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Articles 31  60 of 135
FullText Articles in Physics
Emergence Of The Fuzzy Horizon Through Gravitational Collapse, Anand Murugan '07, Vatche Sahakian
Emergence Of The Fuzzy Horizon Through Gravitational Collapse, Anand Murugan '07, Vatche Sahakian
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For a large enough Schwarzschild black hole, the horizon is a region of space where gravitational forces are weak; yet it is also a region leading to numerous puzzles connected to stringy physics. In this work, we analyze the process of gravitational collapse and black hole formation in the context of lightcone Mtheory. We find that, as a shell of matter contracts and is about to reveal a black hole horizon, it undergoes a thermodynamic phase transition. This involves the binding of D0 branes into D2’s, and the new phase leads to large membranes of the size of the ...
Certifications Offered By Cost Estimating Organizations, Donald S. Remer, Karen M. Ahle, Kevin J. Alley, John Silny, Karen Hsin
Certifications Offered By Cost Estimating Organizations, Donald S. Remer, Karen M. Ahle, Kevin J. Alley, John Silny, Karen Hsin
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There has been an increasing trend in professional and engineering circles to place greater emphasis on official credentials. These credentials commonly come in the form of certificates – documented recognition by a professional body that an engineer or other professional has the qualifications and technical knowledge to be a practitioner in that field. These certificates are somewhat analogous to merit badges in scouting – the certification is evidence that the holder has a certain minimum level of competence in the subject area. This review will help you decide what certifications are applicable to you and the requirements to obtain a certification.
Role Of Beat Noise In Limiting The Sensitivity Of Optical Coherence Tomography, Richard C. Haskell, David Liao, Adam E. Pivonka, Tera L. Bell, Brendan R. Haberle, Barbara M. Hoeling, Daniel C. Petersen
Role Of Beat Noise In Limiting The Sensitivity Of Optical Coherence Tomography, Richard C. Haskell, David Liao, Adam E. Pivonka, Tera L. Bell, Brendan R. Haberle, Barbara M. Hoeling, Daniel C. Petersen
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The sensitivity and dynamic range of optical coherence tomography (OCT) are calculated for instruments utilizing two common interferometer configurations and detection schemes. Previous researchers recognized that the performance of dualbalanced OCT instruments is severely limited by beat noise, which is generated by incoherent light backscattered from the sample. However, beat noise has been ignored in previous calculations of Michelson OCT performance. Our measurements of instrument noise confirm the presence of beat noise even in a simple Michelson interferometer configuration with a single photodetector. Including this noise, we calculate the dynamic range as a function of OCT light source power, and ...
Erratum: The Structure Of Alkali Halide Dimers: A Critical Test Of Ionic Models And New Ab Initio Results, T. Törring, S. Biermann, J. Hoeft, Richard J. Mawhorter, Robert J. Cave, C. Szemenyei
Erratum: The Structure Of Alkali Halide Dimers: A Critical Test Of Ionic Models And New Ab Initio Results, T. Törring, S. Biermann, J. Hoeft, Richard J. Mawhorter, Robert J. Cave, C. Szemenyei
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It has come to our attention that some of the ab initio results presented are incorrect due to errors in the Cs and C1 basis sets, and a small error in the binding energy of Rb2F2. The corrected results are presented below for the species that were affected, modifying the results in Table III of the original paper. Only those values which are different from the results of the original Table III are included. Note that some of these results are used for comparison with the ionic models in later tables. In addition, some HF data quoted in Tables V ...
Transverse Priority Phase Sensitive Optical Coherence Tomography, Jeff Fingler, Jon Williams, Zahid Yaqoob, Changhuei Yang, Richard C. Haskell, Scott E. Fraser
Transverse Priority Phase Sensitive Optical Coherence Tomography, Jeff Fingler, Jon Williams, Zahid Yaqoob, Changhuei Yang, Richard C. Haskell, Scott E. Fraser
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A variation on the standard time domain optical coherence tomography (TDOCT) system is presented. Using an inexpensive piezoelectric stack to modulate the reference mirror position, the amplitude and phase of the sample reflection is determined without scanning. With the primary scan in the transverse direction, en face and Bscan OCT images can be readily produced with phase information. This project plans to use the dynamic phase information to add an extra level of contrast to the images, based on the motion of the scatterers.
Hairy Strings, Vatche Sahakian
Hairy Strings, Vatche Sahakian
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Zero modes of the worldsheet spinors of a closed string can source higher order moments of the bulk supergravity fields. In this work, we analyze various configurations of closed strings focusing on the imprints of the quantized spinor vacuum expectation values onto the tails of bulk fields. We identify supersymmetric arrangements for which all multipole charges vanish; while for others, we find that one is left with NeveuSchwarz–NeveuSchwarz, and RamondRamond dipole and quadrupole moments. Our analysis is exhaustive with respect to all the bosonic fields of the bulk and to all higher order moments. We comment on the relevance ...
The Motion Of A Thin Liquid Film Driven By Surfactant And Gravity, Michael Shearer, Rachel Levy
The Motion Of A Thin Liquid Film Driven By Surfactant And Gravity, Michael Shearer, Rachel Levy
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We investigate wave solutions of a lubrication model for surfactantdriven flow of a thin liquid film down an inclined plane. We model the flow in one space dimension with a system of nonlinear PDEs of mixed hyperbolicparabolic type in which the effects of capillarity and surface diffusion are neglected. Numerical solutions reveal distinct patterns of waves that are described analytically by combinations of traveling waves, some with jumps in height and surfactant concentration gradient. The various waves and combinations are strikingly different from what is observed in the case of flow on a horizontal plane. Jump conditions admit new shock ...
Using Ultrasonic Atomization To Produce An Aerosol Of MicronScale Particles, Thomas D. Donnelly, J. Hogan '03, A. Mugler '04, M. Schubmehl '02, N. Schommer '04, Andrew J. Bernoff, S. Dasnurkar, T. Ditmire
Using Ultrasonic Atomization To Produce An Aerosol Of MicronScale Particles, Thomas D. Donnelly, J. Hogan '03, A. Mugler '04, M. Schubmehl '02, N. Schommer '04, Andrew J. Bernoff, S. Dasnurkar, T. Ditmire
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A device that uses ultrasonic atomization of a liquid to produce an aerosol of micronscale droplets is described. This device represents a new approach to producing targets relevant to laserdriven fusion studies, and to rare studies of nonlinear optics in which wavelengthscale targets are irradiated. The device has also made possible tests of fluid dynamics models in a novel phase space. The distribution of droplet sizes produced by the device and the threshold power required for droplet production are shown to follow scaling laws predicted by fluid dynamics.
Harmonic Generation In Thin Films And Multilayers, William S. Kolthammer '04, Dustin Barnard '03, Nicole Carson, Aaron D. Edens '00, Nathan A. Miller '01, Peter N. Saeta
Harmonic Generation In Thin Films And Multilayers, William S. Kolthammer '04, Dustin Barnard '03, Nicole Carson, Aaron D. Edens '00, Nathan A. Miller '01, Peter N. Saeta
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A general method for computing harmonic generation in reflection and transmission from planar nonmagnetic multilayer structures is described. The method assumes plane waves and treats harmonic generation in the parametric approximation. The method is applied in studying the second and thirdharmonic generation properties of thin crystal silicon layers surrounded by thermal oxide. Most independent components of the nonlinear susceptibility tensor have unique signatures with silicon layer thickness d, allowing their strength to be determined in principle by measuring harmonic generation as a function of d. Surface and bulk contributions to thirdharmonic generation are cleanly distinguished, with the bulk signal dominating ...
XRay Generation From Metal Targets Coated With WavelengthScale Spheres, D. R. Symes, H. A. Sumeruk, I. V. Churina, Thomas D. Donnelly, J. Landry, T. Ditmire
XRay Generation From Metal Targets Coated With WavelengthScale Spheres, D. R. Symes, H. A. Sumeruk, I. V. Churina, Thomas D. Donnelly, J. Landry, T. Ditmire
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Xray yield measurements from targets coated with wavelengthscale spheres are compared with measurements from polished targets. Evidence for a hotter resonant electron temperature due to field enhancements from Mie resonances in the spheres is investigated.
Selectron Mass Reconstruction And The Resolution Of The Linear Collider Detector, Sharon J. Gerbode, Heath Holguin, Troy Lau, Paul Mooser, Adam Pearlstein, Joe Rose, Bruce Schumm
Selectron Mass Reconstruction And The Resolution Of The Linear Collider Detector, Sharon J. Gerbode, Heath Holguin, Troy Lau, Paul Mooser, Adam Pearlstein, Joe Rose, Bruce Schumm
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We have used ISAJET and the JAS LCD fast simulation to explore the precision of Snowmass Point SPS1a selectron mass reconstruction for the Silicon Detector concept. Simulating collisions at E_cm = 1 TeV, we have found that most of the information constraining the selectron mass is carried in the forward (cos(theta) > 0.8) region. We have also found that, for a beam energy spread of 1% (conventional RF design), detector resolution limitations compromise the selectron mass reconstruction only in the forward region. However, for a beam energy spread of less than 0.2% (superconducting RF design), the detector resolution compromises ...
On The Polarization Of Closed Strings By RamondRamond Fluxes, Vatche Sahakian
On The Polarization Of Closed Strings By RamondRamond Fluxes, Vatche Sahakian
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In the GreenSchwarz formalism, the closed string worldsheet of the IIB theory couples to RamondRamond (RR) fluxes through spinor bilinears. We study the effect of such fluxes by analyzing the supersymmetry transformation of the worldsheet in general backgrounds. We show that, in the presence RR fields, the closed string can get `polarized', as the spinors acquire nonzero vevs in directions correlating with the orientation of closeby Dbranes. Reversing the argument, this may allow for worldsheet configurations—with nontrivial spinor structure—that source RR moments.
Immunogold Labeling To Enhance Contrast In Optical Coherence Microscopy Of Tissue Engineered Corneal Constructs, Chris B. Raub, Elizabeth J. Orwin, Richard C. Haskell
Immunogold Labeling To Enhance Contrast In Optical Coherence Microscopy Of Tissue Engineered Corneal Constructs, Chris B. Raub, Elizabeth J. Orwin, Richard C. Haskell
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Our lab has used an optical coherence microscope (OCM) to assess both the structure of tissueengineered corneal constructs and their transparency. Currently, we are not able to resolve cells versus collagen matrix material in the images produced. We would like to distinguish cells in order to determine if they are viable while growing in culture and also if they are significantly contributing to the light scattering in the tissue. In order to do this, we are currently investigating the use of immunogold labeling. Gold nanoparticles are high scatterers and can create contrast in images. We have conjugated gold nanoparticles to ...
Visualizing Early Frog Development With MotionSensitive 3D Optical Coherence Microscopy, Richard C. Haskell, Mary E. Williams, Daniel C. Petersen, Barbara M. Hoeling, Andrew J. Schile, J. D. Pennington, M. G. Seetin, J. M. Castelaz, Scott E. Fraser, Cyrus Papan, Hongwu Ren, Johannes F. De Boer, Zhongping Chen
Visualizing Early Frog Development With MotionSensitive 3D Optical Coherence Microscopy, Richard C. Haskell, Mary E. Williams, Daniel C. Petersen, Barbara M. Hoeling, Andrew J. Schile, J. D. Pennington, M. G. Seetin, J. M. Castelaz, Scott E. Fraser, Cyrus Papan, Hongwu Ren, Johannes F. De Boer, Zhongping Chen
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A motionsensitive enfacescanning 3D optical coherence microscope (OCM) has been designed and constructed to study critical events in the early development of plants and animals. We describe the OCM instrument and present timelapse movies of frog gastrulation, an early developmental event in which three distinct tissue layers are established that later give rise to all major organ systems. OCM images constructed with fringeamplitude data show the mesendoderm migrating up along the blastocoel roof, thus forming the inner two tissue layers. Motionsigma data, measuring the random motion of scatterers, is used to construct complementary images that indicate the presence of Brownian ...
Femtosecond Spectrotemporal MagnetoOptics, J.Y. Bigot, L. Guidoni, E. Beaurepaire, Peter N. Saeta
Femtosecond Spectrotemporal MagnetoOptics, J.Y. Bigot, L. Guidoni, E. Beaurepaire, Peter N. Saeta
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A new method to measure and analyze the time and spectrally resolved polarimetric response of magnetic materials is presented. It allows us to study the ultrafast magnetization dynamics of a CoPt_{3} ferromagnetic film. The analysis of the pumpinduced rotation and ellipticity detected by a broad spectrum probe beam shows that magnetooptical signals predominantly reflect the spin dynamics in ferromagnets.
An Experimental Study Of MicronScale Droplet Aerosols Produced Via Ultrasonic Atomization, Thomas D. Donnelly, J. Hogan '03, A. Mugler '04, N. Schommer '04, M. Schubmehl '02, Andrew J. Bernoff, B. Forrest '02
An Experimental Study Of MicronScale Droplet Aerosols Produced Via Ultrasonic Atomization, Thomas D. Donnelly, J. Hogan '03, A. Mugler '04, N. Schommer '04, M. Schubmehl '02, Andrew J. Bernoff, B. Forrest '02
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In the last 10 years, laserdriven fusion experiments performed on atomic clusters of deuterium have shown a surprisingly high neutron yield per joule of input laser energy. Results indicate that the optimal cluster size for maximizing fusion events should be in the 0.01–μm diameter range, but an appropriate source of droplets of this size does not exist. In an attempt to meet this need, we use ultrasonic atomization to generate micronscale droplet aerosols of high average density, and we have developed and refined a reliable droplet sizing technique based on Mie scattering. Harmonic excitation of the fluid ...
Double Excitations Within TimeDependent Density Functional Theory Linear Response, Neepa T. Maitra, Fan Zhang, Robert J. Cave, Kieron Burke
Double Excitations Within TimeDependent Density Functional Theory Linear Response, Neepa T. Maitra, Fan Zhang, Robert J. Cave, Kieron Burke
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Within the adiabatic approximation, timedependent density functional theory yields only single excitations. Near states of double excitation character, the exact exchange–correlation kernel has a strong dependence on frequency. We derive the exact frequencydependent kernel when a double excitation mixes with a single excitation, well separated from the other excitations, in the limit that the electron–electron interaction is weak. Building on this, we construct a nonempirical approximation for the general case, and illustrate our results on a simple model.
Closed Strings In RamondRamond Backgrounds, Vatche Sahakian
Closed Strings In RamondRamond Backgrounds, Vatche Sahakian
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We write the IIB GreenSchwarz action in certain general classes of curved backgrounds threaded with RamondRamond fluxes. The fixing of the kappa symmetry in the lightcone gauge and the use of supergravity Bianchi identities simplify the task. We find an expression that truncates to quartic order in the spacetime spinors and relays interesting information about the vacuum structure of the worldsheet theory. The results are particularly useful in exploring integrable string dynamics in the context of the holographic duality.
Limits To Performance Improvement Provided By Balanced Interferometers And Balanced Detection In Oct/Ocm Instruments, David Liao, Adam E. Pivonka, Brendan R. Haberle, Daniel C. Petersen, Barbara M. Hoeling, Richard C. Haskell
Limits To Performance Improvement Provided By Balanced Interferometers And Balanced Detection In Oct/Ocm Instruments, David Liao, Adam E. Pivonka, Brendan R. Haberle, Daniel C. Petersen, Barbara M. Hoeling, Richard C. Haskell
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We compare the dynamic range of OCT/OCM instruments configured with unbalanced interferometers, e.g., Michelson interferometers, with that of instruments utilizing balanced interferometers and balanced photodetection. We define the dynamic range (DR) as the ratio of the maximum fringe amplitude achieved with a highly reflecting surface to the rootmeansquare (rms) noise. Balanced systems achieve a dynamic range 2.5 times higher than that of a Michelson interferometer, enabling an image acquisition speed roughly 6 times faster. This maximum improvement occurs at light source powers of a few milliwatts. At light source powers higher than 30 mW, the advantage in ...
Blowup And Dissipation In A CriticalCase Unstable Thin Film Equation, Thomas P. Witelski, Andrew J. Bernoff, Andrea L. Bertozzi
Blowup And Dissipation In A CriticalCase Unstable Thin Film Equation, Thomas P. Witelski, Andrew J. Bernoff, Andrea L. Bertozzi
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We study the dynamics of dissipation and blowup in a criticalcase unstable thin film equation. The governing equation is a nonlinear fourthorder degenerate parabolic PDE derived from a generalized model for lubrication flows of thin viscous fluid layers on solid surfaces. There is a critical mass for blowup and a rich set of dynamics including families of similarity solutions for finitetime blowup and infinitetime spreading. The structure and stability of the steadystates and the compactlysupported similarity solutions is studied.
Holography With RamondRamond Fluxes, Vatche Sahakian
Holography With RamondRamond Fluxes, Vatche Sahakian
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Starting from the nonlinear sigma model of the IIB string in the lightcone gauge, we analyze the role of RR fluxes in Holography. We find that the worldsheet theory of states with only left or right moving modes does not see the presence of RR fields threading a geometry. We use this significant simplification to compute part of the strong coupling spectrum of the two dimensional NCOS theory. We also reproduce the action of a closed string in a PPwave background using this general formalism; and we argue for various strategies to find new systems where the closed string theory ...
Breakdown Of The Slowly Varying Amplitude Approximation: Generation Of Backward Traveling Second Harmonic Light, J. Z. Sanborn '01, C. Hellings '02, Thomas D. Donnelly
Breakdown Of The Slowly Varying Amplitude Approximation: Generation Of Backward Traveling Second Harmonic Light, J. Z. Sanborn '01, C. Hellings '02, Thomas D. Donnelly
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By numerically solving the nonlinear field equations, we simulate secondharmonic generation by laser pulses within a nonlinear medium without making the usual slowlyvaryingamplitude approximation, an approximation which may fail when laser pulses of moderate intensity or ultrashort duration are used to drive a nonlinear process. Under these conditions we show that a backwardtraveling, secondharmonic wave is created, and that the magnitude of this wave is indicative of the breakdown of the slowlyvaryingamplitude approximation. Conditions necessary for experimental detection of this wave are discussed.
Nonlinear Dynamics Of ModeLocking Optical Fiber Ring Lasers, Kristin M. Spaulding, Darryl H. Yong, Arnold D. Kim, J Nathan Kutz
Nonlinear Dynamics Of ModeLocking Optical Fiber Ring Lasers, Kristin M. Spaulding, Darryl H. Yong, Arnold D. Kim, J Nathan Kutz
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We consider a model of a modelocked fiber ring laser for which the evolution of a propagating pulse in a birefringent optical fiber is periodically perturbed by rotation of the polarization state owing to the presence of a passive polarizer. The stable modes of operation of this laser that correspond to pulse trains with uniform amplitudes are fully classified. Four parameters, i.e., polarization, phase, amplitude, and chirp, are essential for an understanding of the resultant pulsetrain uniformity. A reduced set of four coupled nonlinear differential equations that describe the leadingorder pulse dynamics is found by use of the variational ...
Women In Physics In The United States, Megan Urry, Sheila Tobias, Kim Budil, Howard Georgi, Kristine Lang, Dongqi Li, Laurie Mcneil, Peter N. Saeta, Jennifer Sokoloski, Sharon Stephenson, Aparna Venkatesan, Yevgeniya Zastavker
Women In Physics In The United States, Megan Urry, Sheila Tobias, Kim Budil, Howard Georgi, Kristine Lang, Dongqi Li, Laurie Mcneil, Peter N. Saeta, Jennifer Sokoloski, Sharon Stephenson, Aparna Venkatesan, Yevgeniya Zastavker
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Presents an overview of the status of women in physics in the U.S. Underrepresentation of women; Highlights of the report 'Women in Physics, 2000'; Efforts to increase the number of women in the profession; Issues for women activists.
The Large M Limit Of NonCommutative Open Strings At Strong Coupling, Vatche Sahakian
The Large M Limit Of NonCommutative Open Strings At Strong Coupling, Vatche Sahakian
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Twodimensional NonCommutative Open String (NCOS) theory, welldefined perturbatively, may also be studied at strong coupling and for large Dstring charge by making use of the Holographic duality. We analyze the zero mode dynamics of a closed string in the appropriate background geometry and map the results onto a sector of strongly coupled NCOS dynamics. We find an elaborate classical picture that shares qualitative similarities with the SL(2,R) WZW model. In the quantum problem, we compute propagators and part of the energy spectrum of the theory; the latter involves interesting variations in the density of states as a function ...
Scroll Waves In The Presence Of Slowly Varying Anisotropy With Application To The Heart, S. Setayeshgar, Andrew J. Bernoff
Scroll Waves In The Presence Of Slowly Varying Anisotropy With Application To The Heart, S. Setayeshgar, Andrew J. Bernoff
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We consider the dynamics of scroll waves in the presence of rotating anisotropy, a model of the left ventricle of the heart in which the orientation of fibers in successive layers of tissue rotates. By choosing a coordinate system aligned with the fiber rotation and studying the phase dynamics of a straight but twisted scroll wave, we derive a Burgers’ equation with forcing associated with the fiber rotation rate. We present asymptotic solutions for scroll twist, verified by numerics, using a realistic fiber distribution profile. We make connection with earlier numerical and analytical work on scroll dynamics.
Distinguishing Surface And Bulk Contributions To ThirdHarmonic Generation In Silicon, Peter N. Saeta, Nathan A. Miller '01
Distinguishing Surface And Bulk Contributions To ThirdHarmonic Generation In Silicon, Peter N. Saeta, Nathan A. Miller '01
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We report measurements of thirdharmonic generation from ultrathin crystalline silicon layers of gradually varying thickness. Both the angular and thickness dependence of the thirdharmonic light generated in transmission at normal incidence are consistent with negligible surface contribution to thirdharmonic generation in silicon, even under tight focusing. This work illustrates a method for distinguishing surface and bulk contributions to harmonic generation.
Transformation Of Statistics In Fractional Quantum Hall Systems, John J. Quinn, Arkadiusz Wojs, Jennifer J. Quinn, Arthur T. Benjamin
Transformation Of Statistics In Fractional Quantum Hall Systems, John J. Quinn, Arkadiusz Wojs, Jennifer J. Quinn, Arthur T. Benjamin
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A Fermion to Boson transformation is accomplished by attaching to each Fermion a tube carrying a single quantum of flux oriented opposite to the applied magnetic field. When the mean field approximation is made in Haldane’s spherical geometry, the Fermion angular momentum l_{F} is replaced by l_{B }=l_{F} − 1/2 (N −1). The set of allowed total angular momentum multiplets is identical in the two different pictures. The Fermion and Boson energy spectra in the presence of many body interactions are identical only if the pseudopotential V (interaction energy as a function of pair angular momentum ...
Transcribing Spacetime Data Into Matrices, Vatche Sahakian
Transcribing Spacetime Data Into Matrices, Vatche Sahakian
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In certain supergravity backgrounds, D0 branes may polarize into higher dimensional Dp branes. We study this phenomenon in some generality from the perspective of a local inertial observer and explore polarization effects resulting from tidallike forces. We find D2 brane droplets made of D0 branes at an extremum of the BornInfeld action even in scenarios where the RR fields may be zero. These solutions lead us to a local formulation of the UVIR correspondence. A holographic Planck scale bound on the number of D0 branes plays an important role in the analysis. We focus on the impact of higher order ...
On D0 Brane Polarization By Tidal Forces, Vatche Sahakian
On D0 Brane Polarization By Tidal Forces, Vatche Sahakian
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Gravitational tidal forces may induce polarization of D0branes, in analogy to the same effects arising in the context of constant background gauge fields. Such phenomena can teach us about the correspondence between smooth curved spacetime and its underlying noncommutative structure. However, unlike polarization by gauge fields, the gravitational counterpart involves concerns regarding the classical stability of the corresponding polarized states. In this work, we study this issue with respect to the solutions presented in hepth0010237 and find that they are classically unstable. The instability however appears with intricate features with all but a few decay channels being lifted. Through a ...