Large-eddy simulation of heat transfer downstream of a backward-facing step

Large-eddy simulation is used to predict heat transfer in the separated and reattached flow regions downstream of a backward-facing step. Simulations were carried out at a Reynolds number of 28 000 (based on the step height and the upstream centreline velocity) with a channel expansion ratio of 1.25. The Prandtl number was 0.71. Two subgrid-scale models were tested, namely the dynamic eddy-viscosity, eddy-diffusivity model and the dynamic mixed model. Both models showed good overall agreement with available experimental data. The simulations indicated that the peak in heat-transfer coefficient occurs slightly upstream of the mean reattachment location, in agreement with experimental data. The results of these simulations have been analysed to discover the mechanisms that cause this phenomenon. The peak in heat-transfer coefficient shows a direct correlation with the peak in wall shear-stress fluctuations. It is conjectured that the peak in these fluctuations is caused by an impingement mechanism, in which large eddies, originating in the shear layer, impact the wall just upstream of the mean reattachment location. These eddies cause a 'downwash', which increases the local heat-transfer coefficient by bringing cold fluid from above the shear layer towards the wall.

Selective attention for threatening information in anxious mood states

Attention for threatening information was investigated using a computerised version of the emotional Stroop. The study examined the influence of state and trait anxiety in an unselected student sample assigned to high trait anxious (HTA) or low trait anxious (LTA) groups on the basis questionnaire scores. State anxiety was manipulated within participants through the threat of electric shock. Threatening words that were either unrelated (e.g., cancer, danger) or related to the source of the threat (e.g., electrocute, shock) were presented to participants both within and outside of awareness. In the latter condition, a backward masking procedure was used to prevent awareness of the stimulus material. In the masked condition, despite chance performance in identification of the lexical status of stimulus items, HTA participants showed facilitated colour naming for all threat words relative to control items under threat of shock, but this effect was not evident in the shock safe condition. For unmasked trials the HTA group showed significant interference in colour naming for all threat words relative to controls under the threat of shock, but not in the shock safe condition. Neither valence of the items nor the threat of shock influenced colour naming latencies for the LTA group. [ABSTRACT FROM AUTHOR]

Confirmation: Increasing resource availability for transactional workflows

The notion of compensation is widely used in advanced transaction models as means of recovery from a failure. Similar concepts are adopted for providing transaction-like behaviour for long business processes supported by workflows technology. In general, it is not trivial to design compensating tasks for tasks in the context of a workflow. Actually, a task in a workflow process does not have to be compensatable in the sense that the forcibility of reverse operations of the task is not always guaranteed by the application semantics. In addition, the isolation requirement on data resources may make a task difficult to compensate. In this paper, we first look into the requirements that a compensating task has to satisfy. Then we introduce a new concept called confirmation. With the help of confirmation, we are able to modify most non-compensatable tasks so that they become compensatable. This can substantially increase the availability of shared resources and greatly improve backward recovery for workflow applications in case of failures. To effectively incorporate confirmation and compensation into a workflow management environment, a three level bottom-up workflow design method is introduced. The implementation issues of this design are also discussed. (C) 2003 Elsevier Science Inc. All rights reserved.

Subordinate-manager gender combination and perceived leadership style influence on emotions, self-esteem and organizational commitment

A theoretical model was developed to investigate the relationships among subordinate-manager gender combinations, perceived leadership style, experienced frustration and optimism, organization-based self-esteem and organizational commitment. The model was tested within the context of a probabilistic structural model, a discrete Bayesian network, using cross-sectional data from a global pharmaceutical company. The Bayesian network allowed forward inference to assess the relative influence of gender combination and leadership style on the emotions, self-esteem and commitment consequence variables. Further, diagnostics from backward inference were used to assess the relative influence of variables antecedent to organizational commitment. The results showed that gender combination was independent of leadership style and had a direct impact on subordinates' levels of frustration and optimism. Female manager-female subordinate had the largest probability of optimism, while male manager teamed with a male subordinate had the largest probability of frustration. Furthermore, having a female manager teamed up with a male subordinate resulted in the lowest possibility of frustration. However, the findings show that the gender issue is not simply female managers versus male managers, but is concerned with the interaction of the subordinate-manager gender combination and leadership style in a nonlinear manner. (C) 2003 Elsevier Inc. All rights reserved.

Intra-abdominal pressure response to multidirectional support-surface translation

A complex response of the trunk muscles occurs to restore equilibrium in response to movement of the support surface. Intra-abdominal pressure (IAP) is considered to contribute to control of the trunk. This study investigated the contribution of IAP to the postural response to multidirection support-surface translation. IAP was recorded with a thin-film pressure transducer inserted via the nose into the stomach and trunk motion was recorded with an optoelectronic system with markers over the spinous process of L1. A pattern of trunk movement was recorded in response to the support-surface translations that was consistent with a 'hip' strategy of postural control. The trunk moved in a manner appropriate to move the centre of gravity over the new base of support. IAP was increased with movement in each direction, but varied in timing and amplitude between translation directions. In general, the IAP was greater with translations in the sagittal plane compared to the frontal plane and was initiated earlier for translations in the backward direction. These data indicate that IAP contributes to the postural response associated with support-surface translation and suggest that this is consistent with stiffening the spine. (C) 2003 Elsevier B.V. All rights reserved.

Patch and whole of surface mass-transfer rate measurements on a stepped rotating cylinder electrode

A recently developed whole of surface electroplating technique was used to obtain mass-transfer rates in the separated flow region of a stepped rotating cylinder electrode. These data are compared with previously reported mass-transfer rates obtained with a patch electrode. It was found that the two methods yield different results, where at lower Reynolds numbers, the mass-transfer rate enhancement was noticeably higher for the whole of the surface electrode than for the patch electrode. The location of the peak mass transfer behind the step, as measured with a patch electrode, was reported to be independent of the Reynolds number in previous studies, whereas the whole of the surface electrode shows a definite Reynolds number dependence. Large eddy simulation results for the recirculating region behind a step are used in this work to show that this difference in behavior is related to the existence of a much thinner fluid layer at the wall for which the velocity is a linear junction of distance from the wall. Consequently, the diffusion layer no longer lies well within a laminar sublayer. It is concluded that the patch electrode responds to the wall shear stress for smooth wall flow as well as for the disturbed flow region behind the step. When the whole of the surface is electro-active, the response is to mass transfer even when this is not a sole function of wall shear stress. The results demonstrate that the choice of the mass-transfer measurement technique in corrosion studies can have a significant effect on the results obtained from empirical data.

Integrating JERS-1 imaging radar and elevation models for mapping tropical rainforest communities in far North Queensland, Australia

The Wet Tropics World Heritage Area in Far North Queens- land, Australia consists predominantly of tropical rainforest and wet sclerophyll forest in areas of variable relief. Previous maps of vegetation communities in the area were produced by a labor-intensive combination of field survey and air-photo interpretation. Thus,. the aim of this work was to develop a new vegetation mapping method based on imaging radar that incorporates topographical corrections, which could be repeated frequently, and which would reduce the need for detailed field assessments and associated costs. The method employed G topographic correction and mapping procedure that was developed to enable vegetation structural classes to be mapped from satellite imaging radar. Eight JERS-1 scenes covering the Wet Tropics area for 1996 were acquired from NASDA under the auspices of the Global Rainforest Mapping Project. JERS scenes were geometrically corrected for topographic distortion using an 80 m DEM and a combination of polynomial warping and radar viewing geometry modeling. An image mosaic was created to cover the Wet Tropics region, and a new technique for image smoothing was applied to the JERS texture bonds and DEM before a Maximum Likelihood classification was applied to identify major land-cover and vegetation communities. Despite these efforts, dominant vegetation community classes could only be classified to low levels of accuracy (57.5 percent) which were partly explained by the significantly larger pixel size of the DEM in comparison to the JERS image (12.5 m). In addition, the spatial and floristic detail contained in the classes of the original validation maps were much finer than the JERS classification product was able to distinguish. In comparison to field and aerial photo-based approaches for mapping the vegetation of the Wet Tropics, appropriately corrected SAR data provides a more regional scale, all-weather mapping technique for broader vegetation classes. Further work is required to establish an appropriate combination of imaging radar with elevation data and other environmental surrogates to accurately map vegetation communities across the entire Wet Tropics.

A distributed systems approach to secure Internet mail

One of the obstacles to improved security of the Internet is ad hoc development of technologies with different design goals and different security goals. This paper proposes reconceptualizing the Internet as a secure distributed system, focusing specifically on the application layer. The notion is to redesign specific functionality, based on principles discovered in research on distributed systems in the decades since the initial development of the Internet. Because of the problems in retrofitting new technology across millions of clients and servers, any options with prospects of success must support backward compatibility. This paper outlines a possible new architecture for internet-based mail which would replace existing protocols by a more secure framework. To maintain backward compatibility, initial implementation could offer a web browser-based front end but the longer-term approach would be to implement the system using appropriate models of replication. (C) 2005 Elsevier Ltd. All rights reserved.

Deceleration affects anticipatory and reactive components of triggered postural responses

Understanding the physiological and psychological factors that contribute to healthy and pathological balance control in man has been made difficult by the confounding effects of the perturbations used to test balance reactions. The present study examined how postural responses were influenced by the acceleration-deceleration interval of an unexpected horizontal translation. Twelve adult males maintained balance during unexpected forward and backward surface translations with two different acceleration-deceleration intervals and presentation orders (serial or random). SHORT perturbations consisted of an initial acceleration (peak acceleration 1.3 m s(-2); duration 300 ms) followed 100 ms later by a deceleration. LONG perturbations had the same acceleration as SHORT perturbations, followed by a 2-s interval of constant velocity before deceleration. Surface and intra-muscular electromyography (EMG) from the leg, trunk, and shoulder muscles were recorded along with motion and force plate data. LONG perturbations induced larger trunk displacements compared to SHORT perturbations when presented randomly and larger EMG responses in proximal and distal muscles during later (500-800 ms) response intervals. During SHORT perturbations, activity in some antagonist muscles was found to be associated with deceleration and not the initial acceleration of the support surface. When predictable, SHORT perturbations facilitated the use of anticipatory mechanisms to attenuate early (100-400 ms) EMG response amplitudes, ankle torque change and trunk displacement. In contrast, LONG perturbations, without an early deceleration effect, did not facilitate anticipatory changes when presented in a predictable order. Therefore, perturbations with a short acceleration-deceleration interval can influence triggered postural responses through reactive effects and, when predictable with repeated exposure, through anticipatory mechanisms.

Selective processing of masked and unmasked verbal threat material in anxiety: Influence of an immediate acute stressor

Attentional biases for threat were investigated using a computerised version of the emotional Stroop task. The study examined the influence of state and trait anxiety by employing a student sample assigned to high trait anxious (HTA; n = 32) or low trait anxious (LTA; n = 32) groups on the basis of questionnaire scores, and state anxiety was manipulated within participants through the threat of electric shock. Threatening words that were either unrelated (e.g., cancer, danger) or related to the threat of shock (e.g., electrocute, shock) were presented to participants both within and outside of awareness. In the latter condition a backward masking procedure was used to prevent awareness and exposure thresholds between the target and mask were individually set for each participant. For unmasked trials the HTA group showed significant interference in colour naming for all threat words relative to control words when performing under the threat of shock, but not in the shock safe condition. For the masked trials, despite chance performance in being able to identify the lexical status of the items, HTA participants showed facilitated colour naming for all threat words relative to control items when performing under threat of shock, but this effect was not evident in the shock safe condition. Neither valence of the items nor the threat of shock influenced colour naming latencies in either exposure mode for the LTA group.

The influence of natural body sway on neuromuscular responses to an unpredictable surface translation

Previous research has shown that the postural configuration adopted by a subject, such as active leaning, influences the postural response to an unpredictable support surface translation. While those studies have examined large differences in postural conditions, it is of additional interest to examine the effects of naturally occurring changes in standing posture. Thus, it was hypothesized that the normal postural sway observed during quiet standing would affect the responses to an unpredictable support surface translation. Seventeen young adults stood quietly on a moveable platform and were perturbed in either the forward or backward direction when the location of the center of pressure (COP) was either 1.5 standard deviations anterior or posterior to the mean baseline COP signal. Postural responses, in the form of electromyographic (EMG) latencies and amplitudes, were recorded from lower limb and trunk muscles. When the location of the COP at the time of the translation was in the opposite, as compared to the same, direction as the upcoming translation, there was a significantly earlier onset of the antagonists (10-23%, i.e. 15-45 ms) and a greater EMG amplitude (14-39%) in four of the six recorded muscles. Stepping responses were most frequently observed during trials where the position of the COP was opposite to the direction of the translation. The results support the hypothesis that postural responses to unpredictable support surface translations are influenced by the normal movements of postural sway. The results may help to explain the large variability of postural responses found between past studies.

Inflammation, complement activation and endothelial function in stable and unstable coronary artery disease

Background: Endothelial dysfunction plays an important role in the pathogenesis of coronary artery disease (CAD). Apart from traditional risk factors complement activation and inflammation may trigger and sustain endothelial dysfunction. We sought to assess the association between endothelial function, high sensitivity C-reactive protein (hs-CRP) and markers of complement activation in patients with either stable or unstable coronary artery disease. Methods: We prospectively recruited 78 patients, 35 patients with stable angina pectoris (SAP) and 43 patients with unstable angina pectoris (UAP). Endothelial function was assessed as brachial artery reactivity (BAR). Hs-CRP, C3a, C5a, and C1-Inhibitor (C1 inh.) were measured enzymatically. Results: Patients with IJAP showed higher median levels of hs-CRP and C3a compared to patients with SAP, while BAR was not significantly different between patient groups. In UAP patients, hs-CRP was significantly correlated with cholesterol (r = 0.27, p < 0.02), C3a (r = 0.32, p < 0.001) and C1 INH.(r = 0.41, p < 0.003), but not with flow mediated dilatation (r = 0.09, P = 0.41). Hs-CRP and C1 INH.were found to be independant predictors of IJAP in a backward stepwise logistic regression model. Conclusions: We conclude that both hs-CRP, a marker of inflammation and C3a, a marker of complement activation are elevated in patients with UAP, but not in patients with SAP. (c) 2005 Elsevier B.V. All rights reserved.

Batting with occluded vision: An in situ examination of the information pick-up and interceptive skills of high- and low-skilled cricket batsmen

The capability of cricket batsmen of different skill levels to pick-up information from the pre-release movement pattern of the bowler, from pre-bounce ball flight, and from post-bounce ball flight was examined experimentally. Six highly skilled and six low-skilled cricket batsmen batted against three different leg-spin bowlers while wearing liquid crystal spectacles. The spectacles permitted the specific information available to the batsmen on each trial to be manipulated such that vision was either: (i) occluded at a point prior to the point of ball release (thereby only allowing vision of advance information from the bowler's delivery action); (ii) occluded at a point prior to the point of bat[ bounce (thereby permitting the additional vision of pre-bounce ball flight); or (iii) not occluded (thereby permitting the additional vision of post-bounce bat[ flight information). Measurement was made on each trial of both the accuracy of the definitive (forward-backward) foot movements made by the batsmen and their success (or otherwise) in making bat-bat[ contact. The analyses revealed a superior capability of the more skilled players to make use of earlier (pre-bounce) bat[ flight information to guide successful bat-bat[ interception, thus mirroring the greater use of prospective information pick-up by skilled performers observed in other aspects of batting and in other time-constrained performance domains. (c) 2006 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.