On the growth of ammonium nitrate(III) crystals

The growth rate of NH4NO3 phase III crystals is measured and interpreted using two models. The first is a standard crystal growth model based on a spiral growth mechanism, the second outlines the concept of kinetical roughening. As the crystal becomes rough a critical supersaturation can be determined and from this the step free energy. The step free energy versus temperature turns out to be well represented by a Kosterlitz¿Thouless type model. Further a phenomenological treatment of some peculiar growth observations is given

From wave function to crystal morphology: application to urea and alpha-glycine

In this paper the relation between the molecular electron density distribution and the crystal growth morphology is investigated. Accurate charge densities derived from ab initio quantum chemical calculations were partitioned into multipole moments, to calculate the electrostatic contribution to the intermolecular interaction energy. For urea and alpha-glycine the F-faces or connected nets were determined according to the Hartman-Perdok PBC theory. From attachment energy and critical Ising temperature calculations, theoretical growth forms were constructed using different atom-atom potential models. These were compared to the Donnay-Harker model, equilibrium form and experimental growth forms. In the case of alpha-glycine, the theoretical growth forms are in good agreement with crystals grown from aqueous solution. Crystals obtained by sublimation seem to show some faces which are not F-faces sensu stricto

Evaporation and growth of crystals - propagation of step density compression waves at vicinal surfaces

We studied the step dynamics during crystal sublimation and growth in the limit of fast surface diffusion and slow kinetics of atom attachment-detachment at the steps. For this limit we formulate a model free of the quasi-static approximation in the calculation of the adatom concentration on the terraces at the crystal surface. Such a model provides a relatively simple way to study the linear stability of a step train in a presence of step-step repulsion and an absence of destabilizing factors (as Schwoebel effect, surface electromigration etc.). The central result is that a critical velocity of the steps in the train exists which separates the stability and instability regimes. When the step velocity exceeds its critical value the plot of these trajectories manifests clear space and time periodicity (step density compression waves propagate on the vicinal surface). This ordered motion of the steps is preceded by a relatively short transition period of disordered step dynamics.Comment: 18 pages, 6 figure

First records of the sponge crab Dromia personata (Brachyura) in the Netherlands and its historical findings in the North Sea

Only a few records exist of the sponge crab Dromia personata in the North Sea. Most records are in local languages, and have limited availability. On 11 August 2016, D. personata was found by divers in the Eastern Scheldt, a former estuary in the south-western part of the Netherlands. In the months to follow, at least four other individuals were observed by divers at the same and nearby locations. This paper lists these and former records in the North Sea. The distribution pattern, and the possible migration of the sponge crab in relation to environmental conditions such as seawater temperature are discussed, as well as the crab's use of the non-native sponge Celtodoryx ciocalyptoides.</p

On the morphology of ammonium nitrate (III): theory and observation

The aim of this paper is to derive on a theoretical basis the morphology of crystals of ammonium nitrate, phase III, and to compare the results with experimental growth forms. The theory used is based on the concepts of periodic bond chain (PBC), F face and connected net, developed by Hartman and Perdok. Further an Ising model is used to determine roughening temperatures. Based on different criteria theoretical growth forms are predicted and compared with experiments

Optimized Trigger for Ultra-High-Energy Cosmic-Ray and Neutrino Observations with the Low Frequency Radio Array

When an ultra-high energy neutrino or cosmic ray strikes the Lunar surface a radio-frequency pulse is emitted. We plan to use the LOFAR radio telescope to detect these pulses. In this work we propose an efficient trigger implementation for LOFAR optimized for the observation of short radio pulses.Comment: Submitted to Nuclear Instruments and Methods in Physics Research Section

Levantamento de reconhecimento dos solos da região sob influência do Reservatório de Furnas: (contribuição à Carta de Solos do Brasil).

Formacao geologica e material originario; Relevo; Clima; Vegetacao; Relacao entre solos e estado de intemperismo de seus constituintes; Metodos de trabalho de campo; Metodos de trabalho de escritorio; Metodos de trabalho de laboratorio; Podzolico vermelho-amarelo fase floresta tropical sempre-verde; Podzolico vermelho-amarelo fase floresta tropical semi-caducifolia; Podzolico vermelho-amarelo variacao rasa cascalhenta; Mediterranico vermelho-amarelo; Terra roxa estruturada; Latosol vermelho escuro fase floresta tropical sempre-verde; Latosol vermelho escuro fase cerrado; Latosol vermelho escuro humico fase floresta tropical sempre-verde; Latosol vermelho escuro humico fase cerrado; Latosol vermelho-amarelo fase floresta tropical sempre-verde; Latosol vermelho-amarelo fase transicao floresta-cerrado; Solos bruno acidos; Solos podzolizados de Alpinopolis; Solos hidromorficos; Low-Humic glei; Solos organicos; Solos aluviais; Litosol fase substrato argilito; Litosol fase substrato filito-xisto; Litosol fase substrato gnaisse; Litosol fase substrato metaquartzito;Podzol humico; Afloramentos de rocha; Associacao podzolico vermelho-amarelo fase floresta tropical sempre-verde-litosol fase substrato gnaisse; Associacao solos brunos acidos (similar)-litosol fase substrato metaquartzito-litosol fase substrato xisto; Associacao podzol humico-litosol fase substrato metaquartzito-litosol fase substrato xisto; Grupamento nao discriminado de solos hidromorficos e solos aluviais.Acompanha 1 mapa, color. Escala 1:250.000