A new type of streaming in pulse tubes

By numerical simulation a new type of streaming in pulse tubes has been found. The geometry in the simulation consists of the pulse tube with its flow straighteners. The straighteners are described as a porous medium. Viscous effects are taken into account, but heat transfer with the wall is not considered. The gas flow in the pulse tube is periodic. Positive and negative boundary conditions are imposed which result in flow fields with opposing directions. The net flow field is obtained by the superposition of these two flow fields. It turns out that two loops are formed in the tube. This paper analyzes this phenomenon and explains how the flow resistance of the straightener and the viscous effect of the tube wall result in this type of streaming

Is intra-abdominal hypertension a missing factor that drives multiple organ dysfunction syndrome?

In a recent issue of Critical Care, Cheng and colleagues conducted a rabbit model study that demonstrated that intra-abdominal hypertension (IAH) may damage both gut anatomy and function. With only 6 hours of IAH at 25 mmHg, these authors observed an 80% reduction in mucosal blood flow, an exponential increase in mucosal permeability, and erosion and necrosis of the jejunal villi. Such dramatic findings should remind all caring for the critically ill that IAH may severely damage the normal gut barrier functions and thus may be reasonably expected to facilitate bacterial and mediator translocation. The potential contribution of IAH as a confounding factor in the efficacy of selective decontamination of the digestive tract should be considered

Reliability analysis of semi-automatic train door systems in service on today's rolling stock of the SNCB

This article analyses the reliability of semi-automatic train door systems that are in use on today’s rolling stock of the SNCB. For the analysis several databases of the SNCB concerning both operation and maintenance were thoroughly screened. These databases are briefly explained and scaling factors are applied to compare the performance of different series of rolling stock relative to each other. Conclusions are made out of the available data

Failure behaviour of a tumble dryer

A tumble dryer is a rotating heated vessel used to fulfil a poly-condensation process of PETgranules. This step is very crucial in the entire production process of polymer fibres. System failure, causing production loss, cannot be afforded. Unfortunately, since a couple of years, the reactors suffer from severe cracking at weld details. To find the root cause(s) of this problem a detailed study of the vessel construction, the loads induced during the production process and the cracking has been performed. Hereby the influencing parameters and their importance could be determined. Based on this study it is put forward that fatigue, due to the exceptional translation of the granules in the vessel, is responsible for the cracking of the tumble dryer. Two main loading modes and corresponding crack locations could be determined: a cyclic changing torque causes the cracks on the outside of the vessel while the dynamic play of the moving granules around the heating elements is responsible for the cracks at the inside the tumble dryer. The root cause of the cracking problem has been determined but the actual mechanism causing the cracks, still needs to be quantified

Effects of variable amplitude loading on fatigue life

This paper is a review of published research on variable amplitude loading of steels. The use of service spectra for different industrial sectors and specifically for offshore applications is first considered. Constant amplitude fatigue failure models are not representative for these applications. The JONSWAP spectrum shows potential to be used as service spectrum for offshore structures. Further investigation of variable amplitude fatigue is needed to get insight in the various phenomena linked to the variable amplitude. Observed trends in fatigue crack growth rate in variable amplitude fatigue tests on steels, such as the effects of overloads and underloads (occurring as single events, sequential events or block loadings), are discussed. Furthermore, suggestions of the underlying physical phenomena behind the load interaction effects due to variable amplitude loading are presented. It can be concluded that the plasticity induced crack closure mechanism is the most profound explanation for the acceleration effect in overloads and the retardation effect observed in underloads

Awareness and knowledge of intra-abdominal hypertension and abdominal compartment syndrome: results of an international survey

Background: Surveys have demonstrated a lack of physician awareness of intra-abdominal hypertension and abdominal compartment syndrome (IAH/ACS) and wide variations in the management of these conditions, with many intensive care units (ICUs) reporting that they do not measure intra-abdominal pressure (IAP). We sought to determine the association between publication of the 2006/2007 World Society of the Abdominal Compartment Syndrome (WSACS) Consensus Definitions and Guidelines and IAH/ACS clinical awareness and management. Methods: The WSACS Executive Committee created an interactive online survey with 53 questions, accessible from November 2006 until December 2008. The survey was endorsed by the WSACS, the European Society of Intensive Care Medicine (ESICM) and the Society of Critical Care Medicine (SCCM). A link to the survey was emailed to all members of the supporting societies. Participants of the 3rd World Congress on Abdominal Compartment Syndrome meeting (March 2007, Antwerp, Belgium) were also asked to complete the questionnaire. No reminders were sent. Based on 13 knowledge questions, an overall score was calculated (expressed as percentage). Results: A total of 2,244 of the approximately 10,000 clinicians who were sent the survey responded (response rate: 22.4%). Most of the 2,244 respondents (79.2%) completing the survey were physicians or physicians in training and the majority were residing in North America (53.0%). The majority of responders (85%) were familiar with IAP/IAH/ACS, but only 28% were aware of the WSACS consensus definitions for IAH/ACS. Three quarters of respondents considered the cut-off for IAH to be at least 15 mm Hg, and nearly two thirds believed the cut-off for ACS was higher than the currently suggested consensus definition (20 mm Hg). In 67.8% of respondents, organ dysfunction was only considered a problem with IAP of 20 mm Hg or higher. IAP was measured most frequently via the bladder (91.9%), but the majority reported that they instilled volumes well above the current guidelines. Surgical decompression was frequently used to treat IAH/ACS, whereas medical management was only attempted by about half of the respondents. Decisions to decompress the abdomen were predominantly based on the severity of IAP elevation and presence of organ dysfunction (74.4%). Overall knowledge scores were low (43 +/- 15%); respondents who were aware of the WSACS had a better score compared to those who were not (49.6% vs 38.6%, P < 0.001). Conclusions: This survey showed that although most responding clinicians claim to be familiar with IAH and ACS, knowledge of published consensus definitions, measurement techniques, and clinical management is inadequate

Intra-abdominal hypertension and abdominal compartment syndrome in pancreatitis, paediatrics, and trauma

Intra-abdominal hypertension (IAH) is an important contributor to early organ dysfunction in trauma and sepsis. However, relatively little is known about the impact of intra-abdominal pressure (IAP) in general internal medicine, pregnant patients, and those with obesity or burns. The aim of this paper is to review the pathophysiologic implications and treatment options for IAH in these specific situations. A MEDLINE and PubMed search was performed and the resulting body-of-evidence included in the current review on the basis of relevance and scientific merit. There is increasing awareness of the role of IAH in different clinical situations. Specifically, IAH will develop in most (if not all) severely burned patients, and may contribute to early mortality. One should avoid over-resuscitation of these patients with large volumes of fluids, especially crystalloids. Acute elevations in IAP have similar effects in obese patients compared to non-obese patients, but the threshold IAP associated with organ dysfunction may be higher. Chronic elevations in IAP may, in part, be responsible for the pathogenesis of obesity-related co-morbid conditions such as hypertension, pseudotumor cerebri, pulmonary dysfunction, gastroesophageal reflux disease, and abdominal wall hernias. At the bedside, measuring IAP and considering IAH in all critical maternal conditions is essential, especially in preeclampsia/eclampsia where some have hypothesized that IAH may have an additional role. IAH in pregnancy must take into account the precautions for aorto-caval compression and has been associated with ovarian hyperstimulation syndrome. Recently, IAP has been associated with the cardiorenal dilemma and hepatorenal syndrome, and this has led to the recognition of the polycompartment syndrome. In conclusion, IAH and ACS have been associated with several patient populations beyond the classical ICU, surgical, and trauma patients. In all at risk conditions the focus should be on the early recognition of IAH and prevention of ACS. Patients at risk for IAH should be identified early through measurements of IAP. Appropriate actions should be taken when IAP increases above 15 mm Hg, especially if pressures reach above 20 mm Hg with new onset organ failure. Although non-operative measures come first, surgical decompression must not be delayed if these fail. Percutaneous drainage of ascites is a simple and potentially effective tool to reduce IAP if organ dysfunction develops, especially in burn patients. Escharotomy may also dramatically reduce IAP in the case of abdominal burns

Multi-wire submerged arc welding: a study of secondary process parameters

The goal of this thesis is to investigate the effect of secondary process parameters on the geometry of the weld bead in multi-wire submerged arc welding. Bead-on-plate welding experiments will be conducted using 3, 4 and 5 wires. The parameters being varied will be the wire stick out, the angles of the torches and the spacing in between. Primary process parameters like voltage, current and welding speed will be kept constant. Penetration, bead width and height, percentage dilution, HAZ, weld penetration shape factor and weld reinforcement shape factor will be measured and evaluated. Fewer experiments will be needed because of the use of a design of experiments approach, namely a fractional factorial design. This will allow to determine the significance of each single parameter and their mutual interaction with respect to weld bead shape