Quinoidal Azaacenes: 99 % Diradical Character

Quinoidal azaacenes with almost pure diradical character (y=0.95 to y=0.99) were synthesized. All compounds exhibit paramagnetic behavior investigated by EPR and NMR spectroscopy, and SQUID measurements, revealing thermally populated triplet states with an extremely low-energy gap ΔEST′ of 0.58 to 1.0 kcal mol−1. The species are persistent in solution (half-life≈14–21 h) and in the solid state they are stable for weeks

Research of the work of technological compton scattering tomograph on the photon beam of the source ¹³⁷Cs

The results of the works, which have been carried out in NSC KIPT, on creation of a stationary technological Compton scattering tomograph are submitted. Modeling physical processes under program GEANT 3 is carried out, the design of a tomograph for a case of use is determined as a source of photons of the accelerator Van de Graaf on energy 3 MeV. Tests results of a tomograph work on a photon beam of the source ¹³⁷Cs are submitted.Представлено результати виконаних у ННЦ ХФТІ робіт по створенню стаціонарного технологічного комптонівського томографа. Проведено моделювання фізичних процесів по програмі GEANT 3, визначено конструкцію томографа для випадку використання як джерело фотонів прискорювача Ван де Граафа на енергію 3 МеВ. Представлено результати випробування роботи томографа на пучку фотонів джерела ¹³⁷Cs.Представлены разультаты выполненных в ННЦ ХФТИ работ по созданию стационарного технологического комптоновского томографа. Проведено моделирование физических процессов по программе GEANT 3, определена конструкция томографа для случая использования в качестве источника фотонов ускорителя Ван де Граафа на энергию 3 МэВ. Представлены результаты испытания работы томографа на пучке фотонов источника ¹³⁷Cs

Quantum effects in the radial thermal expansion of bundles of single-walled carbon nanotubes doped with ⁴He

The radial thermal expansion αr of bundles of single-walled carbon nanotubes saturated with ⁴He impurities to the molar concentration 9.4% has been investigated in the interval 2.5–9.5 K using the dilatometric method. In the interval 2.1–3.7 K α r is negative and is several times higher than the negative αr for pure nanotube bundles. This most likely points to ⁴He atom tunneling between different positions in the nanotube bundle system. The excess expansion was reduced with decreasing ⁴He concentration

The effect of O₂ impurities on the low-temperature radial thermal expansion of bundles of closed single-walled carbon nanotubes

The effect of oxygen impurities upon the radial thermal expansion αr of bundles of closed single-walled carbon nanotubes has been investigated in the temperature interval 2.2–48 K by the dilatometric method. Saturation of bundles of nanotubes with oxygen caused an increase in the positive αr-values in the whole interval of temperatures used. Also, several peaks appeared in the temperature dependence αr(T) above 20 K. The low temperature desorption of oxygen from powders consisting of bundles of single-walled nanotubes with open and closed ends has been investigated

Quantum phenomena in the radial thermal expansion of bundles of single-walled carbon nanotubes doped with ³He. A giant isotope effect

The radial thermal expansion αr of bundles of single-walled carbon nanotubes saturated with ³He up to the molar concentration 9.4% has been investigated in the temperature interval 2.1–9.5 K by high-sensitivity capacitance dilatometry. In the interval 2.1–7 K a negative αr was observed, with a magnitude which exceeded the largest negative αr values of pure and ⁴He-saturated nanotubes by three and two orders of magnitude, respectively. The contributions of the two He isotope impurities to the negative thermal expansion of the nanotube bundles are most likely connected with the spatial redistribution of ⁴He and ³He atoms by tunneling at the surface and inside nanotube bundles. The isotope effect turned out to be huge, probably owing to the higher tunneling probability of ³He atoms

The low-temperature radial thermal expansion of single-walled carbon nanotube bundles saturated with nitrogen

The effect of a N₂ impurity on the radial thermal expansion coefficient αr of single-walled carbon nanotube bundles has been investigated in the temperature interval 2.2–43K by the dilatometric method. Saturation of nanotube bundles with N₂ caused a sharp increase in the positive magnitudes of αr in the whole temperature range used and a very high and wide maximum in the thermal expansion coefficient αr(T) at T~28 K. The lowtemperature desorption of the impurity from the N₂-saturated powder of bundles of single-walled carbon nanotubes with open and closed ends has been investigated

Radial thermal expansion of single-walled carbon nanotube bundles at low temperatures

For the first time the linear coefficient of the radial thermal expansion has been measured on a system of SWNT bundles at low temperatures (2.2–120 K). The measurements were performed using a dilatometer with a sensitivity of 2·10⁻⁹ cm. The cylindrical sample 7 mm high and 10 mm in diameter was obtained by compressing powder. The resulting bundles of the nanotubes were oriented perpendicular to the sample axis. The starting powder contained over 90% of SWNTs with the outer diameter 1.1 nm, the length varying within 5–30 μm. The change of sign of the radial thermal expansion coefficient at 5.5 K was observed

Measurement of xF3xF_3 and F2F_2 Structure Functions in Low Q2Q^2 Region with the IHEP-JINR Neutrino Detector

The isoscalar structure functions $xF_3$ and $F_2$ are measured as functions of $x$ averaged over all $Q^2$ permissible for the range of 6 to 28 GeV of incident neutrino (anti-neutrino) energy at the IHEP-JINR Neutrino Detector. The QCD analysis of $xF_3$ structure function provides $\Lambda_{\bar{MS}}^{(4)} = (411 \pm 200)$ MeV under the assumption of QCD validity in the region of low $Q^2$. The corresponding value of the strong interaction constant $\alpha_S (M_Z) = 0.123^{+0.010}_{-0.013}$ agrees with the recent result of the CCFR collaboration and with the combined LEP/SLC result.Comment: 11 pages, 1 Postscript figure, LaTeX. Talk given at the 7th International Workshop on Deep Inelastic Scattering and QCD (DIS 99), Zeuthen, Germany, 19-23 Apr 199

Billiards in a general domain with random reflections

We study stochastic billiards on general tables: a particle moves according to its constant velocity inside some domain ${\mathcal D} \subset {\mathbb R}^d$ until it hits the boundary and bounces randomly inside according to some reflection law. We assume that the boundary of the domain is locally Lipschitz and almost everywhere continuously differentiable. The angle of the outgoing velocity with the inner normal vector has a specified, absolutely continuous density. We construct the discrete time and the continuous time processes recording the sequence of hitting points on the boundary and the pair location/velocity. We mainly focus on the case of bounded domains. Then, we prove exponential ergodicity of these two Markov processes, we study their invariant distribution and their normal (Gaussian) fluctuations. Of particular interest is the case of the cosine reflection law: the stationary distributions for the two processes are uniform in this case, the discrete time chain is reversible though the continuous time process is quasi-reversible. Also in this case, we give a natural construction of a chord "picked at random" in ${\mathcal D}$, and we study the angle of intersection of the process with a $(d-1)$-dimensional manifold contained in ${\mathcal D}$.Comment: 50 pages, 10 figures; To appear in: Archive for Rational Mechanics and Analysis; corrected Theorem 2.8 (induced chords in nonconvex subdomains

Recognition of wavefront aberrations types corresponding to single Zernike functions from the pattern of the point spread function in the focal plane using neural networks

В работе осуществлено обучение и распознавание типов аберраций, соответствующих отдельным функциям Цернике, по картине интенсивности функции рассеяния точки с применением свёрточных нейронных сетей. Картины интенсивности функции рассеяния точки в фокальной плоскости моделировались с применением алгоритма быстрого преобразования Фурье. При обучении нейронной сети коэффициент обучения и количество эпох для датасета заданного размера был подобран эмпирически. Средние ошибки предсказания нейронной сети для каждого типа аберраций были получены для набора из 15 функций Цернике по датасету из 15 тысяч картин функции рассеяния точки. В результате обучения для большинства типов аберраций получены усреднённые абсолютные погрешности в диапазоне 0,012 – 0,015, однако определение коэффициента (величины) аберрации требует дополнительных исследований и данных, например, расчёта функции рассеяния точки во внефокальной плоскости. In this work, we carried out training and recognition of the types of aberrations corresponding to single Zernike functions, based on the intensity pattern of the point spread function (PSF) using convolutional neural networks. PSF intensity patterns in the focal plane were modeled using a fast Fourier transform algorithm. When training a neural network, the learning coefficient and the number of epochs for a dataset of a given size were selected empirically. The average prediction errors of the neural network for each type of aberration were obtained for a set of 15 Zernike functions from a data set of 15 thousand PSF pictures. As a result of training, for most types of aberrations, averaged absolute errors were obtained in the range of 0.012 – 0.015. However, determining the aberration coefficient (magnitude) requires additional research and data, for example, calculating the PSF in the extrafocal plane.Исследование выполнено при финансовой поддержке РФФИ в рамках научного проекта № 19-29-09054 в части, касающейся машинного обучения и нейронных сетей, а также Министерства науки и высшего образования РФ в рамках выполнения работ по Государственному заданию ФНИЦ «Кристаллография и фотоника» РАН (соглашение № 007-ГЗ/Ч3363/26) в части моделирования аберрированного волнового фронта и расчёта ФРТ