Repository of works by Caltech published authors.
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Mostrando recursos 1 - 20 de 3.157
Photon-Induced Near Field Electron Microscopy - Park, Sang Tae; Zewail, Ahmed H.
Ultrafast electron microscopy in the space and time domains utilizes a pulsed electron probe to directly map structural dynamics of nanomaterials initiated by an optical pump pulse, in imaging, diffraction, spectroscopy, and their combinations. It has demonstrated its capability in the studies of phase transitions, mechanical vibrations, and chemical reactions. Moreover, electrons can directly interact with photons via the near field component of light scattering by nanostructures, and either gain or lose light quanta discretely in energy. By energetically selecting those electrons that exchanged photon energies, we can map this photon-electron interaction, and the technique is termed photon-induced near field...
Optical Methods for Wireless Implantable Sensing Platforms - Mujeeb-U-Rahman, Muhammad; Chang, Chieh-Feng; Scherer, Axel
Ultra small scale implants have gained lots of importance for both acute and chronic applications. Optical techniques
hold the key to miniaturizing these devices to long sought sub-mm scale. This will lead towards long term use of these
devices for medically relevant applications. It can also allow using multiple of these devices at the same time and
forming a true body area network of sensors. In this paper, we present optical power transfer to such devices and the
techniques to harness this power for different applications, for example high voltage or high current applications. We
also present methods for wireless data transfer from such implants.
Martian oases? Feasibility of orbital thermal emission detection - Haldemann, Albert F. C.; Danielson, G. Edward; Murray, Bruce C.
We review the motivation for searching out modem "oases" on Mars,
and examine methods of detecting them from orbit. We use the term
"oasis" to refer to sites with anomalous thermal behavior at, or near the
planet's surface. Such sites may be more likely than other locations on
Mars to have liquid water nearby, hence the terminology reminiscent of
Earth's deserts. Three types of "oases" are considered here: small-scale
volcanic eruptions, hot springs, and subsurface intrusions. The general
consensus is that such oases are highly unlikely on Mars today, and
probably do not exist at all. How much investment is worthy of such a
high-risk, unlikely return? We argue...
An oxygen and hydrogen isotope study of high-grade metamorphism and anatexis in the Ruby Mountains-East
Humboldt Range core complex, Nevada - Wickham, Stephen M.; Taylor, Hugh P., Jr.; Snoke, Arthur W.; O'Neil, James R.
Oxygen isotope analyses were made of 91 whole rock and mineral separate samples from the Ruby Mountains-East Humboldt Range metamorphic core complex and other nearby areas in eastern Nevada. In addition, ten hydrogen isotope analyses were made of the hydrous minerals muscovite, biotite, and hornblende. The samples include plutonic igneous rocks, high-grade metasedimentary rocks, and low-grade sediments that are thought to be their protoliths. The δ^(18)O values vary systematically in each of these categories. Most of the metasediments were shifted to lower δ^(18)O values than their protoliths, but the magnitude and pervasiveness of this ^(18)O-depletion varies in different geographic areas,...
Target detection using saliency-based attention - Itti, Laurent; Koch, Christof
Most models of visual search, whether involving overt eye movements or covert shifts of attention, are based on the concept of a "saliency map", that is, an explicit two-dimensional map that encodes the saliency or conspicuity of objects in the visual environment. Competition among neurons in this map gives rise to a single winning location that corresponds to the next attended target. Inhibiting this location automatically allows the system to attend to the next most salient location. We describe a detailed computer implementation of such a scheme, focusing on the problem of combining information across modalities, here orientation, intensity and...
Deployable Helical Antennas for CubeSats - Olson, Gina M.; Pellegrino, Sergio; Banik, Jeremy; Constantine, Joseph
This paper explores the behavior of a self-deploying helical pantograph antenna for CubeSats. The helical pantograph concept is described along with concepts for attachment to the satellite bus. Finite element folding simulations of a pantograph consisting of eight helices are presented and compared to compaction force experiments done on a prototype antenna. Reflection coefficient test are also presented, demonstrating the operating frequency range of the prototype antenna. The helical pantograph is shown to be a promising alternative to current small satellite antenna solutions.
Keck Observations of 160 Gamma-Ray Burst Host Galaxies - Perley, D. A.; Bloom, J. S.; Prochaska, J. X.
We present a preliminary data release from our multi-year campaign at Keck Observatory to study the host galaxies of a large sample of Swift-era gamma-ray bursts via multi-color ground-based optical imaging and spectroscopy. With over 160 targets observed to date (and almost 100 host detections, most of which have not previously been reported in the literature) our effort represents the broadest GRB host survey to date. While targeting was heterogeneous, our observations span the known diversity of GRBs including short bursts, long bursts, spectrally soft GRBs (XRFs), ultra-energetic GRBs, X-ray faint GRBs, dark GRBs, SN-GRBs, and other sub-classes. We also...
Block Copolymer Lithography - Boyd, David A.
This chapter presents block copolymer lithography (BCPL) in light of engineering nanoscale architectures for catalytic applications. It begins with an introduction to the basic phenomenology of block copolymers and then follows with highlights of recent advances in block copolymer science. An overview of the methods and materials commonly used in BCPL is provided. Important results involving BCPL in current research including heterogeneous catalysis, advanced material growth, and plasmonics are presented. Finally, challenges and outlook for BCPL are discussed.
Material Design Considerations Based on Thermoelectric Quality Factor - Wang, Heng; Pei, Yanzhong; LaLonde, Aaron D.; Snyder, G. Jeffrey
In this chapter several aspects of the electronic and phonon structure are
considered for the design and engineering of advanced thermoelectric materials. For
a given compound, its thermoelectric figure of merit, zT, is fully exploited only when
the free carrier density is optimized. Achieving higher zT beyond this requires the
improvement in the material quality factor B. Using experimental data on lead chalcogenides
as well as examples of other good thermoelectric materials, we demonstrate
how the fundamental material parameters: effective mass, band anisotropy, deformation
potential, and band degeneracy, among others, impact the thermoelectric
properties and lead to desirable thermoelectric materials. As the quality factor B is
introduced under the...
Spectrum splitting photovoltaics: light trapping filtered concentrator for ultrahigh photovoltaic efficiency - Kosten, Emily D.; Warmann, Emily C.; Lloyd, John; Atwater, Harry A.
While monolithic multijunction solar cell approaches have been quite successful, current and lattice matching requirements limit the maximum possible achievable efficiencies. Spectrum splitting, where light is optically distributed among subcells with differing bandgaps, avoids these constraints and offers a route to achieving higher efficiencies (<50%). We investigate a spectrum splitting approach where concentrated sunlight is trapped in a textured dielectric slab and then selectively coupled into underlying solar cells of different bandgaps through omnidirectional filters. We develop a multipass optical model to find regimes of high optical efficiency based on parameters such as slab refractive index, number of subcells, and...
Complex Modal Decomposition Applied to Nematode Posturing - Feeny, B. F.; Sternberg, P. W.; Cronin, C. J.
The complex orthogonal decomposition (COD), a process of
extracting complex modes from complex ensemble data, is summarized,
as is the use of complex modal coordinates. A brief
assessment is made on how small levels of noise affect the decomposition.
The decomposition is applied to the posturing of
a wild Caenorhabditis elegans nematode. The decomposition
indicates that the worm has a multi-modal posturing behavior,
involving at least a dominant locomotion mode and a secondary,
steering mode. The locomotion mode is closer to a pure traveling
waveform than the steering mode. The characteristic wavelength
of the primary mode was estimated in the complex plane.
Frequency was obtained from the complex modal coordinate's
Orthogonal query recommendation - Vahabi, Hossein; Ackerman, Margareta; Loker, David; Baeza-Yates, Ricardo; Lopez-Ortiz, Alejandro
One important challenge of current search engines is to satisfy the users’ needs when they provide a poorly formulated
query. When the pages matching the user’s original key-
words are judged to be unsatisfactory, query recommendation techniques are used to propose alternative queries and
alter the result set. These techniques search for queries that are semantically similar to the user’s original query, often searching for keywords that are similar to the keywords given
by the user. However, when the original query is sufficiently
ill-posed, the user’s informational need is best met using entirely different keywords, and a substantially different query may be necessary.
We propose a...
Efficient LHC Data Distribution across 100Gbps Networks - Newman, Harvey; Barczyk, Artur; Mughal, Azher; Rozsa, Sandor; Voicu, Ramiro; Legrand, Iosif; Lo, Steven; Kcira, Dorian; Sobie, Randall; Gable, Ian; Leavett-Brown, Colin; Savard, Yvan; Tam, Thomas; Hay, Marilyn; McKee, Shawn; Hocket, Roy; Meekhof, Ben; Timoteo, Sergio
During Supercomputing 2012 (SC12), an international team of high energy physicists, computer scientists, and network engineers led by the California Institute of Technology (Caltech), the University of Victoria, and the University of Michigan, together with Brookhaven National Lab, Vanderbilt and other partners, smashed their previous records for data transfers using the latest generation of wide area network circuitsWith three 100 gigabit/sec (100 Gbps) wide area network circuits  set up by the SCinet, Internet2, CENIC, CANARIE and BCnet, Starlight and US LHCNet network teams, and servers at each of the sites with 40 gigabit Ethernet (40GE) interfaces, the team reached...
Polyhedral Specular Reflector Design for Ultra-High Spectrum
Splitting Solar Module Efficiencies (>50%) - Eisler, Carissa N.; Kosten, Emily D.; Warmann, Emily C.; Atwater, Harry A.
One pathway to achieving ultra-high solar efficiencies (>50%) is employing a spectrum splitting optical element with at
least 6 subcells and significant concentration (100-500 suns). We propose a design to meet these criteria, employing
specular reflection to split and divide the light onto appropriate subcells. The polyhedral specular reflector incorporates
a high index parallelepiped with seven subcells. The subcells are placed around the parallelepiped such that light entering at normal incidence encounters the subcells in order from highest to lowest bandgap, with the ray path reflecting
at a 90° angle until the light is fully absorbed. Previous studies of the design have shown that...
Poll Tax - Kousser, J. Morgan
The poll or capitation (head) tax in the United States was a lump sum tax levied by state
and local governments on individuals, who often had to pay the tax in order to vote. Popularly
associated with racial and class restrictions on suffrage in the South, it actually expanded the
suffrage when it was introduced shortly after the American Revolution, it unintentionally
discouraged voting by white women after 1920, it was exaggeratedly blamed for many of the
South’s ills in the 1930s and 40s, and after a long crusade against it, it was banned in the mid-
1960s as a mere footnote to the civil rights...
Comparison of the effects of millimeter wave irradiation, general bath heating, and localized heating on neuronal activity in the leech ganglion - Romanenko, Sergii; Siegel, Peter H.; Wagenaar, Daniel A.; Pikov, Victor
The use of electrically-induced neuromodulation has grown in importance in the treatment of multiple neurological disorders such as Parkinson’s disease, dystonia, epilepsy, chronic pain, cluster headaches and others. While electrical current can be applied locally, it requires placing stimulation electrodes in direct contact with the neural tissue. Our goal is to develop a method for localized application of electromagnetic energy to the brain without direct tissue contact. Toward this goal, we are experimenting with the wireless transmission of millimeter wave (MMW) energy in the 10-100 GHz frequency range, where penetration and focusing can be traded off to provide non-contact irradiation...
A Framework for piRNA Cluster Manipulation - Olovnikov, Ivan; Le Thomas, Adrien; Aravin, Alexei A.
Piwi proteins and their small-RNA partners, piwi-interacting (pi)RNA, form a natural mechanism that
prevents the deleterious activity of transposable elements in the germ line of metazoan species. The piRNA pathway relies on extended noncoding genomic regions, dubbed piRNA clusters, to produce long precursor transcripts that are subsequently processed into mature piRNAs. The large size and repetitive nature of piRNA clusters provide significant challenges for their dissection using common genetic tools. Here we describe an effective approach for manipulation of piRNA clusters using a combination of BAC recombineering
in E. coli and phiC31-mediated transgenesis in Drosophila. Although the described approach is instrumental for...
Visualization of human retinal and choroidal vascular networks with phase-variance optical coherence tomography - Kim, Dae Yu; Fingler, Jeff; Zawadzki, Robert J.; Verma, Malvika; Schwartz, Daniel M.; Werner, John S.; Fraser, Scott E.
We present in vivo noninvasive retinal and choroidal perfusion maps with phase-variance optical coherence tomography (pvOCT). We acquired a pvOCT volumetric data set of a normal subject and visualized blood circulation in the retina and the choroid. En face projection views of the retina as well as the choroid were generated from a manually segmented volumetric data set. In addition, the processed pvOCT images were compared to current standard imaging modalities used for retinal and choroidal vasculature visualization in clinical settings, including fluorescein angiography (FA) and indocyanine green angiography (ICGA).
Termite Gut Spirochetes - Breznak, John A.; Leadbetter, Jared R.
There are few habitats on earth in which spirochetes
are such prominent members of the
microbial community as in the hindgut of termites.
This was first documented over a century
ago by Joseph Leidy (Leidy, 1874-1881; Leidy,
1877), who was struck by their abundance in
hindgut contents of the eastern subterranean termite,
Termes (now Reticulitermes) flavipes. In
some termites, spirochetes account for up to 50%
of all prokaryotes in the hindgut (Paster et al.,
1996), and even casual phase contrast microscopic
observation of hindgut contents usually
reveals about a dozen different morphological
types, distinguishable on the bases of cell size,
wavelength and amplitude, or pitch (Fig. 1).
Digital Particle Image Thermometry - Dabiri, Dana; Gharib, Morteza
A computerized flow visualization technique capable of automatically
quantifying the temperature field in a two-dimensional cross section of a flow field
is described. The temperature sensors used are fast-response temperature-sensitive
micro-encapsulated liquid crystal particles. Illuminating the flow by a thin sheet
of white light, the reflected colors from the liquid-crystal particles were captured
through a 3-chip video color camera and stored onto a videotape for subsequent data
processing. The temperature flow field was obtained through an automatic color-temperature
calibration scheme in HSI rather than RGB space, thus allowing for
data processing of approximately one-third the time of RGB processing. The
technique is finally applied to the study of a...