Crystal structure and physical properties of half-doped manganite nanocrystals with size < 100nm

In this paper we report the structural and property (magnetic and electrical transport) measurements of nanocrystals of half-doped $\mathrm{La_{0.5}Ca_{0.5}MnO_3}$(LCMO) synthesized by chemical route, having particle size down to an average diameter of 15nm. It was observed that the size reduction leads to change in crystal structure and the room temperature structure is arrested so that the structure does not evolve on cooling unlike bulk samples. The structural change mainly affects the orthorhombic distortion of the lattice. By making comparison with observed crystal structure data under hydrostatic pressure it is suggested that the change in the crystal structure of the nanocrystals occurs due to an effective hydrostatic pressure created by the surface pressure on size reduction. This not only changes the structure but also causes the room temperature structure to freeze-in. The size reduction also does not allow the long supercell modulation needed for the Charge Ordering, characteristic of this half-doped manganite, to set-in. The magnetic and transport measurements also show that the Charge Ordering (CO) does not occur when the size is reduced below a critical size. Instead, the nanocrystals show ferromagnetic ordering down to the lowest temperatures along with metallic type conductivity. Our investigation establishes a structural basis for the destabilization of CO state observed in half-doped manganite nanocrystals.Comment: 11 pages, 13 Figure

Brillouin Scattering Studies of La_{0.77}Ca_{0.23}MnO_3 Across Metal-Insulator Transition

Temperature-dependent Brillouin scattering studies have been carried out on La_{0.77}Ca_{0.23}MnO_3 across the paramagnetic insulator - ferromagnetic metal (I-M) transition. The spectra show a surface Rayleigh wave (SRW) and a high velocity pseudo surface acoustic wave (HVPSAW) besides bulk acoustic waves (BAW). The Brillouin shifts associated with SRW and HVPSAW show blue-shifts, where as the frequencies of the BAW decrease below the I-M transition temperature (T_C) of 230 K. These results can be understood based on the temperature dependence of the elastic constants. We also observe a central peak whose width is maximum at T_C.Comment: 7 pages, 8 figure

NaGdF4:Eu3+ Nanoparticles for Enhanced X-ray Excited Optical Imaging.

X-ray luminescent nanoparticles (NPs), including lanthanide fluorides, have been evaluated for application to deep tissue in vivo molecular imaging using optical tomography. A combination of high material density, higher atomic number and efficient NIR luminescence from compatible lanthanide dopant ions indicates that particles that consist of ALnF4 (A = alkaline, Ln = lanthanide element) may offer a very attractive class of materials for high resolution, deep tissue imaging with X-ray excitation. NaGdF4:Eu3+ NPs produced an X-ray excited luminescence that was among the most efficient of nanomaterials that have been studied thus far. We have systematically studied factors such as (a) the crystal structure that changes the lattice environment of the doped Eu3+ ions within the unit cell; and extrinsic factors such as (b) a gold coating (with attendant biocompatibility) that couples to a plasmonic excitation, and (c) changes in the NPs surface properties via changes in the pH of the suspending medium-all with a significant impact on the X-ray excited luminescence of NaGdF4:Eu3+NPs. The luminescence from an optimally doped hexagonal phase NaGdF4:Eu3+ nanoparticle was 25% more intense compared to that of a cubic structure. We observed evidence of plasmonic reabsorption of midwavelength emission by a gold coating on hexagonal NaGdF4:Eu3+ NPs; fortunately, the NaGdF4:Eu3+ @Au core-shell NPs retained the efficient 5D0→7F4 NIR (692 nm) luminescence. The NaGdF4:Eu3+ NPs exhibited sensitivity to the ambient pH when excited by X-rays, an effect not seen with UV excitation. The sensitivity to the local environment can be understood in terms of the sensitivity of the excitons that are generated by the high energy X-rays (and not by UV photons) to crystal structure and to the surface state of the particles

A Range Query Algorithm to Process KNN Queries in Cloud Computing

In Public Cloud environment, security and data confidentiality is the major problem facing by all the data controller. The service user can take the service from the cloud by getting authorization from the service provider and he can only pay for the service by using the server, for that the service provider lose the control so there may have chances of leaking the information. For that reason the data controller does not want the data to shift to the Cloud. There may have only chance of storing the data is providing the privacy gurantee to the Cloud. The requirement to building privacy is based on CPEL criteria which is confidentiality, privacy, efficiency, low in-house processing cost. By satisfying these requirement will increase the difficulty to store data in the Cloud. In order to eliminate this problem, We are using Random Space Perturbation method for providing the security and efficiency for processing the data. This method is used to building a practical query services in the Cloud. This approach will balance all the requirements by using range query and KNN query services.It provides multifaceted distances , which allows actual listing techniques to increase distances processing. DOI: 10.17762/ijritcc2321-8169.150311

Measurement of Elastic Moduli in Ceramic Composites as a Function fo Porosity Content

Longitudinal and transverse ultrasonic velocity measurements were made to obtain elastic moduli of ceramic compacts and continuous fiber ceramic composites (CMCC) as a function of porosity volume fraction. The ceramic compacts were hot pressed silicon carbide and the CMCC were Nicalon fiber reinforced silicon carbide, manufactured using a forced chemical vapor infiltration (FCVI) process developed at Oak Ridge National Laboratory [1]. The purpose of the SiC powder compact study was to obtain experimental results of elastic moduli for various porosity level and to compare the measured results with predictions based on theoretical models. For chemical vapor infiltrated Nicalon/SiC ceramic composites, elastic constants data at different porosity level were not readily available in the literature. The purpose of the study was therefore to generate a more complete set of modulus data as a function of void content. These results can be used for the optimization of the manufacturing process and for comparison with mechanical testing results

Study of biochemical and nutritional indicators in severe acute malnutrition: A prospective observational study

Background: Malnutrition in children is widely prevalent in developing countries including India. More than 33% of thedeaths in 0-5 years are associated with malnutrition. Children with severe acute malnutrition (SAM) are in danger of death fromhypoglycemia, hypothermia, fluid overload, electrolyte mismanagement, and undetected infections. Hence, biochemical andnutritional indicators in these children are important for management. Objectives: To study the biochemical and nutritional indicatorsin children with SAM. Methods: This hospital based prospective study was conducted on children aged 6-59 months admitted atNutrition Rehabilitation Center attached to a tertiary care teaching institution. 100 consecutive SAM children admitted during2013-2015 were studied. Children were tested for biochemical and nutritional status like complete blood picture with peripheralsmear, liver function tests, renal function tests, serum electrolytes, calcium, phosphorus, and alkaline phosphatase. Results: A totalof 100 cases were included, of these 57 were male and female were 43. Mean age of presentation was 18.45±2.37 months. A lack ofexclusive breastfeeding was seen in 67% of these children and in 78% children complimentary feeds were initiated either early orlater than 6 months. Hypoglycemia was seen in 15% cases, hypokalemia in 22%, and hypocalcemia in 35% of cases. Hyponatremiawas seen in 14% and hypernatremia in 19% of the children. The most common type of anemia was microcytic hypochromictype (55%). Conclusion: The observations in this study confirm a significant association between SAM and faulty feeding andearly introduction of complementary feeds. It was observed that these children have significant alterations in nutritional indicatorsat admission

A-site Ordering versus Electronic Inhomogeneity in CMR-Manganite Films

Epitaxial La3/4Ca1/4MnO3/MgO(100) (LCMO) thin films show unusual rhombohedral (R-3c) structure with a new perovskite superstructure due to unique ordering of La and Ca at the A-site positions. Very sharp insulator-metal and para-ferromagnetic phase transitions at temperatures up to TMI ~ TC=295 K were observed. The ordered films were electronically homogeneous down to 1 nm scale as revealed by scanning tunnelling microscopy/spectroscopy. In contrast, orthorhombic and A-site disordered LCMO demonstrate broadened phase transitions as well as mesoscopic phase separation for T<<TC. The unique La/Ca ordering suppresses cation mismatch stress within one super-cell, a~1.55 nm, enhancing electronic homogeneity. Phase separation scenario seems not to be a unique mechanism for CMR as very large CMR=500 % was also observed in A-site ordered films.Comment: We have added two references and additional sentence