36,561 research outputs found
Epizootiološko istraživanje slinavke i šapa u Sudanu: stanje nakon dva desetljeća
In order to update information on the situation regarding foot and mouth disease (FMD) in the Sudan, a serosurvey and disease survey were conducted. Recently collected data on FMD in the Sudan showed that FMD is a major constraint to animal production in the country. It presents no threat nor does it cause mild disease in sheep and goats. The disease, with obvious clinical signs, has been detected in cattle only, and is caused by serotype O and SAT 2. Seasonal occurrence of the disease in the cold, dry season has been observed and animal
movement seems to play a major role in virus dissemination. A total of 1,069 sera were collected from cattle, sheep, goats, and camel, from seven states in the Sudan, for the detection of antibodies to FMDV. Application of liquid phase blocking (LPB) ELISA revealed that antibodies to four serotypes were present in ruminants; namely O, A, SAT 1 and SAT 2. No antibodies to FMDV were detected in camel sera. The results differed from early reports regarding the prevalence of serotype specifi c antibodies in different species; for instance, in cattle, the antibodies to type A (78.13%) surpassed that of type O (69.39%) and the antibodies to type SAT 2 (44%) surpassed that of type SAT 1 (20.2%). This work elucidates the current epidemiology of FMD in some parts of the Sudan.Radi pružanja informacija o sadašnjem stanju slinavke i šapa u Sudanu provedena su serološka istraživanja te je prikazana njezina pojavnost. Svježe prikupljeni podatci o pojavi slinavke i šapa u Sudanu pokazali su da ona predstavlja veliku prepreku životinjskoj proizvodnji u toj zemlji. U ovaca i koza javlja se kao blaga bolest i ne predstavlja veliku prijetnju, dok se u goveda javlja s očitim kliničkim znakovima, a uzrokovana je serotipovima O i SAT 2. Bolest se javlja sezonski u hladnoj i suhoj sezoni, a promet životinjama ima glavnu ulogu u širenju virusa. Ukupno je bilo prikupljeno 1069 uzoraka seruma goveda, ovaca, koza i deva podrijetlom iz sedam država u Sudanu radi pretrage na prisutnost protutijela za virus slinavke i šapa. Blokirajućim imunonenzimnim testom dokazana su protutijela za četiri serotipa virusa: O, A, SAT 1 i SAT 2. Protutijela za virus slinavke i šapa
nisu bila dokazana u uzorcima seruma deva. Rezultati se razlikuju od ranijih izvješća s obzirom na prevalenciju specifi čnih protutijela u različitih vrsta. Npr., specifi čna protutijela za serotip A dokazana su u 78,13% goveda, za serotip O u 69,39%, serotip SAT 2 u 44% te serotip SAT 1 u 20,2% goveda. U radu je prikazano sadašnje epizootiološko stanje slinavke i šapa u nekim dijelovima Sudana
Mitigation of Side-Effect Modulation in Optical OFDM VLC Systems
Side-effect modulation (SEM) has the potential to be a significant source of
interference in future visible light communication (VLC) systems. SEM is a
variation in the intensity of the light emitted by a luminaire and is usually a
side-effect caused by the power supply used to drive the luminaires. For LED
luminaires powered by a switched mode power supply, the SEM can be at much
higher frequencies than that emitted by conventional incandescent or
fluorescent lighting. It has been shown that the SEM caused by commercially
available LED luminaires is often periodic and of low power. In this paper, we
investigate the impact of typical forms of SEM on the performance of optical
OFDM VLC systems; both ACO-OFDM and DCO-OFDM are considered. Our results show
that even low levels of SEM power can significantly degrade the bit-error-rate
performance. To solve this problem, an SEM mitigation scheme is described. The
mitigation scheme is decision-directed and is based on estimating and
subtracting the fundamental component of the SEM from the received signal. We
describe two forms of the algorithm; one uses blind estimation while the other
uses pilot-assisted estimation based on a training sequence. Decision errors,
resulting in decision noise, limit the performance of the blind estimator even
when estimation is based on very long signals. However, the pilot system can
achieve more accurate estimations, thus better performance. Results are first
presented for typical SEM waveforms for the case where the fundamental
frequency of the SEM is known. The algorithms are then extended to include a
frequency estimation step and the mitigation algorithm is shown also to be
effective in this case
Sidelobe Control in Collaborative Beamforming via Node Selection
Collaborative beamforming (CB) is a power efficient method for data
communications in wireless sensor networks (WSNs) which aims at increasing the
transmission range in the network by radiating the power from a cluster of
sensor nodes in the directions of the intended base station(s) or access
point(s) (BSs/APs). The CB average beampattern expresses a deterministic
behavior and can be used for characterizing/controling the transmission at
intended direction(s), since the mainlobe of the CB beampattern is independent
on the particular random node locations. However, the CB for a cluster formed
by a limited number of collaborative nodes results in a sample beampattern with
sidelobes that severely depend on the particular node locations. High level
sidelobes can cause unacceptable interference when they occur at directions of
unintended BSs/APs. Therefore, sidelobe control in CB has a potential to
increase the network capacity and wireless channel availability by decreasing
the interference. Traditional sidelobe control techniques are proposed for
centralized antenna arrays and, therefore, are not suitable for WSNs. In this
paper, we show that distributed, scalable, and low-complexity sidelobe control
techniques suitable for CB in WSNs can be developed based on node selection
technique which make use of the randomness of the node locations. A node
selection algorithm with low-rate feedback is developed to search over
different node combinations. The performance of the proposed algorithm is
analyzed in terms of the average number of trials required to select the
collaborative nodes and the resulting interference. Our simulation results
approve the theoretical analysis and show that the interference is
significantly reduced when node selection is used with CB.Comment: 30 pages, 10 figures, submitted to the IEEE Trans. Signal Processin
Arrays of optical vortices formed by "fork" holograms
Singular light beams with optical vortices (OV) are often generated by means
of thin binary gratings with groove bifurcation ("fork holograms") that produce
a set of diffracted beams with different OV charges. Usually, only single
separate beams are used and investigated; here we consider the whole set of
diffracted OV beams that, at certain conditions, are involved in efficient
mutual interference to form a characteristic pattern where the ring-like
structure of separate OV beams is replaced by series of bright and dark lines
between adjacent diffraction orders. This pattern, well developed for high
diffraction orders, reflects the main spatial properties of the diffracted
beams as well as of the fork grating used for their generation. In particular,
it confirms the theoretical model for the diffracted beams (Kummer beam model)
and enables to determine the sign and the absolute value of the phase
singularity embedded in the hologram.Comment: 9 pages, 8 figure
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