Contests Hosting Service as a tool to teach programming

Computer science would not exist without the concept of algorithm. Therefore design of algorithms plays an important role in education while implementation is usually considered to be straightforward. Increasing variety of programming languages, wealth of possible constructions, programming environments and tools makes programming difficult for the beginners.Apart from the idea of problem solution, it is important to teach programming skills. Size of classes of 10-20 pupils and a limited number of lessons and their short time are the major problem. The teacher has to check solution of every pupil, compile it and run tests. This is definitely a time-consuming process which makes teaching difficult. In this paper the authors present the use of problem solutions validation systems during classes. With the help of such a system called Zawody WEB, the authors teach algorithms and programming for the secondary school students

Approximation Algorithms for the Joint Replenishment Problem with Deadlines

The Joint Replenishment Problem (JRP) is a fundamental optimization problem in supply-chain management, concerned with optimizing the flow of goods from a supplier to retailers. Over time, in response to demands at the retailers, the supplier ships orders, via a warehouse, to the retailers. The objective is to schedule these orders to minimize the sum of ordering costs and retailers' waiting costs. We study the approximability of JRP-D, the version of JRP with deadlines, where instead of waiting costs the retailers impose strict deadlines. We study the integrality gap of the standard linear-program (LP) relaxation, giving a lower bound of 1.207, a stronger, computer-assisted lower bound of 1.245, as well as an upper bound and approximation ratio of 1.574. The best previous upper bound and approximation ratio was 1.667; no lower bound was previously published. For the special case when all demand periods are of equal length we give an upper bound of 1.5, a lower bound of 1.2, and show APX-hardness

Influence of polymer binder structure on the properties of the graphite anode for lithium-ion batteries

This paper discusses the impact of the structure and properties of three different polymer binders: polyvinylidene fluoride, sodium carboxymethyl cellulose and polyvinyl alcohol, on the electrochemical properties of spherical graphite anodes for Li-ion batteries. Electrochemical tests indicate that the nature of polyvinylidene fluoride contributes in decreasing the cycle life of graphite electrodes in contrast to effective water-based binders. This study demonstrates the possibility of manufacturing graphite-based electrode for Li-ion batteries that cycle longer and use water in the processing, instead of hazardous organic solvents like N-methylpyrrolidone, thereby improving performance, reducing cost and protecting the environment

Potentially positive ageing-related variations of medial smooth muscle cells in the saphenous veins used as aortocoronary bypass grafts

Introduction. Currently, elderly people constitute a large proportion of patients undergoing coronary artery bypass grafting (CABG). Activated smooth muscle cells in the tunica media of saphenous vein (SV) grafts are thought to play a key role in the formation of neointima and development of occluding atherosclerotic plaques. The aim of this study was to identify ageing-related variations in the expression of the smooth muscle cells pro­teins that may impact on patency rate of the grafts and the CABG outcomes. Material and methods. The study involved 216 consecutive patients with the mean of 62.7 ± 8.4 years who underwent isolated CABG with at least one SV aortocoronary bypass graft. Expression of a-smooth muscle actin (a-SM actin), smooth muscle-myosin heavy chain (SM-MHC), calponin (CALP), cytokeratin 8 (CK-8), metalloproteinase-2 (MMP-2) and tissue inhibitors of metalloproteinases-2 and -3 (TIMP-2, TIMP-3) in the SV wall was assessed by immunohistochemistry and correlated with the age of patients. Results. Calponin and a-SM actin were expressed in all studied SV transplants. SM-MHC immunoreactivity was observed in SV segments in 68.5% of patients, whereas MMP-2a and TIMPs expression was found in 75% of cases. In more than 50% of analyzed SV transplants, no expression of cytokeratin-8 was found. Moderate correlations between preexisting expressions of either cytoskeletal or hemostatic proteins in the tunica media of the SV grafts and the age of CABG patients were demonstrated. They were positive for SM-MHC (r = 0.494), CALP (r = 0.548), TIMP-2 (r = 0.413) and TIMP-3 (r = 0.406) whereas negative for CK-8 (r = –0.528) and MMP-2 (r = –0.417). Conclusions. Age-dependent decreases in the expression of MMP-2 and CK-8 accompanied by increases in expression of SM-MHC, TIMP-2 and TIMP-3 may promote SV graft patency and, thus, suggest a rationale for common use of SV grafts in the elderly

Wpływ stopnia nawodnienia oraz zmienności ciśnienia tętniczego krwi i częstości rytmu serca w czasie hemodializy na śróddializacyjne zmiany stężeń wysokoczułej troponiny T

Introduction. High sensitivity troponin T (TnT-hs) is biomarker of myocardial damage and ischemia. Despite its elevation troponin still preserve its usefulness as a marker of the cardiovascular risk and mortality in chronic kidney disease. Variations of hydration status between and during hemodialysis exert significant hemodynamic effects, which may negatively affect cardiovascular system and blood pressure and lead to myocardial damage. The aim of the study was to access the effect of hydration status and variability of blood pressure and heart rate induced by hemodialysis on intradialytic changes of TnT-hs, in chronic hemodialysis patients. Material and methods. In 50 chronic hemodialysis patients (35M, 15F, mean age 64 ± 12 years) blood pressure and heart rate were monitored noninvasively during HD session. Serum concentration of TnT-hs and hydration status were assessed before and after hemodialysis. Results. TnT-hs concentration was above normal range in 98% patients before, and in all after hemodialysis. Median TnT-hs level was 82 ng/L before and 84 ng/L after hemodialysis, which comprised 586% and 600% of the upper limit of normal range. There was a small 2.4%, intradialytic increase of TnT-hs (p = 0.004). TnT-hs levels correlated positively with mean interdialytic weigh gain, before HD (r = 0.43, p = 0.02) and after HD (r = 0.5, p = 0.003). There was also a positive correlation between TnT-hs concentration and mean heart rate (r = 0.37, p = 0.008) and with mean systolic blood pressure during HD, before HD (r = 0.3, p = 0.026) and after HD (r = 0.3, p = 0.031). Conclusions. Hemodialysis can be a risk factor of myocardial injury, especially in overhydrated patients.Wstęp. Wysokoczuła troponina T (TnT-hs) jest przydatnym klinicznie wskaźnikiem uszkodzenia komórek mięśnia sercowego. Stężenia TnT-hs u pacjentów z przewlekłą chorobą nerek są wyższe niż w populacji ogólnej, co wiąże się ze zwiększonym ryzykiem incydentów sercowo-naczyniowych oraz zgonu. Znaczne zmiany stopnia nawodnienia w czasie zabiegu hemodializy mogą niekorzystnie oddziaływać na układ sercowo-naczyniowy i ciśnienie tętnicze, co w efekcie może prowadzić do uszkodzenia kardiomiocytów. Celem pracy była ocena wpływu stanu nawodnienia, zmian częstości rytmu serca (HR) i ciśnienia tętniczego (BP) w trakcie hemodializy (HD) na zmiany stężeń TnT-hs powodowane zabiegiem hemodializy u pacjentów długotrwale hemodializowanych. Materiał i metody. U 50 pacjentów (35M, 15K, średnia wieku 64 ± 12 lat) z rozpoznaniem schyłkowej niewydolności nerek, długotrwale hemodializowanych, nieinwazyjnie monitorowano BP oraz HR podczas HD. Przed i po HD dokonano oceny stanu nawodnienia pacjenta oraz pobrano próbki krwi w celu oznaczenia stężenia TnT-hs. Wyniki. Zwiększone stężenie w surowicy TnT-hs stwierdzono u 98% pacjentów przed zabiegiem HD oraz u 100% pacjentów po zabiegu. Mediana TnT-hs wynosiła 82ng/l przed HD i 84 ng/l po zabiegu, co wyniosło odpowiednio 586% oraz 600% wartości górnego zakresu referencyjnego. Stężenie TnT-hs podczas HD wzrastało nieznacznie o 2,4% (p = 0,04). Stężenie TnT-hs przed HD i po zabiegu korelowało ze średnim HR (r = 0,37; p = 0,008) oraz średnim skurczowym BP podczas zabiegu HD (przed HD r = 0,32; p = 0,026 i po HD r = 0,3; p = 0,031). Wykazano dodatnią korelację między przewodnieniem pomiędzy dializami a stężeniem TnT-hs przed HD (r = 0,43, p = 0,02) i po HD (r = 0,5, p = 0,003). Wnioski. Zabieg hemodializy może zwiększać ryzyko uszkodzenia mięśnia sercowego, w szczególności w przypadku znacznego stopnia przewodnienia

Porównanie przydatności 3D angio-TK z innymi metodami oceny morfologii tętniaka aorty brzusznej przed planowanym zabiegiem przezskórnej implantacji stent-graftu

Background: The purpose of this study was to examine the accuracy of diagnostic methods in the preoperative evaluation of abdominal aortic aneurysm before endovascular treatment. Material/Methods: During the period of January 2002-December 2004, 67 patients with AAA (42 diagnosed in the Department of Radiology of the Central Clinical Hospital of the Ministry of Internal Affairs and Administration and 25 patients diagnosed the in the Department of Radiology of Medical Academy in Bialystok) underwent ultrasonography, spiral CT with 3D reconstructions (3D CTA), and digital subtraction angiography (DSA) following treatment of aortoiliac aneurysms with endoluminal stentgrafts in 36 and 12 patients, respectively. Results/Conclusions: Our experience suggests that spiral computerized tomographic angiography with three-dimensional reconstruction (3D CTA) is a reliable, relatively noninvasive technique to assess the feasibility of endovascular aneurysm repair. DSA allows verification of the measurements from spiral computed scans, but it is a more invasive method than CTA. However, CTA with 3D reconstruction shows a diagnostic effectiveness similar to that of DSA. Thus it may be sufficient as a preoperative imaging technique when evaluating a patient for an endovascular graft procedure