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Transient Events (transient + event)
Selected AbstractsBioassays with caged Hyalella azteca to determine in situ toxicity downstream of two Saskatchewan, Canada, uranium operations,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2007Erin L. Robertson Abstract The main objectives of this in situ study were to evaluate the usefulness of an in situ bioassay to determine if downstream water bodies at the Key Lake and Rabbit Lake uranium operations (Saskatchewan, Canada) were toxic to Hyalella azteca and, if toxicity was observed, to differentiate between the contribution of surface water and sediment contamination to in situ toxicity. These objectives were achieved by performing 4-d in situ bioassays with laboratory-reared H. azteca confined in specially designed, paired, surface water and sediment exposure chambers. Results from the in situ bioassays revealed significant mortality, relative to the respective reference site, at the exposure sites at both Key Lake (p , 0.001) and Rabbit Lake (p = 0.001). No statistical differences were found between survival in surface water and sediment exposure chambers at either Key Lake (p = 0.232) or Rabbit Lake (p = 0.072). This suggests that surface water (the common feature of both types of exposure chambers) was the primary cause of in situ mortality of H. azteca at both operations, although this relationship was stronger at Key Lake. At Key Lake, the primary cause of aquatic toxicity to H. azteca did not appear to be correlated with the variables measured in this study, but most likely with a pulse of organic mill-process chemicals released during the time of the in situ study , a transient event that was caused by a problem with the mill's solvent extraction process. The suspected cause of in situ toxicity to H. azteca at Rabbit Lake was high levels of uranium in surface water, sediment, and pore water. [source] The role of phosphoinositide 3-kinase and phosphatidic acid in the regulation of mammalian target of rapamycin following eccentric contractionsTHE JOURNAL OF PHYSIOLOGY, Issue 14 2009T. K. O'Neil Resistance exercise induces a hypertrophic response in skeletal muscle and recent studies have begun to shed light on the molecular mechanisms involved in this process. For example, several studies indicate that signalling by the mammalian target of rapamycin (mTOR) is necessary for a hypertrophic response. Furthermore, resistance exercise has been proposed to activate mTOR signalling through an upstream pathway involving the phosphoinositide 3-kinase (PI3K) and protein kinase B (PKB); however, this hypothesis has not been thoroughly tested. To test this hypothesis, we first evaluated the temporal pattern of signalling through PI3K,PKB and mTOR following a bout of resistance exercise with eccentric contractions (EC). Our results indicated that the activation of signalling through PI3K,PKB is a transient event (<15 min), while the activation of mTOR is sustained for a long duration (>12 h). Furthermore, inhibition of PI3K,PKB activity did not prevent the activation of mTOR signalling by ECs, indicating that PI3K,PKB is not part of the upstream regulatory pathway. These observations led us to investigate an alternative pathway for the activation of mTOR signalling involving the synthesis of phosphatidic acid (PA) by phospholipase D (PLD). Our results demonstrate that ECs induce a sustained elevation in [PA] and inhibiting the synthesis of PA by PLD prevented the activation of mTOR. Furthermore, we determined that similar to ECs, PA activates mTOR signalling through a PI3K,PKB-independent mechanism. Combined, the results of this study indicate that the activation of mTOR following eccentric contractions occurs through a PI3K,PKB-independent mechanism that requires PLD and PA. [source] A Relativistic Disk in Sagittarius A*ASTRONOMISCHE NACHRICHTEN, Issue S1 2003Siming Liu The detection of a mm/Sub-mm "bump" in Sgr A*'s radio spectrum suggests that at least a portion of its overall emission is produced within a compact accretion disk. This inference is strengthened by observations of strong linear polarization (at the 10 percent level) within this bump. No linear polarization has been detected yet at other wavelengths. Given that radiation from this source is produced on progressively smaller spatial scales with increasing frequency, the mm/Sub-mm bump apparently arises within a mere handful of Schwarzschild radii of the black hole. We have found that a small (10-Schwarzschild-radii) magnetized accretion disk can not only account for the spectral bump via thermal synchrotron processes, but that it can also reproduce the corresponding polarimetric results. In addition, the quiescent X-ray emission appears to be associated with synchrotron self-Comptonization, while X-ray flares detected from Sgr A* may be induced by a sudden enhancement of accretion through this disk. The hardening of the flare-state X-ray spectrum appears to favor thermal bremsstrahlung as the dominant X-ray emission mechanism during the transient event. This picture predicts correlations among the mm, IR, and X-ray flux densities, that appear to be consistent with recent multi-wavelength observations. Further evidence for such a disk in Sgr A* is provided by its radio variability. Recent monitoring of Sgr A* at cm and mm wavelengths suggests that a spectral break is manifested at 3 mm during cm/Sub-mm flares. The flat cm spectrum, combined with a weak X-ray flux in the quiescent state, rules out models in which the radio emission is produced by thermal synchrotron process in a bounded plasma. One possibility is that nonthermal particles may be produced when the large scale quasi-spherical inflow circularizes and settles down into the small accretion disk. Dissipation of kinetic energy associated with radial motion may lead to particle acceleration in shocks or via magnetic reconnection. On the other hand, the identification of a 106-day cycle in Sgr A*'s radio variability may signal a precession of the disk around a spinning black hole. The disk's characteristics imply rigid-body rotation, so the long precession period is indicative of a small black-hole spin with a spin parameter a/M around 0.1. It is interesting to note that such a small value of a/M would be favored if the nonthermal portion of Sgr A*'s spectrum is powered by a Blandford- Znajek type of process; in this situation, the observed luminosity would correspond to an outer disk radius of about 30 Schwarzschild radii. This disk structure is consistent with earlier hydrodynamical and recent MHD simulations and is implied by Sgr A*'s mm/Sub-mm spectral and polarimetric characteristics. For the disk to precess with such a long (106-day) period, the angular momentum flux flowing through it must be sufficiently small that any modulation of the total angular momentum is mostly due to its coupling with the black-hole spin. This requires that the torque exerted on the inner boundary of the disk via magnetic stresses is close to the angular momentum accretion rate associated with the infalling gas. Significant heating at the inner edge of the disk then leaves the gas marginally bounded near the black hole. A strong wind from the central region may ensue and produce a scaled down version of relativistic (possibly magnetized) jets in AGNs. [source] Ventral otic cell lines as developmental models of auditory epithelial and neural precursorsDEVELOPMENTAL DYNAMICS, Issue 4 2004G. Lawoko-Kerali Abstract Conditionally immortal cell lines were established from the ventral otocyst of the Immortomouse at embryonic day 10.5 and selected to represent precursors of auditory sensory neural and epithelial cells. Selection was based upon dissection, tissue-specific markers, and expression of the transcription factor GATA3. Two cell lines expressed GATA3 but possessed intrinsically different genetic programs under differentiating conditions. US/VOT-E36 represented epithelial progenitors with potential to differentiate into sensory and nonsensory epithelial cells. US/VOT-N33 represented migrating neuroblasts. Under differentiating conditions in vitro the cell lines expressed very different gene expression profiles. Expression of several cell- and tissue-specific markers, including the transcription factors Pax2, GATA3, and NeuroD, differed between the cell lines in a pattern consistent with that observed between their counterparts in vivo. We suggest that these and other conditionally immortal cell lines can be used to study transient events in development against different backgrounds of cell competence. Developmental Dynamics 231:801,814, 2004. © 2004 Wiley-Liss, Inc. [source] Distributed control of event floods in a large telecom networkINTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 2 2010Chundury Jagadish Events in a failing system can be generated so rapidly that they adversely impact the network as well as the network management system (NMS) manager. They may fail to get delivered and critical information may get lost. This problem becomes worse in a large and congested network. Today, in practice, a management station is often flooded with a huge number of redundant events, making it difficult for the operator to process them and take corrective actions. Methods are needed to limit the volume of event transmission and number of events presented to the operator, while ensuring delivery of important information to the NMS manager. These methods need to take care of the operators' changing needs in monitoring abstraction level, for various network elements (NE) based on time and NE severity state. In this paper we propose novel techniques for distributed control of events flood, by suppressing transient events at the source. These techniques do not add any delay in communicating a failure, while ensuring that only the important events are presented to the operator. Also, the correctness of event state at the NMS is not compromised. Moreover, these methods give flexibility to the operator to dynamically change the abstraction level needed from a network element, and limit the number of events presented to the operator. The implementation of these techniques is tested with real field event traces from various telecom networks. Results show that there is a substantial reduction in the event traffic in the network. Copyright © 2009 John Wiley & Sons, Ltd. [source] Real-time Monitoring of Force Response Measured in Mechanically Stimulated Tissue-Engineered CartilageARTIFICIAL ORGANS, Issue 4 2009Orahn Preiss-Bloom Abstract:, Mechanical stimulation improves tissue-engineered cartilage development both in terms of biochemical composition and structural properties. However, the link between the compositional changes attributed to mechanical stimulation and the changing structural properties of the engineered cartilage is poorly understood. We hypothesize that transient events associated with construct stiffening can be documented and used to understand milestones in construct development. To do this, we designed and built a mechanical stimulation bioreactor that can continuously record the force response of the engineered construct in real time. This study documents the transient changes of the stiffness of tissue-engineered cartilage constructs over the first 14 days of their development under cyclic loading. Compressive strain stimulation (15%, 1 Hz) was applied to poly(ethylene glycol) (PEG) hydrogels seeded with primary articular chondrocytes. The average compressive modulus of strain-stimulated constructs was 12.7 ± 1.45 kPa after 2 weeks, significantly greater (P < 0.01) than the average compressive moduli of both unstimulated constructs (10.7 ± 0.94 kPa) and nonviable stimulated constructs (11.2 ± 0.91 kPa). The system was able to document that nearly all of the stiffness increase occurred over the last 2 days of the experiment, where live-cell constructs demonstrated a rapid 20% increase in force response. The system's ability to track significant increases in stiffness over time was also confirmed by Instron testing. These results present a novel view of the early mechanical development of tissue-engineering cartilage constructs and suggest that the real-time monitoring of force response may be used to noninvasively track the development of engineered tissue. [source] Are there common triggers of preterm deliveries?BJOG : AN INTERNATIONAL JOURNAL OF OBSTETRICS & GYNAECOLOGY, Issue 6 2001E. Petridou Objective To assess the effect(s) of transient events which are perceived as stressful on the inseption of preterm delivery. Design A case,control study, with immature infants as cases and borderline term babies as controls. Setting A teaching maternity hospital in Athens. Population All infants born at less than 37 weeks of gestation, during a twelve-month period. Methods Information was collected about maternal socio-demographic and lifestyle characteristics, clinical variables and stressful events occurring within two weeks prior to delivery. Main outcome measures Factors affecting the risk of preterm delivery. Results Extreme prematurity (<33 weeks) is more common among younger (<25 years of age) and older (>29 years of age) women and is positively associated with parity, body mass index and smoking, whereas it is inversely associated with educational level, regular physical exercise and serious nausea/vomiting. After controlling for these factors, however, only coitus during the last weeks of pregnancy had a significant triggering effect on prematurity (P= 0.004, odds ratio 3.21, 95% CI 1.45 to 7.09 for very immature babies, and P= 0.04, OR=2.20, 95% CI 1.03 to 4.70 for immature babies). On the contrary, several events perceived as stressful, such as illness of relatives or friends, husband's departure, loss of employment, were unrelated to the onset of premature labour. Conclusions Coitus during the last few weeks of pregnancy appears to increase the risk of preterm delivery, while a possible detrimental effect of physical exertion seems more limited. Stressful events should not receive undue attention as possible causes of preterm delivery. [source] | |||||||||||||