Affine diffractive beam dividers.

Diffractive optical elements that divide an input beam into a set of replicas are used in many optical applications ranging from image processing to communications. Their design requires time-consuming optimization processes, which, for a given number of generated beams, are to be separately treated for one-dimensional and two-dimensional cases because the corresponding optimal efficiencies may be different. After generalizing their Fourier treatment, we prove that, once a particular divider has been designed, its transmission function can be used to generate numberless other dividers through affine transforms that preserve the efficiency of the original element without requiring any further optimization.

Three-dimensional polarization of fields radiated by partially coherent electromagnetic cylindrical sources.

Partially coherent electromagnetic sources with cylindrical symmetry and infinite extent radiating outward are introduced. Their 3 × 3 cross-spectral density matrix is given through expansions of the field components in terms of basis functions related to the Hankel functions. The spectral density and the three-dimensional degree of polarization of such sources and the fields they radiate are examined. Several examples are presented and discussed. Among them, a class of cylindrical sources whose coherent vector modes coincide with the above basis functions is defined and studied.

Epidemiology of bacterial co-infections and risk factors in COVID-19-hospitalized patients in Spain: a nationwide study.

BACKGROUND: We performed a nationwide population-based retrospective study to describe the epidemiology of bacterial co-infections in coronavirus disease 2019 (COVID-19)-hospitalized patients in Spain in 2020. We also analyzed the risk factors for co-infection, the etiology and the impact in the outcome. METHODS: Data were obtained from records in the Minimum Basic Data Set (MBDS) of the National Surveillance System for Hospital Data in Spain, provided by the Ministry of Health and annually published with 2 years lag. COVID-19 circulated in two waves in 2020: from its introduction to 31st June and from 1st July to 31st December. The risk of developing a healthcare-associated bacterial co-infection and the risk for in-hospital and intensive care unit (ICU) mortality in co-infected patients was assessed using an adjusted logistic regression model. RESULTS: The incidence of bacterial co-infection in COVID-19 hospitalized patients was 2.3%. The main risk factors associated with bacterial co-infection were organ failure, obesity and male sex. Co-infection was associated with worse outcomes including higher in-hospital, in-ICU mortality and higher length of stay. Gram-negative bacteria caused most infections. Causative agents were similar between waves, although higher co-infections with Pseudomonas spp. were detected in the first wave and with Haemophilus influenzae and Streptococcus pneumoniae in the second. CONCLUSIONS: Co-infections are not as common as those found in other viral respiratory infections; therefore, antibiotics should be used carefully. Screening for actual co-infection to prescribe antibiotic therapy when required should be performed.

On z-coherence of beams radiated by Schell-model sources with Gaussian profile.

The degree of coherence and the intensity distribution on the axis of the beam radiated by a planar partially coherent source of the Schell-model type are investigated. We present an expression for the on-axis cross-spectral density which is valid for a very general Schell-model source, with the only constraint that the intensity distribution across the source is Gaussian. Furthermore, we show that such an expression takes very simple analytical forms for several commonly used degrees of coherence of the source.

On z-coherence in self-focusing.

Both the intensity distribution and the degree of coherence between pairs of points along the propagation axis (z-coherence) are derived in closed form for a phenomenon of self-focusing produced by circularly coherent light. The first confirms results previously obtained numerically, while the second exhibits new complex features. The physical interpretation is obtained by a suitable pseudo-modal expansion that suggests an analogy with a simple two-mode structure.

Tailoring on-axis spectral density with circularly coherent light beams.

The on-axis cross-spectral density (CSD) of a beam radiated by a stationary source with a circular coherence state and a Gaussian spectral density is obtained in the closed form. It is revealed that the on-axis CSD is expressed via the Laplace transform of the source's degree of coherence or the Hilbert transform of the corresponding pseudo-mode weighting function. Such relations enable efficient tailoring of the on-axis spectral density, as we show with a slew of numerical examples.

On-axis polarization of beams radiated by electromagnetic circularly coherent sources.

On-axis spectral density and degree of polarization of beams radiated by electromagnetic (EM) sources with circular correlations are shown to be finely controlled by changing the source parameters. We reveal, in particular, that in this beam class, unlike for all previously known stationary beams, it is possible to control independently the dynamics of the on-axis spectral density and the degree of polarization. This was enabled by the obtained analytical expression for the on-axis polarization matrix, derived for general EM sources with circular coherence and Gaussian spectral density across the source plane. A simple experimental scheme for generating a broad class of EM circularly coherent sources is devised involving only a line source, a lens, and a transparency, possibly anisotropic.

Cylindrical partially coherent scalar sources.

Partially coherent scalar sources with cylindrical symmetry radiating outwards are introduced. Homogeneous cross-spectral densities are shown to possess angularly modulated Hankel modes, whose amplitudes are subject to a filtering process during propagation. Simple criteria for treating such sources are given. For the case of an incoherent cylinder, the number of effective modes is found and spatial coherence is shown to appear in the radiated light. The radial coherence of the radiated field is then examined. Non-homogeneous cylindrical sources are also introduced.

Partially coherent spherical sources with spherical harmonic modes.

A class of partially coherent spherical sources is introduced whose cross-spectral density across the surface has a modal expansion made up of spherical harmonics. For such sources, the solution of the propagation problem in all the outer spaces can be written through a series of the propagated modes, which maintains the spherical harmonic structure. The main features of this class of cross-spectral densities are derived illustrating their coherence properties with examples. Attention is paid to the properties of radial coherence. In particular, it is clearly shown that sources with perfect radial coherence exist with angular coherence that is only partial.

Nonlinear complexification of periodic orbits in the generalized Landau scenario.

We have found a way for penetrating the space of the dynamical systems toward systems of arbitrary dimension exhibiting the nonlinear mixing of a large number of oscillation modes through which extraordinarily complex time evolutions may arise. The system design is based on assuring the occurrence of a number of Hopf bifurcations in a set of fixed points of a relatively generic system of ordinary differential equations, in which the main peculiarity is that the nonlinearities appear through functions of a linear combination of the system variables. The paper outlines the design procedure and presents a selection of numerical simulations with a variety of designed systems whose dynamical behaviors are really rich and full of unknown features. For concreteness, the presentation is focused on illustrating the oscillatory mixing effects on the periodic orbits, through which the harmonic oscillation born in a Hopf bifurcation becomes successively enriched with the intermittent incorporation of other oscillation modes of higher frequencies while the orbit remains periodic and without the necessity of bifurcating instabilities. Even in the absence of a proper mathematical theory covering the nonlinear mixing mechanisms, we find enough evidence to expect that the oscillatory scenario be truly scalable concerning the phase-space dimension, the multiplicity of involved fixed points, and the range of time scales so that extremely complex but ordered dynamical behaviors could be sustained through it.

Non-Hermitian arrangement for stable semiconductor laser arrays.

We propose and explore a physical mechanism for the stabilization of the complex spatiotemporal dynamics in arrays (bars) of broad area laser diodes taking advantage of the symmetry breaking in non-Hermitian potentials. We show that such stabilization can be achieved by specific pump and index profiles leading to a PT-symmetric coupling between nearest neighboring lasers within the semiconductor bar. A numerical analysis is performed using a complete (2 + 1)-dimensional space-temporal model, including transverse and longitudinal spatial degrees of freedom and temporal evolution of the electric field and carriers. We show regimes of temporal stabilization and light emission spatial redistribution and enhancement. We also consider a simplified (1 + 1)-dimensional model for an array of lasers holding the proposed non-Hermitian coupling with a global axisymmetric geometry. We numerically demonstrate a two-fold benefit: the control over the temporal dynamics over the EELs bar and the field concentration on the central lasers leading to a brighter output beam, facilitating a direct coupling to an optical fiber.

Misalignments measurement of CPV optical components through image acquisition.

Concentrator Photovoltaics (CPV) technology relies on optical systems that concentrate sunlight on solar cells in exchange for a reduction of the permitted angular tolerance when pointing at the sun. A proper alignment between optics and photovoltaic receivers is crucial for the performance of this technology, particularly point focus CPV systems with concentration ratios above 100X that have narrow angular tolerances. This study presents the theoretical fundamentals of a method for evaluating misalignments in a CPV module. The method is based on the acquisition and analysis of images, taken by a camera, of the photovoltaic receivers magnified through the primary optics. The method has been successfully validated by empirical measurements and ray tracing simulations of a single lens-receiver unit.

Uncertainty principle for axial power content of highly focused fields.

In the analysis of the on-axis intensity for a highly focused optical field, it is highly desirable to deal with effective relations aimed at characterizing the field behavior in a rather simple fashion. Here, a novel and adequate measure for the size of the region where the axial power content mainly concentrates is proposed on the basis of an uncertainty principle. Accordingly, a meaningful relationship is provided for both the spread of the incident beam at the entrance of the highly focused optical system and the size of the region where the on-axis power mainly concentrates.

Partially coherent sources with radial coherence.

Partially coherent sources with radial coherence are proposed. They present a circularly symmetric intensity profile and a degree of coherence whose absolute value only depends on the angular difference between the two considered points. In particular, the source is completely coherent at pairs of points belonging to the same radius. The modal structure of such sources is determined in the general case, and conditions are derived under which the field propagated in paraxial approximation remains radially coherent at any transverse plane. In such cases, the angular dependence of the correlation function is preserved upon propagation, although the intensity profile generally changes. An example of this kind of source has been experimentally synthesized by means of a simple setup, and its coherence characteristics have been tested by means of a Young interferometer.

Goos-Hänchen and Imbert-Fedorov shifts: relation with the irradiance moments of a beam.

We present closed and simple expressions of the spatial and angular Goos-Hänchen and Imbert-Fedorov shifts in terms of the second-order irradiance moments of a beam. Our results are applicable to a general totally polarized partially coherent beam. One of the main advantages of this formalism is that it can be applied directly from the knowledge of the cross-spectral density function and the polarization state without using any modal beam expansion. The obtained expressions allow understanding of the relationship between the global spatial characteristics of the incident beam and the experimented shifts in the reflected beam. Cosine-Gaussian Schell-model beams with rectangular symmetry are used to exemplify results.

Partially coherent sources with circular coherence.

A new class of partially coherent light sources is introduced. At the source plane, they exhibit perfect coherence along any annulus that is concentric to the source center. Between two points at different distances from the center, coherence can be partial or even vanishing. Such sources can be synthesized by using a generalized form of van Cittert-Zernike theorem where axial sources are used. Beams radiated by this type of source are analyzed at the source plane and upon free propagation for some simple cases.

Synthesis of circularly coherent sources.

An experiment is presented in which a partially coherent source endowed with circular coherence is generated. The source is synthesized through a time averaging procedure, so that the mutual intensity is used as the basic correlation function. The correlation between points at different radial distances from the source center is tested by means of a Young interferometer. To confirm the perfect coherence among points along a circle concentric with the source center, the Young mask is replaced by an array of equally spaced pinholes arranged along a circle. The observed pattern is identical to that produced by the same mask, illuminated by perfectly coherent light.

A new experimental model of acid- and endotoxin-induced acute lung injury in rats.

The majority of the animal models of acute lung injury (ALI) are focused on the acute phase. This limits the studies of the mechanisms involved in later phases and the effects of long-term treatments. Thus the goal of this study was to develop an experimental ALI model of aspiration pneumonia, in which diffuse alveolar damage continues for 72 h. Rats were intratracheally instilled with one dose of HCl (0.1 mol/l) followed by another instillation of one dose of LPS (0, 10, 20, 30, or 40 µg/g body weight) 2 h later, which models aspiration of gastric contents that progresses to secondary lung injury from bacteria or bacterial products. The rats were euthanized at 24, 48, and 72 h after the last instillation. The results showed that HCl and LPS at all doses caused activation of inflammatory responses, increased protein permeability and apoptosis, and induced mild hypoxemia in rat lungs at 24 h postinstillation. However, this lung damage was present at 72 h only in rats receiving HCl and LPS at the doses of 30 and 40 µg/g body wt. Mortality (∼50%) occurred in the first 48 h and only in the rats treated with HCl and LPS at the highest dose (40 µg/g body wt). In conclusion, intratracheal instillation of HCl followed by LPS at the dose of 30 µg/g body wt results in severe diffuse alveolar damage that continues at least 72 h. This rat model of aspiration pneumonia-induced ALI will be useful for testing long-term effects of new therapeutic strategies in ALI.

Anosognosia in Alzheimer disease: Prevalence, associated factors, and influence on disease progression. / Anosognosia en la enfermedad de Alzheimer: prevalencia, factores asociados e influencia en la evolución de la enfermedad.

INTRODUCTION: Anosognosia is a frequent symptom in Alzheimer disease (AD). The objective of this article is to describe prevalence of this condition at time of diagnosis and analyse any predisposing factors and their influence on disease progression. METHODS: Observational, prospective, and analytical multi-centre study in an outpatient setting. Patients recently diagnosed with AD (NINCDS-ADRDA criteria) were included. Each patient underwent two cognitive, functional, and neuropsychiatric assessments separated by an interval of 18 months. The Clinical Insight Rating Scale was employed as a measure of anosognosia (CIR, scored 0-8). Progression was defined as an increase in the Clinical Dementia Rating Scale-sum of boxes of more than 2.5 points. The predictor variables were analysed using binary logistic regression. RESULTS: The study included 127 patients, and 94 completed both assessments. Of the total, 31.5% displayed severe anosognosia (CIR 7-8); 39.4%, altered level of consciousness (CIR 3-6); and 29.1%, normal awareness (CIR 0-2). The median baseline CIR in this cohort was 4 (Q1-Q3: 1-7), and at 18 months, 6 (Q1-Q3: 3-8), P<.001. Advanced age (odds ratio (OR) 2.43; CI 95%:1.14-5.19), lower educational level (OR 2.15; CI 95%:1.01-4.58), and more marked neuropsychiatric symptoms (OR 2.66; CI 95%:1.23-5.74) were predictor variables of anosognosia. Baseline CIR was similar in the groups with and without significant clinical progression. CONCLUSIONS: The large majority of patients with AD at the time of diagnosis showed significant anosognosia, and this condition was associated with advanced age, lower educational level, and more marked behavioural symptoms. Our results did not show that anosognosia had an effect on the initial clinical progression of AD after diagnosis.

Usefulness of semiquantitative elastography in predicting malignancy in thyroid nodules. / Utilidad de la elastografía semicuantitativa para predecir la malignidad de los nódulos tiroideos.

OBJECTIVE: To retrospectively review the diagnostic capacity of semiquantitative elastography in differentiating between benign and malignant thyroid nodules. PATIENTS AND METHODS: We analyzed 314 thyroid nodules in 295 consecutive patients referred to the endocrinology department for cytological study, studying all by conventional ultrasonography, elastography, and fine-needle aspiration cytology (FNAC). Using a semiquantitative elastography system that portrays tissue stiffness through a color map, we designed our own classification system for thyroid nodules based on their characteristics on elastography. We classified nodules into three groups: predominantly soft, predominantly stiff, and mosaic patterned. We used logistic regression analysis to investigate the relation between elastography and thyroid cancer. RESULTS: We obtained a definite diagnosis of malignancy after surgery in 19 nodules, of which on elastography 8 had the mosaic pattern, 6 were predominantly stiff, and 5 were predominantly soft. We found no significant association between the pattern on elastography and the probability of malignancy in any of the models. CONCLUSION: According to our study, la probability of malignancy in a thyroid nodule is not related to the findings at elastography. Therefore, semiquantitative elastography as used in this study cannot obviate FNAC.