bluuebunny/crossref_metadata_2025 huggingface dataset:
Mucosal Immunization with a Novel Nanoemulsion-Based Recombinant Anthrax Protective Antigen Vaccine Protects againstBacillus anthracisSpore Challenge
Authors: Bielinska Anna U. , Janczak Katarzyna W. , Landers Jeffrey J. , Makidon Paul , Sower Laurie E. , Peterson Johnny W. , Baker James R.
Published: May 2007

The currently available commercial human anthrax vaccine requires multiple injections for efficacy and has side effects due to its alum adjuvant. These factors limit its utility when immunizing exposed populations in emergent situations. We evaluated a novel mucosal adjuvant that consists of a nontoxic, water-in-oil nanoemulsion (NE). This material does not contain a proinflammatory component but penetrates mucosal surfaces to load antigens into dendritic cells. Mice and guinea pigs were intranasally immunized with recombinantBacillus anthracisprotective antigen (rPA) mixed in NE as an adjuvant. rPA-NE immunization was effective in inducing both serum anti-PA immunoglobulin G (IgG) and bronchial anti-PA IgA and IgG antibodies after either one or two mucosal administrations. Serum anti-PA IgG2a and IgG2b antibodies and PA-specific cytokine induction after immunization indicate a Th1-polarized immune response. rPA-NE immunization also produced high titers of lethal-toxin-neutralizing serum antibodies in both mice and guinea pigs. Guinea pigs nasally immunized with rPA-NE vaccine were protected against an intradermal challenge with ∼1,000 times the 50% lethal dose (∼1,000× LD50) ofB. anthracisAmes strain spores (1.38 × 103spores), which killed control animals within 96 h. Nasal immunization also resulted in 70% and 40% survival rates against intranasal challenge with 10× LD50and 100× LD50(1.2 × 106and 1.2 × 107) Ames strain spores. Our results indicate that NE can effectively adjuvant rPA for intranasal immunization. This potentially could lead to a needle-free anthrax vaccine requiring fewer doses and having fewer side effects than the currently available human vaccine.
Mechanisms of
Chlamydia trachomatis
Entry into Nonphagocytic Cells
Authors: Hybiske Kevin , Stephens Richard S.
Published: May 2007

The mechanisms of entry for the obligate intracellular bacterium
C. trachomatis
were examined by functional disruption of proteins essential for various modes of entry. RNA interference was used to disrupt proteins with established roles in clathrin-mediated endocytosis (clathrin heavy chain, dynamin-2, heat shock 70-kDa protein 8, Arp2, cortactin, and calmodulin), caveola-mediated endocytosis (caveolin-1, dynamin-2, Arp2, NSF, and annexin II), phagocytosis (RhoA, dynamin-2, Rac1, and Arp2), and macropinocytosis (Pak1, Rac1, and Arp2). Comparative quantitative PCR analysis was performed on small interfering RNA-transfected HeLa cells to accurately determine the extent of
C. trachomatis
entry after these treatments. Key structural and regulatory factors associated with clathrin-mediated endocytosis were found to be involved in
Chlamydia
entry, whereas those for caveola-mediated endocytosis, phagocytosis, and macropinocytosis were not. Thus, clathrin and its coordinate accessory factors were required for entry of
C. trachomatis
, although additional, uncharacterized mechanisms are also utilized.
Protective Role of
Bacillus anthracis
Exosporium in Macrophage-Mediated Killing by Nitric Oxide
Authors: Weaver John , Kang Tae Jin , Raines Kimberly W. , Cao Guan-Liang , Hibbs Stephen , Tsai Pei , Baillie Les , Rosen Gerald M. , Cross Alan S.
Published: May 2007

The ability of the endospore-forming, gram-positive bacterium
Bacillus anthracis
to survive in activated macrophages is key to its germination and survival. In a previous publication, we discovered that exposure of primary murine macrophages to
B. anthracis
endospores upregulated NOS 2 concomitant with an ·NO-dependent bactericidal response. Since NOS 2 also generates O
2
·
−
, experiments were designed to determine whether NOS 2 formed peroxynitrite (ONOO
−
) from the reaction of ·NO with O
2
·
−
and if so, was ONOO
−
microbicidal toward
B. anthracis
. Our findings suggest that ONOO
−
was formed upon macrophage infection by
B. anthracis
endospores; however, ONOO
−
does not appear to exhibit microbicidal activity toward this bacterium. In contrast, the exosporium of
B. anthracis
, which exhibits arginase activity, protected
B. anthracis
from macrophage-mediated killing by decreasing ·NO levels in the macrophage. Thus, the ability of
B. anthracis
to subvert ·NO production has important implications in the control of
B. anthracis
-induced infection.
ThePseudomonas aeruginosaSecreted Protein PA2934 Decreases Apical Membrane Expression of the Cystic Fibrosis Transmembrane Conductance Regulator
Authors: MacEachran Daniel P. , Ye Siying , Bomberger Jennifer M. , Hogan Deborah A. , Swiatecka-Urban Agnieszka , Stanton Bruce A. , O'Toole George A.
Published: May 2007

We previously reported thatPseudomonas aeruginosaPA14 secretes a protein that can reduce the apical membrane expression of thecysticfibrosistransmembrane conductanceregulator (CFTR) protein. Here we report that we have used a proteomic approach to identify this secreted protein as PA2394, and we have named the genecif, forCFTRinhibitoryfactor. We demonstrate that Cif is a secreted protein and is found associated with outer membrane-derived vesicles. Expression of Cif inEscherichia coliand purification of the C-terminal six-His-tagged Cif protein showed that Cif is necessary and sufficient to mediate the reduction in apical membrane expression of CFTR and a concomitant reduction in CFTR-mediated Cl−ion secretion. Cif demonstrates epoxide hydrolase activity in vitro and requires a highly conserved histidine residue identified in α/β hydrolase family enzymes to catalyze this reaction. Mutating this histidine residue also abolishes the ability of Cif to reduce apical membrane CFTR expression. Finally, we demonstrate that thecifgene is expressed in the cystic fibrosis (CF) lung and that nonmucoid isolates ofP. aeruginosashow greater expression of the gene than do mucoid isolates. We propose a model in which the Cif-mediated decrease in apical membrane expression of CFTR by environmental isolates ofP. aeruginosafacilitates the colonization of the CF lung by this microbe.
Enhanced Immunity toPlasmodium falciparumCircumsporozoite Protein (PfCSP) by UsingSalmonella entericaSerovar Typhi Expressing PfCSP and a PfCSP-Encoding DNA Vaccine in a Heterologous Prime-Boost Strategy
Authors: Chinchilla Magaly , Pasetti Marcela F. , Medina-Moreno Sandra , Wang Jin Yuan , Gomez-Duarte Oscar G. , Stout Rick , Levine Myron M. , Galen James E.
Published: May 2007

TwoSalmonella entericaserovar Typhi strains that express and export a truncated version ofPlasmodium falciparumcircumsporozoite surface protein (tCSP) fused toSalmonellaserovar TyphicytolysinA(ClyA) were constructed as a first step in the development of a preerythrocytic malaria vaccine. Synthetic codon-optimized genes (t-csp1and t-csp2), containing immunodominant B- and T-cell epitopes present in nativeP. falciparumcircumsporozoite surface protein (PfCSP), were fused in frame to the carboxyl terminus of the ClyA gene (clyA::t-csp) in genetically stabilized expression plasmids. Expression and export of ClyA-tCSP1 and ClyA-tCSP2 bySalmonellaserovar Typhi vaccine strain CVD 908-htrAwere demonstrated by immunoblotting of whole-cell lysates and culture supernatants. The immunogenicity of these constructs was evaluated using a “heterologous prime-boost” approach consisting of mucosal priming withSalmonellaserovar Typhi expressing ClyA-tCSP1 and ClyA-tCSP2, followed by parenteral boosting with PfCSP DNA vaccines pVR2510 and pVR2571. Mice primed intranasally on days 0 and 28 with CVD 908-htrA(pSEC10tcsp2) and boosted intradermally on day 56 with PfCSP DNA vaccine pVR2571 induced high titers of serum NANP immunoglobulin G (IgG) (predominantly IgG2a); no serological responses to DNA vaccination were observed in the absence ofSalmonellaserovar Typhi-PfCSP priming. Mice primed withSalmonellaserovar Typhi expressing tCSP2 and boosted with PfCSP DNA also developed high frequencies of gamma interferon-secreting cells, which surpassed those produced by PfCSP DNA in the absence of priming. A prime-boost regimen consisting of mucosal delivery of PfCSP exported from aSalmonella-based live-vector vaccine followed by a parenteral PfCSP DNA boosting is a promising strategy for the development of a live-vector-based malaria vaccine.
PorA Variable Antigenic Regions VR1, VR2, and VR3 of
Neisseria meningitidis
Serogroups B and C Isolated in Brazil from 1999 to 2004
Authors: de Filippis Ivano , de Andrade Claudia Ferreira , Silva Luciete , Prevots D. Rebecca , Vicente Ana Carolina P.
Published: May 2007

The high genetic diversity found among the PorA regions VR1 and VR2 of 101
Neisseria meningitidis
isolates from patients with meningococcal disease and healthy carriers in Brazil contrasts with the stability found in the PorA VR3 of these isolates. The presence of VR3 epitope variant 35 or 36 on the surfaces of 87% of the strains analyzed suggests that these antigens should be considered for inclusion in new formulations of vaccines against serogroup B meningococci in Brazil.
Influence ofMycobacterium aviumsubsp.paratuberculosison Colitis Development and Specific Immune Responses during Disease
Authors: Singh Udai P. , Singh Shailesh , Singh Rajesh , Karls Russell K. , Quinn Frederick D. , Potter Morris E. , Lillard James W.
Published: May 2007

The granulomatous and intramural inflammation observed in cases of inflammatory bowel diseases (IBD) and veterinary Johne's disease suggests thatMycobacterium aviumsubsp.paratuberculosisis a causative agent. However, an incomplete understanding of the immunological steps responsible for the pathologies of IBD makes this conclusion uncertain. Sera from interleukin-10-deficient (IL-10−/−) mice with spontaneous colitis displayed significantly higherM. aviumsubsp.paratuberculosis-specific immunoglobulin G2a antibody responses than did sera from similar mice without disease. Pathogen-free IL-10−/−mice received control vehicle or the vehicle containing heat-killed or liveM. aviumsubsp.paratuberculosis. Mucosal CD4+T cells from the mice that developed colitis proliferated and secreted higher levels of gamma interferon and tumor necrosis factor alpha after ex vivo stimulation with a Vβ11+T-cell receptor-restricted peptide from the MPT59 antigen (Ag85B) than those secreted from cells from mice before the onset of colitis. The data from this study provide important information regarding the mechanisms of colitis in IL-10−/−mice, which are driven in part by Ag85B-specific T cells. The data suggest a plausible mechanism of Ag-specific T-cell responses in colitis driven by potent Ags conserved inMycobacteriumspecies.
Ligand Migration in the Reaction of Titanium Complexes with AlMe3
Authors: Kobyłka Michał J. , Jerzykiewicz Lucjan B. , Patton Jasson T. , Przybylak Szymon , Utko Józef , Sobota Piotr
Published: May 2007

Five different titanium compounds cis-[Ti(η2-hbo)2(OEt)2]·0.5toluene (1), cis-[TiCl2(η2-thp)2] (2), [TiCl2(edbp)2] (3), [Ti2(μ-OMe)2(edbp)2(Me)2] (6), [Ti2(μ-OMe)2(edbp)2(OMe)2] (7) (Hhbo = 2-(2-hydroxyfenyl)benzoxazole, Hthp = tetrahydropyran-2-methanol, H2edbp = 2,2'-ethylidenebis(4,6-di-tert-butylphenol)), have been prepared and tested in combination with MAO as catalysts for propene polymerization and ethene and oct-1-ene copolymerization with the aim of gaining insight into the structure of the active species. Investigation of the 1/AlMe3 or 2/AlMe3 systems resulted in isolation of [Al(η2-hbo)2(Me)] (4) and [Al2(μ2-η2-thp)2(Me)4] (5) in high yields. This indicates that the trimethylaluminum contained in MAO abstracts ligands from 1 or 2, affecting thus the catalytic performance of the 1,2/MAO catalysts. In contrast, compound 3 reacted with MAO affording methylated product 6. Accordingly, the 3/MAO catalyst differed from the above ones, furnishing at 70 °C e.g., narrow molecular weight polypropylene (Mn = 454 000; Mw/Mn = 2.49; Tm = 158.2 °C).
Injuries in the Victorian thoroughbred racing industry
Authors: Cowley S , Bowman B , Lawrance M
Published: May 2007

There is increasing concern in Australia about safety in the thoroughbred racing industry, but there has been no reported analysis of injury data. This review analyses injury and workers’ compensation data recorded in Victoria. On the basis of the results, it is recommended that the injury and incident data collection systems are improved such that they are not only more complete but also accumulate more detailed information about the location of an incident or injury event, the activity at the time of the incident or injury event, and factors that may have influenced the occurrence.
Impact of low-intensity isocapnic hyperpnoea on blood lactate disappearance after exhaustive arm exercise
Authors: Perret Claudio , Mueller Gabi
Published: May 2007

Objective:

To investigate the impact of low-intensity isocapnic hyperpnoea (IH) on blood lactate disappearance after exhaustive arm exercise in comparison with passive and active recovery using the previously loaded muscle group.

Design:

Randomised, crossover trial.

Setting:

Institute for Sports Medicine.

Participants:

18 healthy non-smoking and physically active male subjects.

Interventions:

Subjects performed three arm cranking tests to volitional exhaustion on 3 different days at least 48 h apart. Arm exercise was randomly followed by 30 min of passive recovery (PR), active arm cranking (AC) at 30% of peak power output or ventilatory recovery (VR) by means of IH at 30% of 12 s maximal voluntary ventilation. Blood lactate concentrations were measured every 2 min during recovery.

Main outcome measurements:

Blood lactate disappearance during the three different recovery strategies.

Results:

No significant differences in blood lactate concentrations were found between interventions PR, AC and VR during the whole measurement period. Mean (SD) peak lactate concentrations were 11.09 (1.98) mmol/l for PR, 11.13 (1.44) mmol/l for AC and 11.25 (1.93) mmol/l for VR. At the end of the recovery period measured lactate concentrations were 4.35 (1.56) mmol/l for PR, 3.77 (1.60) mmol/l for AC and 4.09 (1.35) mmol/l for VR. Moreover, all other variables measured were not significantly different, with the exception of higher average recovery heart rates during AC (116 (9) bpm) and VR (111 (17) bpm) compared with PR (93 (11) bpm).

Conclusion:

Low-intensity IH seems not to enhance blood lactate disappearance after exhaustive arm exercise compared with passive or active recovery using the previously loaded muscle group. The magnitude of the involved muscle mass appears critical to effective active recovery.
An approach for the synthesis of duplexes containing N3T-butyl-N3T interstrand cross-links via a bisphosphoramidite strategy
Authors: Wilds Christopher James , Palus Ernest , Noronha Anne Marietta
Published: May 2007

DNA duplexes containing an interstrand cross-link have been synthesized utilizing a bis-3′-O-phosphoramidite deoxythymidine dimer where the N3 atoms are bridged by a butyl linker. With this approach sufficient quantities of high purity cross-linked duplexes are obtained that will enable various biochemical and structural studies to aid in research directed towards understanding the mechanism of interstrand cross-linked DNA repair. This methodology has advantages over a previously reported method to synthesize cross-linked DNA duplexes involving a monophosphoramidite of the same cross-linked thymidine dimer including circumventing the use of costly 5′-O-deoxyphosphoramidites in the assembly of the cross-linked duplex by solid-phase synthesis. This strategy can be employed to produce cross-linked duplexes in which the lesions are engineered to have a directly opposed (1–1) or staggered (1–2 or 2–1) orientations. Biophysical studies of duplexes containing this N3T-butyl-N3T cross-link in staggered 1–2 and 2–1 orientations reveal that both duplexes have a higher Tm than a non-cross-linked duplex suggesting that these linkages do not result in the destabilization of duplex DNA. Circular dichroism spectra of the 1–2 and 2–1 cross-linked duplexes exhibit minor differences from B-form structure, which correlates with molecular modeling studies.Key words: chemically modified oligonucleotides, interstrand cross-link, DNA adduct, DNA repair.
Interactions of platinum(II)-derivatized triplex-forming oligonucleotides with DNA
Authors: Campbell Meghan A , Mason Tracey McGregor , Miller Paul S
Published: May 2007

Polypyrimidine oligonucleotides can bind to tracts of contiguous purines in double-stranded DNA to form triple-stranded complexes. The stability of the triplex is reduced significantly if the target purine tract is interrupted by a single pyrimidine. Previous studies have shown that incorporation of an N4-aminoalkylcytosine into the triplex-forming oligonucleotide (TFO), opposite a single CG interruption, facilitates triplex formation. Examination of molecular models suggested that further modification of the amino group of the aminoalkyl arm might enable adduct formation with the N7 of the guanine of the CG interruption. To test this, we prepared 2′-deoxyribo-and 2′-O-methylribo-TFOs that contained cytosine (C), N4-(2-aminoethyl)cytosine (ae-C), or diethylenetriamineplatinum(II) (DPt-C) or cis-aquodiammineplatinum(II) (cPt-C) derivatives of N4-(2-aminoethyl)cytosine, positioned opposite a CG interruption of a polypurine tract found in the pol gene of HIV-1 proviral DNA. Although the C- and ae-C-derivatized deoxyribo-TFOs formed triplexes of modest stability and the DPt-C-modified TFO failed to form a triplex, the C- and ae-C-derivatized 2′-O-methylribo-TFOs formed remarkably stable triplexes (Tm = 57 °C). The DPt-C- and cPt-C-modified 2′-O-methylribo-TFOs also formed triplexes, although their stabilities were reduced (Tm = 33 °C), suggesting that the tethered platinum group may interfere sterically with TFO binding. Consistent with this hypothesis was the observation that triplex stability was restored (Tm = 57 °C) when the diethylenetriamineplatinum(II) group was tethered to the 5′-end of the 2′-O-methylribo-TFO via a 2-aminoethylcarbamate linkage. Taken together, these results suggest that 2′-O-methylribo-TFOs may be particularly useful in targeting purine tracts in DNA that have CG interruptions, and that further modification with platinum derivatives could lead to the design of TFOs that are capable of covalent binding to their target, thus increasing the effectiveness of the TFO.Key words: triplex-forming oligonucleotide, TFO, cisplatin, interrupted polypurine tract.
Characterization of pH3DZ1 — An RNA-cleaving deoxyribozyme with optimal activity at pH 3
Authors: Ali Md. Monsur , Kandadai Srinivas A , Li Yingfu
Published: May 2007

We previously described a cis-acting RNA-cleaving deoxyribozyme known as pH3DZ1 that exhibits optimal catalytic activity at pH 3.0 (Zhongjie Liu, Shirley H. Mei, John D. Brennan, and Yingfu Li. J. Am. Chem. Soc. 125, 7539 (2003)). This DNA catalyst was made of a 99-nucleotide (nt) catalytic domain covalently linked to a 23-nt DNA–RNA chimeric substrate containing a single ribonucleotide as the cleavage site. In the present work, we conducted an extensive sequence examination of this deoxyribozyme via nucleotide truncation and reselection experiments, with a goal to minimize its size and identify the nucleotides that are crucial to its catalytic function. A trans-acting deoxyribozyme that can process an external substrate was also successfully designed. Stretches of 30 and 17 nucleotides from the 5′ and 3′ ends of the trans catalyst, respectively, were found to be completely dispensable; in contrast, few nucleotides could be deleted internally without producing a detrimental effect. The reselection experiment led to the discovery of 7 and 5 absolutely conserved nucleotides located at the 5′ and 3′ ends of the minimized catalyst, respectively, separated by a 31-nt element in which 14 highly conserved nucleotides were scattered among 17 variable nucleotides. The shortened deoxyribozyme and the original catalyst showed a similar pH profile with the optimal activity at pH 3; however, the minimized deoxyribozyme still exhibited strong catalytic activity at pH 2.5, while the full-length catalyst was barely active at this pH. Finally, it was found that this deoxyribozyme generated two cleavage fragments, one with 2′,3′-cyclic phosphate and the other with 5′-OH.Key words: DNA, deoxyribozyme, RNA cleavage, in vitro selection, catalysis.
Ion-tagged synthesis of an oligoribonucleotide pentamer — The continuing versatility of TBDMS chemistry
Authors: Donga Robert A , Chan Tak-Hang , Damha Masad J
Published: May 2007

An oligoribonucleotide has been synthesized in solution, using an ionic-liquid-based soluble tag at a scale several hundred times that of a standard solid-phase synthesis approach. Ogilvie's 2′-TBDMS strategy was adopted, and because of the resultant increase in lipophilicity, it allowed an easier purification of the growing oligomer compared with the previously observed for DNA, which does not require 2′ protection. The procedure is illustrated by the synthesis of the pentaribonucleotide sequence AGAUC, corresponding to a segment of the tRNAfMet from E. coli.Key words: solution-phase RNA synthesis, ionic-liquid tag.
Hydrophilic modifications in peptide nucleic acid — Synthesis and properties of PNA possessing 5-hydroxymethyluracil and 5-hydroxymethylcytosine
Authors: Hudson Robert HE , Liu Yuhong , Wojciechowski Filip
Published: May 2007

We have investigated the chemistry for the incorporation of C5-hydroxymethyl-uracil and -cytosine in peptide nucleic acid (PNA) and the subsequent effect of this modification on PNA hybridization behavior. Largely based on literature precedent, we prepared a peptide nucleic acid monomer, possessing 5-hydroxymethyuracil, which was compatible with Fmoc-based oligopeptide synthesis. An improved, large-scale synthesis of 5-hydroxymethylcytosine was developed, as a starting point for the synthesis of a monomer containing this nucleobase. In each case, the hydroxyl group was blocked as a t-butyldiphenylsilyl ether, and the exocyclic amino group of cytosine was additionally blocked with the benzoyl-group. The modified monomers were incorporated into isolated positions in the oligomer sequence using standard protocols. The modified oligomers showed that the 5-hydroxymethyl group is compatible with triplex and duplex formation.Key words: peptide nucleic acid, hydroxymethyluracil, hydroxymethylcytosine, modified nucleobase, hybridization.
Kinetic characterization of a cis- and trans-acting M2+-independent DNAzyme that depends on synthetic RNaseA-like functionality — Burst-phase kinetics from the coalescence of two active DNAzyme folds
Authors: Ting Richard , Thomas Jason M , Perrin David M
Published: May 2007

This work describes the kinetics of the DNAzyme 925-11, a combinatorially selected, M2+-independent ribophosphodiesterase that is covalently modified with both cationic amines and imidazoles. At 13 °C, cis- and trans-cleaving constructs of 925-11 demonstrate the highest rate constants reported to date for any M2+-independent nucleic acid catalyst, investigated at physiological ionic strength and pH 7.5 (0.3 min–1for self cleavage and 0.2 min–1for intermolecular cleavage). In contrast to the cis-cleaving species, single-turnover experiments with the trans-cleaving species exhibit biphasic cleavage data, suggesting the presence of two conformations of the catalyst–substrate complex. Pulse–chase experiments demonstrate that both complexes lead to substrate cleavage. Under multiple-turnover conditions, the higher rate constant appears in a burst phase that decays to a slower steady state exhibiting a rate constant of 0.0077 min–1, a value approximating that of the slow-cleaving phase seen in single-turnover experiments. Slow product release is excluded as the source of the burst phase. An integrated rate equation is derived to describe burst-phase kinetics based on the funneling of the initial population of fast-cleaving conformation into a steady-state population composed largely of the slow-cleaving conformation.Key words: RNase mimics, DNAzymes, ribozymes, kinetics, RNA cleavage.
Quantum Hall Effect in Graphene
Authors: Koshino Mikito , Ando Tsuneya
Published: May 2007

The integer quantum Hall effect is studied for a non-interacting electron in a monolayer graphene. We numerically calculate the Hall conductivity in a single Landau level with disorder, and estimate the critical energies for the extended states in thermodynamic limit. We show that a valley-degenerated (K and K′) Landau band has extended levels at two different energies, indicating that an extra Hall plateau appears inside.
MAGNETO-SPECTROSCOPY OF EPITAXIAL GRAPHENE
Authors: SADOWSKI M. L. , MARTINEZ G. , POTEMSKI M. , BERGER C. , DE HEER W. A.
Published: May 2007

We present a far infrared investigation of the optical transitions in epitaxial graphene subjected to a perpendicular magnetic field. Cyclotron-resonance-like transitions between adjacent electron Landau levels are observed, as well as interband transitions. The results are discussed in terms of existing theoretical models of Dirac fermions in graphene, and the relevant optical selection rules.
NOVEL ONE-DIMENSIONAL STATES IN A BENT QUANTUM HALL JUNCTION
Authors: GRAYSON M. , STEINKE L. , HUBER M. , SCHUH D. , BICHLER M. , ABSTREITER G. , HOEPPEL L. , SMET J. , v. KLITZING K. , MAUDE D. K.
Published: May 2007

Using a recently developed crystal growth technique (see Fig. 1), we have succeeded in creating a two-dimensional (2D) electron system that is bent at an atomically sharp angle of 90°1. Naming the two 2D systems after their substrate (S) and precleave (P) facets, we can measure their densities ns and np. In the presence of a tilted magnetic field, this system realizes an abrupt junction between two quantum Hall effect (QH) systems with arbitrary filling factors2νs = nsh/eB cos (θ) and νp = nph/eB sin (θ). When the two filling factors are equal νs = νp, the corner junction represents a multimode wire with the maximum number of forward & reverse moving modes equalling the filling factor ν plus two spin degenerate modes from corner-accumulation wire.

The conductance of this bent QH system dI/dV(V) or G(T) can be characterized with four-point measurements. As long as the excitation energy (V or T, respectively) is smaller than the QH gap energy, there is no scattering of electrons away from the wire system to the 2D bulk and the transport is truly one-dimensional. The devices studied here are from 0.4 - 4 mm long with ohmic contacts alloyed on both facets away from the junction. The resulting 1D wire at the corner junction has exhibited metallic, insulating, and critical phases depending on filling factor, with all 1D conductances of order 0.02e2/h or below. The insulating 1D behavior occurs for ν = 1 and ν = 2, and is manifest in a vanishing 1D conductance at low temperatures and low dc voltage biases. Metallic 1D behavior occurs for ν = 1/3 where the conductance rises with decreasing temperature and the dc bias shows a large zero-bias peak in the differential conductivity. The so-called critical behavior has only weak temperature dependence and a weak zero-bias dip in the dc bias voltage dependence. The conductance G at ν = 3 and ν = 4 goes inversely with the wire length L indicating that scattering is distributed equally along the wire length.

These observations can be partly explained with Hartree calculations of the bent quantum Hall junction. Low magnetic fields (ν = 3 and 4) are expected to manifest a multimode wire, which provides a basis for understanding the critical phase. Higher magnetic fields (ν = 1 and 2) are expected to open up a gap in the 1D energy spectrum at the corner, resulting in the experimentally observed insulating phase. Alternatively, disorder may also explain the 1D insulating behavior via scaling theory of localization. The highest magnetic fields for the fractional state ν = 1/3 show the remarkable metallic phase which might be explained in terms of an antiwire between counterpropagating ν = 1/3 Luttinger liquid edges which are randomly coupled by electron back-scattering events3.
TWO-DIMENSIONAL HOLES IN GaAs HIGFETs: FABRICATION METHODS AND TRANSPORT MEASUREMENTS
Authors: HUANG JIAN , NOVIKOV D. S. , TSUI D. C. , PFEIFFER L. N. , WEST K. W.
Published: May 2007

We present a fabrication process and results of transport measurements of a number of p-channel heterojunction-insulated-gate field-effect transistors (HIGFETs). Without intentional doping in HIGFETs, the disorder is likely to be less than that in the modulation-doped samples. We established a process that eliminates the well-known gate leakage problem. The hole density in our devices can be continuously tuned down to a record low value of 7 × 108 cm -2. Remarkably, such a dilute system (with Fermi wavelength approaching 1 μm) exhibits a non-activated conductivity that grows with temperature approximately as a power law at sufficiently low temperatures. We contrast it with the activated transport found in more disordered samples and discuss possible transport mechanisms in this strongly-interacting regime.
Investigations of the νT=1 Exciton Condensate
Authors: Wiersma R. D. , Lok J. G. S. , Tiemann L. , Dietsche W. , von Klitzing K. , Wegscheider W. , Schuh D.
Published: May 2007

Recent experiments on quantum Hall bilayers in the vicinity of total filling factor 1 (νT=1) have revealed the possibility of a superfluidic exciton condensate. We report on our experimental work involving the νT=1 exciton condensate in independently contacted bilayer two-dimensional electron systems. We reproduce the previously reported zero bias resonant tunneling peak, a quantized Hall drag resistivity, and in counter-flow configuration, the near vanishing of both ρxx and ρxy resistivity components. At balanced electron densities in the layers, we find for both drag and counter-flow current configurations, thermally activated transport with a monotonic increase of the activation energy for d/ℓB < 1.65 with activation energies up to 0.4 K. In the imbalanced system the activation energies show a striking asymmetry around the balance point, implying that the gap to charge excitations is considerably different in the separate layers that form the bilayer condensate. This indicates that the measured activation energy is neither the binding energy of the excitons, nor their condensation energy. We establish a phase diagram of the excitonic condensate showing the enhancement of this state at slight imbalances.
ENHANCEMENT OF THE LONGITUDINAL MAGNETIC MOMENT OF THE EXCITON DUE TO ITS MOTION
Authors: KOCHERESHKO V. P. , PLATONOV A. V. , MIKHAILOV G. V. , DAVIES J. J. , WOLVERSON D. , COX R. T. , CIBERT J. , MARIETTE H. , LOGINOV D. K. , UBYIVOVK E. V. , EFIMOV Yu. P. , ELISEEV S. A.
Published: May 2007

A new physical phenomenon has been found, namely a giant enhancement of the exciton magnetic moment due to its motion. This phenomenon was observed in GaAs , CdTe and ZnSe based quantum wells with QW widths much larger than the exciton Bohr radius. Consequently, it is relevant to any crystal with zinc blende structure.
QUANTUM COMPUTING WITH NON-ABELIAN QUASIPARTICLES
Authors: BONESTEEL N. E. , HORMOZI L. , ZIKOS G. , SIMON S. H.
Published: May 2007

In topological quantum computation quantum information is stored in exotic states of matter which are intrinsically protected from decoherence, and quantum operations are carried out by dragging particle-like excitations (quasiparticles) around one another in two space dimensions. The resulting quasiparticle trajectories define world-lines in three dimensional space-time, and the corresponding quantum operations depend only on the topology of the braids formed by these world-lines. We describe recent work showing how to find braids which can be used to perform arbitrary quantum computations using a specific kind of quasiparticle (those described by the so-called Fibonacci anyon model) which are thought to exist in the experimentally observed ν = 12/5 fractional quantum Hall state.
ANOMALOUS QUANTUM HALL RESISTANCE IN Al0.6Ga0.4As0.1Sb0.9/InAs QUANTUM WELL WITH TUNABLE CARRIER DENSITY
Authors: OTO K. , TAMIYA S. , ISHIDA S. , OKAMOTO A. , SHIBASAKI I.
Published: May 2007

We have investigated magneto-resistance in InAs/Al 0.6 Ga 0.4 As 0.1 Sb 0.9 quantum well (QW), where the lattice mismatch at the interface is less than 2 %. The carrier concentration can be tuned by using positive and negative persistent photoconductivity effect, selected by the wavelength (λ=1.6μ m or 0.95 μm) of illumination. The electrons and holes coexist in the QW structure, and the contribution of both carriers should be taken into account. The observed deviation of Hall plateaus from the quantized value can be understood by considering the carrier transport in both electron and hole edge channels, and the equilibrium of chemical potential at the all electrodes in the sample. The transport properties in quantum Hall regime measured in the samples with the QW thickness of 15, 50 and 150 nm are reported.
CIRCUIT TYPE SIMULATIONS OF MAGNETO-TRANSPORT IN THE QUANTUM HALL EFFECT REGIME
Authors: OSWALD J.
Published: May 2007

A Landauer-Büttiker type representation of bulk current transport is used for the numerical simulation of the magneto-transport of 2-dimensional electron systems. It allows us to build up a network model, which describes the effect of non-equilibrium currents injected via metallic contacts like in real experiments. Our model suggests a peak-like contribution of de-localized states to the bulk conductance, which appears embedded in the density of states (DOS) of the Landau levels (LLs). In contrast, the localization picture of the quantum Hall effect suggests almost sharp boundaries between localized and de-localized states and does not explicitly map out their contribution to the bulk conductance. Most recent experiments by B. A. Piot et al. suggest a similar peak-like contribution of de-localized states near the center of the LLs. Our simulation results for the same parameter values as determined by Piot et al. reproduce their experimental data very well.
QUANTUM EFFICIENCY OF A 2-LEVEL InAs/AlSb QUANTUM CASCADE STRUCTURE
Authors: FAUGERAS CLEMENT , LEULIET AUDE , VASANELLI ANGELA , SIRTORI CARLO , WADE AARON , FEDOROV GEORGY , SMIRNOV DMITRY , TEISSIER ROLAND , BARANOV ALEXEI , BARATE DAVID , DEVENSON JAN
Published: May 2007

The quantum efficiency of an electroluminescent intersubband emitter based on InAs/AlSb has been measured as a function of the magnetic field up to 20T. Two series of oscillations periodic in 1/B are observed, corresponding to the elastic and inelastic scattering of electrons of the upper state of the radiative transitions. Experimental results are accurately reproduced by a calculation of the excited state lifetime as a function of the applied magnetic field. The interpretation of these data gives an exact measure of the relative weight of the scattering mechanisms and allows the extraction of material parameters such as the energy dependent electron effective mass and the optical phonon energy.
MANY-BODY EFFECTS IN LANDAU LEVELS: NON-COMMUTATIVE GEOMETRY AND SQUEEZED CORRELATED STATES
Authors: DZYUBENKO ALEXANDER
Published: May 2007

We discuss symmetry-driven squeezing and coherent states of few-particle systems in magnetic fields. An operator approach using canonical transformations and the SU(1, 1) algebras is developed for considering Coulomb correlations in the lowest Landau levels.
MICROWAVE RESPONSE OF A TWO-DIMENSIONAL ELECTRON STRIPE: ELECTRODYNAMIC EFFECTS AND THE INFLUENCE OF CONTACTS
Authors: MIKHAILOV S. A. , SAVOSTIANOVA N. A.
Published: May 2007

Microwave response of a two-dimensional (2D) electron stripe, supplied by two semi-infinite side contacts, is theoretically studied taking into account retardation and radiative effects. Absorption spectra of the stripe are calculated as a function of the microwave frequency ω, magnetic field B, parameters of the 2D electron gas and of the contacts. It is shown that the contacts substantially modify the position, the linewidth and the strength of the absorption resonances, leading for instance to the inversion of the ab-sorption maxima of the right and left circularly polarized radiation in magnetic fields.
HALL RESISTANCE AND MANY-BODY EFFECTS IN A PARABOLIC WELL
Authors: ORTIZ DE ZEVALLOS A. M. , MAMANI N. C. , GUSEV G. M. , QUIVY A. A. , LAMAS T. E. , PORTAL J. C.
Published: May 2007

We report on Hall effect measurements in 1000-4000 Åwide AlxGax-1As parabolic wells with quasi-two-dimensional electrons and holes in the presence of a perpendicular magnetic field. Above a critical magnetic field B > 3T, the Hall resistance is found to increase when temperature decreases. We attribute such an enhanced Hall slope to the variation of the carrier density. The Hartree and exchange-correlation terms produce a strong variation of the potential well shap: the width of the electronic and hole slabs shrinks as magnetic field increases, which in turn leads to a charge redistribution between the well and impurity layer.
INTERLAYER SURFACE TRANSPORT IN MULTILAYER QUANTUM HALL SYSTEMS UNDER TILTED MAGNETIC FIELDS
Authors: Okui Shinji , Ohmichi Eiji , Osada Toshihito
Published: May 2007

We have studied interlayer surface transport in multilayer quantum Hall systems under tilted magnetic fields. Under the fields normal to layers, edge state of each layer couples with each other due to interlayer tunneling forming the chiral surface state, which causes the surface transport. Once the field is tilted to the normal of the surface, the inter-edge tunneling is suppressed except at the certain magic angles. On the other hands, when the field is tilted in the surface, the inter-edge tunneling reflects the density distribution of the edge state. We carried out the experiments to confirm these features using GaAs/AlGaAs superlattices.
QUANTUM BEATS IN SEMICONDUCTORS
Authors: ZIENER CHRISTIAN H. , KAMPF THOMAS , BAUER WOLFGANG R. , JAKOB PETER M. , GLUTSCH STEPHAN , BECHSTEDT FRIEDHELM
Published: May 2007

In this paper we present a new method to calculate the Faraday rotation using the Jones calculus applicable to light pulses. This result is used to calculate the quantum beats in a magnetic semiconductor generated by pump-probe experiments in Faraday geometry. Considering a six level system and neglecting band dispersion as well as Coulomb interaction we find the Luttinger parameter of the valence band to be the only band parameter contributing to the quantum beat frequency.
MAGNETO-OPTICS OF QUANTUM DOTS IN THE NEAR FIELD
Authors: SIMSERIDES CONSTANTINOS , ZORA ANNA , TRIBERIS GEORGIOS
Published: May 2007

We examine a quantum dot (QD) illuminated in the near field with subwavelength spatial resolution, while simultaneously it is subjected to a magnetic field of variable orientation and magnitude. The magnetic field orientation can conserve or destroy the zero-magnetic-field ("structural") symmetry. The asymmetry induced by the magnetic field -except for specific orientations along symmetry axes- can be uncovered in the near-field (NF) but not in the far-field (FF) spectra. We predict that NF magnetoabsorption experiments of realistic spatial resolution could reveal the QD symmetry. This exceptional symmetry-resolving power of the near-field optics, is lost in the far field.
THE FEASIBLE DOMAINS AND THEIR BIFURCATIONS IN AN EXTENDED LOGISTIC MODEL WITH AN EXTERNAL INTERFERENCE
Authors: GU EN-GUO
Published: May 2007

This paper is devoted to the study of the properties of basins of attraction and the domains of feasible trajectories (discrete trajectories having an ecological sense) generated by a family of two-dimensional map T related to a discrete model of populations generation. The inverse of T has vanishing denominator giving rise to nonclassical singularities: a nondefinition line, a focal point and a prefocal line. Furthermore, the differences and relations between the feasible set, the feasible domains and the basins of attraction are presented. A phenomena of coexistence of attractors is shown. The structure of a chaotic repellor is interpreted by use of the singularities.
NONSTANDARD DISCRETIZATION SCHEMES APPLIED TO THE CONSERVATIVE HÉNON–HEILES SYSTEM
Authors: LETELLIER CHRISTOPHE , MENDES EDUARDO M. A. M. , MICKENS RONALD E.
Published: May 2007

The discretization of ordinary differential equations is investigated for the case of the conservative Hénon–Heiles system. Starting from a discrete Hamiltonian function, which is invariant under time reversal, discrete equations of motion are analytically obtained using three different discretization schemes recently proposed and investigated in the literature. In the case where the discretization scheme successfully provide discrete systems in which the trace of the Jacobian matrix corresponding to the property required by a conservative system is preserved, it is shown that they are not necessarily invariant to time reversal. Such models are however quite robust when the time step is increased. For the schemes where the trace of Jacobian matrix does not match the condition required by conservative systems, it is shown that energy conservation is not achieved and the original dynamics is lost. Steps toward the solution to this problem are given.
A CHAOS-BASED PSEUDO-RANDOM NUMBER GENERATOR AND ITS APPLICATION IN VOICE COMMUNICATIONS
Authors: TANG K. W. , TANG WALLACE K. S. , MAN K. F.
Published: May 2007

In this paper, a fast chaos-based pseudo-random number generator (PRNG) is proposed for secured communications. In order to achieve fast throughput and facilitate hardware realization, 32-bit fixed point representation and arithmetic are used. Even under such configuration with quantization errors which will make the normal chaos-based PRNG impractical, our scheme can pass all the statistical tests in the up-to-date National Institute of Standards and Technology (NIST) test suite with the output bit rate up to 134 Mbps in a 2.6 GHz Pentium-4 machine. With such a fast PRNG, a stream cipher is hence designed for the application of online secure voice communication system with User Datagram Protocol (UDP).
CHARACTERIZATION OF STATIC BIFURCATIONS FOR MAPS IN THE FREQUENCY DOMAIN
Authors: ZENG LI , ZHAO YI
Published: May 2007

In this paper n-dimensional discrete-time systems with static bifurcations are considered from the viewpoint of control theory. This paper presents an adaption of available formulas for bifurcation analysis in two-dimensional continuous-time systems to the case of smooth maps using a frequency domain approach. The analyzed bifurcations are the building blocks to understand other more complex singularities and to propose certain methods for controlling the bifurcation behavior in nonlinear maps in the future.
BIFURCATIONS IN TWO-DIMENSIONAL HINDMARSH–ROSE TYPE MODEL
Authors: TSUJI SHIGEKI , UETA TETSUSHI , KAWAKAMI HIROSHI , FUJII HIROSHI , AIHARA KAZUYUKI
Published: May 2007

We analyze a two-dimensional Hindmarsh–Rose type model exhibiting properties of both Class 1 and Class 2 neurons. Although the system is two-dimensional and contains only four parameters, the obtained bifurcation diagrams show that the bifurcation structure satisfies conditions for emergence of both features with constant stimuli.
OPTIMAL CNN TEMPLATES FOR LINEARLY-SEPARABLE ONE-DIMENSIONAL CELLULAR AUTOMATA
Authors: CHANG P. J. , MUTHUSWAMY BHARATHWAJ
Published: May 2007

In this tutorial, we present optimal Cellular Nonlinear Network (CNN) templates for implementing linearly-separable one-dimensional (1-D) Cellular Automata (CA). From the gallery of CNN templates presented in this paper, one can calculate any of the 256 1-D CA Rules studied by Wolfram using a CNN Universal Machine chip that is several orders of magnitude faster than conventional programming on a digital computer.
Phase I Clinical and Pharmacodynamic Evaluation of Oral CI-1033 in Patients with Refractory Cancer
Authors: Zinner Ralph G. , Nemunaitis John , Eiseman Irene , Shin Hyung Ju C. , Olson Stephen C. , Christensen James , Huang Xin , Lenehan Peter F. , Donato Nicholas J. , Shin Dong M.
Published: May 2007

Purpose: To determine the tolerability and pharmacokinetics of CI-1033 given daily for 7 days of a 21-day cycle. Tumor response and changes in erbB receptor tyrosine kinase activity in tumor and skin tissue were examined, and modulation of potential biomarkers in plasma was explored.

Design: This was a dose-finding phase I study in patients with advanced solid malignancies. Patients were evaluated for safety, pharmacokinetics, and tumor response. Pharmacodynamic markers, such as Ki67, p27, and erbB receptor status, were assessed in tumor and skin tissue using immunohistochemical and immunoprecipitation methodologies. Plasma biomarkers HER2, vascular endothelial growth factor, interleukin-8, and matrix metalloproteinase-9 were evaluated using immunologic techniques.

Results: Fifty-three patients were enrolled in the study. Dose-limiting toxicity (emesis, persistent rash, and mouth ulcer) was observed at 750 mg. The maximum tolerated dose was 650 mg. There were no confirmed objective responses. CI-1033 treatment showed down-regulation of epidermal growth factor receptor, HER2, and Ki67 in a variety of tumor tissues and up regulation of p27 in skin tissue. Plasma HER2 was reduced following CI-1033 administration, but no consistent change in vascular endothelial growth factor, interleukin-8, or matrix metalloproteinase-9 was noted. CI-1033 plasma concentrations were proportional to dose.

Conclusion: The safety and pharmacokinetic profile of CI-1033 was favorable for multidose oral administration. Evidence of modulation of erbB receptor activity in tumor and skin tissue was accompanied by changes in markers of proliferation and cell cycle inhibition. Additional clinical trials are warranted in defining the role of CI-1033 in the treatment of cancer and further assessing the utility of antitumor markers.
Temozolomide as Monotherapy Is Effective in Treatment of Advanced Malignant Neuroendocrine Tumors
Authors: Ekeblad Sara , Sundin Anders , Janson Eva Tiensuu , Welin Staffan , Granberg Dan , Kindmark Henrik , Dunder Kristina , Kozlovacki Gordana , Örlefors Håkan , Sigurd Mattias , Öberg Kjell , Eriksson Barbro , Skogseid Britt
Published: May 2007

Purpose: A retrospective analysis of the toxicity and efficacy of temozolomide in advanced neuroendocrine tumors.

Experimental Design: Thirty-six patients with advanced stages of neuroendocrine tumor (1 gastric, 7 thymic and 13 bronchial carcinoids, 12 pancreatic endocrine tumors, 1 paraganglioma, 1 neuroendocrine foregut, and 1 neuroendocrine cecal cancer) were treated with temozolomide (200 mg/m2) for 5 days every 4 weeks. Patients had previously received a mean of 2.4 antitumoral medical regimens. Tumor response was evaluated radiologically according to the Response Evaluation Criteria in Solid Tumors every 3 months on an intent-to-treat basis. The circulating tumor marker plasma chromogranin A was also assessed. The expression of O6-methylguanine DNA methyltransferase, an enzyme implicated in chemotherapy resistance, was studied by immunohistochemistry (n = 23) and compared with response to temozolomide.

Results: Median overall time to progression was 7 months (95% confidence interval, 3-10). Radiologic response was seen in 14% of patients and stable disease in 53%. Side effects were mainly hematologic; 14% experienced grade 3 or 4 thrombocytopenia (National Cancer Institute toxicity criteria). Ten patients had tumors with O6-methylguanine DNA methyltransferase immunoreactivity in <10% of nuclei, whereas four patients showed radiologic responses.

Conclusions: Temozolomide as monotherapy had acceptable toxicity and antitumoral effects in a small series of patients with advanced malignant neuroendocrine tumors and four of these showed radiologic responses.