Interplay of immune modulation, adaptive response and hormesis: Suggestive of threshold for clinical manifestation of effects of ionizing radiation at low doses?

The health impacts of low-dose ionizing radiation exposures have been a subject of debate over the last three to four decades. While there has been enough evidence of "no adverse observable" health effects at low doses and low dose rates, the hypothesis of "Linear No Threshold" continues to rule and govern the principles of radiation protection and the formulation of regulations and public policies. In adopting this conservative approach, the role of the biological processes underway in the human body is kept at abeyance. This review consolidates the available studies that discuss all related biological pathways and repair mechanisms that inhibit the progression of deleterious effects at low doses and low dose rates of ionizing radiation. It is pertinent that, taking cognizance of these processes, there is a need to have a relook at policies of radiation protection, which as of now are too stringent, leading to undue economic losses and negative public perception about radiation.

Negligible radiological impact of Indian nuclear power plants on the environment and the public: Findings from a 20-year study.

Nuclear power plants, recognized for their extended operational life, minimal greenhouse gas emissions, and high-power density, are deemed as reliable energy sources. Nonetheless, concerns persist regarding the radioactive discharges from these plants and their potential impact on health and the environment. To comprehend the radiological implications of such releases, this study presents, for the first time, an analysis of radiological data from 7 Indian nuclear power plants (NPPs), collected by Indian environmental survey laboratories (ESL) over the past two decades (2000-2020). This dataset encompasses radioactivity concentrations in the atmospheric, aquatic, and terrestrial environments within a 30 km radius of each NPP, as well as the annual cumulative external gamma doses recorded by environmental thermoluminescence dosimeters (TLDs). The analysis yielded several key findings: (i) Radioactivity concentrations around the NPPs were low and comparable to values measured at other nuclear power plant sites worldwide; (ii) Tritium concentrations in receiving water bodies were <1 % of the internationally recommended limit of 10,000 Bq/l; (iii) The estimated total radiation doses to the public were at most 10 % of the stipulated regulatory dose limit of 1000 µSv and consistently decreased over the study period and (iv) Variations in doses among the NPP sites were primarily attributed to legacy technology used in specific reactors. These results indicate efficient and secure reactor operations and the minimal contribution of Indian nuclear power plants to anthropogenic doses in the country. The findings hold potential significance for reinforcing India's commitment to advancing its nuclear power program.

Generation of map on natural environmental background absorbed dose rate in India.

A systematic mapping of natural absorbed dose rate was carried out to assess the existing exposure situation in India. The mammoth nationwide survey covered the entire terrestrial region of the country comprising of 45127 sampling grids (grid size 36 km2) with more than 100,000 data points. The data was processed using Geographic Information System. This study is based on established national and international approaches to provide linkage with conventional geochemical mapping of soil. Majority (93%) of the absorbed dose rate data was collected using handheld radiation survey meters and remaining were measured using environmental Thermo Luminescent Dosimeters. The mean absorbed dose rate of the entire country including several mineralized regions, was found to be 96 ± 21 nGy/h. The median, Geometric Mean and Geometric Standard Deviation values of absorbed dose rate were 94, 94 and 1.2 nGy/h, respectively. Among the High Background Radiation Areas of the country, absorbed dose rate varied from 700 to 9562 nGy/h in Karunagappally area of Kollam district, Kerala. The absorbed dose rate in the present nationwide study is comparable with the global database.

Oxygen Reduction Reaction Activity of Microwave Mediated Solvothermal Synthesized CeO2/g-C3N4 Nanocomposite.

Electrocatalytic active species like transition metal oxides have been widely combined with carbon-based nanomaterials for enhanced Oxygen Reduction Reaction (ORR) studies because of the synergistic effect arising between different components. The aim of the present study is to synthesize CeO2/g-C3N4 system and compare the ORR activity with bare CeO2. Ceria (CeO2) embedded on g-C3N4 nanocomposite was synthesized by a single-step microwave-mediated solvothermal method. This cerium oxide-based nanocomposite displays enhanced ORR activity and electrochemical stability as compared to bare ceria.

Fabrication of plasmonic dye-sensitized solar cells using ion-implanted photoanodes.

Plasmonic dye-sensitized solar cells containing metal nanoparticles suffer from stability issues due to their miscibility with liquid iodine-based electrolytes. To resolve the stability issue, herein, an ion implantation technique was explored to implant metal nanoparticles inside TiO2, which protected these nanoparticles with a thin coverage of TiO2 melt and maintained the localized surface plasmon resonance oscillations of the metal nanoparticles to efficiently enhance their light absorption and make them corrosion resistant. Herein, Au nanoparticles were implanted into the TiO2 matrix up to the penetration depth of 22 nm, and their influence on the structural and optical properties of TiO2 was studied. Moreover, plasmonic dye-sensitized solar cells were fabricated using N719 dye-loaded Au-implanted TiO2 photoanodes, and their power conversion efficiency was found to be 44.7% higher than that of the unimplanted TiO2-based dye-sensitized solar cells due to the enhanced light absorption of the dye molecules in the vicinity of the localized surface plasmon resonance of Au as well as the efficient electron charge transport at the TiO2@Au@N719/electrolyte interface.

Tailoring of the chlorine sensing properties of substituted metal phthalocyanines non-covalently anchored on single-walled carbon nanotubes.

To investigate how central metal tunes the synergetic interactions between substituted metallo-phthalocyanine and single-walled carbon nanotubes in enhancing the gas sensing properties, a comparative study has been performed by varying the central metal ion in fluorinated metal phthalocyanines and single-walled carbon nanotube hybrid. Hybrids of metal(ii)-1,2,3,4,8,9,10,11,15,16,17,18-24,25-hexa-decafluoro-29H,31H-phthalocyanine/single-walled carbon nanotube (F16MPc/SWCNTs-COOH, where M = Co, Zn) have been synthesized through π-π stacking interactions using the solution route. Spectroscopic (FT-IR, UV-vis, XPS and Raman), electron microscopic (TEM and FE-SEM) and TGA investigations have confirmed the successful functionalization and interaction of SWCNTs-COOH with F16MPc. Parts per billion (ppb) level Cl2-selective chemiresistive gas sensors have been fabricated on glass substrates with precoated gold electrodes by using these hybrids. The responses of various F16MPc/SWCNTs-COOH sensors have demonstrated the central metal ion-dependence in the sensitivity of Cl2.

Nanostructured tin oxide films: Physical synthesis, characterization, and gas sensing properties.

Nanostructured tin oxide (SnO2) films are synthesized using physical method i.e. thermal evaporation and are further characterized with X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy measurement techniques for confirming its structure and morphology. The chemiresistive properties of SnO2 films are studied towards different oxidizing and reducing gases where these films have demonstrated considerable selectivity towards oxidizing nitrogen dioxide (NO2) gas with a maximum response of 403% to 100ppm @200°C, and fast response and recovery times of 4s and 210s, respectively, than other test gases. In addition, SnO2 films are enabling to detect as low as 1ppm NO2 gas concentration @200°C with 23% response enhancement. Chemiresistive performances of SnO2 films are carried out in the range of 1-100ppm and reported. Finally, plausible adsorption and desorption reaction mechanism of NO2 gas molecules with SnO2 film surface has been thoroughly discussed by means of an impedance spectroscopy analysis.

Change in the Affinity of Ethylene Glycol Methacrylate Phosphate Monomer and Its Polymer Anchored on a Graphene Oxide Platform toward Uranium(VI) and Plutonium(IV) Ions.

The complexation behavior of the carbonyl and phosphoryl ligating groups bearing ethylene glycol methacrylate phosphate (EGMP) monomer and its polymer fixed on a graphene oxide (GO) platform was studied to understand the coordination ability of segregated EGMP units and polymer chains toward UO2(2+) and Pu(4+) ions. The cross-linked poly(EGMP) gel and EGMP dissolved in solution have a similar affinity toward these ions. UV-initiator induced polymerization was used to graft poly(EGMP) on the GO platform utilizing a double bond of EGMP covalently fixed on it. X-ray photoelectron spectroscopy (XPS) of the GO and GO-EGMP was done to confirm covalent attachment of the EGMP via a -C-O-P- link between GO and EGMP. The extent of poly(EGMP) grafting on GO by thermal analyses was found to be 5.88 wt %. The EGMP units fixed on the graphene oxide platform exhibited a remarkable selectivity toward Pu(4+) ions at high HNO3 conc. where coordination is a dominant mode involved in the sorption of ions. The ratio of distribution coefficients of Pu(IV) to U(VI) (DPu(IV)/DU(VI)) followed a trend as cross-linked poly(EGMP) (0.95) < EGMP in solvent methyl isobutyl ketone (1.3) < GO-poly(EGMP) (25) < GO-EGMP (181); the DPu(IV)/DU(VI) values are given in parentheses. The density functional theory computations have been performed for the complexation of UO2(2+) and Pu(4+) ions with the EGMP molecule anchored on GO in the presence of nitrate ions. This computational modeling suggested that Pu(4+) ion formed a strong coordination complex with phosphoryl and carbonyl ligating groups of the GO-EGMP as compared to UO2(2+) ions. Thus, the nonselective EGMP becomes highly selective to Pu(IV) ions when it interacts as a single unit fixed on a GO platform.

Enhanced thermoelectric properties of selenium-deficient layered TiSe(2-x): a charge-density-wave material.

In the present work, we report on the investigation of low-temperature (300-5 K) thermoelectric properties of hot-pressed TiSe2, a charge-density-wave (CDW) material. We demonstrate that, with increasing hot-pressing temperature, the density of TiSe2 increases and becomes nonstoichiometric owing to the loss of selenium. X-ray diffraction, scanning electron microscopy, and transimission electron microscopy results show that the material consists of a layered microstructure with several defects. Increasing the hot-press temperature in nonstoichiometric TiSe2 leads to a reduction of the resistivity and enhancement of the Seebeck coefficient in concomitent with suppression of CDW. Samples hot-pressed at 850 °C exhibited a minimum thermal conductivity (κ) of 1.5 W/m·K at 300 K that, in turn, resulted in a figure-of-merit (ZT) value of 0.14. This value is higher by 6 orders of magnitude compared to 1.49 × 10(-7) obtained for cold-pressed samples annealed at 850 °C. The enhancement of ZT in hot-pressed samples is attributed to (i) a reduced thermal conductivity owing to enhanced phonon scattering and (ii) improved power factor (α(2)σ).

Thermoelectric performance of layered SrxTiSe2 above 300 K.

In this paper we report the thermoelectric performance of Sr intercalated TiSe(2) above 300 K. Refined x-ray diffraction, high resolution transmission electron microscopy and scanning electron microscopy images show well oriented polycrystalline grains along a (0 0 l) direction and layered growth of the sample. Intercalation of Sr in TiSe(2) shows an improved Seebeck coefficient (α) value without altering the polarity of the majority charge carrier. A drastic reduction in the thermal conductivity (κ) from 3.8 W m K(-1) to 1.2 W m K(-1) (at 650 K) was observed which is ascribed to the: (i) scattering of the phonon by natural layer interfaces, grain boundaries and lattice defects and (ii) rattling of intercalated Sr atoms among weakly bound TiSe(2) layers. This led to the maximum ZT of ~0.08 at 650 K for Sr(x)TiSe(2) (x > 0.1) which is almost twice as high as the parent TiSe(2).

Charge transport in ultrathin iron-phthalocyanine thin films under high electric fields.

The temperature dependent current-voltage (J-V) characteristics of 20 nm thick iron-phthalocyanine films are investigated in the temperature range of 300-30 K, and in the bias range of ±200 V. In the temperature range of 300-100 K, the charge transport is governed by bulk-limited processes with a bias dependent crossover from Ohmic (J∼V) to exponentially distributed shallow trap mediated space-charge-limited conduction (J∼V(α), α ≥ 2) to space-charge-limited conduction with field enhanced mobility (lnµâˆ¼E(1/2)). However, at temperatures less than 100 K, the charge transport is electrode-limited, and undergoes a bias dependent transition from Schottky (lnJ∼V(1/2)) to multistep tunneling. From shallow trap mediated space-charge-limited conduction data the estimated room temperature mobility was found to be ∼1.9 cm(2) V (-1) s(-1). The high mobility of films is attributed to better structural organization due to the face-on stacking of molecules, which is supported by x-ray diffraction and UV-visible spectroscopy data.

Room temperature ppb level Cl2 sensing using sulphonated copper phthalocyanine films.

We present room temperature chemiresistive gas sensing characteristics of drop casted sulphonated copper phthalocyanine (CuTsPc) films. It has been demonstrated that these films are highly selective to Cl(2) and the sensitivity in the 5-2000 ppb range varies linearly between 65 and 625%. However, for concentrations >or=2000 ppb, the response becomes irreversible, which is found to be due to the chemical bond formation between Cl(2) and SO(3)Na group of CuTsPc films. The X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) data confirms the oxidation of SO(3)Na group by Cl(2) gas.

Temperature dependent current-voltage characteristics of iron-phthalocyanine thin films.

The current-voltage (I-V) characteristics of the crystalline alpha-phase iron phthalocyanine (FePc) thin films grown by molecular beam epitaxy have been investigated by using a planar geometry in which the metal electrodes are separated by 15 microm. By carrying out the room temperature I-V measurements on vacuum annealed (200 degrees C for 30 min under 10(-6) torr) FePc thin films under vacuum and after exposing them to the air, we demonstrate that the hysteresis in FePc films is intimately related to the filling and de-filling of surface traps created by chemisorbed oxygen. The presence of chemisorbed oxygen has been confirmed by the X-ray photoelectron spectroscopy. Room temperature I-V characteristics of air exposed films showed ohmic conduction in the lower voltage range and space-charge-limited-conductivity (SCLC) in the relatively high voltage. Temperature dependent measurements show that the hysteresis disappears at 250 K and the surface traps are distributed in energy about 0.22 eV deep.

Electrical characterization of self-assembled monolayers of alkyltrichlorosilanes on native oxide of silicon.

The octadecyltrichlorosilane (C18), dodecyltrichlorosilane (C12) and octyltrichlorosilane (C8) monolayers have been deposited on the native oxide of silicon by self-assembly technique. The morphology of the monolayers studied by atomic force microscopy revealed an average roughness of approximately 1.0 A. The Fourier Transform Infra Red Spectroscopic measurements revealed the presence of peaks at approximately 2848 and 2915 cm(-1) indicating the formation of densely packed monolayers. The current density versus voltage (J-V) measurements using mercury drop as counter electrode showed tunneling current between 10(-5) to 10(-8) A/cm2 at 1 V indicating the excellent dielectric behaviour of these monolayers. The J-V data were fitted to Simmons theory of tunneling which yielded an effective electron energy barrier height of 1.6 +/- 0.2 eV and the effective mass of electron tunneling through the barrier was found to be 0.3 +/- 0.03 m(e). The tunneling decay factor beta was estimated from the current density values measured as a function of thickness of the monolayer and was found to be 0.28 +/- 0.02 A(-1).

Growth, characterization and gas sensing properties of nanotetrapod ZnO.

ZnO nanotetrapods have been obtained in large quantities by carbothermal reduction of ZnO powder. These were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, UV-visible spectroscopy and photoluminescence. Electron microscopy revealed that the overall size of the tetrapods is 1.5-2 microm and legs are 30-50 nm in diameter. The size of tetrapods as well as diameter of the legs was found to increase with deposition temperature. Photoluminescence spectra revealed that green emission originating from oxygen vacancies overwhelmed that of the near-band-edge ultraviolet peak. A band gap of 3.27 eV was calculated from optical absorption spectra which agreed well with that estimated from PL spectra. Gas sensing properties of tetrapods were investigated and these were found to be 5 times more sensitive to H2S gas at room temperature in comparison to ZnO bulk polycrystalline material.

Nanogranular Fe-Cu-Ag thin films: structure, microstructure and giant magnetoresistance.

Fe(x)Cu(y)Ag(z) granular thin films with several compositions were prepared by dc magnetron sputtering. These films consist of small Fe magnetic particles embedded in a nonmagnetic CuAg matrix. Structure, microstructure, morphology and magnetotransport properties were studied. The compositions of these samples were determined by energy-dispersive X-ray analysis. X-ray diffraction results showed strong Ag(111) peaks and broad Cu(111) peaks in all the samples. The variation of the (111) lattice spacings indicates a partial intermixing of Fe, Cu and Ag atoms. Microstructural studies using transmission electron microscopy (TEM) on a selected sample showed only Ag reflections and no reflection from Cu and Fe. Both XRD and TEM studies did not reveal any diffraction peak due to Fe and Cu for this sample. The fitting of the experimental grain size data obtained from TEM micrograph to the lognormal distribution function has allowed an estimation of the average grain diameter of 3.7 nm. The surface image of the Fe22Ag78 film observed using a scanning electron microscope showed the presence of droplet like Ag particles on the film surface. The Cu substitution results in smooth films without any Ag particles on the surface. Surface morphology by atomic force microscopy shows that the Fe39Cu13Ag48 film has a surface roughness of 0.75 nm. Finally, we have obtained a maximum giant magnetoresistance ratio of 3.2% in these films measured at 300 K for an in-plane magnetic field of 20 kOe.

Growth of highly oriented crystalline polyaniline films by self-organization.

Silicon substrates with (100) orientation were modified with amino-silane self-assembled monolayer (SAM) to provide amino (NH(2)) moieties at the substrate surface. Self-organization of polyaniline during chemical polymerization, on this modified surface, leads to the growth of highly oriented films at the substrate-polymer interface. The morphology studied using scanning electron microscopy and atomic force microscopy revealed the formation of polymer film with well faceted pyramidal crystallites. XPS and FTIR spectroscopy were used to analyze the chemical structure of the film. X-ray diffraction measurements show the crystalline nature of the polyaniline, whose lattice parameters are in agreement with the reported values. This study underlines the importance of a SAM in deciding the structure and morphology of the deposited polymer.

Self assembled monolayers on silicon for molecular electronics.

We present an overview of various aspects of the self-assembly of organic monolayers on silicon substrates for molecular electronics applications. Different chemical strategies employed for grafting the self-assembled monolayers (SAMs) of alkanes having different chain lengths on native oxide of Si or on bare Si have been reviewed. The utility of different characterization techniques in determination of the thickness, molecular ordering and orientation, surface coverage, growth kinetics and chemical composition of the SAMs has been discussed by choosing appropriate examples. The metal counterelectrodes are an integral part of SAMs for measuring their electrical properties as well as using them for molecular electronic devices. A brief discussion on the variety of options available for the deposition of metal counterelectrodes, that is, soft metal contacts, vapor deposition and soft lithography, has been presented. Various theoretical models, namely, tunneling (direct and Fowler-Nordheim), thermionic emission, Poole-Frenkel emission and hopping conduction, used for explaining the electronic transport in dielectric SAMs have been outlined and, some experimental data on alkane SAMs have been analyzed using these models. It has been found that short alkyl chains show excellent agreement with tunneling models; while more experimental data on long alkyl chains are required to understand their transport mechanism(s). Finally, the concepts and realization of various molecular electronic components, that is, diodes, resonant tunnel diodes, memories and transistors, based on appropriate architecture of SAMs comprising of alkyl chains (sigma- molecule) and conjugated molecules (pi-molecule) have been presented.