1,779 research outputs found
Short-Chain Fatty Acids in the Metabolism of Heart Failure - Rethinking the Fat Stigma
Heart failure (HF) remains a disease with immense global health burden. During the development of HF, the myocardium and therefore cardiac metabolism undergoes specific changes, with decreased long-chain fatty acid oxidation and increased anaerobic glycolysis, diminishing the overall energy yield. Based on the dogma that the failing heart is oxygen-deprived and on the fact that carbohydrates are more oxygen-efficient than FA, metabolic HF drugs have so far aimed to stimulate glucose oxidation or inhibit FA oxidation. Unfortunately, these treatments have failed to provide meaningful clinical benefits. We believe it is time to rethink the concept that fat is harmful to the failing heart. In this review we discuss accumulating evidence that short-chain fatty acids (SCFAs) may be an effective fuel for the failing heart. In contrast to long-chain fatty acids, SCFAs are readily taken up and oxidized by the heart and could serve as a nutraceutical treatment strategy. In addition, we discuss how SCFAs activate pathways that increase long chain fatty acid oxidation, which could help increase the overall energy availability. Another potential beneficial effect we discuss lies within the anti-inflammatory effect of SCFAs, which has shown to inhibit cardiac fibrosis - a key pathological process in the development of HF
An Experimental and Semi-Empirical Method to Determine the Pauli-Limiting Field in Quasi 2D Superconductors as applied to -(BEDT-TTF)Cu(NCS): Strong Evidence of a FFLO State
We present upper critical field data for -(BEDT-TTF)Cu(NCS)
with the magnetic field close to parallel and parallel to the conducting
layers. We show that we can eliminate the effect of vortex dynamics in these
layered materials if the layers are oriented within 0.3 degrees of parallel to
the applied magnetic field. Eliminating vortex effects leaves one remaining
feature in the data that corresponds to the Pauli paramagnetic limit ().
We propose a semi-empirical method to calculate the in quasi 2D
superconductors. This method takes into account the energy gap of each of the
quasi 2D superconductors, which is calculated from specific heat data, and the
influence of many body effects. The calculated Pauli paramagnetic limits are
then compared to critical field data for the title compound and other organic
conductors. Many of the examined quasi 2D superconductors, including the above
organic superconductors and CeCoIn, exhibit upper critical fields that
exceed their calculated suggesting unconventional superconductivity. We
show that the high field low temperature state in
-(BEDT-TTF)Cu(NCS) is consistent with the Fulde Ferrell Larkin
Ovchinnikov state.Comment: 8 pages, 9 figures, 10 years of dat
Towards understanding the variability in biospheric CO2 fluxes:Using FTIR spectrometry and a chemical transport model to investigate the sources and sinks of carbonyl sulfide and its link to CO2
Understanding carbon dioxide (CO2) biospheric processes is of great importance because the terrestrial exchange drives the seasonal and interannual variability of CO2 in the atmosphere. Atmospheric inversions based on CO2 concentration measurements alone can only determine net biosphere fluxes, but not differentiate between photosynthesis (uptake) and respiration (production). Carbonyl sulfide (OCS) could provide an important additional constraint: it is also taken up by plants during photosynthesis but not emitted during respiration, and therefore is a potential means to differentiate between these processes. Solar absorption Fourier Transform InfraRed (FTIR) spectrometry allows for the retrievals of the atmospheric concentrations of both CO2 and OCS from measured solar absorption spectra. Here, we investigate co-located and quasi-simultaneous FTIR measurements of OCS and CO2 performed at five selected sites located in the Northern Hemisphere. These measurements are compared to simulations of OCS and CO2 using a chemical transport model (GEOS-Chem). The coupled biospheric fluxes of OCS and CO2 from the simple biosphere model (SiB) are used in the study. The CO2 simulation with SiB fluxes agrees with the measurements well, while the OCS simulation reproduced a weaker drawdown than FTIR measurements at selected sites, and a smaller latitudinal gradient in the Northern Hemisphere during growing season when comparing with HIPPO (HIAPER Pole-to-Pole Observations) data spanning both hemispheres. An offset in the timing of the seasonal cycle minimum between SiB simulation and measurements is also seen. Using OCS as a photosynthesis proxy can help to understand how the biospheric processes are reproduced in models and to further understand the carbon cycle in the real world
Field-Orientation Dependent Heat Capacity Measurements at Low Temperatures with a Vector Magnet System
We describe a heat capacity measurement system for the study of the
field-orientation dependence for temperatures down to 50 mK. A "Vector Magnet"
combined with a mechanical rotator for the dewar enables the rotation of the
magnetic field without mechanical heating in the cryostat by friction. High
reproducibility of the field direction, as well as an angular resolution of
better than 0.01 degree, is obtained. This system is applicable to other kinds
of measurements which require a large sample space or an adiabatic sample
environment, and can also be used with multiple refrigerator inserts
interchangeably.Comment: 7 pages, 8 figure
Profiling Sea Ice with a Multiple Altimeter Beam Experimental Lidar (MABEL)
The sole instrument on the upcoming ICESat-2 altimetry mission is a micropulse lidar that measures the time-of-flight of individual photons from laser pulses transmitted at 532 nm. Prior to launch, MABEL serves as an airborne implementation for testing and development. In this paper, we provide a first examination of MABEL data acquired on two flights over sea ice in April 2012: one north of the Arctic coast of Greenland, and the other in the East Greenland Sea.We investigate the phenomenology of photon distributions in the sea ice returns. An approach to locate the surface and estimate its elevation in the distributions is described, and its achievable precision assessed. Retrieved surface elevations over relatively flat leads in the ice cover suggest that precisions of several centimeters are attainable. Restricting the width of the elevation window used in the surface analysis can mitigate potential biases in the elevation estimates due to subsurface returns at 532 nm. Comparisons of nearly coincident elevation profiles from MABEL with those acquired by an analog lidar show good agreement.Discrimination of ice and open water, a crucial step in the determination of sea ice free board and the estimation of ice thickness, is facilitated by contrasts in the observed signal background photon statistics. Future flight lines will sample a broader range of seasonal ice conditions for further evaluation of the year-round profiling capabilities and limitations of the MABEL instrument
Time-resolved dynamics of electron wave packets in chaotic and regular quantum billiards with leads
We perform numerical studies of the wave packet propagation through open
quantum billiards whose classical counterparts exhibit regular and chaotic
dynamics. We show that for t less or similar to tau (tau being the Heisenberg
time), the features in the transmitted and reflected currents are directly
related to specific classical trajectories connecting the billiard leads. In
contrast, the long-time asymptotics of the wave packet dynamics is
qualitatively different for classical and quantum billiards. In particularly,
the decay of the quantum system obeys a power law that depends on the number of
decay channels, and is not sensitive to the nature of classical dynamics
(chaotic or regular).Comment: 5 pages, 4 figure
A de Haas-van Alphen study of the filled skutterudite compounds PrOsAs and LaOsAs
Comprehensive magnetic-field-orientation dependent studies of the
susceptibility and de Haas-van Alphen effect have been carried out on single
crystals of the filled skutterudites PrOsAs and LaOsAs
using magnetic fields of up to 40~T. Several peaks are observed in the
low-field susceptibility of PrOsAs, corresponding to cascades of
metamagnetic transitions separating the low-field antiferromagnetic and
high-field paramagnetic metal (PMM) phases. The de Haas-van Alphen experiments
show that the Fermi-surface topologies of PrOsAs in its PMM phase
and LaOsAs are very similar. In addition, they are in reasonable
agreement with the predictions of bandstructure calculations for
LaOsAs on the PrOsAs lattice. Both observations suggest
that the Pr 4 electrons contribute little to the number of itinerant
quasiparticles in the PMM phase. However, whilst the properties of
LaOsAs suggest a conventional nonmagnetic Fermi liquid, the effects
of direct exchange and electron correlations are detected in the PMM phase of
PrOsAs. For example, the quasiparticle effective masses in
PrOsAs are found to decrease with increasing field, probably
reflecting the gradual suppression of magnetic fluctuations associated with
proximity to the low-temperature, low-field antiferromagnetic state
Size-resolved aerosol composition and its link to hygroscopicity at a forested site in Colorado
Aerosol hygroscopicity describes the ability of a particle to take up water
and form a cloud droplet. Modeling studies have shown sensitivity of
precipitation-producing cloud systems to the availability of aerosol
particles capable of serving as cloud condensation nuclei (CCN), and
hygroscopicity is a key parameter controlling the number of available CCN.
Continental aerosol is typically assumed to have a representative
hygroscopicity parameter, κ, of 0.3; however, in remote locations
this value can be lower due to relatively large mass fractions of organic
components. To further our understanding of aerosol properties in remote
areas, we measured size-resolved aerosol chemical composition and
hygroscopicity in a forested, mountainous site in Colorado during the
six-week BEACHON-RoMBAS (Bio-hydro-atmosphere interactions of Energy, Aerosols,
Carbon, H<sub>2</sub>O, Organics and Nitrogen–Rocky Mountain Biogenic
Aerosol Study) campaign. This campaign followed a year-long
measurement period at this site, and results from the intensive campaign
shed light on the previously reported seasonal cycle in aerosol
hygroscopicity. New particle formation events were observed routinely at
this site and nucleation mode composition measurements indicated that the
newly formed particles were predominantly organic. These events likely
contribute to the dominance of organic species at smaller sizes, where
aerosol organic mass fractions were between 70 and 90%. Corresponding
aerosol hygroscopicity was observed to be in the range κ = 0.15–0.22,
with hygroscopicity increasing with particle size. Aerosol chemical
composition measured by an aerosol mass spectrometer and calculated from
hygroscopicity measurements agreed very well during the intensive study, with
an assumed value of κ<sub>org</sub> = 0.13 resulting in the best
agreement
Reorientation of Anisotropy in a Square Well Quantum Hall Sample
We have measured magnetotransport at half-filled high Landau levels in a
quantum well with two occupied electric subbands. We find resistivities that
are {\em isotropic} in perpendicular magnetic field but become strongly {\em
anisotropic} at = 9/2 and 11/2 on tilting the field. The anisotropy
appears at an in-plane field, 2.5T, with the easy-current
direction {\em parallel} to but rotates by 90 at 10T and points now in the same direction as in single-subband samples.
This complex behavior is in quantitative agreement with theoretical
calculations based on a unidirectional charge density wave state model.Comment: 4 pages, 4 figure
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