Theoretical search for Chevrel phase based thermoelectric materials

We investigate the thermoelectric properties of some semiconducting Chevrel phases. Band structure calculations are used to compute thermopowers and to estimate of the effects of alloying and disorder on carrier mobility. Alloying on the Mo site with transition metals like Re, Ru or Tc to reach a semiconducting composition causes large changes in the electronic structure at the Fermi level. Such alloys are expected to have low carrier mobilities. Filling with transition metals was also found to be incompatible with high thermoelectric performance based on the calculated electronic structures. Filling with Zn, Cu, and especially with Li was found to be favorable. The calculated electronic structures of these filled Chevrel phases are consistent with low scattering of carriers by defects associated with the filling. We expect good mobility and high thermopower in materials with the composition close to (Li,Cu)$_4$Mo$_6$Se$_8$, particularly when Li-rich, and recommend this system for experimental investigation.Comment: 4 two-column pages, 4 embedded ps figure

Lessons from the Great Underground Empire: Pedagogy, computers and False Dawn

The educational use of computers in the UK coincided with growing tensions between educators and government policy. This led to the imposition of a National Curriculum and policy that took scant account of research evidence or the views of professional educators. As a result of this unhappy coincidence, the UK failed to take early advantage of the educational benefits offered by this technology. The exploitation of the unique affordances of computers have seen a false dawn and dashed hopes but, slowly, a body of research has emerged that is now starting to identify where we should look and what we should do. However, the necessary changes would fundamentally alter the roles of teacher and learner within the educational system as well as government policy and this may go some way to explain government reluctance and the systemic inertia in the UK and elsewhere

Respiratory complications in Brazilian patients infected with human immunodeficiency virus Complicações respiratórias em pacientes brasileiros infectados pelo vírus da imunodeficiência humana

PURPOSE: To determine how often and by what means an indentifiable pulmonary pathogen can be recognized in human immunodeficiency virus (HIV) infected patients with respiratory disorders in Brazil, which are the most frequently observed microorganisms and what impact specific therapy has on these agents. PATIENTS AND METHODS: Thirty-five HIV seroposiüve subjects with respiratory complaints were studied. All patients had a complete history, physical examination and blood counts. The pulmonary assessment included chest radiograms; sputum examination for bacterial and fungal pathogens; bronchoscopy with bronchoalveolar lavage and transbronchial biopsy. Patients with treatable complications received standard antimicrobial therapy. RESULTS: One or more microorganisms were found in 24 subjects and another 3 individuals showed nonspecific interstitial pneumonitis. The sputum examination identified the pulmonary pathogens in 7 cases. The bronchoalveolar lavage and the histopathologic examination were diagnostic in 14% and 83%, respectively, of the 28 individuals that were submitted to bronchoscopy. The most frequently identified microorganism was P. carinii (55%), followed by M. tuberculosis (41%) and cytomegalovirus (8%). The clinical, laboratory and radiographic findings failed to distinguish the specific pulmonary pathogens. Twenty-three individuals with P. carinii pneumonitis and/or tuberculosis received specific therapy; among the evaluable patients the therapeutic response rates were 79% for PCP and 100% for TB. CONCLUSIONS: We have determined that tuberculosis, P. carinii and cytomegalovirus pneumonitis are the most common respiratory opportunistic diseases in Brazilian patients infected with HIV. The histologic evaluation was crucial in order to identify the pulmonary pathogens. Tuberculosis in AIDS individuals displayed clinical and radiographic findings atypical for reactivation disease. However, most of the features observed in HIV infected patients had been previously described in infection of the normal host. Furthermore, the AIDS subjects showed a good therapeutic response to anti-tuberculous drugs.<br>OBJETIVO: Determinar a frequência e os meios pelos quais é possível identificar um agente patogênico respiratório em pacientes brasileiros infectados pelo vírus da imunodeficiência humana (HIV); quais são os microorganismos mais comuns; e qual é o impacto da terapêutica específica. PACIENTES E MÉTODOS: Trinta e cinco pacientes HIV positivos, com queixas respiratórias foram estudados. Todos os pacientes tiveram história, exame físico e testes hematólogicos. A avaliação da patologia respiratória incluiu radiografia pulmonar, exame do escarro para bactérias e fungos, broncoscopia com lavagem bronquiolo-alveolar e biopsia transbronquica. Pacientes com patologias tratáveis receberam a terapêutica indicada. RESULTADOS: Um ou mais organismos foram encontrados em 24 pacientes, e outros 3 pacientes mostraram pneumonite intersticial inespecífica. O exame de escarro identificou o agente patogênico pulmonar em 7 casos. O lavado bronquiolo-alveo-lar e o exame histopatológico definiram o diagnóstico em 14% e 83%, respectivamente, entre os 28 pacientes que foram submetidos à broncoscopia. O organismo mais comun foi P.carinii (55%), seguido por M.tuberculosis (41%), e citomegalovírus (8%). Os achados clínicos, laboratoriais e radioló-gicos não discriminaram os agentes patogênicos. Vinte e três pacientes com PCP ou tuberculose receberam terapêutica específica; entre os pacientes que puderam ser avaliados o tratamento foi bem sucedido em 79% dos episódios de PCP e 100% em TB. CONCLUSÕES: Determinamos que TB, PCP e CMV são as causas mais frequentes de infecções respiratórias em pacientes brasileiros infectados pelo HIV. O exame histológico foi essencial para firmar o diagnóstico etiológico. A TB em pacientes aidéticos assumiu formas semelhantes à TB primária em pacientes imunocompetentes e apresentou boa resposta terapêutica