5,129 research outputs found
Dicke quantum spin glass of atoms and photons
Recent studies of strongly interacting atoms and photons in optical cavities
have rekindled interest in the Dicke model of atomic qubits coupled to discrete
photon cavity modes. We study the multimode Dicke model with variable
atom-photon couplings. We argue that a quantum spin glass phase can appear,
with a random linear combination of the cavity modes superradiant. We compute
atomic and photon spectral response functions across this quantum phase
transition, both of which should be accessible in experiment.Comment: 4 pages, 3 figures, v2: described quantum optics set-up in more
detail; extended discussion on photon correlation functions and experimental
signatures; added reference
Enhanced Electron-Phonon Coupling and its Irrelevance to High T Superconductivity
It is argued that the origin of the buckling of the CuO planes in
certain cuprates as well as the strong electron-phonon coupling of the
phonon is due to the electric field across the planes induced by atoms with
different valence above and below. The magnitude of the electric field is
deduced from new Raman results on YBaCuO and
BiSr(CaY)CuO with different O and Y
doping, respectively. In the latter case it is shown that the symmetry breaking
by replacing Ca partially by Y enhances the coupling by an order of magnitude,
while the superconducting drops to about two third of its original value.Comment: 4 pages, 2 figures. This and other papers can be downloaded from
http://gwis2.circ.gwu.edu/~tp
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Unraveling the Impact of High-Order Silk Structures on Molecular Drug Binding and Release Behaviors
Silk continues to amaze: over the past decade, new research threads have emerged that include the use of silk fibroin for advanced pharmaceutics, including its suitability for drug delivery. Despite this ongoing interest, the details of silk fibroin structures and their subsequent drug interactions at the molecular level remain elusive, primarily because of the difficulties encountered in modeling the silk fibroin molecule. Here, we generated an atomistic silk model containing amorphous and crystalline regions. We then exploited advanced well-tempered metadynamics simulations to generate molecular conformations that we subsequently exposed to classical molecular dynamics simulations to monitor both drug binding and release. Overall, this study demonstrated the importance of the silk fibroin primary sequence, electrostatic interactions, hydrogen bonding, and higher-order conformation in the processes of drug binding and release. © Copyright © 2019 American Chemical Society
A real space renormalization group approach to spin glass dynamics
The slow non-equilibrium dynamics of the Edwards-Anderson spin glass model on
a hierarchical lattice is studied by means of a coarse-grained description
based on renormalization concepts. We evaluate the isothermal aging properties
and show how the occurrence of temperature chaos is connected to a gradual loss
of memory when approaching the overlap length. This leads to rejuvenation
effects in temperature shift protocols and to rejuvenation--memory effects in
temperature cycling procedures with a pattern of behavior parallel to
experimental observations.Comment: 4 pages, 4 figure
Multiple scaling regimes in simple aging models
We investigate aging in glassy systems based on a simple model, where a point
in configuration space performs thermally activated jumps between the minima of
a random energy landscape. The model allows us to show explicitly a subaging
behavior and multiple scaling regimes for the correlation function. Both the
exponents characterizing the scaling of the different relaxation times with the
waiting time and those characterizing the asymptotic decay of the scaling
functions are obtained analytically by invoking a `partial equilibrium'
concept.Comment: 4 pages, 3 figure
Ten-Year Minimum Follow-up Study of First Metatarsophalangeal Joint Fusion in Young vs Old Patients
BACKGROUND
Painful degenerative joint disease (DJD) of the first metatarsophalangeal joint (MTP I), or hallux rigidus, mainly occurs in later stages of life. For end-stage hallux rigidus, MTP I arthrodesis is considered the gold standard. As young and active patients are affected considerably less frequently, it currently remains unclear, whether they benefit to the same extent. We hypothesized that MTP I arthrodesis in younger patients would lead to an inferior outcome with decreased rates of overall with lower rates of patient postoperative pain and function compared to an older cohort.
METHODS
All patients aged 60 years. Minimum follow-up was 10 years. Outcome measures were Tegner activity score (TAS), a "Virtual Tegner activity score" (VTAS), the visual analog scale (VAS), and the Foot Function index (FFI).
RESULTS
Sixty-one MTP I fusions (n = 28 young, n = 33 old) in 46 patients were included in our study at an average of 14 years after surgery. Younger patients experienced significantly more pain relief as reflected by changes in VAS and FFI Pain subscale scores. No difference in functional outcomes was found with change in the FFI function subscale or in the ability to have desired functional outcomes using the ratio of TAS to VTAS. Revision rate did not differ between the two groups apart from hardware removal, which was significantly more likely in the younger group.
CONCLUSION
In patients below the age of 50 years with end-stage DJD of the first metatarsal joint, MTP I arthrodesis not only yielded highly satisfactory postoperative results at least equal outcome compared to an older cohort of patients aged >60 years at an average 14 years' follow-up. Based on these findings, we consider first metatarsal joint fusion even for young patients is a valid option to treat end-stage hallux rigidus.
LEVEL OF EVIDENCE
Level III, a case-control study
The expression of the mouse VpreB/λ5 locus in transformed cell lines and tumors of the B lineage differentiation pathway
The expression of RNA transcripts from two pre B lymphocyte related genes, VpreB and λ5, has been studied in a series of transformed cell lines which appear frozen at different states of B lineage differentiation, from early progenitors to surface Ig positive B cells. In the HAFTL-1 cell line, which arose from fetal liver by transformation with a retrovlrus containing the Hras oncogene, Northern analysis of poly A+ mRNA as well as in situ hybridization of RNA In single cells revealed that λ5 and VpreB are already expressed at the progenitor stage and increase in expression as the progenitors differentiate to precursor (preB) cells, or are turned off as the progenitors differentiate to myeloid cells. Continued rearrangements of Ig genes in pre B cell lines leading to Ig expression on the surface of NFS-5 pre B cells do not influence the continued expression of VpreB and λ5. Surface Ig-positive B lineage cell lines also express the pre B-related genes. Both Ly1+ as well as Ly1− pre B cells are VpreB and λ5positlve. Lipopolysaccharide (LPS) stimulation of 70Z/3 pre B cells does not turn off λ5 expression. It therefore appears that, at least In transformed cell lines, the expression of VpreB and λ5, is not directly regulated by the expression of μH, κL, or λL chains, LPS reactivity, or the Ly1 surface antigen. Fusion of plasmacytoma cells with normal pre B cells to generate pre B hybridomas leads to down-regulation of VpreB/λ5 expression. These results suggest that different trans-acting factors in more mature cells might down-regulate the expression of VpreB/λ
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