3,084 research outputs found
Sinus-preserving modification of eversional carotid endarterectomy: early and late results
Universitatea de Stat de Medicină de Sud Ural, Spitalul Clinic Regional, Celiabinsk, Federația Rusă, Al XIII-lea Congres al Asociației Chirurgilor „Nicolae Anestiadi” și
al III-lea Congres al Societății de Endoscopie, Chirurgie miniminvazivă și Ultrasonografie ”V.M.Guțu” din Republica MoldovaIntroducere: Endarterectomia carotidiană (EAEC) și-a demonstrat avantajul în tratamentul stenozelor hemodinamic semnificative
ale arterei carotide interne (ACI). Tehnica prin eversiune este cea mai populară, însă în versiunea sa standard se asociază cu
traumatizarea frecventă a sinusului carotidian, cu impact negativ asupra reglării vegetative a tonusului vascular și hemodinamicii.
Scopul: Evaluarea eficacității EAEC prin eversiune cu prezervarea nervilor sinusului carotid, comparând rezultatele precoce și la
distanță cu cele ale unui lot de control.
Material și metode: Studiul a inclus 375 pacienți supuși tratamentului chirurgical în Spitalul Clinic Regional Celiabinsk în perioada
anilor 2012-2018. În lotul I (208 bolnavi) EAEC prin eversiune s-a efectuat conform tehnicii standard. În lotul II (167 pacienți) s-a
practicat EAEC modificată, cu prezervarea sinusului. Loturile au fost comparabile în funcție de vârstă, gen, statutul neurologic și
hipertensiv inițial, utilizarea șuntului temporar, timpul de clampaj al ACI și gradul leziunii arteriale carotidiene contralaterale. Pe lângă
înregistrarea parametrilor hemodinamici comuni, a fost evaluată și activitatea vegetativă în baza analizei prospective a variabilității
frecvenței cardiace utilizând ritmocardiografia. La etapa de follow-up, parametrii hemodinamici au fost evaluați la 103 pacienți: cu
păstrarea nervilor sinusului carotidian (39) și după secționarea acestora (64).
Rezultate: În prima zi atât presiunea sistolică, diastolică, cât și presiunea pulsului, precum și frecvența cardiacă au fost mai reduse la
bolnavii după EAEC cu prezervarea sinusului în comparație cu lotul de control. În plus, diminuarea influenței simpatice asupra ritmului
conform ritmocardiografiei a fost notabilă. La pacienții operați cu prezervarea nervilor sinusului carotidian elevarea tensiunii arteriale s-a atestat mai rar, iar doza necesară de remedii antihipertensive a fost mai mică.
Concluzii: S-au constatat diferențe semnificative dintre parametrii, evaluați precoce și la distanță, ai hemodinamicii arteriale
postoperatorii și reglării vegetative a tonusului vascular, în funcție de prezervarea nervilor sinusului carotidian. Practicarea EAEC prin
eversiune cu prezervarea sinusului carotid reduce riscul complicațiilor postoperatorii cauzate de dereglările vegetative.Introduction: Carotid endarterectomy (CEAE) has proven its advantage in correcting hemodynamically significant stenoses of the
internal carotid arteries (ICA). The eversion technique is the most popular, but with its standard procedure, traumatization of carotid
sinus nerves occurs, which has a negative effect on the vegetative regulation of vascular tonus and hemodynamics.
Aim: To evaluate the effectiveness of eversional CEAE with preservation of carotid sinus nerves, by comparing of early and long-term
results with a control group of patients.
Materials and methods: The study included 375 patients treated surgically at the Chelyabinsk Regional Clinical Hospital from 2012
to 2018. In the first group (208 patients), eversional CEAE was performed according to standard technique. In the second group (167
patients), a sinus-preserving modification of CEAE was applied. The groups were comparable by age, sex, baseline neurological
status, baseline hypertension, use of a temporary shunt, ICA cross-clamping time, and degree of contralateral lesion of the carotid
arteries. In addition to common hemodynamic parameters, mediator vegetative activity evaluated based on a prospective analysis
of heart rate variability using rhythmocardiography. In the follow-up period, hemodynamic parameters assessed in 103 patients: with
preservation of the carotid sinus nerves (39) and after their transection (64).
Results: On the 1st day, systolic, diastolic and pulse blood pressure, as well as a heart rate were lower in patients after sinuspreserving CEAE as compared with the control group. In addition, a decrease in sympathetic pressure effect on the rhythm according
to rhythmocardiography was noticeable. In patients operated with the preservation of carotid sinus nerves, an increased blood pressure
is less common and they require a lower dosage of antihypertensive drugs.
Conclusions: There are significant differences between early and distant parameters of postoperative arterial hemodynamics and
vegetative regulation of vascular tonus, depending on preservation of the carotid sinus nerves. Practical application of sinus- preserving
eversional CEAE reduces the risk of postoperative complications due to vegetative dysregulation
Thermal deformation of concentrators in an axisymmetric temperature field
Axisymmetric thermal deformations of paraboloid mirrors, due to heating, are examined for a mirror with a optical axis oriented toward the Sun. A governing differential equation is derived using Mushtari-Donnel-Vlasov simplifications, and a solution is presented which makes it possible to determine the principal deformation characteristics
Understanding the dynamical structure of pulsating stars: The Baade-Wesselink projection factor of the delta Scuti stars AI Vel and beta Cas
Aims. The Baade-Wesselink method of distance determination is based on the
oscillations of pulsating stars. The key parameter of this method is the
projection factor used to convert the radial velocity into the pulsation
velocity. Our analysis was aimed at deriving for the first time the projection
factor of delta Scuti stars, using high-resolution spectra of the
high-amplitude pulsator AI Vel and of the fast rotator beta Cas. Methods. The
geometric component of the projection factor (i.e. p0) was calculated using a
limb-darkening model of the intensity distribution for AI Vel, and a
fast-rotator model for beta Cas. Then, using SOPHIE/OHP data for beta Cas and
HARPS/ESO data for AI Vel, we compared the radial velocity curves of several
spectral lines forming at different levels in the atmosphere and derived the
velocity gradient associated to the spectral-line-forming regions in the
atmosphere of the star. This velocity gradient was used to derive a dynamical
projection factor p. Results. We find a flat velocity gradient for both stars
and finally p = p0 = 1.44 for AI Vel and p = p0 = 1.41 for beta Cas. By
comparing Cepheids and delta Scuti stars, these results bring valuable insights
into the dynamical structure of pulsating star atmospheres. They suggest that
the period-projection factor relation derived for Cepheids is also applicable
to delta Scuti stars pulsating in a dominant radial mode
New Metallicities of RR Lyrae Stars in omega Centauri: Evidence for a Non He-Enhanced Metal-Intermediate Population
We present new spectroscopic metal abundances for 74 RR Lyrae stars in omega
Cen obtained with FLAMES. The well-known metallicity spread is visible among
the RR Lyrae variables. The metal-intermediate (MInt) RR Lyrae stars ([Fe/H] ~
-1.2) are fainter than the bulk of the dominant metal-poor population ([Fe/H] ~
-1.7), in good agreement with the corresponding zero-age horizontal branch
models with cosmological helium abundance Y = 0.246. This result conflicts with
the hypothesis that the progenitors of the MInt RR Lyrae stars correspond to
the anomalous blue main-sequence stars, which share a similar metallicity but
whose properties are currently explained by assuming for them a large helium
enhancement. Therefore, in this scenario, the coexistence within the cluster of
two different populations with similar metallicities ([Fe/H] ~ -1.2) and
different helium abundances has to be considered.Comment: 9 pages, 4 figures, accepted for publication by ApJ
Deep learning-based fully automatic segmentation of wrist cartilage in MR images
The study objective was to investigate the performance of a dedicated
convolutional neural network (CNN) optimized for wrist cartilage segmentation
from 2D MR images. CNN utilized a planar architecture and patch-based (PB)
training approach that ensured optimal performance in the presence of a limited
amount of training data. The CNN was trained and validated in twenty
multi-slice MRI datasets acquired with two different coils in eleven subjects
(healthy volunteers and patients). The validation included a comparison with
the alternative state-of-the-art CNN methods for the segmentation of joints
from MR images and the ground-truth manual segmentation. When trained on the
limited training data, the CNN outperformed significantly image-based and
patch-based U-Net networks. Our PB-CNN also demonstrated a good agreement with
manual segmentation (Sorensen-Dice similarity coefficient (DSC) = 0.81) in the
representative (central coronal) slices with large amount of cartilage tissue.
Reduced performance of the network for slices with a very limited amount of
cartilage tissue suggests the need for fully 3D convolutional networks to
provide uniform performance across the joint. The study also assessed inter-
and intra-observer variability of the manual wrist cartilage segmentation
(DSC=0.78-0.88 and 0.9, respectively). The proposed deep-learning-based
segmentation of the wrist cartilage from MRI could facilitate research of novel
imaging markers of wrist osteoarthritis to characterize its progression and
response to therapy
The Baade-Wesselink p-factor applicable to LMC Cepheids
Context. Recent observations of LMC Cepheids bring new constraints on the
slope of the period-projection factor relation (hereafter Pp relation) that is
currently used in the Baade-Wesselink (hereafter BW) method of distance
determination. The discrepancy between observations and theoretical analysis is
particularly significant for short period Cepheids Aims. We investigate three
physical effects that might possibly explain this discrepancy: (1) the
spectroscopic S/N that is systematically lower for LMC Cepheids (around 10)
compared to Galactic ones (up to 300), (2) the impact of the metallicity on the
dynamical structure of LMC Cepheids, and (3) the combination of infrared
photometry/interferometry with optical spectroscopy. Methods. To study the S/N
we use a very simple toy model of Cepheids. The impact of metallicity on the
projection factor is based on the hydrodynamical model of delta Cep already
described in previous studies. This model is also used to derive the position
of the optical versus infrared photospheric layers. Results. We find no
significant effect of S/N, metallicity, and optical-versus-infrared
observations on the Pp relation. Conclusions. The Pp relation of Cepheids in
the LMC does not differ from the Galactic relation. This allows its universal
application to determine distances to extragalactic Cepheids via BW analysis.Comment: accepted in A&A LETTER
Hybrid Group IV Nanophotonic Structures Incorporating Diamond Silicon-Vacancy Color Centers
We demonstrate a new approach for engineering group IV semiconductor-based
quantum photonic structures containing negatively charged silicon-vacancy
(SiV) color centers in diamond as quantum emitters. Hybrid SiC/diamond
structures are realized by combining the growth of nanoand micro-diamonds on
silicon carbide (3C or 4H polytype) substrates, with the subsequent use of
these diamond crystals as a hard mask for pattern transfer. SiV color
centers are incorporated in diamond during its synthesis from molecular diamond
seeds (diamondoids), with no need for ionimplantation or annealing. We show
that the same growth technique can be used to grow a diamond layer controllably
doped with SiV on top of a high purity bulk diamond, in which we
subsequently fabricate nanopillar arrays containing high quality SiV
centers. Scanning confocal photoluminescence measurements reveal optically
active SiV lines both at room temperature and low temperature (5 K) from
all fabricated structures, and, in particular, very narrow linewidths and small
inhomogeneous broadening of SiV lines from all-diamond nano-pillar arrays,
which is a critical requirement for quantum computation. At low temperatures (5
K) we observe in these structures the signature typical of SiV centers in
bulk diamond, consistent with a double lambda. These results indicate that high
quality color centers can be incorporated into nanophotonic structures
synthetically with properties equivalent to those in bulk diamond, thereby
opening opportunities for applications in classical and quantum information
processing
Автоматизация управления электроприводом обитаемого подводного аппарата
Currently, there is an intensive development of manned and unmanned submersibles due to development of offshore oil and gas fields, development of underwater archaeology and exploration activities in transit zones regarding seabed mineral extraction. The depth of immersion and the nature of the underwater technical works performed determine not only the design of the underwater vehicle, its power-to-weight ratio and technical equipment, but also impose high requirements on reliability, survivability, and habitability, if the underwater vehicle implies that the operator is on board inside a pressure hull. The main objectives of the study carried out by the authors were to achieve high reliability and survivability of the main elements of the propulsion-steering complex, which ensure movement of a human-occupied vehicle in the water column, its positioning and retention at a given point in the water area.For this purpose, it was proceeded to development of an automated control system for the electric drive of the propulsive device of manned immersible. The proposed developments include a flowchart of the movement control system, circuitry engineering solutions using power semiconductor devices to maintain operability of the electric drive in extreme and emergency operating conditions, and movement control algorithms. Electromagnetic calculations of the active part of the electric machine were performed by the finite element method, considering the geometric features of the dental zone of the rotor and stator. The proposed mathematical apparatus served to calculate optimal control actions of the electric drive and to quantitatively assess the reduction in electrical losses once optimal control was applied. The calculation of the optimal control parameters was carried out using the maximum principle. The initial conditions for auxiliary functions are determined by the Newton‒ Raphson method. A comparison of various modes of operation of the electric drive was made regarding their influence on duration of the campaign, and other parameters.The calculations did not consider the parameters and geometry of the propulsive device (the propeller) since the developers of electric propulsion systems for manned and unmanned underwater vehicles of various classes often deliberately reduce the efficiency of the propeller to increase speed of the electric motor shaft, resulting in a decrease in the dimensions and weight of the latter.В настоящее время происходит интенсивное развитие обитаемых и необитаемых подводных аппаратов благодаря освоению шельфовых нефтегазовых месторождений, развитию подводной археологии и геологоразведочной деятельности в транзитных зонах относительно добычи полезных ископаемых с морского дна. Глубина погружения и характер выполняемых подводно-технических работ определяют не только конструктивное исполнение подводного аппарата, его энерговооруженность и техническую оснащенность, но и предъявляют высокие требования по надёжности, живучести и обитаемости в случае, если подводный аппарат подразумевает нахождение оператора на борту внутри прочного корпуса. Основные цели проведённого авторами исследования – это достижение высоких показателей надёжности и живучести основных элементов движительно-рулевого комплекса, обеспечивающих движение обитаемого подводного аппарата в толще воды, его позиционирование и удержание в заданной точке акватории.Для этого была проведена разработка автоматизированной системы управления электроприводом движителей обитаемого подводного аппарата. Предложена блок-схема системы управления движением, разработаны схемотехнические решения с использованием силовых полупроводниковых приборов для поддержания работоспособности электропривода в экстремальных и аварийных условиях эксплуатации, разработаны алгоритмы управления движением. Электромагнитные расчёты активной части электрической машины выполнены методом конечных элементов с учётом геометрических особенностей зубцовой зоны ротора и статора. На основе предложенного математического аппарата рассчитаны оптимальные управляющие воздействия электроприводом и дана количественная оценка по снижению электрических потерь при оптимальном управлении. Расчёт оптимальных параметров управления осуществлялся с помощью принципа максимума. Начальные условия для вспомогательных функций определены методом Ньютона–Рафсона. Проведено сравнение различных режимов работы электропривода с их влиянием на продолжительность кампании и другие показатели.В проведённых расчётах не учитывались параметры и геометрия движителя – гребного винта, потому как разработчики систем электродвижения обитаемых и необитаемых подводных аппаратов различного класса часто намеренно идут на снижение коэффициента полезного действия винта в угоду увеличению частоты вращения вала электродвигателя, следствием чего является снижение габаритов и массы последнего
CATHODE DIFFUSION POLARIZATION INFLUENCE MODELING IN COAXIAL SYMMETRY REFINER
The authors represent results of research of diffusion polarization influence on cathode sediment growth on the example of metal refining process in coaxial symmetry electrolyzer
RESEARCH OF ANODE FORM INFLUENCE ON CATHODE SEDIMENT GROWTH IN COAXIAL SYMMETRY REFINER USING IMITATION MODELING METHOD
This article represents results of cathode sediment growth modeling in coaxial symmetry electrolyzer in different forms of cathode and anode matrix. During modeling the authors were solving the problem of cathode matrix form optimization in accordance with performance of the device
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