75,407 research outputs found
Spread spectrum techniques for indoor wireless IR communications
Multipath dispersion and fluorescent light
interference are two major problems in indoor
wireless infrared communications systems. Multipath
dispersion introduces intersymhol interference
at data rates above 10 Mb/s, while
fluorescent light induces severe narrowband
interference to baseband modulation schemes
commonly used such as OOK and PPM. This
article reviews the research into the application
of direct sequence spread spectrum techniques
to ameliorate these key channel impairments
without having to resort to complex signal processing
techniques. The inherent properties of a
spreading sequence are exploited in order to
combat the ISI and narrowband interference. In
addition, to reduce the impact of these impairments,
the DSSS modulation schemes have
strived to be bandwidth-efficient and simple to
implement. Three main DSSS waveform techniques
have been developed and investigated.
These are sequence inverse keying, complementary
sequence inverse keying, and M-ary biorthogonal
keying (MBOK). The operations of
the three systems are explained; their performances
were evaluated through simulations and
experiments for a number of system parameters,
including spreading sequence type and length.
By comparison with OOK, our results show that
SIK, CSIK, and MBOK are effective against
multipath dispersion and fluorescent light interference
becausc the penalties incurred on the
DSSS schemes are between 0-7 dB, while the
penalty on OOK in the same environment is
more than 17 dB. The DSSS solution for IR
wireless transmission demonstrates that a transmission
waveform can he designed to remove
the key channel impairments in a wireless IR
system
Evaluation of electrolytic tilt sensors for measuring model angle of attack in wind tunnel tests
The results of a laboratory evaluation of electrolytic tilt sensors as potential candidates for measuring model attitude or angle of attack in wind tunnel tests are presented. The performance of eight electrolytic tilt sensors was compared with that of typical servo accelerometers used for angle-of-attack measurements. The areas evaluated included linearity, hysteresis, repeatability, temperature characteristics, roll-on-pitch interaction, sensitivity to lead-wire resistance, step response time, and rectification. Among the sensors being evaluated, the Spectron model RG-37 electrolytic tilt sensors have the highest overall accuracy in terms of linearity, hysteresis, repeatability, temperature sensitivity, and roll sensitivity. A comparison of the sensors with the servo accelerometers revealed that the accuracy of the RG-37 sensors was on the average about one order of magnitude worse. Even though a comparison indicates that the cost of each tilt sensor is about one-third the cost of each servo accelerometer, the sensors are considered unsuitable for angle-of-attack measurements. However, the potential exists for other applications such as wind tunnel wall-attitude measurements where the errors resulting from roll interaction, vibration, and response time are less and sensor temperature can be controlled
Robust active heave compensated winch-driven overhead crane system for load transfer in marine operation
Active heave compensation (AHC) is important for load transfer in marine operation using the overhead crane system (OCS). The control of marine OCS aims to continuously regulate the displacement of the cart and the payload sway angle, whilst at the same time, maintaining the gap between the payload and the vessel main deck at a desirable and safe distance. As the marine OHC system is to be operated in a continuously changing environment, with plenty inevitable disturbances and undesirable loads, a robust controller, i.e., active force control (AFC) is thus greatly needed to promote accuracy and robustness features into the controllability of OCS in rough working environment. This paper highlights a novel method for controlling the payload in an OCS based on the combination of both AFC and AHC. Results from the simulation study clearly indicate that the performance of OCS can be greatly improved by the proposed robust AFC controller, as compared with the classical PID controller scheme
Tidal stability of giant molecular clouds in the Large Magellanic Cloud
Star formation does not occur until the onset of gravitational collapse
inside giant molecular clouds. However, the conditions that initiate cloud
collapse and regulate the star formation process remain poorly understood.
Local processes such as turbulence and magnetic fields can act to promote or
prevent collapse. On larger scales, the galactic potential can also influence
cloud stability and is traditionally assessed by the tidal and shear effects.
In this paper, we examine the stability of giant molecular clouds (GMCs) in the
Large Magellanic Cloud (LMC) against shear and the galactic tide using CO data
from the Magellanic Mopra Assessment (MAGMA) and rotation curve data from the
literature. We calculate the tidal acceleration experienced by individual GMCs
and determine the minimum cloud mass required for tidal stability. We also
calculate the shear parameter, which is a measure of a clouds susceptibility to
disruption via shearing forces in the galactic disk. We examine whether there
are correlations between the properties and star forming activity of GMCs and
their stability against shear and tidal disruption. We find that the GMCs are
in approximate tidal balance in the LMC, and that shear is unlikely to affect
their further evolution. GMCs with masses close to the minimal stable mass
against tidal disruption are not unusual in terms of their mass, location, or
CO brightness, but we note that GMCs with large velocity dispersion tend to be
more sensitive to tidal instability. We also note that GMCs with smaller radii,
which represent the majority of our sample, tend to more strongly resist tidal
and shear disruption. Our results demonstrate that star formation in the LMC is
not inhibited by to tidal or shear instability.Comment: 18 pages, 10 Figures, Accepted in PAS
Studies of Neutrino-Electron Scattering at the Kuo-Sheng Reactor Neutrino Laboratory
Studies on electron antineutrino-electron elastic scattering were performed
using a 200-kg CsI(Tl) scintillating crystal detector array at the Kuo-Sheng
Nuclear Power Plant in Taiwan. The measured cross section of R(exp) = [1.00 +-
0.32(stat)]xR(SM) is consistent with the Standard Model expectation and the
corresponding weak mixing angle derived is sin2T = 0.24 +- 0.05 (stat). The
results are consistent with a destructive interference effect between neutral
and charged-currents in this process. Limits on neutrino magnetic moment of
mu(nu_(e)) < 2.0 x 10^(-10) mu_(B) at 90% confidence level and on electron
antineutrino charge radius of r^(2) < (0.12 +- 2.07)x10^(-32) cm^2 were also
derived.Comment: Parallel talk at ICHEP08, Philadelphia, USA, July 2008. 4 pages,
LaTex, 4 eps figure
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Use of colour for hand-filled form analysis and recognition
Colour information in form analysis is currently under utilised. As technology has advanced and computing costs have reduced, the processing of forms in colour has now become practicable. This paper describes a novel colour-based approach to the extraction of filled data from colour form images. Images are first quantised to reduce the colour complexity and data is extracted by examining the colour characteristics of the images. The improved performance of the proposed method has been verified by comparing the processing time, recognition rate, extraction precision and recall rate to that of an equivalent black and white system
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