bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficient n-type doping of diamond using surfactant-mediated epitaxial growth
Authors: Yu Byung Deok , Miyamoto Yoshiyuki , Sugino Osamu
Published: July 2002

Fabrication of n-type diamond was studied by performing extensive first-principles total-energy calculations for a number of possible configurations during the epitaxial growth process. We find that spatially correlated codopant N–Al–N, which acts as a shallow donor in diamond, can be effectively formed by using a surfactant-based growth technique. This technique takes advantage of the difference in the growth modes of diamond which depend on surface species: incorporation of carbon into diamond crystal is promoted by surfactants (Al) but is locally prohibited by surface co-dopants (N–Al–N). Thus, the co-dopants are selectively buried in diamond. This approach provides a possible and very effective way to realize dense n-type doping of diamond which has not been possible using conventional techniques.
Low-temperature preparation and characterization of SrBi2Ta2O9 thin films on (100)-oriented LaNiO3 electrodes
Authors: Hu G. D. , Wilson I. H. , Xu J. B. , Li C. P. , Wong S. P.
Published: July 2002

SrBi 2 Ta 2 O 9 (SBT) ferroelectric thin films were prepared by the metalorganic decomposition technique at annealing temperatures of 600 and 650 °C on Pt/Ti/SiO2/Si substrates coated by (100)-oriented LaNiO3 (LNO) metal oxide thin films, which were fabricated by the sol–gel technique combined with a layer-by-layer annealing method at 600 °C. A (200)-predominant SBT thin film can be formed on LaNiO3(100)/Pt/Ti/SiO2/Si substrate at 600 °C. The effect of the LNO oxide electrode on the dielectric and ferroelectric properties of SBT thin film annealed at 600 °C was studied. Although the remanent polarization of the (200)-predominant SBT thin film is not as large as expected, the film can be uniformly polarized and imaged using an atomic force microscope in the piezoelectric mode.
Manipulation of colloidal gold nanoparticles in the evanescent field of a channel waveguide
Authors: Ng L. N. , Zervas M. N. , Wilkinson J. S. , Luff B. J.
Published: July 2002

Colloidal gold spheres of radius 10 nm are reported to move forward in water, under the influence of radiation pressure forces, due to the evanescent field at the surface of an optical channel waveguide. The velocity is linearly dependent upon the optical power in the waveguide, acquiring a maximum velocity of 4 μm/s for modal power of 500 mW in the TM polarization at a wavelength of λ=1.047 μm.
Strain-dependent magnetic phase diagram of epitaxial La0.67Sr0.33MnO3 thin films
Authors: Tsui F. , Smoak M. C. , Nath T. K. , Eom C. B.
Published: July 2002

Effects of lattice strain on magnetic behavior of epitaxial La0.67Sr0.33MnO3 thin films grown by 90° off-axis sputtering have been studied. The size of epitaxial strain was varied using four different substrates, i.e., (001) LaAlO3, (001) SrTiO3, (001) La0.3Sr0.7Al0.65Ta0.35O9, and (110) NdGaO3. The observed magnetism of coherent epitaxial films grown on these substrates, particularly anisotropy and Curie temperature, exhibit strong correlations with lattice strains. Spin reorientation transitions have been observed. The dependence of Curie temperature on the bulk and Jahn–Teller strains has been determined.
Observation of source-to-drain direct tunneling current in 8 nm gate electrically variable shallow junction metal–oxide–semiconductor field-effect transistors
Authors: Kawaura Hisao , Sakamoto Toshitsugu , Baba Toshio
Published: July 2002

We investigated quantum mechanical effects in electrically variable shallow junction metal–oxide–semiconductor field-effect transistors with an 8 nm long gate. We clearly observed the direct tunneling current from the source to the drain below 77 K, in good agreement with the calculation. We also showed that the direct tunneling current will exceed the thermal current and will become detrimental to low-voltage operation of MOSLSIs in the 5 nm gate generation.
Plasma-induced alignment of carbon nanotubes
Authors: Bower Chris , Zhu Wei , Jin Sungho , Zhou Otto
Published: July 2002

Uniform films of well-aligned carbon nanotubes have been grown using microwave plasma-enhanced chemical vapor deposition. It is shown that nanotubes can be grown on contoured surfaces and aligned in a direction always perpendicular to the local substrate surface. The alignment is primarily induced by the electrical self-bias field imposed on the substrate surface from the plasma environment. It is found that switching the plasma source off effectively turns the alignment mechanism off, leading to a smooth transition between the plasma-grown straight nanotubes and the thermally grown “curly” nanotubes. The nanotubes grow at a surprisingly high rate of ∼100 nm/s in our plasma process, which may be important for large-scale commercial production of nanotubes.
High figure of merit in partially filled ytterbium skutterudite materials
Authors: Nolas G. S. , Kaeser M. , Littleton R. T. , Tritt T. M.
Published: July 2002

We present evidence of a relatively high dimensionless figure of merit (ZT) in a polycrystalline skutterudite partially filled with ytterbium ions. The small-diameter yet heavy-mass Yb atoms partially filling the voids of the host CoSb3 system exhibit low values of thermal conductivity while the quite favorable electronic properties are not substantially perturbed by the addition of Yb. This combination is ideal for thermoelectric applications exemplifying the “phonon-glass electron-crystal” concept of a thermoelectric material, resulting in ZT=0.3 at room temperature and ZT∼1 at 600 K for Yb0.19Co4Sb12.
New results in the variational approach to turbulent Boussinesq convection
Authors: Kerswell R. R.
Published: July 2002

The new “background” variational formulation introduced by Doering and Constantin for bounding the heat transport in Boussinesq convection is related to the classical mean-fluctuation approach pioneered by Malkus, Howard and Busse. Viewed from within a unified variational framework, these methods are seen to be complementary or dual principles. The Doering–Constantin approach seeks to estimate a saddle point value of a functional strictly from above as part of a minimization process whereas the Malkus–Howard–Busse approach estimates it from below as part of a maximization procedure. The best bounds on the Nusselt number available in each approach therefore coincide when the same dynamical constraints are imposed. The current best large-Rayleigh-number bound, Nu⩽0.167Ra1/2−2, is improved fivefold so that the true bound corresponding to the dynamical constraints of global power balance, global entropy balance and mean heat balance is bracketed as follows: 0.031Ra1/2≲Nubound−1⩽0.0335Ra1/2 as Ra→∞. The optimizing solution is shown to possess no mean flow even if additional momentum constraints are imposed. Finally, the effect of an extra plausible smoothness constraint on the Nusselt number bound is examined. If the minimum lengthscale allowed parallel to the plates in the velocity and temperature field is l=λRa(2γ−1)/2d (d is the plate separation and λ is a constant), then (0.606/λ)Ra(1−γ)/2⩽Nubound−1⩽(0.781/λ)Ra(1−γ)/2 as Ra→∞. In particular, if the Kolmogorov length scale (ν3/ε)1/4=d[σ2/((Nu−1)Ra)]1/4 (ν is the kinematic viscosity, ε is energy dissipation per unit mass, σ is the Prandtl number) is used as the minimum lengthscale allowed parallel to the plates in numerical simulations, the Nusselt number can never increase faster than Ra3/7 as Ra→∞.
Bistable reaction-diffusion systems can have robust zero-velocity fronts
Authors: Sepulchre Jacques-Alexandre , Krinsky Valentin I.
Published: July 2002

We show that for a class of bistable reaction-diffusion systems, zero-velocity fronts can be robust in the singular limit where one of the diffusion coefficients vanishes. In this case, stationary fronts can persist along variations of the system parameters. This property contrasts with the standard result that the front velocity v(μ), expressed as a function of a control parameter μ, is zero only at some isolated values μ0, and thus not giving robustness to zero-velocity fronts when μ is varied.
New origin for spin current and current-induced spin precession in magnetic multilayers
Authors: Berger L.
Published: July 2002

In metallic ferromagnets, an electric current is accompanied by a flux of angular momentum, also called spin current. In multilayers, spatial variations of the spin current correspond to drive torques exerted on a magnetic layer. These torques result in spin precession above a certain current threshold. The usual kind of spin current is associated with translation of the spin-up and spin-down Fermi surfaces in momentum space. We discuss a different kind of spin current, associated with expansion and contraction of the Fermi surfaces. It is more nonlocal in nature, and may exist even in locations where the electrical current density is zero. It is larger than the usual spin current, in a ratio of 10 or 100, at least in the case of one-dimensional current flow. The new spin current is proportional to the difference Δμ̄≃10−3 eV between spin-up and spin-down Fermi levels, averaged over the entire Fermi surface. Conduction processes, spin relaxation, and spin-wave emission in the multilayer can be described by an equivalent electrical circuit resembling an unbalanced dc Wheatstone bridge. And Δμ̄ corresponds to the output voltage of the bridge.
Langmuir probe analysis for high density plasmas
Authors: Chen Francis F.
Published: July 2002

High-density, radio-frequency plasmas used in semiconductor processing have progressed to densities n⩾5×1011 cm−3, where the methods used to interpret Langmuir probe characteristics in low-density (109–11 cm−3) plasma reactors are no longer valid. Though theory and computations for arbitrarily dense collisionless plasmas exist, they are difficult to apply in real time. A new parametrization and iteration scheme is given which permits rapid analysis of Langmuir probe data using these theories. However, at high n, measured ion saturation curves are shown which do not agree in shape with the “correct” theory, yielding anomalously high values of n. The discrepancy with independent measures of n, which can exceed a factor of 2, is believed to be caused by charge-exchange collisions well outside the sheath. Probe designs for avoiding this discrepancy are suggested.
High-power resonant measurements of piezoelectric materials: Importance of elastic nonlinearities
Authors: Priya Shashank , Viehland Dwight , Carazo Alfredo Vázquez , Ryu Jungho , Uchino Kenji
Published: July 2002

A resonance method for measuring the complex elastic and electromechanical properties of piezoelectric materials under high-power operational conditions has been developed. In this method, rectangular specimens are piezoelectrically driven into mechanical resonance. The displacement of the transverse resonance mode is measured as a function of frequency (f ) using an optical vibrometer method in conjunction with a frequency response analyzer. Due to the wide amplitude sensitivity range of the detection system, asymmetries in nonlinear resonance curves with mechanical damping can be accurately measured. The method has been applied to the study of Pb(Zr1−xTix)O3. Under resonant high-power drive, it has been found that electromechanical nonlinearities are due to elastic ones, as the elastic and electromechanical properties were both found to scale with the square of the strain amplitude. The temperature (T) and ac electric field (Eac) dependence of the mechanical quality factor Qm were also determined. Iso-Qm curves were constructed that can be used to predict performance criteria for high-power applications of piezoelectric materials.
High-efficiency yellow double-doped organic light-emitting devices based on phosphor-sensitized fluorescence
Authors: D’Andrade Brian W. , Baldo Marc A. , Adachi Chihaya , Brooks Jason , Thompson Mark E. , Forrest Stephen R.
Published: July 2002

We demonstrate high-efficiency yellow organic light-emitting devices (OLEDs) employing [2-methyl-6-[2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene] propane-dinitrile (DCM2) as a fluorescent lumophore, with a green electrophospho- rescent sensitizer, fac tris(2-phenylpyridine) iridium [Ir(ppy)3] co-doped into a 4,4′-N,N′dicarbazole-biphenyl host. The devices exhibit peak external fluorescent quantum and power efficiencies of 9%±1% (25 cd/A) and 17±2 lm/W at 0.01 mA/cm2, respectively. At 10 mA/cm2, the efficiencies are 4.1%±0.5% (11 cd/A) and 3.1±0.3 lm/W. We show that this exceptionally high performance for a fluorescent dye is due to the ∼100% efficient transfer of both singlet and triplet excited states in the doubly doped host to the fluorescent material using Ir(ppy)3 as a sensitizing agent. These results suggest that 100% internal quantum efficiency fluorescent OLEDs employing this sensitization process are within reach.
On resonant heating below the cyclotron frequency
Authors: Chen Liu , Lin Zhihong , White Roscoe
Published: July 2002

Resonant heating of particles by electrostatic and Alfvén waves propagating in a confining uniform magnetic field is examined. It is shown that, with a sufficiently large wave amplitude, significant perpendicular stochastic heating can be obtained with wave frequency at a fraction of the cyclotron frequency. This result may have relevance for the heating of ions in the solar corona, and is a generic phenomenon, independent of the type of wave considered.
Self-focused electron beams produced by pyroelectric crystals on heating or cooling in dilute gases
Authors: Brownridge J. D. , Shafroth S. M.
Published: July 2002

Self-focusing, spatially stable, electron beams are produced by cylindrical pyroelectric crystals such as LiNbO3 in dilute gases on cooling provided that heating is done from the +z base. Beam energies up to 170 keV have been observed. A 4 mm diameter×10 mm crystal heated to 160 °C gives rise to spatially stable beams with a focal length of 22 mm and a 1 mm spot size. Here we present photographic as well as electronic proof of the existence of these electron beams.
Computing memory functions from molecular dynamics simulations
Authors: Kneller G. R. , Hinsen K.
Published: July 2002

We propose a new method to compute reliable estimates for memory functions of dynamical variables from molecular dynamics simulations. The key point is that the dynamical variable under consideration, which we take to be the velocity of a fluid particle, is modeled as an autoregressive stochastic process. The parameters of this stochastic process can be determined from molecular dynamics trajectories using efficient algorithms that are well established in signal processing. The procedure is also referred to as the maximum entropy method. From the autoregressive model of the velocity autocorrelation function we compute the one-sided z transform of the discretized memory function and the memory function itself. Using liquid argon as a simple model system, we demonstrate that the autocorrelation function and its power spectrum can be approximated to almost arbitrary precision. The same is therefore true for the memory function, which is calculated within the same stochastic model.
Adsorption and incorporation of silicon at GaN(0001) surfaces
Authors: Rosa A. L. , Neugebauer J. , Northrup J. E. , Lee Chae-Deok , Feenstra R. M.
Published: July 2002

We have studied the adsorption and incorporation of Si at GaN(0001) surfaces employing density-functional theory and scanning tunneling microscopy (STM). Calculating the surface energy of a large number of structures with various Si concentrations and various III–V ratios, we derive a phase diagram showing the energetically most stable surfaces as a function of the Si and N chemical potentials. Based on these results, we identify the surface reconstructions seen in STM, explain the incorporation mechanism of Si on GaN surfaces, and discuss under which conditions Si acts as an antisurfactant.
Interconnection of carbon nanotubes by chemical functionalization
Authors: Chiu P. W. , Duesberg G. S. , Dettlaff-Weglikowska U. , Roth S.
Published: July 2002

Intermolecular carbon nanotube junctions were formed by coupling chemically functionalized nanotubes with molecular linkers. An end-to-side or end-to-end heterojunction can be formed by reacting chloride terminated nanotubes with aliphatic diamine. The chemically modified nanotube mats were characterized by Raman spectroscopy. The peak shift in the tangential vibration mode reveals that the attached chemical functional groups can behave as either an electron donor or an acceptor, and facilitate charge transfer with the nanotube host. The charge transfer is also verified by transport measurements on individual end-to-side intermolecular junctions, which show diode-like behavior. The charge transfer can be attributed to amide functionality at the junction.
Density relaxation of silicon dioxide on (100) silicon during thermal annealing
Authors: Taniguchi K. , Tanaka M. , Hamaguchi C. , Imai K.
Published: July 2002

Measurements of the refractive index of thermally grown oxide after annealing reveal that the density relaxation of the oxide is well described by a stretched exponential decay function. The experiments of two-step oxidation show that oxygen diffusivity in the oxide exponentially decreases with the oxide density. The relation between the oxide density and the refractive index is well expressed by a simple power relation rather than the Lorenz–Lorenz formula.
Numerical modeling of microscopic fluid distribution in porous media
Authors: Knight Rosemary , Chapman Alice , Knoll Michael
Published: July 2002

Three numerical methods have been developed to model the equilibrium distribution of fluid phases in a multiphase saturated porous medium. The basic assumption made is that the distribution of phases is governed by the static interfacial free energy of the system, such that the equilibrium phase distribution corresponds to a minimum in the total interfacial free energy of the system. The example of determining the distribution of water vapor and liquid water in 2D numerical models of the pore space in a rock is considered. Starting with a numerical model of the pore space, the objective of each method is to obtain the minimum energy configuration of water vapor and liquid water in the pore space for some set level of water saturation. Two of the methods are simple and computationally fast methods that can produce fluid distributions close to, or matching, the equilibrium configuration. These methods can, however, produce metastable configurations due to the simplistic nature of the algorithms. The third method applied to this problem is a simulated annealing method. This method consistently produced the lowest possible energy configuration. It is concluded that simulated annealing can be successfully used to numerically model fluid distribution in multiphase saturated porous media.
Quantum-well infrared photodetectors
Authors: Levine B. F.
Published: July 2002

The extensive literature on quantum-well infrared photodetectors (QWIPs) is reviewed. A detailed discussion is given on the device physics of the intersubband absorption and hot-carrier transport processes for individual detectors, as well as the high performance which has been achieved for large staring arrays. QWIPs having widely different structures, materials, and spectral responses are covered, as is the optimization of the quantum-well parameters for maximum performance.
The spontaneous relaxor-ferroelectric transition of Pb(Sc0.5Ta0.5)O3
Authors: Chu F. , Setter N. , Tagantsev A. K.
Published: July 2002

A zero-field spontaneous relaxor-ferroelectric transition is reported in Pb(Sc0.5Ta0.5)O3 (PST). This behavior is different from that of other relaxors, where such transitions occur only under the field. A highly disordered PST that has the wide relaxation spectrum typical of relaxors is shown to transform spontaneously into a macroscopic ferroelectric state. Introduction of defects (lead vacancies) into the material impedes the transition resulting in the usual relaxor behavior. Dielectric properties of PST, with and without defects, are analyzed. For the interpretation of the observed properties, a model invoking an additional nonpolar phase is proposed. This model does not imply a freezing in the system. At the low-frequency limit, it is possible to account for the Vögel–Fulcher (VF) law for the temperature of the maximum of the dielectric constant, using only the commonly accepted assumption of an exponentially wide relaxation time spectrum that shrinks on heating. The presented approach interprets the observed proximity between the ferroelectric phase transition temperature and that of the freezing temperature obtained from the VF relation.
Cation size-temperature phase diagram of the manganites Ln0.5Sr0.5MnO3
Authors: Damay F. , Maignan A. , Martin C. , Raveau B.
Published: July 2002

We have studied the variation of the paramagnetic to ferromagnetic transition temperature TC and of the ferromagnetic to antiferromagnetic transition temperature TN as a function of the average size of the A site cations (Ln, Sr) in the manganite perovskites Ln0.5Sr0.5MnO3 (Ln=Gd, Sm, Y, Pr, La). For our investigation we used dc resistivity, magnetization, susceptibility and magnetoresistance measurements. Results show that the Curie temperature TC increases from 85 to 310 K when 〈rA〉 varies from 1.221 to 1.263 Å, whereas TN remains stable around 150 K. A magnetic phase diagram temperature-〈rA〉 has been established, allowing five regions with different magnetic behaviours to be evidenced: paramagnetic insulating, ferromagnetic metallic, antiferromagnetic insulating, canted antiferromagnetic metallic, and weak ferromagnetic insulating. The extension of these regions is determined by the value of the applied magnetic field.
Dose effects on amorphous silicon sputtering by argon ions: A molecular dynamics simulation
Authors: Marqués Luis A. , Rubio José E. , Jaraı́z Martı́n , Bailón Luis A. , Barbolla Juan J.
Published: July 2002

We have investigated, using molecular dynamics techniques, the sputtering yield enhancement of amorphous silicon produced by argon ion accumulation within the target. Several amorphous silicon samples, with different argon contents, were bombarded with 1 keV argon ions at normal incidence. To study the influence of the target structure, we considered samples with different argon arrangements, either uniformly distributed or within solid bubbles. We have observed that silicon sputtering yield increases linearly with dose until steady state conditions are reached. This enhancement is produced by the shallow argon atoms through the weakening of Si–Si bonds. We have also observed that argon release takes place even long after the end of the collisional phase, and it is produced by ion-induced desorption and bubble destabilization. This enhanced argon yield determines the dose where target saturation and steady state conditions are reached.
Direct evidence for diffusion and electromigration of Cu in CuInSe2
Authors: Gartsman Konstantin , Chernyak Leonid , Lyahovitskaya Vera , Cahen David , Didik Vladimir , Kozlovsky Vitaliy , Malkovich Roald , Skoryatina Elena , Usacheva Valentina
Published: July 2002

Cu diffusion in chalcopyrite CuInSe2 was studied directly, using 64Cu as a radioactive tracer. For diffusion from a thin surface layer, the Cu diffusion coefficients at 380 and 430 °C, were found to vary from 10−8 to 10−9 cm2/s. In case of diffusion from a volume source at 400 °C, a value of 10−10 cm2/s was calculated from diffusion profiles. Electromigration of Cu was demonstrated, by applying a strong electric field to a sample and following the redistribution of 64Cu, that had been thermally diffused into the sample, prior to electric field application.
Vibrational excitation of D2 by low energy electrons
Authors: Buckman S. J. , Phelps A. V.
Published: July 2002

Excitation coefficients for the production of vibrationally exicted D2 by low energy electrons have been determined from measurements of the intensity of infrared emission from mixtures of D2 and small concentrations of CO2 or CO. The measurements were made using the electron drift tube technique and covered electric field to gas density ratios (E/n) from (5 to 80)×10−21 V m2, corresponding to mean electron energies between 0.45 and 4.5 eV. The CO2 and CO concentrations were chosen to allow efficient excitation transfer from the D2 to the carbon containing molecule, but to minimize direct excitation of the CO2 or CO. The measured infrared intensities were normalized to predicted values for N2–CO2 and N2–CO mixtures at E/n where the efficiency of vibrational excitation is known to be very close to 100%. The experimental excitation coefficients are in satisfactory agreement with predictions based on electron–D2 cross sections at mean electron energies below 1 eV, but are about 50% too high at mean energies above about 2 eV. Application of the technique to H2 did not yield useful vibrational excitation coefficients. The effective coefficients in H2–CO2 mixtures were a factor of about 3 times the predicted values. For our H2–CO mixtures the excitation of CO via excitation transfer from H2 is small compared to direct electron excitation of CO molecules. Published experiments and theories on electron–H2 and electron–D2 collisions are reviewed to obtain the cross sections used in the predictions.
The finite difference thermodynamic integration, tested on calculating the hydration free energy difference between acetone and dimethylamine in water
Authors: Mezei M.
Published: July 2002

A new technique is proposed to compute by Monte Carlo (or molecular dynamics) computer simulation the hydration free energy differences. The method, called finite difference thermodynamic integration, is a combination of the thermodynamic integration and the perturbation method. It was compared with thermodynamic integration over two different paths and the perturbation method on computing the solvation free-energy difference between the dilute aqueous solution of acetone and dimethyl amine. Finite difference thermodynamic integration was found to have the best convergence characteristics among the methods tested.
Raman spectroscopic study on the vibrational and rotational relaxation of OH− ion in molten LiOH
Authors: Okazaki Susumu , Ohtori Norikazu , Okada Isao
Published: July 2002

Raman scattering spectra have been measured for molten LiOH at 773 K. The highly corrosive melt was held as a drop under a silver wire ring. While the Rayleigh wing spread over more than 1000 cm−1, only one distinct peak for the OH− stretching mode appeared at 3607 cm−1, the band shape being asymmetric owing to inhomogeneous broadening. The vibrational and rotational autocorrelation functions for the OH− ion, Gv(t) and Gr(t), respectively, have been evaluated from the Fourier transformation of the observed polarized and depolarized band contours. The Gv(t) is virtually of an exponential form and its decay is faster than that of the NO−3 ion in molten LiNO3. The Gr(t) can be obtained with good accuracy, whereas inhomogeneous broadening is obviously observed. The relaxation rate of Gr (t) is extremely high as compared with that for the NO−3 ion in molten LiNO3 . The difference is explained in terms of the difference mainly in the moments of inertia and partly in the temperatures. The Gr (t) has oscillatory character with a period of ∼0.04 ps at small t. This must be attributed to the precession and/or the pendulum motion of the ion, which supports the M- or J-extended rotational diffusion model rather than Debye’s rotational diffusion model.
Self-, N2, O2, H2, Ar, and He broadening in the ν3 band Q branch of CH4
Authors: Pine A. S.
Published: July 2002

Self-, N2-, O2-, H2-, Ar-, and He-broadening coefficients, pressure shifts, and integrated intensities have been measured for most transitions in the Q branch of the ν3 fundamental band of methane using a difference-frequency laser spectrometer. A systematic dependence of the broadening coefficients on the tetrahedral symmetry species and order index is observed with striking similarities for N2, O2, and Ar and for H2 and He buffer gases. Comparison with earlier measurements on other bands and branches of methane indicates very little vibrational, branch, or carbon isotope dependence. Dicke narrowing is evident at intermediate pressures, yielding an average narrowing coefficient and an optical diffusion constant for each gas mixture. A small amount of line mixing is evident for strongly overlapped lines near atmospheric pressure from nonlinear deviations of the observed spectra from the contours extrapolated from lower pressure measurements.
Stretching frequencies of cation-CO adducts in alkali-metal exchanged zeolites: An elementary electrostatic approach
Authors: Lamberti C. , Bordiga S. , Geobaldo F. , Zecchina A. , Otero Areán C.
Published: July 2002

The C–O stretching frequencies, obtained by a 77 K Fourier transform infrared study of the interaction of CO with the extraframework cations in alkali–metal exchanged M-ZSM-5 and M-mordenites (M=Na,K,Rb,Cs) have been used to evaluate the local electric field strength tested by the probe molecule. For all the investigated zeolites, the dipolar CO molecule was found to interact specifically with extra-framework metal ions, and its stretching frequency was found to increase continuously from Cs+ to Na+ samples. The observed frequency shifts, with respect to that of the free CO molecule (ν̃CO=2143 cm−1), were used to evaluate the electrostatic field created by the cation sites. Electric fields in the range of 2 to 6 V nm−1 were obtained; experimental values are inferior to those expected if generated in vacuo, at the distance of the probe molecule, from a point charge of +‖e‖. The observed fields can be reproduced by the sum of a positive contribution of the cation itself, and by two negative contributions, the first due to the negatively charged oxygen atoms surrounding the cation and the second due to the polarized zeolite framework. The last contribution has been found to increase from ZSM-5 to Mordenite, in agreement with the decreasing Si/Al ratio.
Laser spectroscopy of the ν1+3ν3 absorption band in C212H2. I. Pressure broadening and absolute line intensity measurements
Authors: Herregodts F. , Hurtmans D. , Vander Auwera J. , Herman M.
Published: July 2002

We have developed a Ti:Sa autoscan laser spectrometer and used it to perform a detailed investigation of individual line profiles in the ν1+3ν3 band of C212H2. Pressure self-broadening effects were measured for most lines with J″ values ranging from 0 to 22, and for pressures between 10 and 600 Torr. The high-pressure data points (p>250 Torr) are fitted satisfactorily by a Voigt profile. Line narrowing, characterized by an underestimation of the Lorentz contribution to the Voigt profile, was observed for the low pressures range (p<150 Torr), indicating the influence of molecular confinement. The two usual limit models (soft and hard collisions) were fitted to the observed line shapes in order to extract more precise information concerning the pressure broadening. The present results confirm the absence of strong vibrational dependence in the self-broadening coefficients. Absolute line intensities are also determined in the fitting procedure. No significant differences were found for the two pressure domains if the appropriate model in each range is used.
Ionic conduction and self-diffusion near infinitesimal concentration in lithium salt-organic solvent electrolytes
Authors: Aihara Yuichi , Sugimoto Kyoko , Price William S. , Hayamizu Kikuko
Published: July 2002

The Debye–Hückel–Onsager and Nernst–Einstein equations, which are based on two different conceptual approaches, constitute the most widely used equations for relating ionic conduction to ionic mobility. However, both of these classical (simple) equations are predictive of ionic conductivity only at very low salt concentrations. In the present work the ionic conductivity of four organic solvent-lithium salt-based electrolytes were measured. These experimental conductivity values were then contrasted with theoretical values calculated using the translational diffusion (also known as self-diffusion or intradiffusion) coefficients of all of the species present obtained using pulsed-gradient spin–echo (1H, F19 and Li7) nuclear magnetic resonance self-diffusion measurements. The experimental results verified the applicability of both theoretical approaches at very low salt concentrations for these particular systems as well as helping to clarify the reasons for the divergence between theory and experiment. In particular, it was found that the correspondence between the Debye–Hückel–Onsager equation and experimental values could be improved by using the measured solvent self-diffusion values to correct for salt-induced changes in the solution viscosity. The concentration dependence of the self-diffusion coefficients is discussed in terms of the Jones–Dole equation.
p-adic quantum mechanics with p-adic valued functions
Authors: Khrennikov A. Yu.
Published: July 2002

An extension of the formalism of quantum mechanics to the case where the canonical variables and functions are valued in a field of p-adic numbers is considered. A new p-adic integral calculus is used for the realization of the Gauss representation in p-adic quantum mechanics.
Snapback repellers as a cause of chaotic vibration of the wave equation with a van der Pol boundary condition and energy injection at the middle of the span
Authors: Chen Goong , Hsu Sze-Bi , Zhou Jianxin
Published: July 2002

A wave equation on a one-dimensional interval I has a van der Pol type nonlinear boundary condition at the right end. At the left end, the boundary condition is fixed. At exactly the midpoint of the interval I, energy is injected into the system through a pair of transmission conditions in the feedback form of anti-damping. We wish to study chaotic wave propagation in the system. A cause of chaos by snapback repellers has been identified. These snapback repellers are repelling fixed points possessing homoclinic orbits of the non-invertible map in 2D corresponding to wave reflections and transmissions at, respectively, the boundary and the middle-of-the-span points. Existing literature [F. R. Marotto, J. Math. Anal. Appl. 63, 199–223 (1978)] on snapback repellers contains an error. We clarify the error and give a refined theorem that snapback repellers imply chaos. Numerical simulations of chaotic vibration are also illustrated.
Use of the positron as a plasma particle
Authors: Surko C. M. , Murphy T. J.
Published: July 2002

The use of positrons in laboratory plasma physics experiments is considered. Recent progress in this area is discussed, including the creation of a single-component positron plasma in the laboratory. Specific applications of such antimatter plasmas are also discussed, with emphasis on areas where existing plasma physics technology and that currently under development are likely to produce results in the next few years.
Electrohydrodynamics and electrorotation of a drop with fluid less conductive than that of the ambient fluid
Authors: Ha Jong-Wook , Yang Seung-Man
Published: July 2002

In this article, we investigated the electrohydrodynamic responses of a deformable fluid drop in another immiscible fluid under the action of a dc electric field. Both the ambient and drop fluids considered here were incompressible Newtonian and all of the drop phases were less conductive than their ambient fluids. Under these circumstances, the drops experienced the so-called electrorotation owing to the reverse dipole generated by the external electric field when the electric field strength exceeded a certain threshold value. The experimental observation showed that the threshold electric field strength was dependent on the drop size as well as the viscosity ratio. Also noted was the effect of the electrorotation on both the deformation behavior and the mode of the drop breakup. Specifically, we determined the critical electric capillary number beyond which the steady-state drop shape did not exist and the drop eventually broke up. Finally, the validity of Taylor’s leaky dielectric theory was discussed in the presence of the electrorotation of the drop.
Plasma wakefield generation and electron acceleration in a self-modulated laser wakefield accelerator experiment
Authors: Ting A. , Moore C. I. , Krushelnick K. , Manka C. , Esarey E. , Sprangle P. , Hubbard R. , Burris H. R. , Fischer R. , Baine M.
Published: July 2002

A self-modulated laser wakefield accelerator (SM-LWFA) experiment was performed at the Naval Research Laboratory. Large amplitude plasma wakefields produced by a sub-picosecond, high intensity laser pulse (7×1018 W/cm2) in an underdense plasma (ne≈1019 cm−3) were measured with a pump–probe coherent Thomson scattering (CTS) technique to last for less than 5 ps, consistent with the decay of large amplitude plasma waves due to the modulational instability. A plasma channel was observed to form in the wake of the pump laser pulse, and its evolution was measured with the pump–probe CTS diagnostic. The trailing probe laser pulse was observed to be guided by this channel for about 20 Rayleigh lengths. High energy electrons (up to 30 MeV) have been measured using an electro-magnetic spectrometer, with the energy spectra and divergence of lower energy (up to 4 MeV) electrons obtained using photographic films. Highly nonlinear plasma waves were also detected using forward Raman scattering diagnostics and were observed to correlate with the electron signals. Simulations of self-trapping of plasma electrons from the interaction of the laser wakefield with the slow plasma wave generated by Raman backscattering are also presented.
Pw1/Peg3 is a potential cell death mediator and cooperates with Siah1a in p53-mediated apoptosis
Authors: Relaix Frédéric , Wei Xiao-jun , Li Wei , Pan Jianjing , Lin Yahong , Bowtell David D. , Sassoon David A. , Wu Xiangwei
Published: July 2002

Induction of wild-type p53 in mouse fibroblasts causes cell cycle arrest at the G
1
phase, whereas coexpression of p53 and the protooncogene c-
myc
induces apoptosis. Although p53 transcriptional activity generally is required for both pathways, the molecular components mediating p53-dependent apoptosis are not well understood. To identify factors that could mediate p53-induced cell death, we used a comparative RNA differential display procedure. We have identified Pw1/Peg3 as a gene product induced during p53/c-
myc
-mediated apoptosis. Pw1/Peg3 is not induced during p53-mediated G
1
growth arrest nor by c-
myc
alone. Although it is not clear whether the induction of Pw1/Peg3 depends on p53 activity, we show that Pw1/Peg3 interacts with a p53-inducible gene product Siah1a. We demonstrate that coexpression of Pw1/Peg3 with Siah1a induces apoptosis independently of p53 whereas expression of Pw1/Peg3 or Siah1a separately has no effect on cell death. These data suggest that Siah1a and Pw1/Peg3 cooperate in the p53-mediated cell death pathway. Furthermore, we show that inhibiting Pw1/Peg3 activity blocks p53-induced apoptosis. The observation that Pw1/Peg3 is necessary for the p53 apoptotic response suggests a pivotal role for this gene in determining cell death versus survival.
The hippocampal neurons of neuronal apoptosis inhibitory protein 1 (NAIP1)-deleted mice display increased vulnerability to kainic acid-induced injury
Authors: Holcik Martin , Thompson Charlie S. , Yaraghi Zahra , Lefebvre Charles A. , MacKenzie Alex E. , Korneluk Robert G.
Published: July 2002

The neuronal apoptosis inhibitory protein (NAIP) is a member of a novel family of inhibitor of apoptosis (IAP) proteins. The IAP genes are highly conserved from baculovirus to metazoans and suppress apoptosis induced by a variety of triggers both
in vitro
and
in vivo
. Here we describe the generation and characterization of mice with the targeted deletion of NAIP1. We demonstrate that the NAIP1-deleted mice develop normally. However, the survival of pyramidal neurons in the hippocampus after kainic acid-induced limbic seizures is greatly reduced in the NAIP1 knock-out animals. Thus, although NAIP1 is not necessary for normal development of murine central nervous system, the endogenous NAIP1 is required for neuronal survival in pathological conditions.
Nucleotides and phospholipids compete for binding to the C terminus of K
ATP
channels
Authors: MacGregor Gordon G. , Dong Ke , Vanoye Carlos G. , Tang LieQi , Giebisch Gerhard , Hebert Steven C.
Published: July 2002

Inwardly rectifying, ATP-sensitive K
+
channels (K
ATP
) couple metabolism to either cell excitability (Kir6.x) or potassium secretion (Kir1.1). Phosphatidylinositol phospholipids, like PI(4,5)P
2
, antagonize nucleotide inhibition of K
ATP
channels enhancing the coupling of metabolic events to cell electrical or transport activity. The mechanism by which phospholipids relieve ATP block is unclear. We have shown that maltose-binding fusion proteins (MBP) containing the COOH termini of K
ATP
channels (Kir1.1, Kir6.1, and Kir6.2) form functional tetramers that directly bind at least two ATP molecules with negative cooperativity. Here we show that purified phosphatidylinositol phospholipids compete for 2,4,6,-trinitrophenyl (TNP)-ATP binding to the COOH termini of K
ATP
channels with EC
50
values for PIP
2
between 6–8 μM. The phospholipid potency profile was PIP
3
> PIP
2
= PIP > PI, suggesting that net phospholipid charge was important. A role for head group charge was supported by polycations (neomycin, spermine, and polylysine) reversing the effect of PIP
2
on TNP-ATP binding to the Kir1.1 channel COOH terminal fusion protein. In contrast, the water-soluble charged hydrolytic product of PIP
2
, inositol(1,4,5)P
3
(IP
3
), had no effect on TNP-ATP binding, suggesting that the acyl chain of PIP
2
was also necessary for its effect on TNP-ATP binding. Indeed, neutral and charged lipids had weak, but significant, effects on TNP-ATP binding. Whereas μM concentrations of PIP
2
could compete with TNP-ATP, we found that mM concentrations of MgATP were required to compete with PIP
2
for binding to these K
ATP
channel COOH termini. Thus the COOH termini of K
ATP
channels form a nucleotide- and phospholipid-modulated channel gate on which ATP and phospholipids compete for binding.
Cortex mapping reveals regionally specific patterns of genetic and disease-specific gray-matter deficits in twins discordant for schizophrenia
Authors: Cannon Tyrone D. , Thompson Paul M. , van Erp Theo G. M. , Toga Arthur W. , Poutanen Veli-Pekka , Huttunen Matti , Lonnqvist Jouko , Standerskjold-Nordenstam Carl-Gustav , Narr Katherine L. , Khaledy Mohammad , Zoumalan Chris I. , Dail Rajneesh , Kaprio Jaakko
Published: July 2002

The symptoms of schizophrenia imply disruption to brain systems supporting higher-order cognitive activity, but whether these systems are impacted differentially against a background of diffuse cortical gray-matter deficit remains ambiguous. Some unaffected first-degree relatives of schizophrenics also manifest cortical gray-matter deficits, but it is unclear whether these changes are isomorphic with those in patients, and the answer is critical to understanding the neurobiological conditions necessary for disease expression given a predisposing genotype. Here we report three-dimensional cortical surface maps (probabilistic atlases matching subjects' anatomy point by point throughout cortex) in monozygotic (MZ) and dizygotic (DZ) twins discordant for chronic schizophrenia along with demographically matched control twins. A map encoding the average differences between schizophrenia patients and their unaffected MZ co-twins revealed deficits primarily in dorsolateral prefrontal cortex, superior temporal gyrus, and superior parietal lobule. A map encoding variation associated with genetic proximity to a patient (MZ co-twins > DZ co-twins > control twins) isolated deficits primarily in polar and dorsolateral prefrontal cortex. In each case, the statistical significance was confirmed through analysis of 10,000 Monte Carlo permutations, and the remaining cortex was shown to be significantly less affected by contrast analysis. The disease-related deficits in gray matter were correlated with measures of symptom severity and cognitive dysfunction but not with duration of illness or antipsychotic drug treatment. Genetic and disease-specific influences thus affect gray matter in partially nonoverlapping areas of predominantly heteromodal association cortex, changes that may act synergistically in producing overt behavioral features of the disorder.
Heritability of lobar brain volumes in twins supports genetic models of cerebral laterality and handedness
Authors: Geschwind Daniel H. , Miller Bruce L. , DeCarli Charles , Carmelli Dorit
Published: July 2002

Although the left and right human cerebral hemispheres differ both functionally and anatomically, little is known about the environmental or genetic factors that govern central nervous system asymmetry. Nevertheless, cerebral asymmetry is strongly correlated with handedness, and handedness does have a significant genetic component. To explore the relative contribution of environmental and genetic influences on cerebral asymmetry, we examined the volumes of left and right cerebral cortex in a large cohort of aging identical and fraternal twins and explored their relationship to handedness. Cerebral lobar volumes had a major genetic component, indicating that genes play a large role in changes in brain volume that occur with aging. Shared environment, which likely represents
in utero
events, had about twice the effect on the left hemisphere as on the right, consistent with less genetic control over the left hemisphere. To test the major genetic models of handedness and cerebral asymmetry, twin pairs were divided into those with two right handers and those with at least one left hander (nonright handers). Genetic factors contributed twice the influence to left and right cerebral hemispheric volumes in right-handed twin pairs, suggesting a large decrement in genetic control of cerebral volumes in the nonright-handed twin pairs. This loss of genetic determination of the left and right cerebral hemispheres in the nonright-handed twin pairs is consistent with models postulating a right-hand/left-hemisphere-biasing genetic influence, a “right-shift” genotype that is lost in nonright handers, resulting in decreased cerebral asymmetry.
Inactivation of menin, a Smad3-interacting protein, blocks transforming growth factor type β signaling
Authors: Kaji Hiroshi , Canaff Lucie , Lebrun Jean-Jacques , Goltzman David , Hendy Geoffrey N.
Published: July 2002

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant
disorder characterized by endocrine tumors of parathyroids, pancreatic
islets, and anterior pituitary. The MEN1 gene encodes a nuclear protein
called menin. In MEN1 carriers inactivating mutations give rise to a
truncated product consistent with menin acting as a tumor suppressor
gene. However, the role of menin in tumorigenesis and its physiological
functions are not known. Here, we show that menin inactivation by
antisense RNA antagonizes transforming growth factor type β-mediated
cell growth inhibition. Menin interacts with Smad3, and antisense menin
suppresses transforming growth factor type β-induced and
Smad3-induced transcriptional activity by inhibiting Smad3/4-DNA
binding at specific transcriptional regulatory sites. These results
implicate a mechanism of tumorigenesis by menin inactivation.