171,107 research outputs found
Calandra oryzae
No full text48.Calandra oryzae (Linnaeus). Curculio oryzae Linnaeus, Amoen. Acad. 6: 396, 1763. Curculio frugilegus De Geer, Mem. Ins. 5: 273, 1781. Curculio granarius Stroem (not Linnaeus), Danske Vid. Selsk. Skrift. 2: 256, 1783. Sitophilus oryzae (Linnaeus) Gyllenhal, in Schoenherr's Gen. Spec. Cure. 4: 981, 1837. Cossonus quadriniaculatus Walker, Ann. Mag. Nat. Hist. III, 4: 219, 1859. Sphenophorus quadriguttatus Montrouzier, Soc. Ent. France, Ann. III, 8: 910, 1860. Most of the Guam specimens in the collection belong to the large variety, zea-mais (Motschulsky) and were taken at Agat, Piti, and Merizo; one was swept from grass and two were taken from corn. I understand that formal application is to be made to the International Congress of Nomenclature to stabilize the long used name Calandra in place of TODO TODOPublished as part of Zimmerman, Elwood C., 1942, Curculionidae of Guam, pp. 73-146 in Insects of Guam I, Honolulu, Hawaii :Bernice P. Bishop Museum on page 145, DOI: 10.5281/zenodo.515996
Surface States of the (110) Surface of GaAs
No full textResults are presented of a new calculation of the surface states at the (110) surface of GaAs. By using Koster-Slater parameters fitted to bulk optical and photoemission data, the surface band structure has been calculated with a LCAO method. The main conclusion is the existence of two surface bands, one inside the band gap at about 1 eV from the top of the valence band and the other a few tenths of an eV below it. The results show good agreement with the available experimental data
Hole density and Tc behaviour in YBa2Cu3O7 - x
No full textThe behaviour of the hole number in YBCO systems as a function of the oxygen deficiency x is studied theoretically by calculating the density of electron states for several different superstructures formed by periodic arrangements of the oxygen vacancies. The characteristic features of the electronic properties for chain copper sites with different coordination are pointed out and their relevance in determining the number of carriers for oxygen planes is illustrated. It is shown that the curve of the hole number as a function of x shows plateaus and jumps similar to those found in the Tc versus x curves if the de-oxygenation process takes place by forming fragmented chains. Structures formed by filled and empty chains only give a smooth hole behaviour as a function of the composition. The results of the numerical calculations can be understood by a simple model giving the Fermi energy shift in terms of the concentrations of Cu(1) sites with different coordination. © 1990
Intrinsic Surface States in III-V Compounds
No full textThe electronic structure of the (110) face of GaAs, GaP and InSb is investigated using a realistic tight-binding model. Calculations of the surface band structure are presented and the nature of the various surface bands is discussed. The results are in agreement with the experimental data and provide a quantitative description of the cation-derived surface states lying in the bulk band gap
Il caso Deutsch. Ebrei argentini negli Stati Uniti tra diaspora, rifugio ed esilio politico
No full textRielaborazione delle relazioni presentate in occasione del convegno " Lo sgurado esiliato. Cultura europea e cultura americana fra delocalizzazione e radicamento" presso l'Universitá di Roma TRE nwl luglio del 2007
Evidence for a GABAergic system in rodent and human testis: Local GABA production and GABA receptors
No full textThe major neurotransmitter of the central nervous system, gamma-aminobutyric acid (GABA), exerts its actions through GABA(A), GABA(B) and GABA(C) receptors. GABA and GABA receptors are, however, also present in several non-neural tissues, including the endocrine organs pituitary, pancreas and testis. In the case of the rat testis, GABA appears to be linked to the regulation of steroid synthesis by Leydig cells via GABA(A) receptors, but neither testicular sources of GABA, nor the precise nature of testicular GABA receptors are fully known. We examined these points in rat, mouse, hamster and human testicular samples. RT-PCR followed by sequencing showed that the GABA-synthesizing enzymes glutamate decarboxylase (GAD) 65 and/or GAD67, as well as the vesicular GABA transporter vesicular inhibitory amino acid transporter (VIAAT/VGAT) are expressed. Testicular GAD in the rat was shown to be functionally active by using a GAD assay, and Western blot analysis confirmed the presence of GAD65 and GAD67. Interstitial cells, most of which are Leydig cells according to their location and morphological characteristics, showed positive immunoreaction for GAD and VIAAT/VGAT proteins. In addition, several GABA(A) receptor subunits (alpha1-3, beta1-3, gamma1-3), as well as GABAB receptor subunits R1 and R2, were detected by RT-PCR. Western blot analysis confirmed the results for GABA(A) receptor subunits beta2/3 in the rat, and immunohistochemistry identified interstitial Leydig cells to possess immunoreactive GABA(A) receptor subunits beta2/3 and alpha1. The presence of GABA(A) receptor subunit alpha1 mRNA in interstitial cells of the rat testis was further shown after laser microdissection followed by RT-PCR analysis. In summary, these results describe molecular details of the components of an intratesticular GABAergic system expressed in the endocrine compartment of rodent and human testes. While the physiological significance of this peripheral neuroendocrine system conserved throughout species remains to be elucidated, its mere presence in humans suggests the possibility that clinically used drugs might be able to interfere with testicular function. Copyright (C) 2003 S. Karger AG, Basel
Correlated one-hole spectra of YBa2Cu3O7 in the bulk and at the surface
No full textThe one-hole valence spectrum of YBa2Cu3O7 is calculated using an accurate tight-binding hamiltonian and a Hubbard model to treat correlation effects. Intra-atomic Coulomb integrals for holes sitting on Cu or O sites are considered and the one-hole self-energy is computed in the low density approximation. The calculated spectrum is compared with photoemission and X-ray emission experiments. This allows to point out a number of problems that arise in assigning the observed structures to a specific atom and to understand some aspects of the data. To evaluate the role of the surface in determining the shape of the photoemission energy distribution curves, the one-hole spectrum is calculated for the Ba-O4 surface. Oxygen induced surface states are shown to be important in determining the intensity of the observed structures. © 1989 Springer-Verlag
Charge density wave in single-layer Pb/Ge(111) driven by Pb-substrate exchange interaction
No full textSingle layer Pb on top of (111) surfaces of group IV semiconductors hosts charge density wave and superconductivity depending on the coverage and on the substrate. These systems are normally considered to be experimental realizations of single band Hubbard models and their properties are mostly investigated using lattice models with frozen structural degrees of freedom, although the reliability of this approximation is unclear. Here, we consider the case of Pb/Ge(111) at coverage, for which surface x-ray diffraction and angle-resolved photoemission spectroscopy data are available. By performing first-principles calculations, we demonstrate that the nonlocal exchange between Pb and the substrate drives the system into a charge density wave. The electronic structure of this charge ordered phase is mainly determined by two effects: The magnitude of the Pb distortion and the large spin-orbit coupling. Finally, we show that the effect applies also to the phase of Pb/Si(111) where the Pb-substrate exchange interaction increases the bandwidth by more than a factor with respect to density functional theory , in better agreement with scanning tunneling spectroscopy data. The delicate interplay between substrate, structural, and electronic degrees of freedom invalidates the widespread interpretation available in literature considering these compounds as physical realizations of single band Hubbard models
Charge density wave and spin 1/2 insulating state in single layer 1T-NbS2
No full textIn bulk samples and few layer flakes, the transition metal dichalcogenides NbS 2 and NbSe 2 assume the H polytype structure with trigonal prismatic coordination of the Nb atom. Recently, however, single and few layers of 1T-NbSe 2 with octahedral coordination around the transition metal ion were synthesized. Motivated by these experiments and by using first-principles calculations, we investigate the structural, electronic and dynamical properties of single layer 1T-NbS 2 . We find that single-layer 1T-NbS 2 undergoes a √13 × √13 star-of-David charge density wave. Within the generalized gradient approximation, the weak interaction between the stars leads to an ultraflat band that results to be located at the Fermi level and isolated from all other bands. The spin-polarized generalized gradient approximation stabilizes a total spin 1/2 magnetic state with a 0.21 μ B magnetic moment localized on the central Nb in the star and the opening of a 0.15 eV band gap. In the GGA + U framework, the magnetic moment on the central Nb is enhanced to 0.41 μ B and a larger gap occurs. Most important, this approximation gives a small energy difference between the 1T and 1H polytypes (only +0.5 mRy/Nb), suggesting that the 1T-polytype can be synthesized in a similar way as done for single layer 1T-NbSe 2 . Finally we compute first and second nearest neighbors magnetic inter-star exchange interactions finding J 1 = 9.5 K and J 2 = 0.4 K ferromagnetic coupling constants
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