Multiple Scales in Small-World Networks

Small-world architectures may be implicated in a range of phenomena from networks of neurons in the cerebral cortex to social networks and propogation of viruses. Small-world networks are interpolations of regular and random networks that retain the advantages of both regular and random networks by being highly clustered like regular networks and having small average path length between nodes, like random networks. While most of the recent attention on small-world networks has focussed on the effect of introducing disorder/randomness into a regular network, we show that that the fundamental mechanism behind the small-world phenomenon is not disorder/ randomness, but the presence of connections of many different length scales. Consequently, in order to explain the small-world phenomenon, we introduce the concept of multiple scale networks and then state the multiple length scale hypothesis. We show that small-world behavior in randomly rewired networks is a consequence of features common to all multiple scale networks. To support the multiple length scale hypothesis, novel network architectures are introduced that need not be a result of random rewiring of a regular network. In each case it is shown that whenever the network exhibits small-world behavior, it also has connections of diverse length scales. We also show that the distribution of the length scales of the new connections is significantly more important than whether the new connections are long range, medium range or short range

Development of a Small Satellite Series ISRO Experience

The development of a small Stretched Rohini Satellite Series (SROSS) in the Indian Space Research Organization (ISRO) has moved hand in hand with that of one class of indigenous launch vehicles, the Augmented Satellite Launch Vehicle (ASLV). In other words, these satellites have been developed as compatible payloads for those launch vehicles. The first two satellites SROSS-1 and SROSS-2 although were very versatile satellites carrying space science related payloads could not be orbited owing to failure of launch vehicles. The third satellite in the series, SROSS-C, was a smaller satellite launched by the third developmental flight ASLV-D3 on May 20, 1992. Earlier, the 40kg class rohini satellites (RS) were developed as payloads for the smaller launch vehicles (SLV-3) during the pre-eighties, which were suitably augmented to the Augmented Satellite Launch Vehicles to carry the 150 kg class Stretched Rohini Satellite Series during the pre and post nineties. This new satellite series were configured on the basis of a common bus concept, which are extremely compact, cost effective as well as innovative. It is compact because subsystems are very densely packed, cost effective because the bus is common and hence easily reproducible, and innovative because it is modular and hence easily reconfigurable. The paper describes some of these important aspects giving full narration of the development including pre-launch, launch and on-orbit operations of SROSS-C in detail

Dark and Dairy

notes: Extended version with footnotes available here: http://www.rajesh.io/street-metaphysics/?tag=Dharmapolispublication-status: PublishedCopyright © 2014 The HinduNewspaper - Opinio

SROSS C-2 detections of gamma ray bursts and the SGR 1627-41

The GRB monitor (GRBM) on board the Indian SROSS C-2 satellite has detected 53 classical gamma ray bursts since its launch in May, 1994 till its re-entry in July, 2001. For a subset of 26 events, locations were obtained from simultaneous observations by other gammaray detectors in space. The sky distribution of these 26 SROSS C-2 bursts is consistent with isotropy. The distribution of event durations shows evidence for bimodality. There is an evidence for a moderate hardness ratio-intensity (HIC) correlation in the data. The SROSS C-2 GRBM has also detected three episodes of emission from the SGR 1627-41

Science and technology of imaging from space

Imaging techniques from space, started mainly as a military reconnaissance tool, have come a long way from its early concepts to meet the present day needs of providing a precise metrology of the Earth processes and its features. The first part of the paper deals with the basic concepts of imaging from space. In this, the energy source available and the effect of atmosphere on the radiation are elaborated. Also the signatures of objects for identification and their characteristics in spatial and spectral domain are briefly touched upon. The second part of the paper deals with the challenges in realizing a satellite with limited volume and weight constraints by giving examples of very innovative approaches in the design of the optical systems for telescopes. The challenges associated with high resolution imaging and resulting high amount of data handling through appropriate data compression techniques are highlighted. The work presented here has been primarily carried out at the Indian Space Research Organization (ISRO). The paper concludes with an assessment of the futuristic direction that include improved algorithms for parameter retrieval and improved classification accuracies, improved models for atmospheric correction, new approach in artificial intelligence and expert systems for feature based classification, improved data compression techniques, ultra-light weight mirrors and adaptive optics, optical materials and detector arrays with built-in read out in the infrared region

X-ray variability of GRS 1915+105 during the low-hard state observed with the Indian X-ray astronomy experiment (IXAE)

The galactic superluminal transient X-ray source GRS 1915+105 was observed with the pointed proportional counters (PPCs) onboard the Indian satellite IRS-P3 during 1996 July 23-27. We report here details of the behavior of this source during the relatively quiet and low luminosity state. Large intensity variations by a factor of 2 to 3, generally seen in black-hole candidates, are observed at a time scale of 100 ms to few seconds. No significant variation is detected over larger time scale of minute or more. The intensity variations are described as sum of shots in the light curve, and the number distribution of the shots are found to be exponential function of the fluence and duration of the shots. The cross correlation spectrum between 6-18 keV and 2-6 keV X-rays is found to have asymmetry signifying a delay of the hard X-rays by about 0.2 to 0.4 sec. This supports the idea of hard X-rays being generated by Compton up-scattering from high energy clouds near the source of soft X-rays. Very strong and narrow quasi periodic oscillations in the frequency range 0.62 to 0.82 Hz are observed. We discuss about a model which explains a gradual change in the QPO frequencies with corresponding changes in the mass accretion rate of the disk.Comment: 14 pages including 6 figures. To appear in Astronomy and Astrophysics Supplement Serie

Science and technology of imaging from space

Imaging techniques from space, started mainly as a military reconnaissance tool, have come a long way from its early concepts to meet the present day needs of providing a precise metrology of the Earth processes and its features. The first part of the paper deals with the basic concepts of imaging from space. In this, the energy source available and the effect of atmosphere on the radiation are elaborated. Also the signatures of objects for identification and their characteristics in spatial and spectral domain are briefly touched upon. The second part of the paper deals with the challenges in realizing a satellite with limited volume and weight constraints by giving examples of very innovative approaches in the design of the optical systems for telescopes. The challenges associated with high resolution imaging and resulting high amount of data handling through appropriate data compression techniques are highlighted. The work presented here has been primarily carried out at the Indian Space Research Organization (ISRO). The paper concludes with an assessment of the futuristic direction that include improved algorithms for parameter retrieval and improved classification accuracies, improved models for atmospheric correction, new approach in artificial intelligence and expert systems for feature based classification, improved data compression techniques, ultra-light weight mirrors and adaptive optics, optical materials and detector arrays with built-in read out in the infrared region

A numerical study of natural convection and radiation heat transfer in a thermoelectric couple

Heat transfer plays an important role in the design of efficient thermoelectric (TE) devices. Currently, a TE device constructed from bismuth-telluride with figure of merit, ZT, of unity can achieve an ideal efficiency of about 12%. However, the efficiency achieved in practice is less than 5%. This difference between the ideal and the actual efficiencies can largely be attributed to heat transfer. A numerical study based on three-dimensional CFD analysis was performed to investigate natural convection and radiation heat transfer that take place in the space between the thermoelectric legs in thermoelectric (TE) modules. Parameters studied include staggered and non-staggered arrangement of the TE legs, length of the legs, spacing between legs, and difference between the hot and cold temperatures. Results obtained show natural convection and radiation can both be important. Radiation increases in importance as surface emissivity increases. Also, radiation heat transfer increases as leg length shortens, leg spacing, and temperature difference increases. This data will be used to guide design. Results also show that there is net transfer of heat to TE legs from the hot walls of the cavity. This presents a new design opportunity

The design of space vehicles

In this paper, an attempt has been made to summarise the essential elements of a space vehicle design. After giving an overview of the methodology of spacecraft sizing and configuration, a brief outline of the technical considerations related to the design of different subsystems of the vehicle has been presented. The essential aspects related to manned systems are also discussed. The article concludes with the identification of some of the important payload interfaces, that are relevant to the design of material processing experiments in space