If plant cells and organs are to survive exposure to liquid nitrogen, intracellular crystallization must be avoided. This implies preliminary dehydration of the cells before quenching in liquid nitrogen. Three main procedures have been successively proposed to ensure cryopreservation of cells and organs. In conventional procedures, dehydration of the cells results from extracellular freezing of the cryoprotective medium during the first step of cooling to −40°C. In dehydration procedures, the loss of water is generally achieved after encapsulation of shoottips and somatic embryos in alginate beads (synthetic seeds) by evaporation at room temperature. In the vitrification procedure, dehydration is obtained by placing plant cells and organs in extremely concentrated solutions of permeating and/or non-permeating cryoprotectants. Thermal analysis shows that the two last procedures led to glass transitions of both organs and cryoprotective media, during cooling as well as during rewarming. It appears to be a useful approach for improvement of cryopreservation by perfecting the composition of cryoprotective mixtures.
A new-design conduction microcalorimeter is described, which has been used to measure the heat of cement hydration evolved
in the initial period of hydration. The calorimeter is 30 cm3 in volume; the heat loss coefficient is 27.2700.015 W V–1, the time constant is 300 s.
During the past decade there has been a great emphasis on using multielemental methods to determine heavy metals in solid waste products arising from various industrial, combustion, municipal and mining activities. Furthermore, the study of the leaching characteristics of these solid wastes is of prime importance for environmental and regulatory considerations. We present an overview of neutron activation analysis (NAA), X-ray fluorescence (XRF) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) for the analysis of solid wastes and leachates. In particular we discuss several matrix problems that are usually not considered in routine NAA measurements.
Municipal solid waste incineration (MSWI) significantly reduces volume and mass by as much as 80%, prolonging the life span of landfills. The concentration of heavy metals in the ash and their ability to leach into ground water is a serious concern when siting and designing MSWI ash landfills. Improved technology captures most heavy metals in the ash. The distribution of elements among the different ash particle sizes was determined by NAA. The bottom ash residue was separated into fractions ranging from 9.5 mm to 0.3 mm. The fly ash was separated into fractions from 250 m to 20 m. Landfills usually bury a mixture of both. The combined ash was separated into fractions over the entire range from >9.5 mm to <20 m. Thermal and epithermal neutron irradiations of size fractionated MSW bottom, fly and combined ash were performed to determine the distribution of various metals within the ash. Compared to normal soil, the ashes contained elevated amounts of numerous elements. Concentrations of the more enriched elements (Ag, Cd, Cr, Cu, Hg, Sb, Se, Sr and Zn) in fly ash were of particular interest as source markers.
Titration calorimetry was used in a thermodynamic study on the interactions of pyridine with natural zinc(II) porphyrin derivatives in benzene and chloroform at 298.15 K. The ability of zinc porphyrins to coordinate to pyridine is higher in benzene than in chloroform and also depends on the molecular structure of the metalloporphyrin.
The fabrication of solar cells based on the transfer of a thin silicon film on a foreign substrate is an attractive way to
realise cheap and efficient photovoltaic devices. The aim of this work is to realise a
thin mono-crystalline silicon film on a double porous silicon layer in order to detach and transfer it on mullite. The first
step is the fabrication of a double porous silicon layer by electrochemical
anodisation using two different current densities. The low current leads to a low porosity layer and during annealing, the
recrystallisation of this layer allows epitaxial growth. The second current leads
to a high porosity which permits the transfer on to a low cost substrate. Liquid Phase Epitaxy (LPE) performed with indium
(or In+Ga) in the temperature range of 950–1050C leads to almost homogeneous
layers. Growth rate is about 0.35 μm min−1. Crystallinity of the grown epilayer is similar on porous silicon and on single crystal silicon. In this paper, we focus
on the realisation of porous silicon
sacrificial layer and subsequent LPE growth.
The objective of the study was to examine the expression of the genes coding for proopiomelanocortin (POMC), proenkephalin (PENK) and prodynorphin (PDYN) in porcine luteal cells isolated from corpora lutea (CL) collected on days 3–6, 8–10 and 13–16 of the oestrous cycle. Total RNA was purified from non-incubated cells and from cells incubated for 48 h in the absence or presence of luteinising hormone (LH). The semi-quantitative RT-PCR technique, involving coamplification of the target and control cDNA (β-actin or 18S rRNA), was used to examine gene expression. It was found that the genes coding for opioid precursors are expressed in both non-incubated and incubated porcine luteal cells representing the early, mid- and late luteal phase. In non-incubated cells, only POMC mRNA content changed during CL development, whereas the expression of PENK and PDYN genes remained relatively constant. Additionally, the treatment of cells with LH markedly affected the expression of POMC and PENK, but no influence on PDYN expression was observed. The present study indicates that porcine luteal cells may produce opioid peptides and that gene expression of their precursors (except for PDYN) may be modulated in these cells by LH. Moreover, the present results support the involvement of opioid peptides in local regulation within the CL of the pig.