Model for cone directionality reflectometric measurements based on scattering

Reflectometric measurements provide an objective assessment of the directionality of the photoreceptors in the human retina. Measurements are obtained by imaging the distribution at the pupil plane of light reflected off the human fundus in a bleached condition. We propose that scattering as well as waveguides must be included in a model of the intensity distribution at the pupil plane. For scattering, the cone-photoreceptor array is treated as a random rough surface, characterized by the correlation length T (related to the distance between scatterers, i.e., mean cone spacing) and the roughness standard deviation sigma (assuming random length variations of the cone outer-segment lengths that produce random phase differences). For realistic values of T and sigma we can use the Kirchhoff approximation for computing the scattering distribution. The scattered component of the distribution can be fitted to a Gaussian function whose width depends only on T and lambda. Actual measurements vary with experimental conditions (exposure time, retinal eccentricity, and lambda) in a manner consistent with the scattering model. However, photoreceptor directionality must be included in the model to explain the actual location of the peak of the intensity distribution in the pupil plane and the total angular spread of light.     

Imaging findings in renal hydatid disease

The aim of this work is to describe the image findings of renal hydatid disease, especially on MR. Four cases of echinococcal involvement of the kidney were retrospectively reviewed. All patients had intravenous urography (IVU) and US performed. Computed tomography examination was available in three patients and MR in two cases. Intravenous urography demonstrated communication of the cyst to the collecting system in one case. Ultrasound revealed multicystic appearance in three cases and unilocular in one case. Computed tomography demonstrated unilocular thick-walled or multilocular cysts with well-defined walls, calcified in one case. In multilocular cysts the CT densities of the fluid of daughter cysts was significantly lower than the fluid of mother cysts. This typical appearance was present in three of our cases. The presence of a hypointense rim and a multicystic appearance were distinctive in MR imaging. The combined findings of these different imaging modalities aid greatly in establishing the correct diagnosis. Magnetic resonance imaging is of value in determining the presence of a characteristic rim and enables the evaluation of anatomical relationships.     

Non-monotonic characterization of induction and its application to inductive learning

In this article a new approach to the formalization of inductive inference in terms of non-monotonic inference is proposed. Induction is characterized as closed-world reasoning from the available data, followed by an inductive jump, which consists in assuming that valid conclusions in the database (assuming closed-world) hold also in the rest of the world. This conception of induction results is adequate to characterize those inference processes that could be formalized, that is, those based in analytical procedures of pattern-matching or regularity detection in the available data. the proposed characterization formally describes the implicit deductive processes of induction and its non-monotonic nature, and could be used as an abstract model of the mental process that leads to obtaining inductive hypotheses. This proposal reduces the problem of induction automatization to that of deduction automatization. Also, it constitutes a formal framework that covers several inductive inference methods used in machine learning. Besides it formalizes inductive definitions, which are very common in science and computer science. © 1995 John Wiley & Sons, Inc.     

Dissociation of autonomic and behavioral components of conditioned fear during development in the rat.

Examined classical conditioning of heart rate (HR) in unrestrained preweanling and weanling Sprague-Dawley rats (aged 16, 19, 21, 25, and 28 days old), with tone and light as the conditioned stimulus/stimuli (CS) and electric shock as the unconditioned stimulus/stimuli (UCS). The conditioned cardiac response was a sustained deceleration in HR that did not emerge until Day 21 for the tone CS and until Day 28 for the light CS. In contrast, when suppression of a behavioral response (running in a straight alley for dry suckling as reward) was used as the index of conditioning, the suppressive effects of the CS were evident around Day 16 for the tone and around Day 19 for the light. Findings indicate that during ontogenesis (a) the behavioral and autonomic responses to the same CS do not develop at the same pace; (b) the emergence of conditioned responses (CRs) to tone and light stimuli parallel the sequential order in which the relevant sensory modalities achieve maturity (first audition, next vision); and (c) there is no clear-cut interdependence between development of the HR orienting response and conditionability of HR because unconditioned cardiac deceleration to both auditory and visual stimuli first appears about Day 16 in the developing rat, well before conditioned HR responses can be established to either stimulus. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The control of grain size and distribution of particles in a (6061 alloym/(Al2O3)P composite by solutionizing treatment

The grain growth during an isothermal treatment at a solutionizing temperature of 540°C has been studied in a composite containing 6061 aluminum alloy matrix with A1₂O₃ particles. The grain growth law is generally applicable to the composites containing 0.10, 0.15, and 0.20 volume fraction of the A1₂O₃ particles (VFAP). It has been observed that the grain growth process involves the disintegration of the agglomerated particles first and then particles coalesce at longer solutionizing times in the composite containing 0.20 VFAP. The process of coalescence has not been observed up to a heating time of 20 hours at this temperature in the composites containing 0.10 and 0.15 VFAP. The trans-mission electron microscopy (TEM) study indicates the generation of a large number of dislocations in both the matrix and the area adjacent to the particles. The dislocation densities at these two locations in the composites increase with an increase in VFAP and the particle size. The microhard-ness measurements confirm the microstructural observations, and the hardness values for the com-posite and the matrix appear to be more sensitive to the particle distribution and the particle size compared to the grain size.     

Adult intussusception: demonstration by current MR techniques

We describe magnetic resonance findings in three patients with small bowel intussusception from different etiologies including idiopathic, adenomatous polyps, and hamartomatous polyps. Magnetic resonance findings showed a bowel-within-bowel appearance in two patients and a coiled-spring appearance in one patient. These findings were best shown on T2-weighted images, and clear definition was present on breathing independent T2-weighted images using half fourier acquisition snap shot turbo spin echo T2-weighted images.     

Developmental hematopoiesis

Hematopoiesis is a developmental process that evolves throughout the lifespan of an individual. Most work in the field has focused on events occurring in the adult bone marrow (BM). In the embryo, blood and endothelial cell generation begins very early after gastrulation, in defined intraembryonic mesodermic sites. Recent multidisciplinary studies, taking advantage of classic embryological and gene targeting technology in various species, have provided a new image of embryofetal lymphohemopoiesis, which includes the suggestion of developmental compartmentalization or waves. The first hematopoietic stem cells (HSC) migrate further and home in an ordered sequence of supporting microenvironments depending on scarcely known molecular requirements. These early hematopoietic progenitors show important differences in their cell biology and differentiation potentialities with respect to those present in adult stages; this fact, together with specific microenvironmental influences, define a process that diverges significantly from that occurring in the BM. Here, we update the latest developments in the field, the new understanding of lymphohemopoiesis in prenatal life, and the novel questions that this emerging paradigm is producing.