Microscopic modelling of perpendicular electronic transport in doped multiple quantum wells

We present a microscopic calculation of transport in strongly doped superlattices where domain formation is likely to occur. Our theoretical method is based on a current formula involving the spectral functions of the system, and thus allows, in principle, a systematic investigation of various interaction mechanisms. Taking into account impurity scattering and optical phonons we obtain a good quantitative agreement with existing experimental data from Helgesen and Finstad (J. Appl. Phys. 69, 2689, (1991)). Furthermore the calculated spectral functions indicate a significant increase of the average intersubband spacing compared to the bare level differences which might explain the experimental trend.Comment: 10 pages 5 figure

Tunneling through nanosystems: Combining broadening with many-particle states

We suggest a new approach for transport through finite systems based on the Liouville equation. By working in a basis of many-particle states for the finite system, Coulomb interactions are taken fully into account and correlated transitions by up to two different contact states are included. This latter extends standard rate equation models by including level-broadening effects. The main result of the paper is a general expression for the elements of the density matrix of the finite size system, which can be applied whenever the eigenstates and the couplings to the leads are known. The approach works for arbitrary bias and for temperatures above the Kondo temperature. We apply the approach to standard models and good agreement with other methods in their respective regime of validity is found.Comment: 9 pages, 5 figures included to tex

Current-voltage characteristic and stability in resonant-tunneling n-doped semiconductor superlattices

We review the occurrence of electric-field domains in doped superlattices within a discrete drift model. A complete analysis of the construction and stability of stationary field profiles having two domains is carried out. As a consequence, we can provide a simple analytical estimation for the doping density above which stable stable domains occur. This bound may be useful for the design of superlattices exhibiting self-sustained current oscillations. Furthermore we explain why stable domains occur in superlattices in contrast to the usual Gunn diode.Comment: Tex file and 3 postscript figure

The Dark Matter at the End of the Galaxy

Dark matter density profiles based upon Lambda-CDM cosmology motivate an ansatz velocity distribution function with fewer high velocity particles than the Maxwell-Boltzmann distribution or proposed variants. The high velocity tail of the distribution is determined by the outer slope of the dark matter halo, the large radius behavior of the Galactic dark matter density. N-body simulations of Galactic halos reproduce the high velocity behavior of this ansatz. Predictions for direct detection rates are dramatically affected for models where the threshold scattering velocity is within 30% of the escape velocity.Comment: 10 pages, 5 figure

Phenomenology of Electroweak Symmetry Breaking from Theory Space

Recently, a new class of realistic models for electroweak symmetry breaking have been constructed, without supersymmetry. These theories have naturally light Higgs bosons and perturbative new physics at the TeV scale. We describe these models in detail, and show that electroweak symmetry breaking can be triggered by a large top quark Yukawa coupling. A rich spectrum of particles is predicted, with a pair of light Higgs doublets accompanied by new light weak triplet and singlet scalars. The lightest of these new scalars is charged under a geometric discrete symmetry and is therefore stable, providing a new candidate for WIMP dark matter. At TeV energies, a plethora of new heavy scalars, gauge bosons and fermions are revealed, with distinctive quantum numbers and decay modes.Comment: 22 pages, latex, 6 figures. Numerical results corrected, clarifications added, conclusions unchange

Theory of Transmission through disordered superlattices

We derive a theory for transmission through disordered finite superlattices in which the interface roughness scattering is treated by disorder averaging. This procedure permits efficient calculation of the transmission thr ough samples with large cross-sections. These calculations can be performed utilizing either the Keldysh or the Landauer-B\"uttiker transmission formalisms, both of which yield identical equations. For energies close to the lowest miniband, we demonstrate the accuracy of the computationally efficient Wannier-function approximation. Our calculations indicate that the transmission is strongly affected by interface roughness and that information about scale and size of the imperfections can be obtained from transmission data.Comment: 12 pages, 6 Figures included into the text. Final version with minor changes. Accepted by Physical Review

Liquid Chromatographic Resolution and Bioassay of Napropamide Herbicide Enantiomers

The enantiomers of the herbicide napropamide (1) were separated on a ?g-scale using chiral liquid chromatography and submitted to a bioassay for herbicidal activity using a wheat germ test. Under these conditions, only one enantiomer showed herbicidal activity. The potential for reducing the application rate of pesticides by omitting isomeric ballast is discussed

Developing an Economic Value Model for Delinquent Tax Auctions in South Carolina

Government-administered public auctions of private property to recoup unpaid taxes represent a common tool to collect funds while representing an investment vehicle for tax sale attendees. The problem was that factors such as starting bids, high bids, redemption timing, taxes due from prior years, possible interest earned, assessed land value, property structures, and possible economic gain were not widely understood by tax sale participants. The purpose of this correlational study was to examine the existence of relationships between or among the aforementioned attributes and the interest earned by a bidder or the odds of acquiring a tax deed. Quantitative theory, affords a precise and unbiased evaluation of decision-making with multiple inputs and variables, provided the foundation for secondary source data analysis via the 2017 Florence County, South Carolina, delinquent tax sale. A multiple linear regression analysis of 586 properties showed a statistically significant association between interest earned from the starting bid, highest bid, and days elapsed until the property was redeemed (F = 625, p \u3c .001). A multiple binary logistic regression analysis of 676 properties showed if taxes were due in prior years, a positive relationship of more than six-fold (p \u3c .05, Exp (B) = 6.064, 95% CI [1.637, 22.469]) existed with receiving a tax deed. The results indicate that if a structure was present, the estimated odds ratio showed a decrease of receiving a tax deed of nearly 58% (p \u3c .05, Exp (B) = .426, 95% CI [0.197, 0.919]). The social change implications were that investors may utilize these results to enhance their strategies when attending delinquent tax sales. Positive social change may increase by providing marginalized groups investing options