Experimental investigation of flow pattern around repelling and attracting T-head spur dikes on flat bed

Use of T-head spur dikes is one of the common methods to control erosion of riverbanks. Nevertheless, setting spur dikes in the flow direction leads to modification of flow path and local scour in the site of the spur dike. In case of intensification, this can destruct the structure and the riverbank. Therefore, understanding its mechanism and characteristics are crucial. The main objective of this study is to investigate and compare the flow pattern around submerged attracting and repelling T-head spur dikes in a flat bed. The experimental Flume was a rectangular channel with bed width of 92 cm, bank height of 60 cm and length of 8.7 m. around spur dike at 24 cross sections, 16 profiles and 3 depths velocity was measured by 2-D electromagnetic velocimeter. The results showed that downflow in upstream of repelling spur dike is stronger than the downstream part and the Length of downstream circulation zone is larger in attracting spur dike.Keywords: T-head spur dike; repelling spur dike; attracting spur dike; flat be

Retroperitoneal extramedullary hematopoietic pseudotumor in ataxia-telangiectasia.

Ataxia-telangiectasia confers a significant increase in the development of several cancer types, most commonly leukemia and lymphoma. However, as the natural history for these patients is evolving and their lifespan is increasing, there is the potential for the development of additional uncommon tumors in an already rare patient population. We report the first case, to our knowledge, of an incidental retroperitoneal tumor in a 26-year-old woman undergoing evaluation for hepatic dysfunction. The mass was suspicious for retroperitoneal sarcoma, but proved to be an extramedullary hematopoietic pseudotumor after extensive pathologic evaluation. The changing landscape of neoplasms associated with ataxia-telangiectasia is discussed with emphasis on previously underreported benign and malignant tumors

The long term effects of occupational electromagnetic fields exposure on peripheral blood indexes in workers of aluminum processing factory of Arak

زمینه و هدف: نظریه بیماری زا بودن میدان های الکترومغناطیسی بر روی ساکنان و کارکنان مجاور این میدان ها بخصوص کارسینوژن بودن آنها مورد مطالعات زیادی قرار گرفته است. ولی نتایج آنها قطعیت نیافته و هنوز مناقشات زیادی در این مورد وجود دارد. این تحقیق به منظور بررسی اثر میدان های الکترومغناطیسی با شدت بالا بر شاخص های خون محیطی افرادی که بطور طولانی مدت (حداقل سه سال) در مجاورت این میدان ها بوده اند طراحی و اجرا گردید. روش بررسی: در یک مطالعه آینده نگر کارگرانی که در کارگاه الکترولیز کارخانه آلومینیوم اراک کار می کنند مورد بررسی قرار گرفتند. ابتدا با کمک گروه بهداشت صنعتی از قسمت های مختلف کارگاه الکترولیز گوس متری به عمل آمد و سپس دویست نفر از کارگران شاغل در کارگاه انتخاب و دویست نفر نیز از افرادی که در سایر قسمت ها شاغل بوده و در معرض میدان مغناطیسی نبودند با رعایت معیارهای ورود انتخاب شدند و هر دو گروه از نظر شرح حال، معاینه بالینی بررسی و پرسشنامه برای آنها تکمیل شد. سپس در دو نوبت به فاصله یکسال برای هر دو گروه CBC و شمارش پلاکت انجام شد. نهایتاً داده ها با استفاده از آمار توصیفی و تحلیلی (t مستقل) و نرم افزار SPSS تجزیه و تحلیل گردید. یافته ها: افراد دو گروه از نظر میانگین سنی و جنسی تفاوتی نداشتند. میانگین شاخص های خونی گروه مواجهه یافته در دو سال متوالی در رده گلبول های سفید، نوتروفیل ها، گلبول های قرمز، هموگلوبین، هماتوکریت و MCV بیشتر از گروه مواجهه نیافته بود (05/0

Advances on Matroid Secretary Problems: Free Order Model and Laminar Case

The most well-known conjecture in the context of matroid secretary problems claims the existence of a constant-factor approximation applicable to any matroid. Whereas this conjecture remains open, modified forms of it were shown to be true, when assuming that the assignment of weights to the secretaries is not adversarial but uniformly random (Soto [SODA 2011], Oveis Gharan and Vondr\'ak [ESA 2011]). However, so far, there was no variant of the matroid secretary problem with adversarial weight assignment for which a constant-factor approximation was found. We address this point by presenting a 9-approximation for the \emph{free order model}, a model suggested shortly after the introduction of the matroid secretary problem, and for which no constant-factor approximation was known so far. The free order model is a relaxed version of the original matroid secretary problem, with the only difference that one can choose the order in which secretaries are interviewed. Furthermore, we consider the classical matroid secretary problem for the special case of laminar matroids. Only recently, a constant-factor approximation has been found for this case, using a clever but rather involved method and analysis (Im and Wang, [SODA 2011]) that leads to a 16000/3-approximation. This is arguably the most involved special case of the matroid secretary problem for which a constant-factor approximation is known. We present a considerably simpler and stronger $3\sqrt{3}e\approx 14.12$-approximation, based on reducing the problem to a matroid secretary problem on a partition matroid

Streaming Algorithms for Submodular Function Maximization

We consider the problem of maximizing a nonnegative submodular set function $f:2^{\mathcal{N}} \rightarrow \mathbb{R}^+$ subject to a $p$-matchoid constraint in the single-pass streaming setting. Previous work in this context has considered streaming algorithms for modular functions and monotone submodular functions. The main result is for submodular functions that are {\em non-monotone}. We describe deterministic and randomized algorithms that obtain a $\Omega(\frac{1}{p})$-approximation using $O(k \log k)$-space, where $k$ is an upper bound on the cardinality of the desired set. The model assumes value oracle access to $f$ and membership oracles for the matroids defining the $p$-matchoid constraint.Comment: 29 pages, 7 figures, extended abstract to appear in ICALP 201

A PTAS for planar group Steiner tree via spanner bootstrapping and prize collecting

We present the first polynomial-time approximation scheme (PTAS), i.e., (1 + ϵ)-approximation algorithm for any constant ϵ > 0, for the planar group Steiner tree problem (in which each group lies on a boundary of a face). This result improves on the best previous approximation factor of O(logn(loglogn)O(1)). We achieve this result via a novel and powerful technique called spanner bootstrapping, which allows one to bootstrap from a superconstant approximation factor (even superpolynomial in the input size) all the way down to a PTAS. This is in contrast with the popular existing approach for planar PTASs of constructing lightweight spanners in one iteration, which notably requires a constant-factor approximate solution to start from. Spanner bootstrapping removes one of the main barriers for designing PTASs for problems which have no known constant-factor approximation (even on planar graphs), and thus can be used to obtain PTASs for several difficult-to-approximate problems. Our second major contribution required for the planar group Steiner tree PTAS is a spanner construction, which reduces the graph to have total weight within a factor of the optimal solution while approximately preserving the optimal solution. This is particularly challenging because group Steiner tree requires deciding which terminal in each group to connect by the tree, making it much harder than recent previous approaches to construct spanners for planar TSP by Klein [SIAM J. Computing 2008], subset TSP by Klein [STOC 2006], Steiner tree by Borradaile, Klein, and Mathieu [ACM Trans. Algorithms 2009], and Steiner forest by Bateni, Hajiaghayi, and Marx [J. ACM 2011] (and its improvement to an efficient PTAS by Eisenstat, Klein, and Mathieu [SODA 2012]. The main conceptual contribution here is realizing that selecting which terminals may be relevant is essentially a complicated prize-collecting process: we have to carefully weigh the cost and benefits of reaching or avoiding certain terminals in the spanner. Via a sequence of involved prize-collecting procedures, we can construct a spanner that reaches a set of terminals that is sufficient for an almost-optimal solution. Our PTAS for planar group Steiner tree implies the first PTAS for geometric Euclidean group Steiner tree with obstacles, as well as a (2 + ϵ)-approximation algorithm for group TSP with obstacles, improving over the best previous constant-factor approximation algorithms. By contrast, we show that planar group Steiner forest, a slight generalization of planar group Steiner tree, is APX-hard on planar graphs of treewidth 3, even if the groups are pairwise disjoint and every group is a vertex or an edge

Consistency vs. Availability in Distributed Real-Time Systems

In distributed applications, Brewer's CAP theorem tells us that when networks become partitioned (P), one must give up either consistency (C) or availability (A). Consistency is agreement on the values of shared variables; availability is the ability to respond to reads and writes accessing those shared variables. Availability is a real-time property whereas consistency is a logical property. We have extended the CAP theorem to relate quantitative measures of these two properties to quantitative measures of communication and computation latency (L), obtaining a relation called the CAL theorem that is linear in a max-plus algebra. This paper shows how to use the CAL theorem in various ways to help design real-time systems. We develop a methodology for systematically trading off availability and consistency in application-specific ways and to guide the system designer when putting functionality in end devices, in edge computers, or in the cloud. We build on the Lingua Franca coordination language to provide system designers with concrete analysis and design tools to make the required tradeoffs in deployable software.Comment: 12 pages. arXiv admin note: text overlap with arXiv:2109.0777

Modal Reactors

Complex software systems often feature distinct modes of operation, each designed to handle a particular scenario that may require the system to respond in a certain way. Breaking down system behavior into mutually exclusive modes and discrete transitions between modes is a commonly used strategy to reduce implementation complexity and promote code readability. However, such capabilities often come in the form of self-contained domain specific languages or language-specific frameworks. The work in this paper aims to bring the advantages of modal models to mainstream programming languages, by following the polyglot coordination approach of Lingua Franca (LF), in which verbatim target code (e.g., C, C++, Python, Typescript, or Rust) is encapsulated in composable reactive components called reactors. Reactors can form a dataflow network, are triggered by timed as well as sporadic events, execute concurrently, and can be distributed across nodes on a network. With modal models in LF, we introduce a lean extension to the concept of reactors that enables the coordination of reactive tasks based on modes of operation. The implementation of modal reactors outlined in this paper generalizes to any LF-supported language with only modest modifications to the generic runtime system

THE PERFORMANCE OF THE ICE HOCKEY SLAP SHOT: THE EFFECTS TO STICK CONSTRUCTION AND PLAYER SKILL

The purpose of this study was to examine the interaction of players’ skill level, body strength, and sticks of various construction and stiffness on the performance of the slap shot in ice hockey. Twenty male players were tested: ten skilled, and ten unskilled. Each subject performed three slap shots with three sticks of different construction and shaft stiffness. Ground contact forces were measured while simultaneously video recording at 480 frames/second the stick movement and bending. The results indicated that 1) puck velocity was influenced by skill level and body strength but not stick type and that 2) variability in performance measures across subjects was greater than the variability across the stick stiffness. Further studies are needed to address the specific influence body strength and skill on the slap shot