Body distribution of poly(<Emphasis Type="SmallCaps">d</Emphasis>,<Emphasis Type="SmallCaps">l</Emphasis>-lactide-<Emphasis Type="Italic">co</Emphasis>-glycolide) copolymer degradation products in rats

Poly (d,l-lactide-co-glycolide) (PLGA) copolymers are among the few synthetic polymers approved for human use, but the biocompatibility of PLGA-derived oligomers and particles remains questionable. Here, high molecular weight PLGA (Mw = 32,000) was radiolabeled with ¹²⁵I in chloroform solution, and the body distribution of PLGA copolymer degradation products was examined following subcutaneous implantation of round ¹²⁵I-PLGA films on the back of Sprague Dawley rats. Autoradiographic images of the PLGA implant taken at 2, 4, 6, 8, 10, and 12 weeks revealed that the central portion of the film degraded much more rapidly than the marginal portions. Examination of the body compartment distribution at these time points revealed that over one-half of the radioactivity was recovered from skin. The remaining radioactivity was concentrated in the blood, liver, and kidneys. Radioactivity steadily appeared in the blood and remained elevated up to 12 weeks after implantation, while the liver to kidney distribution began to decrease after 6 weeks. Cumulatively, these results indicate that the clearance of degraded particles and fragments from the implantation site is extremely delayed. Moreover, the degraded particles and fragments were selectively concentrated in the liver and kidneys, following release of degraded products into the bloodstream from the implantation site.     

The thermodynamic properties of liquid binary mixtures of <Emphasis Type="Italic">n</Emphasis>-alkanes: <Emphasis Type="Italic">n</Emphasis>-decane + <Emphasis Type="Italic">n</Emphasis>-hexadecane

Data on sound velocity are used for determining the density, the isobaric expansion coefficient, the isobaric and isochoric heat capacity, and the isothermal compressibility of liquid binary mixture of n-decane + n-hexadecane of three compositions in the temperature range of 298–433 K and pressure range of 0.1–100 MPa. The coefficients of Tait equation are calculated in the above-identified range of parameters. The calculation results are compared with experimental data on density. The divergence does not exceed 0.2% for the most reliable data.     

Electrical impedance of ethylene-carbon monoxide/propylene-carbon monoxide (<Emphasis Type="Italic">EPEC</Emphasis>-<Emphasis Type="Italic">69</Emphasis>) thermoplastic polyketone

Electrical impedance technique was employed to investigate the electrical properties of ethylene-carbon monoxide/propylene-carbon monoxide terpolymer (EPEC-69). The measurements were performed in the frequency range 0.1–10⁵ Hz and in the temperature range 30–110 °C. The results reveal that the dielectric constant, loss factor, modulus, and ac conductivity are dependent of frequency and temperature. A Debye relaxation peak was detected in the plot of Z″ versus frequency where the activation energy was determined and found to be 1.26 eV. When the surface phenomenon effects were separated using the imaginary part of the complex admittance a second dielectric dispersion was observed in the low frequency region. Two models were proposed from the impedance measurements depending on temperature range.     

Pre-exponential factor in<Emphasis Type="Italic">a</Emphasis>-Se<Subscript>75</Subscript>In<Subscript>25-<Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> thin films

Temperature dependence of d.c. conductivity is studied ina- Se₇₅In_25-x Pb _x thin films wherex is varied from 0–10. From these measurements, the values of the pre-exponential factor (σ₀) and activation energy (ΔE) are calculated for each glassy alloy. An approximate linear dependence of ln σ₀ on AE is observed in this glassy system with good agreement between the expected and calculated σ₀ values using Meyer-Neldel rule. Linear dependence of ln σ₀ on ΔE in case of amorphous materials indicates that the conduction band tails a finite energy distance towards the valence band and Fermi level is controlled by fixed dominant hole levels deeper in the gap.     

Dielectric properties of Na<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>K<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>NbO<Subscript>3</Subscript> in orthorhombic phase

Pellets of ceramic Na_1−xK_xNbO₃ (x = 0, 0.2 and 0.5), were prepared by conventional solid-state reaction method. Prepared samples were characterized using XRD and SEM. The frequency and temperature variation of dielectric constant, loss tangent and dielectric conductivity of prepared samples were measured in the frequency range from 10 KHz-1 MHz, and in the temperature range from 50–250°C for x = 0.2 and 0.5, and between 50 and 480°C for x = 0 compositions. It was observed that the dielectric constant and loss tangent decrease, and conductivity increases with increasing frequency. Near the transition temperature the material shows anomalous behaviour for the observed properties, and the peaks of dielectric constant and loss tangent were observed shifting towards lower temperature with increasing frequency.     

<Emphasis Type="Italic">In vivo</Emphasis> assessment of hydroxyapatite and silicate-substituted hydroxyapatite granules using an ovine defect model

Phase pure hydroxyapatite (HA) and two silicate-substituted hydroxyapatites (0.8 and 1.5 wt% Si, or 2.6 and 4.9 wt% SiO₄) were prepared by aqueous precipitation methods. The filter-cakes of HA and silicate-substituted hydroxyapatite (SiHA) compositions were processed into granules 1.0–2.0 mm in diameter and sintered at 1200°C for 2 h. The sintered granules underwent full structural characterisation, prior to assessment in an ovine defect model by implantation for a period of 6 and 12 weeks. The results indicate that HA and SiHA implants were well accepted by the host tissue, with no evidence of inflammation. New bone formation was observed directly on the surfaces and in the spaces between the granular implants. Quantitative histomorphometry as determined by the percentage of bone ingrowth and bone coverage for both SiHA implant compositions was significantly greater than that for phase pure HA. These findings indicate that the in vivo bioactivity of hydroxyapatite was significantly improved by the incorporation of silicate ions into the HA structure, making SiHA ceramics attractive alternatives to conventional HA materials for use as bone graft substitute ceramics.     

Optical band gap in the system ZnO<Subscript>1 – <Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>. An experimental and quantum chemical study

The synthesis of single crystalline and polycrystalline material is reported in the system ZnO_{1 – x} S _x . Substitution of oxygen by sulphur yields hexagonal wurtzite-type mixed crystals in the range 0 ≤ x ≤ 0.05. The cubic zincblende structure is observed for oxygen incorporation into ZnS for 0.96 ≤ x ≤ 1. At intermediate compositions, the system is two-phase. For both types of anion substitution, the band gap energies, as determined from optical transmission and remission experiments, are found to decrease from the pure end members. Quantum chemical calculations at density functional level identify local structural changes as the main factor responsible for the reduction of band gap energies.     

Thomas Fincke und die <Emphasis Type="Italic">Geometria rotundi</Emphasis>

Thomas Fincke (January 6^th, 1561–April 24^th, 1656), born in Flensburg (Germany), was one of the very most important and significant scientists in Denmark during the seventeenth century, a mathematician and astrologer and physician in the beginning of modern science, a representative of humanism and an influentual academic organizer. He studied in Strasbourg (since 1577) and Padua (since 1583) and received his M.D. in Basel (1587), he practised as a physician throughout his life (since 1587 or 1590) and became a professor at Copenhagen (1591). But he was best known because of his Geometriae rotundi libri XIIII (1583), a famous book on plane and spherical trigonometry, based not on Euclid but on Petrus Ramus. In this influentual work, in which Fincke introduced the terms tangent and secant and probable first noticed the Law of Tangents and the so-called Newton-Oppel-Mauduit-Simpson-Mollweide-Gauss-formula, he showed himself to be „abreast of the mathematics of his time“.      

Prediction of fatigue limit reliability of high strength steel with deep notch under mean stress <Emphasis Type="Italic">σ</Emphasis><Subscript><Emphasis Type="Italic">m</Emphasis></Subscript> = 0

Because a fatigue limit of high strength steel with Vickers hardness H _V > 400 is scattered, it is difficult to predict the fatigue limit for S-N curve experimentally. The authors have proposed a nondestructive method for predicting the fatigue limit reliability of plain specimen of the high strength steel by the stress-strength model which consists of “statistical characteristics of hardness of a matrix under a small indentation load” and “statistical characteristics of hardness required for non-propagations of fatigue cracks from microstructural defects in a material”. In this paper, a nondestructive method for predicting the fatigue limit reliability of notched specimen of the high strength steel with microstructural defects such as non-metallic inclusions and pits from characteristics of a stress field near a notch, statistical characteristics of Vickers hardness and defect size is proposed. Especially, the method is applied to a structure with a deep notch under a mean stress σ _m = 0. Then, fatigue tests were carried out on the notched specimens of quenched-tempered 0.5% carbon steels with H _V ≃ 600 changing a notch root radius under a constant notch depth, and the validity of the prediction method is examined by comparing predicted results to experimental ones.     

Fractal structure of precursors and phase transformations in the sol-gel synthesis of nanoparticulate <Emphasis Type="Italic">M</Emphasis>-type barium hexaferrite

We have studied the influence of sol-gel process conditions on the fractal structure of precursors, the phase transformations during the synthesis process, and the morphology of the resulting barium hexaferrite particles and determined the optimal fractal structure of sol-gel derived precursors for the solid-state synthesis of barium hexaferrite. The activity of the precursors is shown to correlate with the fractal dimension of their first structural aggregation level. Nanoparticulate barium hexaferrite can be prepared in the form of anisometric particles: platelets (d _av ∼ 65 nm) and nanorods (d _av ∼ 30 nm, l _av ∼ 70 nm).     

Study of defect states in a-Se<Subscript>85</Subscript>Te<Subscript>15−<Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> thin films by space charge limited conduction mechanism

Current–Voltage (I–V) characteristics have been studied at various temperatures in vacuum evaporated thin films of a-Se₈₅Te_15−x Pb _x (x = 0, 2, 4, 6) alloys. These characteristics show that, at low electric fields, an ohmic behaviour is observed. However, at high electric fields (E ∼ 10⁴ V/cm), the current becomes superohmic. At high fields, in case of samples having 0 and 2 at% of Pb, the experimental data fits well with the theory of space charge limited conduction (SCLC) in case of uniform distribution of localized states in the mobility gap. Such type of behaviour is not observed at higher concentration of Pb in the present glassy system due to high conductivity. In these samples, joule heating due to large currents may prohibit the measurement of SCLC. Using the theory of SCLC for the uniform distribution of the traps, the density of localized defect states near Fermi level is calculated for these compositions. The results indicate that the density of defect states near Fermi level increases on addition of Pb to binary Se₈₅Te₁₅alloy. This is explained in terms of electronegativity of Pb as compared to host elements.     

Local vibrational modes of N<Subscript>2</Subscript>−O<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> defects in Cz-Silicon

In this paper we investigate N₂−O _n defect complexes in Czochralski silicon (Cz-Si) by means of local density functional theory. We consider the N₂O and the N₂O₂ defect and determine their structural, electronic and vibrational properties. The calculated local vibrational modes of the N₂O defect are in good agreement with the experiment. Furthermore the calculated binding energy matches very well with the experimental estimate. Motivated by recent experimental work, where several new absorption lines in IR absorbance spectra were observed, we present first principle studies on the ground state configuration, binding energy and local vibrational modes of the N₂O₂ defect and make a tentative assignment to the experimentally observed lines at 1018 and 810 cm⁻¹.     

Solid state synthesis and structural refinement of polycrystalline La<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> ceramic powder

Perovskite structure based ceramic precursors have a characteristic property of substitution in the “A” site of the ABO₃ structure. This makes them a potential material for nuclear waste management in synthetic rock (SYNROC) technology. In order to simulate the mechanism of rare earth fixation in perovskite, La_x Ca_1−xTiO₃ (wherex = 0.05) has been synthesized through ceramic route by taking calculated quantities of oxides of Ca, Ti and La as starting materials. Solid state synthesis has been carried out by repeated pelletizing and sintering the finely powdered oxide mixture in a muffle furnace at 1050°C. The ceramic phase has been characterized by its powder diffraction pattern. Step analysis data has been used to determine the structure of solid solution of lanthanum substituted calcium titanate. The SEM and EDAX analyses also confirm that the CaTiO₃ can act as a host for lanthanum. X-ray data has been interpreted using CRYSFIRE and POWDERCELL softwares. Theh, k, l values for different lattice planes have been generated from the experimental data. The lanthanum substituted perovskite crystallizes in orthorhombic symmetry with space groupP n m a (#62). Following unit cell parameters have been calculated:a = 5.410,b = 7.631,c = 5.382. The calculated and observed values of corresponding intensities, 2θ, and density show good agreement. GSAS based calculation for bond distances Ti-O, Ca-O, La-O and bond angles Ti-O-Ca, Ca-O-Ca, La-O-Ti have been reported.     

<Emphasis Type="Italic">In vivo</Emphasis> evaluation of an injectable Macroporous Calcium Phosphate Cement

Although Calcium Phosphate Cements (CPC) are highly biocompatible and osteconductive materials, its resorption rate still remains too slow for some applications. In this work the introduction of Macroporosity in an injectable CPC is evaluated as a way to accelerate resorption and to increase bone ingrowth. A Macroporous and a standard CPC were injected just after preparation in a defect drilled in rabbit femur for their in vivo evaluation. The foaming agent used was Albumen, which gave up to a 75% porosity. Sodium Alginate was added to promote the cohesion of the foamed paste after implantation. In the case of the Macroporous Cement, bone growth and neovascularisation was observed inside the pores of the material, not only at the margins of the cement but also in some central pores. After 12 weeks of implantation, the residual material volume of the Macroporous Cement was approximately 35% of the initial value, whereas only the outer layers of non-Macroporous CPC were resorbed, being the residual material volume close to 100%. The higher resorption rate was due to the higher surface contact with body fluids which increased the dissolution rate, and to the enhancement of the cellular activity     

Application of a sensitivity equation method to the <Emphasis Type="Italic">k</Emphasis>–<Emphasis Type="Italic">ε</Emphasis> model of turbulence

In this paper, we present some examples of sensitivity analysis for flows modeled by the standard k–ε model of turbulence with wall functions. The flow and continuous sensitivity equations are solved using an adaptive finite element method. Our examples emphasize a number of applications of sensitivity analysis: identification of the most significant parameters, analysis of the flow model, assessing the influence of closure coefficients, calculation of nearby flows, and uncertainty analysis. The sensitivity parameters considered are closure coefficients of the turbulence model and constants appearing in the wall functions.     

Defects in Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Te-based heterostructures grown by molecular beam epitaxy on GaAs(310) substrates

Cd _x Hg_{1 − x} Te-based epitaxial heterostructures grown on [310]-oriented GaAs substrates by molecular beam epitaxy have been studied by atomic force, scanning electron, and high-resolution field emission microscopy. A mechanism of defect formation has been proposed. The microstructure of the epilayer has been investigated in greatest detail. We have analyzed the key features of V-defect formation, in particular using depth profiling of the heterostructures by ion etching. A comparative analysis of the elemental compositions of V-defects and a defect-free region has been performed. The results indicate that, in the central part of the V-defects, the excess tellurium content is ∼2.5% and mercury deficiency is ∼3%. V-defect formation in the heterostructures is related to tellurium precipitation, which initiates nucleation of polycrystalline clusters and dislocation generation in adjacent regions.     

Sb-doped CuAlO<Subscript>2</Subscript>: widening of band gap and nonlinear <Emphasis Type="Italic">J</Emphasis>–<Emphasis Type="Italic">E</Emphasis> characteristics

The effect of antimony doping on the optical and electrical properties of copper aluminum oxide synthesized by solid state reaction technique was investigated. Formation of single phase CuAlO₂ was confirmed by x-ray diffraction studies. Variation of strain, particle size, and preferred orientation of the crystallites with Sb doping concentrations were analyzed by x-ray diffraction. Using the x-ray photoelectron spectroscopy trivalent state of Sb ions was confirmed. A blue shift in the energy band gap with Sb doping was observed, and it was supported by ab initio calculation based on density functional theory. A nonlinear current–voltage characteristic was observed for the Sb-doped CuAlO₂ samples whereas the same was linear for the undoped samples. The nonlinearity of the current–voltage characteristics changed significantly at higher temperature, and this behavior was explained.     

Synthesis of nano-particle and highly porous conducting perovskites from simple <Emphasis Type="Italic">in situ</Emphasis> sol-gel derived carbon templating process

Nano-sized La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) and La_0.8Sr_0.2MnO_3−δ (LSM) oxides were synthesized by a simple in situ sol-gel derived carbon templating process. Nano-sized LSCF-carbon and LSM-carbon composites were first obtained with a grain size of 20–30 nm. Further calcination of the obtained composites under air resulted in the nano-sized pure-phase perovskites with crystalline size of as small as 14 nm. Such a decrease in crystalline size of perovskite via the indirect calcination process was ascribed to the suppressing effect of carbon in the grain growth of perovskite. Furthermore, when the in situ created carbon was applied as a template for pore forming, a highly porous perovskite sintering body packing from the nano-sized perovskite oxide was obtained.     

Growth and properties of nanostructured layers based on Pb<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se (<Emphasis Type="Italic">x</Emphasis> = 0−0.20) solid solutions

We have produced nanostructured layers based on supersaturated Pb_1−x Cd _x Se (x = 0−0.20) solid solutions with an efficient room-temperature photoluminescence in the range 3–5 μm and studied the effect of growth conditions on their chemical and phase compositions and properties. Their photoluminescence spectra have been measured, and the main radiative recombination mechanisms in activated solid-solution layers have been identified. The role of iodine in the formation of the emitting nanostructures has been discussed.