1,095 research outputs found
Unidirectional Rotation Neurones in the Optomotor System of the Crab, Carcinus
1. Among the optomotor fibres to the eye muscles in Carcinus a class was found which responds to unidirectional fast rotations around various body axes. All had large signals and are therefore of large diameter.
2. In one set of these fibres which fires especially for rotations around the dorsoventral axis, it could be shown that discharges take place especially during accelerations and that, when a rotation in the null direction is suddenly stopped, a short discharge occurs. The fibres for other axes behave in a similar manner.
3. For rotations around the ventro-dorsal axis, but not for other directions, mediumsized fibres are present which, in contrast to the fast fibres, respond to visual stimulation, as well as to body rotations in darkness, thus combining the input properties of the unidirectional fast rotatory and the unidirectional purely optokinetic small fibres. Their sensitivity to visual input is for low rotation velocities, to body rotations is for high rotation velocities
Factors Regulating the Discharge Frequency in Optomotor Fibres Of Carcinus Maenas
The influence of the excited state of the animal on various motor neurone discharges and accompanying muscle action potentials was studied in the eyestalk of the crab, Carcinus maenas.
In most cases large increases in firing frequency could be obtained during such states. An exception is the tonic eye-withdrawal system in which an inhibitory effect is caused.
A pronounced difference in habituation to constant stimuli between spring and summer was found for the position fibres; in spring it was slow and in summer much quicker
Command Interneurons in the Crayfish Central Nervous System
The motor effects evoked by stimulation of each of eight command fibres in the circumoesophageal commissures of the crayfish are described. The fibres obtained appeared to have widespread connexions in all or most of the lower ganglia. For certain fibres the response was stronger on the homolateral side of the animal; for others it was symmetrical. The frequency of stimulation of a command fibre generally had a pronounced influence on the speed of the evoked response. In addition, segments of the total response could be elicited selectively by alteration of the frequency and duration of stimulation. Although the responses associated with most of the fibres were not sensitive to the fine temporal pattern of the applied stimulation, for one fibre the motor output depended clearly on the spacing of the stimulating pulses
Light diffusion and localization in 3D nonlinear disordered media
Using a 3D Finite-Difference Time-Domain parallel code, we report on the
linear and nonlinear propagation of light pulses in a disordered assembly of
scatterers, whose spatial distribution is generated by a Molecular Dynamics
code; refractive index dispersion is also taken into account. We calculate the
static and dynamical diffusion constant of light, while considering a pulsed
excitation. Our results are in quantitative agreement with reported
experiments, also furnishing evidence of a non-exponential decay of the
transmitted pulse in the linear regime and in the presence of localized modes.
By using an high power excitation, we numerically demonstrate the
``modulational instability random laser'': at high peak input powers energy is
transferred to localized states from the input pulse, via third-order
nonlinearity and optical parametric amplification, and this process is signed
by a power-dependent non-exponential time-decay of the transmitted pulse.Comment: 5 pages, 4 figures. Revised version with new figure 4 with localized
state
A Bose-Einstein condensate in a random potential
An optical speckle potential is used to investigate the static and dynamic
properties of a Bose-Einstein condensate in the presence of disorder. For
strong disorder the condensate is localized in the deep wells of the potential.
With smaller levels of disorder, stripes are observed in the expanded density
profile and strong damping of dipole and quadrupole oscillations is seen.
Uncorrelated frequency shifts of the two modes are measured for a weak disorder
and are explained using a sum-rules approach and by the numerical solution of
the Gross-Pitaevskii equation
Probing the eigenfunction fractality with a stop watch
We study numerically the distribution of scattering phases
and of Wigner delay times for the power-law banded random
matrix (PBRM) model at criticality with one channel attached to it. We find
that is insensitive to the position of the channel and
undergoes a transition towards uniformity as the bandwidth of the PBRM
model increases. The inverse moments of Wigner delay times scale as
, where are the multifractal
dimensions of the eigenfunctions of the corresponding closed system and is
the system size. The latter scaling law is sensitive to the position of the
channel.Comment: 5 pages, 4 figure
Effect of optical disorder and single defects on the expansion of a Bose-Einstein condensate in a one-dimensional waveguide
We investigate the one-dimensional expansion of a Bose-Einstein condensate in
an optical guide in the presence of a random potential created with optical
speckles. With the speckle the expansion of the condensate is strongly
inhibited. A detailed investigation has been carried out varying the
experimental conditions and checking the expansion when a single optical defect
is present. The experimental results are in good agreement with numerical
calculations based on the Gross-Pitaevskii equation.Comment: 5 pages, 5 figure
Fluctuations of radiation from a chaotic laser below threshold
Radiation from a chaotic cavity filled with gain medium is considered. A set
of coupled equations describing the photon density and the population of gain
medium is proposed and solved. The spectral distribution and fluctuations of
the radiation are found. The full noise is a result of a competition between
positive correlations of photons with equal frequencies (due to stimulated
emission and chaotic scattering) which increase fluctuations, and a suppression
due to interaction with a gain medium which leads to negative correlations
between photons. The latter effect is responsible for a pronounced suppression
of the photonic noise as compared to the linear theory predictions.Comment: 7 pages, 5 figures; expanded version, to appear in Phys. Rev.
When one size does not fit all:Using <i>ex post</i> subjective ratings to provide parity in risk-adjusted compensation
Firms typically use a ‘one-size-fits-all’ (OSFA) compensation contract that specifies a common formulaic relation between performance and compensation (i.e., a performance bonus) for non-executive managers in similar jobs. However, a contract that is appropriate on average, may be suboptimal for individual managers if heterogeneity in the operating environment creates varying compensation risk. We use field data from a retail firm that introduced an OSFA bonus compensation plan for its store managers. The common bonus formula is based on a weighted sum of objective measures of performance and a subjective rating made by supervisors. The firm intended the supervisors’ discretionary subjective rating to evaluate performance on dimensions that are difficult to measure (e.g., store appearance). We test and find that supervisors give uniformly higher subjective ratings to managers whose objective measure of sales performance is measured with greater noise, and to managers who face higher performance target difficulty, the latter assessed both prior to (ex ante) and subsequent to (ex post) the evaluation period. These results obtain after controlling for manager ability and performance, and for alternative mechanisms to mitigate differences in compensation risk (e.g., salary changes, sales target changes, and bonus adjustments). The evidence suggests that supervisors use discretion in subjective ratings to provide manager-specific risk premiums for non-executive managers who are subject to an OSFA contract
Public trust and global biobank networks.
BACKGROUND: Biobanks provide an important foundation for genomic and personalised medicine. In order to enhance their scientific power and scope, they are increasingly becoming part of national or international networks. Public trust is essential in fostering public engagement, encouraging donation to, and facilitating public funding for biobanks. Globalisation and networking of biobanking may challenge this trust. METHODS: We report the results of an Australian study examining public attitudes to the networking and globalisation of biobanks. The study used quantitative and qualitative methods in conjunction with bioethical analysis in order to determine factors that may contribute to, and threaten, trust. RESULTS: Our results indicate a generally high level of trust in biobanks and in medical research more broadly. Key factors that can reduce perceived trustworthiness of biobanks are commercialisation and involvement in global networking. CONCLUSIONS: We conclude that robust ethical oversight and governance standards can both promote trust in global biobanking and ensure that this trust is warranted
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