Chain-forming zintl antimonides as novel thermoelectric materials

Zintl phases, a subset of intermetallic compounds characterized by covalently-bonded "sub-structures," surrounded by highly electropositive cations, exhibit precisely the characteristics desired for thermoelectric applications. The requirement that Zintl compounds satisfy the valence of anions through the formation of covalent substructures leads to many unique, complex crystal structures. Such complexity often leads to exceptionally low lattice thermal conductivity due to the containment of heat in low velocity optical modes in the phonon dispersion. To date, excellent thermoelectric properties have been demonstrated in several Zintl compounds. However, compared with the large number of known Zintl phases, very few have been investigated as thermoelectric materials.

From this pool of uninvestigated compounds, we selected a class of Zintl antimonides that share a common structural motif: anionic moieties resembling infinite chains of linked <i>Mi>Sb₄ tetrahedra, where $M$ is a triel element. The compounds discussed in this thesis (<italic>Aitalic>₅<italic>Mitalic>₂Sb₆ and <i>Ai>₃<i>Mi>Sb₃, where <i>Ai> = Ca or Sr and <i>Mi> = Al, Ga and In) crystallize as four distinct, but closely related "chain-forming" structure types. This thesis describes the thermoelectric characterization and optimization of these phases, and explores the influence of their chemistry and structure on the thermal and electronic transport properties. Due to their large unit cells, each compound exhibits exceptionally low lattice thermal conductivity (0.4 - 0.6 W/mK at 1000 K), approaching the predicted glassy minimum at high temperatures. A combination of Density Functional calculations and classical transport models were used to explain the experimentally observed electronic transport properties of each compound. Consistent with the Zintl electron counting formalism, <italic>Aitalic>₅<italic>Mitalic>₂Sb₆ and <i>Ai>₃<i>Mi>Sb₃ phases were found to have filled valence bands and exhibit intrinsic electronic properties. Doping with divalent transition metals (Zn²⁺ and Mn²⁺) on the <i>Mi>³⁺ site, or Na¹⁺ on the <i>Ai>³⁺ site allowed for rational control of the carrier concentration and a transition towards degenerate semiconducting behavior. In optimally-doped samples, promising peak <i>zTi> values between 0.4 and 0.9 were obtained, highlighting the value of continued investigations of complex Zintl phases.

The ionic basis of frequency selectivity in hair cells of the bullfrog's sacculus

Hair cells from the bull frog's sacculus, a vestibular organ responding to substrate-borne vibration, possess electrically resonant membrane properties which maximize the sensitivity of each cell to a particular frequency of mechanical input. The electrical resonance of these cells and its underlying ionic basis were studied by applying gigohm-seal recording techniques to solitary hair cells enzymatically dissociated from the sacculus. The contribution of electrical resonance to frequency selectivity was assessed from microelectrode recordings from hair cells in an excised preparation of the sacculus.

Electrical resonance in the hair cell is demonstrated by damped membrane-potential oscillations in response to extrinsic current pulses applied through the recording pipette. This response is analyzed as that of a damped harmonic oscillator. Oscillation frequency rises with membrane depolarization, from 80-160 Hz at resting potential to asymptotic values of 200-250 Hz. The sharpness of electrical tuning, denoted by the electrical quality factor, Q_e, is a bell-shaped function of membrane voltage, reaching a maximum value around eight at a membrane potential slightly positive to the resting potential.

In whole cells, three time-variant ionic currents are activated at voltages more positive than -60 to -50 mV; these are identified as a voltage-dependent, non-inactivating Ca current (I_ca), a voltage-dependent, transient K current (Ia), and a Ca-dependent K current (Ic). The C channel is identified in excised, inside-out membrane patches on the basis of its large conductance (130-200 pS), its selective permeability to Kover Na or Cl, and its activation by internal Ca ions and membrane depolarization. Analysis of open- and closed-lifetime distributions suggests that the C channel can assume at least two open and three closed kinetic states.</sub>

Exposing hair cells to external solutions that inhibit the Ca or C conductances degrades the electrical resonance properties measured under current-clamp conditions, while blocking the A conductance has no significant effect, providing evidence that only the Ca and C conductances participate in the resonance mechanism. To test the sufficiency of these two conductances to account for electrical resonance, a mathematical model is developed that describes I_ca, Ic, and intracellular Ca concentration during voltage-clamp steps. Ica</sub> activation is approximated by a third-order Hodgkin-Huxley kinetic scheme. Ca entering the cell is assumed to be confined to a small submembrane compartment which contains an excess of Ca buffer; Ca leaves this space with first-order kinetics. The Ca- and voltage-dependent activation of C channels is described by a five-state kinetic scheme suggested by the results of single-channel observations. Parameter values in the model are adjusted to fit the waveforms of Ica</sub> and Ic evoked by a series of voltage-clamp steps in a single cell. Having been thus constrained, the model correctly predicts the character of voltage oscillations produced by current-clamp steps, including the dependencies of oscillation frequency and Qe on membrane voltage. The model shows quantitatively how the Ca and C conductances interact, via changes in intracellular Ca concentration, to produce electrical resonance in a vertebrate hair cell.</sub>

Retórica e religiosidade em cena: as moralidades de Gil Vicente

Esta tese analisa as moralidades vicentinas a partir dos preceitos retóricos presentes na Arte Retórica de Aristóteles e na retórica latina a fim de observar possíveis pontos de identifica��ão das moralidades com os sermões medievais. Para tanto, investiga como a retórica influenciou os diversos tratados de prédica que orientaram a produção de sermões no período. O conhecimento das técnicas retóricas, seja em sua formulação antiga, ou em suas atualizações, mostra-se um importante meio de interpretação não só das estratégias persuasivas das moralidades, como também na compreensão do sentido mais profundo do texto. O corpus vicentino de interesse para esta investigação foi delimitado e organizado a partir da distinção dos discursos epidíticos, deliberativo e judiciário no que concerne à identifica��ão dos valores e argumentos predominantes nos autos analisados, quais sejam: a exaltação das virtudes e da Virgem nos autos da Fé e da Mofina Mendes e as vantagens dos discursos que visam à deliberação nos autos da Alma e da Feira, além da construção argumentativa no diálogo das personagens que acusam/defendem nos autos da Barca do Inferno e Purgatório

Factors influencing the timing and frequency of spawning and fecundity of the goldlined seabream (Rhabdosargus sarba) (Sparidae) in the lower reaches of an estuary

We have studied the reproductive biology of the goldlined seabream (Rhabdosargus sarba) in the lower Swan River Estuary in Western Australia, focusing particularly on elucidating the factors influencing the duration, timing, and frequency of spawning and on determining potential annual fecundity. Our results demonstrate that 1) Rhabdosargus sarba has indeterminate fecundity, 2) oocyte hydration commences soon after dusk (ca. 18:30 h) and is complete by ca. 01:30−04:30 h and 3) fish with ovaries containing migratory nucleus oocytes, hydrated oocytes, or postovulatory follicles were caught between July and November. However, in July and August, their prevalence was low, whereas that of fish with ovaries containing substantial numbers of atretic yolk granule oocytes was high. Thus, spawning activity did not start to peak until September (early spring), when salinities were rising markedly from their winter minima. The prevalence of spawning was positively correlated with tidal height and was greatest on days when the tide changed from flood to ebb at ca. 06:00 h, i.e., just after spawning had ceased. Because our estimate of the average daily prevalence of spawning by females during the spawning season (July to November) was 36.5%, individual females were estimated to spawn, on average, at intervals of about 2.7 days and thus about 45 times during that period. Therefore, because female R. sarba with total lengths of 180, 220, and 260 mm were estimated to have batch fecundities of about 4500, 7700, and 12,400 eggs, respectively, they had potential annual fecundities of about 204,300, 346,100 and 557,500 eggs, respectively. Because spawning occurs just prior to strong ebb tides, the eggs of R. sarba are likely to be transported out of the estuary into coastal waters where salinities remain at ca. 35‰. Such downstream transport would account for the fact that, although R. sarba exhibits substantial spawning activity in the lower Swan River Estuary, few of its early juveniles are recruited into the nearshore shallow waters of this estuary.

Effects of physiological doses of vitamin D sub(3) (Cholecalciferol) on induced molting and growth in giant freshwater prawn, Macrobrachium rosenbergii (de Man)

Effects of three different doses of vitamin D sub(3) on molting, growth, and calcium and phosphate composition of tissue and molt during the grow-out of the giant freshwater prawn Macrobrachium rosenbergii (average weight 10.56 ± 0.20 g), obtained from a grow-out pond, were studied. Intramuscular doses of vitamin D sub(3) (100, 500 and 2000 IU/kg body weight) were given on the 1st, 3rd, 5th, 7th, 9th, 11th, 13th, 15th, 20th, 25th and 30th days. All the experimental animals were fed with a basal diet containing fish meal, shrimp meal, wheat flour, groundnut de-oiled cake, soybean meal and wheat bran at 3% of the body weight. The numbers of molts were recorded as 20±0.50, 29±1.16, 51±1.87, and 30±1.60 in control, 100, 500 and 2000 IU/kg body weight physiological doses, respectively. Maximum growth was recorded in prawns given 500 IU/ kg dose. Survival was between 58.33 ± 9.13 and 77.77 ± 8.61%. The ash content and calcium level increased significantly (p<0.05) and recorded the highest values in 500 IU/kg physiological dose. However, the inorganic phosphate (P sub(i)) content recorded the highest values in tissue in 2000 IU/kg dose (p<0.05, F = 50.60613). There is no significant difference in calcium contents (p>0.05) in both tissue and molt at 500 and 2000 IU/kg doses. It was found that a higher physiological dose (2000 IU/kg) of vitamin D sub(3) increased the rate of mortality. Results have shown that vitamin D sub(3) has a positive impact on the growth and survival of M. rosenbergii and it interferes with the metabolism of Ca and P sub(i), in tissue, and alters molting frequency. Results on physiological dose suggest an alternative and effective dietary supplementation method of vitamin D sub(3) in the grow-out phase of M. rosenbergii.

可生物降解聚酯及其共聚物的合成

生物降解高分子材料是当今高分子材料领域的研究热点。本论文引入了一种新型的催化剂－Ca���化剂用于合成生物降解高分子PCL及其嵌段共聚物PEO－PCL、PEO－PCL－PEO、PCL－PEO，另外对嵌段共聚物PLLA－PEO的合成也做了探索性的研究。实验结果表明：1、Ca���化剂从氨钙配合物出发制备，利用各种不同的配体对其配位（如已内酯、环氧丙烷和乙腈），并在适当温度下加热陈化，催化活性得到明显的改善。2、Ca���化剂可以高效催化已内酯的聚合。详细讨论了Ca���化剂催化已内酯聚合的聚全条件。在室温至100 ℃，钙催化剂均能有效催化已内酯聚合，单体转化率接近100%。随着单体与催化剂的比值M／I、聚合温度和时间的变化聚合物的分子量MW发生相应的变化。MW与M／I的线性关系说明了钙催化剂聚合已内酯的准活性特征。高的聚合温度可以获得主的转化率，但聚合物分子量却相应降低。在一定的聚合时间内MW随着聚合时间的增加而增加，但如果聚合时间过长MW会有所降低，分子量分布变宽，说明聚合后期随着单体的减少降解反应和微量的酯交换反应显著。最高分子量出现在25万到30万左右。另外，对聚合物做了几种力学测试（强度S、模量E和伸长率σ），发现随着PCL分子量的增加，上述几种力学性能发生相应的变化。MW在20万左右时S＝28MPa，E=256MPa，σ=743%。3、 Ca���化剂既可以制备PEO－PCL嵌段共聚物，也可以制备PCL－PEO嵌段共聚物。在两种共聚物的基础上还可以继续制备三嵌段共聚物。此外，Ca���化剂还可以用于制备嵌段共聚物PLLA－PEO。通过NMR，GPC，DSC等测试手段证明所得的共聚物确实为嵌段共聚物。

Early-type stars observed in the ESO UVES Paranal Observatory Project - III. Sub-parsec and AU-scale structure in the interstellar medium

UVES interstellar observations from the Paranal Observatory Project are presented for early-type stars located in the line of sight to the nearby open clusters IC 2391 (Omni Vel) and NGC 6475 (M7), with spectroscopic resolution R similar to 80 000 and signal-to-noise ratios in the Ti II (3383 angstrom), Ca II K, CH+ (4232 angstrom), Na I D and K I (7698 angstrom) lines of several hundred. The sightlines are a mixture of cluster and non-cluster objects. A total of 22 early-type stars (A and B type) are present in our sample towards IC 2391, with 21 towards NGC 6475/M7, and enable us to probe for differences in column density on scales from similar to 0.07 to 7.3 and similar to 0.05 to 4.9 pc in the respective clusters. Additionally, towards Praesepe the Na I D interstellar variation only is probed towards 13 sightlines and transverse scales of similar to 0.16-10.7 pc at R = 70 000. Towards IC 2391 variations are found in Ti II, Ca II K and Na I D column density in different sightlines of up to 0.7, 1.0 and 1.8 dex (excluding one star), respectively. This kind of variability correlates well with the Hipparcos parallax of the objects, and probes structure within the Local Bubble. For cluster-only objects the variations are 0.3, 0.3 and 0.5 dex, respectively. For the field of view towards NGC6475 the corresponding maximum variations are somewhat smaller, being 0.5, 0.3, 0.8 and 1.0 dex for Ti II, Ca II K, Na I and K I, respectively, for all objects and 0.4, 0.2, 0.6 and 0.7 dex for the cluster-only objects. These are uncorrelated with parallax, and again demonstrate that Ca II K tends to be more smoothly distributed than Na I D. A few likely cluster sightlines show evidence for CH+ and variations in this molecular species of a factor of 10 in equivalent width over sub-pc scales. Towards Praesepe variation in interstellar Na I D is small, being a maximum of only similar to 0.4 dex (including measurement errors), but with fewer sightlines studied. Overall, the scatter in the data is similar for the singly ionized species Ti II and Ca II, lending more support to the hypothesis that these two species sample similar parts of the interstellar medium (ISM). This also appears to be the case for the neutral species Na I D and K I in the one cluster studied. Finally, multiple-epoch observations from a variety of archive sources are used to search for astronomical unit (au) scale structure in the ISM towards 46 sightlines. There are tentative indications of structure on scales of tens to thousands of au for three sightlines. Future observations will confirm the veracity or otherwise of the time-variable components and others presented.

Early-type stars observed in the ESO UVES Paranal Observatory Project - V. Time-variable interstellar absorption

The structure and properties of the diffuse interstellar medium (ISM) on small scales, sub-au to 1 pc, are poorly understood. We compare interstellar absorption-lines, observed towards a selection of O- and B-type stars at two or more epochs, to search for variations over time caused by the transverse motion of each star combined with changes in the structure in the foreground ISM. Two sets of data were used: 83 VLT- UVES spectra with approximately 6 yr between epochs and 21 McDonald observatory 2.7m telescope echelle spectra with 6 - 20 yr between epochs, over a range of scales from 0 - 360 au. The interstellar absorption-lines observed at the two epochs were subtracted and searched for any residuals due to changes in the foreground ISM. Of the 104 sightlines investigated with typically five or more components in Na I D, possible temporal variation was identified in five UVES spectra (six components), in Ca II, Ca I and/or Na I absorption-lines. The variations detected range from 7\% to a factor of 3.6 in column density. No variation was found in any other interstellar species. Most sightlines show no variation, with 3{\sigma} upper limits to changes of the order 0.1 - 0.3 dex in Ca II and Na I. These variations observed imply that fine-scale structure is present in the ISM, but at the resolution available in this study, is not very common at visible wavelengths. A determination of the electron densities and lower limits to the total number density of a sample of the sightlines implies that there is no striking difference between these parameters in sightlines with, and sightlines without, varying components.

Activitat 5. J.-H. Fragonard

Material didàctic del grup d'investigació Observatori sobre la Didàctica de les Arts (ODAS)

Activitats: Les principals activitats recents a l'EPS

L'objecte d'aquest apartat és que en cada número es faci esment de les principals activitats realitzades a l'EPS des de la publicació del número anterior. Com que aquest és el primer número de la RePiSta s'ha optat per fer una ressenya de les principals activitats que s'han dut a terme entre la inauguració dels curs acadèmic 2006-2007 i la inauguració de l’actual curs 2007-2008

Activitats: Les principals activitats recents a l'EPS

L'objecte d'aquest apartat és que en cada número es faci esment de les principals activitats realitzades a l'EPS des de la publicació del número anterior

Estudio comparado sobre la tutorización de los estudiantes universitarios. Estudios de caso: Universidad de Santiago de Compostela (España) y Università degli Studi di Torino (Italia)

Esta comunicación se ocupa de la descripción del papel de los servicios de tutoría en las instituciones de educación superior de los dos países estudiados: España e Italia. Después de una breve descripción general sobre los principales elementos presentes en este tema (Tutoría universitaria) se realiza la exposición de dos estudios de caso. El primero realizado en la universidad española de Santiago de Compostela y el segundo en la universidad italiana de Turín. A través de los estudios de caso se expone en primer lugar, de modo general, la situación en este ámbito a nivel legal y organizativo en ambos países y a continuación, de modo particular, la situación en las dos universidades elegidas. Ambas instituciones están realizando, en el ámbito de orientación universitaria en general y de la tutoría en particular, avances importantes y muestran un fuerte compromiso en relación con este aspecto. Por último concluimos el artículo realizando una breve síntesis de los aspectos tratados y presentando diferentes interrogantes que puedas suscitar el debate y la reflexión sobre los puntos fuertes y débiles de cada uno de los sistemas de tutoría y su posible transferencia y adaptabilidad a diferentes contextos

La Acción tutorial como elemento dinamizador en la vida universitaria del alumno

La introducción de nuevos modelos de enseñanza más centrados en el alumno es una de las prioridades del nuevo enfoque pedagógico que se pretende desarrollar para la implantación del Espacio Europeo de Educación Superior. Uno de los aspectos claves será la articulación de sistemas de tutorización flexibles e innovadores que despierten mayor interés por parte de nuestros alumnos y dinamicen la vida socio-cultural de los centros. En este trabajo se presenta una síntesis de los resultados obtenidos mediante la puesta en marcha en la Facultad de Ciencias Económicas y Empresariales de la Universidad de Oviedo de tres acciones innovadoras y dinamizadoras de la acción tutorial: el Café Matemático, un sistema de tutorías entre iguales y un ciclo de cine sobre Matemáticas, Economía y Cine. Se efectuaron dos encuestas entre los alumnos que participaron en estas actividades cuyos principales resultados son analizados. Se extraen conclusiones y sintetizan las opiniones que los profesores participantes en estas iniciativas han ido desarrollando

Implantació d’un manual de gestió en una indústria de llescats

Estudi sobre la implantació d’un manual de gestió en una indústria de llescats, realitzat a l’empresa Serra&Mota de la Cellera de Ter (consta d’un sistema APPCC i un manual de qualitat)

Pla d'acció tutorial de l'Escola Universitària d'Estudis Empresarials de la UB

L’acció tutorial constitueix un element més del sistema d’educació superior orientat a maximitzar l’aprofitament que l’estudiant fa del seu pas per la universitat, coneixent les necessitats dels alumnes i adequant els recursos i metodologies al seu procés d’ensenyamentaprenentatge. Un element que cobra una importància fonamental davant els canvis que s’han produït en els darrers anys en el context de l’educació universitària, tant pel que fa al creixement en l’oferta d’estudis i centres que ofereixen carreres, com en el perfil dels estudiants que accedeixen a les aules de les facultats i escoles universitàries. L’escenari actual posa de manifest la necessitat de pensar en accions adreçades a millorar l’adaptació a la universitat, com aquelles dirigides a orientar i assessorar l’estudiant al llarg del estudis fins a la sortida al mercat laboral. De tal manera que, els diferents estudiants que accedeixen a una carrera puguin desenvolupar un procés formatiu i personal d’acord amb les seves capacitats, necessitats i interessos, disposant de la màxima informació i orientació adequada. En aquest sentit, l’objecte d’aquest text és descriure un Pla d’Acció Tutorial, ubicat en un dels ensenyaments més demandats i massificats de la Universitat de Barcelona, la Diplomatura en Ciències Empresarials, amb un perfil d’estudiants amb un nivell d’heterogeneïtat alt i un fracàs acadèmic en el primer any de carrera elevat. S’exposa l’estructura del pla, quina és la seva organització, els instruments de treball emprats, i quines són les diferents actuacions que configuren aquest programa. Finalment s’assenyalen algunes consideracions valoratives sobre la implementació del PAT, i es plantegen algunes qüestions que van apareixent fruit dels anys de funcionament i de les reflexions internes de l’equip de tutors