Search results for "methods"
showing 10 items of 4526 documents
Unraveling the role of the secretor antigen in human rotavirus attachment to histo-blood group antigens
2019
25 Páginas, 7 figuras, 2 tablas
Evolutionary plasticity of SH3 domain binding by Nef proteins of the HIV-1/SIVcpz lentiviral lineage
2021
The accessory protein Nef of human and simian immunodeficiency viruses (HIV and SIV) is an important pathogenicity factor known to interact with cellular protein kinases and other signaling proteins. A canonical SH3 domain binding motif in Nef is required for most of these interactions. For example, HIV-1 Nef activates the tyrosine kinase Hck by tightly binding to its SH3 domain. An archetypal contact between a negatively charged SH3 residue and a highly conserved arginine in Nef (Arg77) plays a key role here. Combining structural analyses with functional assays, we here show that Nef proteins have also developed a distinct structural strategy—termed the "R-clamp”—that favors the formation …
Before and after Science. Radcliffe-Brown e la questione dei rapporti tra metodi di ricerca sul campo, etnografia e teoria
2020
Nella prima parte del capitolo, mi occupo del periodo iniziale della carriera di Radcliffe-Brown che precede la pubblicazione, nel 1922, del suo celebre scritto, di carattere programmatico, su I metodi dell’etnologia e dell’antropologia sociale. Questo periodo di formazione è segnato dal rapporto con Haddon e Rivers, dalle due esperienze di ricerca sul campo nelle isole Andamane e tra gli aborigeni australiani, e dalla riflessione critica sul modello di scienza sociale proposto da Durkheim, riguardante in particolare le teorie formulate da quest’ultimo a proposito dei tipi di morfologia sociale e del ruolo di integrazione sociale svolto dalle credenze e dai rituali religiosi nelle “società …
Characterization of LiF and CaF2 surfaces using MIES and UPS (HeI)
1998
Metastable impact electron spectroscopy (MIES) and UPS (HeI) in combination with ab initio calculations (CRYSTALcode) were applied to study surface and bulk defects in LiF and CaF2. The investigated stoichiometric, defective and doped surfaces are LiF, LiF doped with Mg, and CaF2. The experimental information obtained on the electronic structure of stoichiometric and defective surfaces of LiF (100), LiF on W (110) and CaF2 (111) is discussed on the basis of the ab initio calculations. MIES spectra show features from Li agglomerates on the surface of electron bombarded LiF. The electronic structure of the LiF:Mg single crystal shows additional features above the valence band maximum caused b…
A selective microscale x-ray fluorescence analyzing method for determination of trace elements
1973
Abstract A new selective X-ray fluorescence analyzing method for trace element determination has been developed. In this method each trace element is measured independently. The excitation source is an X-ray tube that has a changeable anode and a variable high voltage. The exciting radiation is shaped with critical absorbers. The sample is viewed at backward angles through an absorber to reduce backscattered radiation. The estimated accuracy of this method is of the order of 10 per cent in thesub-ppm range of trace element concentration in organic samples. Measurement times are of the order of a few minutes.
Theoretical study of the formation reaction of the methyl vinyl ketone: A conformational approach
2005
The formation reaction of both isomers of the methyl vinyl ketone (MVK) from the corresponding alkoxy radicals was investigated by means of theoretical methods based on quantum chemistry. Perturbative unrestricted Moller–Plesset (UMP2) and density functional methods B3LYP and BH and HLYP were used to obtain the stationary points on the potential energy surface. In addition to this, the interconversion reaction between both isomers of the MVK was studied, characterizing the corresponding transition state. A conformational study was done, and the energy and geometry of the stationary points located were analyzed by means of ab initio calculations. © 2005 Wiley Periodicals, Inc. Int J Quantum …
Thermochemical analysis of the OH+C2H4→C2H4OH reaction using accurate theoretical methods
2001
Abstract The radical addition of hydroxyl radical to ethene has been investigated using ab initio methods and density functional theory. The structure and energetics of reactants, prereaction complex, transition state structure and radical product have been optimized and vibrational frequencies have been calculated at the HF, MP2, B88, and B3LYP level using 6-31G* and 6-311G** basis sets. The energetics of the reaction is characterized within the MP2, DFT, G2, CBS, and BAC approaches. The evolution of the barrier height and reaction enthalpy has been systematically investigated with respect to the methodological approach employed. The best agreement with experimental results for the barrier…
The contribution of the Italian Northern Cross Radiotelescope to the Gamma-Ray Observatory Pulsar Timing Network
1992
The observation of pulsars at gamma-ray energy requires updated pulsar parameters in order to fold the gamma-ray data over time intervals of weeks. The Compton Gamma-Ray Observatory Institute has set up an international agreement including several radiotelescopes and pulsar observers in order to provide a suitable timing support at radio wavelengths. In this paper we describe the system used at the Italian Northern Cross for the pulse timing observations related to the GRO mission.
Search for radio pulsations in four anomalous X-ray pulsars and discovery of two new pulsars
2007
We have performed deep searches for radio pulsations from four southern anomalous X-ray pulsars (AXPs) to investigate their physical nature in comparison with the rotation powered pulsars. The data were acquired using the Parkes radio telescope with the 1.4 GHz multibeam receiver. No pulsed emission with periodicity matching the X-ray ephemeris have been found in the observed targets down to a limit of ∼0.1 mJy. A blind search has also been performed on all the 13 beams of the multibeam receiver (the central beam being pointed on the target AXP), leading to the serendipitous discovery of two new radio pulsars and to the further detection of 18 pulsars. Also a search for single dispersed pul…
Progress in ISOL target–ion source systems
2008
The heart of every ISOL (isotope separation on-line) facility is its target and ion source system. Its efficiency, selectivity and rapidity is decisive for the production of intense and pure ion beams of short-lived isotopes. Recent progress in ISOL target and ion source technology is discussed at the examples of radioactive ion beams of exotic zinc and tin isotopes that were purified by isothermal chromatography and molecular sideband separation respectively. An outlook is given to which other elements these purification methods are applicable.