Extension of Classical Nucleation Theory for Uniformly Sheared Systems

Nucleation is an out-of-equilibrium process, which can be strongly affected by the presence of external fields. In this letter, we report a simple extension of classical nucleation theory to systems submitted to an homogeneous shear flow. The theory involves accounting for the anisotropy of the critical nucleus formation, and introduces a shear rate dependent effective temperature. This extended theory is used to analyze the results of extensive molecular dynamics simulations, which explore a broad range of shear rates and undercoolings. At fixed temperature, a maximum in the nucleation rate is observed, when the relaxation time of the system is comparable to the inverse shear rate. In contrast to previous studies, our approach does not require a modification of the thermodynamic description, as the effect of shear is mainly embodied into a modification of the kinetic prefactor and of the temperature.Comment: 6 pages, 4 figure

Crystal nucleation and cluster-growth kinetics in a model glass under shear

Crystal nucleation and growth processes induced by an externally applied shear strain in a model metallic glass are studied by means of nonequilibrium molecular dynamics simulations, in a range of temperatures. We observe that the nucleation-growth process takes place after a transient, induction regime. The critical cluster size and the lag-time associated with this induction period are determined from a mean first-passage time analysis. The laws that describe the cluster growth process are studied as a function of temperature and strain rate. A theoretical model for crystallization kinetics that includes the time dependence for nucleation and cluster growth is developed within the framework of the Kolmogorov-Johnson-Mehl-Avrami scenario and is compared with the molecular dynamics data. Scalings for the cluster growth laws and for the crystallization kinetics are also proposed and tested. The observed nucleation rates are found to display a nonmonotonic strain rate dependency

Desulfovibrio alcoholovorans sp. nov., a sulfate-reducing bacterium able to grow on glycerol, 1,2- and 1,3-propanediol

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Assessment of Nitrogen Nutrition Status of Grasses under Water Deficit and Recovery

Grasslands are rarely irrigated. They are therefore systematically submitted to more or less severe water deficits: as well as mineral deficiencies, water scarcity often also results in a reduction of nitrogen (N) status. Although identified some time ago, qualitatively, the interaction with N still remains difficult to take into account in quantitative analyses of crop physiology under water deficits. This paper illustrates how the nitrogen (N) status of the crop changes under water deficits. A N nutrition index (INN) was defined as the ratio of the actual N concentration of forage with the theoretical N concentration under optimal conditions, the latter only depending on the above ground biomass. The objective of the paper is to describe the effect of water deficits on INN, using a new assay recently proposed by Faruggia et al. ( 2004)

Experimental Demonstration of A Dual-Input/Dual-Output Reflective Impedance Metasurface

This paper presents the experimental demonstration of a dual-input/dual-output reflective impedance metasurface. The design of the metasurface relies on the Method of Moments and leverages auxiliary surface waves to achieve anomalous reflection of two impinging plane waves with controlled sidelobe levels. The two beams are chosen independently compared to those in a conventional phase-gradient metasurface where the design presents a single slope to achieve a certain reflection and all other incident beams would depend on that slope. A prototype that ensures maximum directivity at two prescribed reflection angles for the two input waves is then fabricated on a Rogers RO3003 printed-circuit board using 42 metawires loaded with printed capacitors. The proposed metasurface is capable of reflecting an incident beam from $-20^\circ$ to $-55^\circ$ and a second from $+10^\circ$ to $50^\circ$ at 9.93 GHz. The metasurface is experimentally characterized and an illumination efficiency of at least 89% is calculated for each of the reflected waves, indicating a high multiplexing efficacy