Ising Universality in Three Dimensions: A Monte Carlo Study

We investigate three Ising models on the simple cubic lattice by means of Monte Carlo methods and finite-size scaling. These models are the spin-1/2 Ising model with nearest-neighbor interactions, a spin-1/2 model with nearest-neighbor and third-neighbor interactions, and a spin-1 model with nearest-neighbor interactions. The results are in accurate agreement with the hypothesis of universality. Analysis of the finite-size scaling behavior reveals corrections beyond those caused by the leading irrelevant scaling field. We find that the correction-to-scaling amplitudes are strongly dependent on the introduction of further-neighbor interactions or a third spin state. In a spin-1 Ising model, these corrections appear to be very small. This is very helpful for the determination of the universal constants of the Ising model. The renormalization exponents of the Ising model are determined as y_t = 1.587 (2), y_h = 2.4815 (15) and y_i = -0.82 (6). The universal ratio Q = ^2/ is equal to 0.6233 (4) for periodic systems with cubic symmetry. The critical point of the nearest-neighbor spin-1/2 model is K_c=0.2216546 (10).Comment: 25 pages, uuencoded compressed PostScript file (to appear in Journal of Physics A

Thermal Denaturation and Aggregation of Myosin Subfragment 1 Isoforms with Different Essential Light Chains

We compared thermally induced denaturation and aggregation of two isoforms of the isolated myosin head (myosin subfragment 1, S1) containing different “essential” (or “alkali”) light chains, A1 or A2. We applied differential scanning calorimetry (DSC) to investigate the domain structure of these two S1 isoforms. For this purpose, a special calorimetric approach was developed to analyze the DSC profiles of irreversibly denaturing multidomain proteins. Using this approach, we revealed two calorimetric domains in the S1 molecule, the more thermostable domain denaturing in two steps. Comparing the DSC data with temperature dependences of intrinsic fluorescence parameters and S1 ATPase inactivation, we have identified these two calorimetric domains as motor domain and regulatory domain of the myosin head, the motor domain being more thermostable. Some difference between the two S1 isoforms was only revealed by DSC in thermal denaturation of the regulatory domain. We also applied dynamic light scattering (DLS) to analyze the aggregation of S1 isoforms induced by their thermal denaturation. We have found no appreciable difference between these S1 isoforms in their aggregation properties under ionic strength conditions close to those in the muscle fiber (in the presence of 100 mM KCl). Under these conditions kinetics of this process was independent of protein concentration, and the aggregation rate was limited by irreversible denaturation of the S1 motor domain

Environmental education after the school

An evaluation covering about ten years can now be made of the E.E. at the post-secundary level. The aims and motives of the teaching programmes and their great diversity of contents are emphasized in this article. Two main processes appear training experts dealing with general environmental matters or specialized technicians in the field of nuisances and pollution. The main difficulties which arise are the education of the teachers of the first generation and the interdisciplinary or multidisciplinary problems involved in the Education cursus as well as in the Research Units

Rayonnement de freinage dans les expériences de diffusion muon-proton

In relation with muon-proton scattering experiments in a region where the momentum transfer is several hundred MeV, we have calculated by the method of quasi-real pro-cesses the contribution of bremsstrahlung to the scattering cross-section. Our result has to be combined with the Schwinger correction, which includes both virtual radiative effects and emission of real photons with very low energy. One thus gets the total radiative correction as a function of initial energy of the muon, scattering angle, and resolution width for the final energy. A numerical application is given for an initial energy of 2 GeV and different values of the scattering angle and the resolution width.En vue d'expériences de diffusion muon-proton dans une région où le transfert d'impulsion est de quelques centaines de MeV, nous avons calculé à l'aide de la méthode des processus quasi réels la contribution du rayonnement de freinage à la section efficace de diffusion. Le résultat obtenu doit être additionné avec la correction de Schwinger qui inclut à la fois les effets radiatifs virtuels et l'émission de photons réels de très basse énergie. On obtient ainsi la correction radiative totale, qui est fonction de l'énergie initiale du muon, de l'angle de diffusion, et de la largeur de résolution pour l'énergie finale. Une application numérique est donnée pour une énergie initiale de 2 GeV et différentes valeurs de l'angle de diffusion et de la largeur de résolution

Sur le rayonnement de freinage dans les expériences de diffusion muon-proton à grand transfert

We have recalculated the radiative correction in muon-proton scattering for various experimental conditions, taking into account the form factors determined by Hofstadter for momentum transfers up to 1 GeV/c.Nous avons recalculé la correction radiative dans la diffusion muon-proton pour diverses conditions expérimentales, en tenant compte des facteurs de forme déterminés par Hofstadter pour des transferts de quantité de mouvement allant jusqu'à 1 GeV/c

Swollen lamellar phases between two solid walls : undulation forces and generation of defects

Forces between curved mica surfaces across a brine swollen lamellar phase (CTAB/hexanol/Brine) have been measured. The bilayers oriented spontaneously parallel to the mica surfaces. The force-distance curves show regimes where brine is continuously expelled from between the lamellae, and regimes in which bilayers are ejected over a few seconds. We have investigated the effect on the forces of moving in the phase diagram at constant bulk repeat distance, as well as along the dilution line. We found that the force necessary to squeeze out bilayers becomes smaller as the system approaches the transition to the bicontinuous phase (Lα/L3), i.e. on increasing the hexanol content. Dynamic effects are observed and may be explained in terms of hydrodynamic coupling of the bilayers with the solvent. They may produce surprising behaviors : on decompressing the phase, lamellae are systematically ejected. The equilibrium state of the system is discussed. The data is consistent with the 1/d2 profile calculated by Helfrich for the undulation forces [1]. Least square fits of the data to 1/d2 gives bilayer curvature modulus values of the order of 5.5 ± 3 kB T.Nous avons mesuré les forces entre deux surfaces de mica immergées dans une phase lamellaire gonflée à l'eau (CTAB/hexanol/eau salée). Les bicouches s'orientent parallèlement aux surfaces de mica. Les courbes force-distance présentent des domaines où l'eau est continûment éjectée d'entre les lamelles, et des domaines où le système saute rapidement à une autre distance en éjectant des lamelles. Nous avons étudié l'effet sur les forces d'un déplacement dans le diagramme de phases à période spatiale constante et également le long de la ligne de dilution. Plus on se rapproche de la transition vers la phase bicontinue (Lα/L3), c'est-à-dire plus la concentration en hexanol est grande, plus la force nécessaire à l'éjection des lamelles devient faible. Certains effets dynamiques sont observés et peuvent s'expliquer par un couplage hydrodynamique entre les bicouches et le solvant. Ils peuvent produire des comportements surprenants : en décomprimant la phase lamellaire, des bicouches sont systématiquement éjectées. L'état d'équilibre du système est discuté. Les résultats sont en accord avec le profil en 1/d 2 calculé par Helfrich pour les forces d'ondulation. L'ajustement des courbes force-distance à une loi en 1/d2 nous donne une valeur de la rigidité de courbure des lamelles : kc = 5.5 ± 3 kB T

Phénomènes élémentaires dans un système irradié application a la dosimétrie

L’étude de l’effet des rayonnements sur un système irradié est faite au niveau des interactions élémentaires. Il est montré que les paramètres qu’il est indispensable de connaître pour rendre compte de l’évolution du système sont : d’une part, les sections efficaces d’interaction et, d’autre part, les spectres des particules libres existant dans le milieu. Les paramètres utilisés en dosimétrie tels que : dose, E.B.R., T.L.E., sont explicités dans le cadre du formalisme présenté