Quantal Density Functional Theory of Degenerate States

The treatment of degenerate states within Kohn-Sham density functional theory (KS-DFT) is a problem of longstanding interest. We propose a solution to this mapping from the interacting degenerate system to that of the noninteracting fermion model whereby the equivalent density and energy are obtained via the unifying physical framework of quantal density functional theory (Q-DFT). We describe the Q-DFT of \textit{both} ground and excited degenerate states, and for the cases of \textit{both} pure state and ensemble v-representable densities. This then further provides a rigorous physical interpretation of the density and bidensity energy functionals, and of their functional derivatives, of the corresponding KS-DFT. We conclude with examples of the mappings within Q-DFT.Comment: 10 pages. minor changes made. to appear in PR

Edge Electron Gas

The uniform electron gas, the traditional starting point for density-based many-body theories of inhomogeneous systems, is inappropriate near electronic edges. In its place we put forward the appropriate concept of the edge electron gas.Comment: 4 pages RevTex with 7 ps-figures included. Minor changes in title,text and figure

Using the Military at Home: Yesterday, Today, and Tomorrow

Today the United States is undergoing a great transformation in national security thinking and priorities. Between the end of the Cold War in 1989 and the collapse of the Soviet Union in 1991, the country began to abandon the policy of containment and the strategy of deterrence that had governed American relations with the rest of the world for over four decades. For only the fourth time in its national history, the United States has been changing its national security policies and reconfiguring its military institutions to adapt to a new role in world politics. Once again, for a variety of reasons not least because of technologies Americans themselves pioneered, defense of the American homeland has become central to national security. Protecting the American people inside the United States is the most significant and perplexing of the changes underway in national defense. What should be-must be-the role of the military in homeland defense

Wholeness-Oneness

Perhaps we have a thing going in our church. In a memorable convention in Detroit four years ago our church acted in a most distinctive way. Aside from several bold administrative decisions, such as recognizing the autonomy of developing national churches overseas and creating a unified Board for Missions, our church collectively penned and proclaimed the total mission of the church in six brief resolutions and then summarized them in six concise but meaningful statements. We called them the Affirmations on God\u27s Mission

Quantum-Dot Cellular Automata using Buried Dopants

The use of buried dopants to construct quantum-dot cellular automata is investigated as an alternative to conventional electronic devices for information transport and elementary computation. This provides a limit in terms of miniaturisation for this type of system as each potential well is formed by a single dopant atom. As an example, phosphorous donors in silicon are found to have good energy level separation with incoherent switching times of the order of microseconds. However, we also illustrate the possibility of ultra-fast quantum coherent switching via adiabatic evolution. The switching speeds are numerically calculated and found to be 10's of picoseconds or less for a single cell. The effect of decoherence is also simulated in the form of a dephasing process and limits are estimated for operation with finite dephasing. The advantages and limitations of this scheme over the more conventional quantum-dot based scheme are discussed. The use of a buried donor cellular automata system is also discussed as an architecture for testing several aspects of buried donor based quantum computing schemes.Comment: Minor changes in response to referees comments. Improved section on scaling and added plot of incoherent switching time

Rescue of splicing-mediated intron loss maximizes expression in lentiviral vectors containing the human ubiquitin C promoter.

Lentiviral vectors almost universally use heterologous internal promoters to express transgenes. One of the most commonly used promoter fragments is a 1.2-kb sequence from the human ubiquitin C (UBC) gene, encompassing the promoter, some enhancers, first exon, first intron and a small part of the second exon of UBC. Because splicing can occur after transcription of the vector genome during vector production, we investigated whether the intron within the UBC promoter fragment is faithfully transmitted to target cells. Genetic analysis revealed that more than 80% of proviral forms lack the intron of the UBC promoter. The human elongation factor 1 alpha (EEF1A1) promoter fragment intron was not lost during lentiviral packaging, and this difference between the UBC and EEF1A1 promoter introns was conferred by promoter exonic sequences. UBC promoter intron loss caused a 4-fold reduction in transgene expression. Movement of the expression cassette to the opposite strand prevented intron loss and restored full expression. This increase in expression was mostly due to non-classical enhancer activity within the intron, and movement of putative intronic enhancer sequences to multiple promoter-proximal sites actually repressed expression. Reversal of the UBC promoter also prevented intron loss and restored full expression in bidirectional lentiviral vectors

Hysteretic resistance spikes in quantum Hall ferromagnets without domains

We use spin-density-functional theory to study recently reported hysteretic magnetoresistance \rho_{xx} spikes in Mn-based 2D electron gases [Jaroszy\'{n}ski et al. Phys. Rev. Lett. (2002)]. We find hysteresis loops in our calculated Landau fan diagrams and total energies signaling quantum-Hall-ferromagnet phase transitions. Spin-dependent exchange-correlation effects are crucial to stabilize the relevant magnetic phases arising from distinct symmetry-broken excited- and ground-state solutions of the Kohn-Sham equations. Besides hysteretic spikes in \rho_{xx}, we predict hysteretic dips in the Hall resistance \rho_{xy}. Our theory, without domain walls, satisfactorily explains the recent data.Comment: 4 pages, 4 figures, published version (some changes to the text; same figures as in v1

Time Dependent Floquet Theory and Absence of an Adiabatic Limit

Quantum systems subject to time periodic fields of finite amplitude, lambda, have conventionally been handled either by low order perturbation theory, for lambda not too large, or by exact diagonalization within a finite basis of N states. An adiabatic limit, as lambda is switched on arbitrarily slowly, has been assumed. But the validity of these procedures seems questionable in view of the fact that, as N goes to infinity, the quasienergy spectrum becomes dense, and numerical calculations show an increasing number of weakly avoided crossings (related in perturbation theory to high order resonances). This paper deals with the highly non-trivial behavior of the solutions in this limit. The Floquet states, and the associated quasienergies, become highly irregular functions of the amplitude, lambda. The mathematical radii of convergence of perturbation theory in lambda approach zero. There is no adiabatic limit of the wave functions when lambda is turned on arbitrarily slowly. However, the quasienergy becomes independent of time in this limit. We introduce a modification of the adiabatic theorem. We explain why, in spite of the pervasive pathologies of the Floquet states in the limit N goes to infinity, the conventional approaches are appropriate in almost all physically interesting situations.Comment: 13 pages, Latex, plus 2 Postscript figure