bluuebunny/crossref_metadata_2025 huggingface dataset:
In Vivo Dissection of theHelicobacter pyloriFur Regulatory Circuit by Genome-Wide Location Analysis
Authors: Danielli Alberto , Roncarati Davide , Delany Isabel , Chiarini Valentina , Rappuoli Rino , Scarlato Vincenzo
Published: June 2006

Iron homeostasis is particularly important in pathogenic bacteria, which need to compete with the host for this essential cofactor. InHelicobacter pylori, a causative agent of several gastric pathologies, iron uptake and storage genes are regulated at the transcriptional level by the ferric uptake regulator Fur. The regulatory circuit of Fur has recently come under focus because of an intimate interlink with a broader regulatory network governing metal homeostasis, acidic response, and virulence. To dissect the Fur regulatory circuit and identify in vivo targets of regulation, we developed a genome-wide location analysis protocol which allowed the identification of 200 genomic loci bound by Fur as well as the investigation of the binding efficiency of the protein to these loci in response to iron. Comparative analysis with transcriptomes of wild-type andfurdeletion mutant strains allowed the distinction between targets associated with Fur regulation and genes indirectly influenced by thefurmutation. The Fur regulon includes 59 genes, 25 of which appear to be positively regulated. A case study conducted by primer extension analysis of two oppositely regulated genes,hpn2andflaB, suggests that negative regulation as well as positive regulation occurs at the transcriptional level. Furthermore, the results revealed the existence of 13 Fur targeted loci within polycistronic operons, which were associated with transcript deregulation in thefurmutant strain. This study provides a systematic insight of Fur regulation at the genome-wide level inH. pyloriand points to regulatory functions extending beyond the classical Fur repression paradigm.
Interactions between
Streptomyces coelicolor
and
Bacillus subtilis
: Role of Surfactants in Raising Aerial Structures
Authors: Straight Paul D. , Willey Joanne M. , Kolter Roberto
Published: June 2006

Using mixed-species cultures, we have undertaken a study of interactions between two common spore-forming soil bacteria,
Bacillus subtilis
and
Streptomyces coelicolor
. Our experiments demonstrate that the development of aerial hyphae and spores by
S. coelicolor
is inhibited by surfactin, a lipopeptide surfactant produced by
B. subtilis
. Current models of aerial development by sporulating bacteria and fungi postulate a role for surfactants in reducing surface tension at air-liquid interfaces, thereby removing the major barrier to aerial growth.
S. coelicolor
produces SapB, an amphipathic peptide that is surface active and required for aerial growth on certain media. Loss of aerial hyphae in developmental mutants can be rescued by addition of purified SapB. While a surfactant from a fungus can substitute for SapB in a mutant that lacks aerial hyphae, not all surfactants have this effect. We show that surfactin is required for formation of aerial structures on the surface of
B. subtilis
colonies. However, in contrast to this positive role, our experiments reveal that surfactin acts antagonistically by arresting
S. coelicolor
aerial development and causing altered expression of developmental genes. Our observations support the idea that surfactants function specifically for a given organism regardless of their shared ability to reduce surface tension. Production of surfactants with antagonistic activity could provide a powerful competitive advantage during surface colonization and in competition for resources.
Coregulation by Phenylacetyl-Coenzyme A-Responsive PaaX Integrates Control of the Upper and Lower Pathways for Catabolism of Styrene by
Pseudomonas
sp. Strain Y2
Authors: del Peso-Santos Teresa , Bartolomé-Martín David , Fernández Cristina , Alonso Sergio , García José Luis , Díaz Eduardo , Shingler Victoria , Perera Julián
Published: June 2006

The

P
styA

promoter of
Pseudomonas
sp. strain Y2 controls expression of the
styABCD
genes, which are required for the conversion of styrene to phenylacetate, which is further catabolized by the products of two
paa
gene clusters. Two PaaX repressor proteins (PaaX1 and PaaX2) regulate transcription of the
paa
gene clusters of this strain. In silico analysis of the

P
styA

promoter region revealed a sequence located just within
styA
that is similar to the reported PaaX binding sites of
Escherichia coli
and the proposed PaaX binding sites of the
paa
genes of
Pseudomonas
species. Here we show that protein extracts from some
Pseudomonas
strains that have
paaX
genes, but not from a
paaX
mutant strain, can bind and retard the migration of a

P
styA

specific probe. Purified maltose-binding protein (MBP)-PaaX1 fusion protein specifically binds the

P
styA

promoter proximal PaaX site, and this binding is eliminated by the addition of phenylacetyl-coenzyme A. The sequence protected by MBP-PaaX1 binding was defined by DNase I footprinting. Moreover, MBP-PaaX1 represses transcription from the

P
styA

promoter in a phenylacetyl-coenzyme A-dependent manner in vitro. Finally, the inactivation of both
paaX
gene copies of
Pseudomonas
sp. strain Y2 leads to a higher level of transcription from the

P
styA

promoter, while heterologous expression of the PaaX1 in
E. coli
greatly decreases transcription from the

P
styA

promoter. These findings reveal a control mechanism that integrates regulation of styrene catabolism by coordinating the expression of the styrene upper catabolic operon to that of the
paa
-encoded central pathway and support a role for PaaX as a major regulatory protein in the phenylacetyl-coenzyme A catabolon through its response to the levels of this central metabolite.
Arginine Homeostasis in J774.1 Macrophages in the Context of
Mycobacterium bovis
BCG Infection
Authors: Talaue Meliza T. , Venketaraman Vishwanath , Hazbón Manzour Hernando , Peteroy-Kelly Marcy , Seth Anjali , Colangeli Roberto , Alland David , Connell Nancy D.
Published: June 2006

The competition for
l
-arginine between the inducible nitric oxide synthase and arginase contributes to the outcome of several parasitic and bacterial infections. The acquisition of
l
-arginine, however, is important not only for the host cells but also for the intracellular pathogen. In this study we observe that strain AS-1, the
Mycobacterium bovis
BCG strain lacking the Rv0522 gene, which encodes an arginine permease, perturbs
l
-arginine metabolism in J774.1 murine macrophages. Infection with AS-1, but not with wild-type BCG, induced
l
-arginine uptake in J774.1 cells. This increase in
l
-arginine uptake was independent of activation with gamma interferon plus lipopolysaccharide and correlated with increased expression of the MCAT1 and MCAT2 cationic amino acid transport genes. AS-1 infection also enhanced arginase activity in resting J774.1 cells. Survival studies revealed that AS-1 survived better than BCG within resting J774.1 cells. Intracellular growth of AS-1 was further enhanced by inhibiting arginase and ornithine decarboxylase activities in J774.1 cells using
l
-norvaline and difluoromethylornithine treatment, respectively. These results suggest that the arginine-related activities of J774.1 macrophages are affected by the arginine transport capacity of the infecting BCG strain. The loss of Rv0522 gene-encoded arginine transport may have induced other cationic amino acid transport systems during intracellular growth of AS-1, allowing better survival within resting macrophages.
Characterization of the StcE Protease Activity of
Escherichia coli
O157:H7
Authors: Grys Thomas E. , Walters Laura L. , Welch Rodney A.
Published: June 2006

The StcE zinc metalloprotease is secreted by enterohemorrhagic
Escherichia coli
(EHEC) O157:H7 and contributes to intimate adherence of this bacterium to host cells, a process essential for mammalian colonization. StcE has also been shown to localize the inflammatory regulator C1 esterase inhibitor (C1-INH) to cell membranes. We tried to more fully characterize StcE activity to better understand its role in EHEC pathogenesis. StcE was active at pH 6.1 to 9.0, in the presence of NaCl concentrations ranging from 0 to 600 mM, and at 4°C to 55°C. Interestingly, antisera against StcE or C1-INH did not eliminate StcE cleavage of C1-INH. Treatment of StcE with the proteases trypsin, chymotrypsin, human neutrophil elastase, and
Pseudomonas aeruginosa
elastase did not eliminate StcE activity against C1-INH. After StcE was kept at 23°C for 65 days, it exhibited full proteolytic activity, and it retained 30% of its original activity after incubation for 8 days at 37°C. Together, these results show the StcE protease is a stable enzyme that is probably active in the environment of the colon. Additionally,
k
cat
/
K
m
data showed that StcE proteolytic activity was 2.5-fold more efficient with the secreted mucin MUC7 than with the complement regulator C1-INH. This evidence supports a model which includes two roles for StcE during infection, in which StcE acts first as a mucinase and then as an anti-inflammatory agent by localizing C1-INH to cell membranes.
A Variation of the Translation Attenuation Model Can Explain the Inducible Regulation of the pBC16 Tetracycline Resistance Gene in
Bacillus subtilis
Authors: Lodato Patricia B. , Rogers Elizabeth J. , Lovett Paul S.
Published: June 2006

Expression of the
tet
resistance gene from plasmid pBC16 is induced by the antibiotic tetracycline, and induction is independent of the native promoter for the gene. The nucleotide sequence at the 5′ end of the
tet
mRNA (the leader region) is predicted to assume a complex secondary structure that sequesters the ribosome binding site for the
tet
gene. A spontaneous, constitutively expressed
tet
gene variant contains a mutation predicted to provide the
tet
gene with a nonsequestered ribosome binding site. Lastly, comparable levels of
tet
mRNA can be demonstrated in tetracycline-induced and uninduced cells. These results are consistent with the idea that the pBC16
tet
gene is regulated by translation attenuation, a model originally proposed to explain the inducible regulation of the
cat
and
erm
genes in gram-positive bacteria. As with inducible
cat
and
erm
genes, the pBC16
tet
gene is preceded by a translated leader open reading frame consisting of a consensus ribosome binding site and an ATG initiation codon, followed by 19 sense codons and a stop codon. Mutations that block translation of
cat
and
erm
leaders prevent gene expression. In contrast, we show that mutations that block translation of the
tet
leader result in constitutive expression. We provide evidence that translation of the
tet
leader peptide coding region blocks
tet
expression by preventing the formation of a secondary-structure complex that would, in the absence of leader translation, expose the
tet
ribosome binding site. Tetracycline is proposed to induce
tet
by blocking or slowing leader translation. The results indicate that
tet
regulation is a variation of the translation attenuation model.
Isolation of a High-Affinity Functional Protein Complex between OmcA and MtrC: Two Outer Membrane Decaheme
c
-Type Cytochromes of
Shewanella oneidensis
MR-1
Authors: Shi Liang , Chen Baowei , Wang Zheming , Elias Dwayne A. , Mayer M. Uljana , Gorby Yuri A. , Ni Shuison , Lower Brian H. , Kennedy David W. , Wunschel David S. , Mottaz Heather M. , Marshall Matthew J. , Hill Eric A. , Beliaev Alexander S. , Zachara John M. , Fredrickson James K. , Squier Thomas C.
Published: June 2006

Shewanella oneidensis
MR-1 is a facultatively anaerobic bacterium capable of using soluble and insoluble forms of manganese [Mn(III/IV)] and iron [Fe(III)] as terminal electron acceptors during anaerobic respiration. To assess the structural association of two outer membrane-associated
c
-type decaheme cytochromes (i.e., OmcA [SO1779] and MtrC [SO1778]) and their ability to reduce soluble Fe(III)-nitrilotriacetic acid (NTA), we expressed these proteins with a C-terminal tag in wild-type
S. oneidensis
and a mutant deficient in these genes (i.e., Δ
omcA mtrC
). Endogenous MtrC copurified with tagged OmcA in wild-type
Shewanella
, suggesting a direct association. To further evaluate their possible interaction, both proteins were purified to near homogeneity following the independent expression of OmcA and MtrC in the Δ
omcA mtrC
mutant. Each purified cytochrome was confirmed to contain 10 hemes and exhibited Fe(III)-NTA reductase activity. To measure binding, MtrC was labeled with the multiuse affinity probe 4′,5′-bis(1,3,2-dithioarsolan-2-yl)fluorescein (1,2-ethanedithiol)
2
, which specifically associates with a tetracysteine motif engineered at the C terminus of MtrC. Upon titration with OmcA, there was a marked increase in fluorescence polarization indicating the formation of a high-affinity protein complex (

K
d

< 500 nM) between MtrC and OmcA whose binding was sensitive to changes in ionic strength. Following association, the OmcA-MtrC complex was observed to have enhanced Fe(III)-NTA reductase specific activity relative to either protein alone, demonstrating that OmcA and MtrC can interact directly with each other to form a stable complex that is consistent with their role in the electron transport pathway of
S. oneidensis
MR-1.
Growth Phase-Dependent Regulation of the Extracytoplasmic Stress Factor, σ
E
, by Guanosine 3′,5′-Bispyrophosphate (ppGpp)
Authors: Costanzo Alessandra , Ades Sarah E.
Published: June 2006

The sigma subunit of procaryotic RNA polymerases is responsible for specific promoter recognition and transcription initiation. In addition to the major sigma factor, σ
70
, in
Escherichia coli
, which directs most of the transcription in the cell, bacteria possess multiple, alternative sigma factors that direct RNA polymerase to distinct sets of promoters in response to environmental signals. By activating an alternative sigma factor, gene expression can be rapidly reprogrammed to meet the needs of the cell as the environment changes. Sigma factors are subject to multiple levels of regulation that control their levels and activities. The alternative sigma factor σ
E
in
Escherichia coli
is induced in response to extracytoplasmic stress. Here we demonstrate that σ
E
can also respond to signals other than extracytoplasmic stress. σ
E
activity increases in a growth phase-dependent manner as a culture enters stationary phase. The signaling pathway that activates σ
E
during entry into stationary phase is dependent upon the alarmone guanosine 3′,5′-bispyrophosphate (ppGpp) and is distinct from the pathway that signals extracytoplasmic stress. ppGpp is the first cytoplasmic factor shown to control σ
E
activity, demonstrating that σ
E
can respond to internal signals as well as signals originating in the cell envelope. ppGpp is a general signal of starvation stress and is also required for activation of the σ
S
and σ
54
alternative sigma factors upon entry into stationary phase, suggesting that this is a key mechanism by which alternative sigma factors can be activated in concert to provide a coordinated response to nutritional stress.
Flavin Adenine Dinucleotide-Dependent 4-Phospho-
d
-Erythronate Dehydrogenase Is Responsible for the 4-Phosphohydroxy-
l
-Threonine Pathway in Vitamin B
6
Biosynthesis in
Sinorhizobium meliloti
Authors: Tazoe Masaaki , Ichikawa Keiko , Hoshino Tatsuo
Published: June 2006

The vitamin B
6
biosynthetic pathway in
Sinorhizobium meliloti
is similar to that in
Escherichia coli
K-12; in both organisms this pathway includes condensation of two intermediates, 1-deoxy-
d
-xylulose 5-phosphate and 4-phosphohydroxy-
l
-threonine (4PHT). Here, we report cloning of a gene designated
pdxR
that functionally corresponds to the
pdxB
gene of
E. coli
and encodes a dye-linked flavin adenine dinucleotide-dependent 4-phospho-
d
-erythronate (4PE) dehydrogenase. This enzyme catalyzes the oxidation of 4PE to 3-hydroxy-4-phosphohydroxy-α-ketobutyrate and is clearly different in terms of cofactor requirements from the
pdxB
gene product of
E. coli
, which is known to be an NAD-dependent enzyme. Previously, we revealed that in
S. meliloti
IFO 14782, 4PHT is synthesized from 4-hydroxy-
l
-threonine and that this synthesis starts with glycolaldehyde and glycine. However, in this study, we identified a second 4PHT pathway in
S. meliloti
that originates exclusively from glycolaldehyde (the major pathway). Based on the involvement of 4PE in the 4PHT pathway, the incorporation of different samples of
13
C-labeled glycolaldehyde into pyridoxine molecules was examined using
13
C nuclear magnetic resonance spectroscopy. On the basis of the spectral analyses, the synthesis of 4PHT from glycolaldehyde was hypothesized to involve the following steps: glycolaldehyde is sequentially metabolized to
d
-erythrulose,
d
-erythrulose 4-phosphate, and
d
-erythrose 4-phosphate by transketolase, kinase, and isomerase, respectively; and
d
-erythrose 4-phosphate is then converted to 4PHT by the conventional three-step pathway elucidated in
E. coli
, although the mechanism of action of the enzymes catalyzing the first two steps is different.
Parent involvement in novice teen driving: a review of the literature
Authors: Simons-Morton B , Ouimet M C
Published: June 2006

Motor vehicle crashes remain elevated among novice teen drivers for at least several years after licensure. Licensing policies and driver education are the two primary countermeasures employed to decrease young driver crash risks. Graduated driver licensing policies have proved to be effective in reducing crash rates where evaluated. Driver education is an essential part of teaching teens the rules of the road and operating a vehicle, but requires few hours of professional driver training, relying mainly on parents to provide most of the supervised practice driving teens obtain before independent driving licensure. The few studies that have been conducted to increase parent supervised practice driving have not shown positive results. Moreover, it is unclear that increases in practice would improve independent driving safety. Recent research has shown that parent management of the early independent driving experience of novice teens improves safety outcomes, and other research has shown that it is possible to increase parent management practices. This paper provides a review of the literature on parent involvement in supervised practice and independent driving, and efforts to increase parental management.
Competent independent driving as an archetypal task of adolescence
Authors: Winston F K , Senserrick T M
Published: June 2006

Supplement Editor, Dr Flaura K Winston, and Co-Editor, Dr Teresa Senserrick, introduce 10 papers covering the current science of safe driving among adolescents from the varied viewpoints of an international panel of experts. This Expert Panel, convened by the Center for Injury Research and Prevention (formerly TraumaLink) at the Children’s Hospital of Philadelphia and State Farm Insurance Companies®, working jointly on the Youthful Driver Research Initiative, represents a wide range of expertise, thereby providing a broad understanding of driving, adolescence, and adolescent driving.
Reducing young driver road trauma: guidance and optimism for the future: Figure 1
Authors: Senserrick T M
Published: June 2006

This paper highlights lessons from each of the Expert Panel papers in the present supplement that provide guidance for future research and initiatives. Although some shortfalls still remain in our understanding, it is argued that much has been learned and we are ready for more translation, implementation, and evaluation of multilevel interventions to help reduce young driver road trauma. Non-use of restraints, speeding, driving at night and with passengers, and fatigue are highlighted as key risk factors to address. “Best practice” intervention is proposed as implementing and strengthening graduated driver licensing systems and complementary candidate programs and research, such as hazard perception training programs. A schematic cognitive-perceptual model to explain the crash sequence process is explored. There is optimism that meaningful impacts can be made, especially coupled with the advances in vehicle technologies, but caution is necessary in the absence of targeted “real world” evaluations and broader implementation and diffusion strategies.
Social marketing: an overview of approach and effects
Authors: Smith W A
Published: June 2006

This paper reviews the applicability of commercial and social marketing to teen driving safety. It draws on a wide range of information, including evaluation studies of specific programs as well as standards of practice within these two professions. Social marketing has been widely applied for more than three decades in the fields of public health, environmental protection, and political marketing with significant success. The paper attempts to distinguish between the practice of commercial marketing, whose goal is profit, and the practice of social marketing, whose goal is societal benefit. Issues of sustainability, segmentation, differences in behavioral characteristics, and cultural competence are discussed with specific examples drawn from the transportation safety literature. The paper suggests that social marketing represents a viable companion to control and education approaches to behavior change to promote teen driving safety.
A conceptual framework for reducing risky teen driving behaviors among minority youth: Figure 1
Authors: Juarez P , Schlundt D G , Goldzweig I , Stinson N
Published: June 2006

Teenage drivers, especially males, have higher rates of motor vehicle crashes and engage in riskier driving behavior than adults. Motor vehicle deaths disproportionately impact youth from poor and minority communities and in many communities there are higher rates of risky behaviors among minority youth. In this paper, the authors review the data on teens, risky driving behaviors, and morbidity and mortality. They identify areas in which known disparities exist, and examine strategies for changing teen driving behavior, identifying what has worked for improving the use of seat belts and for reducing other risky behaviors. A multifaceted, multilevel model based on ecological theory is proposed for understanding how teens make choices about driving behaviors, and to understand the array of factors that can influence these choices. The model is used to create recommendations for comprehensive intervention strategies that can be used in minority communities to reduce disparities in risk behaviors, injury, disability, and death.
Bacteriocin-like substance inhibits potato soft rot caused byErwinia carotovora
Authors: Cladera-Olivera Florencia , Caron Geruza R , Motta Amanda S , Souto André A , Brandelli Adriano
Published: June 2006

Soft rot is a major problem encountered in potatoes during postharvest storage. The soft rot bacterium Erwinia carotovora was inhibited by a novel bacteriocin-like substance (BLS) produced by Bacillus licheniformis P40. The BLS caused a bactericidal effect on E. carotovora cells at 30 µg mL–1. Transmission electron microscopy showed that BLS-treated cells presented wrinkled bacterial surfaces and shrinkage of the whole cell, indicating plasmolysis. Erwinia carotovora cells treated with BLS were analyzed by FTIR showing differences in the 1390 cm–1and 1250–1220 cm–1bands, corresponding to assignments of membrane lipids. BLS was effective in preventing E. carotovora spoilage on potato tubers, reducing the symptoms of soft rot at 240 µg mL–1and higher concentrations. Soft rot development was completely blocked at 3.7 mg mL–1. This BLS showed potential to protect potato tubers during storage. Key words: bacteriocin, plant pathogen, potato, soft rot, storage.
Influence of dissolved organic matter and inorganic nutrients on the biofilm bacterial community on artificial substrates in a northeastern Ohio, USA, stream
Authors: Olapade Ola A , Leff Laura G
Published: June 2006

Stream bacteria may be influenced by the composition and availability of dissolved organic matter (DOM) and inorganic nutrients, but knowledge about how individual phylogenetic groups in biofilm are affected is still limited. In this study, the influence of DOM and inorganic nutrients on stream biofilm bacteria was examined. Biofilms were developed on artificial substrates (unglazed ceramic tiles) for 21 days in a northeastern Ohio (USA) stream for five consecutive seasons. Then, the developed biofilm assemblages were exposed, in the laboratory, to DOM (glucose, leaf leachate, and algal exudates) and inorganic nutrients (nitrate, phosphate, and nitrate and phosphate in combination) amendments for 6 days. Bacterial numbers in the biofilms were generally higher in response to the DOM treatments than to the inorganic nutrient treatments. There were also apparent seasonal variations in the response patterns of the individual bacterial taxa to the nutrient treatments; an indication that limiting resources to bacteria in stream biofilms may change over time. Overall, in contrast to the other treatments, bacterial abundance was generally highest in response to the low-molecular-weight DOM (i.e., glucose) treatment. These results further suggest that there are interactions among the different bacterial groups in biofilms that are impacted by the associated nutrient dynamics among seasons in stream ecosystems.Key words: biofilms, nutrients, DOM, bacteria, in situ hybridization.
INDUCED CHANGES OF THERMOTROPIC PROPERTIES OF PHASE TRANSITIONS BETWEEN SMECTIC A MESOPHASE AND ISOTROPIC LIQUID: EFFECT OF SURFACES
Authors: NESRULLAJEV ARIF , OKTIK ŞENER
Published: June 2006

In this work, the effect of thin films on the thermotropic and thermo-optical properties and peculiarities of the phase transitions between the smectic A and isotropic liquid have been investigated. Peculiarities of the heterophase regions of the straight smectic A-isotropic liquid and reverse isotropic liquid-smectic A phase transitions have been studied.

Change of morphologic properties of the heterophase regions, shift of the phase transition temperatures and the change of temperature widths of these heterophase regions under thin film influence have been observed.
ELASTIC BEHAVIOR OF Pr SUBSTITUTED Y-123 SUPERCONDUCTING MATERIALS
Authors: DOLE B. N. , PURUSHOTHAM Y. , REDDY P. VENUGOPAL , SHAH S. S.
Published: June 2006

The longitudinal (Vl) and shear (Vs) wave velocities of Praseodymium substituted YB 2 Cu 3 O 7-δ high temperature superconductors were determined at room temperature by the pulse transmission technique. The values of Young's (E), rigidity (n) and bulk (k) moduli have been corrected to zero porosity. The zero porous corrected values of the elastic moduli are found to increase with increasing Praseodymium concentration. A linear relationship between the Debye temperature (θD) and average sound velocity (Vm) has also been observed and the behavior is explained qualitatively.
Strong convergence of a modified implicit iteration process for a finite family of Z‐operators
Authors: Rafiq Arif
Published: June 2006

The purpose of this note is to establish a strong convergence of a modified implicit iteration process to a common fixed point for a finite family of Z‐operators.
Stability analysis of a ratio‐dependent predator‐prey system with diffusion and stage structure
Authors: Song Xinyu , Ge Zhihao , Wu Jingang
Published: June 2006

A two‐species predator‐prey system with diffusion term and stage
structure is discussed, local stability of the system is studied
using linearization method, and global stability of the system is
investigated by strong upper and lower solutions. The asymptotic
behavior of solutions and the negative effect of stage structure
on the permanence of populations are given.
Dispersion properties of ergodic translations
Authors: Isola Stefano
Published: June 2006

We consider irrational rotations of the circle Tx = x + α

(mod⁡
1) and study the asymptotic behavior of sums of the type

with πk = ±1, the sign being
determined by the location of Tkx
with respect to a binary
partition.
Covariance of the number of real zeros of a random trigonometric polynomial
Authors: Farahmand K. , Sambandham M.
Published: June 2006

For random coefficients aj and bj we consider a random trigonometric polynomial defined as . The expected number of real zeros of Tn(θ) in the interval (0, 2π) can be easily obtained. In this note we show that this number is in fact . However the variance of the above number is not known. This note presents a method which leads to the asymptotic value for the covariance of the number of real zeros of the above polynomial in intervals (0, π) and (π, 2π). It can be seen that our method in fact remains valid to obtain the result for any two disjoint intervals. The applicability of our method to the classical random trigonometric polynomial, defined as , is also discussed. Tn(θ) has the advantage on Pn(θ) of being stationary, with respect to θ, for which, therefore, a more advanced method developed could be used to yield the results.
Vector bundles over three‐dimensional spherical space forms
Authors: Costa Esdras Teixeira , Neto Oziride Manzoli , Spreafico Mauro
Published: June 2006

We consider the problem of enumerating the G‐bundles over
low‐dimensional manifolds (dimension ≤3) and in particular
vector bundles over the three‐dimensional spherical space forms.
We give a complete answer to these questions and we give tables
for the possible vector bundles over the 3‐dimensional spherical
space forms.
Linearization coefficients for Sheffer polynomialsets via lowering operators
Authors: Ben Cheikh Y. , Chaggara H.
Published: June 2006

The lowering operator σ associated with a polynomial set
is an operator not depending on n and satisfying the relation σPn = nPn−1. In this paper, we express explicitly the linearization coefficients for
polynomial sets of Sheffer type using the corresponding lowering
operators. We obtain some well‐known results as particular cases.
Existence of positive periodic solutions for delayed predator‐prey patch systems with stocking
Authors: Fang Hui , Wang Zhicheng
Published: June 2006

A sufficient condition is derived for the existence of positive periodic solutions for a delayed predator‐prey patch system with stocking. Some known results are improved.
Universal mapping properties of some pseudovaluation domains and related quasilocal domains
Authors: Ayache Ahmed , Dobbs David E. , Echi Othman
Published: June 2006

If (R, M) and (S, N)
are quasilocal (commutative integral)
domains and f : R → S is a (unital) ring homomorphism,
then f
is said to be a strong local homomorphism
(resp., radical local homomorphism) if f(M) = N
(resp.,
f(M)⊆N
and for each x ∈ N, there exists a positive
integer t
such that xt ∈ f(M)). It is known that if
f : R → S
is a strong local homomorphism where R
is a
pseudovaluation domain that is not a field and S is a valuation
domain that is not a field, then f factors via a unique strong
local homomorphism through the inclusion map iR
from R to its
canonically associated valuation overring (M : M). Analogues of
this result are obtained which delete the conditions that R and
S are not fields, thus obtaining new characterizations of when
iR
is integral or radicial. Further analogues are obtained in which the “pseudovaluation domain that is not a
field” condition is replaced by the APVDs of Badawi‐Houston and the “strong local homomorphism” conditions are replaced by “radical local homomorphism.”
P‐clean rings
Authors: Chen Weixing
Published: June 2006

In this paper we unify the structures of various clean rings by introducing the notion of P‐clean rings. Some properties of P‐clean rings are investigated, which generalize the known results on clean rings, semiclean rings, n‐clean rings, and so forth. By the way, we answer a question of Xiao and Tong on n‐clean rings in the negative.
Erratum to “Hyperfinite and standard unifications for physical theories”
Authors: Herrmann Robert A.
Published: June 2006

This corrects the major theorem on product consequence operators.
Control of Hypertension 5 Years After Stroke in the North East Melbourne Stroke Incidence Study
Authors: Paul Seana L. , Thrift Amanda G.
Published: June 2006

Control of blood pressure after stroke is important for reducing the risk of recurrent stroke. We examined the control of hypertension in a community-based population of 5-year stroke survivors. Cases of first-ever stroke from the North East Melbourne Stroke Incidence Study were interviewed at 5 years poststroke. Blood pressure, history of hypertension, and antihypertensive medications were recorded. Individuals were classified as normotensive (blood pressure <140/90 mm Hg, no history of hypertension, and no antihypertensive medications), controlled hypertensive (blood pressure <140/90 mm Hg, history of hypertension, and/or taking antihypertensive medications), uncontrolled hypertensive (blood pressure ≥140/90 mm Hg, history of hypertension, and/or taking antihypertensive medications), or uninformed hypertensive (blood pressure ≥140/90 mm Hg, no known history of hypertension, and no antihypertensive medications). At 5 years poststroke, 441 (45%) of 978 first-ever stroke cases were alive. Of these, 305 (69%) had complete data on blood pressure, antihypertensive medication use, and history of hypertension. No statistical differences existed between those with or without these data. Eight-two percent were hypertensive; 63% had controlled hypertension, 30% had uncontrolled hypertension, and 7% were unaware that they were hypertensive. Overall, 67% of individuals classified as uncontrolled or uninformed hypertensive subjects were receiving treatment that was insufficient to achieve target blood pressure levels. Uncontrolled hypertensive subjects were more likely to recall receiving advice to manage their hypertension with medication (
P
<0.02) and diet (
P
<0.09). Although the majority of hypertensive individuals had controlled hypertension at 5 years poststroke, considerable improvement can be made in the control of hypertension after stroke.
Residual Arachidonic Acid–Induced Platelet Activation via an Adenosine Diphosphate–Dependent but Cyclooxygenase-1– and Cyclooxygenase-2–Independent Pathway
Authors: Frelinger Andrew L. , Furman Mark I. , Linden Matthew D. , Li Youfu , Fox Marsha L. , Barnard Marc R. , Michelson Alan D.
Published: June 2006

Background—

Thrombotic events still occur in aspirin-treated patients with coronary artery disease.

Methods and Results—

To better understand aspirin “resistance,” serum thromboxane B
2
(TXB
2
) and flow cytometric measures of arachidonic acid–induced platelet activation (before and after the ex vivo addition of aspirin and indomethacin) were analyzed in 700 consecutive aspirin-treated patients undergoing cardiac catheterization. In 680 of 682 evaluable patients, serum TXB
2
concentrations were reduced compared with nonaspirinated healthy donors. Twelve patients had serum TXB
2
that was lower than nonaspirinated healthy donors but >10 ng/mL. Arachidonic acid stimulated greater platelet activation in patients with high serum TXB
2
(>10 ng/mL) than in patients with low serum TXB
2
. Addition of ex vivo aspirin reduced arachidonic acid–induced platelet activation to similar levels regardless of serum TXB
2
concentrations, which suggests that patients with high residual serum TXB
2
concentrations were either noncompliant or underdosed with aspirin. Among the remaining 98% of patients, ex vivo administration of either aspirin or indomethacin failed to prevent platelet activation across all degrees of arachidonic acid–induced platelet activation and aspirin doses. Although the patients were not randomized with respect to clopidogrel treatment, multivariate analysis showed that arachidonic acid–induced platelet activation was less in patients receiving clopidogrel.

Conclusions—

There is a residual arachidonic acid–induced platelet activation in aspirin-treated patients that (1) is caused by underdosing and/or noncompliance in only &2% of patients and (2) in the remaining patients, occurs via a cyclooxygenase-1 and cyclooxygenase-2 independent pathway, in direct proportion to the degree of baseline platelet activation, and is mediated in part by adenosine diphosphate–induced platelet activation.
Risk of Death or Reinfarction Associated With the Use of Selective Cyclooxygenase-2 Inhibitors and Nonselective Nonsteroidal Antiinflammatory Drugs After Acute Myocardial Infarction
Authors: Gislason Gunnar H. , Jacobsen Søren , Rasmussen Jeppe N. , Rasmussen Søren , Buch Pernille , Friberg Jens , Schramm Tina Ken , Abildstrom Steen Z. , Køber Lars , Madsen Mette , Torp-Pedersen Christian
Published: June 2006

Background—

The selective cyclooxygenase-2 (COX-2) inhibitors and other nonselective nonsteroidal antiinflammatory drugs (NSAIDs) have been associated with increased cardiovascular risk, but the risk in patients with established cardiovascular disease is unknown. We analyzed the risk of rehospitalization for acute myocardial infarction (MI) and death related to the use of NSAIDs including selective COX-2 inhibitors in patients with prior MI.

Methods and Results—

All patients with first-time MI between 1995 and 2002 as well as all prescription claims for NSAIDs after discharge were identified from nationwide Danish administrative registers. The risk of death and rehospitalization for MI associated with the use of selective COX-2 inhibitors and nonselective NSAIDs was studied with the use of multivariable proportional hazards models and case-crossover analysis. A total of 58 432 patients were discharged alive and included in the study; 9773 experienced rehospitalization for MI, and 16 573 died. A total of 5.2% of patients received rofecoxib, 4.3% celecoxib, 17.5% ibuprofen, 10.6% diclofenac, and 12.7% other NSAIDs. For any use of rofecoxib, celecoxib, ibuprofen, diclofenac, and other NSAIDs, the hazard ratios and 95% confidence intervals for death were 2.80 (2.41 to 3.25; for rofecoxib), 2.57 (2.15 to 3.08; for celecoxib), 1.50 (1.36 to 1.67; for ibuprofen), 2.40 (2.09 to 2.80; for diclofenac), and 1.29 (1.16 to 1.43; for other NSAIDS); there were dose-related increases in risk of death for all of the drugs. There were trends for increased risk of rehospitalization for MI associated with the use of both the selective COX-2 inhibitors and the nonselective NSAIDs.

Conclusions—

Selective COX-2 inhibitors in all dosages and nonselective NSAIDs in high dosages increase mortality in patients with previous MI and should therefore be used with particular caution in these patients.
An Adaptive Load Balancer for Multiprocessor Routers
Authors: Shi W. , MacGregor M. H. , Gburzynski P.
Published: June 2006

By investigating flow-level characteristics of Internet traffic, the authors are able to trace the root of load imbalance in hash-based load-splitting schemes. They model flow popularity distributions as Zipf-like and prove that for typical Internet traffic, a hashing scheme cannot balance workload statistically, not even in the long run. They then develop a novel load-balancing packet scheduler for parallel forwarding systems. The scheduler capitalizes on the nonuniform flow reference pattern and especially the presence of a few high-rate flows in Internet traffic. The authors show that detecting and scheduling these flows can be very effective in balancing workloads among network processors. They introduce an important metric, adaptation disruption, to measure the scheduling efficiency of load-balancing mechanisms in parallel forwarding systems. Because there are relatively few large flows, reassigning them in the load balancer results in little disruption to the states of individual processors. The ideas are validated by simulation results. Finally, the authors discuss the effects on cache performance when classifying flows using two different flow definitions: the destination IP address and the five-tuple. The latter results in finer flow granularity but worse route cache hit rate, which can lead to the degradation of routing table lookup performance.
Empire and communication: the media wars of Marshall McLuhan
Authors: MacDonald Michael
Published: June 2006

From his first reflections on advertising as a ‘magical institution’ in 1952 to his last writings on ‘The Brain and Media’ in 1978, Marshall McLuhan was reproached for his utopian view of media technologies as the ‘extensions of man’ and for his failure to understand the new, more formidable rhetorical powers of the electric mass media. These criticisms are not entirely unjust. At times McLuhan does seem to view media machines as vehicles of flight into a ‘cosmic harmony’ that ‘transcends space and time’. But for all his ‘delirious tribal optimism’ (Baudrillard), McLuhan also understood that the global village or ‘global theatre’ has become a theatre of war, a staging area for ‘colossal violence’ and ‘maximal conflict’. In order to shed new light on this darker, more radical vision of the mass media set forth by McLuhan, this article explores his decisive – but largely unacknowledged – contribution to radical media studies today, especially to the work of Paul Virilio, Friedrich Kittler and others concerned with the alliance of war, media and information in modern society. After some reflections on McLuhan's ‘mosaic’ approach to the media ecology and his view of media as the extensions of man, I examine three modulations of his most infamous aphorism: the medium is the message; the medium is the massage; and the medium is the mass-age.
Critical laughter: humor, popular culture and Israeli Holocaust commemoration
Authors: Zandberg Eyal
Published: June 2006

This article explores current trends in the representation of the Holocaust in Israeli popular culture through the analysis of the successful satirical television program: The Chamber Quintet. The article argues that the show's subversive and challenging interpretations of traditional Holocaust commemorations, indicates a major change in the collective memory of the Holocaust. The article explores the cultural role of the show's sketches relating to Holocaust memory by using three perspectives of analysis. The first is a historical–sociological perspective that deals with the development of Holocaust commemoration in Israel. The second perspective deals with the conflict between popular cultural practices and the conventions of Holocaust remembrance. The third perspective deals with the problematic relationship between the content (Holocaust memory) and the form (the genre of humor). Combining these perspectives reveals a dialectical discourse that connects prior voices with new modes of Holocaust representation in popular culture. The article suggests that the use of the popular medium and the genre of humor undermine the program's content. This process indicates a situation of deadlock in collective memory in which new voices criticize the traditional commemoration but can offer no alternative and subvert their own criticism.
Media effects and the question of the rational audience: lessons from the financial markets
Authors: Davis Aeron
Published: June 2006

This article offers evidence for an alternative perspective on the media effects debate. Early work on media influence, be it conservative or critical, assumed a causal link between mass media and mass behaviour. In contrast, decades of effects and audience research has established the inadequacy of this ‘strong effects’ paradigm. The main thrust of this counter-research is the realization that audiences actively consume and use the media for self-serving purposes. The alternative perspective offered here comes from a study of elite fund managers, their communications and decision-making in the London Stock Exchange. The research findings suggest that such individuals do respond actively to media, but, collectively, the results can be both self-defeating and on a mass scale. That is, individuals do not have to be ignorant nor act irrationally to contribute to media-instigated, collective irrationality.
The Estimation Theoretic Sensor Bias Correction Problem in Map Aided Localization
Authors: Perera Linthotage Dushantha Lochana , Wijesoma Wijerupage Sardha , Adams Martin David
Published: June 2006

Simultaneous Localization and Map Building (SLAM) and Map Aided Localization (MAL) are very effective techniques employed extensively in robot navigation tasks. However, biases and drifts in both exteroceptive and proprioceptive sensors adversely impair correct localization (in MAL) and also impair map building (in SLAM). More specifically, accumulated errors as a result of biases in the sensors cause the algorithms to diverge and produce inconsistent and inaccurate results. Although offline calibration of these sensors can reduce the effects to some extent, the process results in longer setup and processing times. Moreover, during operation, the sensors’ calibration may often be subject to changes or drifts requiring regular resetting and initialization. A convenient, appropriate and effective approach to overcome problems associated with biases in sensors has been to explicitly model and estimate the bias parameters concurrently with the vehicle state online using an augmented state space approach. This paper investigates the properties of the concurrent bias estimation in MAL using an augmented, estimation theoretic state space approach for the localization of a large class of mobile robots, consisting of autonomous ground vehicles. This involves a rigorous theoretical study of the issues of observability and convergence, their interrelations and effects on the algorithm’s performance. This paper shows analytically that if sensor biases are estimated jointly with the vehicle pose in a MAL framework: 1) The uncertainties of the estimated errors in the bias parameters of both proprioceptive and exteroceptive sensors diminish in each update. 2) A derived lower bound is reached in each of these estimates. 3) The rate of convergence to this lower bound is also derived. 4) Although often neglected in the literature, observability is a major issue. From the analysis it is derived that in order to guarantee observability in MAL with bias estimation, it is necessary to observe simultaneously at least two distinct landmarks, which are not on a straight line with the vehicle position. Extensive simulations are provided to illustrate the theoretical results established for the general case of nonlinear dynamics and slowly varying sensor biases. The results are further exemplified and verified experimentally using a sophisticated MAL algorithm, utilizing a low cost inertial navigation sensor suite.
On the Probabilistic Foundations of Probabilistic Roadmap Planning
Authors: Hsu David , Latombe Jean-Claude , Kurniawati Hanna
Published: June 2006

Why is probabilistic roadmap (PRM) planning probabilistic? How does the probability measure used for sampling a robot’s configuration space affect the performance of a PRM planner? These questions have received little attention to date. This paper tries to fill this gap and identify promising directions to improve future planners. It introduces the probabilistic foundations of PRM planning and examines previous work in this context. It shows that the success of PRM planning depends mainly and critically on favorable “visibility” properties of a robot’s configuration space. A promising direction for speeding up PRM planners is to infer partial knowledge of such properties from both workspace geometry and information gathered during roadmap construction, and to use this knowledge to adapt the probability measure for sampling. This paper also shows that the choice of the sampling source—pseudo-random or deterministic—has small impact on a PRM planner’s performance, compared with that of the sampling measure. These conclusions are supported by both theoretical and empirical results.