4,703 research outputs found
Testing for Asymmetric Employer Learning and Statistical Discrimination
No full textWe test the implications of a statistical discrimination model with asymmetric learning. Firms receive signals of productivity over time and may use race to infer worker's productivity. Incumbent employers have more information about workers productivity than outside employers. Using data from the NLSY79, we find evidence of asymmetric learning. In addition, employers statistically discriminate against non-college educated black workers at time of hiring. We also find that employers directly observe most of the productivity of college graduates at hiring, and learn very little over time about these workers
Ordering of Ge quantum dots on silicon surfaces via bottom-up and top-down approaches
No full textThe nanoscale ordering of inorganic semiconductor quantum dots (QDs) is crucial to obtain reliable structures for novel nanotechnological applications such as nanomemories, nanolasers and nanoelectronic devices. We have directly grown Ge QDs by physical vapour deposition (PVD) on Si(111), Si(100) and some of its vicinal surfaces and studied innovative bottom up techniques to order such nanostructures. Specifically, we harnessed naturally occurring instabilities due to reconstruction and intrinsic anisotropic diffusion in Si bare surfaces, such as step bunching and natural steps occurring in silicon vicinal surfaces, to order the QDs both in one dimension and in the plane. We have also shown the use of controlled quantities of surfactants, like Sb, dramatically improves the desired ordering. Moreover, we have assisted these self-assembling processes using top-down approaches like Focused Ion Beam (FIB) milling and STM nanoindentation to control the nucleation sites and the density of the Ge QDs. Real-time study of growth and selfassembly has been accomplished using Scanning Tunneling Microscopy imaging in UHV. An explanation of the occurring processes is given, and a software routine is used to quantify the ordering of the QDs both in pre-patterned and bare surfaces. Applications, mainly in the field of Nanocrystal Nonvolatile Memories, are discussed
Ge1-ySny (y=0.01-0.10) alloys on Ge-buffered Si: Synthesis, microstructure, and optical properties
No full textabstract: Novel hydride chemistries are employed to deposit light-emitting Ge [subscript 1- y] Sn [subscript y] alloys with y ≤ 0.1 by Ultra-High Vacuum Chemical Vapor Deposition (UHV-CVD) on Ge-buffered Si wafers. The properties of the resultant materials are systematically compared with similar alloys grown directly on Si wafers. The fundamental difference between the two systems is a fivefold (and higher) decrease in lattice mismatch between film and virtual substrate, allowing direct integration of bulk-like crystals with planar surfaces and relatively low dislocation densities. For y ≤ 0.06, the CVD precursors used were digermane Ge [subscript 2]H[subscript 6] and deuterated stannane SnD[subscript 4]. For y ≥ 0.06, the Ge precursor was changed to trigermane Ge [subscript 3]H[subscript 8], whose higher reactivity enabled the fabrication of supersaturated samples with the target film parameters. In all cases, the Ge wafers were produced using tetragermane Ge [subscript 4]H[subscript 10] as the Ge source. The photoluminescence intensity from Ge [subscript 1− y] Sn [subscript y] /Ge films is expected to increase relative to Ge [subscript 1− y] Sn [subscript y] /Si due to the less defected interface with the virtual substrate. However, while Ge [subscript 1− y] Sn [subscript y] /Si films are largely relaxed, a significant amount of compressive strain may be present in the Ge [subscript 1− y] Sn [subscript y] /Ge case. This compressive strain can reduce the emission intensity by increasing the separation between the direct and indirect edges. In this context, it is shown here that the proposed CVD approach to Ge [subscript 1− y] Sn [subscript y] /Ge makes it possible to approach film thicknesses of about 1 μm, for which the strain is mostly relaxed and the photoluminescence intensity increases by one order of magnitude relative to Ge [subscript 1− y] Sn [subscript y] /Si films. The observed strain relaxation is shown to be consistent with predictions from strain-relaxation models first developed for the Si[subscript 1− x] Ge [subscript x] /Si system. The defect structure and atomic distributions in the films are studied in detail using advanced electron-microscopy techniques, including aberration corrected STEM imaging and EELS mapping of the average diamond–cubic lattice.Copyright 2014 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. along with the following message: The following article appeared in 116, 13 (2014) and may be found at http://dx.doi.org/10.1063/1.489678
Atomic layer deposition of crystalline SrHfO3 directly on Ge (001) for high-k dielectric applications
No full textabstract: The current work explores the crystalline perovskite oxide, strontium hafnate, as a potential high-k gate dielectric for Ge-based transistors. SrHfO3 (SHO) is grown directly on Ge by atomic layer deposition and becomes crystalline with epitaxial registry after post-deposition vacuum annealing at ∼700 °C for 5 min. The 2 × 1 reconstructed, clean Ge (001) surface is a necessary template to achieve crystalline films upon annealing. The SHO films exhibit excellent crystallinity, as shown by x-ray diffraction and transmission electron microscopy. The SHO films have favorable electronic properties for consideration as a high-k gate dielectric on Ge, with satisfactory band offsets (>2 eV), low leakage current (<10[superscript −5] A/cm[superscript 2] at an applied field of 1 MV/cm) at an equivalent oxide thickness of 1 nm, and a reasonable dielectric constant (k ∼ 18). The interface trap density (Dit ) is estimated to be as low as ∼2 × 10[superscript 12] cm[superscript −2] eV[superscript −1] under the current growth and anneal conditions. Some interfacial reaction is observed between SHO and Ge at temperatures above ∼650 °C, which may contribute to increased Dit value. This study confirms the potential for crystalline oxides grown directly on Ge by atomic layer deposition for advanced electronic applications.Copyright 2015 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. along with the following message: The following article appeared in JOURNAL OF APPLIED PHYSICS 117, 5 (2015) and may be found at http://dx.doi.org/10.1063/1.490695
Randomized, controlled trial of breastfeeding versus formula feeding in extremely low birth weight infants
No full textDietary prebiotic oligosaccharides are detectable in the faeces of formula-fed infants
No full textHuman milk oligosaccharides are not digested during intestinal passage and can be detected in stools. In this study it was investigated whether a prebiotic mixture of low-molecular-weight galacto-oligosaccharides (GOS) and high-molecular-weight fructo-oligosaccharides (FOS) can be detected in stool samples of formula-fed infants. The test formula was supplemented with 0.8 g/dl oligosaccharides (GOS+FOS). In the control formula, maltodextrins were used as placebo. Fecal flora was assessed at the beginning (day 1) and at the end of a 28-d feeding period (day 2). At day 2 the content of galacto- and fructo-oligosaccharides in the stool samples were measured. On study day 1, the number of bifidobacteria was not different among the groups (supplemented group: 7.7 (6.2) CFU/g; placebo group: 8.0 (6.0) CFU/g). At the end of the 28-d feeding period, the number of bifidobacteria was significantly higher in the group fed the supplemented formula when compared to placebo (supplemented group: 9.8 (0.7) CFU/g stool; placebo group: 7.1 (4.7) CFU/g stool; p<0.001). In all infants fed the supplemented formula, GOS and FOS could be identified in the stool samples. That was not the case in infants fed the non-supplemented formula. CONCLUSION: The present data confirm the bifidogenicity of oligosaccharides and indicate that dietary galacto-oligosaccharides and long chain fructo-oligosaccharides remain during the whole passage in the lumen of the gastrointestinal tract, similarly to human milk oligosaccharides
OB00040 - Damodarpur Copper Plate 1 (GE 163) of Budhagupta
No full textDamodarpur Copper Plate 1 (GE 163) of Budhagupt
Il sistema finanziario e gli investimenti speculativi
No full textSommario: 1. L’idea di speculazione ed il suo ruolo nel mercato finanziario. - 2. Le pos- sibili conseguenze macroscopiche: le bolle. - 3. Le istituzioni: le borse, gli investitori e le piattaforme. - 4. Il mercato secondario dei titoli obbligazionari. - 5. L’arbitraggio internazionale su titoli a reddito fisso. - 6. L’esposizione dell’investitore: posizioni “corte o scoperte” e “lunghe”. - 7. Il margin trading ed il margin call. - 8. Gli hed- ge funds, fondi speculativi. - 9. Gli strumenti intrinsecamente speculativi. - 10. Le special-purpose acquisition company (SPAC) ed i fondi chiusi. - 11. Conclusione: l’unico speculatore cattivo è quello fallit
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