1,408 research outputs found
The incidence of first stroke in and around pregnancy: A population-based cohort study from Sweden
Introduction:
Research has suggested that delivery is associated with an increased risk of stroke in women; however, there is a lack of contemporary estimates on the incidence of stroke in and after pregnancy compared with the baseline risk in women of childbearing age in Sweden.
Patients and methods:
All women aged 15â49 years with live births/stillbirths in 1992â2011 were identified from the Swedish Medical Birth Registry linked with the National Patient Registry. First stroke during the study period was identified. Incidence rates per 100,000 person-years and adjusted incidence rate ratios (IRRs) were calculated for antepartum, peripartum and early and late postpartum periods, compared with all other available follow-up time (time before pregnancy and after postpartum) using Poisson regression adjusted for maternal age, education attainment and calendar time.
Results:
Of 1,124,541 women, 3094 had a first incident stroke (331 occurred during pregnancy or first 12 weeks postpartum), about half having ischaemic stroke. The incidence was 15.0 per 100,000 person-years (95% confidence interval 14.5â15.6) in non-pregnant time. The incidence was lower antepartum (7.3/100,000 person-years, 6.0â8.9; adjusted IRRâ=â0.7, 0.5â0.8) but higher peripartum (314.4/100,000 person-years, 247.5â399.5; adjusted IRRâ=â27.3, 21.4â34.9) and early postpartum (64.0/100,000 person-years, 54.1â75.7; adjusted IRRâ=â5.5, 4.6â6.6). The increased risk in peripartum was more evident for intracerebral haemorrhage than other types of stroke.
Conclusion:
Overall risk of stroke was low in women of childbearing age, but stroke risk peaks in the peripartum and early postpartum periods. Future work should address factors that contribute to this increased risk in order to develop approaches to attenuate risk
Multi-layered Ruthenium-modified Bond Coats for Thermal Barrier Coatings
Diffusional approaches for fabrication of multi-layered Ru-modified bond coats for thermal
barrier coatings have been developed via low activity chemical vapor deposition and high activity
pack aluminization. Both processes yield bond coats comprising two distinct B2 layers, based on
NiAl and RuAl, however, the position of these layers relative to the bond coat surface is reversed
when switching processes. The structural evolution of each coating at various stages of the
fabrication process has been and subsequent cyclic oxidation is presented, and the relevant
interdiffusion and phase equilibria issues in are discussed. Evaluation of the oxidation behavior of
these Ru-modified bond coat structures reveals that each B2 interlayer arrangement leads to the
formation of α-Al 2 O 3 TGO at 1100°C, but the durability of the TGO is somewhat different and in
need of further improvement in both cases
Solitary wave solution to the generalized nonlinear Schrodinger equation for dispersive permittivity and permeability
We present a solitary wave solution of the generalized nonlinear Schrodinger
equation for dispersive permittivity and permeability using a scaling
transformation and coupled amplitude-phase formulation. We have considered the
third-order dispersion effect (TOD) into our model and show that soliton shift
may be suppressed in a negative index material by a judicious choice of the TOD
and self-steepening parameter.Comment: 6 page
Vibrations of a chain of Xe atoms in a groove of carbon nanotube bundle
We present a lattice dynamics study of the vibrations of a linear chain of Xe
adsorbates in groove positions of a bundle of carbon nanotubes. The
characteristic phonon frequencies are calculated and the adsorbate polarization
vectors discussed. Comparison of the present results with the ones previously
published shows that the adsorbate vibrations cannot be treated as completely
decoupled from the vibrations of carbon nanotubes and that a significant
hybridization between the adsorbate and the tube modes occurs for phonons of
large wavelengths.Comment: 3 PS figure
Continental Crust Rejuvenation Across the PaleoâMesoarchean Transition Resulted From Elevated Mantle Geotherms
The increase in initial Hf isotopes identified in early Mesoarchean detrital zircon is commonly interpreted as a reflection of the geodynamic transition from stagnant-lid to mobile-lid tectonics. However, given the lack of petrogenetic context, interpreting detrital zircon may lead to spurious conclusions. In this contribution, we use zircon U-Pb-Hf-O isotopic and bulk rock compositions of newly identified 3.05â2.9 Ga granitoids from the SW Yangtze Block to posit petrogenesis within an isotopically juvenile magmatic system. A statistical analysis of these data with a global igneous zircon Lu-Hf isotopic compilation reveals an increase in average initial radiogenic Hf isotopes during the Paleoarchean to Mesoarchean transition. We posit that the Earth's continental crust underwent a global rejuvenation across the Paleo-Mesoarchean transition. This rejuvenation can be explained by an independently observed increase in mantle temperatures resulting from mantle thermal evolution and does not require a change in tectonic style
The spectral gap for some spin chains with discrete symmetry breaking
We prove that for any finite set of generalized valence bond solid (GVBS)
states of a quantum spin chain there exists a translation invariant
finite-range Hamiltonian for which this set is the set of ground states. This
result implies that there are GVBS models with arbitrary broken discrete
symmetries that are described as combinations of lattice translations, lattice
reflections, and local unitary or anti-unitary transformations. We also show
that all GVBS models that satisfy some natural conditions have a spectral gap.
The existence of a spectral gap is obtained by applying a simple and quite
general strategy for proving lower bounds on the spectral gap of the generator
of a classical or quantum spin dynamics. This general scheme is interesting in
its own right and therefore, although the basic idea is not new, we present it
in a system-independent setting. The results are illustrated with an number of
examples.Comment: 48 pages, Plain TeX, BN26/Oct/9
Screened Coulomb interactions in metallic alloys: II Screening beyond the single-site and atomic sphere approximations
A quantitative description of the configurational part of the total energy of
metallic alloys with substantial atomic size difference cannot be achieved in
the atomic sphere approximation: It needs to be corrected at least for the
multipole moment interactions in the Madelung part of the one-electron
potential and energy. In the case of a random alloy such interactions can be
accounted for only by lifting the atomic sphere and single-site approximations,
in order to include the polarization due to local environment effects.
Nevertheless a simple parameterization of the screened Coulomb interactions for
the ordinary single-site methods, including the generalized perturbation
method, is still possible. We obtained such a parameterization for bulk and
surface NiPt alloys, which allows one to obtain quantitatively accurate
effective interactions in this system.Comment: 24 pages, 2 figure
A switchable controlled-NOT gate in a spin-chain NMR quantum computer
A method of switching a controlled-NOT gate in a solid-stae NMR quantum
computer is presented. Qubits of I=1/2 nuclear spins are placed periodically
along a quantum spin chain (1-D antiferromagnet) having a singlet ground state
with a finite spin gap to the lowest excited state caused by some quantum
effect. Irradiation of a microwave tuned to the spin gap energy excites a
packet of triplet magnons at a specific part of the chain where control and
target qubits are involved. The packet switches on the Suhl-Nakamura
interaction between the qubits, which serves as a controlled NOT gate. The
qubit initialization is achieved by a qubit initializer consisting of
semiconducting sheets attached to the spin chain, where spin polarizations
created by the optical pumping method in the semiconductors are transferred to
the spin chain. The scheme allows us to separate the initialization process
from the computation, so that one can optimize the computation part without
being restricted by the initialization scheme, which provides us with a wide
selection of materials for a quantum computer.Comment: 8 pages, 5 figure
Immersed boundary-finite element model of fluid-structure interaction in the aortic root
It has long been recognized that aortic root elasticity helps to ensure
efficient aortic valve closure, but our understanding of the functional
importance of the elasticity and geometry of the aortic root continues to
evolve as increasingly detailed in vivo imaging data become available. Herein,
we describe fluid-structure interaction models of the aortic root, including
the aortic valve leaflets, the sinuses of Valsalva, the aortic annulus, and the
sinotubular junction, that employ a version of Peskin's immersed boundary (IB)
method with a finite element (FE) description of the structural elasticity. We
develop both an idealized model of the root with three-fold symmetry of the
aortic sinuses and valve leaflets, and a more realistic model that accounts for
the differences in the sizes of the left, right, and noncoronary sinuses and
corresponding valve cusps. As in earlier work, we use fiber-based models of the
valve leaflets, but this study extends earlier IB models of the aortic root by
employing incompressible hyperelastic models of the mechanics of the sinuses
and ascending aorta using a constitutive law fit to experimental data from
human aortic root tissue. In vivo pressure loading is accounted for by a
backwards displacement method that determines the unloaded configurations of
the root models. Our models yield realistic cardiac output at physiological
pressures, with low transvalvular pressure differences during forward flow,
minimal regurgitation during valve closure, and realistic pressure loads when
the valve is closed during diastole. Further, results from high-resolution
computations demonstrate that IB models of the aortic valve are able to produce
essentially grid-converged dynamics at practical grid spacings for the
high-Reynolds number flows of the aortic root
Characterization and preliminary imaging evaluation of a clinical prototype stationary intraoral tomosynthesis system
Purpose: Technological advancements in dental radiography have improved oral care on many fronts, yet diagnostic efficacy for some of the most common oral conditions, such as caries, dental cracks and fractures, and periodontal disease, remains relatively low. Driven by the clinical need for a better diagnostic yield for these and other dental conditions, we initiated the development of a stationary intraoral tomosynthesis (s-IOT) imaging system using carbon nanotube (CNT) x-ray source array technology. Here, we report the system characterization and preliminary imaging evaluation of a clinical prototype s-IOT system approved for human use. Methods: The clinical prototype s-IOT system is comprised of a multibeam CNT x-ray source array, high voltage generator, control electronics, collimator cone, and dynamic digital intraoral detector. During a tomosynthesis scan, each x-ray source is operated sequentially at fixed, nominal tube current of 7 mA and user-specified pulse width. Images are acquired by a digital intraoral detector and the reconstruction algorithm generates slice information in real time for operator review. In this study, the s-IOT system was characterized for tube output, dosimetry, and spatial resolution. Manufacturer specifications were validated, such as tube current, kVp, and pulse width. Tube current was measured with an oscilloscope on the analog output of the anode power supply. Pulse width, kVp, and peak skin dose were measured with a dosimeter with ion chamber and high voltage accessory. In-plane spatial resolution was evaluated via measurement of MTF and imaging of a line pair phantom. Spatial resolution in the depth direction was evaluated via artifact spread measurement. The size of the collimated radiation field was evaluated for compliance with FDA regulations. A dental phantom and human specimens of varying pathologies were imaged on a clinical 2D intraoral imaging system as well as s-IOT for comparison and to explore potential clinical applications. Results: The measured tube current, kVp, and pulse width values were within 3% of the set values. A cumulative peak skin dose of 1.12 mGy was measured for one complete tomosynthesis scan using a 50-ms pulse per projection view. Projection images and reconstruction slices revealed MTF values ranging from 8.1 to 9.3 cycles/mm. Line pair imaging verified this result. The radiation field was found to meet the FDA requirements for intraoral imaging devices. Tomosynthesis reconstruction slice images of the dental phantom and human specimens provided depth resolution, allowing visibility of anatomical features that cannot be seen in the 2D intraoral images. Conclusions: The clinical prototype s-IOT device was evaluated and found to meet all manufacturer specifications. Though the system capability is higher, initial investigations are targeting a low-dose range comparable to a single 2D radiograph. Preliminary studies indicated that s-IOT provides increased image quality and feature conspicuity at a dose comparable to a single 2D intraoral radiograph
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