A hadron blind detector for the PHENIX experiment at RHIC Fraenkel, Z.; Kozlov, A.; Naglis, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2005, Letnik:
546, Številka:
3
Journal Article
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A Hadron Blind Detector (HBD) is being developed for the PHENIX experiment at RHIC. It consists of a Cherenkov radiator operated with pure
CF
4
directly coupled in a windowless configuration to a ...triple-GEM detector element with a CsI photocathode and pad readout. The HBD operates in the bandwidth 6–11.5
eV (110–200
nm). We studied the detector response to minimum ionizing particles and to electrons. We present measurements of the CsI quantum efficiency, which are in very good agreement with previously published results over the bandwidth 6–8.3
eV and extend them up to 10.3
eV. Discharge probability and aging studies of the GEMs and the CsI photocathode in pure
CF
4
are presented.
Nitration of
N
-acetyl-3-methylaceperidazine with a 2–3-fold excess of nitric acid (
d
1.36, 1.48) in glacial acetic acid results in the exclusive formation of mono- and dinitroderivatives. The ...nitration of 3-methylaceperidazine and its
N
-alkyl- and
N
-acetyl-substituted derivatives with a 6–9-fold excess of fuming nitric acid (
d
1.54) in the same conditions results in the formation of both the expected products of mono- and dinitration and a product of the electrophilic addition of nitric acid to a double bond of acenaphthene scaffold of the molecule of nitration product.
The lipopeptaibol trichogin GA IV is a 10 amino acid-long residue and
α-aminoisobutyric acid-rich antibiotic peptide of fungal origin. TOAC (2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic ...acid) spin-labeled analogs of this membrane active peptide were investigated in hydrated bilayers of dipalmitoylphosphatidylcholine by electron spin echo envelope modulation (ESEEM) spectroscopy and pulsed electron-electron double resonance (PELDOR). Since, the ESEEM of the spin label appears to be strongly dependent on the presence of water molecules penetrated into the membrane, this phenomenon was used to study the location of this peptide in the membrane. This was achieved by comparing the ESEEM spectra for peptides labeled at different positions along the amino acid sequence with spectra known for lipids with spin labels at different positions along the hydrocarbon chain. To increase the ESEEM amplitude and to distinguish the hydrogen nuclei of water from lipid protons, membranes were hydrated with deuterated water. The PELDOR spectroscopy technique was chosen to study peptide aggregation and to determine the mutual distance distribution of the spin-labeled peptides in the membrane. The location of the peptide in the membrane and its aggregation state were found to be dependent on the peptide concentration. At a low peptide/lipid molar ratio (less than 1:100) the nonaggregated peptide chain of the trichogin molecules lie parallel to the membrane surface, with TOAC at the 4th residue located near the 9th–11th carbon positions of the
sn-2 lipid chain. Increasing this ratio up to 1:20 leads to a change in peptide orientation, with the N-terminus of the peptide buried deeper into membrane. Under these conditions peptide aggregates are formed with a mean aggregate number of about
N
=
2. The aggregates are further characterized by a broad range of intermolecular distances (1.5–4
nm) between the labels at the N-terminal residues. The major population exhibits a distance of ∼2.5
nm, which is of the same order as the length of the helical peptide. We suggest that the constituting monomers of the dimer are antiparallel oriented.
Properties of frontier orbitals and low-energy electronic transitions in a d0-organometallic complex have been studied by TDDFT and DFT methods using B3LYP hybrid functional and 3-21G*, 6-31G**, SDD, ...CEP-121G, and DGDZVP basis sets. It has been shown that the electronic transition between frontier orbitals in the excitation and absorption spectra is associated with charge transfer mainly from π-type ligands to a central metal d0-ion. The good agreement of the data (the shape and band position of the spectra of electronic absorption and excitation, energy of electronic transitions, and strength of the harmonic oscillator) of quantum-chemical and photophysical studies is demonstrated.
Properties of the frontier orbitals of a
d
0
-organometallic complex with promising photoluminescent and photosensor characteristics have been systematically studied by modern quantum-chemical ...methods. It has been demonstrated that the lowest electronically excited states are related to charge transfer from high-lying ligand-centered molecular orbitals to the predominantly metal-centered lowest unoccupied molecular orbital. Such an approach makes it possible to predict complexes with promising spectral-luminescent properties, including catalytic precursors of early transition metals.
The impact of pumping pulse duration on four-pulse pulsed electron–electron double resonance (PELDOR) data was experimentally studied. For biradicals with known distances between two spin labels, it ...is shown that refocused echo amplitude decreases with increasing the pumping pulse duration and decreasing the distance between spin labels. The effect becomes substantial when the pumping pulse duration is comparable or exceeds the inverse value of the dipole–dipole interaction between spin labels. This effect is essential for determination of distance distribution between labels in double-labeled molecules and for determination of the number of labels in clusters of spin-labeled molecules. PELDOR signal distortion was observed when the pumping pulse position in the time scale coincided with those of the detecting pulses. An approach of signal correction to eliminate this distortion is proposed.
PELDOR (pulsed electron-electron double resonance) spectroscopy was applied to determine spin-spin distances in spin-labeled DNA duplexes (13-mer and 17-mer) containing the damaged sites 8-oxoguanine ...or uncleavable abasic site analogue tetrahydrofuran. The lesions were located in one strand of the DNA, and two nitroxyl spin labels were attached at the 5'- and 3'-ends of the complementary strand. PELDOR data allow us to obtain distances between the two spin labels in DNAs, which turned out to be around 5 nm for the 13-mer DNA and around 6 nm for 17-mer DNA. Results of PELDOR measurements were supported by molecular dynamics calculations. Study of the interaction of DNA fragments with DNA repair enzyme 8-oxoguanine-DNA glycosylase from E. coli (Fpg protein) showed that this interaction leads to a noticeable decrease of the distance between spin labels, which indicates the enzyme-induced bending of the DNA duplex. This bending may be important for the mechanisms of recognition of damaged sites by DNA repair enzymes.
The good wear-resistance of state-of-the-art liquid lubricants is due to the formation of complex metal and organometallic films onto the friction surface, reducing the friction and wear. For this ...purpose, various additives of metal nanopowders are used, especially ones based on copper. The formation and growth of Cu nanoparticles, as well as the tribotechnical characteristics of lubricants, are mainly affected by the choice of stabilizer, because nanoparticles cannot resist the external conditions without protecting their surface. According to quantum chemical studies, the best stabilizer in the series of gelatin, ammonia, sodium borohydride, and sodium citrate is gelatin due to the very large amount of functional groups in its structure. The characterization of physicochemical properties via dynamic light scattering, atomic force microscopy, and electron microscopy, as well as the tribotechnical characteristics of liquid lubricants with stabilized Cu nanoparticles, are consistent with quantum chemical calculations, confirming that Cu nanoparticles stabilized in gelatin possess the better tribotechnical properties than other stabilizers.
Clusters of atmospheric gases (N
2
, CO, Ar) of different composition comprising 11 and 13 molecules have been systematically studied by means of MP2(full)/6-311+G** calculations. The effect of a ...meduim (a nitrogen or carbon monoxide atmosphere) on the properties of the gas molecule dimers has been revealed, and general trends in the formation of large clusters have been determined.
An attempt was made to determine the influence of the nature of the lubricating medium on the qualitative composition of wear products during long-term frictional interaction of a brass-steel ...friction pair in model media. Copper nanoparticles deposited on the steel surface in the form of a tribo-film are formed in the lubricant composition. Using quantum chemical calculations, it was shown that carboxylic acids form complexes with copper ions and clusters. The concentration of iron ions decreases during the transition from formic to caproic acid in the homologous series of monobasic carboxylic acids. It is shown that particles of wear products agglomerate in a lubricating medium with an increase in the time of frictional interaction of friction pairs.
•The lubricating medium affects the composition of wear products during friction of a brass-steel pair.•A tribo-film is formed from copper nanoparticles deposited on a steel surface.•Particles of wear products agglomerate in a lubricating medium with an increase in friction time.
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