Non Linear Current Response of a Many-Level Tunneling System: Higher Harmonics Generation

The fully nonlinear response of a many-level tunneling system to a strong alternating field of high frequency $\omega$ is studied in terms of the Schwinger-Keldysh nonequilibrium Green functions. The nonlinear time dependent tunneling current $I(t)$ is calculated exactly and its resonance structure is elucidated. In particular, it is shown that under certain reasonable conditions on the physical parameters, the Fourier component $I_{n}$ is sharply peaked at $n=\frac {\Delta E} {\hbar \omega}$, where $\Delta E$ is the spacing between two levels. This frequency multiplication results from the highly nonlinear process of $n$ photon absorption (or emission) by the tunneling system. It is also conjectured that this effect (which so far is studied mainly in the context of nonlinear optics) might be experimentally feasible.Comment: 28 pages, LaTex, 7 figures are available upon request from [email protected], submitted to Phys.Rev.

School-Based Programs to Reduce Bullying and Victimization

School bullying has serious short-term and long-term effects on children’s physical and mental health. Various anti-bullying programs have been implemented world wide and, more rarely, evaluated. Previous narrative reviews, summarizing the work done on bullying prevention, as well as previous meta-analyses of anti-bullying programs, are limited. The definition of school bullying includes several key elements: physical, verbal, or psychological attack or intimidation that is intended to cause fear, distress, or harm to the victim; an imbalance of power (psychological or physical), with a more powerful child (or children) oppressing less powerful ones; and repeated incidents between the same children over a prolonged period. School bullying can occur in school or on the way to or from school. It is not bullying when two persons of the same strength (physical, psychological, or verbal) victimize each other. This report presents a systematic review and meta-analysis of the effectiveness of programs designed to reduce school bullying perpetration and victimization (i.e. being bullied). The authors indicate the pitfalls of previous reviews and explain in detail how the present systematic review and meta-analysis addresses the gaps in the existing literature on bullying prevention

Seleção para aumento de produtividade e qualidade de frutos em abobrinha 'Piramoita' comparando dois métodos de melhoramento Selection for fruit yield and quality in 'Piramoita' summer squash comparing two breeding methods

Este trabalho teve por objetivo comparar dois métodos de melhoramento quanto à seleção visando ao aumento de produtividade e qualidade de frutos na cv. Piramoita. Foram realizados três ciclos de seleção recorrente, com seleção de progênies autofecundadas (S1) e recombinação das melhores progênies para obtenção das populações melhoradas no primeiro (SR-1), segundo (SR-2) e terceiro (SR-3) ciclos. No método do "Single Seed Descent" (SSD) as plantas foram autofecundadas por cinco gerações até a obtenção e avaliação de progênies S5. As nove melhores progênies foram selecionadas obtendo-se progênies endogâmicas selecionadas (SSD-1 a SSD-9) e essas progênies também foram intercruzadas para se obter a população P-SSD. Todas as populações obtidas (SR-1, SR-2, SR-3, P-SSD, SSD-1 a SSD-9), juntamente com a população original (cv. Piramoita), totalizando 14 tratamentos, foram avaliadas em um experimento em blocos ao acaso, com seis repetições e cinco plantas por parcela. As características avaliadas foram: produção de frutos (número e massa) total e comercial, massa média de fruto comercial e taxa de frutos comerciais. Foram obtidos aumentos crescentes de produção de frutos comerciais com os ciclos de seleção recorrente, sendo a população SR-3 superior à 'Piramoita' para número de frutos por planta. Foi obtida uma progênie por SSD melhor que a população inicial e tão produtiva quanto à população SR-3. Deste modo, o método SSD pode vir a ser ótima alternativa no melhoramento genético de abobrinha, sem a necessidade de avaliação e seleção de progênies a cada safra, apenas quando essas já estiverem praticamente homozigotas.<br>The objective of this work was to compare two breeding methods to improve fruit yield and quality in 'Piramoita' summer squash. Three cycles of recurrent selection were made, with evaluation and selection of S1 progenies and recombination of plants from selected progenies to obtain improved populations after one (SR-1), two (SR-2) and three (SR-3) cycles. In the single seed descent (SSD), plants were selfed for five generations untill obtention and evaluation of S5 progenies. The nine best progenies were selected to obtain nine endogamous progenies (SSD-1 to SSD-9) and they were, also, inter-crossed to obtain a improved population by SSD (P-SSD). All obtained populations (SR-1, SR-2, SR-3, P-SSD, SSD-1 to SSD-9) and the original one (cv. Piramoita), resulting 14 treatments, were evaluated in a randomized block design, with six replications and five plants per plot. The following characteristics were evaluated: number and weight of fruits per plant, total and commercial, mean fruit weight and rate of commercial fruits. Improvements were obtained with increased commercial fruit yield along the recurrent selection cycles, and SR-3 population was superior to 'Piramoita' regarding fruit number per plant. It was obtained a SSD progeny better than the original population and as productive as SR-3 population. SSD method is a good alternative for summer squash breeding, allowing evaluation and selection of progenies, only when the progenies are practically homozygous rather than each year