Highly anisotropic mechanical and optical properties of 2D NbOX2 (X = Cl, Br, I) revealed by first-principle

In the latest experimental success, NbOI2 two-dimensional (2D) crystals with anisotropic electronic and optical properties have been fabricated (Adv. Mater. 33 (2021), 2101505). In this work inspired by the aforementioned accomplishment, we conduct first-principles calculations to explore the mechanical, electronic, and optical properties of NbOX2 (X = Cl, Br, I) nanosheets. We show that individual layers in these systems are weakly bonded, with exfoliation energies of 0.22, 0.23, and 0.24 J m-2, for the isolation of the NbOCl2, NbOBr2, and NbOI2 monolayers, respectively, distinctly lower than those of the graphene. The optoelectronic properties of the single-layer, bilayer, and bulk NbOCl2, NbOBr2, and NbOI2 crystals are investigated via density functional theory calculations with the HSE06 approach. Our results indicate that the layered bulk NbOCl2, NbOBr2, and NbOI2 crystals are indirect gap semiconductors, with band gaps of 1.79, 1.69, and 1.60 eV, respectively. We found a slight increase in the electronic gap for the monolayer and bilayer systems due to electron confinement at the nanoscale. Our results show that the monolayer and bilayer of these novel 2D compounds show suitable valence and conduction band edge positions for visible-light-driven water splitting reactions. The first absorption peaks of these novel monolayers along the in-plane polarization are located in the visible range of light which can be a promising feature to design advanced nanoelectronics. We found that the studied 2D systems exhibit highly anisotropic mechanical and optical properties. The presented first-principles results provide a comprehensive vision about direction-dependent mechanical and optical properties of NbOX2 (X = Cl, Br, I) nanosheets

Long-term morphological and power spectral studies of VHF amplitude scintillations recorded over Waltair (17.7°N, 83.3°E), India

This research reports on recently recorded 250 MHz amplitude scintillations at Waltair (17.7°N, 83.3°E), a low-latitude station in India, using the signals radiated from a geostationary satellite (FLEETSAT, 73°E) during a six-year period (2008 - 2013), which covers extremely low and higher solar activity years (2008 and 2013). The morphological features in terms of local time, month, and season during different geophysical conditions are presented. The scintillation patches (segregated based on their occurrence durations) have shown an increasing trend with the increasing sunspot activity. The scintillation patches with 30-min duration show increasing trends with increasing sunspot activity, and their occurrence frequencies also show increasing trends with increasing sunspot activity. The scintillation activity during disturbed epochs (Kp index lies between 3+ and 9) is found to be less compared to its quiet day counterparts. The plausible mechanisms for these observational results are discussed. In addition, power spectral characteristics, including Fresnel frequency, upper role of frequency and spectral slope of scintillations are calculated and the salient results are presented

A study of temperature profiles and trends as revealed by COSMIC RO technique and balloon –borne radiosonde instrument

This research presents atmospheric temperature profiles and trends retrieved using COSMIC RO technique and balloon-borne radiosonde instrument in 2007 and a few cases during 2017. By effectively using ‘wet’ temperature product available at COSMIC Data Analysis and Archive Center (CDAAC) website, an analysis has been made to present temperature profiles and trends at various regions including, Indian, Taiwan and Japan. A one-to-one correspondence is, clearly, seen between temperature profiles retrieved with COSMIC RO and radiosonde instrument. But, few and dominant differences in temperature profiles are found below at an altitude of ~5 km and above around tropopause (~16-17 km). The dominant differences found at below ~5km could be due to the inhomogeneous distribution of humidity present, generally, at the tropical regions, whereas above the tropopause altitudes, differences might be due to the ionospheric residual correction as reported by other researchers. Further, temperature monthly trends at various regions show distinct characteristics including, a sharp temperature inversion up to tropopause altitude. In addition, it is also observed maximum temperatures (peaks) during the northern summer seasons (May, June, July, and August) and minimum temperatures (troughs) during the northern winter seasons (November, December, January, and February) near to the surface of the Earth. Interestingly, although it is generally observed that the tropopause altitude is located at ~ 16-17 km at various regions, a keen observation reveals that distinct seasonal and latitudinal variations can be witnessed. With this case study, it may be concluded that the COSMIC RO technique is able to provide very accurate measurement, which reiterates its importance as a powerful tool to explore the Earth’s atmosphere on the local and global scale

Anomalous wind circulation over Taipei, Taiwan during the northern winter seasons of 2004 and 2005- A case study

This research reports, for the first time, an anomalous wind circulation over Taipei (Latitude 25.030N, Longitude 121.510E), Taiwan during the northern hemisphere winter season (December, January, and February) of years 2004 and 2005. The anomalous wind circulation of meridional winds, which showed southward directions during the winter seasons of 2004 and 2005 instead of northward winds, is noticed from one kilometer altitude range (lower troposphere) and that trend continued till around 20 km altitude range (lower stratosphere). To ascertain whether such a disturbed nature of wind pattern existed over nearby locations to Taipei, we have analyzed radiosonde-measured meridional and zonal winds over four nearby stations station to Taipei including, Roig, Xiamen, Minami and Fuzhou. Surprisingly, no anomalous wind behavior is seen except over Taipei during the northern winter seasons of 2004 and 2005. On the other hand, the European Centre for Medium-Range Weather Forecasts (ECMWF) model-predicted winds do not show any anomalous wind patterns over Taipei and other nearby stations, possibly due to the large averaging of internal variabilities of reanalysis databases. The plausible physical mechanisms of these disturbed meridional wind patterns are not understood at this juncture, but it is believed that local winds and atmospheric pollutants might have created an amicable environment as to provide such a disturbed meridional wind pattern over Taipei, Taiwan in the winter season of 2004 and 2005

Hepatopancreatic lipolytic activity in the aestivated pond snail, Pila globosa

The aestivated snails showed significant increase in the enzymic hydrolysis of Me salicylate and olive oil and significant decrease in the enzymic hydrolysis of coconut oil indicating that relatively more of the unsatd. fats are hydrolyzed than satd. fats in these animals. Accumulation of glycerol in the tissues of the snail during aestivation is discussed with reference to fatty acid metabolism