Vibration reduction of a single cylinder reciprocating compressor based on multi-stage balancing

Basically, a reciprocating compressor consists of three main mechanical subsets: the hermetic housing, the crankcase and the rotor-crankshaft assembly. The counterweight mass located on the rotor-crankshaft is designed to balance the eccentric masses of the slider-crank mechanism which predominate in comparison to the residual distributed unbalance masses due to manufacturing. However, excessive vibration levels can be observed. The objective of the study is to perform a reliable finite element model for balancing the compressor by taking into account the dynamic behavior of the three subsets. The rotor-crankshaft assembly is considered as a flexible body, while the crankcase and the housing are assumed to be rigid. The rotor-crankshaft model is updated by using experimental modal analysis at rest. The characteristics of the fluid film bearings are speed of rotation dependant. The forces of the pressure and of the slider-crank mechanism are expanded by using Fourier transformation. The Influence Coefficient Method is used to investigate several balancing solutions to reduce the vibratory levels of the target plane located on the three main subsets. The experiments carried out show that this multi-stage balancing procedure is rather more efficient than a classical approach based only on the dynamic balancing of the rotor crankshaft assembly.     

Ultrasonographic signs of chromosome aberrations]

Factors predictive of psychiatric outcome in the second 6 months following traumatic brain injury (TBI) in 43 children and adolescents were assessed prospectively. The outcome measure was the presence of a psychiatric disorder not present before the injury ("novel"). Out of six models tested, four were predictive of novel psychiatric disorder: preinjury family function, family psychiatric history, socioeconomic class/intellectual function, and behavior/adaptive function. Post hoc analyses suggested that preinjury family functioning measured by a structured interview was a significant predictive variable. Severity of injury, when reclassified as severe versus mild/moderate TBI, significantly predicted novel psychiatric disorders. These data suggest that some children, identifiable through clinical assessment, are at increased risk for psychiatric disorders following TBI.     

Riparian vegetation restoration: Does social perception reflect ecological value?

Social‐ecological contexts are key to the success of ecological restoration projects. The ecological quality of restoration efforts, however, may not be fully evident to stakeholders, particularly if the desired aesthetic experience is not delivered. Aesthetically pleasing landscapes are more highly appreciated and tend to be better protected than less appealing landscapes, regardless of their ecological value. Positive public perception of restoration actions may therefore facilitate stakeholder involvement and catalyse recognition of ecological improvement. Here we aim to contrast aesthetical perception and ecological condition in headwater river reaches restored through passive ecological restoration in study areas in Portugal (Alentejo) and France (Normandy). We recorded structural and functional indicators of riparian vegetation to monitor the ecological condition of study sites along a passive restoration trajectory. Aesthetical perception indicators were assessed through stakeholder inquiries developed under a semantic differential approach. We analysed perception responses to changes in the riparian ecosystems resulting from passive ecological restoration across different geographical contexts and social groups. The analysed social groups comprised stakeholders (environmental managers and landowners) and university students (landscape architecture and geography students). Results indicate that (a) visual preferences often do not reflect changes in ecological condition, (b) perception of the restoration process is strongly context dependent, and (c) experience and cultural background affect perception of ecological condition across the different social groups analysed. Clear identification of relevant stakeholder groups (those interested in or directly affected by restoration), effective communication, and stakeholder engagement are therefore essential for assuring the success of river restoration projects.     

Association between spinal loads and the psychophysical determination of maximum acceptable force during pushing tasks

The objective of this study was to investigate potential associations between an individual's psychophysical maximum acceptable force (MAF) during pushing tasks and biomechanical tissue loads within the lumbar spine. Ten subjects (eight males, two females) pushed a cart with an unknown weight at one push every two minute for a distance of 3.9 m. Two independent variables were investigated, cart control and handle orientation while evaluating their association with the MAF. Dependent variables of hand force and tissue loads for each MAF determination and preceding push trial were assessed using a validated, electromyography-assisted biomechanical model that calculated spinal load distribution throughout the lumbar spine. Results showed no association between spinal loads and the MAF. Only hand forces were associated with the MAF. Therefore, MAFs may be dependent upon tactile sensations from the hands, not the loads on the spine and thus may be unrelated to risk of low back injury.

Practitioner Summary: Pushing tasks have become common in manual materials handling (MMH) and these tasks impose different tissue loads compared to lifting tasks. Industry has commonly used the psychophysical tables for job assent and decision of MMH tasks. However, due to the biomechanical complexity of pushing tasks, psychophysics may be misinterpreting risk.     

SVET, AFM and AES study of pitting corrosion initiated on MnS inclusions by microinjection

As pitting is a random phenomenon, it is difficult to predict where a pit will appear on the surface and consequently the use of local probes is rendered difficult. In this work, a new method to study pitting corrosion on a MnS inclusion on 316L stainless steel is proposed. It consists in modifying locally the chemistry in its vicinity by injecting with a microcapillary an aggressive solution of NaCl, H₂SO₄ or HCl. Once a pit appears, scanning vibrating electrode technique (SVET) is used to follow the current fluctuations over and around the pit when the metal is polarized at a passive potential. In another series of experiments the effect of local activation of MnS inclusion was studied ex-situ using Auger electron spectroscopy (AES) and atomic force microscopy. It is observed that a single pit can be initiated only when hydrochloric acid is injected, whereas sulphuric acid only partially dissolved the inclusion. On another hand, the surface morphology is not affected when a sodium chloride solution is injected. A significant enrichment in sulphur is detected around the inclusion by AES, and micropits are observed in the metal at the edge of the inclusion after HCl activation. Anodic zones are detected by SVET around the inclusion, whereas a cathodic current flows from the inclusion. The anodic current is clearly ascribed to the breakdown of passivity induced by adsorbed sulphur coming from the MnS dissolution, whereas various assumptions can be proposed for the origin of the cathodic current.     

Proteolysis of type III collagen by collagenase and cathepsin B under high hydrostatic pressure

The effects of high hydrostatic pressures on the kinetics of hydrolysis of type III collagen from calf skin by collagenase and cathepsin B were studied. Collagen hydrolysates sampled at different time intervals (0-90 min) and at different pressures (0.1-300 MPa) were analysed by reverse-phase high pressure liquid chromatography. The rate of collagen hydrolysis decreased up to 300 MPa for both enzymes. The rate of collagen hydrolysis with cathepsin B was drastically reduced between 0.1 and 100 MPa. Significant differences in the populations of the peptides in cathepsin B hydrolysates were observed in chromatograms corresponding to different pressures. This indicated that some amino acid side-chains were less exposed to cathepsin B recognition on the surface of collagen molecules at high pressures. In contrast, the chromatograms of collagenase hydrolysates showed similar patterns, varying only by the peak heights in chromatograms corresponding to the 0.1-300 MPa pressure range. Pressureinduced decreases of the enzyme-apparent activities suggested that the activation volumes for the reaction of both enzymes were positive.     

Foam formation in oxidic pool with application to MCCI real material experiments

Void fraction is an important parameter in molten core concrete interaction (MCCI) study of PWR since it controls the swollen level of the corium pool, the interaction surface between the pool and the concrete and, in turn, the concrete erosion velocity. In recent MCCI real material experiments (OECD-MCCI, VULCANO), it seems that very high void fraction (higher than 50%) might have been obtained leading to low erosion velocity of concrete (e.g. CCI-4) and significant concrete erosion of the upper part of the test section (e.g. CCI-2 and CCI-4). Such void fraction cannot presently be predicted with classical void fraction correlations (e.g. Zuber and Findlay), so that a different phenomenon related to the formation of foam in oxidic pool during core concrete interaction could be considered. The main purpose of this paper is to propose an analysis of MCCI experiments taking into account the foam formation resulting from gas released from concrete in corium pool with SiO₂ and CaO. The first part of this paper is devoted to a review of the available experimental and modeling work performed in the frame of the metallurgical industry R&D. Two of these models have been implemented in the TOLBIAC-ICB code (CEA/EDF) which has then been used to simulate real material MCCI experiments of the OECD-MCCI project, CCI-2 and CCI-3. In the second part of this paper, it will be seen that foam formation could explain some of the phenomena observed in these experiments such as the strong ablation of the upper part of the cavity in Limestone Common Sand (LCS) concrete tests.     

Epidemiological analysis of Salmonella enterica from beef sampled in the slaughterhouse and retailers in Dakar (Senegal) using pulsed-field gel electrophoresis and antibiotic susceptibility testing

Seventy-eight isolates of Salmonella spp. isolated from beef sampled from the official city slaughterhouse and from retailers in Dakar, Senegal were analyzed using serotyping, antimicrobial testing and macrorestriction profiling by Pulsed-Field Gel Electrophoresis (PFGE). These analyses were done to identify clonal relationships and potential transmission routes in beef channel. XbaI macrorestriction allowed defining 17 genotypes among the six main analyzed serotypes: Salmonella bredeney (3 genotypes), S. muenster (6), S. waycross (1), S. corvallis (3), S. kentucky (1) and S. brandenburg (3). The cross analysis of PFGE profiles and origin of the beef samples reveals a wide range of contamination sources in the beef channel in Dakar. Comparison of PFGE and antimicrobial resistance types shows that the Salmonella contamination sources are equally shared by the slaughterhouse (56% of the isolates) and by the distribution channel (44% of the isolates) by handlings and houseflies.     

Comparison of Enterococcus measurements in freshwater at two recreational beaches by quantitative polymerase chain reaction and membrane filter culture analysis

Cell densities of the fecal pollution indicator genus, Enterococcus, were determined by a rapid (3 h or less) quantitative polymerase chain reaction (QPCR) analysis method in 100 ml water samples collected from recreational beaches on Lake Michigan and Lake Erie during the summer of 2003. Measurements by this method were compared with counts of Enterococcus colony-forming units (CFU) determined by Method 1600 membrane filter (MF) analysis using mEI agar. The QPCR method had an estimated 95% confidence, minimum detection limit of 27 Enterococcus cells per sample in analyses of undiluted DNA extracts and quantitative analyses of multiple lake water samples, spiked with known numbers of these organisms, gave geometric mean results that were highly consistent with the spike levels. At both beaches, the geometric means of ambient Enterococcus concentrations in water samples, determined from multiple collection points during each sampling visit, showed approximately lognormal distributions over the study period using both QPCR and MF analyses. These geometric means ranged from 10 to 8548 cells by QPCR analysis and 1-2499 CFU by MF culture analysis in Lake Michigan (N=56) and from 8 to 8695 cells by QPCR and 3-1941 CFU by MF culture in Lake Erie (N=47). Regression analysis of these results showed a significant positive correlation between the two methods with an overall correlation coefficient (r) of 0.68.     

Description et analyse des attitudes et attributions paternelles favorables á la punition corporelle.

To date, few studies have shown a specific interest in parental discipline from the fathers' point of view. The goal of this study is to fill this gap by documenting the factors that are likely to predict attitudes favoring corporal punishment in a representative sampling of Quebec fathers. In total, 953 fathers participated in a telephone survey. Noted among the variables in the analysis model were: father's sensitivity to the consequences of violence for the child, prevalence of physical punishment toward the child, perception of the level of poverty, reports of violent discipline of a physical or psychological nature experienced during the fathers' childhood, number of people in the household and father's stress associated with the child's temperament. However, an apparent contradiction in paternal attitudes was seen: the majority of fathers were opposed to resorting to corporal punishment while remaining tolerant with respect to its use. The discussion paves the way for a more in-depth analysis and for understanding the potential role played by personal and contextual variables in the explanation of attitudes favoring corporal punishment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)