The Approximating Hamiltonian Method for the Imperfect Boson Gas

The pressure for the Imperfect (Mean Field) Boson gas can be derived in several ways. The aim of the present note is to provide a new method based on the Approximating Hamiltonian argument which is extremely simple and very general.Comment: 7 page

The Canonical Perfect Bose Gas in Casimir Boxes

We study the problem of Bose-Einstein condensation in the perfect Bose gas in the canonical ensemble, in anisotropically dilated rectangular parallelpipeds (Casimir boxes). We prove that in the canonical ensemble for these anisotropic boxes there is the same type of generalized Bose-Einstein condensation as in the grand-canonical ensemble for the equivalent geometry. However the amount of condensate in the individual states is different in some cases and so are the fluctuations.Comment: 23 page

Selection Effects, Biases, and Constraints in the Calan/Tololo Supernova Survey

We use Monte Carlo simulations of the Calan/Tololo photographic supernova survey to show that a simple model of the survey's selection effects accounts for the observed distributions of recession velocity, apparent magnitude, angular offset, and projected radial distance between the supernova and the host galaxy nucleus for this sample of Type Ia supernovae (SNe Ia). The model includes biases due to the flux-limited nature of the survey, the different light curve morphologies displayed by different SNe Ia, and the difficulty of finding events projected near the central regions of the host galaxies. From these simulations we estimate the bias in the zero-point and slope of the absolute magnitude-decline rate relation used in SNe Ia distance measurements. For an assumed intrinsic scatter of 0.15 mag about this relation, these selection effects decrease the zero-point by 0.04 mag. The slope of the relation is not significantly biased. We conclude that despite selection effects in the survey, the shape and zero-point of the relation determined from the Calan/Tololo sample are quite reliable. We estimate the degree of incompleteness of the survey as a function of decline rate and estimate a corrected luminosity function for SNe Ia in which the frequency of SNe appears to increase with decline rate (the fainter SNe are more common). Finally, we compute the integrated detection efficiency of the survey in order to infer the rate of SNe Ia from the 31 events found. For a value of Ho=65 km/sec/Mpc we obtain a SN Ia rate of 0.21(+0.30)(-0.13) SNu. This is in good agreement with the value 0.16+/-0.05 SNu recently determined by Capellaro et al. (1997).Comment: 36 pages, 19 figures as extra files, to appear in the A

Comparaison de quelques peuplements nématologiques des Petites Antilles

L'enquête faunistique effectuée sur trois îles des Antilles : Union, Barbade et la Martinique a permis de collecter 63 espèces de nématodes appartenant à 25 genres. Plus de la moitié des genres sont multispécifiques, avec un maximum de 7 espèces pour le genre #Xiphinema. A l'exception de 4 espèces : #Tylenchorhynchus curvus Williams, 1960, #Gracilacus aonli (Misra & Edward, 1971) Raski, 1976, #Helicotylenchus retusus Siddiqi & Brown, 1964 et #Pratylenchus teres Khan & Singh, 1975, toutes les autres existent en Amérique du Sud. Trois espèces seulement sont communes aux trois îles : #Paratylenchus elachistus Steiner, 1949, #Pratylenchus zeae Graham, 1951 et #Rotylenchus reniformis Linford & Oliveira, 1940. C'est à la Martinique, la plus vaste des trois îles, où l'altitude est la plus élevée, la pluviométrie la plus forte, qu'il y a le plus d'espèces et de genres, bien que la plus éloignée du continent américain. Le taux d'endémisme qui atteint 7 % est relativement faible. (Résumé d'auteur

Cappuccino and specific heat versus heat of vaporization

A cappuccino is prepared by adding about 50 mL frothing, foaming milk to a cup of espresso. Whole milk is best for foaming and the ideal milk temperature when adding it to the espresso is 65 °C. The espresso itself may be warmer than that. During the heating the milk should not burn, as that would spoil the taste. The best way is to heat the milk slowly while stirring to froth the milk and create foam. But modern cappuccino machines in restaurants do not have time for slow heating. Could we heat the milk by just adding hot water? That’s the question we pose to our high school students first. How many mL of 90 °C hot water would be needed to heat 50 mL of milk from a refrigerator temperature (say 4 °C) to 65 °C? Assume that the specific heat of milk is the same as that of water. Students answer the question on a worksheet and practice their computation skills. The answer: 122 g. This would mean an unacceptable dilution of the milk, 2.5 mL of water for every mL of milk. What would the answer be if we use boiling hot water of 100 °C? Students calculate again, then the answer is 87 g, still an unacceptable dilution. What then? What if we use steam