New aspects in processing of hydroxyapatite ceramics

Sintering of hydroxyapatite ceramics has been a challenging topic for decades since the material has good bioactivity, proven biocompatibility, low cost, and high availability. Besides its biomaterial applications, hydroxyapatite has been used so far as a catalyst support, sensor material, etc. For improvements in its functional properties, new synthesis and processing routes are certainly required. This work will present current achievements in new processing routes of hydroxyapatite ceramics. In the first part, sintering of hydroxyapatite in the presence of lithium iron phosphate will be presented. Such composition induces formation of liquid phase during sintering and interaction between materials that provides decreasing of the processing temperature and formation of reinforcing Fe-rich phase located along the grain boundaries of the matrix material. Furthermore, an influence of heating rate on pure hydroxyapatite sintering will be presented showing that conventional processing with high heating rates can be beneficial for microstructural refinement without any drawbacks regarding the final density of sintered ceramics. This will be discussed regarding the chemical changes induced due to release of hydroxyapatite structural ionic species

Inhomogeneous Reionization Models in Cosmological Hydrodynamical Simulations

In this work we present a new hybrid method to simulate the thermal effects of the reionization in cosmological hydrodynamical simulations. The method improves upon the standard approach used in simulations of the intergalactic medium (IGM) and galaxy formation without a significant increase of the computational cost allowing for efficient exploration of the parameter space. The method uses a small set of phenomenological input parameters and combines a semi-numerical reionization model to solve for the topology of reionization and an approximate model of how reionization heats the IGM, with the massively parallel \texttt{Nyx} hydrodynamics code, specifically designed to solve for the structure of diffuse IGM gas. We have produced several large-scale high resolution cosmological hydrodynamical simulations ($2048^3$, $L_{\rm box} = 40$ Mpc/h) with different instantaneous and inhomogeneous HI reionization models that use this new methodology. We study the IGM thermal properties of these models and find that large scale temperature fluctuations extend well beyond the end of reionization. Analyzing the 1D flux power spectrum of these models, we find up to $\sim 50\%$ differences in the large scale properties (low modes, $k\lesssim0.01$ s/km) of the post-reionization power spectrum due to the thermal fluctuations. We show that these differences could allow one to distinguish between different reionization scenarios already with existing Ly$\alpha$ forest measurements. Finally, we explore the differences in the small-scale cutoff of the power spectrum and we find that, for the same heat input, models show very good agreement provided that the reionization redshift of the instantaneous reionization model happens at the midpoint of the inhomogeneous model.Comment: 24 pages, 16 figures. Accepted by MNRAS. Minor changes to match published versio

Reliable low-cost experimental setup for material synthesis modification by applying alternating electric fields

Building of laboratory hardware in-house can reduce overall equipment costs and respond to the specific requirements of the experiment. The aim of this contribution is to present the novel design and implementation of the low-cost module for AC electric excitation of chemical systems, mainly intended for modifying wet chemical synthesis of nanomaterials. Results of preliminary modelling and experimental tests indicate good module reliability and applicability of the modification methodology on various material types (ceramics, metals and proteins). Possible underlying mechanisms correlating the influence of alternating electric fields and material properties, as well as potential improvements in module construction are discussed

A New Measurement of the Temperature Density Relation of the IGM From Voigt Profile Fitting

We decompose the Lyman-{\alpha} (Ly{\alpha}) forest of an extensive sample of 74 high signal-to-noise ratio and high-resolution quasar spectra into a collection of Voigt profiles. Absorbers located near caustics in the peculiar velocity field have the smallest Doppler parameters, resulting in a low-$b$ cutoff in the $b$-$N_{\text{HI}}$ set by the thermal state of intergalactic medium (IGM). We fit this cutoff as a function of redshift over the range $2.0\leq z \leq 3.4$, which allows us to measure the evolution of the IGM temperature-density ($T= T_0 (\rho/ \rho_0)^{\gamma-1}$) relation parameters $T_0$ and $\gamma$. We calibrate our measurements against Ly$\alpha$ forest simulations, using 21 different thermal models of the IGM at each redshift, also allowing for different values of the IGM pressure smoothing scale. We adopt a forward-modeling approach and self-consistently apply the same algorithms to both data and simulations, propagating both statistical and modeling uncertainties via Monte Carlo. The redshift evolution of $T_0$ shows a suggestive peak at $z=2.8$, while our evolution of $\gamma$ is consistent with $\gamma\simeq 1.4$ and disfavors inverted temperature-density relations. Our measured evolution of $T_0$ and $\gamma$ are generally in good agreement with previous determinations in the literature. Both the peak in the evolution of $T_0$ at $z = 2.8$, as well as the high temperatures $T_0\simeq 15000-20000\,$K that we observe at $2.4 < z < 3.4$, strongly suggest that a significant episode of heating occurred after the end of HI reionization, which was most likely the cosmic reionization of HeII.Comment: Accepted for publication in ApJ, 23 pages, 26 figures, machine readable tables available onlin

Molecular design of nanoparticles and functional materials by sintering

Nanosized powders present an excellent starting point for the formation of nonporous materials during the sintering process. Narrow particle size distributions and sufficiently small sizes of the precursor powders typically present prerequisites for a successful sintering process. Different wet methods for the synthesis of nanoparticles with controlled physicochemical and morphological properties, alongside the multistep sintering approach at relatively low temperatures applied to convert the nanoparticles to materials with density close to theoretical, will present the focus of this presentation. Special attention will be paid to the design of multifunctional nanoparticles composed of various coexisting components, metallic, ceramic and polymer ones, and the properties resulting from the symmetry of their ordering. Obtainment of dense nanostructured materials from nanosized powders and the corresponding sintering mechanisms will be discussed in light of the general knowledge in this area. The process of densification during sintering of functionally gradient materials, including barium titanates and calcium phosphates, and a detailed correlation between the synthesis parameters, the material structure and characteristics will be elucidated in the course of the lecture

Isomerisation of N-Acyl Benzylpenilloic Acid in Acetic Anhydride and Formation of 7, 7-Dimethyl-6-thia-3,8-diazahicyclo(3,2,1)octan-2-one

The heating of N-acyl benzylpenilloic acids {II) in a cetic anhydride gave an equilibrium mixture of C-4 epimers, due to the epimerisation at C-4 position. Cyclisation of the 2-amidomethyl and 4-carboxylic group of IIb or IIc into a 2-ketopiperazine ring gave 1S,5S or 1R,5R enantiomer of III. Alkaline hydrolysis of III gave IV and II. When N-formyl group was present, IV and II upon acid hydrolysis yielded V and I. The C-4 epimers (lb or le) can be prepared from trans C-2, C-4 substituted C-4 epimers (Id or Ia) via II and III

One–pot synthesis of hydrophobic hydroxyapatite nano particles

A highly hydrophobic oleic acid functionalized hydroxyapatite nanoparticles were obtained by the solvothermal method. Water solutions of reactants were added in mixture of oleic acid, triethanolamine and ethanol, which was then treated in Teflon lined autoclave. The chemical composition, size and morphology of as obtained particles were determined using XRD, FT IR, FE SEM and LD PSA. In addition, sintering behaviour and microstructure of prepared material were also examined

Measurement of the small-scale structure of the intergalactic medium using close quasar pairs

The distribution of diffuse gas in the intergalactic medium (IGM) imprints a series of hydrogen absorption lines on the spectra of distant background quasars known as the Lyman-$\alpha$ forest. Cosmological hydrodynamical simulations predict that IGM density fluctuations are suppressed below a characteristic scale where thermal pressure balances gravity. We measured this pressure-smoothing scale by quantifying absorption correlations in a sample of close quasar pairs. We compared our measurements to hydrodynamical simulations, where pressure smoothing is determined by the integrated thermal history of the IGM. Our findings are consistent with standard models for photoionization heating by the ultraviolet radiation backgrounds that reionized the universe.Comment: Accepted for publication on Scienc

Enhanced high-temperature electrical response of hydroxyapatite upon grain size refinement

Correlation between high-temperature electrical response and microstructural properties of dense hydroxyapatite with average grain size from micrometer to nanometer level in heating/cooling cycle was investigated. Grain interior and grain boundary contributions to overall conductivity were determined. Nanostructured hydroxyapatite exhibited enhanced grain interior conductivity, with significantly higher activation energy (∼2.4 eV) than that of coarsed microstructures (∼1.7 eV). This difference in activation energies is explained by the possible influence of dehydroxylation during materials fabrication procedure, which affected the amount of OH- ions as the main charge carriers. Grain boundary conductivity was similar for all microstructures, with activation energy above ∼2 eV, implying the OH- ions migration across grain boundaries. Electrical response in cooling cycle confirmed the trends found during heating. © 2014 Elsevier B.V. All rights reserved