Gopal Sharma

An A–D–A small molecule based on the 3,6-dithienylcarbazole electron donor (D) unit and nitrophenyl acrylonitrile electron acceptor (A) units for solution processed organic solar cells

A new A–D–A small molecule (SM) based on a 3,6-dithienylcarbazole donor unit at the center and nitrophenyl acrylonitrile acceptor units as the terminal ends was synthesized by the Pd catalyzed Stille coupling reaction for application as a donor material in the organic bulk heterojunction solar cells. The SM possesses a low lying HOMO energy level at −5.34 eV and optical band gap of 1.74 eV. The photovoltaic performance of the SM was investigated with PC60BM and PC70BM as acceptors cast from THF with 3% CN additive and without additive. The power conversion efficiency (PCE) of the organic solar cells based on SM:PC60BM cast from THF solvent reached 1.94% with a high Voc of 0.94 V, a Jsc of 6.08 mA cm−2 and FF of 0.34, where as the PCE of SM:PC70BM cast from THF solvent was 2.65% with a Voc of 0.96 V, a Jsc of 7.26 mA cm−2 and FF of 0.38%, under the illumination intensity of 100 mW cm−2. The higher PCE of the organic solar cells based on PC70BM as an electron acceptor has been attributed to its strong absorption in the visible region than PC60BM. The PCE of the organic solar cells has been further improved to 3.76% and 4.96% for SM:PC60BM and SM:PC70BM, respectively, cast with CN–THF solvent.

Global navigation satellite system detection of preseismic ionospheric total electron content anomalies for strong magnitude ( Mw > 6 ) Himalayan earthquakes

Abstract. Electron content in the ionosphere is very sensitive to temporary disturbances of the Earth’s magnetosphere (geomagnetic storm), solar flares, and seismic activities. The Global Navigation Satellite System (GNSS)-based total electron content (TEC) measurement has emerged as an important technique for computations of earthquake precursor signals. We examined the pre-earthquake signatures for eight strong magnitude (Mw>6: 6.1 to 7.8) earthquakes with the aid of GNSS-based TEC measurement in the tectonically active Himalayan region using International GNSS Service (IGS) stations as well as local GNSS-based continuously operating reference stations (CORS). The results indicate very significant ionospheric anomalies in the vertical total electron content (vTEC) a few days before the main shock for all of the events. Geomagnetic activities were also studied during the TEC observation window to ascertain their role in ionospheric perturbations. It was also inferred that TEC variation due to low magnitude events could also be monitored if the epicenter lies closer to the GNSS or IGS station. Therefore, the study has confirmed TEC anomalies before major Himalayan earthquakes, thereby making it imperative to set up a much denser network of IGS/CORS for real-time data analysis and forewarning.

Ionospheric TEC Monitoring Using Ground Based GNSS Observations for Earthquake Precursor Studies

Summary Measurement of Ionospheric total electron content(TEC) for earthquake precursor studies has emerged as an innovative application of global navigation satellite systems(GNSS) which are gaining popularity. In present study we examine pre-earthquake Ionospheric anomalies with the aid of TEC measurement derived from ground based GNSS receivers. We did an experimental study considering data from two International GNSS Service (IGS) Stations VISO(in Sweden) and MDVJ (in Moscow) located relatively away from known earthquake regions. The data were processed using GPS-TEC for the period of 11 months. In most of the cases anomalies were found 5–10 days prior to earthquakes occurrences and were also studied vis-a-vis solar flares and geomagnetic storms activities to rule out its possible effects. Most importantly the study has critically analyzed epicentral distances of earthquakes from the GNSS location and it was found that anomalies have been detected at a larger distance from the earthquake epicenter as per the earthquake preparation zone defined by Liu(2004). Therefore, the study highlighted that the Ionospheric anomalies due to TEC perturbations in the Ionospheric detected at far off places from earthquake epicenter could provide non-ambiguous precursory signals attributed to earthquakes, thus reducing the chance of false alarms.

Ionospheric Total Electron Content for Earthquake Precursor Detection

Understanding earthquake precursory phenomena based on ionosphere perturbation is a fairly new field in geoscience today and has achieved promising success. Scientists across the globe are now trying to learn insight about the physical and chemical processes involved in the upper atmosphere and beyond during the earthquake preparatory period. One of such studies is based on global navigation satellite system (GNSS) observations. Global Positioning System (GPS) is currently one of the most popular global navigation satellite positioning systems widely available for such society application. GPS has led to technical revolutions in the field of applications like navigation as well as in upper atmospheric/ionospheric studies. GPS signals from the satellites encountered the ionosphere before it is captured by the receiver on the ground. In this process, the free electrons in the ionosphere affect the propagation of the signals by changing their velocity and direction of travel. A number of recent investigations have suggested that satellites and ground-based facilities like that of GNSS may detect earthquake precursors a few hours or days prior to the main event due to ionospheric perturbations induced by initiation of earthquake process. The typical phenomenological features of ionospheric precursors of strong earthquakes are summarised by Pulinets et al. (2003). The parameter of ionosphere that produces most of the effects on radio signals is the total electron content (TEC). The TEC is defined by the integral of electron density in a 1 metre square column along the signal transmission path. The ionosphere causes GPS signal delays to be proportional to the TEC along the path from the GNSS satellite to a receiver. The TEC measurements obtained from dual frequency GNSS receivers are one of the most important parameters to characterise Earth’s ionosphere. The changes in the Earth’s ionosphere can be used to derive the information about an impending earthquake. Therefore, it is very important to monitor the TEC variation due to tectonic deformation prior to an earthquake and its validation in real-world situation.