Ti3AlC2 coated D-shaped fiber saturable absorber for Q-switched pulse generation

In this letter, a titanium aluminum carbide (Ti3AlC2) coated D-shaped fiber is proposed and demonstrated as a new saturable absorber (SA) for Q-switched laser pulse generation. In preparing the SA, the Ti3AlC2 powder is dispersed in liquid polyvinyl alcohol (PVA) before the solution is dropped and left to dry onto a polished surface of D-shape fiber. The SA is added to an erbium-doped fiber laser (EDFL) cavity to modulate the cavity loss for Q-switching. The Q-switched laser is obtained at 1 561 nm. The pulse width of the pulses can be varied between 7.4 µs and 5.1 µs with a corresponding repetition rate range from 41.26 kHz to 54.35 kHz, when the pump power is increased from 42.2 mW to 71.5 mW. At 71.5 mW pump, the pulse energy is obtained at 70.3 nJ. The signal-to-noise ratio (SNR) of the fundamental frequency is recorded at 67 dB, which indicates the stability of the laser.     

Brightness-dependent Tarpley model for global solar radiation estimation using GOES satellite images: Application to Uruguay

A statistical model based on Tarpley’s original solar irradiation model is proposed and evaluated using data from seven new ground stations in Uruguay. The model estimates hourly global solar irradiation on a horizontal surface using GOES-East satellite images. We show that the introduction of a simple brightness dependence in the model parameters drastically improves the accuracy of the estimates. The implementations of the original and the improved models are explained in detail. For each case, the parameters are adjusted using controlled quality solar irradiation data and a comprehensive performance analysis, on an hourly and daily basis, is carried out using data from independent measurement sites. The relative RMS deviations for the estimates of the brightness-dependent model are 7.1% for the daily estimates and 14.0% for the hourly estimates, relative to the mean of the measurements. This represents a reduction of approximately 45% (daily) and 25% (hourly) in the relative RMS deviations of the original model. The improved model provides a good balance between simplicity and accuracy.     

An A Contrario Decision Method for Shape Element Recognition

Shape recognition is the field of computer vision which addresses the problem of finding out whether a query shape lies or not in a shape database, up to a certain invariance. Most shape recognition methods simply sort shapes from the database along some (dis-)similarity measure to the query shape. Their main weakness is the decision stage, which should aim at giving a clear-cut answer to the question: “do these two shapes look alike?” In this article, the proposed solution consists in bounding the number of false correspondences of the query shape among the database shapes, ensuring that the obtained matches are not likely to occur “by chance”. As an application, one can decide with a parameterless method whether any two digital images share some shapes or not.     

Computer-aided lesion diagnosis in automated 3-D breast ultrasound using coronal spiculation

A computer-aided diagnosis (CAD) system for the classification of lesions as malignant or benign in automated 3-D breast ultrasound (ABUS) images, is presented. Lesions are automatically segmented when a seed point is provided, using dynamic programming in combination with a spiral scanning technique. A novel aspect of ABUS imaging is the presence of spiculation patterns in coronal planes perpendicular to the transducer. Spiculation patterns are characteristic for malignant lesions. Therefore, we compute spiculation features and combine them with features related to echotexture, echogenicity, shape, posterior acoustic behavior and margins. Classification experiments were performed using a support vector machine classifier and evaluation was done with leave-one-patient-out cross-validation. Receiver operator characteristic (ROC) analysis was used to determine performance of the system on a dataset of 201 lesions. We found that spiculation was among the most discriminative features. Using all features, the area under the ROC curve (A(z)) was 0.93, which was significantly higher than the performance without spiculation features (A(z)=0.90, p=0.02). On a subset of 88 cases, classification performance of CAD (A(z)=0.90) was comparable to the average performance of 10 readers (A(z)=0.87).     

Long-term monitoring of Neisseria meningitidis carrier state in the nasopharynx and seroprevalence of specific antibodies in immunized and non-immunized persons

Long-term (three-month and one-year) follow-up of nasopharyngeal carriers of Neisseria meningitidis with a frequency of sample collection of once a week and once a month resp. in the healthy population with a mean age of 43 years revealed a 4.8% positivity (2 of 42 subjects). Carriership of the same phenotype and ET-genotype of the N. meningitidis group 29E was stable in one subject, while the other long-term carrier of N. meningitidis group B has changes of the phenotype as well as ET-genotype during the follow-up period. Double (after a 3-month interval) verification of the seroprevalence of specific antimeningococcal antibodies revealed in a group of immunized subjects (vaccine A and C) a considerable degree of anti A immunity. Anti A-seropositivity in subjects immunized within a three-year interval since vaccination was 100%, in those immunized within a four-year interval a decline to 66% was recorded. Anti C antibodies after vaccination within a three-year interval were recorded in 75% subjects, in vaccinated subjects the authors detected antibodies during the first year after vaccination in 86% of the subjects. Natural anti A antibodies of the lowest titre 1:6 were recorded in four non-vaccinated subjects (22%). Naturally acquired anti B antibodies (B:2a:P1.2,P1.5) and anti C (C:2a:P1.2,P1.5) were not detected in any of the subjects.     

A five-component magneto-telluric method in geothermal exploration: the M.T.-5-E.X.

The present paper describes a new method designed both at recording and processing levels for a practical solution of the overall problem of the Earth electromagnetism, in geophysics.Up to now, the random character of the natural signals prevented any measurement of reliable values of the phase shift between the various electromagnetic components at a given place. Hence it is impossible numerically to solve the general linear relations binding these components simply by using the processes of the standard harmonic analysis.In order to overcome this difficulty the writer designed an analysis method based on a hypothesis according to which the natural signals are considered as real exponential functions increasing with time.The writer, thus, was able to work out systematically a magneto-telluric prospection method utilizing the five standard electromagnetic components quantitatively, and in particular the vertical magnetic component.The application of this method — named the M.T.-5-E.X. — to geothermal prospection in Italy in the region of Travale (Tuscany) obtained various practical results of particular interest. They will be described in a paper which will be edited jointly with the researchers of the International Institute for Geothermal Research of Pisa (Italy).     

The Non-parametric Sub-pixel Local Point Spread Function Estimation Is a Well Posed Problem

Most medium to high quality digital cameras (dslrs) acquire images at a spatial rate which is several times below the ideal Nyquist rate. For this reason only aliased versions of the cameral point-spread function (psf) can be directly observed. Yet, it can be recovered, at a sub-pixel resolution, by a numerical method. Since the acquisition system is only locally stationary, this psf estimation must be local. This paper presents a theoretical study proving that the sub-pixel psf estimation problem is well-posed even with a single well chosen observation. Indeed, theoretical bounds show that a near-optimal accuracy can be achieved with a calibration pattern mimicking a Bernoulli(0.5) random noise. The physical realization of this psf estimation method is demonstrated in many comparative experiments. We use an algorithm to accurately estimate the pattern position and its illumination conditions. Once this accurate registration is obtained, the local psf can be directly computed by inverting a well conditioned linear system. The psf estimates reach stringent accuracy levels with a relative error of the order of 2% to 5%. To the best of our knowledge, such a regularization-free and model-free sub-pixel psf estimation scheme is the first of its kind.