Volunteer Management Practices and Retention of Volunteers

This report is the second in a series of briefs on a 2003 survey of volunteer management capacity among public charities in the United States. It focuses on charities' adoption of nine volunteer management practices: supervision and communication, liability coverage, screening and matching, regular collection of volunteer numbers and hours written policies and job descriptions, recognition activities, measurement of volunteer impacts, training and professional development, and training for paid staff in working with volunteers. We report on the extent of adoption of these practices by charities with different characteristics, and the relationship between volunteer management practices and retention of volunteers

Equilibrium Bundle Size of Rodlike Polyelectrolytes with Counterion-Induced Attractive Interactions

Multivalent counterions can induce an effective attraction between like-charged rodlike polyelectrolytes, leading to the formation of polelectrolyte bundles. In this paper, we calculate the equilibrium bundle size using a simple model in which the attraction between polyelectrolytes (assumed to be pairwise additive) is treated phenomenologically. If the counterions are point-like, they almost completely neutralize the charge of the bundle, and the equilibrium bundle size diverges. When the counterions are large, however, steric and short-range electrostatic interactions prevent charge neutralization of the bundle, thus forcing the equilibrium bundle size to be finite. We also consider the possibility that increasing the number of nearest neighbors for each rod in the bundle frustrates the attractive interaction between the rods. Such a frustration leads to the formation of finite size bundles as well, even when the counterions are small.Comment: 4 pages, 2 figures; v2: typos corrected, references added, minor changes made to conten

Extended interface states enhance valley splitting in Si/SiO2

Interface disorder and its effect on the valley degeneracy of the conduction band edge remains among the greatest theoretical challenges for understanding the operation of spin qubits in silicon. Here, we investigate a counterintuitive effect occurring at Si/SiO2 interfaces. By applying tight binding methods, we show that intrinsic interface states can hybridize with conventional valley states, leading to a large ground state energy gap. The effects of hybridization have not previously been explored in details for valley splitting. We find that valley splitting is enhanced in the presence of disordered chemical bonds, in agreement with recent experiments.Comment: 4 pages, 4 figure

Extended interface states enhance valley splitting in Si/SiO2

Interface disorder and its effect on the valley degeneracy of the conduction band edge remains among the greatest theoretical challenges for understanding the operation of spin qubits in silicon. Here, we investigate a counterintuitive effect occurring at Si/SiO2 interfaces. By applying tight binding methods, we show that intrinsic interface states can hybridize with conventional valley states, leading to a large ground state energy gap. The effects of hybridization have not previously been explored in details for valley splitting. We find that valley splitting is enhanced in the presence of disordered chemical bonds, in agreement with recent experiments.Comment: 4 pages, 4 figure

Electromagnetic energy transport along arrays of closely spaced metal rods as an analogue to plasmonic devices

The transport of electromagnetic energy along structures consisting of arrays of closely spaced metal rods (spacing = 0.2 cm) was investigated in the microwave regime at 8.0 GHz (lambda= 3.7 cm). The dispersion relation shows that information transport occurs at a group velocity of 0.6c. The electromagnetic energy is highly confined to the arrays (90% within a distance of 0.05lambda from the array). The propagation loss in a straight array is 3 dB/8 cm. Routing of energy around 90° corners is possible with a power loss of 3–4 dB. Analogies to plasmon wires consisting of arrays of nm-size metal clusters are discussed

Models for quantitative charge imaging by atomic force microscopy

Two models are presented for quantitative charge imaging with an atomic-force microscope. The first is appropriate for noncontact mode and the second for intermittent contact (tapping) mode imaging. Different forms for the contact force are used to demonstrate that quantitative charge imaging is possible without precise knowledge of the contact interaction. From the models, estimates of the best charge sensitivity of an unbiased standard atomic-force microscope cantilever are found to be on the order of a few electrons