Determining efficient temperature sets for the simulated tempering method

In statistical physics, the efficiency of tempering approaches strongly depends on ingredients such as the number of replicas $R$, reliable determination of weight factors and the set of used temperatures, ${\mathcal T}_R = \{T_1, T_2, \ldots, T_R\}$. For the simulated tempering (SP) in particular -- useful due to its generality and conceptual simplicity -- the latter aspect (closely related to the actual $R$) may be a key issue in problems displaying metastability and trapping in certain regions of the phase space. To determine ${\mathcal T}_R$'s leading to accurate thermodynamics estimates and still trying to minimize the simulation computational time, here it is considered a fixed exchange frequency scheme for the ST. From the temperature of interest $T_1$, successive $T$'s are chosen so that the exchange frequency between any adjacent pair $T_r$ and $T_{r+1}$ has a same value $f$. By varying the $f$'s and analyzing the ${\mathcal T}_R$'s through relatively inexpensive tests (e.g., time decay toward the steady regime), an optimal situation in which the simulations visit much faster and more uniformly the relevant portions of the phase space is determined. As illustrations, the proposal is applied to three lattice models, BEG, Bell-Lavis, and Potts, in the hard case of extreme first-order phase transitions, always giving very good results, even for $R=3$. Also, comparisons with other protocols (constant entropy and arithmetic progression) to choose the set ${\mathcal T}_R$ are undertaken. The fixed exchange frequency method is found to be consistently superior, specially for small $R$'s. Finally, distinct instances where the prescription could be helpful (in second-order transitions and for the parallel tempering approach) are briefly discussed.Comment: 10 pages, 14 figure

Comparative Studies of Phytophthora Palmivora from Cocoa and Durian and Their Control

Phytophthora palmivora (But 1.) Butler is known to be a variable or ganism and is considered to be one of the most destructive pathogens of cocoa and durian which are being inter cropped in Malaysia. Studies were under taken to compare the cultural characteristics, sexuality, and pathogenicity of six Phytophthora isolates from these crops as well as the in-vitro and in-vivo efficacy of fungicide s against the pathogen. Preliminary studies on the use of a bio-control agent against the organism were also looked into. Cultural studies established that the Phytophthora isolates belonged to MFI P. palmivora. They produced stellate and striate colonies on carrot, cornmeal, and V-8 juice agar media. Mycelial growth was opt imum at 28 + 1.5C. No growth occurred at 36C. Sporangia were caducous, with length: breadth ratios from 1.22 to 1.8 and possessed short, occluded pedicels. Abundant chlamydospores were produced in culture