14,246 research outputs found
Thermal effects on cephalopod energy metabolism - A case study for Sepia officinalis
Cephalopods are the largest, most active invertebrates and there is considerable evidence for their convergent evolution with fishes. However, most active cephalopods display standard and active metabolic rates that are several-fold higher than comparably sized fishes. Shifting habitat temperatures due to climate change will therefore affect a cephalopods energy metabolism much more than that of a fish. Prediction of the probable outcome of cephalopod-fish competition thus requires quantitative information concerning whole animal energetics and corresponding efficiencies. Migrating cephalopods such as squid and cuttlefish grow rapidly to maturity, carry few food reserves and have little overlap of generations. This "live fast, die young" life history strategy means that they require niches capable of sustaining high power requirements and rapid growth. This presentation aims to draw a bottom-up picture of the cellular basis of energy metabolism of the cuttlefish Sepia officinalis, from its molecular basis to whole animal energetics based on laboratory experiments and field data. We assessed the proportionality of standard vs active metabolic rate and the daily energetic requirements using field tracking data in combination with lab based respirometry and video analysis. Effects of environmental temperature on mitochondrial energy coupling were investigated in whole animals using in vivo 31P-NMR spectroscopy. As efficient energy turnover needs sufficient oxygen supply, also thermal effects on the blood oxygen-binding capacities of the respiratory pigment haemocyanin and the differential expression of its isoforms were investigated.Supported by NERC grant NERC/A/S/2002/00812
The Phase Diagram and Spectrum of Gauge-Fixed Abelian Lattice Gauge Theory
We consider a lattice discretization of a covariantly gauge-fixed abelian
gauge theory. The gauge fixing is part of the action defining the theory, and
we study the phase diagram in detail. As there is no BRST symmetry on the
lattice, counterterms are needed, and we construct those explicitly. We show
that the proper adjustment of these counterterms drives the theory to a new
type of phase transition, at which we recover a continuum theory of (free)
photons. We present both numerical and (one-loop) perturbative results, and
show that they are in good agreement near this phase transition. Since
perturbation theory plays an important role, it is important to choose a
discretization of the gauge-fixing action such that lattice perturbation theory
is valid. Indeed, we find numerical evidence that lattice actions not
satisfying this requirement do not lead to the desired continuum limit. While
we do not consider fermions here, we argue that our results, in combination
with previous work, provide very strong evidence that this new phase transition
can be used to define abelian lattice chiral gauge theories.Comment: 42 pages, 30 figure
Faster k-Medoids Clustering: Improving the PAM, CLARA, and CLARANS Algorithms
Clustering non-Euclidean data is difficult, and one of the most used
algorithms besides hierarchical clustering is the popular algorithm
Partitioning Around Medoids (PAM), also simply referred to as k-medoids. In
Euclidean geometry the mean-as used in k-means-is a good estimator for the
cluster center, but this does not hold for arbitrary dissimilarities. PAM uses
the medoid instead, the object with the smallest dissimilarity to all others in
the cluster. This notion of centrality can be used with any (dis-)similarity,
and thus is of high relevance to many domains such as biology that require the
use of Jaccard, Gower, or more complex distances.
A key issue with PAM is its high run time cost. We propose modifications to
the PAM algorithm to achieve an O(k)-fold speedup in the second SWAP phase of
the algorithm, but will still find the same results as the original PAM
algorithm. If we slightly relax the choice of swaps performed (at comparable
quality), we can further accelerate the algorithm by performing up to k swaps
in each iteration. With the substantially faster SWAP, we can now also explore
alternative strategies for choosing the initial medoids. We also show how the
CLARA and CLARANS algorithms benefit from these modifications. It can easily be
combined with earlier approaches to use PAM and CLARA on big data (some of
which use PAM as a subroutine, hence can immediately benefit from these
improvements), where the performance with high k becomes increasingly
important.
In experiments on real data with k=100, we observed a 200-fold speedup
compared to the original PAM SWAP algorithm, making PAM applicable to larger
data sets as long as we can afford to compute a distance matrix, and in
particular to higher k (at k=2, the new SWAP was only 1.5 times faster, as the
speedup is expected to increase with k)
Thermal Kinetic Inductance Detectors for Millimeter-Wave Astrophysics
Thermal Kinetic Inductance Detectors (TKIDs) combine the excellent noise performance of traditional bolometers with a radio frequency (RF) multiplexing architecture that enables the large detector counts needed for the next generation of millimeter-wave instruments. Here we present dark prototype TKID pixels that demonstrate a noise equivalent power NEP = 2Ă10â»Âčâ·âW/Hz with a 1/f knee at 0.1 Hz, suitable for background-limited noise performance at 150 GHz from a ground-based site. We discuss the optimizations in the device design and fabrication techniques to realize optimal electrical performance and high quality factors at a bath temperature of 250 mK
Impact of anthropogenic ocean acidification on thermal tolerance of the spider crab <i>Hyas araneus</i>
Future scenarios for the oceans project combined developments of CO<sub>2</sub> accumulation and global warming and their impact on marine ecosystems. The synergistic impact of both factors was addressed by studying the effect of elevated CO<sub>2</sub> concentrations on thermal tolerance of the cold-eurythermal spider crab <i>Hyas araneus</i> from the population around Helgoland. Here ambient temperatures characterize the southernmost distribution limit of this species. Animals were exposed to present day normocapnia (380 ppm CO<sub>2</sub>), CO<sub>2</sub> levels expected towards 2100 (710 ppm) and beyond (3000 ppm). Heart rate and haemolymph PO<sub>2</sub> (P<sub>e</sub>O<sub>2</sub>) were measured during progressive short term cooling from 10 to 0°C and during warming from 10 to 25°C. An increase of P<sub>e</sub>O<sub>2</sub> occurred during cooling, the highest values being reached at 0°C under all three CO<sub>2</sub> levels. Heart rate increased during warming until a critical temperature (<i>T<sub>c</sub></i>) was reached. The putative <i>T<sub>c</sub></i> under normocapnia was presumably >25°C, from where it fell to 23.5°C under 710 ppm and then 21.1°C under 3000 ppm. At the same time, thermal sensitivity, as seen in the <i>Q<sub>10</sub></i> values of heart rate, rose with increasing CO<sub>2</sub> concentration in the warmth. Our results suggest a narrowing of the thermal window of <i>Hyas araneus</i> under moderate increases in CO<sub>2</sub> levels by exacerbation of the heat or cold induced oxygen and capacity limitation of thermal tolerance
Z-Spec: A MM-Wave Spectrometer For Measuring Redshifts Of Submillimeter Galaxies
We are building a background-limited, broadband millimeter-wave spectrometer (Z-Spec) for observations of CO rotational transitions from high-redshift dusty galaxies. The large instantaneous bandwidth (195 to 310 GHz) will enable redshifts of dust obscured galaxies to be unambiguously measured. Z-Spec uses a waveguide-coupled grating architecture in which the light propagation is confined within a parallel-plate waveguide. The grating is extremely compact compared to a classical free-space system. An array of silicon nitride bolometers cooled to 100 mK will provide background-limited performance. Z-Spec serves as a technology demonstration for a future space-borne far-infrared grating spectrometer
Observations of [C II] 158 micron Line and Far-infrared Continuum Emission toward the High-latitude Molecular Clouds in Ursa Major
We report the results of a rocket-borne observation of [C II] 158\micron line
and far-infrared continuum emission at 152.5\micron toward the high latitude
molecular clouds in Ursa Major. We also present the results of a follow-up
observation of the millimeter ^{12}CO J=1-0 line over a selected region
observed by the rocket-borne experiment. We have discovered three small CO
cloudlets from the follow-up ^{12}CO observations. We show that these molecular
cloudlets, as well as the MBM clouds(MBM 27/28/29/30), are not gravitationally
bound. Magnetic pressure and turbulent pressure dominate the dynamic balance of
the clouds. After removing the HI-correlated and background contributions, we
find that the [C II] emission peak is displaced from the 152.5\micron and CO
peaks, while the 152.5\micron continuum emission is spatially correlated with
the CO emission. We interpret this behavior by attributing the origin of [C II]
emission to the photodissociation regions around the molecular clouds
illuminated by the local UV radiation field. We also find that the ratio of the
molecular hydrogen column density to velocity-integrated CO intensity is
1.19+-0.29x10^{20} cm^{-2} (K kms^{-1})^{-1} from the FIR continuum and the CO
data. The average [C II] /FIR intensity ratio over the MBM clouds is 0.0071,
which is close to the all sky average of 0.0082 reported by the FIRAS on the
COBE satellite. The average [C II]/CO ratio over the same regions is 420, which
is significantly lower than that of molecular clouds in the Galactic plane.Comment: 15 pages, LaTeX (aaspp4.sty) + 2 tables(apjpt4.sty) + 6 postscript
figures; accepted for publication in the Astrophysical Journal; Astrophys. J.
in press (Vol. 490, December 1, 1997 issue
HerMES: The submillimeter spectral energy distributions of Herschel/SPIRE-detected galaxies
We present colours of sources detected with the Herschel/SPIRE instrument in deep extragalactic surveys of the Lockman Hole, Spitzer-FLS, and GOODS-N fields in three photometric bands at 250, 350 and 500 ÎŒm. We compare these with expectations from the literature and discuss
associated uncertainties and biases in the SPIRE data. We identify a 500 ÎŒm flux limited selection of sources from the HerMES point source catalogue that appears free from neighbouring/blended sources in all three SPIRE bands. We compare the colours with redshift tracks of various
contemporary models. Based on these spectral templates we show that regions corresponding to specific population types and redshifts can be identified better in colour-flux space. The redshift tracks as well as the colour-flux plots imply a majority of detected objects with redshifts at
1 < z < 3.5, somewhat depending on the group of model SEDs used. We also find that a population of sources with S_(250)/S_(350) < 0.8 at fluxes above 50 mJy as observed by SPIRE are not well represented by contemporary models and could consist of a mix of cold and lensed galaxies
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