Collapse of the random phase approximation: examples and counter-examples from the shell model

The Hartree-Fock approximation to the many-fermion problem can break exact symmetries, and in some cases by changing a parameter in the interaction one can drive the Hartree-Fock minimum from a symmetry-breaking state to a symmetry-conserving state (also referred to as a ``phase transition'' in the literature). The order of the transition is important when one applies the random phase approximation (RPA) to the of the Hartree-Fock wavefunction: if first order, RPA is stable through the transition, but if second-order, then the RPA amplitudes become large and lead to unphysical results. The latter is known as ``collapse'' of the RPA. While the difference between first- and second-order transitions in the RPA was first pointed out by Thouless, we present for the first time non-trivial examples of both first- and second-order transitions in a uniform model, the interacting shell-model, where we can compare to exact numerical results.Comment: 8 pages, 7 figure

The Split Window Microwave Radiometer (SWMR) for hurricane wind speed measurement from space

The monitoring of hurricanes demands considerable resources each year by the National Oceanic and Atmospheric Administration. Even with the extensive use of satellite and airborne probing of those storms, there is still much uncertainty involved in predicting landfall for timely evacuation of people subject to the threat. The concept of the Split Window Microwave Radiometer (SWMR) is to add an additional capability of remotely measuring surface winds to hopefully improve prediction capabilities or at least define the severity of the storm while it is far from land. Some of the present science and observational needs are addressed in this report as are remote sensing limitations which impact the design of a minimal system which can be launched into low earth orbit by a low cost launch system. This study has concluded that wind speed and rain rate maps of hurricanes can be generated with an X-Band radiometer system with an antenna whose aperture is 2 m on a side

STUDENT’S ATTITUDE TOWARDS DICTIONARY AND ITS USAGE : A Case of Study for English Department Students Diponegoro University

In learning a foreign language, dictionary is one of learning aids to assist students in making decision about making sense of words in usage –in the target language. This research is conducted to discover how English Department students in Universitas Diponegoro perceive dictionary and use it to assist meaning discovery. The data in this paper is obtained from returned questionnaires previously distributed across four academic years in. The results show that dictionary is not the primary source of English vocabulary intake. Most dictionaries are bilingual (English-Indonesian or Indonesian-English), and may take the form of printed or electronic dictionary. We also discovered that the respondents tend to choose a dictionary based on the number of words listed. Further clarifications of the respondents’ answers indicate the preference of vocabulary intake, where dictionary is not a priority. Bilingual dictionaries are preferred as compared to monolingual ones with the assumption that they are easier to understand. Although the definition of word is still very loose, students seem to be more attracted to dictionaries, which claim to have vast number of entries. For practical purposes, portable dictionary or application dictionary is more preferred as they support mobility. From the results, we may conclude that dictionaries are used by the respondents with restriction in meaning discovery. We suggest that they take it to the next level, where existing linguistic features from dictionaries might also be used to assist writing

A diffuse radar scattering model from Martian surface rocks

Remote sensing of Mars has been done with a variety of instrumentation at various wavelengths. Many of these data sets can be reconciled with a surface model of bonded fines (or duricrust) which varies widely across the surface and a surface rock distribution which varies less so. A surface rock distribution map from -60 to +60 deg latitude has been generated by Christensen. Our objective is to model the diffuse component of radar reflection based on this surface distribution of rocks. The diffuse, rather than specular, scattering is modeled because the diffuse component arises due to scattering from rocks with sizes on the order of the wavelength of the radar beam. Scattering for radio waves of 12.5 cm is then indicative of the meter scale and smaller structure of the surface. The specular term is indicative of large scale surface undulations and should not be causally related to other surface physical properties. A simplified model of diffuse scattering is described along with two rock distribution models. The results of applying the models to a planet of uniform fractional rock coverage with values ranging from 5 to 20% are discussed

Distribution and Emergence Patterns of Mayflies Ephemera simulans (Ephemeroptera: Ephemeridae)

Analyses of collections made during the years 1961-1964 reveal that Ephemera simulans is widely distributed in the lake regions of Minnesota and Wisconsin. The period of maximum emergence in central Minnesota and northern Wisconsin occurs during the last three weeks in June, the peak in extreme northern Minnesota about two weeks later