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Caltech Authors (116,090 recursos)
Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 5,179

1. On the Simple Tensile Deformation of an Incompressible Rubber Matrix Filled with Non-Adherent Rigid Spheres of Uniform Size Distribution - Blatz, P. J.; McQuarrie, D. A.; Shen, M. C.
Two striking features revealed in a photograph (cf Figure 1) of a thin film of rubber binder highly filled with glass beads are: a) that the growth of voids around particles increases with increasing strain and b) that the preferred direction of the void growth seems to be in the direction of the applied macroscopic strain. It is obvious that the local stress field around particles in a deformed composite is not as high as it would be if the binder did not pull away from the filler particles. On the other hand, because of the high rigidity of the particles relative...

2. Time-Dependent Failure of Viscoelastic Materials Under Cyclic Loads - Knauss, W. G.
The problem of failure in viscoelastic materials under cyclic strain histories is treated theoretically by using a fracture model based on the theory of rate processes. Failure times in constant, uniaxial strain tests are compared with failure times encountered in sinusoidal strain histories. The dependence of the latter on the mean strain, the size of the strain variation and its frequency is illustrated. It is pointed out that for certain conditions a difference in the failure times in constant or cyclic strain histories may be masked entirely by statistical data scatter. Finally the failure of solid propellant fuels under cyclic loading is...

3. Fatigue Failure in Linearly Viscoelastic Masterials - Williams, M. L.; Knauss, W. G.; Wagner, F. R.
The thermodynamic approach to the fracture of linearly viscoelastic materials presented earlier is extended to include fatigue. The theoretical analysis of the growth of an internal spherical flaw due to a uniformly distributed, oscillatory input of displacement in the radial direction predicts a growth-rest type of flaw growth which depends upon the properties of the media and the loading frequency. Comparison of these results with experimental crack growth data for a pre-cracked sheet specimen subjected to an oscillatory displacement input discloses a qualitative similarity in behavior. It is, therefore, believed that the analytical model employed is representative of real flaw behavior and...

4. A state-space realization approach to set identification of biochemical kinetic parameters - Hori, Yutaka; Murray, Richard M.
This paper proposes a set-based parameter identification method for biochemical systems. The developed method identifies not a single parameter but a set of parameters that all explain time-series experimental data, enabling the systematic characterization of the uncertainty of identified parameters. Our key idea is to use a state-space realization that has the same input-output behavior as experimental data instead of the experimental data itself for the identification. This allows us to relax the originally nonlinear identification problem to an LMI feasibility problem validating the norm bound of an error system. We show that regions of parameters can be efficiently classified...

5. Compact non-invasive millimeter-wave glucose sensor - Siegel, Peter H.; Tang, Adrian; Virbila, Gabriel; Kim, Yanghyo; Chang, M. C. Frank; Pikov, Victor
The authors describe a compact non-invasive CMOS-circuit-based glucose monitor using millimeter-wave transmission for use on animal and human subjects. Using an earlier device, in vivo measurements were performed through the ear in anesthetized animals and correlated with blood glucose concentration from test strips. In addition, millimeter wave absorption through glucose-containing solutions was measured in specialized liquid transmission cells and is shown to correlate with the animal and separate in vitro data. Design and performance information on the CMOS transceiver are given.

6. Ion Rotational Distributions at Near-Threshold Photoelectron Energies - Wang, K.; Stephens, J.; McKoy, V.
Rotationally resolved photoelectron spectra can provide significant insight into the underlying dynamics of molecular photoionization. Recent advances in experimental techniques now make it possible to readily achieve rotational resolution in molecular photoelectron spectra. Here we present results of theoretical studies of rotationally resolved photoelectron spectra at low and very near-threshold energies for molecules such aa HBr, NH, NO, and CO. These studies serve to reveal the rich dynamics of quantum.state specific studies of molecular photoionization and, where poesible, to provide a robust description of key spectral features of interest in related experimental studies.

7. Multiple glacier surges observed with airborne and spaceborne interferometric synthetic aperture radar - Minchew, Brent; Simons, Mark; Hensley, Scott; Björnsson, Helgi; Pálsson, Finnur; Milillo, Pietro
Mechanical properties of glacier beds impose fundamental constraints on glacier flow across a wide range of timescales [1]. Despite their importance in governing glacier dynamics, basal mechanics are not well understood, particularly where glaciers are underlain by deformable till [2]. While some till samples have been retrieved from beneath several glaciers and tested in laboratories in order to ascertain till rheology [3, 4], limitations on clast sizes imposed by apparatus dimensions and the difficulty of understanding and reproducing subglacial environments in the lab necessitate observations of the mechanical properties of in situ tills [5]. Such observations are sparse, owing to...

8. Monolithic Mach-Zehnder Interferometer Modulator in an unmodified CMOS process - Khachaturian, Aroutin; Abiri, Behrooz; Zhou, Andy; Hajimiri, Ali
A compact monolithically integrated Mach-Zehnder Interferometer Modulator operating above 1Gbps is demonstrated in an unmodified 180nm CMOS SOI process. This 50µm long structure allows for high density integration of photonics modulators and electrical driver circuitry on a single standard CMOS chip.

9. Vector field processing on triangle meshes - de Goes, Fernando; Desbrun, Mathieu; Tong, Yiying
While scalar fields on surfaces have been staples of geometry processing, the use of tangent vector fields has steadily grown in geometry processing over the last two decades: they are crucial to encoding directions and sizing on surfaces as commonly required in tasks such as texture synthesis, non-photorealistic rendering, digital grooming, and meshing. There are, however, a variety of discrete representations of tangent vector fields on triangle meshes, and each approach offers different tradeoffs among simplicity, efficiency, and accuracy depending on the targeted application. This course reviews the three main families of discretizations used to design computational tools for vector field...

10. An extreme-scale implicit solver for complex PDEs: highly heterogeneous flow in earth's mantle - Rudi, Johann; Malossi, A. Cristiano I.; Isaac, Tobin; Stadler, Georg; Gurnis, Michael; Staar, Peter W. J.; Ineichen, Yves; Bekas, Costas; Curioni, Alessandro; Ghattas, Omar
Mantle convection is the fundamental physical process within earth's interior responsible for the thermal and geological evolution of the planet, including plate tectonics. The mantle is modeled as a viscous, incompressible, non-Newtonian fluid. The wide range of spatial scales, extreme variability and anisotropy in material properties, and severely nonlinear rheology have made global mantle convection modeling with realistic parameters prohibitive. Here we present a new implicit solver that exhibits optimal algorithmic performance and is capable of extreme scaling for hard PDE problems, such as mantle convection. To maximize accuracy and minimize runtime, the solver incorporates a number of advances, including...

11. High speed scientific data transfers using software defined networking - Newman, Harvey; Mughal, Azher; Kcira, Dorian; Legrand, Iosif; Voicu, Ramiro; Bunn, Julian
The massive data volumes acquired, simulated, processed and analyzed by globally distributed scientific collaborations continue to grow exponentially. One leading example is the LHC program, now at the start of its second three year data taking cycle, searching for new particles and interactions in a previously inaccessible range of energies, which has experienced a 70% growth in peak data transfer rates over the last 12 months alone. Other major science programs such as LSST and SKA, and other disciplines ranging from earth observation to genomics, are expected to have similar or great needs than the LHC program within the next...

12. Managing scientific data with named data networking - Fan, Chengyu; Shannigrahi, Susmit; Dibenedetto, Steve; Olschanowsky, Catherine; Papadopoulos, Christos; Newman, Harvey
Many scientific domains, such as climate science and High Energy Physics (HEP), have data management requirements that are not well supported by the IP network architecture. Named Data Networking (NDN) is a new network architecture whose service model is better aligned with the needs of data-oriented applications. NDN provides features such as best-location retrieval, caching, load sharing, and transparent failover that would otherwise be painstakingly (re-)implemented by each application using point-to-point semantics in an IP network. We present the first scientific data management application designed and implemented on top of NDN. We use this application to manage climate and HEP data...

13. Studies of Electron-Molecule Collisions on Massively Parallel Computers - Winstead, Carl; McKoy, Vincent
Electron- molecule collisions occur in a wide variety of contexts. The essential ingredients are physical conditions that permit the presence of molecules - which have dissociation energies on the order of a few electron volts or eV (1 eV = 11,600 K) - and that simultaneously permit the presence of free electrons. If these electrons are produced by ionization of neutral matter, their generation requires on the order of 5-15 eV of energy, enough to dissociate most molecules. Thus systems in which electron- molecule collisions are important are generally far from thermal equilibrium.

14. Studies of Molecular Photoionization - McKoy, Vincent; Lucchese, Robert
It is becoming increasingly clear that, due to the availability of high-resolution electron spectrometers utilizing synchrotron light sources, increasing amounts of data containing detailed dynamical information on molecular photoionization are being produced. Such data have already shown that shape and autoionizing resonances play a very important role in molecular photoionization processes. For example, these resonant processes can induce significant deviations of the vibrational branching ratios from those based on Franck-Condon factors and also lead to photoelectron asymmetry parameters which depend strongly on the final vibrational state of the ion. The availability of such data is stimulating the development and application of theoretical methods for studying molecular photoionization processes at...

15. Studies of Electron-Molecule Collisions on Massively Parallel Computers - Winstead, Carl; McKoy, Vincent
Electron-molecule collisions, particularly those leading to dissociation of molecules and hence to production of chemically reactive fragments, play an important role in the modelling of plasmas used in materials processing. The available data base of the cross sections needed in modelling such plasmas is quite fragmentary. In fact, the lack of an adequate data base of relevant cross sections for calculating plasma properties is one of the major obstacles to improved modelling and simulation of plasma processes. In this presentation we review the progress we have made in exploiting the high-performance computing provided by the Intel Delta System to obtain quantitatively useful estimates...

16. Rotationally Resolved Photoelectron Spectra at Near-Threshold Kinetic Energies - Wang, Kwanghsi; McKoy, Vincent
Rotationally resolved photoelectron spectra and their associated photoelectron angular distributions can clearly provide significant insight into the dynamics of molecular photoionization, one of the simplest of molecular fragmentation processes. Such state-resolved spectra are an obvious signature of the exchanges of energy and angular momentum between the photoelectron and molecular ion. With the exception of H2 (Pollard et al., 1982; Anderson et al., 1984; Pratt et al., 1984, 1990; O'Halloran et al. , 1987; McCormack et al., 1990) and D2 (Peatman et al., 1983; O'Halloran et al., 1989; Pratt et al., 1990a) and of higher J levels of diatomic systems such...

17. Equations of state and impact-induced shock-wave attenuation on the moon - Ahrens, Thomas J.; O'Keefe, John D.
Current equation-of-state formulations, used for finite-difference cratering flow calculations, are cast into a framework permitting comparison of peak pressures attained upon impact of a sphere, with a half-space, along the impact symmetry axis, to one-dimensional impedance match solutions. On the basis of this formulation and application of thermochemical data, the regimes of melting and vaporization are examined. For the purpose of identifying material which will, upon isentropic release from the impact-induced shock state, result in a solid just brought to its melting point, i.e., incipiently melted (IM), completely melted (CM), just brought to its boiling point, i.e., incipiently vaporized (IV),...

18. Molecules in Intense Laser Fields - Dixit, S. N.; McKoy, V.
Recent advances in tunable laser sources have stimulated a great deal of interest in the study of intense field-matter interaction physics. Whenever a molecule interacts with an intense radiation field, it can absorb multiple photons from the field and make a transition either to an excited state (excitation) or into the continuum (ionization). If the energy of an integral number of photons equals the energy difference between the initial and an excited state, the multiphoton process becomes resonant and its probability is greatly enhanced. The observation of such resonant enhanced processes requires considerably less intensity than that required for non-resonant...

19. Studies of Elastic and Electronically Inelastic Electron-Molecule Collisions - Lima, Marco A. P.; Gibson, Thomas L.; Brescansin, Luiz M.; McKoy, Vincent; Huo, Winifred M.
Cross-sections for the scattering of low-energy electrons by molecules play an important role in the modeling of swarm and plasma etching systems, gas lasers, and planetary atmospheres. In contrast to the related atomic problem, the progress to date in both theoretical and experimental studies of electron-molecule scattering cross-sections has been limited [1]. On the theoretical side, this situation is primarily due to the additional complexities arising from the nonspherical potential fields of molecular targets. Most studies of electronic excitation of molecules by low-energy electrons have hence been carried out using low-order theories. These include plane-wave theories such as the Born...

20. Electron-Nitrogen Molecule Collisions in High-Temperature Nonequilibrium Air - Hou, W. M.; McKoy, V.; Lima, M. A. P.; Gibson, T. L.
Ab initio calculation of vibrational excitation and de-excitation cross sections of N_2 by low-energy resonant electron impact have been carried out. The calculation includes initial target state in v = 0-12 and final target state in v = 0-17. The calculated cross sections are found to agree with available experimental data to within reported experimental error. Effect of target rotation has been investigated. Comparison of vibrational excitation cross sections at J = 0, 50, and 150 shows that the major effect of target rotation is to lower the resonance energy. Vibrational excitation and de-excitation rate coefficients are tabulated for electron temperatures of 1100-55,000 K. The present tabulation supersedes an earlier...

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