Two-dimensional Bloch electrons in perpendicular magnetic fields: an exact calculation of the Hofstadter butterfly spectrum

The problem of two-dimensional, independent electrons subject to a periodic potential and a uniform perpendicular magnetic field unveils surprisingly rich physics, as epitomized by the fractal energy spectrum known as Hofstadter's Butterfly. It has hitherto been addressed using various approximations rooted in either the strong potential or the strong field limiting cases. Here we report calculations of the full spectrum of the single-particle Schr\"{o}dinger equation without further approximations. Our method is exact, up to numerical precision, for any combination of potential and uniform field strength. We first study a situation that corresponds to the strong potential limit, and compare the exact results to the predictions of a Hofstadter-like model. We then go on to analyze the evolution of the fractal spectrum from a Landau-like nearly-free electron system to the Hofstadter tight-binding limit by tuning the amplitude of the modulation potential

An evaluation of semantic fisheye views for opportunistic search in an annotated image collection

Visual interfaces are potentially powerful tools for users to explore a representation of a collection and opportunistically discover information that will guide them toward relevant documents. Semantic fisheye views (SFEVs) are focus + context visualization techniques that manage visual complexity by selectively emphasizing and increasing the detail of information related to the user's focus and deemphasizing or filtering less important information. In this paper we describe a prototype for visualizing an annotated image collection and an experiment to compare the effectiveness of two distinctly different SFEVs for a complex opportunistic search task. The first SFEV calculates relevance based on keyword-content similarity and the second based on conceptual relationships between images derived using WordNet. The results of the experiment suggest that semantic-guided search is significantly more effective than similarity-guided search for discovering and using domain knowledge in a collectio

Implementation Essays on Decision Support Systems

The "Task Force Meeting on Decision Support Systems (DSS)" held at IIASA in June 1980 has stimulated some new thinking in this area of research in the MMT group (Management and Technology Research Area). The discussion pointed out the important role that DSS can play in assisting decision makers. DSS should be seen as a complicated socio-technical system for solving relevant problems in the wider social context. This paper is oriented towards technical aspects of DSS, but human factors have been taken into account as well. It contains some points of view of implementation; it reviews some basic functions which are to be performed by DSS and techniques which can simplify DSS design. A possible implementation structure based on computer network theory is presented, and in addition, some of the problems involved are discussed The author Jan Janecek participated in the IIASA Young Scientists Summer Program 1980. He was attached to the MMT Research Area for three months. This report is one of the results of his work during that period

Гвинтовий вібраційний змішувач удосконаленої конструкції

The Co-design practices are carried out in different fields of studies. Some of the key advocates of Co-design originate from business. In this study the four steps of Co-design approach is applied. From the first step of Co-design, through interviews, log analysis and a channel survey, findings show that the failed dialogues with Avatar Eva are mainly concerned with five factors: interactivity; dialogue capability; consistency; knowledge; and synonyms. In the second step, carrying out customer workshops, we suggested ten ideal scenarios for Avatar Eva to perform better. In the third step, SAS decision makers decided to implement the first three scenarios: Eva’s synonyms; knowledge and Eva’s consistency. In the fourth step, another channel survey was carried out as well as a new log analysis to know the impact of the redevelopment above three scenarios. An important result of the study was that the company adopted a continuous use of Co-design as an approach of continuous improvement of the service quality performed by the Avatar Eva. It also opens a new set of questions framing the relation and transformation between Co-design as a research approach for knowledge creation and Co-design as a method for innovation and service quality improvements. The study presents an Extended Co-design Model, which illustrates how the Co-design inspires staff to use it for other functions within and without the SAS

A generalized Kiselev crossover approach applied to Soave–Redlich–Kwong equation of state

International audienceThree different variants of the crossover Soave–Redlich–Kwong equation of state are applied to describe the equilibrium behaviour of 72 common non-associating fluids – 27 hydrocarbons (including the first 10 n-alkanes), 36 halogenated refrigerants, 5 cryogenics (fluorine, oxygen, nitrogen, argon and carbon monoxide) and 4 other industrially important inorganic fluids (carbon dioxide, sulfur dioxide, nitrous oxide and sulfur hexafluoride). The model contains six compound dependent parameters.Two of them (a0 and b of the classical part) are adjusted on the critical experimental temperature and the critical pressure. In a first model denoted as model A, the four remaining parameters are fitted to describe the saturated liquid and vapour densities and vapor pressures as well as PVT data at pressures up to P = 3 × Pc. In the second model (model B), the dispersion softness m is expressed as a function of the acentric factor ω and a relation between two of the crossover parameters is employed; the number of fitted parameters is thus reduced to two. Based on model B, we suggested our final Model C, in which all the parameters can be determined from the critical point, acentric factor or rectlinear diameter. This model is superior to the classical Soave–Redlich–Kwong equation of state because it improves considerably the description of the liquid densities over the whole coexistence region. Contrary to equations of state optimized to reproduce the liquid densities at low temperatures, the crossover equation does not overpredict the critical temperature and pressure. Model C is applied to describe the equilibrium behaviour of two compounds not included in the parameterization, hexafluoropropene (HFO1216) and hexafluoropropene oxide (HFPO)