Subspace Leakage Analysis and Improved DOA Estimation with Small Sample Size

Classical methods of DOA estimation such as the MUSIC algorithm are based on estimating the signal and noise subspaces from the sample covariance matrix. For a small number of samples, such methods are exposed to performance breakdown, as the sample covariance matrix can largely deviate from the true covariance matrix. In this paper, the problem of DOA estimation performance breakdown is investigated. We consider the structure of the sample covariance matrix and the dynamics of the root-MUSIC algorithm. The performance breakdown in the threshold region is associated with the subspace leakage where some portion of the true signal subspace resides in the estimated noise subspace. In this paper, the subspace leakage is theoretically derived. We also propose a two-step method which improves the performance by modifying the sample covariance matrix such that the amount of the subspace leakage is reduced. Furthermore, we introduce a phenomenon named as root-swap which occurs in the root-MUSIC algorithm in the low sample size region and degrades the performance of the DOA estimation. A new method is then proposed to alleviate this problem. Numerical examples and simulation results are given for uncorrelated and correlated sources to illustrate the improvement achieved by the proposed methods. Moreover, the proposed algorithms are combined with the pseudo-noise resampling method to further improve the performance.Comment: 37 pages, 10 figures, Submitted to the IEEE Transactions on Signal Processing in July 201

Cramer-Rao Bound for Sparse Signals Fitting the Low-Rank Model with Small Number of Parameters

In this paper, we consider signals with a low-rank covariance matrix which reside in a low-dimensional subspace and can be written in terms of a finite (small) number of parameters. Although such signals do not necessarily have a sparse representation in a finite basis, they possess a sparse structure which makes it possible to recover the signal from compressed measurements. We study the statistical performance bound for parameter estimation in the low-rank signal model from compressed measurements. Specifically, we derive the Cramer-Rao bound (CRB) for a generic low-rank model and we show that the number of compressed samples needs to be larger than the number of sources for the existence of an unbiased estimator with finite estimation variance. We further consider the applications to direction-of-arrival (DOA) and spectral estimation which fit into the low-rank signal model. We also investigate the effect of compression on the CRB by considering numerical examples of the DOA estimation scenario, and show how the CRB increases by increasing the compression or equivalently reducing the number of compressed samples.Comment: 14 pages, 1 figure, Submitted to IEEE Signal Processing Letters on December 201

Seismic behavior of conxl connections in concrete filled steel Tube Columns (CFT)

Steel box-shaped columns are suitable structural members for structures with moment frames in two directions, but plate connections have several construction problems, including inaccessibility of inside of columns, welding difficulties, etc. ConXL  connections are the new proposed details to reduce these problems. This connection consists of collar flange, collar corner, and collar web extension. In this paper, the seismic behavior of these types of connections is investigated using the numerical method. For this purpose, three samples of ConXL connections without concrete filler, with concrete filler and with concrete filler and stiffener plates inside the column were studied using Abaqus software. The results demonstrated that the ductility of the ConXL connection without concrete filler is more than the two other samples, while the strength of this connection is less than the strengths of the two other samples. It was observed that utilizing stiffener plate inside the column has no significant effect on the strength of the connection.Keywords: ConXL moment connection; collar; concrete filled steel tube (CFT); ductility; stiffener plate

The effect of negative excess pore-water pressure on the stability of excavated slopes

Generation of negative excess pore-water pressure (NEPWP) due to the excavation of saturated soils under undrained conditions and the dissipation that follows over time may result in different short- and long-term slope instability. The NEPWP generated due to excavation gradually decreases towards equilibrium or, in some cases, steady seepage. Hence, total pore-water pressures immediately after excavation are lower than the ultimate equilibrium values, leading to a reduction of the average effective stresses in the slope and subsequently threatening stability in the long term. In this research study, the stability of three benchmark civil and mining excavations has been studied, considering the effects of the generation and dissipation of NEPWP. A series of numerical simulations are conducted to determine the role of in situ stresses and time in NEPWP dissipation as well as the consequent effects on the stability of the excavated slopes. To conduct a realistic time-dependent transient analysis, fully coupled hydro-geomechanical formulation has been employed. Results show that in general, higher removal of stress levels lead to higher NEPWP generation and higher factor of safety values in the short term. Thereafter, the dissipation of NEPWP threatens the long-term stability of the excavation

A systemic risk assessment of OTC derivatives reforms and skin-in-the-game for CCPs

The G20 OTC (over-the-counter) derivatives reforms impose large collateral/liquidity demands on clearing members of Central Counterparty (CCP) clearing platforms in the form of initial margins, variation margins and contributions to the default fund. In Heath et al. (2016), it was shown how this introduces a trade-off between liquidity risk and solvency risk with the system manifesting considerable systemic risk from these two sources of risk while CCP penetration is at current levels. The authors extend this analysis to include the European Market Infrastructure Regulation (EMIR) skin-in-the-game requirements for CCPs, which aim to ameliorate the contributions to the default fund by clearing members and also to prevent moral hazard problems associated with the too-interconnected-to-fail (TITF) status of CCPs as more and more derivatives are centrally cleared. The authors provide a systemic risk assessment of these features of the OTC derivatives reforms using network analysis based on 2015-end data on the derivatives positions for 40 globally systemically important banks (G-SIBs)

Silica nanoparticles as a highly efficient catalyst for the one-pot synthesis of sterically congested 2-(dibenzylamino)-2-aryl acetamide derivatives from by phthaldehyde isomers, isocyanides and dibenzylamine

A green and efficient method for the preparation of 2-(dibenzylamino)-2-aryl acetamide derivatives via a three-component reaction of an isocyanide, dibenzylamine and a phthalaldehyde derivative in the presence of silica nanoparticles (silica NPs, ca. 42 nm) as a catalyst under solvent free conditions at room temperature is described. The ease of work-up, green chemistry conditions and high yields of the products make this procedure a useful addition to modern synthetic methods. The silica nanoparticles that used in this reaction as a catalyst were prepared by thermal decomposition of rice hulls. Simple, green and cheap method for the preparation of the nanocatalyst represents a major advantage for this process. The structures of these compounds were confirmed by IR, 1H and 13C NMR spectroscopy. KEY WORDS: Silica nanoparticles, Nanocatalyst, Isocyanide, Phthalaldehyde Bull. Chem. Soc. Ethiop. 2016, 30(3), 413-420DOI: http://dx.doi.org/10.4314/bcse.v30i3.

Application of ground penetrating radar (GPR) to detect joints in organic soft rock

The detection of joints and discontinuities is of particular importance to the stability of a broad range of geostructures, including slopes and underground and open-pit mines. As a common example, the mechanical response of soft rocks observed within open-pit mines is significantly influenced by the existence of joint networks, resulting in a complex stress distribution that governs the stability factor of safety as well as the failure mechanism. In this article, surface geophysics scanning by ground penetrating radar (GPR) is presented for the detection of vertical joints at one of the largest open-pit coal mines in Australia. The optimum soil velocity, point interval, and antenna frequency for joint detection in Victorian Brown Coal (VBC) are presented in comparison with electromagnetic properties of known organic soils. Furthermore, the performance of an assorted set of post-processing signal filtering techniques to successfully identify the underground coal fractures are detailed, along with obstructions affecting the feasibility of GPR vertical joint discovery in this light organic soft rock

“Because It Kind of Falls in Between, Doesn’t It? Like an Acute Thing and a Chronic”: the Psychological Experience of Anaphylaxis in Adulthood

Anaphylaxis is a serious, rare condition increasing in prevalence. This study explored the psychological experience of adult-onset anaphylaxis from patient, family and staff perspectives. Semi-structured interviews were conducted with twelve participants. Two global themes emerged from thematic analysis: ‘controllability’ (‘an unknown and distressing experience’, ‘the importance of control over triggers’ and ‘responsibility but no control: the impact on others’) and ‘conflict’ (‘rejecting illness identity’, ‘minimisation of risk’, ‘accessing specialist care: running in slow motion’ and ‘patient-centred versus service-centred care’). Findings highlight the importance of perceived control and emphasise the presence of conflict in the experience of this complex, episodic condition

Establishment of national primary immunodeficiency network, requisite of health organization and final stage of polio eradication: Review article

Primary immunodeficiency diseases (PIDs) is a diverse group of diseases, characterized by a defect in the immune system. These patients are susceptible to recurrent respiratory infections, gastrointestinal problems, autoimmune diseases, and malignancies. In most cases, patients with primary immunodeficiency disorders have genetic defects and are monogenic disorders that follow a simple Mendelian inheritance, however, some PIDs recognize a more complex polygenic origin. Overall, almost 70 to 90 percent of patients with primary immunodeficiency are undiagnosed. Given that these patients are exposing to respiratory infectious agents and some live-attenuated vaccines, thus they have a high risk to some clinical complications. The administration of oral polio vaccine in patients with PIDs especially can increase the possibility of acute flaccid paralysis. These patients will excrete the poliovirus for a long time through their feces, even though they are not paralyzed. Long-term virus proliferation in the vaccinated individuals causes a mutation in the poliovirus and creates a vaccine-derived polioviruses (VDPVs), which is a major challenge to the final stages of the worldwide eradication of polio. To increase the diagnosis and identification of patients with immunodeficiency and carrying out a national plan for screening patients with immunodeficiency from the fecal excretion of the poliovirus, a possible polio epidemic can be prevented during post-eradication. Development of laboratory facilities in provincial and city centers, improvement of communications among physicians regarding medical consultation and establishment of referring systems for patients by national network lead to improve status of diagnosis and treatment of patients with primary immunodefiicencies. In this context, launching and activating the national network of immunodeficiency diseases is essential for improving the health of children and reducing the cost of the health system of the country. A national network of immunodeficiency can lead to increase awareness of physiciansregarding primary immunodeficiency disorders, improve collaboration among physicians about genetic consultation and establish a practical referral system in Iran that resultsin increased diagnosis and improve treatment of patients with primary immunodeficiency disorders. © 2020 Tehran University of Medical Sciences. All rights reserved