Generally, GaN-based devices are grown on silicon carbide or sapphire substrates. But these substrates are costly and insulating in nature and also are not available in large diameter. Silicon can meet the requirements for a low cost and conducting substrate and will enable integration of optoelectronic or high power electronic devices with Si based electronics. But the main problem that hinders the rapid development of GaN devices based on silicon is the thermal mismatch of GaN and Si, which generates cracks. In 1998, the first MBE grown GaN based LED on Si was made and now the quality of material grown on silicon is comparable to that on sapphire substrate. It is only a question of time before Si based GaN devices appear on the market. This article is a review of the latest developments in GaN based devices on silicon.

This first general population-based epidemiological study of HBV infection from India suggests that HBV acquisition starts in early childhood and peaks in adulthood. Most infections in the community are e-negative and inactive. The point prevalence of PC stop codon and BCP mutants is low in this primarily inactive and asymptomatic HBV-infected population sample in eastern India.

Summary Background CD4+ regulatory T‐cells (Tregs) expand during chronic hepatitis B virus (HBV) infection and inhibit antiviral immunity, although the underlying mechanism remains largely elusive. Myeloid‐derived suppressor cells (MDSC) have been linked with T‐cell dysfunction but questions remain regarding their persistence/profile/function in chronically HBV infected patients. Aim To characterise MDSC in different phases of chronic HBV infection namely, immune‐tolerant (IT), hepatitis B e‐antigen‐positive chronic hepatitis B (EP‐CHB), inactive carriers (IC) and hepatitis B e‐antigen‐negative chronic hepatitis B (EN‐CHB), to investigate their role in Treg induction and evaluate the effect of anti‐viral therapy on these cells. Methods Multiparametric flow cytometry, cell‐sorting and co‐culture assays were performed along with longitudinal immune monitoring of CHB patients receiving tenofovir. Results HLA‐DR‐CD11b+CD33hi‐Monocytic‐MDSC (M‐MDSC) were enhanced in IT, EP‐CHB and EN‐CHB compared with IC, and this was related to increasing hepatitis B surface antigen (HBsAg) concentration. IT and EP‐/EN‐CHB displayed elevated frequency of CD4+CD25+FOXP3+Treg that positively correlated with that of M‐MDSC. However, both M‐MDSC and HLA‐DR‐CD11b+CD33low‐granulocytic‐MDSC from IT and EP‐/EN‐CHB expressed high transforming growth factor beta (TGF‐β) and interleukin‐10 (IL‐10). Co‐culture of sorted HLA‐DR‐CD33+‐MDSC with autologous MDSC depleted‐PBMC from IT and CHB but not from IC, increased CD4+CD25+FOXP3+‐iTreg and CD4+FOXP3‐IL‐10+‐Tr1‐cells through a cell‐contact independent mechanism. While MDSC‐derived TGF‐β and IL‐10 promoted development of iTreg, only IL‐10 appeared to be crucial for Tr1 induction. One year of tenofovir treatment failed to normalise MDSC frequency/function or reduce Treg percentage and serum HBsAg levels, despite reduction in viral load. Conclusions We established a previously unrecognised role of MDSC in Treg development in IT and EP‐/EN‐CHB via TGF‐β/IL‐10‐dependent pathways and both cell‐types persisted after anti‐viral therapy. Hence, therapeutic targeting of MDSC or reducing circulating HBsAg level together with tenofovir‐therapy might be more effective in restricting HBV persistence and disease progression.

Abstract. X-ray photons emitted during solar flares cause ionization in the lower ionosphere (~60 to 100 km) in excess of what is expected to occur due to a quiet sun. Very low frequency (VLF) radio wave signals reflected from the D-region of the ionosphere are affected by this excess ionization. In this paper, we reproduce the deviation in VLF signal strength during solar flares by numerical modeling. We use GEANT4 Monte Carlo simulation code to compute the rate of ionization due to a M-class flare and a X-class flare. The output of the simulation is then used in a simplified ionospheric chemistry model to calculate the time variation of electron density at different altitudes in the D-region of the ionosphere. The resulting electron density variation profile is then self-consistently used in the LWPC code to obtain the time variation of the change in VLF signal. We did the modeling of the VLF signal along the NWC (Australia) to IERC/ICSP (India) propagation path and compared the results with observations. The agreement is found to be very satisfactory.

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