научный журнал по химии Химическая физика ISSN: 0207-401X

ANNI R., CONNOR J.N.L., NOLI C. — 2004 г.

A recently proposed technique is described that provides improved nearsie-farside (NF) decompositions of elastic scattering amplitudes. The technique, involving a new resummation formula for Legendre partial wave series, reduces the importance of unphysical contributions to NF subamplitudes, which can appear in more conventional NF decompositions. Applications are made to a strong absorption model that arises in chemical and nuclear physics, as well as to a 16O + 12C optical potential at E lab = 132 MeV.

BELLENOUE M., CENIAN A., LABUDA S.A., LEYS C. — 2004 г.

Electrical probes have been used for diagnostic of propane/air flames of different equivalence ratios propagating in a cylindrical combustion chamber. The various parameters of combustion plasma, including ionization density and flame temperature have been determined. Electrical probe combined with Schlieren signal allowed measurement of burning velocity and gas velocity of unburned mixture just ahead of combustion front. It was shown also that the measurements of different flame characteristics require electrical probes of specific design. The electron densities obtained for stoichiometric methane/air flame plasma vary in combustion chamber and are of the order of 10 17 m -3 at the pressure 0.15-0.3 MPa and gas temperature ~325 K. The temperature of combustion plasma derived from volt-ampere probe characteristic is ~2200 K for atmospheric-pressure flame. The agreement of our results with available experimental and theoretical data is satisfactory.

MAKAROV D.V., MOLKOV V.V. — 2004 г.

The LES model of flame propagation and pressure build up during gaseous explosions in large-scale closed vessels is suggested. The subgrid scale turbulence modelling is based on the renormalization group approach. The premixed combustion is modelled by the gradient method and based on the filtered progress variable equation. The full three-dimensional compressible Navier-Stokes equations are solved on unstructured tetrahedral meshes in a spherical domain of 2.3-m diameter. The average size of the tetrahedron edges was 0.07 cm for uniform grid and 0.035 m with one level of solution adaptive grid refinement/derifinement around the flame front area. The simulations were validated against experimental data by Kumar et al. on deflagration of a stoichiometric hydrogen-air mixture, initiated at the centre of a closed sphere of 2.3-m diameter at initial temperature 100°C and pressure 97 kPa. The simulated pressure dynamics is in agreement with the experiment. The role of a mesh size on the resolved flame wrinkling factor and pressure build up is demonstrated in the assumption of subgrid scale wrinklin Ξ s sgs = 1. For the first time the resolved cellular structure (wrinkling) of a large-scale explosion flame is obtained by LES. The resolved flame front wrinkling factor increases with flame radius and reaches S = 1.09 on the 0.035 m mesh.

LAVERGNE G., LECOURT R., OUARTI N. — 2004 г.

The study presented in this paper is conducted in the frame of turbojets combustion chambers optimization by the increase of efficiency and the reduction of polluting emissions. The operating critical conditions at high altitude make it more difficult to control both the ignition and the re-light process after an accidental in-flight flameout. In this context, a numerical model has been developed to predict the behavior of a two-phase kernel when submitted to the electrical spark’s discharge inside the combustor. This model is based upon the resolution of the mass species and energy conservation equations linked with the state equation of the gas; it takes account of the various physical and chemical phenomena involved, such as the fuel-drops vaporization, the chemical kinetics and the turbulent transfers. The turbulent two-phase flow field corresponding to an experimental combustion chamber of simple geometry has been computed using an Enlerian-Lagrangian approach and then the kernel’ s ignition model has been applied to determine numerically an optimal location for the spark-plug. This paper presents in detail the kernel’s ignition model and some results of its application that are compared with experimental results.

KOZHUSHNER M.A., MURYASOV R.R., POSVYANSKII V.S. — 2004 г.

The theory of the “bridge” effect, i.e. electron tunneling with the participation of intermediate particles, is developed. It is shown and proved the general incorrectness of the approach that operates with the restricted basis of the bound states on the bridge particles to obtain sub-barrier electron Green function. This approach is adequate only in the energy region near the bound energy of the bridge centers at the large center-to-center distances. Our theory is based on the concept of multiple sub-barrier scattering of tunneling electron on the intermediate particles. The regular method of the calculation of the energies of the collectivized bound states as the poles of the total scattering amplitude is developed. It is shown that probability of the tunneling transition depends on the value and sign of the amplitude of electron sub-barrier scattering on one particle, and this amplitude can be calculated by the variation-asymptotic method developed by the authors earlier. The bridge induced enhancement of the tunneling probability depends exponentially on the length of the bridge, the exponent rises with modulus of the tunneling energy, i.e. with energy decreasing. Such enhancement is possible also in the absence of the bound states on the bridge. Two modes of the tunneling transitions, adiabatic and non-adiabatic ones, are considered.

CONNOR J.N.L., HOBBS C.A. — 2004 г.

Oscillating integrals often arise in the theoretical description of phenomena in chemical physics, in particular in atomic and molecular collisions, and in spectroscopy. A computer code for the numerical evaluation of the oscillatory cuspoid canonical integrals and their first-order partial derivatives is described. The code uses a novel adaptive contour algorithm, which chooses a contour in the complex plane that avoids the violent oscillatory and exponential natures of the integrand and modifies its choice as necessary. Applications are made to the swallowtail canonical integral and to a bessoid integral.

FIGL C., GOLDSTEIN R., GROSSER J., HOFFMANN O., REBENTROST F. — 2004 г.

Optical excitation of collision pairs into a definite molecular state and analysis of the final atomic state gives a direct access to the nonadiabatic processes which occur at the convergence of the molecular potential curves before the collision partners separate. We describe the method, give experimental examples and discuss different nonadiabatic mechanisms.

BOGAERTS A., CENIAN A., CHERNUKHO A., LEYS C. — 2004 г.

Langmuir-probes immersed in a combustion front are effective tools of flame-plasma diagnostics, including determination of flame-front arrival, ion temperature or ionization density. Particle-in-cell Monte-Carlo models, combined with computational fluid-dynamics and ion-kinetics codes may be very helpful in providing some additional information useful in interpretation of probe data. The results of the first particle-in-cell simulation of current-voltage characteristic of Langmuir probe are presented here.

GUÉROUT R., JUNGEN M., LEHNER M. — 2004 г.

We wish to draw the attention to a set of ab initio calculations for the potential energy surfaces of about 20 electronic states of H 3 and H 3 +, carried out for a large range of nuclear arrangements corresponding to the dissociation of the metastable molecule. In the text we give a qualitative discussion of the properties of the surfaces and we present calculations for the vibrational levels of the 2sa 1 excited state.

BUENKER R.J., MUIÑO P.L. — 2004 г.

Attempts to explain the refraction of light in dispersive media in terms of a photon or “corpuscular” model have heretofore been unable to account for the observed decrease in the speed of light as it passes from air into a region of higher refractive index n such as water or glass. In the present work it is argued on the basis of the quantum mechanical relations p = ħk and E = ħω that the energy of photons satisfies the equation E = pc/n. It is possible to obtain an exact prediction of the observed speed of the photons in a given medium by application of Hamilton’s equations of motion to the above formula, but at the same time to conclude, in agreement with the arguments of Newton and other classical physicists, that the photon momentum increases in direct proportion to n, thereby producing the well-known bending of light rays toward the normal when entering water from air. The corresponding relativistic particle theory of light indicates that the potential V encountered by the photons in a given medium is attractive for n > 1 and is momentum-dependent, which suggests the microscopic interactions responsible for the refraction of light are non-Coulombic in nature and are instead akin to the spin-orbit and orbit-orbit terms in the Breit-Pauli Hamiltonian for electrons moving in an external field. The present theory concludes that the reason photons are slowed down upon entering water from air is that their relativistic mass p/v increases faster with n than does their momentum, which in turn requires that Einstein’s famous E = mc 2 formula does not hold for light dispersion because the energy of the photons is expected to be the same in both media. In summary, all the known experimental data regarding light dispersion can be successfully explained in terms of a particle theory of light once it is realized that photons possess exceptional properties by virtue of their zero proper mass and their capacity to undergo electromagnetic interactions with surrounding media.

DE RUYCK J., DYAKOV I.V., KONNOV A.A. — 2004 г.

Probe sampling measurements of the concentrations of nitric oxide in the post-flame zone of methane-oxygen-carbon dioxide flames with admixture of ammonia (0.5% of the fuel) are reported. A Heat Flux method was used for stabilization of non-stretched flames on a perforated plate burner at atmospheric pressure. Dilution ratios of oxygen, O 2/(O 2 + CO 2), were varied from 0.26 to 0.35. Measured burning velocities for these flames agree well with those of the flames of methane-oxygen-carbon dioxide within an experimental accuracy. The concentrations of NO* were measured by means of a non-cooled quartz probe at different axial distances from the burner. The data are compared to modeling. The modeling over-predicts the measured concentrations of NO* however the experimental data trends are well reproduced. The effect of dilution of the flames by ambient air is stronger at smaller dilution ratios of oxygen. Including the downstream heat losses to the modeling does not remarkably alter the predicted concentrations of NO*.

BUENKER R.J. — 2004 г.

It is shown that time intervals ∆t' measured for photons moving with speed v > c can be of the same sign for all observers according to special relativity, thereby avoiding any violation of Einstein causality. Previous assertions to the contrary have led to unnecessarily complicated interpretations of experiments which indicate that single photons do travel with faster-than-c speeds in regions of anomalous dispersion.

SHAKARIYANTS S.A., VAN BUIJTENEN J.P., VISSER W.P.J. — 2004 г.

The year 2003 marks a century of the engine-powered flight. Although being born just 100 years ago, aviation has experienced rapid growth and expansion towards an integral and vital part of modern society. At the same time, this growth has raised worries about the associated environmental impact. An essential area of concern in this respect is a lack of methods and tools for aero-engine exhaust emission prediction and analysis, which would enable to respond the problem of aviation pollution. In a commitment to contribute to the solution of the problem, a Research Project has been launched at the Thermal Power Engineering Section of the Delft University of Technology in July 2002, named “Aero-Gasturbine Emission Reduction and Simulation Technology”. The Project is being conducted in collaboration with the Dutch National Aerospace Laboratory (NLR) and the Netherlands Ministry of Transport, Public Works and Water Management. The Conceptual Study of the Subject is represented in the current paper.

BUENKER R.J., MUIÑO P.L., THOMPSON A.M. — 2004 г.

Traditional methods for measuring the speed of light in dispersive media have been based on the detection of interference between light waves emitted from the same source. In the present study the elapsed times for single photons to move from a laser to a photomultiplier tube are measured electronically. Time-correlated single photon counting detection produces a characteristic instrument response which has the same shape independent of both the path length the light travels and the nature of the transparent media through which it passes. This allows for an accurate calibration of the chronograph by observing shifts in the location of the instrument response for different distances traveled by the light. Measurement of the corresponding shift which occurs when light moves the same distance through air and water then enables an accurate determination of the ratio of the photon velocities in these two media. Three different wavelengths of light have been used. In two cases good agreement is found between the present measured light speeds and those which can be inferred from existing refractive index measurements in water. The shortest wavelength studied is too far in the uv to obtain a reliable estimate on the same basis, and so the n g value (1.463) measured in the present work awaits independent confirmation. A theoretical discussion of the present results is undertaken with reference to Newton’s original corpuscular theory of light. It is argued that his failure to predict that light travels more slowly in water than in air arose from the inadequacy of his mechanical theory rather than his assumptions about the elementary composition of light.

ВАННИКОВ А.В., ЗОЛОТАРЕВСКИЙ В.И., КОЛЕСНИКОВ В.А. — 2004 г.

Аномальные, N-образные вольт-амперные характеристики наблюдались ранее для полимерных слоев толщиной менее 100 нм и для различных органических электролюминесцентных диодов. Они выражались в появлении плохо повторяющихся максимумов тока при напряжениях ниже рабочих напряжений светодиодов. До настоящего времени в литературе отсутствовало достаточно непротиворечивое объяснение данного явления. В настоящей работе мы предполагаем, что за возникновение аномальных вольт-амперных характеристик ответственны различные неоднородности и металлические острия, направленные в глубь полимера на межфазной границе металл/полимер. В аномальной области плотность тока автоэлектронной эмиссии через острия может достигать достаточно больших значений, чтобы вызывать микровзрывы кончиков острий. В данной области мы наблюдали свечение, имеющее спектр излучения абсолютно черного тела с характеристической температурой, значительно превышающей температуру плавления электрода.

ГРИШИН М.В., ДАЛИДЧИК Ф.И., КОВАЛЕВСКИЙ С.А., КОВЫТИН А.В. — 2004 г.

Методами сканирующей туннельной микроскопии и спектроскопии изучено атомное и электронное строение поверхностных наномасштабных структур пиролитического графита - вращательно-смещенных графеновых листов и полулистов (поверхностных и подповерхностных). Впервые найдены примеры новых поверхностных протяженных дефектов - складок типа гофрированного листа. Полученные результаты демонстрируют возможность управления поверхностной проводимостью графита посредством создания наномасштабных дефектов различного типа.

2004

2004

АРХИПОВ В.А., КОРОТКИХ А.Г., КУЗНЕЦОВ В.Т., САВЕЛЬЕВА Л.А. — 2004 г.

Представлены результаты по влиянию дисперсности добавок металлов на скорость горения смесевых композиций в зависимости от давления окружающей среды и содержания металла в составе модельных композиций. Экспериментальные исследования проводились на модельных составах на основе перхлората аммония и бутилкаучука марки БКЛ. В качестве металлического горючего использовали порошки алюминия со средним размером частиц 10 мкм (АСД-1), а также ультрадисперсные порошки алюминия, полученные электровзрывным способом дисперсностью 0.12 мкм. Содержание добавок металлов варьировалось в диапазоне 10-20%. Кроме того, в состав смесевых композиций вводились катализаторы (порошок железа с диаметром частиц ~100 мкм и ультрадисперсные порошки железа, меди и никеля).

ВАХРУШЕВ В.В., ВОЙНОВ В.И., ВОЛКОВ Г.И., ДИДЕНКО Б.Я., ДРАГУНОВА В.В., ИВАНОВ В.А., КУЗНЕЦОВ О.П., ХОДАЛЕВ Г.Ф., ЧЕРНЫШЕВ В.К. — 2004 г.

В статье впервые рассматривается вопрос о влиянии на окружающую природную среду взрыва экспериментального устройства с использованием взрывомагнитного генератора с генерируемой энергией 30 МДж. Приведены расчетные оценки расстояний, на которых реализуются допустимые концентрации окиси углерода, меди, и места расположения безопасной зоны для людей, не причастных к эксперименту.