Recent studies on Schistosoma intercalatum: taxonomic status, puzzling distribution and transmission foci revisited

Schistosoma intercalatum, which causes human rectal schistosomiasis in Africa, still presents a great interest for its imprecise taxonomic status and its puzzling distribution in Africa. Two geographically isolated strains of S. intercalatum are recognized, the Lower Guinea strain and the Congo strain, which differ from each other in a number of morphological, biological and biochemical characteristics. Recent molecular data using RAPD markers indicate high divergence between the two strains, with values of Nei and Li's similarity indice allowing recognition of two genetically distinct taxa: experiments on pre- and post-isolating mechanisms are in progress in order to re-evaluate the taxonomic status of this polytypic species. With regard to its geographical distribution, S. intercalatum is characterized by the existence of two stable endemic areas (localized in Lower Guinea and North East of Democratic Republic of Congo) which correspond to the historical areas of species discovery, and the emergence during the last 15 years of new foci of the Lower Guinea strain outside previously known endemic areas. The absence of local adaptation of the Lower Guinea strain to its intermediate host, supported by experimental studies, may help to facilitate the spread of this strain. Nevertheless, the present restricted distribution of this species remains puzzling, because its potential snail hosts (bulinids) are widely distributed throughout much of Africa. Recent experimental and epidemiological studies suggest that interspecific sexual interactions between human schistosomes could have a role in limiting the distribution of S. intercalatum: the competitive sexual processes acting among human schistosomes show that S. haematobium and S. mansoni are always competitively dominant over S. intercalatum. These epidemiological observations lead the authors to distinguish three kinds of transmission foci for S. intercalatum.

The impact of pre- and post-natal contexts on immunity, glucocorticoids and oxidative stress resistance in wild and domesticated grey partridges

Genetic background, prenatal and post-natal early-life conditions influence the development of interconnected physiological systems and thereby shape the phenotype. Certain combinations of genotypes and pre- and post-natal conditions may provide higher fitness in a specific environmental context. Here, we investigated how grey partridges Perdix perdix of two strains (wild and domesticated) cope physiologically with pre- and post-natal predictable vs. unpredictable food supply. Food unpredictability occurs frequently in wild environments and requires physiological and behavioural adjustments. Well-orchestrated and efficient physiological systems are presumably more vital in a wild environment as compared to captivity. We thus predicted that wild-strain grey partridges have a stronger immunity, glucocorticoid (GC) stress response and oxidative stress resistance (OSR) than domesticated birds, which have undergone adaptations to captivity. We also predicted that wild-strain birds react more strongly to environmental stimuli and, when faced with harsh prenatal conditions, are better able to prepare their offspring for similarly poor post-natal conditions than birds of domesticated origin. We found that wild-strain offspring were physiologically better prepared for stressful situations as compared to the domesticated strain. They had a high GC stress response and a high OSR when kept under predictable food supply. Wild-strain parents reacted to prenatal unpredictable food supply by lowering their offspring's GC stress response, which potentially lowered GC-induced oxidative pressure. No such pattern was evident in the domesticated birds. Irrespective of strain and prenatal feeding scheme, post-natal unpredictable food supply boosted immune indices, and GC stress response was negatively related to antibody response in females and to mitochondrial superoxide production. Wild-strain grey partridge showed fitness-relevant physiological advantages and appeared to prepare their offspring for the prospective environment. Negative relationships between GC stress response, immunity and oxidative indices imply a pivotal role of an organism's oxidative balance and support the importance of considering multiple physiological systems simultaneously.

The sigma factor AlgU (AlgT) controls exopolysaccharide production and tolerance towards desiccation and osmotic stress in the biocontrol agent Pseudomonas fluorescens CHA0.

A variety of stress situations may affect the activity and survival of plant-beneficial pseudomonads added to soil to control root diseases. This study focused on the roles of the sigma factor AlgU (synonyms, AlgT, RpoE, and sigma(22)) and the anti-sigma factor MucA in stress adaptation of the biocontrol agent Pseudomonas fluorescens CHA0. The algU-mucA-mucB gene cluster of strain CHA0 was similar to that of the pathogens Pseudomonas aeruginosa and Pseudomonas syringae. Strain CHA0 is naturally nonmucoid, whereas a mucA deletion mutant or algU-overexpressing strains were highly mucoid due to exopolysaccharide overproduction. Mucoidy strictly depended on the global regulator GacA. An algU deletion mutant was significantly more sensitive to osmotic stress than the wild-type CHA0 strain and the mucA mutant were. Expression of an algU'-'lacZ reporter fusion was induced severalfold in the wild type and in the mucA mutant upon exposure to osmotic stress, whereas a lower, noninducible level of expression was observed in the algU mutant. Overexpression of algU did not enhance tolerance towards osmotic stress. AlgU was found to be essential for tolerance of P. fluorescens towards desiccation stress in a sterile vermiculite-sand mixture and in a natural sandy loam soil. The size of the population of the algU mutant declined much more rapidly than the size of the wild-type population at soil water contents below 5%. In contrast to its role in pathogenic pseudomonads, AlgU did not contribute to tolerance of P. fluorescens towards oxidative and heat stress. In conclusion, AlgU is a crucial determinant in the adaptation of P. fluorescens to dry conditions and hyperosmolarity, two major stress factors that limit bacterial survival in the environment.

Field Instrumentation, Testing, and Long-Term Monitoring of High-Mast Lighting Tower No. 1 at the I-35/US 18 Interchange Near Clear Lake in the State of Iowa Phase 3, TR-562, 2009

The current study was initiated to quantify the stresses induced in critical details on the reinforcing jacket and the tower itself through the use of field instrumentation, load testing, and long-term monitoring. Strain gages were installed on the both the tower and the reinforcing jacket. Additional strain gages were installed on two anchor rods. Tests were conducted with and without the reinforcing jacket installed. Data were collected from all strain gages during static load testing and were used to study the stress distribution of the tower caused by known loads, both with and without the reinforcing jacket. The tower was tested dynamically by first applying a static load, and then quickly releasing the load causing the tower to vibrate freely. Furthermore, the tower was monitored over a period of over 1 year to obtain stress range histograms at the critical details to be used for a fatigue evaluation. Also during the long-term monitoring, triggered time-history data were recorded to study the wind loading phenomena that excite the tower.

The Aspergillus fumigatus septins play pleiotropic roles in septation, conidiation, and cell wall stress, but are dispensable for virulence.

Septins are a conserved family of GTPases that regulate important cellular processes such as cell wall integrity, and septation in fungi. The requirement of septins for virulence has been demonstrated in the human pathogenic yeasts Candida albicans and Cryptococcus neoformans, as well as the plant pathogen Magnaporthe oryzae. Aspergillus spp. contains five genes encoding for septins (aspA-E). While the importance of septins AspA, AspB, AspC, and AspE for growth and conidiation has been elucidated in the filamentous fungal model Aspergillus nidulans, nothing is known on the role of septins in growth and virulence in the human pathogen Aspergillus fumigatus. Here we deleted all five A. fumigatus septins, and generated certain double and triple septin deletion strains. Phenotypic analyses revealed that while all the septins are dispensable in normal growth conditions, AspA, AspB, AspC and AspE are required for regular septation. Furthermore, deletion of only the core septin genes significantly reduced conidiation. Concomitant with the absence of an electron-dense outer conidial wall, the ΔaspB strain was also sensitive to anti-cell wall agents. Infection with the ΔaspB strain in a Galleria mellonella model of invasive aspergillosis showed hypervirulence, but no virulence difference was noted when compared to the wild-type strain in a murine model of invasive aspergillosis. Although the deletion of aspB resulted in increased release of TNF-α from the macrophages, no significant inflammation differences in lung histology was noted between the ΔaspB strain and the wild-type strain. Taken together, these results point to the importance of septins in A. fumigatus growth, but not virulence in a murine model.

Size Effect and Notch Size Effect in Metal Fatigue

It is a well known phenomenon that the constant amplitude fatigue limit of a large component is lower than the fatigue limit of a small specimen made of the same material. In notched components the opposite occurs: the fatigue limit defined as the maximum stress at the notch is higher than that achieved with smooth specimens. These two effects have been taken into account in most design handbooks with the help of experimental formulas or design curves. The basic idea of this study is that the size effect can mainly be explained by the statistical size effect. A component subjected to an alternating load can be assumed to form a sample of initiated cracks at the end of the crack initiation phase. The size of the sample depends on the size of the specimen in question. The main objective of this study is to develop a statistical model for the estimation of this kind of size effect. It was shown that the size of a sample of initiated cracks shall be based on the stressed surface area of the specimen. In case of varying stress distribution, an effective stress area must be calculated. It is based on the decreasing probability of equally sized initiated cracks at lower stress level. If the distribution function of the parent population of cracks is known, the distribution of the maximum crack size in a sample can be defined. This makes it possible to calculate an estimate of the largest expected crack in any sample size. The estimate of the fatigue limit can now be calculated with the help of the linear elastic fracture mechanics. In notched components another source of size effect has to be taken into account. If we think about two specimens which have similar shape, but the size is different, it can be seen that the stress gradient in the smaller specimen is steeper. If there is an initiated crack in both of them, the stress intensity factor at the crack in the larger specimen is higher. The second goal of this thesis is to create a calculation method for this factor which is called the geometric size effect. The proposed method for the calculation of the geometric size effect is also based on the use of the linear elastic fracture mechanics. It is possible to calculate an accurate value of the stress intensity factor in a non linear stress field using weight functions. The calculated stress intensity factor values at the initiated crack can be compared to the corresponding stress intensity factor due to constant stress. The notch size effect is calculated as the ratio of these stress intensity factors. The presented methods were tested against experimental results taken from three German doctoral works. Two candidates for the parent population of initiated cracks were found: the Weibull distribution and the log normal distribution. Both of them can be used successfully for the prediction of the statistical size effect for smooth specimens. In case of notched components the geometric size effect due to the stress gradient shall be combined with the statistical size effect. The proposed method gives good results as long as the notch in question is blunt enough. For very sharp notches, stress concentration factor about 5 or higher, the method does not give sufficient results. It was shown that the plastic portion of the strain becomes quite high at the root of this kind of notches. The use of the linear elastic fracture mechanics becomes therefore questionable.

Fatigue study of the fillet weld waving on weld toe and the penetration in the weld root based on the effective notch stress approach

The fatigue failure of structures under fluctuating loads in fillet weld joints raises a demand to determine the parameters related to this type of loading. In this study, the stress distribution in the susceptible area of weld toe and weld root in fillet welded models analyzed by finite element method applying FEMAP software. To avoid the geometrical singularity on the path of analytical stress analysis in the toe and root area of a weld model the effective notch stress approach applied by which a proper fictitious rounding that mostly depend on the material of structure is applied. The models with different weld toe waving width and radius are analyzed while the flank angle of weld varied in 45 and 30 degrees. The processed results shows that the waving compare to the straight weld toe makes differences in the value of stress and consequently the stress concentration factor between the tip and depth of the waves in the weld toe which helps to protect the crack of propagation and gives enough time and tools to be informed of the crack initiation in the structure during the periodical observation of structure. In the weld root study the analyses among the models with the welding penetration percentage from non-penetration to the full-penetration shows a slightly increase in the root area stress value which comparing with the stiffening effect of penetration conclude that the half-penetration can make an optimization between the stress increase and stiffening effect of deep penetration.

Hyperosmotic Stress and the Impact on Metabolite Formation and Redox Balance in Saccharomyces cerevisiae and Saccharomyces bayanus strains

Wine produced using an appassimento-type process represents a new and exciting innovation for the Ontario wine industry. This process involves drying grapes that have already been picked from the vine, which increases the sugar content due to dehydration and induces a variety of changes both within and on the surface of the grapes. Increasing sugar contents in musts subject wine yeast to conditions of high osmolarity during alcoholic fermentations. Under these conditions, yeast growth can be inhibited, target alcohol levels may not be attained and metabolic by-products of the hyperosmotic stress response, including glycerol and acetic acid, may impact wine composition. The further metabolism of acetic acid to acetylCoA by yeast facilitates the synthesis of ethyl acetate, a volatile compound that can also impact wine quality if present in sufficiently high concentrations. The first objective of this project was to understand the effect of yeast strain and sugar concentration on fermentation kinetics and metabolite formation, notably acetic acid and ethyl acetate, during fermentation in appassimento-type must. Our working hypotheses were that (1) the natural isolate Saccharomyces bayanus would produce less acetic acid and ethyl acetate compared to Saccharomyces cerevisiae strain EC-1118 fermenting the high and low sugar juices; (2) the wine produced using the appassimento process would contain higher levels of acetic acid and lower levels of ethyl acetate compared to table wine; (3) and the strains would be similar in the kinetic behavior of their fermentation performances in the high sugar must. This study determined that the S. bayanus strain produced significantly less acetic acid and ethyl acetate in the appassimento wine and table wine fermentations. Differences in acetic acid and ethyl acetate production were also observed within strains fermenting the two sugar conditions. Acetic acid production was higher in table wine fermented by S. bayanus as no acetic acid was produced in appassimento-style wine, and 1.4-times higher in appassimento wine fermented by EC-1118 over that found in table wine. Ethyl acetate production was 27.6-times higher in table wine fermented by S. bayanus, and 5.2-times higher by EC-1118, compared to that in appassimento wine. Sugar utilization and ethanol production were comparable between strains as no significant differences were determined. The second objective of this project was to bring a method in-house for measuring the concentration of pyridine nucleotides, NAD+, NADP+, NADH and NADPH, in yeast cytosolic extract. Development of this method is of applicative interest for our lab group as it will enable the redox balance of the NAD+/ NADH and NADP+/ NADPH systems to be assessed during high sugar fermentations to determine their respective roles as metabolic triggers for acetic acid production. Two methods were evaluated in this study including a UV-endpoint method using a set of enzymatic assay protocols outlined in Bergmeyer (1974) and a colorimetric enzyme cycling method developed by Sigma-Aldrich® using commercial kits. The former was determined to be limited by its low sensitivity following application to yeast extract and subsequent coenzyme analyses, while the latter was shown to exhibit greater sensitivity. The results obtained from the kits indicated high linearity, accuracy and precision of the analytical method for measuring NADH and NADPH, and that it was sensitive enough to measure the low coenzyme concentrations present in yeast extract samples. NADtotal and NADPtotal concentrations were determined to be above the lower limit of quantification and within the range of the respective calibration curves, making this method suitable for our research purposes.

Damage rate is a predictor of fatigue life and creep strain rate in fatigue of tensile human cortical bone samples

We present results on the growth of damage in 29 fatigue tests of human femoral cortical bone from four individuals, aged 53–79. In these tests we examine the interdependency of stress, cycles to failure, rate of creep strain, and rate of modulus loss. The behavior of creep rates has been reported recently for the same donors as an effect of stress and cycles (Cotton, J. R., Zioupos, P., Winwood, K., and Taylor, M., 2003, "Analysis of Creep Strain During Tensile Fatigue of Cortical Bone," J. Biomech. 36, pp. 943–949). In the present paper we first examine how the evolution of damage (drop in modulus per cycle) is associated with the stress level or the "normalized stress" level (stress divided by specimen modulus), and results show the rate of modulus loss fits better as a function of normalized stress. However, we find here that even better correlations can be established between either the cycles to failure or creep rates versus rates of damage than any of these three measures versus normalized stress. The data indicate that damage rates can be excellent predictors of fatigue life and creep strain rates in tensile fatigue of human cortical bone for use in practical problems and computer simulations.

Design, testing, and simulation of fibre composite leaf springs for heavy axle loads

This paper summarizes the design, manufacturing, testing, and finite element analysis (FEA) of glass-fibre-reinforced polyester leaf springs for rail freight vehicles. FEA predictions of load-deflection curves under static loading are presented, together with comparisons with test results. Bending stress distribution at typical load conditions is plotted for the springs. The springs have been mounted on a real wagon and drop tests at tare and full load have been carried out on a purpose-built shaker rig. The transient response of the springs from tests and FEA is presented and discussed.

The CtsR regulator of Listeria monocytogenes contains a variant glycine repeat region that affects piezotolerance, stress resistance, motility and virulence

A spontaneous high hydrostatic pressure (HHP)-tolerant mutant of Listeria monocytogenes ScottA, named AK01, was isolated previously. This mutant was immotile and showed increased resistance to heat, acid and H2O2 compared with the wild type (wt) (Karatzas, K.A.G. and Bennik, M.H.J. 2002 Appl Environ Microbiol 68: 3183–3189). In this study, we conclusively linked the increased HHP and stress tolerance of strain AK01 to a single codon deletion in ctsR (class three stress gene repressor) in a region encoding a highly conserved glycine repeat. CtsR negatively regulates the expression of the clp genes, including clpP, clpE and the clpC operon (encompassing ctsR itself), which belong to the class III heat shock genes. Allelic replacement of the ctsR gene in the wt background with the mutant ctsR gene, designated ctsRΔGly, rendered mutants with phenotypes and protein expression profiles identical to those of strain AK01. The expression levels of CtsR, ClpC and ClpP proteins were significantly higher in ctsRΔGly mutants than in the wt strain, indicative of the CtsRΔGly protein being inactive. Further evidence that the CtsRΔGly protein lacks its repressor function came from the finding that the Clp proteins in the mutant were not further induced upon heat shock, and that HHP tolerance of a ctsR deletion strain was as high as that of a ctsRΔGly mutant. The high HHP tolerance possibly results from the increased expression of the clp genes in the absence of (active) CtsR repressor. Importantly, the strains expressing CtsRΔGly show significantly attenuated virulence compared with the wt strain; however, no indication of disregulation of PrfA in the mutant strains was found. Our data highlight an important regulatory role of the glycine-rich region of CtsR in stress resistance and virulence.

Safety and quality and stage of distribution

Let 0 denote the level of quality inherent in a food product that is delivered to some terminal market. In this paper, I characterize allocations over 0 and provide an economic rationale for regulating safety and quality standards in the food system. Zusman and Bockstael investigate the theoretical foundations for imposing standards and stress the importance of providing a tractable conceptual foundation. Despite a wealth of contributions that are mainly empirical (for reviews of these works see, respectively, Caswell and Antle), there have been relatively few attempts to model formally the linkages between farm and food markets when food quality and consumer safety are at issue. Here, I attempt to provide such a framework, building on key contributions in the theoretical literature and linking them in a simple model of quality determination in a vertically related marketing channel. The food-marketing model is due to Gardner. Spence provides a foundation for Pareto-improving intervention in a deterministic model of quality provision, and Leland, building on the classic paper by Akerlof, investigates licensing and minimum standards when the information structure is incomplete. Linking these ideas in a satisfactory model of the food markets is the main objective of the paper.

Photoelastic Stress Analysis in Screwed and Cemented Implant-Supported Dentures With External Hexagon Implants

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Evaluation of Stress Patterns Produced by Implant-Retained Overdentures and Implant-Retained Fixed Partial Denture

The purposes of this study were to photoelastically measure the biomechanical behavior of 4 implants retaining different cantilevered bar mandibular overdenture designs and to compare a fixed partial denture (FPD). A photoelastic model of a human edentulous mandible was fabricated, which contained 4 screw-type implants (3.75 x 10 mm) embedded in the parasymphyseal area. An FPD and 3 overdenture designs with the following attachments were evaluated: 3 plastic Hader clips, 1 Hader clip with 2 posterior resilient cap attachments, and 3 ball/O-ring attachments. Vertical occlusal forces of 100 N were applied between the central incisor and unilaterally to the right and left second premolars and second molars. Stresses that developed in the supporting structure were monitored photoelastically and recorded photographically. The results showed that the anterior loading, the overdenture with 3 plastic Hader clips, displayed the largest stress concentration at the medium implant. With premolar loading, the FPD and overdenture with 3 plastic Hader clips displayed the highest stresses to the ipsilateral terminal implant. With molar loading, the overdenture with 3 ball/O-ring attachments displayed the most uniform stress distribution in the posterior edentulous ridge, with less overloading in the terminal implant. It was concluded that vertical forces applied to the bar-clip overdenture and FPD created immediate stress patterns of greater magnitude and concentration on the ipsilateral implants, whereas the ball/O-ring attachments transferred minimal stress to the implants. The increased cantilever in the FPD caused the highest stresses to the terminal implant.

Photoelastic Stress Analysis of Different Attachment Systems on Implant-Retained and Conventional Palatal Obturator Prostheses

Background: Considering that an increasing number of patients are victims of mutilator surgical resections, these studies are important for treatment success of rehabilitation of patients presenting oronasal communication.Purpose: The aim of this study was to assess the stress distribution through photoelasticity in palatal obturator prostheses with different attachment systems for implants.Methods: Two photoelastic models were obtained from an experimental maxillary model presenting an oronasal communication. One model was fabricated without implant, and the other with 2 implants 10 mm in length inserted in the left crest. Four colorless palatal obturator prostheses were fabricated. One prosthesis presented no attachment system, whereas the remaining prostheses were adapted to 3 attachment systems. The assembly was positioned in a circular polariscope for application of axial load.Results: The results were based on photographic records of stress in the photoelastic model submitted to loading. The records revealed higher stress concentration on the bar-clip system followed by the O'ring/bar-clip and O'ring systems, respectively. A homogeneous stress distribution was observed on the photoelastic model with the mucous-supported prosthesis.Conclusions: The attachment systems generated different characteristics of stress distribution that was concentrated surrounding the implants. The bar-clip system exhibited the highest stress concentration on the alveolar crest.