795 research outputs found
Study made of corrosion resistance of stainless steel and nickel alloys in nuclear reactor superheaters
Experiments performed under conditions found in nuclear reactor superheaters determine the corrosion rate of stainless steel and nickel alloys used in them. Electropolishing was the primary surface treatment before the corrosion test. Corrosion is determined by weight loss of specimens after defilming
A systematic comparison of tropical waves over northern Africa. Part II: Dynamics and thermodynamics
This study presents the first systematic comparison of the (thermo-)dynamics
associated with all major tropical wave types causing rainfall modulation over
northern tropical Africa: Madden Julian Oscillation (MJO), Equatorial Rossby
waves (ERs), mixed Rossby-gravity waves (MRGs), Kelvin waves, tropical
disturbances (TDs, including African Easterly Waves), and eastward
inertio-gravity waves (EIGs). Reanalysis and radiosonde data were analyzed for
the period 1981--2013 based on space-time filtering of outgoing longwave
radiation. The identified circulation patterns are largely consistent with
theory. The slow modes, MJO and ER, mainly impact precipitable water, whereas
the faster Kelvin waves, MRGs, and TDs primarily modulate moisture convergence.
Monsoonal inflow intensifies during wet phases of the MJO, ERs, and MRGs,
associated with a northward shift of the intertropical discontinuity for MJO
and ERs. During passages of vertically tilted imbalanced wave modes, such as
MJO, Kelvin waves, and TDs, and partly MRGs, increased vertical wind shear and
improved conditions for up- and downdrafts facilitate the organization of
convection. The balanced ERs are not tilted and rainfall is triggered by
large-scale moistening and stratiform lifting. The MJO and ERs interact with
intraseasonal variations of the Indian monsoon and extratropical Rossby wave
trains. The latter causes a trough over the Atlas Mountains associated with a
tropical plume and rainfall over the Sahara. Positive North Atlantic and Arctic
Oscillation signals precede tropical plumes in case of the MJO. The results
unveil which dynamical processes need to be modeled realistically to represent
the coupling between tropical waves and rainfall in northern tropical Africa.Comment: 33 pages, 11 figures, supplementary material; submitted to Journal of
Climat
A systematic comparison of tropical waves over northern Africa. Part I: Influence on rainfall
Low-latitude rainfall variability on the daily to intraseasonal timescale is
often related to tropical waves, including convectively coupled equatorial
waves, the Madden-Julian Oscillation (MJO), and tropical disturbances. Despite
the importance of rainfall variability for vulnerable societies in tropical
Africa, the relative influence of tropical waves for this region is largely
unknown. This article presents the first systematic comparison of the impact of
six wave types on precipitation over northern tropical Africa during the
transition and full monsoon seasons, using two satellite products and a dense
rain gauge network. Composites of rainfall anomalies in the different datasets
show} comparable modulation intensities in the West Sahel and at the Guinea
Coast, varying from less than 2 to above 7 mm/d depending on the wave type.
African Easterly Waves (AEWs) and Kelvin waves dominate the 3-hourly to daily
timescale and explain 10-30% locally. On longer timescales (7-20d), only the
MJO and equatorial Rossby (ER) waves remain as modulating factors and explain
about up to one third of rainfall variability. Eastward inertio-gravity waves
and mixed Rossby-gravity (MRG) waves are comparatively unimportant. An analysis
of wave superposition shows that low-frequency waves (MJO, ER) in their wet
phase amplify the activity of high-frequency waves (TD, MRG) and suppress them
in the dry phase. The results stress that more attention should be paid to
tropical waves when forecasting rainfall over northern tropical Africa.Comment: 34 pages, 12 figures, supplementary material; submitted to Journal of
Climat
Comparison of the Fermi-surface topologies of kappa-(BEDT-TTF)_2 Cu(NCS)_2 and its deuterated analogue
We have measured details of the quasi one-dimensional Fermi-surface sections
in the organic superconductor kappa-(BEDT-TTF)_2 Cu(NCS)_2 and its deuterated
analogue using angle-dependent millimetre-wave techniques. There are
significant differences in the corrugations of the Fermi surfaces in the
deuterated and undeuterated salts. We suggest that this is important in
understanding the inverse isotope effect, where the superconducting transition
temperature rises on deuteration. The data support models for superconductivity
which invoke electron-electron interactions depending on the topological
properties of the Fermi surface
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