Roberto Marco y el sarcómero del músculo de vuelo

La traducción de este artículo al español ha sido realizada por Raúl Herranz. La versión original en inglés se puede encontrar en la página web de esta revista: www.encuentros-multidisciplinares.or

Stimulus configuration and the perceived rigidity of eight-vertex polyhedra

In a series of four experiments, subjects examined the perceived rigidity of rotating eight-vertex polyhedra. Four different categories of polyhedra were observed under parallel projection: (1) line drawings where the initial orientation appeared to be a cube (LN), though the depth components of the eight vertices were randomly positioned (upon rotation, it could be seen that the stimuli were not cubes); (2) line drawings where the vertices were randomly placed (LR); (3) vertex-only drawings where the initial orientation appeared to be a cube (VN), though the depth components of the eight vertices were randomly positioned; and (4) vertex-only drawings with randomly positioned vertices (VR). Preliminary observations indicated that some of the mathematically rigid configurations were perceived as deforming in a nonrigid manner. Given the different stimulus categories, the following questions were addressed: (1) Could subjects identify stimuli that appeared to deform based on a large set of mathematically rigid objects?; and (2) Was it possible to identify gross qualities about the stimulus that control whether or not the human visual system adopts a rigid versus a nonrigid interpretation? Through several deformation-rating tasks, the results indicated that although most of the configurations maintained a rigid appearance throughout their rotations, the LN stimuli appeared to deform more than the LR, VN, and VR categories of stimuli. In addition, based on a signal detection paradigm, when subjects were asked to detect a physical nonrigidity embedded within mathematically rigid rotations, they had a more difficult time doing so when viewing the LN stimuli, compared to the other three stimulus categories. To account for these findings, a theory was formulated based on the behavior of line segments as they are projected onto the two-dimensional image plane. It seems that when the visual system is forced to interpret such images, two conflicting sources of information may exist: local shape cues formed by the intersecting line segments and motion-induced depth information. In order for the visual system to make sense of these images, the conflicting cues need to be driven into agreement with one another, via the adoption of a nonrigid interpretation

Temperature Determination by Means of Optoacoustic Measurements

The capabilities of the optoacoustic principle as a means of temperature measurement have been explored by means of experiments. In the experiments, a tissue test specimen, biological muscle sample, was positioned in a precisely temperature-controlled environment and irradiated with 532-nm laser light. The absorbed radiation gave rise to thermal expansion whose induced stresses created a sound field which was detected by a piezoelectric sensor. During the course of the experiments, the temperature of the water bath was systematically varied, with ample time being allowed to enable the test specimen to achieve thermal equilibrium. The temperature variation encompassed both increasing and decreasing protocols. Replicate samples were tested to ensure accuracy. It was found that temperature increases gave rise to decreasing acoustic amplitudes. An opposite trend was observed when the temperature was decreased. This outcome, when compared with the published literature, suggested that accurate use of the photoacoustic effect as a means of temperature measurement requires great care in the setup and execution of the experiment

Investigating teaching strategies in mathematics classrooms : a CD-ROM resource enabling teachers to explore teaching strategies in mathematics education

Teaching mathematics has traditionally followed a standard pattern across the world. Students are placed in classrooms where they are seated individually, are required to listen passively and observe the teacher demonstrating mathematical procedure and then s1 end extensive time practicing the newly acquired ski ll s. Generally the content being taught comprises mathematical facts and skills taught sequentially in the order presented by a textbook. Students are then assessed by unseen pencil and paper tests for the purpose of grading and ranking. This cycle is then repeated with another mathematical topic which is viewed by students as discrete from the previous one. The National Council of Teachers of Mathematics offers a new vision of mathematics teaching and learning..

Cardiovascular magnetic resonance of scar and ischemia burden early after acute ST elevation and non-ST elevation myocardial infarction

<p>Abstract</p> <p>Background</p> <p>The acute coronary syndrome diagnosis includes different classifications of myocardial infarction, which have been shown to differ in their pathology, as well as their early and late prognosis. These differences may relate to the underlying extent of infarction and/or residual myocardial ischemia. The study aim was to compare scar and ischemia mass between acute non-ST elevation myocardial infarction (NSTEMI), ST-elevation MI with Q-wave formation (Q-STEMI) and ST-elevation MI without Q-wave formation (Non-Q STEMI) in-vivo, using cardiovascular magnetic resonance (CMR).</p> <p>Methods and results</p> <p>This was a prospective cohort study of twenty five consecutive patients with NSTEMI, 25 patients with thrombolysed Q-STEMI and 25 patients with thrombolysed Non-Q STEMI. Myocardial function (cine imaging), ischemia (adenosine stress first pass myocardial perfusion) and scar (late gadolinium enhancement) were assessed by CMR 2–6 days after presentation and before any invasive revascularisation procedure. All subjects gave written informed consent and ethical committee approval was obtained. Scar mass was highest in Q-STEMI, followed by Non-Q STEMI and NSTEMI (24.1%, 15.2% and 3.8% of LV mass, respectively; p < 0.0001). Ischemia mass showed the reverse trend and was lowest in Q-STEMI, followed by Non-Q STEMI and NSTEMI (6.9%, 14.7% and 19.9% of LV mass, respectively; p = 0.012). The combined mass of scar and ischemia was similar between the three groups (p = 0.17). The ratio of scar to ischemia was 3.5, 1.0 and 0.2 for Q-STEMI, Non-Q STEMI and NSTEMI, respectively.</p> <p>Conclusion</p> <p>Prior to revascularisation, the ratio of scar to ischemia differs between NSTEMI, Non-Q STEMI and Q-STEMI, whilst the combined scar and ischemia mass is similar between these three types of MI. These results provide in-vivo confirmation of the diverse pathophysiology of different types of acute myocardial infarction and may explain their divergent early and late prognosis.</p

Intraretinal Correlates of Reticular Pseudodrusen Revealed by Autofluorescence and En Face OCT.

Purpose We sought to determine whether information revealed from the reflectance, autofluorescence, and absorption properties of RPE cells situated posterior to reticular pseudodrusen (RPD) could provide insight into the origins and structure of RPD. Methods RPD were studied qualitatively by near-infrared fundus autofluorescence (NIR-AF), short-wavelength fundus autofluorescence (SW-AF), and infrared reflectance (IR-R) images, and the presentation was compared to horizontal and en face spectral domain optical coherence tomographic (SD-OCT) images. Images were acquired from 23 patients (39 eyes) diagnosed with RPD (mean age 80.7 ± 7.1 [SD]; 16 female; 4 Hispanics, 19 non-Hispanic whites). Results In SW-AF, NIR-AF, and IR-R images, fundus RPD were recognized as interlacing networks of small scale variations in IR-R and fluorescence (SW-AF, NIR-AF) intensities. Darkened foci of RPD colocalized in SW-AF and NIR-AF images, and in SD-OCT images corresponded to disturbances of the interdigitation (IZ) and ellipsoid (EZ) zones and to more pronounced hyperreflective lesions traversing photoreceptor-attributable bands in SD-OCT images. Qualitative assessment of the outer nuclear layer (ONL) revealed thinning as RPD extended radially from the outer to inner retina. In en face OCT, hyperreflective areas in the EZ band correlated topographically with hyporeflective foci at the level of the RPE. Conclusions The hyperreflective lesions corresponding to RPD in SD-OCT scans are likely indicative of degenerating photoreceptor cells. The darkened foci at positions of RPD in NIR-AF and en face OCT images indicate changes in the RPE monolayer with the reduced NIR-AF and en face OCT signal suggesting a reduction in melanin that could be accounted for by RPE thinning

Evaluating Refractive Outcomes after Cataract Surgery

Purpose To compare methods for evaluating refractive outcomes after cataract surgery to detect outliers. Design Case series database study of the evaluation of diagnostic technology. Participants Consecutive patients who had uneventful cataract operations over a 5-year period. Methods The intended and postoperative refractive outcome and differences between these were analyzed as a spherical equivalent, cylinder, and spherocylinder. The average keratometry and differences between steep and flat keratometric meridians were used to calculate the intended refractive error. Main Outcome Measures Outliers were defined as patients for whom the difference between the intended and postoperative refractive errors was more than 3 standard deviations (SDs) away from the mean. Results A total of 9000 patients were included. Twelve patients had missing data and were excluded. The mean intended refractive outcome was −0.12+0.12×2 (95% lower confidence limit [LCL], −1.94+1.06×44; 95% upper confidence limit [UCL], +0.77+1.05×140). The actual postoperative refractive error was −0.30+0.47×6 (95% LCL, −2.36+1.31×36; 95% UCL, +1.00+1.18×148) with a difference from the intended of −0.18+0.35×7 (95% LCL, −1.91+1.22×38; 95% UCL, +0.75+1.09×145). Treating the components of the refractive error independently, outliers were observed in 82 eyes (0.91%) based on the sphere, 46 eyes (0.51%) based on the spherical equivalent, 115 eyes (1.28%) based on treating the cylinder as a scalar, and 76 eyes (0.85%) based on treating the cylinder as a vector. When the differences between the intended and postoperative refractive errors were calculated as a compound spherocylinder, outliers were observed for 233 eyes (2.59%). Conclusions Treating the intended refractive outcome as a spherocylinder improves the precision for detecting clinically significant refractive outliers