5,913 research outputs found
Weber-like interactions and energy conservation
Velocity dependent forces varying as (such as Weber force), here called Weber-like forces, are examined
from the point of view of energy conservation and it is proved that they are
conservative if and only if . As a consequence, it is shown that
gravitational theories employing Weber-like forces cannot be conservative and
also yield both the precession of the perihelion of Mercury as well as the
gravitational deflection of light.Comment: latex, 11 pages, no figure
Monthly and Diurnal Variability of Rain Rate and Rain Attenuation during the Monsoon Period in Malaysia
Rain is the major source of attenuation for microwave propagation above 10 GHz. In tropical and equatorial regions where the rain intensity is higher, designing a terrestrial and earth-to-satellite microwave links is very critical and challenging at these frequencies. This paper presents the preliminary results of rain effects in a 23 GHz terrestrial point-to-point communication link 1.3km long. The experimental test bed had been set up at Skudai, Johor Bahru, Malaysia. In this area, a monsoon equatorial climate prevails and the rainfall rate can reach values well above 100mm/h with significant monthly and diurnal variability. Hence, it is necessary to implement a mitigation technique for maintaining an adequate radio link performance for the action of very heavy rain. Since we now know that the ULPC (Up Link Power Control) cannot guarantee the desired performance, a solution based on frequency band diversity is proposed in this paper. Here, a secondary radio link operating in a frequency not affected by rain (C band for instance) is placed parallel with the main link. Under no rain or light rain conditions, the secondary link carries without priority radio signals. When there is an outage of the main link due to rain, the secondary link assumes the priority traffic. The outcome of the research shows a solution for higher operating frequencies during rainy events
The importance of the Ising model
Understanding the relationship which integrable (solvable) models, all of
which possess very special symmetry properties, have with the generic
non-integrable models that are used to describe real experiments, which do not
have the symmetry properties, is one of the most fundamental open questions in
both statistical mechanics and quantum field theory. The importance of the
two-dimensional Ising model in a magnetic field is that it is the simplest
system where this relationship may be concretely studied. We here review the
advances made in this study, and concentrate on the magnetic susceptibility
which has revealed an unexpected natural boundary phenomenon. When this is
combined with the Fermionic representations of conformal characters, it is
suggested that the scaling theory, which smoothly connects the lattice with the
correlation length scale, may be incomplete for .Comment: 33 page
Modeling the input history of programs for improved instruction-memory performance
When a program is loaded into memory for execution, the relative position of
its basic blocks is crucial, since loading basic blocks that are unlikely to be
executed first places them high in the instruction-memory hierarchy only to be
dislodged as the execution goes on. In this paper we study the use of Bayesian
networks as models of the input history of a program. The main point is the
creation of a probabilistic model that persists as the program is run on
different inputs and at each new input refines its own parameters in order to
reflect the program's input history more accurately. As the model is thus
tuned, it causes basic blocks to be reordered so that, upon arrival of the next
input for execution, loading the basic blocks into memory automatically takes
into account the input history of the program. We report on extensive
experiments, whose results demonstrate the efficacy of the overall approach in
progressively lowering the execution times of a program on identical inputs
placed randomly in a sequence of varied inputs. We provide results on selected
SPEC CINT2000 programs and also evaluate our approach as compared to the gcc
level-3 optimization and to Pettis-Hansen reordering
Diagonal Ising susceptibility: elliptic integrals, modular forms and Calabi-Yau equations
We give the exact expressions of the partial susceptibilities
and for the diagonal susceptibility of the Ising model in terms
of modular forms and Calabi-Yau ODEs, and more specifically,
and hypergeometric functions. By solving the connection problems we
analytically compute the behavior at all finite singular points for
and . We also give new results for .
We see in particular, the emergence of a remarkable order-six operator, which
is such that its symmetric square has a rational solution. These new exact
results indicate that the linear differential operators occurring in the
-fold integrals of the Ising model are not only "Derived from Geometry"
(globally nilpotent), but actually correspond to "Special Geometry"
(homomorphic to their formal adjoint). This raises the question of seeing if
these "special geometry" Ising-operators, are "special" ones, reducing, in fact
systematically, to (selected, k-balanced, ...) hypergeometric
functions, or correspond to the more general solutions of Calabi-Yau equations.Comment: 35 page
Importância da qualidade e certificação para ampliação do mercado internacional da manga brasileira.
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