50,752 research outputs found
The Co-ordination of Swimmeret Movements in the Crayfish, Procambarus Clarkii (Girard)
1. Electrical activity recorded in the first roots of the abdominal nerve cord show bursts of activity which accompany rhythmic movements of the swimmerets. These bursts persist when a root is cut distal to the electrodes.
2. Proprioceptive impulses have been recorded from the distal portion of these nerves during passive movements of the swimmerets. They have also been recorded in the connectives during both passive and active movements.
3. Cutting all second and third roots of the abdominal ganglia does not interfere with the rhythmic swimmeret movements of the isolated abdomen. Rhythmic efferent bursts persist in first roots even when only a single first root remains intact in such a preparation.
4. Intermittent bursts are also found in the first roots of a completely isolated cord but their pattern, frequency and phase relationships differ from those recorded in the same roots before isolation was completed. Such bursts are very rare in second and third roots.
5. Stimulation of small bundles of fibres in the circumoesophageal commissure produces well-defined inhibitory and excitatory effects on the discharge of single units in the first roots.
6. One specific bundle found in many preparations, when stimulated at 50/sec., caused a tonic retraction of all the swimmerets which then began to beat rhythmically and continued to do so when stimulation was discontinued.
7. Intermittent bursts in the first roots took place with correct phasing during this stimulation even when the abdominal ganglia were isolated except for their connexion with the last thoracic ganglion. Again, such bursts were absent in the second and third roots.
8. It is concluded that both the inflow from peripheral proprioceptors and intrinsic properties of the central ganglia play essential parts in the co-ordination of the metachronal movements of the swimmerets
Neuronal Pathways and Synaptic Connexions in the Abdominal Cord of the Crayfish
1. An investigation has been made into the function and distribution of nerve fibres in the abdominal ganglion chain and its roots in the crayfish, Procambarus clarkii, by leading off action potentials from small prepared bundles following sensory stimulation.
2 .The sensory fields belonging to the first and second roots of each abdominal ganglion were determined, and the antero-posterior pathway of sensory fibres within the cord noted. It was found that the primary sensory fibres of the dorsal muscle receptor organs, entering through the second root, send out an anterior branch to the brain and a posterior one to the last ganglion. For most other sensory fibres much shorter intracentral branches are indicated, though some of them extend for two ganglia in the anterior direction and for one posteriorly. All sensory fibres in the connectives run on the same side as they enter.
3. The segmental divisions of the external skeleton and of the nervous system do not coincide, the neural segment slants in a posterior dorsal direction with respect to the skeletal one.
4. For the majority of the interneurones which innervate more than two abdominal segments it has been proved that they synapse with primary sensory fibres in each of the ganglia that these enter. Depending on the segment stimulated with respect to the leading-off position, both ascending and descending impulses are obtained in such interneurones and collision of the impulses has been observed. Some consequences of this type of integration are discussed.
5. For interneurones responding to bilateral or heterolateral stimulation the course of the impulses proved to be of at least two types. In some, cutting the fibre prevents the arrival of impulses except those set up on the side of the cut from which the recording is made. In others, recording from either side of the cut fibre does not exclude any of the sensory fields to which the fibre normally responded.
6. At least one interneurone is present in which all primary sensory fibres from the different segments to whose activity it responds collect in one ganglion
Photometric Metallicities in Bootes I
We present new Stromgren and Washington data sets for the Bootes I dwarf
galaxy, and combine them with the available SDSS photometry. The goal of this
project is to refine a ground-based, practical, accurate method to determine
age and metallicity for individual stars in Bootes I that can be selected in an
unbiased imaging survey, without having to take spectra. We produce photometric
metallicities from Stromgren and Washington photometry, for stellar systems
with a range of . To avoid the decrease in sensitivity of the
Stromgren metallicity index on the lower red-giant branch, we replace the
Stromgren v-filter with the broader Washington C-filter; we find that
is the most successful filter combination, for individual stars with
, to maintain ~0.2 dex -resolution over the whole
red-giant branch. We demonstrate that we can break the isochrones'
age-metallicity degeneracy with these filters, using stars with log g=2.5-3.0,
which have less than a 2% change in their -colour due to age, over a
range of 11-14 Gyr.Comment: 24 pages, 18 figures, accepted by MNRA
Double-impulse magnetic focusing of launched cold atoms.
We have theoretically investigated three-dimensional focusing of a launched cloud of cold atoms using a pair of magnetic lens pulses (the alternate-gradient method). Individual lenses focus radially and defocus axially or vice versa. The performance of the two possible pulse sequences are compared and found to be ideal for loading both 'pancake' and 'sausage' shaped magnetic/optical microtraps. It is shown that focusing aberrations are considerably smaller for double-impulse magnetic lenses compared to single-impulse magnetic lenses. An analysis of clouds focused by the double-impulse technique is presented
AGAPEROS: Searching for variable stars in the LMC Bar with the Pixel Method. I. Detection, astrometry and cross-identification
We extend the work developed in previous papers on microlensing with a
selection of variable stars. We use the Pixel Method to select variable stars
on a set of 2.5 x 10**6 pixel light curves in the LMC Bar presented elsewhere.
The previous treatment was done in order to optimise the detection of long
timescale variations (larger than a few days) and we further optimise our
analysis for the selection of Long Timescale and Long Period Variables
(LT&LPV). We choose to perform a selection of variable objects as comprehensive
as possible, independent of periodicity and of their position on the colour
magnitude diagram. We detail the different thresholds successively applied to
the light curves, which allow to produce a catalogue of 632 variable objects.
We present a table with the coordinate of each variable, its EROS magnitudes at
one epoch and an indicator of blending in both colours, together with a finding
chart.
A cross-correlation with various catalogues shows that 90% of those variable
objects were undetected before, thus enlarging the sample of LT&LPV previously
known in this area by a factor of 10. Due to the limitations of both the Pixel
Method and the data set, additional data -- namely a longer baseline and near
infrared photometry -- are required to further characterise these variable
stars, as will be addressed in subsequent papers.Comment: 11 pages with 10 figure
Comparison of Nurse Staffing Based on Changes in Unit-level Workload Associated with Patient Churn
Aim
This analysis compares the staffing implications of three measures of nurse staffing requirements: midnight census, turnover adjustment based on length of stay, and volume of admissions, discharges and transfers. Background
Midnight census is commonly used to determine registered nurse staffing. Unit-level workload increases with patient churn, the movement of patients in and out of the nursing unit. Failure to account for patient churn in staffing allocation impacts nurse workload and may result in adverse patient outcomes. Method(s)
Secondary data analysis of unit-level data from 32 hospitals, where nursing units are grouped into three unit-type categories: intensive care, intermediate care, and medical surgical. Result
Midnight census alone did not account adequately for registered nurse workload intensity associated with patient churn. On average, units were staffed with a mixture of registered nurses and other nursing staff not always to budgeted levels. Adjusting for patient churn increases nurse staffing across all units and shifts. Conclusion
Use of the discharges and transfers adjustment to midnight census may be useful in adjusting RN staffing on a shift basis to account for patient churn. Implications for nursing management
Nurse managers should understand the implications to nurse workload of various methods of calculating registered nurse staff requirements
Quantum non-Gaussianity witnesses in the phase space
We address detection of quantum non-Gaussian states, i.e. nonclassical states
that cannot be expressed as a convex mixture of Gaussian states, and present a
method to derive a new family of criteria based on generic linear functionals.
We then specialise this method to derive witnesses based on -parametrized
quasiprobability functions, generalising previous criteria based on the Wigner
function. In particular we discuss in detail and analyse the properties of
Husimi Q-function based witnesses and prove that they are often more effective
than previous criteria in detecting quantum non-Gaussianity of various kinds of
non-Gaussian states evolving in a lossy channel.Comment: 9 pages, 6 figure
Characterizing spiral arm and interarm star formation
Interarm star formation contributes significantly to a galaxy's star
formation budget, and provides an opportunity to study stellar birthplaces
unperturbed by spiral arm dynamics. Using optical integral field spectroscopy
of the nearby galaxy NGC 628 with VLT/MUSE, we construct Halpha maps including
detailed corrections for dust extinction and stellar absorption to identify 391
HII regions at 35pc resolution over 12 kpc^2. Using tracers sensitive to the
underlying gravitational potential, we associate HII regions with either arm
(271) or interarm (120) environments. Using our full spectral coverage of each
region, we find that most HII region physical properties (luminosity, size,
metallicity, ionization parameter) are independent of environment. We calculate
the fraction of Halpha luminosity due to the diffuse ionized gas (DIG)
background contaminating each HII region, and find the DIG surface brightness
to be higher within HII regions compared to the surroundings, and slightly
higher within arm HII regions. Use of the temperature sensitive [SII]/Halpha
line ratio map instead of the Halpha surface brightness to identify HII region
boundaries does not change this result. Using the dust attenuation as a tracer
of the gas, we find depletion times consistent with previous work (2 x 10^9 yr)
with no differences between the arm and interarm, however this is very
sensitive to the DIG correction. Unlike molecular clouds, which can be
dynamically affected by the galactic environment, we see fairly consistent HII
region properties in both arm and interarm environments. This suggests either a
difference in arm star formation and feedback, or a decoupling of dense star
forming clumps from the more extended surrounding molecular gas.Comment: 10 pages, 4 figures, 1 table, accepted for publication in Ap
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