Direction Finding

A sparse uniform Cartesian-grid array suffers cyclic ambiguity in its Cartesian direction-cosine estimates due to the spatial Nyquist sampling theorem. The proposed MUSIC-based or MODE-based algorithm improves and generalizes previous disambiguation schemes that populate the thin array grid with identical subarrays-such as electromagnetic vector sensors, underwater acoustic vector hydrophones, or half-wavelength spaced subarrays.

This novel underwater acoustic azimuth-elevation source localization scheme realizes the eigenstructure-based polynomial rooting procedure for an L-shaped uniformly spaced array of diversely oriented and possibly spatially co-located velocity hydrophones and an optional pressure hydrophone. A velocity hydrophone measures a Cartesian component of the acoustic particle velocity vector of the incident wavefield. At each uniformly spaced array grid, one or more co-located and diversely oriented velocity hydrophones and/or a pressure hydrophone are placed, with the number and orientations of velocity hydrophones possibly varying from grid position to grid position in some known prearranged manner. The diverse orientation of the velocity hydrophones, however, disrupts the Vandermonde array manifold structure in each of the two uniform-linear-array legs of the L-shaped array. Nonetheless, ingenuous mathematical manipulations proposed in this paper restore the disrupted Vandermonde algebraic structure, thereby permitting once again the use of polynomial rooting to estimate the directions of arrival. A proposed pairing procedure matches each source's x x x-axis direction cosine estimate with its corresponding y y y-axis direction cosine estimate. Simulation results verify the efficacy of the proposed scheme.

This paper introduces a new closed-form ESPRITbased algorithm for multisource direction finding and polarization estimation with arbitrarily spaced electromagnetic vector-sensors whose three-dimensional (3-D) locations need not be known. The vector-sensor, already commercially available, consists of six colocated but diversely polarized antennas separately measuring all six electromagnetic-field components of an incident wavefield. ESPRIT exploits the nonspatial interrelations among the six unknown electromagnetic-field components of each source and produces from the measured data a set of eigenvalues, from which the source's electromagnetic-field vector may be estimated to within a complex scalar. Application of a vector cross-product operation to this ambiguous electromagnetic-field vector estimate produces an unambiguous estimate of that source's normalized Poynting vector, which contains as its components the source's Cartesian direction cosines. Monte Carlo simulation results verify the efficacy and versatility of this innovative scheme. This novel method maybe considered as a simplification and a refinement over Li's earlier work in 1993 [8].

This paper introduces a novel ESPRIT-based closedform source localization algorithm applicable to arbitrarily spaced three-dimensional arrays of vector hydrophones, whose locations need not be known. Each vector hydrophone consists of two or three identical but orthogonally oriented velocity hydrophones plus one pressure hydrophone, all spatially co-located in a point-like geometry. A velocity hydrophone measures one Cartesian component of the incident sonar wavefield's velocity vector, whereas a pressure hydrophone measures the acoustic wavefield's pressure. Velocity-hydrophone technology is well established in underwater acoustics and a great variety of commercial models have long been available. ESPRIT is realized herein by exploiting the nonspatial interrelations among each vector hydrophone's constituent hydrophones, such that ESPRIT's eigenvalues become independent of array geometry. Simulation results verify the efficacy and versatility of this innovative scheme. Aspects of this underwater acoustic algorithm are analogous to Li's earlier work with diversely polarized antennas.

A closed-form multi-dimensional multi-invariance generalization of the ESPRIT algorithm is introduced to exploit the entire invariance structure underlying a (possibly) multiparametric data model, thereby greatly improving estimation performance. The multiple-invariance data structure that this proposed method can handle includes: (1) multiple occurrence of one size of invariance along one or multiple parametric dimensions, (2) multiple sizes of invariances along one or multiple parametric dimensions, and (3) invariances that cross over two or more parametric dimensions. The basic (uni-dimensional uni-invariance) ESPRIT algorithm is applied in parallel to each m ultiple pair of matrixpencils characterizing the multiple invariance relationships in the data model, producing multiple sets of cyclically ambiguous estimates over the multi-dimensional parameter space. A weighted least-squares hyper-plane is then tted to these set of estimates to yield very accurate and unambiguous estimates of the signal parameters.

A vector-hydrophone (a.k.a. acoustic vector-sensor) is the diction-cosine along the z-axis, and A symbolizes the source's composed of two or three spatially collocated but orthogonally wavelength. Three special cases exist: oriented velocity-hydrophones, possibly plus a collocated pressurehydrophone. A vector-hydrophone may form azimuth-elevation 1) No reflecting boundary exists near the vector-hydrophone: spatial beams that are invariant with respect to the sources' R(O) = 0 [6]. Thus, (1) degenerates to: [6], [23] frequencies, bandwidths and radial locations (i.e., in near field as opposed to the far field). This paper adopts a multiple-forgetting-Cos 0 Cos (O factor recursive-least-squares (RLS) adaptive algorithm to a single def d def COS 0 sfin

Aperture extension (interferometry baseline extension) is achieved in this novel ESPRIT-based two-dimensional (2-D) arrival angle estimation scheme using a sparse (a.k.a., thin or thinned) uniform rectangular array of electromagnetic vector sensors spaced much farther apart than a half-wavelength. An electromagnetic vector sensor is composed of six spatially co-located, orthogonally oriented, diversely polarized antennas, distinctly measuring all six electromagnetic-field components of an incident multisource wavefield. Each incident source's direction of arrival (DOA) is estimated from the source's electromagnetic-field vector component and serves as a coarse reference to disambiguate the cyclic phase ambiguities in ESPRIT's eigenvalues when the intervector sensor spacing exceeds a half wavelength. Simulations demonstrate the significant performance gain realizable by this method for radar and wireless mobile fading-channel communications.

This paper introduces a new underwater acoustic eigenstructure ESPRIT-based algorithm that yields closed-form direction-of-arrival (DOA) estimates using a single vector hydrophone. A vector hydrophone is composed of two or three spatially co-located but orthogonally oriented velocity hydrophones plus another optional co-located pressure hydrophone. This direction finding algorithm may (under most circumstances) resolve up to four uncorrelated monochromatic sources impinging from the near field or the far field, but it assumes that all signal frequencies are distinct. It requires no a priori knowledge of the signals' frequencies, suffers no frequency-DOA ambiguity, and pairs automatically the x-axis direction cosines with the y-axis direction cosines. It significantly outperforms an array of spatially displaced pressure hydrophones of comparable array-manifold size and computational load but may involve more complex hardware. This work also derives new Cramér-Rao bounds (CRBs) for various vector hydrophone constructions of arrival angle estimates for the incident uncorrelated sinusoidal signals corrupted by spatio-temporally correlated additive noise.

A sparse uniform Cartesian-grid array suffers cyclic ambiguity in its Cartesian direction-cosine estimates due to the spatial Nyquist sampling theorem. The proposed MUSIC-based or MODE-based algorithm improves and generalizes previous disambiguation schemes that populate the thin array grid with identical subarrays-such as electromagnetic vector sensors, underwater acoustic vector hydrophones, or half-wavelength spaced subarrays.

This paper introduces a new closed-form ESPRITbased algorithm for multisource direction finding and polarization estimation with arbitrarily spaced electromagnetic vector-sensors whose three-dimensional (3-D) locations need not be known. The vector-sensor, already commercially available, consists of six colocated but diversely polarized antennas separately measuring all six electromagnetic-field components of an incident wavefield. ESPRIT exploits the nonspatial interrelations among the six unknown electromagnetic-field components of each source and produces from the measured data a set of eigenvalues, from which the source's electromagnetic-field vector may be estimated to within a complex scalar. Application of a vector cross-product operation to this ambiguous electromagnetic-field vector estimate produces an unambiguous estimate of that source's normalized Poynting vector, which contains as its components the source's Cartesian direction cosines. Monte Carlo simulation results verify the efficacy and versatility of this innovative scheme. This novel method maybe considered as a simplification and a refinement over Li's earlier work in 1993 [8].

This paper introduces a novel eigenstructure-based algorithm uni-vector-sensor ESPRIT that yields closed-form direction-of-arrival (DOA) estimates and polarization estimates using one electromagnetic vector sensor. A vector sensor is composed of six spatially co-located nonisotropic polarizationsensitive antennas, measuring all six electromagnetic field components of the incident wave field. Uni-vector-sensor ESPRIT is based on a matrix-pencil pair of temporally displaced data sets collected from a single electromagnetic vector sensor. The closed-form parameter estimates are obtained through a vector cross-product operation on each decoupled signalsubspace eigenvector of the data correlation matrix. This method exploits the electromagnetic sources' polarization diversity in addition to their spatial diversity, requires no a priori knowledge of signal frequencies, suffers no frequency-DOA ambiguity, pairs automatically the x-axis direction cosines with the y-axis direction cosines, eliminates array interelement calibration, can resolve up to five completely polarized uncorrelated monochromatic sources from near field or far field. It impressively out-performs an array of spatially displaced identically polarized antennas of comparable array-manifold size and computational load.

This paper introduces a novel ESPRIT-based closedform source localization algorithm applicable to arbitrarily spaced three-dimensional arrays of vector hydrophones, whose locations need not be known. Each vector hydrophone consists of two or three identical but orthogonally oriented velocity hydrophones plus one pressure hydrophone, all spatially co-located in a point-like geometry. A velocity hydrophone measures one Cartesian component of the incident sonar wavefield's velocity vector, whereas a pressure hydrophone measures the acoustic wavefield's pressure. Velocity-hydrophone technology is well established in underwater acoustics and a great variety of commercial models have long been available. ESPRIT is realized herein by exploiting the nonspatial interrelations among each vector hydrophone's constituent hydrophones, such that ESPRIT's eigenvalues become independent of array geometry. Simulation results verify the efficacy and versatility of this innovative scheme. Aspects of this underwater acoustic algorithm are analogous to Li's earlier work with diversely polarized antennas.

Aperture extension is achieved in this novel ESPRITbased two-dimensional angle estimation scheme using a uniform rectangular array of vector hydrophones spaced much farther apart than a half-wavelength. A vector hydrophone comprises two or three spatially co-located, orthogonally oriented identical velocity hydrophones (each of which measures one Cartesian component of the underwater acoustical particle velocity vector-field) plus an optional pressure hydrophone. Each incident source's directions-of-arrival are determined from the source's acoustical particle velocity components, which are extracted by decoupling the data covariance matrix's signal-subspace eigenvectors using the lower dimensional eigenvectors obtainable by ESPRIT. These direction-cosine estimates are unambiguous but have high variance; they are used as coarse references to disambiguate the cyclic phase ambiguities in ESPRIT's eigenvalues when the intervector-hydrophone spacing exceeds a halfwavelength. In one simulation scenario, the estimation standard deviation decreases with increasing intervector-hydrophone spacing up to 12 wavelengths, effecting a 97% reduction in the estimation standard deviation relative to the half-wavelength case. This proposed scheme and the attendant vector-hydrophone array outperform a uniform half-wavelength spaced pressurehydrophone array with the same aperture and slightly greater number of component hydrophones by an order of magnitude in estimation standard deviation. Other simulations demonstrate how this proposed method improves underwater acoustic communications link performance. The virtual array interpolation technique would allow this proposed algorithm to be used with irregular array geometries.

A vector hydrophone is composed of two or three spatially collocated but orthogonally oriented velocity hydrophones plus an optional collocated pressure hydrophone. A vector hydrophone may form azimuth-elevation beams that are invariant with respect to the sources' frequencies, bandwidths and radial location (in near field as opposed to the far field). This paper characterizes the spatial matched filter beam patterns (a.k.a. fixed or conventional or maximum signal-to-noise ratio beam patterns) and the minimum variance distortionless response (MVDR) beam patterns associated with a single underwater acoustic vector hydrophone distant from any reflecting boundary.

A "figure-8" sensor is so labeled because its spatial pattern resembles the character "8" with regard to the sensor's axis. This figure-8 pattern narrows as the sensor's order increases. Using two such figure-8 directional sensors of higher order, oriented perpendicularly to each other - this paper pioneers closed-form signal-processing algorithms to estimate an incident signal's azimuth-elevation bivariate direction-of-arrival. Monte Carlo simulations verify these proposed algorithms' efficacy and statistical closeness to the corresponding Cramér-Rao bounds.

Non-line-of-sight (NLOS) reception and multipath interference are major causes of poor GNSS positioning accuracy in urban environments. This paper describes three pieces of work to mitigate their effects: a new multipath detection technique using multi-frequency carrier-power-to-noise-density ratio (C/N0) measurements; the first multi-constellation test of the dual-polarization NLOS detection technique; and a proposal for a portfolio approach to multipath and NLOS mitigation. Constructive multipath interference results in an increase in C/N0, whereas destructive interference results in a decrease. As the phase of a reflected signal with respect to its directly received counterpart depends on the wavelength, the multipath interference may be constructive on one frequency and destructive on another. Thus, by comparing the difference in measured C/N0 between two frequencies with what is normally expected for that signal at that elevation angle, strong multipath interference may be dete...

White-light and radio observations are combined to deduce the coronal and interplanetary kinematics of a fast coronal mass ejection (CME) that was ejected from the Sun at about 1700 UT on 2 November 2003. The CME, which was associated with an X8.3 solar flare from W56°, was observed by the Mauna Loa and Solar and Heliospheric Observatory (SOHO) Large-Angle Spectrometric Coronograph (LASCO) coronagraphs to 14 R . The measured plane-of-sky speed of the LASCO CME was 2600 km s À1 . To deduce the kinematics of this CME, we use the plane-of-sky white light observations from both the Solar Mass Ejection Imager (SMEI) all-sky camera on board the Coriolis spacecraft and the SOHO/LASCO coronagraph, as well as the frequency drift rate of the low-frequency radio data and the results of the radio direction-finding analysis from the WAVES experiment on the Wind spacecraft. In agreement with the in situ observations for this event, we find that both the white light and radio observations indicate that the CME must have decelerated significantly beginning near the Sun and continuing well into the interplanetary medium. More specifically, by requiring self-consistency of all the available remote and in situ data, together with a simple, but not unreasonable, assumption about the general characteristic of the CME deceleration, we were able to deduce the radial speed and distance time profiles for this CME as it propagated from the Sun to 1 AU. The technique presented here, which is applicable to mutual SMEI/WAVES CME events, is expected to provide a more complete description and better quantitative understanding of how CMEs propagate through interplanetary space, as well as how the radio emissions, generated by propagating CME/shocks, relate to the shock and CME. This understanding can potentially lead to more accurate predictions for the onset times of space weather events, such as those that were observed during this unique period of intense solar activity.

Direction of arrival (DOA) estimation techniques estimate the angle from which the signal is received. Using multiple antennas, the best DOA estimate is found by comparing the signals from these antennas and their phase shifts. Optimizing the arrangements of these antennas can greatly increase the accuracy of the system and decrease the cost of a Radio Direction Finding (RDF) system. In this paper, a Software-Defined-Radio (SDR) platform is implemented for sparse DOA estimation based on sparse array configurations. The results show that it is possible to estimate the location of more targets without increasing the number of antennas using sparse arrays.

In the modern digital economy, optimal decision support systems, as well as machine learning systems, are becoming an integral part of production processes. Artificial neural network training as well as other engineering problems generate such problems of high dimension that are difficult to solve with traditional gradient or conjugate gradient methods. Relaxation subgradient minimization methods (RSMMs) construct a descent direction that forms an obtuse angle with all subgradients of the current minimum neighborhood, which reduces to the problem of solving systems of inequalities. Having formalized the model and taking into account the specific features of subgradient sets, we reduced the problem of solving a system of inequalities to an approximation problem and obtained an efficient rapidly converging iterative learning algorithm for finding the direction of descent, conceptually similar to the iterative least squares method. The new algorithm is theoretically substantiated, and ...

This study investigates the effectiveness of the interference-handling radio frequency direction finding (RFDF) monitoring system in detecting and localizing interference sources near the BMKG C-Band weather radar in West Kalimantan, Indonesia. We conducted field tests varying interference transmitter power levels (0-30 dBm) and distances (100, 500, and 1,000 m) from the radar. Results indicate the RFDF system's robust performance, consistently detecting interference within 5-20 minutes and accurately localizing sources with minimal deviation from actual positions. The findings confirm the system's superiority over traditional manual methods, offering a reliable solution for interference management in weather radar operations. However, limitations include controlled test conditions and a need for further exploration of the system's efficacy in diverse environmental settings. This research contributes to improving radar reliability and lays the groundwork for future studies to refine RFDF technology for broader meteorological applications.

The expectation maximization (EM) algorithm is presented for the case of estimating direction of arrivals of unknown deterministic wideband signals. Alternative regularized least squares estimation techniques for the required signal estimation and a tree structure for the data mapping in the EM algorithm are proposed. Extensive simulation results are presented for comparison of the proposed algorithms with the conventional EM approach and the current high-resolution methods of wideband direction finding.

A compact low-profile self-isolated Multi Input Multi Output Antenna (MIMO) Array is presented for the 5G smartphone devices. The proposed system consists of eight antenna elements operating on triple bands, which are (1.83-2.21) GHz for the extended Personal Communication Purposes (PCS) n25 and other related applications, the china mobile band n79 (4.8-5) GHz, and the WLAN (5.15-5.97) GHz applications. The proposed antenna element is designed based on a hybrid of modified Minkowski and Peano curves fractal geometries. All antennas are printed on the surface layer of the main mobile board and the size of the antenna is (11.47 mm × 7.19 mm). Good isolation is achieved (better than 10 dB and 13.5 dB in the lower band and the higher bands, respectively) without employing any additional decoupling elements and/or isolation techniques. For evaluating the performance of the proposed antenna element, the Sparameters, antenna gains, antenna efficiencies, and antenna radiation characteristics are considered. To assess the MIMO performance of the proposed antenna array, the Envelope Correlation Coefficients (ECCs) and Mean Effective Gains (MEGs) are investigated. Desirable antenna and MIMO performances are attained so the proposed system can be considered as a good candidate for the 5G mobile smartphones.

Eleven new cases of visceral leishmaniasis (VL) are reported in organ transplant patients in France. The epidemiological, clinical, biological, diagnostic and therapeutic features are reviewed, based on these cases and 46 cases reported in the literature. VL was most commonly associated with renal transplantation (77% of the cases). Most patients were from Southern European countries. The main clinical symptom was fever. Leucopoenia and anaemia were the most frequent haematological disorders. Diagnosis was by direct finding of the parasite in smears of bone marrow (85.2%) or, by positive serology (90.9%). Without antileishmanial treatment, VL in transplant recipients was fatal. Treatment using either antimonials or amphotericine B gave similar cure rates of around 80% of the cases. But toxicity was higher for antimonials. Relapses occurred in 14.3%.

An array antenna system with innovative signal processing can enhance the resolution of a signal direction of arrival (DOA) estimation. The performance of DOA using estimation signal parameter via a rotational invariant technique is investigated in this paper. The DOA angles are derived from the auto-correlation and cross-correlation matrices. Three matrix estimation methods, (1) temporal averaging, (2) spatial smoothing, (3) temporal averaging and spatial smoothing are used to evaluate the performance. Extensive computer simulations are used to demonstrate the performance of the processing algorithms.

An array antenna system with innovative signal processing can enhance the resolution of a signal direction of arrival (DOA) estimation. Super resolution algorithms take advantage of array antenna structures to better process the incoming signals. They also have the ability to identify multiple targets. This paper explores the eigen-analysis category of super resolution algorithm. A class of Multiple Signal Classification (MUSIC) algorithms known as a root-MUSIC algorithm is presented in this paper. The root-MUSIC method is based on the eigenvectors of the sensor array correlation matrix. It obtains the signal estimation by examining the roots of the spectrum polynomial. The peaks in the spectrum space correspond to the roots of the polynomial lying close to the unit circle. Statistical analysis of the performance of the processing algorithm and processing resource requirements are discussed in this paper. Extensive computer simulations are used to show the performance of the algorit...

An array antenna system with innovative signal processing can enhance the resolution of a signal direction of arrival (DOA) estimation. Super resolution algorithms take advantage of array antenna structures to better process the incoming signals. They also have the ability to identify multiple targets. This paper explores the eigen-analysis category of super resolution algorithm. A class of Multiple Signal Classification (MUSIC) algorithms known as a root-MUSIC algorithm is presented in this paper. The root-MUSIC method is based on the eigenvectors of the sensor array correlation matrix. It obtains the signal estimation by examining the roots of the spectrum polynomial. The peaks in the spectrum space correspond to the roots of the polynomial lying close to the unit circle.

In Array signal processing field, the problem of finding the direction of signal sources at the receiving antenna is one of the most important and challenging tasks in many of the applications such as radar, wireless communications, sonar, radio astronomy and navigation. Direction of Arrival (DOA) estimation can be achieved by the antenna array at the receiver side. The resolution of a DOA estimation algorithm depends on the antenna array structures and these algorithms also have the capability to identify the number of signal sources and their directions (multiple signal sources). This paper presents the simulation and performance comparison of all the low and high-resolution DOA estimation algorithms namely Beamforming, Capon/MVDR, MUSIC, Improved-MUSIC, Root-MUSIC and ESPRIT. These algorithms are simulated and investigated using Uniform Linear Array (ULA) in presence of White noise and interference noise. The simulation results shown in this paper investigates that the performance of any DOA estimation algorithm depends on features such as number of array elements, number of signal sources, correlation between the signal sources, Signal-to-noise ratio, array element spacing, number of snapshots and the angle separation between adjacent signal sources.

Rheometry serves as a method for the determination of effective length vectors of short antennas by means of electrolytic tank measurements. This paper reports on the application of rheometry to the three linear monopoles mounted for the purposes of the Radio and Plasma Wave Science Experiment on the Cassini spacecraft, which will fly to planet Saturn. The voltage signals induced by incoming waves from the Saturnian radio emissions will be recorded for further evaluation. By direction‐finding techniques one will trace back from the collected data to the source regions of the received radio waves and determine the wave polarization. An accurate direction finding is only possible if the effective length vectors of the antennas, which are affected by the spacecraft body, are known to a certain degree of accuracy. It is investigated how rheometry enables the determination of the effective length vectors with the help of a scale model. After a detailed discussion of the fundamentals of r...

Relative dynamics of the radio sources of the metric type II burst with three emission lanes and coronal mass ejection (CME) occurred in the lower corona (r K 1:5R ) during the SOL2011-02-16T14:19 event is studied. The observational data of the Nancay Radioheliograph (NRH) and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) are used. These observations are also supplemented by the data sets obtained with the STEREO-A and -B, RHESSI, and GOES spacecraft, as well as with the ground-based solar radio spectrometers. It is found that the sources of the radio burst were located ahead of the expanding CME and had a complex spatial structure. The first and the second lanes were both emitted from the "magnetic funnel" -a bundle of open magnetic field lines separated the south and north systems of magnetic loops of the active region. Due to the projection effect and limited angular resolution of the NRH it is not possible to determine, whether the spatial locations of the radio sources of the two first emission lanes differed or not. It is argued that the observations support the hypothesis that the radio sources of the first and second lanes could be emitted respectively ahead of and behind a front of the same weak (the Alfve ´n Mach number M A % 1:1-1:2), fast mode, quasi-parallel piston MHD shock wave. However, the third lane of the burst was definitely emitted from a different place. Its radio sources were situated ahead of the north-west part of the CME propagated through the north system of magnetic loops. This indicates clearly that different emission lanes of the same type II burst can be a result of propagation of different parts of a single CME through regions with different physical conditions (geometries and plasma densities) in the lower corona.

We provide an algorithm which solves the following problem: given a polygon with edges parallel to the x and y axes, which is convex in the y direction, find a minimum size collection of rectangles, which cover the polygon and are contained within it. The algorithm is quadratic in the number of vertices of the polygon. Our method also yields a new proof of a recent duality theorem equating minimum size rectangle covers to maximum size sets of independent points in the polygon.

An electronically controlled antenna array consisting of one active element and a number of parasitic elements can be used for direction finding. Array directivity is controlled by exchanging the position of the feed and the parasitic elements. An array of four monopoles on a ground plane provides 360 degree azimuthal coverage with no moving parts, provides excellent directional resolution and can be controlled using a simple microcontroller. The antenna design, its application to direction finding and reliability in noisy environments are presented.

This paper deals with the problem of the Direction Of Arrival (DOA) estimation with nonuniform linear arrays. The proposed method is a combination of the Expectation Maximization (EM) and the ESPRIT methods. The EM algorithm interpolates the nonuniform array to an equivalent uniform array, and then, the application of ESPRIT is possible, in order to estimate the DOA. One of this method novelties lies in its capacity of dealing with any nonuniform array geometry. This technique manifests significant performance and computational advantages over previous algorithms such as MUSIC, specially in the preasymptotic domain, and the comparison with the theoretical Cramer-Rao Bounds (CRB) shows its efficiency.

Introduction: Gastro-duodenal perforations may be suspected in patients with history of ulceration, who present with acute pain and abdominal wall rigidity, but radiological findings in these cases may be unable to confirm a clinical diagnosis. The aim of our study was to report our experience in the diagnosis of gastro-duodenal perforation by conventional radiography, US and CT examinations. Material and methods: We retrospectively reviewed medical records of 166 consecutive patients who presented in the last 2 years to our institutions with symptoms of acute abdomen and submitted to surgery at the Emergency Unit of the "A.Cardarelli" Hospital of Naples with a surgical finding of perforated gastro-duodenal ulcer. The evidence of free intraperitoneal air on abdominal plain film was considered as a direct or suggestive finding of perforation. Evidence of intraperitoneal free fluid and/or reduced intestinal peristalsis at sonographic examination were considered indirect signs of gastro-duodenal perforation. Evidence of free peritoneal gas at CT was considered as a direct evidence of gastro-duodenal perforation. Results: Twenty patients underwent immediate surgery with no preoperative imaging evaluation, in 10 of them the site of perforation was found in a juxta-pyloric region and in the others at level of duodenum. In 146 patients submitted to serial radiological investigations before surgery, the site of perforation was in 56 (38.3%) duodenal, in 52 (35.6%) juxta-pyloric, in 28 (19.1%) gastric and in 10 (6.8%) pyloric. The cause of perforation was in all cases gastric or duodenal ulceration, in seven cases involving pancreatic parenchyma. In 110 (75.4%) patients with direct findings of perforation, in 94 cases (85.5%) the correct diagnosis was established on abdominal plain film, in two (1.8%) with radiographic and sonographic examinations and in 14 (12.7%) on CT findings. In 36 (24,6%) patients with no direct findings of perforation, only 24 (16,4%) of them showed indirect findings of perforation. In other 12 patients no direct or indirect finding of free peritoneal air was detected. Conclusions: Our experience documents that in 146 gastroduodenal perforations the free peritoneal air was not evident in 12 cases and in 66% of these patients the presence of intraperitoneal fluid could be the only sign of perforation. If free peritoneal air was detected with conventional radiography, other investigations were not indicated. In the absence of direct or indirect findings of pneumoperitoneum, US examination could help to confirm intestinal paresis and the evidence of intraperitoneal free fluid. Helical CT examination was useless before at least 6 h from the onset of symptomatology, because in the absence of direct or indirect findings of penumoperitoneum at abdominal plain film and sonograpy, CT could not demonstrate any additional diagnostic information.

I hereby declare that 1) The work presented in this paper is original and has been done by myself under the guidance of my supervisor. 2) The work has not been submitted to any other Institute for any degree or diploma. 3) The data used in this work is taken from only free sources and its credit has been cited in references. 4) The materials (data, theoretical analysis, and text) used for this work has been given credit by citing them in the text of the thesis and their details in the references. 5) I have followed the thesis guidelines provided by the Institute.

Estimation of arrival angles and incoming signals is a challenging problem for HF channels where the signals are correlated and the separation between the signals can be as low as a couple of degrees. In this paper, a new algorithm, Multipath Separation-Direction of Arrival (MS-DOA), is developed to estimate both the arrival angles in elevation and azimuth and the incoming signals at the output of the reference antenna with very high accuracy. The MS-DOA algorithm provides reliable angle and signal estimates even with small separation of arrival angles and for low SNRs. The minimum number of antennas that are required by the algorithm is only one more than the number of incoming signals. In a narrowed down region of interest and for a few incoming signals, the computational search time for MS-DOA is only a couple of minutes in a standard PC.

Direction-of-Arrival (DOA) defines the estimation of arrival angles of an electromagnetic wave impinging on a set of sensors. For dispersive and time-varying HF channels, where the propagating wave also suffers from the multipath phenomena, estimation of DOA is a very challenging problem. Multipath Separation-Direction of Arrival (MS-DOA), that is developed to estimate both the arrival angles in elevation and azimuth and the incoming signals at the output of the reference antenna with very high accuracy, proves itself as a strong alternative in DOA estimation for HF channels. In MS-DOA, a linear system of equations is formed using the coefficients of the basis vector for the array output vector, the incoming signal vector and the array manifold. The angles of arrival in elevation and azimuth are obtained as the maximizers of the sum of the magnitude squares of the projection of the signal coefficients on the column space of the array manifold. In this study, alternative Genetic Search Algorithms (GA) for the maximizers of the projection sum are investigated using simulated and experimental ionospheric channel data. It is observed that GA combined with MS-DOA is a powerful alternative in online DOA estimation and can be further developed according to the channel characteristics of a specific HF link.

Electron emission due to grazing scattering of fast protons from LiF and KCl surfaces is studied under axial channeling conditions. The differential electron emission probability is calculated within a distorted-wave formalism, taking into account realistic channeled trajectories. For electronic spectra along low-index crystallographic directions, we find that channeling effects on the electron emission yield depend strongly on the penetration rate of projectiles into the solid.

The formation of a linear array is introduced in (1). When all of the element fields are in phase, we obtained a main beam with its maximum directivity. The phenomenon in which a linear array be able to have a gain which is higher than the maximum directivity of the normal linear array called superdirectivity (2,3,4). In this paper, we study the formation of a supergain array and its application in Radar, some simulations are given to illustrate the array performance and some remark conclusions are given. I. INTRODUCTION In Radar modern, we interested in design a system having a very narrow beam and very high directivity. In general, in order to do so we have use a large array which is inconvenient in electronic-battle now a day. Therefore, the researches about super gain array have much attractive from Radar was born up to now. In this paper, the formation of a supergain array and its applications in Radar are presented. The paper is organized as follows. The directivity of a linea...

Infrasound arrays typically consist of several microbarometers separated by distances that provide predictable signal time separations, forming the basis for processing techniques that estimate the phase velocity direction. The directional resolution depends on the noise level and is proportional to the number of these point sensors; additional sensors help attenuate noise and improve direction resolution. An alternative approach is to form an array of directional line sensors, each of which emulates a line of many microphones that instantaneously integrate pressure change. The instrument response is a function of the orientation of the line with respect to the signal wavefront. Real data recorded at the Piñon Flat Observatory in southern California and synthetic data show that this spectral property can be exploited with multiple line sensors to determine the phase velocity direction with a precision comparable to a larger aperture array of microbarometers. Three types of instrumen...

We have developed a high-resolution ESPRIT-based method for estimating the directions-of-arrival of partially polarized signals with electromagnetic vector sensors, each of which provides measurements of the complete electric and magnetic fields induced by electromagnetic signals. The method is computationally efficient since unlike many high-resolution methods, it does not involve searching across a multidimensional array manifold. In addition, the method has two variants, of which one is applicable to scenarios where a priori information about the array system, such as the sensor positions, is unavailable.

We address the problem of discriminating between two finite point sets A and B in the n-dimensional space by h hyperplanes generating a convex polyhedron. If the intersection of the convex hull of A with B is empty, the two sets can be strictly separated (polyhedral separability). We introduce an error function which is piecewise linear, but not convex nor concave, and define a descent procedure based on the iterative solution of the LP descent direction finding subproblems.