Existence of weak solutions for the generalized Navier-Stokes equations with damping

In this work we consider the generalized Navier-Stokes equations with the presence of a damping term in the momentum equation. The problem studied here derives from the set of equations which govern isothermal flows of incompressible and homogeneous non-Newtonian fluids. For the generalized Navier-Stokes problem with damping, we prove the existence of weak solutions by using regularization techniques, the theory of monotone operators and compactness arguments together with the local decomposition of the pressure and the Lipschitz-truncation method. The existence result proved here holds for any and any sigma > 1, where q is the exponent of the diffusion term and sigma is the exponent which characterizes the damping term.MCTES, Portugal [SFRH/BSAB/1058/2010]; FCT, Portugal [PTDC/MAT/110613/2010]info:eu-repo/semantics/publishedVersio

Scaling exponents and clustering coefficients of a growing random network

The statistical property of a growing scale-free network is studied based on an earlier model proposed by Krapivsky, Rodgers, and Redner [Phys. Rev. Lett. 86, 5401 (2001)], with the additional constraints of forbidden of self-connection and multiple links of the same direction between any two nodes. Scaling exponents in the range of 1-2 are obtained through Monte Carlo simulations and various clustering coefficients are calculated, one of which, $C_{\rm out}$, is of order $10^{-1}$, indicating the network resembles a small-world. The out-degree distribution has an exponential cut-off for large out-degree.Comment: six pages, including 5 figures, RevTex 4 forma

Constrained spin dynamics description of random walks on hierarchical scale-free networks

We study a random walk problem on the hierarchical network which is a scale-free network grown deterministically. The random walk problem is mapped onto a dynamical Ising spin chain system in one dimension with a nonlocal spin update rule, which allows an analytic approach. We show analytically that the characteristic relaxation time scale grows algebraically with the total number of nodes $N$ as $T \sim N^z$. From a scaling argument, we also show the power-law decay of the autocorrelation function C_{\bfsigma}(t)\sim t^{-\alpha}, which is the probability to find the Ising spins in the initial state {\bfsigma} after $t$ time steps, with the state-dependent non-universal exponent $\alpha$. It turns out that the power-law scaling behavior has its origin in an quasi-ultrametric structure of the configuration space.Comment: 9 pages, 6 figure

Fingerprint for Network Topologies

A network's topology information can be given as an adjacency matrix. The bitmap of sorted adjacency matrix(BOSAM) is a network visualisation tool which can emphasise different network structures by just looking at reordered adjacent matrixes. A BOSAM picture resembles the shape of a flower and is characterised by a series of 'leaves'. Here we show and mathematically prove that for most networks, there is a self-similar relation between the envelope of the BOSAM leaves. This self-similar property allows us to use a single envelope to predict all other envelopes and therefore reconstruct the outline of a network's BOSAM picture. We analogise the BOSAM envelope to human's fingerprint as they share a number of common features, e.g. both are simple, easy to obtain, and strongly characteristic encoding essential information for identification.Comment: 12papes, 3 figures, in pres

X-ray and neutron diffraction studies of coupled structural phase transitions in DyBaCo2_{2}O5.5_{5.5}

A structural transition at $T\approx 322$ K from the $Pmmm$ to $Pmma$ phase is found to coincide with an anomaly of resistivity. Another structural phase transition doubling the lattice parameter $c$, which has been postulated earlier to accompany a low-temperature magnetic transition in TbBaCo$_{2}$O$_{5.5}$, is observed in a single crystal DbBaCo$_{2}$O$_{5.5}$ by means of the X-ray and neutron diffraction. The low temperature phase does not belong to the space group $Pcca$ that has been chosen earlier as the highest subgroup of the $Pmma$. The transition is of the first order with the temperature hysteresis, between $T\approx 100$ and $T\approx 200$ K, which probably explains anomalous magnetic properties in this temperature range.Comment: 6 pages, 4 figure

An improved method for automated control of the WWER-1000 power maneuvering

A multizone mathematical model for automated control of the WWER-1000 power maneuvering has been improved by means of considering the power release at fission of both ²³⁵U and ²³⁹Pu nuclei, as well as by using simultaneous control actions of changing the boric acid solution concentration in the reactor coolant and the position of control rods of the reactor control system. This distributed model allows us to control the change of reactor technological parameters in specified core sectors, core axial segments, as well as accounting for fuel assembly groups. A new method for automated control of the WWER-1000 power maneuvering based on using three control loops has been proposed, thereby two reactor power control programs have been improved.Багатозонна математична модель процесів в активній зоні (АКЗ) реактора типу ВВЕР-1000, яка розроблена для автоматизованого управління зміною потужності реактора, вдосконалена за рахунок обліку енерговиділення при розподілі не тільки ядер ²³⁵U, а й ²³⁹Pu, а також шляхом застосування одночасних дій, що управляють по каналах зміни концентрації розчину борної кислоти в теплоносії 1-го контуру і положення керуючих стрижнів системи управління та захисту реактора. Запропонована розподілена модель процесів у АКЗ, яка дозволяє контролювати зміну технологічних параметрів у виділених секторах симетрії і аксіальних сегментах АКЗ, для груп ТВЗ, що відповідають рокам паливного циклу. Новий метод автоматизованого управління зміною потужності реактора типу ВВЕР-1000, заснований на застосуванні трьох контурів управління, дозволив вдосконалити дві відомі програми управління потужністю реактора.Многозонная математическая модель процессов в активной зоне (АКЗ) реактора типа ВВЭР-1000, разработанная для автоматизированного управления изменением мощности реактора, усовершенствована за счет учета энерговыделения при делении не только ядер ²³⁵U, но и ²³⁹Pu, а также путем применения одновременных управляющих воздействий по каналам изменения концентрации раствора борной кислоты в теплоносителе 1-го контура и положения управляющих стержней системы управления и защиты реактора. Предложенная распределенная модель процессов в АКЗ позволяет контролировать изменение технологических параметров в выделенных секторах симметрии и аксиальных сегментах АКЗ, для групп ТВС, соответствующих годам топливного цикла. Новый метод автоматизированного управления изменением мощности реактора типа ВВЭР-1000, основанный на применении трех контуров управления, позволил усовершенствовать две известные программы управления мощностью реактора

Оptimization of power control program switching for a WWER-1000 under transient operating conditions

This paper is devoted to solution of the scientific and technical problem of safe switching of static power control programs for a nuclear power unit with a WWER-1000 under transient operating conditions, so that to minimize the influence of disturbances of external and internal operating parameters, as well as to increase the safety and efficiency of reactor operation. The switching optimization task for static power control programs has been solved by finding a decision of the objective function which allows to switch safely the energy equipment modes in a predetermined range of load variations. The possibility of switching between static power control programs during a 4-year reactor campaign has been studied. The control program optimization problem for anuclear power unit with a WWER-1000 operated under variable loading, considering different power control programs during a 4-year campaign, has been solved.Стаття присвячена вирішенню науково-технічної проблеми безпечного перемикання статичних програм регулювання ядерного енергоблоку з ВВЕР-1000 у змінних режимах навантаження, щоб мінімізувати вплив відхилень зовнішніх і внутрішніх експлуатаційних параметрів, а також підвищити безпеку і ефективність експлуатації реактора. Завдання оптимізації перемикань статичних програм регулювання вирішене шляхом знаходження екстремуму цільової функції, що дозволяє безпечно перемикати режими експлуатації енергетичного обладнання в передбаченому інтервалі зміни навантаження. Вивчена можливість перемикання статичних програм регулювання протягом 4-річної кампанії реактора. Розглядаючи різні програми регулювання потужності ядерного енергоблоку з ВВЕР-1000 у змінному режимі навантаження, вирішена задача оптимізації вибору програми протягом 4-річної кампанії.Статья посвячена решению научно-технической проблемы безопаcрного переключения статических программ регулирования ядерного энергоблока с ВВЭР-1000 в переменных режимах нагружения, чтобы минимизировать влияние отклонений внешних и внутренних эксплуатационных параметров, а также повысить безопасность и эффективность эксплуатации реактора. Задача оптимизации переключений статических программ регулирования решена путем нахождения экстремума целевой функции, что позволяет безопасно переключать режимы эксплуатации энергетического оборудования в предусмотренном интервале изменения нагрузки. Изучена возможность переключения статических программ регулирования в течение 4-годичной кампании реактора. Рассматривая различные программы регулирования мощности ядерного энергоблока с ВВЭР-1000 в переменном режиме нагружения, решена задача оптимизации выбора программы на протяжении 4-годичной кампании

Network Landscape from a Brownian Particle's Perspective

Given a complex biological or social network, how many clusters should it be decomposed into? We define the distance $d_{i,j}$ from node $i$ to node $j$ as the average number of steps a Brownian particle takes to reach $j$ from $i$. Node $j$ is a global attractor of $i$ if $d_{i,j}\leq d_{i,k}$ for any $k$ of the graph; it is a local attractor of $i$, if $j\in E_i$ (the set of nearest-neighbors of $i$) and $d_{i,j}\leq d_{i,l}$ for any $l\in E_i$. Based on the intuition that each node should have a high probability to be in the same community as its global (local) attractor on the global (local) scale, we present a simple method to uncover a network's community structure. This method is applied to several real networks and some discussion on its possible extensions is made.Comment: 5 pages, 4 color-figures. REVTeX 4 format. To appear in PR

Towards the characterization of individual users through Web analytics

We perform an analysis of the way individual users navigate in the Web. We focus primarily in the temporal patterns of they return to a given page. The return probability as a function of time as well as the distribution of time intervals between consecutive visits are measured and found to be independent of the level of activity of single users. The results indicate a rich variety of individual behaviors and seem to preclude the possibility of defining a characteristic frequency for each user in his/her visits to a single site.Comment: 8 pages, 4 figures. To appear in Proceeding of Complex'0

Au-Ag template stripped pattern for scanning probe investigations of DNA arrays produced by Dip Pen Nanolithography

We report on DNA arrays produced by Dip Pen Nanolithography (DPN) on a novel Au-Ag micro patterned template stripped surface. DNA arrays have been investigated by atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) showing that the patterned template stripped substrate enables easy retrieval of the DPN-functionalized zone with a standard optical microscope permitting a multi-instrument and multi-technique local detection and analysis. Moreover the smooth surface of the Au squares (abput 5-10 angstrom roughness) allows to be sensitive to the hybridization of the oligonucleotide array with label-free target DNA. Our Au-Ag substrates, combining the retrieving capabilities of the patterned surface with the smoothness of the template stripped technique, are candidates for the investigation of DPN nanostructures and for the development of label free detection methods for DNA nanoarrays based on the use of scanning probes.Comment: Langmuir (accepted