330 research outputs found
Transport through constricted quantum Hall edge systems: beyond the quantum point contact
Motivated by surprises in recent experimental findings, we study transport in
a model of a quantum Hall edge system with a gate-voltage controlled
constriction. A finite backscattered current at finite edge-bias is explained
from a Landauer-Buttiker analysis as arising from the splitting of edge current
caused by the difference in the filling fractions of the bulk () and
constriction () quantum Hall fluid regions. We develop a hydrodynamic
theory for bosonic edge modes inspired by this model. The constriction region
splits the incident long-wavelength chiral edge density-wave excitations among
the transmitting and reflecting edge states encircling it. The competition
between two interedge tunneling processes taking place inside the constriction,
related by a quasiparticle-quasihole (qp-qh) symmetry, is accounted for by
computing the boundary theories of the system. This competition is found to
determine the strong coupling configuration of the system. A separatrix of
qp-qh symmetric gapless critical states is found to lie between the relevant RG
flows to a metallic and an insulating configuration of the constriction system.
This constitutes an interesting generalisation of the Kane-Fisher quantum
impurity model. The features of the RG phase diagram are also confirmed by
computing various correlators and chiral linear conductances of the system. In
this way, our results find excellent agreement with many recent puzzling
experimental results for the cases of . We also discuss and
make predictions for the case of a constriction system with .Comment: 18 pages, 9 figure
Full counting statistics of Andreev scattering in an asymmetric chaotic cavity
We study the charge transport statistics in coherent two-terminal double
junctions within the framework of the circuit theory of mesoscopic transport.
We obtain the general solution of the circuit-theory matrix equations for the
Green's function of a chaotic cavity between arbitrary contacts. As an example
we discuss the full counting statistics and the first three cumulants for an
open asymmetric cavity between a superconductor and a normal-metal lead at
temperatures and voltages below the superconducting gap. The third cumulant
shows a characteristic sign change as a function of the asymmetry of the two
quantum point contacts, which is related to the properties of the Andreev
reflection eigenvalue distribution.Comment: 8 pages, 4 figure
Energy and emissions modelling in ethiopia’s transport sector
Papers presented virtually at the 41st International Southern African Transport Conference on 10-13 July 2062This paper discusses emissions and energy modelling in Ethiopia’s transport sector as a
component of the development of a wider cross-sectoral Long-term Low Emissions
Development Strategy (LT-LEDS) for the country. The LT-LEDS is a key requirement of
the Paris Agreement 2015 to which Ethiopia is a signatory. It aims to support growth of key
economic sectors while ensuring the alignment of developmental goals with climate
commitments and environmental sustainability. The transport sector is identified as a key
part of this effort given its significant contribution to GHG emissions and climate change
globally. The main activities involved in developing the low emissions pathways are the
modelling of baseline and mitigation scenarios which capture historic emission and energy
trends in the transport sector and estimates future emissions linked with the growth of the
sector respectively. A bottom-up modelling technique is employed for the study. This
involves collecting and analysing disaggregate transport activity data to provide a
fundamental understanding of transport sector energy consumption and how it affects the
long-term transitions. The results of the scenario building highlight the road sector as the
main contributor to transport sector emissions in the country. This calls for the
implementation of strategies and interventions to reduce emissions and guarantee a
climate friendly and environmentally sustainable growth
Ehrenfest time dependent suppression of weak localization
The Ehrenfest time dependence of the suppression of the weak localization
correction to the conductance of a {\em clean} chaotic cavity is calculated.
Unlike in earlier work, no impurity scattering is invoked to imitate
diffraction effects. The calculation extends the semiclassical theory of K.
Richter and M. Sieber [Phys. Rev. Lett. {\bf 89}, 206801 (2002)] to include the
effect of a finite Ehrenfest time.Comment: 3 Pages, 1 Figure, RevTe
Quantum suppression of shot noise in field emitters
We have analyzed the shot noise of electron emission under strong applied
electric fields within the Landauer-Buttiker scheme. In contrast to the
previous studies of vacuum-tube emitters, we show that in new generation
electron emitters, scaled down to the nanometer dimensions, shot noise much
smaller than the Schottky noise is observable. Carbon nanotube field emitters
are among possible candidates to observe the effect of shot-noise suppression
caused by quantum partitioning.Comment: 5 pages, 1 fig, minor changes, published versio
Shot Noise by Quantum Scattering in Chaotic Cavities
We have experimentally studied shot noise of chaotic cavities defined by two
quantum point contacts in series. The cavity noise is determined as 1/4*2e|I|
in agreement with theory and can be well distinguished from other contributions
to noise generated at the contacts. Subsequently, we have found that cavity
noise decreases if one of the contacts is further opened and reaches nearly
zero for a highly asymmetric cavity.Comment: 4 pages, 4 figures, REVTe
Synthesis and evaluation of human phosphodiesterases (PDE) 5 inhibitor analogs as trypanosomal PDE inhibitors. 1. Sildenafil analogs
Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Bioorganic & Medicinal Chemistry Letters 22 (2012): 2579-2581, doi:10.1016/j.bmcl.2012.01.119.Parasitic diseases, such as African sleeping sickness, have a significant impact on the health and well-being in the poorest regions of the world. Pragmatic drug discovery efforts are needed to find new therapeutic agents. In this report we describe target repurposing efforts focused on trypanosomal phosphodiesterases. We outline the synthesis and biological evaluation of analogs of sildenafil (1), a human PDE5 inhibitor, for activities against trypanosomal PDEB1 (TbrPDEB1). We find that, while low potency analogs can be prepared, this chemical class is a sub-optimal starting point for further development of TbrPDE inhibitors.This work was supported by the National Institutes of Health (R01AI082577), Boston University and Northeastern University
Gene Conversion Transfers the GAF-A Domain of Phosphodiesterase TbrPDEB1 to One Allele of TbrPDEB2 of Trypanosoma brucei
Cyclic nucleotide specific phosphodiesterases are important regulators of cyclic nucleotide signalling in eukaryotes. In many organisms, including humans and trypanosomes, some of these enzymes contain specific domains (GAF domains) that bind cyclic nucleotides, and that are involved in the regulation of the catalytic domain. In the parasitic protozoon that causes human sleeping sickness, Trypanosoma brucei, two closely related phosphodiesterases each contain two such GAF domains, GAF-A and GAF-B. Their genes are tandemly located on chromosome 9, spaced by only a few thousand nucleotides. We here show that a gene conversion event has exchanged the region that codes for the GAF-A domain of the downstream gene by the closely similar corresponding sequence of the upstream gene. This domain exchange has no effect on intracellular localization of the two enzymes. The gene conversion event has occurred in one particular strain of trypanosomes (Lister427) and is found in all its derivatives, but not in any other strain or isolate. The presence or absence of this gene conversion represents a useful analytical marker for the stringent discrimination of Lister427 derivatives from other trypanosome strains
Fast-growing till over ancient ice in Beacon Valley, Antarctica
We analyze published cosmogenic 3He depth profiles through the till that covers relict glacier ice in Beacon Valley, Antarctica, in order to derive rigorous constraints on the till thickness history, and on the amount and rate of ice loss by sublimation. The till is a residue of debris-laden ice that sublimed. The 3He profiles show that the lower 80% of the till formed in the past 310–43 k.y. under sublimation rates averaging >7 m·m.y.−1 (meters per million years). Such rapid recent growth of the till contradicts previous interpretations that it is older than 8.1 Ma at an adjacent site, where it encloses volcanic ash of this age. We question whether the ash provides a valid age constraint for the ice. Cosmogenic nuclide analysis of the till where the ash was collected for dating should resolve this question
Proteomic analysis of the Plasmodium male gamete reveals the key role for glycolysis in flagellar motility.
BACKGROUND: Gametogenesis and fertilization play crucial roles in malaria transmission. While male gametes are thought to be amongst the simplest eukaryotic cells and are proven targets of transmission blocking immunity, little is known about their molecular organization. For example, the pathway of energy metabolism that power motility, a feature that facilitates gamete encounter and fertilization, is unknown.
METHODS: Plasmodium berghei microgametes were purified and analysed by whole-cell proteomic analysis for the first time. Data are available via ProteomeXchange with identifier PXD001163.
RESULTS: 615 proteins were recovered, they included all male gamete proteins described thus far. Amongst them were the 11 enzymes of the glycolytic pathway. The hexose transporter was localized to the gamete plasma membrane and it was shown that microgamete motility can be suppressed effectively by inhibitors of this transporter and of the glycolytic pathway.
CONCLUSIONS: This study describes the first whole-cell proteomic analysis of the malaria male gamete. It identifies glycolysis as the likely exclusive source of energy for flagellar beat, and provides new insights in original features of Plasmodium flagellar organization
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