Second Moment Closure Modeling and DNS of Stratified Shear Layers

Buoyant shear layers encountered in many engineering and environmental applications have been studied by researchers for decades. Often, these flows have high Reynolds and Richardson numbers, which leads to significant/intractable space-time resolution requirements for DNS or LES. On the other hand, many of the important physical mechanisms, such as stress anisotropy, wake stabilization, and regime transition, inherently render eddy viscosity-based RANS modeling inappropriate. Accordingly, we pursue second-moment closure (SMC), i.e., full Reynolds stress/flux/variance modeling, for moderate Reynolds number non-stratified, and stratified shear layers for which DNS is possible. A range of sub-model complexity is pursued for the diffusion of stresses, density fluxes and variance, pressure strain and scrambling, and dissipation. These sub-models are evaluated in terms of how well they are represented by DNS in comparison to the exact Reynolds averaged terms, and how well they impact the accuracy of full RANS closure. For the non-stratified case, SMC model predicts the shear layer growth rate and Reynolds shear stress profiles accurately. Stress anisotropy and budgets are captured only qualitatively. Comparing DNS of exact and modeled terms, inconsistencies in model performance and assumptions are observed, including inaccurate prediction of individual statistics, non-negligible pressure diffusion, and dissipation anisotropy. For the stratified case, shear layer and gradient Richardson number growth rates, and stress, flux and variance decay rates, are captured with less accuracy than corresponding flow parameters in the non-stratified case. These studies lead to several recommendations for model improvement.

Governance structures in cooperative slaughterhouses: a study on the chain of differentiated beef in the state of Paraná

This study sought to discuss the governance structures adopted between livestock producers and their cooperative slaughterhouses in the chain of differentiated beef in the state of Paraná. The theoretical basis used was the Transaction Cost Economics and Measurement Costs Economics, complemented by the specificities of cooperatives. We conducted interviews with three key agents and eleven representatives of six cooperative slaughterhouses operating in this system. As result, we observed that the cooperatives have similar objectives and requirements, although there are differences in the levels of formality or flexibility. Although transactions are recurrent and have been successful, they involve a high asset specificity, depend on subjective measurements, and are still exposed to market uncertainties, which leaves room for the generation of conflicts and disincentives to quality. Despite this, the relational and reputational aspects associated with trust and partnership between the parties are elements that enable reduced transaction and measurement costs in these structures. At first, the measurements conducted by the cooperatives had an important role in the construction of trust between the parties and for value distribution. In a second moment, the trust built enabled the reduction of measurement costs.

STRUCTURAL STABILITY OF Ag AND Ag NANOCLUSTERS WITH A CHANGE IN THE INITIAL MORPHOLOGY

В статье методом молекулярной динамики с использованием модифицированного потенциала сильной связи TB-SMA (second moment approximation of tight-binding) проводится сравнительный анализ характера термически индуцированных структурных переходов в нанокластерах серебра, число атомов в которых соответствует «магическим» числам икосаэдрической структуры, при вариации их начальной морфологии. Показано, что в случае начальной ГЦК конфигурации формирование Ih модификации происходит либо на этапе предварительной термической релаксации, либо в ходе дальнейшего нагрева. При начальной аморфной морфологии характер структурных переходов претерпевает значительные изменения. Так, например, формирующаяся Ih модификация обладает большей стабильностью в области высоких температур и точка плавления нанокластеров смещается на величину более 100 К. Такой эффект обусловлен более плавным изменением удельной потенциальной энергии нанокластера в сравнении со случаем, когда устойчивая Ih конфигурация формируется при низких температурах. Полученные данные могут быть использованы при процессах создания нанокластеров серебра с требуемым внутренним строением. This article provides a comparative analysis of thermally induced structural transitions in silver nanoclusters with a change in their initial morphology. The study was executed by the molecular dynamics method using the modified TB-SMA (second moment approximation of tight-binding) tight binding potential. The number of atoms in nanoclusters corresponds to the icosahedral structure «magic» numbers. It is shown that for nanoclusters with the initial FCC configuration, the Ih modification is formed either at the stage of preliminary thermal relaxation or during further heating. For nanoclusters with an initial amorphous morphology, the nature of structural transitions undergoes significant changes. For example, the formed Ih modification is more stable at high temperatures and the melting point of nanoclusters shifts by more than 100 K. This effect is due to a smoother change in the specific potential energy of the nanocluster in comparison with the case when a stable Ih configuration is formed at low temperatures. The data obtained can be used in processes to create silver nanoclusters with the required internal structure.

ROLE OF «MAGIC» HCP NUMBERS IN STABILITY OF THE INTERNAL STRUCTURE OF Ag AND Ag NANOCLUSTERS

В настоящее время серебро активно применяется в микроэлектронике, в основном благодаря своей высокой электро- и теплопроводности. Учет процессов взаимодействия между металлом и световой волной (плазмонные эффекты) дает совершенно новые технические приложения серебра. Эти приложения становятся возможными благодаря сильному взаимодействию между падающим светом и свободными электронами в наноструктурах. К настоящему времени уже стало понятно, что размер, форма и структура наночастиц определяют их плазмонные свойства, в том числе резонансные частоты. Следовательно, подгонкой размера, внешнего вида металлической наноструктуры и ее внутреннего строения, можно управлять светом с очень большой степенью точности. В данной работе методом молекулярной динамики с использованием модифицированного потенциала сильной связи TB-SMA (second moment approximation of tight-binding) были изучены границы термической стабильности различной исходной структурной фазы в малых кластерах серебра с числом атомов, соответствующим «магическим» числам ГПУ структуры. Было показано, что характер термически индуцированных структурных переходов в исследуемых группах нанокластеров резко отличается. Данный факт может позволить создать малые кластеры серебра с требуемым внутренним строением. Currently, silver is actively used in microelectronics, mainly due to its high electrical and thermal conductivity. Taking into account the processes of interaction between a metal and a light wave (plasmon effects) gives completely new technical applications of silver. These applications are made possible by the strong interaction between incident light and free electrons in nanostructures. By now, it has already become clear that the size, shape, and structure of nanoparticles determine their plasmon properties, including resonance frequencies. Therefore, by adjusting the size, appearance of the metal nanostructure and its internal structure, it is possible to control light with a very high degree of accuracy. In this work, the boundaries of thermal stability of various initial structural phases in small silver clusters with the number of atoms corresponding to the «magic» numbers of the hcp structure were studied by the molecular dynamics method using the modified tight-binding potential TB-SMA (second moment approximation of tight-binding). It was shown that the nature of thermally induced structural transitions in the groups of nanoclusters under study differs sharply. This fact can make it possible to create small silver clusters with the required internal structure.

The second moment of Sn(t) on the Riemann hypothesis

Let [Formula: see text] be the argument of the Riemann zeta-function at the point [Formula: see text]. For [Formula: see text] and [Formula: see text] define its antiderivatives as [Formula: see text] where [Formula: see text] is a specific constant depending on [Formula: see text] and [Formula: see text]. In 1925, Littlewood proved, under the Riemann Hypothesis (RH), that [Formula: see text] for [Formula: see text]. In 1946, Selberg unconditionally established the explicit asymptotic formulas for the second moments of [Formula: see text] and [Formula: see text]. This was extended by Fujii for [Formula: see text], when [Formula: see text]. Assuming the RH, we give the explicit asymptotic formula for the second moment of [Formula: see text] up to the second-order term, for [Formula: see text]. Our result conditionally refines Selberg’s and Fujii’s formulas and extends previous work by Goldston in [Formula: see text], where the case [Formula: see text] was considered.

Práticas educativas no ensino de História sobre Judeus/Judaísmo

The theme about Jewish immigration in Brazil gains relevance from the work of the History teacher with themes directly linked to the way of life, adaptation and the result of power relations exercised by the descendents of Jews settled in the city of Ponta Grossa-PR. The educational practices that underlie the teaching of History depend on the historian's ability to contextualize and make references to other themes of interest, in order to allow the student, when inserted in the context, to make readings according to the content of the proposed activities. In a second moment, subthemes such as identity, memory, religion and politics are approached, which interfere in the ways of acceptance by society about historical facts and/or perceptions around the identity of the Jewish community of immigrants and expatriates in Brazil. O tema da imigração judaica no Brasil ganha relevância com o trabalho do professor de História com temas directamente ligados ao modo de vida, adaptação e resultado das relações de poder exercidas pelos descendentes dos judeus instalados na cidade de Ponta Grossa-PR. As práticas educativas subjacentes ao ensino da História dependem da capacidade do historiador de contextualizar e fazer referências a outros temas de interesse, de modo a permitir ao aluno, quando inserido no contexto, fazer leituras de acordo com o conteúdo das actividades propostas. Num segundo momento, são abordados subtemas como identidade, memória, religião e política, que interferem nas formas de aceitação pela sociedade sobre factos históricos e/ou percepções em torno da identidade da comunidade judaica de imigrantes e expatriados no Brasil.

MOMENTS AND HYBRID SUBCONVEXITY FOR SYMMETRIC-SQUARE L-FUNCTIONS

We establish sharp bounds for the second moment of symmetric-square L-functions attached to Hecke Maass cusp forms $u_j$ with spectral parameter $t_j$ , where the second moment is a sum over $t_j$ in a short interval. At the central point $s=1/2$ of the L-function, our interval is smaller than previous known results. More specifically, for $\left \lvert t_j\right \rvert $ of size T, our interval is of size $T^{1/5}$ , whereas the previous best was $T^{1/3}$ , from work of Lam. A little higher up on the critical line, our second moment yields a subconvexity bound for the symmetric-square L-function. More specifically, we get subconvexity at $s=1/2+it$ provided $\left \lvert t_j\right \rvert ^{6/7+\delta }\le \lvert t\rvert \le (2-\delta )\left \lvert t_j\right \rvert $ for any fixed $\delta>0$ . Since $\lvert t\rvert $ can be taken significantly smaller than $\left \lvert t_j\right \rvert $ , this may be viewed as an approximation to the notorious subconvexity problem for the symmetric-square L-function in the spectral aspect at $s=1/2$ .

A variation of the prime k-tuples conjecture with applications to quantum limits

Let $$\mathcal {H}^{*}=\{h_1,h_2,\ldots \}$$ H ∗ = { h 1 , h 2 , … } be an ordered set of integers. We give sufficient conditions for the existence of increasing sequences of natural numbers $$a_j$$ a j and $$n_k$$ n k such that $$n_k+h_{a_j}$$ n k + h a j is a sum of two squares for every $$k\ge 1$$ k ≥ 1 and $$1\le j\le k.$$ 1 ≤ j ≤ k . Our method uses a novel modification of the Maynard–Tao sieve together with a second moment estimate. As a special case of our result, we deduce a conjecture due to D. Jakobson which has several implications for quantum limits on flat tori.

WATER ACTIVITIES WITH THREE AND FOUR-YEAR-OLD CHILDREN:

Contextualization of the objective: Motor experiences in the liquid or terrestrial environment are part of children's behavior, helping children to master the environment, making them autonomous and self-assured. Objective: To report the experience of six months of intervention with water activities for 21 children, of both sexes, aged between three and four years old in an academy in São Luís. Method: The water activities classes lasted forty minutes, they were held twice a week and the classes had an average of eight to ten children aged three to four years. The class was divided into three moments: setting with the environment and with people, the second moment of displacements with floating material and the third moment there were jumps and dives followed by displacements. After a period of six months of intervention, an observational assessment consisting of eight items, with four sub-items each, was applied. The evaluation was applied during a class and the teachers selected a group of children to make the observations and apply the proposed exercises according to the evaluated item. Results: It was found that all children developed the skills proposed in the assessment items, receiving excellent ratings, with the exception of the item "backstroke legs propulsion" in which seven students, four of which had a good rating, three had a very good result. Final considerations: after six months of intervention, it was noticed that there were positive results in the expansion of learning the contents and refinement of the proposed movements, confirming the hypothesis that, within the proposed period, there were benefits in learning to swim.