286 research outputs found
A Restoration Method for Impulsive Functions
A method is presented for enhancing the resolution of impulsive functions which have been degraded by a known convolutional disturbance and by the addition of white noise. An autoregressive model is employed to represent the spectrum of the ideally resolved impulsive function. The method is flexible in that it allows constraints to be incorporated into the resolution scheme. Two quite diverse examples are presented as illustration
Analysis of Unsteady Transonic Flow Fields by Means of the Colour Streak Schlieren Method
This article deals with a new approach to the investigation of unsteady transonic flow fields around aerodynamic models and in blade cascades using a schlieren method of flow visualisation. The principle and the application of the Colour Streak Schlieren Method (CSSM) are defined. The characteristic flow field features were observed and analysed around an oscillating NACA 0012 airfoil under the conditions of transonic free stream Mach number (M∞ = 0.9), initial angle of attack (α = +4 deg), one amplitude of oscillation (Δα=±3 deg), and three frequencies of model oscillation (f = 1, 15, 30 Hz). There is a description of the terminal shock wave hysteresis across the investigated area, which was revealed in particular cases. Application possibilities of CSSM and its further development are discussed
Comment on 'Second-Order Statistical Structure of Geomagnetic Field Reversals' by P. S. Naidu
In a recent paper, Naidu [1975] has proposed that the reversal intervals of the geomagnetic field for the period 0-76 m.y. are not independent. In fact, the author has fitted a first order autoregressive moving average model to the data published by Heirtzler et al. [1968]. This conclusion, if true, is of importance because it suggests that the mechanism governing the reversals of the geomagnetic dynamo possesses a memory
Revision of Scheumann’s classification of melilitic lamprophyres and related melilitic rocks in light of new analytical data
Dykes of the Late Cretaceous to Early Tertiary (79.5 ± 3.5 to 60.7 ± 2.4 Ma) melilitic rock series of the Osečná Com-
plex and the Devil’s Walls dyke swarm, including ultramafic lamprophyres – polzenites – of Scheumann (1913) occur
dispersed in the entire Upper Ploučnice River basin in northern Bohemia.
Polzenites and associated melilitic rocks are characterized by the mineral association of olivine + melilite ± nephe-
line, haüyne, monticellite, phlogopite, calcite, perovskite, spinels and apatite. New data on their mineral and chemical
compositions from original Scheumann’s localities (the Vesec, Modlibohov, Luhov types) argue against the abolition
of the group of ultramafic lamprophyres and the terms ‘polzenite’ and ‘alnöite’ by the Le Maitre (2002) classification.
Marginal facies and numerous flat apophyses of the lopolith-like body known as the Osečná Complex show an olivine
micro-melilitolite composition (lamprophyric facies). The porphyritic texture, chemical composition and the presence of
characteristic minerals such as monticellite and phlogopite point to their affinity with ultramafic lamprophyres – polze-
nites of the Vesec type. Melilite-bearing olivine nephelinites to olivine melilitites (olivine + clinopyroxene + nepheline
+ melilite ± haüyne and spinels with apatite) form a swarm of subparallel dykes known as the Devil’s Walls.
The Scheumann’s non-melilite dyke rock “wesselite”, spatially associated with polzenites and often erroneously attributed
to the polzenite group, is an alkaline lamprophyre of monchiquite to camptonite composition (kaersutite + phlogopite
+ diopside + olivine phenocrysts in groundmass containing clinopyroxene, phlogopite, haüyne, analcime, titanian mag-
netite, apatite ± glass/plagioclase). First K–Ar data show Oligocene ages (30.9 ± 1.2 to 27.8 ± 1.1 Ma) and an affinity to
the common tephrite–basanite rock series
Correlations and the relativistic structure of the nucleon self-energy
A key point of Dirac Brueckner Hartree Fock calculations for nuclear matter
is to decompose the self energy of the nucleons into Lorentz scalar and vector
components. A new method is introduced for this decomposition. It is based on
the dependence of the single-particle energy on the small component in the
Dirac spinors used to calculate the matrix elements of the underlying NN
interaction. The resulting Dirac components of the self-energy depend on the
momentum of the nucleons. At densities around and below the nuclear matter
saturation density this momentum dependence is dominated by the non-locality of
the Brueckner G matrix. At higher densities these correlation effects are
suppressed and the momentum dependence due to the Fock exchange terms is
getting more important. Differences between symmetric nuclear matter and
neutron matter are discussed. Various versions of the Bonn potential are
considered.Comment: 18 pages LaTeX, including 6 figure
Rock forming minerals of alkaline volcanic series association the Cheb-Domažlice Graben, West Bohemia
Long-Term Variations in the Growth and Decay Rates of Sunspot Groups
Using the combined Greenwich (1874-1976) and Solar Optical Observatories
Network (1977-2009) data on sunspot groups, we study the long-term variations
in the mean daily rates of growth and decay of sunspot groups. We find that the
minimum and the maximum values of the annually averaged daily mean growth rates
are ~52% per day and ~183% per day, respectively, whereas the corresponding
values of the annually averaged daily mean decay rates are ~21% per day and
~44% per day, respectively. The average value (over the period 1874-2009) of
the growth rate is about 70% more than that of the decay rate. The growth and
the decay rates vary by about 35% and 13%, respectively, on a 60-year
time-scale. From the beginning of Cycle 23 the growth rate is substantially
decreased and near the end (2007-2008) the growth rate is lowest in the past
about 100 years.Comment: 1 table, 13 figures, accepted by Solar Physic
Search for Short-Term Periodicities in the Sun's Surface Rotation: A Revisit
The power spectral analyses of the Sun's surface equatorial rotation rate
determined from the Mt. Wilson daily Doppler velocity measurements during the
period 3 December 1985 to 5 March 2007 suggests the existence of 7.6 year, 2.8
year, 1.47 year, 245 day, 182 day and 158 day periodicities in the surface
equatorial rotation rate during the period before 1996.
However, there is no variation of any kind in the more accurately measured
data during the period after 1995. That is, the aforementioned periodicities in
the data during the period before the year 1996 may be artifacts of the
uncertainties of those data due to the frequent changes in the instrumentation
of the Mt. Wilson spectrograph. On the other hand, the temporal behavior of
most of the activity phenomena during cycles 22 (1986-1996) and 23 (after 1997)
is considerably different. Therefore, the presence of the aforementioned
short-term periodicities during the last cycle and absence of them in the
current cycle may, in principle, be real temporal behavior of the solar
rotation during these cycles.Comment: 11 pages, 6 figures, accepted for publication in Solar Physic
Quaiselastic scattering from relativistic bound nucleons: Transverse-Longitudinal response
Predictions for electron induced proton knockout from the and
shells in O are presented using various approximations for the
relativistic nucleonic current. Results for the differential cross section,
transverse-longitudinal response () and left-right asymmetry
are compared at (GeV/c) corresponding to TJNAF experiment
89-003. We show that there are important dynamical and kinematical relativistic
effects which can be tested by experiment.Comment: 10 pages, including 2 figures. Removed preliminary experimental data
from the figure
L-moments and C-moments
It is well known that the computation of higher order statistics, like skewness and kurtosis, (which we call C-moments) is very dependent on sample size and is highly susceptible to the presence of outliers. To obviate these difficulties, Hosking (1990) has introduced related statistics called L-moments. We have investigated the relationship of these two measures in a number of different ways. Firstly, we show that probability density functions (pdf ) that are estimated from L-moments are superior estimates to those obtained using C-moments and the principle of maximum entropy. C-moments computed from these pdf's are not however, contrary to what one may have expected, better estimates than those estimated from sample statistics. L-moment derived distributions for field data examples appear to be more consistent sample to sample than pdf 's determined by conventional means. Our observations and conclusions have a significant impact on the use of the conventional maximum entropy procedure which typically uses C-moments from actual data sets to infer probabilities.Facultad de Ciencias Astronómicas y Geofísica
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