Optimal estimation for Large-Eddy Simulation of turbulence and application to the analysis of subgrid models

The tools of optimal estimation are applied to the study of subgrid models for Large-Eddy Simulation of turbulence. The concept of optimal estimator is introduced and its properties are analyzed in the context of applications to a priori tests of subgrid models. Attention is focused on the Cook and Riley model in the case of a scalar field in isotropic turbulence. Using DNS data, the relevance of the beta assumption is estimated by computing (i) generalized optimal estimators and (ii) the error brought by this assumption alone. Optimal estimators are computed for the subgrid variance using various sets of variables and various techniques (histograms and neural networks). It is shown that optimal estimators allow a thorough exploration of models. Neural networks are proved to be relevant and very efficient in this framework, and further usages are suggested

Mean Age of Patients with and without Type 2 Diabetes Mellitus during Surgical Treatment of Age-Related Cataract

Introduction: Age-related cataract is one of the most common causes of preventable blindness. Type 2 diabetes is a non-infectious epidemic disease with an ever-increasing number of diseased patients. Cataract is one of the leading causes of reduced vision in diabetics. The preferred treatment method is phacoemulsification. The aim of the present study was to compare the mean age of patients with and without diabetes type 2 at the time of cataract surgery. Materials and methods: After informed consent and approval by the Ethics Commission of the Medical University of Sofia, 176 patients admitted to the Clinic of Ophthalmology at the University Hospital „Alexandrovska“ for surgical treatment of cataract were randomized. Inclusion criteria: diagnosed age-related cataract, requiring surgical treatment. Patients were divided into two groups – diabetic type 2 and non-diabetic patients. Inclusion criteria for the group of diabetics: medical history of diabetes type 2 and administration of anti diabetic medications. Results: The average age of patients undergoing cataract surgery was 70.81 years. The average ageof patients with diabetes type 2 was 65.89 years, and that of non-diabetics – 71.74 years. Diabetes type 2 was established at 15.91 % of patients (19 men and 9 women). Conclusion: Patients with diabetes type 2 develop age-related cataract, requiring surgical treatment, at an earlier age compared to non-diabetics. The transparency of the lens in diabetic patients is of particular importance for the diagnosis and treatment of the diabetic retinopathy. Follow-up by an ophthalmologist and maintenance of strict blood glucose control are necessary to reduce the incidence of vision loss, caused by cataract and diabetic retinopathy

Towards a feasible implementation of quantum neural networks using quantum dots

We propose an implementation of quantum neural networks using an array of quantum dots with dipole-dipole interactions. We demonstrate that this implementation is both feasible and versatile by studying it within the framework of GaAs based quantum dot qubits coupled to a reservoir of acoustic phonons. Using numerically exact Feynman integral calculations, we have found that the quantum coherence in our neural networks survive for over a hundred ps even at liquid nitrogen temperatures (77 K), which is three orders of magnitude higher than current implementations which are based on SQUID-based systems operating at temperatures in the mK range.Comment: revtex, 5 pages, 2 eps figure

On Security and reliability using cooperative transmissions in sensor networks

Cooperative transmissions have received recent attention and research papers have demonstrated their benefits for wireless networks. Such benefits include improving the reliability of links through diversity and/or increasing the reach of a link compared to a single transmitter transmitting to a single receiver (single-input single-output or SISO). In one form of cooperative transmissions, multiple nodes can act as virtual antenna elements and provide diversity gain or range improvement using space-time coding. In a multi-hop ad hoc or sensor network, a source node can make use of its neighbors as relays with itself to reach an intermediate node with greater reliability or at a larger distance than otherwise possible. The intermediate node will use its neighbors in a similar manner and this process continues till the destination is reached. Thus, for the same reliability of a link as SISO, the number of hops between a source and destination may be reduced using cooperative transmissions as each hop spans a larger distance. However, the presence of ma-licious or compromised nodes in the network impacts the benefits obtained with cooperative transmissions. Using more relays can increase the reach of a link, but if one or more relays are malicious, the transmission may fail. However, the relationships between the number of relays, the number of hops, and success probabilities are not trivial to determine. In this paper, we analyze this problem to understand the conditions under which cooperative transmissions fare better or worse than SISO transmissions. We take into consideration additional parameters such as the path-loss exponent and provide a framework that allows us to evaluate the conditions when cooperative transmissions are better than SISO transmissions. This analysis provides insights that can be employed before resorting to simulations or experimentation. © Springer Science+Business Media, LLC 2012

Exploring the randomness of Directed Acyclic Networks

The feed-forward relationship naturally observed in time-dependent processes and in a diverse number of real systems -such as some food-webs and electronic and neural wiring- can be described in terms of so-called directed acyclic graphs (DAGs). An important ingredient of the analysis of such networks is a proper comparison of their observed architecture against an ensemble of randomized graphs, thereby quantifying the {\em randomness} of the real systems with respect to suitable null models. This approximation is particularly relevant when the finite size and/or large connectivity of real systems make inadequate a comparison with the predictions obtained from the so-called {\em configuration model}. In this paper we analyze four methods of DAG randomization as defined by the desired combination of topological invariants (directed and undirected degree sequence and component distributions) aimed to be preserved. A highly ordered DAG, called \textit{snake}-graph and a Erd\:os-R\'enyi DAG were used to validate the performance of the algorithms. Finally, three real case studies, namely, the \textit{C. elegans} cell lineage network, a PhD student-advisor network and the Milgram's citation network were analyzed using each randomization method. Results show how the interpretation of degree-degree relations in DAGs respect to their randomized ensembles depend on the topological invariants imposed. In general, real DAGs provide disordered values, lower than the expected by chance when the directedness of the links is not preserved in the randomization process. Conversely, if the direction of the links is conserved throughout the randomization process, disorder indicators are close to the obtained from the null-model ensemble, although some deviations are observed.Comment: 13 pages, 5 figures and 5 table

Childhood glaucoma

Въведение: Глаукомата в детска възраст е сравнително рядко, но сериозно застрашаващо зрението заболяване. По литературни данни засяга 1 на 10 000 до 12 500 новородени. Заболяването има значителни различия по отношение на етиопатогенезата, клиниката и лечението в сравнение с глаукомата при възрастни. Цел: Целта на настоящата статия е да представи алгоритъм за диагностика и проследяване на деца с глаукома, както и резултатите от изследване на деца с първична конгенитална глаукома. Материали и Методи: Под обща маскова анестезия са изследвани 18 очи на 9 деца. Изследвани са вътреочното налягане, централната роговична дебелина и хоризонтален роговичен диаметър. Резултати: При 3 от децата заболяването засяга само едното око, a при останалите 6 и двете очи. Средната възраст на изследваните деца е 6 месеца и 5 дни. Заключение: Глаукомата в детска възраст е актуален, значим, широко дискутиран медико-социален проблем. При всички деца с глаукома или съмнение за такава трябва да се предложи пакет от изследвания, които се правят в определена последователност, струват пари и отнемат време. Без тяхна помощ обаче е абсолютно невъзможна правилната диагноза, стадирането на болестта и предлагането на адекватна терапия. Повече от половината от пациентите с ПКГ стигат до слепота.Introduction: Childhood glaucoma is a relatively rare but seriously sight threatening disease. According to the literature it affects 1 out of 10 000 to 12 500 newborns. It has ethiopathological, clinical and therapeutic differences from the adult glaucoma. Aim: The aim of the current study is to present an algorithm for diagnosis and follow-up of patients with glaucoma and the results of the examination of 9 children with primary congenital glaucoma Methods and Materials: We have examined under general mask anestesia 18 eyes of 9 children (3 boys and 6 girls): intraocular pressure of each eye; central corneal sickness and horizontal corneal diameter. Results: Three of the children had unilateral disease and in the rest the diseases affected both eyes. The average age of the examined children was 6 months and 5 days. Conclusion: Childhood glaucoma is a relevant, significant and widely-discussed medico-social problem. In all cases of children with glaucoma or suspicion for such a package of tests should be performed which are costly and time-consuming. However, without these tests it is absolutely impossible to give an accurate diagnosis and hence initiate a proper therapy. More than half of the patients with primary congenital glaucoma become blind

Perturbation spreading in many-particle systems: a random walk approach

The propagation of an initially localized perturbation via an interacting many-particle Hamiltonian dynamics is investigated. We argue that the propagation of the perturbation can be captured by the use of a continuous-time random walk where a single particle is traveling through an active, fluctuating medium. Employing two archetype ergodic many-particle systems, namely (i) a hard-point gas composed of two unequal masses and (ii) a Fermi-Pasta-Ulam chain we demonstrate that the corresponding perturbation profiles coincide with the diffusion profiles of the single-particle L\'{e}vy walk approach. The parameters of the random walk can be related through elementary algebraic expressions to the physical parameters of the corresponding test many-body systems

Spatially Resolved Mapping of Local Polarization Dynamics in an Ergodic Phase of Ferroelectric Relaxor

Spatial variability of polarization relaxation kinetics in relaxor ferroelectric 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 is studied using time-resolved Piezoresponse Force Microscopy. Local relaxation attributed to the reorientation of polar nanoregions is shown to follow stretched exponential dependence, exp(-(t/tau)^beta), with beta~~0.4, much larger than the macroscopic value determined from dielectric spectra (beta~~0.09). The spatial inhomogeneity of relaxation time distributions with the presence of 100-200 nm "fast" and "slow" regions is observed. The results are analyzed to map the Vogel-Fulcher temperatures on the nanoscale.Comment: 23 pages, 4 figures, supplementary materials attached; to be submitted to Phys. Rev. Let

Adaptive filtering techniques for gravitational wave interferometric data: Removing long-term sinusoidal disturbances and oscillatory transients

It is known by the experience gained from the gravitational wave detector proto-types that the interferometric output signal will be corrupted by a significant amount of non-Gaussian noise, large part of it being essentially composed of long-term sinusoids with slowly varying envelope (such as violin resonances in the suspensions, or main power harmonics) and short-term ringdown noise (which may emanate from servo control systems, electronics in a non-linear state, etc.). Since non-Gaussian noise components make the detection and estimation of the gravitational wave signature more difficult, a denoising algorithm based on adaptive filtering techniques (LMS methods) is proposed to separate and extract them from the stationary and Gaussian background noise. The strength of the method is that it does not require any precise model on the observed data: the signals are distinguished on the basis of their autocorrelation time. We believe that the robustness and simplicity of this method make it useful for data preparation and for the understanding of the first interferometric data. We present the detailed structure of the algorithm and its application to both simulated data and real data from the LIGO 40meter proto-type.Comment: 16 pages, 9 figures, submitted to Phys. Rev.

Transmitter-side antennas correlation in SVD-assisted MIMO systems

MIMO techniques allow increasing wireless channel performance by decreasing the BER and increasing the channel throughput and in consequence are included in current mobile communication standards. MIMO techniques are based on benefiting the existence of multipath in wireless communications and the application of appropriate signal processing techniques. The singular value decomposition (SVD) is a popular signal processing technique which, based on the perfect channel state information (PCSI) knowledge at both the transmitter and receiver sides, removes inter-antenna interferences and improves channel performance. Nevertheless, the proximity of the multiple antennas at each front-end produces the so called antennas correlation effect due to the similarity of the various physical paths. In consequence, antennas correlation drops the MIMO channel performance. This investigation focuses on the analysis of a MIMO channel under transmitter-side antennas correlation conditions. First, antennas correlation is analyzed and characterized by the correlation coefficients. The analysis describes the relation between antennas correlation and the appearance of predominant layers which significantly affect the channel performance. Then, based on the SVD, pre- and post-processing is applied to remove inter-antenna interferences. Finally, bit- and power allocation strategies are applied to reach the best performance. The resulting BER reveals that antennas correlation effect diminishes the channel performance and that not necessarily all MIMO layers must be activated to obtain the best performance