8,204 research outputs found
Quasi-Kondo Phenomenon due to Dynamical Jahn-Teller Effect
A mechanism of non-magnetic Kondo effect is proposed on the basis of a
multiorbital Anderson model coupled with dynamical Jahn-Teller (JT) phonons. An
electron system coupled dynamically with JT phonons has a vibronic ground state
with double degeneracy due to clockwise and anti-clockwise rotational modes
with entropy of . When a temperature is lower than a characteristic
energy to turn the rotational direction, the rotational degree of freedom is
eventually suppressed and the corresponding entropy is released,
leading to quasi-Kondo behavior. We discuss possible relevance of this
quasi-Kondo phenomenon to electronic properties of filled skutterudites.Comment: 4 pages, 3 figure
Rad62 protein functionally and physically associates with the Smc5/Smc6 protein complex and is required for chromosome integrity and recombination repair in fission yeast
Smc5 and Smc6 proteins form a heterodimeric SMC (structural maintenance of chromosome) protein complex like SMC1-SMC3 cohesin and SMC2-SMC4 condensin, and they associate with non-SMC proteins Nse1 and Nse2 stably and Rad60 transiently. This multiprotein complex plays an essential role in maintaining chromosome integrity and repairing DNA double strand breaks (DSBs). This study characterizes a Schizosaccharomyces pombe mutant rad62-1, which is hypersensitive to methyl methanesulfonate (MMS) and synthetically lethal with rad2 (a feature of recombination mutants). rad62-1 is hypersensitive to UV and gamma rays, epistatic with rhp51, and defective in repair of DSBs. rad62 is essential for viability and genetically interacts with rad60, smc6, and brc1. Rad62 protein physically associates with the Smc5-6 complex. rad62-1 is synthetically lethal with mutations in the genes promoting recovery from stalled replication, such as rqh1, srs2, and mus81, and those involved in nucleotide excision repair like rad13 and rad16. These results suggest that Rad62, like Rad60, in conjunction with the Smc5-6 complex, plays an essential role in maintaining chromosome integrity and recovery from stalled replication by recombination
Episodic modulations in supernova radio light curves from luminous blue variable supernova progenitor models
Ideally, one would like to know which type of core-collapse SNe is
produced by different progenitors and the channels of stellar evolution leading
to these progenitors. These links have to be very well known to use the
observed frequency of different types of SN events for probing the star
formation rate and massive star evolution in different types of galaxies.
We investigate the link between LBV as SN progenitors and the appearance
of episodic radio light curve modulations of the SN event. We use the
20Msun and 25Msun models with rotation at solar metallicity, part of an
extended grid of stellar models computed by the Geneva team. At their pre-SN
stage, these two models have recently been shown to have spectra similar to
those of LBV stars and possibly explode as Type IIb SNe. Based on the wind
properties before the explosion, we derive the density structure of their
circumstellar medium. This structure is used as input for computing the SN
radio light curve. We find that the 20Msun model shows radio light
curves with episodic luminosity modulations, similar to those observed in some
Type IIb SNe. This occurs because the evolution of the 20Msun model terminates
in a region of the HR diagram where radiative stellar winds present strong
density variations, caused by the bistability limit. The 25Msun model, ending
its evolution in a zone of the HR diagram where no change of the mass-loss
rates is expected, presents no such modulations in its radio SN light curve.
Our results reinforce the link between SN progenitors and LBV
stars. We also confirm the existence of a physical mechanism for a single star
to have episodic radio light curve modulations. In the case of the 25Msun
progenitors, we do not obtain modulations in the radio light curve, but our
models may miss some outbursting behavior in the late stages of massive stars.Comment: 5 pages, 3 figures, accepted by Astronomy & Astrophysics Letter
Interfaces of correlated electron systems: Proposed mechanism for colossal electroresistance
Mott's metal-insulator transition at an interface due to band bending is
studied by the density matrix renormalization group (DMRG). We show that the
result can be recovered by a simple modification of the conventional Poisson's
equation approach used in semi-conductor heterojunctions. A novel mechanism of
colossal electroresistance is proposed, which incorporates the hysteretic
behavior of the transition in higher dimensions.Comment: 5 pages, 3 figures, title change
Gutzwiller study of extended Hubbard models with fixed boson densities
We studied all possible ground states, including supersolid (SS) phases and
phase separations of hard-core- and soft-core-extended Bose--Hubbard models
with fixed boson densities by using the Gutzwiller variational wave function
and the linear programming method. We found that the phase diagram of the
soft-core model depends strongly on its transfer integral. Furthermore, for a
large transfer integral, we showed that an SS phase can be the ground state
even below or at half filling against the phase separation. We also found that
the density difference between nearest-neighbor sites, which indicates the
density order of the SS phase, depends strongly on the boson density and
transfer integral.Comment: 14 pages, 14 figures, to be published in Phys. Rev.
Reliable postprocessing improvement of van der Waals heterostructures
The successful assembly of heterostructures consisting of several layers of
different 2D materials in arbitrary order by exploiting van der Waals forces
has truly been a game changer in the field of low dimensional physics. For
instance, the encapsulation of graphene or MoS2 between atomically flat
hexagonal boron nitride (hBN) layers with strong affinity and graphitic gates
that screen charge impurity disorder provided access to a plethora of
interesting physical phenomena by drastically boosting the device quality. The
encapsulation is accompanied by a self-cleansing effect at the interfaces. The
otherwise predominant charged impurity disorder is minimized and random strain
fluctuations ultimately constitute the main source of residual disorder.
Despite these advances, the fabricated heterostructures still vary notably in
their performance. While some achieve record mobilities, others only possess
mediocre quality. Here, we report a reliable method to improve fully completed
van der Waals heterostructure devices with a straightforward post-processing
surface treatment based on thermal annealing and contact mode AFM. The impact
is demonstrated by comparing magnetotransport measurements before and after the
AFM treatment on one and the same device as well as on a larger set of treated
and untreated devices to collect device statistics. Both the low temperature
properties as well as the room temperature electrical characteristics, as
relevant for applications, improve on average substantially. We surmise that
the main beneficial effect arises from reducing nanometer scale corrugations at
the interfaces, i.e. the detrimental impact of random strain fluctuations
Identifying States of a Financial Market
The understanding of complex systems has become a central issue because
complex systems exist in a wide range of scientific disciplines. Time series
are typical experimental results we have about complex systems. In the analysis
of such time series, stationary situations have been extensively studied and
correlations have been found to be a very powerful tool. Yet most natural
processes are non-stationary. In particular, in times of crisis, accident or
trouble, stationarity is lost. As examples we may think of financial markets,
biological systems, reactors or the weather. In non-stationary situations
analysis becomes very difficult and noise is a severe problem. Following a
natural urge to search for order in the system, we endeavor to define states
through which systems pass and in which they remain for short times. Success in
this respect would allow to get a better understanding of the system and might
even lead to methods for controlling the system in more efficient ways.
We here concentrate on financial markets because of the easy access we have
to good data and because of the strong non-stationary effects recently seen. We
analyze the S&P 500 stocks in the 19-year period 1992-2010. Here, we propose
such an above mentioned definition of state for a financial market and use it
to identify points of drastic change in the correlation structure. These points
are mapped to occurrences of financial crises. We find that a wide variety of
characteristic correlation structure patterns exist in the observation time
window, and that these characteristic correlation structure patterns can be
classified into several typical "market states". Using this classification we
recognize transitions between different market states. A similarity measure we
develop thus affords means of understanding changes in states and of
recognizing developments not previously seen.Comment: 9 pages, 8 figure
Generation of polarization entanglement from spatially-correlated photons in spontaneous parametric down-conversion
We propose a novel scheme to generate polarization entanglement from
spatially-correlated photon pairs. We experimentally realized a scheme by means
of a spatial correlation effect in a spontaneous parametric down-conversion and
a modified Michelson interferometer. The scheme we propose in this paper can be
interpreted as a conversion process from spatial correlation to polarization
entanglement.Comment: 4 pages, 4 figure
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