bluuebunny/crossref_metadata_2025 huggingface dataset:
Negative autoregulation of HNF-4α gene expression by HNF-4α1
Authors: MAGENHEIM Judith , HERTZ Rachel , BERMAN Ina , NOUSBECK Janna , BAR-TANA Jacob
Published: May 2005

HNF-4α (hepatocyte nuclear factor-4α) is required for tissue-specific expression of many of the hepatic, pancreatic, enteric and renal traits. Heterozygous HNF-4α mutants are inflicted by MODY-1 (maturity onset diabetes of the young type-1). HNF-4α expression is reported here to be negatively autoregulated by HNF-4α1 and to be activated by dominant-negative HNF-4α1. Deletion and chromatin immunoprecipitation analysis indicated that negative autoregulation by HNF-4α1 was mediated by its association with the TATA-less HNF-4α core promoter enriched in Sp1, but lacking DR-1 response elements. Also, negative autoregulation by HNF-4α1 was independent of its transactivation function, being similarly exerted by transcriptional-defective MODY-1 missense mutants of HNF-4α1, or under conditions of suppressing or enhancing HNF-4α activity by small heterodimer partner or by inhibiting histone deacetylase respectively. Negative autoregulation by HNF-4α1 was abrogated by overexpressed Sp1. Transcriptional suppression by HNF-4α1 independently of its transactivation function may extend the scope of its transcriptional activity to interference with docking of the pre-transcriptional initiation complex to TATA-less promoters.
Self-assembly of SNARE fusion proteins into star-shaped oligomers
Authors: RICKMAN Colin , HU Kuang , CARROLL Joe , DAVLETOV Bazbek
Published: May 2005

Three evolutionarily conserved proteins known as SNAREs (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptors) mediate exocytosis from single cell eukaryotes to neurons. Among neuronal SNAREs, syntaxin and SNAP-25 (synaptosome-associated protein of 25 kDa) reside on the plasma membrane, whereas synaptobrevin resides on synaptic vesicles prior to fusion. The SNARE motifs of the three proteins form a helical bundle which probably drives membrane fusion. Since studies in vivo suggested an importance for multiple SNARE complexes in the fusion process, and models appeared in the literature with large numbers of SNARE bundles executing the fusion process, we analysed the quaternary structure of the full-length native SNARE complexes in detail. By employing a preparative immunoaffinity procedure we isolated all of the SNARE complexes from brain, and have shown by size-exclusion chromatography and negative stain electron microscopy that they exist as approx. 30 nm particles containing, most frequently, 3 or 4 bundles emanating from their centre. Using highly purified, individual, full-length SNAREs we demonstrated that the oligomerization of SNAREs into star-shaped particles with 3 to 4 bundles is an intrinsic property of these proteins and is not dependent on other proteins, as previously hypothesized. The average number of the SNARE bundles in the isolated fusion particles corresponds well with the co-operativity observed in calcium-triggered neuronal exocytosis.
Pi class glutathione S-transferase genes are regulated by Nrf 2 through an evolutionarily conserved regulatory element in zebrafish
Authors: SUZUKI Takafumi , TAKAGI Yaeko , OSANAI Hitoshi , LI Li , TAKEUCHI Miki , KATOH Yasutake , KOBAYASHI Makoto , YAMAMOTO Masayuki
Published: May 2005

Pi class GSTs (glutathione S-transferases) are a member of the vertebrate GST family of proteins that catalyse the conjugation of GSH to electrophilic compounds. The expression of Pi class GST genes can be induced by exposure to electrophiles. We demonstrated previously that the transcription factor Nrf 2 (NF-E2 p45-related factor 2) mediates this induction, not only in mammals, but also in fish. In the present study, we have isolated the genomic region of zebrafish containing the genes gstp1 and gstp2. The regulatory regions of zebrafish gstp1 and gstp2 have been examined by GFP (green fluorescent protein)-reporter gene analyses using microinjection into zebrafish embryos. Deletion and point-mutation analyses of the gstp1 promoter showed that an ARE (antioxidant-responsive element)-like sequence is located 50 bp upstream of the transcription initiation site which is essential for Nrf 2 transactivation. Using EMSA (electrophoretic mobility-shift assay) analysis we showed that zebrafish Nrf 2–MafK heterodimer specifically bound to this sequence. All the vertebrate Pi class GST genes harbour a similar ARE-like sequence in their promoter regions. We propose that this sequence is a conserved target site for Nrf 2 in the Pi class GST genes.
Sodium-coupled and electrogenic transport of B-complex vitamin nicotinic acid by slc5a8, a member of the Na/glucose co-transporter gene family
Authors: GOPAL Elangovan , FEI You-Jun , MIYAUCHI Seiji , ZHUANG Lina , PRASAD Puttur D. , GANAPATHY Vadivel
Published: May 2005

SMCT (sodium-coupled monocarboxylate transporter; slc5a8) is a Na+-coupled transporter for lactate, pyruvate and short-chain fatty acids. Similar to these already known substrates of SMCT, the water-soluble B-complex vitamin nicotinic acid also exists as a monocarboxylate anion (nicotinate) under physiological conditions. Therefore we evaluated the ability of SMCT to mediate the uptake of nicotinate. In mammalian cells, the cloned mouse SMCT (slc5a8) induced the uptake of nicotinate. The SMCT-induced uptake was Na+-dependent. The Michaelis constant for the uptake process was 296±88 μM. The Na+-activation kinetics indicated that at least two Na+ ions are involved in the process. Among the various structural analogues tested, nicotinate was the most effective substrate. Nicotinamide and methylnicotinate were not recognized by the transporter. 2-Pyrazine carboxylate and isonicotinate interacted with the transporter to a moderate extent. SMCT-mediated uptake of nicotinate was inhibited by lactate and pyruvate. In the Xenopus laevis oocyte expression system, SMCT-mediated nicotinate transport was electrogenic, as evident from the nicotinate-induced inward currents under voltage-clamp conditions. Substrate-induced currents in this expression system corroborated the substrate specificity determined in the mammalian cell expression system. The kinetic parameters with regard to the affinity of the transporter for nicotinate and the Hill coefficient for Na+ activation, determined by using the oocyte expression system, were also similar to those obtained from the mammalian cell expression system. We conclude that SMCT functions not only as a Na+-coupled transporter for short-chain fatty acids and lactate but also as a Na+-coupled transporter for the water-soluble vitamin nicotinic acid.
LEA proteins prevent protein aggregation due to water stress
Authors: GOYAL Kshamata , WALTON Laura J. , TUNNACLIFFE Alan
Published: May 2005

LEA (late embryogenesis abundant) proteins in both plants and animals are associated with tolerance to water stress resulting from desiccation and cold shock. However, although various functions of LEA proteins have been proposed, their precise role has not been defined. Recent bioinformatics studies suggest that LEA proteins might behave as molecular chaperones, and the current study was undertaken to test this hypothesis. Recombinant forms of AavLEA1, a group 3 LEA protein from the anhydrobiotic nematode Aphelenchus avenae, and Em, a group 1 LEA protein from wheat, have been subjected to functional analysis. Heat-stress experiments with citrate synthase, which is susceptible to aggregation at high temperatures, suggest that LEA proteins do not behave as classical molecular chaperones, but they do exhibit a protective, synergistic effect in the presence of the so-called chemical chaperone, trehalose. In contrast, both LEA proteins can independently protect citrate synthase from aggregation due to desiccation and freezing, in keeping with a role in water-stress tolerance; similar results were obtained with lactate dehydrogenase. This is the first evidence of anti-aggregation activity of LEA proteins due to water stress. Again, a synergistic effect of LEA and trehalose was observed, which is significant given that non-reducing disaccharides are known to accumulate during dehydration in plants and nematodes. A model is proposed whereby LEA proteins might act as a novel form of molecular chaperone, or ‘molecular shield’, to help prevent the formation of damaging protein aggregates during water stress.
Synthesis and assembly of thylakoid protein complexes: multiple assembly steps of photosystem II
Authors: ROKKA Anne , SUORSA Marjaana , SALEEM Ammar , BATTCHIKOVA Natalia , ARO Eva-Mari
Published: May 2005

To study the synthesis and assembly of multisubunit thylakoid protein complexes, we performed [35S]Met pulse and chase experiments with isolated chloroplasts and intact leaves of spinach (Spinacia oleracea L.), followed by Blue Native gel separation of the (sub)complexes and subsequent identification of the newly synthesized and assembled protein subunits. PSII (photosystem II) core subunits were the most intensively synthesized proteins, particularly in vitro and at high light intensities in vivo, and could be sequestered in several distinct PSII subassemblies. Newly synthesized D1 was first found in the reaction centre complex that also contained labelled D2 and two labelled low-molecular-mass proteins. The next biggest PSII subassembly contained CP47 also. Then PsbH was assembled together with at least two other labelled chloroplast-encoded low-molecular-mass subunits, PsbM and PsbTc, and a nuclear-encoded PsbR. Subsequently, CP43 was inserted into the PSII complex concomitantly with PsbK. These assembly steps seemed to be essential for the dimerization of PSII core monomers. Intact PSII core monomer was the smallest subcomplex harbouring the newly synthesized 33 kDa oxygen-evolving complex protein PsbO. Nuclear-encoded PsbW was synthesized only at low light intensities concomitantly with Lhcb polypeptides and was distinctively present in PSII–LHCII (where LHC stands for light-harvesting complex) supercomplexes. The PsbH protein, on the contrary, was vigorously synthesized and incorporated into PSII core monomers together with the D1 protein, suggesting an intrinsic role for PsbH in the photoinhibition-repair cycle of PSII.
Fibulin-5 interacts with fibrillin-1 molecules and microfibrils
Authors: FREEMAN Lyle J. , LOMAS Amanda , HODSON Nigel , SHERRATT Michael J. , MELLODY Kieran T. , WEISS Anthony S. , SHUTTLEWORTH Adrian , KIELTY Cay M.
Published: May 2005

Fibulin-5 plays an important role in elastic fibre formation in vivo. We have investigated the molecular interactions between fibulin-5 and components of fibrillin-rich microfibrils which form a template for elastin. Fibulin-5 interacted in a dose-dependent manner with a fibrillin-1 N-terminal sequence and with tropoelastin, but not with MAGP-1 (microfibril-associated glycoprotein-1) or decorin. Fibulin-5 did not inhibit interactions between fibrillin-1 N- and C-terminal fragments, or fibrillin-1 interactions with tropoelastin. Fibulin-5 may provide a link between tropoelastin and microfibrils in the pericellular space during elastic fibre assembly.
Formulating Effective National Strategies for Market Transformation
Authors: Gao Ping , Lyytinen Kalle
Published: May 2005

National initiatives for the development of information infrastructure have become critical to moving nations into the information age. In this paper, we are concerned with the features of information infrastructure development strategy, the social determinants for a country to choose a strategy and the principles of its design. We investigate China's telecommunications market transformation over the last two decades. China's experience is interesting as it is a case par excellence of a large transitory economy. We observe that China's national strategy was based on multiple social elements, not on technological prerogatives alone. This suggests that a national strategy for infrastructure construction should be derived from carefully considering both the technological options available as well as the social and political environment and the situation in the market structure.
Toward Predicting Software Development Success from the Perspective of Practitioners: An Exploratory Bayesian Model
Authors: Procaccino J Drew , Verner June M , Darter Marvin E , Amadio William J
Published: May 2005

Software development project managers may need to focus on particular issues during the development process for a variety of reasons, including limited resources. This study utilized a survey to ask software practitioners, who are at the core of development, to provide insight into some of the important early non-technical issues of software development, including those related to sponsor/senior management, customer/users and requirements management. Proposed relationships among these early items, and their relationship to software practitioners’ perception of project success, were quantitatively represented through a proposed Bayesian Belief Network. The concept of ‘success’ was derived from a pilot study of practitioners and was ‘defined’ as (a) there is a project plan, (b) the project is well planned, (c) practitioners have a sense of achievement while working on a project, (d) practitioners have a sense of doing a good job (i.e. delivered quality) while working on a project, and (e) requirements are accepted by the development team as realistic/achievable. The proposed causal model provided quantitative evidence that reaching agreement with customers/users on requirements, a high level of customer/user participation, and users who make adequate time for requirements gathering have the largest direct impacts on project success among the investigated items. The proposed model identified the following as the critical chain of events for success: (1) Having a sponsor throughout the project, (2) users who make adequate time for requirements gathering, (3) a high level of customer/user participation in the development process, and (4) agreement on requirements between customer/users and the development team.
Stochastic diffusion interactions and coarsening in a system of droplets growing from a supersaturated gas mixture
Authors: Pines V. , Zlatkowski M. , Chait A.
Published: May 2005

In this work we study diffusion interactions among liquid droplets growing in stochastic population by condensation from supersaturated binary gas mixture. During the postnucleation transient regime collective growth of liquid droplets competing for the available water vapor decreases local supersaturation leading to the increase of critical radius and the onset of coarsening process. In coarsening regime the growth of larger droplets is prevailing noticeably broadening the droplet size-distribution function when the condensation process becomes more intensive than the supersaturation yield. Modifications in the kinetic equation are discussed and formulated for a stochastic population of liquid droplets when diffusional interactions among droplets become noteworthy. The kinetic equation for the droplet size-distribution function is solved together with field equations for the mass fraction of disperse liquid phase, mass fraction of water vapor component of moist air, and temperature during diffusion-dominated regime of droplet coarsening. The droplet size and mass distributions are found as functions of the liquid volume fraction, showing considerable broadening of droplet spectra. It is demonstrated that the effect of latent heat of condensation considerably changes coarsening process. The coarsening rate constant, the droplet density (number of droplets per unit volume), the screening length, the mean droplet size, and mass are determined as functions of the temperature, pressure, and liquid volume fraction.
Nematic fluid structure in wall-field geometry
Authors: Sokolovska T. G. , Sokolovskii R. O. , Patey G. N.
Published: May 2005

We describe an integral equation method for obtaining the distribution of a nematic fluid near a wall and interacting with a uniform orienting field. Complete density-orientational profiles are calculated for a model nematic with different wall-particle interactions and different orientations of the wall with respect to the field. For orienting walls we identify particular long-range correlations that are responsible for reorientation of the bulk nematic at zero external field. These correlations become stronger as the wall-particle interaction is increased in range; they become longer ranged as the orienting field is weakened. Special attention is focused on systems where the wall-particle interaction favors orientations perpendicular to the surface. The local director orientation can vary discontinuously with the distance from the surface when the orienting influences of the field and the wall are antagonistic. At high densities smectic-like structures appear. Adsorption phenomena are also discussed. For inert hard walls, the ordered fluid avoids the surface, and a surface layer where the particles tend to orient perpendicular to the bulk director appears. Experimentally, this might be seen as wetting of the wall by a less-ordered fluid.
Novel synthesis of two-dimensional TiS2 nanocrystallites on Au(111)
Authors: Biener Monika M. , Biener Juergen , Friend Cynthia M.
Published: May 2005

We describe a novel approach to synthesize two-dimensional nanocrystalline TiS2 islands on Au(111). Ti is deposited by physical vapor deposition at room temperature on AuS-covered Au(111) surfaces. Subsequent annealing to temperatures between 670 K and 800 K leads to the formation of single-layer, triangular TiS2 islands. These TiS2 nanocrystallites reflect the structure of bulk TiS2, and are composed of S–Ti–S stacking units with hexagonally close-packed layers of sulfur atoms and titanium occupying the octahedral sites in between. The lattice constant of the hexagonal unit cell is 3.45 Å. A superlattice with a repeat distance of 17.3 Å results from the coincidence of five TiS2 units with six Au atoms and is observed in scanning tunneling microscopy and low energy electron diffraction. The triangular shape of the islands indicates a preference for one of the two possible edge terminations. The observation of two island orientations rotated by 60° with respect to each other can be attributed to the formation of twin-related TiS2 domains. The population of the two different island orientations changes during annealing at 800 K indicating a thermodynamic preference for one of the possible stacking sequences.
A density-functional theory study of the interaction of N2O with Rh(110)
Authors: Kokalj Anton , Matsushima Tatsuo
Published: May 2005

The adsorption of nitrous oxide, N2O, on a Rh(110) surface has been characterized by using density-functional theory. N2O was found to bind to the surface in two alternative forms. The first, less stable form is tilted with the terminal N atom attached to the surface, while the second, more stable form lies horizontally on the surface. Adsorption on the on-top site is more stable than that on the bridge site. The tilted form remains linear on adsorption, while the horizontal form is bent, with the terminal-nitrogen and oxygen atoms pointing towards the surface. At lower adsorbate coverage, Θ≲1/4 ML (ML—monolayer), the adsorption of a few horizontal N2O configurations is dissociative, i.e., N2O→N2(a)+O(a). The N2O-surface interaction is discussed in terms of the electronic structure analysis.
Molecular dynamic heterogeneity of confined lipid films by H1 magnetization-exchange nuclear magnetic resonance
Authors: Buda A. , Demco D. E. , Jagadeesh B. , Blümich B.
Published: May 2005

The molecular dynamic heterogeneity of monolayer to submonolayer thin lecithin films confined to submicron cylindrical pores were investigated by H1 magnetization exchange nuclear magnetic resonance. In this experiment a z-magnetization gradient was generated by a double-quantum dipolar filter. The magnetization-exchange decay and buildup curves were interpreted with the help of a theoretical model based on the approximation of a one-dimensional spin-diffusion process in a three-domain morphology. The dynamic heterogeneity of the fatty acid chains and the effects of the surface area per molecule, the diameter of the pores, and the temperature were characterized with the help of local spin-diffusion coefficients. The effect of various parameters on the molecular dynamics of the mobile region of the fatty acid chains was quantified by introducing an ad hoc Gaussian distribution function of the H1 residual dipolar couplings. For the lipid films investigated in this study, the surface induced order and the geometrical confinement affect the chain dynamics of the entire molecule. Therefore, each part of the chain independently reflects the effect of surface coverage, pore size, and temperature.
Microscopic and macroscopic polarization within a combined quantum mechanics and molecular mechanics model
Authors: Jensen L. , Swart Marcel , van Duijnen Piet Th.
Published: May 2005

A polarizable quantum mechanics and molecular mechanics model has been extended to account for the difference between the macroscopic electric field and the actual electric field felt by the solute molecule. This enables the calculation of effective microscopic properties which can be related to macroscopic susceptibilities directly comparable with experimental results. By seperating the discrete local field into two distinct contribution we define two different microscopic properties, the so-called solute and effective properties. The solute properties account for the pure solvent effects, i.e., effects even when the macroscopic electric field is zero, and the effective properties account for both the pure solvent effects and the effect from the induced dipoles in the solvent due to the macroscopic electric field. We present results for the linear and nonlinear polarizabilities of water and acetonitrile both in the gas phase and in the liquid phase. For all the properties we find that the pure solvent effect increases the properties whereas the induced electric field decreases the properties. Furthermore, we present results for the refractive index, third-harmonic generation (THG), and electric field induced second-harmonic generation (EFISH) for liquid water and acetonitrile. We find in general good agreement between the calculated and experimental results for the refractive index and the THG susceptibility. For the EFISH susceptibility, however, the difference between experiment and theory is larger since the orientational effect arising from the static electric field is not accurately described.
A localized basis that allows fast and accurate second-order Møller-Plesset calculations
Authors: Subotnik Joseph E. , Head-Gordon Martin
Published: May 2005

We present a method for computing a basis of localized orthonormal orbitals (both occupied and virtual), in whose representation the Fock matrix is extremely diagonal dominant. The existence of these orbitals is shown empirically to be sufficient for achieving highly accurate second-order Møller-Plesset (MP2) energies, calculated according to Kapuy’s method. This method (which we abbreviate KMP2) involves a different partitioning of the n-electron Hamiltonian and scales at most quadratically, with potential for linearity, in the number of electrons. As such, we believe the KMP2 algorithm presented here could be the basis of a viable approach to local-correlation calculations.
A dielectric fallacy in inferring Tg of water
Authors: Johari G. P.
Published: May 2005

In a recent analysis, Angell [Annu. Rev. Phys. Chem. 55, 559 (2004)] concluded that if water’s Tg is assumed to be 160 K, the plot of dielectric loss tangent tan δ against T/Tg for unsintered amorphous solid water overlaps the corresponding plots for glycerol and propylene carbonate. We point out that such an analysis falsifies both dielectrics and molecular kinetics, and is not useful for ascertaining Tg.
Casimir energy for a wedge with three surfaces and for a pyramidal cavity
Authors: Ahmedov H. , Duru I. H.
Published: May 2005

Casimir energy calculations for the conformally coupled massless scalar field for a wedge defined by three intersecting planes and for a pyramid with four triangular surfaces are presented. The group generated by reflections are employed in the formulation of the required Green functions and the wave functions.
Coverage dependence of oxygen decomposition and surface diffusion on rhodium (111): A DFT study
Authors: Inderwildi Oliver R. , Lebiedz Dirk , Deutschmann Olaf , Warnatz Jürgen
Published: May 2005

A systematic study of oxygen adsorption, decomposition and diffusion on Rh(111) and its dependence on coadsorbed oxygen molecules has been performed using density functional theory calculations. First, the bonding strength between metal surface and adsorbed oxygen molecules has been studied as a function of initial oxygen coverage. The bonding strength decreases with increasing oxygen coverage, which points towards a self-inhibition of the adsorption process. The potential energy hypersurface (PES) for the dissociation of oxygen molecules adsorbed on a threefold fcc position perpendicular to the surface was calculated using a combined linear/quadratic synchronous transit method with conjugate gradient refinements. The results indicate that a minor amount of oxygen on the surface enhances the decomposition of further oxygen molecules, while this process is inhibited at higher coverage. Moreover, PES calculations of a single site jump of atomic oxygen on rhodium (111) indicate that the activation energy increases as well with increasing oxygen coverage. All results are discussed with respect to a rhodium based catalytic NOx reduction/decomposition system proposed by Nakatsuji, which decomposes nitrogen oxides in oxygen excess.
Molecular dynamics simulation of amphiphilic dimers at a liquid-vapor interface
Authors: Kim Hye-Young , Fichthorn Kristen A.
Published: May 2005

Molecular dynamics simulations are utilized to simulate a model liquid-vapor-amphiphile system. Amphiphilic surfactant molecules are modeled as dimers composed of a hydrophilic head and a hydrophobic tail. Three dimer models with three different head sizes and two different head-to-tail size ratios are studied. The surfactant molecules distribute preferentially at the interfaces at low concentrations and form micelles in the bulk liquid phase as the concentration increases. We find that the surface tension decreases as molecular concentration increases, with a reduction in the rate of decrease after micellization occurs. The extent to which a surfactant can reduce the surface tension at a given concentration is found to depend on the head size. Furthermore, the head size and concentration dependence of the surfactant tilt-angle distribution is studied and compared to experimental data.
Pure point spectrum for the time evolution of a periodically rank-N kicked Hamiltonian
Authors: McCaw James , McKellar B. H. J.
Published: May 2005

We find the conditions under which the spectrum of the unitary time evolution operator for a periodically rank-N kicked system remains pure point. This stability result allows one to analyze the onset of, or lack of chaos in this class of quantum mechanical systems, extending the results for rank-1 systems produced by Combescure and others. This work includes a number of unitary theorems equivalent to those well known and used in the self-adjoint theory.
Finite propagation speed for the Camassa–Holm equation
Authors: Constantin Adrian
Published: May 2005

We prove that any classical solution of the Camassa–Holm equation will have compact support if its initial data has this property.
Magnetic and transport properties of Co nanoparticles embedded in a carbon matrix
Authors: Liu P. , Huang Y. , Zhang Y. , Bonder M. J. , Hadjipanayis G. C. , Vlachos D. , Deshmukh S. R.
Published: May 2005

Co nanoparticles embedded in a carbon matrix have been prepared by gas condensation using a cluster gun. The magnetic, microstructural, and transport properties of the Co nanoparticles can be controlled by the volume fraction of Co particles, which is adjusted by the sputtering time of Co. With the decrease of the amount of Co, the transport properties of thin films showed a transition from a metallic to a semiconductorlike behavior. The sample with a semiconductorlike behavior showed a superparamagnetic behavior with a blocking temperature around 130K. The blocking temperature of the Co particles was found to decrease with the decrease of Co sputtering time, indicating a decrease in the average particle size because of the shorter sputtering time.
Template-mediated assembly of FePt L1 clusters under external magnetic field
Authors: Sui Y. C. , Liu W. , Yue L. P. , Li X. Z. , Zhou J. , Skomski R. , Sellmyer D. J.
Published: May 2005

FePt L10-structured clusters were synthesized by hydrogen reduction of Fe(NO3)3∙9H2O and H2PtCl6∙6H2O mixtures within the pores of alumina. They were released by dissolving the alumina matrix and capped with organic surfactants. After a series of chemical treatments, clusters with an average diameter of about 11nm were precipitated. The clusters were drop casted onto ordered nanoporous arrays. Clusters reaching the bottom of the pores formed an ordered magnetic array. The corresponding magnetic film exhibits distinct anisotropic behavior caused by the external magnetic field.
Magnetic properties of YGdFe17−x(Ga,Al)x (x=0–8)
Authors: Srilatha R. , Murty V. S. , Markandeyulu G.
Published: May 2005

The effect of Ga∕Al substitution on the structural and magnetic properties of YGdFe17 has been investigated. A structural transformation from hexagonal to rhombohedral has been observed. The saturation magnetization increases up to x=1 (Ga)∕2 (Al) and then decreases with further increase of x. Curie temperature increases from 476 K for YGdFe17 to 595 K for YGdFe14Ga3 and 495 K for YGdFe14Al3 and decreases with further substitution of Ga∕Al. The easy magnetization direction is planar up to x=6 for Ga- and 7 for Al-substituted compounds and shifts to along c axis for x=8.
Magneto-optical spectra of closely spaced magnetite nanoparticles
Authors: Smith Damon Allen , Barnakov Yu. A. , Scott B. L. , White S. A. , Stokes K. L.
Published: May 2005

The Faraday rotation spectrum of composites containing magnetite nanoparticles is found to be dependent on the interparticle spacing of the constituent nanoparticles. The composite materials are prepared by combining chemically synthesized Fe3O4 (magnetite) nanoparticles (8-nm diameter) and poly(methylmethacrylate). Composites are made containing a range of nanoparticle concentrations. The peak of the main spectral feature depends on nanoparticle concentration; this peak is observed to shift from approximately 470 nm for (dilute composites) to 540 nm (concentrated). We present a theory based on the discrete-dipole approximation which accounts for optical coupling between magnetite particles. Qualitative correlations between theoretical calculations and experimental data suggest that the shifts in spectral peak position depend on both interparticle distance and geometrical configuration.
Pulse shape, resolution, and signal-to-noise ratio in patterned media recording
Authors: Takeo Akihiko , Bertram H. Neal
Published: May 2005

Patterned media is one candidate for high areal density recording near 1 Tbpsi. We propose a coding scheme that utilizes practical giant magnetoresistance dimensions. The scheme defines a “1” as the region between two dots of opposite polarity (nonreturn to zero inverted for patterned media). Expressions for the pulse shape, amplitude, and resolution are given. The signal-to-noise ratio is discussed in terms of minimum patterned dot fluctuations.
Incommensurate transverse anisotropy induced by disorder and spin-orbit-vibron coupling in Mn12 acetate
Authors: Park Kyungwha , Pederson Mark R. , Baruah Tunna , Bernstein Noam , Kortus Jens , Richardson Steven L. , del Barco Enrique , Kent Andrew D. , Hill Steve , Dalal Naresh S.
Published: May 2005

It has been shown within density-functional theory that in Mn12 acetate there are effects due to disorder by solvent molecules and a coupling between vibrational and electronic degrees of freedom. We calculate the in-plane principal axes of the second-order anisotropy caused by the second effect and compare them with those of the fourth-order anisotropy due to the first effect. We find that the two types of the principal axes are not commensurate with each other, which results in a complete quenching of the tunnel-splitting oscillation as a function of an applied transverse field.
Crystallographic texture and angular dependence of coercivity of ordered CoPt thin film
Authors: Oh D. Y. , Park J. K.
Published: May 2005

Effect of crystallographic texture on the angular dependence of coercivity of ordered CoPt thin film was studied by successfully controlling the texture of the ordered CoPt thin film. We have developed, based on the Stoner–Wohlfarth interacting particles model, a micromagnetic simulation technique which can simulate the effect of distribution of magnetocrystalline easy axis on the magnetization behavior of thin film. The good agreement between the experiments and simulation suggested that the magnetization reversal in ordered CoPt thin film occurs not by the domain wall motion but by the Stoner–Wohlfarth interacting particles model.
A new method for direct calculation of total energy of protein
Authors: He Xiao , Zhang John Z. H.
Published: May 2005

A new scheme is developed for efficient quantum mechanical calculation of total energy of protein based on a recently developed MFCC (molecular fractionation with conjugate caps) approach. In this scheme, the linear-scaling MFCC method is first applied to calculate total electron density of protein. The computed electron density is then employed for direct numerical integration in density functional theory (DFT) to yield total energy of protein, with the kinetic energy obtained by a proposed ansatz. Numerical studies are carried out to calculate torsional energies of two polypeptides using this approach and the energies are shown to be in good agreement with the corresponding full system DFT calculation.
The magnetic structure of Nd5Sn4
Authors: Wang H. B. , Altounian Z. , Ryan D. H. , Cadogan J. M. , Swainson I. P.
Published: May 2005

Nd 5 Sn 4 adopts the orthorhombic Pnma structure, and orders antiferromagnetically below 36(3) K. The neutron diffraction pattern at 4 K reveals that the magnetic space group is Pn′m′a′, a complex canted-antiferromagnetic structure. The Nd 4c magnetic mode is AxCz, and the Nd 8d magnetic mode is Ax−Gy−Cz−. The Nd magnetic moments are 1.76(8), 2.44(12), and 2.63(10)μB at 4c, 8d1, and 8d2 sites, respectively. These results are in agreement with our Mössbauer spectroscopy and magnetic measurements.
Current-assisted magnetization switching in submicron permalloy S-shape wires with narrow junctions
Authors: Chen Yi-Chun , Lin Yu-An , Chen Dong-Chen , Yao Yeong-Der , Lee Shang-Fan , Liou Yung
Published: May 2005

We report the results of the current-assisted magnetization switching in submicron permalloy S-shape wires with narrow junctions (or notches). Domain walls were initially formed and pinned in the vicinity of the notches. Two distinct behaviors are observed in the current-assisted magnetization reversal process. When the applied field is near switching field (ΔH<7Oe), the injected current directly switched the wire magnetization, and the needed critical current varied linearly and significantly with the field intensity. In contrast, when the field is relatively far from the switching field (ΔH>7Oe), the current only moves the domain wall to a local stable state, and the critical current varied slightly with the field. Moreover, two resistance jumps during current scanning are observed in the cases with magnetization reversals. These results reveal that the current driven effect is closely related to the initial domain states, and are explained by a theoretical model based on spin transfer effect.
Effects of Ag buffer layer on the microstructure and magnetic properties of nanocomposite FePt∕Ag multilayer films
Authors: Chen S. C. , Kuo P. C. , Chou C. Y. , Sun A. C.
Published: May 2005

The face-centered-tetragonal L10FePt films with (001) preferred orientation has perpendicular coercivity (Hc⊥) of about 2462Oe that can be achieved by stacking a structure of (FePt4nm∕Ag2nm)5 multilayer films on the 5nm thick MgO underlayer and annealing at 600°C for 30min. It is found that both the perpendicular anisotropy and coercivity of (FePt4nm∕Ag2nm)5 multilayer films are enhanced by introducing an Ag buffer layer (≦20nm) between the (FePt4nm∕Ag2nm)5 films and the MgO underlayer. When introducing an Ag buffer layer of 20nm thickness, the Hc⊥ value of the MgO5nm∕Ag20nm∕(FePt4nm∕Ag2nm)5 multilayer films is observed to increase from 2462to4731Oe, which has significant potential as perpendicular magnetic recording media for high-density recording.
The effect of hole depth on the coercivity distribution and domain structure for DyFeCo thin films
Authors: Ye L. X. , Lee J. M. , Wu Te-ho , Wu J. C.
Published: May 2005

In our previous studies, we indicated that the coercivity of patterned magneto-optical thin film is quite different from nonpatterned samples. However, we only compared the hysteresis loop bulk measurements of the samples. In this study, we measured the microhysteresis curves at an arbitrary position while coercivity distribution was mapped, and observed submicron images of the remnant state of domain reversal patterns. The spatial variations of the coercivity over several depths of hole arrays barrier on patterned film will be reported.
Simulation of the collisional sheath structure near the outer wall of the Hall thruster
Authors: Nejoh YasuNori , Yamamura Yuki
Published: May 2005

In order to study the inner structure of the sheath near the outer wall of the Hall thruster, a simulation associated with the equation of momentum transfer with the ion-neutral collision and Poisson’s equation having dust grains and photoelectrons is performed. It is found that the velocity of ions, the potential, the space charge density, and the density distributions of electrons, ions, photoelectrons, and dust grains are different from those of the traditional sheath.
Advantages of superconducting quantum interference device-detected magnetic resonance over conventional high-frequency electron paramagnetic resonance for characterization of nanomagnetic materials
Authors: Cage Brant , Russek Stephen E. , Zipse David , Dalal Naresh S.
Published: May 2005

A dc-detected high-frequency electron paramagnetic resonance (HF-EPR) technique, based on a standard superconducting quantum interference device (SQUID) magnetometer, has significant advantages over traditional HF-EPR based on microwave absorption measurements. The SQUID-based technique provides quantitative determination of the dc magnetic moment as a function of microwave power, magnetic field and temperature. The EPR spectra obtained do not contain variability in the line shape and splittings that are commonly observed in the standard single-pass transmission mode HF-EPR. We demonstrate the improved performance by comparing EPR spectra for Fe8 molecular nanomagnets using both SQUID-based and conventional microwave-absorption EPR systems.
Level shift operator and second order perturbation theory
Authors: Dereziński Jan , Früboes Rafal
Published: May 2005

We give approximate formulas for spectrum and the corresponding spectral projections of perturbed linear operators. The main tool is the so-called level shift operator, which expresses the effects of second order perturbation theory on the point spectrum.
Magnetism and transport in YbMn2Sb2
Authors: Nirmala R. , Morozkin A. V. , Suresh K. G. , Kim H.-D. , Kim J.-Y. , Park B.-G. , Oh S.-J. , Malik S. K.
Published: May 2005

A new ternary intermetallic compound, namely, YbMn2Sb2, has been synthesized and its magnetic and electrical transport properties have been studied in the temperature range of 2–300K. This compound crystallizes in a trigonal, La2O2S-type structure (space-group P3bm1, No. 164) and is found to be ferromagnetically ordered at room temperature. The magnetism is attributed to the ordering of Mn sublattice. M5 x-ray absorption spectrum of YbMn2Sb2 obtained at room temperature suggests that the valency of Yb in this compound is close to 2+. Electrical resistivity of this compound is metal-like and a positive magnetoresistance of 13% is observed at 5K in an applied field of 9T.
Direct synthesis of Pt based L1 structured nanoparticles (invited)
Authors: Takahashi Migaku , Ogawa Tomoyuki , Hasegawa Daiji , Jeyadevan Balachandran
Published: May 2005

Equiatomic FePt and CoPt nanoparticles with the ordered L10 structure are attractive as ultrahigh density magnetic recording media. In a recent work, chemically synthesized fcc-FePt nanoparticles with narrow size distribution and their self-assembled array with close-packed microstructure has been achieved successfully. However, the particles coalesced during the subsequent annealing step necessary to obtain L10 FePt nanoparticles. In the present study, we have successfully demonstrated the direct synthesis of L10 FePt nanoparticles at low temperature of 553K using the “modified polyol method” without subsequent annealing, whose diameter is 5–10nm and intrinsic magnetocrystalline anisotropy field (Hk) is 31kOe. This indicates that precisely controlling the reaction kinetics, especially low reduction rate through optimizing the polyol/Pt mole ratio and type of polyol are very important for directly synthesizing the L10 FePt nanoparticles. Furthermore, we investigated the size, morphology and composition dependence of the magnetic properties of FePt nanoparticles in order to clarify the L10 ordering mechanism. As a result, clear evidence of the existence of the critical diameter for the thermodynamical L10 ordering is not observed in the size range above 2nm. Furthermore, the recrystallization and sintering process can be a driving force for promoting the L10 ordering, and hence, Fe and Pt atom diffusion at the grain boundary plays an important role to the L10 ordering of FePt nanoparticles.
Graphical analysis of electron inertia induced acoustic instability
Authors: Karmakar P. K. , Deka U. , Dwivedi C. B.
Published: May 2005

Recently, the practical significance of the asymptotic limit of me∕mi→0 for electron density distribution has been judged in a two-component plasma system with drifting ions. It is reported that in the presence of drifting ions with drift speed exceeding the ion acoustic wave speed, the electron inertial delay effect facilitates the resonance coupling of the usual fluid ion acoustic mode with the ion-beam mode. In this contribution the same instability is analyzed by graphical and numerical methods. This is to note that the obtained dispersion relation differs from those of the other known normal modes of low frequency ion plasma oscillations and waves. This is due to consideration of electron inertial delay in derivation of the dispersion relation of the ion acoustic wave fluctuations. Numerical calculations of the dispersion relation and wave energy are carried out to depict the graphical appearance of poles and positive-negative enegy modes. It is found that the electron inertia induced ion acoustic wave instability arises out of linear resonance coupling between the negative and positive energy modes. Characterization of the resonance nature of the instability in Mach number space for different wave numbers of the ion acoustic mode is presented.
Size effect on L1 ordering and magnetic properties of chemically synthesized FePt and FePtAu nanoparticles
Authors: Jia Zhiyong , Kang Shishou , Shi Shifan , Nikles David E. , Harrell J. W.
Published: May 2005

There is growing evidence that FePt nanoparticles become increasingly difficult to chemically order as the size approaches a few nanometers. We have studied the chemical ordering of FePt and FePtAu nanoparticle arrays as a function of particle size. Monodisperse Fe49Pt51 and Fe48Pt44Au8 nanoparticles with a size about 6nm were synthesized by the simultaneous decomposition of iron pentacarbonyl and reduction of platinum acetylacetonate and gold (III) acetate in a mixture of phenyl ether and hexadecylamine (HDA), with 1-adamantanecarboxylic acid and HDA as stabilizers. The nanoparticles were dispersed in toluene, films of the particles were cast onto silicon wafers from the dispersion, and the films were annealed in a tube furnace with flowing Ar+5%H2. The magnetic anisotropy and switching volumes were determined from time- and temperature-dependent coercivity measurements. By comparing with 3-nm FePt and FePtAu nanoparticles of comparable composition, the phase transformation is easier for the larger particles. Under the same annealing conditions, the larger particles have higher anisotropy and order parameter. Additive Au is very effective in enhancing the chemical ordering in both small and large particles, with x-ray diffraction superlattice peaks appearing after annealing at 350°C. Dynamic remnant coercivity measurements and magnetic switching volumes suggest particle aggregation at the higher annealing temperatures in both small and large particles.
Magnetocaloric effect in NiMnGa particles produced by spark erosion
Authors: Tang Y. J. , Solomon Virgil C. , Smith D. J. , Harper H. , Berkowitz A. E.
Published: May 2005

The magnetic entropy change of tetragonal and orthorhombic NiMnGa fine particles made by spark erosion was investigated in this paper. It was found that the structure and crystalline phase transformation temperatures can be strongly affected by the compositions of the particles, while Curie temperature is less sensitive to the compositions. Due to the possible distribution of the particle size and compositions in these particles, the magnetic entropy changes observed are much broader and smaller than those of bulk NiMnGa alloys. The maximum absolute value of entropy change ΔS=2JKg−1K−1 was observed for tetragonal structure NiMnGa particles at 95°C in a field of 2T.
Magnetic properties of nanosized iron oxide particles precipitated in alginate hydrogels
Authors: Naik R. , Senaratne U. , Powell N. , Buc E. C. , Tsoi G. M. , Naik V. M. , Vaishnava P. P. , Wenger L. E.
Published: May 2005

Nanoparticles of γ-Fe2O3 (size 2–3nm) were precipitated in alginate hydrogels by cross-linking sodium alginate with Fe ions in a methanol-water solution. The zero-field-cooled and field-cooled magnetization measurements between 5 and 350K and the hysteresis in the M vs H relation below the blocking temperature indicate superparamagnetic behavior. The temperature dependence of the coercive field is not consistent with the T1∕2 behavior predicted by Néel and Brown for the noninteracting particles. The average diameter of the nanoparticles determined from the magnetic data is consistently larger than the corresponding particle size determined by x-ray diffraction, perhaps due to interparticle magnetic interactions.
Analysis of magnetization and magnetocaloric effect in amorphous FeZrMn ribbons
Authors: Min S. G. , Kim K. S. , Yu S. C. , Suh H. S. , Lee S. W.
Published: May 2005

The magnetization behaviors have been measured for amorphous Fe90−xMnxZr10 (x=8 and 10) alloys. The Curie temperature is decreased from 210Kto185K with increasing Mn concentration (x=8 to x=10). The magnetization measurements were conducted at temperatures above the Curie temperature in the paramagnetic region. In both samples, the magnetic properties showed superparamagnetic behavior above Tc where the mean magnetic moment of the superparamagnetic spin clusters decreased with increasing temperature. A large magnetic entropy change ΔSM, which is calculated from H vs M curves associated with the ferromagnetic-paramagnetic transitions in amorphous, has been observed. The maximum ΔSM of Fe82Mn8Zr10 is 2.87J∕kgK at 210K for an applied field of 5T. The peak of magnetic entropy change was observed at the Curie temperature. The ΔSM decreases with increasing Mn concentration to 2.33J∕kgK.