4,501 research outputs found
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
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
Local roughness exponent in the nonlinear molecular-beam-epitaxy universality class in one-dimension
We report local roughness exponents, , for three
interface growth models in one dimension which are believed to belong the
non-linear molecular-beam-epitaxy (nMBE) universality class represented by the
Villain-Lais-Das Sarma (VLDS) stochastic equation. We applied an optimum
detrended fluctuation analysis (ODFA) [Luis et al., Phys. Rev. E 95, 042801
(2017)] and compared the outcomes with standard detrending methods. We observe
in all investigated models that ODFA outperforms the standard methods providing
exponents in the narrow interval consistent
with renormalization group predictions for the VLDS equation. In particular,
these exponent values are calculated for the Clarke-Vvdensky and Das
Sarma-Tamborenea models characterized by very strong corrections to the
scaling, for which large deviations of these values had been reported. Our
results strongly support the absence of anomalous scaling in the nMBE
universality class and the existence of corrections in the form
of the one-loop renormalization group analysis
of the VLDS equation
Poynting Vector Flow in a Circular Circuit
A circuit is considered in the shape of a ring, with a battery of negligible
size and a wire of uniform resistance. A linear charge distribution along the
wire maintains an electrostatic field and a steady current, which produces a
constant magnetic field. Earlier studies of the Poynting vector and the rate of
flow of energy considered only idealized geometries in which the Poynting
vector was confined to the space within the circuit. But in more realistic
cases the Poynting vector is nonzero outside as well as inside the circuit. An
expression is obtained for the Poynting vector in terms of products of
integrals, which are evaluated numerically to show the energy flow. Limiting
expressions are obtained analytically. It is shown that the total power
generated by the battery equals the energy flowing into the wire per unit time.Comment: 19 pages, 8 figure
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