201 research outputs found
Magneto-structural properties of the layered quasi-2D triangular-lattice antiferromagnets CsCuClBr for = 0,1,2 and 4
We present a study of the magnetic susceptibility under variable
hydrostatic pressure on single crystals of CsCuClBr. This
includes the border compounds \textit{x} = 0 and 4, known as good realizations
of the distorted triangular-lattice spin-1/2 Heisenberg antiferromagnet, as
well as the isostructural stoichiometric systems CsCuClBr and
CsCuClBr. For the determination of the exchange coupling
constants and , data were fitted by a
model \cite{Schmidt2015}. Its application, validated for the
border compounds, yields a degree of frustration / = 0.47 for
CsCuClBr and / 0.63 - 0.78 for
CsCuClBr, making these systems particular interesting
representatives of this family. From the evolution of the magnetic
susceptibility under pressure up to about 0.4\,GPa, the maximum pressure
applied, two observations were made for all the compounds investigated here.
First, we find that the overall energy scale, given by +
), increases under pressure, whereas the ratio
/ remains unchanged in this pressure range. These experimental
observations are in accordance with the results of DFT calculations performed
for these materials. Secondly, for the magnetoelastic coupling constants,
extraordinarily small values are obtained. We assign these observations to a
structural peculiarity of this class of materials
Realization of a single Josephson junction for Bose-Einstein condensates
We report on the realization of a double-well potential for Rubidium-87
Bose-Einstein condensates. The experimental setup allows the investigation of
two different dynamical phenomena known for this system - Josephson
oscillations and self-trapping. We give a detailed discussion of the
experimental setup and the methods used for calibrating the relevant
parameters. We compare our experimental findings with the predictions of an
extended two-mode model and find quantitative agreement
Comparative Study of Human and Automated Screening for Antinuclear Antibodies by Immunofluorescence on HEp-2 Cells
Background: Several automated systems had been developed in order to reduce inter-observer variability in
indirect immunofluorescence (IIF) interpretation. We aimed to evaluate the performance of a processing system in
antinuclear antibodies (ANA) screening on HEp-2 cells.
Patients and Methods: This study included 64 ANA-positive sera and 107 ANA-negative sera that underwent IIF on two
commercial kits of HEp-2 cells (BioSystems® and Euroimmun®). IIF results were compared with a novel automated
interpretation system, the “CyclopusCADImmuno®” (CAD).
Results: All ANA-positive sera images were recognized as positive by CAD (sensitivity = 100%), while 17 (15.9%) of the
ANA-negative sera images were interpreted as positive (specificity = 84.1%), =0.799 (SD=0.045). Comparison of IIF
pattern determination between human and CAD system revealed on HEp-2 (BioSystems®), a complete concordance in
6 (9.37%) sera, a partial concordance (sharing of at least 1 pattern) in 42 (65.6%) cases and in 16 (25%) sera the
pattern interpretation was discordant. Similarly, on HEp-2 (Euroimmun®) the concordance in pattern interpretation was
total in 5 (7.8%) sera, partial in 39 (60.9%) and absent in 20 (31.25%). For both tested HEp-2 cells kits agreement was
enhanced for the most common patterns, homogenous, fine speckled and coarse speckled. While there was an issue in
identification of nucleolar, dots and nuclear membranous patterns by CAD.
Conclusion: Assessment of ANA by IIF on HEp-2 cells using the automated interpretation system, the
“CyclopusCADImmuno®” is a reliable method for positive/negative differentiation. Continuous integration of IIF images
would improve the pattern identification by the CAD
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Structure of human frizzled5 by fiducial-assisted cryo-em supports a heterodimeric mechanism of canonical wnt signaling
Frizzleds (Fzd) are the primary receptors for Wnt morphogens, which are essential regulators of stem cell biology, yet the structural basis of Wnt signaling through Fzd remains poorly understood. Here we report the structure of an unliganded human Fzd5 determined by single-particle cryo-EM at 3.7 Å resolution, with the aid of an antibody chaperone acting as a fiducial marker. We also analyzed the topology of low-resolution XWnt8/Fzd5 complex particles, which revealed extreme flexibility between the Wnt/Fzd-CRD and the Fzd-TM regions. Analysis of Wnt/b-catenin signaling in response to Wnt3a versus a ‘surrogate agonist’ that cross-links Fzd to LRP6, revealed identical structure-activity relationships. Thus, canonical Wnt/b-catenin signaling appears to be principally reliant on ligand-induced Fzd/LRP6 heterodimerization, versus the allosteric mechanisms seen in structurally analogous class A G protein-coupled receptors, and Smoothened. These findings deepen our mechanistic understanding of Wnt signal transduction, and have implications for harnessing Wnt agonism in regenerative medicine
Josephson dynamics for coupled polariton modes under the atom-field interaction in the cavity
We consider a new approach to the problem of Bose-Einstein condensation (BEC)
of polaritons for atom-field interaction under the strong coupling regime in
the cavity. We investigate the dynamics of two macroscopically populated
polariton modes corresponding to the upper and lower branch energy states
coupled via Kerr-like nonlinearity of atomic medium. We found out the
dispersion relations for new type of collective excitations in the system under
consideration. Various temporal regimes like linear (nonlinear) Josephson
transition and/or Rabi oscillations, macroscopic quantum self-trapping (MQST)
dynamics for population imbalance of polariton modes are predicted. We also
examine the switching properties for time-averaged population imbalance
depending on initial conditions, effective nonlinear parameter of atomic medium
and kinetic energy of low-branch polaritons.Comment: 10 pages, 6 postscript figures, uses svjour.cl
Inter-subunit coupling enables fast CO2-fixation by reductive carboxylases
Enoyl-CoA carboxylases/reductases (ECRs) are some of the most efficient CO2-fixing enzymes described to date. However, the molecular mechanisms underlying the extraordinary catalytic activity of ECRs on the level of the protein assembly remain elusive. Here we used a combination of ambient-temperature X-ray free electron laser (XFEL) and cryogenic synchrotron experiments to study the structural organization of the ECR from Kitasatospora setae. The K. setae ECR is a homotetramer that differentiates into a pair of dimers of open- and closed-form subunits in the catalytically active state. Using molecular dynamics simulations and structure-based mutagenesis, we show that catalysis is synchronized in the K. setae ECR across the pair of dimers. This conformational coupling of catalytic domains is conferred by individual amino acids to achieve high CO2-fixation rates. Our results provide unprecedented insights into the dynamic organization and synchronized inter- and intrasubunit communications of this remarkably efficient CO2-fixing enzyme during catalysis.
Macroscopic superposition states of ultracold bosons in a double-well potential
We present a thorough description of the physical regimes for ultracold
bosons in double wells, with special attention paid to macroscopic
superpositions (MSs). We use a generalization of the Lipkin-Meshkov-Glick
Hamiltonian of up to eight single particle modes to study these MSs, solving
the Hamiltonian with a combination of numerical exact diagonalization and
high-order perturbation theory. The MS is between left and right potential
wells; the extreme case with all atoms simultaneously located in both wells and
in only two modes is the famous NOON state, but our approach encompasses much
more general MSs. Use of more single particle modes brings dimensionality into
the problem, allows us to set hard limits on the use of the original two-mode
LMG model commonly treated in the literature, and also introduces a new mixed
Josephson-Fock regime. Higher modes introduce angular degrees of freedom and MS
states with different angular properties.Comment: 15 pages, 8 figures, 1 table. Mini-review prepared for the special
issue of Frontiers of Physics "Recent Progresses on Quantum Dynamics of
Ultracold Atoms and Future Quantum Technologies", edited by Profs. Lee, Ueda,
and Drummon
Preliminary results of the project A.I.D.A. (Auto Immunity: Diagnosis Assisted by computer)
In this paper, are presented the preliminary results of the A.I.D.A. (Auto Immunity: Diagnosis
Assisted by computer) project which is developed in the frame of the cross-border cooperation Italy-Tunisia.
According to the main objectives of this project, a database of interpreted Indirect ImmunoFluorescence (IIF)
images on HEp 2 cells is being collected thanks to the contribution of Italian and Tunisian experts involved in
routine diagnosis of autoimmune diseases. Through exchanging images and double reporting; a Gold Standard
database, containing around 1000 double reported IIF images with different patterns including negative tests,
has been settled. This Gold Standard database has been used for optimization of a computing solution (CADComputer
Aided Detection) and for assessment of its added value in order to be used along with an
immunologist as a second reader in detection of auto antibodies for autoimmune disease diagnosis. From the
preliminary results obtained, the CAD appeared more powerful than junior immunologists used as second
readers and may significantly improve their efficacy
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