The positron annihilation lifetimes were measured using a 48V positron source in noncentrosymmetric cubic single crystals of CoSi, FeSi and MnSi. The following lifetimes were determined from the ...positron annihilation time spectra: 168(1) ps for CoSi, 114(1) ps for FeSi and 111(1) ps for MnSi. For single-crystal CoSi, the positron annihilation lifetime was also determined with a 22Na positron source. For CoSi, the lifetimes obtained from different positron sources are consistent. The differences in the positron annihilation lifetimes in MnSi and FeSi, on the one hand, and in the Weyl semimetal CoSi, on the other hand, are possibly caused by the formation of a positron + electron bound state (positronium).
The study of the gas discharge in quasioptical beams of electromagnetic radiation of the terahertz (THz) frequency band is attractive for fundamental and applied research. The study of this discharge ...was made possible by the emergence of unique and reliable sources of radiation of the THz frequency band. Electrovacuum radiation sources of THz band (gyrotrons) have been created at the Institute of Applied Physics (IAP RAS) (Nizhny Novgorod) with a power order of 100 kW in pulsed mode of operation (pulse duration ~ several dozens of µs) and a kilowatt in continuous mode, and investigations of gas discharge phenomena in various gases have been started. Even the first experimental studies of the discharge in noble gases (argon) showed a significant difference in the THz discharge from the discharge at lower frequencies, even in the dynamics of discharge glow. The maximum of the discharge glow was observed after the end of the THz pulse and the afterglow duration was hundreds of microseconds. This paper is devoted to the theoretical and experimental study of the breakdown thresholds of various gases by radiation at 263 and 670 GHz and the study of discharge dynamics in noble and molecular gases under the action of 670 GHz radiation.
Superconductivity in diamond Sidorov, V. A; Ekimov, E. A; Bauer, E. D ...
Nature,
04/2004, Volume:
428, Issue:
6982
Journal Article
Peer reviewed
Open access
Diamond is an electrical insulator well known for its exceptional hardness. It also conducts heat even more effectively than copper, and can withstand very high electric fields. With these physical ...properties, diamond is attractive for electronic applications, particularly when charge carriers are introduced (by chemical doping) into the system. Boron has one less electron than carbon and, because of its small atomic radius, boron is relatively easily incorporated into diamond; as boron acts as a charge acceptor, the resulting diamond is effectively hole-doped. Here we report the discovery of superconductivity in boron-doped diamond synthesized at high pressure (nearly 100,000 atmospheres) and temperature (2,500-2,800 K). Electrical resistivity, magnetic susceptibility, specific heat and field-dependent resistance measurements show that boron-doped diamond is a bulk, type-II superconductor below the superconducting transition temperature Tc 4 K; superconductivity survives in a magnetic field up to Hc2(0) ≥ 3.5 T. The discovery of superconductivity in diamond-structured carbon suggests that Si and Ge, which also form in the diamond structure, may similarly exhibit superconductivity under the appropriate conditions.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This study was aimed at studying the effect of heavy metals and arsenic on the survival and biofilm formation of some saprotrophic microorganisms:
Bacillus megaterium
var.
phosphaticum
,
Bacillus ...mucilaginosus
,
Pectobacterium carotovorum
, and
Escherichia coli
. As a source of heavy metals and arsenic, we used aqueous solutions of NaAsO
2
, Cd(CH
3
COO)
2
, and Pb(NO
3
)
2
(2.5, 25, 250 mg L
−1
). The cultures in the liquid medium had different resistance to the toxicants under study:
B. megaterium
>
B. mucilaginosus
>
P. carotovorum
>
E. coli
. The toxicity of the tested solutions of heavy metals and arsenic for microorganisms can be arranged (decreasing toxicity) as follows: cadmium acetate > lead nitrate > sodium metaarsenite. These experiments revealed some regularities related to the mechanisms of toxic effect of As, Pb, and Cd solutions on the formation of biofilms of soil bacteria, changes in bacterial cellular forms, and their survival.
Bacillus megaterium
strain was the most resistant to high As concentrations and was able to influence the formation of highly structured colonies of bacterial cells with the honeycomb-like structure. The immobilization of heavy metals can be achieved due to their binding into strong compounds with the matrix substances of biofilms and polymeric organic compounds formed during the sporulation of rhizobacteria. It can increase the resistance of bacteria to high concentrations of heavy metals and arsenic. The results obtained can be of great practical importance in the development of biotechnologies related to soil bioremediation, in the field of nanotechnology, crop production, and medicine.
We have used the time differential perturbed angular correlation (TDPAC) spectroscopy to measure the electric and magnetic hyperfine fields in RhGe crystallized in the B20 cubic lattice structure and ...weakly doped with Hf (0.5–2 atomic %) in the temperature range from 5 K to 295 K. Two most commonly used nuclei probes, 111In→111Cd and 181Hf→181Ta, have been used. The experimental results combined with theoretical density functional calculations indicate that the In/Cd impurities substitute into the Ge-site whereas the Ta/Hf probes substitute into the Rh-site. It has also been found that the Ta/Hf impurity strongly distorts the local crystal environment, whereas the effect from the In/Cd probe is weak. There are no reliable evidences of the magnetic order in the studied alloys at low temperatures.
•Novel high-pressure phases.•Local studies of both lattice sites in RhGe.•Study of the very weak magnetism in noncentrosymmetric superconductor.•TDPAC measurements on two most commonly used nuclei probes.•TDPAC measurements at low temperatures.•Digital TDPAC spectrometer.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Plasma created in focused beams of electromagnetic waves in the terahertz frequency range is a fairly new object in gas discharge physics. The specified range, located between the microwave ...and infrared regions of the spectrum of electromagnetic waves, is currently being actively developed. However, until recently, the study of discharge phenomena in it was practically inaccessible. Recent advances in its development are associated primarily with the creation of powerful sources of terahertz radiation—gyrotrons and free electron lasers. This article presents an overview of the latest results of studies of a gaseous terahertz discharge: gas breakdown, discharge propagation, features of the discharge glow, and prospects for a gaseous terahertz discharge as a point source of UV radiation.
The influence of deionized water and heat treatments of samples of epitaxial Cd
x
Hg
1 −
x
Te films on the Hall and ellipsometric parameters is investigated. Water treatment reduces the refractive ...index of natural Cd
x
Hg
1 −
x
Te oxide from 2.1 to 1.2–1.4. This means that a substance with a low refractive index, such as water, is introduced into the oxide. Boiling in water leads to the formation of acceptors with concentrations of up to 10
19
cm
–3
in Cd
x
Hg
1 −
x
Te. Changing the acidity of the medium from alkaline to acidic decelerates the formation of acceptors. Heat treatments after holding in water also lead to the formation of acceptors. It is concluded that an aqueous medium, including water that is absorbed by the natural oxide layer, leads to the formation of acceptors in Cd
x
Hg
1 −
x
Te. The acceptor concentration increases with the temperature of treatments and the amount of available water.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Abstract
Various methods for limiting the plasma volume made it possible to produce a continuous point-like high-temperature terahertz discharge at the Novosibirsk free-electron laser (NovoFEL). When ...a krypton-nitrogen jet was injected into the focus of the NovoFEL radiation, as compressed as possible and having an average power of about 200 W, a spherical plasma with a diameter of 1 mm, temperature of 4–4.5 eV (46 000–52 000 K), and density of 3.5 × 10
17
cm
−3
was obtained. The ion composition of the plasma is represented mainly by triply and doubly ionized krypton atoms (Kr IV and Kr III). The absolute stability of the plasma, which tends to self-oscillate, is achieved through the use of a special negative optical feedback.
A recombinant form of pneumolysin from
Streptococcus pneumoniae
was obtained. By using Vector NTI Advance 11.0 bioinformatic analysis software, specific primers were designed in order to amplify the ...genome fragment of strain No. 3358
S. pneumoniae
serotype 19F containing the nucleotide sequence encoding the full-length pneumolysin protein. A PCR product with a molecular weight corresponding to the nucleotide sequence of the
S. pneumoniae
genome fragment encoding the full-length pneumolysin was obtained. An expression system for recombinant pneumolysin in
E. coli
was constructed. Sequencing confirmed the identity of the inserted nucleotide sequence encoding the full-length recombinant pneumolysin synthesized in
E. coli
M15 strain. Purification of the recombinant protein was performed by affinity chromatography using Ni-Sepharose in 8 M urea buffer solution. Confirmation of the recombinant protein was performed by immunoblotting with monoclonal antibodies to pneumolysin.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Filamentation of ultrashort laser pulses in the atmosphere offers unique opportunities for long-range transmission of high-power laser radiation and standoff detection. With the critical power of ...self-focusing scaling as the laser wavelength squared, the quest for longer-wavelength drivers, which would radically increase the peak power and, hence, the laser energy in a single filament, has been ongoing over two decades, during which time the available laser sources limited filamentation experiments in the atmosphere to the near-infrared and visible ranges. Here, we demonstrate filamentation of ultrashort mid-infrared pulses in the atmosphere for the first time. We show that, with the spectrum of a femtosecond laser driver centered at 3.9 μm, right at the edge of the atmospheric transmission window, radiation energies above 20 mJ and peak powers in excess of 200 GW can be transmitted through the atmosphere in a single filament. Our studies reveal unique properties of mid-infrared filaments, where the generation of powerful mid-infrared supercontinuum is accompanied by unusual scenarios of optical harmonic generation, giving rise to remarkably broad radiation spectra, stretching from the visible to the mid-infrared.
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