430 research outputs found
Adiabatic non-equilibrium steady states in the partition free approach
Consider a small sample coupled to a finite number of leads, and assume that
the total (continuous) system is at thermal equilibrium in the remote past. We
construct a non-equilibrium steady state (NESS) by adiabatically turning on an
electrical bias between the leads. The main mathematical challenge is to show
that certain adiabatic wave operators exist, and to identify their strong limit
when the adiabatic parameter tends to zero. Our NESS is different from, though
closely related with the NESS provided by the Jak{\v s}i{\'c}-Pillet-Ruelle
approach. Thus we partly settle a question asked by Caroli {\it et al} in 1971
regarding the (non)equivalence between the partitioned and partition-free
approaches
Geometrical effects and signal delay in time-dependent transport at the nanoscale
The nonstationary and steady-state transport through a mesoscopic sample
connected to particle reservoirs via time-dependent barriers is investigated
within the reduced density operator method. The generalized Master equation is
solved via the Crank-Nicolson algorithm by taking into account the memory
kernel which embodies the non-Markovian effects that are commonly disregarded.
We propose a physically reasonable model for the lead-sample coupling which
takes into account the match between the energy of the incident electrons and
the levels of the isolated sample, as well as their overlap at the contacts.
Using a tight-binding description of the system we investigate the effects
induced in the transient current by the spectral structure of the sample and by
the localization properties of its eigenfunctions. In strong magnetic fields
the transient currents propagate along edge states. The behavior of populations
and coherences is discussed, as well as their connection to the tunneling
processes that are relevant for transport.Comment: 26 pages, 13 figures. To appear in New Journal of Physic
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So you call that research? : mending methodological biases in strategy and organization departments of top business schools
We believe that all strategy and organization (SO) scholars should be able to decide for themselves whether to specialize in certain parts of the knowledge cycle or adopt a broader, multi-method view on the scientific process. In a situation of ―methodological pluralism‖, individuals might choose to contribute to the construction of new administrative theories by means of qualitative works like case studies, ethnographies, biographies, or grounded theory studies (e.g., see Denzin and Lincoln, 2000). Others could then specialize in testing these theories by means of experiments, surveys, or longitudinal econometric studies (e.g., see Lewis-Beck, 1987-2004). Again others could combine both approaches in Herculean attempts to conduct high-impact, integrative research with the potential to change the way we understand the field as a whole
Coherent manipulation of charge qubits in double quantum dots
The coherent time evolution of electrons in double quantum dots induced by
fast bias-voltage switches is studied theoretically. As it was shown
experimentally, such driven double quantum dots are potential devices for
controlled manipulation of charge qubits. By numerically solving a quantum
master equation we obtain the energy- and time-resolved electron transfer
through the device which resembles the measured data. The observed oscillations
are found to depend on the level offset of the two dots during the manipulation
and, most surprisingly, also the on initialization stage. By means of an
analytical expression, obtained from a large-bias model, we can understand the
prominent features of these oscillations seen in both the experimental data and
the numerical results. These findings strengthen the common interpretation in
terms of a coherent transfer of electrons between the dots.Comment: 18 pages, 4 figure
Is complexity leadership theory complex enough? A critical appraisal, some modifications and suggestions for further research
Scholars are increasingly seeking to develop theories that explain the underlying processes whereby leadership is enacted. This shifts attention away from the actions of ‘heroic’ individuals and towards the social contexts in which people with greater or lesser power influence each other. A number of researchers have embraced complexity theory, with its emphasis on non-linearity and unpredictability. However, some complexity scholars still depict the theory and practice of leadership in relatively non-complex terms. They continue to assume that leaders can exercise rational, extensive and purposeful influence on other actors to a greater extent than is possible. In effect, they offer a theory of complex organizations led by non-complex leaders who establish themselves by relatively non-complex means. This testifies to the enduring power of ‘heroic’ images of leader agency. Without greater care, the terminology offered by complexity leadership theory could become little more than a new mask for old theories that legitimize imbalanced power relationships in the workplace. This paper explores how these problems are evident in complexity leadership theory, suggests that communication and process perspectives help to overcome them, and outlines an agenda for further research on these issues
The Neonatal Fc Receptor (FcRn) Enhances Human Immunodeficiency Virus Type 1 (HIV-1) Transcytosis across Epithelial Cells
The mechanisms by which human immunodeficiency virus type 1 (HIV-1) crosses mucosal surfaces to establish infection are unknown. Acidic genital secretions of HIV-1-infected women contain HIV-1 likely coated by antibody. We found that the combination of acidic pH and Env-specific IgG, including that from cervicovaginal and seminal fluids of HIV-1-infected individuals, augmented transcytosis across epithelial cells as much as 20-fold compared with Env-specific IgG at neutral pH or non-specific IgG at either pH. Enhanced transcytosis was observed with clinical HIV-1 isolates, including transmitted/founder strains, and was eliminated in Fc neonatal receptor (FcRn)-knockdown epithelial cells. Non-neutralizing antibodies allowed similar or less transcytosis than neutralizing antibodies. However, the ratio of total:infectious virus was higher for neutralizing antibodies, indicating that they allowed transcytosis while blocking infectivity of transcytosed virus. Immunocytochemistry revealed abundant FcRn expression in columnar epithelia lining the human endocervix and penile urethra. Acidity and Env-specific IgG enhance transcytosis of virus across epithelial cells via FcRn and could facilitate translocation of virus to susceptible target cells following sexual exposure
Calpain Cleavage Prediction Using Multiple Kernel Learning
Calpain, an intracellular -dependent cysteine protease, is known to play a role in a wide range of metabolic pathways through limited proteolysis of its substrates. However, only a limited number of these substrates are currently known, with the exact mechanism of substrate recognition and cleavage by calpain still largely unknown. While previous research has successfully applied standard machine-learning algorithms to accurately predict substrate cleavage by other similar types of proteases, their approach does not extend well to calpain, possibly due to its particular mode of proteolytic action and limited amount of experimental data. Through the use of Multiple Kernel Learning, a recent extension to the classic Support Vector Machine framework, we were able to train complex models based on rich, heterogeneous feature sets, leading to significantly improved prediction quality (6% over highest AUC score produced by state-of-the-art methods). In addition to producing a stronger machine-learning model for the prediction of calpain cleavage, we were able to highlight the importance and role of each feature of substrate sequences in defining specificity: primary sequence, secondary structure and solvent accessibility. Most notably, we showed there existed significant specificity differences across calpain sub-types, despite previous assumption to the contrary. Prediction accuracy was further successfully validated using, as an unbiased test set, mutated sequences of calpastatin (endogenous inhibitor of calpain) modified to no longer block calpain's proteolytic action. An online implementation of our prediction tool is available at http://calpain.org
The Role of Bound States in Time-Dependent Quantum Transport
Charge transport through a nanoscale junction coupled to two macroscopic
electrodes is investigated for the situation when bound states are present. We
provide numerical evidence that bound states give rise to persistent,
non-decaying current oscillations in the junction. We also show that the
amplitude of these oscillations can exhibit a strong dependence on the history
of the applied potential as well as on the initial equilibrium configuration.
Our simulations allow for a quantitative investigation of several transient
features. We also discuss the existence of different time-scales and address
their microscopic origin.Comment: 10 pages, 8 figure
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