Classical derivation of Bose-Einstein statistics

When its temperature is low enough, the motion of any stable classical mechanical system is a superposition of {\em quasi}-independent harmonic oscillations of its normal modes, which are standing waves if the system is a crystal or a bounded continuous medium. Without invoking quantum mechanics I prove that, at thermal equilibrium, the observed distribution of energy among these oscillations is a Bose-Einstein distribution, albeit with an unknown constant $h_?$ in place of Planck's constant, $h$. I identify characteristics of the classical independent-oscillator Hamiltonian that make my derivation of the Bose-Einstein distribution possible, and I point out that other classical physical systems, such as an ideal gas, have Hamiltonians that can be transformed canonically into forms with these characteristics. If ${h_?=h}$, among the implications of this work are that (i) there is no discrepancy between the experimentally-observed spectrum of a blackbody and what should be expected if light was a mechanical wave in a bounded medium; (ii) there is no discrepancy between the experimentally-observed temperature dependence of a crystal's heat capacity and what should be expected of classical lattice waves; and (iii) when a cluster of massive particles is cold enough, the classical expectation should be that almost all of its vibrational energy is possessed by its lowest-frequency normal mode. Therefore, below a certain temperature, all but one of its degrees of freedom are almost inactive and it is a Bose-Einstein condensate

Factors influencing the distribution of charge in polar nanocrystals

We perform first-principles calculations of wurtzite GaAs nanorods to explore the factors determining charge distributions in polar nanostructures. We show that both the direction and magnitude of the dipole moment $\mathbf{d}$ of a nanorod, and its electic field, depend sensitively on how its surfaces are terminated and do not depend strongly on the spontaneous polarization of the underlying lattice. We identify two physical mechanisms by which $\mathbf{d}$ is controlled by the surface termination, and we show that the excess charge on the nanorod ends is not strongly localized. We discuss the implications of these results for tuning nanocrystal properties, and for their growth and assembly.Comment: Accepted for publication in Phys. Rev. B Rapid Communication

Breakdown of phonon band theory in MgO

We present a series of detailed images of the distribution of kinetic energy among frequencies and wavevectors in the bulk of an MgO crystal as it is heated slowly until it melts. These spectra, which are Fourier transforms of velocity-velocity correlation functions calculated from accurate molecular dynamics (MD) simulations, provide a valuable perspective on the growth of thermal disorder in ionic crystals. We use them to explain why the most striking and rapidly-progressing departures from a band structure occur among longitudinal optical (LO) modes, which would be the least active modes at low temperature ($T$) if phonons did not interact. The degradation of the LO band begins, at low $T$, as an anomalously-large broadening of modes near the center of the Brillouin zone (BZ), which gradually spreads towards the BZ boundary. The LO band all but vanishes before the crystal melts, and transverse optical (TO) modes' spectral peaks become so broad that the TO branches no longer appear band-like. Acoustic bands remain relatively well defined until melting of the crystal manifests in the spectra as their sudden disappearance. We argue that, even at high $T$, the long wavelength acoustic (LWA) phonons of an ionic crystal can remain partially immune to disorder generated by its LO phonons; whereas, even at low $T$, its LO phonons can be strongly affected by LWA phonons. This is because LO displacements average out in much less than the period of an LWA phonon; whereas during each period of an LO phonon an LWA phonon appears as a quasistatic perturbation of the crystal, which warps the LO mode's intrinsic electric field. LO phonons are highly sensitive to acoustic warping of their intrinsic fields because their frequencies depend strongly on them: They cause the large frequency difference between LO and TO bands known as {\em LO-TO splitting}

DNA vaccination for prostate cancer, from preclinical to clinical trials - where we stand?

Development of various vaccines for prostate cancer (PCa) is becoming an active research area. PCa vaccines are perceived to have less toxicity compared with the available cytotoxic agents. While various immune-based strategies can elicit anti-tumour responses, DNA vaccines present increased efficacy, inducing both humoural and cellular immunity. This immune activation has been proven effective in animal models and initial clinical trials are encouraging. However, to validate the role of DNA vaccination in currently available PCa management paradigms, strong clinical evidence is still lacking. This article provides an overview of the basic principles of DNA vaccines and aims to provide a summary of preclinical and clinical trials outlining the benefits of this immunotherapy in the management of PCa

Temperature Dependence of the Band Gap of Semiconducting Carbon Nanotubes

The temperature dependence of the band gap of semiconducting single-wall carbon nanotubes (SWNTs) is calculated by direct evaluation of electron-phonon couplings within a ``frozen-phonon'' scheme. An interesting diameter and chirality dependence of $E_g(T)$ is obtained, including non-monotonic behavior for certain tubes and distinct ``family'' behavior. These results are traced to a strong and complex coupling between band-edge states and the lowest-energy optical phonon modes in SWNTs. The $E_g(T)$ curves are modeled by an analytic function with diameter and chirality dependent parameters; these provide a valuable guide for systematic estimates of $E_g(T)$ for any given SWNT. Magnitudes of the temperature shifts at 300 K are smaller than 12 meV and should not affect $(n,m)$ assignments based on optical measurements.Comment: To appear in Phys. Rev. Let

Anti-Salmonella lacatic acid bacteria from porcine intestinal sources

The aim of this study was to isolate lactic acid bacteria (LAB) with anti-Salmonella activity from the porcine gastrointestinal tract (GIT) and to characterise these for potentially probiotic properties using in vitro assays. Porcine caecal and faecal samples were screened for the presence of anti-Salmonella LAB; the ten most promising isolates belonged to the genera Lactobacillus and Pediococcus. The LAB exhibited large variation in their ability to survive in simulated gastric juice at pH 1.85. While Lactobacillus acidophilus species survived at up to 80% for 30 min, Lb. pentosus species declined to less than 0.001%. All isolates tolerated porcine bile at a concentration of 0.3%, with some capable of growth in the presence of up to 5% bile. The ability of the LAB isolates to prevent Salmonella invasion of intestinal epithelial cells varied, with reductions of 55% (Lb. acidophilus spp.) to 82% (Lb. salivarius spp.) observed. The data demonstrates that some porcine intestinal LAB isolates may offer potential as probiotics for the reduction of Salmonella carriage in pigs

An interpretative phenomenological analysis of stress and coping in first year undergraduates

In the UK, changes to the higher education system have increased the range of stressors experienced by students above those traditionally associated with the transition to university. Despite this, there is little qualitative research examining how students experience and cope with the adjustment to university. The experience of the transition was investigated in depth amongst 10 first year UK undergraduates. Purposive sampling resulted in a group with demographics similar to national statistics on UK undergraduates. Semi-structured interviews were used beginning with a content specific vignette to develop rapport. Interpretative phenomenological analysis was utilised to analyse the transcripts and quality checks were implemented to increase the validity of the analysis. Five main themes were identified: all the change, with subthemes of independent living, homesickness, differences between post-compulsory education and university; expectations of university; academic focus with subthemes of self-discipline, motivation, learning from experience; support network with subthemes of establishing a support network, support for coping with problems; and difficulties with subthemes of difficulties experienced with housemates, finances and employment, and academic difficulties. Students used a range of coping strategies. By identifying the role of positive psychological strengths such as optimism, hope, self-efficacy and self-control in coping with stress and facilitating positive adaptation, the study locates positive psychological strengths within a transactional understanding of stress and provides depth and relevance to their role in facilitating adjustment. Such qualitative research is rare in the positive psychology and stress literature. Suggestions for easing the transition are made