Physics Commons^™

Asymptotic Solitons For A Higher-Order Modified Korteweg–De Vries Equation, T. Marchant

Tim Marchant

Solitary wave interaction for a higher-order modified Korteweg–de Vries (mKdV) equation is examined. The higher-order mKdV equation can be asymptotically transformed to the mKdV equation, if the higher-order coefficients satisfy a certain algebraic relationship. The transformation is used to derive the higher-order two-soliton solution and it is shown that the interaction is asymptotically elastic. Moreover, the higher-order phase shifts are derived using the asymptotic theory. Numerical simulations of the interaction of two higher-order solitary waves are also performed. Two examples are considered, one satisfies the algebraic relationship derived from the asymptotic theory, and the other does not. For the example …

Heat Transport In Sb2àXvxte3 Single Crystals, Jeffrey Dyck, W. Chen, C. Uher, Č. DrašAr, P. LošŤÁK

Jeffrey Dyck

Antimony telluride doped with small concentrations of vanadium was recently identified as a diluted magnetic semiconductor. We present a study of the heat transport in single crystals of [formula] with [formula] 0.01, 0.02, and 0.03. Thermopower and thermal conductivity were measured from 1.5 K to 300 K. The thermopower is positive for all samples investigated and has a modest dependence on vanadium content. At low temperatures, the lattice thermal conductivity has an approximate [formula] dependence and the data up to 100 K can be fitted well assuming that phonons scatter on boundaries, point defects, charge carriers, and other phonons. Theoretical …

Calorimetric Study Of Nematic Prewetting, Xuewu Liu, David W. Allender, D. Finotello

David W Allender

We report specific-heat measurements for a series of liquid crystals imbedded in a porous cylindrical geometry. Above the nematic-to-isotropic transition and dependent on nematic width (or chain length), the specific heat shows a small peak. In analogy to known ellipsometry results, the peak is believed to be the signature of a nematic prewetting transition.

Ultrafast Measurement Of Two-Photon Absorption By Loss Modulation, Peifang Tian, Warren Warren

Peifang Tian

We demonstrate a direct and sensitive technique for measuring two-photon absorption (TPA).An intensity- modulated femtosecond laser beam passes through a sample exhibiting TPA.A TPA signal at twice the modulation frequency is then generated and subsequently measured by a lock-in amplifier. The absolute TPA cross section of Rhodamine 6G at 800nm is found to be 15.32.010 -50 cm 4 s / photon and agrees well with previously published results obtained with much higher intensity [J.Chem.Phys. 112, 9201 (2000)]. Our method may be especially useful in measuring nonlinear absorptions of nonfluorescent materials.

Infrared Depletion Spectroscopy Of Aniline-Acetonitrile Cation And Aniline-Acetonitrile-Water Cation Clusters, H. Nagai, Naveed Piracha, T. Nakanaga

Naveed K. Piracha

The vibrational spectra of the aniline-acetonitrile^+ and the aniline-acetonitrile-water^+ cluster cations have been measured by the infrared depletion spectroscopy in the frequency region of NH and OH stretching vibrations. One absorption band was observed at 3437cm^-^1 in the infrared spectrum of the aniline-acetonitrile^+ cluster cation, and was assigned to the NH stretching vibration of free NH of aniline. As for the aniline-water-acetonitrile^+ cluster cation, three absorptions were observed at 3722, 3634 and 3247cm^-^1, which were assigned to the anti-symmetric stretching and symmetric stretching vibrations of OH of water and the stretching vibrations of NH bond interacting with water, respectively. In …

Maximization Of The Open Circuit Voltage For Hydrogenated Amorphous Silicon N–I–P Solar Cells By Incorporation Of Protocrystalline Silicon P-Type Layers, R. J. Koval, Chi Chen, G. M. Ferreira, A. S. Ferlauto, Joshua M. Pearce, P. I. Rovira, C. R. Wronski, R. W. Collins

Joshua M. Pearce

Electrical Conductivity And Thermopower Of Cu–Sio[Sub 2] Nanogranular Films., W. Chen, J. Lin, X. Zhang, H. Shin, Jeffrey Dyck, C. Uher

Jeffrey Dyck

We have measured the thermopower S and electrical conductivity σ in a series of Cu[sub x](SiO[sub 2])[sub 1-x] nanogranular films between 2 and 300 K with Cu volume fraction x varying from 0.43 up to 1.0. At low temperatures, disorder-enhanced electron-electron interaction effects dictate the behavior of σ. A crossover of the temperature dependence from σ∝ √T to σ∝ T[sup 1/3] is observed as x is lowered and the metal-insulator transition is approached. S is small, shows linear temperature dependence, and is rather insensitive to the change of x. Effects of annealing are also discussed.

Highly Anisotropic Crystal Growth And Thermoelectric Properties Of K2bi8_Xsbxse13 Solid Solutions: Band Gap Anomaly At Low X, Jeffrey S. Dyck, Theodora Kyratsi, Wei Chan, Duck-Young Chung, Ctirad Uher, Konstantinos Paraskevopoulos, Mercouri Kanatzidis

Jeffrey Dyck

The thermoelectric properties of solid solutions of the type B -K2Bi8_xSbxSe13 (0

Infrared Spectroscopy Of Aniline–Ne Clusters And The Corresponding Cluster Cations In The Nh2-Stretching Vibration Region, Naveed Piracha, T. Nakanaga

Naveed K. Piracha

The vibrational spectra of the NH2-stretching modes of aniline–Ne and aniline–Ne+ have been measured using infrared depletion spectroscopy and REMPI–TOF mass spectrometry. In the NH2-stretching vibration region of the aniline–Ne clusters, two absorption bands at 3422 and 3508cm−1 were observed. The frequency shifts from the monomer was found to be negligibly small. As for the aniline–Ne+ cluster cations, the observed frequencies of the vibrational modes were 3394 and 3488cm−1. These values agreed with ones observed for aniline–Ar+ cluster within the error limit. This fact suggests that the effect of neon to aniline in forming the cluster is not significant in …

Thermal-Lens Model Compared With The Sheik-Bahae Formalism In Interpreting Z-Scan Experiments On Lyotropic Liquid Crystals, Fabio Luiz Sant'anna Cuppo, Antonio Martins Figueiredo Neto, Sergio Leonardo Gomez, Peter Palffy-Muhoray

Peter Palffy-Muhoray

We carried out Z-scan measurements on lyotropic liquid crystals and on lyotropic liquid crystals doped with ferrofluid. In these experiments, the sample is translated through the focal region of a focused Gaussian laser beam. The dependence of the far-field intensity on sample position due to intensity-dependent optical nonlinearities has been analyzed on the basis of the thermal-lens model of Gordon et al. and the Gaussian decomposition analysis of Sheik-Bahae et al. The thermal-lens model is nonlocal in space and time, whereas the Gaussian decomposition is predicated on a strictly local response. We compare the goodness of fit of the predictions …

Direct And Sensitive Measurement Of Two-Photon Absorption Cross Sections, Peifang Tian, D. Keusters, Warren Warren

Peifang Tian

Summary form only given. We present a direct method to detect weak two-photon absorption (TPA) signals. As a proof of principle, we have measured the TPA cross section δ for rhodamine 6G (R6G) in methanol and obtained a value which agrees with other results. The technique may be very useful in biomedical imaging.

Transport Properties Of Polycrystalline Type-I Sn Clathrates, G. S. Nolas, J. L. Cohn, Jeffrey Dyck, C. Uher, J. Lang

Jeffrey Dyck

Thermal conductivity, resistivity, Seebeck coefficient, and Hall measurements on polycrystalline Sn-clathrate compounds with the type-I hydrate crystal structure are reported. Interstitial alkali-metal atoms in these compounds reside inside polyhedral cavities formed by the tetrahedrally bonded Sn network atoms. Localized disorder associated with “rattling” motion of these interstitial atoms contributes to the low thermal conductivity of these semiconducting compounds. The Hall coefficient and resistivity for some compounds exhibit nonmonotonic temperature dependences consistent with a crossover with decreasing temperature from conduction-band to impurity-band conduction. The carrier mobility is found to be low even in the absence of interstitial atoms within the Sn …

Three-Dimensional Dye Distribution In Photo-Oriented Liquid-Crystal Alignment Layers, S. Bardon, D. Coleman, N. A. Clark, T. Kosa, H. Yuan, Peter Palffy-Muhoray

Peter Palffy-Muhoray

The three-dimensional optical anisotropy of photo-buffed dye-doped polymer films and the resulting orientation imparted to a liquid crystal in contact are probed using total internal reflection. Although the linearly polarized writing light generates a uniaxial distribution of dye molecules, the polymer films are biaxial, a result of symmetry breaking by the film surface.

Thermoelectric Properties Of The N-Type Filled Skutterudite Ba0.3co4sb12 Doped With Ni, Jeffrey Dyck, Wei Chen, Ctirad Uher, Lidong Chen, Xinfeng Tang, Toshio Hirai

Jeffrey Dyck

Synthesis and electrical and thermal transport properties are reported for several filled skutterudite compounds doped with Ni: Ba0.3NixCo4_xSb12 with 0

Diluted Magnetic Semiconductors Based On Sb2àXvxte3 „0.01ïXï0.03., Jeffrey Dyck, Pavel Hájek, Petr LošŤÁK, Ctirad Uher

Jeffrey Dyck

We report on a diluted magnetic semiconductor based on the [formula] tetradymite structure doped with very low concentrations of vanadium (1—3 at. %). The anomalous transport behavior and robust magnetic hysteresis loops observed in magnetotransport and magnetic measurements are experimental manifestations of the ferromagnetic state in these materials. The [formula] exchange between holes and vanadium [formula] spins is estimated from the behavior of the magnetoresistance. A Curie temperature of at least 22 K is observed for [formula] This discovery offers possibilities for exploring magnetic properties of other tetradymite structure semiconductors doped with a wide range of [formula] transition metals.

Effect Of Ni On The Transport And Magnetic Properties Of Co1àXnixsb3, Jeffrey Dyck, Wei Chen, Jihui Yang, Gregory P. Meisner, Ctirad Uher

Jeffrey Dyck

The filled skutterudite compounds based on the binary skutterudite [formula] are currently being investigated for their potential applications as thermoelectric materials. One route to optimization of these compounds is by doping on the Co site. An obvious candidate for an n-type dopant is Ni, since it has one more electron in its valence shell than Co. Up to now, however, only high concentrations of Ni in [formula] have been studied; and the valence of Ni in this compound and its influence on the transport and magnetic properties has been an open question. We present electrical resistivity, thermopower, Hall effect, magnetoresistance, …

Low-Temperature Ferromagnetism And Magnetic Anisotropy In The Novel Diluted Magnetic Semiconductor Sb2−Xvxte3, Jeffrey Dyck, Wei Chen, Pavel Hájek, Petr Lošt’Ák, Ctirad Uher

Jeffrey Dyck

We report on a novel diluted magnetic semiconductor based on the Sb2Te3 tetradymite structure doped with very low concentrations of vanadium (1–3at%). Anisotropy in the magnetic hysteresis loops and magnetoresistance are observed at temperatures below the ferromagnetic ordering temperature. A Curie temperature of 24K is observed for Sb1.97V0.03Te3.

Influence Of Electron-Phonon Interaction On The Lattice Thermal Conductivity Of Co1àXnixsb3, J. Yang, D. T. Morelli, G. P. Meisner, W. Chen, Jeffrey Dyck, C. Uher

Jeffrey Dyck

We have investigated the effect of electron-phonon scattering in a series of n-type nickel-doped [formula] skutterudite materials. Samples were polycrystalline of the form [formula] with [formula] 0.001, 0.003, 0.005, 0.0075, and 0.01. The lattice thermal conductivity decreases dramatically with increasing Ni doping for [formula] For higher Ni concentration the reduction of the lattice thermal conductivity saturates. Our theoretical analysis indicates that this reduction of the lattice thermal conductivity cannot be explained solely by point-defect scattering of the phonons. Rather, we can fit the lattice thermal conductivity of Ni-doped [formula] by introducing an electron-phonon scattering mechanism, and this demonstrates that the …

High-Order Interaction Of Solitary Waves On Shallow Water, Prof. Tim Marchant

Tim Marchant

The interaction of solitary waves on shallow water is examined to fourth order. At first order the interaction is governed by the Korteweg-de Vries (KdV) equation, and it is shown that the unidirectional assumption, of right-moving waves only, is incompatible with mass conservation at third order. To resolve this, a mass conserving system of KdV equations, involving both right- and left-moving waves, is derived to third order. A fourth-order interaction term, in which the right- and left-moving waves are coupled, is also derived as this term is crucial in determining the fourth-order change in solitary wave amplitude. The form of …

The Occurrence Of Limit-Cycles During Feedback Control Of Microwave Heating, Prof. Tim Marchant

Tim Marchant

The microwave heating of one- and two-dimensional slabs, subject to linear feedback control, is examined. A semianalytical model of the microwave heating is developed using the Galerkin method. A local stability analysis of the model indicates that Hopf bifurcations occur; the regions of parameter space in which limit-cycles exist are identified. An efficient numerical scheme for the solution of the governing equations, which consist of the forced heat equation and a Helmholtz equation describing the electric-field amplitude, is also developed. An excellent comparison between numerical solutions of the semianalytical model and the governing equations is obtained for the temporal evolution …

Cubic Autocatalytic Reaction-Diffusion Equations: Semi-Analytical Solutions, Prof. Tim Marchant

Tim Marchant

The Gray-Scott model of cubic-autocatalysis with linear decay is coupled with diffusion and considered in a one-dimensional reactor (a reaction-diffusion cell). The boundaries of the reactor are permeable, so diffusion occurs from external reservoirs that contain fixed concentrations of the reactant and catalyst. The Galerkin method is used to approximate the spatial structure of the reactant and autocatalyst concentrations in the reactor. Ordinary differential equations are then obtained as an approximation to the governing partial differential equations. The ordinary differential equations are then analysed to obtain semi-analytical results for the reaction-diffusion cell. Steady-state concentration profiles and bifurcation diagrams are obtained …

Semi-Analytical Solutions For Continuous-Flow Microwave Reactors, Prof. Tim Marchant

Tim Marchant

A prototype chemical reaction is examined in both one and two-dimensional continuous-flow microwave reactors, which are unstirred so the effects of diffusion are important. The reaction rate obeys the Arrhenius law and the thermal absorptivity of the reactor contents is assumed to be both temperature- and concentration-dependent. The governing equations consist of coupled reaction-diffusion equations for the temperature and reactant concentration, plus a Helmholtz equation describing the electric-field amplitude in the reactor. The Galerkin method is used to develop a semi-analytical microwave reactor model, which consists of ordinary differential equations. A stability analysis is performed on the semi-analytical model. This …

The Initial Boundary Problem For The Korteweg-De Vries Equation On The Negative Quarter-Plane, Prof. Tim Marchant

Tim Marchant

The initial boundary-value problem for the Korteweg-de Vries (KdV) equation on the negative quarter-plane, x < 0 and t > 0, is considered. The formulation of this problem is different to the usual initial boundary-value problem on the positive quarter-plane, for which x > 0 and t > 0. Two boundary conditions are required at x = 0 for the negative quarter-plane problem, in contrast to the one boundary condition needed at x = 0 for the positive quarter-plane problem. Solutions of the KdV equation on the infinite line, such as the soliton, cnoidal wave, mean height variation and undular bore solution, are used to find approximate …

The Microwave Heating Of Three-Dimensional Blocks: Semi-Analytical Solutions, Prof. Tim Marchant

Tim Marchant

The microwave heating of three-dimensional blocks, by the transverse magnetic waveguide mode TM11, is considered in a long rectangular waveguide. The governing equations are the forced heat equation and a steady-state version of Maxwell's equations, while the boundary conditions take into account both convective and radiative heat loss. Semi-analytical solutions, valid for small thermal absorptivity, are found using the Galerkin method. The electrical conductivity and the thermal absorptivity are assumed to be temperature dependent, while both the electrical permittivity and magnetic permeability are taken to be constant. Both a quadratic relation and an Arrhenius-type law are used for the temperature …

Thermoelectric Properties Of K[Subscript 2]Bi[Subscript 8-X]Sb[Subscript X]Se[Subscript 13] Solid Solutions And Se Doping [Et Al.], Theodora Kyratski, Jeffrey Dyck, Wei Chen

Jeffrey Dyck

Our efforts to improve the thermoelectric properties of β-K2Bi8Se13, led to systematic studies of solid solutions of the type β-K2Bi8−xSbxSe13. The charge transport properties and thermal conductivities were studied for selected members of the series. Lattice thermal conductivity decreases due to the mass fluctuation generated in the lattice by the mixed occupation of Sb and Bi atoms. Se excess as a dopant was found to increase the figure-of merit of the solid solutions.

Numerical Solitary Wave Interaction: The Order Of The Inelastic Effect, Prof. Tim Marchant

Tim Marchant

Solitary wave interaction is examined using an extended Benjamin-Bona-Mahony (eBBM) equation. This equation includes higher-order nonlinear and dispersive effects and is is asymptotically equivalent to the extended Korteweg-de Vries (eKdV) equation. The eBBM formulation is preferable to the eKdV equation for the numerical modelling of solitary wave collisions, due to the stability of its finite-difference scheme. In particular, it allows the interaction of steep waves to be modelled, which due to numerical instability, is not possible using the eKdV equation. Numerical simulations of a number of solitary wave collisions of varying nonlinearity are performed for two special cases corresponding to …

Analysis And Classification Of Nonlinear Dispersive Evolution Equations In The Potential Representation, Andrei Ludu

Andrei Ludu

No abstract provided.

What Do We Learn From The Local Geometry Of Glass-Forming Liquids?, Francis W. Starr, S. Sastry, J. F. Douglas, S. C. Glotzer

Francis Starr

No abstract provided.

The Single Particle Potential In Mean-Field Theory, Peter Palffy-Muhoray

Peter Palffy-Muhoray

The problem of determining the single particle energy in a mean-field description of interacting particles is considered. It is shown that the single particle energy must satisfy two consistency conditions, and a general procedure for obtaining the single particle energy from the pair energy is proposed. Interacting dipolar systems are examined, current approaches in the literature are discussed, and the usefulness of the proposed method is demonstrated.

Translational And Rotational Diffusion In Stretched Water, P. A. Netz, Francis Starr, M. C. Barbosa, H. E. Stanley

Francis Starr

No abstract provided.