Bachia heteropa

Number of Pages: 10Integrative BiologyGeological Science

Static and dynamic XY-like short-range order in a frustrated magnet with exchange disorder

A single crystal of the Co2+ based pyrochlore NaCaCo2F7 was studied by inelastic neutron scattering. This frustrated magnet with quenched exchange disorder remains in a strongly correlated paramagnetic state down to one 60th of the Curie-Weiss temperature. Below T_f = 2.4 K, diffuse elastic scattering develops and comprises 30 +/- 10% of the total magnetic scattering, as expected for J_{eff} = 1/2 moments frozen on a time scale that exceeds \hbar/\delta E=3.8 ps. The diffuse scattering is consistent with short range XY antiferromagnetism with a correlation length of 16 \AA. The momentum (Q) dependence of the inelastic intensity indicates relaxing XY-like antiferromagnetic clusters at energies below ~ 5.5 meV, and collinear antiferromagnetic fluctuations above this energy. The relevant XY configurations form a continuous manifold of symmetry-related states. Contrary to well-known models that produce this continuous manifold, order-by-disorder does not select an ordered state in NaCaCo2F7 despite evidence for weak (~12 %) exchange disorder. Instead, NaCaCo2F7 freezes into short range ordered clusters that span this manifold.Comment: 9 pages, 9 figures. This updated version features modified figures and some new discussio

La responsabilidad civil medica. La responsabilidad del equipo medico y el consentimiento informado

57 p.La Responsabilidad médica ha sido objeto de numerosos estudios tanto en el Derecho comparado como en la doctrina nacional. El interés de esta es producto del aumento en los tribunales de Justicia de demandas donde se involucren médicos. El presente trabajo pretendemos analizar la naturaleza de la responsabilidad en general; la responsabilidad profesional; la responsabilidad médica y el ámbito de su aplicación. Luego se analizará las teorías al respecto,tanto la contractual como la extracontractual. Continuando con el equipo médico, revisando las teorías esgrimidas con respecto a su responsabilidad, para finalizar con el examen del principio del consentimiento informado

Effect of specimen geometry and test configuration on the fracture process zone for asphalt materials

In the United States and elsewhere in the world, recycled materials are commonly incorporated into asphalt mixtures, to provide environmental and economic benefits by decreasing the use of virgin materials, such as natural or quarried aggregates and asphalt binder, in newly designed asphalt mixtures. However, recycled materials such as reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) have resulted in asphalt mixtures prone to early cracking. In addition, Superpave volumetric design requirements are no longer sufficient to design asphalt mixtures because of the inconsistent properties of RAP or RAS. Consequently, agencies have been adopting performance tests to assess the cracking and rutting vulnerability of asphalt mixtures to achieve a balance mix design. The Illinois Flexibility Index Test (I-FIT) protocol was developed at the Illinois Center for Transportation (ICT) and published as American Association of State Highway and Transportation Officials provisional standards (AASHTO TP 124) to evaluate the cracking vulnerability of asphalt concrete. The test consists of a semi-circular asphalt concrete sample that has a vertical notch loaded along the symmetric axis resulting in mode-I type of fracture similar to, the typical three-point bending beam tests. The I-FIT global response refers to the load-versus-displacement curve that is characterized using the fracture energy (FE), strength, and post-peak slope. The microstructural response refers to the deformation occurring in the fracture process zone (FPZ). FPZ is the region surrounding the notch tip that develops micro cracks before a macro crack is observed. Hence, the energy dissipation due to the deformation that occurs in this region eventually controls the global response of the specimen. I-FIT outputs are influenced by specimen geometry and test conditions (e.g., thickness, and loading rate, as well field aging). For this reason, there is a need to understand the effect of test parameters on global and microstructural responses to calibrate the I-FIT results when test parameters are altered. Therefore, this work investigates the effect of the notch length, specimen thickness, loading rate, air void content, and asphalt binder on I-FIT global results and microstructural response. Multiple samples with varying notch lengths, thicknesses, and loading rates were evaluated to observe the effect of the test parameters. Then, samples with varying air void content and asphalt binder were tested to observe the mixture properties effect. The tests were recorded with high-resolution cameras to allow for digital image correlation (DIC) measurements. DIC measured the strain and displacement fields at a resolution of 8 microns/pixels. The resolution allows to evaluate the local characterization of fracture mechanisms and the interaction between the asphalt mastic and aggregate phases. It was found that an increase in the thickness or loading rate resulted in an increase of the post-peak slope without affecting the FE. On the other hand, an increase in the notch length or air voids content resulted in lower post-peak slope values. The FE was affected by the notch length and the loading rate. From, DIC results, it was seen that a decrease in the FPZ area correlated to a decrease in the FE and lower post-peak slope. The results from varying the notch length did not follow this trend because, as the notch length gets longer, the compressive strain (not included in the FPZ definition) interacts as an energy dissipation mechanism at failure. It can be concluded that existing correction factors that address the variation due to specimen thickness and air void content are appropriate. A new correction factor to account for the notch length is proposed. Finally, the specimen properties affect the microstructural response of the specimen. As the one of the test parameter (thickness, notch length, loading rate, or air voids) is modified, the size of the FPZ changed

Tropical milkweed herbivore and predator dynamics in suburban South Texas

Tropical milkweed is commonly grown to conserve pollinators, but the presence of non-caterpillar herbivores may prompt treatment. Management is limited to non-chemical methods like biological control, but potential natural enemies have not been well studied in the Lower Rio Grande Valley (LRGV). We documented the arthropod community on tropical milkweed in garden and potted settings then analyzed associations between organisms. In the garden, oleander aphids and large milkweed bugs were the primary herbivores, overlapping on seedpods. Natural enemies (lady beetles, syrphid fly larvae, and aphid parasitoids) were positively associated with oleander aphids but not milkweed bugs. The arthropod community experienced similar associations but with reduced natural enemy abundance and richness on potted plants

Adenosine Thallium-201 Tomography in Evaluation of Graft Patency Late After Coronary Artery Bypass Graft Surgery

AbstractObjectives. We sought to ascertain the utility of adenosine thallium-201 tomography for assessing graft stenoses late after coronary artery bypass graft surgery.Background. Although pharmacologic perfusion imaging has been increasingly used in the assessment of patients with coronary artery disease, the value of this stress modality for detecting coronary artery bypass graft stenosis late after surgery is unknown.Methods. We studied 109 patients who underwent both adenosine thallium-201 tomography and coronary angiography at 6.7 ± 4.8 (mean ± SD) years after coronary artery bypass graft surgery. Adenosine thallium-201 tomography was assessed quantitatively by computer-generated polar maps of the myocardial thallium-201 activity.Results. On coronary angiography, significant graft stenoses were present in 68 patients, 65 of whom had a corresponding perfusion defect as shown by thallium-201 tomography (sensitivity 96%). Significant stenoses were present in 107 (37.8%) of 283 grafts. The overall specificity by quantitative tomography was 61%. Seventy percent of the apparently false positive perfusion defects could be explained on the basis of unbypassed native disease or by the presence of fixed defects in patients with previous myocardial infarction.Conclusions. Thus, results of adenosine thallium-201 tomography are nearly always abnormal in patients with late coronary graft stenosis. Most of the false positive defects appear to be due to either unbypassed native disease or a previous myocardial infarction.(J Am Coll Cardiol 1997;29:1290–5