Investigation of MBH4–VCl2, M = Li,Na or K

Systematic investigations of MBH₄−VCl₂, M = Li, Na, or K, 2:1 or 3:1, samples prepared by mechano-chemistry and different milling time in order to gain insight in the phase stability and search for novel borohydrides. The samples were investigated using powder X-ray diffraction and Raman spectroscopy. Subsequently, the samples were exposed to heat treatment and investigated by in-situ synchrotron radiation powder X-ray diffraction (SR-PXD). These studies reveal formation of numerous compounds during decomposition of the samples, which contrasts with previous investigations. In several cases the formed compounds were in a less well-crystalline state, which did not allow identification. One of the unidentified compounds was observed both in the LiBH₄−VCl₂ and NaBH₄−VCl₂ systems and appeared to decompose at T ∼ 190 °C and is assumed to be a new vanadium borohydride. Crystalline Li₂VCl₄ was observed, but a major fraction of the decomposition products appeared to be amorphous. The KBH₄−VCl₂ system revealed formation of well-crystalline solid solutions of K(BH₄)_1−xCl_x.     

Synthesis of an orthorhombic high pressure boron phase

The densest boron phase (2.52 g cm^-3) was produced as a result of the synthesis under pressures above 9 GPa and temperatures up to ∼1800 °C. The x-ray powder diffraction pattern and the Raman spectra of the new material do not correspond to those of any known boron phases. A new high-pressure high-temperature boron phase was defined to have an orthorhombic symmetry (Pnnm (No. 58)) and 28 atoms per unit cell.     

Pressure jump relaxation setup with IR detection and millisecond time resolution

An instrument is described that allows the use of Fourier transform infrared (FTIR) spectroscopy as a detection system for kinetic processes after a pressure jump of up to 100 bars. The pressure is generated using a high performance liquid chromatography (HPLC) pump and water as a pressure transducing medium. A flexible membrane separates the liquid sample in the IR cell from the pressure transducing medium. Two electromagnetic switching valves in the setup enable pressure jumps with a decay time of 4 ms. The FTIR spectrometer is configured to measure time resolved spectra in the millisecond time regime using the rapid scan mode. All components are computer controlled. For a demonstration of the capability of the method first results on the kinetics of a phase transition between two lamellar phases of an aqueous phospholipid dispersion are presented. This combination of FTIR spectroscopy with the pressure jump relaxation technique can also be used for other systems which display cooperative transitions with concomitant volume changes.     

Assuming exponential decay by incorporating viscous damping improves the prediction of the coefficient of friction in pendulum tests of whole articular joints

A pendulum test with a whole articular joint serving as the fulcrum is commonly used to measure the bulk coefficient of friction (COF). In such tests it is universally assumed that energy loss is due to frictional damping only, and accordingly the decay of pendulum amplitude is linear with time. The purpose of this work was to determine whether the measurement of the COF is improved when viscous damping and exponential decay of pendulum amplitude are incorporated into a lumped-parameter model. Various pendulum models with a range of values for COF and for viscous damping were constructed. The resulting decay was fitted with an exponential function (including both frictional and viscous damping) and with a linear decay function (frictional damping only). The values predicted from the fit of each function were then compared to the known values. It was found that the exponential decay function was able to predict the COF values within 2 per cent error. This error increased for models in which the damping coefficient was relatively small and the COF was relatively large. On the other hand, the linear decay function resulted in large errors in the prediction of the COF, even for small values of viscous damping. The exponential decay function including both frictional and constant viscous damping presented herein dramatically increased the accuracy of measuring the COF in a pendulum test of modelled whole articular joints.     

Effect of Chromium on the Structure and Properties of Boride Diffusion Coatings

We have studied the effect of the chromium concentration in an impregnating borochromating powder mixture on the change in the lattice parameters of the rhombic FeB phase of boride coatings on carbon steels, their microhardness, and the BK _α energy spectra. An increase in the microhardness of the boride phases for chromium concentration 3.5-6 mass% in powder boron-impregnating mixtures is accompanied by a decrease in the FeB lattice parameters. Interpretation of the BK _α spectra has allowed us to establish that this fact is due to an increase in the covalent component of the Fesd ― Bp bond.     

Image presentation in digital radiology: perspectives on the emerging DICOM display function standard and its application

DICOM (Digital Imaging and Communications in Medicine) Working Group XI, formerly called ACR/NEMA (American College of Radiology/National Electrical Manufacturers' Association) Working Group XI, is currently developing a display function standard. The main objective of the standard is to define mathematically a display function for all image presentation systems. As a secondary objective, the standard aims at providing similarity in gray-scale perception for a given image between display systems of different luminance and at facilitating efficient utilization of the available digital input levels of a display system. The design of the display function incorporates the concept of perceptual linearization. The proposed standard applies to monochrome image presentation devices such as cathode ray tube monitor-display controller systems and digital laser image printers. The standard does not eliminate the use of application-specific display functions but rather ensures their effectiveness. Neither does the standard guarantee equal information transfer between image presentation devices with different physical properties; it does, however, from the basis for applying image processing to compensate for such differences.     

Effect of decohesion and sliding on bimaterial crack-tip fields

This work is concerned with the analytical characterization of the effect of bond decohesion and sliding on the fields surrounding the tip of an interface crack. We consider the two-dimensional problem of an interface crack along the bond between a pair of linearly elastic materials. The interface itself has a nonlinear constitutive property: it has maximum load carrying capacities in both tension normal to the bond and in shear. The interface therefore has the ability to slide and separate inelastically without loss of integrity. The effects of these physically motivated assumptions are deduced and discussed. Further impetus for this study stems from the recent resurgence of interest in interfacial fracture mechanics. This interest is partly driven by the desire to understand and alleviate the pathological difficulties associated with the crack-tip fields predicted by the linear theory of elasticity. By accounting for possible interfacial nonlinear behavior, we are able to find that near-tip fields are free of the offensive properties alluded to above.

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Résumé On considère le problème à deux dimensions d'une fissure d'interface suivant la liaison entre deux matériaux élastiques linéaires, et la caractérisation analytique de l'effet d'une décohésion et d'un glissement de cette liaison sur le champ entourant l'extrémité de la fissure d'interface.Ce dernier possède lui-même une propriété constitutive non linéaire et présente une capacité de chargement maximum à la fois suivant une traction normale par rapport au joint et en cisaillement. Dès lors, l'interface peut glisser ou se séparer de manière inélastique sans perte de l'intégrité de la liaison. Ces hypothèses physiques ont des effets qui sont discutés. Une telle étude est stimulée par le regain récent d'intérêt pour la mécanique de rupture des interfaces, en partie dû au désir de comprendre et d'alléger les difficultés auxquelles conduit une prédiction des champs à l'extrémité d'une fissure en se basant sur la théorie linéaire de l'élasticité. En prenant en compte la possibilité d'un comportement non linéaire de l'interface, on est à même de trouver que les champs au voisinage de l'extrémité de la fissure ne présentent pas de propriétés adverses.

     

Synthesis and Characterization of Novel Succinyl Chitosan-Dexamethasone Conjugates for Potential Intravitreal Dexamethasone Delivery

The development of intravitreal glucocorticoid delivery systems is a current global challenge for the treatment of inflammatory diseases of the posterior segment of the eye. The main advantages of these systems are that they can overcome anatomical and physiological ophthalmic barriers and increase local bioavailability while prolonging and controlling drug release over several months to improve the safety and effectiveness of glucocorticoid therapy. One approach to the development of optimal delivery systems for intravitreal injections is the conjugation of low-molecular-weight drugs with natural polymers to prevent their rapid elimination and provide targeted and controlled release. This study focuses on the development of a procedure for a two-step synthesis of dexamethasone (DEX) conjugates based on the natural polysaccharide chitosan (CS). We first used carbodiimide chemistry to conjugate DEX to CS via a succinyl linker, and we then modified the obtained systems with succinic anhydride to impart a negative ζ-potential to the polymer particle surface. The resulting polysaccharide carriers had a degree of substitution with DEX moieties of 2–4%, a DEX content of 50–85 μg/mg, and a degree of succinylation of 64–68%. The size of the obtained particles was 400–1100 nm, and the ζ-potential was −30 to −33 mV. In vitro release studies at pH 7.4 showed slow hydrolysis of the amide and ester bonds in the synthesized systems, with a total release of 8–10% for both DEX and succinyl dexamethasone (SucDEX) after 1 month. The developed conjugates showed a significant anti-inflammatory effect in TNFα-induced and LPS-induced inflammation models, suppressing CD54 expression in THP-1 cells by 2- and 4-fold, respectively. Thus, these novel succinyl chitosan-dexamethasone (SucCS-DEX) conjugates are promising ophthalmic carriers for intravitreal delivery.