Monte Carlo simulations of magnetovolume instabilities in anti-Invar systems

We perform constant pressure Monte Carlo simulations of a spin-analogous model which describes coupled spatial and magnetic degrees of freedom on an fcc lattice. Our calculations qualitatively reproduce magnetovolume effects observed in some rare earth manganese compounds, especially in the anti-Invar material YMn₂. These are a sudden collapse of the magnetic moment which is connected with a huge volume change, and a largely enhanced thermal expansion coefficient.     

Thermodynamic data of the formation of titanium nitride in iron

The solubility of titanium nitride in liquid iron is described by the solubility product log([%Ti][%N])₁ = ?17040/T + 6.40 reported by Turkdogan. The solubility in δ ferrite measured by Kunze is log<[%Ti][%N])_δ = ?17205/T + 5.56. Combining the solubilities in both phases and the solubilities of nitrogen the distribution equilibrium of titanium can be derived. It is characterized by the thermodynamic distribution coefficient k^δ/I_o,Ti = [%Ti]_δ/[%Ti] = 0.40. By zone melting and secondary ion mass spectrometry of the titanium distribution k^δ/I_Ti = 0.53 was measured. An analysis of all known data led to k^δ/I_o,Ti = 0.40…0.50. Measurements of the TiN solubility in austenite by heat treatment were not significant. They led to distribution coefficients between 0.07 and > 1. By zone melting in a carburizing atmosphere a distribution coefficient k^γ/I_Ti = 0.12 was measured. From a thermodynamic analysis performed by Ohtani et al., from the TiN solubility in the melt, and from the solubilities of nitrogen k^γ/I_o,Ti = 0.13 was deduced. Basing on the distribution equilibria of titanium and nitrogen and on the measured temperature dependence the solubility product log([%Ti][%N])_γ = ?15000/T + 4.06 was obtained.     

Variable use of standards-based IOS enabling technologies in Australian SMEs: an examination of deliberate and emergent decision making processes

Use of inter-organizational systems (IOS) is widely recognized as pivotal to organizational success. However, the nature of decision making processes regarding the adoption and use of IOS-enabling technologies has received little research attention. The authors explore approaches to decision making relating to SMEs’ use of these technologies and outline the drivers and implications of such decision making. Data were collected through two crosssectional surveys and multiple case studies. The surveys allowed for the identification of two groups of three SMEs each—the first group increased and the second group decreased the use of IOS-enabling technologies over time. This identification provided the context of strategic change or transition in the use of these technologies over time. The study’s results challenge widely held assumptions about the performance benefits of higher-level, deliberate planning over functional-level, emergent decision making regarding SMEs’ technological choices. Results also show that SME managers mainly use flexible IOS technology adoption and implementation strategies to promote organizational performance. Further, two main factors drive flexible decision making: a lack of managerial power and a lack of financial resources. Overall, the study offers insights into the link between IOS-enabling technology use and organizational strategy, and advances research concerning the contingencies influencing SMEs’ decision making in this context.     

The small left colon syndrome. 3 cases

In the light of three cases of neonatal obstruction related to a small calibre descending colon, the authors review the main clinical and radiological signs and compare them with the data in the literature. This functional disturbance is related to immaturity of the intrinsic innervation of the colon which is especially common in low birth weight neonates or of diabetic mothers. Diagnosis is dependent upon enema using diluted uroangiographic hydrosoluble iodine contrast medium, which shows a disparity in calibre at the left colic angle. The differential diagnosis lies with Hirschsprung's disease. Functional ileus in premature infants, meconium ileus and the "small left colon syndrome" are related to the same pathogenisis: functional immaturity of the colon.     

Chemical and Morphological Changes of Vacuum-Plasma-Sprayed Hydroxyapatite Coatings during Immersion in Simulated Physiological Solutions

The purpose of this investigation was to study the behavior of vacuum-plasma-sprayed hydroxyapatite (VPS-HA) coatings in a defined simulated physiological environment that mimics the conditions that the material experiences after implantation in the human body. Commercially available and clinically used HA coatings on titanium alloy substrates were immersed in an inorganic simulated body fluid (SBF) with ion concentrations that were almost equal to those of human blood plasma and in fetal calf serum (FCS) for time periods of 1, 3, 7, 14, and 28 days. At each time interval, the VPS-HA coatings were analyzed using scanning electron microscopy, X-ray diffractometry, Fourier transform infrared spectroscopy, and inductively coupled plasma-atomic emission spectroscopy. The as-received VPS coatings consisted of HA as the main phase component; in addition, small concentrations of tricalciumphosphate (TCP) were determined to be present. During immersion in SBF, transformation of the peripheral area of the VPS coating to a regular spherical shape was observed. Concentration measurements of the immersion solution indicated that dissolution of the more-soluble TCP started within the first day. At the same time, precipitation of a carbonate-containing, marginally crystalline calcium phosphate with very small coherently scattering domains was observed. In FCS, the dissolution of calcium and phosphorus was observed; however, the precipitation of the new calcium phosphate layer was retarded by the presence of proteins, which indicates their important role in the ion-exchange mechanisms. In both solutions, the coating integrity was not adversely affected, which indicates the high stability of VPS-HA coatings in a simulated physiological environment.     

Elektrochemische Charakterisierung von TiC- und Ti(C,N)-Schichten auf WC/Co-Hartmetallen

Electrochemical characterization of TiC and Ti(C,N) layers on WC/Co hard metals TiC and Ti(C,N)layers deposited on WC/Co hard-metal substrates by Chemical Vapour Deposition (CVD) can be characterized using a combination of electrochemically controlled dissolution and voltammetric signals with respect to stoichiometry (C/N ratio) and depth profile. A regular layer-by-layer dissolution with proportionality between charge and depth as well as with a good etching quality (edges, lateral homogenity) could be realized in sulphuric acid. The influence of the C/N ratio in Ti(C,N) on the electrochemical signal has been investigated with defined powders using the Carbon-Paste-Electrode. These results were used for calibration of the signals at CVD layers.     

Role of phosphatidylethanolamine lipids in the stabilization of protein-lipid contacts

We have investigated the effect of lipids with phosphatidylethanolamine (PE) head groups on the stabilization of contacts between the tryptophan side chains of gramicidin and the lipid head groups. We initially developed two fluorescence methods that can be correlated to the spontaneous curvature of DOPC/DOPE and DOPC/DOPEme. One is based on bilayer structure and measures the rotational motion of a probe located close to the membrane surface relative to a more deeply-buried probe. The second is based on surface hydration/polarity and measures the emission energy of a polarity-sensitive probe located on the membrane surface. We used these methods to estimate the pseudo-curvature (i.e., curvature obtained by fluorescence measurements) of lipids with dimyristyl chains, and their pressure and temperature dependence. We then investigated the stability of gramicidin tryptophan-lipid contacts in DMPC/DMPE as a function of temperature and pressure. Stability was assessed by tryptophan rotational motion as determined by fluorescence anisotropy, since rotational motion is limited when the indoles are hydrogen bonded to the lipid head groups. The results suggest that the presence of PE lipids destabilizes these contacts due to either their smaller size relative to PC head groups, or their tendency to self-interact. Fluorescence quenching studies support these results.     

Thermodynamic investigation of the austenite and the delta ferrite in the system Fe-Cr-Mn-N

The nitrogen solubility was measured in a wide range of temperatures including both the austenitic and the ferritic phase of iron-chromium-manganese alloys. The mass contents of the samples were 6.0 to 20.5 % Cr and 5.7 to 16.6 % Mn. Parameters describing the austenite and the delta ferrite in the system Fe-Cr-Mn-N were calculated analyzing all available experimental data. This evaluation yielded an improvement of the known parameters describing the austenitic phase by means of the regular solution model. At the first time, accurate thermodynamic parameters describing the delta phase both in the systems Fe-Mn-N and Fe-Cr-Mn-N could be deduced. By means of the phase diagram program package PD-pp the austenite-delta ferrite phase boundaries of the investigated alloys were calculated. They were compared with experimentally determined temperatures and nitrogen concentrations in the two-phase region. There is a good correspondence between theory and experiment. Using published data describing the melt a calculation of phase diagrams in the high temperature region can be performed.