Home About us Contact
|
Home About us Contact | ||
|
|
||
Average Speed (average + speed)
Selected AbstractsMembrane associated nonmuscle myosin II functions as a motor for actin-based vesicle transport in clam oocyte extractsCYTOSKELETON, Issue 10 2007Ana S. DePina Abstract Nonmuscle myosin II (Myo2) has been shown to associate with membranes of the trans -Golgi network and to be involved in Golgi to ER retrograde protein transport. Here, we provide evidence that Myo2 not only associates with membranes but functions to transport vesicles on actin filaments (AFs). We used extracts from unactivated clam oocytes for these studies. AFs assembled spontaneously in these extracts and myosin-dependent vesicle transport was observed upon activation. In addition, actin bundles formed and moved relative to each other at an average speed of ,0.30 ,m/s. Motion analysis revealed that vesicles moved on the spontaneously assembled AFs at speeds greater than 1 ,m/s. The motor on these vesicles was identified as a member of the nonmuscle Myo2 family based on sequence determination by Edman chemistry. Vesicles in these extracts were purified by sucrose gradient centrifugation and movement was reconstituted in vitro using skeletal muscle actin coated coverslips. When peripheral membrane proteins of vesicles including Myo2 were removed by salt stripping or when extracts were treated with an antibody specific to clam oocyte nonmuscle Myo2, vesicle movement was inhibited. Blebbistatin, a Myo2 specific inhibitor, also blocked vesicle movement. Myo2 light chain kinase activity was found to be essential for vesicle movement and sliding of actin bundles. Together, our data provide direct evidence that nonmuscle Myo2 is involved in actin-dependent vesicle transport in clam oocytes. Cell Motil. Cytoskeleton 2007. © 2007 Wiley-Liss, Inc. [source] The migratory behavior of immature enteric neuronsDEVELOPMENTAL NEUROBIOLOGY, Issue 1 2009M.M. Hao Abstract While they are migrating caudally along the developing gut, around 10%,20% of enteric neural crest-derived cells start to express pan-neuronal markers and tyrosine hydroxylase (TH). We used explants of gut from embryonic TH-green fluorescence protein (GFP) mice and time-lapse microscopy to examine whether these immature enteric neurons migrate and their mode of migration. In the gut of E10.5 and E11.5 TH-GFP mice, around 50% of immature enteric neurons (GFP+ cells) migrated, with an average speed of around 15 ,m/h. This is slower than the speed at which the population of enteric neural crest-derived cells advances along the developing gut, and hence neuronal differentiation seems to slow, but not necessarily halt, the caudal migration of enteric neural crest cells. Most migrating immature enteric neurons migrated caudally by extending a long-leading process followed by translocation of the cell body. This mode of migration is different from that of non-neuronal enteric neural crest-derived cells and neural crest cells in other locations, but resembles that of migrating neurons in many regions of the developing central nervous system (CNS). In migrating immature enteric neurons, a swelling often preceded the movement of the nucleus in the direction of the leading process. However, the centrosomal marker, pericentrin, was not localized to either the leading process or swelling. This seems to be the first detailed report of neuronal migration in the developing mammalian peripheral nervous system. © 2008 Wiley Periodicals, Inc. Develop Neurobiol, 2009. [source] The workload of riding-school horses during jumpingEQUINE VETERINARY JOURNAL, Issue S36 2006M. M. SLOET Van OLDRUITENBORGH-OOSTERBAAN Summary Reasons for performing the study: As there are no reports on the real workload of horses that jump fences, this study was undertaken in riding-school horses. Objective: To compare the workload of horses jumping a course of fences with that of horses cantering over the same course at the same average speed without jumping fences. The workload variables included heart rate (HR), packed cell volume (PCV), acid-base balance (venous pH, pCO2, HCO3,) and blood lactate (LA), glucose, total protein and electrolyte concentrations. Methods: Eight healthy riding-school horses performed test A (a course of approximately 700 m with 12 jumps from 0.8-1.0 m high at an average speed of approximately 350 m/min) and test B (same course at the same speed, but without the rails) in a crossover study with at least 4 h between the 2 tests. Before each test the horses were fitted with a heart rate meter (Polar Electro)1. Blood samples were taken from the jugular vein at rest prior to the test, after warm-up before starting the course, immediately after the course and after recovery. All samples were analysed immediately. Results: The mean ± s.d maximal HR (beats/min) during the course (184 ± 17 and 156 ± 21, respectively) and the mean HR after recovery (75 ± 6 and 63 ± 7, respectively) were significantly higher in test A compared to test B (P=0.001 and P=0.007 respectively). The mean LA concentrations after the course and after recovery (mmol/1) were significantly higher in test A (3.6 ± 2.7 and 1.0 ± 0.9, respectively) compared to test B (0.9 ± 0.5 and 0.3 ± 0.1, respectively), (P=0.016 and P = 0.048 respectively). The mean PCV (1/1) after the course and after recovery was also significantly different between tests A (0.48 ± 0.04 and 0.39 ± 0.03, respectively) and B (0.42 ± 0.04 and 0.36 ± 0.03, respectively) (P<0.01). The mean pH and the mean HCO3, (mmol/1) after the course were significantly lower in test A (7.40 ± 0.04 and 28.9 ± 1.4, respectively) compared to test B (7.45 ± 0.03 and 30.4 ± 2.3, respectively) (P<0.05). Conclusions: This study indicates that in riding-school horses jumping fences, even at a low level competition, provokes a significant workload compared to cantering the same distance and speed without fences. Potential relevance: This study makes it clear that the extra workload of jumping fences should be taken into account in the training programmes of jumping horses. Further research with more experienced horses jumping higher fences will reveal the workload for top-level jumping horses. [source] Determining the relationship between drivers' level of education, training, working conditions, and job performance in KenyaHUMAN RESOURCE DEVELOPMENT QUARTERLY, Issue 3 2003Fredrick Muyia Nafukho One major issue in human resource development (HRD) is to determine factors that predict the performance of employees. The primary purpose of this study was to determine how level of education, training, and the working conditions of matatu (public service vehicle) drivers determined their job performance in terms of reduced road traffic accidents. Proportionate and simple random sampling techniques were employed to select 143 drivers who completed and returned the questionnaires. Multiple regression analysis was used to test the hypotheses stated. The findings indicate that the variables of driver experience and hours worked had a significant relationship with the dependent variable rates of traffic accidents per driver as hypothesized. The variables of education level, training, salary earned, and average speed traveled did not have a significant relationship with the dependent variable. [source] Numerical simulation of a dam break for an actual river terrain environmentHYDROLOGICAL PROCESSES, Issue 4 2007C. B. Liao Abstract A two-dimensional (2D) finite-difference shallow water model based on a second-order hybrid type of total variation diminishing (TVD) approximate solver with a MUSCL limiter function was developed to model flooding and inundation problems where the evolution of the drying and wetting interface is numerically challenging. Both a minimum positive depth (MPD) scheme and a non-MPD scheme were employed to handle the advancement of drying and wetting fronts. We used several model problems to verify the model, including a dam break in a slope channel, a dam break flooding over a triangular obstacle, an idealized circular dam-break, and a tide flow over a mound. Computed results agreed well with the experiment data and other numerical results available. The model was then applied to simulate the dam breaking and flooding of Hsindien Creek, Taiwan, with the detailed river basin topography. Computed flooding scenarios show reasonable flow characteristics. Though the average speed of flooding is 6,7 m s,1, which corresponds to the subcritical flow condition (Fr < 1), the local maximum speed of flooding is 14·12 m s,1, which corresponds to the supercritical flow condition (Fr , 1·31). It is necessary to conduct some kind of comparison of the numerical results with measurements/experiments in further studies. Nevertheless, the model exhibits its capability to capture the essential features of dam-break flows with drying and wetting fronts. It also exhibits the potential to provide the basis for computationally efficient flood routing and warning information. Copyright © 2006 John Wiley & Sons, Ltd. [source] Living on the bottom: Kinematics of benthic station-holding in darter fishes (Percidae: Etheostomatinae)JOURNAL OF MORPHOLOGY, Issue 1 2010Rose L. Carlson Abstract Darters represent a substantial radiation of freshwater fishes that live in close association with the substrate in North American streams and rivers. A key feature of any darter species is therefore its ability to stay in place or to "hold station" in flowing water. Here, we quantify the station-holding performance of two morphologically divergent darter species, the fantail darter Etheostoma flabellare and the Missouri saddled darter Etheostoma tetrazonum. We also characterize the primary kinematic responses of the two species when holding station in flow speeds ranging from 4 to 56 cm s,1 in a flow tank on either plexiglas or small rock substrate. We then present a series of hypotheses about the potential hydrodynamic and functional consequences of the observed postural changes and the links among morphology, posture, and station-holding performance. On both substrates, E. tetrazonum was able to hold station at higher flow speeds than E. flabellare. On rocks, E. tetrazonum slipped at an average speed of 55.7 cm s,1 whereas E. flabellare slipped at 40.2 cm s,1. On plexiglas, E. tetrazonum slipped at an average speed of 24.7 cm s,1 whereas E. flabellare slipped at 23.1 cm s,1. We measured body and fin positions of the two species from individual frames of high-speed video while holding station on rocks and plexiglas. We found that on both substrates, the two species generally exhibited similar kinematic responses to increasing flow: the head was lowered and angled downward, the back became more arched, and the median and caudal fin rays contracted as water flow speed increased. The ventral halves of the pectoral fins were also expanded and the dorsal halves contracted. These changes in posture and fin position likely increase negative lift forces thereby increasing substrate contact forces and reducing the probability of downstream slip. J. Morphol., 2010. © 2009 Wiley-Liss, Inc. [source] Automated classification of Plasmodium sporozoite movement patterns reveals a shift towards productive motility during salivary gland infectionBIOTECHNOLOGY JOURNAL, Issue 6 2009Stephan Hegge Abstract The invasive stages of malaria and other apicomplexan parasites use a unique motility machinery based on actin, myosin and a number of parasite-specific proteins to invade host cells and tissues. The crucial importance of this motility machinery at several stages of the life cycle of these parasites makes the individual components potential drug targets. The different stages of the malaria parasite exhibit strikingly diverse movement patterns, likely reflecting the varied needs to achieve successful invasion. Here, we describe a Tool for Automated Sporozoite Tracking (ToAST) that allows the rapid simultaneous analysis of several hundred motile Plasmodium sporozoites, the stage of the malaria parasite transmitted by the mosquito. ToAST reliably categorizes different modes of sporozoite movement and can be used for both tracking changes in movement patterns and comparing overall movement parameters, such as average speed or the persistence of sporozoites undergoing a certain type of movement. This allows the comparison of potentially small differences between distinct parasite populations and will enable screening of drug libraries to find inhibitors of sporozoite motility. Using ToAST, we find that isolated sporozoites change their movement patterns towards productive motility during the first week after infection of mosquito salivary glands. [source] Evolution of capital structure in east Asia,corporate inertia or endeavours?JOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES A (STATISTICS IN SOCIETY), Issue 1 2010Nigel Driffield Summary., The paper examines the capital structure adjustment dynamics of listed non-financial corporations in seven east Asian countries before, during and after the crisis of 1997,1998. Our methodology allows for speeds of adjustment to vary, not only among firms, but also over time, distinguishing between cases of sudden and smooth adjustment. Whereas, compared with firms in the least affected countries, average leverages were much higher, generalized method-of-moments analysis of the Worldscope panel data suggests that average speeds of adjustment were lower in the worst affected countries. This holds also for the severely financially distressed firms in some worst affected countries, though the trend reversed in the post-crisis period. These findings have important implications for the regulatory environment as well as access to market finance. [source] | ||||||||||