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Caltech Authors (99,974 recursos)
Repository of works by Caltech published authors.

Type = Article

Mostrando recursos 481 - 500 de 500

481. Stabilized lasers for advanced gravitational wave detectors - Willke, B.; Danzmann, K.; Frede, M.; King, P.; Kracht, D.; Kwee, P. K.; Puncken, O.; Savage, R. L., Jr.; Schulz, B.; Seifert, F.; Veltkamp, C.; Wagner, S.; Weßels, P.; Winkelmann, L.
Second generation gravitational wave detectors require high power lasers with more than 100 W of output power and with very low temporal and spatial fluctuations. To achieve the demanding stability levels required, low noise techniques and adequate control actuators have to be part of the high power laser design. In addition feedback control and passive noise filtering is used to reduce the fluctuations in the so-called prestabilized laser system (PSL). In this paper, we discuss the design of a 200 W PSL which is under development for the Advanced LIGO gravitational wave detector and will present the first results. The...

482. Demonstration of displacement-noise-free interferometry using bi-directional Mach–Zehnder interferometers - Sato, S.; Kokeyama, K.; Kawamura, S.; Ward, R. L.; Nishizawa, A.; Chen, Yanbei; Pai, A.; Somiya, K.
We have demonstrated displacement- and frequency-noise-free laser interferometry (DFI) by partially implementing a recently proposed optical configuration using bi-directional Mach–Zehnder interferometers (MZIs). This partial implementation, the minimum necessary to be called DFI, has confirmed the essential feature of DFI: the combination of two MZI signals can be carried out in a way that cancels the displacement noise of the mirrors and beam splitters while maintaining gravitational-wave signals. The attained maximum displacement noise suppression was 45 dB.

483. Robust Bayesian detection of unmodelled bursts - Searle, Antony C.; Sutton, Patrick J.; Tinto, Massimo; Woan, Graham
We develop a Bayesian treatment of the problem of detecting unmodelled gravitational wave bursts using the new global network of interferometric detectors. We also compare this Bayesian treatment with existing coherent methods, and demonstrate that the existing methods make implicit assumptions on the distribution of signals that make them sub-optimal for realistic signal populations.

484. Ground-based gravitational-wave detection: now and future - Whitcomb, Stanley E.
In the past three years, the first generation of large gravitational-wave interferometers has begun operation near their design sensitivities, taking up the mantle from the bar detectors that pioneered the search for the first direct detection of gravitational waves. Even as the current ground-based interferometers were reaching their design sensitivities, plans were being laid for the future. Advances in technology and lessons learned from the first generation devices have pointed the way to an order of magnitude improvement in sensitivity, as well as expanded frequency ranges and the capability to tailor the sensitivity band to address particular astrophysical sources. Advanced...

485. Transmission Electron Microscope Studies of LiNi1/3Mn1/3Co1/3O2 before and after Long-Term Aging at 70°C - Gabrisch, Heike; Yi, Tanghong; Yazami, Rachid
LiNi1/3Mn1/3Co1/3O2 is a potential cathode material for high-power applications in lithium-ion batteries. While cation ordering on a sqrt(3)×sqrt(3) R30° in-plane superlattice was proposed for the layered structure, the experimental data do not fully support this model. Here, we present a systematic electron diffraction study of LiNi1/3Mn1/3Co1/3O2 in the pristine state and after aging. Our results show that a mixture of different phases in the starting material transforms to the O3-type phase and the cubic spinel phase after aging, accompanied by an increase in the percentage of polycrystals.

486. Vibrational overtone initiated unimolecular dissociation of HOCH2OOH and HOCD2OOH: Evidence for mode selective behavior - Matthews, Jamie; Fry, Julie L.; Roehl, Coleen M.; Wennberg, Paul O.; Sinha, Amitabha
The vibrational overtone induced unimolecular dissociation of HMHP (HOCH2OOH) and HMHP-d2 (HOCD2OOH) into OH and HOCH2O (HOCD2O) fragments is investigated in the region of the 4nuOH and 5nuOH bands. The unimolecular dissociation rates in the threshold region, corresponding to the 4nuOH band, exhibit measurable differences associated with excitation of the OH stretch of the alcohol versus the peroxide functional group, with the higher energy alcohol OH stretching state exhibiting a slower dissociation rate compared to the lower energy peroxide OH stretch in both HMHP and HMHP-d2. Predictions using the Rice–Ramsperger–Kassel–Marcus theory give rates that are in reasonably good agreement with...

487. Belief propagation algorithm for computing correlation functions in finite-temperature quantum many-body systems on loopy graphs - Poulin, David; Bilgin, Ersen
Belief propagation —- a powerful heuristic method to solve inference problems involving a large number of random variables—was recently generalized to quantum theory. Like its classical counterpart, this algorithm is exact on trees when the appropriate independence conditions are met and is expected to provide reliable approximations when operated on loopy graphs. In this paper, we benchmark the performances of loopy quantum belief propagation (QBP) in the context of finite-temperature quantum many-body physics. Our results indicate that QBP provides reliable estimates of the high-temperature correlation function when the typical loop size in the graph is large. As such, it is...

488. Neurophysiological defects in temperature-sensitive paralytic mutants of Drosophila melanogaster - Siddiqi, Obaid; Benzer, Seymour
A new temperature-sensitive paralytic mutant of Drosophila, comatose, is compared behaviorally and physiologically with the previously known types, para and shi. All three have different properties with respect to kinetics of paralysis at high temperature and recovery from paralysis; com is hypersensitive to paralysis by cooling. Neurophysiological experiments indicate different mechanisms for paralysis in each of the mutants.

489. Models of earth structure inferred from neodymium and strontium isotopic abundances - Wasserburg, G. J.; DePaolo, D. J.
A simplified model of earth structure based on the Nd and Sr isotopic characteristics of oceanic and continental tholeiitic flood basalts is presented, taking into account the motion of crustal plates and a chemical balance for trace elements. The resulting structure that is inferred consists of a lower mantle that is still essentially undifferentiated, overlain by an upper mantle that is the residue of the original source from which the continents were derived.

490. Synthesis of immunoglobulin µ chain gene products precedes synthesis of light chains during B-lymphocyte development - Siden, E.; Alt, F. W.; Shinefeld, L.; Sato, V.; Baltimore, D.
Immunoglobulin (Ig) gene expression has been followed during the later stages of development of the murine fetal liver. Biosynthetic labeling and immunoprecipitation were used to isolate Ig-related polypeptides from fetal and neonatal livers. By examination of the specific immune precipitates, the earliest detectable Ig was shown to consist only of µ heavy chain. At about the time of birth, when light chain synthesis became evident, separation of surface Ig-positive cells from surface Ig-negative cells by using anti-Ig-coated dishes showed that cells lacking surface Ig (pre-B lymphocytes) synthesized only µ chains. Thus, commencement of light chain synthesis was closely coordinated with...

491. Galactic substructure and direct detection of dark matter - Kamionkowski, Marc; Koushiappas, Savvas M.
We study the effects of substructure in the Galactic halo on direct detection of dark matter, on searches for energetic neutrinos from weakly interacting massive particles (WIMP) annihilation in the Sun and Earth, and on the enhancement in the WIMP annihilation rate in the halo. Our central result is a probability distribution function (PDF) P(rho) for the local dark-matter density. This distribution must be taken into account when using null dark-matter searches to constrain the properties of dark-matter candidates. We take two approaches to calculating the PDF. The first is an analytic model that capitalizes on the scale-invariant nature of...

492. Quantum reference frames and deformed symmetries - Girelli, Florian; Poulin, David
In the context of constrained quantum mechanics, reference systems are used to construct relational observables that are invariant under the action of the symmetry group. Upon measurement of a relational observable, the reference system undergoes an unavoidable measurement “back-action” that modifies its properties. In a quantum-gravitational setting, it has been argued that such a back-action may produce effects that are described at an effective level as a form of deformed (or doubly) special relativity. We examine this possibility using a simple constrained system that has been extensively studied in the context of quantum information. While our conclusions support the idea...

493. Acidity enhances the formation of a persistent ozonide at aqueous ascorbate/ozone gas interfaces - Enami, Shinichi; Hoffmann, M. R.; Colussi, A. J.
The pulmonary epithelium, like most aerial biosurfaces, is naturally protected against atmospheric ozone (O3) by fluid films that contain ascorbic acid (AH2) and related scavengers. This mechanism of protection will fail, however, if specific copollutants redirect AH2 and O3(g) to produce species that can transduce oxidative damage to underlying tissues. Here, the possibility that the synergistic adverse health effects of atmospheric O3(g) and acidic particulate matter revealed by epidemiological studies could be mediated by hitherto unidentified species is investigated by electrospray mass spectrometry of aqueous AH2 droplets exposed to O3(g). The products of AH2 ozonolysis at the relevant air–water interface...

494. Numerical Analysis at the National Bureau of Standards - Todd, John
In 1946/47, Dr. E. U. Condon (1902–1974), the fourth director of the National Bureau of Standards, arranged for the organization of a Division of Applied Mathematics, under the leadership of Dr. John H. Curtiss. A principal objective of this division was the development of the mathematics appropriate for the automatic digital computing machines then being constructed. An account is given here of some of the activities in numerical analysis carried out by that division in its first 25 years.

495. Atomic aftereffects and the line shape of muonic x-rays - Vogel, P.
The muonic x-ray energy, by virtue of the electron screening, depends on the depletion of the electron states by Auger transitions and on the time needed for the refilling of the electron vacancies. The effect of these processes on the line shape of the muonic x rays is studied here. Equations for the electron 1s-level population and for the muonic-x-ray center of gravity are derived and applied to representative examples of medium- and high-Z muonic atoms. It is shown that the atomic aftereffects (i.e., refilling of the 1s state) result in almost full screening in wide range of atomic numbers....

496. Multiscale Analysis and Computation for the Three-Dimensional Incompressible Navier–Stokes Equations - Hou, Thomas Y.; Yang, Danping; Ran, Hongyu
In this paper, we perform a systematic multiscale analysis for the three-dimensional incompressible Navier–Stokes equations with multiscale initial data. There are two main ingredients in our multiscale method. The first one is that we reparameterize the initial data in the Fourier space into a formal two-scale structure. The second one is the use of a nested multiscale expansion together with a multiscale phase function to characterize the propagation of the small-scale solution dynamically. By using these two techniques and performing a systematic multiscale analysis, we derive a multiscale model which couples the dynamics of the small-scale subgrid problem to the...

497. Electron screening in muonic atoms - Vogel, P.
Screening corrections to the muon binding energies are computed for Pb, Tl, Ba, and O. Available methods of calculation are compared. It is shown that in a broad range of atomic charges and muon states the screening of nuclear charge by the muon is almost complete, and therefore the electron density of the Z-1 element can be used in most applications. The effect of the muon on the electron cloud and the effect of the vacancies in electron shells on the screening corrections are calculated and discussed. The degree of ionization of the electron 1s1/2 orbit is determined by a...

498. Atmospheric turbulence profiling with SLODAR using multiple adaptive optics wavefront sensors - Wang, Lianqi; Schöck, Matthias; Chanan, Gary
The slope detection and ranging (SLODAR) method recovers atmospheric turbulence profiles from time averaged spatial cross correlations of wavefront slopes measured by Shack-Hartmann wavefront sensors. The Palomar multiple guide star unit (MGSU) was set up to test tomographic multiple guide star adaptive optics and provided an ideal test bed for SLODAR turbulence altitude profiling. We present the data reduction methods and SLODAR results from MGSU observations made in 2006. Wind profiling is also performed using delayed wavefront cross correlations along with SLODAR analysis. The wind profiling analysis is shown to improve the height resolution of the SLODAR method and in...

499. A 6.0-mW 10.0-Gb/s Receiver With Switched-Capacitor Summation DFE - Emami-Neyestanak, Azita; Varzaghani, Aida; Bulchacchelli, John F.; Rylyakov, Alexander; Yang, Chih-Kong Ken; Friedman, Daniel J.
A low-power receiver with a one-tap decision feedback equalization (DFE) was fabricated in 90-nm CMOS technology. The speculative equalization is performed using switched-capacitor-based addition at the front-end sample-hold circuit. In order to further reduce the power consumption, an analog multiplexer is used in the speculation technique implementation. A quarter-rate-clocking scheme facilitates the use of low-power front-end circuitry and CMOS clock buffers. The receiver was tested over channels with different levels of ISI. The signaling rate with BER<10^-12 was significantly increased with the use of DFE for short- to medium-distance PCB traces. At 10-Gb/s data rate, the receiver consumes less than...

500. A 90 nm CMOS 16 Gb/s Transceiver for Optical Interconnects - Palermo, Samuel; Emami-Neyestanak, Azita; Horowitz, Mark
Interconnect architectures which leverage high-bandwidth optical channels offer a promising solution to address the increasing chip-to-chip I/O bandwidth demands. This paper describes a dense, high-speed, and low-power CMOS optical interconnect transceiver architecture. Vertical-cavity surface-emitting laser (VCSEL) data rate is extended for a given average current and corresponding reliability level with a four-tap current summing FIR transmitter. A low-voltage integrating and double-sampling optical receiver front-end provides adequate sensitivity in a power efficient manner by avoiding linear high-gain elements common in conventional transimpedance-amplifier (TIA) receivers. Clock recovery is performed with a dual-loop architecture which employs baud-rate phase detection and feedback interpolation to...

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