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Articles 1  30 of 2588
FullText Articles in Physics
ViscoElastic Properties Of Duct Tape, Ashley Brown, Ulrich Zurcher
ViscoElastic Properties Of Duct Tape, Ashley Brown, Ulrich Zurcher
Ulrich Zurcher
A simple experiment for determining the nonlinear stress–strain relation of duct tape is described. After weights are added and subsequently removed, the tape does not return to its original state and is no longer taut. The tape exhibits hysteresis, which implies the loss of work during the cyclical process. The exponent describing the nonlinearity is related to the fractional work loss.
Torque Around The Center Of Mass: Dynamic Stability During Quadrupedal Arboreal Locomotion In The Siberian Chipmunk (Tamias Sibiricus), Andrew R. Lammers, Ulrich Zurcher
Torque Around The Center Of Mass: Dynamic Stability During Quadrupedal Arboreal Locomotion In The Siberian Chipmunk (Tamias Sibiricus), Andrew R. Lammers, Ulrich Zurcher
Ulrich Zurcher
When animals travel on tree branches, avoiding falls is of paramount importance. Animals swiftly running on a narrow branch must rely on movement to create stability rather than on static methods. We examined how Siberian chipmunks (Tamias sibiricus) remain stable while running on a narrow tree branch trackway. We examined the pitch, yaw, and rolling torques around the center of mass, and hypothesized that within a stride, any angular impulse (torque during step time) acting on the center of mass would be canceled out by an equal and opposite angular impulse. Three chipmunks were videotaped while running on a 2 ...
Thermal Fluctuations In Systems With Continuous Symmetry, Ulrich Zürcher
Thermal Fluctuations In Systems With Continuous Symmetry, Ulrich Zürcher
Ulrich Zurcher
We investigate relaxation and thermal fluctuations in systems with continuous symmetry in arbitrary spatial dimensions. For the scalar order parameter ζ(r, t) with r∈ℛd, the deterministic relaxation is caused by hydrodynamic modes η∂ζ(r, t)/∂t= K∇2ζ(r, t). For a finite volume V, we expand the scalar field in a discrete Fourier series and then we study the behavior in the limit V→∞. We find that the second moment is well defined for dimensions d≥3, while it diverges for d=1, 2. Furthermore, we show that for d<4, the decay of the scalar field does not define an "effective" relaxation time. For dimensions d<4, these two properties suggest scaleinvariant properties of the scalar field in the limit V→∞. We show that thermal fluctuations are described by fractional Brownian motion for d ≤ 3 and by ordinary Brownian motion for d ≥ 4. The spectral density of the stochastic force follows 1/f for d=1 and d=2, for d=3, and "white noise," f0 for d≥4. We find explicit representation of the equilibrium distribution of the conserved scalar field. For d≥4 it is a Gaussian distribution, while for d=1 and d=2, it is the Cauchy distribution.
Thermally Activated Escape Over Fluctuating Barriers, Ulrich Zürcher, Charles R. Doering
Thermally Activated Escape Over Fluctuating Barriers, Ulrich Zürcher, Charles R. Doering
Ulrich Zurcher
We investigate the thermally activated escape of a Brownian particle over a potential barrier whose height fluctuates with a rate α between the values E+ and E−. We are mainly interested in the lowtemperature behavior where E+/T≫E−/T. We calculate the mean exit time as a function of the rate of the barrier fluctuations for the piecewise linear and the piecewise constant barrier, τ=τ(α). For the piecewise constant potential we find three different regimes: τ∼τ+ for α<τ−1+=exp(E+/T), τ∼2τ− for α>τ−1−=exp(E−/T), and τ∼α−1 for τ−1+<α<τ−1−. The mean exit time for the piecewise linear potential has a different behavior for fast barrier fluctuations, α>τ−1−; τ(α) is a ...
Scaling Behavior Of Fluctuations In Systems With Continuous Symmetry, Ulrich Zürcher
Scaling Behavior Of Fluctuations In Systems With Continuous Symmetry, Ulrich Zürcher
Ulrich Zurcher
In nematic liquid crystals, director fluctuations correpond to the dynamical mode that is critical for all temperatures in zero external fields. The Hurst exponent characterizes the temporal behavior of the mean square displacement of director fluctuations, 〈[δn(r,t)δn(r,0)]2〉∼t2H. We find H=1/2 in finite fields and H=3/4 in zero field. This result differs from that of Zhang et al. [Phys. Rev. Lett. 70, 1834 (1993)] who find a Hurst exponent that varies continuously from H≃1 in zero field to H≃1/2 in moderate fields.
Radial Motion In A Central Potential For Singular Mass Densities, Ulrich Zürcher, Miron Kaufman
Radial Motion In A Central Potential For Singular Mass Densities, Ulrich Zürcher, Miron Kaufman
Ulrich Zurcher
We study the radial motion of an object in the gravitational field produced by an isotropic mass density that is singular at the origin. This problem applies to elliptical galaxies and can be used to illustrate motion in a central field appropriate for an intermediatelevel mechanics course.
QuantumMechanical Harmonic Chain Attached To Heat Baths Ii: Nonequilibrium Properties, Ulrich Zürcher, Peter Talkner
QuantumMechanical Harmonic Chain Attached To Heat Baths Ii: Nonequilibrium Properties, Ulrich Zürcher, Peter Talkner
Ulrich Zurcher
We study nonequilibrium properties of a onedimensional harmonic chain to whose ends independent heat baths are attached which are kept at different temperatures. Using the quantum Langevin equation approach, we determine the stationary nonequilibrium state for arbitrary temperatures and coupling strength to the heat baths. This allows us to discuss several typical nonequilibrium properties. We find that the heat flux through the chain is finite as the length of the chain goes to infinity, i.e., we recover the wellknown fact that the lattice thermal conductivity of the perfect harmonic chain is infinite. In the quantal case, the heat flux ...
QuantumMechanical Harmonic Chain Attached To Heat Baths I: Equilibrium Properties, Ulrich Zürcher, Peter Talkner
QuantumMechanical Harmonic Chain Attached To Heat Baths I: Equilibrium Properties, Ulrich Zürcher, Peter Talkner
Ulrich Zurcher
Starting from quantum Langevin equations for operators we study thermal properties of a onedimensional harmonic chain to whose ends independent heat baths are attached. In this paper, we mainly discuss the thermal equilibrium state that the chain eventually approaches if the heat baths are at equal temperatures. In the classical limit, this state is determined by the Gibbs ensemble of the free chain, whereas in the quantal case, this is only true if the strength of coupling between chain and heat baths is made infinitely small. We find that corrections for finite coupling strength are appreciable only in boundary layers ...
Geometric Constructions For Image Formation By A Converging Lens, Ulrich Zürcher
Geometric Constructions For Image Formation By A Converging Lens, Ulrich Zürcher
Ulrich Zurcher
Light rays emerge from an object in all directions. In introductory texts, three 'special' rays are selected to draw the image produced by lenses and mirrors. This presentation may suggest to students that these three rays are necessary for the formation of an image. We discuss that the three rays attain their 'special status' from the geometric solution of the equation of a hyperbola x−1 + y−1 = c−1 (mirror/lens equation). The material is suitable for use in introductory courses for science majors.
Electrostatics At The Molecular Level, Ulrich Zurcher
Electrostatics At The Molecular Level, Ulrich Zurcher
Ulrich Zurcher
In molecular systems, positive and negative charges are separated, making them ideal systems to examine electrostatic interactions. The attractive force between positive and negative charges is balanced by repulsive ‘forces’ that are quantummechanical in origin. We introduce an ‘effective’ potential energy that captures the repulsion; it allows us to obtain fairly accurate estimates of the bonding properties of molecular systems. We use units (e.g., kcal mol–1 for energy) that emphasize the relevance of electrostatics to macroscopic behavior.
Comment On A Critique Of The Instantaneous Normal Mode (Inm) Approach To Diffusion, T. Keyes, Wu Xiong Li, Ulrich Zurcher
Comment On A Critique Of The Instantaneous Normal Mode (Inm) Approach To Diffusion, T. Keyes, Wu Xiong Li, Ulrich Zurcher
Ulrich Zurcher
A critique of the instantaneous normal mode (INM) theory of diffusion by Gezelter, Rabani, and Berne (GRB) [J. Chem. Phys. 107, 4618 (1997)] is analyzed. GRB assert that imaginaryfrequency INM are corrupted with modes unrelated to barrier crossing, that proposals for removing such nondiffusive (ND) modes are inadequate, and thus that INM cannot be used to predict the selfdiffusion constant, D. In rebuttal it is argued that LennardJones, the system studied by GRB, is anamolously rich in ND modes. INM in molecular liquids are shown to behave as excellent indicators of barrier crossing. Even in LJ NDINM, while plentiful, do ...
An Instantaneous Normal Mode Description Of Relaxation In Supercooled Liquids, T. Keyes, G. V. Vijayadamodar, Ulrich Zurcher
An Instantaneous Normal Mode Description Of Relaxation In Supercooled Liquids, T. Keyes, G. V. Vijayadamodar, Ulrich Zurcher
Ulrich Zurcher
Relaxation in supercooled liquids is formulated from the instantaneous normal modes (INM) point of view. The frequency and temperature dependence of the unstable, imaginary frequency lobe of the INM density of states, ⟨ρu(ω,T)⟩ (for simplicity we write ω instead of iω), is investigated and characterized over a broad temperature range, 10⩾T⩾0.42, in the unit density LennardJones liquid. INM theories of diffusion invoke Imω modes descriptive of barrier crossing, but not all imaginary frequency modes fall into this category. There exists a cutoff frequency ωc such that modes with ω<ωc correspond to “shoulder potentials,” whereas the potential profiles include barriercrossing double wells for ω>ωc. Given that only modes with ...
Anharmonic Potentials In Supercooled Liquids: The SoftPotential Model, Ulrich Zürcher, T. Keyes
Anharmonic Potentials In Supercooled Liquids: The SoftPotential Model, Ulrich Zürcher, T. Keyes
Ulrich Zurcher
Instantaneous normal modes (INM) are the harmonic approximation to liquid dynamics. This is an extension of the phonon description of lattice dynamics, in which case Bloch's theorem shows that all modes are extended. Longrange order is destroyed in liquids and glasses, and the INM spectrum has contributions from both extended and localized modes. We use the softpotential mode to describe localized modes. This model is a hightemperature extension of the standard twolevelsystem model for glasses. The equilibrium position of any atom in the liquid has only temporary character, and relaxation processes in the liquid are associated with particles hopping ...
Dephasing Processes In Glasses With Strong Strain Interactions, Ulrich Zürcher, R. Silbey
Dephasing Processes In Glasses With Strong Strain Interactions, Ulrich Zürcher, R. Silbey
Ulrich Zurcher
Spectral diffusion decay is calculated for a glass modeled by two level systems which are strongly coupled to phonons. The spinphonon interaction induces an effective spinspin interaction which dominates the energy scale. We show that spectral diffusion is a property of macroscopic local fields which fluctuate on time scales that are much longer than the spinphonon relaxation time T1. We assume for the spectral diffusion a Gaussian distribution and derive a selfconsistent equation for its variance which is nonlocal in time. At high temperatures, the variance grows linearly with time while at low temperatures, we find strong deviations from simple ...
Configurational Entropy And Collective Modes In Normal And Supercooled Liquids, Ulrich Zürcher, T. Keyes
Configurational Entropy And Collective Modes In Normal And Supercooled Liquids, Ulrich Zürcher, T. Keyes
Ulrich Zurcher
Soft vibrational modes have been used to explain anomalous thermal properties of glasses above 1 K. The softpotential model consists of a collection of doublewell potentials that are distorted by a linear term representing local stress in the liquid. Doublewell modes contribute to the configurational entropy of the system. Based on the AdamGibbs theory of entropically driven relaxation in liquids, we show that the presence of stress drives the transition from Arrhenius to ZwanzigBässler temperature dependence of relaxation times. At some temperature below the glass transition, the energy scale is dominated by local stress, and soft modes are described by ...
A Stochastic Theory Of Inhomogeneously Broadened Linewidths In Solids, Ulrich Zürcher
A Stochastic Theory Of Inhomogeneously Broadened Linewidths In Solids, Ulrich Zürcher
Ulrich Zurcher
We investigate spectral diffusion decay using a model for solids that consists of twolevelsystems (TLSs) interacting via strain fields. For the case when the rate of TLS flips vanishes, we find algebraic decay of correlation functions of the local field. We show that properties of equilibrium fluctuations are in agreement with the hierarchical picture proposed by Basché and Moerner: TLSs far away produce fast fluctuations that are small in magnitude, and close TLSs produce large fluctuations that are less frequent.
Use Of Grooved Microchannels To Improve The Performance Of MembraneLess Fuel Cells, J. D'Alessandro, Petru S. Fodor
Use Of Grooved Microchannels To Improve The Performance Of MembraneLess Fuel Cells, J. D'Alessandro, Petru S. Fodor
Petru S. Fodor
In this work, the fluid dynamics within a membraneless microchannel fuel cell is analyzed computationally. The membraneless design is a result of the laminar nature of the fluid flow at small Reynolds numbers, restricting the fuel and oxidant to the vicinity of the corresponding electrodes, without the need of a proton exchange membrane (PEM). However, the performance of such cells is limited by the slow diffusive mass transport near the electrodes, with a large fraction of the reactants leaving the channel without coming in contact with the catalytic surfaces, and thus not being used. We mitigate this problem through the ...
XRay Photoelectron Spectroscopy (Xps) And Magnetization Studies Of Iron–Vanadium Phosphate Glasses, M. A. Salim, G. D. Khattak, Petru S. Fodor, Lowell E. Wenger
XRay Photoelectron Spectroscopy (Xps) And Magnetization Studies Of Iron–Vanadium Phosphate Glasses, M. A. Salim, G. D. Khattak, Petru S. Fodor, Lowell E. Wenger
Petru S. Fodor
Vanadium phosphate glasses containing Fe2O3 with the chemical composition [(Fe2O3)x(V2O5)0.6−x(P2O5)0.4], where x=0.00, 0.10, 0.20, 0.25 and 0.30, have been prepared and investigated by Xray photoelectron spectroscopy (XPS) and magnetic susceptibility measurements. The core level binding energies of V 2p, Fe 2p, P 2p and P 2s in the Fe2O3–vanadium phosphate glasses have been measured and shifts from the corresponding binding energies measured for V2O5, Fe2O3 and P2O5 powders are accounted for by changes in the nextnearest neighbor environment of these atoms in the P4O10 local ...
VariableTemperature Scanning Optical And Force Microscope, Petru S. Fodor, H. Zhu, N. G. Patil, J. Levy
VariableTemperature Scanning Optical And Force Microscope, Petru S. Fodor, H. Zhu, N. G. Patil, J. Levy
Petru S. Fodor
The implementation of a scanning microscope capable of working in confocal, atomic force and apertureless near field configurations is presented. The microscope is designed to operate in the temperature range 4–300 K, using conventional helium flow cryostats. In atomic force microscope(AFM) mode, the distance between the sample and an etchedtungsten tip is controlled by a selfsensing piezoelectrictuning fork. The vertical position of both the AFM head and microscope objective can be accurately controlled using piezoelectric coarse approach motors. The scanning is performed using a compact XYZ stage, while the AFM and optical head are kept fixed, allowing scanning ...
Zero Magnetization States In Electrodeposited Co0.45fe0.55 Nanowire Arrays, Petru S. Fodor, Georgy M. Tsoi, Lowell E. Wenger
Zero Magnetization States In Electrodeposited Co0.45fe0.55 Nanowire Arrays, Petru S. Fodor, Georgy M. Tsoi, Lowell E. Wenger
Petru S. Fodor
Co0.45Fe0.55 alloy nanowires with 12 to 35 nm diameter and 12 μm length were fabricated by electrodeposition in porous anodic alumina templates. The initial magnetization curves reveal that the zero magnetization state is not unique and is determined by the field history (acdemagnetization process) leading to the zero average moment state. For acdemagnetization processes with the field applied parallel to the nanowire axis, the subsequent magnetization curves suggest that an individual nanowire behaves as a single domain with neighboring nanowires being antiparallel to each other in the zero magnetization state. However, for a demagnetization process with the field ...
Thermal Hysteresis In The ChargeDensityWave Transition Of Lu5rh4si10, C. S. Lue, Y. K. Kuo, F. H. Hsu, H. H. Li, H. D. Yang, Petru S. Fodor, Lowell E. Wenger
Thermal Hysteresis In The ChargeDensityWave Transition Of Lu5rh4si10, C. S. Lue, Y. K. Kuo, F. H. Hsu, H. H. Li, H. D. Yang, Petru S. Fodor, Lowell E. Wenger
Petru S. Fodor
We report the detailed studies of resistivity, magnetic susceptibility, heat capacity, thermal conductivity, and thermoelectric power on the chargedensitywave (CDW) material Lu5Rh4Si10 in the vicinity of its transition temperature T0 ∼ 147 K. Pronounced thermal hystereses loops between heating and cooling cycles have been observed in all measured quantities, making this system very unique as compared to other isostructural compounds such as Lu5Ir4Si10. The thermal hysteresis features in Lu5Rh4Si10 are attributed to the presence of metastable states arising from pinning of the CDW phase to impurities. In addition, the measured physical quantities are magnetic field independent up to 8 T, which ...
Modeling Of Hysteresis And Magnetization Curves For Hexagonally Ordered Electrodeposited Nanowires, Petru S. Fodor, Georgy M. Tsoi, Lowell E. Wenger
Modeling Of Hysteresis And Magnetization Curves For Hexagonally Ordered Electrodeposited Nanowires, Petru S. Fodor, Georgy M. Tsoi, Lowell E. Wenger
Petru S. Fodor
A computational model has been developed to investigate how the magnetostatic interactions affect the hysteresis and magnetization curves for hexagonal arrays of magnetic nanowires. The magnetization coupling between nanowires arises from the stray fields produced by the other nanowires composing the array such that the field at each nanowire is the sum of the external field and the interaction field with the other nanowires. Using only two adjustable parameters: the interaction between nearest neighbors and the width of the Gaussian distribution in switching fields centered around the measuredcoercivity, simulations are compared with the experimentally measuredhysteresis and magnetization curves for electrodepositedCo0 ...
320Channel Dual Phase LockIn Optical Spectrometer, Petru S. Fodor, S. Rothenberger, J. Levy
320Channel Dual Phase LockIn Optical Spectrometer, Petru S. Fodor, S. Rothenberger, J. Levy
Petru S. Fodor
The development of a multiplechannel lockin optical spectrometer (LIOS) is presented, which enables parallel phasesensitive detection at the output of an optical spectrometer. The light intensity from a spectrally broad source is modulated at the reference frequency, and focused into a highresolution imaging spectrometer. The height at which the light enters the spectrometer is controlled by an acoustooptic deflector, and the height information is preserved at the output focal plane. A twodimensional InGaAs focal plane array collects light that has been dispersed in wavelength along the horizontal direction, and in time along the vertical direction. The data is demodulated using ...
Fabrication And Characterization Of Co1−Xfex Alloy Nanowires, Petru S. Fodor, Georgy M. Tsoi, Lowell E. Wenger
Fabrication And Characterization Of Co1−Xfex Alloy Nanowires, Petru S. Fodor, Georgy M. Tsoi, Lowell E. Wenger
Petru S. Fodor
Co1−xFex alloy nanowires with 40 nm diam and x=0–1.0 were fabricated by electrodeposition in nanopores of alumina templates. The crystalline structure of the nanowires is concentration dependent and shows a transition from the cobalt hexagonalclosedpacked structure (hcp) to a facecenteredcubic structure (fcc) in the concentration range 0
Determination Of Magnetic Exchange Stiffness And Surface Anisotropy Constants In Epitaxial Ni_ {1X} Co_ {X}(001) Films, P. Talagala, Petru S. Fodor, Haddad R. Naik, Lowell E. Wenger, P. P. Vaishnava, V. M. Naik
Determination Of Magnetic Exchange Stiffness And Surface Anisotropy Constants In Epitaxial Ni_ {1X} Co_ {X}(001) Films, P. Talagala, Petru S. Fodor, Haddad R. Naik, Lowell E. Wenger, P. P. Vaishnava, V. M. Naik
Petru S. Fodor
Magnetic characteristics of epitaxial Ni1xCox(001) (x=0, 0.16, and 0.50) films with nominal 200 nm thickness on Cu(001)/Si(100) substrates have been investigated by magnetization and ferromagnetic resonance measurements in order to better clarify the rationale for the large variation in the magnetic exchange stiffness constant A, previously determined from different measurements. The exchange constant as well as the saturation magnetization, effective demagnetizing field, fourthorder magnetocrystalline, and secondorder perpendicular uniaxial magnetic anisotropy fields has been determined. The analyses of lowtemperature saturation magnetization data on these films yield A values that increase from 0.82×106erg ...
Use Of Optical Tweezers For Colloid Science, Andrew Resnick
Use Of Optical Tweezers For Colloid Science, Andrew Resnick
Andrew Resnick
A spaceborne optical tweezer apparatus for use with colloidal crystallization experiments has been characterized. The trapping force has been measured as a function of index mismatch between colloidal microspheres and the surrounding fluid and as a function of particle size. This work also presents a method to determine the refractive index of a colloidal microsphere, which is then used to calculate the applied trapping force for the case of an arbitrary background fluid. This is useful for work with dense colloidal suspensions when the usual (e.g., Stokes flow) trap force measurement methods do not apply, as well as microrheological ...
Plateau Tank Apparatus For The Study Of Liquid Bridges, Andrew Resnick, J. Iwan D. Alexander
Plateau Tank Apparatus For The Study Of Liquid Bridges, Andrew Resnick, J. Iwan D. Alexander
Andrew Resnick
An apparatus has been constructed and used to study the equilibrium and dynamical behavior of liquid bridges under reduced effective gravity. Liquid bridges are created and manipulated using six independent computer controlled stepper motors which drive linear motion tables. The bridges are visualized with a high magnification coherent Fourier optical system and in an orthogonal view using incoherent white light. By calibrating a density hydrometer and measuring the interfacial energy between the bridge and bath, reliable Bond numbers as low as 10−4 can be created and held stable for extended periods of time. Dimensional control of the liquid bridges ...
Near RealTime Measurement Of Forces Applied By An Optical Trap To A Rigid Cylindrical Object, Joseph Glaser, David Hoeprich, Andrew Resnick
Near RealTime Measurement Of Forces Applied By An Optical Trap To A Rigid Cylindrical Object, Joseph Glaser, David Hoeprich, Andrew Resnick
Andrew Resnick
An automated data acquisition and processing system is established to measure the force applied by an optical trap to an object of unknown composition in real time. Optical traps have been in use for the past 40 years to manipulate microscopic particles, but the magnitude of applied force is often unknown and requires extensive instrument characterization. Measuring or calculating the force applied by an optical trap to nonspherical particles presents additional difficulties which are also overcome with our system. Extensive experiments and measurements using wellcharacterized objects were performed to verify the system performance.
ForceResponse Considerations In Ciliary Mechanosensation, Andrew Resnick, Ulrich Hopfer
ForceResponse Considerations In Ciliary Mechanosensation, Andrew Resnick, Ulrich Hopfer
Andrew Resnick
Considerable experimental evidence indicates that the primary, nonmotile cilium is a mechanosensory organelle in several epithelial cell types. As the relationship between cellular responses and nature and magnitude of applied forces is not well understood, we have investigated the effects of exposure of monolayers of renal collecting duct chief cells to orbital shaking and quantified the forces incident on cilia. An exposure of 24 h of these cells to orbital shaking resulted in a decrease of amiloridesensitive sodium current by ∼60% and ciliary length by ∼30%. The sensitivity of the sodium current to shaking was dependent on intact cilia. The ...
Chronic Fluid Flow Is An Environmental Modifier Of Renal Epithelial Function, Andrew Resnick
Chronic Fluid Flow Is An Environmental Modifier Of Renal Epithelial Function, Andrew Resnick
Andrew Resnick
Although solitary or sensory cilia are present in most cells of the body and their existence has been known since the sixties, very little is been known about their functions. One suspected function is fluid flow sensing physical bending of cilia produces an influx of Ca++, which can then result in a variety of activated signaling pathways. Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a progressive disease, typically appearing in the 5th decade of life and is one of the most common monogenetic inherited human diseases, affecting approximately 600,000 people in the United States. Because ADPKD is a slowly ...