1,878 research outputs found
Time-dependent embedding: surface electron emission
An embedding method for solving the time-dependent Schr\"odinger equation is
developed using the Dirac-Frenkel variational principle. Embedding allows the
time-evolution of the wavefunction to be calculated explicitly in a limited
region of space, the region of physical interest, the embedding potential
ensuring that the wavefunction satisfies the correct boundary conditions for
matching on to the rest of the system. This is applied to a study of the
excitation of electrons at a metal surface, represented by a one-dimensional
model potential for Cu(111). Time-dependent embedding potentials are derived
for replacing the bulk substrate, and the image potential and vacuum region
outside the surface, so that the calculation of electron excitation by a
surface perturbation can be restricted to the surface itself. The excitation of
the Shockley surface state and a continuum bulk state is studied, and the
time-structure of the resulting currents analysed. Non-linear effects and the
time taken for the current to arrive outside the surface are discussed. The
method shows a clear distinction between emission from the localized surface
state, where the charge is steadily depleted, and the extended continuum state
where the current emitted into the vacuum is compensated by current approaching
the surface from the bulk.Comment: 15 figure
Deformations of conformal theories and non-toric quiver gauge theories
We discuss several examples of non-toric quiver gauge theories dual to
Sasaki-Einstein manifolds with U(1)^2 or U(1) isometry. We give a general
method for constructing non-toric examples by adding relevant deformations to
the toric case. For all examples, we are able to make a complete comparison
between the prediction for R-charges based on geometry and on quantum field
theory. We also give a general discussion of the spectrum of conformal
dimensions for mesonic and baryonic operators for a generic quiver theory; in
the toric case we make an explicit comparison between R-charges of mesons and
baryons.Comment: 51 pages, 12 figures; minor corrections in appendix B, published
versio
A-D-E Quivers and Baryonic Operators
We study baryonic operators of the gauge theory on multiple D3-branes at the
tip of the conifold orbifolded by a discrete subgroup Gamma of SU(2). The
string theory analysis predicts that the number and the order of the fixed
points of Gamma acting on S^2 are directly reflected in the spectrum of
baryonic operators on the corresponding quiver gauge theory constructed from
two Dynkin diagrams of the corresponding type. We confirm the prediction by
developing techniques to enumerate baryonic operators of the quiver gauge
theory which includes the gauge groups with different ranks. We also find that
the Seiberg dualities act on the baryonic operators in a non-Abelian fashion.Comment: 46 pages, 17 figures; v2: minor corrections, note added in section 1,
references adde
Comments on Anomalies and Charges of Toric-Quiver Duals
We obtain a simple expression for the triangle `t Hooft anomalies in quiver
gauge theories that are dual to toric Sasaki-Einstein manifolds. We utilize the
result and simplify considerably the proof concerning the equivalence of
a-maximization and Z-minimization. We also resolve the ambiguity in defining
the flavor charges in quiver gauge theories. We then compare coefficients of
the triangle anomalies with coefficients of the current-current correlators and
find perfect agreement.Comment: 22 pages, 3 figure
Hilbert Series for Flavor Invariants of the Standard Model
The Hilbert series is computed for the lepton flavor invariants of the
Standard Model with three generations including the right-handed neutrino
sector needed to generate light neutrino masses via the see-saw mechanism. We
also compute the Hilbert series of the quark flavor invariants for the case of
four generations.Comment: 6 page
Comparison between continuous grazing and rotational grazing on roller chopped rangeland in central-west of La Pampa province
El control de la vegetación leñosa y la planificación posterior del pastoreo contribuirían a aumentar la oferta forrajera y la producción ganadera en pastizales del centro-oeste de la Provincia de La Pampa. El objetivo del presente trabajo fue comparar la dinámica de la vegetación y la respuesta animal en un pastizal rolado sometido a pastoreo continuo o pastoreo rotativo. La mitad de un área rolada de 200 ha se pastoreo en forma continua con terneros de recría, mientras que la restante mitad se pastoreo en forma rotativa mediante la subdivisión en cuatro parcelas de igual tamaño. Durante cuatro años consecutivos se realizaron mediciones sobre la vegetación (herbácea y leñosa) y sobre los animales. En el periodo de mediciones las lluvias fueron similares o superaron (hasta en un 33%) el promedio anual histórico. Los tratamientos de pastoreo (continuo y rotativo) no afectaron en forma diferencial la densidad de las gramíneas perennes palatables ni la cobertura de la vegetación leñosa, mientras que la disponibilidad de MS total promedio de las gramíneas perennes palatables fue mayor bajo pastoreo rotativo. La ganancia diaria de peso promedio de los animales en recría fue mayor bajo pastoreo continuo en tres de los cuatro años de medición. En el contexto del presente estudio no se expresó el potencial esperado del pastoreo rotativo, lo cual se interpreta en relación a las lluvias y a una potencial desmejora de la calidad del forraje consumido por los animales.Woody vegetation control and further grazing planning would contribute to increase forage availability and livestock production in rangelands of central-west La Pampa Province. The objective of present study was to compare vegetation dynamics and animal response in a roller chopped rangeland under continuous or rotational grazing. Half of a roller chopped area of 200 ha was continuously grazed with stocker cattle, whereas the other half was rotationally grazed through its subdivision in four parcels of equal size. Vegetation (herbaceous, woody) and animal responses were measured along a period of four consecutive years. During the study period rainfall was similar or above (up to 33%) the long-term annual average. Grazing treatments (continuous, rotational) did not differentially affect either density of palatable perennial grasses or woody vegetation cover, whereas total average DM availability of palatable perennial grasses was higher under rotational grazing. Average daily gain of stockers was higher under continuous grazing on three out of the four years of measurements. The expected potential of rotation grazing was not expressed under the context of present study, which is interpreted in relation to rainfall conditions and a potential deterioration in forage quality ingested by animals.Fil: Adema, E. O.. Instituto Nacional de Tecnología Agropecuaria. Centro Regional La Pampa-San Luis. Estación Experimental Agropecuaria Anguil; ArgentinaFil: Butti, L. R.. Instituto Nacional de Tecnología Agropecuaria. Centro Regional La Pampa-San Luis. Estación Experimental Agropecuaria Anguil; ArgentinaFil: Babinec, Francisco José. Instituto Nacional de Tecnología Agropecuaria. Centro Regional La Pampa-San Luis. Estación Experimental Agropecuaria Anguil; Argentina. Universidad Nacional de La Pampa. Facultad de Agronomía; ArgentinaFil: Distel, Roberto Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiarida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiarida; Argentin
Characterization and modeling of CMOS-compatible acoustical particle velocity sensors for applications requiring low supply voltages
Acoustic particle velocity sensors have been obtained applying simple low resolution micromachining steps to chips fabricated using a standard microelectronic process. Each sensor consists of four silicided polysilicon wires, suspended over cavities etched into the substrate, and connected to form a heatstone bridge. Full compatibility of the micromachining procedure with the original process is demonstrated by integrating a simple pre-amplifier on the same chip as the sensors and showing that both blocks are functional. Proper design of the sensing structures allows them to operate with a single 3.3 V power supply. Sensitivity and noise measurements, performed to estimate the sensor detection limit, are described. Excess noise with a flicker-like behavior, not ascribable to the amplifier, is found when the bridges are biased in working conditions. In addition, the dependence of the sensitivity on the dc bias voltage of the bridges is investigated, comparing the experimental data with the results of a simple analytical model and finite element method simulations
New Einstein-Sasaki and Einstein Spaces from Kerr-de Sitter
In this paper, which is an elaboration of our results in hep-th/0504225, we
construct new Einstein-Sasaki spaces L^{p,q,r_1,...,r_{n-1}} in all odd
dimensions D=2n+1\ge 5. They arise by taking certain BPS limits of the
Euclideanised Kerr-de Sitter metrics. This yields local Einstein-Sasaki metrics
of cohomogeneity n, with toric U(1)^{n+1} principal orbits, and n real
non-trivial parameters. By studying the structure of the degenerate orbits we
show that for appropriate choices of the parameters, characterised by the (n+1)
coprime integers (p,q,r_1,...,r_{n-1}), the local metrics extend smoothly onto
complete and non-singular compact Einstein-Sasaki manifolds
L^{p,q,r_1,...,r_{n-1}}. We also construct new complete and non-singular
compact Einstein spaces \Lambda^{p,q,r_1,...,r_n} in D=2n+1 that are not
Sasakian, by choosing parameters appropriately in the Euclideanised Kerr-de
Sitter metrics when no BPS limit is taken.Comment: latex, 26 page
Type IIB Flows with N=1 Supersymmetry
We write general and explicit equations which solve the supersymmetry
transformations with two arbitrary complex-proportional Weyl spinors on
supersymmetric type IIB strings backgrounds with all R-R ,
, and NS-NS fluxes turned on using SU(3) structures. The
equations are generalizations of the ones found for specific relations between
the two spinors by Grana, Minasian, Petrini and Tomasiello in [1] and by Butti,
Grana, Minasian, Petrini and Zaffaroni in [2]. The general equations allow to
study systematically generic type IIB backgrounds with
supersymmetry. We then explore some specific classes of flows with constant
axion, flows with constant dilaton, flows on conformally Calabi-Yau
backgrounds, flows with imaginary self-dual 3-form flux, flows with constant
ratio of the two spinors, the corresponding equations are written down and some
of their features and relations are discussed.Comment: 28 page
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