Broadband performance of superdirective delay-and-sum beamformers steered to end-fire.

Linear arrays steered to end-fire provide superdirective robust performance if a constraint is imposed on the white-noise gain. Filter-and-sum beamformers achieve the maximum constrained directivity by tuning their complex weights over the frequency. Delay-and-sum beamformers have simpler structures, but their weights are fixed and optimized at a given frequency. This letter investigates the constrained directivity provided over a broad band by different delay-and-sum techniques. Complex weights and analytic signals attain near-optimal broadband performance over four octaves. Oversteered arrays using real weights and signals were found to attain superdirective performance over approximately two octaves. Hearing aids and directional hydrophones are potential applications for the considered arrays.

[Occurrence of ticks (Acari: Ixodidae) in public parks in Cuneo province (Piemonte, Italy)]. / Zecche (Acari: Ixodidae) nelle aree verdi urbane destinate ad attività ricreative: indagine in 17 comuni della provincia di Cuneo (Piemonte, Italia).

Mites Ixodidae (hard ticks) may represent an important public health problem even in urban green areas. In the present study, by doing weekly samples, the green areas (playgrounds, parks, picnic areas for dogs, etc.) of 17 municipalities in the province of Cuneo (Piedmont, Italy) have been inspected, for a total of about 18,710 m2 monitored. No sample was found positive for mites Ixodidae. From this study it can be concluded that the green areas surveyed do not pose a risk to the population, while probably the greatest risk of infestation for humans has to be found in domestic spaces and areas of woodland and forests.

A preliminary in vitro assessment of polymer-shelled microbubbles in contrast-enhanced ultrasound imaging.

This paper focuses on the use of poly (vinyl alcohol)-shelled microbubbles as a contrast agent in ultrasound medical imaging. The objective was an in vitro assessment of the different working conditions and signal processing methods for the visual detection (especially in small vessels) of such microbubbles, while avoiding their destruction. Polymer-shelled microbubbles have recently been proposed as ultrasound contrast agents with some important advantages. The major drawback is a shell that is less elastic than that of the traditional lipidic microbubbles. Weaker echoes are expected, and their detection at low concentrations may be critical. In vitro experiments were performed with a commercial ultrasound scanner equipped with a dedicated acquisition board. A concentration of 100bubbles/mm(3), excitation pressure amplitudes from 120kPa to 320kPa, and a central frequency of 3MHz or 4.5MHz were used. Three multi-pulse techniques (i.e., pulse inversion, contrast pulse sequence based on three transmitted signals, and contrast pulse sequence in combination with the chirp pulse) were compared. The results confirmed that these microbubbles produce a weaker ultrasound response than lipidic bubbles with a reduced second-order nonlinear component. Nevertheless, these microbubbles can be detected by the contrast pulse sequence technique, especially when the chirp pulse is adopted. The best value of the contrast-to-tissue ratio was obtained at an excitation pressure amplitude of 230kPa: although this pressure amplitude is higher than what is typically used for lipidic microbubbles, it does not cause the rupture of the polymeric contrast agent.

A comparative analysis of multi-pulse techniques in contrast-enhanced ultrasound medical imaging.

One of the important issues in the field of ultrasound medical imaging using contrast agents is the development of techniques able to separate the response of the contrast media from that of the biological tissues. In the literature, one can find various solutions involving the use of multiple transmitted signals and the combination of related echoes. However, the quality of these techniques may be reduced due to some undesired effects that are seldom considered, despite the fact that they are always present in real systems. These effects are the signal distortions introduced by the hardware equipment, the thermal noise in the electronic circuitry, and body motion between successive pulses. In this paper we propose a simulation tool that will allow the calculation of the backscattered echo from a population of contrast agents immersed in a biological tissue, considering all the mentioned effects. With this tool, an assessment of the comparative robustness of three well-known multi-pulse techniques has been carried out under realistic working conditions and the performance of the three techniques has been evaluated in terms of contrast-to-tissue ratio and signal-to-noise ratio. The results show that the undesired effects have a strong impact on these techniques and that there are notable differences in their robustness. Finally, some suggestions on the choice of the particular technique to be applied are provided on the basis of the specific work conditions.

Immunogenicity of a 23-valent pneumococcal polysaccharide vaccine in elderly residents of a long-term care facility

S. pneumoniae is a significant cause of community-acquired pneumonia in the elderly, and accounts for the majority of the pneumonia deaths among the elderly. We conducted this randomized double-blind study to evaluate the immune response to a 23-valent pneumococcal polysaccharide vaccine and the persistence of antibodies two years after the vaccination in an elderly population in Santiago, Chile. A total of 118 elderly nursing home residents received either the pneumococcal or a tetanus control vaccine. Serum samples were taken at enrolment, at two months, and at two years post-vaccination. Pre-vaccination anti-pneumococcal antibody geometric mean concentrations (GMC) were similar in both study groups, with increased levels of antibodies found only against serotype 14. The pneumococcal vaccine was highly immunogenic at 2 months, and titers remained high two years after the vaccination for the 10 serotypes studied in this elderly population. The results thus support the benefits of this pneumococcal vaccine in this elderly population who are at increased risk of invasive pneumococcal disease.

[Nasal carriage of Streptococcus pneumoniae in elderly subjects according to vaccination status]. / Portación nasal de Streptococcus pneumoniae en adulto mayor y su respuesta frente a la vacunación antineumocócica.

BACKGROUND: S pneumoniae is the main cause of community-acquired pneumonia in the elderly, group that concentrates 95% of deaths. AIM: To assess the prevalence of nasal carriage of S pneumoniae in institutionalized elderly patients. MATERIAL AND METHODS: One hundred eighteen institutionalized subjects aged over 60 years (65 males) were enrolled. Since they were also participating in a controlled protocol related to the immunogenicity of an anti-pneumococcal vaccine, our investigation was also blind and randomized. According to randomization, they received pneumococcal or tetanic vaccine. Nasal swab cultures were taken at the beginning of the trial and two months after vaccination. According to recommended methods, we identified S pneumoniae, the serotypes and their antimicrobial susceptibility. RESULTS: In the first nasal sample, 16% of subjects were positive for S pneumoniae. The second sample was positive in 12%. Of the 33 isolated serotypes, 9.1% demonstrated intermediate resistance to penicillin and 3.3% were resistant to chloramphenicol. CONCLUSIONS: The study demonstrated a greater percentage of colonized patients than in the general population. The isolated serotypes are the same that cause invasive diseases in this age group, according to data of the Institute of Public Health of Chile. There were no differences in the percentage of colonization between subjects vaccinated against S pneumoniae and control groups, after two months of follow up. Isolated strains had a low resistance to penicillin. High level resistance was not observed.

Portación nasal de Streptococcus pneumoniae en adulto mayor y su respuesta frente a la vacunación antineumocócica / Nasal carriage of Streptococcus pneumoniae in elderly subjects according to vaccination status

Background: S pneumoniae is the main cause of community-acquired pneumonia in the elderly, group that concentrates 95 percent of deaths. Aim: To assess the prevalence of nasal carriage of S pneumoniae in institutionalized elderly patients. Material and methods: One hundred eighteen institutionalized subjects aged over 60 years (65 males) were enrolled. Since they were also participating in a controlled protocol related to the immunogenicity of an anti-pneumococcal vaccine, our investigation was also blind and randomized. According to randomization, they received pneumococcal or tetanic vaccine. Nasal swab cultures were taken at the beginning of the trial and two months after vaccination. According to recommended methods, we identified S pneumoniae, the serotypes and their antimicrobial susceptibility. Results: In the first nasal sample, 16 percent of subjects were positive for S pneumoniae. The second sample was positive in 12 percent. Of the 33 isolated serotypes, 9.1 percent demonstrated intermediate resistance to penicillin and 3.3 percent were resistant to chloramphenicol. Conclusions: The study demonstrated a greater percentage of colonized patients than in the general population. The isolated serotypes are the same that cause invasive diseases in this age group, according to data of the Institute of Public Health of Chile. There were no differences in the percentage of colonization between subjects vaccinated against S pneumoniae and control groups, after two months of follow up. Isolated strains had a low resistance to penicillin. High level resistance was not observed.

A stochastic approach for the apodization of very short arrays.

The problem addressed in this paper is the synthesis of the weight coefficients to be assigned to the elements of a linear array that has a spatial aperture shorter than one wavelength. The aim is to obtain a data-independent beam pattern that fulfills some a priori fixed constraints. The analytical approach, expressed in terms of a linear least-squares problem, has been attempted, resulting in very large noise sensitivity and beam pattern instability. To overcome this problem a mixed methodology, based on a combination of a stochastic technique and a local descent method that provides very robust weight coefficients with reduced noise sensitivity, is proposed. Here, robust means that, even if unavoidable fluctuations occur in the transducer gains, the beam pattern obtained maintains the desired features.

Extraction of 3D information from sonar image sequences.

This paper describes a set of methods that make it possible to estimate the position of a feature inside a three-dimensional (3D) space by starting from a sequence of two-dimensional (2D) acoustic images of the seafloor acquired with a sonar system. Typical sonar imaging systems are able to generate just 2D images, and the acquisition of 3D information involves sharp increases in complexity and costs. The front-scan sonar proposed in this paper is a new equipment devoted to acquiring a 2D image of the seafloor to sail over, and allows one to collect a sequence of images showing a specific feature during the approach of the ship. This fact seems to make it possible to recover the 3D position of a feature by comparing the feature positions along the sequence of images acquired from different (known) ship positions. This opportunity is investigated in the paper, where it is shown that encouraging results have been obtained by a processing chain composed of some blocks devoted to low-level processing, feature extraction and analysis, a Kalman filter for robust feature tracking, and some ad hoc equations for depth estimation and averaging. A statistical error analysis demonstrated the great potential of the proposed system also if some inaccuracies affect the sonar measures and the knowledge of the ship position. This was also confirmed by several tests performed on both simulated and real sequences, obtaining satisfactory results on both the feature tracking and, above all, the estimation of the 3D position.

Implementación de una red nacional para la vigilancia de resistencia de agentes patógenos a antimicrobianos según sÝndromes clÝnicos / Starting a national surveillance network on antibiotic resistance

El Instituto de Salud Pública de Chile y la Sociedad Chilena de InfectologÝa han aunado sus esfuerzos para coordinar y co-dirigir una red nacional para la vigilancia de resistencia de agentes patógenos a antimicrobianos según sÝndromes clÝnicos. El objetivo de esta red es establecer un sistema nacional de vigilancia de la resistencia a antimicrobianos, estandarizado y coordinado, que proporcione información actualizada acerca de los agentes infecciosos mßs relevantes por sÝndromes clÝnicos bien definidos, por edad y por lugar de origen: hospitalaria o de la comunidad. Nos parece fundamental la participación de todos los Servicios de Salud del paÝs en esta red, para obtener datos de calidad, representativos de nuestra realidad nacional, que sean de real utilidad en el manejo de los pacientes.

Determination of virus abundance in marine sediments.

In this study, we optimized procedures to enumerate viruses from marine sediments by epifluorescence microscopy using SYBR Green I as a stain. The highest virus yields from the bulk of the sediments were obtained by utilizing pyrophosphate and 3 min of sonication. The efficiency of extraction benthic viruses by pyrophosphate-ultrasound treatment was about 60% of the extractable virus particles. Samples treated with nucleases had increased virus counts, suggesting a masking effect of extracellular DNA. No significant differences were observed between virus counts obtained by epifluorescence microscopy and transmission electron microscopy. Both formaldehyde and glutaraldehyde gave significant reductions of virus counts after only 24 h of sediment storage, but no further loss occurred after 7 days.

Small cargo proteins and large aggregates can traverse the Golgi by a common mechanism without leaving the lumen of cisternae.

Procollagen (PC)-I aggregates transit through the Golgi complex without leaving the lumen of Golgi cisternae. Based on this evidence, we have proposed that PC-I is transported across the Golgi stacks by the cisternal maturation process. However, most secretory cargoes are small, freely diffusing proteins, thus raising the issue whether they move by a transport mechanism different than that used by PC-I. To address this question we have developed procedures to compare the transport of a small protein, the G protein of the vesicular stomatitis virus (VSVG), with that of the much larger PC-I aggregates in the same cell. Transport was followed using a combination of video and EM, providing high resolution in time and space. Our results reveal that PC-I aggregates and VSVG move synchronously through the Golgi at indistinguishable rapid rates. Additionally, not only PC-I aggregates (as confirmed by ultrarapid cryofixation), but also VSVG, can traverse the stack without leaving the cisternal lumen and without entering Golgi vesicles in functionally relevant amounts. Our findings indicate that a common mechanism independent of anterograde dissociative carriers is responsible for the traffic of small and large secretory cargo across the Golgi stack.

Aperture and element minimization in linear sparse arrays with desired beam patterns

In this paper, an optimization method aimed at designing aperiodic linear sparse arrays is proposed that is based on the stochastic optimization methodology called simulated annealing. Such a method optimizes the positions and the weight coefficients of each element of a linear array in order to obtain a beam pattern that meets given requirements. Moreover, while positions and weights are optimized, minimization of both the number of elements and the spatial aperture is carried out. In this way, a beam pattern without grating lobes and close to the desired one is produced using a small number of elements and a short aperture. The results obtained are impressive in terms of improvement of array characteristics and performance over those reported in the literature, while a great flexibility in defining the desired beam pattern is allowed. Finally, it is proved that the array configurations need a number of elements very close to the absolute minimum to achieve the desired beam pattern.

Thinning and weighting of large planar arrays by simulated annealing.

Two-dimensional arrays offer the potential for producing three-dimensional acoustic imaging. The major problem is the complexity arising from the large number of elements in such arrays. In this paper, a synthesis method is proposed that is aimed at designing an aperiodic sparse two-dimensional array to be used with a conventional beam-former. The stochastic algorithm of simulated annealing has been utilized to minimize the number of elements necessary to produce a spatial response that meets given requirements. The proposed method is highly innovative, as it can design very large arrays, optimize both positions and weight coefficients, synthesize asymmetric arrays, and generate array configurations that are valid for every steering direction. Several results are presented, showing notable improvements in the array characteristics and performances over those reported in the literature.

A confidence-based approach to enhancing underwater acoustic image formation.

This paper describes a flexible technique to enhance the formation of short-range acoustic images so as to improve image quality and facilitate the tasks of subsequent postprocessing methods. The proposed methodology operates as an ideal interface between the signals formed by a focused beamforming technique (i.e., the beam signals) and the related image, whether a two-dimensional (2-D) or three-dimensional (3-D) one. To this end, a reliability measure has been introduced, called confidence, which allows one to perform a rapid examination of the beam signals and is aimed at accurately detecting echoes backscattered from a scene. The confidence-based approach exploits the physics of the process of image formation and generic a priori knowledge of a scene to synthesize model-based signals to be compared with actual backscattered echoes, giving, at the same time, a measure of the reliability of their similarity. The objectives that can be attained by this method can be summarized in a reduction in artifacts due to the lowering of the side-lobe level, a better lateral resolution, a greater accuracy in range determination, a direct estimation of the reliability of the information acquired, thus leading to a higher image quality and hence a better scene understanding. Tests on both simulated and actual data (concerning both 2-D and 3-D images) show the higher efficiency of the proposed confidence-based approach, as compared with more traditional techniques.

Difusión de H. influenzae tipo B (HI B) en contactos intrafamiliares de niños con infecciones sistémicas por este agente / Spread of haemophilus type B in household contacts of patients with invasive infections

Actualmente está bien documentada la difusibilidad de Hi b especialmente en niños y se ha planteado quimioprofilaxis a los menores de 4 años que son contactos de infecciones sistémicas. Para conocer nuestra situación epidemiológica, se estudiaron 31 infecciones sistémicas por Hi b en pacientes ingresados a los hospitales L. Calvo Mackenna y Exequiel González Cortés (24 meningitis, 3 celulitis faciales, 1 neumonía abscesada, 3 pleuroneumonías, una de las cuales presentó además pericarditis) y se investigó la presencia de portadores entre los contactos intrafamiliares. Se estudiaron 191 contactos (X 6,4 por cada caso índice), encontrándose 18% de portadores entre los niños y 5,9% entre los adultos. Se detectó un caso secundario en un contacto de 7 meses de edad. Se logró la erradicación de todos los portadores mediante tratamiento con rifampicina durante 4 días. Se determinó el perfil de sensibilidad a los antimicrobianos de las cepas de Hi aisladas de pacientes y portadores, observándose 12% de cepas resistentes a ampicilina y cloramfenicol entre las cepas de los casos índices. No se observó resistencia en Hi b aislados de portadores