The self-similar solution that characterizes the water impact, with a constant vertical velocity, of a wedge entering the free surface with an arbitrary orientation is derived analytically. The study ...is carried out by assuming the fluid to be ideal, weightless and with negligible surface tension effects. The solution is based on the complex analysis of nonlinear two-dimensional problems of unsteady free boundary flows and is written in terms of two governing functions, which are the complex velocity and the derivative of the complex potential defined in a parameter domain. The boundary value problem is reduced to the system of an integral and an integro-differential equation in terms of the velocity modulus and of the velocity angle to the free surface, both written as functions of a parameter variable. The system of equations is solved through a numerical procedure which is validated in the case of symmetric wedges. Comparisons with data available in literature are established for this purpose. Results are presented in terms of free surface shape, contact angles at the intersection with the wedge boundary, pressure distribution, force and moment coefficients. For a given wedge angle, the changes induced by the heel angle on the above quantities are discussed. A criterion is proposed to determine the limit conditions beyond which flow separation from the wedge apex occurs. Comparisons with experimental results available in literature are presented.
Brownian motion with general drift Kinzebulatov, D.; Semënov, Yu. A.
Stochastic processes and their applications,
20/May , Letnik:
130, Številka:
5
Journal Article
Recenzirano
Odprti dostop
We construct and study the weak solution to stochastic differential equation dX(t)=−b(X(t))dt+2dW(t), X(0)=x, for every x∈Rd, d≥3, with b in the class of weakly form-bounded vector fields, ...containing, as proper subclasses, a sub-critical class Ld+L∞d, as well as critical classes such as weak Ld class, Kato class, Campanato–Morrey class.
In
R
d
,
d
≥
3
, consider the divergence and the non-divergence form operators
-
Δ
-
∇
·
(
a
-
I
)
·
∇
+
b
·
∇
,
-
Δ
-
(
a
-
I
)
·
∇
2
+
b
·
∇
,
where the second-order perturbations are given by the ...matrix
a
-
I
=
c
|
x
|
-
2
x
⊗
x
,
c
>
-
1
.
The vector field
b
:
R
d
→
R
d
is form-bounded with form-bound
δ
>
0
. (This includes vector fields with entries in
L
d
, as well as vector fields having critical-order singularities.) We characterize quantitative dependence on
c
and
δ
of the
L
q
→
W
1
,
q
d
/
(
d
-
2
)
regularity of solutions of the corresponding elliptic and parabolic equations in
L
q
,
q
≥
2
∨
(
d
-
2
)
.
In this article a precedent is described of the role of the Scientific Council on the Complex Problem of Cybernetics of the USSR Academy of Sciences as a foundation for forming a consortium of ...research organizations, Provisional Scientific and Research Group (PSRG) “School-1” to support the creation of a new national education system.
Chest MRI of patients with COVID-19 Vasilev, Yu A.; Sergunova, K.A.; Bazhin, A.V. ...
Magnetic resonance imaging,
06/2021, Letnik:
79
Journal Article
Recenzirano
Odprti dostop
During the pandemic of novel coronavirus infection (COVID-19), computed tomography (CT) showed its effectiveness in diagnosis of coronavirus infection. However, ionizing radiation during CT studies ...causes concern for patients who require dynamic observation, as well as for examination of children and young people. For this retrospective study, we included 15 suspected for COVID-19 patients who were hospitalized in April 2020, Russia. There were 4 adults with positive polymerase chain reaction (PCR) test for COVID-19. All patients underwent magnetic resonance imaging (MRI) examinations using MR-LUND PROTOCOL: Single-shot Fast Spin Echo (SSFSE), LAVA 3D and IDEAL 3D, Echo-planar imaging (EPI) diffusion-weighted imaging (DWI) and Fast Spin Echo (FSE) T2 weighted imaging (T2WI). On T2WI changes were identified in 9 (60,0%) patients, on DWI – in 5 (33,3%) patients. In 5 (33,3%) patients lesions of the parenchyma were visualized on T2WI and DWI simultaneously. At the same time, 4 (26.7%) patients had changes in lung tissue only on T2WI. (P(McNemar) = 0,125; OR = 0,00 (95%); kappa = 0,500). In those patients who had CT scan, the changes were comparable to MRI. The results showed that in case of CT is not available, it is advisable to conduct a chest MRI for patients with suspected or confirmed COVID-19. Considering that T2WI is a fluid-sensitive sequence, if imaging for the lung infiltration is required, we can recommend the abbreviated MRI protocol consisting of T2 and T1 WI. These data may be applicable for interpreting other studies, such as thoracic spine MRI, detecting signs of viral pneumonia of asymptomatic patients. MRI can detect features of viral pneumonia.
The effect of oxidizing and nitriding on the structure, tribological properties and corrosion resistance of alloy VT18u with zirconium, niobium and tin additions used to replace the cytotoxic ...vanadium for biomedical applications is studied. The thermochemical treatment is shown to affect positively the wear resistance of the alloy. The wear resistance is the highest after nitriding, but the corrosion resistance of the nitrided specimens is somewhat lower than in the initial condition. The corrosion resistance of the oxidized coatings is somewhat lower than in the initial state. However, both coatings reduce the resistance of VT18u to preferential corrosion. The results obtained make it possible to recommend the alloy for biomedical applications. The final choice of the method of surface hardening of the alloy will depend in the results of an additional check of its biocompatibility.
In the present study, we have investigated the effect of hydroxyectoine (Ect-OH), a heterocyclic amino acid, on oxygen evolution in photosystem II (PS II) membrane fragments and on photoinhibition of ...Mn-depleted PS II (apo-WOC-PS II) preparations. The degree of photoinhibition of apo-WOC-PS II preparations was estimated by the loss of the capability of exogenous electron donor (sodium ascorbate) to restore the amplitude of light-induced changes of chlorophyll fluorescence yield (∆F). It was found that Ect-OH (i) stimulates the oxygen-evolving activity of PS II, (ii) accelerates the electron transfer from exogenous electron donors (K
4
Fe(CN)
6
, DPC, TMPD, Fe
2+
, and Mn
2+
) to the reaction center of apo-WOC-PS II, (iii) enhances the protective effect of exogenous electron donors against donor-side photoinhibition of apo-WOC-PS II preparations. It is assumed that Ect-OH can serve as an artificial electron donor for apo-WOC-PS II, which does not directly interact with either the donor or acceptor side of the reaction center. We suggest that the protein conformation in the presence of Ect-OH, which affects the extent of hydration, becomes favorable for accepting electrons from exogenous donors. To our knowledge, this is the first study dealing with redox activity of Ect-OH towards photosynthetic pigment–protein complexes.
We establish sharp two‐sided bounds on the heat kernel of the fractional Laplacian, perturbed by a drift having critical‐order singularity, by transferring it to appropriate weighted space with ...singular weight.
PDF
