Bi2Te_xSe_y series studied by resistivity and thermopower

We study the detailed temperature and composition dependence of the resistivity, $\rho(T)$, and thermopower, $S(T)$, for a series of layered bismuth chalcogenides Bi$_2$Te$_{3-x}$Se$_x$, and report the stoichiometry dependence of the optical band gap. In the resistivity of the most compensated member, Bi$_2$Te$_{2.1}$Se$_{0.9}$, we find a low-temperature plateau whose onset temperature correlates with the high-temperature activation energy. For the whole series $S(T)$ can be described by a simple model for an extrinsic semiconductor. By substituting Se for Te, the Fermi level is tuned from the valence band into the conduction band. The maximum values of $S(T)$, bulk band gap as well the activation energy in the resistivity are found for $x \approx 0.9$

BiOCuS: A new superconducting compound with oxypnictide - related structure

The discovery of about 50 K superconductivity in the tetragonal Fe-based pnictides has stimulated the search for superconductivity in a wide class of materials with similar structure. Copper forms compounds isostructural to LaOFeAs. Single phase BiOCuS can be prepared by a solid state reaction at temperature lower than 500 C from a mixture of Bi2O3, Bi2S3 and Cu2S. The samples have been characterized by means of EDX analysis, X-ray diffraction, magnetic and electrical measurements. The cell parameters are a = 3.8708 A, c = 8.565 A. Charge carrier doping can be realized either by F substitutions for O, or by Cu off-stoichiometry. The latter doping route leads to the occurrence of superconductivity below Tc = 5.8 K

SARCOFAGI NORD-ADRIATICI: ALCUNI ESEMPI ATIPICI

Ovaj kratak pregled sjevernojadranskih sarkofaga zeli prikazati << atipicne» slucajeve u odnosu na kodificirane sheme Ravene i Akvileje. Dobiveni podaci podvlace izvjesnu autonomiju periferije u odnosu na spomenute glavne centre takve produkcije. U ovom kontekstu predstavljena su cetiri sarkofaga koji jasno dokazuju, po mom misljenju, takvu situaciju. Sarkofag Svete Eufemije u Rovinju, datiran iz druge cetvrtine III stoljeéa n.e. a moze se uvrstiti u tip III A arhitektonskih sarkofaga G(abelmann), predlaze zanimljivu varijantu centralne osmerokutne tabule. ldenticno rjesenje prisutno je i na istodobnom sarkofagu F. Hostilius- a Sertorianus-a u Bellunu. Analogan motiv nalazi se na sarkofagu Valerius-a Dinens-a i Attia-e Valeria-e u Splitu, iako je sarkofag tipoloski neslican predasnjima; no, i on vjerojatno pod akvilejskim utjecajem. naljnji poziv na Akvileju nalazi se na neobjavljenom sarkofagu u Riva del Garda, koji predstavlja analognu ali slozeniju soluciju i moze se uvrstiti u grupu sarkofaga Val Policelle, datiranih u druguj polovici II stoljeéa n.e

Optical properties of Bi2Te2Se at ambient and high pressure

The temperature dependence of the complex optical properties of the three-dimensional topological insulator Bi2Te2Se is reported for light polarized in the a-b planes at ambient pressure, as well as the effects of pressure at room temperature. This material displays a semiconducting character with a bulk optical gap of 300 meV at 295 K. In addition to the two expected infrared-active vibrations observed in the planes, there is additional fine structure that is attributed to either the removal of degeneracy or the activation of Raman modes due to disorder. A strong impurity band located at 200 cm^{-1} is also observed. At and just above the optical gap, several interband absorptions are found to show a strong temperature and pressure dependence. As the temperature is lowered these features increase in strength and harden. The application of pressure leads to a very abrupt closing of the gap above 8 GPa, and strongly modifies the interband absorptions in the mid-infrared spectral range. While ab initio calculations fail to predict the collapse of the gap, they do successfully describe the size of the band gap at ambient pressure, and the magnitude and shape of the optical conductivity.Comment: 8 pages, 7 figure

Prenatal exposure to serotonin reuptake inhibitors: a case report

Two premature twins (33 weeks gestation) were born to a woman who had used paroxetine during pregnancy for an anxiety-depression disorder. They were admitted to the NICU, where they showed prolonged RDS, cardiovascular malformations, and facial dysmorphisms. Soon after birth, they also presented abnormal neurobehavioral and motor signs, which partially disappeared during the following weeks, although alterations of tone persisted even at discharge

Internet, el nuevo consumidor y un cambio del paradigma del marketing

En el siguiente trabajo se analiza el impacto de Internet y las nuevas tecnologías en las personas como consumidores, y el impacto en el mercado y los negocios. Se realiza una descripción de estas nuevas tecnologías, cómo es el nuevo consumidor y se analiza si las bases del marketing actual han quedado relegadas por estos cambios.Fil: Yanchina Ubaldini, Ezequiel. Universidad Nacional de Cuyo. Facultad de Ciencias Económicas

Doping nature of native defects in 1T-TiSe2

The transition metal dichalcogenide 1T-TiSe2 is a quasi two-dimensional layered material with a charge density wave (CDW) transition temperature of TCDW 200 K. Self-doping effects for crystals grown at different temperatures introduce structural defects, modify the temperature dependent resistivity and strongly perturbate the CDW phase. Here we study the structural and doping nature of such native defects combining scanning tunneling microscopy/spectroscopy and ab initio calculations. The dominant native single atom dopants we identify in our single crystals are intercalated Ti atoms, Se vacancies and Se substitutions by residual iodine and oxygen.Comment: 5 pages, 3 figure