bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonparallel local spatial stability analysis of pipe entrance swirling flows
Authors: Herrada M. A. , Pérez-Saborid M. , Barrero A.
Published: May 2004

A spatial local viscous stability analysis of a swirling flow developing in a cylindrical pipe has been carried out numerically. Even at moderately low swirl strengths, we have found the existence of centrifugal modes in addition to the shear ones found in previous stability analysis of nonswirling flows developing in pipes. It is found that these centrifugal instabilities develop at Reynolds numbers that are much lower than those required for the growing of the shear instability. Moreover, the extent of the region where centrifugal instabilities appear is much larger than that where the shear layer instability grows. We have found from the analysis that the most unstable mode was the counter-rotating one (n=−1). The critical Reynolds number for which linear analysis predicts the growth of the convective instabilities is for the centrifugal modes one hundred times smaller than for the shear layer ones.
Drop coalescence through a liquid/liquid interface
Authors: Mohamed-Kassim Zulfaa , Longmire Ellen K.
Published: May 2004

Particle image velocimetry (PIV) experiments were conducted to study the coalescence of single drops through planar liquid/liquid interfaces. Sequences of velocity vector fields were obtained with a high-speed video camera and subsequent PIV analysis. Two ambient liquids with different viscosity but similar density were examined resulting in Reynolds numbers based on a surface tension velocity of 10 and 26. Prior to rupture, the drops rested on a thin film of ambient liquid above an underlying interface. After rupture, which was typically off-axis, the free edge of the thin film receded rapidly allowing the drop fluid to sink into the bulk liquid below. Vorticity generated in the collapsing fluid developed into a vortex ring straddling the upper drop surface. The ring core traveled radially inward with a ring-shaped capillary wave effectively pinching the upper drop surface and increasing the drop collapse speed. The inertia of the collapse deflected the interface downward before it rebounded upward. During this time, the vortex core split so that part of its initial vorticity moved inside the drop fluid while part remained in the ambient fluid above it. A second ring-shaped capillary wave formed along the interface outside of the drop and propagated radially outward during the collapse. Changing the ambient fluid viscosity resulted in several effects. First, the velocity of the receding free edge was smaller for higher ambient viscosity. Second, the pinching of the upper drop surface caused by the shrinking capillary ring wave was stronger when the ambient viscosity was lower, and this resulted in a higher maximum collapse speed and higher vorticity values in the dominant vortex ring.
Calculation of the self force using the extended-object approach
Authors: Ori Amos , Rosenthal Eran
Published: May 2004

We present the extended-object approach for the explanation and calculation of the self-force phenomenon (often called “radiation-reaction force”). In this approach, one considers a charged extended object of a finite size ε that accelerates in a nontrivial manner, and calculates the total force exerted on it by the electromagnetic field (whose source is the charged object itself). We show that at the limit ε→0 this overall electromagnetic field yields a universal result, independent of the object’s shape, which agrees with the standard expression for the self force acting on a point-like charge. Previous implementation of this approach ended up with expressions for the total electromagnetic force that include O(1/ε) terms which do not have the form required by mass-renormalization. (In the special case of a spherical charge distribution, this ∝1/ε term was found to be 4/3 times larger than the desired quantity.) We show here that this problem was originated from a too naive definition of the notion of “total electromagnetic force” used in previous analyses. We then derive the correct notion of total electromagnetic force. This completely cures the problematic O(1/ε) term, for any object’s shape, and yields the correct self force at the limit ε→0. In particular, for a spherical charge distribution, the above “4/3 problem” is resolved.
Nonlinear frequency shift of the dust ion-acoustic wave
Authors: Yi Sumin , Ryu Chang-Mo , Yoon Peter H.
Published: May 2004

The nonlinear frequency shift of a low-frequency, coherent dust ion-acoustic wave in the presence of higher-frequency dust ion-acoustic turbulence is investigated in the framework of weak turbulence theory. It is found that the frequency shift of the dust ion-acoustic wave in an unmagnetized dusty plasma is always positive irrespective of the propagation direction of the coherent wave, as in the case of the customary ion-acoustic wave in the absence of dust particles. It is also found that the magnitude of the frequency shift decreases with increasing dust density.
Gyrokinetic global three-dimensional simulations of linear ion-temperature-gradient modes in Wendelstein 7-X
Authors: Kornilov V. , Kleiber R. , Hatzky R. , Villard L. , Jost G.
Published: May 2004

Using a global approach for solving an ion gyrokinetic model in three-dimensional geometry the linear stability and structure of ion-temperature-gradient (ITG) modes in the configuration of the stellarator Wendelstein 7-X (W7-X) [G. Grieger et al., in Plasma Physics and Controlled Nuclear Fusion Research 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 525.] is studied. The time evolution of electrostatic perturbations is solved as an initial value problem with a particle-in-cell δf method. The vacuum magnetohydrodynamic equilibrium is calculated by the code VMEC [S. P. Hirshman and D. K. Lee, Comput. Phys. Commun. 39, 161 (1986)]. In this work the most unstable ITG mode in W7-X is presented. This mode has a pronounced ballooning-type structure; however, it is not tokamak-like. A driving mechanism analysis using the energy transfer shows that the contribution of curvature effects is non-negligible. The growth rate and the mixing-length estimate for transport are compared with those for ITG modes found in axisymmetric geometries.
Analytical eigenvalue solution for ηi modes of general modewidth
Authors: Weiland Jan
Published: May 2004

The eigenvalue problem of ion temperature gradient modes in a reactive advanced fluid model has been solved analytically for general mode width. The solution is iterative and suitable for use in transport codes. The solution is made for the simple electrostatic mode but can be generalized to more complex systems. The solution has been tested against a shooting code with good agreement.
Ion acceleration in expanding multispecies plasmas
Authors: Bychenkov V. Yu. , Novikov V. N. , Batani D. , Tikhonchuk V. T. , Bochkarev S. G.
Published: May 2004

The acceleration of light and heavy ions in an expanding plasma slab with hot electrons produced by an intense and short laser pulse is studied by using the hybrid Boltzmann–Vlasov–Poisson model. Spatial profiles, energy distributions, and maximum energies of accelerated ions are analyzed in function of the plasma and hot electron parameters. The crucial parameter for ion acceleration is found to be the ratio of the foil thickness to the hot electron Debye length. Special attention is paid to characterization of protons accelerated from a thin hydrogenated layer at the target surface. The evolution of the proton spectrum is studied for the cases of isothermal and cooling hot electron distributions. The obtained dependencies of the ion energy on the pulse duration and the target characteristics allow one to define the optimal conditions for the ion acceleration with lasers.
d
3
=0,
d2=0 differential calculi on certain noncommutative (super) spaces
Authors: El Baz M. , El Hassouni A. , Hassouni Y. , Zakkari E. H.
Published: May 2004

In this paper, we construct a covariant differential calculus on a quantum plane with two-parametric quantum group as a symmetry group. The two cases d2=0 and d3=0 are completely established. We also construct differential calculi n=2 and n=3 nilpotent on super quantum spaces with one and two-parametric symmetry quantum supergroup.
Hydrodynamic reductions of multidimensional dispersionless PDEs: The test for integrability
Authors: Ferapontov E. V. , Khusnutdinova K. R.
Published: May 2004

A (d+1)-dimensional dispersionless PDE is said to be integrable if its n-component hydrodynamic reductions are locally parametrized by (d−1)n arbitrary functions of one variable. The most important examples include the four-dimensional heavenly equation descriptive of self-dual Ricci-flat metrics and its six-dimensional generalization arising in the context of sdiff(Σ2) self-dual Yang–Mills equations. Given a multidimensional PDE which does not pass the integrability test, the method of hydrodynamic reductions allows one to effectively reconstruct additional differential constraints which, when added to the equation, make it an integrable system in fewer dimensions. As an example of this phenomenon we discuss the second commuting flow of the dispersionless KP hierarchy. Considered separately, this is a four-dimensional PDE which does not pass the integrability test. However, the method of hydrodynamic reductions generates additional differential constraints which reconstruct the full (2+1)-dimensional dispersionless KP hierarchy.
Soliton lattice and single soliton solutions of the associated Lamé and Lamé potentials
Authors: Bena Ioana , Khare Avinash , Saxena Avadh
Published: May 2004

We obtain the exact nontopological soliton lattice solutions of the associated Lamé equation in different parameter regimes and compute the corresponding energy for each of these solutions. We show that in specific limits these solutions give rise to nontopological (pulse-like) single solitons, as well as to different types of topological (kink-like) single soliton solutions of the associated Lamé equation. Following Manton, we also compute, as an illustration, the asymptotic interaction energy between these soliton solutions in one particular case. Finally, in specific limits, we deduce the soliton lattices, as well as the topological single soliton solutions of the Lamé equation, and also the sine-Gordon soliton solution.
Position and momentum observables on R and on R3
Authors: Carmeli Claudio , Heinonen Teiko , Toigo Alessandro
Published: May 2004

We characterize all position and momentum observables on ↛ and on R3. We study some of their operational properties and discuss their covariant joint observables.
2D conformal field theories and holography
Authors: Freidel Laurent , Krasnov Kirill
Published: May 2004

It is known that the chiral part of any 2D conformal field theory defines a 3D topological quantum field theory: quantum states of this TQFT are the CFT conformal blocks. The main aim of this paper is to show that a similar CFT/TQFT relation exists also for the full CFT. The 3D topological theory that arises is a certain “square” of the chiral TQFT. Such topological theories were studied by Turaev and Viro; they are related to 3D gravity. We establish an operator/state correspondence in which operators in the chiral TQFT correspond to states in the Turaev–Viro theory. We use this correspondence to interpret CFT correlation functions as particular quantum states of the Turaev–Viro theory. We compute the components of these states in the basis in the Turaev–Viro Hilbert space given by colored 3-valent graphs. The formula we obtain is a generalization of the Verlinde formula. The later is obtained from our expression for a zero colored graph. Our results give an interesting “holographic” perspective on conformal field theories in two dimensions.
Three-halves harmonic emission from femtosecond laser produced plasmas with steep density gradients
Authors: Veisz L. , Theobald W. , Feurer T. , Schwoerer H. , Uschmann I. , Renner O. , Sauerbrey R.
Published: May 2004

Detailed measurements of the angular distribution of 3 ω0/2 radiation are presented in short scale length plasmas (0.8–7 μm) generated by laser radiation at intensities reaching the relativistic level (1016–6×1018 W/cm2). The experimental results are in very good agreement with theoretical predictions based on two-plasmon decay and stimulated Raman scattering instabilities. New three-halves harmonic generation mechanisms are an identified characteristic of femtosecond laser induced parametric instabilities. These are the joint interaction of incident and reflected laser beams as well as stimulated Raman scattering. It is shown both experimentally and theoretically that the three-halves harmonic radiation is a useful preplasma diagnostic tool.
High-mobility thin InSb films grown by molecular beam epitaxy
Authors: Zhang T. , Clowes S. K. , Debnath M. , Bennett A. , Roberts C. , Harris J. J. , Stradling R. A. , Cohen L. F. , Lyford T. , Fewster P. F.
Published: May 2004

The problem of preparing high-mobility thin InSb films is revisited for magnetoresistive and spintronic sensor applications. We introduce a growth process that significantly improves the electrical properties of thin unintentionally doped InSb layers (60–300 nm) epitaxially grown on GaAs(100) substrates by reducing the density of dislocations within the interfacial layer. The epilayer properties are well described by a differential two-layer model. This model confirms that the contribution of the interface can only be donor-like. Moreover, the electrical properties of the InSb layers change continuously away from the interface up to sample thickness of the order of 1 μm.
X-ray absorption study of the electronic structure of Li-excess spinel Li1+xTi2−xO4 (0⩽x⩽0.33)
Authors: Ra Wonkyung , Nakayama Masanobu , Ikuta Hiromasa , Uchimoto Yoshiharu , Wakihara Masataka
Published: May 2004

Li-excess spinel oxide, Li1+xTi2−xO4 (0⩽x⩽0.33), was investigated by x-ray absorption spectra (XAS) technique. XAS results revealed that both oxygen and titanium ions affect electronic structural changes in the system. Early transition metal compounds are considered to have smaller d–d Coulomb correlation energy (Udd) than p–d Charge-transfer energy (Δ), indicating that electronic transfer for charge compensation occurs mainly on transition metal. However, present XAS results show that considerable charge-transfer character due to strong hybridization between titanium 3d and oxygen 2p orbitals exists in this early transition metal oxide system.
Intermittent distribution of heavy particles in a turbulent flow
Authors: Falkovich Gregory , Pumir Alain
Published: May 2004

The retardation of weakly inertial particles depends on the acceleration of the ambient fluid, so the particle concentration n is determined by the divergence of Lagrangian acceleration which we study by direct numerical simulations. We demonstrate that the second moment of the concentration coarse-grained over the scale r behaves as an approximate power law: 〈n̄r2〉∼rα. We study the dependencies of the exponent α on the Reynolds number, of the Stokes number, and on the settling velocity. We find numerically that the theoretical lower bound previously suggested [Falkovich et al., Nature 419, 151 (2002)] correctly estimates the order of magnitude (within a factor 2 to 4) as well as the dependencies on the Reynolds, Stokes, and Froude numbers. The discrepancy grows with the Reynolds number and the Froude number. We analyze the possible physical mechanism responsible for that behavior.
Nanomachining carbon nanotubes with ion beams
Authors: Raghuveer M. S. , Ganesan P. G. , D’Arcy-Gall J. , Ramanath G. , Marshall M. , Petrov I.
Published: May 2004

We demonstrate the use of 10 and 30 keV focused beams of Ga+ ions to thin, slice, weld, and alter the structure and composition of multiwalled carbon nanotubes at precise locations along the nanotube axis. This strategy of harnessing ion-beam-induced defect generation and doping could be attractive for modulating chemical and electrical properties along the nanotube length, and fabricate nanotube heterostructures and networks for device applications.
Wave interactions in buckling: Self-organization of a metal surface on a structured polymer layer
Authors: Kwon S. Joon , Yoo Pil J. , Lee Hong H.
Published: May 2004

We report on self-organized metal surface patterns that result when a thin bilayer of a metal on a periodically corrugated polymer layer is annealed. A theoretical basis is provided for the self-organization that is verified by experiment. The wave number of the surface pattern is determined by a square law relationship involving the corrugation wave number and the intrinsic wave number of the bilayer. The phase shift between the wave on the ridge and that on the groove is related to an uncertainty in the corrugation wave number. Free energy minimization dictates connectivity of the two waves and fidelity of the metal surface pattern.
Characterization of laser-produced aluminum plasma in ambient atmosphere of nitrogen using fast photography
Authors: Sharma A. K. , Thareja R. K.
Published: May 2004

We report on the pulsed-laser ablation of aluminum in ambient pressure of nitrogen varying from 0.01 to 70 Torr using images of the expanding plasma plume. At pressures ⩾1 Torr plasma–gas interface showed severe distortion in the front of the expanding plume. The plasma expansion velocity showed oscillatory behavior with delay time beyond 260 ns and is attributed to Rayleigh–Taylor instability. The effect of background gas on inducing polarization in the ablated plasma is also reported. At low pressure of 0.1 Torr the degree of polarization of Al III transition 4s 2S1/2–4p 2P3/20 at 569.6 nm increased with delay time. At pressures ⩾1 Torr it showed an oscillatory behavior. The observed steep pressure gradient at the plasma–gas interface may result in strong self-generated magnetic field due to Rayleigh–Taylor instability.
Interaction of Fe+ with the C60 surface: A study about the feasibility of endohedral doping
Authors: Reinke P. , Eyhusen S. , Büttner M. , Oelhafen P.
Published: May 2004

The feasibility of endohedral iron doping of C60 is studied using a mass selected ion beam to create an Fe+ beam with variable energy (60–380 eV, 1.2×10−3 C) which is directed at a C60 thin film. The surface is characterized by x-ray photoelectron spectroscopy, and oxidation of the samples is used to discriminate between Fe@C60 and carbides. The fullerene cages are damaged during the irradiation, and participate in direct Fe–C bond formation. The reaction with oxygen indicates the absence of sizable amount of Fe@C60. Comparison with reference samples composed of iron and damaged fullerene layers (by Ar+ irradiation) supports this interpretation. The experiment serves as a model study for the investigation of different metal-fullerene combinations.
Enhancement of the green, visible Tb3+ luminescence from Tb-doped silicon-rich silicon oxide by C co-doping
Authors: Seo Se-Young , Shin Jung H.
Published: May 2004

The effect of C co-doping on the Tb3+ luminescence from Tb-doped silicon-rich silicon oxide (SRSO) films is investigated. Tb-doped SRSO films co-doped with C (SRSO:C) were deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition. The Tb3+ photoluminescence intensity is enhanced by the presence of nanocluster Si (nc-Si), and C co-doping further increases the Tb3+ photoluminescence intensity by more than an order of magnitude. The maximum enhancement is observed at the C content of ∼5 at. %, at which the Tb3+ luminescence is bright enough to be observed by the naked eye under ambient conditions. The 543 nm Tb3+ lifetimes were in the range of 0.5–1.2 ms, comparable to those from Tb-doped silica. Based on the results, we conclude that nanometer-sized nc-Si can excite Tb3+ ions via an Auger-type energy transfer, and that C co-doping greatly increases the efficiency of such exciton-mediated excitation of Tb3+.
Controlling the crystallization and magnetic properties of melt-spun Pr2Fe14B/α-Fe nanocomposites by Joule heating
Authors: Jin Z. Q. , Cui B. Z. , Liu J. P. , Ding Y. , Wang Z. L. , Thadhani N. N.
Published: May 2004

Pr 2 Fe 14 B /α- Fe based nanocomposites have been prepared through crystallization of melt-spun amorphous Pr7Tb1Fe85Nb0.5Zr0.5B6 ribbons by means of ac Joule heating while simultaneously monitoring room-temperature electrical resistance R. The R value shows a strong variation with respect to applied current I, and is closely related to the amorphous-to-nanocrystalline phase transformation. The curve of R versus I allows one to control the crystallization behavior during Joule heating and to identify the heat-treatment conditions for optimum magnetic properties. A coercivity of 550 kA/m and a maximum energy product of 128 kJ/m3 have been obtained upon heating the amorphous ribbons at a current of 2.0 A. These properties are around 30% higher than the values of samples prepared by conventionally (furnace) annealed amorphous ribbons.
Minimization of germanium penetration, nanocrystal formation, charge storage, and retention in a trilayer memory structure with silicon nitride/hafnium dioxide stack as the tunnel dielectric
Authors: Ng T. H. , Chim W. K. , Choi W. K. , Ho V. , Teo L. W. , Du A. Y. , Tung C. H.
Published: May 2004

Trilayer structures, consisting of a rapid thermal oxide (RTO) layer (2.5 or 5 nm thick) grown on silicon, a sputtered Ge middle layer (3–20 nm thick), and a 50-nm-thick sputtered silicon oxide capping layer, exhibit significant penetration of Ge atoms into the silicon substrate for devices with the smaller (2.5 nm) RTO thickness, resulting in negligible nanocrystal formation and hence no charge storage or memory effect. The Ge penetration is minimized by replacing the RTO layer with a high dielectric constant (high-κ) silicon nitride/hafnium dioxide stack (grown by metalorganic chemical vapor deposition) having a larger physical thickness but smaller equivalent oxide thickness of 1.9 nm. Results show that the high-κ trilayer structure exhibits better charge storage capability (in terms of a lower program voltage) and better charge retention performance as compared to the RTO trilayer structure.
GaInN light-emitting diodes with RuO2/SiO2/Ag omni-directional reflector
Authors: Kim Jong Kyu , Gessmann Thomas , Luo Hong , Schubert E. Fred
Published: May 2004

A GaInN light-emitting diode (LED) employing an omni-directional reflector (ODR) is presented. The ODR consists of a RuO2 ohmic contact to p-type GaN, a quarter-wave thick SiO2 low-index layer perforated by an array of micro-contacts, and an Ag layer. Calculations predict a 98% angle-averaged reflectivity at λ=450 nm for an GaN/SiO2/Ag ODR, much higher than that for a 20 period Al0.25Ga0.75N/GaN distributed Bragg reflector (49%) and an Ag reflector (94%). It is shown that the RuO2/SiO2/Ag ODR has higher reflectivity than Ni/Au and even Ag reflectors, leading to a higher light extraction efficiency of GaInN LEDs with ODR. The electrical properties of the ODR-LED are comparable to those LEDs with a conventional Ni/Au contact.
Doping-level-dependent optical properties of GaN:Mn
Authors: Gelhausen O. , Malguth E. , Phillips M. R. , Goldys E. M. , Strassburg M. , Hoffmann A. , Graf T. , Gjukic M. , Stutzmann M.
Published: May 2004

The optical properties of molecular-beam-epitaxy-grown GaN with different Mn-doping levels (5–23×1019 cm−3) were studied by cathodoluminescence (CL) and optical transmission spectroscopy. Transmission measurements at 2 K revealed an absorption peak at 1.414±0.002 eV, which was attributed to an internal 5T2→5E transition of the neutral Mn3+ state. The intensity of this Mn-related transmission peak was found to scale with the Mn3+ concentration. The CL measurements showed that Mn-doping concentrations around 1020 cm−3 reduced the near band edge emission intensity by around one order of magnitude. A complete quenching of the donor–acceptor-pair band at 3.27 eV and strong decrease of the yellow luminescence centered at 2.2 eV were attributed to a reduced concentration of VGa. In the infrared spectral range of 0.8–1.4 eV three broad, Mn-doping related CL emission bands centered at 1.01±0.02, 1.09±0.02, and 1.25±0.03 eV were observed. Their origin is attributed to deep donor complexes, which are generated as a result of the heavy Mn-doping.
Probing local coordination environments in high-k materials for gate stack applications
Authors: McComb D. W. , Craven A. J. , Hamilton D. A. , MacKenzie M.
Published: May 2004

Using electron energy-loss spectroscopy, the oxygen K-edge excitation in a range of crystalline standards relevant to candidate high-k materials has been examined. The spectra have been modeled using electronic structure calculations in order to understand the influence of the local coordination environment on the data. The knowledge obtained is used to probe the local atomic structure in thin amorphous films of “HfSiO.”
High spatial resolution subsurface thermal emission microscopy
Authors: Ippolito S. B. , Thorne S. A. , Eraslan M. G. , Goldberg B. B. , Ünlü M. S. , Leblebici Y.
Published: May 2004

We apply the numerical aperture increasing lens technique to subsurface thermal emission microscopy of Si integrated circuits. We achieve improvements in the amount of light collected and the spatial resolution, well beyond the limits of conventional thermal emission microscopy. We experimentally demonstrate a lateral spatial resolution of 1.4 μm and a longitudinal spatial resolution of 7.4 μm, for thermal imaging at free space wavelengths up to 5 μm.
Determination of the optical energy gap of Ge1−xSnx alloys with 0<x<0.14
Authors: Ladrón de Guevara H. Pérez , Rodrı́guez A. G. , Navarro-Contreras H. , Vidal M. A.
Published: May 2004

The optical energy gap of Ge1−xSnx alloys has been determined from transmittance measurements, using a fast-Fourier-transform infrared interferometer. Our results show that the change from indirect to direct band gap occurs at a lower critical Sn concentration (xc) than the value predicted from the virtual crystal approximation, tight binding, and pseudopotential models. However, a close agreement between the experimental results and the predictions with deformation potential theory is observed. The concentration xc, which is theoretically expected to be 0.09, actually it is observed to lie between 0.10<xc<0.13.
First-order quasi-phase-matched blue light generation in surface-poled Ti:indiffused lithium niobate waveguides
Authors: Busacca A. C. , Sones C. L. , Eason R. W. , Mailis S.
Published: May 2004

We demonstrate efficient first-order quasi-phase-matched second-harmonic generation in a surface periodically poled Ti:indiffused lithium niobate waveguide; 6 mW of continuous-wave blue radiation (λ=412.6 nm) was produced showing the potential of surface domain inversion for efficient nonlinear waveguide interactions.
Magnetic-field-induced structural homogeneity of a phase-separated manganite
Authors: Gagliardi M. S. , Ren Y. , Mitchell J. F. , Beno M. A.
Published: May 2004

Magnetic field (MF) dependence of the phase separation (PS) in the manganite Pr0.65(Ca0.7Sr0.3)0.35MnO3 was studied using high-energy x-ray powder diffraction. The compound shows intrinsic inhomogeneities in the form of coexisting competing phases below a temperature Tc. Application of MFs not only eliminates the multiple phases below Tc but also significantly affects the structure above Tc. The MF-induced structural phase transition occurs abruptly at 2 K but is smooth at higher temperatures. Moreover, the MF dependence of some reflection intensities clearly indicates a complicated PS. This MF-induced homogeneity should play a key role in the colossal magnetoresistance effect.
Random laser action in self-organized para-sexiphenyl nanofibers grown by hot-wall epitaxy
Authors: Quochi F. , Cordella F. , Orrù R. , Communal J. E. , Verzeroli P. , Mura A. , Bongiovanni G. , Andreev A. , Sitter H. , Sariciftci N. S.
Published: May 2004

We report on the observation of amplified spontaneous emission and random lasing in self-organized crystalline para-sexiphenyl nanofibers. Using subpicosecond excitation, a lasing threshold is observed on the 0–1 emission band near 425 nm at excitation fluences as low as 0.5 μJ/cm2 (6×1016 cm−3 equivalent density), near the onset of density-dependent recombination processes. The dependence of the nonlinear emission spectrum on both the pump intensity and position of the excitation area are attributed to the interplay between random lasing and amplified spontaneous emission occurring along the nanofibers.
NFAM1, an immunoreceptor tyrosine-based activation motif-bearing molecule that regulates B cell development and signaling
Authors: Ohtsuka Makoto , Arase Hisashi , Takeuchi Arata , Yamasaki Sho , Shiina Ritsuko , Suenaga Tadahiro , Sakurai Daiju , Yokosuka Tadashi , Arase Noriko , Iwashima Makio , Kitamura Toshio , Moriya Hideshige , Saito Takashi
Published: May 2004

A functional cDNA cloning system was developed by using a retrovirus library encoding CD8-chimeric proteins and a nuclear factor of activated T cells (NFAT)-GFP reporter cell line to identify molecules inducing NFAT activation. By using this strategy, NFAT activating molecule 1 (NFAM1) was cloned as an immunoreceptor tyrosine-based activation motif (ITAM)-bearing cell surface molecule belonging to the Ig superfamily and is predominantly expressed in spleen B and T cells. NFAM1 crosslinking induced ITAM phosphorylation, ZAP-70/Syk recruitment, NFAT activation, and cytokine production.In vivooverexpression of NFAM1 in bone marrow chimeras and transgenic mice induced severe impairment of early B cell development in an ITAM-dependent manner. In NFAM1-expressing B cells, B cell antigen receptor stimulation induced NFAM1 translocation to lipid raft, and NFAM1 co-crosslinking augmented B cell antigen receptor signaling. The results suggest that NFAM1 modulates B cell signaling through its ITAM, which regulates B cell development.
CELL STRUCTURE AND THE METABOLISM OF INSECT FLIGHT MUSCLE
Authors: Sacktor Bertram
Published: May 2004

The biochemical properties of insect flight muscle were investigated to ascertain the mechanisms whereby energy is made available for the contractile processes. It was found:

1. The endogenous respiration of muscle homogenates was diminished by starving the flies. The substrate for this respiration was probably glycogen.

2. To obtain the maximal rate of oxidation of glucose, the homogenate had to be fortified with inorganic phosphate, Mg ions, ATP, and cytochrome c. The nucleotides, AMP and ADP, were not as effective as ATP. The addition of DPN or TPN was not necessary for this system.

3. Flight muscle homogenates oxidized glycogen, some sugars, and amino acids, as well as the intermediates of the glycolytic and tricarboxylic acid cycles. Other evidence demonstrated the substrate specificity of the muscle.

4. By centrifugation, the muscle homogenate was divided into two fractions: one, a soluble fraction representing the sarcoplasm; the other, the particulate fraction which contained the fibrils and the sarcosomes.

5. The particulate fraction, alone, oxidized all the citric acid cycle intermediates, α-glycerophosphate, phosphopyruvate, and the amino acids, glutamic, proline, and cysteine. Regardless of the substrate, no oxygen uptake was found with the sarcoplasm by itself.

6. A recombination of the sarcoplasm and the particulate component was required for the oxidation of glycogen, the hexoses, and all the phosphorylated intermediates of glycolysis, except phosphopyruvate.

7. Isolated mitochondria accounted for all the enzymatic activity of the particulate fraction.

These results demonstrate that the enzymes of intermediate metabolism are localized in the sarcoplasm or sarcosomes. The third cytological entity, the myofibrils, plays no role in the energy-providing scheme. From a functional viewpoint, the sarcoplasm and the mitochondria, in combination, furnish the energy for the actomyosin contraction.

The results are discussed in relation to analogous findings in other insects and vertebrates.
SOME FEATURES OF THE SUBMICROSCOPIC MORPHOLOGY OF SYNAPSES IN FROG AND EARTHWORM
Authors: De Robertis Eduardo D. P. , Bennett H. Stanley
Published: May 2004

Electron micrographs are presented of synaptic regions encountered in sections of frog sympathetic ganglia and earthworm nerve cord neuropile. Pre- and postsynaptic neuronal elements each appear to have a membrane 70 to 100 A thick, separated from each other over the synaptic area by an intermembranal space 100 to 150 A across. A granular or vesicular component, here designated the synaptic vesicles, is encountered on the presynaptic side of the synapse and consists of numerous oval or spherical bodies 200 to 500 A in diameter, with dense circumferences and lighter centers. Synaptic vesicles are encountered in close relationship to the synaptic membrane. In the earthworm neuropile elongated vesicles are found extending through perforations or gaps in the presynaptic membrane, with portions of vesicles appearing in the intermembranal space. Mitochondria are encountered in the vicinity of the synapse, and in the frog, a submicroscopic filamentary component can be seen in the presynaptic member extending up to the region where the vesicles are found, but terminating short of the synapse itself.
ANTAGONISTIC EFFECTS OF 6-MERCAPTOPURINE AND COENZYME A ON MITOCHONDRIA AND MITOSIS IN TISSUE CULTURE
Authors: Biesele John J.
Published: May 2004

The partial mitotic inhibition caused by 6-mercaptopurine in tissue cultures of Crocker mouse sarcoma 180 and embryonic mouse skin is blocked by co-enzyme A. 6-Mercaptopurine and coenzyme A also have opposite effects on mitochondrial morphology. Mitochondria in cells treated with 6-mercaptopurine become thin and fragmented. Coenzyme A blocks this effect, and alone coenzyme A makes for longer and thicker mitochondria. 6-Mercaptopurine inhibits lipogenesis in embryo skin fibroblasts, and this inhibition is partly counteracted by coenzyme A, which by itself makes for a greater accumulation of lipid droplets in the cytoplasm.

It is suggested that at least one part of the action by which 6-mercaptopurine decreases mitotic incidence in tissue cultures may be an interference on the part of 6-mercaptopurine, acting as an antimetabolite of coenzyme A, in mitochondrial function related to cell division.
A METHOD FOR ISOLATING INTACT MITOCHONDRIA AND NUCLEI FROM THE SAME HOMOGENATE, AND THE INFLUENCE OF MITOCHONDRIAL DESTRUCTION ON THE PROPERTIES OF CELL NUCLEI
Authors: Dounce Alexander L. , Witter Robert F. , Monty Kenneth J. , Pate Sidney , Cottone Mary A.
Published: May 2004

1. An improved type of ground glass homogenizer for soft tissues has been described which brings about a high degree of cell disruption and liberation of nuclei without causing appreciable damage to mitochondria. The gentleness and effectiveness of the new homogenizer in respect to isolation of mitochondria have been ascertained by comparing the ATP-ase activities of mitochondria isolated in 0.25 M sucrose solution without pH adjustment using a previous type of homogenizer with those of mitochondria isolated under the same conditions with the aid of the new homogenizer. In these experiments sucrose of 0.25 molarity without pH adjustment has been used in order to maintain the mitochondria in a rather sensitive state so as to make slightly deleterious effects of homogenization readily apparent.

2. A new method is described for the isolation of morphologically intact mitochondria and cell nuclei from the same homogenate. In this procedure the pH of the homogenate in 0.44 M sucrose is maintained at 6.0–6.2 with citric acid during the homogenization. An alternative method employing 0.44 M sucrose plus 0.005 M CaCl2 is given for the isolation of nuclei from tumor cells. However, the latter method does not produce unaltered mitochondria.

3. The α-ketoglutarate, malate, succinate, and hexanoate oxidases of the "intact" mitochondria isolated in 0.44 M sucrose adjusted to pH 6.0–6.2 with very dilute citric acid as described in this paper have been investigated, and it has been shown that the mitochondria compare favorably to those isolated in 0.25 M sucrose by a previously described method.

4. Mitochondria have been found to contain an enzyme which causes nuclei to lose their ability to form gels in dilute alkali. This enzyme is released from the mitochondria when the latter are disrupted.

5. Some properties of nuclei isolated by the new method have been briefly discussed.
ADHESION PARTITIONING: INTRASOMATIC OBSERVATIONS ON NORMAL ESCHERICHIA COLI AND T2 BACTERIOPHAGE
Authors: Backus Robert C.
Published: May 2004

Adhesion partitioning is a method for progressively dismantling small biological entities for observation of their internal structures. The method is particularly well suited to use with the electron microscope. Objects to be partitioned are air-dried between two preformed plastic films resulting in envelopment of the objects. On separating the films the objects are partitioned. Partitioned E. coli bacteria reveal a variety of structures which change markedly with culture age. Organisms from young cultures have a water-retaining gelatinous matrix in which radially striated discs, fabric-like structures, and microsomes are found. Older cultures are less anatomically complex. The T2 bacteriophage is shown to be composed of an outer limiting membrane and a cohesive semisolid fibrillar body substance, presumably nucleic acid, which can be drawn as a strand from the bacteriophage body.
INVESTIGATION OF THE STRUCTURE OF THE CORNIFIED EPITHELIUM OF THE HUMAN SKIN
Authors: Matoltsy A. Gedeon , Odland George F.
Published: May 2004

To explore the submicroscopic structure of the human callus by the polarization optical method, serial sections were prepared in three principal planes and the sign of double refraction as well as optic axes of various regions of the sections was determined. It was concluded that in areas under the grooves keratin is oriented parallel to the surface plane of the callus and to the direction of the grooves. In component structures of ridge areas such as in sweat duct areas a circumferential, in cross-band areas a linear, and in other parts a random structure was seen. The cross-bands of ridge areas in association with groove areas revealed a regular lattice-like submicroscopic pattern which was considered as an important mechanical system of the cornified epithelium.
THE NUCLEAR ENVELOPE
Authors: Watson Michael L.
Published: May 2004

An electron microscope study of thin sections of interphase cells has revealed the following:—

Circular pores are formed in the double nuclear envelope by continuities between the inner and outer membranes which permit contact between the nucleoplasm and the cytoplasm unmediated by a well defined membrane.

The pores, seen in sections normal to the nuclear envelope, are profiles of the ring-shaped structures described by others and seen in tangential section.

The inner and outer nuclear membranes are continuous with one another and enclose the perinuclear space.

The pores contain a diffuse, faintly particulate material.

A survey of cells of the rat derived from the embryonic ectoderm, mesoderm, and endoderm, and of a protozoan and an alga has revealed pores in all tissues examined, without exception. It is concluded that pores in the nuclear envelope are a fundamental feature of all resting cells.

In certain cells, the outer nuclear membrane is continuous with membranes of the endoplasmic reticulum, hence the perinuclear space is continuous with cavities enclosed by those membranes. There are indications that this is true for all resting cells, at least in a transitory way.

On the basis of these observations, the hypothesis is made that two pathways of exchange exist between the nucleus and the cytoplasm; by way of the perinuclear space and cavities of the endoplasmic reticulum and by way of the pores in the nuclear envelope.
INTRACELLULAR DISTRIBUTION OF ALKALINE PHOSPHATASE IN RAT LIVER CELLS
Authors: Emery Arthur J. , Dounce Alexander L.
Published: May 2004

1. Cytochemical studies of the intracellular distribution of alkaline phosphatase in rat liver have been made, using a fractionation procedure recently developed in this laboratory (8) and a similar but modified method not described previously. Aqueous media were used in both cases.

2. The alkaline phosphatase was found to consist of two forms, one of which is strongly activated by magnesium and one of which is not sensitive to this metal.

3. The form of the enzyme that is not activated by magnesium occurs mainly in the nuclear fraction, where it seems to be rather firmly bound. Some of this form of the enzyme is also found in the microsomes, but very little if any occurs in the soluble supernatant fraction.

4. The form of alkaline phosphatase which is activated by magnesium occurs mainly in the soluble supernatant fraction, but what is believed are significant amounts also occur in nuclei. A significant portion of this form of the enzyme can be extracted from the isolated nuclei with cold, isotonic saline solution. Some activity of this form of the enzyme is also found in the microsomal fraction.

5. Mitochondria appear to contain relatively little alkaline phosphatase of either kind.

6. The concept of a porous nuclear membrane has been invoked to explain some of the results obtained in this work. It is postulated that part at least of the form of the enzyme that is activated by magnesium is free to diffuse back and forth through pores in the nuclear membrane, whereas this is considered not to be possible for the form of the enzyme that is insensitive to magnesium as a result of the firm binding of the latter to nuclear substance.
A STUDY OF THE COMPONENTS OF THE CORNIFIED EPITHELIUM OF HUMAN SKIN
Authors: Matoltsy A. Gedeon , Balsamo Constance A.
Published: May 2004

Pulverized cornified epithelium of human skin was divided into a "soluble fraction" and a "residue." About half of the "soluble fraction" proved to be soluble epidermal keratin (keratin A); the remainder, dialyzable substances of low molecular weight. The "residue" contained epidermal keratin and resistant cell membranes of cornified cells. Epidermal keratin was found to form an oriented and dense submicroscopic structure in the cornified cells. It showed high resistance toward strong acid and moderately strong alkali solutions as well as concentrated urea. In strong alkali, reducing substances, alkaline urea, and mixtures of reducing substance with alkali, epidermal keratin dissociated and yielded a non-dialyzable derivative of high molecular weight (keratin B) which resembled true proteins. The cell membranes of cornified cells showed higher resistance toward strong alkali and reducing substance than did epidermal keratin.
STUDIES ON THE STRUCTURE OF MUSCLE
Authors: Hodge A. J.
Published: May 2004

1. The flight muscles of blowflies are easily dispersed in appropriate media to form suspensions of myofibrils which are highly suitable for phase contrast observation of the band changes associated with ATP-induced contraction.

2. Fresh myofibrils show a simple band pattern in which the A substance is uniformly distributed throughout the sarcomere, while the pattern characteristic of glycerinated material is identical with that generally regarded as typical of relaxed vertebrate myofibrils (A, I, H, Z, and M bands present).

3. Unrestrained myofibrils of both fresh and glycerinated muscle shorten by not more than about 20 per cent on exposure to ATP. In both cases the A substance migrates during contraction and accumulates in dense bands in the Z region, while material also accumulates in the M region. It is proposed that these dense contraction bands be designated the Cz, and Cm bands respectively. In restrained myofibrils, the I band does not disappear, but the Cz and Cm bands still appear in the presence of ATP.

4. The birefringence of the myofibrils decreases somewhat during contraction, but the shift of A substance does not result in an increase of birefringence in the Cz and Cm bands. It seems therefore that the A substance, if it is oriented parallel with the fibre axis in the relaxed myofibril, must exist in a coiled or folded configuration in the C hands of contracted myofibrils.

5. The fine structure of the flight muscle has been determined from electron microscopic examination of ultrathin sections. The myofibrils are of roughly hexagonal cross-section and consist of a regular single hexagonal array of compound myofilaments the cores of which extend continuously throughout all bands of the sarcomere in all states of contraction or relaxation so far investigated.

6. Each myofilament is joined laterally with its six nearest neighbours by thin filamentous bridges which repeat at regular intervals along the fibre axis and are present in the A, I, and Z, but not in the H or M bands. When stained with PTA, the myofilaments display a compound structure. In the A band, a lightly staining medullary region about 40 A in diameter is surrounded by a densely staining cortex, the over-all diameter of the myofilament being about 120 A. This thick cortex is absent in the I and H bands, but a thinner cortex is often visible.

7. It is suggested that the basic structure is a longitudinally continuous framework of F actin filaments, which are linked periodically by the lateral bridges (possibly tropomyosin). The A substance is free under certain conditions to migrate to the Z bands to form the Cz bands. The material forming the Cm bands possibly represents another component of the A substance. The results do not clearly indicate whether myosin is confined to the A bands or distributed throughout the sarcomere.
HISTOCHEMICAL STUDIES ON MUCOPROTEINS IN NERVE CELLS OF THE DOG
Authors: Sulkin Norman M.
Published: May 2004

Autonomic and sensory ganglion cells in the senile dog contain a deposition of PAS-positive substances which has been shown to be mucoprotein in nature.

Data are presented to show that this PAS-positive mucoprotein can be demonstrated by metachromatic staining with toluidine blue after the mucoprotein is sulfated. This procedure indicates that mucoprotein is also present in a granular form in all nerve cells in both senile and young dogs.

The evidence for this is further substantiated by the use of the aldehyde-fuchsin stain following both periodic acid oxidation and sulfation. The granular and non-granular deposition can be demonstrated by the periodic acid-aldehyde-fuchsin method due to the affinity of the aldehyde-fuchsin stain for aldehydes. It can be demonstrated following the sulfation-aldehyde-fuchsin method owing to the affinity of the stain for the sulfuric group. The evidence for this latter phenomenon has been reported by Scott and Clayton (6).

It is concluded that mucoprotein is present in a granular form in all nerve cells in both senile and young dogs but is not concentrated enough in the latter to be demonstrated by the PAS method.