Long-Lived Non-Equilibrium Interstitial-Solid-Solutions in Binary Mixtures

We perform particle resolved experimental studies on the heterogeneous crystallisation process of two compo- nent mixtures of hard spheres. The components have a size ratio of 0.39. We compared these with molecular dynamics simulations of homogenous nucleation. We find for both experiments and simulations that the final assemblies are interstitial solid solutions, where the large particles form crystalline close-packed lattices, whereas the small particles occupy random interstitial sites. This interstitial solution resembles that found at equilibrium when the size ratios are 0.3 [Filion et al., Phys. Rev. Lett. 107, 168302 (2011)] and 0.4 [Filion, PhD Thesis, Utrecht University (2011)]. However, unlike these previous studies, for our system sim- ulations showed that the small particles are trapped in the octahedral holes of the ordered structure formed by the large particles, leading to long-lived non-equilibrium structures in the time scales studied and not the equilibrium interstitial solutions found earlier. Interestingly, the percentage of small particles in the crystal formed by the large ones rapidly reaches a maximum of around 14% for most of the packing fractions tested, unlike previous predictions where the occupancy of the interstitial sites increases with the system concentration. Finally, no further hopping of the small particles was observed

Continuum variational and diffusion quantum Monte Carlo calculations

This topical review describes the methodology of continuum variational and diffusion quantum Monte Carlo calculations. These stochastic methods are based on many-body wave functions and are capable of achieving very high accuracy. The algorithms are intrinsically parallel and well-suited to petascale computers, and the computational cost scales as a polynomial of the number of particles. A guide to the systems and topics which have been investigated using these methods is given. The bulk of the article is devoted to an overview of the basic quantum Monte Carlo methods, the forms and optimisation of wave functions, performing calculations within periodic boundary conditions, using pseudopotentials, excited-state calculations, sources of calculational inaccuracy, and calculating energy differences and forces

Why metallic surfaces with grooves a few nanometers deep and wide may strongly absorb visible light

It is theoretically shown that nanometric silver lamellar gratings present very strong visible light absorption inside the grooves, leading to electric field intensities by several orders of magnitude larger than that of the impinging light. This effect, due to the excitation of long wave vector surface plasmon polaritons with particular small penetration depth in the metal, may explain the abnormal optical absorption observed a long time ago on almost flat Ag films. Surface enhanced Raman scattering in rough metallic films could also be due to the excitation of such plasmon polaritons in the grain boundaries or notches of the films.Comment: 5 pages, 5 figure, submitted to Phys. Rev. Let

Quantum Monte Carlo study of a positron in an electron gas

Quantum Monte Carlo calculations of the relaxation energy, pair-correlation function, and annihilating-pair momentum density are presented for a positron immersed in a homogeneous electron gas. We find smaller relaxation energies and contact pair-correlation functions in the important low-density regime than predicted by earlier studies. Our annihilating-pair momentum densities have almost zero weight above the Fermi momentum due to the cancellation of electron-electron and electron-positron correlation effects

Sustainable management in pecan cultivation in Argentina

243-248Pecan nut "Carya illinoinensis" is native from central and western U.S.A. and arrived in Argentina in the nineteenth century. The difference with other nuts is that it presents an 80 percent oil composition, with polyunsaturated fatty acids omega 3 and 6 that help to reduce cholesterol and also prevent the risk of cardiovascular disease. It contains an antioxidant: vitamin E, and has a high content of fibre that helps to prevent colon cancer. Reduces bad cholesterol, helps keep blood pressure low and is recommended especially for patients with cancer and cardiac problems. A pecan sustainable farming system intends to be productive but at the same time, to preserve enviromental quality, favouring the use of biological practices over chemical inputs. Surface application of compost to pecan trees, is a common practice in organic orcharding. The objectives of the work were to compare compost and vermicompost with liquid fertilizer and a control without fertilization in a completely random block design with four replications, in a one-year crop with a planting frame of 8m x 8m. The application of organic amendments produced statistically significant changes in soil properties with reference to inorganic fertilizer, especially in the total carbon, microbial biomass carbon and phosphorus. Compost and vermicompost treatments produced statistically significant increases in factors related to production as tree height and diameter

Framework for constructing generic Jastrow correlation factors

We have developed a flexible framework for constructing Jastrow factors which allows for the introduction of terms involving arbitrary numbers of particles. The use of various three- and four-body Jastrow terms in quantum Monte Carlo calculations is investigated, including a four-body van der Waals-like term, and anisotropic terms. We have tested these Jastrow factors on one- and two-dimensional homogeneous electron gases, the Be, B, and O atoms, and the BeH, H$_2$O, N$_2$, and H$_2$ molecules. Our optimized Jastrow factors retrieve more than 90% of the fixed-node diffusion Monte Carlo correlation energy in variational Monte Carlo for each system studied.Comment: 17 pages, 4 figure

Intrinsic point defects and volume swelling in ZrSiO4 under irradiation

The effects of high concentration of point defects in crystalline ZrSiO4 as originated by exposure to radiation, have been simulated using first principles density functional calculations. Structural relaxation and vibrational studies were performed for a catalogue of intrinsic point defects, with different charge states and concentrations. The experimental evidence of a large anisotropic volume swelling in natural and artificially irradiated samples is used to select the subset of defects that give similar lattice swelling for the concentrations studied, namely interstitials of O and Si, and the anti-site Zr(Si), Calculated vibrational spectra for the interstitials show additional evidence for the presence of high concentrations of some of these defects in irradiated zircon.Comment: 9 pages, 7 (color) figure

Efecto de la lactancia reducida sobre la performance reproductiva en vaquillonas de primera parición

Con el fin de evaluar el efecto de la lactancia reducida (60 días) sobre la performance reproductiva en vaquilIonas de primera parición a los 2 años de edad producto de un entore precoz (a los 15 meses de edad), se realizó en el Campo de Enseñanza de la Facultad de Agronomía de la Universidad Nacional de La Pampa un ensayo entre el 05 de octubre de 1993 y el 31 de diciembre de 1995. Se utilizaron 30 vaquillonas Abeerden Angus entoradas en el primer servicio con un toro F l Jersey por Abeerden Angus, se agruparon al azar en dos lotes luego del tacto a los cuales se les aplicó 2 duraciones distintas de lactancia: 60 y 210 días. Los parámetros evaluados fueron: porcentaje de preñez, evolución del peso vivo, condición corporal e intervalo parto-concepción. Se encontraron diferencias altamente significativas en el porcentaje de preñez, en la evolución del peso vivo y en la condición corporal, y no se encontraron diferencias en el intervalo parto-concepción. Los resultados obtenidos indican que la aplicación de la técnica de destete precoz en vaquillonas de primera parición a los 2 años de edad y que deben recibir su segundo servicio usando pasto llorón como recurso forrajero, tiene un claro efecto mejorador sobre la performance reproductiva.Director: lng. Agr. Gustavo D. Fernández e Ing. Agr. Abel E. Zuccari. Cátedra de Zootecnia Especial I

O mercado da tilápia - 1° trimestre de 2016.

Comportamento do mercado de varejo nacional. Evolução dos preços. O setor externo.bitstream/item/142435/1/CNPASA-2016-mt.pd