bluuebunny/crossref_metadata_2025 huggingface dataset:
C-rotational echo double resonance: Heteronuclear dipolar recoupling with homonuclear dipolar decoupling
Authors: Chan Jerry C. C. , Eckert Hellmut
Published: July 2002

We propose a series of heteronuclear dipolar recoupling schemes which are insensitive to the presence of homonuclear dipolar interaction. The schemes are based on the pulse symmetry CNnν. The optimum choices for N, n, and ν were determined with the help of Average Hamiltonian Theory (AHT). The lowest-order AHT shows that the pulse symmetries with n=N and ν=1 are suitable for the recoupling of heteronuclear dipolar interactions. Together with the parabolic approximation of the dephasing curve, we develop a powerful experimental strategy to characterize the van Vleck’s second moments for multiple-spin systems under conditions of very fast magic-angle spinning. These new pulse symmetries are superior to the rotational echo double resonance (REDOR) method and other recoupling schemes as far as the interference of the homonuclear dipolar interaction is concerned. Preliminary experimental results on crystalline model compounds are given to illustrate the utility of our approach.
Steady-state characteristics of lateral p-n junction vertical-cavity surface-emitting lasers
Authors: Ryzhii V. , Tsutsui N. , Khmyrova I. , Ikegami T. , Vaccaro P. O. , Taniyama H. , Aida T.
Published: July 2002

We developed an analytical device model for lateral p-n junction vertical-cavity surface-emitting lasers (LJVCSELs) with a quantum well active region. The model takes into account the features of the carrier injection, transport, and recombination in LJVCSELs as well as the features of the photon propagation in the cavity. This model is used for the calculation and analysis of the LJVCSEL steady-state characteristics. It is shown that the localization of the injected electrons primarily near the p-n junction and the reabsorption of lateral propagating photons significantly effects the LJVCSELs performance, in particular, the LJVCSEL threshold current and power-current characteristics. The reincarnation of electrons and holes due to the reabsorption of lateral propagating photons can substantially decrease the threshold current.
Stationary quantum source coding
Authors: Petz Dénes , Mosonyi Milán
Published: July 2002

In this article the quantum version of the source coding theorem is obtained for a completely ergodic source. This result extends Schumacher’s quantum noiseless coding theorem for memoryless sources. The control of the memory effects requires some earlier results of Hiai and Petz on high probability subspaces. Our result is equivalently considered as a compression theorem for noiseless stationary channels.
New type of frequency-domain four-wave mixing spectroscopy using a quasicontinuous wave probe
Authors: Watanabe Yukio , Kinoshita Shuichi
Published: July 2002

Frequency-domain four-wave mixing (FD-4WM) spectroscopy is developed using an amplified Ti:sapphire laser as pump pulses and a Q-switched yttrium lithium fluoride laser locked to the Ti:sapphire laser as a probe. The diffracted beam is spectrally analyzed by a monochromator and detected by a charge coupled device camera. The signal obtained by this spectroscopy is expressed by the product of the square of the material response function and the second-order cross correlation function of the two pump pulses. We propose the following two applications of this spectroscopy: One is to obtain directly frequency information on the material response, which is difficult to obtain by means of usual homodyne-detected time-domain 4WM spectroscopy. The FD-4WM spectra obtained for liquid samples agree well with the results obtained by optically heterodyne-detected optical Kerr effect measurement. Besides, we have demonstrated the polarization-selected FD-4WM. The other application is the pulse diagnostic use of this spectroscopy: We have measured the FD-4WM spectra for a frequency-modulated pulse, a chirped pulse, and a frequency-modulated, linearly chirped pulse, and have demonstrated that the tempo-spectral relationship between the two pump pulses is very well expressed by the two-dimensional FD-4WM spectra.
Comment on “High order finite difference algorithms for solving the Schrödinger equation in molecular dynamics” [J. Chem. Phys. 111, 10827 (1999)]
Authors: Mazziotti David A.
Published: July 2002

The spectral difference methods [D. A. Mazziotti, Chem. Phys. Lett. 299, 473 (1999)] for solving differential equations in chemical physics combine the useful features of matrix sparsity and rapid convergence. In their recent article [J. Chem. Phys. 111, 10827 (1999)] Guantes and Farantos incorrectly classify the Lagrange distributed approximating functional (LDAF) method in the category of finite differences. This comment clarifies the connections among higher-order finite difference, Lagrange distributed approximating functionals, and other spectral difference methods.
Dependence of electrical properties on nitrogen profile in ultrathin oxynitride gate dielectrics formed by using oxygen and nitrogen radicals
Authors: Watanabe Koji , Tatsumi Toru , Togo Mitsuhiro , Mogami Tohru
Published: July 2002

We studied nitrogen incorporation in ultrathin oxynitride films by using oxygen and nitrogen radicals, and investigated the dependence of the electrical properties on the nitrogen profile. We found that the nitrogen position in the films could be controlled by using different processing sequences, and that the N concentration could be controlled at values up to 16%. In this process, the interface roughness depends on nitrogen position and nitrogen concentration: the interface roughness tends to increase as the N position close to the SiO2–Si interface and increase with N concentration. The results of an analysis of the electrical properties of these oxynitride films indicated that the best way to form the film was by radical nitridation after radical oxidation. These results show that the nitrogen position should be kept away from the SiO2–Si interface and nitrogen amount should be localized at the surface. Using this process, we have successfully achieved a low-leakage 1.5 nm oxynitride (equivalent oxide thickness) and maintained good device performance. This 1.5-nm-thick oxynitride has a leakage current two orders of magnitude less than that of 1.5-nm-thick SiO2 without decreasing the drain current. Radical oxynitridation should thus be very useful in making high-quality ultrathin gate-insulator films.
Electrostatic complexation of spheres and chains under elastic stress
Authors: Schiessel H. , Bruinsma R. F. , Gelbart W. M.
Published: July 2002

We consider the complexation of highly charged semiflexible polyelectrolytes with oppositely charged macroions. On the basis of scaling arguments we discuss how the resulting complexes depend on the persistence length of the polyelectrolyte, the salt concentration, and the sizes and charges of the chain and the macroions. We study first the case of complexation with a single sphere and calculate the wrapping length of the chain. We then extend our consideration to complexes involving many wrapped spheres and study cooperative effects. The mechanical properties of such a complex under an external deformation are evaluated.
Structure and dynamics of I2−(N2O)n: Monte Carlo and molecular dynamics simulations
Authors: Cho Eunseog , Shin Seokmin
Published: July 2002

The structures and relaxation dynamics of I2− embedded in clusters of N2O molecules are studied by Monte Carlo and molecular dynamics simulations. The equilibrium structures of I2−(N2O)n clusters are obtained as a function of cluster size and the closing of the first solvation shell is found to occur at n=13, consistent with experimental observation. By comparing with the previous studies with different types of solvent molecules, it is found that differences in solvent polarity lead to noticeable changes in equilibrium structures and caging dynamics of clusters. N2O clusters tend to form more symmetric, spread-out solvent configurations, resulting in a weaker solvent electric field being exerted on the solute. The localization of the charge distribution for large internuclear separations happens for longer bond length and much more rapidly in I2−(N2O)16 than in I2−(CO2)16 clusters. Molecular dynamics simulations showed that I2− vibrational relaxation is very rapid, losing almost 90% of its internal energy within 1 ps of recombination. It is suggested that the change of I2− charge distribution provides an efficient mechanism for energy transfer from the anion to the surrounding solvents. The N2O solvent with permanent dipole moment exhibits a slightly shorter relaxation time than the nonpolar CO2 solvent. The electrostatic interactions are found to be major driving forces for the compression of the solute throughout the relaxation processes. The effects of solvent flexibility on the relaxation dynamics are investigated for I2− embedded in clusters of flexible N2O solvents. It is found that including the flexibility of the N2O molecules has minimal effect on the vibrational relaxation dynamics of I2−(N2O)16 clusters.
Energy transfer via a thermal capillary
Authors: Huang T. X. , Zheng Zh. J. , Ding Y. K.
Published: July 2002

Thermal radiation transfer in a cylindrical hohlraum is discussed. The mass and energy conservation equations for the ablated wall material, derived from the self-similar solution for ablative heat wave [R. Pakula and R. Sigel, Phys. Fluids 28, 232 (1985)], and coupled flux conservation equation, are solved to investigate energy redistribution inside the hohlraum. A similarity solution is obtained for a gold capillary heated by a uniform disc source, with which the re-emission flux from the wall and the energy transfer efficiency through the thermal capillary are calculated for different parametric conditions.
Dipole-oscillons generating wakefields in a dusty plasma
Authors: Shukla P. K.
Published: July 2002

It is shown that oscillating dipoles of elongated grains (dipole oscillons) can create oscillatory wake potentials which can focus ions and attract nonspherical grains having the same polarity. This may provide the possibility for the formation of a linear ordered structure, which has been observed in association with ultra-low low-frequency oscillations in a liquid plasma crystal [V. Molotkov et al., JETP Lett. 71, 102 (2000); Rahman et al., Phys. Scr. T 89, 186 (2001)].
Intracluster photodimerization of thymine: Size-dependent modes of cluster ion fragmentation
Authors: Kim Nam Joon , Kang Hyuk , Jeong Gawoon , Kim Yung Sam , Lee Kang Taek , Kim Seong Keun
Published: July 2002

Clusters of thymine were found to undergo facile and extensive photodimerization upon strong UV irradiation. Multiphoton excitation/ionization yields cluster ions with excess energy, which undergo thermal fragmentation during flight in time-of-flight mass spectrometer. Reflectron mass spectrometry was employed to investigate the fragmentation dynamics. Remarkably size-specific modes of fragmentation were found: a cluster ion that consists of an even number of molecules tends to lose two molecules, while one that consists of an odd number of molecules loses one molecule. The strong alternation of intensity in the cluster mass spectrum was found to be due to such distinct fragmentation modes. The two-molecule loss was found to be a single fission process of a dimeric unit, which was in accord with a model of the cluster ion that consists of mostly dimeric units. The culprit was extensive intracluster photodimerization, which was shown to occur through absorption of anomalously large numbers of photons by the cluster system during excitation/ionization.
Locality of ion-drift wave spectra in weakly-turbulent dusty plasmas
Authors: Onishchenko Oleg G. , Pokhotelov Oleg A. , Pavlenko Vladimir P. , Sagdeev Roald Z. , Stenflo Lennart , Shukla Padma K.
Published: July 2002

The locality of weakly turbulent Kolmogorov spectra for the ion-drift waves in dusty plasmas and the flute waves in electron-ion plasmas is analyzed. Using a standard kinetic approach for the description of the wave turbulence it is shown that the wave spectrum associated with the enstrophy flux is nonlocal whereas that related to the energy flux is local. The nonlocality of the wave enstrophy spectrum is associated with the long wavelength part of the turbulence. It is found that the wave energy flux is directed to smaller spatial scales.
Interface reactions of high-κ Y2O3 gate oxides with Si
Authors: Busch B. W. , Kwo J. , Hong M. , Mannaerts J. P. , Sapjeta B. J. , Schulte W. H. , Garfunkel E. , Gustafsson T.
Published: July 2002

Ultrathin Y2O3 films were electron beam evaporated in an ultrahigh vacuum onto Si(100) and investigated by high-resolution medium energy ion scattering. Selected films were capped in situ with amorphous Si. Uncapped films that were exposed to air prior to analysis contained excess oxygen compared to a stoichiometric Y2O3 film, and showed a 6–8 Å interfacial layer. Si uptake from the substrate occurred in these films after a 700 °C vacuum anneal, presumably by reacting with the excess oxygen. Si-capped Y2O3 films on the other hand were stoichiometric, and the substrate interface was sharp (⩽2 Å), even after 900 °C vacuum anneals. No change was seen at the Y2O3 capping layer interface until ⩾800 °C for vacuum anneals. These measurements indicate that control of the interface composition is not possible after exposure of ultrathin Y2O3 films to air.
Singularity induced exterior and interior Stokes flows
Authors: Daripa Prabir , Palaniappan D.
Published: July 2002

In this paper, the two-dimensional Stokes flow inside and outside a circular cylinder induced by a pair of line singularities (rotlet and stokeslet) is studied. Analytical solutions for the flow field are obtained by straightforward application of the Fourier method. The streamline patterns are sketched for a number of special cases where the cylinder is either stationary or rotating about its own axis. In particular, some interesting flow patterns are observed in the parameter space which may have potential significance in studies of various flows including flows in journal bearing, mixing flows, chaotic flows, etc. We also investigate into the way the streamline topologies change as the parameters are varied.
Thermal stability and contact degradation mechanisms of TaC ohmic contacts with W/WC overlayers to n-type 6H SiC
Authors: Jang T. , Odekirk B. , Madsen L. D. , Porter L. M.
Published: July 2002

Ohmic contacts comprised of the layer sequence of W/WC/TaC/SiC showed excellent thermal stability after testing at 600 °C for 1000 h. No degradation of the specific contact resistance nor a reaction of the film with the SiC substrate was observed. From Auger electron spectroscopy depth profiles, it was found that W and WC reacted to form W2C on TaC after annealing. After annealing for several hundred hours at 1000 °C, the specific contact resistance of the W/WC/TaC/SiC contacts displayed noticeable degradation. According to secondary ion mass spectrometry (SIMS) analysis, after annealing at 1000 °C for 600 h, small but measurable changes in the electrical characteristics were associated with O incorporation at the interface between TaC and SiC. Investigation of the W/WC/TaC/SiC interface by transmission electron microscopy (TEM) indicated that a reaction between the W and WC had occurred, but there was no observed reaction with the SiC substrate. After annealing for 1000 h, substantial changes in the chemistry, the microstructure, the specific contact resistance, and the spreading resistance of the contacts were observed. To understand the mechanisms associated with the degradation of the electrical properties, SIMS and TEM analyses were performed on samples annealed for 600, 700, 800, 900, and 1000 h at 1000 °C. These findings indicated that both oxidation and metallurgical reactions played important roles in the degradation of the electrical properties.
Reduction of the electron thermal conductivity produced by ion Bernstein waves on the Frascati Tokamak Upgrade tokamak
Authors: Cesario R. , Cardinali A. , Castaldo C. , Leigheb M. , Marinucci M. , Pericoli-Ridolfini V. , Zonca F. , Apruzzese G. , Borra M. , De Angelis R. , Giovannozzi E. , Gabellieri L. , Kroegler H. , Mazzitelli G. , Micozzi P. , Panaccione L. , Papitto P. , Podda S. , Ravera G. , Angelini B. , Apicella M. L. , Barbato E. , Bertalot L. , Bertocchi A. , Buceti G. , Cascino S. , Centioli C. , Chuilon P. , Ciattaglia S. , Cocilovo V. , Crisanti F. , Marco F. De , Esposito B. , Gatti G. , Gormezano C. , Grolli M. , Iannone F. , Maddaluno G. , Monari G. , Orsitto P. , Pacella D. , Panella M. , Pieroni L. , Righetti G. B. , Romanelli F. , Sternini E. , Tartoni N. , Trevisanutto P. , Tuccillo A. A. , Tudisco O. , Vitale V. , Vlad G. , Zerbini M.
Published: July 2002

Operating with a high frequency and a wave guide antenna, the ion Bernstein wave (IBW) experiment on the Frascati Tokamak Upgrade is not dominated, as expected, by nonlinear plasma edge phenomena. By coupling IBW power, a simultaneous increase of plasma density and central electron temperature (⩾2 keV) is produced when the confinement magnetic field is adjusted to set an ion cyclotron resonant layer in the plasma bulk. Transport analysis indicates a reduction of the electron thermal transport inside the internal resonant layer larger than a factor of 2.
A hybrid ion temperature gradient and Kelvin–Helmholtz instability
Authors: Sen A. K. , Reva V. , Avinash K.
Published: July 2002

It is shown that Kelvin–Helmholtz drive due to shear in parallel flow can modestly enhance the ion temperature gradient (ITG) driven modes in the Columbia Linear Machine [R. Scarmozzino et al., Phys. Fluids 31, 1773 (1988)]. However, this modest enhancement does not substantially alter the large discrepancy between our experimental results and the theoretical estimates of stabilizing levels of transverse flow shear, necessary for stabilization of ITG modes.
Phase diagram of dilute lattice surfactant solution
Authors: Shida Cláudio S. , Henriques Vera B.
Published: July 2002

We have studied the temperature–composition phase diagram for a dilute surfactant model solution on the square lattice through Monte Carlo simulations. A micellar region and a solubility line were identified from the measurement of different properties, among which the volume fraction of aggregate, specific heat, and convergence of relaxation from different initial conditions. We have compared properties of the above system with those of a symmetric lattice solution in the dilute regime. Comparison of data allow an interpretation of the micellar phase as a transition region between a microscopically homogeneous phase and a solid phase.
Rate of steady-state reconnection in an incompressible plasma
Authors: Erkaev Nikolai V. , Semenov Vladimir S. , Alexeev Ilya V. , Biernat Helfried K.
Published: July 2002

The reconnection rate is obtained for the simplest case of two-dimensional (2D) symmetric reconnection in an incompressible plasma. In the short note [Erkaev et al., Phys. Rev. Lett. 84, 1455 (2000)], the reconnection rate is found by matching the outer Petschek solution and the inner diffusion region solution. Here the details of the numerical simulation of the diffusion region are presented and the asymptotic procedure which is used for deriving the reconnection rate is described. The reconnection rate is obtained as a decreasing function of the diffusion region length. For a sufficiently large diffusion region scale, the reconnection rate becomes close to that obtained in the Sweet–Parker solution with the inverse square root dependence on the magnetic Reynolds number Rem, determined for the global size of the current sheet. On the other hand, for a small diffusion region length scale, the reconnection rate turns out to be very similar to that obtained in the Petschek model with a logarithmic dependence on the magnetic Reynolds number Rem. This means that the Petschek regime seems to be possible only in the case of a strongly localized conductivity corresponding to a small scale of the diffusion region.
Selective laser desorption of ionic surfaces: Resonant surface excitation of KBr
Authors: Hess Wayne P. , Joly Alan G. , Gerrity Daniel P. , Beck Kenneth M. , Sushko Peter V. , Shluger Alexander L.
Published: July 2002

We demonstrate evidence of selective laser-induced desorption of ground state Br(2P3/2) and spin–orbit excited state Br(2P1/2) atoms from KBr single crystals following 6.4 eV irradiation. Laser excitation tuned selectively to a surface resonance below the first bulk absorption band excites surface states preferentially leading to surface specific reactions while inducing relatively insignificant bulk reaction. The experimental results are supported by embedded cluster ab initio calculations that indicate a reduced surface exciton energy compared to that of the bulk exciton with a slight further reduction for steps and kink sites. Low fluence irradiation of cleaved KBr crystals, near the calculated surface exciton energy of 6.2 eV, produces hyperthermal Br(2P3/2) emission without a significant thermal or Br(2P1/2) component. The hyperthermal emission is shown theoretically to be characteristic of surface induced reaction of exciton decomposition while thermal emission is attributed to bulk photoreaction.
Anisotropy of a thermal field at dissipative scales in the case of small-scale injection
Authors: Rosset L. , Paranthoën P. , Lecordier J.-C. , Gonzalez M.
Published: July 2002

The anisotropy of a thermal field at the level of dissipation has been studied experimentally and by means of modeling, downstream of a heated line source placed, successively, in a turbulent boundary layer and a turbulent plane jet. This situation represents anisotropic small-scale injection of a passive scalar in a turbulent medium. All three instantaneous temperature gradients have been measured. In the central region of the thermal sheet, experimental data reveal a high degree of anisotropy of temperature dissipation near the line source and return to isotropy further downstream. Comparison of measurements with modeling allows interpreting the data and estimating the return-to-isotropy time scale.
Re-analysis of the ultraviolet absorption spectrum of ozone
Authors: O’Keeffe Patrick , Ridley Trevor , Lawley Kenneth P. , Donovan Robert J.
Published: July 2002

A re-analysis of the Huggins and Hartley bands in the ultraviolet absorption spectrum of O3 is presented in which the structure in both bands is assigned to vibrational progressions in the symmetric stretching mode ν1 and the bending mode ν2 but not the asymmetric stretching mode ν3. The present improved fit of a larger range of bands results in relatively large anharmonicity terms, whereas previous assignments have relied on the motion being largely harmonic in the upper state. From a consideration of the shape of single surface required to support both sets of vibrational data, it is concluded that the Huggins bands almost certainly terminate on the 2 1A1 state rather than the 1 1B2 state.
Synthesis of carbon nanotube bridges on patterned silicon wafers by selective lateral growth
Authors: Han Young-Soo , Shin Jin-Koog , Kim Sung-Tae
Published: July 2002

Floated carbon nanotube bridges were synthesized on a patterned silicon wafer by thermal chemical vapor deposition of acetylene. A conventional photolithography was used to define the catalytic nickel line patterns. The carbon nanotubes grow laterally from the side face to side face of the nickel catalyst by a SiO2 vertical growth barrier deposited on the nickel layer. The typical diameter of carbon nanotube bridges is 10–30 nm and it depends on the thickness of the catalytic nickel layer. Our laterally grown carbon nanotubes have a bamboo structure in which the spacing of compartment layers increases with an increase in temperature. We can control the length, linearity, and density of the carbon nanotube bridges by adjusting various synthetic process parameters and find they may possibly be applied to nanoelectronic devices.
Extreme thermal expansion, piezoelectricity, and other coupled field properties in composites with a negative stiffness phase
Authors: Wang Y. C. , Lakes R. S.
Published: July 2002

Particulate composites with negative stiffness inclusions in a viscoelastic matrix are shown to have higher thermal expansion than that of either constituent and exceeding conventional bounds. It is also shown theoretically that other extreme linear coupled field properties including piezoelectricity and pyroelectricity occur in layer- and fiber-type piezoelectric composites, due to negative inclusion stiffness effects. The causal mechanism is a greater deformation in and near the inclusions than the composite as a whole. A block of negative stiffness material is unstable, but negative stiffness inclusions in a composite can be stabilized by the surrounding matrix and can give rise to extreme viscoelastic effects in lumped and distributed composites. In contrast to prior proposed composites with unbounded thermal expansion, neither the assumptions of void spaces nor slip interfaces are required in the present analysis.
Protonic and Bjerrum defect activity near the surface of ice at T<145 K
Authors: Uras-Aytemiz Nevin , Joyce Charles , Devlin J. Paul
Published: July 2002

The activity of point defects within cubic-ice nanocrystals has been probed using isotopic exchange of D2O molecules isolated intact within H2O aerosol particles of average radii ranging from 12 to 45 nm. The observed rates of conversion of D2O to dynamically coupled HDO molecules, and ultimately to isolated HDO, offer a direct evaluation of the activity of both the protonic and orientational (Bjerrum) defects within a few nm of the ice surface. We have sought answers to two interesting questions related to proton transport in cubic ice: (1) is Bjerrum-defect activity enhanced near the ice surface as a consequence of the structural defects associated with the surface, and (2) does proton trapping in the disordered surface region lead to a reduced proton activity, as reported for amorphous solid water? The new data indicate that Bjerrum defect activity within ice nanocrystals exceeds that of bulk ice for similar temperatures by more than an order of magnitude. In contrast, the observed behavior of protonic defects matched closely that of thick ice films.
Isotope exchange of D2O on H2O ice: Surface versus bulk reactivity
Authors: Everest Michael A. , Pursell Christopher J.
Published: July 2002

The nature of the surface of crystalline water ice is investigated by monitoring isotope exchange in the first few bilayers. Near-monolayer amounts of D2O are deposited on thin films of H2O ice and isotope exchange at 145 K is monitored with Fourier-Transform infrared spectroscopy as a function of time. No exchange occurs on the surface of pure ice, however, exchange is readily observed on the surface of ice doped with small amounts of hydrogen chloride (HCl). The lack of exchange at the surface of pure ice stands in contrast to similar experiments performed of D2O embedded in the bulk. This suggests a depletion of mobile defects on the surface of pure crystalline ice at 145 K. This relative depletion may cause a significant difference between reactivity on the ice surface and in the ice bulk for other systems.
Magnetotunneling spectroscopy of an individual quantum dot in a gated tunnel diode
Authors: Hill R. J. A. , Patanè A. , Main P. C. , Eaves L. , Gustafson B. , Henini M. , Tarucha S. , Austing D. G.
Published: July 2002

We use an array of gate electrodes to control the electrostatic profile in a layer of self-assembled InAs quantum dots. In combination with magnetotunneling spectroscopy, this allows us to identify and measure the energy levels and wave functions associated with the ground and excited state of an individual quantum dot.
Inertial effects in the nonlinear transient relaxation of Brownian particles in strong external electric fields
Authors: Coffey W. T. , Kalmykov Yu. P. , Titov S. V.
Published: July 2002

A method of calculation of the nonlinear transient response of an assembly of fixed axis (two-dimensional) rotators due to sudden changes of a strong external dc electric field is presented. The infinite hierarchy of differential-recurrence relations for the decay functions describing the relaxation of the system is derived by averaging the underlying inertial Langevin equation. The solution for the one-sided Fourier transform of this hierarchy is obtained in terms of matrix continued fractions. The integral relaxation time and the spectrum of the electric polarization for various kinds of nonlinear transient responses (step-on, step-off, rapidly rotating field) are calculated for typical values of the model parameters. Both exhibit pronounced nonlinear effects due to the strong dc field. Analytical equations for the quantities of interest are presented for particular cases (in the overdamped and low damping limits, etc.).
A time pickup system for monitoring cyclotron beam bursts
Authors: Okumura S. , Fukuda M. , Ishibori I. , Arakawa K.
Published: July 2002

We have developed a time pickup system for monitoring the beam bursts from a cyclotron. The time pickup can measure the phase and the width of the beam bursts by detecting secondary electrons emitted from a foil or a wire target inserted into the beam with time resolutions around 200 ps full width at half maximum in spite of its simple structure. By using the foil and the wire targets appropriately, monitoring the bursts of a variety of beams can be achieved. In addition, by adjusting the position of the target, a high enough detection rate of the beam burst is obtained with a minimum of interference with the beam. The present investigation shows that it is needed to adjust the collection voltage of the time pickup because the optimum collection voltages for high resolution measurement are in the range from −0.5 to −1.0 kV and those for high efficiency measurement are not less than −4.0 kV.
Tunable surface plasmon resonance silver films
Authors: Weimer W. A. , Dyer M. J.
Published: July 2002

Precise control of thermal evaporation deposition parameters allows the production of silver island films on glass substrates with tunable surface plasmon resonance wavelengths. Specific combinations of substrate temperature, deposition rate, and film thickness produce films exhibiting surface plasmon resonance wavelengths that can be adjusted throughout the visible and into the near-IR regions of the electromagnetic spectrum. These films are shown to be useful as substrates for surface enhanced Raman spectroscopy.
Nonlinear development of flow patterns in an annulus with decelerating inner cylinder
Authors: Watanabe Takashi , Furukawa Hiroyuki , Nakamura Ikuo
Published: July 2002

Decelerating Taylor vortex flow between two concentric cylinders is investigated by using the time-dependent numerical method. The lengths of the rotating inner cylinder and the stationary outer cylinder are finite. We focus on the mode transitions from well-developed flows during the gradual decrease in the angular velocity of the inner cylinder. In the range of the Reynolds number from 50 to 1000 and the range of the aspect ratio Γ from 2.6 to 7.2, the exchanges of flow pattern from normal secondary modes to primary modes are clarified, and the Reynolds numbers at which the flow modes exchange are determined. The reduction of the number of cells in the flow of the normal mode begins with the weakening of a pair of counter-rotating cells with an inward radial flow at their boundary. An anomalous cell has two extra cells at corners of the end wall and the cylinder walls. In the transient process from the flow of the anomalous mode, extra cells grow and merge into a normal cell, and a saddle point appears in the working fluid. As the merged cell enlarges, the saddle point vanishes and the global normal flow mode appears. The result shows good agreement with experimental observations.
Shape-dependent magnetization reversal processes and flux-closure configurations of microstructured epitaxial Fe(110) elements
Authors: König C. , Sperlich M. , Heinesch R. , Calarco R. , Hauch J. O. , Rüdiger U. , Güntherodt G. , Kirsch S. , Özyilmaz B. , Kent A. D.
Published: July 2002

The magnetization reversal processes and magnetic domain states of microstructured epitaxial Fe(110) elements have been investigated by magnetic-force microscopy and longitudinal Kerr hysteresis loop measurements. The characteristic micromagnetic behavior, such as coercive and nucleation fields, can be tailored by taking advantage of the pronounced uniaxial anisotropy and by varying the shape of the elements. The magnetic domain states of rectangular and diamond-shaped elements with lateral dimensions of 1.5 μm×0.5 μm have been investigated after magnetic saturation along the long and short axes of the elements. The observed flux-closure domain states have been compared with micromagnetic simulations.
In situ magnetoelastic coupling and stress-evolution studies of epitaxial Co35Pd65 alloy films in the monolayer regime
Authors: Jeong Jong-Ryul , Kim Jonggeol , Lee Jeong-Won , Kim Sang-Koog , Shin Sung-Chul
Published: July 2002

We report in situ measurements of magnetoelastic coupling, B2, and stress, σ, in Co35Pd65 alloy films epitaxially grown on a Cu/Si(001) substrate in a thickness range of 1–10 ML by means of a highly sensitive optical deflection-detecting system. It was found that the value of B2 increases from 0.72×107 J/m3 at 2 ML to 3.31×107 J/m3 at 10 ML. A second-order strain correction of B2=Bb+C1ε+C2ε2 rather than a first-order one of B2=Bb+C1ε provides a better fit for the observed behavior of B2 versus film strain, ε, where Bb is the bulk value. The relationship between B2 and ε observed in the present study reveals that the second-order correction is crucial for understanding the dependence of B2 on ε in an ultrathin regime.
Electronic spectroscopy of jet-cooled CFCl: Laser-induced fluorescence, dispersed fluorescence, lifetimes, and C–Cl dissociation barrier
Authors: Guss Joseph S. , Votava Ondrej , Kable Scott H.
Published: July 2002

The Ã(1A″)–X̃(1A′) transition of jet-cooled chlorofluorocarbene (CFCl) has been measured by laser-induced fluorescence (LIF) excitation and dispersed fluorescence spectroscopy. Over 170 vibronic transitions were measured in the LIF spectrum, consisting of cold bands and hot bands of carbenes containing both Cl35 and Cl37 isotopes. Dispersed fluorescence spectroscopy was used both to map the ground-state vibrational levels and to provide confirmation of the vibronic identity of the emitting level. A predictor–corrector method was used to progressively assign almost all of the vibronic transitions, resulting in the positive assignment and measurement of almost every bound vibrational state within the Ã-state manifold. The vibrational structure is modeled well by a Morse potential with frequencies ν1′=1229 cm−1, ω2′=399.2 cm−1, and ω3′=748.0 cm−1 for CF 35Cl and 1235 cm−1, 397.0 cm−1, and 744.5 cm−1 for the same three vibrations in CF 37Cl. The standard diagonal and cross-anharmonicity constants for a three-coordinate Morse potential were also measured for each isotopic species. Dispersed fluorescence spectroscopy provided a map of ground-state vibrational levels up to about 4000 cm−1. Franck–Condon factors were modeled well by a simple, one-dimensional harmonic potential, and these were also used to confirm assignment of many transitions. The fluorescence lifetime of the excited vibronic states decreased markedly from a consistent 650 ns for most states, to <20 ns for the highest lying observed state. In addition, the Franck–Condon analysis indicates that higher lying members of progressions were missing in the LIF spectrum. This strongly indicated the presence of a nonradiative pathway that opens for energies above T00+4073 cm−1. Analysis of the rotational structure of many transitions indicated that the molecule was not reaching the Renner–Teller intersection, where the Ã and X̃ states are degenerate. We attribute the nonradiative channel to cleavage of the C–Cl bond directly on the Ã state, in exact analogy with the observed process in CFBr. The height of the barrier, and the vibrational frequencies are all in reasonable agreement with recent ab initio values.
Design and test of a beam profile monitoring device for low intensity radioactive beams
Authors: Ostroumov P. N. , Billquist P. , Portillo M. , Shen W. Q.
Published: July 2002

Development efforts have gone into the construction and performance testing of a device that can be used to provide snap shot images of the beam profile. It is intended to function even at very low ion intensities, such as those expected from a rare-isotope accelerator. Intensity profiles and emittance analysis are among the most critical tools used for optimizing beam transport through accelerators. This article describes the design and performance of a beam image monitor. The device is sensitive at a wide dynamic range which spans from ∼102 to ∼1012 pps. With the advent of double-plane slits or a pepper pot plate, this system can be used to scan transverse emittance profiles in both the x–x′ and y–y′ phase space planes, simultaneously. Conventional diagnostic devices used for heavy ion accelerators generally require at least 109 pps intensity to carry out similar diagnostics, which is not practical when considering beams with very low intensities, such as rare isotope beams. Furthermore, the detection system used here can be used for a wide range of incident ion velocities. Compared with solid-state detectors and scintillators that are inserted directly into the beam, this type of detection system is less susceptible to beam induced damage resulting in longer lifetimes and less maintenance. The test was done using single charge state Kr beams at energies ranging from 3.6 to 18 keV/u. The device’s sensitivity was monitored for intensities below 1012 pps and an emittance scan was recorded and analyzed. The spatial resolution was characterized by comparing the emittance profile with that obtained by a wire scanning device which had better resolution but was sensitive only to intensities above 1011 pps. Recently, the device has been used to aid in the transport of ∼6 MeV/u radioactive beams, such as F17, produced by pickup reactions with a gas cell target at the ATLAS accelerator facility.
Failure of exchange-biased low resistance magnetic tunneling junctions upon thermal treatment
Authors: Lee J. H. , Jeong H. D. , Kyung H. , Yoon C. S. , Kim C. K. , Park B. G. , Lee T. D.
Published: July 2002

Transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS) were used to characterize low resistance (100–1000 Ω μm2) tunneling junctions consisting of Ta/NiFe/Cu/NiFe/IrMn/CoFe/Al (6.6 and 7.7 Å)–oxide/CoFe/NiFe/Ta multilayers after annealing at temperatures ranging from 250 to 500 °C. The Al (7.7 Å) junction showed continual improvement in the magnetoresistance (MR) ratio when annealed up to 300 °C while the MR ratio of the Al (6.6 Å) junction dropped sharply above 250 °C in spite of the only 1 Å difference in the deposited thickness of aluminum metal prior to plasma oxidation. TEM measurement provided evidence that the annealing process improves, in general, structural uniformity in the insulation layer, but thermal treatment can also degrade junction performance at a relatively low temperature due to current leakage through the electrodes. Current leakage can be problematic for a junction whose insulation barrier may be too thin (less than ∼10 Å). Both RBS and TEM analyses indicated that the maximum annealing temperature of exchange biased junctions lies between 400 and 500 °C above which the multilayer structure in the pinned electrode is destroyed by interdiffusion.
Intermolecular potential and second virial coefficient of the water–helium complex
Authors: Hodges Matthew P. , Wheatley Richard J. , Harvey Allan H.
Published: July 2002

A potential-energy surface for the water–helium complex is constructed from scaled perturbation theory calculations, and calibrated using accurate supermolecule methods. At the global minimum, the helium atom lies in the plane of the water molecule with an interaction energy corresponding to about 35 cm−1 (−160 microhartree). The potential is used to calculate second virial coefficients, including first-order quantum corrections, from 100 to 2000 K. The estimated uncertainties in the calculated values are much smaller than the uncertainties in the available experimental data; the calculated values also cover a much wider range of temperature. The quantum corrections are found to be smaller in magnitude than the uncertainty in the calculated second virial coefficient.
On the applicability of the Redfield high-temperature theory for proton dipolar order relaxation in liquid crystals
Authors: Mensio O. , González C. E. , Zamar R. C.
Published: July 2002

Nuclear magnetic resonance experiments on the Larmor frequency dependence of the intrapair dipolar order relaxation time T1D showed the existence of discrepancies between the usual two-spin theory and the experimental data. Field-cycling experiments of T1D in methyl deuterated para azoxyanisole (PAA-d6) in the nematic phase [J. Chem. Phys. 110, 8155 (1999)] showed that the difference cannot be assigned to the common assumption of isolated spin pairs or to the neglecting of the alkyl chain protons in the theoretical interpretation. Though the applicability of the spin temperature and short correlation time assumptions have not been justified for nematic liquid crystals, they have been used in all the available theoretical approaches for dipolar order relaxation. In this work, we calculate T1D of PAA-d6 within the Redfield high-temperature theory of spin–lattice relaxation but avoid the usual assumptions of short correlation times and random phase. First, we find that this fact does not alter the expression for T1D in the simple case of an ensemble of isolated spin pairs. Then we take the four benzene protons as the spin system and find that this refinement gives no relevant contribution able to explain the discrepancies between theory and experiments. Also, we find that the random phase assumption becomes redundant in the calculation of T1D, whenever the relevant spin Hamiltonian is nondegenerate. Thus, in these cases the spin temperature hypothesis is justified in liquid crystals, where the spin system contains few spins. We conclude that the Redfield high-temperature relaxation theory fails to describe T1D in thermotropic liquid crystals, since it underestimates the prominent role of the slow cooperative motions.
Time-of-flight neutral mass and velocity spectrometer for atmospheric research
Authors: Fujikawa N. , Tsuruda K. , Hayakawa H.
Published: July 2002

We have developed a prototype time-of-flight neutral gas mass spectrometer that simultaneously measures the density and the velocity distribution function of each mass species, using the time-of-flight and the two-dimensional spatial distribution of the ionized particles on a charge-coupled device (CCD). We confirmed the feasibility of the velocity distribution measurement in a vacuum chamber using room-temperature Ar gas, by measuring the spatial distribution of the ionized Ar on the CCD and inferring the corresponding velocity distribution of the incident Ar.
Time and phase control of x-rays in stroboscopic diffraction experiments
Authors: Zolotoyabko E. , Quintana J. P.
Published: July 2002

Time-resolved diffraction experiments with a LiNbO3-based surface acoustic wave (SAW) device were carried out at the 5BMD station of the APS. X-ray diffraction was measured using a 0.58 GHz standing SAW excitation. We observed well-defined diffraction satellites about the main diffraction maximum due to inelastic multiphonon scattering. The satellite intensity oscillated, as a function of the delay time, at 1.16 GHz (i.e., twice the SAW frequency). The maximum satellite contribution reached 40% of the main peak intensity, and proves that the SAW device acts as a fast and effective modulator for coming x-rays. In this study, the phase shift between the x-ray bursts and the acoustic deformation was changed both by electronic delay line (in steps of 18 ps) and by translating the diffractometer along the incident x-ray beam. We demonstrate that the later method can be used to produce very precise delay times in the fs- and ps-scale range. By using a motorized Thomson stage and a laser scan micrometer (Mitutoyo LSM-6000), the translations can be done in steps of 100 nm and monitored with the same precision. The measured positional fluctuations of the diffractometer at rest were within 200–400 nm, which yields the jitter of the corresponding time delay of about 1 fs.
Solvable model of kinetic control
Authors: Fraser Simon J.
Published: July 2002

A two-step nonlinear sequential reaction mechanism is studied as a dimensionless model of kinetic control. In this mechanism the unimolecular step is: A→B1, and the bimolecular step is: A+B→Cε, with normalized initial conditions. For ε≪1, little C is formed, whereas for ε≫1, the concentration of B approaches a steady state and C is the main product. Because of the coupling between the two reaction steps the steady-state approximation (SSA) is both a nullcline and a solution of the ordinary differential equations (ODEs) for the model. All concentrations can be expressed in terms of a timelike, real phase variable φ, whose evolution is described by a first-order, nonlinear ODE. Algorithms for the systematic perturbation solution of this ODE for large and small ε are given.
Motion of an inclined plate supported by a sessile two-dimensional drop
Authors: Reznik S. N. , Zussman E. , Yarin A. L.
Published: July 2002

Motion of an inclined plate supported by a two-dimensional sessile drop on a second plate is studied in the inertialess approximation. It is shown that the upper plate can be equilibrated horizontally, parallel to the lower plate supporting the drop, when the Bond number exceeds a certain threshold value. The dependence of this threshold value on the parameters of the plate and liquid is found and discussed. Small oscillations of the plate near its equilibrium horizontal position on top of the drop are investigated analytically in the case of low liquid viscosity. The periods of the vertical (translational) and angular oscillations are determined. Comparison with experimental data demonstrates reasonable agreement between the characteristic times of the process predicted analytically and observed experimentally.
Coexistence of paramagnetic-charge-ordered and ferromagnetic-metallic phases in La0.5Ca0.5MnO3 evidenced by electron spin resonance
Authors: Rivadulla F. , Freita-Alvite M. , López-Quintela M. A. , Hueso L. E. , Miguéns D. R. , Sande P. , Rivas J.
Published: July 2002

Throughout a complete electron spin resonance (ESR) and magnetization study of La0.5Ca0.5MnO3, we discuss about the nature of the complex phase-segregated state established in this compound below T∼210 K. Between TN⩽T⩽TC, the ESR spectra shows two lines characteristic of two different magnetic phases. From the resonance field (Hr) derived for each line, we argue that the incommensurate-charge-ordering phase (ICO) which coexists with ferromagnetic–metallic (FMM) clusters in this temperature interval, is mainly paramagnetic and not antiferromagnetic. The FMM/ICO ratio can be tuned with a relatively small field, which suggests that the internal energy associated with those phases is very similar. Below TN, there is an appreciable ferromagnetic (FM) contribution to the magnetization and the ESR spectra indicates the presence of FM clusters in an antiferromagnetic matrix (canted). Our results show that ESR could be a very useful tool to investigate the nature of the phase-separated state now believed to play a fundamental role in the physics of mixed valent manganites.
Structure and growth modes of (BaO)n (n⩽9) clusters
Authors: Chen G. , Liu Z. F. , Gong X. G.
Published: July 2002

Using density functional theory with the generalized gradient approximation, we have studied the structures of small (BaO)n (n⩽9) clusters. We find that there are three different growth modes (cubic-like, ring-like and anti-tetragonal prism based) for the (BaO)n clusters. Although the cubic-like structure is prevailing for the clusters, the energy difference from other growth modes is small. The anti-tetragonal prism based structures are found to be ground states for (BaO)5 and (BaO)7.