bluuebunny/crossref_metadata_2025 huggingface dataset:
Hamiltonian description of convective-cell generation
Authors: Krommes J. A. , Kolesnikov R. A.
Published: May 2004

The nonlinear statistical growth rate γq for convective cells driven by drift-wave (DW) interactions is studied with the aid of a covariant Hamiltonian formalism for the gyrofluid nonlinearities. A statistical energy theorem is proven that relates γq to a second functional tensor derivative of the DW energy. This generalizes to a wide class of systems of coupled partial differential equations a previous result for scalar dynamics. Applications to (i) electrostatic ion-temperature-gradient-driven modes at small ion temperature, and (ii) weakly electromagnetic collisional DWs are noted.
Anomalous skin effect for anisotropic electron velocity distribution function
Authors: Kaganovich Igor , Startsev Edward , Shvets Gennady
Published: May 2004

The anomalous skin effect in a plasma with a highly anisotropic electron velocity distribution function (EVDF) is very different from the skin effect in a plasma with isotropic EVDF. An analytical solution was derived for the electric field penetrated into plasma with the EVDF described as a Maxwellian with two temperatures Tx≫Tz, where x is the direction along the plasma boundary and z is the direction perpendicular to the plasma boundary. The skin layer was found to consist of two distinct regions of width of order vTx/ω and vTz/ω, where vTx,z=Tx,z/m is the thermal electron velocity and ω is the incident wave frequency.
Experimental evaluation of the migration of spherical particles in three-dimensional Poiseuille flow
Authors: Eloot Sunny , De Bisschop Frank , Verdonck Pascal
Published: May 2004

Convective transport of 10 μm nearly neutrally buoyant spherical particles (polystyrene vinyl dibenzene) is studied in 220 μm and 530 μm diameter capillaries using an on-line particle detector of the electronic gate type. The detector, connected to the capillary outlet, monitors the elution and translates the passage of individual particles into pulsed signals. The measuring technique requires the use of an electrically conductive carrier liquid, such as physiological saline (0.9%NaCl). Passage times are registered for discrete capillary lengths varying between 0.25 m and 5 m. Mean particle and fluid velocities are used to calculate the preferential radius of particle transport. The equilibrium position of the particles is found to shift towards the capillary wall for higher Reynolds numbers, for longer and smaller capillaries, and for more dilute suspensions. However, the higher the particle to capillary diameter ratio, the more pronounced wall effects. Moreover, as the Stokes number is small (E-2), adhesion at the capillary walls turns out to be non-negligible and to have an impact on the final quantitative results.
Co- and counter-helicity interaction between two adjacent laboratory prominences
Authors: Hansen J. F. , Tripathi S. K. P. , Bellan P. M.
Published: May 2004

The interaction between two side-by-side solar prominence-like plasmas has been studied using a four-electrode magnetized plasma source that can impose a wide variety of surface boundary conditions. When the source is arranged to create two prominences with the same helicity (co-helicity), it is observed that helicity transfer from one prominence to the other causes the receiving prominence to erupt sooner and faster than the transmitting prominence. When the source is arranged to create two prominences with opposite helicity (counter-helicity), it is observed that upon merging, prominences wrap around each other to form closely spaced, writhing turns of plasma. This is followed by appearance of a distinct bright region in the middle and order of magnitude higher emission of soft x rays. The four-electrode device has also been used to change the angle of the neutral line and so form more pronounced S-shapes.
Motions of ultrarelativistic particles accelerated in an oblique plasma wave
Authors: Usami Shunsuke , Ohsawa Yukiharu
Published: May 2004

The motion of ultrarelativistic particles in an oblique plasma wave is theoretically studied. Making use of the relation vdγ/dt≫γdv/dt, where γ is the Lorentz factor, the zeroth-order velocity and energy increase rate are obtained. This solution is applicable to any particle species. The particle velocity is nearly parallel to the external magnetic field when vsh∼c cos θ, where vsh is the wave propagation speed and θ is the angle between the wave normal and the external magnetic field. The perturbed motions of ions and of positrons are then separately discussed. Their perturbations are both nearly perpendicular to the zeroth-order velocity. The ion perturbation is one dimensional with the frequency ω∼Ωi0γ−1/2, while that of the positrons is elliptic with ω∼Ωp0γ−1, where Ωi0 and Ωp0 are the nonrelativistic gyrofrequencies of ions and positrons, respectively.
Phase state and transport of non-Yukawa interacting macroparticles (complex plasma)
Authors: Vaulina O. S. , Vladimirov S. V. , Petrov O. F. , Fortov V. E.
Published: May 2004

Phase state and transport of macroparticles forming fluid-like structures in a complex plasma is numerically studied for radial pair potentials of various types. Special attention is paid to non-Yukawa-type screening potentials. The parameters responsible for the phase state and microscopic dynamics of macroparticle motions are determined and investigated. Consequences for the particle condensation are discussed.
White organic light-emitting devices using 2,5,2′,5′-tetrakis(4′-biphenylenevinyl)-biphenyl as blue light-emitting layer
Authors: Cheng Gang , Zhao Yi , Zhang Yingfang , Liu Shiyong , He Feng , Zhang Haiquan , Ma Yuguang
Published: May 2004

White organic light-emitting devices (OLEDs) have been fabricated using a trimeric phenylenvinylene derivative, 2,5,2′,5′-tetrakis(4′-biphenylenevinyl)-biphenyl (TBVB), as blue light-emitting layer. The structure of devices is simple, in which tris(8-hydroxyquinoline) aluminum (Alq), N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine, TBVB, and an ultrathin layer of 5,6,11,12-tetraphenylnaphthacene (rubrene), which is inserted between Alq and TBVB layers, are used as electron-transporting, hole-transporting, blue, and yellow light-emitting layers, respectively. A fairly pure white OLED with Commission Internationale De L’Eclairage coordinates of (0.33,0.34) at 4000 cd/m2 is realized when the thickness of TBVB is 10 nm and that of rubrene is 0.15 nm. The maximum luminance and efficiency of this device are 4025 cd/m2 and 3.2 cd/A, respectively.
Cyclic statistics in three dimensions
Authors: Surya Sumati
Published: May 2004

The existence of anyons in two-dimensional systems is a well-known example of nonpermutation group statistics. In higher dimensions, however, it is expected that statistics is dictated solely by representations of the permutation group. Using basic elements from representation theory we show that this expectation is false in three-dimensions for a certain nongravitational system. Namely, we demonstrate the existence of “cyclic,” or Zn, nonpermutation group statistics for a system of n>2 identical, unknotted rings embedded in R3. We make crucial use of a theorem due to Goldsmith in conjunction with the Fuchs–Rabinovitch relations for the automorphisms of the free product group on n elements.
On the higher-order solution of the dust-acoustic solitary waves in a warm magnetized dusty plasma with dust charge variation
Authors: El-Labany S. K. , Moslem Waleed M. , El-Taibany W. F. , Mahmoud M.
Published: May 2004

The higher-order contribution in reductive perturbation theory is studied for small-butfinite-amplitude dust-acoustic solitary waves in warm magnetized three-component dusty plasmas comprised of variational charged dust grains, isothermal ions, and electrons. The basic set of fluid equations is reduced to the Zakharov–Kuznetsov equation for the first-order perturbed potential and a linear inhomogeneous Zakharov–Kuznetsov-type equation for the second-order perturbed potential. Stationary solutions of both equations are obtained using a renormalization method. The effects of the higher-order contribution, external magnetic field, dust charge variation, dust grain temperature, ratios of temperature and density of positive ions to electrons, and directional cosine of the wave vector k along the x axis on the nature of the solitary waves are investigated.
Dynamical magnetic relaxation: A nonlinear magnetically driven dynamo
Authors: Blackman Eric G. , Field George B.
Published: May 2004

A nonlinear, time-dependent, magnetically driven dynamo theory that shows how magnetically dominated configurations can relax to become helical on the largest scale available is presented. Coupled time-dependent differential equations for large-scale magnetic helicity, small-scale magnetic helicity, velocity, and the electromotive force are solved. The magnetic helicity on small scales relaxes to drive significant large-scale helical field growth on dynamical (Alfvén crossing) time scales, independent of the magnitude of finite microphysical transport coefficients, after which the growing kinetic helicity slows the growth to a viscously limited pace. This magnetically driven dynamo complements the nonlinear kinetic helicity-driven dynamo; for the latter, the growing magnetic helicity fluctuations suppress, rather than drive, large-scale magnetic helicity growth. A unified set of equations accommodates both types of dynamos.
Superconformal primary fields on a graded Riemann sphere
Authors: Nagi Jasbir
Published: May 2004

Primary superfields for a two-dimensional Euclidean superconformal field theory are constructed as sections of a sheaf over a graded Riemann sphere. The transformation law is found to be the same as that of an O(N) extended primary field. The construction is then applied to the N=3 Neveu–Schwarz case. Various quantities in the N=3 theory are calculated, such as elements of the super-Möbius group, and the two-point function. Applications of the construction to calculate three-point functions and fusion rules in a manifestly supersymmetric fashion are discussed.
Novel low-frequency oscillation in a radio-frequency inductively coupled plasma with tuned substrate
Authors: Ding Z. F. , Huo W. G. , Wang Y. N.
Published: May 2004

The rf self-bias on the substrate in a rf inductively coupled plasma is controlled by varying the impedance of an external tuning inductor and capacitor network inserted between the substrate and the ground. In term of variations of tuned substrate self-bias (Vtsb) with tuning capacitance (Ct), three characteristic regions, namely continuous, instable, and bistable regions are found, corresponding to low, moderate, and high discharge power at a constant gas pressure, respectively. A novel self-oscillation observed in the instable region occurs only within a limited domain of Ct. With the increment in Ct, the self-oscillation frequency increases while its amplitude decreases. Near the boundary of the instable and bistable regions, the self-oscillations shift downward and upward at lower and higher Ct, respectively. The possible mechanism for the self-oscillation is discussed.
On bosonic limits of two recent supersymmetric extensions of the Harry Dym hierarchy
Authors: Sakovich S. Yu.
Published: May 2004

Two generalized Harry Dym equations, recently found by Brunelli, Das, and Popowicz in the bosonic limit of new supersymmetric extensions of the Harry Dym hierarchy [J. Math. Phys. 44, 4756 (2003)], are transformed into previously known integrable systems: one, into a pair of decoupled KdV equations, the other one, into a pair of coupled mKdV equations from a bi-Hamiltonian hierarchy of Kupershmidt.
Impossibility of Vedenov–Rudakov’s plasma modulational instability as one more illustration of the inappropriateness of the recipes of nonequilibrium statistical mechanics
Authors: Erofeev V. I.
Published: May 2004

It is shown that collisionless dissipation of Langmuir turbulence is always sufficient for suppression of Vedenov–Rudakov’s plasma modulational instability, i.e., the plasma hydrodynamic instability with respect to long-wavelength spatial modulation in plasma density and coordinated modulation in the density of Langmuir turbulence.
Ultrasensitive nanoelectromechanical mass detection
Authors: Ekinci K. L. , Huang X. M. H. , Roukes M. L.
Published: May 2004

We describe the application of nanoelectromechanical systems (NEMS) to ultrasensitive mass detection. In these experiments, a modulated flux of atoms was adsorbed upon the surface of a 32.8 MHz NEMS resonator within an ultrahigh-vacuum environment. The mass-induced resonance frequency shifts by these adsorbates were then measured to ascertain a mass sensitivity of 2.53×10−18 g. In these initial measurements, this sensitivity is limited by the noise in the NEMS displacement transducer; the ultimate limits of the technique are set by fundamental phase noise processes. Our results and analysis indicate that mass sensing of individual molecules will be realizable with optimized NEMS devices.
Blue-light emission from molecular-beam-epitaxially grown GaN/Al0.5Ga0.5N multiple quantum wells with a perturbating layer of Al0.5Ga0.5N monolayers
Authors: Park Y. S. , Lee Seung-Ho , Oh Jae-Eung , Park Chang-Mo , Kang Tae-Won
Published: May 2004

We have studied the influence of AlGaN inserting layer into GaN well region on the light emission from a strained GaN/AlGaN multiple-quantum-well system. We have found that, by simply inserting thin AlGaN layer, the luminescence is dramatically redshifted with respect to that of the normal GaN/AlGaN quantum well, which is centered at 2.96 eV, nearly 0.52 eV below the bulk GaN band gap. We attribute this enormous redshift to an additional 0.7 MV/cm field present in the well due to the perturbation of the well region by inserting AlGaN layer. The result is revealed to be of great importance in the design and analysis of nitride heterostructure devices which can be exploited to advantage in nitride materials and device engineering.
Temperature-dependent emptying of grain-boundary charge traps in chemical vapor deposited diamond
Authors: Hearne S. M. , Jamieson D. N. , Trajkov E. , Prawer S. , Butler J. E.
Published: May 2004

We have used the technique of ion beam induced charge with a 2 MeV He+ microprobe to image particle detectors fabricated from polycrystalline chemical vapor deposited diamond as a function of temperature. We find that detectors which display a thermally stimulated current peak at 190 °C display increased charge collection efficiency when heated above that temperature. The probability of detecting the impact of a single ion at room temperature was less than 2%, but this probability rises to over 80% at 170 °C. We model this effect by showing that charge trapped at grain boundaries is liberated at elevated temperatures and this results in an increased electric field within the detector volume and hence a raised charge collection efficiency.
Quantum confinement for large light output from pure semiconducting scintillators
Authors: Shibuya Kengo , Koshimizu Masanori , Asai Keisuke , Shibata Hiromi
Published: May 2004

A method for creating a fast scintillator is proposed. Recently, much attention has been paid to pure semiconductors during development of subnanosecond fast solid scintillators. However, the bulky samples rarely exhibit high light yields at room temperature because of thermal instability at the excitonic levels. The authors employed the optimum three- and two-dimensional semiconducting systems provided by lead-halide-based compounds to demonstrate the advantage of low dimensionality in the scintillating efficiency. Their dimensional and temperature dependencies were investigated using a high-energy proton beam. Consequently, the quantum confinement system clearly prevented thermal quenching from excitonic level even at room temperature, and the result proposes the next breakthrough to create ultrafast solid scintillators.
Scanning ferromagnetic resonance microscopy and resonant heating of magnetite nanoparticles: Demonstration of thermally detected magnetic resonance
Authors: Sakran F. , Copty A. , Golosovsky M. , Davidov D. , Monod P.
Published: May 2004

We report a 9 GHz microwave scanning probe based on a slit aperture for spatially resolved magnetic resonance detection. We use patterned layers of dispersed magnetite Fe3O4 nanoparticles and demonstrate low-field ferromagnetic resonance images with a spatial resolution of 15 μm. We also demonstrate localized heating of magnetite nanoparticles via ferromagnetic resonance absorption which can be controlled by an external dc magnetic field. Using our microwave probe as a transmitter and a temperature sensor (thermocouple or infrared detector), we show thermally detected magnetic resonance at room temperature.
Scaling law in liquid drop coalescence driven by surface tension
Authors: Wu Mingming , Cubaud Thomas , Ho Chih-Ming
Published: May 2004

This Letter reports experimental results on the coalescence of two liquid drops driven by surface tension. Using a high speed imaging system, we studied the early-time evolution of the liquid bridge that is formed upon the initial contact of two liquid drops in air. Experimental results confirmed the scaling law that was proposed by Eggers et al. based on a simple and yet elegant physical argument. We found that the liquid bridge radius rb follows the scaling law rb∝t1/2 in the inertial regime. Further experiments demonstrate that such scaling law is robust when using fluids of different viscosities and surface tensions. The prefactor of the scaling law, rb/t1/2, is shown to be ∝R1/4, where R is the inverse of the drop curvature at the point of contact. The dimensionless prefactor is measured to be in the range of 1.03–1.29, which is lower than 1.62, a prefactor predicted by the numerical simulation of Duchemin et al. for inviscid drop coalescence.
Negative bias-temperature instabilities in metal–oxide–silicon devices with SiO2 and SiOxNy/HfO2 gate dielectrics
Authors: Zhou X. J. , Tsetseris L. , Rashkeev S. N. , Fleetwood D. M. , Schrimpf R. D. , Pantelides S. T. , Felix J. A. , Gusev E. P. , D’Emic C.
Published: May 2004

Negative bias-temperature instability (NBTI) in metal–oxide–semiconductor capacitors with SiOxNy/HfO2 gate dielectrics is compared to those with thermal SiO2 oxides. Activation energies for interface and oxide-trap charge densities for each device type, estimated from capacitance–voltage measurements versus temperature and electric field, lie in the range 0.2–0.4 eV. This suggests that the release of hydrogen from, e.g., oxide protrusions in Si, followed by the lateral motion of protons along the interface (activation energy ∼0.3 eV), may play a key role in NBTI. Passivation reactions between protons and Si–H can create interface traps, and proton capture by sub-oxide bonds (O vacancies) can lead to positive trapped-oxide charge.
Vertically aligned liquid crystal light valve controlled by double-side fringe-field switching with memory effect
Authors: Xiang C. Y. , Sun X. W.
Published: May 2004

A vertically aligned liquid crystal light valve with negative dielectric anisotropy driven by vertical field and double-side fringe field is described. The transmission of this device is not determined by the vertical field, but by the relative strength of the two fringe fields at the surfaces of top and bottom substrates. When a voltage is applied on the two plane electrodes, by connecting or disconnecting the two floating stripe electrodes, the corresponding transmission is high or low, respectively. An optical memory device based on this mechanism has been demonstrated.
Guiding and bending of acoustic waves in highly confined phononic crystal waveguides
Authors: Khelif A. , Choujaa A. , Benchabane S. , Djafari-Rouhani B. , Laude V.
Published: May 2004

We demonstrate experimentally the guiding and the bending of acoustic waves in highly confined waveguides formed by removing rods from a periodic two-dimensional lattice of steel cylinders immersed in water. Full transmission is observed for a one-period-wide straight waveguide within the full band gap of the perfect phononic crystal. However, when the waveguide width is doubled, destructive interference causes the transmission to vanish in the center of the passband. Waveguiding over a wide frequency range is obtained for a one-period-wide waveguide with two sharp 90° bends. Finite-difference time-domain computations are found to be in good agreement with the measurements.
Submicron imaging with a planar silver lens
Authors: Melville David O. S. , Blaikie Richard J. , Wolf Conrad R.
Published: May 2004

Optical imaging through a thin planar silver layer has been achieved by utilizing near-field lithography techniques. A 120 nm thick silver lens that was placed 60 nm below a patterned mask, imaged the mask’s features onto a photosensitive material located 60 nm below the silver. The entire structure was exposed from above with a mercury lamp. Features sizes as small as 350 nm (at a 700 nm period) were imaged onto the photosensitive material, demonstrating the lensing ability of the planar silver slab.
Supersonic dense granular materials in a duct flow
Authors: Soleymani Azita , Zamankhan Piroz , Polashenski William
Published: May 2004

Both large-scale three-dimensional molecular-dynamics-type simulation and integration of hydrodynamic equations relevant to dense granular flows were performed to investigate the formation of shock waves in granular flows past a stationary wedge in a rectangular duct. No signature of supersonic flows was found at grain speeds as small as 0.1 m/s. Upon increasing the speed of the grains, the flow became supersonic where complex solid structures were observed to form in both upstream and downstream flow regions. In addition, the compression shock formed on the upper edges of the channel adjacent to the wedge and the expansion fan formed adjacent to the rear face of the wedge. Both the compression shock and expansion fan appear to be analogous to those in supersonic gases with some fundamental differences arising due to the inelastic collisions between particles in granular media.
Microstructures formed in recrystallized Si
Authors: Watanabe K. , Anzai Y. , Nakanishi N. , Yamazaki T. , Kuramochi K. , Mitsuishi K. , Furuya K. , Hashimoto I.
Published: May 2004

Our study using systematic transmission electron microscopy observation and simulation shows that microstructures formed in recrystallized Si are characterized as microtwin or lamellar microtwin. Detailed analysis leads to their atomic structures. The discovery of exceptional diffraction spots offers direct evidence of long-periodic-order structures and antiphase boundaries, due to the ordering of projected lamellar microtwins.
Degenerate layers in epitaxial ZnO films grown on sapphire substrates
Authors: Tampo H. , Yamada A. , Fons P. , Shibata H. , Matsubara K. , Iwata K. , Niki S. , Nakahara K. , Takasu H.
Published: May 2004

ZnO films were grown on low-temperature (LT) buffer layers on sapphire a-plane (11–20) substrates by radical source molecular-beam epitaxy. The LT buffer layers were found to effect the electrical properties of subsequently grown undoped ZnO films, and their presence was found to be indispensable for the growth of films with low carrier concentrations and high mobilities. Temperature-dependent Hall measurements showed the existence of a degenerate region related to the LT buffer layers. It was found that the effects of degenerate layers could be reduced by using annealing treatments and nitrogen doping of the LT buffer layers. The dominant residual donor energy of 110 meV was found to be different than previously reported. The carrier concentration of a ZnO film fabricated using a nitrogen-doped buffer layer was 7.5×1016 cm−3 with a mobility of 132 cm2/V s at room temperature.
Midinfrared difference frequency generation in quasi-phase matched diffusion bonded ZnSe plates
Authors: Mustelier A. , Rosencher E. , Kupecek Ph. , Godard A. , Baudrier M. , Lefebvre M. , Poulat M. , Mennerat G. , Pasquer C. , Lemasson Ph.
Published: May 2004

We present the results on tunable midinfrared radiation (8–12 μm) generated in diffusion-bonded ZnSe slabs by difference frequency mixing of optical-parametric-oscillator output waves (≈2 μm).
Direct observation of laser level occupation and injector coupling in undoped GaAs/(Al,Ga)As quantum-cascade structures
Authors: Schrottke L. , Hey R. , Grahn H. T.
Published: May 2004

The occupation of the laser levels in an undoped GaAs/(Al,Ga)As quantum-cascade structure is directly detected by interband photoluminescence spectroscopy. The upper laser level and the injector state exhibit an anticrossing behavior with a splitting of about 10 meV, which is attributed to a strong coupling between them. The energy splitting matches well the oscillation period observed in recent, ultrafast, coherent electron-transport experiments by F. Eickemeyer et al. [Phys. Rev. Lett. 89, 047402 (2002)]. A comparison with the calculated transition energies qualitatively confirms the anticrossing behavior in the vicinity of the threshold field strength. Furthermore, the measured energy difference between the upper and lower laser level agrees with the lasing energies of a set of complete quantum-cascade lasers. At the same time, the variation of the lasing energies corresponds to the energy splitting between the upper laser level and the injector state.
Resonant photoemission in Cr silicide at the absorption energy Cr 2p
Authors: Galán L. , Garcı́a M. , Ripalda J. M. , Montero I. , Román E. , Batchelor D. R. , Bressler P. R.
Published: May 2004

Valence band photoemission has been measured in chromium silicide as a function of the photon energy near the Cr 2p3/2 absorption threshold. Evidence of resonant photoemission is observed for the 3d valence band and the two-hole satellite. The threshold for normal Auger regime is 2.8 eV below the absorption peak and 0.8 eV below the Cr 2p3/2 binding energy, even lower than in pure Cr metal where it is already at extreme levels. The requirement for good resolution in photon energy relative to absorption width for the resonant Raman Auger to be observed is found to be less restrictive than expected.
Quantum grid infrared spectrometer
Authors: Choi K. K. , Dang G. , Little J. W. , Leung K. M. , Tamir T.
Published: May 2004

We have designed and characterized an infrared spectrometer, which uses a linear array of quantum grid infrared photodetectors (QGIPs) as its spectral sensing elements. Each QGIP element shares the same detector material but has a different grid geometry. The detector material, which is based on a binary superlattice design, provides an 8–14 μm broadband absorption medium for the spectrometer. The geometry of the grid, which is the light coupling structure under normal incidence, selects individual absorption wavelength for each element. Using a linear array of QGIPs of different geometries, multiple wavelengths can be detected simultaneously, and the array thus forms a spectrometer. Multicolor infrared imaging can then be achieved by integrating such QGIPs in unit cells of a two-dimensional array.
Structure of grain boundaries in nanostructured ZnO
Authors: Wu Zhihao , Zhou Yingxue , Zhang Xinyi , Wei Shiqiang , Chen Dongliang
Published: May 2004

The grain boundary (GB) of nanocrystalline ZnO films is investigated using the x-ray absorption fine structure technique. With the advantage of the dominant GB volume fraction in our samples, the GB structure is found to be neither simply “gas-like” nor “similar to that of coarse-grained phase,” but experiences a transition from the modestly ordered innermost coordination shell around centered atoms to partly disordered second coordination shell and then to completely disordered higher coordination shells.
Nanowire transistors with ferroelectric gate dielectrics: Enhanced performance and memory effects
Authors: Lei Bo , Li Chao , Zhang Daihua , Zhou Q. F. , Shung K. K. , Zhou Chongwu
Published: May 2004

Integration of ferroelectric materials into nanoscale field-effect transistors offers enormous promise for superior transistor performance and also intriguing memory effects. In this study, we have incorporated lead zirconate titanate (PZT) into In2O3 nanowire transistors to replace the commonly used SiO2 as the gate dielectric. These transistors exhibited substantially enhanced performance as a result of the high dielectric constant of PZT, as revealed by a 30-fold increase in the transconductance and a 10-fold reduction in the subthreshold swing when compared to similar SiO2-gated devices. Furthermore, memory effects were observed with our devices, as characterized by a counter-clockwise loop in current-versus-gate-bias curves that can be attributed to the switchable remnant polarization of PZT. Our method can be easily generalized to other nanomaterials systems and may prove to be a viable way to obtain nanoscale memories.
Electronic transport through individual ZnO nanowires
Authors: Li Q. H. , Wan Q. , Liang Y. X. , Wang T. H.
Published: May 2004

Electronic transport through individual ZnO nanowires has been investigated. The current increases linearly with the bias and the conductance jumps upon ultraviolet illumination. The increase rate upon the illumination is much faster than the decrease rate as the light is off. The decrease rate under vacuum is slower than that in air. These phenomena are related to the surface oxygen species and further confirmed by in situ current–voltage measurements as a function of oxygen pressure at room temperature. Also, the conductance increases greatly as the temperature is raised. These results demonstrate that the surface oxygen species dominate the transport process through individual ZnO nanowires, which indicates their potential application to room temperature gas sensors.
Jamming phase diagram of colloidal dispersions by molecular dynamics simulations
Authors: Kumar Anil , Wu Jianzhong
Published: May 2004

We report a three-dimensional jamming phase diagram of a model colloidal system obtained from molecular dynamics simulations where the inter-colloidal forces are represented by the Derjaguin–Landau–Verwey–Overbeek potential. The jamming threshold is uniquely defined in terms of the critical volume fraction, the critical temperature, and the critical yield stress. The simulation results indicate that near the jamming transition the shear viscosity diverges following a critical-like scaling law as observed for realistic colloids. These results offer a convincing proof for unifying different nonequilibrium transitions in colloids under the concepts of jamming.
Initial growth mechanism of atomic layer deposited TiN
Authors: Satta A. , Vantomme A. , Schuhmacher J. , Whelan C. M. , Sutcliffe V. , Maex K.
Published: May 2004

We have investigated the role of the substrate in the growth mechanism of TiN films grown by atomic layer deposition. The early stage of the film formation is dominated by a Volmer–Weber-type growth mode, driven by the ligand exchange of reactant molecules with preferential surface function groups. The density of function groups on the initial surface dictates the density and the vertical dimension of TiN islands, the evolution of the substrate coverage, and the minimum thickness at which the films become continuous.
A model for Ure2p prion filaments and other amyloids: The parallel superpleated β-structure
Authors: Kajava Andrey V. , Baxa Ulrich , Wickner Reed B. , Steven Alasdair C.
Published: May 2004

In its prion form, Ure2p, a regulator of nitrogen catabolism in
Saccharomyces cerevisiae
, polymerizes into filaments whereby its C-terminal regulatory domain is inactivated but retains its native fold. The filament has an amyloid fibril backbone formed by the Asn-rich, N-terminal, “prion” domain. The prion domain is also capable of forming fibrils when alone or when fused to other proteins. We have developed a model for the fibril that we call a parallel superpleated β-structure. In this model, the prion domain is divided into nine seven-residue segments, each with a four-residue strand and a three-residue turn, that zig-zag in a planar serpentine arrangement. Serpentines are stacked axially, in register, generating an array of parallel β-sheets, with a small and potentially variable left-hand twist. The interior of the filament is mostly stabilized not by packing of apolar side chains but by H-bond networks generated by the stacking of Asn side chains: charged residues are excluded. The model is consistent with current biophysical, biochemical, and structural data (notably, mass-per-unit-length measurements by scanning transmission electron microscopy that gave one subunit rise per 0.47 nm) and is readily adaptable to other amyloids, for instance the core of Sup35p filaments and glutamine expansions in huntingtin.
Uterine Smooth Muscle Tumors in Potbellied Pigs (Sus scrofa) Resemble Human Fibroids: A Potential Animal Model
Authors: Mozzachio Kristie , Linder Keith , Dixon Darlene
Published: May 2004

Uterine leiomyomas, commonly termed fibroids, clinically affect approximately 25% of women of reproductive age in the United States, with a subclinical incidence as high as 77%. The pathogenesis of fibroid formation remains poorly understood, due in large part to the lack of a suitable animal model. This retrospective study characterizes the clinical, gross, and histopathologic features of similar, spontaneously occurring uterine tumors in potbellied pigs. Medical records available through a local Potbellied Pig Spay/Neuter Program, pig sanctuaries, and the Duchess Fund database were reviewed for evidence of reproductive disease or surgery. One-hundred and six female potbellied pigs were evaluated and uterine neoplasia was identified in 17 animals; tissues were available for 13 of these. Uterine leiomyoma was diagnosed in 11 of 13 cases, leiomyosarcoma in 1 of 13 cases, and undifferentiated sarcoma in 1 case. Pigs presented with clinical signs including abdominal distension or vaginal bleeding or were subclinical and identified during ovariohysterectomy. Tumors ranged from microscopic to 45 kg, were often multiple, and primarily involved the uterine horns. Hematoxylin and eosin and trichrome-stained sections were evaluated for morphological features of human and animal leiomyomas; immunohistochemistry to detect smooth muscle actin was also performed. The cellular pattern/morphology and variable degree of fibroplasia of the leiomyomas were similar to that reported for human fibroids. These results support further investigation of uterine leiomyomas in potbellied pigs as a potentially valuable animal model for studying human fibroids.
HISTOLOGY AND CYTOCHEMISTRY OF HUMAN SKIN
Authors: Montagna William
Published: May 2004

1. In the epidermis non-specific esterase activity outlines a strongly reactive band between the stratum granulosum and the stratum corneum. In the epidermis of the palm, there is no such esterase-rich band.

2. The outer sheath of active hair follicles has strong enzyme activity. The degenerating hair bulb in catagen follicles is very strongly reactive, and clusters of cells around the hair club in quiescent follicles are rich in enzyme activity.

3. Strong enzyme activity is found in young sebaceous cells, while decaying sebaceous cells and newly formed sebum are unreactive. Old sebum, however, is very intensely reactive.

4. Only the "dark" cells of eccrine sweat glands show a reaction; the "clear" cells are negative.

5. The cells of axillary apocrine glands abound in enzyme.
MORPHOLOGY AND ATP-ASE OF ISOLATED MITOCHONDRIA
Authors: Witter Robert F. , Watson Michael L. , Cottone Mary A.
Published: May 2004

Changes in the morphology of rat liver mitochondria brought about by different methods of isolation and the concomitant changes in ATP-ase activity were studied. The morphology was investigated with the electron microscope. It was found that the ATP-ase activity of the isolated mitochondria cannot be readily correlated with the morphology of the mitochondria. The ATP-ase found in these preparations was latent, resembling the enzyme described in mitochondria prepared in 0.25 M sucrose. In confirmation of earlier results the use of 0.88 M sucrose yielded preparations with a higher initial ATP-ase than did other methods. Preparation in 0.25 M sucrose resulted in round, swollen mitochondria of which 30 to 40 per cent appeared to have lost a substantial part of the mitochondrial matrix. Preparations in 0.44 to 0.88 M sucrose contained mainly rod-shaped mitochondria plus a small amount of another type of swollen mitochondria. The matrix of mitochondria isolated in 0.88 M sucrose was highly condensed. By the use of 0.44 M sucrose adjusted to pH 6.2 with citric acid, it was possible to isolate, for the first time, mitochondria closely resembling those in situ and containing latent ATP-ase.
SILVER DEPOSITION IN THE CENTRAL NERVOUS SYSTEM AND THE HEMATOENCEPHALIC BARRIER STUDIED WITH THE ELECTRON MICROSCOPE
Authors: van Breemen V. L. , Clemente C. D.
Published: May 2004

For the purpose of studying the hematoencephalic barrier as it is concerned with silver circulating in the blood stream, silver nitrate was vitally administered to rats in their drinking water over periods of 6 to 8 months. The cerebrum, cerebellum, medulla, area postrema, and choroid plexus were prepared for light and electron microscopy. Silver deposition was found in the perivascular spaces in the choroid plexus, area postrema, in the medulla surrounding the area postrema, and in minute quantities in the cerebrum, cerebellum, and most of the medulla. Two levels of the hematoencephalic barrier were apparently demonstrated in our investigations. The endothelial linings of the vessels in the cerebrum, cerebellum, and medulla constitute the first threshold of the hematoencephalic barrier (specifically here, blood-brain barrier). The cell membranes adjacent to the perivascular spaces form the second threshold, as follows:—the neuroglial cell membranes in the cerebrum, cerebellum, and medulla (blood-brain barrier); the membranes of the neuroglial cells in the area postrema (blood-brain barrier); and the membranes of the epithelial cells of the choroid plexus (blood-cerebrospinal fluid barrier). This study deals with silver deposition and does not infer that the penetration of ionic silver, if present in the blood stream, would necessarily be limited to the regions described.

Bleb-like structures were observed to cover the epithelial cell surfaces in the choroid plexus. They may be cellular projections increasing the cell surface area or they may be secretory droplets.
THYMINE IN THE ACID-SOLUBLE FRACTION OF ARBACIA EGGS
Authors: Marshak A. , Marshak C.
Published: May 2004

Mature Arbacia eggs were extracted with cold dilute perchloric acid, the extract concentrated, and the concentrate digested in hot perchloric acid. Thymine was recovered from the digest by paper chromatography, and the amount per egg found to be about 5 times the amount per sperm. This was the amount expected from previous experiments and is believed to represent all or almost all of the thymine in the egg. The result supports previous observations that DNA is absent from the mature egg although present in the nucleus of the egg in the germinal vesicle stage. No thymine could be recovered from a similar extract of 5,000 times as many sperm of the same species. The observations are consistent with the theory that DNA and its derivatives act as metabolic antagonists of the corresponding ribose compounds.
VITROSIN: A MEMBER OF THE COLLAGEN CLASS
Authors: Gross Jerome , Matoltsy A. Gedeon , Cohen Carolyn
Published: May 2004

Vitrosin, a fibrous protein obtained from the vitreous humor of the eye in the form of an indefinitely long fibril about 100 to 150 A in diameter, has been identified as a member of the collagen class of proteins. It is characterized by the collagen wide-angle x-ray diffraction pattern, and axial periodicity of about 640 A determined by electron microscopy and small-angle x-ray diffraction, an amino acid pattern characteristic of collagen as determined by paper chromatography, and a hydroxyproline and glycine content also typical of collagen. The glycine-hydroxyproline ratio is somewhat lower than that for most vertebrate collagens.
PEPTIDASE DISTRIBUTION IN LYMPHATIC TISSUE
Authors: Doyle William L.
Published: May 2004

The lymphatic tissue of the rabbit contains a labile peptidase as measured by the hydrolysis of alanylglycine. Some characteristics of the enzyme were determined. This enzyme increases in amount when the numbers of macrophages in the tissue are increased and it is also present in the extracellular fluid in high concentration. The extracellular fluid value for this activity is calculated to be about 8 times the value for serum. Based on a correlation between the types of cells present and the amount of peptidase found in the tissue the following relative activities are assigned to the tissue components per unit volume: lymphocytes 1.0, tissue fluid 11.0, serum 1.4, phagocytes (macrophages) 30.0, reticular cells 12.0. The amount of chloride space varied from 35 to 55 per cent.

The relative amounts of acid phosphatase per unit volume in the same elements were calculated to be: lymphocytes 1.0, tissue fluid 0, phagocytes 20.0, and reticular cells 4.0.

Analysis of the distribution of peptidase was facilitated by simultaneous determination of acid phosphatase whose primary localization in one cell type was known.

The over-all contribution of lymphocytes to the labile peptidase content of lymphatic tissue is relatively minor and was not found to exceed 5 per cent of the average value for the entire nodular tissue. In the absence of large numbers of macrophages the intercellular fluid of the nodule accounts for half or more of the peptidase content of the nodules.
EFFECTS OF CORTISONE ON RAT LIVER MITOCHONDRIA
Authors: Lowe Charles Upton , MacKinney Deloris , Sarkaria Daljit
Published: May 2004

Experiments were designed to determine the effects of parenteral administration of cortisone on mitochondrial numbers of rat liver cells. Observations were made in three ways: (1) after osmic acid fixation and appropriate stain, (2) by phase microscopy on intact cells, (3) by actual enumeration of mitochondria and nuclei to provide data on mitochondria per cell. The results of the experiments indicate that the mitochondria per cell are significantly reduced under the conditions used. Each experimental approach provided similar data, and each tended to support the results obtained from the others.
AN ELECTRON MICROSCOPIC STUDY OF THE BLOOD-BRAIN BARRIER IN THE RAT, EMPLOYING SILVER NITRATE AS A VITAL STAIN
Authors: Dempsey Edward W. , Wislocki George B.
Published: May 2004

The intravital deposition of silver in the chorioid plexuses, area postrema, intercolumnar tubercle, neurohypophysis, and pineal body of rats, given 1.5 gm. of silver nitrate per liter of drinking water for periods of up to one year, has been investigated by electron microscopy. Unlike other parts of the central nervous system, these regions store large amounts of silver. In all of these structures, silver is deposited in the form of dense granules in the basement membrane upon which the capillary endothelium rests, in and upon the connective tissue cells and fibers constituting a loose pericapillary sheath, and in an outer membrane separating this sheath from the parenchymatous cells. Parts of the central nervous system which do not store silver, for example the spinal cord, cerebellar cortex, cerebral cortex, and reticular formation, lack a connective tissue investment of the capillaries. In these locations, the glial processes or end-feet are closely applied to the walls of the capillaries. Only a narrow space, filled by an amorphous, moderately electron-dense substance, separates the plasma membranes of the endothelial cells and glial processes. The significance of these observations is discussed with respect to the questions of the Virchow-Robin perivascular spaces, the interstitial ground-substance of the brain, and the location of the hematoencephalic barrier.
THE ULTRASTRUCTURE OF ADULT VERTEBRATE PERIPHERAL MYELINATED NERVE FIBERS IN RELATION TO MYELINOGENESIS
Authors: Robertson J. David
Published: May 2004

Adult chameleon myelinated peripheral nerve fibers have been studied with the electron microscope in thin sections. The outer lamella of the myelin sheath has been found to be connected as a double membrane to the surface of the Schwann cell. The inner lamella is connected as a similar double membrane with the double axon-Schwann membrane. The relations of these double connecting membranes suggest that the layered myelin structure is composed of a double membrane which is closely wound about the axon as a helix. These findings support the new theory of myelinogenesis proposed recently by Geren. The possible significance of these results with respect to cell surface membranes and cytoplasmic double membranes is discussed.
BUFFERED OSMIUM TETROXIDE (OsO4) FIXATION FOR CYTOLOGICAL AND FEULGEN MICROSPECTROPHOTOMETRIC STUDIES OF HUMAN RECTAL POLYPS
Authors: Leuchtenberger Cecilie , Doolin Paul F. , Kutsakis Anne H.
Published: May 2004

Evidence has been presented that when human rectal mucosa and polyps are fixed with buffered OsO4 according to the method of Palade, staining of paraffin sections by basic and acidic dyes results in a distinct color difference between chromatin and cytoplasm. Furthermore, the Feulgen reaction also can be carried out successfully and such OsO4-fixed Feulgen-stained sections are especially suitable for microspectrophotometric determinations of DNA in individual nuclei.
CYTOLOGICAL STUDIES ON THE ANTIMETABOLITE ACTION OF 2,6-DIAMINOPURINE IN VICIA FABA ROOTS
Authors: Setterfield George , Duncan Robert E.
Published: May 2004

At a concentration of 9.6 x 10–5 M, 2,6-diaminopurine (DAP) completely inhibited cell enlargement, cell division, and DNA synthesis (determined by microphotometric measurement of Feulgen dye) in Vicia faba roots.

Inhibition of cell enlargement was partially reversed by adenine, guanine, xanthine, adenosine, and desoxyadenosine. Guanine and the nucleosides gave the greatest reversal, suggesting that one point of DAP action upon cell enlargement is a disruption of nucleoside or nucleotide metabolism, possibly during pentosenucleic acid synthesis.

DAP inhibited cell division by preventing onset of prophase. At the concentrations used it had no significant effect on the rate or appearance of mitoses in progress. Inhibition of entrance into prophase was not directly due to inhibition of DNA synthesis since approximately half of the inhibited nuclei had the doubled (4C) amount of DNA. Adenine competitively reversed DAP inhibition of cell division, giving an inhibition index of about 0.5. Guanine gave a slight reversal while xanthine, hypoxanthine, adenosine, and desoxyadenosine were inactive. A basic need for free adenine for the onset of mitosis was suggested by this reversal pattern.

Meristems treated with DAP contained almost no nuclei with intermediate amounts of DNA, indicating that DAP prevented the onset of DNA synthesis while allowing that underway to reach completion. The inhibition of DNA synthesis was reversed by adenine, adenosine, and desoxyadenosine although synthesis appeared to proceed at a slower rate in reversals than in controls. Inhibition of DNA synthesis by DAP is probably through nucleoside or nucleotide metabolism.

A small general depression of DNA content of nuclei in the reversal treatments was observed. This deviation from DNA "constancy" cannot be adequately explained at present although it may be a result of direct incorporation of DAP into DNA.

The possible purine precursor, 4-amino-5-imidazolecarboxamide gave no reversal of DAP inhibition of cell elongation and cell division and only a slight possible reversal of inhibition of DNA synthesis.