Electron capture in GaAs quantum wells via electron-electron and optic phonon scattering

Electron capture times in a separate confinement quantum well (QW) structure with finite electron density are calculated for electron-electron (e-e) and electron-polar optic phonon (e-pop) scattering. We find that the capture time oscillates as function of the QW width for both processes with the same period, but with very different amplitudes. For an electron density of 10^11 cm^-2 the e-e capture time is 10-1000 times larger than the e-pop capture time except for QW widths near the resonance minima, where it is only 2-3 times larger. With increasing electron density the e-e capture time decreases and near the resonance becomes smaller than the e-pop capture time. Our e-e capture time values are two-to-three orders of magnitude larger than previous results of Blom et al. [Appl. Phys. Lett. 62, 1490 (1993)]. The role of the e-e capture in QW lasers is therefore readdressed.Comment: 5 pages, standard LaTeX file + 5 PostScript figures (tarred, compressed and uuencoded) or by request from [email protected], accepted to Appl. Phys. Let

Dermal denticles and morphometrics of the sailfin roughshark Oxynotus paradoxus (Elasmobranchii, Oxynotidae), with comments on its geographic distribution

The dermal denticles of the sailfin roughshark Oxynotus paradoxus are described and illustrated with SEM pictures, based on two specimens captured at the Azores. The flank denticles are similar to those of O. centrina, with a central cusp flanked by two smaller lateral cusps, rising from the lateral ridges, and a secondary median cusp posterior to the main one. Differences in squamation between both species are described. Body proportions of the Azorean specimens are given and found to be consistent with those reported by previous authors. The published information shows depth of capture to have a mode at 570 m. A bathybenthic habitat has been suggested, with spring reproductive migrations to the continental shelf. The presence of this species in the Azores and Mid-Atlantic Ridge represents a significant westward extension of its previously known geographic distribution, the continental shelf and upper slope of the north and eastern Atlantic. It is possible that O. paradoxus is continuously distributed along the north-eastern Atlantic floor, deeper than presently known. Alternatively, separate slope and ridge populations may exist

African-specific molecular taxonomy of prostate cancer

Prostate cancer is characterized by considerable geo-ethnic disparity. African ancestry is a signifcant risk factor, with mortality rates across sub-Saharan Africa of 2.7-fold higher than global averages1 . The contributing genetic and non-genetic factors, and associated mutational processes, are unknown2,3 . Here, through whole-genome sequencing of treatment-naive prostate cancer samples from 183 ancestrally (African versus European) and globally distinct patients, we generate a large cancer genomics resource for sub-Saharan Africa, identifying around 2 million somatic variants. Signifcant African-ancestry-specifc fndings include an elevated tumour mutational burden, increased percentage of genome alteration, a greater number of predicted damaging mutations and a higher total of mutational signatures, and the driver genes NCOA2, STK19, DDX11L1, PCAT1 and SETBP1. Examining all somatic mutational types, we describe a molecular taxonomy for prostate cancer diferentiated by ancestry and defned as global mutational subtypes (GMS). By further including Chinese Asian data, we confrm that GMS-B (copy-number gain) and GMS-D (mutationally noisy) are specifc to African populations, GMS-A (mutationally quiet) is universal (all ethnicities) and the African–European-restricted subtype GMS-C (copy-number losses) predicts poor clinical outcomes. In addition to the clinical beneft of including individuals of African ancestry, our GMS subtypes reveal diferent evolutionary trajectories and mutational processes suggesting that both common genetic and environmental factors contribute to the disparity between ethnicities. Analogous to gene–environment interaction—defned here as a diferent efect of an environmental surrounding in people with diferent ancestries or vice versa—we anticipate that GMS subtypes act as a proxy for intrinsic and extrinsic mutational processes in cancers, promoting global inclusion in landmark studies

The Rockefeller Foundation and the Training of Agricultural Specialists for Latin America: a Profile of Scholars from Latin American Scholarship Program in Agriculture (1951-1962)

Between 1951 and 1962, the Rockefeller Foundation (RF) maintained a scholarship program, the Latin American Scholarships program in agriculture (LAS), which financed the training of 226 Latin American students and researchers who, together, received 297 scholarships for short study periods at leading research centers in countries in the region. These centers were, above all, structures linked to the Office of Special Studies (OSS), a partnership between the Rockefeller Foundation and the Mexican government, and North American universities. The LAS provided the training and circulation of Latin American scholars in a period of great technological advancement in agricultural research and sought to give continental scope to RF’s main and most successful laboratory in the area: Mexico. The profile analysis of 226 LAS scholars is made from a database of 9057 minibiographies of scholars available in the Directory of Fellowships and Scholarships published by the Rockefeller Foundation in the 1970s.Between 1951 and 1962, the Rockefeller Foundation (RF) maintained a scholarship program, the Latin American Scholarships program in agriculture (LAS), which financed the training of 226 Latin American students and researchers who, together, received 297 scholarships for short study periods at leading research centers in countries in the region. These centers were, above all, structures linked to the Office of Special Studies (OSS), a partnership between the Rockefeller Foundation and the Mexican government, and North American universities. The LAS provided the training and circulation of Latin American scholars in a period of great technological advancement in agricultural research and sought to give continental scope to RF’s main and most successful laboratory in the area: Mexico. The profile analysis of 226 LAS scholars is made from a database of 9057 minibiographies of scholars available in the Directory of Fellowships and Scholarships published by the Rockefeller Foundation in the 1970s.Between 1951 and 1962, the Rockefeller Foundation (RF) maintained a scholarship program, the Latin American Scholarships program in agriculture (LAS), which financed the training of 226 Latin American students and researchers who, together, received 297 scholarships for short study periods at leading research centers in countries in the region. These centers were, above all, structures linked to the Office of Special Studies (OSS), a partnership between the Rockefeller Foundation and the Mexican government, and North American universities. The LAS provided the training and circulation of Latin American scholars in a period of great technological advancement in agricultural research and sought to give continental scope to RF’s main and most successful laboratory in the area: Mexico. The profile analysis of 226 LAS scholars is made from a database of 9057 minibiographies of scholars available in the Directory of Fellowships and Scholarships published by the Rockefeller Foundation in the 1970s

Chemical composition and minerals in pyrite ash of an abandoned sulphuric acid production plant

The extraction of sulphur produces a hematite-rich waste, known as roasted pyrite ash, which contains significant amounts of environmentally sensitive elements in variable concentrations and modes of occurrence. Whilst the mineralogy of roasted pyrite ash associated with iron or copper mining has been studied, as this is the main source of sulphur worldwide, the mineralogy, and more importantly, the characterization of submicron, ultrafine and nanoparticles, in coal-derived roasted pyrite ash remain to be resolved. In this work we provide essential data on the chemical composition and nanomineralogical assemblage of roasted pyrite ash. XRD, HR-TEM and FE-SEM were used to identify a large variety of minerals of anthropogenic origin. These phases result from highly complex chemical reactions occurring during the processing of coal pyrite of southern Brazil for sulphur extraction and further manufacture of sulphuric acid. Iron-rich submicron, ultrafine and nanoparticles within the ash may contain high proportions of toxic elements such as As, Se, U, among others. A number of elements, such as As, Cr, Cu, Co, La, Mn, Ni, Pb, Sb, Se, Sr, Ti, Zn, and Zr, were found to be present in individual nanoparticles and submicron, ultrafine and nanominerals (e.g. oxides, sulphates, clays) in concentrations of up to 5%. The study of nanominerals in roasted pyrite ash from coal rejects is important to develop an understanding on the nature of this by-product, and to assess the interaction between emitted nanominerals, ultra-fine particles, and atmospheric gases, rain or body fluids, and thus to evaluate the environmental and health impacts of pyrite ash materials