Incoherent dynamics of vibrating single-molecule transistors

We study the tunneling conductance of nano-scale quantum ``shuttles'' in connection with a recent experiment (H. Park et al., Nature, 407, 57 (2000)) in which a vibrating C^60 molecule was apparently functioning as the island of a single electron transistor (SET). While our calculation starts from the same model of previous work (D. Boese and H. Schoeller, Europhys. Lett. 54, 66(2001)) we obtain quantitatively different dynamics. Calculated I-V curves exhibit most features present in experimental data with a physically reasonable parameter set, and point to a strong dependence of the oscillator's potential on the electrostatics of the island region. We propose that in a regime where the electric field due to the bias voltage itself affects island position, a "catastrophic" negative differential conductance (NDC) may be realized. This effect is directly attributable to the magnitude of overlap of final and initial quantum oscillator states, and as such represents experimental control over quantum transitions of the oscillator via the macroscopically controllable bias voltage.Comment: 6 pages, LaTex, 6 figure

Stochastic programming approaches to stochastic scheduling

Practical scheduling problems typically require decisions without full information about the outcomes of those decisions. Yields, resource availability, performance, demand, costs, and revenues may all vary. Incorporating these quantities into stochastic scheduling models often produces diffculties in analysis that may be addressed in a variety of ways. In this paper, we present results based on stochastic programming approaches to the hierarchy of decisions in typical stochastic scheduling situations. Our unifying framework allows us to treat all aspects of a decision in a similar framework. We show how views from different levels enable approximations that can overcome nonconvexities and duality gaps that appear in deterministic formulations. In particular, we show that the stochastic program structure leads to a vanishing Lagrangian duality gap in stochastic integer programs as the number of scenarios increases.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44935/1/10898_2004_Article_BF00121682.pd

Two-electron elastic tunneling in low-dimensional conductors

This article was published in the journal, Physical Review B [© American Physical Society]. It is also available at: http://link.aps.org/abstract/PRB/v65/e155209.We solve the Lippmann-Schwinger equation describing one-dimensional elastic scattering of preformed pairs (e.g., bipolarons) off a short-range scattering center, and find the two-particle transmission through a thin potential barrier. While the pair transmission is smaller than the single-electron transmission in the strong-coupling limit, it is remarkably larger in the weak-coupling limit. We also calculate current-voltage characteristics of a molecule-barrier-molecule junction. They show unusual temperature and voltage behaviors which are experimentally verifiable at low temperatures in bulk and nanoscale molecular conductors

Two apple repetitive sequence elements: characterisation and potential use as genetic markers

Within the 5? flanking regions of two ripening-related genes from apple (Malus pumila), two short repeat sequences were identified and named Ars1 andArs2 (Apple repetitivesequences). Both elements were present in the promoter of the Md-ACS1-1 ACC synthase gene and Ars2was also found in the promoter of a gene homologous to the ABG1 ?-galactosidase gene. Database searches revealed other examples of each element in apple genomic sequences and a partial Ars2element in a sequence from Asian pear (Pyrus pyrifolia). DNA dot blot analysis demonstrated that both elements are present in high numbers in the apple genome. Ars1 is thought to represent a MITEminiature inverted-repeat transposable element) related to the MITE Alien, while the identity ofArs2, though it is undoubtedly a transposable element, remains undetermined. DNA dot blot analysis and PCR amplification using primers designed from Ars1and Ars2 showed that elements similar to Ars1 and Ars2 are present across the Rosaceae. The amplification patterns obtained using Ars1- and Ars2-specific primers with genomic DNA from different cultivars or mapping populations suggest that these elements could be used for finger printing and segregation analysis in Rosaceae. Evidence from DNA database searches suggests that they may be applicable to genetic studies in a wide range of other organisms

Using heterologous and homologous promoters to study tissue specific transgene expression in fruit crops

It is desirable that the expression of transgenes in genetically improved crops is restricted to the tissue requiring the encoded activity. To this end, the ability of several heterologous and homologous gene promoters to drive expression of the ?-glucuronidase (gusA) marker gene in the vegetative tissues of transgenic apple (Malus pumila Mill.) and commercial strawberry (Fragaria x ananassa) was tested. These promoters originally drove expression in leaves (Rubisco) small subunit (SSU), RBCS3CP from tomato, SRS1P from soybean, vascular tissue, rolCP, and CoYMVP and tissue root, extAP (Brassica) and PsMTAP (Pisum). Homologous promoters from apple were cloned for expression in fruit and from strawberry for expression in stamens, petals and roots. Transgenic lines were produced by Agrobacterium-mediated transformation and the level of gusA expression in the vegetative tissues of young plants was compared with that using the CaMV 35S promoter. Quantitative GUS data were related to the copy number of transgene loci assessed by Southern blotting. The precise location of GUS activity in each tissue was identified by staining of whole leaves and tissue sections with the chromogenic substrate X-Gluc. Light-regulation and patterns of expression are recorderd in various vegetative tissues of apple

Reforming asylums, reforming public attitudes : J. R. Lord and Montagu Lomax's representations of mental hospitals and the community, 1921–1931

J.R. Lord and Montagu Lomax offered competing visions of the relationship between mental hospitals and the community in a decade when asylums were subjected to extensive official and public scrutiny. The background of both men arguably informed their divergent outlook on mental hospitals. Lomax's work targeted reform at mental hospitals, through public and governmental intervention. Lord, however, advocated a leading role for mental hospitals in community mental health, and called for reform of public attitudes and laws inhibiting mental hospital development. This paper suggests that Lord effectively inverted Lomax's core arguments, selectively focusing on aspects of social service and aftercare to present a more positive picture of mental hospitals. Targeting different (public/professional) audiences, Lord and Lomax each based their case for reform on a particular perspective of the public. It is argued that to appreciate their respective attitudes to asylums one must also consider their representations of the public