bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron-propagator calculations on the photoelectron spectrum of ethylene
Authors: Dolgounitcheva O. , Zakrzewski V. G. , Ortiz J. V.
Published: July 2002

Electron-propagator calculations are performed on the vertical ionization energies of ethylene with a sequence of correlation-consistent basis sets. Two methods are employed: the nondiagonal, renormalized, second-order (NR2) approximation and the third-order, algebraic, diagrammatic construction. The computational efficiency of the NR2 method permits the use of the correlation-consistent, pentuple ζ basis, which contains 402 contracted Gaussian functions. As the size of the basis set grows, NR2 results for outer-valence ionization energies steadily increase; NR2 errors with the largest basis set are less than ∼0.15 eV. Agreement with prominent, inner-valence peaks is also satisfactory and the ratio of two pole strengths corresponding to inner-valence, Ag2 states is in close agreement with observed intensity ratios.
A simple treatment of the sine-Gordon equation
Authors: Chen Shi-Rong , Huang Nian-Ning
Published: July 2002

To avoid difficulties due to the complexity of the Lax pair of the sine-Gordon equation, the orthogonality relations of the squared Jost solutions is derived simply using the 1+1 dimensional Green’s theorem. The direct perturbation theory for sine-Gordon in the laboratory reference is re-developed, correcting some numerical coefficients in published orthogonality relationships.
An experimental and ab initio reinvestigation of the Lyman-α photodissociation of H2S and D2S
Authors: Cook Phillip A. , Langford Stephen R. , Dixon Richard N. , Ashfold Michael N. R.
Published: July 2002

The Lyman-α (λH=121.6 nm) photodissociation of both H2S and D2S has been reinvestigated using the experimental technique of H/D atom photofragment translational spectroscopy. Their total kinetic energy release profiles consist of two distinct components. The first, which is highly structured, is assigned to two body dissociation to H/D(2S)+SH/SD(A 2Σ+) fragments, with the latter formed in a range of rovibrational states. By assigning these various levels the dissociation energy of D2S (measured relative to the lowest rovibrational level of the products) is determined to be D0(D-SD)⩾31 874±22 cm−1. The second contribution, which is broad and relatively unstructured, is modeled in terms of two likely fragmentation pathways; secondary predissociation of SH/SD(A 2Σ+) partner fragments associated with the structured contour, and primary three-body dissociation to 2H/D(2S)+S(1D) atomic products. The presented data allow determination of the kinetic energy-dependent anisotropy parameter (β), which is positive over both profiles. This indicates a preferentially parallel distribution of H/D atom recoil velocities about the laser polarization axis. These data are presented in tandem with ab initio and classical trajectory calculations which seek to explain the lack of branching to ground state H/D+SH/SD(X 2ΠΩ) molecular products. The analogous channel is important in the Lyman-α dissociation of the lighter homologue, H2O.
Enhancement of magnetic properties of nanocomposite Pr2Fe14B/α-Fe magnets by small substitution of Dy for Pr
Authors: Chen Zhongmin , Okumura Hideyuki , Hadjipanayis George C. , Chen Qun
Published: July 2002

Nanocomposite (Pr,Dy)2Fe14B/α-Fe magnets with compositions Pr8−xDyxFe86B6 (x=0, 0.5, 1, 1.5, and 2) have been synthesized by melt spinning using low wheel speeds in the range from 18 to 21.7 m/s. It has been found that the coercivity is significantly increased by Dy substitution. An optimum coercivity of 6.6 kOe is obtained in the Pr7Dy1Fe86B6 magnet as compared to 4.3 kOe in the Pr8Fe86B6 magnet. As a result, the energy product is increased from 9.1 MGOe in the Pr8Fe86B6 magnet to 16.9 MGOe in the Pr7Dy1Fe86B6 magnet. The reason for this is the finer and more uniform 2:14:1/α-Fe nanoscale microstructure developed in the magnets with Dy substitution. Because of the low wheel speed spinning, the majority of the nanoscale microstructure is crystallized directly out of the melt. The enhancement of magnetic properties by Dy substitution is mainly due to the microstructure refinement which leads to an enhanced exchange coupling between the Pr2Fe14B and α-Fe, whereas the anisotropy increase by the Dy substitution provides only a minor contribution to the enhanced coercivity.
The scenario of three-dimensional instabilities of the cylinder wake in an external magnetic field: A linear stability analysis
Authors: Mutschke G. , Gerbeth G. , Shatrov V. , Tomboulides A.
Published: July 2002

A more detailed look is given on the scenario of three-dimensional (3-D) instabilities in the magnetohydrodynamic cylinder flow when the oncoming flow and the magnetic field are parallel. The results presented here are in the frame of linear stability analysis in the range 100<Re<250 and extend the results in our previous letter [Phys. Fluids 9, 3114 (1997)]. As the strength of the magnetic field is increased, a nonmonotonic behavior of the 3-D instability is found. This is mainly due to the fact that the underlying two-dimensional (2-D) flow changes considerably from periodic to steady while different instability mechanisms are counteracting. The behavior at weak magnetic fields depends on the Reynolds number and has either a damping or an enhancing influence on 3-D instability. A local maximum is observed in the 3-D instability curve, close to the critical value for 2-D instability, Nc2-D, leading to 3-D instability at Reynolds numbers as low as Re∼150, i.e., lower than the critical Reynolds number for the onset of three dimensionality, Rec3-D, in the pure hydrodynamic cylinder flow. By increasing the magnetic field strength further, the 3-D instability is first damped while for larger values of N it is generally amplified. Therefore, for strong magnetic fields, 3-D steady flows may exist at Re which are considerably lower than Rec3-D of the pure hydrodynamic cylinder flow. In the case of a transverse magnetic field, a stronger and approximately monotonic damping of three dimensionality was observed with increasing magnetic field strength.
Gray track formation in KTiOPO4 by swift ion irradiation
Authors: Deepthy A. , Rao K. S. R. K. , Bhat H. L. , Kumar Ravi , Asokan K.
Published: July 2002

Potassium titanyl phosphate single crystals were irradiated with 48 MeV lithium ions at fluences varying from 5×1012 to 1016 ions/cm2. The defects created in the crystal have been characterized using x-ray rocking curve measurements, optical transmittance, and photoluminescence spectroscopy. From x-ray rocking curve studies, the full width at half maximum for the irradiated samples was observed to increase, indicating lattice strain caused by the energetic ions. Optical transparency of these samples was found to decrease upon irradiation. The irradiated samples exhibited a broadband luminescence in the 700–900 nm region, for fluences above 5×1013 ions/cm2. The results indicate that ion-beam-induced optical effects in KTiOPO4 single crystals are very similar to the ones obtained for crystals with “gray tracks,” which are attributed to the electronic transitions in the Ti3+ levels.
Microwave interferometer for steady-state plasmas
Authors: Scime Earl E. , Boivin Robert F. , Kline John L. , Balkey Matthew M.
Published: July 2002

Standard single frequency, “fringe-counting,” microwave interferometers are of limited use for steady-state plasma experiments. We have constructed a swept frequency microwave interferometer, similar to a classic zebra-stripe interferometer, optimized for electron density measurements in steady-state plasma experiments. The key element in the system is a frequency doubled YIG oscillator capable of sweeping from 20 to 40 GHz. As the source frequency is swept, the sum of the reference and plasma leg signals exhibits a series of beats. Both the frequency shift and phase shift of the beat pattern due to the addition of plasma in one leg of the interferometer is used to determine the line-integrated electron density.
Microstructure and magnetoelastic properties of FeCo/Ag multilayers
Authors: Wang L. C. , Hatton H. J. , Cooke M. D. , Gibbs M. R. J. , Rainforth W. M. , Hetherington C. J. D.
Published: July 2002

There is growing evidence that in magnetic films of thickness less than 20 nm there can be significant change in the values of magnetic anisotropy constant and magnetoelastic coupling from those of bulk materials. While phenomenological models based on Néel’s idea of surface anisotropy may offer a partial explanation, it is vital to develop a more mechanistic understanding. Recently the potential contribution of interface and surface strains to the observed property change has been highlighted. Here we report the field emission gun TEM and electron spectroscopic images of the structure of the interface region between Fe50Co50 and Ag, the local crystallographic texture and the distribution of Ag in magnetostrictive Fe50Co50/Ag multilayers. The results are correlated with the bulk measurements of coercivity and the saturation magnetostriction constant. For the first time it is possible to provide a degree of microstructural interpretation of the magnetic data.
Comparison of defect density measurements in magnetic tunnel junctions
Authors: Allen D. , Schad R. , Zangari G. , Zana I. , Tondra M. , Wang D. , Reed D.
Published: July 2002

Magnetic tunnel junctions may experience failure due to local shortcuts in the insulating layers of such devices. The quality of the insulating layers of these devices must be analyzed. We use electrodeposition to decorate pinholes and analyze the density of pinholes and pinhole precursors. Electrical breakdown measurements can also be performed on magnetic tunnel junctions to predict the probability of such devices failing. We discuss both experimental methods and compare the results obtained. It is observed that the two methods yield the same results for the areal defect density.
Experimental study of ion heating and acceleration during magnetic reconnection
Authors: Hsu S. C. , Carter T. A. , Fiksel G. , Ji H. , Kulsrud R. M. , Yamada M.
Published: July 2002

Ion heating and acceleration has been studied in the well-characterized reconnection layer of the Magnetic Reconnection Experiment [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)]. Ion temperature in the layer rises substantially during null-helicity reconnection in which reconnecting field lines are anti-parallel. The plasma outflow is sub-Alfvénic due to a downstream back pressure. An ion energy balance calculation based on the data and including classical viscous heating indicates that ions are heated largely via nonclassical mechanisms. The Ti rise is much smaller during co-helicity reconnection in which field lines reconnect obliquely. This is consistent with a slower reconnection rate and a smaller resistivity enhancement over the Spitzer value. These observations show that nonclassical dissipation mechanisms can play an important role both in heating the ions and in facilitating the reconnection process.
Thermal stability of Ta-pinned spin valves
Authors: Fry Richard A. , McMichael R. D. , Bonevich J. E. , Chen P. J. , Egelhoff W. F. , Lee C.-G.
Published: July 2002

It has recently been found that large uniaxial anisotropy fields in excess of 120 kA/m (1500 Oe) can be created in thin (3–5 nm) films of Co by obliquely sputtered Ta underlayers. This anisotropy can be used to pin the bottom film of a spin valve while having only a modest effect on the top “free” film, separated by a 2.5 nm Cu spacer layer. This article describes measurements of thermal stability in these Ta-pinned spin valves. Using room temperature giant magnetoresistance (GMR) as a measure, we find that the structure is stable under cumulative 20 min anneals at 25 °C intervals up to 300 °C; GMR decreases to zero upon further anneals up to 450 °C. Measurements taken at elevated temperatures reveal that GMR decreases linearly with temperature, extrapolating to zero at approximately 425 °C, while the anisotropy field is much less temperature dependent, remaining nearly constant up to 150 °C and gradually decreasing to 50% of its room temperature value at 325 °C.
Nonequilibrium molecular dynamics simulations of confined fluids in contact with the bulk
Authors: Zhang Luzheng , Balasundaram Ramkumar , Gehrke Stevin H. , Jiang Shaoyi
Published: July 2002

A nonequilibrium molecular dynamics (MD) simulation study is reported of the structural and rheological properties of confined n-decane between two Au(111) surfaces in contact with its bulk under constant normal loads or constant heights. In the constant-load MD simulations, it was observed that fluid molecules were squeezed out of the pore continuously in a single simulation upon compression, whereas fluid molecules in the bulk were soaked into the pore when applied normal load was released. Pore separation depends on bulk pressure under the same normal load and approaches a steady value as normal load increases. In the constant-height simulations, density, velocity, and orientational profiles of the confined film were accumulated along the Z (perpendicular to the walls) and Y (parallel to the walls and finite due to the bulk) directions. These distributions are not uniform not only along the Z direction but also along the Y direction, particularly for weak fluid–wall interactions. The shear-thinning behavior and “slip” boundary conditions were also studied in this work. Even though the shear-thinning behavior was reported by several previous studies, the number of particles was fixed and the bulk condition was unknown in those simulations. The simulation geometry employed in this work is closer to that of surface-force apparatus (SFA) experiments and of engine lubricating systems where confined liquid is in contact with its bulk.
Magnetic stability in exchange-spring and exchange-bias systems after multiple switching cycles
Authors: Jiang J. S. , Inomata A. , You C.-Y. , Pearson J. E. , Bader S. D.
Published: July 2002

We have studied the magnetic stability in exchange-bias and exchange-spring systems during repeated reversal of the pinned layer. The samples were prepared by epitaxial sputter deposition. The exchange-biased system consists of a combination of ferromagnetic and antiferromagnetic Fe/Cr superlattices. The exchange-spring system is a bilayer structure made of hard Sm–Co and soft Fe ferromagnetic layers. The magnetic properties were investigated using the magneto-optic Kerr effect during repeated reversal of the soft layer magnetization by field cycling up to 107 times. The experimentally observed decay behaviors are discussed in terms of microstructure and spin configuration of the pinning layers.
Effects of Ag2O doping on the electromagnetic properties of a BiPbSrCaCuO superconductor
Authors: Lee Sang Heon , Kim H. C.
Published: July 2002

Electromagnetic properties of an Ag2O doped and an undoped BiPbSrCaCuO superconductor were evaluated to investigate the effect of the pinning center on the magnetic shielding and suspension/levitation phenomena. The residual magnetization M=M+–M− increased with the dopant concentration, a maximum for 2% doping, wherein a fine uniform dispersion of Ag particles was observed. The fine Ag particles form a cluster with increasing dopant as the particles condense with each other and grow, consequently does the number of flux passing through decreases, so the magnetization M decreases. This result indicates that M is proportional to the number of magnetic flux lines passing through the sample, because the smaller the particle size the larger the ratio of the surface area to the volume. Magnetic shielding was evaluated by measuring the induced voltage in the secondary coil by placing the sample in between the primary coil. The voltage was initially set to 0.5 V, and decreased to 0.17 and 0.28 V, respectively, for the undoped and 2% Ag2O doped samples. The much less change in the induced voltage for the 2% doped sample is attributed to increased flux shielding by shielding the vortex current. Simultaneous stable levitation and suspension of 2% Ag2O doped disk samples weighing 0.3 g were observed, respectively, above (3 mm) and beneath (2 mm) a toroidal permanent magnet under a field cooled condition. The role of flux pinning is discussed to account for the phenomena by considering the hysteretic force function.
Fabrication and characteristics of submicron tunneling junctions on high Tc superconducting c-axis thin films and single crystals
Authors: Kim S.-J. , Yamashita T.
Published: July 2002

We report successful fabrication and characteristics of submicron-size tunneling junctions using c-axis YBa2Cu3O7−y (YBCO) thin films of 800 nm thickness and Bi2Sr2CaCu2O8+δ(Bi-2212) single-crystal whiskers. The junctions were made using a three-dimensional focused-ion-beam etching method. First, a microbridge was patterned in a required junction width by normal direction etching. By tilting the sample stage up to 90°, two grooves on the bridge were etched from the lateral direction in order to create the required junction size. The 60 K YBCO junctions did not show any degradation of critical current density (Jc) down to an in-plane area of 0.5 μm2 and showed current–voltage (I–V) characteristics of the collective switching transition from the zero voltage state to the resistive state. For Bi-2212 stacks smaller than 1 μm2, we identified some of the features of charging effects on the I–V characteristics.
Low-temperature noncontact atomic-force microscope with quick sample and cantilever exchange mechanism
Authors: Suehira N. , Tomiyoshi Y. , Sugawara Y. , Morita S.
Published: July 2002

We present the design and performance of a noncontact atomic-force microscope (AFM) operating at low temperatures (LTNCAFM). For the first time, a “top bath” cryostat is used to avoid long-distance translation of the AFM unit, while protecting the fragile optical fiber, and to reduce outgassing. The top bath cryostat is optimized by using three radiation shields with two shutters. The AFM unit is cooled down to 5 K for 14 h with 4.6 l liquid helium. The quick sample and cantilever exchange is performed even at low temperatures. The optimal positioning of the optical fiber with respect to a cantilever can be performed with a three-dimensional micropositioner within 10 min. The high performance of the LTNCAFM is demonstrated with an atomically resolved image of a Si(111)7×7 surface.
Molecular quantum dynamics in a thermal system: Fractional wave packet revivals probed by random-phase fluorescence interferometry
Authors: Warmuth Ch. , Tortschanoff A. , Milota F. , Leibscher M. , Shapiro M. , Prior Y. , Averbukh I. Sh. , Schleich W. , Jakubetz W. , Kauffmann H. F.
Published: July 2002

The method of coherence observation by interference noise (COIN) [Kinrot et al., Phys. Rev. Lett. 75, 3822 (1995)] has been shown to be a useful tool for measurements of wave packet motion at the quantum-classical border. We present the first systematic interferometric study of fractional vibrational revivals in the B state of thermal iodine (I2) vapor. Experimental COIN interferograms ranging from 200 fs to 40 ps are presented for various excitation wavelengths. The complex temporal structure of the observed fluorescence includes rapid initial damping in the short-time regime and the appearance of quarter- and half-revivals on the quantum-mechanical long-time scale. These features arise from a delicate balance between rotational and vibrational molecular coherences. The clear observation of the wave packets on the long time scale is possible due to the long-time stability of the COIN interferometer. Lowest-order perturbative solutions nicely recover the experimental results, and closed-form analytical expressions based upon the factorization approach and the Poisson summation give insights into the nature of dephasing and rephasing of vibrational wave packets subject to rotational inhomogeneous broadening.
Observation of submicron dust particles trapped in a diffused region of a low pressure radio frequency plasma
Authors: Hayashi N.
Published: July 2002

Submicron dust particles (Cu, φ 50 nm) were observed to be trapped in an rf plasma at relatively low pressure. The laser light scattering by particles shows the time evolution of the dust particles for several hours after pulsed injection of the particles. The dust particles were localized in the diffused region as a large volume cloud. The suspension mechanism of the dust particles in the diffused plasma was explained by an electrostatic force due to the potential structure. The spatial distribution of the charge of the dust particles was determined by this potential structure. The dispersion relations of the self-excited dust acoustic waves were adopted to confirm the spatial distribution and the time evolution of the charge of the dust particles.
A Landau fluid model for electromagnetic plasma microturbulence
Authors: Snyder P. B. , Hammett G. W.
Published: July 2002

A fluid model is developed for the description of microturbulence and transport in magnetized, long mean-free-path plasmas. The model incorporates both electrostatic and magnetic fluctuations, as well as finite Larmor radius and kinetic effects. Multispecies Landau fluid equations are derived from moments of the electromagnetic gyrokinetic equation, using fluid closures which model kinetic effects. A reduced description of electron dynamics, appropriate for the study of microturbulence on characteristic ion drift and Alfvén scales, is derived via an expansion in the electron to ion mass ratio. The reduced electron equations incorporate curvature, ∇B, and linear and nonlinear E×B drift effects, needed to model the electron contribution to the drive and damping of ion gyroradius scale instabilities in tokamaks. The Landau fluid model is linearly benchmarked against gyrokinetic codes, and found to reproduce the toroidal finite beta ion temperature gradient and kinetic ballooning instabilities.
A theoretical study of the effects of insulators on electron transport through electrostatic tube lenses
Authors: Anderson T. G. , Birdsey B. G. , Woeher S. M. , Rosenberry M. A. , Gay T. J.
Published: July 2002

Using the computer program SIMION 6, we have studied the effects of spurious insulator charging on the trajectories of electrons through electrostatic tube lenses. We considered lens elements with flat ends, spaced a distance g apart, whose inner diameter D=10g. For the standard cases of drift tubes, two-element lenses, and einzel lenses, we found that charging effects are eliminated if t/g>3.5, where t is the distance between the lens inner diameter and the charged spacing insulator.
Particle acceleration for delivery deoxyribonucleic acid vaccine into skin in vivo
Authors: Xinglong Yu , Xiwen Zhang , Yuan Wang , Junshi Xie , Pengfei Hao
Published: July 2002

Skin represents an important immunogenic inductive site, 3%–4% epidermis cells are special antigen-presenting cells. Deoxyribonucleic acid (DNA) vaccine can elicit vigorous immune responses in epidermis cells. The means of delivering DNA vaccine into epidermis cells becomes an important step in DNA vaccine applications. This article presents a new type of gene gun based on the principle of two-stage injector acceleration. DNA coated particles are attached on an screen-type carrier located at the negative pressure inlet, the particles will be sucked into the accelerating channel by negative pressure and be accelerated at a great speed. FLUENT, a computation fluid dynamic application software is used to simulate the flow condition of the injector. Distribution of Mach number, total pressure on exit cross section, and negative pressure on negative pressure inlet are analyzed, by which the process of acceleration of particles is determined. We also measured these parameters in this study. The data show that the particle velocity can be up to 500 m/s and the particles distribute evenly over a circle of Φ 20 mm. The numerical simulation results coincide with experimental data well. Therefore, the results of numerical simulation can be served as guidance for an optimal design of the gene gun and for practical operations. When gene coated particles are distributed evenly, they can penetrate into or even through epidermis cells where the gene can be expressed and subsequently elicits host immune responses. This device may be evaluated in human objects in future.
Development of an ultrahigh vacuum scanning tunneling microscope cooled by superfluid 4He
Authors: Kondo Y. , Foley E. T. , Amakusa T. , Shibata N. , Chiba S. , Iwatsuki M. , Tokumoto H.
Published: July 2002

We have developed an ultrahigh vacuum (UHV) scanning tunneling microscope (STM) cooled by superfluid 4He. This microscope is integrated with a solenoid and split-pair superconducting magnet. The STM can be operated at 300>T>4 K in a rotatable magnetic field of up to 8 T perpendicular to, and 1.5 T parallel to the sample surface. Moreover, tips and samples may be changed without venting the UHV system. The performance of the STM was confirmed by obtaining atomic resolution images of Si reconstructed surfaces at low temperatures. The STM performance was unaffected by the application of high magnetic fields.
Theory of the virtual cathode oscillator
Authors: Jiang Weihua , Kristiansen Magne
Published: July 2002

A one-dimensional analytical theory is developed to describe the behavior of the virtual cathode oscillator. Theoretical predictions for the microwave frequency and efficiency have been obtained. The results suggested that the feedback of the microwave field to the virtual cathode is very important for the microwave efficiency which, under optimum conditions, can be as high as 30%–40%. In addition, the dependence of the microwave efficiency on the electron-beam energy spread and the electron lifetime was determined. The threshold value of the cavity Q, which is necessary to enhance the microwave field, is also estimated.
Magnetic probe construction using thick-film technology
Authors: Takahashi H. , Sakakibara S. , Kubota Y. , Yamada H.
Published: July 2002

Thick-film technology has been successfully adapted for the design and fabrication of magnetic probes of a new type suitable for use in the simultaneous ultrahigh vacuum and high temperature environment of a nuclear fusion device. The maximum usable temperature is expected to be around 900 °C. This new probe has a specific sensitivity (coupling area per unit volume) an order of magnitude higher than a conventional coil. The new probe in one implementation is capable of simultaneously measuring magnetic field in three orthogonal directions about a single spatial point and in two frequency ranges. Low frequency coils have a measured coupling area of 296–323 cm2, and a frequency response of about 300 kHz. High frequency coils have a design coupling area of 12–15 cm2.
State-to-state dynamics of the H+c-C6H12→H2(v′,j′)+c-C6H11 reaction
Authors: Srivastava Abneesh , Picconatto Carl A. , Valentini James J.
Published: July 2002

The rovibrational state distributions for the H2 product of the H+c-C6H12→H2+c-C6H11 abstraction reaction have been measured at 1.6 eV collision energy under single-collision conditions. The state distributions are compared to those for the H2 product of the reaction of H atoms with CD3(CH2)4CD3 and n-C6H14 that we have measured previously. Abstraction of secondary H atoms from the cyclic C6 alkane produces H2(v′=0,j′) and H2(v′=1,j′) rotational state distributions that are significantly colder than those from the reaction of the linear C6 alkane. These results are interpreted within a simple phenomenological local reaction model that we have developed for these atom+polyatom reactions. The substantial differences between the state distributions for the reactions of the cyclic and linear alkanes indicate that reactions of cyclohexane are not representative of reactions at all secondary C–H.
Displacement measurement based on Fourier transform method with external laser cavity modulation
Authors: Wang Ming , Lai Guanming
Published: July 2002

Smart optical sensors for the displacement measurement in submicron, have been developed by using the self-mixing effect of a laser diode. In this article, we propose a new type of self-mixing interferometry (SMI) to measure microscopic displacement. The phase of the SMI signal is modulated with external cavity length and demodulated by the Fourier transform analysis technique. Some errors for this method are discussed. We have demonstrated this system to measure the microscopic displacement of a remote target. The experiment results reveal that phase extraction error for the method is ∼2π×10−3 rad, and the displacement measurement error is approximately 8 nm.
Molecular dynamics studies of the effects of branching characteristics on the crystalline structure of polyethylene
Authors: Doran Michael , Choi Phillip
Published: July 2002

Molecular dynamics simulations were carried out on single chain models of linear low-density polyethylene in vacuum to study the effects of branch length, branch content, and branch distribution on the polymer’s crystalline structure at 300 K. The trans/gauche (t/g) ratios of the backbones of the modeled molecules were calculated and utilized to characterize their degree of crystallinity. The results show that the t/g ratio decreases with increasing branch content regardless of branch length and branch distribution, indicating that branch content is the key molecular parameter that controls the degree of crystallinity. Although t/g ratios of the models with the same branch content vary, they are of secondary importance. However, our data suggests that branch distribution (regular or random) has a significant effect on the degree of crystallinity for models containing 10 hexyl branches/1,000 backbone carbons. The fractions of branches that resided in the equilibrium crystalline structures of the models were also calculated. On average, 9.8% and 2.5% of the branches were found in the crystallites of the molecules with ethyl and hexyl branches while C13 NMR experiments showed that the respective probabilities of branch inclusion for ethyl and hexyl branches are 10% and 6% [Hosoda et al., Polymer 1990, 31, 1999–2005]. However, the degree of branch inclusion seems to be insensitive to the branch content and branch distribution.
High temperature miniature oven with low thermal gradient for processing fiber Bragg gratings
Authors: Fokine M.
Published: July 2002

A miniature oven for processing fiber Bragg gratings in excess of 1000 °C has been projected and evaluated. The dimensions and the design of the oven allow rapid insertion and removal of the fiber during heating and minimizes mechanical degradation of the fiber. The 22 mm long oven has a flat zone at 1000 °C of 16 mm with a temperature variation of less than 2% and 20 mm with a temperature variation of 10%. The long term stability (hours) is ±20 °C measured at the center of the oven at 1000 °C. Rapid heating is possible, and heating optical fibers to 1000 °C shows a delay of approximately 400 ms before the core reaches thermal equilibrium.
Design of a hypersonic waterjet apparatus driven by high explosives
Authors: Weeks Brandon L. , Klosterman John , Worsey Paul N.
Published: July 2002

The design and construction of a hypersonic waterjet apparatus is described. Jet velocities from 0.5 to 5 km/s have been achieved using a high explosive charge. Images are obtained in situ on various target substrates using a high-speed framing camera. Experimental results are shown for the impact of high velocity waterjets on propellants and high explosive samples. By observing the impact of the waterjet at a wide range of velocities a safety threshold can be determined where no reaction takes place.
The absolute definition of the phase-shift in potential scattering
Authors: Chadan Khosrow , Kobayashi Reido , Kobayashi Takao
Published: July 2002

The variable phase approach to potential scattering with regular spherically symmetric potentials satisfying Eq. (1), and studied by Calogero in his book [Variable Phase Approach to Potential Scattering (Acadamic, New York, 1967)] is revisited, and we show directly that it gives the absolute definition of the phase-shifts, i.e., the one which defines δl(k) as a continuous function of k for all k⩾0, up to infinity, where δl(∞)=0 is automatically satisfied. This removes the usual ambiguity ±nπ, n integer, attached to the definition of the phase-shifts through the partial wave scattering amplitudes obtained from the Lippmann–Schwinger integral equation, or via the phase of the Jost functions. It is then shown rigorously, and also on several examples, that this definition of the phase-shifts is very general, and applies as well to all potentials which have a strong repulsive singularity at the origin, for instance those which behave like gr−m, g>0, m⩾2, etc. We also give an example of application to the low-energy behavior of the S-wave scattering amplitude in two dimensions, which leads to an interesting result.
Effect of lithium ion irradiation on the transport and optical properties of Bridgman grown n-type InSb single crystals
Authors: Dixit V. K. , Rodrigues B. V. , Bhat H. L. , Kumar Ravi , Venkataraghavan R. , Chandrasekaran K. S. , Arora B. M
Published: July 2002

Single crystal (100) wafers of n-InSb were implanted with 50 MeV Li3+ ions at various fluences ranging from 1010 to 1014 ions/cm2 at room temperature. Investigations of the optical, electrical, and structural properties of the as-grown, irradiated, annealed wafers were carried out by infrared and Raman spectroscopies, Hall measurements, and high resolution x-ray diffraction (HRXRD). In the case of samples irradiated with an ion fluence of 1.6×1014 ions/cm2, electrical measurements at 80 K reveal that there is a decrease in carrier concentration from 8.5×1015 (for unirradiated) to 1.1×1015/cm3 and an increase in mobility from 5.4×104 to 1.67×105 cm2/V s. The change in carrier concentration is attributed to the creation of electron trap centers induced by ion beam irradiation and the increase in mobility to the formation of electrical inactive complexes. Nevertheless, even with the irradiation at 1.6×1014 ions/cm2 fluence the crystalline quality remains largely unaffected, as is seen from HRXRD and Raman studies.
Computer-aided modeling of superconducting striplines with ground planes using critical state models
Authors: Dasgupta T. , Derov J. S. , Sridhar S.
Published: July 2002

The effect of ground planes on the current-induced critical states and flux penetration for a thin superconducting strip carrying a microwave current has been calculated numerically. The nonlinear response represented by the dependence of the surface resistance and reactance were also calculated. We find that when the distance d between the ground planes is smaller than the width a of the strip, i.e., d⩽a, the ground planes affect the nonlinear response significantly. In particular we study the effects of ground planes placed at a distance d=a/5. We compare and contrast these effects with the results of similar models without the ground planes. The ground planes reduce the current crowding at the film edges, thus reducing the nonlinearities arising from critical state flux motion. The numerical procedure can be incorporated into computer-aided design of superconducting microwave circuits.
Orbital free ab initio molecular dynamics study of liquid Al near melting
Authors: González D. J. , González L. E. , López J. M. , Stott Malcolm J.
Published: July 2002

The orbital free ab initio molecular dynamics method is applied to study the static and dynamic structure of liquid Al near the triple point. The method uses a new kinetic energy functional, along with a local pseudopotential constructed within the same kinetic energy functional. The results obtained for the dynamic structure factor are compared with recent experimental data.
Quantization of longitudinal excitons in CuCl thin films
Authors: Silva-Castillo A. , Pérez-Rodrı́guez F.
Published: July 2002

The quantization of the exciton translational motion in CuCl thin films, having a thickness much less than the photon wavelength and overlying a substrate, is theoretically investigated by employing the 45° reflectometry. We show that the resonances associated with quantized longitudinal excitons can be directly measured by means of such a polarization-modulation technique despite the relatively large damping factors for very thin films.
Variation of spin densities and the solid-phase crystallization of amorphous Si1−xGex:H films
Authors: Roh O. H. , Yun W. J. , Lee J.-K.
Published: July 2002

We have investigated the solid-phase crystallization (SPC) of hydrogenated amorphous silicon–germanium (a-Si1−xGex:H) alloy films by using x-ray diffraction and electron spin resonance measurements. The films were deposited on glass in a plasma-enhanced chemical vapor deposition system by using SiH4 and GeH4 gases. The deposited films were then annealed at 600 °C, which resulted in crystallization. The variation of the spin densities with annealing time was found to be strongly correlated with the structural changes in the SPC process, and the Ge dangling bonds were the dominant defects involved in the SPC process for Si1−xGex:H films (for x>0.05). The incubation time and the final grain size of the recrystallized films depended on the Ge composition and were closely related to the variations of the Si–H and the Ge–H dissociation energies. The SPC process is thought to be influenced by the initial structural disorder of the a-Si1−xGex:H films, and by the Ge composition.
Quantum degeneracy effect on the work output from a Stirling cycle
Authors: Saygin Hasan , Şişman Altuğ
Published: July 2002

The effect of quantum degeneracy on the work output from a Stirling cycle working at quantum degeneracy conditions (QDCs) is analyzed. Expressions for net work outputs of Stirling power cycles working with monatomic ideal Bose and Fermi gases are derived by using the quantum ideal gas equation of state. Ratios of net work outputs of Stirling cycles working with Bose and Fermi gases to the net work output of a classical Stirling cycle (RWB and RWF, respectively) are obtained. Variations of RWB and RWF with TH are examined for a given temperature ratio (τ=TL/TH) and a specific volume ratio (rν=νH/νL). At QDC, it is seen that RWB has a maximum value, which is greater than unity. On the other hand, there is no maximum or minimum point for RWF and RWF⩽1 for any values of TH. Consequently, the use of Bose gas as a working fluid in a Stirling cycle provides an advantage since it causes the net work output per cycle to increase by consuming more heat energy. This fact is seen to be in the opposite direction for a Stirling cycle working with Fermi gas.
Linear phase demodulation in photorefractive crystals with nonlocal response
Authors: Päiväsaari Kimmo , Kamshilin Alexei A. , Prokofiev Victor V. , Sturman Boris , Calvo Gabriel F. , Carrascosa Mercedes , Agullo-Lopez Fernando
Published: July 2002

On the basis of the vectorial theory of light diffraction in cubic photorefractive crystals, we derive analytical expressions to describe the output intensities and polarization states of two coherent beams coupled via a dynamic index grating and subjected at the input to a fast phase modulation. It is shown that the linear transformation of fast phase excursions into intensity modulation can be achieved in the case of a nonlocal ac response by means of proper polarization filtering. Theoretical results are supported by the data obtained in experiments with Bi12TiO20 crystals of different orientations. The polarization technique is used for the evaluation of the space-charge fields created in different crystals.
Surface photovoltaic properties of sputtered Mo/Si multilayers
Authors: Li Wenming , Gong Hao , Cao Yaan , Du Hui
Published: July 2002

Structural and photovoltaic properties of magnetron sputtered Mo/Si multilayers were studied. Low-angle x-ray diffraction patterns demonstrated that the films had sharp interfaces and good periodicity. Surface photovoltage spectroscopy (SPS) was employed to investigate the electronic transport properties of the multilayers. It was found that the photovoltaic response depended on the composition, the monolayer thickness, and the number of periods. The electronic confinement effects of the semiconductor layers were discussed with an energy band model. SPS results were related to the film structure of the multilayers determined through x-ray diffraction.
Ab initio studies of dissociation pathways on the ground- and excited-state potential energy surfaces for HFCO
Authors: Fang Wei-Hai , Liu Ruo-Zhuang
Published: July 2002

Potential energy surfaces of the HFCO dissociation to H+FCO and F+HCO in the lowest three electronic states (S0, S1, and T1) have been investigated with ab initio molecular orbital method at the level of the complete active space self-consistent field. An insight into the dynamics of the HFCO photodissociation at the range of 193–248 nm was provided in the present work. Radiationless transfer from S1 to T1 and subsequent dissociation on the T1 surface was predicted to be the mechanism for the C–H bond cleavage, which is consistent with that proposed by experimentalists. The experimental investigations of the HFCO photodissociation suggest that the F–C bond fission also occurs as a result of intersystem crossing (ISC) from S1 to T1, which is not supported by the present calculations. This has been discussed in detail.
A theoretical model for molecules interacting with intense laser pulses: The Floquet-based quantum-classical Liouville equation
Authors: Horenko Illia , Schmidt Burkhard , Schütte Christof
Published: July 2002

The Floquet-based quantum-classical Liouville equation (F-QCLE) is presented as a novel theoretical model for the interaction of molecules with intense laser pulses. This equation efficiently combines the following two approaches: First, a small but spectroscopically relevant part of the molecule is treated quantum-mechanically while the remaining degrees of freedom are modeled by means of classical molecular dynamics. The corresponding nonadiabatic dynamics is given by the quantum-classical Liouville equation which is a first-order approximation to the partial Wigner transform of full quantum dynamics. Second, the dynamics of the quantum subsystem is described in terms of instantaneous Floquet states thus eliminating highly oscillatory terms from the equations of motion. The resulting F-QCLE is shown to have a well defined adiabatic limit: For infinitely heavy classical particles and for infinitely slow modulation the dynamics adiabatically follows the Floquet quasi-energy surfaces for a strictly time-periodic field. Otherwise, nonadiabtic effects arise both from the motion of the classical particles and from the modulation of the field which is assumed to be much slower than the carrier frequency. A numerical scheme to solve the F-QCLE is based on a Trotter splitting of the time evolution. The simplest implementation can be realized by an ensemble of trajectories stochastically hopping between different Floquet surfaces. As a first application we demonstrate the excellent agreement of quantum-classical and fully quantum-mechanical dynamics for a two-state model of photodissociation of molecular fluorine. In summary, due to the favorable scaling of the numerical effort the F-QCLE provides an efficient tool for the simulation of medium to large molecules interacting with intense fields beyond the perturbative regime.
Giant relaxation oscillations in a very strongly hysteretic superconductive quantum interference device ring-tank circuit system
Authors: Clark T. D. , Prance R. J. , Whiteman R. , Prance H. , Everitt M. J. , Bulsara A. R. , Ralph J. F.
Published: July 2002

In this article, we show that the radio frequency (rf) dynamical characteristics of a very strongly hysteretic superconducting quantum interference device (SQUID) ring, coupled to a rf tank circuit resonator, display relaxation oscillations. We demonstrate that the overall form of these characteristics, together with the relaxation oscillations, can be modeled accurately by solving the quasiclassical nonlinear equations of motion for the system. We suggest that in these very strongly hysteretic regimes, SQUID ring-resonator systems may find application in logic and memory devices.
Magnetic response of hard superconductors subjected to parallel rotating magnetic fields
Authors: Carballo-Sánchez A. F. , Pérez-Rodrı́guez F. , Pérez-González A.
Published: July 2002

The manifestation of flux-line cutting in the magnetic behavior of a type-II superconductor, either (i) subjected to a rotating magnetic field, or (ii) undergoing slow oscillations in a static magnetic field, is investigated theoretically. We have applied both the generalized double critical-state model and the two-velocity hydrodynamic one to interpret available experimental results for oscillating disks of Nb. The hydrodynamic model generates only closed hysteresis loops, after the first full oscillation, in accordance with the experimental hysteresis loops observed at a relatively small amplitude of oscillation, θmax=45°. However, at larger amplitudes of oscillation, several measured loops are evidently open. This behavior as well as their asymmetric form could be reproduced only by the generalized double critical-state model. The limits of applicability of both models are discussed.
Distribution kinetics theory of Ostwald ripening
Authors: Madras Giridhar , McCoy Benjamin J.
Published: July 2002

Ostwald ripening occurs near equilibrium conditions when larger clusters grow at the expense of dissolving smaller clusters. We propose that ripening kinetics for growth and dissolution can be represented by a general population balance equation (PBE) for the cluster size distribution (CSD). This PBE can also describe cluster growth or dissolution in the absence of ripening. The Kelvin equation provides the effect of interfacial energy on solubility in terms of the cluster radius. The continuity equation conventionally applied to ripening or cluster growth is obtained as a Taylor series expansion of the governing PBE. Numerical and moment solutions of the PBE show the evolution of the CSD. The cluster number density declines, and the average cluster mass increases. The variance can initially increase as the CSD broadens by growth of large clusters, and then decrease until eventually vanishing. The final state after a long time is a single large cluster in equilibrium with the fluid solution.
Fluorescence and phosphorescence resulting from electrochemical generation of triplet excitations
Authors: Burshtein A. I. , Neufeld A. A. , Ivanov K. L.
Published: July 2002

The biexcitonic annihilation of triplet products of ion recombination is incorporated in the kinetic description of electrochemiluminescence. This process resulting in excitation and fluorescencence of singlets is the dominant mechanism of the initial quenching of triplets, while their concentration is still high. Therefore, the contribution of triplets in subsequent phosphorescence is never as high as expected even at a large exergonicity of inter-ion electron transfer when the recombination to the triplet state prevails on recombination to the ground state of neutral products. The kinetics and quantum yields of fluorescence and phosphorescence are calculated by means of integral encounter theory.