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 /

Chronic Dermal Ulcer Healing Enhanced with Monophasic Pulsed Electrical Stimulation

The purposes of this randomized, double-blind, multicenter study were to compare healing of chronic dermal ulcers treated with pulsed electrical stimulation with healing of similar wounds treated with sham electrical stimulation and to evaluate patient tolerance to the therapeutic protocol. Forty-seven patients, aged 29 to 91 years, with 50 stage II, III, and IV ulcers were randomly assigned to either a treatment group (n=26) or a control (sham treatment) group (n=24). Treated wounds received 30 minutes of pulsed cathodal electrical stimulation twice daily at a pulse frequency of 128 pulses per second (pps) and a peak amplitude of 29.2 mA if the wound contained necrotic tissue or any drainage that was not serosanguinous. A saline-moistened nontreatment electrode was applied 30.5 cm (12 in) cephalad from the wound. This protocol was continued for 3 days after the wound was debrided or exhibited serosanguinous drainage. Thereafter, the polarity of the treatment electrode on the wound was changed every 3 days until the wound progressed to a stage II classification. The pulse frequency was then reduced to 64 pps, and the treatment electrode polarity was changed daily until the wound was healed. Patients in the control group were treated with the same protocol, except they received sham electrical stimulation. After 4 weeks, wounds in the treatment and control groups were 44% and 67% of their initial size, respectively. The healing rates per week for the treatment and control groups were 14% and 8.25%, respectively. The results of this study indicate that pulsed electrical stimulation has a beneficial effect on healing stage II, III, and IV chronic dermal ulcers

A game-theoretic model of kleptoparasitic behavior in polymorphic populations

Kleptoparasitism, the stealing of food by one animal from another, is a widespread biological phenomenon. In this paper we build upon earlier models to investigate a population of conspecifics involved in foraging and, potentially, kleptoparasitism. We assume that the population is composed of four types of individuals, according to their strategic choices when faced with an opportunity to steal and to resist an attack. The fitness of each type of individual depends upon various natural parameters, for example food density, the handling time of a food item and the probability of mounting a successful attack against resistance, as well as the choices that they make. We find the evolutionarily stable strategies (ESSs) for all parameter combinations and show that there are six possible ESSs, four pure and two mixtures of two strategies, that can occur. We show that there is always at least one ESS, and sometimes two or three. We further investigate the influence of the different parameters on when each type of solution occurs

Teaching Theories on Origins Without Controversy

Thirty years of intensive efforts by creationists have produced little substantiate prog ress in bringing about open academic inquiry in the teaching of origins theories in public schools because the opposition has convinced the courts that this would violate the First Amendment. The author has developed a secular approach to origins teaching that avoids all possible objections on constitutional grounds. It informs students about the true nature of the relevant scientific data which reveal great difficulties with evolution theory and show that all basic types of life first appeared abruptly on Earth

Teaching Theories on Origins: An Approach That Works

An effective approach to teaching about theories on origins defines the two general concepts, gives the requirements of a scientific theory, and examines the direct scientific evidence found in the fossil record to see if it supports common ancestry of all life or the sudden appearance of complete organisms. No legal objection on constitutional grounds is possible since religious doctrine is not promoted or even discussed

The Monroe Doctrine as the transparent veil of isolation during the League of Nations debate

In June 1919, President Woodrow Wilson returned from Paris after several months of negotiating the Treaty of Versailles to end World War One. At the peace conference, Wilson achieved his goal of establishing the League of Nations. However, he had one more hurdle: convince the Republican Senate to ratify the treaty. This was no easy task as Republicans claimed the treaty nullified the Monroe Doctrine, even though the century-old foreign policy was recognized, by name, in the League of Nations Covenant. Why, then, did opponents of the League of Nations in the United States claim isolation and refuse to ratify the treaty even though the Monroe Doctrine was included in the diplomatic agreement? The answer lies with the Republican foreign policy of expansionism that thrust the United States onto the world stage as a colonial power in 1898. Evidence from letters, diaries, and published articles by major Republican leaders, such as Theodore Roosevelt and Henry Cabot Lodge, proves that the United States wished to maintain its authority over the Western Hemisphere and other areas controlled by the colonial power. Further, an examination of the interactions between Democratic and Republican leaders illustrates the urgency with which those opposed to the League placed on the protection of the Monroe Doctrine’s authority within the Western Hemisphere. While one cannot disregard the political drama that unfolded during the League of Nations debate in 1919, it is necessary to look at a broader picture in order to understand why opponents wished to include the Monroe Doctrine in the treaty and pretend to be in isolation. The conclusion that the United States wished to remain sovereign with authority over the Western Hemisphere provides the notion that Americans wanted to be on par with European imperial powers, but also provides answers as to why many in 1919 argued that the United States was an isolationist nation, even when it clearly was not