4,571 research outputs found
Acetylene terminated matrix resins
The synthesis of resins with terminal acetylene groups has provided a promising technology to yield high performance structural materials. Because these resins cure through an addition reaction, no volatile by-products are produced during the processing. The cured products have high thermal stability and good properties retention after exposure to humidity. Resins with a wide variety of different chemical structures between the terminal acetylene groups are synthesized and their mechanical properties studied. The ability of the acetylene cured polymers to give good mechanical properties is demonstrated by the resins with quinoxaline structures. Processibility of these resins can be manipulated by varying the chain length between the acetylene groups or by blending in different amounts of reactive deluents. Processing conditions similar to the state-of-the-art epoxy can be attained by using backbone structures like ether-sulfone or bis-phenol-A. The wide range of mechanical properties and processing conditions attainable by this class of resins should allow them to be used in a wide variety of applications
Quantum System Identification by Bayesian Analysis of Noisy Data: Beyond Hamiltonian Tomography
We consider how to characterize the dynamics of a quantum system from a
restricted set of initial states and measurements using Bayesian analysis.
Previous work has shown that Hamiltonian systems can be well estimated from
analysis of noisy data. Here we show how to generalize this approach to systems
with moderate dephasing in the eigenbasis of the Hamiltonian. We illustrate the
process for a range of three-level quantum systems. The results suggest that
the Bayesian estimation of the frequencies and dephasing rates is generally
highly accurate and the main source of errors are errors in the reconstructed
Hamiltonian basis.Comment: 6 pages, 3 figure
Prepyramid-to-pyramid transition of SiGe islands on Si(001)
The morphology of the first three-dimensional islands appearing during
strained growth of SiGe alloys on Si(001) was investigated by scanning
tunneling microscopy. High resolution images of individual islands and a
statistical analysis of island shapes were used to reconstruct the evolution of
the island shape as a function of size. As they grow, islands undergo a
transition from completely unfacetted rough mounds (prepyramids) to partially
{105} facetted islands and then they gradually evolve to {105} facetted
pyramids. The results are in good agreement with the predictions of a recently
proposed theoretical model
An AC susceptometer for the characterization of large, bulk superconducting samples
The main purpose of this work was to design, develop and construct a simple,
low-cost AC susceptometer to measure large, bulk superconducting samples (up to
32 mm in diameter) in the temperature range 78-120 K. The design incorporates a
double heating system that enables a high heating rate (25 K/hour) while
maintaining a small temperature gradient (< 0.2 K) across the sample. The
apparatus can be calibrated precisely using a copper coil connected in series
with the primary coil. The system has been used successfully to measure the
temperature dependence of the AC magnetic properties of entire RE-Ba-Cu-O
[(RE)BCO] bulk superconducting domains. A typical AC susceptibility measurement
run from 78 K to 95 K takes about 2 hours, with excellent temperature
resolution (temperature step ~ 4 mK) around the critical temperature, in
particular.Comment: 25 pages, 7 figures. Accepted for publication in Measurement Science
and Technolog
A focused telephonic nursing intervention delivers improved adherence to A1c testing
Compliance with hemoglobin A1c (A1c) testing is suboptimal despite the clear national recommendations and guidelines established for care of patients with diabetes. Recent studies have demonstrated a relationship between participation in a diabetes disease management (DM) program and improved adherence to A1c testing. A focused intervention study was initiated to investigate the ability of a DM program to drive improvement in A1c testing. A cohort of 36,327 members experienced a statistically significant increase (29%) in A1c testing while participating in the 6-month focused intervention. This finding demonstrated that a focused DM intervention is able to deliver improvement in a clinical process metric critical for managing patients with diabetes, thereby reducing their risk of disease exacerbation
Severe infantile-onset cardiomyopathy associated with a homozygous deletion in desmin
Desminopathy is a genetically heterogeneous disorder with autosomal dominant pattern of inheritance in most affected families; the age of disease onset is on average 30 years. We studied a patient with a history of recurrent episodes of syncope from infancy who later developed second-degree AV block and restrictive cardiomyopathy; she subsequently suffered several episodes of ventricular tachyarrhythmia requiring implantation of bicameral defibrillator. Neurological examination revealed rapidly progressive bilateral facial weakness, winging of the scapulae, symmetric weakness and atrophy of the trunk muscles, shoulder girdle and distal muscles of both upper and lower extremities. Muscle biopsy demonstrated signs of myofibrillar myopathy with prominent subsarcolemmal desmin-reactive aggregates. Molecular analysis identified a homozygous deletion in DES resulting in a predicted in-frame obliteration of seven amino acids (p.R173_E179del) in the 1B domain of desmin. We describe the youngest known desminopathy patient with severe cardiomyopathy and aggressive course leading to the devastation of cardiac, skeletal and smooth musculature at an early age
Mammalian Adaptation of an Avian Influenza A Virus Involves Stepwise Changes in NS1
Influenza A viruses (IAVs) are common pathogens of birds that occasionally establish endemic infections in mammals. The processes and mechanisms that result in IAV mammalian adaptation are poorly understood. The viral non-structural 1 (NS1) protein counteracts the interferon (IFN) response, a central component of the host-species barrier.
We characterised the NS1 proteins of equine influenza virus (EIV), a mammalian IAV lineage of avian origin. We showed that evolutionary distinct NS1s counteract the IFN response using different and mutually exclusive mechanisms: while the NS1s of early EIVs block general gene expression by binding to the cellular polyadenylation specific factor 30 (CPSF30), NS1s from more evolved EIVs specifically block the induction of IFN-stimulated genes by interfering with the JAK/STAT pathway. These contrasting anti-IFN strategies are associated with two mutations that appeared sequentially and became rapidly selected during EIV evolution, highlighting the importance of evolutionary processes on immune evasion mechanisms during IAV adaptation
Meshless methods for ‘gas ‐ evaporating droplet’ flow modelling
The main ideas of simulation of two-phase flows, based on a combination of the conventional Lagrangian method or fully Lagrangian method (FLM) for the dispersed phase and the mesh-free vortex and thermal blob methods for the carrier phase, are summarised. A meshless method for modelling of 2D transient, non-isothermal, gasdroplet flows with phase transitions, based on a combination of the viscous-vortex and thermal-blob methods for the carrier phase with the Lagrangian approach for the dispersed phase, is described. The one-way coupled, two-fluid approach is used in the analysis. The method makes it possible to avoid the `remeshing' procedure (recalculation of flow parameters from Eulerian to Lagrangian grids) and reduces the problem to the solution of three systems of ordinary differential equations, describing the motion of viscous-vortex blobs, thermal blobs, and evaporating droplets. The gas velocity field is restored using the Biot-Savart integral. The numerical algorithm is verified against the analytical solution for a non-isothermal Lamb vortex. The method is applied to modelling of an impulse two-phase cold jet injected into a quiescent hot gas, taking into account droplet evaporation. Various flow patterns are obtained in the calculations, depending on the initial droplet size: (i) low-inertia droplets, evaporating at a higher rate, form ring-like structures and are accumulated only behind the vortex pair; (ii) large droplets move closer to the jet axis, with their sizes remaining almost unchanged; and (iii) intermediate-size droplets are accumulated in a curved band whose ends trail in the periphery behind the head of the cloud, with larger droplets being collected at the front of the two-phase region
Study of coupling loss on bi-columnar BSCCO/Ag tapes by a.c. susceptibility measurements
Coupling losses were studied in composite tapes containing superconducting
material in the form of two separate stacks of densely packed filaments
embedded in a metallic matrix of Ag or Ag alloy. This kind of sample geometry
is quite favorable for studying the coupling currents and in particular the
role of superconducting bridges between filaments. By using a.c. susceptibility
technique, the electromagnetic losses as function of a.c. magnetic field
amplitude and frequency were measured at the temperature T = 77 K for two tapes
with different matrix composition. The length of samples was varied by
subsequent cutting in order to investigate its influence on the dynamics of
magnetic flux penetration. The geometrical factor which takes into
account the demagnetizing effects was established from a.c. susceptibility data
at low amplitudes. Losses vs frequency dependencies have been found to agree
nicely with the theoretical model developed for round multifilamentary wires.
Applying this model, the effective resistivity of the matrix was determined for
each tape, by using only measured quantities. For the tape with pure silver
matrix its value was found to be larger than what predicted by the theory for
given metal resistivity and filamentary architecture. On the contrary, in the
sample with a Ag/Mg alloy matrix, an effective resistivity much lower than
expected was determined. We explain these discrepancies by taking into account
the properties of the electrical contact of the interface between the
superconducting filaments and the normal matrix. In the case of soft matrix of
pure Ag, this is of poor quality, while the properties of alloy matrix seem to
provoke an extensive creation of intergrowths which can be actually observed in
this kind of samples.Comment: 20 pages 11 figure, submitted to Superconductor Science and
Technolog
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