Abstract
An experimental study of the possibility of using the acoustic emission signal during turning to assess the machinability of steel by cutting has been carried out. According to the results ...of previous studies, it has been shown that the use of the total acoustic energy of the cutting process to assess the machinability does not have sufficient resolution. The article presents the results of measurements of the acoustic emission signal in comparison with the results of measuring the tool wear during resistance tests. A group of samples of six steels with a known chemical composition and mechanical properties were used as materials. The group includes steels that differ a priori in machinability and steels whose machinability cannot be predicted in advance. Endurance tests were carried out for face turning with a tool made of highspeed steel with a variable cutting speed. The maximum height of the wear area in the direction perpendicular to the cutting edge was used as a criterion for machinability. The acquisition of the acoustic emission signal was carried out by a broadband sensor built into the tool holder with a preamplifier of 60 dB and a bandwidth of 50...1000 kHz. The integral energy characteristic of the RMS signal is used as a criterion for predicting the processability. As a result of the experiments, it was found that the use of an acoustic emission signal has a good resolution in assessing the machinability by turning steels.
The heaviest elements to have been chemically characterized are seaborgium (element 106), bohrium (element 107) and hassium (element 108). All three behave according to their respective positions in ...groups 6, 7 and 8 of the periodic table, which arranges elements according to their outermost electrons and hence their chemical properties. However, the chemical characterization results are not trivial: relativistic effects on the electronic structure of the heaviest elements can strongly influence chemical properties. The next heavy element targeted for chemical characterization is element 112; its closed-shell electronic structure with a filled outer s orbital suggests that it may be particularly susceptible to strong deviations from the chemical property trends expected within group 12. Indeed, first experiments concluded that element 112 does not behave like its lighter homologue mercury. However, the production and identification methods used cast doubt on the validity of this result. Here we report a more reliable chemical characterization of element 112, involving the production of two atoms of 283112 through the alpha decay of the short-lived 287114 (which itself forms in the nuclear fusion reaction of 48Ca with 242Pu) and the adsorption of the two atoms on a gold surface. By directly comparing the adsorption characteristics of 283112 to that of mercury and the noble gas radon, we find that element 112 is very volatile and, unlike radon, reveals a metallic interaction with the gold surface. These adsorption characteristics establish element 112 as a typical element of group 12, and its successful production unambiguously establishes the approach to the island of stability of superheavy elements through 48Ca-induced nuclear fusion reactions with actinides.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Combined Thomson scattering (TS) and laser-induced fluorescence (LIF) diagnostics are being developed. The Thomson scattering and laser-induced fluorescence are laser diagnostics, with joint both ...probing and c-ollecting optical systems, which are the most complex and expensive parts of the diagnostic systems of large tokamaks, can be combined. Thomson scattering by free electrons is the use-proven diagnostic method for measuring profiles of important parameters of the plasma electron component (electron tempera-ture
T
e
and electron density
n
e
), which requires a minimum of model assumptions. Almost all existing tokamaks are equipped with one or more TS systems, and by now, considerable experience has been accumulated in practical methods for implementation of these systems. The use of laser-induced fluorescence for measuring parameters of ion and neutral plasma components is less common, also because it requires knowledge of electron parameters to calculate populations of excited levels. The joint diagnostics of the Thomson scattering and laser-induced fluorescence in divertor plasma will be used to simultaneously measure the plasma parameters necessary for fundamental understanding physics of plasma detachment from divertor plates. These parameters are: the local parameters of plasma electrons (
T
e
,
n
e
), ion temperature (
T
i
) measured from the data on emission of helium ions (HeII), as well as densities of helium atoms (
n
a
(He)) and hydrogen isotopes (
n
a
(H,D,T)). The measured parameters make it possible to calculate the following characteristics: (i) the ionization and recombination rates (using the data on
T
e
,
n
e
,
T
i
, and
n
a
(H, D, T)); (ii) the friction force of the plasma flow due to collisions with neutral particles (using the data on
T
i
,
n
i
(assuming
n
i
=
n
e
), and
n
a
(H, D, T)); and (iii) the pressure of the oncoming plasma flow (using the data on
T
e
,
n
e
,
T
i
, and
n
i
). The article discusses advantages of combining laser diagnostics and ways of further development of the joint diagnostcs, based on the experience of creating similar diagnostics for domestic tokamaks and the similar diagnostics developed for ITER.
The possibilities are considered of using the Thomson scattering diagnostics of core and edge plasmas in the tokamak with reactor technologies, which is under design. The problems are described that ...can be solved using the Thomson scattering diagnostics, including the possibility of controlling the plasma current profile. Technical requirements for the diagnostics are formulated. The possibilities are analyzed of its arrangement in the tokamak vacuum chamber. The accuracies are estimated of measuring the electron temperature and density of the plasma created in the tokamak. Particular attention is paid to ensuring the operability of the proposed diagnostics in the reactor regime of the tokamak operation.
Studies of radioactive ions (RIs) are the most thriving field of low-energy nuclear physics. In this paper, the concept and the scientific agenda of the prospective accelerator and storage ring ...facility for RI beam (RIB) research are proposed for a large-scale international project based at the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research. The motivation for the new facility is discussed and its characteristics are briefly presented and shown to be comparable to those of advanced world centers, the so-called "RIB factories". In the project, the emphasis is made on studies with short-lived RIBs in storage rings. A unique feature of the project is the possibility of studying electron-RI interactions in a collider experiment to determine the fundamental properties of nuclear matter, in particular, electromagnetic form factors of exotic nuclei.
Temperature and optical power density dependences of the photovoltage at a p-GaN(Cs) photocathode surface were measured in the temperature range 90-295 K. The study demonstrated that band bending at ...the p-GaN(Cs) photocathode surface can be reduced by ∼ 0.5 eV without modifying the surface atomic structure. The surface photovoltage impact on the p-GaN(Cs) photocathode quantum efficiency and photoelectron energy distributions was analyzed.
The effect of neutron irradiation on the photosensitivity of the InAs/GaAs quantum dots has been investigated. It was shown that after neutron irradiation with a fluence of 1.5×1015 cm-2 the ...photosensitivity at the room temperature has been decreased at 3 times, whereas the shape of the photosensitivity's temperature dependence didn't reveal any visible changes, despite an appearance of defects in quantum dot layer. The effect was explained by the difficulty of a motion of photoexcited carriers in quantum dot layer to the recombination centres arised after irradiation.
Aim To study the clinical course of non-ST segment elevation myocardial infarction (NSTEMI) in hospitalized patients after COVID-19 and to evaluate the effect of baseline characteristics of ...patients on the risk of complications.Material and methods The study included 209 patients with NSTEMI; 104 of them had had COVID-19. The course of myocardial infarction (MI) was analyzed at the hospital stage, including evaluation of the incidence rate of complications (fatal outcome, recurrent MI, life-threatening arrhythmias and conduction disorders, pulmonary edema, cardiogenic shock, ischemic stroke, gastrointestinal bleeding).Results Mean age of patients after COVID-19 was 61.8±12.2 years vs. 69.0±13.0 in the comparison group (p<0.0001). The groups were comparable by risk factors, clinical data, and severity of coronary damage. Among those who have had СOVID-19, there were fewer patients of the GRACE high risk group (55.8 % vs. 74.3 %; p<0.05). Convalescent COVID-19 patients had higher levels of C-reactive protein and troponin I (p<0.05). The groups did not significantly differ in the incidence of unfavorable NSTEMI course (p>0.05). However, effects of individual factors (postinfarction cardiosclerosis, atrial fibrillation, decreased SpO2, red blood cell concentration, increased plasma glucose) on the risk of complications were significantly greater for patients after COVID-19 than for the control group (p<0.05).Conclusion Patients with NSTEMI, despite differences in clinical history and laboratory data, are characterized by a similar risk of death at the hospital stage, regardless of the past COVID-19. Despite the absence of statistically significant differences in the incidence of in-hospital complications, in general, post-COVID-19 patients showed a higher risk of complicated course of NSTEMI compared to patients who had not have COVID-19. In addition, for this category of patients, new factors were identified that previously did not exert a clinically significant effect on the incidence of complications: female gender, concentration of IgG to SARS-CoV-2 ≥200.0 U/l, concentration of С-reactive protein ≥40.0 mg/l, total protein <65 g/l. These results can be used for additional stratification of risk for cardiovascular complications in patients with MI and also for development of individual protocols for evaluation and management of NSTEMI patients with a history of COVID-19.
The article discusses the technology of manufacturing low-stiff long multistage shafts made of stainless steels. A feature of this technology is the cutting of annular cooling fins on the entire ...surface of the shaft blank during machining and their use in thermal operations and further to finishing turning. To implement the technology, self-centering steady rests with double rollers were used during machining.
The article proposes a method for improving the quality of cold straightening of non-rigid shafts. The essence of the solution is to change the sequence of traditional technological operations by ...introducing dynamic straightening of the workpiece with subsequent application of a given depth of the deformed layer, immediately before roughing and finishing, and after them, in addition, in the process of roughing and finishing, the depth and nature of stresses are preserved. due to the exclusion and redistribution of surface stresses arising directly in the process of machining non-rigid parts, taking into account the changing dynamic characteristics of the cutting process itself. A complex functional diagram of the automatic control system has been developed. The results of straightening a non-rigid shaft, without a system and using automatic control, are presented. Decrease of processing error by 2..3 times is shown.
PDF
