Motivational change during shell fights in the hermit crab Pagurus bernhardus

During agonistic interactions the motivation of each contestant is expected to vary because of increased information and changes in fighting ability. In shell fights between hermit crabs over gastropod shells, attackers rap their shell in a series of bouts against that of the defender whereas defenders remain withdrawn into their shells until the encounter is resolved; either the defender is evicted from its shell or the attacker 'gives up' and the defender retains its shell. We assessed the motivational state of attackers for performing rapping by measuring the duration of startle responses elicited by a novel stimulus. We staged fights between pairs of crabs in six different groups defined by the potential gain in shell quality available to attackers (high or low) and by the point at which the novel stimulus was applied (prior to rapping, after one bout or after four bouts). Startle response duration decreased during the first four bouts of fighting and showed a U-shaped relationship with the relative difference in size between the crabs. There was, no difference in startle response duration between high- and low-gain groups. Individuals showing short startle responses were likely to be victorious and we conclude that the relationship between the relative size difference of the opponents and. startle duration reflects that between size difference and the cost of gaining an eviction. (C) 2001 The Association for the Study of Animal Behaviour.

Measurement of the duration of X-ray lasing pumped by an optical laser pulse of picosecond duration

Measurements of the duration of X-ray lasing pumped with picosecond pulses from the VULCAN optical laser are obtained using a streak camera with 700 fs temporal resolution. Combined with a temporal smearing due to the spectrometer employed, we have measured X-ray laser pulse durations for Ni-like silver at 13.9 nm with a total time resolution of 1.1 ps. For Ni-like silver, the X-ray laser output has a steep rise followed by an approximately exponential temporal decay with measured full-width at half-maximum (FWHM) of 3.7 (+/-0.5) ps. For Ne-like nickel lasing at 23.1 nm, the measured duration of lasing is approximate to10.7 (+/-1) ps (FWHM). An estimate of the duration of the X-ray laser gain has been obtained by temporally resolving spectrally integrated continuum and resonance line emission. For Ni-like silver, this time of emission is approximate to22 (+/-2) ps (FWHM), while for Ne-like nickel we measure approximate to35 (+/-2) ps (FWHM). Assuming that these times of emission correspond to the gain duration, we show that a simple model consistently relates the gain durations to the measured durations of X-ray lasing. (C) 2002 Elsevier Science B.V. All rights reserved.

Modelling Patient Duration of Stay to Facilitate Resource Management of Geriatric Hospitals

A fundamental aspect of health care management is the effective allocation of resources. This is of particular importance in geriatric hospitals where elderly patients tend to have more complex needs. Hospital managers would benefit immensely if they had advance knowledge of patient duration of stay in hospital. Managers could assess the costs of patient care and make allowances for these in their budget. In this paper, we tackle this important problem via a model which predicts the duration of stay distribution of patients in hospital. The approach uses phase-type distributions conditioned on a Bayesian belief network.

Using Coxian Phase-Type Distributions to Identify Patient Characteristics for Duration of Stay in Hospital

Coxian phase-type distributions are a special type of Markov model that describes duration until an event occurs in terms of a process consisting of a sequence of latent phases. This paper considers the use of Coxian phase-type distributions for modelling patient duration of stay for the elderly in hospital and investigates the potential for using the resulting distribution as a classifying variable to identify common characteristics between different groups of patients according to their (anticipated) length of stay in hospital. The identification of common characteristics for patient length of stay groups would offer hospital managers and clinicians possible insights into the overall management and bed allocation of the hospital wards.

Appearance of the frequency-doubling stimulus at threshold.

PURPOSE. It has been argued that the threshold for detecting frequency-doubling (FD) technology perimeter stimuli differs from the threshold for perceiving spatial structure (pattern) in the same targets. Thresholds for perceiving spatial structure have typically been assessed using orientation-identification experiments. The authors investigated the influence of orientation, edge profile, and psychophysical method on the origin of the reported differences in detection and orientation-identification thresholds for FD gratings.

METHODS. Detection and orientation-identification thresholds were determined in 12 observers with the use of FD stimuli (0.25 cyc/deg, 25 Hz) presented centrally and at 15° eccentricity. Edge profile (square- and Gaussian-windowed) and orientation (horizontal, vertical, and oblique) were independently modified. Detection thresholds were also measured for spatially uniform flickering targets (25 Hz). Orientation-identification thresholds using a two-alternative forced choice (2-AFC) and a two-interval forced choice (2-IFC) method were also compared in five experienced observers.

RESULTS. Orientation-identification and detection thresholds did not significantly differ under any condition tested. Orientation-identification thresholds obtained with 2-AFC were not significantly different from those obtained with 2-IFC. Thresholds for spatially uniform flicker were significantly lower than for FD stimuli.

CONCLUSIONS. The authors found that orientation-identification and detection thresholds for FD gratings did not differ and argue that recent findings to the contrary arise from the inappropriate use of spatially uniform flicker targets as alternatives in 2-IFC experiments.