3,051 research outputs found
Unpulsed UBV Optical Emission from the Crab Pulsar
Based on observations of the Crab pulsar using the TRIFFID high speed imaging
photometer in the UBV bands using the Special Astrophysical Observatory's 6m
telescope in the Russian Caucasus, we report the detection of pronounced
emission during the so-called `off' phase of emission. Following de-extinction,
this unpulsed component of emission is shown to be consistent with a power law
with an exponent of alpha = -0.60 +/- 0.37, the uncertainty being dominated by
the error associated with the independent CCD photometry used to reference the
TRIFFID data. This suggests a steeper power law form than that reported
elsewhere in the literature for the total integrated spectrum, which is
essentially flat with alpha ~ 0.1, although the difference in this case is only
significant at the ~ 2 sigma level. Deeper reference integrated and TRIFFID
phase-resolved photometry in these bands in conjunction with further
observations in the UV and R region would constrain this fit further.Comment: 26 pages, 2 figures, uses aasms4.sty, accepted for publication in the
Astrophysical Journa
Implications of the Optical Observations of Neutron Stars
We show that observations of pulsars with pulsed optical emission indicate
that the peak flux scales according to the magnetic field strength at the light
cylinder. The derived relationships indicate that the emission mechanism is
common across all of the observed pulsars with periods ranging from 33ms to 385
ms and ages of 1000-300,000 years. It is noted that similar trends exist for
ray pulsars. Furthermore the model proposed by Pacini (1971) and
developed by Pacini and Salvati (1983,1987) still has validity and gives an
adequate explanation of the optical phenomena.Comment: 23 pages, 6 figures, accepted for publication in the Astrophysical
Journa
Multi-Robot System Control Architecture (MRSCA) for Agricultural Production
Coordinating multiple autonomous robots for achieving an assigned collective task presents a complex engineering challenge. In this paper multi robot system control architecture (MRSCA) for the coordination of multiple agricultural robots is developed. The two important aspects of MRSCA; coordination strategy and inter-robot communication were discussed with typical agricultural tasks as examples. Classification of MRS into homogeneous and heterogeneous robots was done to identify appropriate form of cooperative behavior and inter-robot communication. The framework developed, proposes that inter-robot communication is not always required for a MRS. Three types of cooperative behaviors; No-cooperation, modest cooperation and absolute cooperation for a MRS were devised for accomplishing a variety of coordinated operations in agricultural productio
Cut Crop Edge Detection Using a Laser Sensor
An off-the-shelf low cost laser sensor was tested and evaluated both in laboratory and field conditions. The sensor identified the angular and straight edges of the laboratory test surface and replicated the straight edge profile with an error of 4%. In field conditions, the sensor identified three types of cut crop edges (wheat, alfalfa and corn) and replicated distinct shapes (triangle, curved and rectangular edges). The sensor was tested at two sensor path offset distances and three tractor/sensor speeds (3.2, 6.4 and 9.6 km/h). In all test runs the sensor detected the cut-crop edges. Standard deviations and RMSE values in determining the actual cut-crop edges for the entire field test were within 210 cm and 13 cm respectively. The sensor performed the best in the case of wheat cut-crop edge where the RMSE was 4.2 cm (sensor path offset = 1m, speed 3.2 km/h) and performed the worst in the case of alfalfa cut-crop edge where the RMSE was 16.7 cm (sensor path offset = .30 m and speed 9.6 km/h)
Guidance Directrix Generation Using Laser Sensors
A sensor array consisting of two laser sensors was utilized to determine the guidance directrix (offset distance-d, heading angle-ø) that are required as reference inputs for an automated guidance system. The sensor array was evaluated in both laboratory and field conditions. Under laboratory conditions the sensor array replicated the physical profile of the target surface with a 4% error in determining the heading angle. Field tests were conducted in two types of crops; corn and alfalfa. The sensor array identified the cut-crop edge profile ahead of the tractor and replicated distinct shapes of the cut-crop edge. RMSE values in determining the offset distances and heading angles of the cut-crop edge in corn were within 5.5 cm and 4.39°. In the case of alfalfa cut-crop edge the RMSE values were within 6.6 cm and 4.32°
Automatic Guidance System Development Using Low Cost Ranging Devices
Autonomous guidance of agricultural vehicles for various field operations serves to increase productivity. Low cost infra-red ranging devices were used in this study to estimate the guidance directrix (offset distance (d) and heading error angle (Ø)). Two kinds of tracks were used for evaluating the performance of the infra-red sensors, one track was made of a cardboard in the laboratory and the other track was made of wheat crop in the field. The cardboard track consisted of straight parallel and non parallel edges whereas the wheat crop track had a series of different edges including few curves. From the results it was concluded that the sensor consistently detected the profile of the tracks with good repeatability .Errors of 6% were observed in detecting the straight edges and errors 6.6% and 13% were obtained in detecting two different angled surfaces. The reasons for the errors were detected and explained briefly in the paper
Guidance Directrix Generation Using Laser Sensors
A sensor array consisting of two laser sensors was utilized to determine the guidance directrix (offset distance-d, heading angle-ø) that are required as reference inputs for an automated guidance system. The sensor array was evaluated in both laboratory and field conditions. Under laboratory conditions the sensor array replicated the physical profile of the target surface with a 4% error in determining the heading angle. Field tests were conducted in two types of crops; corn and alfalfa. The sensor array identified the cut-crop edge profile ahead of the tractor and replicated distinct shapes of the cut-crop edge. RMSE values in determining the offset distances and heading angles of the cut-crop edge in corn were within 5.5 cm and 4.390. In the case of alfalfa cut-crop edge the RMSE values were within 6.6 cm and 4.320
Sensor Ranging Technique for Determining Corn Plant Population
Mapping of corn plant population can provide useful information for making field management decisions. This research focused on using low cost infra-red sensors to count plants. The voltage output data from the sensors were processed using an algorithm developed to extract plant populations. Preliminary investigations were conducted using sensors mounted on a stationary track for laboratory testing and on a row crop tractor for field testing. Repeated measurements were taken on a manually counted corn row. Visual inspection of the data from the field test indicated the potential to identify corn stalks based on approximate physical widths of the stalks. Corn plant populations tended to be overestimated for all eight field trials, with errors ranging from +0.7% to +4.4%. Overestimation was most likely due to leaves or other objects detected by the sensors during the field trials wrongly identified as corn stalks
A candidate optical counterpart to the middle-aged gamma-ray pulsar PSR J1741-2054
We carried out deep optical observations of the middle-aged -ray
pulsar PSR J1741-2054 with the Very Large Telescope (VLT). We identified two
objects, of magnitudes and , at positions
consistent with the very accurate Chandra coordinates of the pulsar, the
faintest of which is more likely to be its counterpart. From the VLT images we
also detected the known bow-shock nebula around PSR J1741-2054. The nebula is
displaced by \sim 0\farcs9 (at the confidence level) with respect
to its position measured in archival data, showing that the shock propagates in
the interstellar medium consistently with the pulsar proper motion. Finally, we
could not find evidence of large-scale extended optical emission associated
with the pulsar wind nebula detected by Chandra, down to a surface brightness
limit of magnitudes arcsec. Future observations are needed
to confirm the optical identification of PSR J1741-2054 and characterise the
spectrum of its counterpart.Comment: 8 pages, 3 figures, Astrophysical Journal, in pres
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