Harish Verma

Bio: Harish Verma is an academic researcher from World Health Organization. The author has contributed to research in topics: Magnetization & Coercivity. The author has an hindex of 31, co-authored 132 publications receiving 2831 citations. Previous affiliations of Harish Verma include Indian Council of Agricultural Research & Patna University.

Cation distribution in nanosized Ni-Zn ferrites

Abstract: Nanoparticles of Ni1−xZnxFe2O4 (x=0.0, 0.25, 0.50, 0.75, and 1.0) in the size range of 6–12 nm have been synthesized by chemical precipitation followed by hydrothermal treatment. A strong correlation between the particle size and the zinc concentration has been identified. Mossbauer studies on these systems show that the cation distribution not only depends on the particle size but also on the preparation route. There are indications that in the present nanophase samples Fe occupies more tetrahedral sites as compared to the normal occupancy in the spinel ferrite structure. The occupancy returns to normal values after heat treatment at 1000 °C. Low-temperature Mossbauer studies indicate a significant amount of deviation of cation distribution from their bulk preferences.

Characteristic length scales of nanosize zinc ferrite

Abstract: Nanosize zinc ferrite samples with an average particle size of 6–65 nm were prepared by a new chemical reaction involving nitrates of Zn and Fe and investigated for magnetic behaviour and defect structure. The sample with an average particle size of 6 nm has considerable inversion in cation distribution as shown by its hysteresis loop and increased magnetization. Mossbauer spectroscopy gives a single doublet for all the samples. Mossbauer parameters like quadrupole splitting and linewidth change sharply as the average particle size increases from 6 to 7 nm and then afterwards the changes are slow. The total Mossbauer absorption, on the average, increases with increase in particle size, the change from 6 to 65 nm being by a factor of 3. Positron parameters too change sharply as the particle size varies. The changes are related to inversion of the cation distribution, agglomeration of particles and annihilation at the surface and in the interior. The picture that emerges from the lifetime studies and supported by Mossbauer spectroscopy and magnetization studies suggests that there are at least two characteristic particle size length scales for nanosize ZnFe2O4 particles prepared by the nitrate route.

Efficacy of inactivated poliovirus vaccine in India

Abstract: Inactivated poliovirus vaccine (IPV) is efficacious against paralytic disease, but its effect on mucosal immunity is debated. We assessed the efficacy of IPV in boosting mucosal immunity. Participants received IPV, bivalent 1 and 3 oral poliovirus vaccine (bOPV), or no vaccine. A bOPV challenge was administered 4 weeks later, and excretion was assessed 3, 7, and 14 days later. Nine hundred and fifty-four participants completed the study. Any fecal shedding of poliovirus type 1 was 8.8, 9.1, and 13.5% in the IPV group and 14.4, 24.1, and 52.4% in the control group by 6- to 11-month, 5-year, and 10-year groups, respectively (IPV versus control: Fisher's exact test P < 0.001). IPV reduced excretion for poliovirus types 1 and 3 between 38.9 and 74.2% and 52.8 and 75.7%, respectively. Thus, IPV in OPV-vaccinated individuals boosts intestinal mucosal immunity.

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Superparamagnetic Colloids: Controlled Synthesis and Niche Applications**

Abstract: The aim of this article is to provide a comprehensive review of current research activities that center on superparamagnetic colloids. We begin with an overview of synthetic strategies that have been developed for generating both nanoscale and mesoscale superparamagnetic colloids, with a focus on those systems that can be prepared as monodisperse samples and in relatively large quantities. We then discuss a variety of techniques that have been exploited for modifying surface properties, as well as for controlling the assembly and patterning of these magnetically active colloids. Towards the end, we highlight a range of innovative applications enabled by the unique combination of superparamagnetism and colloidal suspension. We conclude this review article with personal remarks and perspectives on the directions toward which future research in this area might be directed.

The ecotoxicology of nanoparticles and nanomaterials: current status, knowledge gaps, challenges, and future needs

Abstract: This paper introduces a special issue on the ecotoxicology and environmental chemistry of nanoparticles (NPs), and nanomaterials (NMs), in the journal Ecotoxicology. There are many types of NMs and the scientific community is making observations on NP ecotoxicity to inform the wider debate about the risks and benefits of these materials. Natural NPs have existed in the environment since the beginning of Earth’s history, and natural sources can be found in volcanic dust, most natural waters, soils and sediments. Natural NPs are generated by a wide variety of geological and biological processes, and while there is evidence that some natural NPs can be toxic, organisms have also evolved in an environment containing natural NPs. There are concerns that natural nano-scale process could be influenced by the presence of pollution. Manufactured NPs show some complex colloid and aggregation chemistry, which is likely to be affected by particle shape, size, surface area and surface charge, as well as the adsorption properties of the material. Abiotic factors such as pH, ionic strength, water hardness and the presence of organic matter will alter aggregation chemistry; and are expected to influence toxicity. The physico-chemistry is essential to understanding of the fate and behaviour of NPs in the environment, as well as uptake and distribution within organisms, and the interactions of NPs with other pollutants. Data on biological effects show that NPs can be toxic to bacteria, algae, invertebrates and fish species, as well as mammals. However, much of the ecotoxicological data is limited to species used in regulatory testing and freshwater organism. Data on bacteria, terrestrial species, marine species and higher plants is particularly lacking. Detailed investigations of absorption, distribution, metabolism and excretion (ADME) remain to be performed on species from the major phyla, although there are some data on fish. The environmental risk assessment of NMs could be performed using the existing tiered approach and regulatory framework, but with modifications to methodology including chemical characterisation of the materials being used. There are many challenges ahead, and controversies (e.g., reference substances for ecotoxicology), but knowledge transfer from mammalian toxicology, colloid chemistry, as well as material and geological sciences, will enable ecotoxicology studies to move forward in this new multi-disciplinary field.

Increasing Vaccination: Putting Psychological Science Into Action:

Abstract: Vaccination is one of the great achievements of the 20th century, yet persistent public-health problems include inadequate, delayed, and unstable vaccination uptake. Psychology offers three general propositions for understanding and intervening to increase uptake where vaccines are available and affordable. The first proposition is that thoughts and feelings can motivate getting vaccinated. Hundreds of studies have shown that risk beliefs and anticipated regret about infectious disease correlate reliably with getting vaccinated; low confidence in vaccine effectiveness and concern about safety correlate reliably with not getting vaccinated. We were surprised to find that few randomized trials have successfully changed what people think and feel about vaccines, and those few that succeeded were minimally effective in increasing uptake. The second proposition is that social processes can motivate getting vaccinated. Substantial research has shown that social norms are associated with vaccination, but few int...