22,827 research outputs found
Josephson Effect in Pb/I/NbSe2 Scanning Tunneling Microscope Junctions
We have developed a method for the reproducible fabrication of
superconducting scanning tunneling microscope (STM) tips. We use these tips to
form superconductor/insulator/superconductor tunnel junctions with the STM tip
as one of the electrodes. We show that such junctions exhibit fluctuation
dominated Josephson effects, and describe how the Josephson product IcRn can be
inferred from the junctions' tunneling characteristics in this regime. This is
first demonstrated for tunneling into Pb films, and then applied in studies of
single crystals of NbSe2. We find that in NbSe2, IcRn is lower than expected,
which could be attributed to the interplay between superconductivity and the
coexisting charge density wave in this material.Comment: 3 pages, 2 figures. Presented at the New3SC-4 meeting, San Diego,
Jan. 16-21 200
The fabrication of reproducible superconducting scanning tunneling microscope tips
Superconducting scanning tunneling microscope tips have been fabricated with
a high degree of reproducibility. The fabrication process relies on sequential
deposition of superconducting Pb and a proximity-coupled Ag capping layer onto
a Pt/Ir tip. The tips were characterized by tunneling into both normal-metal
and superconducting films. The simplicity of the fabrication process, along
with the stability and reproducibility of the tips, clear the way for tunneling
studies with a well-characterized, scannable superconducting electrode.Comment: 4 pages, 3 figures, REVTeX. Submitted to Rev. Sci. Instru
Disseminated Nocardia cyriacigeorgia causing pancreatitis in a haploidentical stem cell transplant recipient.
We report the first published case of acute pancreatitis secondary to disseminated nocardiosis in a hematopoietic stem cell transplant (HSCT) recipient on chronic immunosuppression for graft-versus-host disease (GVHD). Nocardiosis in the HSCT population is relatively rare, and has not yet been described in haploidentical HSCT recipients. Our patient is a 28-year-old male with a history of haploidentical HSCT and GVHD of the skin and lung who was admitted to the hospital with acute pancreatitis. The workup for the etiology of his pancreatitis was initially unrevealing. He subsequently developed worsening sepsis and respiratory failure despite broad spectrum antimicrobials. After multiple bronchoscopies and pancreatic fluid sampling, he was found to have disseminated nocardiosis with Nocardia cyriacigeorgia
Hierarchical ResNeXt Models for Breast Cancer Histology Image Classification
Microscopic histology image analysis is a cornerstone in early detection of
breast cancer. However these images are very large and manual analysis is error
prone and very time consuming. Thus automating this process is in high demand.
We proposed a hierarchical system of convolutional neural networks (CNN) that
classifies automatically patches of these images into four pathologies: normal,
benign, in situ carcinoma and invasive carcinoma. We evaluated our system on
the BACH challenge dataset of image-wise classification and a small dataset
that we used to extend it. Using a train/test split of 75%/25%, we achieved an
accuracy rate of 0.99 on the test split for the BACH dataset and 0.96 on that
of the extension. On the test of the BACH challenge, we've reached an accuracy
of 0.81 which rank us to the 8th out of 51 teams
Unique Thermal Properties of Clothing Materials.
Cloth wearing seems so natural that everyone is self-deemed knowledgeable and has some expert opinions about it. However, to clearly explain the physics involved, and hence to make predictions for clothing design or selection, it turns out to be quite challenging even for experts. Cloth is a multiphased, porous, and anisotropic material system and usually in multilayers. The human body acts as an internal heat source in a clothing situation, thus forming a temperature gradient between body and ambient. But unlike ordinary engineering heat transfer problems, the sign of this gradient often changes as the ambient temperature varies. The human body also perspires and the sweat evaporates, an effective body cooling process via phase change. To bring all the variables into analysis quickly escalates into a formidable task. This work attempts to unravel the problem from a physics perspective, focusing on a few rarely noticed yet critically important mechanisms involved so as to offer a clearer and more accurate depiction of the principles in clothing thermal comfort
Josephson scanning tunneling microscopy
We propose a set of scanning tunneling microscopy experiments in which the
surface of superconductor is scanned by a superconducting tip. Potential
capabilities of such experimental setup are discussed. Most important
anticipated results of such an experiment include the position-resolved
measurement of the superconducting order parameter and the possibility to
determine the nature of the secondary component of the order parameter at the
surface. The theoretical description based on the tunneling Hamiltonian
formalism is presented.Comment: 6 pages, 7 figures, submitted to Phys. Rev.
Geometric, electronic properties and the thermodynamics of pure and Al--doped Li clusters
The first--principles density functional molecular dynamics simulations have
been carried out to investigate the geometric, the electronic, and the finite
temperature properties of pure Li clusters (Li, Li) and Al--doped
Li clusters (LiAl, LiAl). We find that addition of two Al
impurities in Li results in a substantial structural change, while the
addition of one Al impurity causes a rearrangement of atoms. Introduction of
Al--impurities in Li establishes a polar bond between Li and nearby Al
atom(s), leading to a multicentered bonding, which weakens the Li--Li metallic
bonds in the system. These weakened Li--Li bonds lead to a premelting feature
to occur at lower temperatures in Al--doped clusters. In LiAl, Al
atoms also form a weak covalent bond, resulting into their dimer like behavior.
This causes Al atoms not to `melt' till 800 K, in contrast to the Li atoms
which show a complete diffusive behavior above 400 K. Thus, although one Al
impurity in Li cluster does not change its melting characteristics
significantly, two impurities results in `surface melting' of Li atoms whose
motions are confined around Al dimer.Comment: 9 pages, 7 figure
Fluctuation Dominated Josephson Tunneling with a Scanning Tunneling Microscope
We demonstrate Josephson tunneling in vacuum tunnel junctions formed between
a superconducting scanning tunneling microscope tip and a Pb film, for junction
resistances in the range 50-300 k. We show that the superconducting
phase dynamics is dominated by thermal fluctuations, and that the Josephson
current appears as a peak centered at small finite voltages. In the presence of
microwave fields (f=15.0 GHz) the peak decreases in magnitude and shifts to
higher voltages with increasing rf power, in agreement with theory.Comment: 4 pages, REVTeX, submitted to PR
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