1,745 research outputs found
Suppressed Andreev Reflection at the Normal-Metal / Heavy-Fermion Superconductor CeCoIn Interface
Dynamic conductance spectra are taken from Au/CeCoIn point contacts in
the Sharvin limit along the (001) and (110) directions. Our conductance
spectra, reproducibly obtained over wide ranges of temperature, constitute the
cleanest data sets ever reported for HFSs. A signature for the emerging
heavy-fermion liquid is evidenced by the development of the asymmetry in the
background in the normal state. Below , an enhancement of the sub-gap
conductance arising from Andreev reflection is observed, with the magnitude of
13.3 % and 11.8 % for the (001) and the (110) point contacts,
respectively, an order of magnitude smaller than those observed in conventional
superconductors but consistent with those in other HFSs. Our zero-bias
conductance data for the (001) point contacts are best fit with the extended
BTK model using the d-wave order parameter. The fit to the full conductance
curve of the (001) point contact indicates the strong coupling nature
(). However, our observed suppression of both the
Andreev reflection signal and the energy gap indicates the failure of existing
models. We provide possible directions for theoretical formulations of the
electronic transport across an N/HFS interface. Several qualitative features
observed in the (110) point contacts provide the first clear spectroscopic
evidence for the symmetry.Comment: 13 pages, 7 figures, LaTeX, paper invited and submitted to SPIE
Conference on Strongly Correlated Electron Materials: Physics and
Nanoengineering, in San Diego, California, July 31 - August 4, 200
Andreev reflection spectroscopy of the heavy-fermion superconductor CeCoIn along three different crystallographic orientations
Andreev reflection spectroscopy has been performed on the heavy-fermion
superconductor (HFS) CeCoIn single crystals along three different
crystallographic orientations, (001), (110), and (100), using Au tips as
counter-electrodes. Dynamic conductance spectra are reproducible over wide
temperature ranges and consistent with each other, ensuring the spectroscopic
nature. Features common to all directions are: i) asymmetric behaviors of the
background conductance, which we attribute to the emerging coherent
heavy-fermion liquid; ii) energy scales (~1 meV) for conductance enhancement
due to Andreev reflection; iii) magnitudes of enhanced zero-bias conductance
(10 - 13 %). These values are an order of magnitude smaller than the predicted
value by the Blonder-Tinkham-Klapwijk (BTK) theory, but comparable to those for
other HFSs. Using the d-wave BTK model, we obtain an energy gap of ~ 460 ueV.
However, it is found that extended BTK models considering the mismatch in Fermi
surface parameters do not account for our data completely, which we attribute
to the shift of spectral weight to low energy as well as to the suppressed
Andreev reflection. A qualitative comparison of the conductance spectra with
calculated curves shows a consistency with d-symmetry, providing
the first spectroscopic evidence for the order parameter symmetry and resolving
the controversy over the location of the line nodes.Comment: invited talk submitted to the 8th M2S conference to be held in
Dresden Germany, July 9-14, 2006, 4 pages, 3 figure
Elevated intracellular cAMP exacerbates vulnerability to oxidative stress in optic nerve head astrocytes.
Glaucoma is characterized by a progressive loss of retinal ganglion cells and their axons, but the underlying biological basis for the accompanying neurodegeneration is not known. Accumulating evidence indicates that structural and functional abnormalities of astrocytes within the optic nerve head (ONH) have a role. However, whether the activation of cyclic adenosine 3',5'-monophosphate (cAMP) signaling pathway is associated with astrocyte dysfunction in the ONH remains unknown. We report here that the cAMP/protein kinase A (PKA) pathway is critical to ONH astrocyte dysfunction, leading to caspase-3 activation and cell death via the AKT/Bim/Bax signaling pathway. Furthermore, elevated intracellular cAMP exacerbates vulnerability to oxidative stress in ONH astrocytes, and this may contribute to axonal damage in glaucomatous neurodegeneration. Inhibition of intracellular cAMP/PKA signaling activation protects ONH astrocytes by increasing AKT phosphorylation against oxidative stress. These results strongly indicate that activation of cAMP/PKA pathway has an important role in astrocyte dysfunction, and suggest that modulating cAMP/PKA pathway has therapeutic potential for glaucomatous ONH degeneration
Limits of Binaries That Can Be Characterized by Gravitational Microlensing
Due to the high efficiency of planet detections, current microlensing planet
searches focus on high-magnification events. High-magnification events are
sensitive to remote binary companions as well and thus a sample of
wide-separation binaries are expected to be collected as a byproduct. In this
paper, we show that characterizing binaries for a portion of this sample will
be difficult due to the degeneracy of the binary-lensing parameters. This
degeneracy arises because the perturbation induced by the binary companion is
well approximated by the Chang-Refsdal lensing for binaries with separations
greater than a certain limit. For binaries composed of equal mass lenses, we
find that the lens binarity can be noticed up to the separations of
times of the Einstein radius corresponding to the mass of each lens. Among
these binaries, however, we find that the lensing parameters can be determined
only for a portion of binaries with separations less than times of
the Einstein radius.Comment: 5 pages, 3 figures, 1 tabl
Efficacy and safety of primary posterior capsulotomy during phaco-vitrectomy for epiretinal membrane
Abstract
Purpose
To evaluate the necessity and safety of primary posterior capsulotomy during phaco-vitrectomy for idiopathic epiretinal membrane (ERM).
Setting
Seoul National University Bundang Hospital, Seongnam, Korea.
Design
Retrospective consecutive cohort analysis.
Methods
This study enrolled 219 patients (228 eyes) who underwent combined 25-gauge phaco-vitrectomy for idiopathic ERM and cataract, divided into capsulotomy (−) group (152 eyes, 144 patients) and capsulotomy (+) group (76 eyes, 75 patients). The main outcomes were rate of posterior capsular opacity (PCO) occurrence and postoperative complications. Ophthalmic examinations were performed at baseline, 1, 3, 6, and 12 months postoperatively.
Results
PCO only occurred in capsulotomy (−) group (20 eyes, 13.2%), with mean onset of 10.59 months. Visually-significant PCO that needed Nd:YAG posterior capsulotomy was present in 9 eyes (45.0% of PCO eyes). The rate of cystoid macular edema (CME) was higher in capsulotomy (+) group (6.6% vs. 15.8%, p= 0.026) with longer duration (1.50 vs. 3.36 months, p= 0.019). Female sex and posterior capsulotomy were significant risk factors for CME occurrence (p< 0.05).
Conclusion
Primary posterior capsulotomy during phaco-vitrectomy for idiopathic ERM obviated the need for Nd:YAG posterior capsulotomy, but visually-significant PCO that needed Nd:YAG laser was not common. Considering the low rate of visually-significant PCO and high rate of postoperative CME, routine posterior capsulotomy during phaco-vitrectomy may not be necessary for preventing PCO in ERM
Divided disk cache and SSD FTL for improving performance in storage
Although there are many efficient techniques to minimize the speed gap between processor and the memory, it remains a bottleneck for various commercial implementations. Since secondary memory technologies are much slower than main memory, it is challenging to match memory speed to the processor. Usually, hard disk drives include semiconductor caches to improve their performance. A hit in the disk cache eliminates the mechanical seek time and rotational latency. To further improve performance a divided disk cache, subdivided between metadata and data, has been proposed previously. We propose a new algorithm to apply the SSD that is flash memory-based solid state drive by applying FTL. First, this paper evaluates the performance of such a disk cache via simulations using DiskSim. Then, we perform an experiment to evaluate the performance of the proposed algorithm.clos
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