bluuebunny/crossref_metadata_2025 huggingface dataset:
Chaperone properties of Escherichia coli thioredoxin and thioredoxin reductase
Authors: KERN Renée , MALKI Abderrahim , HOLMGREN Arne , RICHARME Gilbert
Published: April 2003

Thioredoxin, thioredoxin reductase and NADPH form the thioredoxin system and are the major cellular protein disulphide reductase. We report here that Escherichia coli thioredoxin and thioredoxin reductase interact with unfolded and denatured proteins, in a manner similar to that of molecular chaperones that are involved in protein folding and protein renaturation after stress. Thioredoxin and/or thioredoxin reductase promote the functional folding of citrate synthase and α-glucosidase after urea denaturation. They also promote the functional folding of the bacterial galactose receptor, a protein without any cysteines. Furthermore, redox cycling of thioredoxin/thioredoxin reductase in the presence of NADPH and cystine stimulates the renaturation of the galactose receptor, suggesting that the thioredoxin system functions like a redox-powered chaperone machine. Thioredoxin reductase prevents the aggregation of citrate synthase under heat-shock conditions. It forms complexes that are more stable than those formed by thioredoxin with several unfolded proteins such as reduced carboxymethyl α-lactalbumin and unfolded bovine pancreatic trypsin inhibitor. These results suggest that the thioredoxin system, in addition to its protein disulphide isomerase activity possesses chaperone-like properties, and that its thioredoxin reductase component plays a major role in this function.
Nonlinear conductivity of a compensated polycrystalline metal in high magnetic field
Authors: Logvinov I. I. , Chiang Yu. N.
Published: April 2003

The current–voltage (I–V) characteristics in a magnetic field are studied at helium temperatures for thin polycrystalline samples of a metal (pure tin) embedded in a solid-state medium in order to create reproducible experimental conditions. In these samples a nonlinear S-shaped I–V characteristic is obtained for the first time with this type of heat sinking at the surface of the metal. The conditions for the onset of a temperature–electric instability in a metal with an S-shaped I–V characteristic are investigated in relation to the reactive parameters of the circuit.
Quantitative analysis of the creep deformation jump stimulated by the superconducting transition in β-tin
Authors: Natsik V. D. , Soldatov V. P. , Kirichenko G. I. , Ivanchenko L. G.
Published: April 2003

The detailed study begun earlier (V. P. Soldatov et al., Fiz. Nizk. Temp. 27, 1421 (2001) [Low Temp. Phys. 27, 1048 (2001)]) on the kinetics of transient creep stimulated by the n–s superconducting transition in single crystals of pure β-Sn is continued. The samples are oriented for slip in the (100)〈010〉 system. In that case the kinetics of creep is governed by the motion of dislocations through the barriers of the Peierls potential relief. Experiments are carried out at temperatures of T1=1.6 K and T2=3.2 K, which are lower than the critical temperature of tin, Tc=3.72 K; the n–s and s–n transitions are brought about by turning a magnetic field off and on. The staged character of the creep curves δεns(t) after an n–s transition is confirmed: at T1=1.6 K one can distinguish a transient, a dynamic, and a fluctuation stage, and at T2=3.2 K, a transient and a fluctuation stage. The quantitative characteristics of each stage are investigated as functions of the creep rate at the time of the n–s transition and the total prestrain of the sample. The method of small loads is used to construct the macroscopic stress–strain diagram of β-Sn for the temperatures indicated and the work-hardening coefficients characterizing the intensity of the hardening on a macroscopic scale are determined. In the Appendix a theory of low-temperature creep in metals is set forth which involves the quantum (tunneling), dynamic, and thermally activated motion of dislocations in the Peierls potential relief. The features and characteristics of the dynamic and fluctuation stages of the experimental creep curves δεns(t) of tin are compared with the theory. It is established that the fluctuation stage of creep in tin is of a quantum character in the temperature interval studied. An analysis of the creep curves allows estimation of the work-hardening coefficient on the macro- and microscopic scales. It is found that the transient creep of β-Sn at temperatures in the liquid-helium region is due to low-energy dislocation processes involving a tunneling through effective potential barriers of the order of 10−3 eV in height.
Collisional and radiative processes in fluorescent lamps
Authors: Lister Graeme G.
Published: April 2003

Since electrode life is the major limiting factor in operating fluorescent lamps, many lighting companies have introduced “electrodeless” fluorescent lamps, using inductively coupled discharges. These lamps often operate at much higher power loadings than standard lamps and numerical models have not been successful in reproducing experimental measurements in the parameter ranges of interest. A comprehensive research program was undertaken to study the fundamental physical processes of these discharges, co-funded by the Electric Power Research Institute (EPRI) and OSRAM SYLVANIA under the name of ALITE. The program included experiments and modeling of radiation transport, computations of electron–atom and atom–atom cross sections and the first comprehensive power balance studies of a highly loaded fluorescent lamp. Results from the program and their importance to the understanding of the physics of fluorescent lamps are discussed, with particular emphasis on the important collisional and radiative processes. Comparisons between results of experimental measurements and numerical models are presented.
Molecular dynamics simulations of strongly coupled plasmas: Localization and microscopic dynamics
Authors: Donkó Z. , Hartmann P. , Kalman G. J.
Published: April 2003

The spatial–temporal localization of particles in the local minima of the potential surface is a prominent feature of strongly coupled plasmas. The duration of localization is investigated by molecular dynamics simulation, through monitoring of the decorrelation of the surroundings of individual particles. Three- and two-dimensional systems of particles interacting through Coulomb and Yukawa potentials are studied over a wide range of the plasma coupling (Γ) and screening (κ) parameters in the liquid phase. The oscillation spectrum of the caged particles in the equilibrium system as well as in the frozen environment of other particles (Einstein frequency spectrum) is determined.
Generalized forms and Einstein’s equations
Authors: Robinson D. C.
Published: April 2003

Generalized differential forms of different types are defined and their algebra and calculus are discussed. Complex generalized p-forms, a particular class of type two generalized forms, are considered in detail. It is shown that Einstein’s vacuum field equations for Lorentzian four-metrics are satisfied if and only if a complex generalized one-form on the bundle of two component spinors is closed. A similar result for half-flat and anti self-dual holomorphic four-metrics is also presented.
Mini-conference on Hamiltonian and Lagrangian methods in fluid and plasma physics
Authors: Brizard Alain J. , Tracy Eugene R.
Published: April 2003

A mini-conference on Hamiltonian and Lagrangian methods in fluid and plasma physics was held on 14 November 2002, as part of the 44th meeting of the Division of Plasma Physics of the American Physical Society. This paper summarizes the material presented during the talks scheduled during the Mini-Conference, which was held to honor Allan Kaufman on the occasion of his 75th birthday.
Periodic orbits and bifurcation diagrams of acetylene/vinylidene revisited
Authors: Prosmiti Rita , Farantos Stavros C.
Published: April 2003

Transitions from normal-mode to local-mode states in the two bending oscillations of acetylene observed in spectroscopic studies, as well as the existence of localized vibrational states in vinylidene above the isomerization barrier to acetylene, are examined by constructing continuation/bifurcation diagrams of periodic orbits on a global potential-energy surface. The principal families of periodic orbits, which provide a faithful representation of the overtone vibrational states, show pitchfork bifurcations for the asymmetric stretch and the two bending families of acetylene, the fingerprints of the normal- to local-mode transitions, whereas for vinylidene most of the principal families of periodic orbits remain stable above the isomerization potential barrier, thus supporting the existence of localized vinylidene states.
A combined time correlation function and instantaneous normal mode study of the sum frequency generation spectroscopy of the water/vapor interface
Authors: Perry Angela , Ahlborn Heather , Space Brian , Moore Preston B.
Published: April 2003

Theoretical approximations to the interface specific sum frequency generation (SFG) spectrum of O–H stretching at the water/vapor interface are constructed using time correlation function (TCF) and instantaneous normal mode (INM) methods. Both approaches lead to a (SSP polarization geometry) signal in excellent agreement with experimental measurements; the SFG spectrum of the entire water spectrum, both intermolecular and intramolecular, is reported. The observation that the INM spectrum is in agreement with the TCF result implies that motional narrowing effects play no role in the interfacial line shapes, in contrast to the O–H stretching dynamics in the bulk that leads to a narrowed line shape. This implies that (SSP) SFG spectroscopy is a probe of structure with dynamics not represented in the signal. The INM approach permits the elucidation of the molecular basis for the observed signal, and the motions responsible for the SFG line shape are well approximated as local O–H stretching modes. The complexity of the broad structured SFG signal is due to O–H stretching motions facing toward the bulk or vacuum environments that are characteristic of the interface. The success of both approaches suggests that theory can play a crucial role in interpreting SFG spectroscopy at more complex interfaces. It is also found that many-body polarization effects account for most of the observed signal intensity.
Comment on “X-transport: A baseline nonambipolar transport in a diverted tokamak plasmas edge” [Phys. Plasmas 9, 3884 (2002)]
Authors: Shaing K. C.
Published: April 2003

It is shown that the usual flux–force relation in neoclassical theory and the density conservation law are violated in a recent transport theory called X-transport. The latter violation leads to a surprisingly large radial flux in the calculations.
Percolation-based vibrational picture to estimate nonrandom N substitution in GaAsN alloys
Authors: Pagès O. , Tite T. , Bormann D. , Tournié E. , Maksimov O. , Tamargo M. C.
Published: April 2003

The number of N atoms in N-rich regions mostly due to nonrandom N incorporation in GaAsN (N∼4%), referred to as the Nr rate, is studied using a nonstandard Raman setup that addresses transverse symmetry. The Ga–N optical range shows a two-mode signal which discriminates between the N-poor (Np) and N-rich (Nr) regions. This is discussed via a percolation-based picture for Be-chalcogenide alloys, which exhibit mechanical contrast with regard to the shear modulus. This applies to GaAs–GaN even though the contrast is in the bulk modulus. The balance of Nr/Np strength provides a Nr rate of ∼30%, i.e., much larger than the corresponding Be rate of ∼4% in random Be-based alloys.
Precession of toroidally passing particles in tokamaks and spherical tori
Authors: Kolesnichenko Ya. I. , White R. B. , Yakovenko Yu. V.
Published: April 2003

The toroidal precession of the circulating particles and semitrapped particles (toroidally passing but poloidally trapped particles) is studied. Expressions for the precession frequency, which are convenient for practical use, are obtained and analyzed. It is found that the key parameters that determine the magnitude and the direction of the precession velocity are the plasma elongation, the magnitudes and profiles of the safety factor and β defined as the ratio of the local plasma pressure to the magnetic field pressure at the magnetic axis. An important role of the “paramagnetic” precession in highly elongated plasmas is revealed. The analysis carried out is based on the obtained expressions for the equilibrium magnetic field strength and the field line curvature.
Extended wavelength InGaAs on GaAs using InAlAs buffer for back-side-illuminated short-wave infrared detectors
Authors: Zimmermann Lars , John Joachim , Degroote Stefan , Borghs Gustaaf , Van Hoof Chris , Nemeth Stefan
Published: April 2003

We conducted an experimental study of back-side-illuminated InGaAs photodiodes grown on GaAs and sensitive in the short-wave infrared up to 2.4 μm. Standard metamorphic InGaAs or IR-transparent InAlAs buffers were grown by molecular-beam epitaxy. We studied dark current and photocurrent as a function of buffer thickness, buffer material, and temperature. A saturation of the dark current with buffer thickness was not observed. The maximum resistance area product was ∼10 Ω cm2 at 295 K. The dark current above 200 K was dominated by generation–recombination current. A pronounced dependence of the photocurrent on the buffer thickness was observed. The peak external quantum efficiency was 46% (at 1.6 μm) without antireflective coating.
Atomic layer deposition of ZrO2 on W for metal–insulator–metal capacitor application
Authors: Lee Sang-Yun , Kim Hyoungsub , McIntyre Paul C. , Saraswat Krishna C. , Byun Jeong-Soo
Published: April 2003

A metal–insulator–metal (MIM) capacitor using ZrO2 on tungsten (W) metal bottom electrode was demonstrated and characterized in this letter. Both ZrO2 and W metal were synthesized by an atomic layer deposition (ALD) method. High-quality 110∼115 Å ZrO2 films were grown uniformly on ALD W using ZrCl4 and H2O precursors at 300 °C, and polycrystalline ZrO2 in the ALD regime could be obtained. A 13∼14-Å-thick interfacial layer between ZrO2 and W was observed after fabrication, and it was identified as WOx through angle-resolved x-ray photoelectron spectroscopy analysis with wet chemical etching. The apparent equivalent oxide thickness was 20∼21 Å. An effective dielectric constant of 22∼25 including an interfacial WOx layer was obtained by measuring capacitance and thickness of MIM capacitors with Pt top electrodes. High capacitance per area (16∼17 fF/μm2) and low leakage current (10−7 A/cm2 at ±1 V) were achieved.
Structural and optical properties of coherent GaN islands grown on 6H-SiC(0001)-(√3×√3)
Authors: Hu C.-W. , Bell A. , Shi L. , Ponce F. A. , Smith D. J. , Tsong I. S. T.
Published: April 2003

Coherent islands of GaN with base widths in the range of 100 to 500 nm were grown on 6H-SiC(0001)-(√3×√3) surfaces via the vapor–liquid–solid (VLS) mechanism. The microstructure of GaN islands was studied by high-resolution cross-sectional transmission electron microscopy. The morphological details of the islands were imaged by atomic force microscopy and the same assembly of islands was identified in a scanning electron microscope in which site-specific cathodoluminescence (CL) spectroscopy was conducted on individual islands. The broadening of the CL linewidths together with the shift to lower wave numbers in the E2 Raman mode detected by micro-Raman spectroscopy suggest the existence of tensile strain in the GaN islands. The strain is due to the heavy Si doping of the GaN islands by Si adatoms on the (√3×√3) substrate surface during the VLS growth process.
Three-level picture for chirp-dependent fluorescence yields under femtosecond optical pulse irradiation
Authors: Hashimoto Naoyuki T. , Misawa Kazuhiko , Lang Roy
Published: April 2003

We propose a simple model to account for chirp-dependent fluorescence yields from a substance under femtosecond optical pulse irradiation. The model is simple, consisting of a three-level system, and yet it explains the essential feature of the chirp-dependent fluorescence yields experimentally observed, for example, with cyanine dye molecules. Based on the model, the dependence of the fluorescence on the excitation pulse properties such as the chirp rate and pulse intensity has been examined in detail. The results indicate that chirp-dependent fluorescence can be utilized as a convenient means for characterizing phase distortions in optical pulses such as those in optical fiber communication systems.
Decrease of the resonance bandwidth of micromechanical oscillators by phase control of the driving force
Authors: Tamayo Javier , Lechuga Laura M.
Published: April 2003

A method for controlling the amplitude response of micromechanical oscillators is presented. The micromechanical oscillator is driven by two forces acting both in phase, a fixed sinusoidal force and a feedback force whose amplitude depends on the phase shift. This dependence exhibits a pronounced maximum when the phase shift is 90°, i.e., at the resonant frequency. Experiments performed with a microcantilever prove that this class of active control decreases the bandwidth of the amplitude response about two orders of magnitude. The noise of the microcantilever, mainly of a thermal nature, is not increased at resonance, and it is moderately increased at both sides of the amplitude peak. Moreover, the noise can be tuned by adjusting the ratio between the two driving forces.
FeRh/FePt exchange spring films for thermally assisted magnetic recording media
Authors: Thiele Jan-Ulrich , Maat Stefan , Fullerton Eric E.
Published: April 2003

The temperature-dependent magnetic response of exchange-coupled FePt/FeRh thin films is described. The FePt forms a high magnetocrystalline anisotropy, high-coercivity ferromagnetic layer. The FeRh layer is antiferromagnetic at room temperature but, upon heating above a transition temperature, becomes ferromagnetic with a large magnetic moment and low magnetocrystalline anisotropy, forming an exchange–spring system and significantly lowering the coercive field of the composite system. This feature opens intriguing possibilities for media applications for thermally assisted magnetic recording where the ferromagnetic phase of FeRh is exploited to help write the media while the antiferromagnetic phase supports the long-time stability.
Anomalous diamagnetism in the intermetallic compounds CaPb3 and YbPb3
Authors: Baranovskiy A. E. , Grechnev G. E. , Mikitik G. P. , Svechakarev I. V.
Published: April 2003

A theoretical study is made of the features of the band structure and orbital magnetic susceptibility χ of the intermetallic compounds CaPb3 and YbPb3. It is shown that the anomalous, strongly temperature-dependent diamagnetism observed earlier in experiments on these compounds is of an interband origin and is due to the presence of degenerate electronic states in the immediate vicinity of the Fermi level. The characteristics of the degenerate states for the two compounds are determined by reconciling the calculated χ(T) dependence with experiment in the temperature range 5 K⩽T⩽300 K.
Corporate entrepreneurship: teaching managers to be entrepreneurs
Authors: Thornberry Neal E.
Published: April 2003

In good and bad economic times, innovation is a requisite for companies seeking to remain competitive especially in uncertain and turbulent times. Many organizations are increasingly looking to “corporate entrepreneurship” as a way of combating the lethargy and bureaucracy that often accompany size. But can mangers, who are expected to act like entrepreneurs really be trained to do so? The purpose of this study, then, was to determine whether large companies, through management education and action learning projects, could indeed turn mangers into corporate entrepreneurs. Four large organizations, that had embarked on formalized “corporate entrepreneurship” management development programs formed the basis for this field research. Results indicate that many managers can indeed be trained to act like entrepreneurs and that these actions can result in significant new value creation. However, companies who embark on corporate entrepreneurial development programs also need to be aware of the pitfalls and problems that can happen, when newly trained corporate entrepreneurs re‐enter the organization.
Roles of conformational stability and colloidal stability in the aggregation of recombinant human granulocyte colony‐stimulating factor
Authors: Chi Eva Y. , Krishnan Sampathkumar , Kendrick Brent S. , Chang Byeong S. , Carpenter John F. , Randolph Theodore W.
Published: April 2003

We studied the non‐native aggregation of recombinant human granulocyte stimulating factor (rhGCSF) in solution conditions where native rhGCSF is both conformationally stable compared to its unfolded state and at concentrations well below its solubility limit. Aggregation of rhGCSF first involves the perturbation of its native structure to form a structurally expanded transition state, followed by assembly process to form an irreversible aggregate. The energy barriers of the two steps are reflected in the experimentally measured values of free energy of unfolding (ΔGunf) and osmotic second virial coefficient (B22), respectively. Under solution conditions where rhGCSF conformational stability dominates (i.e., large ΔGunf and negative B22), the first step is rate‐limiting, and increasing ΔGunf (e.g., by the addition of sucrose) decreases aggregation. In solutions where colloidal stability is high (i.e., large and positive B22 values) the second step is rate‐limiting, and solution conditions (e.g., low pH and low ionic strength) that increase repulsive interactions between protein molecules are effective at reducing aggregation. rhGCSF aggregation is thus controlled by both conformational stability and colloidal stability, and depending on the solution conditions, either could be rate‐limiting.
Cyclic coordinate descent: A robotics algorithm for protein loop closure
Authors: Canutescu Adrian A. , Dunbrack Roland L.
Published: April 2003

In protein structure prediction, it is often the case that a protein segment must be adjusted to connect two fixed segments. This occurs during loop structure prediction in homology modeling as well as in ab initio structure prediction. Several algorithms for this purpose are based on the inverse Jacobian of the distance constraints with respect to dihedral angle degrees of freedom. These algorithms are sometimes unstable and fail to converge. We present an algorithm developed originally for inverse kinematics applications in robotics. In robotics, an end effector in the form of a robot hand must reach for an object in space by altering adjustable joint angles and arm lengths. In loop prediction, dihedral angles must be adjusted to move the C‐terminal residue of a segment to superimpose on a fixed anchor residue in the protein structure. The algorithm, referred to as cyclic coordinate descent or CCD, involves adjusting one dihedral angle at a time to minimize the sum of the squared distances between three backbone atoms of the moving C‐terminal anchor and the corresponding atoms in the fixed C‐terminal anchor. The result is an equation in one variable for the proposed change in each dihedral. The algorithm proceeds iteratively through all of the adjustable dihedral angles from the N‐terminal to the C‐terminal end of the loop. CCD is suitable as a component of loop prediction methods that generate large numbers of trial structures. It succeeds in closing loops in a large test set 99.79% of the time, and fails occasionally only for short, highly extended loops. It is very fast, closing loops of length 8 in 0.037 sec on average.
Effects of Aeroderivative Combustor Turbulence on Endwall Heat Transfer Distributions Acquired in a Linear Vane Cascade
Authors: Ames Forrest E. , Barbot Pierre A. , Wang Chao
Published: April 2003

Vane endwall heat transfer distributions are documented for a mock aeroderivative combustion system and for a low turbulence condition in a large-scale low speed linear cascade facility. Inlet turbulence levels range from below 0.7% for the low turbulence condition to 14% for the mock combustor system. Stanton number contours are presented at both turbulence conditions for Reynolds numbers based on true chord length and exit conditions ranging from 500,000 to 2,000,000. Low turbulence endwall heat transfer shows the influence of the complex three-dimensional flow field, while the effects of individual vortex systems are less evident for the high turbulence cases. Turbulent scale has been documented for the high turbulence case. Inlet boundary layers are relatively thin for the low turbulence case, while inlet flow approximates a nonequilibrium or high turbulence channel flow for the mock combustor case. Inlet boundary layer parameters are presented across the inlet passage for the three Reynolds numbers and both the low turbulence and mock combustor inlet cases. Both midspan and 95% span pressure contours are included. This research provides a well-documented database taken across a range of Reynolds numbers and turbulence conditions for assessment of endwall heat transfer predictive capabilities.
Reversing the Inactivation of Peroxiredoxins Caused by Cysteine Sulfinic Acid Formation
Authors: Woo Hyun Ae , Chae Ho Zoon , Hwang Sung Chul , Yang Kap-Seok , Kang Sang Won , Kim Kanghwa , Rhee Sue Goo
Published: April 2003

The active-site cysteine of peroxiredoxins is selectively oxidized to cysteine sulfinic acid during catalysis, which leads to inactivation of peroxidase activity. This oxidation was thought to be irreversible. However, by metabolic labeling of mammalian cells with
35
S, we show that the sulfinic form of peroxiredoxin I, produced during the exposure of cells to H
2
O
2
, is rapidly reduced to the catalytically active thiol form. The mammalian cells' ability to reduce protein sulfinic acid might serve as a mechanism to repair oxidatively damaged proteins or represent a new type of cyclic modification by which the function of various proteins is regulated.
Roles of NPM2 in Chromatin and Nucleolar Organization in Oocytes and Embryos
Authors: Burns Kathleen H. , Viveiros Maria M. , Ren Yongsheng , Wang Pei , DeMayo Francesco J. , Frail Donald E. , Eppig John J. , Matzuk Martin M.
Published: April 2003

Upon fertilization, remodeling of condensed maternal and paternal gamete DNA occurs to form the diploid genome. In
Xenopus laevis
, nucleoplasmin 2 (NPM2) decondenses sperm DNA in vitro. To study chromatin remodeling in vivo, we isolated mammalian NPM2 orthologs. Mouse NPM2 accumulates in oocyte nuclei and persists in preimplantation embryos.
Npm2
knockout females have fertility defects owing to failed preimplantation embryo development. Although sperm DNA decondensation proceeds without NPM2, abnormalities are evident in oocyte and early embryonic nuclei. These defects include an absence of coalesced nucleolar structures and loss of heterochromatin and deacetylated histone H3 that normally circumscribe nucleoli in oocytes and early embryos, respectively. Thus,
Npm2
is a maternal effect gene critical for nuclear and nucleolar organization and embryonic development.
Laser-Induced Ferroelectric Structural Order in an Organic Charge-Transfer Crystal
Authors: Collet Eric , Lemée-Cailleau Marie-Hélene , Buron-Le Cointe Marylise , Cailleau Hervé , Wulff Michael , Luty Tadeusz , Koshihara Shin-Ya , Meyer Mathias , Toupet Loic , Rabiller Philippe , Techert Simone
Published: April 2003

We report the direct observation by x-ray diffraction of a photoinduced paraelectric-to-ferroelectric structural phase transition using monochromatic 100-picosecond synchrotron pulses. It occurs in tetrathiafulvalene-
p
-chloranil, a charge-transfer molecular material in which electronic and structural changes are strongly coupled. An optical 300-femtosecond laser pulse switches the material from a neutral to an ionic state on a 500-picosecond time scale and, by virtue of intrinsic cooperativity, generates self-organized long-range structural order. The x-ray data indicate a macroscopic ferroelectric reorganization after the laser irradiation. Refinement of the structures before and after laser irradiation indicates structural changes at the molecular level.
Requirement of Cks2 for the First Metaphase/Anaphase Transition of Mammalian Meiosis
Authors: Spruck Charles H. , de Miguel Maria P. , Smith Adrian P. L. , Ryan Aimee , Stein Paula , Schultz Richard M. , Lincoln A. Jeannine , Donovan Peter J. , Reed Steven I.
Published: April 2003

We generated mice lacking Cks2, one of two mammalian homologs of the yeast Cdk1-binding proteins, Suc1 and Cks1, and found them to be viable but sterile in both sexes. Sterility is due to failure of both male and female germ cells to progress past the first meiotic metaphase. The chromosomal events up through the end of prophase I are normal in both

CKS2
–/–

males and females, suggesting that the phenotype is due directly to failure to enter anaphase and not a consequence of a checkpoint-mediated metaphase I arrest.
Axially Chiral 3,3'-Bi(1-benzothiophene)-2,2'-dicarboxylic Acid and Its Derivatives
Authors: Mézlová Marie , Petříčková Hana , Maloň Petr , Kozmík Václav , Svoboda Jiří
Published: April 2003

Ullmann dimerization of substituted methyl 3-X-1-benzothiophene-2-carboxylates 1-7 (X = Cl, Br) gave rise to the corresponding dimeric 3,3'-bi(1-benzothiophene) esters 8-13. Resolution of the title acid 20 by fractional crystallization of its mono- and bisquininium salt afforded pure (R)- and (S)-enantiomers, the optical purity and absolute configuration of which was confirmed by CD spectrometry and by X-ray crystallography. Ullmann dimerization of chiral oxazolines 23 and 24 derived from 2 proceeded without any diastereodifferentiation. Reduction of (R)- and (S)-20 afforded the corresponding (R)- and (S)-diols 29, which served as chiral ligands in a model enantioselective reduction of acetophenone. (R)- and (S)-1-phenylethan-1-ol were formed in 28 and 29% e.e., respectively.
INTRODUCTION TO THE MALDACENA CONJECTURE ON AdS/CFT
Authors: PETERSEN JENS LYNG
Published: April 2003

These lectures do not at all provide a general review of this rapidly growing field. Instead a rather detailed account is presented of a number of the most elementary aspects.
TRANSPORT IN EXCITED STATES OF SEMICONDUCTOR SUPERLATTICES
Authors: SIBILLE A. , MINOT C. , LARUELLE F.
Published: April 2003

The electronic conduction processes in the minibands and excited states of semiconductor superlattices are reviewed and discussed. The paper includes an introduction on miniband conduction and hopping conduction between localized states. It focusses subsequently on interminiband transport, both in the context of theoretical approaches and of experimental observations of these effects. Rabi oscillations between interacting Wannier–Stark levels are considered in detail. The role of scattering, and the manifestation of multipeaked velocity-field relationships on carrier and electric field profiles are evidenced. The final part concerns transport above the superlattice barriers, and quasi-ballistic transport in excited superlattice minibands.
ERROR CORRECTING ANALYSIS FOR TREE LANGUAGES
Authors: LÓPEZ DAMIÁN , SEMPERE JOSÉ M. , GARCÍA PEDRO
Published: April 2003

To undertake a syntactic approach to a pattern recognition problem, it is necessary to have good grammatical models as well as good parsing algorithms that allow distorted samples to be classified. There are several methods that obtain, by taking two trees as input, the editing distance between them. In the following work, a polynomial time algorithm which processes the distance between a tree and a tree automaton is presented. This measure can be used in pattern recognition problems as an error model inside a syntactic classifier.
A MODIFIED IMAGE REPRESENTATION FOR BINCODES AND ITS MANIPULATIONS
Authors: WU JUNG-GEN , CHUNG KUO-LIANG
Published: April 2003

It has been shown that using bincodes (BCs) to represent binary images is storage-saving and easy to be manipulated. Given a set of BCs, this paper presents improved codes, namely, the modified BCs (MBCs) to represent binary images. We first transform the given BCs into a set of logical expressions, then an improved encoding scheme is employed to reduce the storage space required for representing these logical expressions, thus obtaining the MBCs. Given twenty different types of real images, experimental results show that the proposed MBCs has 25% to 28% improvement when compared to BCs. By adopting the level-compact scheme on MBCs, storage space can be reduced further. It is shown that in some cases the storage-saving improvement is more than 50%. Some image manipulations, such as computing geometrical properties and set operations, on the MBCs are also investigated.
CHAOTIC MODULATION FOR ROBUST DIGITAL COMMUNICATIONS OVER MULTIPATH CHANNELS
Authors: KENNEDY MICHAEL PETER , KOLUMBÁN GÉZA , KIS GÁBOR
Published: April 2003

This tutorial work identifies the characteristic properties of chaotic digital modulation schemes and shows how the unique features of chaotic basis functions can be exploited to competitive advantage in selected application domains. Two robust noncoherent chaotic digital modulation schemes (DCSK and FM-DCSK) are described in detail and the performance of FM-DCSK is examined critically for communication channels where systems using conventional coherent and narrow-band modulation schemes fail. Since the FM-DCSK signal is a wide-band signal and its demodulation is performed without synchronization, the FM-DCSK modulation scheme is especially suitable for operation in multipath channel such as Wireless Local Area Networks (WLANs).
BIFURCATION DYNAMICS OF THREE-DIMENSIONAL SYSTEMS
Authors: PHILLIPSON PAUL E. , SCHUSTER PETER
Published: April 2003

Oscillations described by autonomous three-dimensional differential equations display multiple periodicities and chaos at critical parameter values. Regardless of the subsequent scenario the key instability is often an initial bifurcation from a single period oscillation to either its subharmonic of period two, or a symmetry breaking bifurcation. A generalized third-order nonlinear differential equation is developed which embraces the dynamics vicinal to these bifurcation events. Subsequently, an asymptotic averaging formalism is applied which permits an analytic development of the bifurcation dynamics, and, within quantifiable limits, prediction of the instability of the period one orbit in terms of the system control parameters. Illustrative applications of the general formalism, are made to the Rössler equations, Lorenz equations, three-dimensional replicator equations and Chua's circuit equations. The results provide the basis for discussion of the class of systems which fall within the framework of the formalism.
PHASE SYNCHRONIZATION IN REGULAR AND CHAOTIC SYSTEMS
Authors: PIKOVSKY ARKADY , ROSENBLUM MICHAEL , KURTHS JÜRGEN
Published: April 2003

In this contribution we present a brief introduction to the theory of synchronization of self-sustained oscillators. Classical results for synchronization of periodic motions and effects of noise on this process are reviewed and compared with recently found phase synchronization phenomena in chaotic oscillators. The basic notions of phase and frequency locking are reconsidered within a common framework. The application of phase synchronization to data analysis is discussed.
ADAPTIVE SYNCHRONIZATION OF CHAOTIC SYSTEMS VIA STATE OR OUTPUT FEEDBACK CONTROL
Authors: HONG YIGUANG , QIN HUASHU , CHEN GUNARONG
Published: April 2003

This letter addresses the problem of robust adaptive control for synchronization of continuous-time coupled chaotic systems, which may be subjected to disturbances. A general model is studied via two different approaches, using either state feedback or measured output feedback controls. Adaptive controllers are designed, in which a sliding mode structure is employed to increase the robustness of the closed-loop systems. When only output variables are measurable for synchronization, the adaptive controllers are designed by incorporating with a filter and using the so-called σ-modification technique. Several numerical examples are presented to show the effectiveness of the proposed chaos synchronization methods.
OBSERVING QUARK-GLUON PLASMA WITH STRANGE HADRONS
Authors: LETESSIER JEAN , RAFELSKI JOHANN
Published: April 2003

We review the methods and results obtained in an analysis of the experimental heavy ion collision research program at nuclear beam energy of 160–200 A GeV. We study strange, and more generally, hadronic particle production experimental data. We discuss present expectations concerning how these observables will perform at other collision energies. We also present the dynamical theory of strangeness production and apply it to show that it agrees with available experimental results. We describe strange hadron production from the baryon-poor quark-gluon phase formed at much higher reaction energies, where the abundance of strange baryons and antibaryons exceeds that of nonstrange baryons and antibaryons.
NEAR EDGE X-RAY ABSORPTION AND X-RAY PHOTOELECTRON DIFFRACTION STUDIES OF THE STRUCTURAL ENVIRONMENT OF Ge–Si SYSTEMS
Authors: CASTRUCCI P. , GUNNELLA R. , PINTO N. , BERNARDINI R. , DE CRESCENZI M. , SACCHI M.
Published: April 2003

Near edge X-ray absorption spectroscopy (XAS), X-ray photoelectron diffraction (XPD) and Auger electron diffraction (AED) are powerful techniques for the qualitative study of the structural and electronic properties of several systems. The recent development of a multiple scattering approach to simulating experimental spectra opened a friendly way to the study of structural environments of solids and surfaces. This article reviews recent X-ray absorption experiments using synchrotron radiation which were performed at Ge L edges and core level electron diffraction measurements obtained using a traditional X-ray source from Ge core levels for ultrathin Ge films deposited on silicon substrates. Thermodynamics and surface reconstruction have been found to play a crucial role in the first stages of Ge growth on Si(001) and Si(111) surfaces. Both techniques show the occurrence of intermixing processes even for room-temperature-grown Ge/Si(001) samples and give a straightforward measurement of the overlayer tetragonal distortion. The effects of Sb as a surfactant on the Ge/Si(001) interface have also been investigated. In this case, evidence of layer-by-layer growth of the fully strained Ge overlayer with a reduced intermixing is obtained when one monolayer of Sb is predeposited on the surface.
QUANTUM CHEMISTRY OF OXIDE SURFACES: FROM CO CHEMISORPTION TO THE IDENTIFICATION OF THE STRUCTURE AND NATURE OF POINT DEFECTS ON MgO
Authors: PACCHIONI GIANFRANCO
Published: April 2003

The electronic structure and chemisorption properties of the surface of ionic crystals are reviewed, with emphasis on two topics: a critical overview of the experimental and theoretical studies of the adsorption of CO on single crystal and polycrystalline MgO, and a discussion on the most important defect centers at the MgO surface — low-coordinated sites, single oxygen and magnesium vacancies, divacancies, and impurity or substitutional atoms. The two subjects are to some extent interconnected. From the detailed theoretical and experimental study of the adsorption of a nonreactive molecule like CO and from the comparison of experiments done on single crystal or thin films and on powder samples, one can learn about the nature and concentration of the defects at the surface. A more precise characterization of defects requires, however, a careful spectroscopic investigation and a direct comparison with quantum-chemical calculations of both geometric structure and observable properties. The combined theoretical–experimental approach offers new opportunities for a better understanding of the complexity of oxide surfaces.
WAVELENGTH CONVERSION OF AN INFRARED SIGNAL THROUGH CASCADED SECOND-ORDER NONLINEARITY IN A LITHIUM-NIOBATE CHANNEL WAVEGUIDE
Authors: CRISTIANI I. , RINI M. , RAMPULLA A. , BANFI G. P. , DEGIORGIO V.
Published: April 2003

We describe a wavelength conversion experiment (generation of a pulse at the wavelength λp - Δλ from a signal at λp+Δλ under the action of a pump at λp) performed through cascaded second-order process in a lithium niobate channel waveguide. With a 58-mm-long Ti diffused channel waveguide, λp=1.1 μ m (the wavelength of phase matching for the first step of sh generation), Δλ of several nanometers and 20 ps pulse duration, wavelength conversion with unit efficiency is obtained with a pump pulse energy of the order of 102 pJ. The experimental results are successfully interpreted by making use of modal analysis and solving the appropriate nonlinear equations.
DISTRIBUTION OF THE EFFECTIVE CONJUGATION LENGTH OF POLYTHIOPHENE DETERMINED BY ITS ABSORPTION AND |χ(3)| SPECTRA
Authors: KOBAYASHI T. , HAMAZAKI J. , KUNUGITA H. , EMA K. , OCHIAI K. , RIKUKAWA M. , SANUI K.
Published: April 2003

We measured the absorption and |χ(3)| spectra around the excitonic resonance for Langmuir–Blodgett (LB) film of polythiophene derivative, poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene) at 10 K and room temperature. We derived a theoretical distribution function for the effective conjugation length taking the molecular weight distribution into consideration, and fitted the calculated absorption and |χ(3)| spectra to the experimental ones. From the fits, we estimated the average effective conjugation length to be 21 thiophene rings at 10 K, and 15 thiophene rings at room temperature.
PERCOLATION AND FRACTAL COMPOSITES: OPTICAL STUDIES
Authors: DUCOURTIEUX S. , GRÉSILLON S. , BOCCARA A. C. , RIVOAL J. C. , QUELIN X. , GADENNE P. , DRACHEV V. P. , BRAGG W. D. , SAFONOV V. P. , PODOLSKIY V. A. , YING Z. C. , ARMSTRONG R. L. , SHALAEV VLADIMIR M.
Published: April 2003

Local field distributions are studied in random metal–dielectric films near percolation (percolation films) and fractal aggregates of colloidal particles. For both systems, it is shown that optical excitations are localized in small nanometer-scale areas, "hot spots," where the local fields are much larger than the field of an incident electromagnetic wave. The large local fields result in giant enhancement of various optical phenomena. The surface-enhanced white-light generation and second-harmonic generation have been obtained in percolation films. For fractal aggregates of silver particles, a giant effect of local optical activity has been observed. The effect is due to surface-plasmon excitations localized on chiral-active particle configurations in fractals.
THE LIQUID CRYSTAL LIGHT VALVE WITH OPTICAL FEEDBACK: A CASE STUDY IN PATTERN FORMATION
Authors: ARECCHI F. T. , BOCCALETTI S. , DUCCI S. , PAMPALONI E. , RAMAZZA P. L. , RESIDORI S.
Published: April 2003

A nonlinear optical system, consisting of a liquid crystal light valve with feedback, can display an enormous variety of spatial patterns. Starting from the basic principles of operation, we review several physical configurations enlighting the specificity of each one and the mechanism by which it leads to certain rules of pattern selection.
1/f NOISE DUE TO ATOMIC DIFFUSION OF IMPURITY CENTERS IN SEMICONDUCTORS
Authors: GRÜNEIS FERDINAND
Published: April 2003

Atomic diffusion of impurity centers is investigated as a possible origin of 1/f noise in semiconductors. Following the trace of an individual impurity center, the noise produced at a certain site is calculated; due to diffusion of centers this is an intermittent process. Besides generation-recombination (= g-r) noise, an excess noise is obtained which is attributed to diffusion of impurity centers. This excess noise exhibits 1/f noise and g-r burst noise. 1/f noise is attributed to the return time of a center to the origin; g-r burst noise is the noise produced by centers residing at a certain site. For a n-type strongly extrinsic semiconductor, the Hooge coefficient α of the present model is derived and impact of compensating acceptors or additional doping by shallow centers is investigated. Increasing the concentration of additional shallow centers α is decreased; an increase of concentration of compensating acceptors results in an increase of α. The temperature dependence of the Hooge coefficient α(T) is calculated and is compared with empirical findings.
Umbilical Cord Ulcer Associated with Fetal Jejunal Atresia: Report of 2 Cases
Authors: Kimura Takuya , Usui Noriaki , Kamata Shinkichi , Kawahara Hisayoshi , Sawai Toshio , Hirano Shinya , Wada Kazuko , Tomimatsu Takuji , Fukuda Hirotsugu , Okada Akira
Published: April 2003

We report 2 cases of umbilical cord ulcer associated with fetal jejunal atresia. Both of them developed a severe intrauterine hemorrhage, followed by fetal heart rate decelerations, and underwent emergency cesarean section. Bloody amniotic fluid and umbilical cord ulcers were observed in both cases. Although both cases were successfully resuscitated, neurological impairment and renal failure developed in 1 case due to prolonged asphyxia. In a review of the literature, umbilical cord ulcer was associated only with congenital duodenal atresia or jejunal atresia, but not with ileal atresia. Although the prenatal diagnosis of duodenal or upper jejunal atresia has been established, the prenatal diagnosis of this complication has not been reported. In such cases, detailed examination of the umbilical cord by ultrasonography may be useful for the prenatal diagnosis of this disease.
Arterial and Ductus venosus Doppler in Fetuses with Absent or Reverse End-Diastolic Flow in the Umbilical Artery: Longitudinal Analysis
Authors: Müller Thomas , Nanan Ralph , Rehn Monika , Kristen Peter , Dietl Johannes
Published: April 2003

Objective: To evaluate alterations of arterial and ductus venosus blood flow velocities during deterioration and their interdependence. Methods: 37 high-risk pregnancies complicated by umbilical absent or reverse end-diastolic flow velocities (AREDV) were monitored by measurement of the pulsatility index of the umbilical artery, middle cerebral artery and ductus venosus waveforms. Results: The mean observation period was 16.5 days. There was a significant change in the pulsatility of waveforms in all vessels over the observation period. Compared with the ductus venosus, pulsatility of waveforms in the middle cerebral artery diverged from the normal range 2.2 weeks earlier. Increase in pulsatility in the umbilical artery was concomitant with venous but not with cerebral flow alterations. In addition, there was a correlation between the increase of venous but not arterial pulsatility and perinatal acidemia. Variability of pulsatility index values of the umbilical artery and the ductus venosus but not of the middle cerebral artery increased towards delivery. Conclusions: Ductus venosus Doppler allows detection of further deterioration in centralized fetuses with umbilical AREDV. However, striking short-term variability has to be taken into account when considering this parameter.
Fetal Subependymal Cysts with Normal Neonatal Outcome
Authors: D’Addario Vincenzo , Selvaggio Saverio , Pinto Vincenzo , Resta Maurizio , Di Cagno Luca , Famà Antonio
Published: April 2003

The authors report the prenatal sonographic diagnosis of subependymal cysts, confirmed by in utero MRI, in an apparently uneventful pregnancy. The sonographic appearance of the lesions, the obstetric management and the postnatal follow-up to one year are described. Special attention is paid to prenatal factors of neurological morbidity, rather than intrapartum and postnatal, thus emphasizing the importance of early and sequential evaluation of the developing fetal brain. Diagnosis, clinical significance and outcome of prenatal subependymal cysts are necessary for parental counselling and obstetric management. Furthermore, the detection of a prenatal brain injury may have remarkable medico-legal implications.