Effective Hamiltonians for fastly driven many-body lattice systems

We consider 1D lattices described by Hubbard or Bose-Hubbard models, in the presence of periodic high-frequency perturbations, such as uniform ac force or modulation of hopping coefficients. Effective Hamiltonians for interacting particles are derived using an averaging method resembling classical canonical perturbation theory. As is known, a high-frequency force may renormalize hopping coefficients, causing interesting phenomena such as coherent destruction of tunnelling and creation of artificial gauge fields. We find explicitly additional corrections to the effective Hamiltonians due to interactions, corresponding to non-trivial processes such as single-particle density-dependent tunnelling, correlated pair hoppings, nearest neighbour interactions, etc. Some of these processes arise also in multiband lattice models, and are capable to give rise to a rich variety of quantum phases. The apparent contradiction with other methods, e.g. Floquet-Magnus expansion, is explained. The results may be useful for designing effective Hamiltonian models in experiments with ultracold atoms, as well as in the field of ultrafast nonequilibrium magnetism. An example of manipulating exchange interaction in a Mott-Hubbard insulator is considered, where our corrections play an essential role

A Study of the Duties of the Elders of Local Seventh-day Adventist Churches in Chile: a Needs Assessment

Problem. Many Seventh-day Adventist churches in Chile, South America, do not have the assistance of a resident pastor, and most of the work in the church is done by volunteer lay leaders. The highest officer of the church is the elder, who usually has no training in leadership nor in theology. What is the work of the elder of the local church? How well is he performing his tasks? No specific study of this problem was found in the literature, and because the elders in Chile appeared to be eager and willing to be trained, this study was designed to investigate these questions and to offer recommendations to aid in the development of a curriculum for the training of elders based on their perceived needs. Method. Information about the duties of the elders was obtained by a study of the Seventh-day Adventist Church Manual. Twelve basic duties were identified, and for each one of them indicators were selected and standards established to measure the performance of the elders. Information about the elders was gathered by a questionnaire developed on the basis of the above-mentioned indicators and mailed to a representative randomly selected sample of 147 elders of the two conferences and one mission which comprise the Chile Union Mission of the Seventh-day Adventist Church. In spite of the distance from the re­ search population, the response rate was 88 percent. Data obtained included the frequency of task performance, level of agreement on a number of statements related to their duties, and self-evaluation of their perceived preparation to perform selected tasks. Findings. The answers the elders gave to the questions indicated that in a number of areas they felt reasonably well prepared to fulfill their duties. This may account for the measure of success they appear to have in their churches. In areas such as teaching adult Sabbath School classes, giving Bible studies, participating in different lay activities, helping members with counseling and advice, and in their concern for the spiritual welfare of the members, they felt they were performing well. There were other areas in which the elders felt they were not perform ing as well as they would like, thus disclosing specific needs. Some of these areas were: (1) understanding of and ability to explain the purpose and organization of an elementary church school; (2) the organization and functioning of a stewardship plan; (3) the planning of various activities; (4) writing objectives; (5) evaluating plans, pro­ grams, and activities; (6) adapting general plans to local situations; (7) advising the treasurer and the clerk; (8) leading out in a communion service; and (9) explaining youth work. From the data it was concluded that the elders felt best pre­ pared to care for the duties they have been familiar with through the years. Some technical administrative skills, such as writing objectives and preparing plans, are conspicuous among their needs. Most of the needs discovered were instructional, but a few related to their personal habits and example, and some pertained to the congregation in general. Recommendations. It was recommended, based on the needs discovered in this study, that (1) an instructional program for the elders be encouraged; (2) special emphasis be given to the concept that elders should not only know how to perform their duties, but should also be prepared to teach others; (3) the instructional program take into consideration the individual characteristics of the elders and local circumstances, using andragogical techniques such as problem-centered instruction and mutual assistance for problem solving in a group setting; and (4) pastors and elders engage in a serious continuing study on an ideal spiritual growth and nurture program for new believers in their churches

Fermi acceleration in time-dependent rectangular billiards due to multiple passages through resonances

We consider a slowly rotating rectangular billiard with moving boundaries and use the canonical perturbation theory to describe the dynamics of a billiard particle. In the process of slow evolution certain resonance conditions can be satisfied. Correspondingly, phenomena of scattering on a resonance and capture into a resonance happen in the system. These phenomena lead to destruction of adiabatic invariance and to unlimited acceleration of the particle.Comment: 20 pages. Presented on School-Conference "Mathematics and Physics of Billiard-Like Systems" (Ubatuba, 2011). Accepted to Chao

Identification of human papillomavirus DNA in cutaneous lesions of Cowden syndrome

Background: Cowden syndrome (CS) or multiple hamartoma syndrome is a cancer-associated genodermatosis inherited in an autosomal dominant pattern. One of the diagnostic criteria is facial papules which are felt to be trichilemmomas, benign hair follicle tumors, which some consider to be induced by human papillomavirus (HPV). Objective: To search for HPV in skin tumors, especially trichilemmomas, from patients with CS. Methods: Skin lesions from patients with CS were classified histologically. Each tumor was then analyzed for HPV DNA by polymerase chain reaction with different primer sets; positive amplicons were typed by direct sequencing. Results: Twenty-nine biopsies from 7 patients with CS were investigated. Only 2 of 29 tumors clinically suspected of being trichilemmomas were confirmed histologically. In addition, 3 sclerotic fibromas, also typical of CS, were found, as well as 1 sebaceous hyperplasia. The other 23 lesions showed histological features of HPV-induced tumors in various stages of development. HPV DNA was found in 19 of 29 cutaneous lesions. Tumors without any histological signs of HPV induction were negative for HPV DNA. Two tumors which were histologically classified as common warts contained HPV types 27 and 28. All the 17 other HPV types belong to the group of epidermodysplasia-verruciformis-associated types. Conclusions: The majority of cutaneous lesions in CS contain HPV DNA. They may have a variety of histological patterns. Trichilemmomas are not clinically distinctive and can be difficult to identify in CS patients. Copyright (C) 2003 S. Karger AG, Basel