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Peltier cells are commonly used in low-power cooling applications, such as automotive refrigerators and electronics temperature regulation systems. These applications are typically low-energy in nature. There is currently a growing emphasis on energy conservation and waste heat utilization in the energy industry. This paper explores the possibility of improving the heating or cooling coefficient of performance (COP) of Peltier cells through intelligent serial and parallel connections. The purpose of this work is to raise the question of whether it would be possible to reconsider the concept of harnessing the “energy” potential of Peltier cells. The utilized model is in line with the current state of the art, and the case study is based on parameters measured on a commercially available Peltier cell. The resulting COP, when considering current materials, remains inferior to the COP of compressor-based heat pumps. For low-power devices, it can represent a technically and economically comparable solution.

Background The association between cardiovascular mortality and winter cold spells was evaluated in the population of the Czech Republic over 21-yr period 1986–2006. No comprehensive study on cold-related mortality in central Europe has been carried out despite the fact that cold air invasions are more frequent and severe in this region than in western and southern Europe. Methods Cold spells were defined as periods of days on which air temperature does not exceed -3.5°C. Days on which mortality was affected by epidemics of influenza/acute respiratory infections were identified and omitted from the analysis. Excess cardiovascular mortality was determined after the long-term changes and the seasonal cycle in mortality had been removed. Excess mortality during and after cold spells was examined in individual age groups and genders. Results Cold spells were associated with positive mean excess cardiovascular mortality in all age groups (25–59, 60–69, 70–79 and 80+ years) and in both men and women. The relative mortality effects were most pronounced and most direct in middle-aged men (25–59 years), which contrasts with majority of studies on cold-related mortality in other regions. The estimated excess mortality during the severe cold spells in January 1987 (+274 cardiovascular deaths) is comparable to that attributed to the most severe heat wave in this region in 1994. Conclusion The results show that cold stress has a considerable impact on mortality in central Europe, representing a public health threat of an importance similar to heat waves. The elevated mortality risks in men aged 25–59 years may be related to occupational exposure of large numbers of men working outdoors in winter. Early warnings and preventive measures based on weather forecast and targeted on the susceptible parts of the population may help mitigate the effects of cold spells and save lives.

An abstract topological graph (briefly an AT-graph) is a pair A=(G,X) where G=(V,E) is a graph and X⊆E2 is a set of pairs of its edges. The AT-graph A is simply realizable if G can be drawn in the plane so that each pair of edges from X crosses exactly once and no other pair crosses. We show that simply realizable complete AT-graphs are characterized by a finite set of forbidden AT-subgraphs, each with at most six vertices. This implies a straightforward polynomial algorithm for testing simple realizability of complete AT-graphs, which simplifies a previous algorithm by the author. We also show an analogous result for independent Z2-realizability, where only the parity of the number of crossings for each pair of independent edges is specified.

Background: The Global Influenza Hospital Surveillance Network is an international platform whose primary objective is to study severe cases of influenza requiring hospitalization. Methods: During the 2015-2016 influenza season, 11 sites in the Global Influenza Hospital Surveillance Network in nine countries (Russian Federation, Czech Republic, Turkey, France, China, Spain, Mexico, India, and Brazil) participated in a prospective, active-surveillance, hospital-based epidemiological study. Influenza infection was confirmed by reverse transcription-polymerase chain reaction. Influenza vaccine effectiveness (IVE) against laboratory-confirmed influenza was estimated using a test-negative approach. Results: 9882 patients with laboratory results were included of which 2415 (24.4%) were positive for influenza, including 1415 (14.3%) for A(H1N1)pdm09, 235 (2.4%) for A(H3N2), 180 (1.8%) for A not subtyped, 45 (0.5%) for B/Yamagata-lineage, 532 (5.4%) for B/Victoria-lineage, and 33 (0.3%) for B not subtyped. Of included admissions, 39% were < 5 years of age and 67% had no underlying conditions. The odds of being admitted with influenza were higher among pregnant than non-pregnant women (odds ratio, 2.82 [95% confidence interval (CI), 1.90 to 4.19]). Adjusted IVE against influenza-related hospitalization was 16.3% (95% CI, 0.4 to 29.7). Among patients targeted for influenza vaccination, adjusted IVE against hospital admission with influenza was 16.2% (95% CI, - 3.6 to 32.2) overall, 23.0% (95% CI, - 3.3 to 42.6) against A(H1N1)pdm09, and - 25.6% (95% CI, - 86.3 to 15.4) against B/Victoria lineage. Conclusions: The 2015-2016 influenza season was dominated by A(H1N1)pdm09 and B/Victoria-lineage. Hospitalization with influenza often occurred in healthy and young individuals, and pregnant women were at increased risk of influenza-related hospitalization. Influenza vaccines provided low to moderate protection against hospitalization with influenza and no protection against the predominant circulating B lineage, highlighting the need for more effective and broader influenza vaccines.

Background To improve national influenza vaccination recommendations, additional data on influenza A and B virus circulation are needed. Here, we describe the circulation of influenza A and B in the Czech Republic during 16 seasons. Methods This was a retrospective analysis of data collected from the 2000–2001 to 2015–2016 influenza seasons by the Czech Republic national influenza surveillance network. Influenza was confirmed and viral isolates subtyped by virological assays followed by antigen detection or by reverse transcriptase-polymerase chain reaction. Results Of 16,940 samples collected, 5144 (30.4%) were influenza-positive. Influenza A represented 78.6% of positive cases overall and accounted for more than 55.0% of all influenza cases in every season, except for 2005–2006 (6.0%). Both A/H1N1 and A/H3N2 were detected in most seasons, except for 2001–2002 and 2003–2004 (only A/H3N2), and 2007–2008 and 2009–2010 (only A/H1N1). Influenza B represented 21.4% of positive cases overall (range, 0.0–94.0% per season). Both influenza B lineages were detected in three seasons, a single B lineage in 11, and no B strain in two. For the 11 seasons where influenza B accounted for ≥20% of positive cases, the dominant lineage was Yamagata in six and Victoria in four. In the remaining season, the two lineages co-circulated. For two seasons (2005–2006 and 2007–2008), the B lineage in the trivalent influenza vaccine did not match the dominant circulating B lineage. Conclusions In the Czech Republic, during the 2000–2001 to 2015–2016 influenza seasons, influenza virus circulation varied considerably. Although influenza A accounted for the most cases in almost all seasons, influenza B made a substantial, sometimes dominant, contribution to influenza disease.

A simple topological graph T = ( V ( T ) , E ( T ) ) is a drawing of a graph in the plane where every two edges have at most one common point (an endpoint or a crossing) and no three edges pass through a single crossing. Topological graphs G and H are isomorphic if H can be obtained from G by a homeomorphism of the sphere, and weakly isomorphic if G and H have the same set of pairs of crossing edges. We generalize results of Pach and Tóth and the author’s previous results on counting different drawings of a graph under both notions of isomorphism. We prove that for every graph G with n vertices, m edges and no isolated vertices the number of weak isomorphism classes of simple topological graphs that realize G is at most 2 O ( n 2 log ( m / n ) ) , and at most 2 O ( m n 1 / 2 log n ) if m ≤ n 3 / 2 . As a consequence we obtain a new upper bound 2 O ( n 3 / 2 log n ) on the number of intersection graphs of n pseudosegments. We improve the upper bound on the number of weak isomorphism classes of simple complete topological graphs with n vertices to 2 n 2 · α ( n ) O ( 1 ) , using an upper bound on the size of a set of permutations with bounded VC-dimension recently proved by Cibulka and the author. We show that the number of isomorphism classes of simple topological graphs that realize G is at most 2 m 2 + O ( m n ) and at least 2 Ω ( m 2 ) for graphs with m > ( 6 + ε ) n .

A drawing of a graph on a surface is independently even if every pair of nonadjacent edges in the drawing crosses an even number of times. The Z2-genus of a graph G is the minimum g such that G has an independently even drawing on the orientable surface of genus g. An unpublished result by Robertson and Seymour implies that for every t, every graph of sufficiently large genus contains as a minor a projective t×t grid or one of the following so-called t-Kuratowski graphs: K3,t, or t copies of K5 or K3,3 sharing at most two common vertices. We show that the Z2-genus of graphs in these families is unbounded in t; in fact, equal to their genus. Together, this implies that the genus of a graph is bounded from above by a function of its Z2-genus, solving a problem posed by Schaefer and Štefankovič, and giving an approximate version of the Hanani–Tutte theorem on orientable surfaces. We also obtain an analogous result for Euler genus and Euler Z2-genus of graphs.

COVID-19 is likely to be the 2020s’ deadliest pandemic according to the World Health Organization (WHO). There have been more than 3.7 million confirmed deaths after 15 months spread. Besides the loss of human lives, COVID-19 has other unfavorable impacts on society, education, and the economy. Due to successive lockdowns and the continuous quarantines, the demands on power resources have reduced. Therefore, there is a need to investigate the impacts of the COVID-19 pandemic on electricity prices (EP). In this paper, a set of six economic factors that are affected by COVID-19 and affect EP are considered. These factors were fed into a functional link artificial neural network (FLANN) to model the relationships between them and the EP. An empirical equation was formulated to help decision makers and strategic developers in the electricity markets come up with more appropriate plans. Italy, the Czech Republic, and China were used as case studies in this research.

Background In temperate climates, influenza follows a seasonal pattern with peak incidence in winter and contributes significantly to excess winter mortality. The relationships among weather variability, influenza, and human health are complex, and the underlying mechanisms remain uncertain. This study investigated how influenza epidemics and all-cause mortality in the nationwide population of the Czech Republic are linked to weather characteristics. Methods A quasi-Poisson regression model was used to quantify excess mortality during 25 influenza epidemics over 1982–2020. Mean seasonal deviations of meteorological variables were calculated for periods from six weeks before to four weeks after the peak of influenza epidemics, categorised by their impact on excess mortality (mild, moderate or severe) and by the predominant influenza virus (A/H3N2, A/H1N1 or B). Temporal associations between individual meteorological variables and the onset of influenza epidemics were evaluated by bootstrapping and logistic regression-based explanatory model analysis. Results The analysis revealed that temperature, followed by absolute humidity, was the most significant weather indicator associated with the epidemic onset. Severe epidemics with the highest mortality impacts, predominantly associated with the A/H3N2 virus, occurred during prolonged periods of significantly below-average temperatures, while mild epidemics with lower mortality impacts, typically associated with the A/H1N1 virus, occurred during prevailing average or above-average temperatures. In non-epidemic seasons, corresponding periods with increased influenza activity were characterised by significantly above-average temperatures. Conclusions The findings suggest that weather indicators, particularly air temperature and absolute humidity, play an important role in the timing and severity of epidemics, and that these parameters differ with the predominant influenza virus. In the temperate climate of Central Europe, the circulation of the A/H3N2 virus in the population, combined with prolonged periods of low temperatures, results in influenza epidemics with the largest excess mortality. These findings highlight the need for a better understanding of weather conditions that increase influenza transmission and survival, and for distinguishing between predominant virus subtypes when informing at-risk populations, implementing preventive measures, and mitigating negative impacts.

An topological graph (briefly an AT-graph ) is a pair where G =( V , E ) is a graph and is a set of pairs of its edges. An AT-graph A is simply realizable if G can be drawn in the plane in such a way that each pair of edges from crosses exactly once and no other pair crosses. We present a polynomial algorithm which decides whether a given complete AT-graph is simply realizable. On the other hand, we show that other similar realizability problems for (complete) AT-graphs are NP-hard.