Exercise stimulates the release of proteins with autocrine, paracrine, or endocrine functions produced in skeletal muscle, termed myokines. Based on the current state of knowledge, the major physiological function of myokines is to protect the functionality and to enhance the exercise capacity of skeletal muscle. Myokines control adaptive processes in skeletal muscle by acting as paracrine regulators of fuel oxidation, hypertrophy, angiogenesis, inflammatory processes, and regulation of the extracellular matrix. Endocrine functions attributed to myokines are involved in body weight regulation, low-grade inflammation, insulin sensitivity, suppression of tumor growth, and improvement of cognitive function. Muscle-derived regulatory RNAs and metabolites, as well as the design of modified myokines, are promising novel directions for treatment of chronic diseases.

/pdf/skeletal-muscle-as-an-endocrine-organ-the-role-of-myokines-4rrxre4ock.pdf

Skeletal Muscle as an Endocrine Organ: The Role of Myokines in Exercise Adaptations

THE charge-coupled device (CCD) has become the detector of choice in optical astronomy. CCDs provide a very linear response to detected photons, are very efficient at some wavelengths, and can now provide coverage of a relatively wide field of view1–3. But they become quite inefficient with decreasing wavelength, and they lack intrinsic wavelength and time resolution. The only way to select specific wavelengths is to place filters in front of the detector, which makes the total system less efficient. Time resolution can be achieved only with short exposures, which are possible only with very bright sources. Here we report a superconducting device that can overcome these limitations, and which has performance characteristics far superior to existing photon counting systems4–7. Our superconducting tunnel junction can detect individual photons at rates up to 2.5 kHz in the wavelength range 200–500 nm, with an intrinsic spectral resolution of 45 nm and a quantum efficiency estimated to be about 50 per cent. The theoretical resolution of the present device is ∼ 20 nm, but use of superconductors with lower transition temperature could improve that to 8 nm.

Single optical photon detection with a superconducting tunnel junction

We discuss the prospects and challenges for implementing a quantum computer using superconducting electronics. It appears that Josephson junction devices operating at milli-Kelvin temperatures can achieve a quantum dephasing time of milliseconds, allowing quantum coherent computations of 10/sup 10/ or more steps. This figure of merit is comparable to that of atomic systems currently being studied for quantum computation.

Prospects for quantum coherent computation using superconducting electronics

We have developed a theory of quasiparticle and phonon energy downconversion in nonequilibrium superconductors following the absorption of an energetic photon. This stage of energy downconversion cascade is important for the production of quasiparticles and is shown to split into two phases. The first is controlled by the evolution of the phonon distribution while the second is dominated by quasiparticle downconversion. The relative durations of the two phases and hence the rates of quasiparticle generation depend on material parameters, and most common superconductors could be classified into three different groups. For typical superconductors used for x-ray detection the downconversion cascade was shown to be fast compared to various time scales in the tunneling regime.

/pdf/quasiparticle-phonon-downconversion-in-nonequilibrium-3azfjsn7us.pdf

Quasiparticle-phonon downconversion in nonequilibrium superconductors

The hunting and gathering lifestyle adopted by human ancestors around 2 Ma required a large increase in aerobic activity. High levels of physical activity altered the shape of the human body, enabling access to new food resources (e.g. animal protein) in a changing environment. Recent experimental work provides strong evidence that both acute bouts of exercise and long-term exercise training increase the size of brain components and improve cognitive performance in humans and other taxa. However, to date, researchers have not explored the possibility that the increases in aerobic capacity and physical activity that occurred during human evolution directly influenced the human brain. Here, we hypothesize that proximate mechanisms linking physical activity and neurobiology in living species may help to explain changes in brain size and cognitive function during human evolution. We review evidence that selection acting on endurance increased baseline neurotrophin and growth factor signalling (compounds responsible for both brain growth and for metabolic regulation during exercise) in some mammals, which in turn led to increased overall brain growth and development. This hypothesis suggests that a significant portion of human neurobiology evolved due to selection acting on features unrelated to cognitive performance.

/pdf/linking-brains-and-brawn-exercise-and-the-evolution-of-human-4wrrzcve56.pdf

Linking brains and brawn: exercise and the evolution of human neurobiology.

Recent experimental results show a linear energy response in high quality Nb‐Al‐AlOx‐Nb superconducting tunnel junction detectors for photon energies between 1.5 and 6.4 keV. The experimental data are based on both direct x‐ray illumination and on the escape and re‐absorption of fluorescent photons created in the junction electrodes and in the silicon substrate. The observed linearity of the energy response raises questions on the validity of some theoretical models which describe the relaxation process occurring in a superconducting thin film after x‐ray photoabsorption. Such models generally predict nonlinear effects due to large quasiparticle number densities and short recombination times.

Response linearity of Nb tunnel junction detectors for photon energies from 1.5 to 6.4 keV

Response of niobium-based superconducting tunnel junctions in the soft-x-ray region 0.15-6.5 keV.

Superconducting Tunnel Junctions (STJ) are promising as X-ray detectors. However, they still do not reach their theoretical energy resolution due to various loss processes such as the diffusion of quasiparticles out of the electrode volume and trapping in regions of reduced energy gap. Low Temperature Scanning Electron Microscopy (LTSEM) allows the investigation of inhomogeneities in the response of superconducting Nb/AlO x /Nb tunnel junctions with high spatial resolution. In this way diffusion of quasiparticles and local trapping sites can be identified directly. The impact of these processes on the homogeneity of the signal height and the energy resolution can be visualized. Furthermore, the diffusion length and the lifetime of the quasiparticles is derived. Numerical simulations show that it is necessary to further reduce signal inhomogeneities due to diffusion processes and local traps to ensure a mayor improvement in the energy resolution.

Quasiparticle diffusion and loss processes in superconducting tunnel junctions

X-ray spectra at 6 keV from niobium based superconducting tunnel junctions with highly transmissive tunnel barriers are presented. Signals from the two films can clearly by discriminated by their different temporal and pulse height characteristics. Levels of tunneled charge as high as 2.7 X 106 electrons at 5.9 keV are observed. The best energy resolution obtained at T equals 1.2 K is 53 eV FWHM including electronic noise, for a 50 X 50 micrometers 2 device in a configuration where the x-ray source is collimated to selectively illuminate the center part of the device. Non-linearity is observed which appears dependent on film volume, implying that self recombination may play an important role in these devices. The energy resolution is found to degrade with increasing magnetic field. The spectra from the polycrystalline top film appear significantly degraded if magnetic flux is deliberately trapped in the device.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

High-resolution x-ray detection at 1.2 K with niobium superconducting tunnel junctions

The performance of photon detectors based on superconducting tunnel junctions are related to their current ‐ voltage (I‐V) curve characteristics and, ultimately, to the quality of the thin tunnel barriers (of order 1 nm) which separate the two superconducting thin films. Both the optimization of the spectroscopic performance of these detectors and the development of a reproducible and high yield fabrication route, require a better understanding of barrier quality and growth techniques. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) provide valuable tools for the investigation of the barrier region and for the control of the quality of the different thin films and related interfaces. In this paper, the results of a TEM and AFM evaluation of Nb‐Al‐AlOx‐Nb tunnel junctions are reported, together with their interpretation on the basis of the I‐V curve performance at low temperature (T≥0.3 K). Thickness disuniformities of the Al plus AlOx overlayer and evidence of barrier defects have...

Transmission electron microscopy and atomic force microscopy analysis of Nb‐Al‐AlOx‐Nb superconducting tunnel junction detectors

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