bluuebunny/crossref_metadata_2025 huggingface dataset:
Debonding in Overmolded Integrated Circuit Packages
Authors: Hunt S. , Carlsson L. A.
Published: April 2008

Recently introduced overmolded pad array chip carrier (OMPAC) electronic packages sometimes suffer from debonding between the overmold material and the printed circuit board. In this study, bond strength is characterized by a combination of experimental and analytical methods. Test specimens representative for OMPAC structures were designed, manufactured, and tested to failure in tension and torsion. Finite element stress analysis of the specimens was performed in conjunction with a combined interfacial stress failure criterion to determine interfacial tensile and shear strengths from the measured failure loads.
Application of Stochastic Finite Element Method to Thermal Analysis for Computer Cooling
Authors: Kieda Shigekazu , Ashiwake Noriyuki , Daikoku Takahiro , Zushi Shizuo
Published: April 2008

A stochastic finite element method is applied to thermal analysis of cooling in large-scale computers using a multi-fin flexible thermal contactor. The stochastic finite element method is a general technique to incorporate the effect of stochastic or statistical features of parameters into a finite element method by means of sensitivity analysis. Using this method, the temperature distribution of the chip is calculated, and also temperature variations associated with variations of thermal properties, heat generation rates, and uncertainties involved in real systems are estimated. Following presentation of the results obtained, the thermal performance of this system and applicability of the stochastic finite element method to computer cooling problems are discussed.
Thermal Characteristics of Two-Layered Bodies With Embedded Thin-Film Heat Source
Authors: Yan Ling , Haji-Sheikh A. , Beck J. V.
Published: April 2008

Exact series solutions for three-dimensional temperature distribution in two-layer bodies subject to various types of boundary conditions are presented. Special consideration is given to the case when one layer is a thin diamond film. The computation emphasizes the temperature effect of an embedded thin heat source of the type used in electronic devices. The mathematical formulation employs the Green’s function solution method. The solution is time partitioned in order to achieve a high degree of accuracy. Time partitioning greatly improves the convergence of three-dimensional heat conduction solutions. Time-partitioned series solutions with a reduced number of terms yield highly accurate temperature data. A two-layer model is chosen for simplicity of presentation; however, the method can be extended to more than two layers.
Component Rearrangement on Printed Wiring Boards to Maximize the Fundamental Natural Frequency
Authors: Chang Tien-Sheng , Magrab E. B.
Published: April 2008

A methodology to attain the highest fundamental natural frequency of a printed wiring board by rearranging its components has been developed. A general two-dimensional rearrangement algorithm is developed by which the rearrangement of the component-lead-board (CLB) assemblies is performed automatically for any combination of equal size, unequal size, movable and immovable CLBs. This algorithm is also capable of incorporating two design restrictions: fixed (immovable) components and prohibited (non-swappable) areas. A highly computationally efficient objective function for the evaluation of the automatic rearrangement process is introduced, which is a linear function of the size of the individual CLBs that have been selected for each interchange. The simulated annealing method is adapted to solve the combinatorial rearrangement of the CLBs. Using 61 combinations of boundary conditions, equal and unequal sized CLBs, movable and immovable CLBs, various CLB groupings and sets of material properties, it is found that, when compared to the exact solution obtained by an exhaustive search method, the simulated annealing method obtained the highest fundamental natural frequency within 1 percent for 87 percent of the cases considered, within 0.5 percent for 72 percent of the cases and the true maximum in 43 percent of them. To further increase the fundamental natural frequency the introduction of a single interior point support is analyzed. Depending on the boundary conditions an additional increase in the maximum fundamental natural frequency of 44 to 198 percent can be obtained.
Reliability of Fine Pitch Plastic Quad Flat Pack Leads and Solder Joints Under Bending, Twisting, and Thermal Conditions
Authors: Lau John , Erasmus Steve
Published: April 2008

The thermal and mechanical responses of a 304-Pin, 0.5 mm pitch, 40 mm by 40 mm body size plastic quad flat pack (QFP) solder joints and leads have been determined in this study. The thermal stress and strain in the leads and solder joints have been obtained by a 3-D nonlinear finite element method and the thermal fatigue life of the QFP corner solder joint was then estimated based on the calculated plastic strains, Coffin-Manson law, and isothermal fatigue data of solders. The effects of overload environmental stress factors on the mechanical responses of the leads and solder joints have been determined by bending and twisting experiments.
Finding the Constitutive Relation for a Specific Elastomer
Authors: Ling Yun , Engel Peter A. , Brodskey Wm. L. , Guo Yifan
Published: April 2008

The main purpose of this study was to determine a suitable strain energy function for a specific elastomer. A survey of various strain energy functions proposed in the past was made. For natural rubber, there were some specific strain energy functions which could accurately fit the experimental data for various types of deformations. The process of determining a strain energy function for the specific elastomer was then described. The second-order invariant polynomial strain energy function (James et al., 1975) was found to give a good fit to the experimental data of uniaxial tension, uniaxial compression, equi-biaxial extension, and pure shear. A new form of strain energy function was proposed; it yielded improved results. The equi-biaxial extension experiment was done in a novel way in which the moire techniques (Pendleton, 1989) were used. The obtained strain energy functions were then utilized in a finite element program to calculate the load-deflection relation of an electrometric spring used in an electrical connector.
An Efficient Numerical Technique for Thermal Characterization of Printed Wiring Boards
Authors: Stefani G. G. , Goel N. S. , Jenks D. B.
Published: April 2008

Thermal modeling of Surface Mount Technology (SMT) microelectronics packages is difficult due to the complexity of the printed wiring board (PWB) plates through hole (PTH) structure. A simple, yet powerful finite difference based approach, called EPIC (Equivalent Parameter for Interfacial Cells), for modelling complex 2-D and 3-D geometries with multiple materials is used to model the PTH structure. A technique for computing an effective thermal conductivity for the PWB is presented. The results compare favorably with those from a commercially available finite element package but require far less computer time.
Modeling of Heat Transfer in the Surface Mounting of Electronic Components
Authors: Rastogi S. K. , Poulikakos D.
Published: April 2008

In this paper a heat transfer model is presented for the determination of the temperature field of a circuit board with electronic components placed upon it and undergoing the process of surface mounting. The model is solved for a simple board configuration and the effect of the major parameters of the problem on the temperature field of the board and the components is obtained. Regions of sharp thermal gradients (causing thermal stresses and possible cracking) are identified. These regions are usually located around the edges of the electronic components as well as underneath the edges of these components within the board material.
Some Modeling Issues on the Finite Element Computation of Thermal Stresses in Metal Lines
Authors: Cifuentes Arturo O. , Shareef Iqbal A.
Published: April 2008

Thermal stresses are a major concern in the reliability of metal lines. This paper addresses some modeling issues concerning the determination of thermal stresses in such structures. Specifically, a finite element technique that allows one to follow the evolution of the stress field as a function of the steps of the manufacturing process is discussed. In addition, comparisons between several modeling strategies, namely, plane stress versus plane strain, geometric nonlinearity versus geometric linearity, “frozen view” models versus “evolving” models, etc., are presented. A detailed example describing the manufacturing of a copper line is included to illustrate these points.
Modeling the Effects of Mixed Flowing Gas (MFG) Corrosion and Stress Relaxation on Contact Interface Resistance
Authors: Bhagath Shrikar , Pecht Michael G.
Published: April 2008

This paper presents the development of an initial, “first-cut”, mathematical model for the prediction of electrical interface reliability trends. The model pertains to gold plated contacts subject to loss of normal force and environmental corrosion with time. Stress relaxation over time and temperature in the base metal of the contact is accounted for. Utilizing the results of Mixed Flowing Gas (MFG) tests, the model can be used to estimate the statistical contact resistance at a particular load (normal force), aging and operating temperature in the class II and III environments. An attempt is made to correlate experimental data with the classical Holm’s equation and to introduce time dependence into the equation. Further work is proposed to correlate results with experimental connector performance data.
A Numerical Study of Fatigue Life of J-Leaded Solder Joints Using the Energy Partitioning Approach
Authors: Verma S. , Dasgupta A. , Barker D.
Published: April 2008

A surface-mount J-leaded device is modeled in this study, to investigate the effects of selected design, loading and manufacturing variables on solder joint fatigue life. The solder is modeled as a viscoplastic material, while the remaining materials are assumed to be linear elastic, as a first order approximation. Finite element analysis is used to determine the stress and strain history in the solder, due to temperature cycling. A “typical” temperature cycle with uniform dwell periods is applied to the solder joint. The computed stress and strain histories are utilized to construct hysteresis plots at each location in the solder joint. The hysteresis plots are then partitioned into elastic strain energy, plastic work and creep work dissipation. The fatigue life of the solder joint is then estimated through the energy partitioning technique. Parametric studies are conducted to investigate qualitatively the dependence of solder joint fatigue life on selected material properties, geometric variables, life cycle as well as accelerated loads, and manufacturing variabilities.
A Finite Element and Experimental Investigation of a Clamp Plate for a Disk Stack in a Winchester Disk Drive
Authors: Morris C. P. , Bert C. W.
Published: April 2008

This paper provides a numerical tool to calculate the load provided by the clamp plate which anchors the disk stack of a Winchester disk drive and the distribution of that load circumferentially around the plate support. The analysis is verified by comparison with experimental data.
Fitness Trade-Offs inblaTEMEvolution
Authors: Mroczkowska Joanna E. , Barlow Miriam
Published: April 2008

blaTEM-1expression results in penicillin resistance, whereas expression of manyblaTEM-1descendants, called extended-spectrum β-lactamases (ESBLs), results simultaneously in resistance to penicillins and extended-spectrum cephalosporins. Despite the expanded resistance phenotypes conferred by many ESBLs,blaTEM-1is still the most abundantblaTEMallele in many microbial populations. This study examines the fitness effects of the two amino acid substitutions, R164S and E240K, that have occurred repeatedly among ESBLblaTEM-1descendants. Using a single-nucleotide polymorphism-specific real-time quantitative PCR method, we analyzed the fitness of strains expressingblaTEM-1,blaTEM-10, andblaTEM-12. Our results show that bacteria expressing the ancestralblaTEM-1allele have a fitness advantage over those expressing eitherblaTEM-10orblaTEM-12when exposed to ampicillin. This observation, combined with the fact that penicillins are the most prevalent antimicrobials prescribed worldwide, may explain whyblaTEM-1has persisted as the most frequently encounteredblaTEMallele in bacterial populations.
The Human CXC Chemokine Granulocyte Chemotactic Protein 2 (GCP-2)/CXCL6 Possesses Membrane-Disrupting Properties and Is Antibacterial
Authors: Linge Helena M. , Collin Mattias , Nordenfelt Pontus , Mörgelin Matthias , Malmsten Martin , Egesten Arne
Published: April 2008

Granulocyte chemotactic protein 2 (GCP-2)/CXCL6 is a CXC chemokine expressed by macrophages and epithelial and mesenchymal cells during inflammation. Through binding and activation of its receptors (CXCR1 and CXCR2), it exerts neutrophil-activating and angiogenic activities. Here we show that GCP-2/CXCL6 itself is antibacterial. Antibacterial activity against gram-positive and gram-negative pathogenic bacteria of relevance to mucosal infections was seen at submicromolar concentrations (minimal bactericidal concentration at which 50% of strains tested were killed, 0.063 ± 0.01 to 0.37 ± 0.03 μM). In killed bacteria, GCP-2/CXCL6 associated with bacterial surfaces, which showed membrane disruption and leakage. A structural prediction indicated the presence of three antiparallel NH2-terminal β-sheets and a short amphipathic COOH-terminal α-helix; the latter feature is typical of antimicrobial peptides. However, when the synthetic derivatives corresponding to the NH2-terminal (50 amino acids) and COOH-terminal (19 amino acids, corresponding to the putative α-helix) regions were compared, higher antibacterial activity was observed for the NH2-terminus-derived peptide, indicating that the holopeptide is necessary for full antibacterial activity. An artificial model of bacterial membranes confirmed these findings. The helical content of GCP-2/CXCL6 in the presence or absence of lipopolysaccharide or negatively charged membranes was studied by circular dichroism. As with many antibacterial peptides, membrane disruption by GCP-2/CXCL6 was dose-dependently reduced in the presence of NaCl, which, we here demonstrate, inhibited the binding of the peptide to the bacterial surface. Compared with CXC chemokines ENA-78/CXCL5 and NAP-2/CXCL7, GCP-2/CXCL6 showed a 90-fold-higher antibacterial activity. Taken together, GCP/CXCL6, in addition to its chemotactic and angiogenic properties, is likely to contribute to direct antibacterial activity during localized infection.
ramR
Mutations Involved in Efflux-Mediated Multidrug Resistance in
Salmonella enterica
Serovar Typhimurium
Authors: Abouzeed Yousef M. , Baucheron Sylvie , Cloeckaert Axel
Published: April 2008

In the sequenced genome of
Salmonella enterica
serovar Typhimurium strain LT2, an open reading frame (STM0580) coding for a putative regulatory protein of the TetR family is found upstream of the
ramA
gene. Overexpression of
ramA
results in increased expression of the AcrAB efflux pump and, consequently, multidrug resistance (MDR) in several bacterial species. The inactivation of the putative regulatory protein gene upstream of
ramA
in a susceptible serovar Typhimurium strain resulted in an MDR phenotype with fourfold increases in the MICs of unrelated antibiotics, such as quinolones/fluoroquinolones, phenicols, and tetracycline. The inactivation of this gene also resulted in a fourfold increase in the expression of
ramA
and a fourfold increase in the expression of the AcrAB efflux pump. These results indicated that the gene encodes a local repressor of
ramA
and was thus named
ramR
. In contrast, the inactivation of
marR
,
marA
,
soxR
, and
soxS
did not affect the susceptibilities of the strain. In quinolone- or fluoroquinolone-resistant strains of serovar Typhimurium overexpressing AcrAB, several point mutations which resulted in amino acid changes or an in-frame shift were identified in
ramR
; in addition, mutations interrupting
ramR
with an IS
1
element were identified in high-level fluoroquinolone-resistant serovar Typhimurium DT204 strains. One serovar Typhimurium DT104 isolate had a 2-nucleotide deletion in the putative RamR binding site found upstream of
ramA
. These mutations were confirmed to play a role in the MDR phenotype by complementing the isolates with an intact
ramR
gene or by inactivating their respective
ramA
gene. No mutations in the
mar
or
sox
region were found in the strains studied. In conclusion, mutations in
ramR
appear to play a major role in the upregulation of RamA and AcrAB and, consequently, in the efflux-mediated MDR phenotype of serovar Typhimurium.
Stronger Activity of Human Immunodeficiency Virus Type 1 Protease Inhibitors against Clinical Isolates of
Plasmodium vivax
than against Those of
P. falciparum
Authors: Lek-Uthai U. , Suwanarusk R. , Ruengweerayut R. , Skinner-Adams T. S. , Nosten F. , Gardiner D. L. , Boonma P. , Piera K. A. , Andrews K. T. , MacHunter B. , McCarthy J. S. , Anstey N. M. , Price R. N. , Russell B.
Published: April 2008

Recent studies using laboratory clones have demonstrated that several antiretroviral protease inhibitors (PIs) inhibit the growth of
Plasmodium falciparum
at concentrations that may be of clinical significance, especially during human immunodeficiency virus type 1 (HIV-1) and malaria coinfection. Using clinical isolates, we now demonstrate the in vitro effectiveness of two HIV-1 aspartic PIs, saquinavir (SQV) and ritonavir (RTV), against
P. vivax
(
n
= 30) and
P. falciparum
(
n
= 20) from populations subjected to high levels of mefloquine and artesunate pressure on the Thailand-Myanmar border. The median 50% inhibitory concentration values of
P. vivax
to RTV and SQV were 2,233 nM (range, 732 to 7,738 nM) and 4,230 nM (range, 1,326 to 8,452 nM), respectively, both within the therapeutic concentration range commonly found for patients treated with these PIs. RTV was fourfold more effective at inhibiting
P. vivax
than it was at inhibiting
P. falciparum
, compared to a twofold difference in SQV sensitivity. An increased
P. falciparum mdr1
copy number was present in 33% (3/9) of isolates and that of
P. vivax mdr1
was present in 9% of isolates (2/22), but neither was associated with PI sensitivity. The inter-
Plasmodium
sp. variations in PI sensitivity indicate key differences between
P. vivax
and
P. falciparum
. PI-containing antiretroviral regimens may demonstrate prophylactic activity against both vivax and falciparum malaria in HIV-infected patients who reside in areas where multidrug-resistant
P. vivax
or
P. falciparum
is found.
Low β-Lactamase-Negative Ampicillin-Resistant
Haemophilus influenzae
Strains Are Best Detected by Testing Amoxicillin Susceptibility by the Broth Microdilution Method
Authors: García-Cobos Silvia , Campos José , Román Federico , Carrera Cristina , Pérez-Vázquez María , Aracil Belén , Oteo Jesús
Published: April 2008

Ampicillin resistance in
Haemophilus influenzae
due to alterations in penicillin-binding proteins (β-lactamase negative ampicillin resistant [BLNAR]) is acquiring increasing clinical and epidemiological importance. BLNAR strains with low ampicillin MICs (0.5 to 4 μg/ml) represent the majority of this population in Europe and the United States, but separating them from susceptible isolates is challenging. To investigate the best method to identify low-BLNAR strains, we studied the antibiotic susceptibilities of 94 clinical isolates of
H. influenzae
by microdilution, Etest, and disk diffusion: 25 had no resistance mechanisms (gBLNAS), 34 had mutations in the
ftsI
gene only (gBLNAR), 20 were β-lactamase producers only (gBLPAR), and 15 showed β-lactamase production and mutations in the
ftsI
gene (gBLPACR). By current CLSI breakpoints, most gBLNAR isolates were ampicillin susceptible by microdilution (76.5%) or by Etest (88.2%). Most gBLNAR strains (79.4%) were nonsusceptible to amoxicillin (the most widely used community antibiotic in the United States and Europe) when tested by microdilution. By Etest, 15% of β-lactamase-positive isolates were nonresistant to ampicillin or amoxicillin. The poorest agreement between Etest and microdilution results was for the gBLPAR isolates (25% for ampicillin, 15% for amoxicillin, and 10% for cefaclor). Low-strength disks of ampicillin and amoxicillin-clavulanic acid poorly identified low-BLNAR isolates and are not recommended as a screening method. We suggest new amoxicillin breakpoints for BLNAR isolates as follows: susceptible, MIC ≤ 0.5 μg/ml (no resistance mechanisms; pharmacokinetic/pharmacodynamic [PK/PD] data favorable); intermediate, MICs = 1 to 2 μg/ml (resistance mechanisms present but PK/PD data favorable), and resistant, MICs ≥ 4 μg/ml (resistance mechanisms present and PK/PD data unfavorable).
Species Distribution and In Vitro Antifungal Susceptibility Patterns of 75 Clinical Isolates of
Fusarium
spp. from Northern Italy
Authors: Tortorano Anna Maria , Prigitano Anna , Dho Giovanna , Esposto Maria Carmela , Gianni Claudia , Grancini Anna , Ossi Cristina , Viviani Maria Anna
Published: April 2008

Fusarium
isolates from 75 Italian patients were identified by molecular methods, and their susceptibilities to antifungals were tested in vitro.
Fusarium verticillioides
was the species most frequently isolated from deep-seated infections, and
F. solani
was the species most frequently isolated from superficial infections.
F. solani
isolates showed high azole MICs, while
F. verticillioides
isolates showed low posaconazole MICs.
Connection between Trimethoprim-Sulfamethoxazole Use and Resistance in
Streptococcus pneumoniae, Haemophilus influenzae
, and
Moraxella catarrhalis
Authors: Kärpänoja Pauliina , Nyberg Solja T. , Bergman Miika , Voipio Tinna , Paakkari Pirkko , Huovinen Pentti , Sarkkinen Hannu
Published: April 2008

The association between trimethoprim-sulfamethoxazole use and resistance among the major respiratory tract pathogens was investigated by comparing regional consumption of the drug to regional resistance in the following year in 21 central hospital districts in Finland. A total of 23,530
Streptococcus pneumoniae
isolates, 28,320
Haemophilus influenzae
isolates, and 14,138
Moraxella catarrhalis
isolates were tested for trimethoprim-sulfamethoxazole susceptibility during the study period (1998-2004). Among the
S. pneumoniae
isolates, a statistically significant connection was found between regional consumption and resistance. No statistically significant connection was found between regional trimethoprim-sulfamethoxazole use and resistance among
H. influenzae
and
M. catarrhalis
isolates. According to our results, it seems that only in pneumococci can the development of trimethoprim-sulfamethoxazole resistance be influenced by restricting its use. However, trimethoprim-sulfamethoxazole remains an important antimicrobial agent because of its reasonable price. Hence, resistance to trimethoprim-sulfamethoxazole among these pathogens needs continuous monitoring.
Suppression of Dualtropic Human Immunodeficiency Virus Type 1 by the CXCR4 Antagonist AMD3100 Is Associated with Efficiency of CXCR4 Use and Baseline Virus Composition
Authors: Fransen Signe , Bridger Gary , Whitcomb Jeannette M. , Toma Jonathan , Stawiski Eric , Parkin Neil , Petropoulos Christos J. , Huang Wei
Published: April 2008

In a phase I/II evaluation of the CXCR4 antagonist AMD3100, human immunodeficiency virus RNA levels were significantly reduced in a single study subject who harbored CXCR4 (X4)-tropic virus, but not in subjects who harbored either dual/mixed (DM)-tropic or CCR5 (R5)-tropic virus (C. W. Hendrix et al., J. Acquir. Immune Defic. Syndr.
37
:1253-1262, 2004). In this study, we analyzed the envelope clones of DM-tropic virus in baseline and treated virus populations from 14 subjects. Ten subjects exhibited significant reductions in CXCR4-mediated infectivity after 10 days of AMD3100 therapy relative to baseline (X4 suppressor group), while four subjects had no reduction of CXCR4-mediated infectivity (X4 nonsuppressor group). The baseline viruses of the X4 suppressor group infected CXCR4-expressing cells less efficiently than those of the X4 nonsuppressor group. Clonal analysis indicated that the baseline viruses from the X4 suppressor group contained a higher proportion of R5-tropic variants mixed with CXCR4-using variants, while the X4 nonsuppressor group was enriched for CXCR4-using variants. AMD3100 suppressed X4-tropic variants in all subjects studied, but not all dualtropic variants. Furthermore, dualtropic variants that used CXCR4 efficiently were suppressed by AMD3100, while dualtropic variants that used CXCR4 poorly were not. This study demonstrated that AMD3100 has the ability to suppress both X4-tropic and certain dualtropic variants in vivo. The suppression of CXCR4-using variants by AMD3100 is dependent on both the tropism composition of the virus population and the efficiency of CXCR4 usage of individual variants.
Synergy of Human Immunodeficiency Virus Protease Inhibitors with Chloroquine against
Plasmodium falciparum
In Vitro and
Plasmodium chabaudi
In Vivo
Authors: He Zhengxiang , Qin Li , Chen Lili , Peng Nanzheng , You Jianlan , Chen Xiaoping
Published: April 2008

The synergy of the activities between chloroquine and various human immunodeficiency virus protease inhibitors was investigated in chloroquine-resistant and -sensitive malaria parasites. In both in vitro and in vivo assay systems, ritonavir was found to be the most potent in potentiating the antimalarial action of chloroquine.
Gene Amplification of the Multidrug Resistance 1 Gene of
Plasmodium vivax
Isolates from Thailand, Laos, and Myanmar
Authors: Imwong Mallika , Pukrittayakamee Sasithon , Pongtavornpinyo Wirichada , Nakeesathit Supatchara , Nair Shalini , Newton Paul , Nosten Francois , Anderson Timothy J. C. , Dondorp Arjen , Day Nicholas P. J. , White Nicholas J.
Published: April 2008

Plasmodium vivax mdr1
gene amplification, quantified by real-time PCR, was significantly more common on the western Thailand border (6 of 66 samples), where mefloquine pressure has been intense, than elsewhere in southeast Asia (3 of 149;
P
= 0.02). Five coding mutations in
pvmdr1
, independent of gene amplification, were also found.
Convergence of Regulatory Networks on the Pilus Locus of
Streptococcus pneumoniae
Authors: Rosch Jason W. , Mann Beth , Thornton Justin , Sublett Jack , Tuomanen Elaine
Published: April 2008

The
rlrA
pilus locus of
Streptococcus pneumoniae
is an example of a pathogenicity island acquired through genetic recombination. Many acquired genetic elements commandeer preexisting networks of the new organism for transcriptional regulation. We hypothesized that the
rlrA
locus has integrated into transcriptional regulatory networks controlling expression of virulence factors important in adhesion and invasion. To test this hypothesis, we determined the impact on pilus expression of known regulators controlling adherence, including the two-component systems CbpR/S and HK/RR03 and the transcriptional regulators of divalent cation transporters MerR and PsaR in vitro and in vivo. It was determined that the pilus locus is down-regulated by preexisting networks designed for adhesion and cation transport/response and that its regulation occurs through RlrA. The pilus locus was found to participate in invasion specifically restricted to lung epithelial cells in vitro. While expression of pili had only a small effect on virulence with an intranasal infection model, pili were critically important with an intratracheal infection model. Thus, expression of pili appears to have become integrated into the regulatory circuits for lung-specific invasion by pneumococci.
Burkholderia pseudomallei
Type III Secretion System Mutants Exhibit Delayed Vacuolar Escape Phenotypes in RAW 264.7 Murine Macrophages
Authors: Burtnick Mary N. , Brett Paul J. , Nair Vinod , Warawa Jonathan M. , Woods Donald E. , Gherardini Frank C.
Published: April 2008

Burkholderia pseudomallei
is a facultative intracellular pathogen capable of surviving and replicating within eukaryotic cells. Recent studies have shown that
B. pseudomallei
Bsa type III secretion system 3 (T3SS-3) mutants exhibit vacuolar escape and replication defects in J774.2 murine macrophages. In the present study, we characterized the interactions of a
B. pseudomallei bsaZ
mutant with RAW 264.7 murine macrophages. Following uptake, the mutant was found to survive and replicate within infected RAW 264.7 cells over an 18-h period. In addition, high levels of tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), granulocyte-macrophage colony-stimulating factor (GM-CSF), and RANTES, but not IL-1α and IL-1β, were detected in culture supernatants harvested from infected monolayers. The subcellular location of
B. pseudomallei
within infected RAW 264.7 cells was determined, and as expected, the
bsaZ
mutant demonstrated early-vacuolar-escape defects. Interestingly, however, experiments also indicated that this mutant was capable of delayed vacuolar escape. Consistent with this finding, evidence of actin-based motility and multinucleated giant cell formation were observed between 12 and 18 h postinfection. Further studies demonstrated that a triple mutant defective in all three
B. pseudomallei
T3SSs exhibited the same phenotype as the
bsaZ
mutant, indicating that functional T3SS-1 and T3SS-2 did not appear to be responsible for the delayed escape phenotype in RAW 264.7 cells. Based upon these findings, it appears that
B. pseudomallei
may not require T3SS-1, -2, and -3 to facilitate survival, delayed vacuolar escape, and actin-based motility in activated RAW 264.7 macrophages.
Pathogenesis of Renal Disease Due to Enterohemorrhagic
Escherichia coli
in Germ-Free Mice
Authors: Eaton Kathryn A. , Friedman David I. , Francis Gayle J. , Tyler Jessica S. , Young Vincent B. , Haeger Jennifer , Abu-Ali Galeb , Whittam Thomas S.
Published: April 2008

Enterohemorrhagic
Escherichia coli
(EHEC) is a food-borne pathogen that causes hemorrhagic colitis and acute renal failure. We used a germ-free mouse model to investigate the role of host factors, Shiga toxin 2 (Stx2), and bacterial strain in disease due to EHEC. Germ-free male and female Swiss-Webster mice that were 3 days to 12 weeks old were orally inoculated with 1 of 10 EHEC strains or derivatives of two of these strains with Stx2 deleted. All inoculated mice became infected regardless of the inoculum dose. All bacterial strains colonized the intestines, reaching levels of 10
9
to 10
12
CFU/g of feces by 4 days after inoculation. Seven of the 10 wild-type strains caused disease. However, the two Stx2 deletion mutants, unlike the Stx2
+
parental strains, did not cause disease. The clinical signs of disease in mice included lethargy, dehydration, polyuria, polydypsia, and death. Postmortem examination of affected mice revealed dehydration and luminal cecal fluid accumulation. Histologic examination revealed close adherence of bacteria to the intestinal epithelium in the ileum and cecum but not in the colon. Other lesions included progressive renal tubular necrosis, glomerular fibrin thrombosis, and red blood cell sludging. The severity of disease varied according to the bacterial strain and age, but not sex, of the host. This study demonstrated that EHEC colonizes germ-free mice in large numbers, adheres to the intestinal epithelium, and causes luminal cecal fluid accumulation and progressive renal failure. The disease in mice was Stx2 and bacterial strain dependent. This animal model should be a useful tool for studying the pathogenesis of renal disease secondary to EHEC infection.
The
Streptococcus pneumoniae
Competence Regulatory System Influences Respiratory Tract Colonization
Authors: Kowalko J. E. , Sebert M. E.
Published: April 2008

The
Streptococcus pneumoniae
ComDE two-component signaling system controls the development of genetic competence in the bacterium and affects virulence in models of pneumonia and bacteremia. We have investigated the impact of the competence pathway during colonization of the nasopharynx, the principal ecological niche of the pneumococcus. Previous work showed that deletion of the pneumococcal CiaRH signaling system inhibited colonization and increased expression of genes required for competence. We anticipated that signaling by the competence pathway might similarly reduce carriage. Consistent with this expectation, a
comE
deletion that blocked transformation increased colonization fitness such that the mutant outcompeted the wild type in an infant rat model of asymptomatic carriage. Deletion of
comD
—immediately upstream of
comE
and likewise required for competence—similarly increased colonization fitness if the orientation of the antibiotic resistance cassette inserted into the
comD
locus was such that it reduced transcription of
comE
. However, an alternative
comD
deletion mutation that caused an increase in
comE
transcription impaired colonization instead. Activation of the competence system through a
comE
(
D143Y
) mutation did not affect colonization, but an inability to secrete the competence-stimulating peptide due to deletion of
comAB
produced a density-dependent reduction in colonization fitness. These results suggest a model in which signaling by the unactivated form of ComE reduces colonization fitness compared to that of bacteria in which it is either activated or absent entirely, with the most substantial fitness gain accompanying deletion of
comE
. This observation demonstrates that the pneumococcus incurs a substantial fitness cost in order to retain a functional competence regulatory system.
Using structural equation modeling to analyze relationships among key causes of delay in construction
Authors: Yang Jyh-Bin , Ou Shen-Fen
Published: April 2008

Schedule delays frequently occur in construction projects. The first step in resolving delay problems is to identify the main causes of delay. Previous studies identifying significant causes of delay have not examined how different causes work together to influence project schedule delays. Structural equation modeling (SEM) of causes of delay in construction has been developed for describing and quantifying the influence of different causes. Although this empirical study is based on a survey in Taiwan’s construction environment, the proposed model is applicable to construction industries in other countries. The analytical results clearly show the correlations among key causes of delay, which is the basis for resolving future schedule delays. This study proved that SEM is capable of quantifying the comprehensive relationships among investigated factors. Additionally, SEM has a high potential to resolve experience-oriented problems in the construction industry.
Relationship between methylene blue values of concrete aggregate fines and some concrete properties
Authors: Topçu İlker Bekir , Demir Abdullah
Published: April 2008

The fine granular structure and surface activity of clay minerals increase the amount of mixing water needed to provide workability in concrete. Even when the microfine material percentage in fine aggregate is low, the methylene blue value of the fine aggregate increases when materials of clay origin are present. In this study, methylene blue values were determined in fine aggregate samples used to produce ready-mixed concrete. Samples were taken from four different aggregate quarries, and relationships between methylene blue values of the concrete samples produced with these aggregates and some of their properties were investigated. Tests were done to determine the quality of microfine material (i.e., passing 0.063 mm sieve). Slump, ultrasonic pulse velocity, compressive strength, and surface abrasion resistance tests were performed on concretes made with these aggregate fines. It is shown that clay content, as indicated by the methylene blue value test, affects the concrete properties, but the microfine material percentage does not give any hint about clay content.
Jet impact geometry and plunge pool dimensions effects on dynamic pressures at pool sidewalls
Authors: Borghei S. M. , Zarnani P.
Published: April 2008

A plunge pool is one of the energy dissipater structures for high head dams, which ensures stability of the dam under extreme hydrodynamic pressure, due to falling jet impacts. The excess energy of the jet is dissipated, together with significant impact pressure exerted on the floor and pool walls. Thus, appropriate assessment of jet dynamic characteristics in the plunge pool is essential. This research presents experimental results focusing on the distribution of mean and extreme pressure fluctuations on the sidewalls, due to circular and rectangular plunging jets, and the effects of pool dimension, especially in narrow valleys. The experimental variables are discharge, geometry of jet, pool depth, pool width, and sidewall slope. Hydrodynamic pressure on the sidewalls due to decreasing bottom width from 6 to 3 times the jet impact diameter, or width, is quite different for core and developed jets. For core jets, it increases the maximum pressure, while decreasing the minimum and mean dynamic pressure on the sidewalls, while, in cases of developed jet impact, a reverse effect is observed for mean dynamic pressure. Finally, the results of pressure variation on plunge pool walls for different jet geometry and pool dimensions are presented graphically and design suggestions for pool optimum dimensions are provided.
Siloxanes in biogases from landfills and wastewater digesters
Authors: McBean Edward A.
Published: April 2008

Volatile methylsiloxanes and linear polydimethylsiloxanes (siloxanes), generated as components of biogases from digesters at wastewater treatment plants and solid waste landfills, have been identified as potentially causing significant operational problems. The problems are demonstrated as being an issue of “sand in the transmission” and are the reason for the changing of engine warrantees. Examples of monitored concentrations of siloxanes at a series of facilities are described, demonstrating degrees of variability both spatially and temporally, for different biogas sources. Wastewater digesters are shown to be generally producing biogases with higher siloxane concentrations than landfills. With a trend toward some landfills being operated as bioreactors, where the temperatures in the refuse are elevated to levels comparable to those within wastewater treatment digesters, there is potential that landfill-derived biogases may result in increased concentrations of siloxanes and hence more operating problems.
Estimating the age of juvenile loggerhead sea turtles in the North Atlantic
Authors: Hays G. C. , Marsh R.
Published: April 2008

Analysis of previously published records shows that the modal size of juvenile loggerhead sea turtles (Caretta caretta) found around the United Kingdom (the area north of 49°N and east of 12°W) is a carapace length of 20.5 cm. These turtles are believed to originate from nesting beaches in North America (principally Florida). We estimated their trans-Atlantic drift time using data from satellite-tracked buoys and from a mathematical model and, hence, estimated that the modal age of these juvenile turtles was between 1.80 and 3.75 years.
Food density, song rate, and body condition in territory-establishing willow warblers (Phylloscopus trochilus)
Authors: Nyström K. G. Kenneth
Published: April 2008

Early-arriving small male willow warblers (Phylloscopus trochilus) in good body condition were relatively successful at defending their territories. Later arriving neighbouring males tended to be larger but had poorer body condition. When males arrived, food resources were limited but increasing. The song rate varied among males during the period before pair formation and was positively correlated with the male body condition index. Song phrase length and song rate decreased after the performance of other activities, which suggests that singing was energy demanding. The sequence of pairing correlated well with male arrival, song rate, and food abundance. Females apparently take food abundance into account when selecting a mate. A model is presented to explain the adaptation of male and female willow warblers to the availability of food resources in time and space and the role of the male in securing a high-quality breeding territory.
Adult survival pattern of the sexually dimorphic Alpine ibex (Capra ibex ibex)
Authors: Toïgo Carole , Gaillard Jean-Michel , Michallet Jacques
Published: April 2008

Using recent developments in capture – recapture modeling, we analyzed the adult survival pattern of an Alpine ibex (Capra ibex ibex) population recently established in the northern Alps of France. Survival rates varied little over time and did not differ between the sexes. The survival rate was 0.97 (SE = 0.011). Recapture probabilities were stable over time but differed according to sex: 0.71 (SE = 0.035) for males versus 0.88 (SE = 0.033) for females. The absence of a between-sex difference in survival was not expected for a highly sexually dimorphic species. Environmental conditions, such as a low population density and a low pressure of limiting factors on population dynamics, could explain this absence of a survival cost of sexual selection for males. The high and rather constant survival rate of ibex over time is consistent with the idea that, in large mammals, individuals should be selected for maximizing their own adult survivorship.
Distribution of iron during embryogenesis and early larval life in sea lampreys (Petromyzon marinus)
Authors: Tsioros Kelly K. , Youson John H.
Published: April 2008

The distribution of ferric iron was examined in eggs, embryos, and early larvae (up to 77 d post fertilization (PF)) of the sea lamprey, Petromyzon marinus, using the Prussian blue staining technique. Iron was not detected in eggs and embryos but was detected in the lumen of the oesophagus at 17 – 33 days PF, when the newly hatched larvae burrow and commence exogenous feeding. The posterior intestine and hindgut became the primary location of iron absorption by 36 days PF, and subsequent development (36 – 63 days PF) showed an iron distribution suggesting elimination of excess metal through exfoliation of epithelial cells of the posterior intestine. The deposition of iron in macrophages of the intestine and liver (Kupffer cells) by 40 days PF may be related to both erythrophagocytosis and erythropoiesis at this time. Iron deposits in the macrophages of the pronephros and the atrium of the heart at 42 – 44 days PF were likely a consequence of endocytosis/filtration of the metal from circulating plasma. The commencement of iron deposition in specific tissues of larval lampreys seems to be correlated with the time they begin filter-feeding. Macrophages play an important role in iron metabolism in early larval life of lampreys.
A predicted in vivo muscle force – velocity trajectory
Authors: Cheng J.-Y. , DeMont M. E.
Published: April 2008

The in vivo stress–strain and stress – strain rate relationships of the adductor muscle in a swimming scallop (Placopecten magellanicus) were predicted on the basis of detailed measured swimming movements and a recently developed dynamic model that integrates all important mechanical elements in the process. The in vivo behaviour of the muscle was found to be quite different than the in vitro properties measured on isolated muscle fibres, which suggests that in general the latter might not be directly used to predict the in vivo mechanical events.
Thermal environment for overwintering hatchlings of the painted turtle (Chrysemys picta)
Authors: Packard Gary C. , Fasano Sarah L. , Attaway Marcus B. , Lohmiller Leslie D. , Lynch Trina L.
Published: April 2008

We monitored temperatures during the winter of 1995–1996 inside 18 nests containing hatchling painted turtles (Chrysemys picta). The study was performed at the Valentine National Wildlife Refuge in north-central Nebraska to assess survival of neonatal turtles in relation to the thermal environment inside their hibernacula. Minimum temperatures in the nests varied from −3 to −21 °C, and were better predictors of survival of hatchlings than other measures of the thermal environment. All hatchlings survived in nests where the temperature never went below −7 °C, some animals survived in nests where the minimum was between −7 and −13 °C, but no turtle survived in a nest where the minimum was below −14 °C. Hatchlings probably survived the cold by sustaining a state of supercooling, because the duration of exposure to low temperatures was far too long for animals in most nests to have survived in a frozen state.
Initial defecation time and rate of passage of digesta in adult Hawaiian monk seals, Monachus schauinslandi
Authors: Goodman-Lowe Gwen D. , Atkinson Shannon , Carpenter James R.
Published: April 2008

In an effort to gain a better understanding of the digestive physiology of the Hawaiian monk seal, Monachus schauinslandi, we measured initial defecation time and rate of passage of digesta using chromic oxide (Cr2O3) and frozen corn kernels as markers. Initial defecation time ranged from 9,5 to 19 h (mean 14 ± 4,8 h), which was a longer period of time than that reported for any other pinniped. The rate of passage of digesta measured using a single-pulse dose of Cr2O3 was approximately 39 h for two of the three seals, which is also longer than that reported for other pinnipeds. Possible reasons for these longer rates include morphological and physiological differences, age of the seals, and feeding regime. Percent Cr2O3 recovery was low (52.7–74.8%), reflecting the difficulty in collecting liquid stools. Levels of protein and ash (dry matter basis) were 21.70 and 34.79%, respectively, which reflects the high protein and mineral contents of the herring diet. This study yielded essential base-line data that will provide further insight into the digestive physiology of the Hawaiian monk seal.
The fine structure of the egg shells of the cabbage maggot,Delia radicumL. (Diptera: Anthomyiidae), and its relation with developmental conditions and oviposition site
Authors: Neveu N. , Allo M. R. , Nénon J. P. , Langlet X. , Brunel E. , Lahmer M. , Boivin G.
Published: April 2008

The fine structure and evolution of the egg shells of the cabbage maggot, Delia radicum, were studied in a French strain. The chorion did not undergo any modification at oviposition and consisted of three layers, except for the longitudinal strip, where the outer layer was lacking. The vitelline membrane of the oocyte was transformed by densification after oviposition. Differences in the longitudinal strip of the chorion were found between three strains of D. radicum. The strip was 650 μm long in the French strain and a Canadian strain, but only 250 μm long in a Moroccan strain. We also studied the effect of relative humidity on the hatching rate of eggs of the French strain and found that low relative humidity decreased the hatching rate. Finally, the function of the longitudinal strip was discussed in relation to climatic conditions.