99,485 research outputs found
Study of 0- phase transition in hybrid superconductor-InSb nanowire quantum dot devices
Hybrid superconductor-semiconducting nanowire devices provide an ideal
platform to investigating novel intragap bound states, such as the Andreev
bound states (ABSs), Yu-Shiba-Rusinov (YSR) states, and the Majorana bound
states. The competition between Kondo correlations and superconductivity in
Josephson quantum dot (QD) devices results in two different ground states and
the occurrence of a 0- quantum phase transition. Here we report on
transport measurements on hybrid superconductor-InSb nanowire QD devices with
different device geometries. We demonstrate a realization of continuous
gate-tunable ABSs with both 0-type levels and -type levels. This allow us
to manipulate the transition between 0 and junction and explore charge
transport and spectrum in the vicinity of the quantum phase transition regime.
Furthermore, we find a coexistence of 0-type ABS and -type ABS in the same
charge state. By measuring temperature and magnetic field evolution of the
ABSs, the different natures of the two sets of ABSs are verified, being
consistent with the scenario of phase transition between the singlet and
doublet ground state. Our study provides insights into Andreev transport
properties of hybrid superconductor-QD devices and sheds light on the crossover
behavior of the subgap spectrum in the vicinity of 0- transition
Enhanced critical current density of MgB2 superconductor synthesized in high magnetic fields
The effect of high magnetic fields on the current carrying properties of both
MgB2 bulks and Fe-sheathed tapes was investigated following different thermal
sequences. It is found that application of a large magnetic field during
processing results in the quite uniform microstructure and the better
connectivity between the MgB2 grains. As a result, the Jc of these samples has
shown much higher value than that of the MgB2 samples in the absence of
magnetic field. The possible mechanism of the Jc enhancement under an external
magnetic field is also discussed.Comment: Presented at ISS2005, Tsukuba, 24-26 Oct., 2005; Revised versio
Stochastic Modeling of Hybrid Cache Systems
In recent years, there is an increasing demand of big memory systems so to
perform large scale data analytics. Since DRAM memories are expensive, some
researchers are suggesting to use other memory systems such as non-volatile
memory (NVM) technology to build large-memory computing systems. However,
whether the NVM technology can be a viable alternative (either economically and
technically) to DRAM remains an open question. To answer this question, it is
important to consider how to design a memory system from a "system
perspective", that is, incorporating different performance characteristics and
price ratios from hybrid memory devices.
This paper presents an analytical model of a "hybrid page cache system" so to
understand the diverse design space and performance impact of a hybrid cache
system. We consider (1) various architectural choices, (2) design strategies,
and (3) configuration of different memory devices. Using this model, we provide
guidelines on how to design hybrid page cache to reach a good trade-off between
high system throughput (in I/O per sec or IOPS) and fast cache reactivity which
is defined by the time to fill the cache. We also show how one can configure
the DRAM capacity and NVM capacity under a fixed budget. We pick PCM as an
example for NVM and conduct numerical analysis. Our analysis indicates that
incorporating PCM in a page cache system significantly improves the system
performance, and it also shows larger benefit to allocate more PCM in page
cache in some cases. Besides, for the common setting of performance-price ratio
of PCM, "flat architecture" offers as a better choice, but "layered
architecture" outperforms if PCM write performance can be significantly
improved in the future.Comment: 14 pages; mascots 201
Formation of X-Ray Cavities by the Magnetically Dominated Jet-Lobe System in a Galaxy Cluster
We present cosmological magnetohydrodynamic simulations of the formation of a
galaxy cluster with magnetic energy feedback from an active galactic nuclei
(AGN). We demonstrate that X-ray cavities can be produced by the magnetically
dominated jet-lobe system that is supported by a central axial current. The
cavities are magnetically dominated and their morphology is determined
jointedly by the magnetic fields and the background cluster pressure profile.
The expansion and motion of the cavities are driven initially by the Lorentz
force of the magnetic fields, and the cavities only become buoyant at late
stages ( Myr). We find that up to of the injected magnetic
energy goes into doing work against the hot cluster medium, heating it, and
lifting it in the cluster potential.Comment: 11 pages, 3 figures, minor correction
Does financial regulation matter? Market volatility and the US 1933/34 Acts
The impact of the US 1933/34 Acts, the rst national nancial regulation acts in the world, on nancial markets have been under debates since Stigler (1964). Major fi ndings in the literature is that nancial regulation enacted by these laws is at best being ine¤ective to improve nancial markets until some recent studies imply indirectly that they could be e¤ective. By studying daily returns of NYSE data from 1890 to1970, this paper provides systematic evidence that the 1933/34 Acts have substantially
reduced market volatilities after controlling for Great Depression e¤ect and macroeco-nomic variables. Moreover, we show that even when we treat the existence and the date of the volatility changes as unknown, statistically identi ed structural changes are fully consistent with the above results that the volatility reduction time coincide with the enacting of the Acts.postprin
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