Three Dimensional Quantum Gravity Coupled to Ising Matter

We establish the phase diagram of three--dimensional quantum gravity coupled to Ising matter. We find that in the negative curvature phase of the quantum gravity there is no disordered phase for ferromagnetic Ising matter because the coordination number of the sites diverges. In the positive curvature phase of the quantum gravity there is evidence for two spin phases with a first order transition between them.Comment: 12 page

First order phase transitions: equivalence between bimodalities and the Yang-Lee theorem

First order phase transitions in finite systems can be defined through the bimodality of the distribution of the order parameter. This definition is equivalent to the one based on the inverted curvature of the thermodynamic potential. Moreover we show that it is in a one to one correspondence with the Yang Lee theorem in the thermodynamic limit. Bimodality is a necessary and sufficient condition for zeroes of the partition sum in the control intensive variable complex plane to be distributed on a line perpendicular to the real axis with a uniform density, scaling like the number of particles.Comment: 10 pages, no figure

Secondary Crystallization of Isotactic Polystyrene

When isotactic polystyrene (i-PS) is crystallized from the melt or from the glassy state at rather large supercooling an additional melting peak appears on the curve during scanning in a differential calorimeter. The overall rate of crystallization deduced from the total peak areas as a function of crystallization time did not fit the Avrami equation well. When we omit the area of the additional melting peak in the kinetic analysis a much better fit is obtained. We also observed that no lamellar thickening occurs during isothermal crystallization. In view of the low degree of crystallinity of i-PS these results lead to the idea that a secondary crystallization process takes place within the amorphous parts of the spherulites resulting in this additional melting peak on the DSC curve. The large supercooling needed and the increase in peak area with increasing molecular weight make us suppose that intercrystalline links are probably responsible for the additional melting peak of bulk-crystallized i-PS. Electron microscopic studies of surface replicas of i-PS support this view.

A simulation study on the interactive effects of radiation and plant density on growth of cut chrysanthemum

In the present study, we used a photosynthesis-driven crop growth model to determine acceptable plant densities for cut chrysanthemum throughout the year at different intensities of supplementary light. Dry matter partitioning between leaves, stems, and flowers was simulated as a function of crop developmental stage. Leaf area index was simulated as leaf dry mass multiplied by specific leaf area, the latter being a function of season. Climatic data (hourly global radiation, greenhouse temperature, and CO2 concentration) and initial organ dry mass were model inputs. Assimilation lights were switched on and off based on time and ambient global radiation intensity. Simulated plant fresh mass with supplementary light (49 µmol m-2 s-1) for 52 cultivations (weekly plantings, reference plant densities, and length of the long and short day period) was used as reference plant fresh mass. For four other supplementary light intensities (31, 67, 85, and 104 µmol m-2 s-1), dry matter production was simulated with the reference plant density and length of the long and short day period for each planting week and plant fresh mass was calculated. The acceptable plant density was then calculated as the ratio between plant fresh mass and reference plant fresh mass multiplied by the reference density. Under low natural light intensities, plant density could be increased substantially (>30%) at increased supplementary light intensities, while maintaining the desired plant mass. Simulated light use efficiency (g additional dry mass ¿ MJ-1 additional supplementary light) was higher in winter (4.7) than in summer (3.5), whereas it hardly differed between the supplementary light intensities. This type of simulations can be used to support decisions on the acceptable level of plant density at different intensities of supplementary lighting or lighting strategies and on optimum supplementary light intensities