18,105 research outputs found
Source Regions of Coronal Mass Ejections
Observations of the solar corona with the Large Angle Spectrometric
Coronograph (LASCO) and Extreme ultraviolet Imaging Telescope (EIT) instruments
on the Solar and Heliospheric Observatory (SOHO) provide an unprecedented
opportunity to study coronal mass ejections (CMEs) from their initiation
through their evolution out to 30 \rsun. The objective of this study is to gain
an understanding of the source regions from which the CMEs emanate. To this
end, we have developed a list of 32 CMEs whose source regions are located on
the solar disk and are well observed in EIT 195 {\AA} data during the period
from so lar minimum in January 1996 through the rising part of the cycle in May
1998. We compare the EIT source regions with photospheric magnetograms from the
Michelson Doppler Imager (MDI) instrument on SOHO and the NSO/Kitt Peak
Observatory and also with H data from various sources. The overall
results of our study show that 41% of the CME related transients observed are
associated with active regions and have no prominence eruptions, 44% are
associated with eruptions of prominences embedded in active regions and 15% are
associated with eruptions of prominences outside active regions. Those CMEs
that do not involve prominence eruptions originate in active regions both with
and without prominences. We describe 6 especially well observed events. These
case studies suggest that active region CMEs (without eruptive prominences) are
associated with active regions with lifetimes between 11--80 days. They are
also often associated with small scale emerging or cancelling flux over
timescales of 6--7 hours. CMEs associated with active region prominence
eruptions, on the other hand, are typically associated with old active regions
with lifetimes 6-7 months.Comment: Accepted for publication in ApJ, scheduled for Nov 1, 2001 issu
Challenges in video based object detection in maritime scenario using computer vision
This paper discusses the technical challenges in maritime image processing
and machine vision problems for video streams generated by cameras. Even well
documented problems of horizon detection and registration of frames in a video
are very challenging in maritime scenarios. More advanced problems of
background subtraction and object detection in video streams are very
challenging. Challenges arising from the dynamic nature of the background,
unavailability of static cues, presence of small objects at distant
backgrounds, illumination effects, all contribute to the challenges as
discussed here
Visualisation of an entangled channel spin-1 system
Co-variance matrix formalism gives powerful entanglement criteria for
continuous as well as finite dimensional systems. We use this formalism to
study a mixed channel spin-1 system which is well known in nuclear reactions. A
spin-j state can be visualized as being made up of 2j spinors which are
represented by a constellation of 2j points on a Bloch sphere using Majorana
construction. We extend this formalism to visualize an entangled mixed spin-1
system.Comment: 4 pages,4 figure
Unsteady convective boundary layer flow of a viscous fluid at a vertical surface with variable fluid properties
In this paper we present numerical solutions to the unsteady convective boundary layer flow of a viscous fluid at a vertical stretching surface with variable transport properties and thermal radiation. Both assisting and opposing buoyant flow situations are considered. Using a similarity transformation, the governing time-dependent partial differential equations are first transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by a second order finite difference scheme known as the Keller-Box method. The numerical results thus obtained are analyzed for the effects of the pertinent parameters namely, the unsteady parameter, the free convection parameter, the suction/injection parameter, the Prandtl number, the thermal conductivity parameter and the thermal radiation parameter on the flow and heat transfer characteristics. It is worth mentioning that the momentum and thermal boundary layer thicknesses decrease with an increase in the unsteady parameter. © 2012 Published by Elsevier Ltd
Comparative study of various methods of fetal weight estimation at term pregnancy in a tertiary hospital in Kanchipuram, Tamil Nadu, India
Background: Prediction of fetal weight is one of the methods towards effective management of pregnancy and delivery. Ultrasonography is the standard method to monitor the weight, but in the absence of such facility it becomes difficult particularly in the primary care setting. Clinical methods can be considered as an option and this requires selection of the valid method in deriving the fetal weight. In the present study, an effort is made to compare two different clinical methods and USG and relate to the actual weight of the baby at birth.Methods: One hundred pregnant women satisfying the criteria, consenting for the study were recruited. Both USG and clinical methods were done and estimated the fetal weight. Weight of the baby at birth was measured.Results: All the three methods had significant relationship with the baby weight. Results indicated that estimation of fetal weight by Dare’s formula could predict 69% of the cases correctly followed by Johnson’s method which could predict 61% of the cases correctly. USG predicted 67% of the cases correctly. Percentage error was least with USG and the standard deviation of error was lower with Dare’s formula.Conclusions: It can be concluded that Dare’s formula of clinical methods can be a potential option to be promoted in predicting the fetal weight in the absence of USG facilities. Training in this method is very important and can be an integral part in managing pregnancy during delivery in primary care setting
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