The influence of the presence and value of the radius of curvature at the junctions of the toneholes of woodwind instruments with the main air duct (undercutting) on the shift of its eigenfrequencies ...is considered. A methodology and formulas for numerical calculation are presented, which allow one to determine the value of the effective radius for open and closed toneholes with a variable cross-section. Based on the dependences obtained, using the transmission-matrix method, a calculation of the eigenfrequencies of an air bore with a single tonehole was carried out and compared with the results of computer simulation in the COMSOL Multiphysics 5.6 program. It is shown that an increase in the degree of undercutting of the tonehole leads to an increase in its effective radius, which increases the resonance frequencies in the case of an open hole and decrease it in the case of a closed tonehole. Averaging the acoustic mass (for open hole) and volume (for closed hole) over the longitudinal sections of the hole, which doesn’t have rotational circular symmetry in the area of connection with the main bore, gives better results in finding eigenfrequencies in comparison with the computer simulation.
Abstract
The article discusses the influence of geometric parameters (the presence and magnitude of the radius of curvature) at the junction of the toneholes with the main bore of the air column on ...the frequency characteristics of woodwind musical instruments. A theoretical calculation of the eigenfrequencies of an air column with one tonehole in the case of sharp edges has been carried out. The resonance frequencies were also found using computer simulation in the COMSOL Multiphysics 5.5 program for the case of sharp edges and joints with a radius of curvature. An empirical dependence of the frequency of the main tone of the air column on the radius of curvature of the edges of the tonehole is obtained. All simulation were carried out for two models: excluding and including viscous drag and thermal exchange losses.
The ratio of the elastic e(+)p to e(-)p scattering cross sections has been measured precisely, allowing the determination of the two-photon exchange contribution to these processes. This neglected ...contribution is believed to be the cause of the discrepancy between the Rosenbluth and polarization transfer methods of measuring the proton electromagnetic form factors. The experiment was performed at the VEPP-3 storage ring at beam energies of 1.6 and 1.0 GeV and at lepton scattering angles between 15° and 105°. The data obtained show evidence of a significant two-photon exchange effect. The results are compared with several theoretical predictions.
ABSTRACT
In the fourth paper of this series, we present – and publicly release – the state-of-the-art catalogue and atlases for the two remaining parallel fields observed with the Hubble Space ...Telescope for the large programme on ω Centauri. These two fields are located at ∼12 arcmin from the centre of the globular cluster (in the west and south-west directions) and were imaged in filters from the ultraviolet to the infrared. Both fields were observed at two epochs separated by about 2 yr that were used to derive proper motions and to compute membership probabilities.
The structure function approach and the parton picture, developed for the theoretical description of the deep inelastic electron-proton scattering, also proved to be very effective for calculation of ...radiative corrections in Quantum Electrodynamics. We use them to calculate radiative corrections to the cross section of electron-proton scattering due to electron-photon interaction, in the experimental setup with the recoil proton detection, proposed by A. A. Vorobyev to measure the proton radius. In the one-loop approximation, explicit expressions for these corrections are obtained for arbitrary momentum transfers. It is shown that, at momentum transfers small compared with the proton mass, various contributions to the corrections mutually cancel each other with power accuracy. In two loops, the corrections are obtained in the leading logarithmic approximation.
ABSTRACT
We present our final study of the white dwarf cooling sequence (WD CS) in the globular cluster NGC 6752. The investigation is the main goal of a dedicated Hubble Space Telescope large ...program, for which all the observations are now collected. The WD CS luminosity function (LF) is confirmed to peak at mF606W ≃ 29.3 ± 0.1, consistent within uncertainties with what has been previously reported, and is now complete down to mF606W ≃ 29.7. We have performed robust and conclusive comparisons with model predictions that show how the theoretical LF for hydrogen envelope WD models closely follow the shape of the empirical LF. The magnitude of the peak of the observed LF is matched with ages between 12.7 and 13.5 Gyr, consistent with the cluster age derived from the main sequence turn off and subgiant branch. We also find that the impact of multiple populations within the cluster on the WD LF for mF606W below 27.3 is negligible, and that the presence of a small fraction of helium envelope objects is consistent with the data. Our analysis reveals a possible hint of an underestimate of the cooling time-scales of models in the magnitude range 28.1 < mF606W < 28.9. Finally, we find that hydrogen envelope models calculated with a new tabulation of electron conduction opacities in the transition between moderate and strong degeneracy provide WD ages that are too small in comparison to the main sequence turnoff age.
A cancellation of leading contributions to radiative corrections to the cross section for elastic electron–proton scattering for experiments devoted to measuring the proton charge radius is studied. ...The cancellations occur in the contribution of electron interaction with the electromagnetic field. It is shown that, under experimental conditions where the recoil proton is detected, there occurs cancellation in the one-loop approximation not only for the terms containing large logarithms but also for the constants at these logarithms and that a nonzero electron contribution to radiative corrections appears starting from terms that are proportional to
, where
is the momentum transfer and
is the electron energy in the rest frame of the primary proton.
The differential cross section for elastic electron-proton scattering has been calculated taking into account the two-photon exchange within the phenomenological description of the electromagnetic ...electron-proton interactions. The calculation is based on the consistent evaluation of the matrix elements of the proton current in a diagonal spin basis, which makes it possible to naturally obtain expressions for the generalized Sachs form factors. A new method has been proposed to independently measure these form factors in the elastic
e
p
→
→
e
p
→
process in the case where the initial proton at rest is fully polarized along the direction of the motion of the final proton.
The paper presents the results of experimental studies on the synthesis of silicon carbide based on micro and nano-sized silicon dioxide powder using thermal plasma energy. Powder synthesis was ...carried out at an average temperature of 5600 ± 26 K using an indirect action plasma torch with the following characteristics: current strength 40 A, voltage 100 V, plasma-forming gas flow rate 1 g/s, and thermal efficiency of 72%. According to the results of X-ray diffraction analysis, when using silicon dioxide of different dispersion compositions, 53.9 to 95.5 wt % silicon carbide is formed, and the remaining component of the synthesized powders is silicon dioxide SiO
2
in various states (crystalline, amorphous). It is worth noting that the Si−O bonds in the silicon-oxygen tetrahedra of the amorphous phase are similar to the alpha-tridymite bonds in the crystalline phase. Experimental results have shown that under similar synthesis conditions, the yield of silicon carbide using nano-sized powder increases by 41.6%. This is due to the high dispersion of the nanopowder, which contributes to the creation of multiple local sources of silicon carbide formation on the contact surfaces of particles. This statement is confirmed by SEM results, which show the formation of cubic SiC particles against a branched system of mesoporous areas with particle sizes not exceeding 1 micron. The obtained research results are of interest for the production of porous high-temperature ceramic materials.
The new method proposed in this research is based on the spectral registration of the microwave range radiation by means of a wideband scanning receiver. The experiments have proved its accuracy ...sufficient for the spectrum frequency determination. Sensitivity of 5-6 Hz/nm level is achieved. The obtained spectra are analyzed using a specialized hardware-software complex. The evidence from practice has shown that the method in question, apart from detecting the substances qualitative composition, helps determine the presence and propagation of cracks.
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