10,553 research outputs found
A digitally controlled very high frequency synthesizer
Breadboard model of digitally controlled very high frequency synthesizer for use in aviation navigation receive
Technique for extending the frequency range of digital dividers
A technique for extending the frequency range of a presettable digital divider is described. The conventional digital divider consists of several counter stages with the count of each stage compared to a preselected number. When the counts for all stages are equal to the preselected numbers, an output pulse is generated and all stages are reset. For high input frequencies, the least significant stage of the divider has to be reset in a very short time. This limits the frequency that can be handled by the conventional digital divider. This invention provides a technique in which the second least significant and higher stages are reset and the least significant stage is permitted to free-run. Hence, the time in which the reset operation can be performed is increased thereby extending the frequency range of the divider
Critical psychiatry: A brief overview
Critical psychiatry has often been confused with what is widely known as 'anti-psychiatry'. In this article the distinction is clarified and the particular contribution critical psychiatry makes is outlined. That contribution is constructive criticism: of the relationship between medicine and mental health practice, of the way drug and psychotherapeutic treatments for mental health difficulties might be better understood. These have implications for everyday clinical practice and there is much to be gained by openly embracing the controversies critical psychiatry highlights
Effect of wind on continental shelf carbon fluxes off southeast Australia: A numerical model
A coupled physical-biological-chemical model is used to study the effect of upwelling-favorable and downwelling-favorable winds on carbon biogeochemistry on the continental shelf off the southeast Australian mainland. Along the continental shelf, from 30?S to 34?S, upwelling-favorable winds, with the aid of bottom Ekman transport, bring dissolved-inorganic-carbon (DIC)-rich slope waters onto the shelf, increasing the carbon held in shelf waters. For downwelling-favorable winds, bottom Ekman transport still lifts slope waters onto the shelf, but the slope water transport, and therefore carbon held, is reduced compared with the upwelling scenario. Under upwelling-favorable winds, filaments of DIC and dissolved-inorganic-nitrogen (DIN)-rich water reaching the surface produce an outgassing near the site of upwelling and absorption downstream due to primary productivity. In a region of the ocean that is generally absorbing, the net effect of upwelling is a reduced absorption of atmospheric CO2 as a result of the ratio of deep DIC and DIN (12.2:1 mol C:mol N) being greater than the Redfield ratio (6.625). Carbon fluxes in the waters off the southeast Australian mainland are variable in space, with the transport of continental shelf waters to deep waters occurring mainly where alongshore currents separate from the coast and flow over the 200-m isobath
Mean winds of the mesosphere and lower thermosphere at 52° N in the period 1988?2000
International audienceA meteor radar in the UK (near 52° N) has been used to measure the mean winds of the mesosphere/lower-thermosphere (MLT) region over the period 1988?2000. The seasonal course and interannual variability is characterised and comparisons are made with a number of models. Annual mean wind trends were found to be + 0.37 ms-1 yr-1 for the zonal component and + 0.157 ms-1 yr-1 for the meridional component. Seasonal means revealed significant trends in the case of meridional winds in spring ( + 0.38 ms-1 yr-1) and autumn ( + 0.29 ms-1 yr-1), and zonal winds in summer ( + 0.48 ms-1 yr-1) and autumn ( + 0.38 ms-1 yr-1). Significant correlation coefficients, R, between the sunspot number and seasonal mean wind are found in four instances. In the case of the summer zonal winds, R = + 0.732; for the winter meridional winds, R = - 0.677; for the winter zonal winds, R = - 0.472; and for the autumn zonal winds R = + 0.508
Statistical Topography of Glassy Interfaces
Statistical topography of two-dimensional interfaces in the presence of
quenched disorder is studied utilizing combinatorial optimization algorithms.
Finite-size scaling is used to measure geometrical exponents associated with
contour loops and fully packed loops. We find that contour-loop exponents
depend on the type of disorder (periodic ``vs'' non-periodic) and they satisfy
scaling relations characteristic of self-affine rough surfaces. Fully packed
loops on the other hand are unaffected by disorder with geometrical exponents
that take on their pure values.Comment: 4 pages, REVTEX, 4 figures included. Further information can be
obtained from [email protected]
Ground-State Roughness of the Disordered Substrate and Flux Line in d=2
We apply optimization algorithms to the problem of finding ground states for
crystalline surfaces and flux lines arrays in presence of disorder. The
algorithms provide ground states in polynomial time, which provides for a more
precise study of the interface widths than from Monte Carlo simulations at
finite temperature. Using systems up to size , with a minimum of
realizations at each size, we find very strong evidence for a
super-rough state at low temperatures.Comment: 10 pages, 3 PS figures, to appear in PR
Energetics and geometry of excitations in random systems
Methods for studying droplets in models with quenched disorder are critically
examined. Low energy excitations in two dimensional models are investigated by
finding minimal energy interior excitations and by computing the effect of bulk
perturbations. The numerical data support the assumptions of compact droplets
and a single exponent for droplet energy scaling. Analytic calculations show
how strong corrections to power laws can result when samples and droplets are
averaged over. Such corrections can explain apparent discrepancies in several
previous numerical results for spin glasses.Comment: 4 pages, eps files include
First excitations in two- and three-dimensional random-field Ising systems
We present results on the first excited states for the random-field Ising
model. These are based on an exact algorithm, with which we study the
excitation energies and the excitation sizes for two- and three-dimensional
random-field Ising systems with a Gaussian distribution of the random fields.
Our algorithm is based on an approach of Frontera and Vives which, in some
cases, does not yield the true first excited states. Using the corrected
algorithm, we find that the order-disorder phase transition for three
dimensions is visible via crossings of the excitations-energy curves for
different system sizes, while in two-dimensions these crossings converge to
zero disorder. Furthermore, we obtain in three dimensions a fractal dimension
of the excitations cluster of d_s=2.42(2). We also provide analytical droplet
arguments to understand the behavior of the excitation energies for small and
large disorder as well as close to the critical point.Comment: 17 pages, 12 figure
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