585 research outputs found
Ocean climate and seal condition
BACKGROUND: The condition of many marine mammals varies with fluctuations in productivity and food supply in the ocean basin where they forage. Prey is impacted by physical environmental variables such as cyclic warming trends. The weaning weight of northern elephant seal pups, Mirounga angustirostris, being closely linked to maternal condition, indirectly reflects prey availability and foraging success of pregnant females in deep waters of the northeastern Pacific. The aim of this study was to examine the effect of ocean climate on foraging success in this deep-diving marine mammal over the course of three decades, using cohort weaning weight as the principal metric of successful resource accrual. RESULTS: The mean annual weaning weight of pups declined from 1975 to the late 1990s, a period characterized by a large-scale, basin-wide warm decadal regime that included multiple strong or long-duration El Niños; and increased with a return to a cool decadal regime from about 1999 to 2004. Increased foraging effort and decreased mass gain of adult females, indicative of reduced foraging success and nutritional stress, were associated with high ocean temperatures. CONCLUSION: Despite ranging widely and foraging deeply in cold waters beyond coastal thermoclines in the northeastern Pacific, elephant seals are impacted significantly by ocean thermal dynamics. Ocean warming redistributes prey decreasing foraging success of females, which in turn leads to lower weaning mass of pups. Annual fluctuations in weaning mass, in turn, reflect the foraging success of females during the year prior to giving birth and signals changes in ocean temperature cycles
Respiration and Heart Rate at the Surface between Dives in Northern Elephant Seals
All underwater activities of diving mammals are constrained by the need for surface gas exchange. Our aim was to measure respiratory rate (fb) and heart rate (fh) at the surface between dives in free-ranging northern elephant seals Mirounga angustirostris. We recorded fb and fh acoustically in six translocated juveniles, 1.8-2. 4 years old, and three migrating adult males from the rookery at Ano Nuevo, California, USA. To each seal, we attached a diving instrument to record the diving pattern, a satellite tag to track movements and location, a digital audio tape recorder or acoustic datalogger with an external hydrophone to record the sounds of respiration and fh at the surface, and a VHF transmitter to facilitate recovery. During surface intervals averaging 2.2+/−0.4 min, adult males breathed a mean of 32.7+/−5.4 times at a rate of 15. 3+/−1.8 breaths min(−)(1) (means +/− s.d., N=57). Mean fh at the surface was 84+/−3 beats min(−)(1). The fb of juveniles was 26 % faster than that of adult males, averaging 19.2+/−2.2 breaths min(−)(1) for a mean total of 41.2+/−5.0 breaths during surface intervals lasting 2.6+/−0.31 min. Mean fh at the surface was 106+/−3 beats min(−)(1). fb and fh did not change significantly over the course of surface intervals. Surface fb and fh were not clearly associated with levels of exertion, such as rapid horizontal transit or apparent foraging, or with measures of immediately previous or subsequent diving performance, such as diving duration, diving depth or swimming speed. Together, surface respiration rate and the duration of the preceding dive were significant predictors of surface interval duration. This implies that elephant seals minimize surface time spent loading oxygen depending on rates of oxygen uptake and previous depletion of stores
Semimetalic antiferromagnetism in the half-Heusler compound CuMnSb
The half-Heusler compound CuMnSb, the first antiferromagnet (AFM) in the
Mn-based class of Heuslers and half-Heuslers that contains several conventional
and half metallic ferromagnets, shows a peculiar stability of its magnetic
order in high magnetic fields. Density functional based studies reveal an
unusual nature of its unstable (and therefore unseen) paramagnetic state, which
for one electron less (CuMnSn, for example) would be a zero gap semiconductor
(accidentally so) between two sets of very narrow, topologically separate bands
of Mn 3d character. The extremely flat Mn 3d bands result from the environment:
Mn has four tetrahedrally coordinated Cu atoms whose 3d states lie well below
the Fermi level, and the other four tetrahedrally coordinated sites are empty,
leaving chemically isolated Mn 3d states. The AFM phase can be pictured
heuristically as a self-doped CuMnSb compensated semimetal
with heavy mass electrons and light mass holes, with magnetic coupling
proceeding through Kondo and/or antiKondo coupling separately through the two
carrier types. The ratio of the linear specific heat coefficient and the
calculated Fermi level density of states indicates a large mass enhancement
, or larger if a correlated band structure is taken as the
reference
Enhancement of Rabi Splitting in a Microcavity with an Embedded Superlattice
We have observed a large coupling between the excitonic and photonic modes of
an AlAs/AlGaAs microcavity filled with an 84-({\rm {\AA}})/20({\rm {\AA}})
GaAs/AlGaAs superlattice. Reflectivity measurements on the coupled
cavity-superlattice system in the presence of a moderate electric field yielded
a Rabi splitting of 9.5 meV at T = 238 K. This splitting is almost 50% larger
than that found in comparable microcavities with quantum wells placed at the
antinodes only. We explain the enhancement by the larger density of optical
absorbers in the superlattice, combined with the quasi-two-dimensional binding
energy of field-localized excitons.Comment: 5 pages, 4 figures, submitted to PR
Subtractive gene expression profiling of articular cartilage and mesenchymal stem cells: serpins as cartilage-relevant differentiation markers
SummaryObjectiveMesenchymal stem cells (MSCs) are a population of cells broadly discussed to support cartilage repair. The differentiation of MSCs into articular chondrocytes is, however, still poorly understood on the molecular level. The aim of this study was to perform an almost genome-wide screen for genes differentially expressed between cartilage and MSCs and to extract new markers useful to define chondrocyte differentiation stages.MethodsGene expression profiles of MSCs (n=8) and articular cartilage from OA patients (n=7) were compared on a 30,000 cDNA-fragment array and differentially expressed genes were extracted by subtraction. Expression of selected genes was assessed during in vitro chondrogenic differentiation of MSCs and during dedifferentiation of expanded chondrocytes using quantitative and semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Protein secretion was measured by enzyme-linked immunosorbent assay.ResultsEighty-seven genes were differentially expressed between MSCs and cartilage with a more than three-fold difference. Sixty-seven of them were higher expressed in cartilage and among them 15 genes were previously not detected in cartilage. Differential expression was confirmed for 69% of 26 reanalysed genes by RT-PCR. The profiles of three unknown transcripts and six protease-related molecules were characterised during differentiation. SERPINA1 and SERPINA3 mRNA expression correlated with chondrogenic differentiation of MSCs and dedifferentiation of chondrocytes, and SERPINA1 protein levels in culture supernatants could be correlated alike.ConclusionscDNA-array analysis identified SERPINA1 and A3 as new differentiation-relevant genes for cartilage. Since SERPINA1 secretion correlated with both chondrogenesis of MSCs and dedifferentiation during chondrocyte expansion, it represents an attractive marker for refinement of chondrocyte differentiation
Transition from Townsend to glow discharge: subcritical, mixed or supercritical
The full parameter space of the transition from Townsend to glow discharge is
investigated numerically in one space dimension in the classical model: with
electrons and positive ions drifting in the local electric field, impact
ionization by electrons ( process), secondary electron emission from
the cathode ( process) and space charge effects. We also perform a
systematic analytical small current expansion about the Townsend limit up to
third order in the total current that fits our numerical data very well.
Depending on and system size pd, the transition from Townsend to glow
discharge can show the textbook subcritical behavior, but for smaller values of
pd, we also find supercritical or some intermediate ``mixed'' behavior. The
analysis in particular lays the basis for understanding the complex
spatio-temporal patterns in planar barrier discharge systems.Comment: 12 pages, 10 figures, submitted to Phys. Rev.
Multi-photon, multi-mode polarization entanglement in parametric down-conversion
We study the quantum properties of the polarization of the light produced in
type II spontaneous parametric down-conversion in the framework of a multi-mode
model valid in any gain regime. We show that the the microscopic polarization
entanglement of photon pairs survives in the high gain regime (multi-photon
regime), in the form of nonclassical correlation of all the Stokes operators
describing polarization degrees of freedom
Engineering hydrophobin DewA to generate surfaces that enhance adhesion of human but not bacterial cells
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