bluuebunny/crossref_metadata_2025 huggingface dataset:
Developmental shift from long‐term depression to long‐term potentiation in the rat medial vestibular nuclei: role of group I metabotropic glutamate receptors
Authors: Puyal Julien , Grassi Silvarosa , Dieni Cristina , Frondaroli Adele , Demêmes Danielle , Raymond Jaqueline , Pettorossi Vito Enrico
Published: September 2003

The effects of high frequency stimulation (HFS) of the primary vestibular afferents on synaptic transmission in the ventral part of the medial vestibular nuclei (vMVN) were studied during postnatal development and compared with the changes in the expression of the group I metabotropic glutamate receptor (mGluR) subtypes, mGluR1 and mGluR5. During the first stages of development, HFS always induced a mGluR5‐ and GABAA‐dependent long‐term depression (LTD) which did not require NMDA receptor and mGluR1 activation. The probability of inducing LTD decreased progressively throughout the development and it was zero at about the end of the second postnatal week. Conversely, long‐term potentiation (LTP) appeared at the beginning of the second week and its occurrence increased to reach the adult value at the end of the third week. Of interest, the sudden change in the LTP frequency occurred at the time of eye opening, about the end of the second postnatal week. LTP depended on NMDA receptor and mGluR1 activation. In parallel with the modifications in synaptic plasticity, we observed that the expression patterns and localizations of mGluR5 and mGluR1 in the medial vestibular nuclei (MVN) changed during postnatal development. At the earlier stages the mGluR1 expression was minimal, then increased progressively. In contrast, mGluR5 expression was initially high, then decreased. While mGluR1 was exclusively localized in neuronal compartments and concentrated at the postsynaptic sites at all stages observed, mGluR5 was found mainly in neuronal compartments at immature stages, then preferentially in glial compartments at mature stages. These results provide the first evidence for a progressive change from LTD to LTP accompanied by a distinct maturation expression of mGluR1 and mGluR5 during the development of the MVN.
The DsbA Signal Sequence Directs Efficient, Cotranslational Export of Passenger Proteins to the
Escherichia coli
Periplasm via the Signal Recognition Particle Pathway
Authors: Schierle Clark F. , Berkmen Mehmet , Huber Damon , Kumamoto Carol , Boyd Dana , Beckwith Jon
Published: September 2003

The
Escherichia coli
cytoplasmic protein thioredoxin 1 can be efficiently exported to the periplasmic space by the signal sequence of the DsbA protein (DsbAss) but not by the signal sequence of alkaline phosphatase (PhoA) or maltose binding protein (MBP). Using mutations of the signal recognition particle (SRP) pathway, we found that DsbAss directs thioredoxin 1 to the SRP export pathway. When DsbAss is fused to MBP, MBP also is directed to the SRP pathway. We show directly that the DsbAss-promoted export of MBP is largely cotranslational, in contrast to the mode of MBP export when the native signal sequence is utilized. However, both the export of thioredoxin 1 by DsbAss and the export of DsbA itself are quite sensitive to even the slight inhibition of SecA. These results suggest that SecA may be essential for both the slow posttranslational pathway and the SRP-dependent cotranslational pathway. Finally, probably because of its rapid folding in the cytoplasm, thioredoxin provides, along with gene fusion approaches, a sensitive assay system for signal sequences that utilize the SRP pathway.
Genome-Wide Analyses Revealing a Signaling Network of the RcsC-YojN-RcsB Phosphorelay System in
Escherichia coli
Authors: Hagiwara Daisuke , Sugiura Masahito , Oshima Taku , Mori Hirotada , Aiba Hirofumi , Yamashino Takafumi , Mizuno Takeshi
Published: September 2003

In
Escherichia coli
, capsular colanic acid polysaccharide synthesis is regulated through the multistep RcsC→YojN→RcsB phosphorelay. By monitoring a hallmarked
cps
::
lacZ
reporter gene, we first searched for physiological stimuli that propagate the Rcs signaling system. The expression of
cps
::
lacZ
was activated when cells were grown at a low temperature (20°C) in the presence of glucose as a carbon source and in the presence of a relatively high concentration of external zinc (1 mM ZnCl
2
). In this Rcs signaling system, the
rcsF
gene product (a putative outer membrane-located lipoprotein) was also an essential signaling component. Based on the defined signaling pathway and physiological stimuli for the Rcs signaling system, we conducted genome-wide analyses with microarrays to clarify the Rcs transcriptome (i.e., Rcs regulon). Thirty-two genes were identified as putative Rcs regulon members; these genes included 15 new genes in addition to 17 of the previously described
cps
genes. Using a set of 37 two-component system mutants, we performed alternative genome-wide analyses. The results showed that the propagation of the zinc-responsive Rcs signaling system was largely dependent on another two-component system, PhoQ/P. Considering the fact that the PhoQ/P signaling system responds to external magnesium, we obtained evidence which supports the view that there is a signaling network that connects the Rcs system with the PhoQ/P system, which coordinately regulates extracellular polysaccharide synthesis in response to the external concentrations of divalent cations.
Characterization of a Spontaneous Nonmagnetic Mutant ofMagnetospirillum gryphiswaldenseReveals a Large Deletion Comprising a Putative Magnetosome Island
Authors: Schübbe Sabrina , Kube Michael , Scheffel André , Wawer Cathrin , Heyen Udo , Meyerdierks Anke , Madkour Mohamed H. , Mayer Frank , Reinhardt Richard , Schüler Dirk
Published: September 2003

Frequent spontaneous loss of the magnetic phenotype was observed in stationary-phase cultures of the magnetotactic bacteriumMagnetospirillum gryphiswaldenseMSR-1. A nonmagnetic mutant, designated strain MSR-1B, was isolated and characterized. The mutant lacked any structures resembling magnetosome crystals as well as internal membrane vesicles. The growth of strain MSR-1B was impaired under all growth conditions tested, and the uptake and accumulation of iron were drastically reduced under iron-replete conditions. A large chromosomal deletion of approximately 80 kb was identified in strain MSR-1B, which comprised both the entiremamABandmamDCclusters as well as further putative operons encoding a number of magnetosome-associated proteins. A bacterial artificial chromosome clone partially covering the deleted region was isolated from the genomic library of wild-typeM. gryphiswaldense. Sequence analysis of this fragment revealed that all previously identifiedmamgenes were closely linked with genes encoding other magnetosome-associated proteins within less than 35 kb. In addition, this region was remarkably rich in insertion elements and harbored a considerable number of unknown gene families which appeared to be specific for magnetotactic bacteria. Overall, these findings suggest the existence of a putative large magnetosome island inM. gryphiswaldenseand other magnetotactic bacteria.
Role of 2-Phosphoglycolate Phosphatase ofEscherichia coliin Metabolism of the 2-Phosphoglycolate Formed in DNA Repair
Authors: Pellicer Maria Teresa , Nuñez Maria Felisa , Aguilar Juan , Badia Josefa , Baldoma Laura
Published: September 2003

The enzyme 2-phosphoglycolate phosphatase fromEscherichia coli, encoded by thegphgene, was purified and characterized. The enzyme was highly specific for 2-phosphoglycolate and showed good catalytic efficiency (kcat/Km), which enabled the conversion of this substrate even at low intracellular concentrations. A comparison of the structural and functional features of this enzyme with those of 2-phosphoglycolate phosphatases of different origins showed a high similarity of the sequences, implying the use of the same catalytic mechanism. Western blot analysis revealed constitutive expression of thegphgene, regardless of the carbon source used, growth stage, or oxidative stress conditions. We showed that this housekeeping enzyme is involved in the dissimilation of the intracellular 2-phosphoglycolate formed in the DNA repair of 3′-phosphoglycolate ends. DNA strand breaks of this kind are caused by agents such as the radiomimetic compound bleomycin. The differential response between a 2-phosphoglycolate phosphatase-deficient mutant and its parental strain after treatment with bleomycin allowed us to connect the intracellular formation of 2-phosphoglycolate with the production of glycolate, which is subsequently incorporated into general metabolism. We thus provide evidence for a salvage function of 2-phosphoglycolate phosphatase in the metabolism of a two-carbon compound generated by the cellular DNA repair machinery.
Complete Sequence of Virulence Plasmid pJM1 from the Marine Fish PathogenVibrio anguillarumStrain 775
Authors: Di Lorenzo Manuela , Stork Michiel , Tolmasky Marcelo E. , Actis Luis A. , Farrell David , Welch Timothy J. , Crosa Lidia M. , Wertheimer Anne M. , Chen Qian , Salinas Patricia , Waldbeser Lillian , Crosa Jorge H.
Published: September 2003

The virulence plasmid pJM1 enables the fish pathogenVibrio anguillarum, a gram-negative polarly flagellated comma-shaped rod bacterium, to cause a highly fatal hemorrhagic septicemic disease in salmonids and other fishes, leading to epizootics throughout the world. The pJM1 plasmid 65,009-nucleotide sequence, with an overall G+C content of 42.6%, revealed genes and open reading frames (ORFs) encoding iron transporters, nonribosomal peptide enzymes, and other proteins essential for the biosynthesis of the siderophore anguibactin. Of the 59 ORFs, approximately 32% were related to iron metabolic functions. The plasmid pJM1 confers onV. anguillarumthe ability to take up ferric iron as a complex with anguibactin from a medium in which iron is chelated by transferrin, ethylenediamine-di(o-hydroxyphenyl-acetic acid), or other iron-chelating compounds. ThefatDCBA-angRToperon as well as other downstream biosynthetic genes is bracketed by the homologous ISV-A1 and ISV-A2 insertion sequences. Other clusters on the plasmid also show an insertion element-flanked organization, including ORFs homologous to genes involved in the biosynthesis of 2,3-dihydroxybenzoic acid. Homologues of replication and partition genes are also identified on pJM1 adjacent to this region. ORFs with no known function represent approximately 30% of the pJM1 sequence. The insertion sequence elements in the composite transposon-like structures, corroborated by the G+C content of the pJM1 sequence, suggest a modular composition of plasmid pJM1, biased towards acquisition of modules containing genes related to iron metabolic functions. We also show that there is considerable microheterogeneity in pJM1-like plasmids from virulent strains ofV. anguillarumisolated from different geographical sources.
Monomeric NarB Is a Dual-Affinity Nitrate Reductase, and Its Activity Is Regulated Differently from That of Nitrate Uptake in the Unicellular Diazotrophic Cyanobacterium
Synechococcus
sp. Strain RF-1
Authors: Wang Tung-Hei , Fu Hongyong , Shieh Yuh-Jang
Published: September 2003

Synechococcus
sp. strain RF-1 is a unicellular freshwater cyanobacterium that fixes N
2
aerobically and exhibits a circadian rhythm for nitrogenase activity under a light-dark regimen.
Synechococcus
sp. strain RF-1 also utilizes nitrate, nitrite, or ammonium for growth. Under the diazotrophic growth, the nitrate uptake in
Synechococcus
sp. strain RF-1 was induced by nitrate or nitrite but repressed by ammonium. In contrast, a prominent nitrate reductase (NR) activity was detected in diazotrophically grown cells using the reduced methyl viologen assay. The NR activity was not inhibited by ammonium and only slightly enhanced by nitrate. The different expression patterns of nitrate uptake and NR in
Synechococcus
sp. strain RF-1 were reflected in general at the transcript level determined by reverse transcriptase PCR. Under both nitrate-induced and uninduced conditions, the in situ NR activity exhibited similar biphasic kinetics for nitrate. The recombinant NR encoded by the
narB
gene of
Synechococcus
sp. strain RF-1, expressed in
E. coli
, also showed the biphasic kinetics with similar pH and temperature profiles. By in-gel NR activity assay, the recombinant NarB was found to exist as a single form. Both the high- and low-affinity NR activities of the recombinant NarB showed the same thermostability. When modified at the N terminus by a polyhistidine tag, the recombinant NR activity was shifted from biphasic to hyperbolic kinetics and showed only a single

K
m

for nitrate, indicating the functional importance of the NarB N-terminal structure in NR kinetics.
Slave Boson Description of CuO2 Planes of the High-Temperature Superconductors
Authors: Mrkonjić Ivana , Barišić Slaven
Published: September 2003

Slave-boson mean-field calculation is carried out analytically for doped CuO 2 conduction planes, described by the extended Emery model which is parameterized by Cu–O charge transfer energy Δpd, Cu–O hopping t0, O–O hopping t′ and Coulomb repulsion U localized on Cu site, taken as infinite. At zero doping δ, finite small t′ expands the range of stability of the covalent, conducting state, characterized by renormalized band parameters Δpf and t, on the expense of insulating t=0 state, which, however, remains stable at larger Δpd. For sufficiently large Δpd, Δpf saturates at 4|t′|. Finite doping suppresses the insulating state nearly symmetrically with respect to its sign. The regime with Δpf close to 4|t′| fits remarkably well ARPES spectra of Y123, Bi2212 and LSCO, and, in the latter case, explains the observed strong doping-dependence of the effective Cu–O hopping.
Metallochloronitrides: Electronic Pairing Mechanism in a New Class of Superconductors
Authors: Bill Andreas , Morawitz Hans , Kresin Vladimir Z.
Published: September 2003

A new class of doped layered superconductors has been discovered recently: the metallochloronitrides. Intercalating metallic atoms (Na, Li) into the layered parent compounds M N X (M= Zr , Hf and X= Cl , Br ) superconductivity was found below a transition temperature that can be as high as Tc~26 K. We show that the dominant contribution to the pairing interaction is electronic and comes from the screened dynamical Coulomb interaction characteristic of layered systems. With use of parameters for Li 0.48 (THF) y HfNCl we show that the calculated Tc is in quantitative agreement with experiment.
Scanning Tunneling Spectroscopy in Anisotropic s-Wave Superconductors
Authors: Suderow H. , Rodrigo J. G. , Martinez-Samper P. , Vieira S. , Brison J. P. , Lejay P. , Canfield P. C. , Lee S. I. , Tajima S.
Published: September 2003

We discuss Scanning Tunneling Microscopy and Spectroscopy (STM/S) measurements at very low temperatures in single crystals of the non magnetic borocarbide superconductors RNi 2 B 2 C ( R = Y , Lu , T c=15.5 and 16.5 K) and in MgB 2. The tunneling spectra in some regions of the surface show a clear reduction of the anisotropy of the superconducting gap.
Quarter-Filled Extended Hubbard Model at Strong Coupling
Authors: Lee W. F. , Lin H. Q.
Published: September 2003

We apply a perturbation approach to study the quarter-filled extended Hubbard model at strong coupling limit. An effective Hamiltonian up to sixth order in t/U and t/V (t defines electron hopping, U defines on-site Coulomb interaction, and V defines nearest-neighbor Coulomb interaction) for one-dimensional chains was obtained. The spin-spin correlation functions were involved, which can be obtained after comparing to the ground state energy numerically obtained from the phase diagram.
Two Structural Blocks in HgBa2CuO4+δ
Authors: Liu W. L. , Han S. H. , Zhang H.
Published: September 2003

All the high Tc superconductors are structurally composed of two different blocks, the perovskite and the rock salt. Based on this fact, we developed a model to calculate the interaction between the two structural blocks. But the model could not deal with the superconductors with one Cu–O plane, such as Bi 2 Sr 2 CuO y (2201) phase and HgBa 2 CuO 4+δ (1201) phase. Here we modify our model, dealing with HgBa 2 CuO 4+δ in a different way in which the unit cell is still divided into two blocks, and the combinative energy between the blocks in HgBa 2 CuO 4+δ with different δ value is calculated. It is shown that the reaction of the different blocks also closely related with the superconductivity in this compound.
Photogenerated States in a Highly Correlated Electron System
Authors: Aihara M. , Takahashi A. , Gomi H.
Published: September 2003

We study the properties of photogenerated states of strongly correlated electron systems (SCES) with using the 'excited-state' t-J Hamiltonian. The lowest energy state in the two-photon excited manifold is calculated for the 20 site two-dimensional square lattice at half filling. The analysis of the off-diagonal order suggests that the d-wave superconducting state is photogenerated. We propose an optical method using the virtual transition to avoid the temperature growth arising from the optical excitation. We also investigate the transient behavior of the photoexcited state in SCES, which distinctively reflects the spin-charge separation in SCES.
Thermodynamics of the Planar Hubbard Model
Authors: Bonča J. , Prelovšek P.
Published: September 2003

The thermodynamic properties: specific heat and entropy are studied as a function of temperature and doping within the two-dimensional Hubbard model with various U/t=4-12. Quantities are calculated using the finite-temperature Lanczos method with additional phase-averaging for a system of 4×4 sites. Results show that the entropy at low T reaches a maximum near half-filling at the electron density n~1±0.15 in the whole regime of studied U/t.
Wilson's Numerical Renormalization Group Calculation of the Anderson–Holstein Model: Phonon Propagator
Authors: Choi Han-Yong , Park Tae-Ho , Jeon Gun Sang
Published: September 2003

We study the symmetric Anderson–Holstein (AH) model at zero temperature with Wilson's numerical renormalization group (NRG) technique to study the interplay between the electron-electron and electron-phonon interactions. An improved method for calculating the phonon propagator using the NRG technique is presented and applied to the AH model as the onsite Coulomb repulsion U and electron-phonon coupling constant g are varied. As g is increased, the phonon propagator is successively renormalized, and for g≳gco crosses over to the regime where the mode splits into two components, one of which approaches back to the bare frequency and the other develops into a soft mode. The initial renormalization of the phonon mode, as g is increased from 0, can be either positive or negative depending on U and the hybridization Δ.
13C NMR Study of Vortex Dynamics in LuNi2B2C
Authors: Lee K. H. , Kang K. H. , Mean B. J. , Hahn K. S. , Kim S. H. , Hahn K. H. , Kwak C. Y. , Lee Moohee , Cho B. K.
Published: September 2003

13 C pulsed nuclear magnetic resonance (NMR) measurements have been performed on LuNi 2 B 2 C single crystals to investigate the vortex structure and dynamical behavior. The spectrum in the superconducting state significantly broadens by local field inhomogeneity due to a vortex lattice and then evolves to double peaks at low temperature. Both peaks shift toward low magnetic field due to imperfect field penetration whereas linewidth increases because of larger field inhomogeneity. Both the linewidth, reflecting vortex fluctuation, and the transverse relaxation rate 1/T2, probing slow motion of vortices, indicates significant thermal fluctuation of vortices in this low Tc and isotropic superconductor.
Visualization and Control of Vortex Chains in Bi2Sr2CaCu2O8+y
Authors: Tamegai T. , Matsui M. , Tokunaga Y. , Kameda N. , Aoki H. , Tokunaga M.
Published: September 2003

We visualize the vortex chains in Bi 2 Sr 2 CaCu 2 O 8+y by Bitter decorations and differential magneto-optical observations. Bitter decorations on a sample with intentionally introduced field gradient enable us to determine the transition field from the vortex chain state to chain + lattice state. We also demonstrate using magneto-optical technique that we can control the density and the direction of vortex chains by the strength and the direction of the in-plane field. Precise determination of the spacing between vortex chains offers a unique way to quantitatively estimate the anisotropy parameter in highly anisotropic superconductors.
Modified Josephson Relation
Authors: Koláček Jan , Lipavský Pavel
Published: September 2003

For type II superconductors, Josephson has shown that vortices moving with velocity v L create an effective electric field E′= -v L ×B V . By definition the effective electric field is gradient of the electrochemical potential, what is the quantity corresponding to voltage observed with the use of Ohmic contacts. It relates to the true electric field E via the local chemical potential μ as E′=E-∇μ/e. We argue that at low temperatures the true electric field in the bulk can be approximated by a modified Josephson relation E=(v S -v L )×B V , where v S is the condensate velocity.
Bragg–Bose Glass Phase in Vortex States of High-Tc Superconductors with Sparse Columnar Defects
Authors: Nonomura Yoshihiko , Hu Xiao
Published: September 2003

Phase diagram of vortex states of high-T c superconductors with sparse columnar defects is obtained by Monte Carlo simulations. The Bragg–Bose glass phase characterized by hexagonal Bragg peaks and the diverging tilt modulus is observed at low doses for the first time. As the density of defects increases, the melting temperature increases. When the density of defects further increases, the transition to the Bose glass phase occurs. The interstitial liquid is observed between these glass phases and the vortex liquid phase.
Flux Pinning and Current-Induced Vortex Motion at T→0 in Two-Dimensional Vortex Glass
Authors: Morita M. , Okuma S.
Published: September 2003

We investigate the roles of flux pinning on vortex motion at low temperatures (T) in two-dimensional (2D) superconductors using two thin (4 nm) amorphous Mo x Si 1-x films with different pinning strength. We measure the T dependence of resistance R at fields B below the critical field Bc of the 2D superconductor-insulator (SI) transition. For both films we observe the very small T-independent R at T→0 in certain field regions below Bc, suggesting quantum motion of a small number of vortices (dislocations) in the 2D vortex-glass phase in the presence of current. For the film with weaker pinning, the activation energy decreases at T<0.1 K .
Magnetic Superconductors: Thermal Conductivity Studies
Authors: Naugle D. G. , Belevtsev B. I. , Hennings B. D.
Published: September 2003

The coexistence of magnetic and superconducting order in rare-earth-nickel-borocarbides ( RNi 2 B 2 C with R = Tm, Er, Ho, Dy ) and in Ru-2122 rutheno-cuprates ( R = Eu and Gd) has been recently reported. Thermal conductivity measurements for magnetic superconductors from these families are discussed.
Direct Spectroscopic Evidence of Holons in a Quantum Antiferromagnetic Spin-1/2 Chain
Authors: Hasan M. Z. , Chuang Y.-D. , Li Y. , Montano P. , Beno M. , Hussain Z. , Eisaki H. , Uchida S. , Gog T. , Casa D. M.
Published: September 2003

We report charge dynamics of a quantum spin-1/2 chain ( SrCuO 2) over the complete Brillouin zone using the momentum tunability of inelastic X-ray scattering. Excitations at the insulating gap edge are found to be highly dispersive. Observed dispersions are consistent with charge fluctuations involving holons unique to 1-D spin-1/2 quantum systems.
Study of Different Dislocations in YBCO Thin Film
Authors: Wang S. X. , Liu W. L. , Han S. H. , Zhang H.
Published: September 2003

A series thin film sample of YBCO with different value of Tc was studied by high-resolution X-ray diffraction. Two different threading dislocations, the in-plane twist and the out-of-plane tilt, were studied carefully. It is found that the value of Tc is much more sensitive to the substrate normal tilt than to the in-plane twist. Dislocations with different Burgers vectors are suggested to exert different influence on the value of Tc of the YBCO thin film. The screw dislocation in the film is strongly influences the properties of the YBCO.
Self-Energy Analysis of Infrared Conductivity of Normal State MgB2
Authors: Choi Han-Yong , Gimm Tae-Hyoung
Published: September 2003

The self-energy analysis of the frequency-dependent infrared conductivity σ(ω) of MgB 2 in normal state is presented. Experimentally obtained σ(ω) is inverted to yield the self-energy of electrons. From the extracted self-energy, other physical properties such as the effective interaction between electrons can also be computed. We suggest from the self-energy analysis that the small electron-phonon coupling constant of MgB 2 obtained previously can be attributed to an underestimate of the plasma frequency.
Possible Route from Stripes and Other Spatially Structures Many-Electron States to Superconductivity
Authors: Tanaka Akihiro , Hu Xiao
Published: September 2003

We discuss how superconductivity can emerge from (1)quasi–1D spin-Peierls system and (2) stripe-ordered state, with an emphasis on the role played by global antiferromagnetic fluctuations. A parallelism between the two cases based on physical and symmetry considerations is noted.
Non-Universal Pairing Symmetry and Pseudogap Phenomena in Hole- and Electron-Doped Cuprate Superconductors
Authors: Yeh N.-C. , Chen C.-T.
Published: September 2003

Experimental studies of the pairing state of cuprate superconductors reveal asymmetric behaviors of the hole-doped (p-type) and electron-doped (n-type) cuprates. The pairing symmetry, pseudogap phenomenon, low-energy spin excitations and the spatial homogeneity of the superconducting order parameter appear to be non-universal among the cuprates, which may be attributed to competing orders. We propose that the non-universal pseudogap and nano-scale variations in the quasiparticle spectra may be the result of a charge nematic (CN) phase stabilized by disorder in highly two-dimensional (2D) p-type cuprates. The CN phase is accompanied by gapped spin excitations and competes with superconductivity (SC). In contrast, gapless spin excitations may be responsible for the absence of pseudogap and the presence of excess sub-gap spectral weight in the momentum-independent quasiparticle spectra of n-type cuprates. The physical implications and further verifications for these conjectures are discussed.
Pseudogap Induced by the SC Fluctuation: Higher Order Correction Beyond the T-Matrix Approximation
Authors: Yanase Y.
Published: September 2003

We discuss the pseudogap phenomena in High-T c superconductors. The superconducting fluctuation is taken into account as an origin of the pseudogap. Then, the T-matrix approach has been widely used. We report a development along this line. The higher order correction, which is important to capture the effects of the SC fluctuation more precisely, is investigated. It is shown that the vertex correction, which is not included in the self-consistent T-matrix approximation, enhances the pseudogap.
Fluctuating Order Parameter in Doped Cuprate Superconductors
Authors: Loktev V. M. , Pogorelov Yu. G. , Turkowski V. M.
Published: September 2003

We discuss the static fluctuations of the d-wave superconducting order parameter Δ in CuO 2 planes, due to quasiparticle scattering by charged dopants. The analysis of two-particle anomalous Green functions at T = 0 permits to estimate the mean-square fluctuation δ2 = <Δ2> - <Δ>2, averaged in random dopant configurations, to the lowest order in doping level c. Since Δ is found to saturate with growing doping level while δ remains to grow, this can explain the collapse of Tc at overdoping. Also we consider the spatial correlations <Δ(0)Δ(R)> for order parameter in different points of the plane.
Kinetic Study on the Reaction of YBa2Cu3Oy Powder with Water
Authors: Yu F. C. , Lin C. H. , Wang C. M. , Kao H.-C. I.
Published: September 2003

The reaction of superconducting YBa 2 Cu 3 O y powder with water is studied kinetically. The initial rate law is found as [Formula: see text] where [S] o is the initial surface area of the solid, a and b is found to be 0.94 ± 0.02 and 0.318 ± 0.002, respectively. For 100.7 mg powder with a mean radius of 0.0265 mm at pH 7.00 and 298 K, R o is 2.21 × 10-4 mol · min -1. Using a = 1 and b = 0.3, the rate constant, k, obtained at 283, 298 and 313 K is 0.64, 1.84 and 4.91 × 10-3 mol · min -1 · cm -2 · M -0.3, respectively. The activation energy is 50.0 kJ · mol -1 and pre-exponential factor is 1.09 × 106 mol · min -1 · cm -2· M -0.3, as calculated from the Arrhenius equation.
Electronic Properties of Magnetic Superconductor HoNi2B2C Under High Pressure
Authors: Oomi G. , Matsuda N. , Kagayama T. , Cho C. K. , Canfield P. C.
Published: September 2003

The electrical resistivity of single crystalline HoNi 2 B 2 C has been measured at high pressure and magnetic fields. The three anomalies in the magnetoresistance due to metamagnetic transitions are observed both at ambient and high pressures. It is found that the metamagnetic transition fields increase with increasing pressure. The temperature dependence of electrical resistivity is strongly dependent on magnetic field. Non Fermi liquid behavior is observed near the metamagnetic transition fields. But the normal Fermi liquid behavior recovers after completing the phase transition. The Grüneisen parameters are also calculated to examine the stability of electronic state.
Superconducting Properties and Possible Vortex Phase Diagram in a Thick Amorphous MgxB1-xFilm
Authors: Okuma S. , Togo S. , Amemori K.
Published: September 2003

We report on the superconducting properties in a thick amorphous Mg x B 1-x film, which was prepared by coevaporation of pure Mg and B. Measurements of the current-voltage characteristics and the AC complex resistivity in magnetic fields indicate the presence of the vortex-glass transition. Based on the data, we construct the possible phase diagram in the field-temperature plane. We find that there is the large vortex-liquid phase, which persists down to low temperatures.
Transient Dynamics of Pulsed-Current-Biased YBa2Cu3O7-δ Superconducting Photoswitches
Authors: Jukna Artūras , Sobolewski Roman
Published: September 2003

Studies on time-resolved dynamics of optically-thick YBa 2 Cu 3 O 7-δ microbridges biased with supercritical current pulses I of nanosecond duration and synchronously excited by femtosecond optical pulses have been carried out. The switching process is explained by the transient vortex dynamics in the superconducting stripe. It was found that the amplitude of the photoresponse increased linearly with the increase of laser fluence up to < 30 μ J / cm 2 and with the increase of the bias current up to ~ 1.9Ic. Calculations of quantum responsivity showed that our YBa 2 Cu 3 O 7-δ bridges biased with I > Ic could driven by optical pulses of comparatively weak fluence in the range of few tens of mW.
Effects of Quantum and Thermal Fluctuations on the Stability of Mutual Phase-Locking in Long Josephson Junction Stacks
Authors: Kim Ju H.
Published: September 2003

We report the effects of quantum and thermal fluctuations on the stability of phase-locking in one-dimensional long Josephson junction (LJJ) devices, involving high temperature superconductors. Accounting for both the magnetic induction effect and the charging effect, we determine the zero temperature (T = 0) stability phase diagram using renormalization group (RG) analysis. This phase diagram shows that the in-phase mode is stable but some out-of-phase modes are unstable against quantum fluctuations. At finite T, all stable phase-locked modes (at T = 0) are unstable, but its stability is maintained within the decoherence length which decreases inversely with T.
Magnetic Nanorods/Superconductor Hybrids
Authors: Lyuksyutov I. F. , Naugle D. G.
Published: September 2003

We discuss properties of hybrid systems which consist of an array of magnetic nanorods (nanowires) embedded in/or covered by a superconductor film. Such hybrid nanostructures are expected to exhibit fascinating characteristics, which are important from both fundamental and applications point of view.
Spin Polarized Tunneling at the Metal-Insulator Transition
Authors: Teizer W. , Hellman F. , Dynes R. C.
Published: September 2003

We have determined the spin polarized density of states (DOS) of 3-d amorphous Gd x Si 1-x in the quantum critical regime of a tunable Metal-Insulator Transition (MIT). Using a spin polarized BCS DOS we fit the data and extract the spin polarization P.
Valence State of Ru at the Mn Sites in Pr0.5Sr0.5MnO3
Authors: Kim B. H. , Kim J. S. , Kim D. C. , Park Y. W. , Maignan A. , Raveau B
Published: September 2003

Valence state of the doped Ru at the Mn sites in Pr 0.5 Sr 0.5 MnO 3 has been studied using Ru K-edge X-ray absorption near-edge structure (XANES) spectroscopy. In comparison with XANES of reference ruthenates, it is found that the Mn-site doped Ru is dominantly in tetravalent state. This result suggests that the change of charge carrier density by Ru doping is not sufficient to understand drastic enhancement of ferromagnetism observed in the transport properties of Ru-doped Pr 0.5 Sr 0.5 MnO 3. The prime role of Ru in Mn 3+– O – Mn 4+ networks is discussed in terms of the valency effect and the magnetic interactions between doped Ru and Mn ions.
Fractal Image Coding and Magnification Using Invariant Features
Authors: Götting Detlef , Ibenthal Achim , Grigat Rolf-Rainer
Published: September 2003

Fractal image coding has significant potential for the compression of still and moving images and also for scaling up images. The objective of our investigations was twofold. First, compression ratios of factor 60 and more for still images have been achieved, yielding a better quality of the decoded picture material than standard methods like JPEG. Second, image enlargement up to factors of 16 per dimension has been realized by means of fractal zoom, leading to natural and sharp representation of the scaled image content. Quality improvements were achieved due to the introduction of an extended luminance transform. In order to reduce the computational complexity of the encoding process, a new class of simple and suited invariant features is proposed, facilitating the search in the multidimensional space spanned by image domains and affine transforms.
Zooming Using Iterated Function Systems
Authors: Polidori Eric , Dugelay Jean-Luc
Published: September 2003

Iterated Function Systems (I.F.S.) have been recently studied in the field of image coding. In addition to compression, I.F.S. possess some properties of fractals which can be used to sub/oversample an image. In this paper, we review how I.F.S. can be used for image zooming, directly from basic algorithms of still image compression. This study shows that results obtained in such a way do not produce better results than those obtained by using classical spatial interpolators such as the linear one. However, in this paper we also show that modified versions of the basic approach provide a better use of I.F.S.'s coding for zooming.
Geometrical Interpretation of IFS Based Image Coding
Authors: Signes Julien
Published: September 2003

In most classical coding methods, a global optimization is carried out to ensure a given bit-rate or a given quality. In IFS based coding, some heuristic choices are made at each step of the algorithm: No method has, for instance, been proposed to optimize the domain blocks position, or the quantization of the transformations parameters. In this article we first analyze the limits of the existing algorithms, then define a new geometrical interpretation of the classical Jacquin-like method. Through the above analysis, we will answer some of these important questions.
Voice Recognition from Spectrograms: A Wavelet Based Approach
Authors: van de Wouwer G. , Scheunders P. , van Dyck D. , de Bodt M. , Wuyts F. , van de Heyning P. H.
Published: September 2003

The performance of a pattern recognition technique is usually determined by the ability of extracting useful features from the available data so as to effectively characterize and discriminate between patterns. We describe a novel method for feature extraction from speech signals. For this purpose, we generate spectrograms, which are time-frequency representations of the original signal. We show that, by considering this spectrogram as a textured image, a wavelet transform can be applied to generate useful features for recognizing the speech signal. This method is used for the classification of voice dysphonia. Its performance is compared with another technique taken from the literature. A recognition accuracy of 98% is achieved for the classification between normal an dysphonic voices.
A Multiresolution Approximation Theory of Fractal Transform
Authors: Cheng Bing , Zhu Xiaokun
Published: September 2003

In this paper, we show that the fractal transform (FT) constitutes a multiresolution approximation to the square-integrable space L2(Td) for d≥1, where T is the interval (-∞,∞). This provides a theoretical basis for the successful applications of the fractal transform algorithms in signal/image encoding. There are many similarities between fractal-based and wavelet-based approximations. However, they are undamentally different from each other in many aspects. Fractal-based multiresolution approximation to signals/images is by a way of self-increasing model complexity, and wavelet-based multiresolution approximation to signals/images is by a way of decomposing data complexity into single (time domain) components.
Orthonormal Fractal Image Encoding Using Overlapping Blocks
Authors: Bone Donald J.
Published: September 2003

This paper presents a novel approach to partitioned fractal image encoding. In this we seek to address a number of problems with earlier fractal encodings. These are: the artefacts associated with the block based approaches at high compression ratios; accuracy limitations imposed by the constraint that only one domain block is used to construct each range block; convergence problems which have required that constraints be imposed on the scaling coefficients to ensure that the mapping functions are contractive. These problems are addressed with a technique based on an orthonormal basis expansion using overlapping blocks, where the basis is partly fixed and partly derived from the image in such a way as to take advantage of local interscale self similarity. A fractal image codec based on this technique, which we call the Lapped Orthogonal Fractal Transform (LOFT), is described and tested, and the results are compared to those of other codecs.
Multiresolution Analysis of Fractal Image Compression
Authors: Caso Gregory , Kuo C.-C. Jay
Published: September 2003

In this research, we perform a multiresolution analysis of the mappings used in fractal image compression. We derive the transform-domain structure of the mappings and demonstrate a close connection between fractal image compression and wavelet transform coding using the Haar basis. We show that under certain conditions, the mappings correspond to a hierarchy of affine mappings between the subbands of the transformed image. Our analysis provides new insights into the mechanism underlying fractal image compression, leads to a new non-iterative transform-domain decoding algorithm, and suggests a new transform-domain encoding method with extensions to wavelets other than the Haar transform.
Acceleration of Fractal Image Compression by Fast Nearest-Neighbor Search
Authors: Ciepliński Leszek , Jȩdrzejek Czesław , Major Tomasz
Published: September 2003

In this paper we investigate the effect of fast nearest neighbor search method on acceleration of fractal image compression. First we follow the Saupe1 encoding step of fractal image compression that uses the multi-dimensional nearest neighbor search in a projected space. Then we investigate performance of a method for finding the nearest vector called partial distortion elimination. We also propose some supplementary accelerating concepts. For all inspected methods the impact of the tolerance criterion for mean square error of block matching is examined.
Estimation of qth-Order Fractal Dimensions
Authors: Fioravanti Stefano , Giusto Daniele D.
Published: September 2003

The paper deals with the theory of qth-order fractal dimensions and its application to texture analysis. In particular, the state-of-the-art regarding the fractal dimension estimation for characterizing textures is presented. After, the insufficiency of the single fractal dimension is proven and the qth order fractal dimensions are introduced to overcome such drawback. The multifractality spectrum function D(q) is described, a novel algorithm for estimating such dimensions is then proposed, and its use in digital-image processing is addressed. Results on real SAR image textures are reported and discussed.
Harmful Effects of Increased LDLR Expression in Mice With Human
APOE*4
But Not
APOE*3
Authors: Malloy Sudi I. , Altenburg Michael K. , Knouff Christopher , Lanningham-Foster Lorraine , Parks John S. , Maeda Nobuyo
Published: September 2003

Objective—

Increased expression of the low-density lipoprotein receptor (LDLR) is generally considered beneficial for reducing plasma cholesterol and atherosclerosis, and its downregulation has been thought to explain the association between apolipoprotein (apo) E4 and increased risk of coronary heart disease in humans.

Methods and Results—

Contrary to this hypothesis, doubling
Ldlr
expression caused severe atherosclerosis with marked accumulation of cholesterol-rich, apoE-poor remnants in mice with human apoE4, but not apoE3, when the animals were fed a Western-type diet. The increased
Ldlr
expression enhanced in vivo clearance of exogenously introduced remnants in mice with apoE4 only when the remnants were already enriched with apoE4. The rates of nascent lipoprotein production were the same. The adverse effects of increased LDLR suggest a possibility that the receptor can trap apoE4, reducing its availability for the transfer to nascent lipoproteins needed for their rapid clearance, thereby increasing the production of apoE-poor remnants that are slowly cleared. The lower affinity for the LDLR of apoE3 compared with apoE4 could then explain why increased receptor expression had no adverse effects with apoE3.

Conclusions—

Our results emphasize the occurrence of important and unexpected interactions between
APOE
genotype,
LDLR
expression, and diet.
Fractalkine in Vascular Biology
Authors: Umehara Hisanori , Bloom Eda T. , Okazaki Toshiro , Nagano Yutaka , Yoshie Osamu , Imai Toshio
Published: September 2003

Fractalkine (now also called CX3CL1) is a unique chemokine that functions not only as a chemoattractant but also as an adhesion molecule and is expressed on endothelial cells activated by proinflammatory cytokines, such as interferon-γ and tumor necrosis factor-α. The fractalkine receptor, CX3CR1, is expressed on cytotoxic effector lymphocytes, including natural killer (NK) cells and cytotoxic T lymphocytes, which contain high levels of intracellular perforin and granzyme B, and on macrophages. Soluble fractalkine causes migration of NK cells, cytotoxic T lymphocytes, and macrophages, whereas the membrane-bound form captures and enhances the subsequent migration of these cells in response to secondary stimulation with other chemokines. Furthermore, stimulation through membrane-bound fractalkine activates NK cells, leading to increased cytotoxicity and interferon-γ production. Recently, accumulating evidence has shown that fractalkine is involved in the pathogenesis of various clinical disease states or processes, such as atherosclerosis, glomerulonephritis, cardiac allograft rejection, and rheumatoid arthritis. In addition, polymorphisms in CX3CR1, which reduce its binding activity to fractalkine, have been reported to increase the risk of HIV disease and to reduce the risk of coronary artery disease. This review will examine new concepts underlying fractalkine-mediated leukocyte migration and tissue damage, focusing primarily on the pathophysiological roles of fractalkine in various clinical conditions, especially in atherosclerosis and vascular injury.
Visceral Adiposity and the Prevalence of Hypertension in Japanese Americans
Authors: Hayashi Tomoshige , Boyko Edward J. , Leonetti Donna L. , McNeely Marguerite J. , Newell-Morris Laura , Kahn Steven E. , Fujimoto Wilfred Y.
Published: September 2003

Background—

Visceral adiposity is generally considered to play a key role in the metabolic syndrome, including hypertension. The purpose of this study was to evaluate cross-sectionally whether visceral adiposity is associated with prevalence of hypertension independent of other adipose depots and fasting plasma insulin.

Methods and Results—

Study subjects included 563 Japanese Americans with normal or impaired glucose tolerance or diabetes but not taking oral hypoglycemic medication or insulin at entry. Variables included plasma glucose and insulin measured after an overnight fast and during an oral glucose tolerance test, and abdominal, thoracic, and thigh fat areas by CT. Total fat area (TFA) was calculated as the sum of these fat areas. Hypertension was defined as having a systolic blood pressure ≥140 mm Hg, having a diastolic blood pressure ≥90 mm Hg, or taking antihypertensive medications. Intra-abdominal fat area (IAFA) was associated with a higher prevalence of hypertension. Adjusted odds ratio of hypertension by IAFA was 1.68 for a 1-SD increase (95% CI, 1.20 to 2.37) after adjusting for age, sex, fasting plasma insulin, a nonlinear transformation of 2-hour plasma glucose, and TFA. IAFA remained a significant predictor of prevalence of hypertension even after adjustment for total subcutaneous fat area, abdominal subcutaneous fat area, body mass index, or waist circumference, but no measure of regional or total adiposity was associated with the odds of prevalence of hypertension in models that contained IAFA.

Conclusions—

Greater visceral adiposity increases the odds of hypertension in Japanese Americans independent of other adipose depots and fasting plasma insulin.
Disease-Specific Health Status After Stent-Assisted Percutaneous Coronary Intervention and Coronary Artery Bypass Surgery
Authors: Zhang Zefeng , Mahoney Elizabeth M. , Stables Rodney H. , Booth Jean , Nugara Fiona , Spertus John A. , Weintraub William S.
Published: September 2003

Background—

Functional status and quality of life are important outcomes in the evaluation of revascularization approaches for symptomatic coronary artery disease. Few data are available regarding the comparative improvement in disease-specific health status after CABG versus percutaneous coronary intervention (PCI) in the era of coronary stenting.

Methods and Results—

Cardiac-specific health status was evaluated at baseline and at 6 and 12 months after intervention with the Seattle Angina Questionnaire (SAQ) in patients randomized to stent-assisted PCI (n=488) versus CABG (n=500) in the Stent or Surgery trial. Scores for physical limitation, angina frequency, and quality of life improved significantly for both treatment groups at 6 months (range of improvement from 13.6 to 34.7 points) and 12 months (14.3 to 38.2 points; all
P
<0.001). CABG patients had greater improvement than those assigned to PCI, although the magnitude of the difference decreased over time (difference at 6 months, 4.03 to 6.48 points; 12 months, 2.05 to 2.93 points). A component of this reduction is accounted for by PCI-arm patients who required repeat intervention. Differences between treatment groups were greatest for the 6-month angina frequency scores (difference=6.48 points; 95% CI 3.96 to 8.99). Overall, treatment satisfaction was high and did not differ significantly between groups.

Conclusions—

Both CABG and stent-assisted PCI dramatically improved cardiac-related health status in patients with multivessel disease at 6- and 12-month follow-up. During the first postprocedure year, patients’ angina burden and physical limitations were alleviated to a greater extent with CABG.