Intrinsic and Cosmological Signatures in Gamma-Ray Burst Time Profiles: Time Dilation

The time profiles of many gamma-ray bursts consist of distinct pulses, which offers the possibility of characterizing the temporal structure of these bursts using a relatively small set of pulse shape parameters. We have used a pulse decomposition procedure to analyze the Time-to-Spill (TTS) data for all bursts observed by BATSE up through trigger number 2000, in all energy channels for which TTS data is available. We obtain amplitude, rise and decay timescales, a pulse shape parameter, and the fluences of individual pulses in all of the bursts. We investigate the correlations between brightness measures (amplitude and fluence) and timescale measures (pulse width and separation) which may result from cosmological time dilation of bursts, or from intrinsic properties of burst sources or from selection effects. The effects of selection biases are evaluated through simulations. The correlations between these parameters among pulses within individual bursts give a measure of the intrinsic effects while the correlations among bursts could result both from intrinsic and cosmological effects. We find that timescales tend to be shorter in bursts with higher peak fluxes, as expected from cosmological time dilation effects, but also find that there are non-cosmological effects contributing to this inverse correlation. We find that timescales tend to be longer in bursts with higher total fluences, contrary to what is expected from cosmological effects. We also find that peak fluxes and total fluences of bursts are uncorrelated, indicating that they cannot both be good distance indicators for bursts.Comment: 39 pages, 17 figures composed of 30 EPS files. Submitted to Astrophysical Journal. PostScript and PDF with un-bitmapped figures available at http://www.slac.stanford.edu/pubs/slacpubs/8000/slac-pub-8365.html . Accompanies astro-ph/000221

Properties of Gamma-Ray Burst Time Profiles Using Pulse Decomposition Analysis

The time profiles of many gamma-ray bursts consist of distinct pulses, which offers the possibility of characterizing the temporal structure of these bursts using a relatively small set of pulse shape parameters. This pulse decomposition analysis has previously been performed on a small sample of bright long bursts using binned data from BATSE, which comes in several data types, and on a sample of short bursts using the BATSE Time-Tagged Event (TTE) data type. We have developed an interactive pulse-fitting program using the phenomenological pulse model of Norris, et al. and a maximum-likelihood fitting routine. We have used this program to analyze the Time-to-Spill (TTS) data for all bursts observed by BATSE up through trigger number 2000, in all energy channels for which TTS data is available. We present statistical information on the attributes of pulses comprising these bursts, including relations between pulse characteristics in different energy channels and the evolution of pulse characteristics through the course of a burst. We carry out simulations to determine the biases that our procedures may introduce. We find that pulses tend to have shorter rise times than decay times, and tend to be narrower and peak earlier at higher energies. We also find that pulse brightness, pulse width, and pulse hardness ratios do not evolve monotonically within bursts, but that the ratios of pulse rise times to decay times tend to decrease with time within bursts.Comment: 40 pages, 19 figures. Submitted to Astrophysical Journal. PostScript and PDF with un-bitmapped figures available at http://www.slac.stanford.edu/pubs/slacpubs/8000/slac-pub-8364.html . Accompanying paper astro-ph/0002218 available at http://www.slac.stanford.edu/pubs/slacpubs/8000/slac-pub-8365.htm

Seasonal differences in soil CO2 efflux and carbon storage in Ntwetwe Pan, Makgadikgadi Basin, Botswana

The carbon cycle in salt pans is complex and poorly understood. Field-based data are needed to improve regional estimates of C storage and land-atmosphere CO2 fluxes from dryland environments where pans are prevalent. This paper provides a first estimate of C stores and CO2 efflux within the salt pan, grassland and woodland of Ntwetwe Pan in the Makgadikgadi Basin, Botswana. C fluxes and stores associated with cyanobacteria-salt crusts are also determined. Total C stores are approximately an order of magnitude greater than on neighbouring Kalahari Sands at 675±41, 760±94 and 274±15 tonsha-1 to 1m depth in the woodland, grassland and salt pan respectively. Most of the C is found as carbonate, with organic C comprising 4.6-10% of total C. CO2 efflux increased with temperature and also increased for a few hours after flooding of the pan surface. Crusts were a small net contributor to CO2 efflux in the dry season but could be a net CO2 sink in the wet season. The biogeochemistry of the sediment is likely to facilitate rapid conversion of organic C from aquatic organisms, biological crusts and algal mats into inorganic carbonates. Although further work is required to improve estimates of the spatial and temporal distribution of C, our data have demonstrated the substantial C store with the Makgadikgadi environment and the important role of biological crusts in the C cycle

Complimentary lower-level and higher-order systems underpin imitation learning

We examined whether the temporal representation developed during motor training with reduced-frequency knowledge of results (KR; feedback available on every other trial) was transferred to an imitation learning task. To this end, four groups first practised a three-segment motor sequence task with different KR protocols. Two experimental groups received reduced-frequency KR, one group received high-frequency KR (feedback available on every trial), and one received no-KR. Compared to the no-KR group, the groups that received KR learned the temporal goal of the movement sequence, as evidenced by increased accuracy and consistency across training. Next, all groups learned a single-segment movement that had the same temporal goal as the motor sequence task but required the imitation of biological and nonbiological motion kinematics. Kinematic data showed that whilst all groups imitated biological motion kinematics, the two experimental reduced-frequency KR groups were on average ∼800 ms more accurate at imitating movement time than the high-frequency KR and no-KR groups. The interplay between learning biological motion kinematics and the transfer of temporal representation indicates imitation involves distinct, but complementary lower-level sensorimotor and higher-level cognitive processing systems

Niche partitioning of bacterial communities in biological crusts and soils under grasses, shrubs and trees in the Kalahari

The Kalahari of southern Africa is characterised by sparse vegetation interspersed with microbe-dominated biological soil crusts (BSC) which deliver a range of ecosystem services including soil stabilisation and carbon fixation. We characterised the bacterial communities of BSCs (0–1 cm depth) and the subsurface soil (1–2 cm depth) in an area typical of lightly grazed Kalahari rangelands, composed of grasses, shrubs, and trees. Our data add substantially to the limited amount of existing knowledge concerning BSC microbial community structure, by providing the first bacterial community analyses of both BSCs and subsurface soils of the Kalahari region based on a high throughput 16S ribosomal RNA gene sequencing approach. BSC bacterial communities were distinct with respect to vegetation type and soil depth, and varied in relation to soil carbon, nitrogen, and surface temperature. Cyanobacteria were predominant in the grass interspaces at the soil surface (0–1 cm) but rare in subsurface soils (1–2 cm depth) and under the shrubs and trees. Bacteroidetes were significantly more abundant in surface soils of all areas even in the absence of a consolidated crust, whilst subsurface soils yielded more sequences affiliated to Acidobacteria, Actinobacteria, Chloroflexi, and Firmicutes. The common detection of vertical stratification, even in disturbed sites, suggests a strong potential for BSC recovery after physical disruption, however severe depletion of Cyanobacteria near trees and shrubs may limit the potential for natural BSC regeneration in heavily shrub-encroached areas

OPTIMISING KINETICS IN THE FREESTYLE FLIP TURN PUSH-OFF

INTRODUCTION: Turning technique is an important component in swimming performance with turn times positively correlating with final event time. However, little is known about the mechanics of an effective turn. This study sought to provide an exploratory analysis of how various kinetic and hydrodynamic variables during wall push-off are related to the wall exit velocity. METHODS: Thirty experienced male swimmers with body types of within one SD of the mean for selected anthropometric parameters reported for elite male adult swimmers (Mazza et al., 1994) were recruited for the study. During three freestyle flip turns, selected kinetic, hydrodynamic and kinematic variables of the wall pushoff were recorded. The wall push-off phase was measured from the point of maximum knee flexion during wall contact until the feet left the wall. Kinetics were recorded via a 2D vertically mounted forceplate which recorded peak push-off force and total impulse. The acceleration of each swimmer’s centre of gravity (CG) and wall exit velocity of the CG were calculated from underwater videography. Hydrodynamic peak drag force and drag impulse were calculated from the kinetic and kinematic data using a derivative of Newton’s second law. RESULTS: A stepwise regression was performed with wall exit velocity as the criterion variable and push-off time, peak propulsive force, total propulsive impulse, peak drag force, and total drag impulse as the independent variables. The stepwise regression yielded peak drag force, peak propulsive force and push-off time in the equation, with beta values indicating that the peak drag force carried the highest weighting of the three variables. CONCLUSIONS: The results of the stepwise regression indicated that an optimal combination of a low peak drag force, high peak propulsive force and increased wall time produced the fastest wall exit velocity. The inclusion of the peak drag force in the regression equation as the most important predictor of wall exit velocity highlights the importance of drag in turning technique. Factors such as very high push-off forces and exaggerated movements during wall push-off may lead to higher peak drag forces which, in turn, could be detrimental to the overall turning performance

Exposure of benthic invertebrates to sediment vibration: From laboratory experiments to outdoor simulated pile-driving

Activities directly interacting with the seabed, such as pile-driving, can produce vibrations that have the potential to impact benthic invertebrates within their vicinity. This stimuli may interfere with crucial behaviors such as foraging and predator avoidance, and the sensitivity to vibration is largely unknown. Here, the responsiveness of benthic invertebrates to sediment vibration is discussed in relation to laboratory and semi-field trials with two marine species: the mussel (Mytilus edulis) and hermit crab (Pagurus bernhardus). Sensory threshold curves were produced for both species in controlled laboratory conditions, followed by small-scale pile-driving exposures in the field. The merits of behavioral indicators are discussed, in addition to using physiological measures, as a method of determining reception and measuring responses. The measurement and sensors required for sediment vibration quantification are also discussed. Response and threshold data were related to measurements taken in the vicinity of anthropogenic sources, allowing a link between responsiveness and actual operations. The impact of pile-driving on sediment-dwelling invertebrates has received relatively little research, yet the data here suggest that such activities are likely to impact key coastal species which play important roles within the marine environment

Effect of the velopharynx on intraluminal pressures in reconstructed pharynges derived from individuals with and without sleep apnea

The most collapsible part of the upper airway in the majority of individuals is the velopharynx which is the segment positioned behind the soft palate. As such it is an important morphological region for consideration in elucidating the pathogenesis of obstructive sleep apnea (OSA). This study compared steady flow properties during inspiration in the pharynges of nine male subjects with OSA and nine body-mass index (BMI)- and age-matched control male subjects without OSA. The k–ωωSST turbulence model was used to simulate the flow field in subject-specific pharyngeal geometric models reconstructed from anatomical optical coherence tomography (aOCT) data. While analysis of the geometry of reconstructed pharynges revealed narrowing at velopharyngeal level in subjects with OSA, it was not possible to clearly distinguish them from subjects without OSA on the basis of pharyngeal size and shape alone. By contrast, flow simulations demonstrated that pressure fields within the narrowed airway segments were sensitive to small differences in geometry and could lead to significantly different intraluminal pressure characteristics between subjects. The ratio between velopharyngeal and total pharyngeal pressure drops emerged as a relevant flow-based criterion by which subjects with OSA could be differentiated from those without