Interacting Electrons on a Square Fermi Surface

Electronic states near a square Fermi surface are mapped onto quantum chains. Using boson-fermion duality on the chains, the bosonic part of the interaction is isolated and diagonalized. These interactions destroy Fermi liquid behavior. Non-boson interactions are also generated by this mapping, and give rise to a new perturbation theory about the boson problem. A case with strong repulsions between parallel faces is studied and solved. There is spin-charge separation and the square Fermi surface remains square under doping. At half-filling, there is a charge gap and insulating behavior together with gapless spin excitations. This mapping appears to be a general tool for understanding the properties of interacting electrons on a square Fermi surface.Comment: 25 pages, Nordita preprint 94/22

A scale-model room as a practical teaching experiment

A practical experiment is described which was used to help university students increase their understanding of the effect of construction methods and window design on passive solar heating and electrical heating. A number of one tenth scale model rooms were constructed by students and sited out-of-doors in the late autumn. The models were fabricated to mimic available commercial construction techniques with careful consideration being given to window size and placement for solar access. Each model had a thermostatically controlled electric heating element. The temperatures and electricity use of the models were recorded using data-loggers over a two week period. The performances of the models based on energy consumption and internal temperature were compared with each other and with predictions based upon thermal mass and R-values. Examples of questions used by students to facilitate this process are included. The effect of scaling on thermal properties was analysed using Buckingham&rsquo;s p-theorem.<br /

Economy and Protein Malnutrition Among the Digo

In short, even where protein malnutrition is primarily a result of poor environment, economy, and technology, other, often less obvious, traditional cultural patterns must be taken into account in any development and improvement program. If kwashiorkor is to be eliminated satisfactorily, and if contingent problems are to be kept to a minimum, these other patterns must often also be modified. The importance of traditional cultural patterns is perhaps best illustrated by an example of a people who suffer from protein malnutrition primarily because of them. The Digo tribe of coastal Kenya and Tanganyika, among whom this writer conducted anthropological field research from October, 1958 to May, 1960, provide an excellent case in point. In spite of an adequate food supply perhaps as many as 25 % of Digo infants up to the age of about five or six suffer from kwashiorkor. Few individuals older than six have kwashiorkor, presumably both because of a change in diet at about this age, and because infants seriously afflicted die. In analyzing this situation, let us first briefly survey Digo environment, economy and diet. Then let us examine Digo concepts about and means of dealing with kwashiorkor. In conclusion, let us consider ways of combating kwashiorkor among the Digo

Defining and developing an energy retrofitting approach

This paper identifies the dilemma faced by the stakeholders of existing buildings in regards to a decision making process for energy retrofitting. This paper also identifies the missing stage viewed as the &ldquo;integrity audit &ldquo;which can lead to substantial savings in the area of building operation. The methodology is centered on identifying energy waste first, reducing the overall peak electrical demand and then retrofitting for energy-efficiency. A proposed &ldquo;integrity audit&rdquo; leads to the classification of three main energy culprits: the identification of waste, missed opportunities, and rescheduling the operation of equipment use. A case study indicating the financial advantages of applying this methodology for a commercial building are presented. The energy retrofitting strategy is divided into two main categories, namely building control improvements and building component implementation. The payback periods are often within months if not immediate

Raman spectra of GexAsySe1−x−y glasses

Various Ge–As–Se glasses spanning a mean coordination number (MCN) from 2.2 to 2.94 have been investigated using differential scanning calorimetry and Raman spectroscopy. The glass transition temperature Tg was found to increase with increasing MCN, except for those glasses located within the nanoscale phase-separated region of the phase diagram. The evolution of Raman features at wavenumbers from 150 to 350 cm⁻¹ exhibits two transitionlike features. Merging of the 225 and 250 cm⁻¹ modes at MCN=2.5 is a symbol of the extinction of Se–Se bonds. Additionally, the appearance of two modes at 280–290 and 170 cm⁻¹ at MCN>2.7 come from the defect modes of ethanelike Ge₂Se₆/₂. The increase in the scattering from these defects is an important factor leading to enhanced optical loss in the glasses with high MCN.This research was partly supported by the Australian Research Council through its Centres of Excellence and Federation Fellow Programs

Preliminary tools assisting collected building performance measurements

Investigating on-site building performance in architectural science is increasing. However, the simplest forms of measurement often lack any analytical support other than presentation on a time-series plot. Here, we present instrumentation and analytical tools to assist in reporting building performance. The intention is to explore formats for observing performance of buildings based on collected data. Sometimes data are presented directly, but more often, information is revealed by calculation. We introduce examples of tools pertaining to interior-exterior climatic comparisons, occupant comfort and thermal performance, such as weather data plotted against a neutral temperature so that adaptive model comfort tolerances can be illustrated. We plot the interior and exterior air condition on the ASHRAE psychrometric chart to understand conditioning requirements. Other tools calculate the ISO 7730 (Fanger) comfort model, and an adaptive model of comfort is provided for the interior measurements alongside an 80 &ndash; 90% comfort band. These tools add value to reporting data by displaying in several formats, so the researcher can observe and report quickly and clearly on the potential of various conditioning periods within a building.A case study is presented for a house in Darwin during the wet-season

Study of heat flow through a rammed earth wall building

In 1999, a 2100 m2 (GFA) two-storey rammed earth building was built on the Thurgoona campus of Charles Sturt University. The climate at Thurgoona is considered Mediterranean &ndash; hot dry summers and cool winters. The internal and external walls of the building are constructed from 300-mm thick rammed earth (pise) and are load bearing. The thermal performance of the building has been investigated, both experimentally and theoretically over the summer and winter seasons of 2000/1. As part of these investigations heat flux sensors and thermistors were embedded in one of the external walls of a ground floor office, and data from the transducers has been used to determine the heat flow at the internal and external wall surfaces. The simulation software, TRNSYS, has been used to model the thermal performance of the same office. The programme allows the user to calculate the heat flow at the walls, which define any particular thermal zone. A comparison of measured and predicted values of heat flows and air temperatures has been used to validate the model. The model has then been used to simulate the effect of shading and added insulation on the thermal performance of the external walls in both summer and winter and these results are also presented in this paper.<br /