Diurnal restratification events in the southeast Pacific trade wind regime

Author Posting. © American Meteorological Society, 2014. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 44 (2014): 2569–2587, doi:10.1175/JPO-D-14-0026.1.This paper describes the occurrence of diurnal restratification events found in the southeast trade wind regime off northern Chile. This is a region where persistent marine stratus clouds are found and where there is a less than complete understanding of the dynamics that govern the maintenance of the sea surface temperature. A surface mooring deployed in the region provides surface meteorological, air–sea flux, and upper-ocean temperature, salinity, and velocity data. In the presence of steady southeast trade winds and strong evaporation, a warm, salty surface mixed layer is found in the upper ocean. During the year, these trade winds, at times, drop dramatically and surface heating leads to the formation of shallow, warm diurnal mixed layers over one to several days. At the end of such a low wind period, mean sea surface temperature is warmer. Though magnitudes of the individual diurnal warming events are consistent with local forcing, as judged by running a one-dimensional model, the net warming at the end of a low wind event is more difficult to predict. This is found to stem from differences between the observed and predicted near-inertial shear and the depths over which the warmed water is distributed. As a result, the evolution of SST has a dependency on these diurnal restratification events and on near-surface processes that govern the depth over which the heat gained during such events is distributed.RAW was supported by the NOAA Climate Program Office. SM and AT were supported by NASA Grant NNX12AD47G,ONR Grant N000140910196, and NSF-OCE 0928138 RAW.2015-03-0

Investigation of Ultrafast Demagnetization and Gilbert Damping and their Correlation in Different Ferromagnetic Thin Films Grown Under Identical Conditions

Following the demonstration of laser-induced ultrafast demagnetization in ferromagnetic nickel, several theoretical and phenomenological propositions have sought to uncover its underlying physics. In this work we revisit the three temperature model (3TM) and the microscopic three temperature model (M3TM) to perform a comparative analysis of ultrafast demagnetization in 20-nm-thick cobalt, nickel and permalloy thin films measured using an all-optical pump-probe technique. In addition to the ultrafast dynamics at the femtosecond timescales, the nanosecond magnetization precession and damping are recorded at various pump excitation fluences revealing a fluence-dependent enhancement in both the demagnetization times and the damping factors. We confirm that the Curie temperature to magnetic moment ratio of a given system acts as a figure of merit for the demagnetization time, while the demagnetization times and damping factors show an apparent sensitivity to the density of states at the Fermi level for a given system. Further, from numerical simulations of the ultrafast demagnetization based on both the 3TM and the M3TM, we extract the reservoir coupling parameters that best reproduce the experimental data and estimate the value of the spin flip scattering probability for each system. We discuss how the fluence-dependence of inter-reservoir coupling parameters so extracted may reflect a role played by nonthermal electrons in the magnetization dynamics at low laser fluences

Near-inertial kinetic energy budget of the mixed layer and shear evolution in the transition layer in the Arabian Sea during the monsoons

Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 120 (2015): 6492–6507, doi:10.1002/2014JC010198.We present the horizontal kinetic energy (KE) balance of near-inertial currents in the mixed layer and explain shear evolution in the transition layer using observations from a mooring at 15.26° N in the Arabian Sea during the southwest monsoon. The highly sheared and stratified transition layer at the mixed-layer base varies between 5 m and 35 m and correlates negatively with the wind stress. Results from the mixed layer near-inertial KE (NIKE) balance suggest that wind energy at times can energize the transition layer and at other times is fully utilized within the mixed layer. A simple two layer model is utilized to study the shear evolution in the transition layer and shown to match well with observations. The shear production in this model arises from alignment of wind stress and shear. Although the winds are unidirectional during the monsoon, the shear in the transition layer is predominantly near-inertial. The near-inertial shear bursts in the observations show the same phasing and magnitude at near-inertial frequencies as the wind-shear alignment term.NASA Grant Number: NNX12AD47G, NSF Grant Number: 0928138, ONR Grant Numbers: N00014-11-1-0429 and N00014-10-1-0273, NSF Grant Number: OCE-07455082016-03-2

Multilayered and Chemiresistive Thin and Thick Film Gas Sensors for Air Quality Monitoring

Selective detection of gases such as nitrogen dioxide (NO2), carbon monoxide (CO), carbon dioxide (CO2), and various volatile organic components (VOCs) is necessary for air quality monitoring. Detection of hydrogen (H2) is equally important as it is a flammable gas and poses serious threat of explosion when exposed to oxygen gas. We have studied the sensing characteristics of these gases using thin film deposited by chemical solution deposition as well as relatively thicker films deposited by atmospheric plasma spray (APS) process. The chapter starts with the sensing mechanism of chemiresistive sensors followed by the definition of gas sensing parameters. Subsequently, we have demonstrated selective NO2 sensing characteristics of zinc oxide-graphene (ZnO-G) multilayered thin film followed by CO and H2 sensing characteristics of ZnO thin film and SnO2 thick film. Cross-sensitivity among CO and H2 gases has been addressed through the analysis of conductance transients with the determination of activation energy, Ea, and heat of adsorption, Q. The concepts of reversible and irreversible sensing have also been discussed in relation to CO and H2 gases. CO2 sensing characteristics of LaFe0.8Co0.2O3 (LFCO)-ZnO thin film have been elucidated. Interference from CO has been addressed with principal component analyses and the ascertaining of Ea and Q values. Additionally, the variation of response with temperature for each gas was simulated to determine distinct parameters for the individual gases. Further, VOC sensing characteristics of copper oxide (CuO) thin film and WO3-SnO2 thick film were investigated. Principal component analysis was performed to discriminate the gases in CuO thin film. The interaction of WO3-SnO2 thick film with various VOCs was found to obey the Freundlich adsorption isotherm based on which Ea and Q values were determined

Role of polyvinyl pyrrolidone as a capping agent in the synthesis of magnetite (Fe3O4) nanoparticles

Uncapped magnetite (Fe3O4) and magnetite capped with polyvinyl pyrrolidone (PVP) (Fe3O4-PVP) have been synthesized by a rapid, cost effective aqueous precipitation method. The nanoparticles are characterized by powder X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and UV spectroscopy. The role of PVP as a capping agent in the synthesis of magnetite nanoparticles has been investigated. Thermal stability and surface charge of the nanoparticles have been characterized by thermogravimetric analysis, differential scanning calorimetry (DSC) and zeta potential measurements. Results suggest that PVP as a capping agent reduces the grain size, regularizes the shape, and increases the crystallinity of Fe3O4 nanoparticles. Thermal stability and surface charge of Fe3O4-PVP nanoparticles are also significantly higher as compared to the uncapped Fe3O4 nanoparticles. Magnetic characterization by vibrating sample magnetometry of both Fe3O4 and Fe3O4-PVP nanoparticles indicates the superparamagnetic behavior of the nanoparticles.

Unusual redox activity of composite alkaline earth metal oxides and reduced graphene oxide system

Reduced Graphene Oxide (rGO) impregnated on alkaline earth oxides (Group 2) (CaO, SrO, BaO) matrix following mechanical mixing, thermal annealing and subsequent cold shock has synthesized a new electrochemical material. The characterization has been carried out by Fourier Transformation Infrared (FTIR) Spectroscopy, Scanning Electron Microscopy (SEM) and Powder X-Ray Diffraction (PXRD) measurements in µm dimension. Thermal stability has been checked by Thermal Gravimetric Analysis and Differential Scanning Calorimetry (TGA-DSC). Cyclic Voltammetry (CV) of the composites show anodic peak potential (Epa) order rGO-CaO (-0.6 V) < rGO-SrO (-0.4 V) < rGO-BaO (-0.3 V) which also follows ordering of ionic size, Ca2+ (100 pm) < Sr2+ (118 pm) < Ba2+ (135 pm). This character becomes more prominent as we move down the Group 2. Thermal stability of these coupled systems also increases down the group

Diversity and Distribution of Archaea in the Mangrove Sediment of Sundarbans

Mangroves are among the most diverse and productive coastal ecosystems in the tropical and subtropical regions. Environmental conditions particular to this biome make mangroves hotspots for microbial diversity, and the resident microbial communities play essential roles in maintenance of the ecosystem. Recently, there has been increasing interest to understand the composition and contribution of microorganisms in mangroves. In the present study, we have analyzed the diversity and distribution of archaea in the tropical mangrove sediments of Sundarbans using 16S rRNA gene amplicon sequencing. The extraction of DNA from sediment samples and the direct application of 16S rRNA gene amplicon sequencing resulted in approximately 142 Mb of data from three distinct mangrove areas (Godkhali, Bonnie camp, and Dhulibhashani). The taxonomic analysis revealed the dominance of phyla Euryarchaeota and Thaumarchaeota (Marine Group I) within our dataset. The distribution of different archaeal taxa and respective statistical analysis (SIMPER, NMDS) revealed a clear community shift along the sampling stations. The sampling stations (Godkhali and Bonnie camp) with history of higher hydrocarbon/oil pollution showed different archaeal community pattern (dominated by haloarchaea) compared to station (Dhulibhashani) with nearly pristine environment (dominated by methanogens). It is indicated that sediment archaeal community patterns were influenced by environmental conditions

Motivation for TV white space: An explorative study on Africa for achieving the rural broadband gap

Emergence of digital broadcasting is the key index of the new horizons of communication and media environment. In this paper we will discuss how TVWS, the resultant of digital switchover is approaching for becoming a financially rewarding solution in terms of rural areas than the other cellular technologies i.e 3G and 4G or even for upcoming 5G. We will analyze the standpoint of digital switchover around the globe and will try to the look at the white space capacity. There has been several TVWS pilot testing all over the world, specially in Africa region and we will try to evaluate their inclusive performance as they match the needs to deploy mobile broadband in rural and low-density areas. After shortly presenting the case, we will try to measure the potential of TVWS technology in terms of the other regions around the world which share the same teletraffic profile and socio-economic condition. Also we will try to present the importance of regulatory issues with ICT strategies and market development with propo