bluuebunny/crossref_metadata_2025 huggingface dataset:
Bivoltinism as an Antecedent to Eusociality in the Paper Wasp Genus
Polistes
Authors: Hunt James H. , Amdam Gro V.
Published: April 2005

To learn the evolutionary trajectories of caste differentiation in eusocial species is a major goal of sociobiology. We present an explanatory framework for caste evolution in the eusocial wasp genus
Polistes
(Vespidae), which is a model system for insect eusocial evolution. We hypothesize that
Polistes
worker and gyne castes stem from two developmental pathways that characterized the bivoltine life cycle of a solitary ancestor. Through individual-based simulations, we show that our mechanistic framework can reproduce colony-level characteristics of
Polistes
and, thereby, that social castes can emerge from solitary regulatory pathways. Our explanatory framework illustrates, by specific example, a changed perspective for understanding insect social evolution.
Functional Characterization of an α-Factor-Like
Sordaria macrospora
Peptide Pheromone and Analysis of Its Interaction with Its Cognate Receptor in
Saccharomyces cerevisiae
Authors: Mayrhofer Severine , Pöggeler Stefanie
Published: April 2005

The homothallic filamentous ascomycete
Sordaria macrospora
possesses genes which are thought to encode two pheromone precursors and two seven-transmembrane pheromone receptors. The pheromone precursor genes are termed
ppg1
and
ppg2.
The putative products derived from the gene sequence show structural similarity to the α-factor precursors and
a
-factor precursors of the yeast
Saccharomyces cerevisiae.
Likewise, sequence similarity has been found between the putative products of the pheromone receptor genes
pre2
and
pre1
and the
S. cerevisiae
Ste2p α-factor receptor and Ste3p
a
-factor receptor, respectively. To investigate whether the α-factor-like pheromone-receptor pair of
S. macrospora
is functional, a heterologous yeast assay was used. Our results show that the
S. macrospora
α-factor-like pheromone precursor PPG1 is processed into an active pheromone by yeast
MATα
cells. The
S. macrospora
PRE2 protein was demonstrated to be a peptide pheromone receptor. In yeast
MAT
a
cells lacking the endogenous Ste2p receptor, the
S. macrospora
PRE2 receptor facilitated all aspects of the pheromone response. Using a synthetic peptide, we can now predict the sequence of one active form of the
S. macrospora
peptide pheromone. We proved that
S. macrospora
wild-type strains secrete an active pheromone into the culture medium and that disruption of the
ppg1
gene in
S. macrospora
prevents pheromone production. However, loss of the
ppg1
gene does not affect vegetative growth or fertility. Finally, we established the yeast assay as an easy and useful system for analyzing pheromone production in developmental mutants of
S. macrospora
.
Structural Elements in the 5′-Untranslated Region of Giardiavirus Transcript Essential for Internal Ribosome Entry Site-Mediated Translation Initiation
Authors: Garlapati Srinivas , Wang Ching C.
Published: April 2005

Translation of uncapped giardiavirus (GLV) mRNA in
Giardia lamblia
requires the presence of a 5′-untranslated region (5′-UTR) and a viral capsid coding region. We used dicistronic viral constructs to show that the downstream 253 nucleotides (nt) of the 5′-UTR plus the initial 264-nt capsid coding region constitute an internal ribosome entry site (IRES). Predicted secondary structures in the 253-nt 5′-UTR include stem-loops U3, U4a, U4b, U4c, and U5. Chemical and enzymatic probing analysis confirmed the presence of all predicted stem-loops except U4a. Disruption of stem-loop structures U3 and U5 by site-directed mutagenesis resulted in a drastic reduction in translation of a monocistronic viral transcript, which could be restored by compensatory sequence changes. Mutations disrupting stem-loops U4b and U4c do not exert an appreciable effect on translation, but certain sequences in the U4a region and in U4b do appear to play important roles in the IRES. Structural analysis also suggests that an 8-nt U3 loop sequence (nt 147 to 154) pairs with an 8-nt downstream sequence (nt 168 to 175) to form a pseudoknot. Disruption of this pseudoknot by mutagenesis resulted in a drastic reduction in translation, which could be restored by compensatory sequence changes. This study has defined the secondary structure in the 5′-UTR of the IRES. Together with the previous results, we have now completed analysis of the entire structure of GLV IRES and fully defined the functionally essential structural elements in it.
Mitochondrial DNA Ligases of
Trypanosoma brucei
Authors: Downey Nick , Hines Jane C. , Sinha Krishna M. , Ray Dan S.
Published: April 2005

The mitochondrial DNA of
Trypanosoma brucei
, termed kinetoplast DNA or kDNA, consists of thousands of minicircles and a small number of maxicircles catenated into a single network organized as a nucleoprotein disk at the base of the flagellum. Minicircles are replicated free of the network but still contain nicks and gaps after rejoining to the network. Covalent closure of remaining discontinuities in newly replicated minicircles after their rejoining to the network is delayed until all minicircles have been replicated. The DNA ligase involved in this terminal step in minicircle replication has not been identified. A search of kinetoplastid genome databases has identified two putative DNA ligase genes in tandem. These genes (
LIG k
α and
LIG k
β) are highly diverged from mitochondrial and nuclear DNA ligase genes of higher eukaryotes. Expression of epitope-tagged versions of these genes shows that both LIG kα and LIG kβ are mitochondrial DNA ligases. Epitope-tagged LIG kα localizes throughout the kDNA, whereas LIG kβ shows an antipodal localization close to, but not overlapping, that of topoisomerase II, suggesting that these proteins may be contained in distinct structures or protein complexes. Knockdown of the
LIG k
α mRNA by RNA interference led to a cessation of the release of minicircles from the network and resulted in a reduction in size of the kDNA networks and rapid loss of the kDNA from the cell. Closely related pairs of mitochondrial DNA ligase genes were also identified in
Leishmania major
and
Crithidia fasciculata
.
S
t
, a Truncated Envelope Protein Derived from the S Protein of Duck Hepatitis B Virus, Acts as a Chaperone for the Folding of the Large Envelope Protein
Authors: Grgacic Elizabeth V. L. , Anderson David A.
Published: April 2005

Envelope proteins of hepadnaviruses undergo a unique folding mechanism which results in the posttranslational translocation of 50% of the large envelope protein (L) chains across the endoplasmic reticulum. This mechanism is essential for the eventual positioning of the receptor-binding domain on the surface of the virus particle and in duck hepatitis B virus (DHBV) is dependent on the small (S) envelope protein as part of the assembly process. In this study, we report the identification of a third envelope protein, S
t
, derived from the S protein and carrying functions previously attributed to S. Antibody mapping and mutagenesis studies indicated S
t
to be C terminally truncated, spanning the N-terminal transmembrane domain (TM1) plus the adjacent cysteine loop. We have previously shown that the mutation of two conserved polar residues in TM1 of S (S
AA
) eliminates L translocation and assembly. A plasmid expressing a functional equivalent of S
t
was able to rescue assembly, demonstrating that this assembly defect is due to mutations of the corresponding residues in S
t
and not in S per se. Immunofluorescence analysis showed that S
t
directly affects L protein cellular localization. These results indicate that S
t
acts as a viral chaperone for L folding, remaining associated with the DHBV envelope upon secretion. The presence of S
t
at a molar ratio of half that of L suggests that it is S
t
which regulates L translocation to 50%.
Effects of Nonstructural Proteins NS1 and NS2 of Human Respiratory Syncytial Virus on Interferon Regulatory Factor 3, NF-κB, and Proinflammatory Cytokines
Authors: Spann Kirsten M. , Tran Kim C. , Collins Peter L.
Published: April 2005

Human respiratory syncytial virus (HRSV) is the leading cause of serious pediatric acute respiratory tract infections, and a better understanding is needed of the host response to HRSV and its attenuated vaccine derivatives. It has been shown previously that HRSV nonstructural proteins 1 and 2 (NS1 and NS2) inhibit the induction of alpha/beta interferon (IFN-α/β) in A549 cells and human macrophages. Two principal transcription factors for the early IFN-β and -α1 response are interferon regulatory factor 3 (IRF-3) and nuclear factor κB (NF-κB). At early times postinfection, wild-type HRSV and the NS1/NS2 deletion mutants were very similar in the ability to activate IRF-3. However, once NS1 and NS2 were expressed significantly, they acted cooperatively to suppress activation and nuclear translocation of IRF-3. Since these viruses differed greatly in the induction of IFN-α/β, NF-κB activation was evaluated in Vero cells, which lack the structural genes for IFN-α/β and would preclude confounding effects of IFN-α/β. This showed that deletion of the NS2 gene sharply reduced the ability of HRSV to induce activation of NF-κB. Since recombinant HRSVs from which the NS1 or NS2 genes have been deleted are being developed as vaccine candidates, we investigated whether the changes in activation of host transcription factors and increased IFN-α/β production had an effect on the epithelial production of proinflammatory factors. Viruses lacking NS1 and/or NS2 stimulated modestly lower production of RANTES (Regulated on Activation Normal T-cell Expressed and Secreted), interleukin 8, and tumor necrosis factor alpha compared to wild-type recombinant RSV, supporting their use as attenuated vaccine candidates.
Highly Protective In Vivo Function of Cytomegalovirus IE1 Epitope-Specific Memory CD8 T Cells Purified by T-Cell Receptor-Based Cell Sorting
Authors: Pahl-Seibert Marcus-Folker , Juelch Markus , Podlech Jürgen , Thomas Doris , Deegen Petra , Reddehase Matthias J. , Holtappels Rafaela
Published: April 2005

Reconstitution of antiviral CD8 T cells is essential for controlling cytomegalovirus (CMV) infection after bone marrow transplantation. Accordingly, polyclonal CD8 T cells derived from BALB/c mice infected with murine CMV protect immunocompromised adoptive transfer recipients against CMV disease. The protective population comprises CD8 T cells with T-cell receptors (TCRs) specific for defined and for as-yet-unknown viral epitopes, as well as a majority of nonprotective cells with unrelated specificities. Defined epitopes include IE1/m123 and m164, which are immunodominant in terms of the magnitude of the CD8 T-cell response, and a panel of subordinate epitopes (m04, m18, M45, M83, and M84). While cytolytic T-lymphocyte lines (CTLLs) were shown to be protective regardless of the immunodominance of the respective epitope, the individual contributions of in vivo resident epitope-specific CD8 T cells to the antiviral control awaited investigation. The IE1 peptide 168-YPHFMPTNL-176 is generated from the immediate-early protein 1 (IE1) (pp89/76) of murine CMV and is presented by the major histocompatibility complex class I (MHC-I) molecule Ld. To quantitate its contribution to the protective potential of a CD8-T memory (CD8-TM) cell population, IE1-TCR+and IE1-TCR−CD8-TMcells were purified by epitope-specific cell sorting with IE1 peptide-loaded MHC-immunoglobulin G1 dimers as ligands of cognate TCRs. Of relevance for clinical approaches to an adoptive cellular immunotherapy, sorted IE1 epitope-specific CD8-TMcells were found to be exceedingly protective upon adoptive transfer. Compared with CTLLs specific for the same epitope and of comparable avidity and TCR β-chain variable region (Vβ)-defined polyclonality, sorted CD8-TMcells proved to be superior by more than 2 orders of magnitude.
Cross-Reactive Cytotoxic T Lymphocytes against Human Immunodeficiency Virus Type 1 Protease and Gamma Interferon-Inducible Protein 30
Authors: Mason R. D. , Bowmer M. I. , Howley C. M. , Grant M. D.
Published: April 2005

The gamma interferon (IFN-γ)-inducible protein 30 (IP-30) signal peptide −11 to −3 (LLDVPTAAV) is a prominent self peptide expressed with the class I human histocompatibility leukocyte antigen A2 (HLA-A2). Stimulation of peripheral blood mononuclear cells (PBMC) from HLA-A2 human immunodeficiency virus type 1 (HIV-1)-infected individuals with an HLA-A2-restricted HIV protease (PR) peptide 76-84 (LVGPTPVNI) activated cytotoxic T lymphocytes (CTL) against the IP-30 signal peptide. Since HIV-1 PR 76-84 stimulated CD8+T cells from these individuals to secrete IFN-γ, we tested whether the activation of IP-30-specific CTL in vitro resulted from T-cell cross-reactivity or from up-regulation of IP-30 by IFN-γ. Neither high levels of exogenous IFN-γ nor incubation of PBMC with other HIV peptides triggering substantial IFN-γ release activated IP-30-specific CTL. Although the IP-30 signal peptide did not stimulate IFN-γ release from freshly isolated PBMC, it activated CTL in vitro against itself and HIV PR 76-84. Peptide-stimulated IFN-γ release, cold target inhibition, and HLA-A2/immunoglobulin dimer-mediated binding and depletion of effector cells all indicated that in vitro stimulation with HIV PR 76-84 or the IP-30 signal peptide activated a comparable population of cross-reactive effector cells. Neither IP-30 nor HIV PR 76-84 activated CTL against themselves following in vitro stimulation of PBMC from non-HIV-infected HLA-A2 individuals. Peptide titrations indicated higher-avidity T-cell interactions with HIV PR 76-84 than with the IP-30 signal peptide. These data indicate that HIV PR 76-84 is a heteroclitic variant of the IP-30 signal peptide −11 to −3, which has implications for immune memory and autoimmunity.
Rift Valley Fever Virus Nonstructural Protein NSs Promotes Viral RNA Replication and Transcription in a Minigenome System
Authors: Ikegami Tetsuro , Peters C. J. , Makino Shinji
Published: April 2005

Rift Valley fever virus
(RVFV), which belongs to the genus
Phlebovirus
, family
Bunyaviridae
, has a tripartite negative-strand genome (S, M, and L segments) and is an important mosquito-borne pathogen for domestic animals and humans. We established an RVFV T7 RNA polymerase-driven minigenome system in which T7 RNA polymerase from an expression plasmid drove expression of RNA transcripts for viral proteins and minigenome RNA transcripts carrying a reporter gene between both termini of the M RNA segment in 293T cells. Like other viruses of the
Bunyaviridae
family, replication and transcription of the RVFV minigenome required expression of viral N and L proteins. Unexpectedly, the coexpression of an RVFV nonstructural protein, NSs, with N and L proteins resulted in a significant enhancement of minigenome RNA replication. Coexpression of NSs protein with N and L proteins also enhanced minigenome mRNA transcription in the cells expressing viral-sense minigenome RNA transcripts. NSs protein expression increased the RNA replication of minigenomes that originated from S and L RNA segments. Enhancement of minigenome RNA synthesis by NSs protein occurred in cells lacking alpha/beta interferon (IFN-α/β) genes, indicating that the effect of NSs protein on minigenome RNA replication was unrelated to a putative NSs protein-induced inhibition of IFN-α/β production. Our finding that RVFV NSs protein augmented minigenome RNA synthesis was in sharp contrast to reports that Bunyamwera virus (genus
Bunyavirus
) NSs protein inhibits viral minigenome RNA synthesis, suggesting that RVFV NSs protein and Bunyamwera virus NSs protein have distinctly different biological roles in viral RNA synthesis.
Peptide Mimetics of Gamma Interferon Possess Antiviral Properties against Vaccinia Virus and Other Viruses in the Presence of Poxvirus B8R Protein
Authors: Ahmed Chulbul M. I. , Burkhart Marjorie A. , Subramaniam Prem S. , Mujtaba Mustafa G. , Johnson Howard M.
Published: April 2005

We have developed peptide mimetics of gamma interferon (IFN-γ) that play a direct role in the activation and nuclear translocation of STAT1α transcription factor. These mimetics do not act through recognition by the extracellular domain of IFN-γ receptor but rather bind to the cytoplasmic domain of the receptor chain 1, IFNGR-1, and thereby initiate the cellular signaling. Thus, we hypothesized that these mimetics would bypass the poxvirus virulence factor B8R protein that binds to intact IFN-γ and prevents its interaction with the receptor. Human and murine IFN-γ mimetic peptides were introduced into an adenoviral vector for intracellular expression. Murine IFN-γ mimetic peptide was also expressed via chemical synthesis with an attached lipophilic group for penetration of cell plasma membrane. In contrast to intact human IFN-γ, the mimetics did not bind poxvirus B8R protein, a homolog of the IFN-γ receptor extracellular domain. Expression of B8R protein in WISH cells did not block the antiviral effect of the mimetics against encephalomyocarditis or vesicular stomatitis virus, while the antiviral activity of human IFN-γ was neutralized. Consistent with the antiviral activity, the upregulation of MHC class I molecules on WISH cells by the IFN-γ mimetics was not affected by B8R protein, while IFN-γ-induced upregulation was blocked. Finally, the mimetics, but not IFN-γ, inhibited vaccinia virus replication in African green monkey kidney BSC-40 cells. The data presented demonstrate that small peptide mimetics of IFN-γ can avoid the B8R virulence factor for poxviruses and, thus, are potential candidates for antivirals against smallpox virus.
TRACE ELEMENTAL ANALYSIS OF PERMIAN GONDWANA COALS IN BANGLADESH BY PIXE TECHNIQUE
Authors: PODDER J. , TAREK S. A. , HOSSAIN T.
Published: April 2005

The study of trace elements level in coal arouses much interest in recent days to assess and evaluate the environmental impact related to its benefit and usage in applying it to the problem of mining site. Further, it is more important during the coal combustion in thermal power stations particularly in relation to the emission of air toxic, disposal and utilization of fly ash. The paper describes the level of nineteen environmentally significant trace elements found in recently discovered Permian Gondwana coals in Barapukuria and Khalaspir of Northwestern Bangladesh using Proton Induced X-ray Emission (PIXE) spectroscopy. Both the mineral species and trace elements are expected to be due to sedimentary and aerobic environmental condition where the Permian coals have been generated depending on their degree of evolution.
DETERMINATION OF HEAVY METALS IN SALTS BY PROTON INDUCED X-RAY EMISSIONS
Authors: BOLORMAA O. , TSUJI M. , KAWASAKI K. , HATTORI T.
Published: April 2005

The samples of common salts available in Japan and Mongolia were analyzed for the presence of heavy elements by PIXE spectrometry using 2.5 MeV proton beam at the Tokyo Institute of Technology Van de Graaff Laboratory. The samples were dissolved in water and insoluble and soluble fractions were determined separately. The soluble constituents were treated with pre-concentration method by using DBDTC to form the complexes appropriate to percolation through a Nuclepore Track - etch Membrane. Insoluble particles were precipitated on the filter surface for subsequent direct irradiation. Combined As and Pb concentrations in insoluble portion of salts were found in the range of 7.2 – 102 ppm based on mass analysis of insoluble materials collected on Nuclepore Track - etch Membrane of the pore diameter 0.4μm. This level of toxic heavy metals makes a caution from the view-point of their safe intake.
FINDING OF HIGH LEVEL ARSENIC FOR MONGOLIAN VILLAGERS' HAIR
Authors: MURAO S. , TUMENBAYAR B. , SERA K. , FUTATSUGAWA S. , WAZA T.
Published: April 2005

In recent years, the number of artisanal gold miners in Mongolia is drastically increasing. They use mercury to extract gold from ore and release it to the environment and this fact has been an issue of concern in the nation. In order to monitor the degree of exposure to mercury, artisanal miners' hairs from a typical mining site, Boroo, were analyzed by PIXE at Nishina Memorial Cyclotron Center, Japan. The result indicated that mercury content in the hairs is very low in spite of the miners' practice to work in mercury fume for smelting. However the result showed high level of arsenic, up to 3.2 ppm, although miners' do not use arsenic in the smelting process.
PIXE STUDIES ON GOLD STANDARDS BY PROTONS OF ENERGY 3.3 MeV
Authors: JOSEPH DAISY , SAXENA A. , GUPTA S. K. , KAILAS S.
Published: April 2005

Proton Induced X-ray Emission Technique (PIXE) has been used in analyzing Gold standards of 22, 20, 18, and 14 karats with a proton beam of Energy 3.3 MeV at the newly commissioned Folded Tandem Ion Accelerator (FOTIA) at B.A.R.C, Trombay. Well resolved Au and Ag X-rays were detected at a current of 3 nA . Percentage values of gold and silver were calculated and were checked with those obtained by Energy Dispersive X-ray Fluorescence (EDXRF) Method and were found to be in agreement with the certified values as well as those obtained by XRF.
ON THE DEFORMATION QUANTIZATION OF AFFINE ALGEBRAIC VARIETIES
Authors: FIORESI R. , LLEDÓ M. A. , VARADARAJAN V. S.
Published: April 2005

We compute an explicit algebraic deformation quantization for an affine Poisson variety described by an ideal in a polynomial ring, and inheriting its Poisson structure from the ambient space.
THE CONNECTION BETWEEN LOW-ENERGY LEPTONIC CP-VIOLATION AND LEPTOGENESIS
Authors: PASCOLI SILVIA
Published: April 2005

Within the context of the seesaw mechanism, we review the possible connection between the CP-violating phases which appear in the lepton unitary mixing matrix and are measurable in neutrino oscillations and other low-energy processes, with the ones which play a role in the generation of the baryon asymmetry of the universe through the leptogenesis mechanism.
FERMI SURFACE STUDIES OF QUASI-1D and QUASI-2D ORGANIC SUPERCONDUCTORS USING PERIODIC ORBIT RESONANCE IN HIGH MAGNETIC FIELDS
Authors: TAKAHASHI S. , KOVALEV A. E. , HILL S. , TAKASAKI S. , YAMADA J. , ANZAI H. , QUALLS J. S. , KAWANO K. , TAMURA M. , NAITO T. , KOBAYASHI H.
Published: April 2005

We have studied periodic orbit resonances (PORs) in order to probe the topology of the Fermi surface (FS) of the quasi-1D organic conductor ( TMTSF )2 ClO 4 and the quasi-2D organic conductors κ-( ET )2 Cu ( NCS )2 and κ-( ET )2 I 3. The FS of ( TMTSF )2 ClO 4 consists of a pair of weakly corrugated open sheets, while κ-( ET )2 Cu ( NCS )2 and κ-( ET )2 I 3 additionally possess warped cylindrical FS sections. In this paper, we review the POR technique for the straightforward case of ( TMTSF )2 ClO 4. We then report on a detailed study of the FS topology for κ-( ET )2 Cu ( NCS )2.
PINNING AND SLIDING OF QUANTUM HALL STRIPES AND BUBBLES
Authors: CÔTÉ RENÉ , LI MEIRONG , FERTIG HERBERT A. , FARIBAULT ALEXANDRE , YI HANGMO
Published: April 2005

We report on the calculation of the frequency-dependent conductivity of the quantum Hall stripes and bubble crystals that form in high Landau level. We use the replica and Gaussian variational methods (GVM) with a dynamical matrix obtained from the time-dependent Hartree-Fock approximation. In the stripe state, we go beyond the semiclassical approximation of the saddle point equations obtained with the GVM and demonstrate the existence of a quantum depinning transition as a function of filling factor. Below a critical filling factor, the pinned state is described by a replica symmetry breaking (RSB) solution that gives resonant peaks in the frequency-dependent conductivity in both directions, parallel and perpendicular to the stripes orientation. These peaks shift to zero frequency as the critical filling is approached. Above the critical filling, we find a depinned stripe state described by a partial replica symmetry breaking solution in which there is free sliding only along the stripe direction. The transition has a Kosterlitz-Thouless character and includes a jump in the low-frequency exponent of the dynamical conductivity. In the bubble crystals a semiclassical approximation yields a pinning peak frequency and resonance width that generally decrease with increasing filling factor, in accordance with recent microwave absorption experiments.
HIGH-CURRENT BREAKDOWN OF THE QUANTUM HALL EFFECT
Authors: MATTHEWS A. J. , KAVOKIN K. V. , USHER A. , PORTNOI M. E. , GETHING J. D. , ZHU M. , RITCHIE D. A.
Published: April 2005

We have recently developed a model for the high-current breakdown of the integer quantum Hall effect, as measured in contactless experiments using a highly-sensitive torsion balance magnetometer. The model predicted that, for low-mobility samples, the critical current for breakdown should decrease linearly with temperature. This prediction was verified experimentally with the addition of a low-temperature (≲ 300 mK) saturation of the critical current. This saturation is consistent with quasi-elastic inter-Landau-level scattering when the maximum electric field in the sample reaches a large enough value. In this paper we extend this model to nearly integer filling factors to show how the model may account for the shape of the magnetisation signal.
FURTHER EVIDENCE FOR A COLLAPSE OF THE EXCHANGE-ENHANCED SPIN SPLITTING IN TWO DIMENSIONAL SYSTEMS
Authors: PIOT B. A. , MAUDE D. K. , WASILEWSKI Z. R. , FRIEDLAND K. J. , HEY R. , PLOOG K. H. , EAVES L. , HENINI M. , AIREY R. , HILL G.
Published: April 2005

The collapse of spin splitting in the integer quantum Hall effect is investigated for a series of Al x Ga 1-x As / GaAs heterojunctions and quantum wells. Magnetoresistance measurements are performed at mK temperature, and a simple model is developed to simulate spin splitting. As expected a single-electron picture cannot reproduce the observed spin splitting, whereas a phenomenological enhanced-spin gap taking into account exchange interactions between electrons provides a good description. The phenomenological spin gap, which is linear in B at high magnetic field, collapses when the spin splitting collapses. This is consistent with previously proposed disorder-driven destruction of exchange interactions with decreasing magnetic field.
RESONANT TRANSPORT IN SEMICONDUCTOR SUPERLATTICES IN A TILTED MAGNETIC FIELD
Authors: MORI N. , HAMAGUCHI C. , PATANÈ A. , FROMHOLD T. M. , EAVES L.
Published: April 2005

We study electron transport in a GaAs /( AlGa ) As superlattice with a magnetic field applied at an angle θ to the superlattice axis. Solving quantum transport equations derived from a non-equilibrium Green's function method, we simulate the velocity-field curves of the superlattice. These curves show interesting similarities with those measured experimentally and those calculated using a semi-classical model.
NUMERICAL KUBO FORMULA STUDY OF FRICTIONAL DRAG IN THE INTEGER QUANTUM HALL REGIME
Authors: NOMURA K. , MACDONALD A. H.
Published: April 2005

We study interlayer frictional drag between two-dimensional electron systems in the strong magnetic field limit by evaluating the weak-coupling Kubo formula for interlayer drag numerically. The key quantity in this theory is the disorder averaged "triangle function", a product of three Greens functions of electrons that represents the dc current response of electrons in one layer to charge fluctuations in a remote current-carrying layer. We find that the disorder averaged triangle functions are proportional to the momentum transfer [Formula: see text] at small [Formula: see text] and that they change sign under a ν→1-ν particle-hole transformations, vanishing for half-filled Landau levels.
MULTI-VALENCE-SUBBAND MAGNETOTRANSPORT IN A MODULATION-DOPED p-TYPE Ge1-xSix/Ge/Ge1-xSix QUANTUM WELL
Authors: YAKUNIN M. V. , ALSHANSKII G. A. , NEVEROV V. N. , ARAPOV YU. G. , HARUS G. I. , SHELUSHININA N. G. , KUZNETSOV O. A. , DE VISSER A. , PONOMARENKO L.
Published: April 2005

We show, from self-consistent calculations, that the effective mass for motion of holes along a two-dimensional (111) Ge layer is almost an order of magnitude smaller than the bulk heavy hole mass, which determines the intersubband distances. This creates a unique situation of multiple populated electric subbands at moderate hole densities ps and layer widths. Depopulation of two or more upper subbands in a 38 nm wide p- Ge layer with ps=5×1015 m -2 has been revealed from the magnetoresistance in high parallel magnetic fields, while a collapse of the quantum Hall state for filling factor ν=1 indicates that two ground subbands merge in a self-formed double-quantum-well potential profile. The latter effect in the valence band is shown to be sensitive to the layer deformation.
POSSIBLE NEW BUBBLE PHASES OF TWO-DIMENSIONAL ELECTRONS IN HIGHER LANDAU LEVELS
Authors: ETTOUHAMI A. M. , KLIRONOMOS F. D. , DORSEY A. T.
Published: April 2005

We argue that, due to the specific form of the interaction potential between electronic guiding centers, a bubble crystal (BC) with basis may be energetically more favorable than the usual bubble solid. This new BC has well-defined normal eigenmodes, and remains energetically favorable when the effects of finite sample thickness and of screening by electrons in lower LLs are taken into account.
MAGNETOCONDUCTANCE THROUGH A CHAIN OF RINGS IN THE PRESENCE OF SPIN-ORBIT INTERACTION
Authors: VASILOPOULOS P. , MOLNÁR B. , PEETERS F. M.
Published: April 2005

Ballistic electron transport through a finite chain of quantum circular rings is studied in the presence of the Rashba coupling, of strength α, and of a perpendicular magnetic field B. The transmission and reflection coefficients for a single ring, obtained analytically, help obtain the conductance through a chain of rings as a function of the strength α, the field B, and of the wave vector k of the incident electron. Due to destructive spin interferences caused by the Rashba coupling the chain can be totally opaque for certain ranges of k the width of which depends on values of α and B. Outside these ranges the conductance oscillates with high values between e2/h and 2e2/h. The effect of a periodic modulation of α or B on the conductance gaps is investigated. A periodic, square-wave conductance pattern, pertinent to the development of the spin transistor, results within wide stripes in the parameter space spanned by k, α, and B. Finite temperatures smoothen the square-wave profile of the conductance but do not alter its periodic character.
COUNTERFLOW MEASUREMENTS IN GaAs HOLE BILAYERS: POSSIBLE EVIDENCE FOR EXCITONIC CONDENSATION
Authors: TUTUC EMANUEL , SHAYEGAN MANSOUR
Published: April 2005

We study interacting GaAs bilayer hole systems, with very small interlayer tunneling, in a counterflow geometry where equal currents are passed in opposite directions in the two, independently contacted layers. In the quantum Hall state at total bilayer filling ν=1 both the longitudinal and Hall counterflow resistances tend to vanish in the limit of zero temperature. This observation demonstrates the pairing of oppositely charged carriers in opposite layers (excitons), and implies that the ground state of the system is an excitonic condensate.
MAGNETIZATION AND MAGNETIC PHASES OF CONDUCTION-BAND DILUTE-MAGNETIC-SEMICONDUCTOR QUANTUM WELLS WITH NON-STEP-LIKE DENSITY OF STATES
Authors: SIMSERIDES CONSTANTINOS
Published: April 2005

We study the magnetization and the magnetic phases of II-VI-based n-doped non-magnetic-semiconductor (NMS) / narrow to wide dilute-magnetic-semiconductor (DMS) / n-doped NMS quantum wells under in-plane magnetic field. The parallel magnetic field is used as a tool, in order to achieve non-step-like density of states in these -appropriate for conduction-band spintronics- structures.
OBSERVATION OF PHOTOLUMINESCENCE FROM MAGNETO-PLASMAS UNDER INTENSE FEMTOSECOND EXCITATION IN STRONG MAGNETIC FIELDS
Authors: JHO Y. D. , WANG X. , SANDERS G. D. , REITZE D. H. , STANTON C. J. , KONO J. , WEI X. , SOLOMON G. S.
Published: April 2005

We report results on measurements of magneto-photoluminescence at 4.2 K in In x Ga 1-x As multiple quantum wells in high magnetic fields (25 Tesla) and laser intensities (25 GW/cm 2) using 150 fs pulses. Novel magneto-plasma phenomena are observed, including strikingly narrow emission lines of Landau levels above a threshold intensity and the suppression of exciton-mixing-induced anti-crossings.
MACROSCOPIC SIZE EFFECT OF INTER-LANDAU-LEVEL SCATTERING IN QUANTUM HALL SYSTEMS
Authors: KAWANO Y. , OKAMOTO T.
Published: April 2005

We present the experimental demonstration of a remarkable size effect of inter-Landau-level scattering (ILLS) in a quantum Hall bar. This observation has become possible by imaging cyclotron emission. The images obtained clearly reveal that spatial distribution of ILLS macroscopically depends on channel width of the device.
MAGNETO-LUMINESCENCE OF A SINGLE LATERAL ISLAND FORMED IN A TYPE - II GaAs/AlAs QW
Authors: CHWALISZ BARBARA , WYSMOLEK ANDRZEJ , STȨPNIEWSKI ROMAN , BABINSKI ADAM , POTEMSKI MAREK , THIERRY-MIEG VERONIQUE
Published: April 2005

Ensembles of sharp emission lines present in the macro-luminescence of type-II GaAs / AlAs double quantum well structures were studied. Micro-luminescence experiments allowed us to conclude that the sharp emission lines originate from lateral GaAlAs islands of a few μm in diameter, formed in the structure. They serve as efficient type-I recombination centers for indirect excitons and/or carriers diffusing in the GaAs / AlAs QW structure. Magneto-luminescence spectra from single islands resemble those observed for natural quantum dots formed in narrow GaAs quantum wells. The observed emission is assigned to the recombination of neutral excitons as well as excitonic molecules.
Bile acid signaling through FXR induces intracellular adhesion molecule-1 expression in mouse liver and human hepatocytes
Authors: Qin Pu , Borges-Marcucci Lisa A. , Evans Mark J. , Harnish Douglas C.
Published: April 2005

Previous studies have demonstrated a dramatic induction of inflammatory gene expression in livers from mice fed a high-fat, high-cholesterol diet containing cholate after 3–5 wk. To determine the contribution of cholate in mediating these inductions, C57BL/6 mice were fed a chow diet supplemented with increasing concentrations of cholic acid (CA) for 5 days. A dose-dependent induction in the hepatic levels of TNF-α, VCAM-1, ICAM-1, and SAA-2 mRNA were observed. As positive controls, a dose-dependent repression of cholesterol 7α-hydroxylase and a dose-dependent induction of small heterodimer partner (SHP) expression were also observed, suggesting that farnesoid X receptor (FXR) was activated. In addition, ICAM-1 and SHP mRNA levels were also induced in primary human hepatocytes when treated with chenodeoxycholic acid or GW4064, a FXR-selective agonist. The involvement of FXR in CA-induced inflammatory gene expression was further investigated in the human hepatic cell line HepG2. Both ICAM-1 and SHP expression were induced in a dose- and time- dependent manner by treatment with the FXR-selective agonist GW4064. Moreover, the induction of ICAM-1 by GW4064 was inhibited by the FXR antagonist guggulsterone or with transfection of FXR siRNA. Finally, the activity of FXR was mapped to a retinoic acid response element (RARE) site containing an imbedded farnesoid X response element (FXRE) on the human ICAM-1 promoter and FXR and retinoid X receptor were demonstrated to bind to this site. Finally, FXR-mediated activation of ICAM-1 could be further enhanced by TNF-α cotreatment in hepatocytes, suggesting a potential cooperation between cytokine and bile acid-signaling pathways during hepatic inflammatory events.
Acute hepatic steatosis in mice by blocking β-oxidation does not reduce insulin sensitivity of very-low-density lipoprotein production
Authors: Grefhorst Aldo , Hoekstra Jildou , Derks Terry G. J. , Ouwens D. Margriet , Baller Julius F. W. , Havinga Rick , Havekes Louis M. , Romijn Johannes A. , Kuipers Folkert
Published: April 2005

Accumulation of triglycerides (TG) in the liver is generally associated with hepatic insulin resistance. We questioned whether acute hepatic steatosis induced by pharmacological blockade of β-oxidation affects hepatic insulin sensitivity, i.e., insulin-mediated suppression of VLDL production and insulin-induced activation of phosphatidylinositol 3-kinase (PI3-kinase) and PKB. Tetradecylglycidic acid (TDGA), an inhibitor of carnitine palmitoyl transferase-1 (CPT1), was used for this purpose. Male C57BL/6J mice received 30 mg/kg TDGA or its solvent intraperitoneally and were subsequently fasted for 12 h. CPT1 inhibition resulted in severe microvesicular hepatic steatosis (19.9 ± 8.3 vs. 112.4 ± 25.2 nmol TG/mg liver, control vs. treated, P < 0.05) with elevated plasma nonesterified fatty acid (0.68 ± 0.25 vs. 1.21 ± 0.41 mM, P < 0.05) and plasma TG (0.39 ± 0.16 vs. 0.60 ± 0.10 mM, P < 0.05) concentrations. VLDL-TG production rate was not affected on CPT1 inhibition (74.9 ± 15.2 vs. 79.1 ± 12.8 μmol TG·kg−1·min−1, control vs. treated) although treated mice secreted larger VLDL particles (59.3 ± 3.6 vs. 66.6 ± 4.5 nm diameter, P < 0.05). Infusion of insulin under euglycemic conditions suppressed VLDL production rate in control and treated mice by 43 and 54%, respectively, with formation of smaller VLDL particles (51.2 ± 2.5 and 53.2 ± 2.8 nm diameter). Insulin-induced insulin receptor substrate (IRS)1- and IRS2-associated PI3-kinase activity and PKB-phosphorylation were not affected on TDGA treatment. In conclusion, acute hepatic steatosis caused by pharmacological inhibition of β-oxidation is not associated with reduced hepatic insulin sensitivity, indicating that hepatocellular fat content per se is not causally related to insulin resistance.
S-nitroso-albumin carries a thiol-labile pool of nitric oxide, which causes venodilation in the rat
Authors: Orie Nelson N. , Vallance Patrick , Jones Dean P. , Moore Kevin P.
Published: April 2005

It is now established that S-nitroso-albumin (SNO-albumin) circulates at low nanomolar concentrations under physiological conditions, but concentrations may increase to micromolar levels during disease states (e.g., cirrhosis or endotoxemia). This study tested the hypothesis that high concentrations of SNO-albumin observed in some diseases modulate vascular function and that it acts as a stable reservoir of nitric oxide (NO), releasing this molecule when the concentrations of low-molecular-weight thiols are increased. SNO-albumin was infused into rats to increase the plasma concentration from <50 nmol/l to ∼4 μmol/l. This caused a 29 ± 6% drop in blood pressure, 20 ± 4% decrease in aortic blood flow, and a 25 ± 14% reduction of renal blood flow within 10 min. These observations were in striking contrast to those of an infused arterial vasodilator (hydralazine), which increased aortic blood flow, and suggested that SNO-albumin acts primarily as a venodilator in vivo. This was confirmed by the observations that glyceryl trinitrate (a venodilator) led to similar hemodynamic changes and that the hemodynamic effects of SNO-albumin are reversed by infusion of colloid. Infusion of N-acetylcysteine into animals with artificially elevated plasma SNO-albumin concentrations led to the rapid decomposition of SNO-albumin in vivo and reproduced the hemodynamic effects of SNO-albumin infusion. These data demonstrate that SNO-albumin acts primarily as a venodilator in vivo and represents a stable reservoir of NO that can release NO when the concentrations of low-molecular-weight thiols are elevated.
Expression of membrane-associated carbonic anhydrase isoforms IV, IX, XII, and XIV in the rabbit: induction of CA IV and IX during maturation
Authors: Purkerson Jeffrey M. , Schwartz George J.
Published: April 2005

Several carbonic anhydrase (CA) isoforms are associated with plasma membranes. It is probable that these enzymes interact with anion transporters to facilitate the movement of HCO3− into or out of the cell. A better knowledge of CA isoform expression in a given tissue would facilitate a systematic examination of any associations with such transporters. We examined the expression of CAs IV, IX, XII, and XIV mRNAs in rabbit tissues, including kidney, heart, lung, skeletal muscle, liver, pancreas, gall bladder, stomach, small intestine, colon, and spleen, using quantitative real-time reverse transcription polymerase chain reaction (RT-PCR). CA IV mRNA was mainly in kidney, heart, lung, colon, and gall bladder. CA IX mRNA was restricted to stomach, gall bladder, duodenum, and early jejunum. CA XII mRNA was found in kidney and colon. CA XIV mRNA was localized to heart, lung, skeletal muscle, and liver. The data indicate that there are different patterns of CA expression in various tissues: CA IX was expressed in the proximal gastrointestinal tract, whereas CA XII and CA IV were more distal. CA IV and CA XII are important kidney isoforms. CA XIV was abundant in metabolically active tissues such as liver, heart, lung, and skeletal muscle. Some significant species differences were noted in the expression of some of these isoforms; for example, CA XIV is not expressed in rabbit kidney, despite being abundant in mouse kidney. Maturational studies showed that the expression of CA IX mRNA and protein increased markedly with weaning (∼3–4 postnatal wk) and was well correlated with the maturational expression of the α-subunit of the gastric H+,K+-ATPase, suggesting that function of CA IX and the gastric H+ pump might be linked in the digestion of adult foodstuffs. The unique pattern of membrane-bound CA isoforms suggests different functional associations with transporters, depending on the physiological demands on the tissue.
Intramembranous absorption rate is unaffected by changes in amniotic fluid composition
Authors: Anderson D. , Yang Q. , Hohimer A. , Faber J. , Giraud G. , Davis L.
Published: April 2005

Experiments were performed to determine the effect of amniotic fluid dilution on the rate of intramembranous absorption. Seven fetal sheep at 118 days gestation were instrumented with a shunt between the trachea and esophagus and arterial and venous vascular catheters. In addition, the urachus of the fetal bladder was ligated, and a catheter was placed in the bladder. Ligation of the urachus does not interfere with urine flow into the amnion. After 5 days of recovery, fetuses were randomly assigned to one of two protocols; all fetuses completed both protocols. In the fetuses in the control period, continuous urine flow measurement was begun. In the fetuses assigned to the isovolumic dilution protocol, continuous urine flow measurement was also begun and, in addition, amniotic fluid was continually exchanged with lactated Ringer solution on an isovolumic basis. After 3–4 days, fetal blood pressures and amniotic fluid volumes were determined. Amniotic fluid volumes were determined by drainage. Each fetus was then assigned to the remaining protocol. The presence of the tracheal-esophageal shunt and the ligation of the urachus allowed the rate of intramembranous absorption to be calculated. Isovolumic exchange showed no effect on fetal vascular pressures, blood-gas values, or urine production. We could demonstrate no effect of isovolumic dilution of amniotic fluid on its volume. However, we were able to demonstrate an inverse relationship between amniotic fluid volume and intramembranous absorption ( P < 0.02).
Neuronal Activity Dependent on Anticipated and Elapsed Delay in Macaque Prefrontal Cortex, Frontal and Supplementary Eye Fields, and Premotor Cortex
Authors: Roesch Matthew R. , Olson Carl R.
Published: April 2005

In macaque monkeys performing a memory-guided saccade task for a reward of variable size, neuronal activity in several areas of frontal cortex is stronger when the monkey anticipates a larger reward. This effect might depend on either the size or the value of the reward. To distinguish between these possibilities, we recorded from neurons in frontal cortex while controlling value through a manipulation of time rather than amount. A cue presented at the beginning of each trial, predicted the length of the delay during which the monkey would have to maintain fixation before performing a saccade and receiving a reward of fixed size. Predicting a short delay had effects closely similar to those of predicting a large reward: 1) monkeys were more motivated when working for a reward at short delay, 2) neurons tended to fire more strongly before a short delay, 3) individual neurons firing more strongly before a short delay tended also to fire more strongly before a large reward, and 4) the tendency to fire more strongly before a short delay was far more pronounced in premotor areas caudal to the arcuate sulcus than in association areas rostral to it. The association areas, in contrast, were marked by a tendency for neurons to fire more strongly at the end of the long delay. We conclude that predicting a short delay, like predicting a large reward, induces an enhancement of neuronal activity related to motivational modulation of the monkey's preparatory state.
Prediction of Pancreatic Cancer by Serum Biomarkers Using Surface-Enhanced Laser Desorption/Ionization-Based Decision Tree Classification
Authors: Yu Yun , Chen Sheng , Wang Li-Shun , Chen Wen-Li , Guo Wei-Jian , Yan Hua , Zhang Wei-Hua , Peng Cheng-Hong , Zhang Sheng-Dao , Li Hong-Wei , Chen Guo-Qiang
Published: April 2005

Objective: In order to improve the prognosis of pancreatic cancer patients, it is crucial to explore novel tools for its early diagnosis. Here, we attempted to screen serum biomarkers to distinguish pancreatic cancer from non-cancer individuals. Methods: 47 serum samples from pancreatic cancer patients, 39 of whom had small surgically resectable cancers, were collected before surgery, and an additional 53 serum samples from age- and sex-matched individuals without cancer were used as controls. The surface-enhanced laser desorption/ionization (SELDI) ProteinChip was applied to analyze serum protein profiling. 54 samples (27 with pancreatic cancer and 27 controls) were analyzed in the training set by a decision tree algorithm to be able to separate pancreatic cancer from controls. A double-blind test was used to determine the sensitivity and specificity of the classification model. Results: A panel of six biomarkers was selected to set up a decision tree as the classification model. The model separated effectively pancreatic cancer from control samples, achieving a sensitivity of 88.9% and a specificity of 74.1%. The double-blind test challenged the model with a sensitivity of 80% and a specificity of 84.6%. Conclusion: The SELDI ProteinChip combined with an artificial intelligence classification algorithm shows great potential for the diagnosis of pancreatic cancer.