Application of simulated annealing to the biclustering of gene expression data.

In a gene expression data matrix, a bicluster is a submatrix of genes and conditions that exhibits a high correlation of expression activity across both rows and columns. The problem of locating the most significant bicluster has been shown to be NP-complete. Heuristic approaches such as Cheng and Church's greedy node deletion algorithm have been previously employed. It is to be expected that stochastic search techniques such as evolutionary algorithms or simulated annealing might improve upon such greedy techniques. In this paper we show that an approach based on simulated annealing is well suited to this problem, and we present a comparative evaluation of simulated annealing and node deletion on a variety of datasets. We show that simulated annealing discovers more significant biclusters in many cases. Furthermore, we also test the ability of our technique to locate biologically verifiable biclusters within an annotated set of genes.     

Coherent and incoherent dynamics of excitons in semiconductor microcavities

Il Nuovo Cimento D - We have investigated the dynamics of impulsively excited planar microcavities in the strongly couple regime. With resonant, coherent excitation, the emitted light shows...     

Between d-stability and sign-stability: the 3 × 3 case

[2] introduced a decreasing sequence of sets of real n × n matrices, which begins with the D-stable matrices and stops at the sign-stable matrices. It is not clear how many of the n sets in the sequence are distinct. This article documents the disappointment that in the first case where the sequence could contain a set which is neither the D-stable matrices nor the sign-stable matrices(viz., the case n = 3) it doesn't.     

Planning Deep-Water Ports

The paper describes how a number of proposed deep-water port developments for importing ore for the British Steel Corporation were assessed. The study was divided into two stages: the first stage was used to identify the best available options against a background of uncertainty by considering one year in a changing future; the second stage was used to evaluate the best proposals in detail and plan a course of action.The investigating team was heavily involved throughout in the managerial aspects of planning and decision-making. Where appropriate the effects of this participation are described and from them corresponding lessons drawn.     

Endor frequencies of randomly oriented triplets by electron spin echo spectroscopy

ENDOR frequencies of randomly oriented triplets have been measured from the fast Fourier transform of electron spin echo envelope modulation. Important experimental conditions are low temperatures, high microwave power and long phase memory time in a proper form of solvent. The technique is exemplified by using diphenylmethylenes in rigid glasses, polycrystalline forms and single crystals of benzophenones.     

Electron spin echo envelope modulation of trapped radicals in disordered systems: nitrogen modulation from isotopically substituted chlorophyll a cations

The electron spin echo envelope modulation of the chlorophyll a radical cation has been examined for radicals containing ¹⁴N and ¹⁵N. The modulation is found to be due primarily to the nitrogen nuclei in the heterocycle and the nuclear quadrupole interaction plays a large part in determining the modulation from ¹⁴N. The modulation from ¹⁵N allows limits to be set on the isotropic and anisotropic hyperfine interactions.     

Electrical effects of clustered defects in heteroepitaxial Si films

Our work indicates that the behavior of injected majority and minority carriers in representative Si/spinel samples is dominated by deep-level defects that are agglomerated into defect clusters rather than being uniformly distributed in the volume of the Si layer. Since these defect clusters will be surrounded by space-charge regions, the resulting trap occupancy-dependent potential barriers result in slow, nonexponential majority carrier trapping effects but subnanosecond minority carrier lifetimes. Accurate numerical calculations of the electrical properties of a sheet of clustered defects are shown to agree with detailed measurements at 90 and 300°K of the transient conductance decay in P- and N-type films following pulsed carrier injection from electron bombardment. A significant conclusion of the theoretical calculations is that the electrical behavior of a defect cluster is insensitive to any of the model parameters chosen as long as there are a sufficient number of defects to completely deplete the material in the vicinity of the defect plane. Our results show that the observed short minority carrier lifetimes, long-term majority carrier trapping effects and mobility temperature dependences can all be explained by the same cluster defect model and cannot be explained by uniformly distributed point defects. Our calculations also imply that minority carrier lifetime in these films should be strongly injection level dependent. Thus, lifetime measured by the MOS transient capacitance technique will not be the lifetime needed to evaluate the material for bipolar device applications.     

Relative contributions of spectral and temporal cues for phoneme recognition

Cochlear implants provide users with limited spectral and temporal information. In this study, the amount of spectral and temporal information was systematically varied through simulations of cochlear implant processors using a noise-excited vocoder. Spectral information was controlled by varying the number of channels between 1 and 16, and temporal information was controlled by varying the lowpass cutoff frequencies of the envelope extractors from 1 to 512 Hz. Consonants and vowels processed using those conditions were presented to seven normal-hearing native-English-speaking listeners for identification. The results demonstrated that both spectral and temporal cues were important for consonant and vowel recognition with the spectral cues having a greater effect than the temporal cues for the ranges of numbers of channels and lowpass cutoff frequencies tested. The lowpass cutoff for asymptotic performance in consonant and vowel recognition was 16 and 4 Hz, respectively. The number of channels at which performance plateaued for consonants and vowels was 8 and 12, respectively. Within the above-mentioned ranges of lowpass cutoff frequency and number of channels, the temporal and spectral cues showed a tradeoff for phoneme recognition. Information transfer analyses showed different relative contributions of spectral and temporal cues in the perception of various phonetic/acoustic features.