Collectivity in the optical response of small metal clusters

The question whether the linear absorption spectra of metal clusters can be interpreted as density oscillations (collective ``plasmons'') or can only be understood as transitions between distinct molecular states is still a matter of debate for clusters with only a few electrons. We calculate the photoabsorption spectra of Na2 and Na5+ comparing two different methods: quantum fluid-dynamics and time-dependent density functional theory. The changes in the electronic structure associated with particular excitations are visualized in ``snapshots'' via transition densities. Our analysis shows that even for the smallest clusters, the observed excitations can be interpreted as intuitively understandable density oscillations. For Na5+, the importance of self-interaction corrections to the adiabatic local density approximation is demonstrated.Comment: 6 pages, 3 figures. To appear in special issue of Applied Physics B, "Optical properties of Nanoparticles

Operational Model of the Alliance for Grassland Renewal

Novel endophyte tall fescue was developed over 20 years ago, and novel endophyte cultivars are among the most innovative cultivars developed in recent decades. Yet adoption of novel endophyte technology is slow. In order to expedite adoption, a diverse group of stakeholders self assembled as the Alliance for Grassland Renewal, a nonprofit organization that includes colleagues from the sectors of industry, university, government, and production. Since 2012, the Alliance has held workshops for producers, educators, and industry across the southeastern US, where tall fescue is the predominant pasture grass. Also since 2012, the Alliance has monitored and reported endophyte purity and viability in novel endophyte cultivars. Activities of the Alliance are self-funded according to a fee structure developed by its Board of Directors. At present, the Alliance has expanded to include seven land-grant universities and seven private companies, along with partners in the federal government, livestock production, and nonprofit organization

Time resolved fission in metal clusters

We explore from a theoretical point of view pump and probe (P&P) analysis for fission of metal clusters where probe pulses are generalized to allow for scanning various frequencies. We show that it is possible to measure the time the system needs to develop to scission. This is achieved by a proper choice of both delay and frequency of the probe pulse. A more detailed analysis even allows to access the various intermediate stages of the fission process.Comment: 4 pages, 4 figure

Dynamics of metal clusters in rare gas clusters

We investigate the dynamics of Na clusters embedded in Ar matrices. We use a hierarchical approach, accounting microscopically for the cluster's degrees of freedom and more coarsely for the matrix. The dynamical polarizability of the Ar atoms and the strong Pauli-repulsion exerted by the Ar-electrons are taken into account. We discuss the impact of the matrix on the cluster gross properties and on its optical response. We then consider a realistic case of irradiation by a moderately intense laser and discuss the impact of the matrix on the hindrance of the explosion, as well as a possible pump probe scenario for analyzing dynamical responses.Comment: Proceedings of the 30th International Workshop on Condensed Matter Theories, Dresden, June 05 - 10, 2006, World Scientific. 3 figure

Contrasting levels of fructose and urea added to an annual ryegrass based diet: effects on microbial protein synthesis, nutrient digestibility and fermentation parameters in continuous culture fermenters

El objetivo de este experimento fue evaluar los efectos de la adición de fructosa cristalina y urea a una dieta basada en raigrás anual sobre la síntesis de proteína microbiana, la fermentación y la digestibilidad de los nutrientes, usando fermentadores de flujo continuo. Se usaron seis fermentadores de flujo continuo en un arreglo factorial 3x2, con tres niveles de hidratos de carbono solubles (WSC) obtenidos por la adición de fructosa cristalina (21, 24 y 27 g.100 g MS1; LWSC, MWSC y HWSC, respectivamente) y dos niveles de proteína bruta (CP) obtenidos por la adición de urea (14,6 y 18,6 g.100 g MS1, LCP y HCP, respectivamente). Se corrieron sucesivamente cuatro períodos de 10d (7d para adaptación, 3d para muestreo). La síntesis de proteína microbiana se estimó por la relación purinas: N. Hubo una interacción significativa entre niveles de WSC y CP para síntesis de proteína microbiana (P<0,001). El nivel de WSC no afectó el pH, la concentración de amonio ni la concentración de ácidos grasos volátiles (VFA). Niveles más altos de CP aumentaron la proporción de ácido acético y tendieron a aumentar la relación acético propiónico, mientras que el nivel de WSC no afectó las proporciones de VFA. Los tratamientos no afectaron la digestibilidad de los nutrientes. Concluimos que la adición de fructosa cristalina a dietas basadas en raigrás anual aumentó la síntesis de proteína microbiana a los niveles más altos de CP en la dieta.The objective of this experiment was to evaluate the effects of the addition of crystalline fructose and urea to an annual ryegrassbased diet on microbial protein synthesis, fermentation profile and nutrient apparent digestibility, using continuous culture fermenters. Six fermenters were used in a 3 x 2 factorial arrangement with three levels of water soluble carbohydrates (WSC) obtained by crystalline fructose addition (21, 24 and 27 g.100 g DM1; LWSC, MWSC and HWSC, respectively) and two levels of CP obtained by urea addition (14.6 and 18.6 g.100 g DM1, LCP and HCP, respectively). Four 10d periods were ran sequentially (7d for adaptation, 3d for sampling). Microbial protein synthesis was assessed by purine to N ratio. There was a positive interaction between WSC and CP level on microbial protein synthesis (P<0.001). Water soluble carbohydrate level did not affect fermentation pH, ammonia concentration or total volatile fatty acids concentration (VFA). Greater CP levels also increased acetic acid proportion and tended to increase acetic to propionic acid ratio, whereas WSC level did not affect VFA proportions. Treatments did not affect nutrient digestibility. We conclude that the addition of crystalline fructose to annual ryegrass samples increased microbial protein synthesis at the greater levels of CP in diet

Use of anabolic implants in calves to increase weaning weight and backgrounding gains

The main component of the beef industry in South Carolina is cow/calf operations. Recent advances in implant technology are being utilized to help these producers increase weights at time of sale to feedlots. The objective of this study was to determine how the use of anabolic implants in steer calves at 4 mo of age and at weaning altered weight gain at two different farm locations in South Carolina. Steers ( year 1; n= 161, year 2 n=116) from Edisto REC and Simpson REC were randomly allotted into two treatment groups: 1) no implant or 2) implant at 4 mo of age plus implant at weaning. Weights were obtained at implanting, weaning, and the end of backgrounding. Real-time ultrasound measurements of the ribeye area and fat thickness were collected at the end of the backgrounding period. Data were analyzed with the treatment, location, year, and the interaction in the model. Implanting the steers increased (P\u3c0.001) average daily gains from implanting to weaning, weaning to the end of the backgrounding, and overall by 0.36, 0.15, 0.25 lb/hd/d respectively. Implanting also increased ribeye area by 0.34 in2. Weight and gains of the steers differed by location and year but there were no interactions between location, year, and implant treatment. The use of anabolic implants in steer calves at 4 mo of age and then again at weaning helped to increase weight gain, other desirable carcass traits and produced heavier steers for marketing

Use of anabolic implants in calves to increase weaning weight and backgrounding gains

The main component of the beef industry in South Carolina is cow/calf operations. Recent advances in implant technology are being utilized to help these producers increase weights at time of sale to feedlots. The objective of this study was to determine how the use of anabolic implants in steer calves at 4 mo of age and at weaning altered weight gain at two different farm locations in South Carolina. Steers ( year 1; n= 161, year 2 n=116) from Edisto REC and Simpson REC were randomly allotted into two treatment groups: 1) no implant or 2) implant at 4 mo of age plus implant at weaning. Weights were obtained at implanting, weaning, and the end of backgrounding. Real-time ultrasound measurements of the ribeye area and fat thickness were collected at the end of the backgrounding period. Data were analyzed with the treatment, location, year, and the interaction in the model. Implanting the steers increased (P\u3c0.001) average daily gains from implanting to weaning, weaning to the end of the backgrounding, and overall by 0.36, 0.15, 0.25 lb/hd/d respectively. Implanting also increased ribeye area by 0.34 in2. Weight and gains of the steers differed by location and year but there were no interactions between location, year, and implant treatment. The use of anabolic implants in steer calves at 4 mo of age and then again at weaning helped to increase weight gain, other desirable carcass traits and produced heavier steers for marketing

Nano-optical concept design for light management

Efficient light management in optoelectronic devices requires nanosystems where high optical qualities coincide with suitable device integration. The requirement of chemical and electrical passivation for integrating nanostrutures in e.g. thin film solar cells points towards the use of insulating and stable dielectric material, which however has to provide high scattering and near-fields as well. We investigate metal@dielectric core-shell nanoparticles and dielectric nanorods. Whereas core-shell nanoparticles can be simulated using Mie theory, nanorods of finite length are studied with the finite element method. We reveal that a metallic core within a thin dielectric shell can help to enhance scattering and near-field cross sections compared to a bare dielectric nanoparticle of the same radius. A dielectric nanorod has the benefit over a dielectric nanosphere in that it can generate much higher scattering cross sections and also give rise to a high near-field enhancement along its whole length. Electrical benefits of e.g. Ag@oxide nanoparticles in thin-film solar cells and ZnO nanorods in hybrid devices lie in reduction of recombination centers or close contact of the nanorod material with the surrounding organics, respectively. The optical benefit of dielectric shell material and elongated dielectric nanostructures is highlighted in this paper

Hindered Coulomb explosion of embedded Na clusters -- stopping, shape dynamics and energy transport

We investigate the dynamical evolution of a Na$_8$ cluster embedded in Ar matrices of various sizes from N=30 to 1048. The system is excited by an intense short laser pulse leading to high ionization stages. We analyze the subsequent highly non-linear motion of cluster and Ar environment in terms of trajectories, shapes, and energy flow. The most prominent effects are: temporary stabilization of high charge states for several ps, sudden stopping of the Coulomb explosion of the embedded Na$_8$ clusters associated with an extremely fast energy transfer to the Ar matrix, fast distribution of energy throughout the Ar layers by a sound wave. Other ionic-atomic transfer and relaxation processes proceed at slower scale of few ps. The electron cloud is almost thermally decoupled from ions and thermalizes far beyond the ps scale.Comment: 12 pages, 10 figures, accepted in Euro. Phys. J.

Non-local Thermodynamic Equilibrium Stellar Spectroscopy with 1D and 〈3D〉 Models. II. Chemical Properties of the Galactic Metal-poor Disk and the Halo

From exploratory studies and theoretical expectations it is known that simplifying approximations in spectroscopic analysis (local thermodynamic equilibrium (LTE), 1D) lead to systematic biases of stellar parameters and abundances. These biases depend strongly on surface gravity, temperature and, in particular, for LTE versus non-LTE (NLTE), on metallicity of the stars. Here we analyze the [Mg/Fe] and [Fe/H] plane of a sample of 326 stars, comparing LTE and NLTE results obtained using 1D hydrostatic models and averaged $\langle 3{\rm{D}}\rangle$ models. We show that compared to the $\langle 3{\rm{D}}\rangle$ NLTE benchmark, the other three methods display increasing biases toward lower metallicities, resulting in false trends of [Mg/Fe] against [Fe/H], which have profound implications for interpretations by chemical evolution models. In our best $\langle 3{\rm{D}}\rangle$ NLTE model, the halo and disk stars show a clearer behavior in the [Mg/Fe]–[Fe/H] plane, from the knee in abundance space down to the lowest metallicities. Our sample has a large fraction of thick disk stars and this population extends down to at least [Fe/H] ~ −1.6 dex, further than previously proven. The thick disk stars display a constant [Mg/Fe] ≈ 0.3 dex, with a small intrinsic dispersion in [Mg/Fe] that suggests that a fast SN Ia channel is not relevant for the disk formation. The halo stars reach higher [Mg/Fe] ratios and display a net trend of [Mg/Fe] at low metallicities, paired with a large dispersion in [Mg/Fe]. These indicate the diverse origin of halo stars from accreted low-mass systems to stochastic/inhomogeneous chemical evolution in the Galactic halo