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Selected Works

2007

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Articles 1 - 30 of 30

Full-Text Articles in Physics

Growth-Temperature Optimization For Low Carrier-Density In0.75Ga0.25As-Based High Electron Mobility Transistors On Inp, Paul J. Simmonds, H. E. Beere, D. A. Ritchie, S. N. Holmes Oct 2007

Growth-Temperature Optimization For Low Carrier-Density In0.75Ga0.25As-Based High Electron Mobility Transistors On Inp, Paul J. Simmonds, H. E. Beere, D. A. Ritchie, S. N. Holmes

Paul J. Simmonds

Two-dimensional electron gases (2DEGs) were formed in undoped In0.75Al0.25As / In0.75Ga0.25As / In0.75Al0.25As quantum wells. The optimal growth temperature for this structure is 410°C, with peak 2DEG electron mobility and density values of μ = 221000 cm2/V s and n = 1.36 × 1011 cm−2 at 1.5 K. This electron mobility is equal to the highest previously published for these undoped structures but with a factor of 2 reduction in n. This has been achieved through the use of a ...


Quantum Dot Resonant Tunneling Diodes For Telecom Wavelength Single Photon Detection, H. W. Li, Paul J. Simmonds, H. E. Beere, B. E. Kardynał, D. A. Ritchie, A. J. Shields Sep 2007

Quantum Dot Resonant Tunneling Diodes For Telecom Wavelength Single Photon Detection, H. W. Li, Paul J. Simmonds, H. E. Beere, B. E. Kardynał, D. A. Ritchie, A. J. Shields

Paul J. Simmonds

Single photon detection was realized at a telecom wavelength with quantum dot resonant tunneling diodes grown on an InP substrate. The structure contains a AlAs/In0.53Ga0.47As/AlAs quantum well with InAs quantum dots grown on the top AlAs barrier. The single photon detection efficiency of the device under 1310 nm illumination was measured to be about 0.35% ± 0.07% with a dark count rate of 1.58×10-6 ns-1. This corresponds to an internal efficiency of 6.3%.


Enhanced Tunable Bragg Diffraction In Large-Pore Inverse Opals Using Dual-Frequency Liquid Crystal, Elton Graugnard, S. N. Dunham, J. S. King, D. Lorang, S. Jain, C. J. Summers Aug 2007

Enhanced Tunable Bragg Diffraction In Large-Pore Inverse Opals Using Dual-Frequency Liquid Crystal, Elton Graugnard, S. N. Dunham, J. S. King, D. Lorang, S. Jain, C. J. Summers

Elton Graugnard

Large-pore TiO2 inverse opals were fabricated by atomic layer deposition in sintered polystyrene colloidal crystal templates and infiltrated with dual-frequency liquid crystal. The optical properties of the hybrid organic/inorganic structure were characterized by reflectance measurements of the Bragg peak, the position of which was tuned using a frequency dependent applied electric field. A 6 nm blueshift was observed for frequencies less than 13 kHz and a 13 nm redshift for frequencies above 13 kHz. These results demonstrate enhanced optical tunability in three-dimensional photonic crystals and are important for the development of active photonic devices.


Quantum Dot Resonant Tunneling Diode For Telecommunication Wavelength Single Photon Detection, H. W. Li, B. E. Kardynał, P. See, A. J. Shields, P. Simmonds, H. E. Beere, D. A. Ritchie Aug 2007

Quantum Dot Resonant Tunneling Diode For Telecommunication Wavelength Single Photon Detection, H. W. Li, B. E. Kardynał, P. See, A. J. Shields, P. Simmonds, H. E. Beere, D. A. Ritchie

Paul J. Simmonds

The authors present a quantum dot (QD) based single photon detector operating at a fiber optic telecommunication wavelength. The detector is based on an AlAs/In0.53Ga0.47As/AlAs double-barrier resonant tunneling diode containing a layer of self-assembled InAs QDs grown on an InP substrate. The device shows an internal efficiency of about 6.3% with a dark count rate of 1.58 × 10−6 ns−1 for 1310 nm photons.


A Liquid Xenon Ionization Chamber In An All-Fluoropolymer Vessel, F. Leport, Andrea Pocar, L. Bartoszek, R. Devoe, P. Fierlinger, B. Flatt, G. Gratta, M. Green, T. Koffas, M. Montero Diez, R. Neilson, K. O'Sullivan, S. Waldman, J. Wodin, D. Woisard, E. Baussan, M. Breidenbach, R. Conley, W. Fairbank Jr., J. Farine, C. Hall, K. Hall, D. Hallman, C. Hargrove, J. Hodgson, S. Jeng, D. S. Leonard, D. Mackay, Y. Martin, A. Odian, L. Ounalli, A. Piepke, C. Y. Prescott, P. C. Rowson, K. Skarpaas, D. Schenker, D. Sinclair, V. Stekhanov, V. Strickland, C. Virtue, J.-L. Vuilleumier, K. Wamba, P. Weber Jul 2007

A Liquid Xenon Ionization Chamber In An All-Fluoropolymer Vessel, F. Leport, Andrea Pocar, L. Bartoszek, R. Devoe, P. Fierlinger, B. Flatt, G. Gratta, M. Green, T. Koffas, M. Montero Diez, R. Neilson, K. O'Sullivan, S. Waldman, J. Wodin, D. Woisard, E. Baussan, M. Breidenbach, R. Conley, W. Fairbank Jr., J. Farine, C. Hall, K. Hall, D. Hallman, C. Hargrove, J. Hodgson, S. Jeng, D. S. Leonard, D. Mackay, Y. Martin, A. Odian, L. Ounalli, A. Piepke, C. Y. Prescott, P. C. Rowson, K. Skarpaas, D. Schenker, D. Sinclair, V. Stekhanov, V. Strickland, C. Virtue, J.-L. Vuilleumier, K. Wamba, P. Weber

Andrea Pocar

A novel technique has been developed to build vessels for liquid xenon ionization detectors entirely out of an ultra-clean fluoropolymer. One such detector was operated inside a welded, He leak tight, all-fluoropolymer chamber. The measured energy resolution for 570 keV gamma rays is σ/E=5.1% at a drift field of 1.5 kV/cm, in line with the best values obtained for ionization only detectors run in LXe using conventional, metal vessels.


A Role For Huntingtin In Dynein/Dynactin-Mediated Vesicle Trafficking, Jennifer Ross, Juliane P. Caviston, Sheila M. Antony, Mariko Tokito, Erika L.F Holzbaur May 2007

A Role For Huntingtin In Dynein/Dynactin-Mediated Vesicle Trafficking, Jennifer Ross, Juliane P. Caviston, Sheila M. Antony, Mariko Tokito, Erika L.F Holzbaur

Jennifer Ross

Cytoplasmic dynein is a multisubunit microtubule motor complex that, together with its activator, dynactin, drives vesicular cargo toward the minus ends of microtubules. Huntingtin (Htt) is a vesicle-associated protein found in both neuronal and nonneuronal cells that is thought to be involved in vesicular transport. In this study, we demonstrate through yeast two-hybrid and affinity chromatography assays that Htt and dynein intermediate chain interact directly; endogenous Htt and dynein coimmunoprecipitate from mouse brain cytosol. Htt RNAi in HeLa cells results in Golgi disruption, similar to the effects of compromising dynein/dynactin function. In vitro studies reveal that Htt and dynein ...


Director Dynamics In Liquid-Crystal Physical Gels, Rafael Verduzco, Neal R. Scruggs, Samuel Sprunt, Peter Palffy-Muhoray, Julia A. Kornfield May 2007

Director Dynamics In Liquid-Crystal Physical Gels, Rafael Verduzco, Neal R. Scruggs, Samuel Sprunt, Peter Palffy-Muhoray, Julia A. Kornfield

Peter Palffy-Muhoray

Nematic liquid- crystal (LC) elastomers and gels have a rubbery polymer network coupled to the nematic director. While LC elastomers show a single, non- hydrodynamic relaxation mode, dynamic light- scattering studies of self- assembled liquid- crystal gels reveal orientational fluctuations that relax over a broad time scale. At short times, the relaxation dynamics exhibit hydrodynamic behavior. In contrast, the relaxation dynamics at long times are non-hydrodynamic, highly anisotropic, and increase in amplitude at small scattering angles. We argue that the slower dynamics arise from coupling between the director and the physically associated network, which prevents director orientational fluctuations from decaying ...


Parametrization Dependence Of The Energy-Momentum Tensor And The Metric, Nej Bjerrum-Bohr, Jf Donoghue, Br Holstein May 2007

Parametrization Dependence Of The Energy-Momentum Tensor And The Metric, Nej Bjerrum-Bohr, Jf Donoghue, Br Holstein

Barry R Holstein

We use results by Kirilin to comment that in general relativity the nonleading terms in the energy-momentum tensor of a particle depends on the parameterization of the gravitational field. The classical observables are parameterization independent after a change in coordinates. The quantum effects that emerge within the same calculation of the metric also depend on the parameterization and a full quantum calculation requires the inclusion of further diagrams. However, within a given parameterization the quantum effects calculated by us in a previous paper are well defined. Flaws of Kirilin’s proposed alternate metric definition are described and we explain why ...


On The Parameterization Dependence Of The Energy Momentum Tensor And The Metric, N. E. J. Bjerrum-Bohr, John Donoghue, Barry R. Holstein May 2007

On The Parameterization Dependence Of The Energy Momentum Tensor And The Metric, N. E. J. Bjerrum-Bohr, John Donoghue, Barry R. Holstein

John Donoghue

We use results by Kirilin to show that in general relativity the nonleading terms in the energy-momentum tensor of a particle depends on the parameterization of the gravitational field. While the classical metric that is calculated from this source, used to define the leading long-distance corrections to the metric, also has a parameteriztion dependence, it can be removed by a coordinate change. Thus the classical observables are parameterization independent. The quantum effects that emerge within the same calculation of the metric also depend on the parameterization and a full quantum calculation requires the inclusion of further diagrams. However, within a ...


Depleted Carbon Monoxide In Fragment C Of The Jupiter-Family Comet 73p/Schwassmann-Wachmann 3, M. A. Disanti, W. M. Anderson, G. L. Villanueva, B. P. Bonev, K. Magee-Sauer, E. L. Gibb, M. J. Mumma May 2007

Depleted Carbon Monoxide In Fragment C Of The Jupiter-Family Comet 73p/Schwassmann-Wachmann 3, M. A. Disanti, W. M. Anderson, G. L. Villanueva, B. P. Bonev, K. Magee-Sauer, E. L. Gibb, M. J. Mumma

Erika Gibb

Carbon monoxide emission was targeted in fragment C of the recently split Jupiter-family comet 73P/Schwassmann-Wachmann 3 during its 2006 apparition, using the Cryogenic Echelle Spectrograph (CSHELL) at the NASA IRTF on Mauna Kea, Hawaii. Simultaneous sounding with H2O near 4.65 μm revealed highly depleted CO, consistent with a mixing ratio of 0.5% ± 0.13%. Along with depleted CH3OH but nearly normal HCN, this may indicate that this comet formed in the inner giant planets' region or, alternatively, that it formed relatively late, after significant clearing of the protosolar nebula.


The Shape Of Galaxy Cluster Dark Matter Haloes: Systematics Of Its Imprint On Cluster Gas And Comparison To Observations, Ricardo A. Flores, Brandon Allgood, Andrey V. Kravtsov, Joel R. Primack, David A. Buote, James S. Bullock May 2007

The Shape Of Galaxy Cluster Dark Matter Haloes: Systematics Of Its Imprint On Cluster Gas And Comparison To Observations, Ricardo A. Flores, Brandon Allgood, Andrey V. Kravtsov, Joel R. Primack, David A. Buote, James S. Bullock

Ricardo Flores

We study predictions for galaxy cluster observables that can test the statistics of dark matter halo shapes expected in a flat Λ cold dark matter (CDM) universe. We present a simple analytical model for the prediction of cluster-scale X-ray observations, approximating clusters as isothermal systems in hydrostatic equilibrium, and dark matter haloes as ellipsoids with uniform axial ratios (homeoidal ellipsoids). We test the model against high-resolution, hydrodynamic cluster simulations to gauge its reliability. We find that this simple prescription does a good job of predicting cluster X-ray ellipticities compared to the simulations as long as one focuses on cluster regions ...


Warm Hcn, C2h2, And Co In The Disk Of Gv Tau, Erika Gibb, K. A. Van Brunt, S. D. Brittain, T W. Rettig May 2007

Warm Hcn, C2h2, And Co In The Disk Of Gv Tau, Erika Gibb, K. A. Van Brunt, S. D. Brittain, T W. Rettig

Erika Gibb

We present the first high-resolution, ground-based observations of HCN and C2H2 toward the T Tauri binary star system GV Tau. We detected strong absorption due to HCN ν3 and weak C2H2 [ν3 and ν2 + (ν4 + ν5)img1.gif] absorption toward the primary (GV Tau S) but not the infrared companion. We also report CO column densities and rotational temperatures, and present abundances relative to CO of HCN/CO ~ 0.6% and C2H/CO ~ 1.2% and an upper limit for CH4/CO < 0.37% toward GV Tau S. Neither HCN nor C2H2 were detected toward the infrared companion, and results ...


Soft Spheres Make More Mesophases, Mattew A. Glaser, Gregory M. Granson, Randall D. Kamien, A. Kosmrlj, Christian Santangelo, P. Ziherl May 2007

Soft Spheres Make More Mesophases, Mattew A. Glaser, Gregory M. Granson, Randall D. Kamien, A. Kosmrlj, Christian Santangelo, P. Ziherl

Christian Santangelo

We use both mean-field methods and numerical simulation to study the phase diagram of classical particles interacting with a hard core and repulsive, soft shoulder. Despite the purely repulsive and isotropic interaction, this system displays a remarkable array of aggregate phases arising from the competition between the hard-core and soft-shoulder length scales, including fluid and crystalline phases with micellar, lamellar, and inverse micellar morphology. In the limit of large shoulder width to core size, we argue that this phase diagram has a number of universal features, and classify the set of repulsive shoulders that lead to aggregation at high density ...


Prepare For Landing, Gregory A. Dilisi, Richard A. Rarick Apr 2007

Prepare For Landing, Gregory A. Dilisi, Richard A. Rarick

Gregory A. DiLisi

An ad-hoc experiment that the author constructed during a flight to measure the airplane's motion during its descent is described. The apparatus comprised a pendulum formed from a USB memory stick with a string attached, which was fixed to the airplane's window using medical tape, with a Post-it note used as a backdrop for measuring the position of the pendulum. Pictures of the pendulum were taken with a digital camera, so that the angular displacement could later be measured using a computer. From a spec sheet that lists a range of performance and flight parameters of the airplane ...


Growth By Molecular Beam Epitaxy Of Self-Assembled Inas Quantum Dots On Inalas And Ingaas Lattice-Matched To Inp, Paul J. Simmonds, H W. Li, H E. Beere, P See, A J. Shields, D A. Ritchie Apr 2007

Growth By Molecular Beam Epitaxy Of Self-Assembled Inas Quantum Dots On Inalas And Ingaas Lattice-Matched To Inp, Paul J. Simmonds, H W. Li, H E. Beere, P See, A J. Shields, D A. Ritchie

Paul J. Simmonds

The authors report the results of a detailed study of the effect of growth conditions, for molecular beam epitaxy, on the structural and optical properties of self-assembled InAs quantum dots (QDs) on In0.524Al0.476As. InAs QDs both buried in, and on top of, In0.524Al0.476As were analyzed using photoluminescence (PL) and atomic force microscopy. InAs QD morphology and peak PL emission wavelength both scale linearly with deposition thickness in monolayers (MLs). InAs deposition thickness can be used to tune QD PL wavelength by 170 nm/ML, over a range of ...


Dynamic Reorganization Of Eg5 In The Mammalian Spindle Throughout Mitosis Requires Dynein And Tpx2, Jennifer Ross, C. Fagerstrom, G. Yang, E. S. Collins, N. Ma, N. P. Ferenz, S. Balchand, P. Wadsworth, J. Titus, M. Qiu, A. Gabel Mar 2007

Dynamic Reorganization Of Eg5 In The Mammalian Spindle Throughout Mitosis Requires Dynein And Tpx2, Jennifer Ross, C. Fagerstrom, G. Yang, E. S. Collins, N. Ma, N. P. Ferenz, S. Balchand, P. Wadsworth, J. Titus, M. Qiu, A. Gabel

Jennifer Ross

Kinesin-5 is an essential mitotic motor. However, how its spatial-temporal distribution is regulated in mitosis remains poorly understood. We expressed localization and affinity purification-tagged Eg5 from a mouse bacterial artificial chromosome (this construct was called mEg5) and found its distribution to be tightly regulated throughout mitosis. Fluorescence recovery after photobleaching analysis showed rapid Eg5 turnover throughout mitosis, which cannot be accounted for by microtubule turnover. Total internal reflection fluorescence microscopy and high-resolution, single-particle tracking revealed that mEg5 punctae on both astral and midzone microtubules rapidly bind and unbind. mEg5 punctae on midzone microtubules moved transiently both toward and away from ...


The Abundance Of Carbon Dioxide Ice In The Quiescent Intracloud Medium, D. C. B. Whittet, S. S. Shenoy, E. A. Bergin, J. E. Chiar, P. A. Gerakines, E. L. Gibb, G. J. Melnick, D. A. Neufeld Jan 2007

The Abundance Of Carbon Dioxide Ice In The Quiescent Intracloud Medium, D. C. B. Whittet, S. S. Shenoy, E. A. Bergin, J. E. Chiar, P. A. Gerakines, E. L. Gibb, G. J. Melnick, D. A. Neufeld

Erika Gibb

We present new observations with the Infrared Spectrograph on board the Spitzer Space Telescope of the solid-CO2 absorption feature near 15 μm in the spectra of eight field stars behind the Taurus complex of dark clouds. Solid CO2 is detected in six lines of sight. New results are combined with previous data to investigate the correlation of CO2 column density with those of other major ice constituents (H2O and CO) and with extinction. CO2 is shown to display a "threshold extinction" effect, i.e., a minimum extinction (A0 = 4.3 ± 1.0 mag) required for detection, behavior similar to that ...


Triply-Periodic Smectic Liquid Crystals, Christian Santangelo, Randall D. Kamien Jan 2007

Triply-Periodic Smectic Liquid Crystals, Christian Santangelo, Randall D. Kamien

Christian Santangelo

Twist-grain-boundary phases in smectics are the geometrical analogs of the Abrikosov flux lattice in superconductors. At large twist angles, the nonlinear elasticity is important in evaluating their energetics. We analytically construct the height function of a π∕2 twist-grain-boundary phase in smectic-A liquid crystals, known as Schnerk’s first surface. This construction, utilizing elliptic functions, allows us to compute the energy of the structure analytically. By identifying a set of heretofore unknown defects along the pitch axis of the structure, we study the necessary topological structure of grain boundaries at other angles, concluding that there exist a set of privileged ...


Measurement Of Cp-Violating Asymmetries In The B0 --> K+K−K0 Dalitz Plot, Stefan Spanier Dec 2006

Measurement Of Cp-Violating Asymmetries In The B0 --> K+K−K0 Dalitz Plot, Stefan Spanier

stefan spanier

No abstract provided.


Dust And Atomic Gas In Dwarf Irregular Galaxies Of The M81 Group: The Sings And Things View, F. Walter, John Cannon, H. Roussel, G. Bendo, D. Calzetti, D. Dale, B. Draine, G. Helou, R. Kennicutt, G. Rieke, L. Armus, C. Engelbracht, K. Gordon, D. Hollenbach, J. Lee, A. Li, M. Meyer, J. Moustakas, E. Murphy, M. Regan, J-D. Smith, E. Brinks, W.J. Deblok, F. Bigiel, M. Thornley Dec 2006

Dust And Atomic Gas In Dwarf Irregular Galaxies Of The M81 Group: The Sings And Things View, F. Walter, John Cannon, H. Roussel, G. Bendo, D. Calzetti, D. Dale, B. Draine, G. Helou, R. Kennicutt, G. Rieke, L. Armus, C. Engelbracht, K. Gordon, D. Hollenbach, J. Lee, A. Li, M. Meyer, J. Moustakas, E. Murphy, M. Regan, J-D. Smith, E. Brinks, W.J. Deblok, F. Bigiel, M. Thornley

John Cannon

No abstract provided.


An Ultraviolet-To-Radio Broadband Spetral Atlas Of Nearby Galaxies, D. A. Dale, A. Gil De Paz, K. D. Gordon, H. M. Hanson, L. Armus, G. J. Bendo, L. Bianchi, M. Block, S. Boisser, A. Boselli, B. A. Buckalew, V. Buat, D. Burgarella, D. Calzetti, John M. Cannon, C. W. Engelbracht, G. Helou, D. J. Hollenbach, T. H. Jarett, R. C. Kennicutt, C. Leitherer, A. Li, B. F. Madore, D. C. Martin, M. J. Meyer, E. J. Murphy, M. W. Regan, H. Roussel, J-D. T. Smith, M. L. Sosey, D. A. Tilker, F. Walter Dec 2006

An Ultraviolet-To-Radio Broadband Spetral Atlas Of Nearby Galaxies, D. A. Dale, A. Gil De Paz, K. D. Gordon, H. M. Hanson, L. Armus, G. J. Bendo, L. Bianchi, M. Block, S. Boisser, A. Boselli, B. A. Buckalew, V. Buat, D. Burgarella, D. Calzetti, John M. Cannon, C. W. Engelbracht, G. Helou, D. J. Hollenbach, T. H. Jarett, R. C. Kennicutt, C. Leitherer, A. Li, B. F. Madore, D. C. Martin, M. J. Meyer, E. J. Murphy, M. W. Regan, H. Roussel, J-D. T. Smith, M. L. Sosey, D. A. Tilker, F. Walter

John Cannon

No abstract provided.


Imaging Voltage-Dependent Cell Motions With Heterodyne Mach-Zehnder Phase Microscopy, Christopher Fang-Yen, S Oh, Y Park, S Song, H S. Seung, M S. Feld Dec 2006

Imaging Voltage-Dependent Cell Motions With Heterodyne Mach-Zehnder Phase Microscopy, Christopher Fang-Yen, S Oh, Y Park, S Song, H S. Seung, M S. Feld

Christopher Fang-Yen

No abstract provided.


Tomographic Phase Microscopy, W Choi, Christopher Fang-Yen, K Badizadegan, S Oh, N Lue, R R. Dasari, M S. Feld Dec 2006

Tomographic Phase Microscopy, W Choi, Christopher Fang-Yen, K Badizadegan, S Oh, N Lue, R R. Dasari, M S. Feld

Christopher Fang-Yen

No abstract provided.


Significant Suppression Of Ferromagnetism By Hydrostatic Pressure In The Diluted Magnetic Semiconductor Sb2-Xvxte3 With X <~ 0.03, Jeffrey Dyck, T J. Mitchell, A J. Luciana, P C. Quayle, C DrašAr, P LošŤÁK Dec 2006

Significant Suppression Of Ferromagnetism By Hydrostatic Pressure In The Diluted Magnetic Semiconductor Sb2-Xvxte3 With X <~ 0.03, Jeffrey Dyck, T J. Mitchell, A J. Luciana, P C. Quayle, C DrašAr, P LošŤÁK

Jeffrey Dyck

The authors report on the hydrostatic pressure dependence of the magnetotransport properties of ferromagnetic Sb2-xVxTe3 single crystals with x=0.02—0.03. Pressure significantly increases the free hole concentration in these compounds. In turn, the Curie temperature is suppressed by roughly 40%, which goes against many models that would predict an increase in Curie temperature with increasing carrier concentration. These results indicate that the ferromagnetism in these materials is carrier mediated and that a full Ruderman-Kittel-Kasuya-Yosida model that takes into account the oscillatory nature of the indirect exchange interaction among localized spins is needed in order to explain the ...


The Low Co Content Of The Extremely Metal-Poor Galaxy I Zw 18, A. Leroy, John M. Cannon, F. Walter, A. Bolatto, A. Weiss Dec 2006

The Low Co Content Of The Extremely Metal-Poor Galaxy I Zw 18, A. Leroy, John M. Cannon, F. Walter, A. Bolatto, A. Weiss

John Cannon

No abstract provided.


Second Born Approximation And Coulomb Scattering, Br Holstein Dec 2006

Second Born Approximation And Coulomb Scattering, Br Holstein

Barry R Holstein

We examine the problem of calculating higher order contributions to the Coulomb scattering amplitude. To make contact with the well known result, it is necessary to modify the conventional definition of the scattering amplitude.


Geometric Theory Of Columnar Phases On Curved Substrates, Christian Santangelo, Vincenzo Vitelli, Randall D. Kamien, David R. Nelson Dec 2006

Geometric Theory Of Columnar Phases On Curved Substrates, Christian Santangelo, Vincenzo Vitelli, Randall D. Kamien, David R. Nelson

Christian Santangelo

We study thin self-assembled columns constrained to lie on a curved, rigid substrate. The curvature presents no local obstruction to equally spaced columns in contrast with curved crystals for which the crystalline bonds are frustrated. Instead, the vanishing compressional strain of the columns implies that their normals lie on geodesics which converge (diverge) in regions of positive (negative) Gaussian curvature, in analogy to the focusing of light rays by a lens. We show that the out of plane bending of the cylinders acts as an effective ordering field.


Modeling Innovation By A Kinetic Description Of The Patent Citation System, Gabor Csardi, Katherine J. Strandburg, Jan Tobochnik, Peter Erdi, Laszlo Zalanyi Dec 2006

Modeling Innovation By A Kinetic Description Of The Patent Citation System, Gabor Csardi, Katherine J. Strandburg, Jan Tobochnik, Peter Erdi, Laszlo Zalanyi

Katherine J. Strandburg

This paper reports results of a network theory approach to the study of the United States patent system. We model the patent citation network as a discrete time, discrete space stochastic dynamic system. From patent data we extract an attractiveness function, A(k, l), which determines the likelihood that a patent will be cited. A(k, l) shows power law aging and perferential attachment, the exponent of the latter is increasing since 1993, suggesting that patent citations are increasingly concentrated on a relatively small number of patents. In particular, our results appear consistent with an increasing patent “thicket”, in which ...


Membrane Fluctuations Around Inclusions, Christian Santangelo, Oded Farago Dec 2006

Membrane Fluctuations Around Inclusions, Christian Santangelo, Oded Farago

Christian Santangelo

The free energy of inserting a protein into a membrane is determined by considering the variation in the spectrum of thermal fluctuations in response to the presence of a rigid inclusion. Both numerically and through a simple analytical approximation, we find that the primary effect of fluctuations is to reduce the effective surface tension, hampering the insertion at low surface tension. Our results, which should also be relevant for membrane pores, suggest (in contrast to classical nucleation theory) that a finite surface tension is necessary to facilitate the opening of a pore.


Digital Elevation Accuracy And Grid Cell Size: Effects On Computed Topographic Attributes, Rob H. Erskine, Timothy R. Green Dec 2006

Digital Elevation Accuracy And Grid Cell Size: Effects On Computed Topographic Attributes, Rob H. Erskine, Timothy R. Green

Timothy R. Green

Terrain attributes are commonly used to explain the spatial variability of agronomic, pedologic, and hydrologic variables. The terrain attributes studied here (elevation, slope, aspect, and curvature) are estimated readily from digital elevation models (DEMs), but questions remain about how the accuracy and sample spacing of the elevation data affect the estimated attributes. The main objective of this study was to quantify differences in each terrain attribute due to factors affecting DEM accuracy and grid cell size. Three data sources were compared: (i) real-time kinematic global positioning system (RTKGPS); (ii) satellite-differentially corrected global positioning system (DGPS); and (iii) U.S. Geological ...