525 research outputs found
Shaping Current Waveforms for direct Modulation of Semiconductor Lasers
We demonstrate a technique for shaping current inputs for the direct
modulation of a semiconductor laser for digital communication. The introduction
of shaped current inputs allows for the suppression of relaxation oscillations
and the avoidance of dynamical memory in the physical laser device, i.e., the
output will not be influenced by previously communicated information. On the
example of time-optimized bits, the possible performance enhancement for high
data rate communications is shown numerically.Comment: 8 pages, 6 figures, to be published in IEEE Journal of Quantum
Electronic
Physiology can contribute to better understanding, management, and conservation of coral reef fishes
Coral reef fishes, like many other marine organisms, are affected by anthropogenic stressors such as fishing and pollution and, owing to climate change, are experiencing increasing water temperatures and ocean acidification. Against the backdrop of these various stressors, a mechanistic understanding of processes governing individual organismal performance is the first step for identifying drivers of coral reef fish population dynamics. In fact, physiological measurements can help to reveal potential cause-and-effect relationships and enable physiologists to advise conservation management by upscaling results from cellular and individual organismal levels to population levels. Here, we highlight studies that include physiological measurements of coral reef fishes and those that give advice for their conservation. A literature search using combined physiological, conservation and coral reef fish key words resulted in similar to 1900 studies, of which only 99 matched predefined requirements. We observed that, over the last 20 years, the combination of physiological and conservation aspects in studies on coral reef fishes has received increased attention. Most of the selected studies made their physiological observations at the whole organism level and used their findings to give conservation advice on population dynamics, habitat use or the potential effects of climate change. The precision of the recommendations differed greatly and, not surprisingly, was least concrete when studies examined the effects of projected climate change scenarios. Although more and more physiological studies on coral reef fishes include conservation aspects, there is still a lack of concrete advice for conservation managers, with only very few published examples of physiological findings leading to improved management practices. We conclude with a call to action to foster better knowledge exchange between natural scientists and conservation managers to translate physiological findings more effectively in order to obtain evidence-based and adaptive management strategies for the conservation of coral reef fishes
Boosting clinical performance: The impact of enhanced final year placements.
BACKGROUND: This study follows on from a study that investigated how to develop effective final year medical student assistantship placements, using multidisciplinary clinical teams in planning and delivery. AIMS: This study assessed the effects on objective structured clinical examination (OSCE) performance of the in-course enhanced "super-assistantship" placement introduced to a randomly selected sample of 2013-14 final year medical students at Leeds medical school. METHODS: Quantitative data analysis was used to compare the global grades of OSCE stations between students who undertook this placement against those who did not. RESULTS: There was a small overall improvement in the "super-assistantship" student scores across the whole assessment (effect size = 0.085). "Pre-op Capacity", "Admissions Prescribing" and "Hip Pain" stations had small-medium effect sizes (0.226, 0.215, and 0.214) in favor of the intervention group. Other stations had small effect sizes (0.107-0.191), mostly in favor of the intervention group. CONCLUSIONS: The "super-assistantship" experience characterized by increasing student responsibility on placement can help to improve competence and confidence in clinical decision-making "in a simulated environment". The clinical environment and multidisciplinary team must be ready and supported to provide these opportunities effectively. Further in-course opportunities for increasing final year student responsibility should be developed
Downflows in sunspot umbral dots
We study the velocity field of umbral dots at a resolution of 0.14". Our
analysis is based on full Stokes spectropolarimetric measurements of a pore
taken with the CRISP instrument at the Swedish 1-m Solar Telescope. We
determine the flow velocity at different heights in the photosphere from a
bisector analysis of the Fe I 630 nm lines. In addtion, we use the observed
Stokes Q, U, and V profiles to characterize the magnetic properties of these
structures. We find that most umbral dots are associated with strong upflows in
deep photospheric layers. Some of them also show concentrated patches of
downflows at their edges, with sizes of about 0.25", velocities of up to 1000
m/s, and enhanced net circular polarization signals. The downflows evolve
rapidly and have lifetimes of only a few minutes. These results appear to
validate numerical models of magnetoconvection in the presence of strong
magnetic fields.Comment: Final published version. For best quality figures, please download
the PS versio
Self-Consistent MHD Modeling of a Coronal Mass Ejection, Coronal Dimming, and a Giant Cusp-Shaped Arcade Formation
We performed magnetohydrodynamic simulation of coronal mass ejections (CMEs)
and associated giant arcade formations, and the results suggested new
interpretations of observations of CMEs. We performed two cases of the
simulation: with and without heat conduction. Comparing between the results of
the two cases, we found that reconnection rate in the conductive case is a
little higher than that in the adiabatic case and the temperature of the loop
top is consistent with the theoretical value predicted by the Yokoyama-Shibata
scaling law. The dynamical properties such as velocity and magnetic fields are
similar in the two cases, whereas thermal properties such as temperature and
density are very different.In both cases, slow shocks associated with magnetic
reconnectionpropagate from the reconnection region along the magnetic field
lines around the flux rope, and the shock fronts form spiral patterns. Just
outside the slow shocks, the plasma density decreased a great deal. The soft
X-ray images synthesized from the numerical results are compared with the soft
X-ray images of a giant arcade observed with the Soft X-ray Telescope aboard
{\it Yohkoh}, it is confirmed that the effect of heat conduction is significant
for the detailed comparison between simulation and observation. The comparison
between synthesized and observed soft X-ray images provides new interpretations
of various features associated with CMEs and giant arcades.Comment: 39 pages, 18 figures. Accepted for publication in the Astrophysical
Journal. The PDF file with high resplution figures can be downloaded from
http://www.kwasan.kyoto-u.ac.jp/~shiota/study/ApJ62426.preprint.pdf
Chaotic Free-Space Laser Communication over Turbulent Channel
The dynamics of errors caused by atmospheric turbulence in a
self-synchronizing chaos based communication system that stably transmits
information over a 5 km free-space laser link is studied experimentally.
Binary information is transmitted using a chaotic sequence of short-term pulses
as carrier. The information signal slightly shifts the chaotic time position of
each pulse depending on the information bit. We report the results of an
experimental analysis of the atmospheric turbulence in the channel and the
impact of turbulence on the Bit-Error-Rate (BER) performance of this chaos
based communication system.Comment: 4 pages, 5 figure
Fluxtube model atmospheres and Stokes V zero-crossing wavelengths
First results of the inversion of Stokes I and V profiles from plage regions
near disk center are presented. Both low and high spatial resolution spectra of
FeI 6301.5 and FeI 6302.5 A obtained with the Advanced Stokes Polarimeter (ASP)
have been considered for analysis. The thin flux tube approximation,
implemented in an LTE inversion code based on response functions, is used to
describe unresolved magnetic elements. The code allows the simultaneous and
consistent inference of all atmospheric quantities determining the radiative
transfer with the sole assumption of hydrostatic equilibrium. By considering
velocity gradients within the tubes we are able to match the full ASP Stokes
profiles. The magnetic atmospheres derived from the inversion are characterized
by the absence of significant motions in high layers and strong velocity
gradients in deeper layers. These are essential to reproduce the asymmetries of
the observed profiles. Our scenario predicts a shift of the Stokes V
zero-crossing wavelengths which is indeed present in observations made with the
Fourier Transform Spectrometer.Comment: To appear in ApJ Letters (1997) (in press
Photoluminescence and photoluminescence excitation studies of lateral size effects in Zn_{1-x}Mn_xSe/ZnSe quantum disc samples of different radii
Quantum disc structures (with diameters of 200 nm and 100 nm) were prepared
from a Zn_{0.72}Mn_{0.28}Se/ZnSe single quantum well structure by electron beam
lithography followed by an etching procedure which combined dry and wet etching
techniques. The quantum disc structures and the parent structure were studied
by photoluminescence and photoluminescence excitation spectroscopy. For the
light-hole excitons in the quantum well region, shifts of the energy positions
are observed following fabrication of the discs, confirming that strain
relaxation occurs in the pillars. The light-hole exciton lines also sharpen
following disc fabrication: this is due to an interplay between strain effects
(related to dislocations) and the lateral size of the discs. A further
consequence of the small lateral sizes of the discs is that the intensity of
the donor-bound exciton emission from the disc is found to decrease with the
disc radius. These size-related effects occur before the disc radius is reduced
to dimensions necessary for lateral quantum confinement to occur but will
remain important when the discs are made small enough to be considered as
quantum dots.Comment: LaTeX2e, 13 pages, 6 figures (epsfig
Importance of health assessments for conservation in noncaptive wildlife
Wildlife health assessments help identify populations at risk of starvation, disease, and decline from anthropogenic impacts on natural habitats. We conducted an overview of available health assessment studies in noncaptive vertebrates and devised a framework to strategically integrate health assessments in population monitoring. Using a systematic approach, we performed a thorough assessment of studies examining multiple health parameters of noncaptive vertebrate species from 1982 to 2020 (n = 261 studies). We quantified trends in study design and diagnostic methods across taxa with generalized linear models, bibliometric analyses, and visual representations of study location versus biodiversity hotspots. Only 35% of studies involved international or cross‐border collaboration. Countries with both high and threatened biodiversity were greatly underrepresented. Species that were not listed as threatened on the International Union for Conservation of Nature Red List represented 49% of assessed species, a trend likely associated with the regional focus of most studies. We strongly suggest following wildlife health assessment protocols when planning a study and using statistically adequate sample sizes for studies establishing reference ranges. Across all taxa blood analysis (89%), body composition assessments (81%), physical examination (72%), and fecal analyses (24% of studies) were the most common methods. A conceptual framework to improve design and standardize wildlife health assessments includes guidelines on the experimental design, data acquisition and analysis, and species conservation planning and management implications. Integrating a physiological and ecological understanding of species resilience toward threatening processes will enable informed decision making regarding the conservation of threatened species
Rapid physiological and transcriptomic changes associated with oxygen delivery in larval anemonefish suggest a role in adaptation to life on hypoxic coral reefs
Connectivity of coral reef fish populations relies on successful dispersal of a pelagic larval phase. Pelagic larvae must exhibit high swimming abilities to overcome ocean and reef currents, but once settling onto the reef, larvae transition to endure habitats that become hypoxic at night. Therefore, coral reef fish larvae must rapidly and dramatically shift their physiology over a short period of time. Taking an integrative, physiological approach, using swimming respirometry, and examining hypoxia tolerance and transcriptomics, we show that larvae of cinnamon anemonefish (Amphiprion melanopus) rapidly transition between "physiological extremes" at the end of their larval phase. Daily measurements of swimming larval anemonefish over their entire early development show that they initially have very high mass-specific oxygen uptake rates. However, oxygen uptake rates decrease midway through the larval phase. This occurs in conjunction with a switch in haemoglobin gene expression and increased expression of myoglobin, cytoglobin, and neuroglobin, which may all contribute to the observed increase in hypoxia tolerance. Our findings indicate that critical ontogenetic changes in the gene expression of oxygen-binding proteins may underpin the physiological mechanisms needed for successful larval recruitment to reefs
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