560 research outputs found
Doping effect on the evolution of the pairing symmetry in n-type superconductor near antiferromagnetic phase boundary
We present the investigation results of the in-plane \{rho}(T) resistivity
tensor at the temperature range 0.4-40 K in magnetic fields up to 90kOe (H||c,
J||ab) for electron-doped Nd{2-x}Ce{x}CuO{4+{\delta}} with different degree of
disorder near antiferromagnetic - superconducting phase boundary. We have
experimentally found that for optimally doped compound both the upper critical
field slope and the critical temperature decrease with increasing of the
disorder parameter (d-wave pairing) while in the case of the underdoped system
the critical temperature remains constant and (dHc2/dT)|Tc increases with
increasing of the disorder (s-wave pairing). These features suggest a possible
implementation of the complex mixture state as the (s+id)-pairing.Comment: 9 pages, 2 figure
Alternative splicing and protein function
BACKGROUND: Alternative splicing is a major mechanism of generating protein diversity in higher eukaryotes. Although at least half, and probably more, of mammalian genes are alternatively spliced, it was not clear, whether the frequency of alternative splicing is the same in different functional categories. The problem is obscured by uneven coverage of genes by ESTs and a large number of artifacts in the EST data. RESULTS: We have developed a method that generates possible mRNA isoforms for human genes contained in the EDAS database, taking into account the effects of nonsense-mediated decay and translation initiation rules, and a procedure for offsetting the effects of uneven EST coverage. Then we computed the number of mRNA isoforms for genes from different functional categories. Genes encoding ribosomal proteins and genes in the category "Small GTPase-mediated signal transduction" tend to have fewer isoforms than the average, whereas the genes in the category "DNA replication and chromosome cycle" have more isoforms than the average. Genes encoding proteins involved in protein-protein interactions tend to be alternatively spliced more often than genes encoding non-interacting proteins, although there is no significant difference in the number of isoforms of alternatively spliced genes. CONCLUSION: Filtering for functional isoforms satisfying biological constraints and accountung for uneven EST coverage allowed us to describe differences in alternative splicing of genes from different functional categories. The observations seem to be consistent with expectations based on current biological knowledge: less isoforms for ribosomal and signal transduction proteins, and more alternative splicing of interacting and cell cycle proteins
Nonlinear spectroscopy of excitonic states in transition metal dichalcogenides
Second-harmonic generation (SHG) is a well-known nonlinear spectroscopy
method to probe electronic structure, specifically, in transition metal
dichalcogenide (TMDC) monolayers. This work investigates the nonlinear dynamics
of a strongly excited TMDC monolayer by solving the time evolution equations
for the density matrix. It is shown that the presence of excitons qualitatively
changes the nonlinear dynamics leading, in particular, to a huge enhancement of
the nonlinear signal as a function of the dielectric environment. It is also
shown that the SHG polarization angular diagram and its dependence on the
driving strength are very sensitive to the type of exciton state. This
sensitivity suggests that SHG spectroscopy is a convenient tool for analyzing
the fine structure of excitonic states.Comment: 13 pages, 5 figure
The key role of smooth impurity potential in formation of hole spectrum for p-Ge/Ge_{1-x}Si_x heterostructures in the quantum Hall regime
We have measured the temperature (0.1 <= T <= 15 K) and magnetic field (0 <=
B <= 12 T) dependences of longitudinal and Hall resistivities for the
p-Ge_0.93Si_0.07/Ge multilayers with different Ge layer widths 10 <= d_w <= 38
nm and hole densities p_s = (1-5)10^11 cm^-2. Two models for the long-range
random impurity potential (the model with randomly distributed charged centers
located outside the conducting layer and the model of the system with a spacer)
are used for evaluation of the impurity potential fluctuation characteristics:
the random potential amplitude, nonlinear screening length in vicinity of
integer filling factors nu = 1 and nu = 2 and the background density of state
(DOS). The described models are suitable for explanation of the unusually high
value of DOS at nu = 1 and nu = 2, in contrast to the short-range impurity
potential models. For half-integer filling factors the linear temperature
dependence of the effective QHE plateau-to-plateau transition width nu_0(T) is
observed in contrast to scaling behavior for systems with short-range disorder.
The finite T -> 0 width of QHE transitions may be due to an effective low
temperature screening of smooth random potential owing to Coulomb repulsion of
electrons.Comment: Accepted for publication in Nanotechnolog
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