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 …

Stationary Correlations For A Far-From-Equilibrium Spin Chain, Beate Schmittmann, F. Schmüser

Beate Schmittmann

A kinetic one-dimensional Ising model on a ring evolves according to a generalization of Glauber rates, such that spins at even (odd) lattice sites experience a temperature Te (To). Detailed balance is violated so that the spin chain settles into a nonequilibrium stationary state, characterized by multiple interactions of increasing range and spin order. We derive the equations of motion for arbitrary correlation functions and solve them to obtain an exact representation of the steady state. Two nontrivial amplitudes reflect the sublattice symmetries; otherwise, correlations decay exponentially, modulo the periodicity of the ring. In the long-chain limit, they factorize into …

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

Magnetochemical Origin For Invar Anomalies In Iron-Nickel Alloys, V. Crisan, P. Entel, H. Ebert, H. Akai, Duane D. Johnson, J. B. Staunton

Duane D. Johnson

Zero- and finite-temperature (T) first-principles calculations versus composition (c) show that magnetochemical effects lead to Invar anomalies in Fe-(Ni, Co, Pt) alloys. Chemical short- or long-range order and negative interatomic exchange interaction of electrons in antibonding majority-spin states force the face-centered-cubic lattice to compete simultaneously for a smaller volume (from antiferromagnetic tendencies) and a larger volume (from Stoner ferromagnetic tendencies). The resulting additional negative lattice anharmonicity is very large for Fe-(Ni, Co) while absent for Fe-Pt. Our results explain the T- and c-dependent behavior of Invar properties, including the lattice softening and thermal expansion of Fe-Ni. In addition, the occurrence …

Longitudinal Ionosphericeffects In The South Atlantic Sector During Solar Maximum, E. R. De Paula, J. R. Souza, Bela G. Fejer, G. J. Bailey, R. A. Heelis

Bela G. Fejer

[1] Large-scale horizontal gradients in ion density and vertical drift observed by the Atmospheric Explorer E satellite in the South Atlantic region (latitudes 10°S–20°S, longitudes 50°W–10°E) during the June solstice at solar maximum are presented and analyzed. These features occur during the nighttime period. The observations near 450-km altitude show vertically downward ion drift velocities exceeding 120 m s−1 and depleted regions where the ion density is around 2 × 104 cm−3. It is shown, using values modeled by the Sheffield University Plasmasphere Ionosphere Model (SUPIM) along the satellite trajectory, that the large ion density depletions appear as a result …

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 …

Polarization Jet Events And Excitation Of Weak Sar Arcs, S. Sazykin, Bela G. Fejer, Y. I. Galperin, S. A. Grigoriev, L. V. Zinin, M. Mendillo

Bela G. Fejer

[1] Polarization Jet (PJ), also known as Sub-Auroral Ion Drift (SAID), events are supersonic westward plasma drifts on the equatorward edge of the diffuse aurora in the evening and nighttime sector. Their optical F-region signatures are weak 630.0 nm red arcs colocated with regions of fast convection. These weak arcs resemble Stable Auroral Red (SAR) arcs observed during the recovery phase of magnetic storms, but have lower intensities, shorter lifetimes, and occur without a significant heat flux from the magnetosphere. Previous model studies underestimated the brightness of weak SAR arcs. We present calculations showing that ion-neutral collisional heating and ion …

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 …

Absolute Tin(111) Step Energies From Analysis Of Anisotropic Island Shape Fluctuations, S. Kodambaka, V. Petrova, S. V. Khare, Duane D. Johnson, I. Petrov, J. E. Greene

Duane D. Johnson

In situ high-temperature (1165–1248 K) scanning tunneling microscopy was used to measure fluctuations around the equilibrium shape of two-dimensional vacancy islands on TiN(111) terraces. From the equilibrium shape, the ratio of the two ⟨110⟩ step energies was found to be 0.72±0.02. Combining this with the results of an exact approach for analysis of shape fluctuations, applicable to highly anisotropic islands, we obtain absolute values for step energies and step stiffnesses as a function of orientation.

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 …

First-Principles Theory Of The Temperature And Compositional Dependence Of Atomic Short-Range Order In Disordered Cu-Pd Alloys, R. V. Chepulskii, J. B. Staunton, Ezio Bruno, B. Ginatempo, Duane D. Johnson

Duane D. Johnson

We combine the first-principles, Korringa-Kohn-Rostoker coherent potential approximation based calculations of compositional fluctuations with a statistical mechanical ring approximation to study the temperature (T) and composition (c) dependence of the atomic short-range order (SRO) in disordered, face-centred cubic, Cu-Pd alloys. The fourfold splitting of SRO peaks around the equivalent X(0,1,0) points in reciprocal space is obtained in a wide T−c region. Such splitting is shown to be an “energy” effect caused by the absolute minima of the Fourier transform of the effective atomic interactions and related previously to the existence of nested sheets of the disordered alloy’s Fermi surface. However, …

Dust In I Zw 18 From Hubble Space Telescope Narrowband Imaging, John M. Cannon, E D. Skillman, D R. Garnett, R J. Dufour

John Cannon

No abstract provided.

Multispectrum, Spatially Addressable Polarization Interference Filter, Salman Saeed, Philip Bos

Philip J. Bos

We review current synthesis techniques for generating and improving birefringent filters. The relationship between wave-plate orientation and the resulting spectral output is shown to be that of a simple Fourier transform. By using this relationship and starting from the fan Sole configuration, we easily generated plate orientations providing lower sidelobe levels and improved finesse. We outline a method by which filters can be constructed to provide from 0 to 100% of the desired passband in a continuous fashion. Such a filter can be stacked to allow rapid control of any number of passbands and is shown, as an example in …

Laplace Transform Of Spherical Bessel Functions, Andrei Ludu

Andrei Ludu

No abstract provided.

A Comparison Of Haloe V19 With Sage Ii V6.00 Ozone Observations Using Trajectory Mapping, Gary A. Morris, James F. Gleason, James M. Russell Iii, Mark R. Schoeberl, M. Patrick Mccormick

Gary A. Morris

We apply trajectory mapping to an 8-year intercomparison of ozone observations from the Halogen Occultation Experiment (HALOE) (V19) and Stratospheric Aerosol and Gas Experiment (SAGE) II (V6.00) for the months March, May, June, September, October, and December from the period December 1991 to October 1999. Our results, which represent the most extensive such intercomparison of these two data sets to date, suggest a root-mean-square difference between the two data sets of >15% below 22 km in the tropics and of 4–12% throughout most of the rest of the stratosphere. In addition, we find a bias with HALOE ozone low relative …

Growing Correlation Length On Cooling Below The Onset Of Caging In A Simulated Glass-Forming Liquid, N. Lacevic, Francis W. Starr, T. B. Schrøder, V. N. Novikov, S. C. Glotzer

Francis Starr

No abstract provided.

Molecular Dynamics Simulation Of A Polymer Melt With A Nanoscopic Particle, Francis W. Starr, T. B. Schroder, S. C. Glotzer

Francis Starr

No abstract provided.