Precision Synthesis of Silicon Nanowires with Crystalline Core and Amorphous Shell

A synthetic route to crystalline silicon (Si) nanowires with an amorphous Si shell is reported. Trisilane (Si3H8) and Sn(HMDS)(2) are decomposed in supercritical toluene at 450 degrees C. Sn(HMDS)(2) creates Sn nanoparticles that seed Si nanowire growth by the supercritical fluid-liquid-solid (SFLS) mechanism. The Si : Sn ratio in the reaction determines the growth of amorphous Si shell. No amorphous shell forms at relatively low Si : Sn ratios of 20 : 1, whereas higher Si : Sn ratio of 40 : 1 leads to significant amorphous shell. We propose that hydrogen evolved from trisilane decomposition etches away the Sn seed particles as nanowires grow, which promotes the amorphous Si shell deposition when the higher Si : Sn ratios are used.Robert A. Welch Foundation F-1464U.S. Department of Energy Office of Science, Office of Basic Energy Sciences DE-SC0001091National Defense Science and Engineering Graduate FellowshipChemistr

Operator bases, SS-matrices, and their partition functions

Relativistic quantum systems that admit scattering experiments are quantitatively described by effective field theories, where $S$-matrix kinematics and symmetry considerations are encoded in the operator spectrum of the EFT. In this paper we use the $S$-matrix to derive the structure of the EFT operator basis, providing complementary descriptions in (i) position space utilizing the conformal algebra and cohomology and (ii) momentum space via an algebraic formulation in terms of a ring of momenta with kinematics implemented as an ideal. These frameworks systematically handle redundancies associated with equations of motion (on-shell) and integration by parts (momentum conservation). We introduce a partition function, termed the Hilbert series, to enumerate the operator basis--correspondingly, the $S$-matrix--and derive a matrix integral expression to compute the Hilbert series. The expression is general, easily applied in any spacetime dimension, with arbitrary field content and (linearly realized) symmetries. In addition to counting, we discuss construction of the basis. Simple algorithms follow from the algebraic formulation in momentum space. We explicitly compute the basis for operators involving up to $n=5$ scalar fields. This construction universally applies to fields with spin, since the operator basis for scalars encodes the momentum dependence of $n$-point amplitudes. We discuss in detail the operator basis for non-linearly realized symmetries. In the presence of massless particles, there is freedom to impose additional structure on the $S$-matrix in the form of soft limits. The most na\"ive implementation for massless scalars leads to the operator basis for pions, which we confirm using the standard CCWZ formulation for non-linear realizations.Comment: 75 pages plus appendice

Electroproduction of Λ\Lambda(1405)

The electroproduction of $K^+ \Lambda$ (1405) was studied by analyzing the E1F data set collected in Hall B at Jefferson Lab. The analysis utilized the decay channel $\Sigma^+ \pi^-$ of the $\Lambda$ (1405) and $p \pi^0$ of the $\Sigma^+$. Simulations of background, $\Lambda$ (1405) and $\Lambda$ (1520) production according to PDG values were performed by using standard CLAS analysis tools adapted for the E1F run. Fits of the acceptance-corrected simulations were made to the acceptance-corrected data to determine contributions from signal and background processes. The line shape of $\Lambda$ (1405) varies with the four momentum transfer, $Q^2$, and does not match the line shape based on PDG resonance parameters. It corresponds approximately to predictions of a recent two-pole meson-baryon picture of this state.Comment: 4 pages, 6 figures, Contribution to the Proceedings of "NSTAR2011 - The 8th International Workshop on the Physics of Excited Nucleons," Thomas Jefferson National Accelerator Facility, Newport News, Virginia USA, 17-20 May 201

How to use the Standard Model effective field theory

We present a practical three-step procedure of using the Standard Model effective field theory (SM EFT) to connect ultraviolet (UV) models of new physics with weak scale precision observables. With this procedure, one can interpret precision measurements as constraints on a given UV model. We give a detailed explanation for calculating the effective action up to one-loop order in a manifestly gauge covariant fashion. This covariant derivative expansion method dramatically simplifies the process of matching a UV model with the SM EFT, and also makes available a universal formalism that is easy to use for a variety of UV models. A few general aspects of RG running effects and choosing operator bases are discussed. Finally, we provide mapping results between the bosonic sector of the SM EFT and a complete set of precision electroweak and Higgs observables to which present and near future experiments are sensitive. Many results and tools which should prove useful to those wishing to use the SM EFT are detailed in several appendices.Comment: 99 pages, 11 figures. V2: Typos corrected, references added. Fixed a link to Mathematica notebook for download. Substantial text changes for clarification with no change in results. In particular, sections 2.5, 3, and 5 received clarifying edits. Additionally, results from part of appendix A have been separated out to a new appendi

COMPETENCE ACQUISITION IN RETAIL FOOD: EFFICIENT CONSUMER RESPONSE AND ENVIRONMENTAL MANAGEMENT

Based on interviews with retail food store managers and a subsequent survey, this paper traces the pathways that spawn competence acquisition in the retail food industry. It finds that having an essential capability for learning, that is, obtaining new ideas, concepts, methods, tends to breed competencies in a number of areas which are of both business and social significance. In this study, the capacity of this essential capability to generate competencies in efficient consumer response (ECR) and environmental management (EM) are examined. These competencies have attracted the attention of the retail food industry in its efforts to become more competitive with alternative retail food channels. The results show that firms possessing the essential capability of generating new ideas are more likely to have higher sales per square foot. Ties with suppliers lead to higher sales per square foot through improved environmental practices and more consumer education. Technical assistance helps retail grocers acquire a social competence in environmental management.Agribusiness, Environmental Economics and Policy, Industrial Organization, Marketing,