Superconductivity in Boron under pressure - why are the measured Tc_c's so low?

Using the full potential linear muffin-tin orbitals (FP-LMTO) method we examine the pressure-dependence of superconductivity in the two metallic phases of Boron: bct and fcc. Linear response calculations are carried out to examine the phonon frequencies and electron-phonon coupling for various lattice parameters, and superconducting transition temperatures are obtained from the Eliashberg equation. In both bct and fcc phases the superconducting transition temperature T$_c$ is found to decrease with increasing pressure, due to stiffening of phonons with an accompanying decrease in electron-phonon coupling. This is in contrast to a recent report, where T$_c$ is found to increase with pressure. Even more drastic is the difference between the measured T$_c$, in the range 4-11 K, and the calculated values for both bct and fcc phases, in the range 60-100 K. The calculation reveals that the transition from the fcc to bct phase, as a result of increasing volume or decreasing pressure, is caused by the softening of the X-point transverse phonons. This phonon softening also causes large electron-phonon coupling for high volumes in the fcc phase, resulting in coupling constants in excess of 2.5 and T$_c$ nearing 100 K. We discuss possible causes as to why the experiment might have revealed T$_c$'s much lower than what is suggested by the present study. The main assertion of this paper is that the possibility of high T$_c$, in excess of 50 K, in high pressure pure metallic phases of boron cannot be ruled out, thus substantiating the need for further experimental investigations of the superconducting properties of high pressure pure phases of boron.Comment: 16 pages, 8 figures, 1 Tabl

Undergraduate student aspirations, awareness and knowledge of postgraduate study options: A preliminary, qualitative investigation

Little attention has been directed to the attitudes of undergraduate university students towards postgraduate studies and little is known about the extent of undergraduates awareness of postgraduate degrees. Research in the careers arena has revealed inconsistencies in factors that impact on a students decision to pursue postgraduate study. Using focus groups across different levels of Bachelor of Business students, this study examines the attitudes of university undergraduate students towards postgraduate study. Factors that impact on an undergraduate decision to pursue postgraduate study are also explored

Gender differences in organizational justice predicting the key employee outcomes of organizational commitment, job satisfaction and turnover intention

All four types of organizational justice &ndash; distributive, procedural, interpersonal and informational &ndash; were included in this study of gender differences. Both male and female respondents perceived the distributive-procedural justice and interpersonal-informational justice pairings similarly and weakly. Females consistently discriminated more clearly across the pairings, however. The effect of the four justices was also found to be gender-dependent. Males&rsquo; perception of distributive justice directly predicted their turnover intentions and commitment to the organization, while females&rsquo; perception of distributive justice predicted only job satisfaction. Males&rsquo; perceptions of procedural and information justice both predicted job satisfaction. Females&rsquo; informational justice perceptions predicted job satisfaction and commitment to the organization. The paper contributes to the literature by presenting results from all four justice types and the simultaneous use of the three outcomes of job satisfaction, organizational commitment and intention to quit. Overall, the males had a diffuse set of relationships between the justice types and the outcomes, whereas the relationships between the justice types andthe outcomes for females tended more to follow a limited number of pathways. The study was validated with data collected on two separate occasions.<br /

Key behavioural and cognitive employee outcomes : a social exchange model

This paper serves to integrate social exchange with organisational justice and performance theory. Social exchange relationships are represented by employees&rsquo; perceptions of workplace inequity and evaluated using justice rules. Employees are expected to have in-role and extra-role behavioural responses and cognitive responses to inequity. It is theorised that behavioural and cognitive responses are moderated by the employee&rsquo;s perceptions of organisational justice. Much employee performance, commitment, engagement, retention and turnover may be explained by this comprehensive model.<br /

Convergent interviewing : a qualitative diagnostic technique for researchers

Purpose &ndash; This paper aims to widen knowledge of and explore how convergent interviewing can be used to identify key issues within an organization.Design/methodology/approach &ndash; This paper introduces the convergent interviewing technique and describes the method of selecting the interview subjects. The construction of a round of interviews is explained. The content of the interviews is described and the particular probing nature of the questions demanded by the convergent interview process is explained. The ways to analyze the full set of interviews for groupings or categories is also described. The case study example of a broad research question about influences on work behaviors in a local government council is used to illustrate the convergent interviewing technique.Findings &ndash; The key issues revealed by using the technique can be subsequently used for a variety of research and consulting purposes and settings. Convergent interviewing is an effective research method, which conserves resources.Originality/value &ndash; Convergent interviewing enables researchers to determine the most important and/or key issues within a population rather than a full list of issues in an organization or barriers to change in a particular organizational context. <br /

The Prevalence of Latent Mycobacterium Tuberculosis Infection Based on an Interferon-γ Release Assay: A Cross-Sectional Survey Among Urban Adults in Mwanza, Tanzania.

One third of the world's population is estimated to be latently infected with Mycobacterium tuberculosis (LTBI). Surveys of LTBI are rarely performed in resource poor TB high endemic countries like Tanzania although low-income countries harbor the largest burden of the worlds LTBI. The primary objective was to estimate the prevalence of LTBI in household contacts of pulmonary TB cases and a group of apparently healthy neighborhood controls in an urban setting of such a country. Secondly we assessed potential impact of LTBI on inflammation by quantitating circulating levels of an acute phase reactant: alpha-1-acid glycoprotein (AGP) in neighborhood controls. The study was nested within the framework of two nutrition studies among TB patients in Mwanza, Tanzania. Household contacts- and neighborhood controls were invited to participate. The study involved a questionnaire, BMI determination and blood samples to measure AGP, HIV testing and a Quantiferon Gold In tube (QFN-IT) test to detect signs of LTBI. 245 household contacts and 192 neighborhood controls had available QFN-IT data. Among household contacts, the proportion of QFT-IT positive was 59% compared to 41% in the neighborhood controls (p = 0.001). In a linear regression model adjusted for sex, age, CD4 and HIV, a QFT-IT positive test was associated with a 10% higher level of alpha-1-acid glycoprotein(AGP) (10(B) 1.10, 95% CI 1.01; 1.20, p = 0.03), compared to individuals with a QFT-IT negative test. LTBI is highly prevalent among apparently healthy urban Tanzanians even without known exposure to TB in the household. LTBI was found to be associated with elevated levels of AGP. The implications of this observation merit further studies

Lattice vibrations and structural instability in Cesium near the cubic to tetragonal transition

Under pressure cesium undergoes a transition from a high-pressure fcc phase (Cs-II) to a collapsed fcc phase (Cs-III) near 4.2GPa. At 4.4GPa there follows a transition to the tetragonal Cs-IV phase. In order to investigate the lattice vibrations in the fcc phase and seek a possible dynamical instability of the lattice, the phonon spectra of fcc-Cs at volumes near the III-IV transition are calculated using Savrasov's density functional linear-response LMTO method. Compared with quasiharmonic model calculations including non-central interatomic forces up to second neighbours, at the volume $V/V_0= 0.44$ ($V_0$ is the experimental volume of bcc-Cs with $a_0$=6.048{\AA}), the linear-response calculations show soft intermediate wavelength $T_{[1\bar{1}0]}[{\xi}{\xi}0]$ phonons. Similar softening is also observed for short wavelength $L[\xi\xi\xi]$ and $L[00\xi]$ phonons and intermediate wavelength $L[\xi\xi\xi]$ phonons. The Born-von K\'{a}rm\'{a}n analysis of dispersion curves indicates that the interplanar force constants exhibit oscillating behaviours against plane spacing $n$ and the large softening of intermediate wavelength $T_{[1\bar{1}0]}[{\xi}{\xi}0]$ phonons results from a negative (110)-interplanar force-constant $\Phi_{n=2}$. The frequencies of the $T_{[1\bar{1}0]}[{\xi}{\xi}0]$ phonons with $\xi$ around 1/3 become imaginary and the fcc structure becomes dynamically unstable for volumes below $0.41V_0$. It is suggested that superstructures corresponding to the $\mathbf{q}{\neq}0$ soft mode should be present as a precursor of tetragonal Cs-IV structure.Comment: 12 pages, 5 figure

Combined density-functional and dynamical cluster quantum Monte Carlo calculations for three-band Hubbard models for hole-doped cuprate superconductors

Using a combined local density functional theory (LDA-DFT) and quantum Monte Carlo (QMC) dynamic cluster approximation approach, the parameter dependence of the superconducting transition temperature Tc of several single-layer hole-doped cuprate superconductors with experimentally very different Tcmax is investigated. The parameters of two different three-band Hubbard models are obtained using the LDA and the downfolding Nth-order muffin-tin orbital technique with N=0 and 1 respectively. QMC calculations on 4-site clusters show that the d-wave transition temperature Tc depends sensitively on the parameters. While the N=1 MTO basis set which reproduces all three $pd\sigma$ bands leads to a d-wave transition, the N=0 set which merely reproduces the LDA Fermi surface and velocities does not