2,340 research outputs found
Suppression of Shot Noise in Quantum Point Contacts in the "0.7" Regime
Experimental investigations of current shot noise in quantum point contacts
show a reduction of the noise near the 0.7 anomaly. It is demonstrated that
such a reduction naturally arises in a model proposed recently to explain the
characteristics of the 0.7 anomaly in quantum point contacts in terms of a
quasi-bound state, due to the emergence of two conducting channels. We
calculate the shot noise as a function of temperature, applied voltage and
magnetic field, and demonstrate an excellent agreement with experiments. It is
predicted that with decreasing temperature, voltage and magnetic field, the dip
in the shot noise is suppressed due to the Kondo effect.Comment: 4 pages, 1 figur
Tunneling Spectroscopy of Disordered Two-Dimensional Electron Gas in the Quantum Hall Regime
Recently, Dial et al. presented measurements of the tunneling density of
states into the bulk of a two dimensional electron gas under strong magnetic
fields. Several high energy features appear in the measured spectrum showing a
distinct dependence on filling factor and a unique response to temperature. We
present a quantitative account of the observed structure, and argue it results
from the repulsive Coulomb interactions between the tunneling electron and
states localized at disorder potential wells. The quenching of the kinetic
energy by the applied magnetic field leads to an electron addition spectrum
that is primarily determined by the external magnetic field and is nearly
independent of the disorder potential. Using a Hartree-Fock model we reproduce
the salient features of the observed structure
Andreev Tunneling in Strongly Interacting Quantum Dots
We review recent work on resonant Andreev tunneling through a strongly
interacting quantum dot connected to a normal and to a superconducting lead. We
derive a general expression for the current flowing in the structure and
discuss the linear and non-linear transport in the nonperturbative regime. New
effects associated to the Kondo resonance combined with the two-particle
tunneling arise. The Kondo anomaly in the characteristics depends on the
relative size of the gap energy and the Kondo temperature.Comment: 8 pages, 4 figures; submitted to Superlattices and Microstructure
A simple stochastic model for the evolution of protein lengths
We analyse a simple discrete-time stochastic process for the theoretical
modeling of the evolution of protein lengths. At every step of the process a
new protein is produced as a modification of one of the proteins already
existing and its length is assumed to be random variable which depends only on
the length of the originating protein. Thus a Random Recursive Trees (RRT) is
produced over the natural integers. If (quasi) scale invariance is assumed, the
length distribution in a single history tends to a lognormal form with a
specific signature of the deviations from exact gaussianity. Comparison with
the very large SIMAP protein database shows good agreement.Comment: 12 pages, 4 figure
Adenoid cystic carcinoma: emerging role of translocations and gene fusions.
Adenoid cystic carcinoma (ACC), the second most common salivary gland malignancy, is notorious for poor prognosis, which reflects the propensity of ACC to progress to clinically advanced metastatic disease. Due to high long-term mortality and lack of effective systemic treatment, the slow-growing but aggressive ACC poses a particular challenge in head and neck oncology. Despite the advancements in cancer genomics, up until recently relatively few genetic alterations critical to the ACC development have been recognized. Although the specific chromosomal translocations resulting in MYB-NFIB fusions provide insight into the ACC pathogenesis and represent attractive diagnostic and therapeutic targets, their clinical significance is unclear, and a substantial subset of ACCs do not harbor the MYB-NFIB translocation. Strategies based on detection of newly described genetic events (such as MYB activating super-enhancer translocations and alterations affecting another member of MYB transcription factor family-MYBL1) offer new hope for improved risk assessment, therapeutic intervention and tumor surveillance. However, the impact of these approaches is still limited by an incomplete understanding of the ACC biology, and the manner by which these alterations initiate and drive ACC remains to be delineated. This manuscript summarizes the current status of gene fusions and other driver genetic alterations in ACC pathogenesis and discusses new therapeutic strategies stemming from the current research
Evidence for localization and 0.7 anomaly in hole quantum point contacts
Quantum point contacts implemented in p-type GaAs/AlGaAs heterostructures are
investigated by low-temperature electrical conductance spectroscopy
measurements. Besides one-dimensional conductance quantization in units of
a pronounced extra plateau is found at about which
possesses the characteristic properties of the so-called "0.7 anomaly" known
from experiments with n-type samples. The evolution of the 0.7 plateau in high
perpendicular magnetic field reveals the existence of a quasi-localized state
and supports the explanation of the 0.7 anomaly based on self-consistent charge
localization. These observations are robust when lateral electrical fields are
applied which shift the relative position of the electron wavefunction in the
quantum point contact, testifying to the intrinsic nature of the underlying
physics.Comment: 4.2 pages, 3 figure
Origins of conductance anomalies in a p-type GaAs quantum point contact
Low temperature transport measurements on a p-GaAs quantum point contact are
presented which reveal the presence of a conductance anomaly that is markedly
different from the conventional `0.7 anomaly'. A lateral shift by asymmetric
gating of the conducting channel is utilized to identify and separate different
conductance anomalies of local and generic origins experimentally. While the
more generic 0.7 anomaly is not directly affected by changing the gate
configuration, a model is proposed which attributes the additional conductance
features to a gate-dependent coupling of the propagating states to localized
states emerging due to a nearby potential imperfection. Finite bias
conductivity measurements reveal the interplay between the two anomalies
consistently with a two-impurity Kondo model
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