713 research outputs found
The control of body position in the stick insect (Carausius morosus), when walking over uneven surfaces
Hitchhiking transport in quasi-one-dimensional systems
In the conventional theory of hopping transport the positions of localized
electronic states are assumed to be fixed, and thermal fluctuations of atoms
enter the theory only through the notion of phonons. On the other hand, in 1D
and 2D lattices, where fluctuations prevent formation of long-range order, the
motion of atoms has the character of the large scale diffusion. In this case
the picture of static localized sites may be inadequate. We argue that for a
certain range of parameters, hopping of charge carriers among localization
sites in a network of 1D chains is a much slower process than diffusion of the
sites themselves. Then the carriers move through the network transported along
the chains by mobile localization sites jumping occasionally between the
chains. This mechanism may result in temperature independent mobility and
frequency dependence similar to that for conventional hopping.Comment: a few typos correcte
Transport Properties of Highly Aligned Polymer Light-Emitting-Diodes
We investigate hole transport in polymer light-emitting-diodes in which the
emissive layer is made of liquid-crystalline polymer chains aligned
perpendicular to the direction of transport. Calculations of the current as a
function of time via a random-walk model show excellent qualitative agreement
with experiments conducted on electroluminescent polyfluorene demonstrating
non-dispersive hole transport. The current exhibits a constant plateau as the
charge carriers move with a time-independent drift velocity, followed by a long
tail when they reach the collecting electrode. Variation of the parameters
within the model allows the investigation of the transition from non-dispersive
to dispersive transport in highly aligned polymers. It turns out that large
inter-chain hopping is required for non-dispersive hole transport and that
structural disorder obstructs the propagation of holes through the polymer
film.Comment: 4 pages, 5 figure
Theory of Exciton Migration and Field-Induced Dissociation in Conjugated Polymers
The interplay of migration, recombination, and dissociation of excitons in
disordered media is studied theoretically in the low temperature regime. An
exact expression for the photoluminescence spectrum is obtained. The theory is
applied to describe the electric field-induced photoluminescence-quenching
experiments by Kersting et al. [Phys. Rev. Lett. 73, 1440 (1994)] and Deussen
et al. [Synth. Met. 73, 123 (1995)] on conjugated polymer systems. Good
agreement with experiment is obtained using an on-chain dissociation mechanism,
which implies a separation of the electron-hole pair along the polymer chain.Comment: 4 pages, RevTeX, 2 Postscript figure
Temperature and Field Dependence of the Mobility in Liquid-Crystalline Conjugated Polymer Films
The transport properties of organic light-emitting diodes in which the
emissive layer is composed of conjugated polymers in the liquid-crystalline
phase have been investigated. We have performed simulations of the current
transient response to an illumination pulse via the Monte Carlo approach, and
from the transit times we have extracted the mobility of the charge carriers as
a function of both the electric field and the temperature. The transport
properties of such films are different from their disordered counterparts, with
charge carrier mobilities exhibiting only a weak dependence on both the
electric field and temperature. We show that for spatially ordered polymer
films, this weak dependence arises for thermal energy being comparable to the
energetic disorder, due to the combined effect of the electrostatic and thermal
energies. The inclusion of spatial disorder, on the other hand, does not alter
the qualitative behaviour of the mobility, but results in decreasing its
absolute value.Comment: 9 pages, 8 figures, submitted to Phys. Rev.
Анализ современных технологий заводнения при разработке нефтяных месторождений
Объектом исследования являются системы заводнения применяемые на месторождениях России
Цель работы – анализ современных технологий заводнения при разработке нефтяных месторождений, а также обоснование применения технологий заводнения с целью увеличения темпов отбора, коэффициента нефтеизвлечения, технико-экономических показателей.
В выпускной квалификационной работе приведены сведения о современных технологиях заводнения, применяемых на месторождениях России. Проведены расчеты экономической эффективности при внедрении нестационарного метода заводнения. Проанализирован процесс работы методов заводнения в условиях месторождений России. Бакалаврская работа выполнена в текстовом редакторе Microsoft Word, и Microsoft Excel.The object of the study are the waterflooding systems used in the fields of Russia
The aim of the work is the analysis of modern flooding technologies in the development of oil fields, as well as the rationale for using flooding technologies to increase the rate of selection, the oil recovery factor, and the technical and economic indicators. In the final qualification work information on modern water flooding technologies used in the fields of Russia is given. Calculations of economic efficiency are implemented in the introduction of the non-stationary flooding method. The process of work of flooding methods in the conditions of Russian deposits is analyzed. Bachelor's work is executed in the text editor Microsoft Word, and Microsoft Excel
Temperature Dependence of Exciton Diffusion in Conjugated Polymers
The temperature dependence of the exciton dynamics in a conjugated polymer is studied using time-resolved spectroscopy. Photoluminescence decays were measured in heterostructured samples containing a sharp polymer-fullerene interface, which acts as an exciton quenching wall. Using a 1D diffusion model, the exciton diffusion length and diffusion coefficient were extracted in the temperature range of 4-293 K. The exciton dynamics reveal two temperature regimes: in the range of 4-150 K, the exciton diffusion length (coefficient) of ~3 nm (~1.5 × 10-4 cm2/s) is nearly temperature independent. Increasing the temperature up to 293 K leads to a gradual growth up to 4.5 nm (~3.2 × 10-4 cm2/s). This demonstrates that exciton diffusion in conjugated polymers is governed by two processes: an initial downhill migration toward lower energy states in the inhomogenously broadened density of states, followed by temperature activated hopping. The latter process is switched off below 150 K.
Theory of Electric Field-Induced Photoluminescence Quenching in Disordered Molecular Solids
The dynamics of excitons in disordered molecular solids is studied
theoretically, taking into account migration between different sites,
recombination, and dissociation into free charge carriers in the presence of an
electric field. The theory is applied to interpret the results of electric
field-induced photoluminescence (PL) quenching experiments on molecularly doped
polymers by Deussen et al. [Chem. Phys. 207, 147 (1996)]. Using an
intermolecular dissociation mechanism, the dependence of the PL quenching on
the electric field strength and the dopant concentration, and the time
evolution of the transient PL quenching can be well described. The results
constitute additional proof of the distinct exciton dissociation mechanisms in
conjugated polymer blends and molecularly doped polymers.Comment: 4 pages RevTeX, 3 Postscript figure
Технологические решения для реконструкции добывающей скважины глубиной 2170 метров методом зарезки бокового ствола на нефтяном месторождении Томской области
Обоснование технологических решений для реконструкции добывающей скважины глубиной 2170 метров методом зарезки бокового ствола на нефтяном месторождении Томской области. В процессе исследования проводился анализ предоставленных геологических данных для принятия решений при разработке проекта. В результате исследования представлен комплекс технологических решений для строительства бокового ствола. Основные конструктивные, технологические и технико-эксплуатационные характеристики: обоснование и расчет профиля бокового ствола, расчет процессов углубления и заканчивания скважины, определение времени и стоимости проведения работ. Область применения: работа может быть использованы при составлении проектов на скважины, а данные из специальной части – при разработке состава эластомера ВЗД.Substantiation of technological solutions for reconstruction of a production well with a depth of 2,170 meters by the method of sidetracking at an oil field in the Tomsk region. In the course of the study, the analysis of the provided geological data for decision making during project development was carried out. As a result of the research, a set of technological solutions for the construction of the lateral trunk is presented. The main design, technological and technical and operational characteristics: justification and calculation of the sidetrack profile, calculation of the deepening and completion of the well, determination of the time and cost of work. Scope: the work can be used in the design of wells, and data from a special part - when developing the composition of an elastomer
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