5,133 research outputs found

    Finite size Berezinski-Kosterlitz-Thouless transition at grain boundaries in solid 4^4He and role of 3^3He impurities

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    We analyze the complex phenomenology of the Non-Classical Rotational Inertia (NCRI) observed at low temperature in solid 4^4He within the context of a two dimensional Berezinski-Kosterlitz-Thouless transition in a premelted 4^4He film at the grain boundaries. We show that both the temperature and 3^3He doping dependence of the NCRI fraction (NCRIF) can be ascribed to finite size effects induced by the finite grain size. We give an estimate of the average size of the grains which we argue to be limited by the isotopic 3^3He impurities and we provide a simple power-law relation between the NCRIF and the 3^3He concentration.Comment: Final version, as appearing on prin

    Connections Between Adaptive Control and Optimization in Machine Learning

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    This paper demonstrates many immediate connections between adaptive control and optimization methods commonly employed in machine learning. Starting from common output error formulations, similarities in update law modifications are examined. Concepts in stability, performance, and learning, common to both fields are then discussed. Building on the similarities in update laws and common concepts, new intersections and opportunities for improved algorithm analysis are provided. In particular, a specific problem related to higher order learning is solved through insights obtained from these intersections.Comment: 18 page

    Microcorrosion Casts in the Microcirculation of Skeletal Muscle

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    The authors review the contribution of microcorrosion cast studies towards clarifying the structure of skeletal muscle microcirculation. Former studies performed on naturally contracted muscles show the presence of a primary and a secondary arterial network and a capillary network. At the level of the capillary network pericyte imprints are present. Muscles characterized by different types of metabolism show different features of the capillary pattern. Other authors have affirmed that the extended muscle is characterized by long and straight capillaries, while the contracted one features clusters of vessels all around a muscle fiber. The authors have made the present observations in order to determine how the capillary pattern of muscles with different metabolism is modified by extension and shortening of the muscle belly. The capillary pattern observed appears very similar to that observed in former studies. The differences between the oxidative and the glycolytic muscle are evident in every condition of the muscle belly. These data confirm the theory that there is a permanent endogenous difference in microcirculation between oxidative and glycolytic muscle, determined by muscle fiber metabolism

    Zero sound in a single component fermion - Bose Einstein Condensate mixture

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    The resonant dynamics of mediated interactions supports zero-sound in a cold atom degenerate mixture of a single component fermion gas and a Bose-Einstein condensate (BEC). We characterize the onset of instability in the phase separation of an unstable mixture and we find a rich collective mode structure for stable mixtures with one undamped mode that exhibits an avoided crossing and a Landau-damped mode that terminates.Comment: 4 pages, 2 figure

    A Three-Dimensional Study of the Morphology and Topography of Pericytes in the Microvascular Bed of Skeletal Muscle

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    Digested tissue specimens and corrosion casts of rat soleus and tibialis anterior muscles were employed for this Scanning Electron Microscopy (SEM) study. The shape, morphology, and position of pericytes were compared to corresponding imprints on the cast surfaces. Pericytes, observed in digested tissue specimens, showed a typical morphological pattern: a central body with two primary processes that run along the capillary in opposite directions. From these primary processes, secondary ones arise and often encircle the vessel almost completely. On the surface of corrosion casts, roundish imprints were found in the microvascular tree at the same level where digested tissue specimens showed the presence of pericyte bodies. Along and around the cast surface, shallow grooves reproduced the course of the primary and secondary processes. The peculiar tridimensional arrangement of pericytes at the level of capillary bifurcations underlines their role in red cell flow regulation. However, if the mechanical linkage of the pericytes to the endothelium and their contractability is taken into account, additional roles of these perivascular cells may be hypothesized

    Microcorrosion Casting in Normal and Pathological Biliary Tree Morphology

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    The organization of the intrahepatic biliary tree was studied in three dimensions by scanning electron microscopic (SEM) corrosion casts, in normal and cholestatic rat liver. In the normal liver the observation revealed the features of the biliary passages from the bile canaliculi to the canaliculo-ductular junction, to the ductules and the bile ducts, confirming previous SEM observations. In cholestatic liver, the modifications and the proliferation of bile ductules appear clearly. Resin flow from canalicular to sinusoidal network was never observed. The method was found to be very useful in the evaluation of the architecture of the intrahepatic biliary tree, under normal as well as under pathological conditions

    A novel ultrafast-low-dose computed tomography protocol allows concomitant coronary artery evaluation and lung cancer screening

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    BACKGROUND:Cardiac computed tomography (CT) is often performed in patients who are at high risk for lung cancer in whom screening is currently recommended. We tested diagnostic ability and radiation exposure of a novel ultra-low-dose CT protocol that allows concomitant coronary artery evaluation and lung screening. METHODS: We studied 30 current or former heavy smoker subjects with suspected or known coronary artery disease who underwent CT assessment of both coronary arteries and thoracic area (Revolution CT, General Electric). A new ultrafast-low-dose single protocol was used for ECG-gated helical acquisition of the heart and the whole chest. A single IV iodine bolus (70-90 ml) was used. All patients with CT evidence of coronary stenosis underwent also invasive coronary angiography. RESULTS: All the coronary segments were assessable in 28/30 (93%) patients. Only 8 coronary segments were not assessable in 2 patients due to motion artefacts (assessability: 98%; 477/485 segments). In the assessable segments, 20/21 significant stenoses (> 70% reduction of vessel diameter) were correctly diagnosed. Pulmonary nodules were detected in 5 patients, thus requiring to schedule follow-up surveillance CT thorax. Effective dose was 1.3 ± 0.9 mSv (range: 0.8-3.2 mSv). Noteworthy, no contrast or radiation dose increment was required with the new protocol as compared to conventional coronary CT protocol. CONCLUSIONS:The novel ultrafast-low-dose CT protocol allows lung cancer screening at time of coronary artery evaluation. The new approach might enhance the cost-effectiveness of coronary CT in heavy smokers with suspected or known coronary artery disease
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