52,470 research outputs found
Characterization of a thermoplastic polyimidesulfone
The detailed characterization of an experimental thermoplastic polyimidesulfone adhesive based on 3,3 prime-diaminodiphenylsulfone and 3,3 prime,4,4 prime-benzophenone tetracarboxylic dianhydride was studied. Model compounds were also examined. Thermal cyclization of the amide-acid to the imide was studied by a variety of techniques including DSC, TGA, MS, in situ diffuse reflectance-FTIR, and flow mearsurement. Characterizations were continued during the processing of adhesive tapes and the fabrication, bonding, and testing of lap shear specimens. Results provide fundamental insights into the role of cure chemistry, and the effects of residual solvent and volatile produces on processing and performance. These insights and the resulting chemical models should lead to more efficient processing cycles for these and other related thermoplastic adhesive systems
Satellite observations of reconnection between emerging and pre-existing small-scale magnetic fields
We report multi-wavelength ultraviolet observations taken with the IRIS
satellite, concerning the emergence phase in the upper chromosphere and
transition region of an emerging flux region (EFR) embedded in the unipolar
plage of active region NOAA 12529. The photospheric configuration of the EFR is
analyzed in detail benefitting from measurements taken with the
spectropolarimeter aboard the Hinode satellite, when the EFR was fully
developed. In addition, these data are complemented by full-disk, simultaneous
observations of the SDO satellite, relevant to the photosphere and the corona.
In the photosphere, magnetic flux emergence signatures are recognized in the
fuzzy granulation, with dark alignments between the emerging polarities,
cospatial with highly inclined fields. In the upper atmospheric layers, we
identify recurrent brightenings that resemble UV bursts, with counterparts in
all coronal passbands. These occur at the edges of the EFR and in the region of
the arch filament system (AFS) cospatial to the EFR. Jet activity is also found
at chromospheric and coronal levels, near the AFS and the observed brightness
enhancement sites. The analysis of the IRIS line profiles reveals the heating
of dense plasma in the low solar atmosphere and the driving of bi-directional
high-velocity flows with speeds up to 100 km/s at the same locations.
Furthermore, we detect a correlation between the Doppler velocity and line
width of the Si IV 1394 and 1402 \AA{} line profiles in the UV burst pixels and
their skewness. Comparing these findings with previous observations and
numerical models, we suggest evidence of several long-lasting, small-scale
magnetic reconnection episodes between the emerging bipole and the ambient
field. This process leads to the cancellation of a pre-existing photospheric
flux concentration of the plage with the opposite polarity flux patch of the
EFR. [...]Comment: 4 pages, 2 figures, to be published in "Nuovo Cimento C" as
proceeding of the Third Meeting of the Italian Solar and Heliospheric
Communit
Quantum oscillations observed in graphene at microwave frequencies
We have measured the microwave conductance of mechanically exfoliated
graphene at frequencies up to 8.5 GHz. The conductance at 4.2 K exhibits
quantum oscillations, and is independent of the frequency
Control/structures interaction study of two 300 KW dual-keel space station concepts
The results of an investigation of the influence of structural stiffness of the space station framework on the controllability of two 300 kw class, solar dynamic powered, dual-keel space station designs are presented. The two design concepts differed only in the truss bay dimensions of the structural framework of the stations. Two control studies were made: (1) A study of the interaction of the framework structural response with the reaction control system used for attitude control during an orbital reboost maneuver; and (2) A study of the stability of the space station attitude control system with sensors influenced by the elastic deformations of the station framework. Although both configurations had acceptable control characteristics, the configuration with the larger truss bay dimension and its increased structural stiffness had more attractive characteristics for pointing control of the solar dynamic system during reboost and for attitude control during normal in-orbit operations
Fractional Chern insulator edges and layer-resolved lattice contacts
Fractional Chern insulators (FCIs) realized in fractional quantum Hall
systems subject to a periodic potential are topological phases of matter for
which space group symmetries play an important role. In particular, lattice
dislocations in an FCI can host topology-altering non-Abelian topological
defects, known as genons. Genons are of particular interest for their potential
application to topological quantum computing. In this work, we study FCI edges
and how they can be used to detect genons. We find that translation symmetry
can impose a quantized momentum difference between the edge electrons of a
partially-filled Chern band. We propose {\it layer-resolved lattice contacts},
which utilize this momentum difference to selectively contact a particular FCI
edge electron. The relative current between FCI edge electrons can then be used
to detect the presence of genons in the bulk FCI. Recent experiments have
demonstrated graphene is a viable platform to study FCI physics. We describe
how the lattice contacts proposed here could be implemented in graphene subject
to an artificial lattice, thereby outlining a path forward for experimental
dectection of non-Abelian topological defects.Comment: 5+7 pages, 10 figures, v2: modified figure
The twisted fourth moment of the Riemann zeta function
We compute the asymptotics of the fourth moment of the Riemann zeta function
times an arbitrary Dirichlet polynomial of length Comment: 28 pages. v2: added reference
Patterns of Treatment for Psychiatric Disorders Among Children and Adolesecents in Mississippi Medicaid
The nature of services for psychiatric disorders in public health systems has been understudied, particularly with regard to frequency, duration, and costs. The current study examines patterns of service reception and costs among Medicaid-covered youth newly diagnosed with anxiety, depression, or behavioral disturbance in a large data set of provider billing claims submitted between 2015–2016. Eligibility criteria included: 1) identification of an initial diagnosis of a single anxiety, unipolar mood, or specific behavioral disorder; 2) continuous Medicaid eligibility over the duration of the time period studied; and 3) under 18 years of age on the date of initial psychiatric diagnosis. The final cohort included 7,627 cases with a mean age of 10.65 (±4.36), of which 58.04% were male, 57.09% were Black, 38.97% were White, and 3.95% were of other ethnicities. Data indicated that 65.94% of the cohort received at least some follow-up services within a median 18 days of diagnosis. Of those, 54.27% received a combination of medical and psychosocial services, 32.01% received medical services only, and 13.72% received psychosocial services only. Overall median costs for direct treatment were 308.41) and highest (behavioral disturbance = $653.59) diagnostic categories. Across all categories the frequency and duration of psychosocial services were much lower than would be expected in comparison to data from a well-known effectiveness trial. Overall, follow-up to psychiatric diagnosis could be characterized as highly variable, underutilized, and emphasizing biomedical treatment. Understanding more about these patterns may facilitate systematic improvements and greater cost efficiency in the future
Ensemble dependence in the Random transverse-field Ising chain
In a disordered system one can either consider a microcanonical ensemble,
where there is a precise constraint on the random variables, or a canonical
ensemble where the variables are chosen according to a distribution without
constraints. We address the question as to whether critical exponents in these
two cases can differ through a detailed study of the random transverse-field
Ising chain. We find that the exponents are the same in both ensembles, though
some critical amplitudes vanish in the microcanonical ensemble for correlations
which span the whole system and are particularly sensitive to the constraint.
This can \textit{appear} as a different exponent. We expect that this apparent
dependence of exponents on ensemble is related to the integrability of the
model, and would not occur in non-integrable models.Comment: 8 pages, 12 figure
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