82 research outputs found
Metabolic, hygric and ventilatory physiology of a hypermetabolic marsupial, the honey possum (Tarsipes rostratus)
The honey possum is the only non-volant mammal to feed exclusively on a diet of nectar and pollen. Like other mammalian and avian nectarivores, previous studies indicated that the honey possum's basal metabolic rate was higher than predicted for a marsupial of equivalent body mass. However, these early measurements have been questioned. We re-examined the basal metabolic rate (2.52 +/- A 0.222 ml O(2) g(-1) h(-1)) of the honey possum and confirm that it is indeed higher (162%) than predicted for other marsupials both before and after accounting for phylogenetic history. This, together with its small body mass (5.4 +/- A 0.14 g; 1.3% of that predicted by phylogeny) may be attributed to its nectarivorous diet and mesic distribution. Its high-basal metabolic rate is associated with a high-standard body temperature (36.6 +/- A 0.48A degrees C) and oxygen extraction (19.4%), but interestingly the honey possum has a high point of relative water economy (17.0A degrees C) and its standard evaporative water loss (4.33 +/- A 0.394 mg H(2)O g(-1) h(-1)) is not elevated above that of other marsupials, despite its mesic habitat and high dietary water intake.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP
Muscle Fiber Viability, a Novel Method for the Fast Detection of Ischemic Muscle Injury in Rats
Acute lower extremity ischemia is a limb- and life-threatening clinical problem. Rapid detection of the degree of injury is crucial, however at present there are no exact diagnostic tests available to achieve this purpose. Our goal was to examine a novel technique - which has the potential to accurately assess the degree of ischemic muscle injury within a short period of time - in a clinically relevant rodent model. Male Wistar rats were exposed to 4, 6, 8 and 9 hours of bilateral lower limb ischemia induced by the occlusion of the infrarenal aorta. Additional animals underwent 8 and 9 hours of ischemia followed by 2 hours of reperfusion to examine the effects of revascularization. Muscle samples were collected from the left anterior tibial muscle for viability assessment. The degree of muscle damage (muscle fiber viability) was assessed by morphometric evaluation of NADH-tetrazolium reductase reaction on frozen sections. Right hind limbs were perfusion-fixed with paraformaldehyde and glutaraldehyde for light and electron microscopic examinations. Muscle fiber viability decreased progressively over the time of ischemia, with significant differences found between the consecutive times. High correlation was detected between the length of ischemia and the values of muscle fiber viability. After reperfusion, viability showed significant reduction in the 8-hour-ischemia and 2-hour-reperfusion group compared to the 8-hour-ischemia-only group, and decreased further after 9 hours of ischemia and 2 hours of reperfusion. Light- and electron microscopic findings correlated strongly with the values of muscle fiber viability: lesser viability values represented higher degree of ultrastructural injury while similar viability results corresponded to similar morphological injury. Muscle fiber viability was capable of accurately determining the degree of muscle injury in our rat model. Our method might therefore be useful in clinical settings in the diagnostics of acute ischemic muscle injury
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Detection of cosmic structures using the bispectrum phase. II. First results from application to cosmic reionization using the Hydrogen Epoch of Reionization Array
Characterizing the epoch of reionization (EoR) at via the
redshifted 21 cm line of neutral Hydrogen (HI) is critical to modern
astrophysics and cosmology, and thus a key science goal of many current and planned low-frequency radio telescopes. The primary challenge to detecting this signal is the overwhelmingly bright foreground emission at these frequencies, placing stringent requirements on the knowledge of the instruments and inaccuracies in analyses. Results from these experiments have largely been limited not by thermal sensitivity but by systematics, particularly caused by the inability to calibrate the instrument to high accuracy. The interferometric bispectrum phase is immune to antenna-based calibration and errors therein, and presents an independent alternative to detect the EoR HI fluctuations while largely avoiding calibration systematics. Here, we provide a demonstration of this technique on a subset of data from the Hydrogen Epoch of Reionization Array (HERA) to place approximate constraints on the IGM brightness temperature. From this limited data, at we infer "" upper limits on the IGM brightness temperature to be "pseudo" mK at Mpc (data-limited) and
"pseudo" mK at
Mpc (noise-limited). The "pseudo" units denote only an approximate and not an exact correspondence to the actual distance scales and brightness temperatures. By propagating models in parallel to the data analysis, we confirm that the dynamic range required to separate the cosmic HI signal from the foregrounds is similar to that in standard approaches, and the power spectrum of the bispectrum phase is still data-limited (at dynamic range) indicating scope for further improvement in sensitivity as the array build-out continues
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Detection of cosmic structures using the bispectrum phase. II. First results from application to cosmic reionization using the Hydrogen Epoch of Reionization Array
Characterizing the epoch of reionization (EoR) at via the
redshifted 21 cm line of neutral Hydrogen (HI) is critical to modern
astrophysics and cosmology, and thus a key science goal of many current and planned low-frequency radio telescopes. The primary challenge to detecting this signal is the overwhelmingly bright foreground emission at these frequencies, placing stringent requirements on the knowledge of the instruments and inaccuracies in analyses. Results from these experiments have largely been limited not by thermal sensitivity but by systematics, particularly caused by the inability to calibrate the instrument to high accuracy. The interferometric bispectrum phase is immune to antenna-based calibration and errors therein, and presents an independent alternative to detect the EoR HI fluctuations while largely avoiding calibration systematics. Here, we provide a demonstration of this technique on a subset of data from the Hydrogen Epoch of Reionization Array (HERA) to place approximate constraints on the IGM brightness temperature. From this limited data, at we infer "" upper limits on the IGM brightness temperature to be "pseudo" mK at Mpc (data-limited) and
"pseudo" mK at
Mpc (noise-limited). The "pseudo" units denote only an approximate and not an exact correspondence to the actual distance scales and brightness temperatures. By propagating models in parallel to the data analysis, we confirm that the dynamic range required to separate the cosmic HI signal from the foregrounds is similar to that in standard approaches, and the power spectrum of the bispectrum phase is still data-limited (at dynamic range) indicating scope for further improvement in sensitivity as the array build-out continues
Imaging and Modeling Data from the Hydrogen Epoch of Reionization Array
We analyze data from the Hydrogen Epoch of Reionization Array. This is the
third in a series of papers on the closure phase delay-spectrum technique
designed to detect the HI 21cm emission from cosmic reionization. We present
the details of the data and models employed in the power spectral analysis, and
discuss limitations to the process. We compare images and visibility spectra
made with HERA data, to parallel quantities generated from sky models based on
the GLEAM survey, incorporating the HERA telescope model. We find reasonable
agreement between images made from HERA data, with those generated from the
models, down to the confusion level. For the visibility spectra, there is broad
agreement between model and data across the full band of MHz. However,
models with only GLEAM sources do not reproduce a roughly sinusoidal spectral
structure at the tens of percent level seen in the observed visibility spectra
on scales MHz on 29 m baselines. We find that this structure is
likely due to diffuse Galactic emission, predominantly the Galactic plane,
filling the far sidelobes of the antenna primary beam. We show that our current
knowledge of the frequency dependence of the diffuse sky radio emission, and
the primary beam at large zenith angles, is inadequate to provide an accurate
reproduction of the diffuse structure in the models. We discuss implications
due to this missing structure in the models, including calibration, and in the
search for the HI 21cm signal, as well as possible mitigation techniques
Understanding the HERA Phase i receiver system with simulations and its impact on the detectability of the EoR delay power spectrum
The detection of the Epoch of Reionization (EoR) delay power spectrum using a
"foreground avoidance method" highly depends on the instrument chromaticity.
The systematic effects induced by the radio-telescope spread the foreground
signal in the delay domain, which contaminates the EoR window theoretically
observable. Applied to the Hydrogen Epoch of Reionization Array (HERA), this
paper combines detailed electromagnetic and electrical simulations in order to
model the chromatic effects of the instrument, and quantify its frequency and
time responses. In particular, the effects of the analogue receiver,
transmission cables, and mutual coupling are included. These simulations are
able to accurately predict the intensity of the reflections occurring in the
150-m cable which links the antenna to the back-end. They also show that
electromagnetic waves can propagate from one dish to another one through large
sections of the array due to mutual coupling. The simulated system time
response is attenuated by a factor after a characteristic delay which
depends on the size of the array and on the antenna position. Ultimately, the
system response is attenuated by a factor after 1400 ns because of the
reflections in the cable, which corresponds to characterizable
-modes above 0.7 at 150 MHz. Thus, this new
study shows that the detection of the EoR signal with HERA Phase I will be more
challenging than expected. On the other hand, it improves our understanding of
the telescope, which is essential to mitigate the instrument chromaticity
Automated Detection of Antenna Malfunctions in Large-N Interferometers: A case study With the Hydrogen Epoch of Reionization Array
We present a framework for identifying and flagging malfunctioning antennas in large radio
interferometers. We outline two distinct categories of metrics designed to detect outliers along known failure
modes of large arrays: cross-correlation metrics, based on all antenna pairs, and auto-correlation metrics, based
solely on individual antennas. We define and motivate the statistical framework for all metrics used, and present
tailored visualizations that aid us in clearly identifying new and existing systematics. We implement these
techniques using data from 105 antennas in the Hydrogen Epoch of Reionization Array (HERA) as a case study.
Finally, we provide a detailed algorithm for implementing these metrics as flagging tools on real data sets
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