3,853 research outputs found
Transient technique for measuring heat transfer coefficients on stator airfoils in a jet engine environment
A transient technique was used to measure heat transfer coefficients on stator airfoils in a high-temperature annular cascade at real engine conditions. The transient response of thin film thermocouples on the airfoil surface to step changes in the gas stream temperature was used to determine these coefficients. In addition, gardon gages and paired thermocouples were also utilized to measure heat flux on the airfoil pressure surface at steady state conditions. The tests were conducted at exit gas stream Reynolds numbers of one-half to 1.9 million based on true chord. The results from the transient technique show good comparison with the steady-state results in both trend and magnitude. In addition, comparison is made with the STAN5 boundary layer code and shows good comparison with the trends. However, the magnitude of the experimental data is consistently higher than the analysis
Study of outgassing and decomposition of Space Shuttle heat protection tiles, fillers and adhesive
A purge and trap technique which was employed to collect and separate the chemicals desorbing from the space shuttle heat protection tiles is described. The instrumentation included a mass spectrometer and gas chromatograph
Double-diffusive instabilities of a shear-generated magnetic layer
Previous theoretical work has speculated about the existence of
double-diffusive magnetic buoyancy instabilities of a dynamically evolving
horizontal magnetic layer generated by the interaction of forced vertically
sheared velocity and a background vertical magnetic field. Here we confirm
numerically that if the ratio of the magnetic to thermal diffusivities is
sufficiently low then such instabilities can indeed exist, even for high
Richardson number shear flows. Magnetic buoyancy may therefore occur via this
mechanism for parameters that are likely to be relevant to the solar
tachocline, where regular magnetic buoyancy instabilities are unlikely.Comment: Submitted to ApJ
The Evolution of a Double Diffusive Magnetic Buoyancy Instability
Recently, Silvers, Vasil, Brummell, & Proctor (2009), using numerical
simulations, confirmed the existence of a double diffusive magnetic buoyancy
instability of a layer of horizontal magnetic field produced by the interaction
of a shear velocity field with a weak vertical field. Here, we demonstrate the
longer term nonlinear evolution of such an instability in the simulations. We
find that a quasi two-dimensional interchange instability rides (or "surfs") on
the growing shear-induced background downstream field gradients. The region of
activity expands since three-dimensional perturbations remain unstable in the
wake of this upward-moving activity front, and so the three-dimensional nature
becomes more noticeable with time.Comment: 9 pages; 3 figures; accepted to appear in IAU symposium 27
Charge Stripping Reactions in Mass Spectrometry: A Study of Diatomic and Triatomic Inorganic and Organic Ions
Charge stripping reactions of the type m⢠+ N--+ m2⢠+ N + ehave
been studied for a variety of diatomic and triatomic inorganic
and organic ions. Ionisation energies of the m⢠ions, IE (m+--+ m2⢠),
have been determined, most of them for the first time. The method
is fast and straightforward; it is applicable to both molecular and
fragment .ions. The relative cross-sections for the charge stripping
processes have been also determined; they show llrge variations
from one species to another. Cases of possible interferences, which
are fairly infrequent, are described and discussed
Magnetic diffusivity tensor and dynamo effects in rotating and shearing turbulence
The turbulent magnetic diffusivity tensor is determined in the presence of
rotation or shear. The question is addressed whether dynamo action from the
shear-current effect can explain large-scale magnetic field generation found in
simulations with shear. For this purpose a set of evolution equations for the
response to imposed test fields is solved with turbulent and mean motions
calculated from the momentum and continuity equations. The corresponding
results for the electromotive force are used to calculate turbulent transport
coefficients. The diagonal components of the turbulent magnetic diffusivity
tensor are found to be very close together, but their values increase slightly
with increasing shear and decrease with increasing rotation rate. In the
presence of shear, the sign of the two off-diagonal components of the turbulent
magnetic diffusion tensor is the same and opposite to the sign of the shear.
This implies that dynamo action from the shear--current effect is impossible,
except perhaps for high magnetic Reynolds numbers. However, even though there
is no alpha effect on the average, the components of the alpha tensor display
Gaussian fluctuations around zero. These fluctuations are strong enough to
drive an incoherent alpha--shear dynamo. The incoherent shear--current effect,
on the other hand, is found to be subdominant.Comment: 12 pages, 13 figures, improved version, accepted by Ap
Bone marrow examination in newly diagnosed Hodgkin's disease: current practice in the United Kingdom.
In the UK Hodgkin's disease is usually treated by either clinical oncologists or haematologists. A national study of the performance of bone marrow examination in newly diagnosed Hodgkin's disease was undertaken to establish current practice. A total of 620 questionnaires were despatched, and replies were received from 60% of consultants (45% of clinical oncologists and 70% of haematologists). Bone marrow examination was performed in all new cases significantly more often by haematologists than by clinical oncologists (74% vs 40%, P < 0.001). Among haematologists, there was no correlation between the number of new patients seen annually and practice, however clinical oncologists were even less likely to perform routine bone marrow biopsies if they saw more than ten patients per year (P < 0.02). Where bone marrow examination was performed selectively, the most common criteria used were peripheral blood cytopenia and advanced-stage disease. These criteria were applied in the same way by both clinical oncologists and haematologists. Bone marrow biopsy, an invasive and often painful procedure, is currently performed more frequently in Hodgkin's disease than can be recommended on the basis of recent studies in the literature and associated guidelines. There is a significant difference in practice between clinical oncologists and haematologists, and this raises the wider issue of the influence of hospital specialisation on patient management
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