We report the results of a search for a new vector boson (
A
′
) decaying into two dark matter particles
χ
1
χ
2
of different mass. The heavier
χ
2
particle subsequently decays to
χ
1
and an ...off-shell Dark Photon
A
′
∗
→
e
+
e
-
. For a sufficiently large mass splitting, this model can explain in terms of new physics the recently confirmed discrepancy observed in the muon anomalous magnetic moment at Fermilab. Remarkably, it also predicts the observed yield of thermal dark matter relic abundance. A detailed Monte-Carlo simulation was used to determine the signal yield and detection efficiency for this channel in the NA64 setup. The results were obtained re-analyzing the previous NA64 searches for an invisible decay
A
′
→
χ
χ
¯
and axion-like or pseudo-scalar particles
a
→
γ
γ
. With this method, we exclude a significant portion of the parameter space justifying the muon g-2 anomaly and being compatible with the observed dark matter relic density for
A
′
masses from 2
m
e
up to 390 MeV and mixing parameter
ε
between
3
×
10
-
5
and
2
×
10
-
2
.
An integrated approach is applied to reveal fine changes in the surface-normal structure of 1,2-dimyristoyl-sn-glycero-3-phospho-l-serine (DMPS) monolayers at the air–lipid–water interface occurring ...in a liquid expanded (LE)–liquid condensed (LC) transition. The combination of the Langmuir monolayer technique, X-ray reflectometry, and molecular dynamics (MD) modeling provides new insight into the molecular nature of electrostatic phenomena in different stages of lipid compression. A homemade setup with a laboratory X-ray source (λ = 1.54 Å) offers a nondestructive way to reveal the structural difference between the LE and LC phases of the lipid. The electron density profile in the direction normal to the interface is recovered from the X-ray reflectivity data with the use of both model-independent and model-based approaches. MD simulations of the DMPS monolayer are performed for several areas per lipid using the all-atom force field. Using the conventional theory of capillary waves, a comparison is made between the electron density profiles reconstructed from the X-ray data and those calculated directly from MD modeling, which demonstrates remarkable agreement between the experiment and simulations for all selected lipid densities. This confirms the validity of the simulations and allows an analysis of the contributions of the hydrophobic tails and hydrated polar groups to the electron density profile and to the dipole component of the electric field at the interface. According to the MD data, the dependence of the Volta potential on the area per lipid in the monolayer has a different molecular nature below and above the phase transition. In the LE state of the monolayer, the potential is determined mostly by the oriented water molecules in the polar region of the lipid. In the LE–LC transition, these molecules are displaced to the bulk, and their effect on the Volta potential becomes insignificant compared with the contribution of the hydrophobic tails. The hydrophobic tails are highly ordered in the state of the liquid crystal so that their dipole moments entirely determine the growth of the potential upon compression up to the monolayer collapse.
Hunting down the X17 boson at the CERN SPS Depero, E.; Andreev, Yu. M.; Banerjee, D. ...
The European physical journal. C, Particles and fields,
12/2020, Letnik:
80, Številka:
12
Journal Article
Recenzirano
Odprti dostop
Recently, the ATOMKI experiment has reported new evidence for the excess of
e
+
e
-
events with a mass
∼
17 MeV in the nuclear transitions of
4
He, that they previously observed in measurements with
...8
Be. These observations could be explained by the existence of a new vector
X
17
boson. So far, the search for the decay
X
17
→
e
+
e
-
with the NA64 experiment at the CERN SPS gave negative results. Here, we present a new technique that could be implemented in NA64 aiming to improve the sensitivity and to cover the remaining
X
17
parameter space. If a signal-like event is detected, an unambiguous observation is achieved by reconstructing the invariant mass of the
X
17
decay with the proposed method. To reach this goal an optimization of the
X
17
production target, as well as an efficient and accurate reconstruction of two close decay tracks, is required. A dedicated analysis of the available experimental data making use of the trackers information is presented. This method provides independent confirmation of the NA64 published results
1
, validating the tracking procedure. The detailed Monte Carlo study of the proposed setup and the background estimate show that the goal of the proposed search is feasible.
Abstract
Until now, planetary rotary hydraulic machines with floating planetary gears were rarely produced and remained poorly studied. One of the main problems was the lack of a simple and ...affordable method for geometric design of non-circular gear rims of such machines. The article discusses an engineering method for profiling non-circular gear rims of volumetric planetary rotary hydraulic machines. The proposed method begins with the choice of the geometric parameters of the round-link planetary mechanism - the prototype of the designed hydraulic machine. Next, the number of waves of the sun gears and the form of the cyclic function characterizing the paths of the planetary gear center in the coordinates associated with the sun gear and the epicycle are selected. The preliminary calculation of the angle of rotation of the planetary gear and the polar coordinates of its center on the path relative to the given sun gear in the variety of the planetary gear positions is performed at the next stage. In this case, the positions of the planetary gear relative to the one of the sun gears correspond to its rolling along the calculated centroid of this gear at a constant angular velocity of the imaginary carrier. Next, the difference between the obtained angles of rotation of the planetary gear is calculated in the coordinates associated with the imaginary carrier. This difference is halved and distributed as a correction between the rotation angles of the planetary gear relative to the sun gear and the epicycle. In conclusion, the profile of the rim of each non-circular sun gear is obtained graphically as an envelope of the family of profile curves of the planetary gear in a variety of its positions. The proposed method provides an accurate solution to the problem and is available for the designers of any machine-building enterprise.
One of the most common ways to assess the activity of acoustic emission (AE) sources and their hazard under mechanical loading of materials and structures is to use the local-dynamic criterion. To ...verify the latter, specimens of various materials, namely fiberglass, corundum refractory, and steel, were tested under static loading during three-point bending. A special software AE-Criterion was developed to determine the AE parameters, including the current parameters of source activity, based on the local dynamic criterion using both the force factor and the time since the beginning of the test. Taking into account the multiplicity and stochastic nature of AE events during the loading of materials, it is proposed to determine the average values of
M
S
,
M
T
, and the values of the indices
I
AS
and
I
AT
of the activity degree of AE sources when applying the force parameter and time, respectively. The analysis of the data obtained during the bending tests of the above-mentioned specimens and, accordingly, the calculation of the parameters of source activity showed that the value of the index I
AS
, when using the force factor, satisfactorily reflects the deformation and fracture processes of these materials. The study’s results indicate the suitability of the local dynamic criterion for diagnosing the deformation and fracture processes of the above materials.
A modification of the quadratic interpolation method for finding the root of a continuous function is proposed. Two quadratic interpolation polynomials are simultaneously constructed. It is shown ...that if the third derivative of the original function does not change sign on the considered interval of localization of the required root, then the root lies between the roots of the quadratic functions. This allows one to substantially narrow the localization interval and reduce the number of steps to calculate the root with a given accuracy. The proposed modification of the quadratic interpolation method is used in the problem of calculating isolines when modeling the hill diagram of hydraulic turbines.
The system for monitoring acoustic emission (AE) parameters in mechanical testing of materials built up from electronic equipment and corresponding software is described. The electronic equipment ...based on a high-speed data storage module with a USB interface provides conversion of AE signals, their amplification, filtering, and digital input to a personal computer. The AEMonitor software performs continuous analog-digital conversion of AE signals, evaluation of their spectral distribution (fast Fourier transform), online display, accumulation, and storage of experimental data with load parameters for their further analysis. The software features an online automatic display of the spectral distribution of signals and corresponding stresses against the number of AE pulses from tested materials. The functional potentials of the system were verified in bending tests of corundum refractory and glass fiber plastic specimens with recording AE parameters. The relations between major AE parameters, form, and spectral distribution of pulses under loading of those materials were greatly different due to varied fracture mechanisms.
•Electron beam modifies the structure of the surface layer (100 µm) in the aluminum alloy AA2024.•The passage of deformation processes induced by irradiation, occurred by grain boundary sliding.•The ...level of residual stresses in the remelted layer has a relatively low value (34 MPa).
AA2024 aluminum alloy was irradiated by a high-current pulsed electron beam with the following parameters: beam energy ∼0.3 MeV, current ∼2000A, pulse duration ∼5·10−6 s, beam diameter ∼3 cm. The thickness of the surface remelted layer reached 100 μm. Dynamic thermal stresses caused by irradiation, induced the development of deformation processes in the irradiated layer. Based on the study of surface morphology and structural state of the remelted layer, it was shown that deformation processes occur in the surface layer by the grain boundary sliding mechanism. The level of residual stresses in the irradiated layer was low and amounted to 34 MPa.
An approach based on the computational search for the extrapolated upper boundary of the core and accounting for the axial asymmetry of the assembly that models a high-temperature gas-cooled reactor ...with an annular core is considered, and its applicability for the development of 3D calculation models of the ASTRA critical facility is justified. Owing to the presence of the lower reflector and absence of the upper one, 2D models based on experimentally determined buckling cannot be used; therefore, an alternative approach based on the use of the extrapolated assembly height is suggested. The use of this method is shown by the example of the computational analysis of the experiments for measuring the efficiency of the control and protection system unit is presented.
The article presents the concept of a channel-type reactor with a combined cooled moderator. The moderator consists of ceramic beryllium oxide and a liquid moderator—water with a possible variation ...in its composition due to the ratio between light water and heavy water components. Variants of fuel cycles based on the combination of “power” plutonium with depleted uranium, regenerated uranium, and thorium are analyzed. Quantitative estimates of the consumption of raw materials and the transformation of the isotopic composition of the irradiated fuel components are presented. The issues of safety and the possibility of controlling the reactivity coefficient by the density of the boiling coolant when changing the fuel cycle are discussed.
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