Numerical Modelling of Optical Trapping

Optical trapping is a widely used technique, with many important applications in biology and metrology. Complete modelling of trapping requires calculation of optical forces, primarily a scattering problem, and non-optical forces. The T-matrix method is used to calculate forces acting on spheroidal and cylindrical particles.Comment: 4 pages, 4 figure

Calculation and optical measurement of laser trapping forces on non-spherical particles

Optical trapping, where microscopic particles are trapped and manipulated by light is a powerful and widespread technique, with the single-beam gradient trap (also known as optical tweezers) in use for a large number of biological and other applications. The forces and torques acting on a trapped particle result from the transfer of momentum and angular momentum from the trapping beam to the particle. Despite the apparent simplicity of a laser trap, with a single particle in a single beam, exact calculation of the optical forces and torques acting on particles is difficult. Calculations can be performed using approximate methods, but are only applicable within their ranges of validity, such as for particles much larger than, or much smaller than, the trapping wavelength, and for spherical isotropic particles. This leaves unfortunate gaps, since wavelength-scale particles are of great practical interest because they are readily and strongly trapped and are used to probe interesting microscopic and macroscopic phenomena, and non-spherical or anisotropic particles, biological, crystalline, or other, due to their frequent occurance in nature, and the possibility of rotating such objects or controlling or sensing their orientation. The systematic application of electromagnetic scattering theory can provide a general theory of laser trapping, and render results missing from existing theory. We present here calculations of force and torque on a trapped particle obtained from this theory and discuss the possible applications, including the optical measurement of the force and torque.Comment: 10 pages, 5 figure

Calculation of the T-matrix: general considerations and application of the point-matching method

The T-matrix method is widely used for the calculation of scattering by particles of sizes on the order of the illuminating wavelength. Although the extended boundary condition method (EBCM) is the most commonly used technique for calculating the T-matrix, a variety of methods can be used. We consider some general principles of calculating T-matrices, and apply the point-matching method to calculate the T-matrix for particles devoid of symmetry. This method avoids the time-consuming surface integrals required by the EBCM.Comment: 10 pages. 2 figures, 1 tabl

Multipole expansion of strongly focussed laser beams

Multipole expansion of an incident radiation field - that is, representation of the fields as sums of vector spherical wavefunctions - is essential for theoretical light scattering methods such as the T-matrix method and generalised Lorenz-Mie theory (GLMT). In general, it is theoretically straightforward to find a vector spherical wavefunction representation of an arbitrary radiation field. For example, a simple formula results in the useful case of an incident plane wave. Laser beams present some difficulties. These problems are not a result of any deficiency in the basic process of spherical wavefunction expansion, but are due to the fact that laser beams, in their standard representations, are not radiation fields, but only approximations of radiation fields. This results from the standard laser beam representations being solutions to the paraxial scalar wave equation. We present an efficient method for determining the multipole representation of an arbitrary focussed beam.Comment: 13 pages, 7 figure

Optical application and measurement of torque on microparticles of isotropic nonabsorbing material

We show how it is possible to controllably rotate or align microscopic particles of isotropic nonabsorbing material in a TEM00 Gaussian beam trap, with simultaneous measurement of the applied torque using purely optical means. This is a simple and general method of rotation, requiring only that the particle is elongated along one direction. Thus, this method can be used to rotate or align a wide range of naturally occurring particles. The ability to measure the applied torque enables the use of this method as a quantitative tool--the rotational equivalent of optical tweezers based force measurement. As well as being of particular value for the rotation of biological specimens, this method is also suitable for the development of optically-driven micromachines.Comment: 8 pages, 6 figure

Endocannabinoid System Participates in Neuron-Glial Networks Adaptation to Modeled Ischemia Factors in vitro

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Лікування хворих з пошкодженням нирок при політравмі

Around 4.5 million of people suffer from traumas in Ukraine. Renal injuries in case of polytrauma are observed in 26.4% of cases and occupy second or third place among injuries of organs of abdominal cavity and retroperitoneal space. To study and prove the influence of the lymph stimulation therapy on functional condition of kidneys and vital organs and systems at suffered people with renal injuries in case of polytrauma we observed 218 patients, who were divided into two groups. In the first main group the lymph stimulation therapy was conducted and the patients of the second group took traditional therapy. The main clinical and biochemical indicators of blood and urine were studied by laboratory methods; ultrasound diagnostics and CT scan of kidneys and organs of abdominal cavity were done. It was proved that in patients, who received the lymph stimulation therapy, indicators of creatinine and indicators of other organs and systems normalized at 7 days earlier than in patients, who receive traditional therapy.В Украине вследствие травм страдают до 4,5 млн. человек. Повреждения почек при политравме наблюдаются у 26,4% случав и занимают 2–3 места среди повреждений органов брюшной полости и забрюшинного пространства. С целью обоснования и изучения влияния лимфостимулирующей терапии на функциональное состояние почек и жизненноважных органов и систем у потерпевших с повреждением почек при политравме наблюдали 218 больных, которые были разделены на две группи. В 1-й основной группе проводилась лимфостимулирующая терапия, а больные 2-й группы получали традиционную терапию. Лабораторными методами изучены основные клинико-биохимические показатели крови и мочи, УЗИ та КТ почек и органов брюшной полости. Доказано, что у больных, которые получали лимфостимулирующую терапию, показатели креатинина и показатели других органов и систем нормализуются на 7 суток раньше, чем при традиционной терапии.В Україні внаслідок травм страждають до 4,5 млн. чоловік. Пошкодження нирок при політравмі спостерігаються у 26,4% випадків і займають 2-3 місця серед пошкоджень органів черевної порожнини і заочеревинного простору. З метою обґрунтування і вивчення впливу лімфостимулювальним терапії на функціональний стан нирок і життєвоважливих органів і систем у потерпілих з ушкодженням нирок при політравмі спостерігали 218 хворих, які були розділені на дві группи. У 1-й основній групі проводилася лімфостимулювальним терапія, а хворі 2-ї групи отримували традиційну терапію. Лабораторними методами вивчені основні клініко-біохімічні показники крові і сечі, УЗД та КТ нирок і органів черевної порожнини. Доведено, що у хворих, які отримували лімфостимулювальним терапію, показники креатиніну та показники інших органів і систем нормалізуються на 7 діб раніше, ніж при традиційній терапії

FEATURES OF THE ELECTRICAL CONDUCTIVITY AND RESISTANCE OF CEMENT FOR FIXATION OF NON-REMOVABLE PROSTHETIC

Our studies show different resistance and consequently different electrical conductivity of dry and wet samples of studied cements. Particular attention is drawn to the fact of reducing the relative value of the resistance of cements to fix after humidification. It can be evidence of higher hydrophobicity of the samples which have greater resistance after humidification. Thus, it is possible to recommend the use for fixing sintered structures made with reference bits according to our proposed method “Tsemion” and polycarboxylate cement. Since these cements have high electrical resistance and a corresponding lower electric conductivity, there is a slight decrease in the resistance after wetting the samples

Adaptive Role of Glial Cell Line-Derived Neurotrophic Factor in Cerebral Ischemia

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