FIELDS EXCITED AND PROVIDING A UNIFORM FOCUSING OF SHORT RELATIVISTIC ELECTRON BUNCHES IN PLASMA

Plasma wake lens in which all short relativistic electron bunches of sequence are focused identically and uniformly is studied analytically and by numerical simulation. For two types of lenses necessary for these parameters of focused sequence of relativistic electron bunches are formulated. Verification of these parameters is performed by numerical simulation

TRANSFORMATION RATIO AT PLASMA WAKEFIELD EXCITATION BY LONG ELECTRON BUNCH WITH SHAPING OF ITS CHARGE ACCORDING COSINE

Possibility of increase of the transformation ratio at plasma wakefield excitation by long relativistic electron bunch, which charge is shaped according to cosine, with purpose to provide the absence of oscillating (on length of bunch) decelerating wakefield, usually attainable, using bunch - precursor, is considered. Length of bunch is selected more larger than wavelength. It is shown analytically that at the choice of charge shaping of long bunch according to cosine distribution one can do without a bunch – precursor to eliminate oscillating decelerating wakefield. Thus the transformation ratio is just in one and a half times less than in the case with a precursor

Uveal melanoma dissemination within the scleral tract in fine needle aspiration biopsy

Introduction. Fine needle aspiration biopsy (FNAB) of uveal melanoma (UM) is an invasive procedure. Many authors consider UM FNAB to be safe procedure, however extraocular extension of the tumor through the scleral tracts may occur. Current studies of scleral tracts after FNAB do not compare different biopsy techniques (cannula-assisted and without cannula) in terms of UM cells.Purpose. To assess morphology of scleral tracts for the presence of malignant cells when different biopsy techniques are approached.Material and methods. Forty-four scleral samples were analyzed after transvitreal FNAB performed in 22 enucleated eyes with UM. Cannula-assisted FNAB was performed in 22 cases. In the same eyes FNAB (n=22) was performed without cannula.Results. FNAB material was adequate for cytological examination in all cases. UM was confirmed in 22 eyes pathologically. UM cell implantation was detected in 5 scleral samples after FNAB without cannula. No signs of cell implantation were seen after cannula-assisted FNAB. The risk of scleral tract UM cell implantation was statistically lower in cannula-assisted FNAB technique (p=0.018, Pearson Chi-square test).Conclusions. UM FNAB performed directly through the sclera without cannula is associated with tumor cells implantation in scleral tract. Cannula-assisted FNAB significantly reduces the incidence of UM implantation in scleral tract

The Hitting Times with Taboo for a Random Walk on an Integer Lattice

For a symmetric, homogeneous and irreducible random walk on d-dimensional integer lattice Z^d, having zero mean and a finite variance of jumps, we study the passage times (with possible infinite values) determined by the starting point x, the hitting state y and the taboo state z. We find the probability that these passages times are finite and analyze the tails of their cumulative distribution functions. In particular, it turns out that for the random walk on Z^d, except for a simple (nearest neighbor) random walk on Z, the order of the tail decrease is specified by dimension d only. In contrast, for a simple random walk on Z, the asymptotic properties of hitting times with taboo essentially depend on the mutual location of the points x, y and z. These problems originated in our recent study of branching random walk on Z^d with a single source of branching

Gamma Knife stereotactic radiosurgery for intraocular retinoblastoma: a 5-year experience

External beam radiotherapy (EBR) remained for a long time the only method of treatment in children with recurrent and resistant retinoblastoma (RB). This method often leads to serious complications, including the occurrence of secondary malignant tumors. Currently, EBR is used as second-line (salvage) therapy. There is no data in the literature of using Gamma Knife stereotactic radiosurgery (GKRS) in RB treatment.Purpose. To present 5-year experience of using GKRS in patients with RB.Material and methods. 16 children (17 eyes) were treated using GKRS in the period from 2015 to 2019. Mean patient age was 34.7 months (range, 12–114 months). The eyes were classified as group B (n=4), C (n=1), D (n=12). 3 children had the last eye. All patients received systemic and local chemotherapy, all types of local treatment modalities before using GKRS. Recurrent and resistant RB was the indication for GKRS. Marginal 50% mean dose was 22 Gу (range, 20–24 Gу), depending on tumour type and location. Radiation doses were evaluated accounting critical eye structures and the orbit bones.Results. Complete regression was achieved in 11 patients, partial in 2. Four patients underwent enucleation after GKRS. Indications for enucleation were retinoblastoma recurrence (n=2) and vitreous hemorrhage with total retinal detachment (n=2). 13 eyes were salvaged with no signs of keratopathy, uveitis or damage of orbital and surrounding tissues during mean follow-up 30.6 months (range, 7–60 months). Сomplications of different severity occurred in 13 patients, including vitreous hemorrhage in 6 patients, which was successfully treated both conservative (n=3) and using pars plana vitrectomy with simultaneous melphalan irrigation (n=3).Conclusion. The first experience of GKRS as an alternative to enucleation in patients with RB was proved to be reasonable and successful

Single-stage combined urethroplasty for extended strictures of the anterior urethra of tuberculous origin

Background. Urethral strictures are currently one of the most complex pathologies in reconstructive urology. The most promising direction in this area is the development of single-stage surgical interventions that meets modern requirements for the quality of life of patients.The aim of the study. To evaluate the possibility and the effectiveness of surgical treatment of extended recurrent tuberculous urethral strictures in men using a combination of a skin flap and a buccal graft. In the literature, there is no description of the use of this technique in patients with urethral tuberculosis.Materials and methods. We observed 44 patients with urethral tuberculosis. Three men from this group of patients were diagnosed with tuberculous (post-tuberculous) extended recurrent stricture of the anterior urethra and they underwent combined single-stage urethroplasty with a ventral fasciocutaneous flap and a buccal graft using the inlay method in the penile region and with a buccal graft using the ventral onlay method in the bulbous urethra. Ultrasound of the urethra served as a method that determines the possibility of performing this surgery in case of maintaining a sufficient width of the urethral plate with a moderate degree of spongiofibrosis.Results. Patients were under observation for 34, 50 and 54 months and have good long-term functional results – all patients have unassisted urination and no residual urine. Post-micturition dribbling persists in 1 patient. The overall effectiveness of the treatment of these strictures, taking into account the treatment of repeated cases of the disease recurrence, is high.Conclusion. This technique demonstrates the possibility of performing a single-stage reconstruction of the anterior urethra in patients with extended recurrent tuberculous (post-tuberculous) urethral strictures and is also applicable for the surgical treatment of urethral strictures of other origins

Survival prognosis in individuals with a high spatial QRS-T angle

Aim. To evaluate medium-term survival without irreversible and fatal cardiovascular events in individuals with a high spatial QRS-T angle (sQRS-Ta) from a regional Russian sample.Material and methods. We analyzed 1394 electrocardiographic records from a random regional sample of men (30%) and women aged 25-64, which were included in the ESSE-RF1 study. Women were on average 5 years older than men, but there was no difference in mean age in the 45-64 groups. The follow-up period lasted 7 year; 26 irreversible events (cardiovascular death, non-fatal myocardial infarction or stroke) and 63 composite endpoints (CEs) (irreversible event or heart failure progression or revascularization) were identified. Irreversible events and composite endpoint in men were noted more often than in women as follows: 3,7% vs 1,1% (p=0,003) and 6,9% vs 3,6% (p=0,01), respectively. sQRS-Ta was estimated as the angle between the integral QRS and T vectors in the orthogonal leads. Survival was assessed by Kaplan-Meier curves using a log-rank test. Differences were considered significant at p≤0,05. Results. Sex groups did not differ in mean sQRS-Ta. sQRS-Ta ≥90o was considered to be increased. The divergence of survival curves by the end of follow-up period in men with increased sQRS-Ta relative to men with sQRS-Ta <900 was greater than in women as follows: 0,88 vs 0,96 for CE (p=0,0026) and 0,93 vs 0,96 for irreversible events (p=0,009); in women — 0,94 vs 0,98 for CE only (p=0,0016). Initial event and CE in men with increased sQRS-Ta occurred earlier than those with normal sQRS-Ta and then in women with increased sQRS-Ta. There were no differences in the frequency of sQRS-Ta increase among 45-64-year-old men and women, but irreversible events in men with increased sQRS-Ta occurred 5 times more often than in women. According to two-stage logistic regression, the probability of irreversible event in men is 4,35 times higher than in women (p=0,0002). After adjusting for sex, in individuals with increased sQRS-Ta, it is 2,75 times higher than in individuals with sQRS-Ta <90o (p=0,015).Conclusion. In men with increased sQRS-Ta (≥90o), survival without irreversible and fatal cardiovascular events was worse, and life expectancy was shorter than in men with normal sQRS-Ta or women with increased sQRS-Ta. The prognosis of irreversible events was significantly affected by male sex and sQRS-Ta increase