Driven quantum transport on the nanoscale

We explore the prospects to control by use of time-dependent fields quantum transport phenomena in nanoscale systems. In particular, we study for driven conductors the electron current and its noise properties. We review recent corresponding theoretical descriptions which are based on Floquet theory. Alternative approaches, as well as various limiting approximation schemes are investigated and compared. The general theory is subsequently applied to different representative nanoscale devices, like the non-adiabatic pumps, molecular gates, molecular quantum ratchets, and molecular transistors. Potential applications range from molecular wires under the influence of strong laser fields to microwave-irradiated quantum dots.Comment: 82 pages, 19 figures, elsart.cls, solved LaTeX/hyperref problem

Cromakalim (BRL 34915) restores in vitro the membrane potential of depolarized human skeletal muscle fibres

The purpose of the present study was to analyze the effects of cromakalim (BRL 34915), a potent drug from a new class of drugs characterized as K+ channel openers, on the electrical activity of human skeletal muscle. Therefore, intracellular recordings were used to measure the effects of cromakalim on the membrane potential and input conductance of fibres from human skeletal muscle biopsies. Cromakalim in a concentration above 1 mol/l induced an increase in membrane K+ conductance. This effect resulted in a membrane hyperpolarization. The magnitude of this polarization depended on the difference between resting and K+ equilibrium potential. The effect had a rapid onset and was quickly reversible after washing. Fibres from two patients with hyperkalaemic periodic paralysis showed an excessive membrane depolarization during and also after exposure to an slightly elevated extracellular K+ concentration. In the latter situation, cromakalim repolarized the fibres to the normal resting potential. Tolbutamide (1 mmol/l) and Ba2+ (3 mmol/l) strongly antagonized the effect of cromakalim. The data show that cromakalim hyperpolarizes depolarized human skeletal muscle fibres maintained in vitro. The underlying mechanism is probably an activation of otherwise silent, ATP-regulated K+ channels. Such an effect may be of therapeutic benefit in a situation in which a membrane depolarization causes muscle paralysis

Role of multi-level states on quantum-dot emission in photonic-crystal cavities

Semiconductor quantum dots embedded in photonic-crystal nanostructures have been the subject of intense study. In this context, quantum dots are often considered to be simple two-level emitters, i.e., the complexities arising from the internal finestructure are neglected. We show that due to the intricate spatial variations of the electric field polarization found in photonic crystal, the two orthogonal finestructure states of quantum dots in general both couple significantly to a cavity mode, implying that the two-level description is not sufficient. As a consequence the emission dynamics and spectra, which are often recorded in experiments, are modified both in the weak- and strong-coupling regimes. The proposed effects are found to be significant for system parameters of current state-of-the-art photonic-crystal cavities

Rectification of laser-induced electronic transport through molecules

We study the influence of laser radiation on the electron transport through a molecular wire weakly coupled to two leads. In the absence of a generalized parity symmetry, the molecule rectifies the laser induced current, resulting in directed electron transport without any applied voltage. We consider two generic ways of dynamical symmetry breaking: mixing of different harmonics of the laser field and molecules consisting of asymmetric groups. For the evaluation of the nonlinear current, a numerically efficient formalism is derived which is based upon the Floquet solutions of the driven molecule. This permits a treatment in the non-adiabatic regime and beyond linear response.Comment: 12 pages, 10 figures, REVTeX

Explaining the Conversion to Organic Farming of Farmers of the Obwalden Canton, Switzerland - Extension of the Theory of Planned Behavior within a Structural Equation Modeling Approach

Farmers' decisions about conversion to organic farming are analyzed with a structural equation model. The Theory of Planned Behavior (ToPB), one of the prominent theories in the social psychology, is used as the theoretical basis of this study. Though ToPB is a well-defined theory, it is static rather than procedural and cannot model the individual decision-making as a process. Therefore, we first examine the general applicability of ToPB in an agricultural context and explain the variance in intentions of farmers to convert to organic farming. Second, we extend the ToPB to make it more procedural. For this purpose, research findings from the Diffusion Theory are included as part of the behavioral model. The empirical results indicate that, overall, the model has an acceptable fit to the data. The effects of the additional variables "Goal" and "Communication" are highly significant. This illustrates the importance of forming personal goals in the behavior domain and that people act in a goal-directed, rational way. Moreover, it gives empirical evidence that communication through personal channels has a great impact on individual decision-making. Altogether, this study shows that the extended ToPB provides an appropriate approach to investigate individual decision-making processes in agriculture.behavior research, conversion to particularly animal friendly stabling system, theory of planned behavior, diffusion theory, structural equation modelling, Farm Management, C8, D1, Q12, Z13,

Escape rates in periodically driven Markov processes

We present an approximate analytical expression for the escape rate of time-dependent driven stochastic processes with an absorbing boundary such as the driven leaky integrate-and-fire model for neural spiking. The novel approximation is based on a discrete state Markovian modeling of the full long-time dynamics with time-dependent rates. It is valid in a wide parameter regime beyond the restraining limits of weak driving (linear response) and/or weak noise. The scheme is carefully tested and yields excellent agreement with three different numerical methods based on the Langevin equation, the Fokker-Planck equation and an integral equation.Comment: 10 pages, 5 figure

Strategies to mitigate greenhouse gas and nitrogen emissions in Swiss agriculture: the application of an integrated sector model

Environmental impacts of agricultural production, such as greenhouse gas (GHG) and nitrogen emissions, are of major concern for scientists and policy makers throughout the world. Global agricultural activities account for about 60% of nitrous oxide and about 50% of methane emissions. From a global perspective, methane and nitrous oxide constitute crucial GHGs. They contribute substantially to climate change due to their high potential for effecting global warming compared to carbon dioxide. Emissions of these gases depend on the extent of agricultural production and applied technologies. Therefore, analysis of potential mitigation opportunities is challenging and requires an integrated approach in order to link agricultural economic perspectives to environmental aspects. In view of this, a mathematical programming model has been developed which enables assessment of cost-effective strategies for mitigating GHG and nitrogen emissions in the agricultural sector in Switzerland. This model is applied to improve understanding of the agricultural sector and its behavior with changing conditions in technology and policy. The presented recursive-dynamic model mimics the structure and inter- dependencies of Swiss agriculture and links that framework to core sources of GHG and nitrogen emissions. Calculated results for evaluation and application indicate that employed flexibility constraints provide a feasible approach to sufficiently validate the described model. Recursive-dynamic elements additionally enable adequate modeling of both an endogenous development of livestock dynamics and investments in buildings and machinery, also taking sunk costs into account. The presented findings reveal that the specified model approach is suitable to accurately estimate agricultural structure, GHG and nitrogen emissions within a tolerable range. The model performance can therefore be described as sufficiently robust and satisfactory. Thus, the model described here appropriately models strategies for GHG and nitrogen abatement in Swiss agriculture. The results indicate that there are limits to the ability of Swiss agriculture to contribute substantially to the mitigation of GHG and nitrogen emissions. There is only a limited level of mitigation available through technical approaches, and these approaches have high cost.resource use, environmental economics, greenhouse gas emission, nitrogen emission, integrated modeling

Children who witness mother-assault: An expanded posttraumatic stress disorder conceptualization

The impact on children who witness mother-assault was conceptualized as an expanded posttraumatic stress disorder (PTSD) and an exploratory research study testing this formulation was carried out. The current conceptualization was based in part on the work of V. Wolfe and associates who utilized a model whereby a number of mediating factors were thought to determine adjustment to traumatic. An important part of their model was the utilization of the Type I and II trauma typologies of Terr (1990, 1991). These typologies were used to measure the PTSD symptoms of children in response to the severity and course of mother-assault. In this study, a Type I sequelae consisted of the PTSD responses of reexperiencing, hyperarousal, and avoidance, and was related to the severity of mother-assault and child witnessing. The Type II sequelae consisted of the PTSD symptoms in addition to the coping responses of denial, rage, dissociation, sadness, and negative attributions. The Type II typology was related to the course of mother-assault which included the frequency of assaults and the duration of witnessing. Mediators included social support family disadvantage, and family functioning. Finally, this study tested the construct validity of two new instruments related to the child witness. The major questions posed for this exploratory research study were: a) would children who witness mother-assault exhibit Type I symptoms in response to the severity of mother-assault, b) would such children exhibit Type II symptoms in response to the course of mother-assault, and last, c) would the History Of Violence Witnessed By Child Questionnaire (HVWCQ) and the Children’s Impact of Traumatic Events Scale-Family Violence Form (CITES-FVF) be valid instruments. Eighty-four children and their mothers volunteered to be participants. Initial findings yielded a curvilinear relationship between the Type I and II responses and the severity and course of the mother-assault. Consequently, children were divided into a three group design whereby children in groups one and two reported gradual increases in symptoms. However, in the midst of the most severe mother-assault, the third group of children reported a decrease in all behaviours measuring the Type I and II PTSD typologies. A series of two factor group X age multivariate analyses of variance (MANOVA) were carried out. Mediating variables were not significant and were not added to the MANOVA models. There was no support for the research question that children would exhibit PTSD symptoms (Type I trauma) in response to the severity of mother-assault. Despite these findings, 56% (n=47) of the child population met the diagnostic criteria for PTSD. Also, there was no support for the research question that children would exhibit PTSD symptoms and maladaptive coping behaviours (Type II trauma) in response to the course of mother-assault. However, the PTSD responses of hyperarousal, avoidance, and assault anxiety were significant for age. As well, the only significant Type II coping responses were negative childhood attributions. Again, age not group was significant. Also, gender did not have an overall multivariate effect on Type I and Type II responses. Finally, two series of principal components factor analyses were conducted on the CITES-FVF and the HVWCQ. The first series of analyses did not support the research question that the CITES-FVF would be a valid measure. There were, however, similarities in the underlying structures of both instruments. The second series of factor analyses supported the question that the HVWCQ would be a valid instrument. At the same time reservations were raised given one of the factors had only a single variable. This exploratory study suggested a number of implications with respect to theory, clinical practice, and policy development. Primarily, it was argued that the current expanded PTSD conceptualization has some merit with respect to the child witness to mother-assault, and that furthermore, a broadened PTSD may also have some theoretical potential. In addition, the ramifications for group, individual, and family therapies were considered. Finally, policy developments by way of written protocols for shelter staff were highlighted