850 research outputs found
High order fluid model for streamer discharges. II. Numerical solution and investigation of planar fronts
The high order fluid model developed in the preceding paper is employed here
to study the propagation of negative planar streamer fronts in pure nitrogen.
The model consists of the balance equations for electron density, average
electron velocity, average electron energy and average electron energy flux.
These balance equations have been obtained as velocity moments of Boltzmann's
equation and are here coupled to the Poisson equation for the space charge
electric field. Here the results of simulations with the high order model, with
a PIC/MC (Particle in cell/Monte Carlo) model and with the first order fluid
model based on the hydrodynamic drift-diffusion approximation are presented and
compared. The comparison with the MC model clearly validates our high order
fluid model, thus supporting its correct theoretical derivation and numerical
implementation. The results of the first order fluid model with local field
approximation, as usually used for streamer discharges, show considerable
deviations. Furthermore, we study the inaccuracies of simulation results caused
by an inconsistent implementation of transport data into our high order fluid
model. We also demonstrate the importance of the energy flux term in the high
order model by comparing with results where this term is neglected. Finally,
results with an approximation for the high order tensor in the energy flux
equation is found to agree well with the PIC/MC results for reduced electric
fields up to 1000 Townsend, as considered in this work.Comment: 26 pages, 11 figure
Testicular dermoid cyst in a 14-year-old child
ДЕРМОИДНАЯ КИСТА /ДИАГНДЕРМОИД /ДИАГНЯИЧКИ /УЛЬТРАСОНДЕТИКЛИНИЧЕСКИЕ СЛУЧАИВ работе представлен клинический случай ребенка, 14 лет, с дермоидной кистой правого яичка. Образование впервые было выявлено при профилактическом осмотре в поликлинике. В последующем пациенту неоднократно проводилось ультразвуковое исследование наружных половых органов, при котором в верхнем полюсе правого яичка выявлялась неоднородная эхоструктура размерами 14 мм, 13,7 мм и 12 мм с четким, ровным контуром. Результаты иммуноферментного анализа крови не показали увеличение основных маркеров опухолевого процесса. При биохимическом тестировании крови отмечалось незначительное повышение уровня прямого билирубина и сывороточного железа. Для уточнения диагноза проведена магнитно-резонансная томография органов малого таза с внутривенным контрастированием. После проведения указанного обследования был выставлен диагноз "кистозное образование правого яичка". После проведения необходимых дополнительных диагностических мероприятий (УЗИ периферических лимфатических узлов, обследование брюшной полости с внутривенным контрастным усилением) выполнена операция, заключавшаяся в ревизии правой половины мошонки и удалении образования правого яичка. Интраоперационно по данным экспресс-биопсии диагностировалась дермоидная киста правого яичка, что подтвердилось при последующем гистологическом исследовании. Послеоперационный период протекал гладко. Пациент выписался в удовлетворительном состоянии. Таким образом, представленное клиническое наблюдение подчеркивает необходимость оптимизации профилактической работы медицинского персонала первичного звена по своевременной диагностике опухолевых процессов наружных половых органов, особенно у детей пубертатного возраста.The paper presents a clinical case of a 14-year-old child with a dermoid cyst of the right testicle. The formation was first detected during a routine check-up in the polyclinic. Then the external genitalia ultrasound examination was repeatedly performed to the patient, which revealed an inhomogeneous echostructure with dimensions of 14 mm, 13.7 mm and 12 mm with a clear, even contour in the upper pole of the right testicle. The enzyme-linked immunosorbent assay (ELISA) did not show an increase in the main tumour markers. The biochemical blood test revealed an insignificant rise in conjugated bilirubin and serum iron. To clarify the diagnosis, magnetic resonance tomography of the pelvic organs with intravenous contrast was recommended. After examination, the cystic lesion of the right testicle was diagnosed. After carrying out the necessary additional diagnostic measures (ultrasound examination of the peripheral lymphatic nodes, the abdominal cavity exploration with intravenous contrast enhancement), the child underwent an operation consisting in revising the right half of the scrotum and removing the formation of the right testicle. Intraoperatively, according to the express biopsy test, the dermoid cyst of the right testicle was diagnosed, which was confirmed by the subsequent histological examination. The postoperative period was uneventful. The patient was discharged in satisfactory state. Thus, the presented clinical observation emphasizes the need to optimize the preventive work of primary care medical personnel for timely diagnosis of tumor processes in the external genital organs, especially in children of puberty
Derivation and test of high order fluid model for streamer discharges
A high order fluid model for streamer dynamics
is developed by closing the system after the 4th moment
of the Boltzmann equation in local mean energy approximation.
This is done by approximating the high order
pressure tensor in the heat flux equation through the previous
moments. Mathematical characteristics of the system is
studied. Then planar ionization fronts for negative streamers
in Nsub2 are simulated with the classical streamer model,
MC-PIC particle model, and with the present higher order
model
High order fluid model for streamer discharges
A high order fluid model for streamer discharges is developed and used to investigate propagation of negative streamer fronts in N2 . Mo- mentum transfer theory is employed to evaluate the collision terms and close the system of moment/balance equations. The results of simulations are compared with those obtained by a PIC/MC method and by the classical first order fluid model based on the drif
Comparing plasma fluid models of different order for 1D streamer ionization fronts
We evaluate the performance of three plasma fluid models: the first order
reaction-drift-diffusion model based on the local field approximation; the second order
reaction-drift-diffusion model based on the local energy approximation and a recently
developed high order fluid model by Dujko et al (2013 J. Phys. D 46 475202) We first review
the fluid models: we briefly discuss their derivation, their underlying assumptions and the
type of transport data they require. Then we compare these models to a particle-in-cell/Monte
Carlo (PIC/MC) code, using a 1D test problem. The tests are performed in neon and nitrogen
at standard temperature and pressure, over a wide range of reduced electric fields. For the fluid
models, transport data generated by a multi-term Boltzmann solver are used. We analyze the
observed differences in the model predictions and address some of the practical aspects when
using these plasma fluid models
Magnetic Properties of J-J-J' Quantum Heisenberg Chains with Spin S=1/2, 1, 3/2 and 2 in a Magnetic Field
By means of the density matrix renormalization group (DMRG) method, the
magnetic properties of the J-J-J quantum Heisenberg chains with spin
, 1, 3/2 and 2 in the ground states are investigated in the presence of
a magnetic field. Two different cases are considered: (a) when is
antiferromagnetic and is ferromagnetic (i.e. the AF-AF-F chain),
the system is a ferrimagnet. The plateaus of the magnetization are observed. It
is found that the width of the plateaus decreases with increasing the
ferromagnetic coupling, and disappears when passes over a
critical value. The saturated field is observed to be independent of the
ferromagnetic coupling; (b) when is ferromagnetic and is
antiferromagnetic (i.e. the F-F-AF chain), the system becomes an
antiferromagnet. The plateaus of the magnetization are also seen. The width of
the plateaus decreases with decreasing the antiferromagnetic coupling, and
disappears when passes over a critical value. Though the ground
state properties are quite different, the magnetization plateaus in both cases
tend to disappear when the ferromagnetic coupling becomes more dominant.
Besides, no fundamental difference between the systems with spin half-integer
and integer has been found.Comment: 8 pages, 9 figures, to be published in J. Phys.: Condens. Matte
Structure and morphology of low mechanical loss TiO₂-doped Ta₂O₅
The exceptional stability required from high finesse optical cavities and high precision interferometers is fundamentally limited by Brownian motion noise in the interference coatings of the cavity mirrors. In amorphous oxide coatings these thermally driven fluctuations are dominant in the high index layer compared to those in the low index SiO₂ layer in the stack. We present a systematic study of the evolution of the structural and optical properties of ion beam sputtered TiO₂-doped Ta₂O₅ films with annealing temperature. We show that low mechanical loss in TiO₂-doped Ta₂O₅ with a Ti cation ratio = 0.27 is associated with a material that consists of a homogeneous titanium-tantalum-oxygen mixture containing a low density of nanometer sized Ar-filled voids. When the Ti cation ratio is 0.53, phase separation occurs leading to increased mechanical loss. These results suggest that amorphous mixed oxides with low mechanical loss could be identified by considering the thermodynamics of ternary phase formation
Structure and morphology of low mechanical loss TiO₂-doped Ta₂O₅
The exceptional stability required from high finesse optical cavities and high precision interferometers is fundamentally limited by Brownian motion noise in the interference coatings of the cavity mirrors. In amorphous oxide coatings these thermally driven fluctuations are dominant in the high index layer compared to those in the low index SiO₂ layer in the stack. We present a systematic study of the evolution of the structural and optical properties of ion beam sputtered TiO₂-doped Ta₂O₅ films with annealing temperature. We show that low mechanical loss in TiO₂-doped Ta₂O₅ with a Ti cation ratio = 0.27 is associated with a material that consists of a homogeneous titanium-tantalum-oxygen mixture containing a low density of nanometer sized Ar-filled voids. When the Ti cation ratio is 0.53, phase separation occurs leading to increased mechanical loss. These results suggest that amorphous mixed oxides with low mechanical loss could be identified by considering the thermodynamics of ternary phase formation
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