Tailoring the carrier mobility of semiconducting nanowires by remote dielectrics

The dielectric environment of thin semiconductor nanowires can affect the charge transport properties inside the wire. In this work, it is shown that Coulomb impurity scattering inside thin nanowires can be damped strongly by coating the wire with a high-k dielectric. This will lead to an increase in the mobility of free charges inside the wire.Comment: 4 pages, 3 figure

Who Benefits from New Medical Technologies? Estimates of Consumer and Producer Surpluses for HIV/AIDS Drugs

The social value of an innovation is comprised of the value to consumers and the value to innovators. We estimate that for the HIV/AIDS therapies that entered the market from the late 1980's onwards, innovators appropriated only 5% of the social surplus arising from these new technologies. Despite the high annual costs of these drugs to patients, the low share of social surplus going to innovators raises concerns about advocating cost-effectiveness criteria that would further reduce this share, and hence further reduce incentives for innovation.

Surplus Appropriation from R&D and Health Care Technology Assessment Procedures

Given the rapid growth in health care spending that is often attributed to technological change, many private and public institutions are grappling with how to best assess and adopt new health care technologies. The leading technology adoption criteria proposed in theory and used in practice involve so called "cost-effectiveness" measures. However, little is known about the dynamic efficiency implications of such criteria, in particular how they influence the R&D investments that make technologies available in the first place. We argue that such criteria implicitly concern maximizing consumer surplus, which many times is consistent with maximizing static efficiency after an innovation has been developed. Dynamic efficiency, however, concerns aligning the social costs and benefits of R&D and is therefore determined by how much of the social surplus from the new technology is appropriated as producer surplus. We analyze the relationship between cost-effectiveness measures and the degree of surplus appropriation by innovators driving dynamic efficiency. We illustrate how to estimate the two for the new HIV/AIDS therapies that entered the market after the late 1980's and find that only 5% of the social surplus is appropriated by innovators. We show how this finding can be generalized to other existing cost-effectiveness estimates by deriving how those estimates identify innovator appropriation for a set of studies of over 200 drugs. We find that these studies implicitly support a low degree of appropriation as well. Despite the high annual cost of drugs to patients, very low shares of social surplus may go to innovators, which may imply that cost-effectiveness is too high in a dynamic efficiency sense.

Evolution of the electronic structure and properties of neutral and charged aluminum clusters: A comprehensive analysis

Density-functional theory with generalized gradient approximation for the exchange-correlation potential has been used to calculate the global equilibrium geometries and electronic structure of neutral, cationic, and anionic aluminumclusters containing up to 15 atoms. The total energies of these clusters are then used to study the evolution of their binding energy, relative stability, fragmentation channels, ionization potential, and vertical and adiabatic electron affinities as a function of size. The geometries are found to undergo a structural change from two dimensional to three dimensional when the cluster contains 6 atoms. An interior atom emerges only when clusters contain 11 or more atoms. The geometrical changes are accompanied by corresponding changes in the coordination number and the electronic structure. The latter is reflected in the relative concentration of the s and p electrons of the highest occupied molecular orbital. Aluminum behaves as a monovalent atom in clusters containing less than seven atoms and as a trivalent atom in clusters containing seven or more atoms. The binding energy evolves monotonically with size, but Al7, Al+7, Al−7, Al−11, and Al−13 exhibit greater stability than their neighbors. Although the neutral clusters do not conform to the jellium model, the enhanced stability of these charged clusters is demonstrated to be due to the electronic shell closure. The fragmentation proceeds preferably by the ejection of a single atom irrespective of the charge state of the parent clusters. While odd-atom clusters carry a magnetic moment of 1μB as expected, clusters containing even number of atoms carry 2μB for n⩽10 and 0 μB for n\u3e10.The calculated results agree very well with all available experimental data on magnetic properties,ionization potentials,electron affinities, and fragmentation channels. The existence of isomers of Al13 cluster provides a unique perspective on the anomaly in the intensity distribution of the mass spectra. The unusual stability of Al7 in neutral, cationic, and anionic form compared to its neighboring clusters is argued to be due to its likely existence in a mixed-valence state

Hippocampal Global Remapping Can Occur without Input from the Medial Entorhinal Cortex.

The high storage capacity of the episodic memory system relies on distinct representations for events that are separated in time and space. The spatial component of these computations includes the formation of independent maps by hippocampal place cells across environments, referred to as global remapping. Such remapping is thought to emerge by the switching of input patterns from specialized spatially selective cells in medial entorhinal cortex (mEC), such as grid and border cells. Although it has been shown that acute manipulations of mEC firing patterns are sufficient for inducing hippocampal remapping, it remains unknown whether specialized spatial mEC inputs are necessary for the reorganization of hippocampal spatial representations. Here, we examined remapping in rats without mEC input to the hippocampus and found that highly distinct spatial maps emerged rapidly in every individual rat. Our data suggest that hippocampal spatial computations do not depend on inputs from specialized cell types in mEC

Molecular view of the interfacial adhesion in aluminum‐silicon carbide metal‐matrix composites

The binding energies, electron charge transfer,bond lengths, and core level shifts of Al‐Al, Al‐Si, Al‐C, and Si‐C dimers have been calculated self‐consistently using the linear combination of atomic orbitals‐molecular orbital theory. The exchange interactions are treated using the unrestricted Hartree–Fock theory and correlation corrections are included through the Möller–Plesset perturbation scheme up to fourth order. The results are used to understand the nature and strength of bonding at the interface of Al and SiC crystals. The strong bonding of Al‐C dimers compared to Al‐Al and Al‐Si is shown to be responsible for the aluminumcarbide formation at the interface. The charge transfer between the constituent atoms in the dimer and the accompanying core level shifts are also shown to be characteristic of what has been observed at the Al/SiC interface

On the quantum and classical scattering times due to charged dislocations in an impure electron gas

We derive the ratio of transport and single particle relaxation times in three and two - dimensional electron gases due to scattering from charged dislocations in semiconductors. The results are compared to the respective relaxation times due to randomly placed charged impurities. We find that the ratio is larger than the case of ionized impurity scattering in both three and two-dimensional electron transport.Comment: 4 pages, 3 figure