bluuebunny/crossref_metadata_2025 huggingface dataset:
In Situ Activation of the Quorum-Sensing Transcription Factor TraR by Cognate and Noncognate Acyl-Homoserine Lactone Ligands: Kinetics and Consequences
Authors: Luo Zhao-Qing , Su Shengchang , Farrand Stephen K.
Published: September 2003

Conjugal transfer of Ti plasmids ofAgrobacterium tumefaciensis controlled by a quorum-sensing system composed of the transcriptional activator TraR and its acyl-homoserine lactone quormoneN-(3-oxo-octanoyl)-l-homoserine lactone (3-oxo-C8-HSL). The population density dependence of quorum-sensing systems can often be circumvented by addition of the quormone to cultures at low cell numbers. However, the quorum-dependent activation of Ti plasmid conjugal transfer exhibited a lag of almost 8 h when the quormone was added to donor cells at low population densities (Piper and Farrand, J. Bacteriol. 182:1080-1088, 2000). As measured by activation of a TraR-dependenttraG::lacZreporter fusion, TraR in cells exposed to the cognate signal for 5 min showed detectable activity, while exposure for 15 min resulted in full activity. Thus, the lag in activation is not due to some intrinsic property of TraR. Cells exposed to the agonistic analogN-(3-oxo-hexanoyl)-l-homoserine lactone (3-oxo-C6-HSL) exhibited similar induction kinetics. However, activation of the reporter in cells exposed to the poorly effective alkanoyl acyl-HSLN-hexanoyl-l-homoserine lactone (C6-HSL) required the continued presence of the signal. As measured by an in vivo repressor assay, TraR activated by 3-oxo-C6-HSL or by 3-oxo-C8-HSL remained active for as long as 8 h after removal of exogenous signal. However, TraR activated by the alkanoyl quormone C6-HSL rapidly lost activity following removal of the signal. In quormone retention assays, which measure signal binding by TraR, cells grown with either of the two 3-oxo-acyl-HSL quormones retained the ligand after washing, while cells grown with C6-HSL lost the alkanoyl-HSL concomitant with the rapid loss of TraR activity. We conclude that TraR rapidly binds its quormone and that, once bound, the cognate signal and its close homologs are tightly retained. Moreover, in the absence of other regulatory factors, activated TraR remains functional after removal of the signal. On the other hand, poorly active signals are not tightly bound, and their removal by washing leads to rapid loss of TraR activity.
Secretion of LamB-LacZ by the Signal Recognition Particle Pathway of
Escherichia coli
Authors: Bowers Christina Wilson , Lau Fion , Silhavy Thomas J.
Published: September 2003

LamB-LacZ fusion proteins have classically been used in studies of the general secretion pathway of
Escherichia coli
. Here we describe how increasing signal sequence hydrophobicity routes LamB-LacZ Hyb42-1 to the signal recognition particle (SRP) pathway. Secretion of this hydrophobic fusion variant (H*LamB-LacZ) was reduced in the absence of fully functional Ffh and Ffs, and the translocator jamming caused by Hyb42-1 was prevented by efficient delivery of the fusion to the periplasm. Finally, we found that in the absence of the ribosome-associated chaperone, trigger factor (Tig), LamB-LacZ localized to the periplasm in a SecA-dependent, SRP-independent fashion. Collectively, our results provide compelling in vivo evidence that there is an SRP-dependent cotranslational targeting mechanism in
E. coli
and argue against a role for trigger factor in pathway discrimination.
Listeria monocytogenesσBRegulates Stress Response and Virulence Functions
Authors: Kazmierczak Mark J. , Mithoe Sharon C. , Boor Kathryn J. , Wiedmann Martin
Published: September 2003

While the stress-responsive alternative sigma factor σBhas been identified in different species ofBacillus,Listeria, andStaphylococcus, theσBregulon has been extensively characterized only inB. subtilis.We combined biocomputing and microarray-based strategies to identify σB-dependent genes in the facultative intracellular pathogenListeria monocytogenes. Hidden Markov model (HMM)-based searches identified 170 candidateσB-dependent promoter sequences in the strain EGD-e genome sequence. These data were used to develop a specialized, 208-gene microarray, which included 166 genes downstream of HMM-predicted σB-dependent promoters as well as selected virulence and stress response genes. RNA for the microarray experiments was isolated from both wild-type and ΔsigBnull mutantL. monocytogenescells grown to stationary phase or exposed to osmotic stress (0.5 M KCl). Microarray analyses identified a total of 55 genes with statistically significantσB-dependent expression under the conditions used in these experiments, with at least 1.5-fold-higher expression in the wild type over thesigBmutant under either stress condition (51 genes showed at least 2.0-fold-higher expression in the wild type). Of the 55 genes exhibiting σB-dependent expression, 54 were preceded by a sequence resembling the σBpromoter consensus sequence. Rapid amplification of cDNA ends-PCR was used to confirm the σB-dependent nature of a subset of eight selected promoter regions. Notably, theσB-dependentL. monocytogenesgenes identified through this HMM/microarray strategy included both stress response genes (e.g.,gadB,ctc, and the glutathione reductase genelmo1433) and virulence genes (e.g.,inlA,inlB, andbsh). Our data demonstrate that, in addition to regulating expression of genes important for survival under environmental stress conditions, σBalso contributes to regulation of virulence gene expression inL. monocytogenes.These findings strongly suggest thatσBcontributes toL. monocytogenesgene expression during infection.
In Vivo Evidence for TonB Dimerization
Authors: Sauter Annette , Howard S. Peter , Braun Volkmar
Published: September 2003

TonB, in complex with ExbB and ExbD, is required for the energy-dependent transport of ferric siderophores across the outer membrane ofEscherichia coli, the killing of cells by group B colicins, and infection by phages T1 and φ80. To gain insights into the protein complex, TonB dimerization was studied by constructing hybrid proteins from complete TonB (containing amino acids 1 to 239) [TonB(1-239)] and the cytoplasmic fragment of ToxR which, when dimerized, activates the transcription of the cholera toxin genectx. ToxR(1-182)-TonB(1-239) activated the transcription oflacZunder the control of thectxpromoter (Pctx::lacZ). Replacement of the TonB transmembrane region by the ToxR transmembrane region resulted in the hybrid proteins ToxR(1-210)-TonB(33-239) and ToxR(1-210)-TonB(164-239), of which only the latter activated Pctx::lacZtranscription. Dimer formation was reduced but not abolished in a mutant lacking ExbB and ExbD, suggesting that these complex components may influence dimerization but are not strictly required and that the N-terminal cytoplasmic membrane anchor and the C-terminal region are important for dimer formation. The periplasmic TonB fragment, TonB(33-239), inhibits ferrichrome and ferric citrate transport and induction of the ferric citrate transport system. This competition provided a means to positively screen for TonB(33-239) mutants which displayed no inhibition. Single point mutations of inactive fragments selected in this manner were introduced into complete TonB, and the phenotypes of the TonB mutant strains were determined. The mutations located in the C-terminal half of TonB, three of which (Y163C, V188E, and R204C) were obtained separately by site-directed mutagenesis, as was the isolated F230V mutation, were studied in more detail. They displayed different activity levels for various TonB-dependent functions, suggesting function-related specificities which reflect differences in the interactions of TonB with various transporters and receptors.
Temperature-Sensitive Growth and Decreased Thermotolerance Associated with
relA
Mutations in
Escherichia coli
Authors: Yang Xiaoming , Ishiguro Edward E.
Published: September 2003

The
relA
gene of
Escherichia coli
encodes guanosine 3′,5′-bispyrophosphate (ppGpp) synthetase I, a ribosome-associated enzyme that is activated during amino acid starvation. The stringent response is thought to be mediated by ppGpp. Mutations in
relA
are known to result in pleiotropic phenotypes. We now report that three different
relA
mutant alleles,
relA1
,
relA2
, and
relA251
::
kan
, conferred temperature-sensitive phenotypes, as demonstrated by reduced plating efficiencies on nutrient agar (Difco) or on Davis minimal agar (Difco) at temperatures above 41°C. The
relA
-mediated temperature sensitivity was osmoremedial and could be completely suppressed, for example, by the addition of NaCl to the medium at a concentration of 0.3 M. The temperature sensitivities of the
relA
mutants were associated with decreased thermotolerance; e.g.,
relA
mutants lost viability at 42°C, a temperature that is normally nonlethal. The
spoT
gene encodes a bifunctional enzyme possessing ppGpp synthetase and ppGpp pyrophosphohydrolase activities. The introduction of the
spoT207
::
cat
allele into a strain bearing the
relA251
::
kan
mutation completely abolished ppGpp synthesis. This ppGpp null mutant was even more temperature sensitive than the strain carrying the
relA251
::
kan
mutation alone. The
relA
-mediated thermosensitivity was suppressed by certain mutant alleles of
rpoB
(encoding the β subunit of RNA polymerase) and
spoT
that have been previously reported to suppress other phenotypic characteristics conferred by
relA
mutations. Collectively, these results suggest that ppGpp may be required in some way for the expression of genes involved in thermotolerance.
Control of Enzyme II
scr
and Sucrose-6-Phosphate Hydrolase Activities in
Streptococcus mutans
by Transcriptional Repressor ScrR Binding to the
cis
-Active Determinants of the
scr
Regulon
Authors: Wang Bing , Kuramitsu Howard K.
Published: September 2003

In
Streptococcus mutans
, enzyme II
scr
and sucrose-6-phosphate hydrolase are two important enzymes in the transport and metabolism of dietary sucrose. The
scr
regulon of
S. mutans
is composed of three genes,
scrA
and
scrB
, which code for enzyme II
scr
and sucrose-6-phosphate hydrolase, respectively, and
scrR
, which codes for a GalR-LacI-type transcription regulator. It was previously shown that expression of both
scrA
and
scrB
is similarly induced by sucrose. Mutation in the
scrR
gene resulted in increased expression of
scrB
relative to that in the wild-type strain. In this study, we employed DNA mobility shift and DNase I protection assays with a purified ScrR-histidine tag fusion protein to examine the DNA binding properties of ScrR to the promoter regions of the
scrA
and
scrB
genes. The results showed that ScrR bound specifically to the promoter regions of both
scrA
and
scrB
. Two regions with high affinity for ScrR in the promoter sequences of the
scrA
and
scrB
genes were identified by DNase I protection assays. One,
O
C
, which includes a 20-bp imperfect inverted-repeat sequence, is located between the two promoters, and the other,
O
B
, is located within the
scrB
promoter region containing a 37-bp imperfect direct-repeat sequence. Mutations of
O
B
and
O
C
resulted in constitutive transcription and expression of both the
scrA
and
scrB
genes. Our results indicated that
S. mutans
coordinates the activities of enzyme II
scr
and sucrose-6-phosphate hydrolase by transcriptional repressor ScrR binding to the promoter regions of the
scr
regulon.
Sigma 32-Dependent Promoter Activity In Vivo: Sequence Determinants of the
groE
Promoter
Authors: Wang Yang , deHaseth Pieter L.
Published: September 2003

The
Escherichia coli
transcription factor sigma 32 binds to core RNA polymerase to form the holoenzyme responsible for transcription initiation at heat shock promoters, utilized upon exposure of the cell to higher temperatures. We have developed two ways to assay sigma 32-dependent RNA synthesis in
E. coli
. The plasmid-borne reporter gene for both is
lacZ
(β-galactosidase), driven by the
groE
promoter. In one application, the cells are exposed to a temperature of 42°C in order to induce accumulation of endogenous sigma 32. The other involves isopropylthiogalactopyranoside (IPTG)-induced synthesis of sigma 32 at 30°C from a gene contained on a second plasmid. The latter employs DnaK
−
cells, which additionally contained a second mutation, inactivating the endogenous sigma 32 gene (Bukau and Walker, EMBO J. 9:4027-4036, 1990). These assays were used to delineate the sequences CTTGA (−37 to −33) and GNCCCCATNT (−18 to −9) as important for sigma 32 promoter activity. At each of the specified base pairs, substitutions were found which reduced promoter activity by greater than 75%. Activity was also dependent upon the number of base pairs separating the two regions.
Regulation of
fur
Expression by RpoS and Fur in
Vibrio vulnificus
Authors: Lee Hyun-Jung , Park Kyung-Je , Lee Ah Young , Park Sung Goo , Park Byoung Chul , Lee Kyu-Ho , Park Soon-Jung
Published: September 2003

In a proteomic analysis of
rpoS
-deficient
Vibrio vulnificus
versus the wild type, one of the down-regulated proteins in the
rpoS
mutant strain was identified as a Fur protein, a ferric uptake regulator. The expression of a
fur
::
luxAB
fusion was significantly influenced by sigma factor S, the
rpoS
gene product, and positively regulated by Fur under iron-limited conditions.
Global Regulation of the
Salmonella enterica
Serovar Typhimurium Major Porin, OmpD
Authors: Santiviago Carlos A. , Toro Cecilia S. , Hidalgo Alejandro A. , Youderian Philip , Mora Guido C.
Published: September 2003

The OmpD porin is the most abundant outer membrane protein in
Salmonella enterica
serovar Typhimurium and represents about 1% of total cell protein. Unlike the case with the less abundant OmpC and OmpF porins, the stoichiometry of OmpD in the outer membrane does not change in response to changes in osmolarity. The abundance of OmpD increases in response to anaerobiosis and decreases in response to low pH, conditions encountered by serovar Typhimurium during the infection of its murine host. By constructing an operon fusion of the
lacZY
genes with the
ompD
promoter, we show that the abundance of OmpD in the outer membrane is regulated primarily at the level of transcription and is subject to catabolite repression. In response to anaerobiosis, the abundance of OmpD in the outer membrane also appears to be controlled posttranscriptionally by a function dependent on Fnr.
Formation of a Bound State in the Presence of Repulsive Interaction
Authors: Fan J. D. , Malozovsky Y. M.
Published: September 2003

We have examined the effective interaction of two fermions in terms of the T-matrix and shown that there are two different series of ladder diagrams in describing the effective interaction: (1) the exchange ladder diagrams giving rise to the T-matrix for the triplet state with poles for attractive interaction and (2) the Hartree ladder diagrams describing the multiple scattering on the Hartree potential and producing the T-matrix for the singlet state with poles for repulsive interaction. It is verified that a bound state of two fermions in the singlet state exists only in the presence of repulsive interaction between them. We further argue that the potential in the Schrodinger equation should be spin-dependent to describe both the singlet and triplet states.
Binding from Repulsive Interaction in a Degenerate Fermi Gas
Authors: Malozovsky Y. M. , Fan J. D.
Published: September 2003

The binding of two fermions in a degenerate Fermi gas is examined in terms of the T-matrix. We deal with effective T-matrix of two fermions in the degenerate Fermi gas in terms of the scattering amplitude. This makes approach valid for the retarded as well as non-retarded interactions. We show that for the interaction of a pair of fermions in a quiescent Fermi sea there are two different series of the ladder diagrams-Exchange and Hartree diagrams, describing a bound state and producing two different T-scattering matrices. The exchange series of the ladder diagrams corresponds to the T-matrix in the triplet-state. This T-matrix contains the pole solution corresponding to the bound state for the attractive interaction only. In contrast, the Hartree diagrams lead to the T-matrix of a pair of fermions in the singlet-state, which have a pole solution corresponding to the bound state of a pair of fermions for the repulsive interaction. Thus, we are led to assert that the bound state of a pair of fermions in the singlet-state in the quiescent Fermi sea can form for the repulsive interaction only and there is no bound state in the singlet-state from the attractive interaction.
Generalized BCS-Bose Crossover Picture of Superconductivity
Authors: Batle J. , Casas M. , de Llano M. , Fortes M. , Sevilla F. J.
Published: September 2003

A recent unification of the BCS theory with that of the Bose–Einstein condensation (BEC) through a "complete" boson-fermion model is discussed as a generalization of the "BCS-Bose crossover" picture of superconductivity. Good first-principles Tc predictions in 2D are calculated with no adjustable parameters for the so-called "exotic" cuprate superconductors of the "Uemura plot", without abandoning the phonon interaction mechanism. The only condition is that one depart moderately from the perfect electron-/hole-Cooper-pair symmetry to which BCS (as well as the "crossover") theory are restricted by construction.
A KT Phase of Interlayer Josephson Vortex Systems in High-Tc Superconductors
Authors: Hu Xiao , Tachiki Masashi
Published: September 2003

A novel Kosterlitz–Thouless phase and continuous melting transitions are proposed for Josephson vortex systems induced in layered superconductors by strong parallel magnetic fields. The mechanism of the phenomenon is revealed and the phase diagram with a multicritical point is presented.
Plausiblity of Antiferromagnetism in and near RBCO Vortex Cores: An ME-μSR Analysis
Authors: Boekema C. , Tien Y. , Hughes L. , Ruiz E. J. , Cavanaugh S. X.
Published: September 2003

Maximum-Entropy (ME) analysis is applied to muon-spin-rotation (μSR) data of RBa 2 Cu 3 O y (RBCO; R = Ho , Eu) vortex states. Our focus is on the prospect of antiferromagnetism (AF) associated with the vortex core. The ME transforms are fitted by two μSR signals: the vortex signal and the grain-boundary (GB) signal. Below Tc, the GB signals are well fitted by Gaussians for both EuBCO (Tc = 94 K ) and underdoped HoBCO (Tc = 66 K ). Below 0.5Tc, EuBCO and HoBCO vortex signals are best fitted using Lorentzians, instead of expected Gaussians. An estimate for an effective Neél temperature of an AF vortex core is about 30 K. Our AF-core search results for RBCO vortex states are discussed considering a magnetic origin of cuprate superconductivity.
Magnet/Superconductor Nanostructures
Authors: Lyuksyutov I. F. , Naugle D. G.
Published: September 2003

In Magnet/Superconductor Nanostructures it is possible to control magnetism and conductivity at the nanoscale by using localized magnetic fields from structural (dots, stripes, wires) and topological (vortices's, skyrmions and domain walls) textures in magnet and/or superconductor subsystems of the hybrid material. We review experimental and theoretical results in the field of nanostructured magnet/superconductor systems.
Negative Isotope Effect in Superconductivity from Non-Retarded Repulsive Interaction
Authors: Fan J. D. , Malozovsky Y. M.
Published: September 2003

We have examined the isotope effect in superconductivity due to the repulsive interaction. The equation for the temperature of transition to the superconducting state is derived in terms of the temperature Bethe–Salpeter equation for a bound state of two fermions in the spin-singlet state. The effective interaction in the equation for Tc is written in terms of the effective scattering amplitude, thus providing the validity of the equation for the non-retarded interaction. The superconducting phase transition occurs due to non-retarded repulsive inter-particle interaction. In contrast, additional retarded electron-phonon interaction contributes to the pair-breaking effect. We have shown that the isotope effect coefficient α is negative in this case.
Superconducting Fluctuations Above TC and the Uncertainty Principle: How Small may the Coherence Length be?
Authors: Vidal F. , Ramallo M. V. , Mosqueira J. , Carballeira C.
Published: September 2003

We summarize here some of our recent results on the superconducting fluctuation effects above TC in different low- and high-TC superconductors, at high reduced-temperatures and magnetic fields. These results confirm our proposal that the collective behaviour of the fluctuating Cooper pairs in the short-wavelength fluctuation regime is dominated by the uncertainty principle, which imposes a limit to the shrinkage of the superconducting wave function when T increases well above TC or H becomes of the order of Hc2(0), the upper critical magnetic field amplitude extrapolated to T = 0 K .
Transport Properties and Upper Critical Field of Single Crystal Non-Magnetic LuxY1-xNi2B2C and Magnetic LuxGd1-xNi2B2C
Authors: Rathnayaka K. D. D. , Naugle D. G. , Dumar A. C. , Anatska M. P. , Canfield P. C.
Published: September 2003

The in-plane resistance of single crystal non-magnetic Lu x Y 1-x Ni 2 B 2 C and magnetic Lu x Gd 1-x Ni 2 B 2 C samples as a function of the magnitude and direction of the magnetic field and temperature have been measured. The superconducting upper critical field Hc2(T) is anisotropic for both. A positive curvature in Hc2(T) near Tc(x) is clearly observed only for the non-magnetic impurity. At low temperature Hc2(T) for the sample with magnetic impurities is strongly reduced. Thermopower, thermal conductivity and resistivity as a function of temperature are also reported for Lu x Gd 1-x Ni 2 B 2 C .
Synthesis and Characterization of Double Perovskites Sr2FeMO6 (M = Mo, W)
Authors: Chan T. S. , Liu R. S. , Guo G. Y. , Huang C. Y.
Published: September 2003

We have investigated the magnetic and magnetotransport properties of monophasic double perovskites Sr 2 FeMO 6( M = Mo , W ). Magnetic measurements indicate that SFMO is a ferromagnet and SFWO is an antiferromagnet with TN = 35 K at H = 5 T . Large magnetoresistance ratio (MR) of ~ 22% (H = 3 T ) at room temperature (RT) was observed in the SFWO compound. However, the SFMO compound did not show any significant MR even at high fields and RT (MR~1%; H = 3 T and 300 K). The changes observed by physical measurements are supported by band structure calculations to explain the interaction between the 3d (Fe) , 4d (Mo) and 5d (W) orbitals of transition metal ions and oxygen ions.
Particle-Hole Pair Excitations in a Quasi-Zero-Dimensional Mott Insulator
Authors: Hasan M. Z. , Li Y. , Chuang Y.-D. , Montano P. A. , Hussain Z. , Eisaki H. , Motoyama N. , Uchida S.
Published: September 2003

We investigate momentum dependence of charge excitations across the effective Mott gap in a quasi-zero dimensional (q-ZD) model cuprate Li 2 CuO 2, using high resolution inelastic X-ray scattering by working near a resonance. In comparison to quasi-one dimensional (q-1D) systems such as Sr 2 CuO 3 or SrCuO 2, momentum dependence is much weaker in Li 2 CuO 2. Particle-hole pair excitations at the gap edge in these low dimensional Mott systems are found to be strongly dependent on the effective dimensionality (or topology) of the lattice and the strength of electron–electron interaction.
Point Contact Spectroscopy on RuSr2GdCu2O8
Authors: Giubileo F. , Bobba F. , Gombos M. , Uthayakumar S. , Vecchione A. , Akimenko A. I. , Cucolo A. M.
Published: September 2003

We report the first tunneling experiments performed by means of point-contact technique on the ruthenate-cuprate RuSr 2 GdCu 2 O 8 (Ru1212) compound. Spectroscopy has been carried out on polycrystals characterized by superconducting transition at TC(ρ = 0) ≃ 26 K and magnetic transition at TM ≃ 133 K . A chemically etched copper tip has been used like normal counterelectrode. Very stable N-S contacts (N = Cu, S = Ru1212) have been obtained, clearly showing dI/dV spectra in the Andreev reflection regime. Temperature behaviour of the spectra has been measured in the range 4.2 K ≤ T ≤ 30 K . The dI/dV spectra seem to indicate important depairing effects in the Ru1212 and we discuss possible explanation.
Magnetism of Multi-Layer HgBa2Ca4Cu5Oy Superconductor Studied by μSR Measurements
Authors: Tokiwa K. , Okumoto H. , Imamura T. , Mikusu S. , Yuasa K. , Higemoto W. , Nishiyama K. , Iyo A. , Tanaka Y. , Watanabe T.
Published: September 2003

μSR measurements were performed on HgBa 2 Ca 4 Cu 5 O y (Hg-1245) samples with Tc of 108 K. Rapid enhancement of muon-spin depolarization rate and losses of initial asymmetry were found in ZF-μSR time spectra below 60 K. These indicate enhancement of magnetic correlation between Cu spins. Moreover, muons precession signals were observed below 45 K, indicating that the Hg-1245 samples were in long range ordered state. These results reveal that antiferromagnetic order is developing in the Hg-1245 superconductor below Tc.
Numerical Simulation of Explosive Consolidation of Superconducting Bulk Components
Authors: Mamalis A. G. , Vottea I. N. , Manolakos D. E. , Szalay A. , Kladas A.
Published: September 2003

The explosive compaction technique has been used for manufacturing bulk superconducting components, e.g. three dimensional plates and axisymmetric billets, rods, discs and tubes, with high density and good electrical and magnetic characteristics. The high pressures and temperatures developed in a very short time result in sintering and in fracturing of the original grains, inducing primarily line defects that would provide flux pinning centers in Type II superconductors. Densified superconducting ceramic YBCO bulk components of various geometries were produced by this dynamic technique and the whole process was simulated by the explicit finite element code LS-DYNA3D. In this paper, experimental and numerical results of the fabricated superconducting bulks are reported and discussed. Applications are also briefly outlined.
Josephson Effect in Pb/I/NbSe2 Scanning Tunneling Microscope Junctions
Authors: Naaman O. , Dynes R. C. , Bucher E.
Published: September 2003

We have developed a method for the reproducible fabrication of superconducting scanning tunneling microscope (STM) tips. We use these tips to form superconductor/insulator/superconductor tunnel junctions with the STM tip as one of the electrodes. We show that such junctions exhibit fluctuation dominated Josephson effects, and describe how the Josephson product IcRN can be inferred from the junctions' tunneling characteristics in this regime. This is first demonstrated for tunneling into Pb films, and then applied in studies of single crystals of NbSe 2. We find that in NbSe 2, IcRN is lower than expected, which could be attributed to the interplay between superconductivity and the coexisting charge density wave in this material.
Impurity State of Nickel in the Vortex Core of d-Wave Superconductor
Authors: Han Qiang , Xia Tian-Long , Wang Z. D. , Li X.-G.
Published: September 2003

Using Anderson impurity model to describe the magnetic moments of Ni doped in high-T c d-wave cuprates, the impurity state of Ni at the vortex core is studied. We find that the existence of the impurity resonance is insensitive to the vortex core although the resonant energy is sightly changed, which might help to examine the dominant mechanism of experimentally observed impurity state.
Tunneling Studies of Multilayered Superconducting Cuprate (Cu,C)Ba2Ca3Cu4O12+δ
Authors: Miyakawa N. , Tokiwa K. , Mikusu S. , Zasadzinski J. F. , Ozyuzer L. , Ishihara T. , Kaneko T. , Watanabe T. , Gray K. E.
Published: September 2003

Point contact tunneling data are reported in a multilayered high-T c cuprate (Cu,C)Ba 2 Ca 3 Cu 4 O 12+δ with T c = 117 K . The tunneling spectra in the superconducting state (T ≪ T c ) display spectral features such as well-defined superconducting gap peak at ±Δ as well as dip-hump structures beyond the peaks. In some cases, the spectra with two-gaps have been observed, indicating the coexistence of two inequivalent superconducting layers. The statistical distribution of superconducting gap magnitude suggests two distinct kinds of superconducting gaps that may originate from two inequivalent CuO 2 planes, a characteristics of multilayered cuprates with n ≥ 3.
Decoupling of the Magnetic State in RuSr2Eu1.5Ce0.5Cu2O10-δ
Authors: Felner I. , Galstyan E.
Published: September 2003

We have studied the effect of Zn substitution for Cu, on the superconducting (SC) and magnetic properties of RuSr 2 Eu 2-x Ce x( Cu 1-x Zn x)2 O 10 (Ru-1222) for x = 0, 0.01 and 0.025. Similar to all other Zn doped HTSC materials, Zn reduces TC, from TC = 38 to 26 K for x = 0 and 0.01 respectively. The system with x = 0.025 is not SC down to 4.2 K. On the other hand, the magnetic state of the Ru sublattice is not significantly affected by the presence or absence the SC State. Thus, the two states are practically decoupled. The wide ferromagnetic hysteresis loops which open at 5 K close themselves at elevated temperatures and the remanent magnetizations (Mrem) and the coercive fields (HC) become zero around Tirr = 80 K . Surprisingly, at Tirr < T < TM a reappearance of the Mrem and HC (with a peak at 120 K) is observed for all three samples studied. We argue that the Ru-1222 system becomes (i) Anti-ferromagnetically (AFM) ordered at TM. (ii) At Tirr < TM, weak-ferromagnetism (W–FM) is induced by the canting of the Ru moments. (iii) At TC (TM/TC ~ 4), the system becomes SC and both SC and W–FM states coexist.
Coulomb Blockade Effect in a Nano-Sized Gold Chain
Authors: Hu S. F. , Yeh R. L. , Liu R. S.
Published: September 2003

Single electron transistors (SETs) has been proposed as a future basis for nanoelectric components. SETs, which utilize Coulomb blockade effect arising from the electrostatic charging energy of a single electron, are one of the promising candidates for future integrated circuits due to their extremely low power consumption and high-density integration. Here, we report on the study of the formation mechanism of a nanometer-scale Au chain on a patterned SiO 2 based wafer by controlling the reaction of raw materials to form citrate Au sol and aminosilane/dithiol treated SiO 2/ Si wafer. Three gold colloidal particles (~15 nm) were aligned in a chain to form a one-dimensional current path which was bridged on a 80 nm gap between source and drain metal electrode. The SET device exhibited a Coulomb blockade effect at 40 K.
Electron Correlation in Carbon Nanotubes: Superconductivity Versus Localization
Authors: Malozovsky Y. M. , Fan J. D. , Rambabu B.
Published: September 2003

We study the effect of electron correlation in the armchair carbon nanotubes (CNT). We model the carbon nanotube as a tubule with electrons confined to the surface of the tubule by an attractive δ-function potential. We derived the pair interaction potential between two electrons in the tubule incorporating short-range and exchange correlation. Dispersions of plasmon modes at different values of orbital momentum (ℓ) and single-particle excitations are derived as well. We find that the plasma modes are not Landau damped and the lowest mode has acoustic behavior. We also find that the multiple scattering of an electron on the plasma acoustic mode leads to the so-called plasmaron quasiparticle and self-localization of an electron in the polarization well. We also show that there is a competition between superconducting correlation and self-localization due to the electron plasma interaction.
Structure and Transport Studies on PrBa2(Cu1-xMx)3O7: M = Al, Fe, and Ni
Authors: Chen T.-P. , Yang X. , Tipparach U. , Zhou A. , Chen B. , Chen Q. Y. , Wang J. T.
Published: September 2003

We have fabricated metal doped PrBa 2 Cu 3 O 7 (PBCO), i.e. PrBa 2( Cu 1-x M x)3 O 7 (PBCMO) with M = Al , Fe, and Ni, and x = 0.05, 0.10, 0.15, and 0.20. X-ray data indicate no significant second phase for Ni-doped samples until 15% doping level is reached. No second phase was found in Al- and Fe-doped samples up to the 20% doping level. All the doped samples are in orthorhombic structure and their lattice parameters are very close to those of YBa 2 Cu 3 O 7-δ (YBCO). However, for Al or Fe doped samples the difference in lattice parameters a-b has decreased from that of PBCO. At 77 K the electrical resistivity for Al- or Fe-doped samples is several orders in magnitude higher than that of PBCO. Therefore these compounds may be better buffer-layer materials for YBCO superconducting electronic circuits and devices.
Transport, AC-Susceptibility and PQR Measurements of Strongly Electron Correlated Compound YbInCu4 at High Pressures
Authors: Wada S. , Mito T. , Koyama T. , Kobayashi T. C. , Muramatsu T. , Sarrao J. L.
Published: September 2003

We have investigated physical properties of the valence fluctuating compound YbInCu 4 at high pressures and low temperatures. The first-order valence transition temperature TV ~ 42 K at ambient pressure is completely suppressed for pressures above 2.49 GPa. Present electrical resistivity data in the pressure-stabilized high-temperature (HT) phase exhibit successive shoulders at around 20 and 2.4 K. The former can reasonably be compared with the Kondo temperature TK ~ 25 K estimated from the static-susceptibility data at ambient pressure. For pressures above 2.27 GPa, the ac-susceptibility showed a clear peak at 2.4 K, which can be explained as the onset of a long-range ferromagnetic ordering. 63 Cu pure-quadrupole-resonance in the HT phase showed that the value of spin-lattice relaxation time T1 and the almost T-independent behavior are hardly affected with pressure up to 1.3 GPa, in contrast to the large increase in quadrupole frequency.
Origin of Diversified Transport Properties of MgB2
Authors: Kim Kijoon H. P. , Jung C. U. , Kim Heon-Jung , Park Min-Seok , Kim Mun-Seog , Kim Kyung Hee , Lee Sung-Ik , Kim K. H. , Betts J. B. , Jaime M. , Lacerda A. H. , Boebinger G. S.
Published: September 2003

We investigated the transport properties of MgB 2 while changing the contents of excess Mg. The samples containing almost no excess Mg showed the highest Tc and the sharpest transition width (ΔTc). A residual resistivity ratio (RRR) of ~ 5.8, and a magnetoresistance (MR) of 12%, at 40 K, were obtained for this stoichiometric sample. Moreover, no upturn of resistivity in a low temperature region at 10 Tesla was observed. However, the samples containing appreciable amounts of excess Mg showed quite different behaviors; the values of ΔTc, RRR and MR were much larger. Surprisingly, big upturn appeared in this Mg-excess MgB 2
Dielectric, Piezoelectric and Magnetic Properties of Ferroelectromagnet Pb(Fe1/3Nb2/3)O3(PFN) Ceramics
Authors: Wang Jin. T. , Mbonye Marx K. , Zhang Cheng
Published: September 2003

Ferroelecromagnet Pb ( Fe 1/3 Nb 2/3) O 3 has been synthesized and its crystal structure and dielectric, electrostrictive and magnetic properties have been investigated. The structure of PFN ceramics examined by X-ray diffraction was found perovskite-like. The dielectric constant and dielectric loss as a function of temperature at different frequencies was measured. A para-ferroelectric transition at a temperature of 403 K was found and the maximum dielectric constant at a frequency of 500 Hz at the transition temperature is as high as 9050. The piezoelectric strain at room temperature was examined. The magnetization measurements as a function of temperature in the temperature region from room temperature to 648 K with different applied magnetic fields revealed that the compound is antiferromagnetic.
Low-Energy Charge Excitations in an Undoped Cuprate: Description Beyond the Standard pdσ-Model?
Authors: Drechsler S.-L. , Málek J. , Hayn R. , Knupfer M. , Moskvin A. S. , Fink J.
Published: September 2003

Within a joint experimental and theoretical study the density-density response of the prototypical linear chain compound Sr 2 CuO 3 has been investigated by means of polarization and momentum dependent electron energy loss spectroscopy (EELS) and exact diagonalizations including also the continued fraction technique for the determination of spectral densities such as the optical conductivity and the loss function, respectively. It has been shown that the lowest charge excitations of this 1D charge transfer insulator cannot be described properly within the usual pdσ-model for cuprates which is based on the Cu 3dx2-y2 and the corresponding O 2pσ states, only. The lowest energy charge excitations are dominated by O 2pπ final states within the CuO 4 plaquette plane. A detailed analysis of the EELS-data allows a classification into two types of charge transfer excitations with predominant π and σ character and various sizes of internal localization and dispersion.
Cooper Pairing and Ladder Correlations in a BCS Ground State
Authors: Aguilera-Navarro V. C. , Fortes M. , de Llano M.
Published: September 2003

A Bethe–Salpeter treatment of Cooper pairs (CPs) based on an ideal Fermi gas (IFG) "sea" produces unstable CPs if holes are not ignored. Stable CPs with damping emerge when the BCS ground state replaces the IFG, and are positive-energy, finite-lifetime resonances for nonzero center-of-mass momentum with a linear dispersion leading term. Bose–Einstein condensation of such pairs may thus occur in exactly two dimensions as it cannot with quadratic dispersion.
A Small Angle Neutron Scattering Study of the Vortex Matter in La2-xSrxCuO4 (x=0.17)
Authors: Gilardi R. , Streule S. , Mesot J. , Drew A. J. , Divakar U. , Lee S. L. , Brown S. P. , Forgan E. M. , Momono N. , Oda M.
Published: September 2003

The magnetic phase diagram of slightly overdoped La 2-x Sr x CuO 4 (x=0.17) is characterised by a field-induced hexagonal to square transition of the vortex lattice at low fields (~ 0.4 Tesla) [R. Gilardi et al., Phys. Rev. Lett.88, 217003 (2002)]. Here we report on a small angle neutron scattering study of the vortex lattice at higher fields, that reveals no further change of the coordination of the square vortex lattice up to 10.5 Tesla applied perpendicular to the CuO 2 planes. Moreover, it is found that the diffraction signal disappears at temperatures well below Tc, due to the melting of the vortex lattice.
A Novel Approach to Large Scale Applications of Superconductivity: The Concept of an All Superconducting Mini Power Plant
Authors: Vajda Istvan
Published: September 2003

The widespread use of energy-efficient, environmental-friendly and secure local power stations, or mini power plants (MPPs) has become a world-wide trend. Disperse power generation has been developed against centralized generation in central power stations/plants with a particular view on the utilization of renewable energy sources. Exceeding the stage of the development of individual superconducting power devices (SPDs), more and more concern is being focused around all superconducting (AS) integrated systems (ASIS) consisting of a set of individual SPDs being integrated into one system with a common cryogenic environment. Such a system possesses with substantial additional benefits compared to and exceeding those of the individual SPDs. The concept of AS MPP model of the order of 10 kW developed by the author's team is presented in this paper.
Fractal Coding of Video Sequence by Circular Prediction Mapping
Authors: Kim Chang-Su , Lee Sang-Uk
Published: September 2003

We propose a novel algorithm for fractal video sequence coding, based on the Circular Prediction Mapping (CPM), in which each range block is approximated by a domain block in the circularly previous frame. In our approach, the size of the domain block is set to be same as that of the range block for exploiting the high temporal correlation between the adjacent frames, while most other fractal coders use the domain block larger than the range block. Therefore the domain-range mapping in the CPM becomes similar to the block matching algorithm in the motion compensation techniques, and the advantages from this similarity are discussed. Also the modified collage theorem, which yields better prediction method for the CPM than the conventional collage theorem, is provided by linear systematic analysis. The computer simulation results on real video-conferencing image sequences demonstrate that the average compression ratios ranging from 60 to 70 can be obtained with good subjective quality.
Multiscale Fractal Texture Analysis Using Morphological Techniques
Authors: Popov Antony T.
Published: September 2003

Fractal dimension is used to analyse texture images. Since the fractal dimension remains unchanged under linear transformations, presented method is robust for dismissing effects caused by lighting and other extrinsic factors. The methods of mathematical morphology are used to calculate the fractal (Bouligand) dimension. A parallel implementation of morphological blanket covering is proposed.
Trans-Cellular Proliferating Cell Nuclear Antigen Gene Activation in Cerebral Vascular Smooth Muscle by Endothelial Oxidative Injury In Vivo
Authors: Gerzanich Volodymyr , Ivanova Svetlana , van der Heijden Michiel S. , Zhou Hui , Simard J. Marc
Published: September 2003

Objective—

This study was undertaken to assess the role of vascular smooth muscle cell (VSMC) Ca
2+
channels and Ca
2+
/calmodulin-dependent protein kinase II (CaMKII) in gene regulation after oxidative endothelial injury (OEI).

Methods and Results—

OEI was produced by infusion of Na fluorescein (NaFluo) photoactivated by UV light immediately before intravenous injection. Posterior cerebral arteries were studied using immunofluorescence imaging, Western blotting, or patch clamping of isolated cells. After infusion of photoactivated NaFluo, but not NaFluo, (1) superoxide dismutase-1 (SOD-1) was upregulated in endothelium, consistent with oxidant stress; (2) the fraction of VSMC nuclei labeled for proliferating cell nuclear antigen (PCNA) increased 7-fold at 6 hours, preceded by a several-fold increase in nuclear phospho-cAMP-response element binding protein, with PCNA upregulation prevented by pretreatment with polyethylene glycol (PEG)-SOD; (3) in VSMCs, phospho-CaMKII increased 20-fold 5 minutes after OEI, with a 2-fold increase in peak Ca
2+
channel currents; and (4) changes in cAMP-response element binding protein and PCNA were blocked by systemic administration of lipophilic (nifedipine) or hydrophilic (amlodipine) 1,4-dihydropyridine Ca
2+
channel blockers, the calmodulin inhibitor trifluoperazine, or the CaMKII inhibitor KN-93, with none of these agents preventing SOD-1 upregulation in endothelium.

Conclusions—

Activation of VSMC Ca
2+
channels and CaMKII is a key early signaling event required for upregulation of PCNA gene expression in VSMCs after oxidative injury to endothelium.
Enhanced G
i
Signaling Selectively Negates β
2
-Adrenergic Receptor (AR)– but Not β
1
-AR–Mediated Positive Inotropic Effect in Myocytes From Failing Rat Hearts
Authors: Xiao Rui-Ping , Zhang Sheng-Jun , Chakir Khalid , Avdonin Pavel , Zhu Weizhong , Bond Richard A. , Balke C. William , Lakatta Edward G. , Cheng Heping
Published: September 2003

Background—

Myocardial contractile response to β
1
- and β
2
-adrenergic receptor (AR) stimulation is severely impaired in chronic heart failure, in which G
i
signaling and the ratio of β
2
/β
1
are often increased. Because β
2
-AR but not β
1
-AR couples to G
s
and G
i
with the G
i
coupling negating the G
s
-mediated contractile response, we determined whether the heart failure–associated augmentation of G
i
signaling contributes differentially to the defects of these β-AR subtypes and, if so, whether inhibition of G
i
or selective activation of β
2
-AR/G
s
by ligands restores β
2
-AR contractile response in the failing heart.

Methods and Results—

Cardiomyocytes were isolated from 18- to 24-month-old failing spontaneously hypertensive (SHR) or age-matched Wistar-Kyoto (WKY) rat hearts. In SHR cardiomyocytes, either β-AR subtype–mediated inotropic effect was markedly diminished, whereas G
i
proteins and the β
2
/β
1
ratio were increased. Disruption of G
i
signaling by pertussis toxin (PTX) enabled β
2
- but not β
1
-AR to induce a full positive inotropic response in SHR myocytes. Furthermore, screening of a panel of β
2
-AR ligands revealed that the contractile response mediated by most β
2
-AR agonists, including zinterol, salbutamol, and procaterol, was potentiated by PTX, indicating concurrent G
s
and G
i
activation. In contrast, fenoterol, another β
2
-AR agonist, induced a full positive inotropic effect in SHR myocytes even in the absence of PTX.

Conclusions—

We conclude that enhanced G
i
signaling is selectively involved in the dysfunction of β
2
- but not β
1
-AR in failing SHR hearts and that disruption of G
i
signaling by PTX or selective activation of β
2
-AR/G
s
signaling by fenoterol restores the blunted β
2
-AR contractile response in the failing heart.
Donor Spontaneous Intracerebral Hemorrhage Is Associated With Systemic Activation of Matrix Metalloproteinase-2 and Matrix Metalloproteinase-9 and Subsequent Development of Coronary Vasculopathy in the Heart Transplant Recipient
Authors: Yamani Mohamad H. , Starling Randall C. , Cook Daniel J. , Tuzcu E. Murat , Abdo Ashraf , Paul Philip , Powell Kimerly , Ratliff Norman B. , Yu Yang , McCarthy Patrick M. , Young James B.
Published: September 2003

Background—

Matrix metalloproteinase (MMP)-2 and MMP-9 have been shown to play a role in the progression of hemorrhagic stroke. We hypothesized that donor intracerebral hemorrhage (ICH) is associated with activation of the metalloproteinases before transplantation that play a key role in the subsequent development of transplant vasculopathy.

Methods and Results—

We evaluated mRNA expressions of MMP-2 and MMP-9 in donor spleen lymphocytes (before transplantation) and in heart biopsies at 1 week after transplantation in 20 recipients from ICH donors and 20 recipients from trauma donors. Patients underwent serial coronary intravascular ultrasound, and interstitial myocardial fibrosis was quantified at 1 year. The baseline characteristics were similar except for increased donor age in the ICH group. Heart biopsies from the ICH group showed significant increased expression of MMP-2 (17-fold,
P
<0.0001) and MMP-9 (20-fold,
P
<0.0001) compared with the trauma group. Furthermore, the ICH group showed 1.8-fold (
P
=0.016) increased mRNA expression of MMP-2 and 1.7-fold (
P
=0.015) increased mRNA expression of MMP-9 in the donor spleen lymphocytes, suggesting the presence of systemic activation of metalloproteinases before transplantation. At 1 year, the ICH group showed increased myocardial fibrosis and accelerated coronary vasculopathy. Using multivariate regression analysis, MMP-9 was found to be associated with increased risk for vasculopathy independent of donor age (OR, 2.41;
P
=0.01; 95% CI, 1.24 to 4.69).

Conclusions—

This is the first report to describe systemic activation of MMP-2 and MMP-9 in donors with intracerebral hemorrhage and subsequent development of allograft vasculopathy.