The detailed studies of the surface structure of synthetic boron-doped diamond single crystals using both conventional X-ray and synchrotron nano- and microbeam diffraction, as well as atomic force ...microscopy and micro-Raman spectroscopy, were carried out to clarify the recently discovered features in them. The arbitrary shaped islands towering above the (111) diamond surface are formed at the final stage of the crystal growth. Their lateral dimensions are from several to tens of microns and their height is from 0.5 to 3 μm. The highly nonequilibrium conditions of crystal growth enhance the boron solubility and, therefore, lead to an increase of the boron concentrations in the islands on the surface up to 10
22
cm
−3
, eventually generating significant stresses in them. The stress in the islands is found to be the volumetric tensile stress. This conclusion is based on the stepwise shift of the diamond Raman peak toward lower frequencies from 1328 to 1300 cm
−1
in various islands and on the observation of the shift of three low-intensity reflections at 2-theta Bragg angles of 41.468°, 41.940° and 42.413° in the X-ray diffractogram to the left relative to the (111) diamond reflection at 2theta = 43.93°. We believe that the origin of the stepwise tensile stress is a discrete change in the distances between boron–carbon layers with the step of 6.18 Å. This supposition explains also the stepwise (step of 5 cm
−1
) behavior of the diamond Raman peak shift. Two approaches based on the combined application of Raman scattering and X-ray diffraction data allowed determination of the values of stresses both in lateral and normal directions. The maximum tensile stress in the direction normal to the surface reaches 63.6 GPa, close to the fracture limit of diamond, equal to 90 GPa along the 111 crystallographic direction. The presented experimental results unambiguously confirm our previously proposed structural model of the boron-doped diamond containing two-dimensional boron–carbon nanosheets and bilayers.
The paper presents the results of calculations of the sampling fluctuations in Pb–LAr electromagnetic sandwich calorimeters. The GEANT4 package was used to generate showers initiated by electrons ...with energies
E
0
from 20 to 500 GeV. It is shown that the dependence of the sampling fluctuations on
E
0
and the thickness of the lead absorber
x
can be described by the formula
kx
b
/
. The exponent
b
weakly depends on the LAr gap width
d
and is close to 2/3 and
k
= 0.1985−0.0363ln
d
mm.
The theory of the magnetotransport in a two-component electron system with rare macroscopic defects has been developed. In such a system, the classical memory effects in the scattering of electrons ...by defects and a slow transfer of electrons between the components of the liquid occurring due to the electron–electron scattering play a decisive role. It has been shown that the flow regime depends on the ratio of the sample width to the characteristic internal length, which is determined by the rate of electron transfer between the components. In samples wider than the internal length, the flow of the two-component liquid as a whole is formed within the bulk of the sample and is described by the corresponding Drude formulas taking into account memory effects. In this case, the magnetoresistance is positive at low magnetic fields and negative at high fields. In samples narrower than the characteristic length, the transfers involving a change in the type of electrons do not provide enough time to form a unified liquid. As a result, the flows of different components are independent and described by their own conductivities, taking into account the memory effects, while the magnetoresistance is strictly negative.
This paper, written to mark the twentieth anniversary of the discovery of the top quark, offers some insight into how the understanding of this heaviest known particle has developed from prediction ...through search to discovery to the current knowledge of its production mechanisms and properties. The central role of the top quark in the Standard Model is considered, and the window of opportunity it opens for seeking new physics beyond the Standard Model is discussed.
The results of calculations of the charged particles multiplicity, energy, radial and time distributions in the electromagnetic showers initiated by electrons with energies from 5 to 1000 GeV in Fe, ...W and Pb are presented. It is shown that the multiplicity distributions are well fitted by the inverse sum of two exponents in a wide range of energy and lead depth. The shapes of energy and radial distributions at the shower maximum weakly depend on the electron energy. Radial distributions for all materials studied are similar if radius is expressed in g/cm2. The time spread of the charged particles at the shower maximum turned out to be in the picosecond range.
A study of the amplitude-frequency characteristics of working bodies taking the form of thin rectangular plates working in a granular medium is presented. Results were obtained for the case of ...elastic oscillations having large deflections using Bolotin’s asymptotic method. The solution to the problem is obtained in the form of Jacobi elliptic functions. The amplitude-frequency characteristics of the vibration mechanism’s plate working body are given for various specific gravity coefficient values. A “pseudofluid” model is adopted as a simulated granular medium. An “attached mass” model is used to estimate the influence of the granular medium on the amplitude-frequency characteristics.
The key properties of Cherenkov radiation are briefly discussed, together with various types of Cherenkov counters used to identify relativistic particles in accelerator studies. Specific examples of ...the application of Cherenkov counters in experiments are discussed. Particular attention is given to the role of Cherenkov counters in antinuclei observations, including the discovery of the antiproton.
In this paper, the development of catalytic technologies used aboard a vehicle for purifying exhaust gases is estimated and forecasted. According to forecasts, in the next decade, the total ...production of vehicles will exceed 1 billion units and 75% of them will be equipped with internal combustion engines, which should necessarily be accompanied by an exhaust gas purification system. The development of catalytic technologies for purifying vehicle exhaust gases is mutually stimulated by the tightening of environmental standards and improving the internal combustion engines. For example, to date, the European standards have gone from Euro 1 to Euro 6d. The introduction of Euro 7 standards in Europe and the introduction of their counterparts in a number of countries by 2025 is planned. In addition, this paper discusses the concepts of systems that purify the exhaust gases of gasoline and diesel engines to meet the Euro 7 standards.
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