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  • richardmitnick 3:50 pm on September 22, 2014 Permalink | Reply
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    From Caltech: “Variability Keeps The Body In Balance” 

    Caltech Logo
    Caltech

    09/22/2014
    Jessica Stoller-Conrad

    Although the heart beats out a very familiar “lub-dub” pattern that speeds up or slows down as our activity increases or decreases, the pattern itself isn’t as regular as you might think. In fact, the amount of time between heartbeats can vary even at a “constant” heart rate—and that variability, doctors have found, is a good thing.

    runner

    Reduced heart rate variability (HRV) has been found to be predictive of a number of illnesses, such as congestive heart failure and inflammation. For athletes, a drop in HRV has also been linked to fatigue and overtraining. However, the underlying physiological mechanisms that control HRV—and exactly why this variation is important for good health—are still a bit of a mystery.

    By combining heart rate data from real athletes with a branch of mathematics called control theory, a collaborative team of physicians and Caltech researchers from the Division of Engineering and Applied Sciences have now devised a way to better understand the relationship between HRV and health—a step that could soon inform better monitoring technologies for athletes and medical professionals.

    The work was published in the August 19 print issue of the Proceedings of the National Academy of Sciences.

    To run smoothly, complex systems, such as computer networks, cars, and even the human body, rely upon give-and-take connections and relationships among a large number of variables; if one variable must remain stable to maintain a healthy system, another variable must be able to flex to maintain that stability. Because it would be too difficult to map each individual variable, the mathematics and software tools used in control theory allow engineers to summarize the ups and downs in a system and pinpoint the source of a possible problem.

    Researchers who study control theory are increasingly discovering that these concepts can also be extremely useful in studies of the human body. In order for a body to work optimally, it must operate in an environment of stability called homeostasis. When the body experiences stress—for example, from exercise or extreme temperatures—it can maintain a stable blood pressure and constant body temperature in part by dialing the heart rate up or down. And HRV plays an important role in maintaining this balance, says study author John Doyle, the Jean-Lou Chameau Professor of Control and Dynamical Systems, Electrical Engineering, and Bioengineering.

    “A familiar related problem is in driving,” Doyle says. “To get to a destination despite varying weather and traffic conditions, any driver—even a robotic one—will change factors such as acceleration, braking, steering, and wipers. If these factors suddenly became frozen and unchangeable while the car was still moving, it would be a nearly certain predictor that a crash was imminent. Similarly, loss of heart rate variability predicts some kind of malfunction or ‘crash,’ often before there are any other indications,” he says.

    To study how HRV helps maintain this version of “cruise control” in the human body, Doyle and his colleagues measured the heart rate, respiration rate, oxygen consumption, and carbon dioxide generation of five healthy young athletes as they completed experimental exercise routines on stationary bicycles.

    By combining the data from these experiments with standard models of the physiological control mechanisms in the human body, the researchers were able to determine the essential tradeoffs that are necessary for athletes to produce enough power to maintain an exercise workload while also maintaining the internal homeostasis of their vital signs.

    Because monitors in hospitals can already provide HRV levels and dozens of other signals and readings, the integration of such mathematical analyses of control theory into HRV monitors could, in the future, provide a way to link a drop in HRV to a more specific and treatable diagnosis. In fact, one of Doyle’s students has used an HRV application of control theory to better interpret traditional EKG signals.

    Control theory could also be incorporated into the HRV monitors used by athletes to prevent fatigue and injury from overtraining, he says.

    “Physicians who work in very data-intensive settings like the operating room or ICU are in urgent need of ways to rapidly and acutely interpret the data deluge,” says Marie Csete, MD (PhD, ’00), chief scientific officer at the Huntington Medical Research Institutes and a coauthor on the paper. “We hope this work is a first step in a larger research program that helps physicians make better use of data to care for patients.”

    “For example, the heart, lungs, and circulation must deliver sufficient oxygenated blood to the muscles and other organs while not raising blood pressure so much as to damage the brain,” Doyle says. “This is done in concert with control of blood vessel dilation in the muscles and brain, and control of breathing. As the physical demands of the exercise change, the muscles must produce fluctuating power outputs, and the heart, blood vessels, and lungs must then respond to keep blood pressure and oxygenation within narrow ranges.”

    Once these trade-offs were defined, the researchers then used control theory to analyze the exercise data and found that a healthy heart must maintain certain patterns of variability during exercise to keep this complicated system in balance. Loss of this variability is a precursor of fatigue, the stress induced by exercise. Today, some HRV monitors in the clinic can let a doctor know when variability is high or low, but they provide little in the way of an actionable diagnosis.

    Because monitors in hospitals can already provide HRV levels and dozens of other signals and readings, the integration of such mathematical analyses of control theory into HRV monitors could, in the future, provide a way to link a drop in HRV to a more specific and treatable diagnosis. In fact, one of Doyle’s students has used an HRV application of control theory to better interpret traditional EKG signals.

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 8:15 pm on September 14, 2014 Permalink | Reply
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    From Caltech: “Slimy Fish and the Origins of Brain Development” 

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    Caltech

    09/14/2014
    Jessica Stoller-Conrad

    Lamprey—slimy, eel-like parasitic fish with tooth-riddled, jawless sucking mouths—are rather disgusting to look at, but thanks to their important position on the vertebrate family tree, they can offer important insights about the evolutionary history of our own brain development, a recent study suggests.

    eel
    A sea lamprey held by postdoctoral scholar Stephen Green in the Caltech Zebrafish/Xenopus/Lamprey Facility. Credit: Lance Hayashida/Caltech Marketing and Communications

    The work appears in a paper in the September 14 advance online issue of the journal Nature.

    “Lamprey are one of the most primitive vertebrates alive on Earth today, and by closely studying their genes and developmental characteristics, researchers can learn more about the evolutionary origins of modern vertebrates—like jawed fishes, frogs, and even humans,” says paper coauthor Marianne Bronner, the Albert Billings Ruddock Professor of Biology and director of Caltech’s unique Zebrafish/Xenopus/Lamprey facility, where the study was done.

    mb
    Marianne Bronner, the Albert Billings Ruddock Professor of Biology, with the tanks where the sea lamprey are kept during their time at Caltech.
    Credit: Lance Hayashida/Caltech Marketing and Communications

    The facility is one of the few places in the world where lampreys can be studied in captivity. Although the parasitic lamprey are an invasive pest in the Great Lakes, they are difficult to study under controlled conditions; their lifecycle takes up to 10 years and they only spawn for a few short weeks in the summer before they die.

    Each summer, Bronner and her colleagues receive shipments of wild lamprey from Michigan just before the prime of breeding season. When the lamprey arrive, they are placed in tanks where the temperature of the water is adjusted to extend the breeding season from around three weeks to up to two months. In those extra weeks, the lamprey produce tens of thousands of additional eggs and sperm, which, via in vitro fertilization, generate tens of thousands of additional embryos for study. During this time, scientists from all over the world come to Caltech to perform experiments with the developing lamprey embryos.

    tank
    Lamprey embryos are sorted for observation at a microscope in the Caltech Zebrafish/Xenopus/Lamprey facility.
    Credit: Lance Hayashida/Caltech Marketing and Communications

    In the current study, Bronner and her collaborators—who traveled to Caltech from Stower’s Institute for Medical Research in Kansas City, Missouri—studied the origins of the vertebrate hindbrain.

    The hindbrain is a part of the central nervous system common to chordates—or organisms that have a nerve cord like our spinal cord. During the development of vertebrates—a subtype of chordates that have backbones—the hindbrain is compartmentalized into eight segments, each of which becomes uniquely patterned to establish networks of neuronal circuits. These segments eventually give rise to adult brain regions like the cerebellum, which is important for motor control, and the medulla oblongata, which is necessary for breathing and other involuntary functions.

    br
    A lamprey embryo expressing the Hox gene Hoxb3 (green). In the study, Bronner and her colleagues found that Hox genes are important for hindbrain segmentation during lamprey development.
    Credit: Hugo Parker

    However, this segmentation is not present in so-called “invertebrate chordates”—a grouping of chordates that lack a backbone, such as sea squirts and lancelets.

    “The interesting thing about lampreys is that they occupy an intermediate evolutionary position between the invertebrate chordates and the jawed vertebrates,” says Hugo Parker, a postdoc at Stower’s Institute and first author on the study. “By investigating aspects of lamprey embryology, we can get a picture of how vertebrate traits might have evolved.”

    hp
    Hugo Parker, a postdoctoral scholar from the Stowers Institute for Medical Research, works with lamprey embryos at a microscope in the Caltech Zebrafish/Xenopus/Lamprey facility.
    Credit: Lance Hayashida/Caltech Marketing and Communications

    In the vertebrates, segmental patterning genes called Hox genes help to determine the animal’s head-to-tail body plan—and those same Hox genes also control the segmentation of the hindbrain. Although invertebrate chordates also have Hox genes, these animals don’t have segmented hindbrains. Because lampreys are centered between these two types of organisms on the evolutionary tree, the researchers wanted to know whether or not Hox genes are involved in patterning of the lamprey hindbrain.

    To their surprise, the researchers discovered that the lamprey hindbrain was not only segmented during development but the process also involved Hox genes—just like in its jawed vertebrate cousins.

    “When we started, we thought that the situation was different, and the Hox genes were not really integrated into the process of segmentation as they are in jawed vertebrates,” Parker says. “But in actually doing this project, we discovered the way that lamprey Hox genes are expressed and regulated is very similar to what we see in jawed vertebrates.” This means that hindbrain segmentation—and the role of Hox genes in this segmentation—happened earlier on in evolution than was once thought, he says.

    Parker, who has been spending his summers at Caltech studying lampreys since 2008, is next hoping to pinpoint other aspects of the lamprey hindbrain that may be conserved in modern vertebrate information that will help contribute to a fundamental understanding of vertebrate development. And although those investigations will probably mean following the lamprey for a few more summers at Caltech, Parker says his time in the lamprey facility continually offers a one-of-a-kind experience.

    “The lamprey system here is unique in the world—and it’s not just the water tanks and how we’ve learned to maintain the animals. It’s the small nucleus of people who have particular skills, people who come in from all over the world to work together, share protocols, and develop the field together,” he says. “That’s one of the things I’ve liked ever since I first came here. I really felt like I was a part of something very special.

    These results were published in a paper titled A Hox regulatory network of hindbrain segmentation is conserved to the base of vertebrates. Robb Krumlauf, a scientific director at the Stower’s Institute and professor at the Kansas University Medical Center, was also a coauthor on the study. The Zebrafish/Xenopus/Lamprey facility at Caltech is a Beckman Institute facility.

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 2:41 pm on August 20, 2014 Permalink | Reply
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    From Caltech: “Programmed to Fold: RNA Origami” 

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    Caltech

    08/20/2014
    Katie Neith

    Researchers from Aarhus University in Denmark and Caltech have developed a new method for organizing molecules on the nanoscale. Inspired by techniques used for folding DNA origami—first invented by Paul Rothemund, a senior research associate in computation and neural systems in the Division of Engineering and Applied Science at Caltech—the team, which includes Rothemund, has fabricated complicated shapes from DNA’s close chemical cousin, RNA.

    Unlike DNA origami, whose components are chemically synthesized and then folded in an artificial heating and cooling process, RNA origami are synthesized enzymatically and fold up as they are being synthesized, which takes place under more natural conditions compatible with living cells. These features of RNA origami may allow designer RNA structures to be grown within living cells, where they might be used to organize cellular enzymes into biochemical factories.

    “The parts for a DNA origami cannot easily be written into the genome of an organism. An RNA origami, on the other hand, can be represented as a DNA gene, which in cells is transcribed into RNA by a protein machine called RNA polymerase,” explains Rothemund.

    So far, the researchers have demonstrated their method by designing RNA molecules that fold into rectangles and then further assemble themselves into larger honeycomb patterns. This approach was taken to make the shapes recognizable using an atomic force microscope, but many other shapes should be realizable.

    fold
    This illustration is an artist’s impression of RNA nanostructures that fold up while they are being synthesized by polymerase enzymes, which read instructions from DNA templates. Once formed, the RNAs assemble into honeycomb-shaped lattices on the mica surface below. Credit: Cody Geary

    A paper describing the research appears in the August 15 issue of the journal Science.

    “What is unique about the method is that the folding recipe is encoded into the molecule itself, through its sequence.” explains first author Cody Geary, a postdoctoral scholar at Aarhus University.

    In other words, the sequence of the RNAs defines both the final shape, and the order in which different parts of the shape fold. The particular RNA sequences that were folded in the experiment were designed using software called NUPACK, created in the laboratory of Caltech professor Niles Pierce. Both the Rothemund and Pierce labs are funded by a National Science Foundation. Molecular Programming Project (MPP) Expeditions in Computing grant.

    “Our latest research is an excellent example of how tools developed by one part of the MPP are being used by another,” says Rothemund.

    “RNA has a richer structural and functional repertoire than DNA, and so I am especially interested in how complex biological motifs with special 3-D geometries or protein-binding regions can be added to the basic architecture of RNA origami,” says Geary, who completed his BS in chemistry at Caltech in 2003.

    The project began with an extended visit by Geary and corresponding author Ebbe Andersen, also from Aarhus University, to Rothemund’s Caltech lab.

    “RNA origami is still in its infancy,” says Rothemund. “Nevertheless, I believe that RNA origami, because of their potential to be manufactured by cells, and because of the extra functionality possible with RNA, will have at least as big an impact as DNA origami.”

    Rothemund (BS ’94) reported the original method for DNA origami in 2006 in the journal Nature. Since then, the work has been cited over 6,000 times and DNA origami have been made in over 50 labs worldwide for potential applications such as drug delivery vehicles and molecular computing.

    “The payoff is that unlike DNA origami, which are expensive and have to be made outside of cells, RNA origami should be able to be grown cheaply in large quantities, simply by growing bacteria with genes for them,” he adds. “Genes and bacteria cost essentially nothing to share, and so RNA origami will be easily exchanged between scientists.”

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 4:52 pm on August 1, 2014 Permalink | Reply
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    From Caltech: “Biology Made Simpler With ‘Clear’ Tissues” 

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    Caltech

    08/01/2014
    Jessica Stoller-Conrad

    In general, our knowledge of biology—and much of science in general—is limited by our ability to actually see things. Researchers who study developmental problems and disease, in particular, are often limited by their inability to look inside an organism to figure out exactly what went wrong and when.

    Now, thanks to techniques developed at Caltech, scientists can see through tissues, organs, and even an entire body. The techniques offer new insight into the cell-by-cell makeup of organisms—and the promise of novel diagnostic medical applications.

    mass
    A 3-D visualization of fluorescently-labeled brain cells within an intact brain tissue. Through the use of this novel whole-body clearing and staining method, researchers can make an organism’s tissues transparent—allowing them to look through the tissues of an organism for specific cells that have been labeled or stained.
    Credit: Bin Yang and Viviana Gradinaru/Caltech

    “Large volumes of tissue are not optically transparent—you can’t see through them,” says Viviana Gradinaru, an assistant professor of biology at Caltech and the principal investigator whose team has developed the new techniques, which are explained in a paper appearing in the journal Cell. Lipids throughout cells provide structural support, but they also prevent light from passing through the cells. “So, if we need to see individual cells within a large volume of tissue”—within a mouse kidney, for example, or a human tumor biopsy—”we have to slice the tissue very thin, separately image each slice with a microscope, and put all of the images back together with a computer. It’s a very time-consuming process and it is error prone, especially if you look to map long axons or sparse cell populations such as stem cells or tumor cells,” she says.

    The researchers came up with a way to circumvent this long process by making an organism’s entire body clear, so that it can be peered through—in 3-D—using standard optical methods such as confocal microscopy.

    The new approach builds off a technique known as CLARITY that was previously developed by Gradinaru and her collaborators to create a transparent whole-brain specimen. With the CLARITY method, a rodent brain is infused with a solution of lipid-dissolving detergents and hydrogel—a water-based polymer gel that provides structural support—thus “clearing” the tissue but leaving its three-dimensional architecture intact for study.

    The refined technique optimizes the CLARITY concept so that it can be used to clear other organs besides the brain, and even whole organisms. By making clever use of an organism’s own network of blood vessels, Gradinaru and her colleagues—including scientific researcher Bin Yang and postdoctoral scholar Jennifer Treweek, coauthors on the paper—can quickly deliver the lipid-dissolving hydrogel and chemical solution throughout the body.

    Gradinaru and her colleagues have dubbed this new technique PARS, or perfusion-assisted agent release in situ.

    Once an organ or whole body has been made transparent, standard microscopy techniques can be used to easily look through a thick mass of tissue to view single cells that are genetically marked with fluorescent proteins. Even without such genetically introduced fluorescent proteins, however, the PARS technique can be used to deliver stains and dyes to individual cell types of interest. When whole-body clearing is not necessary the method works just as well on individual organs by using a technique called PACT, short for passive clarity technique.

    To find out if stripping the lipids from cells also removes other potential molecules of interest—such as proteins, DNA, and RNA—Gradinaru and her team collaborated with Long Cai, an assistant professor of chemistry at Caltech, and his lab. The two groups found that strands of RNA are indeed still present and can be detected with single-molecule resolution in the cells of the transparent organisms.

    The Cell paper focuses on the use of PACT and PARS as research tools for studying disease and development in research organisms. However, Gradinaru and her UCLA collaborator Rajan Kulkarni, have already found a diagnostic medical application for the methods. Using the techniques on a biopsy from a human skin tumor, the researchers were able to view the distribution of individual tumor cells within a tissue mass. In the future, Gradinaru says, the methods could be used in the clinic for the rapid detection of cancer cells in biopsy samples.

    The ability to make an entire organism transparent while retaining its structural and genetic integrity has broad-ranging applications, Gradinaru says. For example, the neurons of the peripheral nervous system could be mapped throughout a whole body, as could the distribution of viruses, such as HIV, in an animal model.

    Gradinaru also leads Caltech’s Beckman Institute BIONIC center for optogenetics and tissue clearing and plans to offer training sessions to researchers interested in learning how to use PACT and PARS in their own labs.

    “I think these new techniques are very practical for many fields in biology,” she says. “When you can just look through an organism for the exact cells or fine axons you want to see—without slicing and realigning individual sections—it frees up the time of the researcher. That means there is more time to the answer big questions, rather than spending time on menial jobs.”

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 5:50 pm on July 28, 2014 Permalink | Reply
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    From Caltech: “TMT Construction Gets Green Light” 

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    Caltech

    07/28/2014
    Kathy Svitil

    The Hawaii Board of Land and Natural Resources has given the official green light for construction of the Thirty Meter Telescope (TMT) on the summit of Mauna Kea, home to many of the world’s premier astronomical observatories. TMT—which will be the world’s largest ground-based telescope when it begins operations in 2022 [ESO's E-ELT will be a 39m behemoth and will see first light in the early 2020's]—will shed light on fundamental questions about the characteristics of exoplanets, the birth of stars and galaxies, and the composition and expansion of the universe, among other elusive cosmic mysteries.

    Thirty Meter Telescope
    TMT

    The TMT project was conceived more than a decade ago by a group of astronomers at Caltech and other institutes as the logical follow-up to the W. M. Keck Observatory, arguably the most prominent and productive ground-based observatory in astronomy today [ the writer seems to not know about ESO's VLT in Chile].

    Keck Observatory
    Keck

    Since the TMT project’s inception, Caltech—in collaboration with the University of California and the Association of Canadian Universities for Research in Astronomy, and with major funding provided by the Gordon and Betty Moore Foundation—has been a core partner and has played a vital role in “defining the scientific objectives and technical capabilities, designing the observatory and its first-light instruments, and building the international partnership that is at the heart of this Pacific Rim observatory,” says Tom Soifer, chair of the Division of Physics, Mathematics and Astronomy. “I am very happy that we’ve made it this far,” Soifer adds. “Having been part of the building of Keck and its first science, I know the thrill of building and commissioning a new, state-of-the-art astronomy facility. I look forward to celebrating the first light of TMT in the future.”

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 10:02 am on July 23, 2014 Permalink | Reply
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    From Caltech: “50 Years of Quarks” 

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    Caltech

    07/22/2014
    A Milestone in Physics

    Douglas Smith

    Caltech’s Murray Gell-Mann simplified the world of particle physics in 1964 by standing it on its head. He theorized that protons—subatomic particles as solid as billiard balls and as stable as the universe—were actually cobbled together from bizarre entities, dubbed “quarks,” whose properties are unlike anything seen in our world. Unlike protons, quarks cannot be separated from their fellows and studied in isolation; despite this, our understanding of the universe is built on their amply documented existence.

    proton
    he quark structure of the proton. (The color assignment of individual quarks is not important, only that all three colors are present.)

    mgm
    Nobel Laureate Murray Gell-Mann

    These days, the subatomic particle catalog has hundreds of entries. Back in the 1920s, there were only two—the massive proton, which had a charge of +1 and was found in the atom’s nucleus; and the electron, which had very little mass, a charge of –1, and orbited the nucleus. Every proton occupied one of two possible spin states in relation to the surrounding space. These spins could easily be flipped in a behavior described by a mathematical construct called the SU(2) symmetry group. “Quantum spin states do not have a familiar analog in everyday experience,” says Caltech’s Steven Frautschi, professor of theoretical physics, emeritus. “However, they can be turned into one another by 180-degree rotations in ordinary space, which is what SU(2) does.”

    In 1932, the neutron was discovered.

    neut
    The quark structure of the neutron. (The color assignment of individual quarks is not important, only that all three colors are present.)

    This new particle appeared to be the proton’s close relative—even its mass was the same, to within 0.2 percent—but the neutron had no electric charge. SU(2) symmetry in ordinary space could not account for the neutron’s existence, but quantum mechanic Werner Heisenberg fixed the problem by declaring that the two particles were indeed fraternal twins . . . if you took SU(2) from another point of view. Frautschi explains: “Like rotating a physical object in ordinary space, Heisenberg extended SU(2) by rotating the symmetry group in a ‘space’ that quantum theorists made up.”

    Heisenberg gave his rotation a quantum number, now called isospin, which described the particle’s interaction with the so-called strong nuclear force. (The strong force overcomes the mutual repulsion between positively charged protons, binding them and neutrons to one another and allowing stable atomic nuclei to exist.) The mathematical treatment of isospin in Heisenberg’s theoretical space was identical to that of the proton’s spin in ordinary space, allowing neutrons to turn into protons and vice versa. In the physical world, Heisenberg’s version of SU(2) is like a slowly spinning roulette wheel after the ball has come to rest—if the white ball (a proton) could transmute itself into a black ball (a neutron) and then back again to a white ball once every revolution.

    A comprehensive theory of the strong force was published three years later by Hideki Yukawa of Osaka University. Quantum-mechanical forces need particles to carry them, and Yukawa calculated that the strong-force carriers would be much more massive than electrons but not nearly as massive as protons. Soon after, in 1937, Caltech research fellow Seth Neddermeyer (PhD ’35) and Nobel laureate physics professor Carl Anderson (BS ’27, PhD ’30) stumbled upon a likely candidate: a new particle with about 200 times the electron’s mass and about one-ninth the mass of the proton.

    Although it was widely assumed that Neddermeyer and Anderson had found the force-carrying particles that would prove Yukawa’s theory, the paper announcing the discovery merely described them as “higher mass states of ordinary electrons.” This proved to be the case—the new particles, now called muons, did not behave as Yukawa had predicted but instead behaved exactly like electrons. This offered the first inkling that otherwise identical particles came in multigenerational “families” of very different masses.

    The search for Yukawa’s strong-force carriers did not bear fruit until 1947, when particles dubbed pions finally turned up…

    pion
    The quark structure of the pion.

    …as did kaons, the massive second-generation members of the pion family. These kaons, however, were oddly long-lived, lasting a quadrillion times longer than expected. (“Long-lived” is relative, as the average kaon decayed into other particles in less than a millionth of a second.)

    Then, in 1953, Murray Gell-Mann, then at the University of Chicago, and Kazuhiko Nishijima (also at Osaka University) independently demystified the kaons’ strange longevity by proposing yet another new quantum number to explain it. This number, imaginatively called “strangeness,” permits particles possessing it to decay—but only by shedding one strangeness unit at a time. This relatively slow process created stepwise cascades of successively less-strange particles, ultimately ending in particles whose strangeness is zero.

    Unfortunately, strangeness and SU(2) did not mesh mathematically. The theorists remained at an impasse; meanwhile, the experimentalists built ever-more-powerful machines that created ever-more-massive, ever-more-exotic particles whose ever-briefer existences could only be inferred by working backward from the collections of mundane particles into which they decayed.

    The mushrooming catalog of discoveries defied all attempts at organization until 1961, when Gell-Mann—who had moved to Caltech in 1955—and Israeli physicist Yuval Ne’eman independently proposed sorting particles into mini-periodic tables organized by electric charge and strangeness number. Gell-Mann dubbed his version the “Eightfold Way,” after Buddhism’s Eightfold Path to enlightenment, because the tables tended to contain eight members each.

    The Eightfold Way brought physicists full circle, as it proved to be a rotating SU(3) symmetry group. Just as charge had driven the isospin axis in Heisenberg’s SU(2) symmetry, strangeness provided a second, perpendicular rotation. In other words, SU(2) spun only around the y axis, as it were, but SU(3) spun on both the x and y axes simultaneously. It was as if the roulette wheel had morphed into a globe spinning around the poles while the polar axis itself spun around two points on the equator. Relationships between particles could be represented as rotations in isospin, in strangeness, or in both.

    Although the Eightfold Way solved one problem, it created another. Whereas SU(2) manifests itself through doublets—the proton-neutron dichotomy—SU(3)’s hallmark is the triplet. “Nature is likely to use this fundamental representation,” says physics professor Frautschi, “but there was no sign of triplets in the data.” Triplets could be conjured into existence, however, if the rock-solid proton could be broken apart. In that case, SU(3)’s fundamental triplet could be a menu of three hypothetical entities, each with its own unique set of quantum numbers.

    If the menu choices were truly independent—much like allowing a diner to order an enchilada with all beans and no rice on the side, for example—a fundamental triplet offered enough possibilities to build every massive particle known, and then some. Intermediate-mass pions and kaons would contain two menu selections; protons, neutrons, and a slew of more massive particles would be three-item combos. “It’s all about making patterns,” Frautschi explains. “You write down sets of quantum numbers, add them up, and see what fits.”

    However, the numbers refused to add up. Both the two-piece kaon and a three-piece particle called the sigma came in positive, negative, and electrically neutral versions. But if the only charges available to the triplet’s members were –1, 0, and +1, no conceivable combination of choices allowed all the other quantum numbers to come out right.

    This should have been the end of the story. Robert Millikan, Caltech’s first Nobel laureate, had won his prize for showing that electric charge came only in whole-numbered units. But in 1964, Gell-Mann and George Zweig (PhD ’64) independently flew in the face of all that was known by proposing that the fundamental triplet had one member with a +2/3 charge and two members with charges of –1/3.

    Gell-Mann called the members of his triplet “quarks,” after the sentence “Three quarks for Muster Mark!” in James Joyce’s Finnegan’s Wake. Everything found in the old SU(2) symmetry group could be fashioned from +2/3 “up” quarks and –1/3 “down” quarks, both of which had a strangeness number of zero. A proton was up-up-down, for example; a neutron was down-down-up. The other –1/3 quark had a quantum of strangeness; adding these “strange” quarks to the mix took care of the particles that SU(2) couldn’t handle. Since this proposal was so heretical, Gell-Mann presented quarks as no more than an expedient accounting system, writing, “It is fun to speculate about the way quarks would behave if they were physical particles of finite mass (instead of purely mathematical entities . . . ).”

    Zweig, meanwhile, called his theoretical constructs “aces,” as they were put together into “deuces” and “treys” to make pions and protons. He was also less circumspect than Gell-Mann. “The results . . . seem somewhat miraculous,” Zweig wrote. “Perhaps the model is . . . a rather elaborate mnemonic device. [But] there is also the outside chance that the model is a closer approximation to nature than we may think, and that fractionally charged aces abound within us.” Sadly, Zweig’s paper met a very different fate than Gell-Mann’s. Since Zweig was working as a very junior postdoctoral fellow at CERN, the European Center for Particle Physics, all his manuscripts had to be reviewed by his superiors before publication. The senior staff considered Zweig’s ideas too outré, and his paper got sent to a file room instead of a journal. He returned to Caltech soon after, joining the faculty.

    Gell-Mann went on to win the Nobel Prize for Physics in 1969—although not for the quark model per se, which was still on thin ice. (The very first experiments demonstrating that protons might contain something else had been run at the Stanford Linear Accelerator the preceding year.) Instead, he was cited “for contributions and discoveries concerning the classification of elementary particles and their interactions.”

    Quarks have since been shown to be physical particles with finite masses. The up quark has been found to have about half the mass of the down, while the strange quark has been shown to be some 50 times more massive—a sure sign that it represented a second generation of quarks, just as muons had turned out to be second-generation electrons. In 1974, the other second-generation quark turned up—the “charm” quark—followed three years later by the third-generation “bottom” quark. It then took nearly two decades to find what is called the “top” quark—which, as far as we know, completes the quark family tree.

    Gell-Mann was named the Robert Andrews Millikan Professor of Theoretical Physics in 1967—a fitting irony that the man who showed that fractional electric charges are necessary holds the chair named for the man who showed that electric charge is indivisible.

    Gell-Mann’s paper introducing the quark was all of two pages long; what has been written about quarks since then would fill warehouses. This half-century of discoveries was celebrated at a conference in the 84-year-old Gell-Mann’s honor, hosted by Caltech’s theoretical high-energy physics group in December, 2013 –

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 7:46 pm on July 17, 2014 Permalink | Reply
    Tags: , Caltech, , Quartz technology   

    From Caltech: “Future Electronics May Depend on Lasers, Not Quartz” 

    Caltech Logo
    Caltech

    07/17/2014
    Jessica Stoller-Conrad

    Nearly all electronics require devices called oscillators that create precise frequencies—frequencies used to keep time in wristwatches or to transmit reliable signals to radios. For nearly 100 years, these oscillators have relied upon quartz crystals to provide a frequency reference, much like a tuning fork is used as a reference to tune a piano. However, future high-end navigation systems, radar systems, and even possibly tomorrow’s consumer electronics will require references beyond the performance of quartz.

    three
    Vahala’s new laser frequency reference (left) is a small 6 mm disk; the quartz “tuning fork” (middle) is the frequency reference commonly used today in wristwatches to set the second. The dime (right) is for scale.
    Credit: Jiang Li/Caltech

    Now, researchers in the laboratory of Kerry Vahala, the Ted and Ginger Jenkins Professor of Information Science and Technology and Applied Physics at Caltech, have developed a method to stabilize microwave signals in the range of gigahertz, or billions of cycles per second—using a pair of laser beams as the reference, in lieu of a crystal.

    Quartz crystals “tune” oscillators by vibrating at relatively low frequencies—those that fall at or below the range of megahertz, or millions of cycles per second, like radio waves. However, quartz crystals are so good at tuning these low frequencies that years ago, researchers were able to apply a technique called electrical frequency division that could convert higher-frequency microwave signals into lower-frequency signals, and then stabilize these with quartz.

    The new technique, which Vahala and his colleagues have dubbed electro-optical frequency division, builds off of the method of optical frequency division, developed at the National Institute of Standards and Technology more than a decade ago. “Our new method reverses the architecture used in standard crystal-stabilized microwave oscillators—the ‘quartz’ reference is replaced by optical signals much higher in frequency than the microwave signal to be stabilized,” Vahala says.

    Jiang Li—a Kavli Nanoscience Institute postdoctoral scholar at Caltech and one of two lead authors on the paper, along with graduate student Xu Yi—likens the method to a gear chain on a bicycle that translates pedaling motion from a small, fast-moving gear into the motion of a much larger wheel. “Electrical frequency dividers used widely in electronics can work at frequencies no higher than 50 to 100 GHz. Our new architecture is a hybrid electro-optical ‘gear chain’ that stabilizes a common microwave electrical oscillator with optical references at much higher frequencies in the range of terahertz or trillions of cycles per second,” Li says.

    The optical reference used by the researchers is a laser that, to the naked eye, looks like a tiny disk. At only 6 mm in diameter, the device is very small, making it particularly useful in compact photonics devices—electronic-like devices powered by photons instead of electrons, says Scott Diddams, physicist and project leader at the National Institute of Standards and Technology and a coauthor on the study.

    “There are always tradeoffs between the highest performance, the smallest size, and the best ease of integration. But even in this first demonstration, these optical oscillators have many advantages; they are on par with, and in some cases even better than, what is available with widespread electronic technology,” Vahala says.

    The new technique is described in a paper that will be published in the journal Science on July 18. Other authors on this paper include Hansuek Lee, who is a visiting associate at Caltech. The work was sponsored by the DARPA’s ORCHID and PULSE programs; the Caltech Institute for Quantum Information and Matter (IQIM), an NSF Physics Frontiers Center with support of the Gordon and Betty Moore Foundation; and the Caltech Kavli NanoScience Institute.

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 5:41 pm on May 1, 2014 Permalink | Reply
    Tags: , , , Caltech, ,   

    From Caltech: “To Supernova or Not to Supernova: A 3-D Model of Stellar Core Collapse” 

    Caltech Logo
    Caltech

    05/01/2014
    Cynthia Eller

    What happens when massive stars collapse? One potential result is a core-collapse supernova. Astronomers can make observations of such events that tell us what is happening on the surface of a star when it explodes in a supernova, but it is considerably more difficult to know what is driving the process inside the star at its hot, dense core.

    star
    A massive stellar core not quite managing to transition to a supernova explosion because of a small “kink” instability in its rotational axis.Credit: Philipp Mösta and Sherwood Richers

    Astrophysicists attempt to simulate these events based on the properties of different kinds of stars and knowledge of the fundamental interactions of mass and energy, hopefully providing astronomers with ready predictions that can be tested with observational data.

    In a recent publication, Caltech postdoctoral scholar Philipp Mösta and Christian Ott, professor of theoretical astrophysics, present a three-dimensional model of a rapidly rotating star with a strong magnetic field undergoing the process of collapse and explosion . . . or at least trying to.

    Stars with a very rapid spin and a strong magnetic field are comparatively rare: no more than one in a hundred massive stars (those at least 10 times the mass of our sun) have these features. According to Mösta and Ott’s research, when these bodies undergo core collapse, small perturbations around its axis of rotation may inhibit the process that would ordinarily lead to a supernova explosion.

    Previous models of the collapse of rapidly rotating magnetized stellar cores assumed perfect symmetry around the axis of rotation. In effect, these models were two-dimensional. The models yielded the expectation that as these cores collapsed, the strong magnetic field combined with the rapid spin would squeeze the stellar material out into two narrow “jets” along the axis of symmetry, as shown [below].

    core

    Assuming perfect symmetry around the axis of rotation can be excused in part as a matter of simplifying the scenario so that it could be simulated on an ordinary computer rather than the kind of supercomputer that Mösta and Ott’s three-dimensional simulations require: 20,000 processors to output 500 terabytes—over 500 trillion bytes—of data that represent only some 200 milliseconds in time. But, says Ott, “Even working with paper and pencil, writing down equations and discussing them with other theoretical astrophysicists, we should have known that small perturbations can trigger an instability in the stellar core. Nothing in nature is perfect. As we learn from this model, even small asymmetries can have a dramatic effect on the process of stellar collapse and the subsequent supernova explosion.

    stars

    “When Mösta and Ott took on the ambitious task of simulating a magnetorotational core collapse in three dimensions, they introduced a small asymmetry into their initial conditions: a 1 percent perturbation (a kink) around the axis of symmetry. “You can think of it like the vertebrae in your spine,” says Ott. “If one vertebra is slightly offset, there will be greater pressure on one side of the spinal column, and less pressure on the other side. This causes the disk and the material between the vertebrae to be squeezed toward the side with less pressure. The same thing happens when you introduce a kink in the axis of symmetry of a collapsing star with a strong magnetic field.”

    With an ever-so-slightly distorted magnetic field, the core is still constrained in the middle, just as it is in the axially symmetric model. But instead of producing two perfectly matched jets, the magnetic distortion—it is called a “kink instability”—produces two asymmetric, misshapen lobes, as shown at right. “Even more noteworthy,” says Mösta, “is the fact that in the three-dimensional model, the explosion—the supernova—never quite gets off the ground.

    This slideshow illustrates the three-dimensional simulation in a step-by-step fashion.

    Setting the two simulations—two-dimensional and three-dimensional—alongside one another provide a dramatic visualization of the impact of even a small asymmetry in a rapidly-rotating, magnetized body. In a video that compares the two, 186 milliseconds of core collapse are slowed to fill two minutes of real time. The two events look very similar for about 20 milliseconds, before the kink instability in the three-dimensional model begins to deform the stellar core and constrain its progress toward supernova.

    The kink instability in the three-dimensional simulation leads to a “wobbling” of the central funnel of material that is pushed out by the ultra-dense and hot stellar core, a proto-neutron star. “As the material expands, it gets wound in tubes around the spin axis of the star, like water being expelled vigorously from a garden hose left lying on the ground,” says Mösta. In the three-dimensional view illustrated here, regions in which the magnetic field pressure dominates are yellow, while regions that are dominated by the normal pressure of the stellar gas are blue, red, and black.

    unstable

    Unlike the two-dimensional, axially symmetric simulations with their uniform jets along the axis of rotation, the three-dimensional simulations of Mösta and Ott result in two lobes of twisted and highly magnetized material that are only slowly pushed outward and do not show signs of a runaway explosion at the end of the simulation. More and longer simulations on more powerful supercomputers will be needed to determine the final fate of core collapse in a rapidly rotating magnetized star.

    “We can be smarter in our simulations now,” says Ott. “We are wrestling with a more interesting if less perfect universe—the one we actually live in.”

    The paper, Magnetorotational Core-collapse Supernovae in Three Dimensions, appeared in the April 3, 2014, issue of Astrophysical Journal Letters and is authored by Mösta, Ott, Sherwood Richers, Roland Haas, Anthony Piro, Kristen Boydstun, Ernazar Abdikamalov, and Christian Reisswig, all of Caltech, and Erik Schnetter of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada. This research was funded by the National Science Foundation, the Sherman Fairchild Foundation, the U.S. Department of Energy, and NASA.

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 8:23 pm on April 29, 2014 Permalink | Reply
    Tags: , , , Caltech,   

    From Caltech: “The Intergalactic Medium Unveiled: Caltech’s Cosmic Web Imager Directly Observes ‘Dim Matter'” 

    Caltech Logo
    Caltech

    04/29/2014
    Cynthia Eller

    Caltech astronomers have taken unprecedented images of the intergalactic medium (IGM)—the diffuse gas that connects galaxies throughout the universe—with the Cosmic Web Imager, an instrument designed and built at Caltech.

    Caltech Cosmic Web Imager
    Cosmic Web Imager

    Until now, the structure of the IGM has mostly been a matter for theoretical speculation. However, with observations from the Cosmic Web Imager, deployed on the Hale 200-inch telescope at Palomar Observatory, astronomers are obtaining our first three-dimensional pictures of the IGM. The Cosmic Web Imager will make possible a new understanding of galactic and intergalactic dynamics, and it has already detected one possible spiral-galaxy-in-the-making that is three times the size of our Milky Way.

    Caltech Hale Telescope at Palomar

    Caltech Hale Telescope at Palomar
    Hale Telescope

    image
    Comparison of Lyman alpha blob observed with Cosmic Web Imager and a simulation of the cosmic web based on theoretical predictions.Credit: Christopher Martin, Robert Hurt

    The Cosmic Web Imager was conceived and developed by Caltech professor of physics Christopher Martin. “I’ve been thinking about the intergalactic medium since I was a graduate student,” says Martin. “Not only does it comprise most of the normal matter in the universe, it is also the medium in which galaxies form and grow.”

    Since the late 1980s and early 1990s, theoreticians have predicted that primordial gas from the Big Bang is not spread uniformly throughout space, but is instead distributed in channels that span galaxies and flow between them. This “cosmic web”—the IGM—is a network of smaller and larger filaments crisscrossing one another across the vastness of space and back through time to an era when galaxies were first forming and stars were being produced at a rapid rate.

    Martin describes the diffuse gas of the IGM as ,” to distinguish it from the bright matter of stars and galaxies, and the dark matter and energy that compose most of the universe. Though you might not think so on a bright sunny day or even a starlit night, fully 96 percent of the mass and energy in the universe is dark energy and dark matter (first inferred by Caltech’s Fritz Zwicky in the 1930s), whose existence we know of only due to its effects on the remaining 4 percent that we can see: normal matter. Of this 4 percent that is normal matter, only one-quarter is made up of stars and galaxies, the bright objects that light our night sky. The remainder, which amounts to only about 3 percent of everything in the universe, is the IGM.

    As Martin’s name for the IGM suggests, dim matter is hard to see. Prior to the development of the Cosmic Web Imager, the IGM was observed primarily via foreground absorption of light—indicating the presence of matter—occurring between Earth and a distant object such as a quasar (the nucleus of a young galaxy).

    “When you look at the gas between us and a quasar, you have only one line of sight,” explains Martin. “You know that there’s some gas farther away, there’s some gas closer in, and there’s some gas in the middle, but there’s no information about how that gas is distributed across three dimensions.”

    Matt Matuszewski, a former graduate student at Caltech who helped to build the Cosmic Web Imager and is now an instrument scientist at Caltech, likens this line-of-sight view to observing a complex cityscape through a few narrow slits in a wall: “All you would know is that there is some concrete, windows, metal, pavement, maybe an occasional flash of color. Only by opening the slit can you see that there are buildings and skyscrapers and roads and bridges and cars and people walking the streets. Only by taking a picture can you understand how all these components fit together, and know that you are looking at a city.

    “Martin and his team have now seen the first glimpse of the city of dim matter. It is not full of skyscrapers and bridges, but it is both visually and scientifically exciting.The first cosmic filaments observed by the Cosmic Web Imager are in the vicinity of two very bright objects: a quasar labeled QSO 1549+19 and a so-called Lyman alpha blob in an emerging galaxy cluster known as SSA22. These objects were chosen by Martin for initial observations because they are bright, lighting up the surrounding IGM and boosting its detectable signal.

    Observations show a narrow filament, one million light-years long, flowing into the quasar, perhaps fueling the growth of the galaxy that hosts the quasar. Meanwhile, there are three filaments surrounding the Lyman alpha blob, with a measured spin that shows that the gas from these filaments is flowing into the blob and affecting its dynamics.

    The Cosmic Web Imager is a spectrographic imager, taking pictures at many different wavelengths simultaneously. This is a powerful technique for investigating astronomical objects, as it makes it possible to not only see these objects but to learn about their composition, mass, and velocity. Under the conditions expected for cosmic web filaments, hydrogen is the dominant element and emits light at a specific ultraviolet wavelength called Lyman alpha. Earth’s atmosphere blocks light at ultraviolet wavelengths, so one needs to be outside Earth’s atmosphere, observing from a satellite or a high-altitude balloon, to observe the Lyman alpha signal.

    However, if the Lyman alpha emission lies much further away from us—that is, it comes to us from an earlier time in the universe—then it arrives at a longer wavelength (a phenomenon known as redshifting). This brings the Lyman alpha signal into the visible spectrum such that it can pass through the atmosphere and be detected by ground-based telescopes like the Cosmic Web Imager.

    The objects the Cosmic Web Imager has observed date to approximately 2 billion years after the Big Bang, a time of rapid star formation in galaxies. “In the case of the Lyman alpha blob,” says Martin, “I think we’re looking at a giant protogalactic disk. It’s almost 300,000 light-years in diameter, three times the size of the Milky Way.”

    The Cosmic Web Imager was funded by grants from the NSF and Caltech. Having successfully deployed the instrument at the Palomar Observatory, Martin’s group is now developing a more sensitive and versatile version of the Cosmic Web Imager for use at the W. M. Keck Observatory atop Mauna Kea in Hawaii. “The gaseous filaments and structures we see around the quasar and the Lyman alpha blob are unusually bright. Our goal is to eventually be able to see the average intergalactic medium everywhere. It’s harder, but we’ll get there,” says Martin.

    Keck Observatory
    Keck Observatory twin 10m telescopes

    Plans are also under way for observations of the IGM from a telescope aboard a high-altitude balloon, FIREBALL (Faint Intergalactic Redshifted Emission Balloon); and from a satellite, ISTOS (Imaging Spectroscopic Telescope for Origins Surveys). By virtue of bypassing most, if not all, of our atmosphere, both instruments will enable observations of Lyman alpha emission—and therefore the IGM—that are closer to us; that is, that are from more recent epochs of the universe.

    Two papers describing the initial data from the Cosmic Web Imager have been published in the Astrophysical Journal: Intergalactic Medium Observations with the Cosmic Web Imager: I. The Circum-QSO Medium of QSO 1549+19, and Evidence for a Filamentary Gas Inflow and Intergalactic Medium Observations with the Cosmic Web Imager: II. Discovery of Extended, Kinematically-linked Emission around SSA22 Lyα Blob 2. The Cosmic Web Imager was built principally by three Caltech graduate students—the late Daphne Chang, Matuszewski, and Shahinur Rahman—and by Caltech principal research scientist Patrick Morrissey, who are all coauthors on the papers. Additional coauthors are Christopher Martin, Anna Moore, Charles Steidel, and Yuichi Matsuda.

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 8:23 am on April 17, 2014 Permalink | Reply
    Tags: , Caltech, ,   

    From Caltech: “Made-to-Order Materials” 

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    Caltech

    09/05/2013
    Kimm Fesenmaier

    Caltech engineers focus on the nano to create strong, lightweight materials

    The lightweight skeletons of organisms such as sea sponges display a strength that far exceeds that of manmade products constructed from similar materials. Scientists have long suspected that the difference has to do with the hierarchical architecture of the biological materials—the way the silica-based skeletons are built up from different structural elements, some of which are measured on the scale of billionths of meters, or nanometers. Now engineers at the California Institute of Technology (Caltech) have mimicked such a structure by creating nanostructured, hollow ceramic scaffolds, and have found that the small building blocks, or unit cells, do indeed display remarkable strength and resistance to failure despite being more than 85 percent air.

    mat
    Three-dimensional, hollow titanium nitride nanotruss with tessellated octahedral geometry. Each unit cell is on the order of 10 microns, each strut length within the unit cell is about three to five microns, the diameter of each strut is less than one micron, and the thickness of titanium nitride is roughly 75 nanometers.Credit: Dongchan Jang and Lucas Meza

    “Inspired, in part, by hard biological materials and by earlier work by Toby Schaedler and a team from HRL Laboratories, Caltech, and UC Irvine on the fabrication of extremely lightweight microtrusses, we designed architectures with building blocks that are less than five microns long, meaning that they are not resolvable by the human eye,” says Julia R. Greer, professor of materials science and mechanics at Caltech. “Constructing these architectures out of materials with nanometer dimensions has enabled us to decouple the materials’ strength from their density and to fabricate so-called structural metamaterials which are very stiff yet extremely lightweight.

    “At the nanometer scale, solids have been shown to exhibit mechanical properties that differ substantially from those displayed by the same materials at larger scales. For example, Greer’s group has shown previously that at the nanoscale, some metals are about 50 times stronger than usual, and some amorphous materials become ductile rather than brittle. “We are capitalizing on these size effects and using them to make real, three-dimensional structures,” Greer says.

    In an advance online publication of the journal Nature Materials, Greer and her students describe how the new structures were made and responded to applied forces.

    The largest structure the team has fabricated thus far using the new method is a one-millimeter cube. Compression tests on the the entire structure indicate that not only the individual unit cells but also the complete architecture can be endowed with unusually high strength, depending on the material, which suggests that the general fabrication technique the researchers developed could be used to produce lightweight, mechanically robust small-scale components such as batteries, interfaces, catalysts, and implantable biomedical devices.

    Greer says the work could fundamentally shift the way people think about the creation of materials. “With this approach, we can really start thinking about designing materials backward,” she says. “I can start with a property and say that I want something that has this strength or this thermal conductivity, for example. Then I can design the optimal architecture with the optimal material at the relevant size and end up with the material I wanted.”

    The team first digitally designed a lattice structure featuring repeating octahedral unit cells—a design that mimics the type of periodic lattice structure seen in diatoms. Next, the researchers used a technique called two-photon lithography to turn that design into a three-dimensional polymer lattice. Then they uniformly coated that polymer lattice with thin layers of the ceramic material titanium nitride (TiN) and removed the polymer core, leaving a ceramic nanolattice. The lattice is constructed of hollow struts with walls no thicker than 75 nanometers.

    “We are now able to design exactly the structure that we want to replicate and then process it in such a way that it’s made out of almost any material class we’d like—for example, metals, ceramics, or semiconductors—at the right dimensions,” Greer says.

    In a second paper, scheduled for publication in the journal Advanced Engineering Materials, Greer’s group demonstrates that similar nanostructured lattices could be made from gold rather than a ceramic. “Basically, once you’ve created the scaffold, you can use whatever technique will allow you to deposit a uniform layer of material on top of it,” Greer says.

    In the Nature Materials work, the team tested the individual octahedral cells of the final ceramic lattice and found that they had an unusually high tensile strength. Despite being repeatedly subjected to stress, the lattice cells did not break, whereas a much larger, solid piece of TiN would break at much lower stresses. Typical ceramics fail because of flaws—the imperfections, such as holes and voids, that they contain. “We believe the greater strength of these nanostructured materials comes from the fact that when samples become sufficiently small, their potential flaws also become very small, and the probability of finding a weak flaw within them becomes very low,” Greer says. So although structural mechanics would predict that a cellular structure made of TiN would be weak because it has very thin walls, she says, “we can effectively trick this law by reducing the thickness or the size of the material and by tuning its microstructure, or atomic configurations.”

    Additional coauthors on the Nature Materials paper, Fabrication and Deformation of Three-Dimensional Hollow Ceramic Nanostructures, are Dongchan Jang, who recently completed a postdoctoral fellowship in Greer’s lab, Caltech graduate student Lucas Meza, and Frank Greer, formerly of the Jet Propulsion Laboratory (JPL). The work was supported by funding from the Dow-Resnick Innovation Fund at Caltech, DARPA’s Materials with Controlled Microstructural Architecture program, and the Army Research Office through the Institute for Collaborative Biotechnologies at Caltech. Some of the work was carried out at JPL under a contract with NASA, and the Kavli Nanoscience Institute at Caltech provided support and infrastructure.

    The lead author on the Advanced Engineering Materials paper, Design and Fabrication of Hollow Rigid Nanolattices Via Two-Photon Lithography, is Caltech graduate student Lauren Montemayor. Meza is a coauthor. In addition to support from the Dow-Resnick Innovation Fund, this work received funding from an NSF Graduate Research Fellowship.

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”


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