11,198 research outputs found

    Determination of convective diffusion heat/mass transfer rates to burner rig test targets comparable in size to cross-stream jet diameter

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    Two sets of experiments have been performed to be able to predict the convective diffusion heat/mass transfer rates to a cylindrical target whose height and diameter are comparable to, but less than, the diameter of the circular cross-stream jet, thereby simulating the same geometric configuration as a typical burner rig test specimen located in the cross-stream of the combustor exit nozzle. The first set exploits the naphthalene sublimation technique to determine the heat/mass transfer coefficient under isothermal conditions for various flow rates (Reynolds numbers). The second set, conducted at various combustion temperatures and Reynolds numbers, utilized the temperature variation along the surface of the above-mentioned target under steady-state conditions to estimate the effect of cooling (dilution) due to the entrainment of stagnant room temperature air. The experimental information obtained is used to predict high temperature, high velocity corrosive salt vapor deposition rates in burner rigs on collectors that are geometrically the same. The agreement with preliminary data obtained from Na2SO4 vapor deposition experiments is found to be excellent

    Minor salivary gland sialolithiasis: a clinical diagnostic challenge

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    Sialolithiasis is a non-neoplastic salivary gland disease that rarely affects the minor salivary glands. There are no guidelines in the literature which can suggest which is the best surgical approach to treat Minor Salivary Glands Sialolithiasis (MSGL). The present case was of a 48-year-old male patient complaining of painful swelling localized in the left back-commissural zone which was 0.5 mm in diameter, for which surgical enucleation approach was done and in that some small calcific masses ranging from 0.2 to 4 mm in diameter were found. They were surrounded by granulation tissue and associated with small pus oozing. Histopathological examination was carried out leading to a final diagnosis of MSGL

    Distributed Approximation Algorithms for Weighted Shortest Paths

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    A distributed network is modeled by a graph having nn nodes (processors) and diameter DD. We study the time complexity of approximating {\em weighted} (undirected) shortest paths on distributed networks with a O(logn)O(\log n) {\em bandwidth restriction} on edges (the standard synchronous \congest model). The question whether approximation algorithms help speed up the shortest paths (more precisely distance computation) was raised since at least 2004 by Elkin (SIGACT News 2004). The unweighted case of this problem is well-understood while its weighted counterpart is fundamental problem in the area of distributed approximation algorithms and remains widely open. We present new algorithms for computing both single-source shortest paths (\sssp) and all-pairs shortest paths (\apsp) in the weighted case. Our main result is an algorithm for \sssp. Previous results are the classic O(n)O(n)-time Bellman-Ford algorithm and an O~(n1/2+1/2k+D)\tilde O(n^{1/2+1/2k}+D)-time (8klog(k+1)1)(8k\lceil \log (k+1) \rceil -1)-approximation algorithm, for any integer k1k\geq 1, which follows from the result of Lenzen and Patt-Shamir (STOC 2013). (Note that Lenzen and Patt-Shamir in fact solve a harder problem, and we use O~()\tilde O(\cdot) to hide the O(\poly\log n) term.) We present an O~(n1/2D1/4+D)\tilde O(n^{1/2}D^{1/4}+D)-time (1+o(1))(1+o(1))-approximation algorithm for \sssp. This algorithm is {\em sublinear-time} as long as DD is sublinear, thus yielding a sublinear-time algorithm with almost optimal solution. When DD is small, our running time matches the lower bound of Ω~(n1/2+D)\tilde \Omega(n^{1/2}+D) by Das Sarma et al. (SICOMP 2012), which holds even when D=Θ(logn)D=\Theta(\log n), up to a \poly\log n factor.Comment: Full version of STOC 201

    Lubricated friction between incommensurate substrates

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    This paper is part of a study of the frictional dynamics of a confined solid lubricant film - modelled as a one-dimensional chain of interacting particles confined between two ideally incommensurate substrates, one of which is driven relative to the other through an attached spring moving at constant velocity. This model system is characterized by three inherent length scales; depending on the precise choice of incommensurability among them it displays a strikingly different tribological behavior. Contrary to two length-scale systems such as the standard Frenkel-Kontorova (FK) model, for large chain stiffness one finds that here the most favorable (lowest friction) sliding regime is achieved by chain-substrate incommensurabilities belonging to the class of non-quadratic irrational numbers (e.g., the spiral mean). The well-known golden mean (quadratic) incommensurability which slides best in the standard FK model shows instead higher kinetic-friction values. The underlying reason lies in the pinning properties of the lattice of solitons formed by the chain with the substrate having the closest periodicity, with the other slider.Comment: 14 pagine latex - elsart, including 4 figures, submitted to Tribology Internationa

    "Credit Cycle" in an OLG Economy with Money and Bequest

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    In the late '90s Kiyotaki and Moore (KM) put forward a new framework (Kiyotaki and Moore,1997) to explore the Financial Accelerator hypothesis. The original model was framed in an Infinitely Lived Agent context (ILA-KM economy). As in KM we develop a dynamic model in which the durable asset ("land") is not only an input but also collateralizable wealth to secure lenders from the risk of borrowers' default. In this paper, however, we model an OLG-KM economy whose novel feature is the role of money as a store of value and of bequest as a vehicle of resources to be "invested" in landholding. The dynamics generated by the model are complex. Not only cyclical patterns are routinely generated but the periodicity and amplitude are irregular. A route to chaotic dynamics is open.

    Meeting in a Polygon by Anonymous Oblivious Robots

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    The Meeting problem for k2k\geq 2 searchers in a polygon PP (possibly with holes) consists in making the searchers move within PP, according to a distributed algorithm, in such a way that at least two of them eventually come to see each other, regardless of their initial positions. The polygon is initially unknown to the searchers, and its edges obstruct both movement and vision. Depending on the shape of PP, we minimize the number of searchers kk for which the Meeting problem is solvable. Specifically, if PP has a rotational symmetry of order σ\sigma (where σ=1\sigma=1 corresponds to no rotational symmetry), we prove that k=σ+1k=\sigma+1 searchers are sufficient, and the bound is tight. Furthermore, we give an improved algorithm that optimally solves the Meeting problem with k=2k=2 searchers in all polygons whose barycenter is not in a hole (which includes the polygons with no holes). Our algorithms can be implemented in a variety of standard models of mobile robots operating in Look-Compute-Move cycles. For instance, if the searchers have memory but are anonymous, asynchronous, and have no agreement on a coordinate system or a notion of clockwise direction, then our algorithms work even if the initial memory contents of the searchers are arbitrary and possibly misleading. Moreover, oblivious searchers can execute our algorithms as well, encoding information by carefully positioning themselves within the polygon. This code is computable with basic arithmetic operations, and each searcher can geometrically construct its own destination point at each cycle using only a compass. We stress that such memoryless searchers may be located anywhere in the polygon when the execution begins, and hence the information they initially encode is arbitrary. Our algorithms use a self-stabilizing map construction subroutine which is of independent interest.Comment: 37 pages, 9 figure

    Retroperitoneal fibrosis: a case of a patient (63y/o) treated with low-dose methotrexate (MTX) and 6-methylprednisolone (6-MP)

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    Retroperitoneal fibrosis (RPF), is a rare fibroinflammatory disease. The pathogenesis of RPF is still unclear and numerous theories have been reported such as environmental factors, immunologic process, genetic component, local inflammation and advanced atherosclerosis. RPF is characterized by the presence of a particular retroperitoneal fibrotic tissue which is white, woody and involving retroperitoneal structures such as the great vessels, ureters and psoas muscle. The main complication of RPF is the obstruction of local structures such as the ureters due to the fibrosis and the treatment of this aspect represents the main challenge for this pathology. RPF medical treatment consists of corticosteroids or/and immunosuppressive therapy. We report a case of a patient (63y/o) affected by idiopathic RPF treated with low-dose methotrexate (MTX) and 6-methylprednisolone (6-MP) for two years, describing and confirming the effectiveness and safety of a long-term low-dose MTX and 6-MP treatment
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