bluuebunny/crossref_metadata_2025 huggingface dataset:
Mitigation Emerges as Major Strategy for Reducing Losses Caused by Natural Disasters
Authors:   Board on Natural Disasters
Published: July 2002

The International Decade for Natural Disaster Reduction, a United Nations program for the 1990s, focused attention on the increasing losses caused by natural hazards and promoted actions to reduce their impacts. During this period in the United States, disaster managers and other officials increased emphasis on mitigation relative to response and recovery, especially in programs of the Federal Emergency Management Agency. Many other nations and international organizations undertook similar efforts. Beyond the Decade, efforts should focus on improving risk assessments; implementing mitigation strategies; improving technologies supporting warnings and the dissemination of, and response to, warnings; improving the basis for natural disaster insurance; and assisting developing nations.
Regulation of Lineage Commitment Distinct from Positive Selection
Authors: Keefe Robert , Dave Vibhuti , Allman David , Wiest David , Kappes Dietmar J.
Published: July 2002

Developing αβ T cells diverge into the CD4 and CD8 lineages as they mature in the thymus. It is unclear whether lineage commitment is mechanistically distinct from the process that selects for the survival of T cells with useful T cell receptor (TCR) specificities (positive selection). In HD mice, which lack mature CD4
+
T cells, major histocompatibility complex (MHC) class II–restricted T cells are redirected to the CD8 lineage independent of MHC class I expression. However, neither TCR-mediated signaling nor positive selection is impaired. Thus, the HD mutation provides genetic evidence that lineage commitment may be mechanistically distinct from positive selection.
Frequent Association between Alteration of the
rdxA
Gene and Metronidazole Resistance in French and North African Isolates of
Helicobacter pylori
Authors: Tankovic Jacques , Lamarque Dominique , Delchier Jean-Charles , Soussy Claude-James , Labigne Agnes , Jenks Peter J.
Published: July 2002

Mutations in the
rdxA
gene have been associated with the acquisition of resistance to metronidazole in
Helicobacter pylori
. This gene encodes an NADPH nitroreductase whose expression is necessary for intracellular activation of the drug. We wished to examine whether mutations in
rdxA
were present in resistant
H. pylori
isolates infecting either French or North African patients. We determined the complete nucleotide sequences of the
rdxA
genes from seven French and six North African patients infected with paired resistant and sensitive strains. Genotyping by random amplified polymorphic DNA analysis confirmed the close genetic relatedness of the susceptible and resistant isolates from individual biopsies. Eight French and five North African individual resistant strains were also studied. For the French strains, an alteration in
rdxA
most probably implicated in resistance was found in 10 cases (seven frameshift mutations, two missense mutations, and one deletion of 211 bp). One to three putative missense mutations were identified in four cases, and a missense mutation possibly not implicated in resistance was discovered in the last case. For the North African strains, an alteration in
rdxA
was found in eight cases (three frameshift mutations, three missense mutations, one deletion of 6 bp, and one insertion of a variant of IS
605
). Two strains contained putative missense mutations, and no change was observed in
rdxA
of the last strain. Thus, inactivation of the
rdxA
gene is frequently, but not always, associated with resistance to metronidazole in French and North African clinical isolates of
H. pylori
. In addition, a variety of alterations of
rdxA
are associated with the resistant phenotype.
Molecular and Biochemical Analysis of AST-1, a Class A β-Lactamase from
Nocardia asteroides
Sensu Stricto
Authors: Poirel Laurent , Laurent Frederic , Naas Thierry , Labia Roger , Boiron Patrick , Nordmann Patrice
Published: July 2002

A β-lactamase gene was cloned from a
Nocardia asteroides
sensu stricto clinical isolate. A recombinant plasmid, pAST-1, expressed the β-lactamase AST-1 in
Escherichia coli
JM109. Its pI was 4.8, and its relative molecular mass was 31 kDa.
E. coli
JM109(pAST-1) was resistant to penicillins and narrow-spectrum cephalosporins. The β-lactamase AST-1 had a restricted hydrolytic activity spectrum. Its activity was partially inhibited by clavulanic acid but not by sulbactam and tazobactam. AST-1 is an Ambler class A β-lactamase sharing 65% amino acid identity with β-lactamase FAR-1, the most closely related enzyme.
Starvation Improves Survival of Bacteria Introduced into Activated Sludge
Authors: Watanabe Kazuya , Miyashita Mariko , Harayama Shigeaki
Published: July 2002

A phenol-degrading bacterium,
Ralstonia eutropha
E2, was grown in Luria-Bertani (LB) medium or in an inorganic medium (called MP) supplemented with phenol and harvested at the late-exponential-growth phase. Phenol-acclimated activated sludge was inoculated with the E2 cells immediately after harvest or after starvation in MP for 2 or 7 days. The densities of the E2 populations in the activated sludge were then monitored by quantitative PCR. The E2 cells grown on phenol and starved for 2 days (P-2 cells) survived in the activated sludge better than those treated differently: the population density of the P-2 cells 7 days after their inoculation was 50 to 100 times higher than the population density of E2 cells without starvation or that with 7-day starvation. LB medium-grown cells either starved or nonstarved were rapidly eliminated from the sludge. The P-2 cells showed a high cell surface hydrophobicity and retained metabolic activities. Cells otherwise prepared did not have one of these two features. From these observations, it is assumed that hydrophobic cell surface and metabolic activities higher than certain levels were required for the inoculated bacteria to survive in the activated sludge. Reverse transcriptase PCR analyses showed that the P-2 cells initiated the expression of phenol hydroxylase within 1 day of their inoculation into the sludge. These results suggest the utility of a short starvation treatment for improving the efficacy of bioaugumentation.
Molecular and Immunological Analyses of the
Borrelia turicatae
Bdr Protein Family
Authors: Carlyon Jason A. , Roberts David M. , Theisen Michael , Sadler Christina , Marconi Richard T.
Published: July 2002

Here, we describe the molecular and immunological characterization of the
bdr
gene family of
Borrelia turicatae
, a relapsing-fever spirochete. Nine
bdr
alleles belonging to two different subfamilies were sequenced and localized to linear plasmids. Anti-Bdr antiserum was generated and used to analyze Bdr expression in pre- and postinfection isogenic populations. The analyses presented here provide a detailed characterization of the Bdr proteins in a relapsing-fever spirochete species, enhancing our understanding of these proteins at the genus-wide level.
Lyme Arthritis Resolution with Antiserum to a 37-KilodaltonBorrelia burgdorferiProtein
Authors: Feng Sunlian , Hodzic Emir , Barthold Stephen W.
Published: July 2002

A 37-kDa protein fromBorrelia burgdorferi(the agent of Lyme disease) was identified as a target for immune-mediated resolution of Lyme arthritis. Studies in a mouse model have shown that arthritis resolution can be mediated by antibodies (against unknown target antigens) within immune sera from actively infected mice. Immune sera from infected mice were therefore used to screen aB. burgdorferigenomic expression library. A gene was identified whose native product is a putative lipoprotein of approximately 37 kDa, referred to here as arthritis-related protein (Arp). Active and passive immunization of mice with recombinant Arp or Arp antiserum, respectively, did not protect mice from challenge inoculation. However, when Arp antiserum was administered to severe combined immunodeficient (SCID) mice with established infections and with ongoing arthritis and carditis, treatment selectively induced arthritis resolution without affecting the status of carditis or influencing the status of infection, including spirochetemia. The selective arthritis-resolving effect of Arp antiserum mimics the activity of immune serum from immunocompetent mice when such serum is transferred into SCID mice with established infections. Thearpgene could not be amplified from unrelatedB. burgdorferiisolates but hybridized with those isolates only under very-low-stringency conditions. Arp antiserum reacted against proteins of similar size in a wide range ofB. burgdorferiisolates.
Helicobacter pylori
Pore-Forming Cytolysin Orthologue TlyA Possesses In Vitro Hemolytic Activity and Has a Role in Colonization of the Gastric Mucosa
Authors: Martino M. Celeste , Stabler Richard A. , Zhang Zun W. , Farthing Michael J. G. , Wren Brendan W. , Dorrell Nick
Published: July 2002

Hemolysins have been found to possess a variety of functions in bacteria, including a role in virulence.
Helicobacter pylori
demonstrates hemolytic activity when cultured on unlysed blood agar plates which is increased under iron-limiting conditions. However, the role of an
H. pylori
hemolysin in virulence is unclear. Scrutiny of the
H. pylori
26695 genome sequence suggests the presence of at least two distinct hemolysins, HP1086 and HP1490, in this strain. Previous studies have shown that the in vitro hemolytic activity of
H. pylori
is reduced when it is coincubated with dextran 5000, suggesting the presence of a pore-forming cytolysin. HP1086 has homology to pore-forming cytolysins (TlyA) from other bacterial species, and the introduction of the cloned
H. pylori tlyA
gene into a nonhemolytic
Escherichia coli
strain conferred hemolytic activity. An
H. pylori tlyA
defined mutant showed reduced in vitro hemolytic activity, which appears to be due to pore formation, as the hemolytic activity of the wild-type strain is reduced to the same level as the
tlyA
mutant by the addition of dextran 5000. The mutant also showed reduced adhesion to human gastric adenocarcinoma cells and failed to colonize the gastric mucosa of mice. These data clearly suggest a role in virulence for
H. pylori
TlyA, contrary to the suggestion that hemolytic activity is an in vitro phenomenon for this pathogen.
Site-Specific Mutational Analysis of a Novel Cysteine Motif Proposed To Ligate the 4Fe-4S Cluster in the Iron-Sulfur Flavoprotein of the Thermophilic Methanoarchaeon
Methanosarcina thermophila
Authors: Leartsakulpanich Ubolsree , Antonkine Mikhail L. , Ferry James G.
Published: July 2002

Isf (iron-sulfur flavoprotein) from
Methanosarcina thermophila
has been produced in
Escherichia coli
as a dimer containing two 4Fe-4S clusters and two FMN (flavin mononucleotide) cofactors. The deduced sequence of Isf contains six cysteines (Cys 16, Cys 47, Cys 50, Cys 53, Cys 59, and Cys 180), four of which (Cys 47, Cys 50, Cys 53, and Cys 59) comprise a motif with high identity to a motif (CX
2
CX
2
CX
4–7
C) present in all homologous Isf sequences available in the databases. The spacing of the motif is highly compact and atypical of motifs coordinating known 4Fe-4S clusters; therefore, all six cysteines in Isf from
M. thermophila
were altered to either alanine or serine to obtain corroborating biochemical evidence that the motif coordinates the 4Fe-4S cluster and to further characterize properties of the cluster dependent on ligation. All except the C16S variant were produced in inclusion bodies and were void of iron-sulfur clusters and FMN. Reconstitution of the iron-sulfur cluster and FMN was attempted for each variant. The UV-visible spectra of all reconstituted variants indicated the presence of iron-sulfur clusters and FMN. The reduced C16A/S variants showed the same electron paramagnetic resonance (EPR) spectra as wild-type Isf, whereas the reduced C180A/S variants showed EPR spectra identical to those of one of the two 4Fe-4S species present in the wild-type Isf spectrum. Conversely, EPR spectra of the oxidized C50A and C59A variants showed
g
values characteristic of a 3Fe-4S cluster. The spectra of the C47A and C53A variants indicated a 4Fe-4S cluster with
g
values and linewidths different from those for the wild type. The combined results of this study support a role for the novel CX
2
CX
2
CX
4–7
C motif in ligating the 4Fe-4S clusters in Isf and Isf homologues.
Function-Based Selection and Characterization of Base-Pair Polymorphisms in a Promoter of
Escherichia coli
RNA Polymerase-ς
70
Authors: Xu Jian , McCabe Barbara C. , Koudelka Gerald B.
Published: July 2002

We performed two sets of in vitro selections to dissect the role of the −10 base sequence in determining the rate and efficiency with which
Escherichia coli
RNA polymerase-ς
70
forms stable complexes with a promoter. We identified sequences that (i) rapidly form heparin-resistant complexes with RNA polymerase or (ii) form heparin-resistant complexes at very low RNA polymerase concentrations. The sequences selected under the two conditions differ from each other and from the consensus −10 sequence. The selected promoters have the expected enhanced binding and kinetic properties and are functionally better than the consensus promoter sequence in directing RNA synthesis in vitro. Detailed analysis of the selected promoter functions shows that each step in this multistep pathway may have different sequence requirements, meaning that the sequence of a strong promoter does not contain the optimal sequence for each step but instead is a compromise sequence that allows all steps to proceed with minimal constraint.
Characterization of an rRNA Operon (
rrnB
) of
Mycobacterium fortuitum
and Other Mycobacterial Species: Implications for the Classification of Mycobacteria
Authors: Menendez M. C. , Garcia M. J. , Navarro M. C. , Gonzalez-y-Merchand J. A. , Rivera-Gutierrez S. , Garcia-Sanchez L. , Cox R. A.
Published: July 2002

Mycobacteria are thought to have either one or two rRNA operons per genome. All mycobacteria investigated to date have an operon, designated
rrnA
, located downstream from the
murA
gene. We report that
Mycobacteriun fortuitum
has a second
rrn
operon, designated
rrnB
, which is located downstream from the
tyrS
gene;
tyrS
is very close to the 3" end of a gene (
3-mag
) coding for 3-methylpurine-DNA-glycosylase. The second
rrn
operon of
Mycobacterium smegmatis
was shown to have a similar organization, namely, 5"
3-mag
-
tyrS
-
rrnB
3". The
rrnB
operon of
M. fortuitum
was found to have a single dedicated promoter. During exponential growth in a rich medium, the
rrnB
and
rrnA
operons were the major and minor contributors, respectively, to pre-rRNA synthesis. Genomic DNA was isolated from eight other fast-growing mycobacterial species. Samples were investigated by Southern blot analysis using probes for
mur
A,
tyrS
, and 16S rRNA sequences. The results revealed that both
rrnA
and
rrnB
operons were present in each species. The results form the basis for a proposed new scheme for the classification of mycobacteria. The approach, which is phylogenetic in concept, is based on particular properties of the
rrn
operons of a cell, namely, the number per genome and a feature of 16S rRNA gene sequences.
The Simian Virus 40 Core Origin Contains Two Separate Sequence Modules That Support T-Antigen Double-Hexamer Assembly
Authors: Sreekumar K. R. , Prack Andrea E. , Winters Danielle R. , Barbaro Brett A. , Bullock Peter A.
Published: July 2002

Using subfragments of the simian virus 40 (SV40) core origin, we demonstrate that two alternative modules exist for the assembly of T-antigen (T-ag) double hexamers. Pentanucleotides 1 and 3 and the early palindrome (EP) constitute one assembly unit, while pentanucleotides 2 and 4 and the AT-rich region constitute a second, relatively weak, assembly unit. Related studies indicate that on the unit made up of pentanucleotide 1 and 3 and the EP assembly unit, the first hexamer forms on pentanucleotide 1 and that owing to additional protein-DNA and protein-protein interactions, the second hexamer is able to form on pentanucleotide 3. Oligomerization on the unit made up of pentanucleotide 2 and 4 and the AT-rich region is initiated by assembly of a hexamer on pentanucleotide 4; subsequent formation of the second hexamer takes place on pentanucleotide 2. Given that oligomerization on the SV40 origin is limited to double-hexamer formation, it is likely that only a single module is used for the initial assembly of T-ag double hexamers. Finally, we discuss the evidence that nucleotide hydrolysis is required for the remodeling events that result in the utilization of the second assembly unit.
Human Immunodeficiency Virus Type 1 Nef Mediates Sustained Membrane Expression of Tumor Necrosis Factor and the Related Cytokine LIGHT on Activated T Cells
Authors: Lama Juan , Ware Carl F.
Published: July 2002

Human immunodeficiency virus (HIV) Nef downregulates the antigen recognition molecules major histocompatibility complex class I and CD4. Downregulation of surface CD4 by Nef relies on the ability of this viral protein to redirect the endocytic machinery to CD4. However, by redirecting the endocytic machinery, Nef may affect the internalization rates of other proteins. Here we show that Nef simultaneously enhances surface expression of the effector cytokines tumor necrosis factor (TNF) and LIGHT, leading to enhanced cytokine activity. A dileucine motif in Nef, which is essential for CD4 downregulation and is involved in the recruitment of adapter protein complexes by Nef, was required to increase surface levels of both cytokines. The physiological impact of the Nef-mediated interference with endocytosis was demonstrated by the fact that a TNF-responsive T-cell line chronically infected with HIV produced higher levels of p24 viral protein following expression of a Nef-green fluorescent protein (GFP) fusion protein. This enhancement was dependent on the levels of membrane-bound TNF, since it was abrogated by a recombinant soluble TNF receptor. Expression of Nef-GFP in human 293T cells reduced the endocytosis of LIGHT, whereas at the same time CD4 internalization was accelerated. Taken together, these results suggest that in infected cells Nef interferes with the internalization of these effector cytokines. By increasing TNF expression, Nef could accelerate disease progression in infected individuals. These findings may help explain the pleiotropic functions that Nef plays during infection and disease.
The E1 Initiator Recognizes Multiple Overlapping Sites in the Papillomavirus Origin of DNA Replication
Authors: Chen Grace , Stenlund Arne
Published: July 2002

A common feature of replicator sequences from a variety of organisms is multiple binding sites for an initiator protein. By binding to the replicator, initiators mark the site and contribute to melting or distortion of the DNA. We have defined the recognition sequence for the papillomavirus E1 initiator and determined the arrangement of binding sites in the viral origin of replication. We show that E1 recognizes a hexanucleotide sequence which is present in overlapping arrays in virtually all papillomavirus replicators. Binding of the initiator to these sites would result in the formation of a closely packed array of E1 molecules that wrap around the double helix.
In Vivo Selection of a Lymphocytic Choriomeningitis Virus Variant That Affects Recognition of the GP33-43 Epitope by H-2Dbbut Not H-2Kb
Authors: Puglielli Maryann T. , Zajac Allan J. , van der Most Robbert G. , Dzuris John L. , Sette Alessandro , Altman John D. , Ahmed Rafi
Published: July 2002

CD8 T cells drive the protective immune response to lymphocytic choriomeningitis virus (LCMV) infection and are thus a determining force in the selection of viral variants. To examine how escape mutations affect the presentation and recognition of overlapping T-cell epitopes, we isolated an LCMV variant that is not recognized by T-cell receptor (TCR)-transgenic H-2Db-restricted LCMV GP33-41-specific cytotoxic T lymphocytes (CTL). The variant virus carried a single-amino-acid substitution (valine to alanine) at position 35 of the viral glycoprotein. This region of the LCMV glycoprotein encodes both the Db-restricted GP33-43 epitope and a second epitope (GP34-42) presented by the Kbmolecule. We determined that the V-to-A CTL escape mutant failed to induce a DbGP33-43-specific CTL response and that Db-restricted GP33-43-specific CTL induced by the wild-type LCMV strain were unable to kill target cells infected with the variant LCMV strain. In contrast, the Kb-restricted response was much less affected. We found that the V-to-A substitution severely impaired peptide binding to Dbbut not to Kbmolecules. Strikingly, the V-to-A mutation did not change any of the anchor residues, and the dramatic effect on binding was therefore unexpected. The strong decrease in Dbbinding explains why the variant virus escapes the DbGP33-43-specific response but still elicits the Kb-restricted response. These findings also illustrate that mutations within regions encoding overlapping T-cell epitopes can differentially affect the presentation and recognition of individual epitopes.
Plasmid Vectors Encoding Cholera Toxin or the Heat-Labile Enterotoxin fromEscherichia coliAre Strong Adjuvants for DNA Vaccines
Authors: Arrington Joshua , Braun Ralph P. , Dong Lichun , Fuller Deborah H. , Macklin Michael D. , Umlauf Scott W. , Wagner Sarah J. , Wu Mary S. , Payne Lendon G. , Haynes Joel R.
Published: July 2002

Two plasmid vectors encoding the A and B subunits of cholera toxin (CT) and two additional vectors encoding the A and B subunits of theEscherichia coliheat-labile enterotoxin (LT) were evaluated for their ability to serve as genetic adjuvants for particle-mediated DNA vaccines administered to the epidermis of laboratory animals. Both the CT and the LT vectors strongly augmented Th1 cytokine responses (gamma interferon [IFN-γ]) to multiple viral antigens when codelivered with DNA vaccines. In addition, Th2 cytokine responses (interleukin 4 [IL-4]) were also augmented by both sets of vectors, with the effects of the LT vectors on IL-4 responses being more antigen dependent. The activities of both sets of vectors on antibody responses were antigen dependent and ranged from no effect to sharp reductions in the immunoglobulin G1 (IgG1)-to-IgG2a ratios. Overall, the LT vectors exhibited stronger adjuvant effects in terms of T-cell responses than did the CT vectors, and this was correlated with the induction of greater levels of cyclic AMP by the LT vectors following vector transfection into cultured cells. The adjuvant effects observed in vivo were due to the biological effects of the encoded proteins and not due to CpG motifs in the bacterial genes. Interestingly, the individual LT A and B subunit vectors exhibited partial adjuvant activity that was strongly influenced by the presence or absence of signal peptide coding sequences directing the encoded subunit to either intracellular or extracellular locations. Particle-mediated delivery of either the CT or LT adjuvant vectors in rodents and domestic pigs was well tolerated, suggesting that bacterial toxin-based genetic adjuvants may be a safe and effective strategy to enhance the potency of both prophylactic and therapeutic DNA vaccines for the induction of strong cellular immunity.
Cyclization Dichotomy of Esters of 3-Ureido-2-cyano-2-propenoic and 3-Ureido-2-acyl-2-propenoic Acids
Authors: Ledvina Miroslav , Farkaš Jiří
Published: July 2002

The preparation of E and Z isomers of 3-ureido-2-cyano-2-propenoates Ia - Id and their base-catalyzed isomerization and cyclization to 5-carboxycytosine derivatives IIa - IIf and 5-cyanouracil derivatives IIIa and IIIb is described. Also described is the preparation of 3-ureido-2-acyl-2-propenoates Va - Vd and their base-catalyzed cyclization to 5-carboxy-2(1H)-pyrimidone derivatives VIa - VIc and 5-acyluracils VIIa - VIIc.
Synthesis of 9-(2-Phosphinomethoxyethyl)adenine and Related Compounds
Authors: Alexander Petr , Holý Antonín , Masojídková Milena
Published: July 2002

Alkyl 2-chloroethoxymethyl(diethoxymethyl)phosphinates VII and XIII were prepared by reaction of silyl esters of dialkoxymethylphosphinic acid with 2-chloroethyl chloromethyl ether. Adenine was alkylated with VII and XIII to give [2-(adenin-9-yl)ethoxy]methyl(diethoxymethyl)phosphinates VIII and XIV, bearing the dialkoxymethyl protecting group on the phosphorus atom. Acid hydrolysis of compounds VIII and XIV afforded 9-(2-phosphinoethoxymethyl)adenine (X). Alkyl dialkoxymethylphosphinates V and XI reacted with paraformaldehyde to give hydroxymethylphosphinates XV and XIX which were converted into the synthons XVI, XVII and XVIII capable of introducing a protected hydroxymethylphosphino group on a hydroxy or amino group.
Synthesis via Ultrasound: A Convenient Synthesis of 6-(4-Tolyl)hept-1-ene and 6-(2-Oxo-4-methylcyclohex-3-en-1-yl)hept-1-ene
Authors: Trehan Inder R. , Singh Jasvinder , Arora Ajay K. , Kaur Jasamrit , Kad Goverdhan L.
Published: July 2002

6-(4-Tolyl)hept-1-ene (I) and 6-(2-oxo-4-methylcyclohex-3-en-1-yl)hept-1-ene (II), monocyclic norsesquiterpenes from aerial parts of South African Senecio digitalifolius, have been synthesized using ultrasonic waves and tandem phenylation reduction.
Structure of Reaction Products of Some Substituted Quinoxaline N-Oxides with Carbanions
Authors: Toman Jaromír , Mindl Jaromír , Lyčka Antonín , Klicnar Jiří , Srovnalová Ivana , Koníček Miloš
Published: July 2002

1,2,3-Triazolo[1,5-a]- (II) and 1,2,4-triazolo[4,3-a]quinoxaline 5-oxide (III) react with the carbanions of β-diketones and β-keto esters to give enaminones in the same way as their tetrazolo analogue. The difference in mechanism of reactions of these N-oxides with carbanions of 3-alkylpentane-2,4-dione and ethyl methyl acetoacetate giving aziridinopolyazoloquinoxalines and ethyl 2-(polyazoloquinoxalin-4-yl)propanoates, respectively, is discussed. It was shown that the reaction with carbanion including the aziridine ring closure proceeds with 3,4-dihydro-3-oxoquinoxaline-1-oxide as well.
Dynamic Light Scattering from Polymer Solutions: The Subtraction Technique
Authors: Štěpánek Petr , Johnsen Robert M.
Published: July 2002

Correlation functions measured in dynamic light scattering on polymer solutions often contain a strong sharp decay which obscures and renders difficult a reliable analysis of other decay processes. We demonstrate that this problem can be circumvented by performing a two-step inverse Laplace transformation. The strong component obtained in the first step is subtracted from the correlation function which is then re-analyzed in the second step. We illustrate this technique on semidilute solutions of polystyrene in cyclohexane and tetrahydrofuran.
THE SPECTRUM OF A HYDROGEN ATOM IN AN INTENSE MAGNETIC FIELD
Authors: FROESE RICHARD , WAXLER ROGER
Published: July 2002

We consider a hydrogen atom in a constant and very large magnetic field. For bounded angular momentum about the direction of the magnetic field we obtain asymptotics for all eigenvalues and eigenfunctions.
HURWITZ THEOREM AND PARALLELIZABLE SPHERES FROM TENSOR ANALYSIS
Authors: NIETO J. A. , ALEJO-ARMENTA L. N.
Published: July 2002

By using tensor analysis, we find a connection between normed algebras and the parallelizability of the spheres S 1, S 3 and S 7. In this process, we discovered the analog of Hurwitz theorem for curved spaces and a geometrical unified formalism for the metric and the torsion. In order to achieve these goals we first develop a proof of Hurwitz theorem based on tensor analysis. It turns out that in contrast to the doubling procedure and Clifford algebra mechanism, our proof is entirely based on tensor algebra applied to the normed algebra condition. From the tersor analysis point of view our proof is straightforward and short. We also discuss a possible connection between our formalism and the Cayley–Dickson algebras and Hopf maps.
SPIN FILTERING IN MAGNETIC HETEROSTRUCTURES
Authors: Demchenko D. O. , Chantis A. N. , Petukhov A. G.
Published: July 2002

Several techniques were proposed to achieve solid state spin filtering such as magnetic tunnel junctions comprised of half-metallic compounds or solid state Stern-Gerlach apparatus. Another alternative consists in using spin-dependent resonant tunneling through magnetically active quantum wells. Recent advances in molecular beam epitaxial growth made it possible to fabricate exotic heterostructures comprised of magnetic films or buried layers (ErAs, GaxMn1-xAs) integrated with conventional semiconductors (GaAs) and to explore quantum transport in these heterostructures. It is particularly interesting to study spin-dependent resonant tunneling in double-barrier resonant tunneling diodes (RTD) with magnetic elements such as GaAs/AlAs/ErAs/AlAs/ErAs/AlAs/GaAs, GaxMn1-xAs/AlAs/GaAs/AlAs/GaAs, and GaAs/AlAs/GaxMn1-xAs/AlAs/GaAs. We present the results of our theoretical studies and computer simulations of transmission coefficients and current-voltage characteristics of resonant tunneling diodes based on these double-barrier structures. Resonant tunneling of holes (GaxMn1-xAs-based RTDs) is considered. Our approach is based on k·p perturbation theory with exchange splitting effects taken into account. We analyze exchange splitting of different resonant channels as a function of magnetization as well as spin polarization of the transmitted current as a function of bias. We found that resonant tunneling I – V characteristics of the double-barrier magnetic hererostructures strongly depend on the doping level in the emitter as well as on the orientation of the magnetization.
QUANTUM AND THERMAL STATE FOR EXPONENTIALLY DAMPED HARMONIC OSCILLATOR WITH AND WITHOUT INVERSE QUADRATIC POTENTIAL
Authors: CHOI J. R.
Published: July 2002

By taking advantage of dynamical invariant operator, we derived Schrödinger solution for exponentially damped harmonic oscillator with and without inverse quadratic potential. We investigated quantum mechanical energy expectation value, uncertainty relation, partition function and density operator of the system. The various expectation values in thermal state are calculated using the diagonal element of density operator.
ON THE HOPF–PITCHFORK BIFURCATION IN THE CHUA'S EQUATION
Authors: ALGABA A. , MERINO M. , FREIRE E. , GAMERO E. , RODRÍGUEZ-LUIS A. J.
Published: July 2002

We study some periodic and quasiperiodic behaviors exhibited by the Chua's equation with a cubic nonlinearity, near a Hopf–pitchfork bifurcation. We classify the types of this bifurcation in the nondegenerate cases, and point out the presence of a degenerate Hopf–pitchfork bifurcation. In this degenerate situation, analytical and numerical study shows a diversity of bifurcations of periodic orbits. We find a secondary Hopf bifurcation of periodic orbits, where invariant torus appears. This secondary Hopf bifurcation is bounded by a Takens–Bogdanov bifurcation of periodic orbits. Here, a sequence of period-doubling bifurcations of invariant tori is detected. Resonance phenomena are also analyzed. In the case of strong resonance 1:4, we show a new sequence of period-doubling bifurcations of 4T invariant tori.
NONIDENTICAL SYNCHRONIZATION OF IDENTICAL SYSTEMS
Authors: PARLITZ U. , JUNGE L. , KOCAREV L.
Published: July 2002

Different notions of generalized synchronization of uni-directionally coupled dynamical systems are briefly discussed. An example is given demonstrating that generalized synchronization may not only occur for pairs of different systems but also for identical systems that do not synchronize in the usual sense.
MOLECULAR-DYNAMICS STUDY OF THIN IRON FILMS ON COPPER
Authors: KADAU K. , MEYER R. , ENTEL P.
Published: July 2002

We have studied the structural stability of thin γ-iron films on Cu(001) and Cu(111) substrates using molecular-dynamics simulations in combination with a semiempirical model. Experimentally, the stability of such films has turned out to depend on (growth) temperature and film thickness. On increasing the thickness or decreasing the temperature the films undergo a structural change to the bcc structure, which is well reproduced by our simulations. An analysis of the local atomic environment of the films after the structural transformation shows that, especially on Cu(001), only parts of the film accomplish the transformation into the bcc structure. Considerations of the atomic displacements during the transformation allow us to give an explanation of the different stability of the films on Cu(001) and Cu(111) as well as the observed orientational relationships.
A VARIATIONAL FORMULATION FOR THE TWO-SIDED OBSTACLE PROBLEM WITH MEASURE DATA
Authors: BREZIS HAÏM , SERFATY SYLVIA
Published: July 2002

We give a new variational formulation for the two-sided obstacle problem with measure data. This formulation allows to prove in particular that the solution does not depend on the part of the data which is concentrated on a set of zero newtonian capacity.
LYAPUNOV SPECTRUM OF NONAUTONOMOUS LINEAR STOCHASTIC DIFFERENTIAL EQUATIONS
Authors: CONG NGUYEN DINH
Published: July 2002

We introduce a concept of Lyapunov exponents and Lyapunov spectrum for nonautonomous linear stochastic differential equations. The Lyapunov exponents are defined samplewise via the two-parameter flow generated by the equation. We prove that Lyapunov exponents are finite and nonrandom. Lyapunov exponents are used for investigation of Lyapunov regularity and stability of nonautonomous stochastic differential equations. The results show that the concept of Lyapunov exponents is still very fruitful for stochastic objects and gives us a useful tool for investigating sample stability as well as qualitative behavior of nonautonomous linear and nonlinear stochastic differential equations.
ON STOCHASTIC PERTURBATIONS OF DYNAMICAL SYSTEMS WITH FAST AND SLOW COMPONENTS
Authors: FREIDLIN MARK
Published: July 2002

Dynamical systems with fast and slow components are considered. We show that small random perturbations of the fast component can lead to essential changes in the limiting slow motion. For example, new stable equilibria or deterministic oscillations with amplitude and frequency of order 1 can be introduced by the perturbations. These are stochastic resonance type effects, and they are considered from the point of view of large deviations theory.
Building integrated software development environments. Part I
Authors: Engels G. , Lewerentz C. , Nagl M. , Schäfer W. , Schürr A.
Published: July 2002

The conceptual modeling approach of the IPSEN (Integrated Project Support Environment) project for building highly integrated environments is based on using attributed graphs to model and implement arbitrary object structures, in particular all kinds of software documents and their relationships. A language based on graph grammars, called PROGRESS (PROgrammed Graph REwriting SyStems), and a suitable method for the application of this language, called graph grammar engineering, have been developed over the last ten years. This language and method are being extensively used for specifying the complex graph structures of internal document representations as well as for specifying the functionality of all tools (editors, browsers, analyzers, debuggers) working on these internal rpresentations. This paper explains the language and the method for applying the language based on a pragmatic nontrivial example of a software production process and its corresponding documents. In particular, it is shown why and how a graph grammar-based strongly typed language is perfectly suitable to formally specify highly integrated software tools. In addition, it is shown that the implementation of these tools (i.e., an environment composed of these tools) is systematically being derived from the formal specifications.
A reappraisal of structured analysis
Authors: Bansler Jorgen P. , Bødker Keld
Published: July 2002

We review Structured Analysis as presented by Yourdon and DeMarco. First, we examine the implicit assumptions embodied in the method about the nature of organizations, work processes, and design. Following this we present the results of an exploratory study, conducted to find out how the method is applied in practice. This study reveals that while some of the tools of Structured Analysis—notably the data flow diagrams—are used and combined with other tools, the designers do not follow the analysis and design procedures prescribed by the method. Our findings suggest that there is a gap between the way systems development is portrayed in the normative technical literature and the way in which it is carried out.
TAE Plus: Transportable Applications Environment Plus
Authors: Szczur Martha R. , Sheppard Sylvia B.
Published: July 2002

The Transportable Applications Environment Plus (TAE Plus) is a NASA-developed user interface development environment (UIDE) for the rapid prototyping, evaluation, implementation, and management of user interfaces. TAE Plus provides an intuitive What You See Is What You Get (WYSIWYG) WorkBench for designing an application's user interface. The WorkBench supports the creation and sequencing of displays, including real-time, data-driven display objects. Users can define context-sensitive help for a target application. They can rehearse the user interface and also generate code automatically. In addition TAE Plus contains application services for the runtime manipulation and management of the user interface. Based on Motif and the MIT X Window System, TAE Plus runs on a variety of Unix- or VMS-based workstations. TAE Plus is an evolving system. User-defined requirements and new technology guide the development of each new version. Advances in virtual operating systems, human factors, computer graphics, command language design, standardization, and software portability are monitored and incorporated as they become available.
Data structures for efficient broker implementation
Authors: Tomasic Anthony , Gravano Luis , Lue Calvin , Schwarz Peter , Haas Laura
Published: July 2002

With the profusion of text databases on the Internet, it is becoming increasingly hard to find the most useful databases for a given query. To attack this problem, several existing and proposed systems employ brokers to direct user queries, using a local database of summary information about the available databases. This summary information must effectively distinguish relevant databases and must be compact while allowing efficient access. We offer evidence that one broker,
GlOSS
, can be effective at locating databases of interest even in a system of hundreds of databased and can examine the performance of accessing the
GlOSS
summeries for two promising storage methods: the grid file and partitioned hashing. We show that both methods can be tuned to provide good performance for a particular workload (within a broad range of workloads), and we discuss the tradeoffs between the two data structures. As a side effect of our work, we show that grid files are more broadly applicable than previously thought; inparticular, we show that by varying the policies used to construct the grid file we can provide good performance for a wide range of workloads even when storing highly skewed data.
Implementing a relational database by means of specialzed hardware
Authors: Babb E.
Published: July 2002

New hardware is described which allows the rapid execution of queries demanding the joining of physically stored relations. The main feature of the hardware is a special store which can rapidly remember or recall data. This data might be pointers from one file to another, in which case the memory helps with queries on joins of files. Alternatively, the memory can help remove redundant data during projection, giving a considerable speed advantage over conventional hardware.
Computers Then and Now
Authors: Wilkes Maurice V.
Published: July 2002

Reminiscences on the early developments leading to large scale electronic computers show that it took much longer than was expected for the first of the more ambitious and fully engineered computers to be completed and prove themselves in practical operation. Comments on the present computer field assess the needs for future development.
The Purdue University network-computing hubs
Authors: Kapadia Nirav H. , Fortes José A. B. , Lundstrom Mark S.
Published: July 2002

This paper describes the Web interface management infrastructure of a functioning network-computing system (PUNCH) that allows users to run unmodified simulation packages at geographically dispersed sites. The system currently contains more than fifty university and commercial simulation tools, and has been used to carry out more than two hundred thousand simulations via the World Wide Web. Dynamically-constructed virtual URLs allow the Web interface management infrastructure to support the semantics associated with an interface to computing services without requiring any changes to Web browsers or WWW protocols. Virtual URLs also facilitate customizable control of access to networked resources. Simulation tools with text-based interfaces are supported via dynamically-generated, virtual interfaces, whereas tools with graphical interfaces are supported by leveraging available remote display-management technologies. Virtual interface generation and interactivity emulation are handled by a programmable state machine in conjunction with a mechanism to embed variables and ovjects within standard HTML.
Method for partial rewriting of magnetic tape
Authors: Miller James A.
Published: July 2002

In simulating the operation of a large storage computer on the IBM 7094, a technique was developed whereby sections of the computer memory which were stored on magnetic tape (IBM 729 Mod II tape drive) could be rewritten without affecting other sections stored on the same tape.
Comment on Brent's scatter storage algorithm
Authors: Feldman Jerome A. , Low James R.
Published: July 2002

R.P. Brent in his presentation of a modification to the linear quotient algorithm [1] shares the common misconception that dynamic chaining requires larger table entries because of the space required for link fields.
An improved hash code for scatter storage
Authors: Maurer W. D.
Published: July 2002

Introduced is a hash coding method based on fixed-point division rather than multiplication or logical operations. This new method allows the hash table to have almost any length. Also a new method of handling collisions is discussed. Known as quadratic search, this method is faster than random search and free from the “clusters” that build up with a linear search.
The UNIX time-sharing system
Authors: Ritchie Dennis M. , Thompson Ken
Published: July 2002

UNIX is a general-purpose, multi-user, interactive operating system for the Digital Equipment Corporation PDP-11/40 and 11/45 computers. It offers a number of features seldom found even in a larger operating systems, including: (1) a hierarchical file system incorporating demountable volumes; (2) compatible file, device, and inter-process I/O; (3) the ability to initiate asynchronous processes; (4) system command language selectable on a per-user basis; and (5) over 100 subsystems including a dozen languages. This paper discusses the nature and implementation of the file system and of the user command interface.
Regulation of electronic funds transfer
Authors: Zaki Ahmed S.
Published: July 2002

This paper investigates the implications and impact of current legislation on the future of the electronic funds transfer systems (EFT). The relevant statutes are introduced and analyzed. Problem areas are discussed together with examples of court rulings. The investigation reveals that the regulations do not provide enough safeguards for the consumer and do not clear up the ambiguities from a combination of competing laws, regulations, and conflicting jurisdictions. Legislators, on both the national and state level, and federal and state governments need to cooperate more closely to produce uniform legislation that specifically addresses the current problems in an EFT environment. Courts need to realize the legislature's intent and the benefits that can be gained before ruling on the current issues.
From Washington: Scientific communications and national security
Authors: Steier Rosalie
Published: July 2002

The Reagan Administration has given considerable attention to the issue of “technology transfer,” by which they mean the dissemination of unclassified, but militarily sensitive U.S. technology to Eastern Bloc countries. There are some 44 separate groups in 10 or more U.S. departments either studying the subject or executing present policy, according to Louis T. Montulli, formerly of the White House Office of Science and Technology Policy.
Development and application of NASA's first standard spacecraft computer
Authors: Trevathan Charles E. , Taylor Thomas D. , Hartenstein Raymond G. , Merwarth Ann C. , Stewart William N.
Published: July 2002

To provide the autonomy needed by low, earth-orbiting satellites, NASA's first standard on-board processor requires changing only interfacing hardware from mission to mission.
Searching in a dynamic memory with fast sequential access
Authors: Vikas Om , Rajaraman V.
Published: July 2002

This communication presents an algorithm for searching in the Aho-Ullman dynamic memory consisting of (2

m

- 1) cells. Mean search time of 1.5
m
steps to the first specified record is obtained with a subsequent sequential access capability. Thus, in such a dynamic memory, the mean access time for content addressing is the same as the mean access time for random addressing.
U.S. computer export control policies
Authors: Goodman S. E.
Published: July 2002

The formulation of a balanced and effective export control policy for computer products and know-how has been an important and difficult task for both the U.S. Government and the computing community. External pressures force national security concerns to conflict with the values and interests of private enterprise and academic freedom. This paper has two primary objectives: the first is to present the computing community with a reasonably equitable and detailed perspective on this important public policy problem; the second is to present and analyze a range of policy choices.
Another spelling correction program
Authors: Robinson Peter , Singer Dave
Published: July 2002

We read James L. Peterson's article, “Computer Programs for Detecting and Correcting Spelling Errors” with great interest. We too have recently developed a spelling correction program as part of a tutorial on programming techniques and style. Our basic modesty inhibited us from publishing the details—there was, after all, little research involved in making the program. However, on reflection, there are several features in our design that we feel merit wider circulation.
Response to the Federal Trade Commission's proposed ruling on standards and certification
Authors: Lee John A. N.
Published: July 2002

In December 1978, the Federal Trade Commission issued a notice of intention of rulemaking in regard to the matter of Standards and Certification. In cooperation with the American National Standards Institute, of which ACM is a member, the ACM Standards Committee prepared a response to that notice and submitted it to the Commission in April 1979. The response gives a summary of the ACM Standards Committee position on a standards regulation and affords insights into the process by which procedures evolve in this area. For this reason, the response is reproduced here as a report.
MINI-EXEC
Authors: Wicklund Thomas L.
Published: July 2002

As microprocessor systems and single-chip microcomputers become more complex, so do the software systems developed for them. In many cases, software is being designed that incorporates multiple control functions running asynchronously on a single microprocessor. Here, discussion focuses on the motivation for running such multiple functions under the control of a real-time multitasking executive. A successfully implemented executive whose design is portable and suitable for use on most 8-bit microprocessors is presented.
A comment on English neologisms and programming language keywords
Authors: Eastman Caroline M.
Published: July 2002

The choice of keywords in the design of programming languages is compared to the formation of neologisms, or new words, in natural languages. Examination of keywords in high-level programming languages shows that they are formed using mechanisms analogous to those observed in English. The use of mirror words as closing keywords is a conspicuous exceptions.