78 research outputs found
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On the long-wave instability of natural-convection boundary layers
This paper considers the stability of the one-dimensional boundary
layer generated by
sudden heating of an infinite vertical wall. A quasi-steady approximation
is used to
analyse the asymptotic form of the lower branch of the neutral curve, corresponding
to disturbances of wavelength much greater than the boundary-layer width.
This leads
to predictions of the critical wavenumber for neutral stability and the
maximum
phase speed of the travelling waves. Results are obtained for a range of
Prandtl numbers and
are compared with solutions of the full stability equations and with numerical
simulations and experimental observations of cavity flows driven by sudden
heating of the sidewalls.</jats:p
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On the boundary-layer structure of cavity flow in a porous medium driven by differential heating
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On finite-amplitude patterns of convection in a rectangular-planform container
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On the boundary-layer structure of patterns of convection in rectangular-planform containers
This paper considers the structure of steady-state solutions of the Swift–Hohenberg
equation describing convection in shallow rectangular-planform containers heated
from below. The lateral dimensions of the planform are assumed to be much larger
than the characteristic wavelength of convection. Results are restricted to patterns
composed of rolls orthogonal to the sides of the rectangle in which case convection
sets in at a critical value of the Rayleigh number in the form of rolls parallel to
the shorter sides. This primary bifurcation from the conductive state of no motion
produces a solution which subsequently undergoes a secondary bifurcation in which
the low-amplitude motion near the shorter sides is replaced locally by cross-rolls
perpendicular to the sides. This results in the formation of grain boundaries (or
domain boundaries) within the fluid which mark the division between the different
roll orientations.With increasing Rayleigh number the grain boundaries approach the sides of the
rectangle and a boundary-layer structure is formed. In the present paper the method
of matched asymptotic expansions is used to determine this boundary-layer structure
and to predict the location of the grain boundaries. An interesting feature of the
solution is that the grain boundaries develop significant curvature and bend into the
corners of the rectangle, where the local solution is also determined.The results are compared with numerical computations of the secondary solution
branch and with previous numerical and experimental work.</jats:p
Curvature correction to the mobility of fluid membrane inclusions
For the first time, using rigorous low-Reynolds-number hydrodynamic theory on curved surfaces via a Stokeslet-type approach, we provide a general and concise expression for the leading-order curvature correction to the canonical, planar, Saffman-Delbrück value of the diffusion constant for a small inclusion embedded in an arbitrarily (albeit weakly) curved fluid membrane. In order to demonstrate the efficacy and utility of this wholly general result, we apply our theory to the specific case of calculating the diffusion coefficient of a locally curvature inducing membrane inclusion. By including both the effects of inclusion and membrane elasticity, as well as their respective thermal shape fluctuations, excellent agreement is found with recently published experimental data on the surface tension dependent mobility of membrane bound inclusions
Classification of maltreatment-related mortality by Child Death Review teams: How reliable are they?
Accurate estimation of the incidence of maltreatment-related child mortality depends on reliable child fatality review. We examined the inter-rater reliability of maltreatment designation for two Alaskan Child Death Review (CDR) panels. Two different multidisciplinary CDR panels each reviewed a series of 101 infant and child deaths (ages 0–4 years) in Alaska. Both panels independently reviewed identical medical, autopsy, law enforcement, child welfare, and administrative records for each death utilizing the same maltreatment criteria. Percent agreement for maltreatment was 64.7% with a weighted Kappa of 0.61 (95% CI 0.51, 0.70). Across maltreatment subtypes, agreement was highest for abuse (69.3%) and lowest for negligence (60.4%). Discordance was higher if the mother was unmarried or a smoker, if residence was rural, or if there was a family history of child protective services report(s). Incidence estimates did not depend on which panel's data were used. There is substantial room for improvement in the reliability of CDR panel assessment of maltreatment related mortality. Standardized decision guidance for CDR panels may improve the reliability of their data
Modal scattering at an impedance transition in a lined flow duct
An explicit Wiener-Hopf solution is derived to describe the scattering of duct modes at a hard-soft wall impedance transition in a circular duct with uniform mean flow. Specifically, we have a circular duct r = 1,-8 <x <8 with mean flow Mach number M > 0 and a hard wall along x <0 and a wall of impedance Z along x > 0. A minimum edge condition at x = 0 requires a continuous wall streamline r = 1 + h(x, t ), no more singular than h = O(x1/2) for x ¿ 0. A mode, incident from x <0, scatters at x = 0 into a series of reflected modes and a series of transmitted modes. Of particular interest is the role of a possible instability along the lined wall in combination with the edge singularity. If one of the "upstream" running modes is to be interpreted as a downstream-running instability, we have an extra degree of freedom in the Wiener-Hopf analysis that can be resolved by application of some form of Kutta condition at x = 0, for example a more stringent edge condition where h = O(x3/2) at the downstream side. The question of the instability requires an investigation of the modes in the complex frequency plane and therefore depends on the chosen impedance model, since Z = Z(¿) is essentially frequency dependent. The usual causality condition by Briggs and Bers appears to be not applicable here because it requires a temporal growth rate bounded for all real axial wave numbers. The alternative Crighton-Leppington criterion, however, is applicable and confirms that the suspected mode is usually unstable. In general, the effect of this Kutta condition is significant, but it is particularly large for the plane wave at low frequencies and should therefore be easily measurable. For ¿ ¿ 0, the modulus tends to |R001| ¿ (1 + M)/(1 - M) without and to 1 with Kutta condition, while the end correction tends to8without and to a finite value with Kutta condition. This is exactly the same behaviour as found for reflection at a pipe exit with flow, irrespective if this is uniform or jet flow
P-Type Silicon Strip Sensors for the new CMS Tracker at HL-L-HC
Abstract: The upgrade of the LHC to the High-Luminosity LHC (HL-LHC) is expected to increase
the LHC design luminosity by an order of magnitude. This will require silicon tracking detectors
with a significantly higher radiation hardness. The CMS Tracker Collaboration has conducted an
irradiation and measurement campaign to identify suitable silicon sensor materials and strip designs
for the future outer tracker at the CMS experiment. Based on these results, the collaboration has
chosen to use n-in-p type silicon sensors and focus further investigations on the optimization of that
sensor type
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