Third harmonic generation in LiKB4O7 single crystal

The third order nonlinear optical properties of the lithium potassium borate (LiKB4O7) single crystal have been investigated by means of the rotational Maker fringe technique using Nd:YAG laser at 1064 nm working in picosecond regime. The value of the third order nonlinear optical susceptibility was calculated using the theoretical model of Kajzar et al. and was found to be about 1.4 × 10−21 m2 V−2 that is one order higher than that of fused silica

Discrete solvent effects on the effective interaction between charged colloids

Using computer simulations of two charged colloidal spheres with their counterions in a hard sphere solvent, we show that the granular nature of the solvent significantly influences the effective colloidal interaction. For divalent counterions, the total effective force can become attractive generated by counterion hydration, while for monovalent counterions the forces are repulsive and well-described by a solvent-induced colloidal charge renormalization. Both effects are not contained in the traditional "primitive" approaches but can be accounted for in a solvent-averaged primitive model.Comment: 4 pages, 3 figure

Electrostatic Interactions of Asymmetrically Charged Membranes

We predict the nature (attractive or repulsive) and range (exponentially screened or long-range power law) of the electrostatic interactions of oppositely charged and planar plates as a function of the salt concentration and surface charge densities (whose absolute magnitudes are not necessarily equal). An analytical expression for the crossover between attractive and repulsive pressure is obtained as a function of the salt concentration. This condition reduces to the high-salt limit of Parsegian and Gingell where the interaction is exponentially screened and to the zero salt limit of Lau and Pincus in which the important length scales are the inter-plate separation and the Gouy-Chapman length. In the regime of low salt and high surface charges we predict - for any ratio of the charges on the surfaces - that the attractive pressure is long-ranged as a function of the spacing. The attractive pressure is related to the decrease in counter-ion concentration as the inter-plate distance is decreased. Our theory predicts several scaling regimes with different scaling expressions for the pressure as function of salinity and surface charge densities. The pressure predictions can be related to surface force experiments of oppositely charged surfaces that are prepared by coating one of the mica surfaces with an oppositely charged polyelectrolyte

DNA-condensation, redissolution and mesocrystals induced by tetravalent counterions

The distance-resolved effective interaction potential between two parallel DNA molecules is calculated by computer simulations with explicit tetravalent counterions and monovalent salt. Adding counterions first yields an attractive minimum in the potential at short distances which then disappears in favor of a shallower minimum at larger separations. The resulting phase diagram includes a DNA-condensation and redissolution transition and a stable mesocrystal with an intermediate lattice constant for high counterion concentration.Comment: 4 pages, 4 figure

On the Properties of Two Pulses Propagating Simultaneously in Different Dispersion Regimes in a Nonlinear Planar Waveguide

Properties of two pulses propagating simultaneously in different dispersion regimes, anomalous and normal, in a Kerr-type planar waveguide are studied in the framework of the nonlinear Schroedinger equation. Catastrophic self-focusing and spatio-temporal splitting of the pulses is investigated. For the limiting case when the dispersive term of the pulse propagating in the normal dispersion regime can be neglected an indication of a possibility of a stable self-trapped propagation of both pulses is obtained.Comment: 18 pages (including 15 eps figures

Комплексна профілактика тромбоемболічних ускладнень у хворих із гострою хірургічною абдомінальною патологією, поєднаною з хронічними захворюваннями вен нижніх кінцівок

The work studied the effect of anticoagulant comprehensive prevention of thromboembolic complications in patients with acute abdominal surgical pathology combined with chronic venous disease of lower extremities for changes in coagulation and tissue microcirculation. It was found out significant improvement tissue microcirculation by drug hypocoagulation, reducing the risk of thromboembolic complications.В работе изучено влияние комплексной антикоагулянтной профилактики тромбоэмболических осложнений у больных с острой хирургической абдоминальной патологией, сочетанной с хроническими заболеваниями вен нижних конечностей, на изменения коагуляции и тканевой микроциркуляции. Выявлено существенное улучшение тканевой микроциркуляции за счет медикаментозной гипокоагуляции, снижение рисков тромбоэмболических осложнений.У роботі вивчено вплив комплексної антикоагулянтної профілактики тромбоемболічних ускладнень у хворих із гострою хірургічною абдомінальною патологією, поєднаною з хронічними захворюваннями вен нижніх кінцівок, на зміни коагуляції та тканинної мікроциркуляції. Виявлено суттєве покращення тканинної мікроциркуляції за рахунок медикаментозної гіпокоагуляції, зниження ризиків тромбоемболічних ускладнень

ДОСВІД ПРОВЕДЕННЯ ДИСТАНЦІЙНИХ ОНЛАЙН-СЕМІНАРІВ ПІД ЧАС КАРАНТИНУ НА КАФЕДРІ ХІРУРГІЇ № 1 З УРОЛОГІЄЮ, МАЛОІНВАЗИВНОЮ ХІРУРГІЄЮ ТА НЕЙРОХІРУРГІЄЮ ІМЕНІ Л. Я. КОВАЛЬЧУКА

The article considers the initial experience of conducting distance online seminars at the L. Ya. Kovalchuk Department of Surgery No.1 with Urology, Minimally Invasive Surgery and Neurosurgery. The analysis of the conducted work showed a number of significant advantages and some disadvantages of this form of education. The biggest advantage is the possibility of personal multimedia access to the proposed materials during the online seminar discussion of the lesson topic. The use of chat programs allows students to interactively participate in discussions, ask questions and also makes it possible for the teacher to provide access to files, treatment protocols and spread links to online resources relevant to the lesson. Significant disadvantage of conducting an online seminar is the lack of ability to perform practical and communicative skills near the patient’s bedside. Conducting distance online seminars can be a separate point in ensuring the quality of educational services in a pandemic for higher medical schools in Ukraine.У статті розглянуто первинний досвід проведення дистанційних онлайн-семінарів на кафедрі хірургії № 1 з урологією, малоінвазивною хірургією та нейрохірургією ім. Л. Я. Ковальчука. Аналіз проведеної роботи показав ряд суттєвих переваг та деяких недоліків такої форми навчання. Найбільшою перевагою є можливість персонального мультимедійного доступу до пропонованих матеріалів під час семінарського онлайн-обговорення теми заняття. Використання чату програм дозволяє студентам інтерактивно брати участь у дискусії, ставити питання, а також викладачеві робить можливим надавати доступ до файлів, протоколів лікування та поширювати посилання на інтернет-ресурси, актуальні для заняття. Явним суттєвим недоліком проведення онлайн-семінару залишається відсутність можливості виконувати практичні та комунікативні навички роботи біля ліжка хворого. Проведення дистанційних онлайн-семінарів може бути окремим  пунктом у забезпеченні якості надання освітніх послуг в умовах пандемії для вищих медичних шкіл України

DNA condensation and redissolution: Interaction between overcharged DNA molecules

The effective DNA-DNA interaction force is calculated by computer simulations with explicit tetravalent counterions and monovalent salt. For overcharged DNA molecules, the interaction force shows a double-minimum structure. The positions and depths of these minima are regulated by the counterion density in the bulk. Using two-dimensional lattice sum and free energy perturbation theories, the coexisting phases for DNA bundles are calculated. A DNA-condensation and redissolution transition and a stable mesocrystal with an intermediate lattice constant for high counterion concentration are obtained.Comment: 26 pages, 10 figure

Attraction between DNA molecules mediated by multivalent ions

The effective force between two parallel DNA molecules is calculated as a function of their mutual separation for different valencies of counter- and salt ions and different salt concentrations. Computer simulations of the primitive model are used and the shape of the DNA molecules is accurately modelled using different geometrical shapes. We find that multivalent ions induce a significant attraction between the DNA molecules whose strength can be tuned by the averaged valency of the ions. The physical origin of the attraction is traced back either to electrostatics or to entropic contributions. For multivalent counter- and monovalent salt ions, we find a salt-induced stabilization effect: the force is first attractive but gets repulsive for increasing salt concentration. Furthermore, we show that the multivalent-ion-induced attraction does not necessarily correlate with DNA overcharging.Comment: 51 pages and 13 figure