Energy level statistics for models of coupled single-mode Bose-Einstein condensates

We study the distribution of energy level spacings in two models describing coupled single-mode Bose-Einstein condensates. Both models have a fixed number of degrees of freedom, which is small compared to the number of interaction parameters, and is independent of the dimensionality of the Hilbert space. We find that the distribution follows a universal Poisson form independent of the choice of coupling parameters, which is indicative of the integrability of both models. These results complement those for integrable lattice models where the number of degrees of freedom increases with increasing dimensionality of the Hilbert space. Finally, we also show that for one model the inclusion of an additional interaction which breaks the integrability leads to a non-Poisson distribution.

Valerian does not appear to reduce symptoms for patients with chronic insomnia in general practice using a series of randomised n-of-I trials

Objectives: To investigate the effectiveness of valerian for the management of chronic insomnia in general practice. Design: Valerian versus placebo in a series of n-of-1 trials, in Queensland, Australia. Results: Of 42 enrolled patients, 24 (57%) had sufficient data for inclusion into the n-of-1 analysis. Response to valerian was fair for 23 (96%) participants evaluating their 'energy level in the previous day' but poor or modest for all 24 (100%) participants' response to 'total sleep time' and for 23 (96%) participants' response to 'number of night awakenings' and 'morning refreshment'. As a group, the proportion of treatment successes ranged from 0.35 (95% CI 0.23, 0.47) to 0.55 (95% CI 0.43, 0.67) for the six elicited outcome sleep variables. There was no significant difference in the number (P = 0.06), distribution (P = 1.00) or severity (P = 0.46) of side effects between valerian and placebo treatments. Conclusions: Valerian was not shown to be appreciably better than placebo in promoting sleep or sleep-related factors for any individual patient or for all patients as a group. (C) 2003 Elsevier Ltd. All rights reserved.

Direct observation of mixed-parity excited states in surface-passivated PbS nanocrystals

Photoluminescent emission is observed from surface-passivated PbS nanocrystals following the two-photon excitation of high-energy excitonic states. The emission appears directly at the excitation energy with no detectable Stokes-shift for a wide range of excitation energies. The observation of direct emission from states excited by two-photon absorption indicates that the parity of the excited states of surface-passivated PbS nanocrystals is partially mixed.

Comparative study of Li, Na, and K adsorptions on graphite by using ab initio method

A comprehensive study has been conducted to compare the adsorptions of alkali metals (including Li, Na, and K) on the basal plane of graphite by using molecular orbital theory calculations. All three metal atoms prefer to be adsorbed on the middle hollow site above a hexagonal aromatic ring. A novel phenomenon was observed, that is, Na, instead of Li or K, is the weakest among the three types of metal atoms in adsorption. The reason is that the SOMO (single occupied molecular orbital) of the Na atom is exactly at the middle point between the HOMO and the LUMO of the graphite layer in energy level. As a result, the SOMO of Na cannot form a stable interaction with either the HOMO or the LUMO of the graphite. On the other hand, the SOMO of Li and K can form a relatively stable interaction with either the HOMO or the LUMO of graphite. Why Li has a relatively stronger adsorption than K on graphite has also been interpreted on the basis of their molecular-orbital energy levels.

Radiative relaxation in synthetic pheomelanin

We report a detailed photoluminescence study of cysteinyldopa-melanin ( CDM), the synthetic analogue of pheomelanin. Emission spectra are shown to be a far more sensitive probe of CDM's spectroscopic behavior than are absorption spectra. Although CDM and dopa-melanin ( DM, the synthetic analogue of eumelanin) have very similar absorption spectra, we find that they have very different excitation and emission characteristics; CDM has two distinct photoluminescence peaks that do not shift with excitation wavelength. Additionally, our data suggest that the radiative quantum yield of CDM is excitation energy dependent, an unusual property among biomolecules that is indicative of a chemically disordered system. Finally, we find that the radiative quantum yield for CDM is similar to 0.2%, twice that of DM, although still extremely low. This means that 99.8% of the energy absorbed by CDM is dissipated via nonradiative pathways, consistent with its role as a pigmentary photoprotectant.

Quantitative fluorescence spectra and quantum yield map of synthetic pheomelanin

Spectroscopic studies of pheomelanin and its constituents have been sparse. These data present what is by far the most complete description of the fluorescence characteristics of synthetic pheomelanin. Emission spectra between 260 and 600 nm were acquired,for excitation wavelengths between 250 and 500 nm at 1-nm intervals. A quantum yield map is also presented, correcting the fluorescence intensities for differences in species concentration and molar absorptivity. These fluorescence features exhibit interesting similarities and differences to eumelanin, and these data are interpreted with respect to possible chemical structures. Overall, these data suggest that pheomelanin oligomers may be more tightly coupled than those of eumelanin. Finally, the quantum yield is shown to be on the order of 10(-4) and exhibit a complex dependence on excitation energy, varying by a factor of 4 across the energies employed here. (c) 2006 Wiley Periodicals, Inc.

XSophe, a computer simulation software suite for the analysis of electron paramagnetic resonance spectra

The XSophe computer simulation software suite consisting of a daemon, the XSophe interface and the computational program Sophe is a state of the art package for the simulation of electron paramagnetic resonance spectra. The Sophe program performs the computer simulation and includes a number of new technologies including; the SOPHE partition and interpolation schemes, a field segmentation algorithm, homotopy, parallelisation and spectral optimisation. The SOPHE partition and interpolation scheme along with a field segmentation algorithm greatly increases the speed of simulations for most systems. Multidimensional homotopy provides an efficient method for accurately tracing energy levels and hence tracing transitions in the presence of energy level anticrossings and looping transitions and allowing computer simulations in frequency space. Recent enhancements to Sophe include the generalised treatment of distributions of orientational parameters, termed the mosaic misorientation linewidth model and a faster more efficient algorithm for the calculation of resonant field positions and transition probabilities. For complex systems the parallelisation enables the simulation of these systems on a parallel computer and the optimisation algorithms in the suite provide the experimentalist with the possibility of finding the spin Hamiltonian parameters in a systematic manner rather than a trial-and-error process. The XSophe software suite has been used to simulate multifrequency EPR spectra (200 MHz to 6 00 GHz) from isolated spin systems (S > ~½) and coupled centres (Si, Sj _> I/2). Griffin, M.; Muys, A.; Noble, C.; Wang, D.; Eldershaw, C.; Gates, K.E.; Burrage, K.; Hanson, G.R."XSophe, a Computer Simulation Software Suite for the Analysis of Electron Paramagnetic Resonance Spectra", 1999, Mol. Phys. Rep., 26, 60-84.

Oxygen sensors and energy sensors act synergistically to achieve a graded alteration in gene expression: Consequences for assessing the level of neuroprotection in response to stressors

Changes in gene expression are associated with switching to an autoprotected phenotype in response to environmental and physiological stress. Ubiquitous molecular chaperones from the heat shock protein (HSP) superfamily confer neuronal protection that can be blocked by antibodies. Recent research has focused on the interactions between the molecular sensors that affect the increased expression of neuroprotective HSPs above constitutive levels. An examination of the conditions under which the expression of heat shock protein 70 (Hsp70) was up regulated in a hypoxia and anoxia tolerant tropical species, the epaulette shark (Hemiscyllium ocellatum), revealed that up-regulation was dependent on exceeding a stimulus threshold for an oxidative stressor. While hypoxic-preconditioning confers neuroprotective changes, there was no increase in the level of Hsp70 indicating that its increased expression was not associated with achieving a neuroprotected state in response to hypoxia in the epaulette shark. Conversely, there was a significant increase in Hsp70 in response to anoxic-preconditioning, highlighting the presence of a stimulus threshold barrier and raising the possibility that, in this species, Hsp70 contributes to the neuroprotective response to extreme crises, such as oxidative stress. Interestingly, there was a synergistic effect of coincident stressors on Hsp70 expression, which was revealed when metabolic stress was superimposed upon oxidative stress. Brain energy charge was significantly lower when adenosine receptor blockade, provided by treatment with aminophylline, was present prior to the final anoxic episode, under these circumstances, the level of Hsp70 induced was significantly higher than in the pair-matched saline treated controls. An understanding of the molecular and metabolic basis for neuroprotective switches, which result in an up-regulation of neuroprotective Hsp70 expression in the brain, is needed so that intervention strategies can be devised to manage CNS pathologies and minimise damage caused by ischemia and trauma. In addition, the current findings indicate that measurements of HSP expression per se may provide a useful correlate of the level of neuroprotection achieved in the switch to an autoprotected phenotype.