Various Tasks (various + task)

Distribution by Scientific Domains

Selected Abstracts

Magnetic Control of Tubular Catalytic Microbots for the Transport, Assembly, and Delivery of Micro-objects

Alexander A. Solovev
Abstract Recently a significant amount of attention has been paid towards the development of man-made synthetic catalytic micro- and nanomotors that can mimic biological counterparts in terms of propulsion power, motion control, and speed. However, only a few applications of such self-propelled vehicles have been described. Here the magnetic control of self-propelled catalytic Ti/Fe/Pt rolled-up microtubes (microbots) that can be used to perform various tasks such as the selective loading, transportation, and delivery of microscale objects in a fluid is shown; for instance, it is demonstrated for polystyrene particles and thin metallic films ("nanoplates"). Microbots self-propel by ejecting microbubbles via a platinum catalytic decomposition of hydrogen peroxide into oxygen and water. The fuel and surfactant concentrations are optimized obtaining a maximum speed of 275,m,s,1 (5.5 body lengths per second) at 15% of peroxide fuel. The microbots exert a force of around 3.77,pN when transporting a single 5,m diameter particle; evidencing a high propulsion power that allows for the transport of up to 60 microparticles. By the introduction of an Fe thin film into the rolled-up microtubes, their motion can be fully controlled by an external magnetic field. [source]

Bigger is better: implications of body size for flight ability under different light conditions and the evolution of alloethism in bumblebees

Summary 1In social insects, reproductive success and survival of the colony critically depend on the colony's ability to efficiently allocate workers to the various tasks which need to be performed. In bumblebees, workers show a large variation of body size within a colony. Large workers tend to leave the nest and forage for nectar and pollen, whereas small workers stay inside the nest and fulfill nest duties. It was speculated that size-related differences of the sensory system might contribute to alloethism found in bumblebee colonies. 2In the first part, we investigated how body size determines eye morphology. We measured several eye parameters of Bombus terrestris workers and drones. In both, workers and drones, larger individuals had larger eyes with larger facet diameters, more ommatidia and larger ocelli. At similar body size, drones exhibited larger eyes and ocelli compared to workers. Due to theoretical considerations, we predict that large individuals with large eyes should be better able to operate in illumination conditions of lower intensity than small individuals, since ommatidial sensitivity is proportional to the square of facet diameter. 3In the second part, we tested this prediction. In a behavioural experiment, we first caught bumblebees of various sizes in the field and then determined the lowest light intensity level at which they are just able to fly under controlled laboratory conditions. We tested workers of B. terrestris and B. pascuorum, and workers and drones of B. lapidarius. Large bumblebees were able to fly under lower light levels compared to small bees, with light intensity thresholds ranging from 11 to 55 lux. 4Our results indicate that the increased light sensitivity of the visual system of large bumblebees allows them to fly under poor light conditions, for example, very early in the morning or late at dusk. This is of potential benefit to the survival of a bumblebee colony since flowers that open early in the morning usually have accumulated a relatively high amount of nectar and pollen throughout the night, and large bumblebees can utilize these resources earlier than most other bees. Thus, our findings have important implications for the understanding of the functional significance and evolution of alloethism in bumblebee colonies. [source]

Neurogenesis may relate to some but not all types of hippocampal-dependent learning

HIPPOCAMPUS, Issue 5 2002
Tracey J. Shors
Abstract The hippocampal formation generates new neurons throughout adulthood. Recent studies indicate that these cells possess the morphology and physiological properties of more established neurons. However, the function of adult generated neurons is still a matter of debate. We previously demonstrated that certain forms of associative learning can enhance the survival of new neurons and a reduction in neurogenesis coincides with impaired learning of the hippocampal-dependent task of trace eyeblink conditioning. Using the toxin methylazoxymethanol acetate (MAM) for proliferating cells, we tested whether reduction of neurogenesis affected learning and performance associated with different hippocampal dependent tasks: spatial navigation learning in a Morris water maze, fear responses to context and an explicit cue after training with a trace fear paradigm. We also examined exploratory behavior in an elevated plus maze. Rats were injected with MAM (7 mg/kg) or saline for 14 days, concurrent with BrdU, to label new neurons on days 10, 12, and 14. After treatment, groups of rats were tested in the various tasks. A significant reduction in new neurons in the adult hippocampus was associated with impaired performance in some tasks, but not with others. Specifically, treatment with the antimitotic agent reduced the amount of fear acquired after exposure to a trace fear conditioning paradigm but did not affect contextual fear conditioning or spatial navigation learning in the Morris water maze. Nor did MAM treatment affect exploration in the elevated plus maze. These results combined with previous ones suggest that neurogenesis may be associated with the formation of some but not all types of hippocampal-dependent memories. Hippocampus 2002;12:578,584. 2002 Wiley-Liss, Inc. [source]

Predicting Treatment Seekers' Readiness to Change Their Drinking Behavior in the COMBINE Study

ALCOHOLISM, Issue 5 2009
Carlo C. DiClemente
Background:, Initial motivation and readiness to change (RTC) are complex constructs and have been important but inconsistent predictors of treatment attendance and drinking outcomes in studies of alcoholism treatment. Motivation can be described in multiple ways as simply the accumulation of consequences that push change, a shift in intentions, or engagement in various tasks that are part of a larger process of change. Method:, Using baseline data from participants in the COMBINE Study, this study reevaluated the psychometric properties of a 24-item measure of motivation derived from the University of Rhode Island Change Assessment Scale that yielded 4 subscales representing attitudes and experiences related to tasks of stages of Precontemplation, Contemplation, Action, and Maintenance Striving as well as a second-order factor score representing a multidimensional view of RTC drinking. A variety of hypothesized predictors of readiness and the stage subscales were examined using multiple regression analyses to better understand the nature of this measure of motivation. Results:, Findings supported the basic subscale structure and the overall motivational readiness score derived from this measure. RTC drinking behavior was predicted by baseline measures of perceived stress, drinking severity, psychiatric comorbidity, self-efficacy, craving, and positive treatment outcome expectancies. However, absolute values were small, indicating that readiness for change is not explained simply by demographic, drinking severity, treatment, change process, or contextual variables. Conclusion:, This measure demonstrated good psychometric properties and results supported the independence as well as convergent and divergent validity of the measured constructs. Predictors of overall readiness and subscale scores indicate that a variety of personal and contextual factors contribute to treatment seekers' motivation to change in an understandable but complex manner. [source]

Acidosis and Catecholamine Evaluation Following Simulated Law Enforcement "Use of Force" Encounters

Jeffrey D. Ho MD
ACADEMIC EMERGENCY MEDICINE 2010; 17:E60,E68 2010 by the Society for Academic Emergency Medicine Abstract Objectives:, Law enforcement authorities are often charged with controlling resisting suspects. These encounters sometimes result in the sudden and unexpected death of the suspect. Drug intoxication, excited delirium syndrome, or excessive uses of force are factors that are often blamed, but sometimes the mechanism of these deaths is not fully understood. It is possible that worsening acidosis or excessive catecholamine release play a part. The objective of this study was to determine the effect on markers of acidosis and catecholamines of various tasks intended to simulate common arrest-related situations. Methods:, Subjects were assigned to one of five task groups: 1) a 150-meter sprint and wall hurdle (simulated flight from arrest); 2) 45 seconds of striking a heavy bag (simulated physical resistance); 3) a 10-second TASER X26 electronic control device exposure; 4) a fleeing and resistance exercise involving a law enforcement dog (K-9); or 5) an oleoresin capsicum (OC) exposure to the face and neck. Baseline serum pH, lactate, potassium, troponin I, catecholamines, and creatine kinase (CK) were evaluated. Serum catecholamines, pH, lactate, and potassium were sampled immediately after the task and every 2 minutes for 10 minutes posttask. Vital signs were repeated immediately after the task. Serum CK and troponin I were evaluated again at 24 hours posttask. Results:, Sixty-six subjects were enrolled; four did not complete their assigned task. One subject lost the intravenous (IV) access after completing the task and did not have data collected, and one subject only received a 5-second TASER device exposure and was excluded from the study, leaving 12 subjects in each task group. The greatest changes in acidosis markers occurred in the sprint and heavy bag groups. Catecholamines increased the most in the heavy bag group and the sprint group and increased to a lesser degree in the TASER, OC, and K-9 groups. Only the sprint group showed an increase in CK at 24 hours. There were no elevations in troponin I in any group, nor any clinically important changes in potassium. Conclusions:, The simulations of physical resistance and fleeing on foot led to the greatest changes in markers of acidosis and catecholamines. These changes may be contributing or causal mechanisms in sudden custodial arrest-related deaths (ARDs). This initial work may have implications in guiding applications of force for law enforcement authorities (LEAs) when apprehending resisting subjects. [source]