On the existence of an upper critical dimension for systems within the KPZ universality class

In this work we extend the etching model to $d+1$ dimensions. This permits us to investigate its exponents behaviour on higher dimensions, to try to verify the existence of an upper critical dimension for the KPZ equations, with our results sugesting that $d=4$ is not an upper critical dimension for the etching model

Increasing the number of students in university basic courses : how to take advantage of this situation

A queda na qualidade de ensino é muitas vezes considerada uma consequência inevitável do aumento no número de alunos atendidos por uma disciplina universitária. No entanto, unificar a avaliação e outros elementos envolvidos com as disciplinas pode trazer ganhos em vários níveis do processo pedagógico. Para tratar desse assunto, esse artigo divide-se em duas partes: a primeira discute a implementação da unificação das disciplinas de Física-1 e Física-2, e a segunda analisa, estatisticamente, os resultados obtidos. São apresentadas técnicas que podem ser utilizadas para lidar com um grande número de alunos de maneira satisfatória, a maior parte delas baseadas no uso de ferramentas computacionais, adotadas no Instituto de Física da Universidade de Brasília para melhorar a formação dos alunos e a utilização dos recursos humanos. É apresentada a demanda de trabalho envolvida na unificação, permitindo avaliar a sua viabilidade em outras instituições. Diversas análises são realizadas a partir dos dados dos alunos da unificação, para determinar como a taxa de abandono e o desempenho dos alunos depende do professor, do comprometimento dos alunos com a disciplina, da existência de uma prova final e da formação pregressa do aluno. Ao final, fica demonstrado que o aumento na quantidade de alunos, aliado à adoção de práticas pedagógica unificadas, pode trazer benefícios ao processo como um todo.The decline in the quality of education is often considered an inevitable consequence of increasing the number of students of the university courses. However, the unification of assessments and other changes in the courses can bring gains at various levels of the educational process. In order to address this issue, this article is divided into two parts: the first part discusses the implementation of the unification of the disciplines of Physics 1 and Physics 2, and the second part is a statistical analysis of results. Techniques are presented that can be used to satisfactorily handle a large number of students. Most of them are based on computational tools, and were used at the Physics Institute at the University of Brasilia to improve the training of students and the use of human resources. It is discussed the effort to propose this unification in other institutions. Several analyzes are performed from the data of students, in order to determine how the dropout rate and student performance depends on the teacher, on the commitment of students with the course, on the existence of a final exam, and on the educational background of the students. Finally, it is shown that the increase in the number of students, coupled with the adoption of unified pedagogical practices, can bring benefits to the whole educational process

One-way pedestrian traffic is a means of reducing personal encounters in epidemics

Minimizing social contact is an important tool to reduce the spread of diseases but harms people's well-being. This and other more compelling reasons urge people to walk outside periodically. The present work explores how organizing the traffic of pedestrians affects the number of walking or running people passing by each other. By applying certain rules, this number can be significantly reduced, potentially reducing the contribution of person-to-person contagion to the basic reproductive number, R0. One example is the traffic of pedestrians on sidewalks. Another is the use of walking or running tracks in parks. It is obtained here that the number of people encountering each other can be drastically reduced if one-way traffic is enforced and runners are separated from walkers

When does contacting more people lessen the transmission of infectious diseases?

A primary concern in epidemics is to minimize the probability of contagion, often resorting to reducing the number of contacted people. However, the success of that strategy depends on the shape of the dose-response curve, which relates the response of the exposed person to the pathogen dose received from surrounding infected people. If the reduction is achieved by spending more time with each contacted person, the pathogen charge received from each infected individual will be larger. The extended time spent close to each person may worsen the expected response if the dose-response curve is convex for small doses. This is the case when the expected response is negligible below a certain dose threshold and rises sharply above it. This study proposes a mathematical model to calculate the expected response and uses it to identify the conditions when it would be advisable to reduce the contact time with each individual even at the cost of increasing the number of contacted people

Resolving the binding-kinase discrepancy in bacterial chemotaxis: A nonequilibrium allosteric model and the role of energy dissipation

The Escherichia coli chemotaxis signaling pathway has served as a model system for studying the adaptive sensing of environmental signals by large protein complexes. The chemoreceptors control the kinase activity of CheA in response to the extracellular ligand concentration and adapt across a wide concentration range by undergoing methylation and demethylation. Methylation shifts the kinase response curve by orders of magnitude in ligand concentration while incurring a much smaller change in the ligand binding curve. Here, we show that this asymmetric shift in binding and kinase response is inconsistent with equilibrium allosteric models regardless of parameter choices. To resolve this inconsistency, we present a nonequilibrium allosteric model that explicitly includes the dissipative reaction cycles driven by ATP hydrolysis. The model successfully explains all existing measurements for both aspartate and serine receptors. Our results suggest that while ligand binding controls the equilibrium balance between the ON and OFF states of the kinase, receptor methylation modulates the kinetic properties (e.g., the phosphorylation rate) of the ON state. Furthermore, sufficient energy dissipation is necessary for maintaining and enhancing the sensitivity range and amplitude of the kinase response. We demonstrate that the nonequilibrium allosteric model is broadly applicable to other sensor-kinase systems by successfully fitting previously unexplained data from the DosP bacterial oxygen-sensing system. Overall, this work provides a new perspective on cooperative sensing by large protein complexes and opens up new research directions for understanding their microscopic mechanisms through simultaneous measurements and modeling of ligand binding and downstream responses.Comment: 12 (main text) + 4 (supplemental information) pages, 6+4 figure