Al–Al2O3 Composites with Interpenetrating Network Structures: Composite Modulus Estimation

The effective Young's moduli of co-continuous Al–Al₂O₃ composites over the 5–97 vol% Al₂O₃ composition range were experimentally measured and compared with theoretical composite modulus values predicted using the methods of Ravichandran, Tuchinskii, Hashin-Shtrikman, and the effective medium approximation (EMA). The influence of phase morphology and the modulus ratio ( E ₁/ E ₂) of the constituent phases on the resulting experimental and calculated Young's modulus is discussed. For two-phased co-continuous composites with a modulus ratio greater than 5, the EMA, with an appropriate microstructural shape factor, was the most consistent method for approximating the composite Young's modulus over the entire composition range.     

中国几种油页岩超临界萃取研究

用甲苯为溶剂对八种中国油页岩样进行了非等温的超临界萃取实验.进行了不同萃取压力、终温、样品粒度、溶剂速率和溶剂中供氢组分含量等参数的系统实验.结果表明,甲苯溶剂超临界萃取油类产物产率是一般干馏方法的二倍.溶剂中加入供氢组分,能使油页岩中有机质回收完全.由不同温度下萃取溶液中萃取物浓度的变化得出,油页岩的超临界萃取动力学可用一级反应描述,过程分两段,活化能分别为120和180kJ·mol~(-1)左右.     

Temperature dependant dielectric breakdown of sputter-deposited AlN thin films using a time-zero approach

In MEMS (micro electromechanical system) devices, piezoelectric aluminum nitride (AlN) thin films are commonly used as functional material for sensing and actuating purposes. Additionally, AlN features excellent dielectric properties as well as a high chemical and thermal stability, making it also a good choice for passivation purposes for microelectronic devices. With those aspects and current trends towards minimization in mind, the dielectric reliability of thin AlN films is of utmost importance for the realization of advanced device concepts. In this study, we present results on the transversal dielectric strength of 100 nm AlN thin films deposited by dc magnetron sputtering. The dielectric strength is measured using a time-zero approach, using a fast voltage ramp to stress the film up to the point of breakdown. The measurements are performed at different device temperatures. In order to achieve statistical significance, at least 12 measurements are performed for each environment parameter set and the results are analyzed using the Weibull approach. Basically, lower breakdown fields are observed with increasing temperatures up to 300 °C with a characteristic breakdown field strength E ₀ following the relationship $\sqrt {E_{0} } \propto T$ as reported in literature for similar measurements performed at silicon nitride thin films. From the intersection of this linear behavior, the Poole–Frenkel (PF) barrier height ? _B is determined to 0.54 eV, which is reasonable for AlN thin films. The slope of this relation is similar to values reported for silicon nitride thin films. This allows an estimation of the breakdown field at higher temperatures by extrapolation. Leakage current measurements show a dominant PF type conduction mechanism, verifying the applicability of $\sqrt {E_{0} } \propto T$ . No breakdown occurs in negative field direction, which is attributed to the metal–insulator–semiconductor configuration of the sample and hence, the presence of a depletion layer forming in the n-doped silicon and dominating the leakage current behavior.     

Interaction between a Fab fragment against gp41 of human immunodeficiency virus 1 and its peptide epitope: characterization using a peptide epitope library and molecular modeling

The molecular interaction of the Fab fragment of the human monoclonalantibody 3D6, directed against the transmembrane protein gp41of human immunodeficiency virus (HTV) 1, with its peptide epitopeis characterized by a panel of overlapping peptides, a peptideepitope library and molecular modeling techniques. The sequenceCSGKLICTTAVPW, corresponding to amino acids 605–617 ofgp41, was identified as the best binding peptide (K_D = 1x10^-8mol/1). This peptide served as a starting point to prepare acellulose-bound peptide epitope library in which each residueof the epitope is substituted by all L- and D-amino acids, resultingin 494 epitope peptide variants which were subsequently analyzedfor binding 3D6. The library was synthesized to identify residuescritical for binding and to obtain information about the molecularenvironment of the epitope peptide bound to 3D6. Both cysteineresidues, as well as isoleucine 6, threonine 8 and proline 12,of the epitope were highly sensitive to substitution. Usingthe data obtained from the epitope characterization, as wellas a low-resolution electron density map of a 3D6 Fab-peptidecomplex, a 3-D model of the Fab-peptide complex was generatedby molecular modeling. The modeling experiments predict bindingof the peptide, which is cyclized via the two cysteine residues,to a pocket formed dominantly by the hypervariable loops complementaritydetermining regions CDR3L, CDR2H and CDR3H.     

Modell zur beschreibung der viskoelastischen eigenschaften von synthetischen fasern

The evaluation of the viscoelastic response of synthetic fibres from stress-relaxation data over a wide range of time at different strain rates is very time-consuming. Therefore, mathematical models are used to describe the viscoelastic response. The characteristic of synthetic fibres is that already at very low deformation rates like an elongation < 1% a nonlinear viscoelasticity has to be considered. Based on the analytical representation of isothermal viscoelastic behaviour by Boltzmann a new model making an assertion to the nonlinear viscoelasticity is proposed. Applying this model, the calculated values of moduli and relaxation tensions of the fibres Nomex® and PEEK are in good agreement with the experimental values.     

Simple adaptive stabilization of high-gain stabilizable systems

It is shown that the simple adaptive feedback strategy

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is a universal adaptive stabilizer for the class of single-input, single-output, finite-dimensional, linear systems which are stabilizable by either negative or positive high-gain feedback.     

Coupled Continuous Chromatography and Racemization Processes for the Production of Pure Enantiomers

Combining an enantioseparation by continuous chromatography with the racemization of the undesired enantiomer in a recycle is a promising approach. Two different cases were considered: limited conversion of the reaction with moderate product purity requirements and high conversion with high product purity requirements. For the first case, a simple plantwide control strategy is presented, manipulating the solvent removal in front of the racemization reactor. It is shown that the various disturbances can be compensated with this strategy without performing the more complex readjustment of the chromatographic unit. Further, it is shown that this strategy is likely to fail in the second scenario and that readjustment of the chromatographic unit is required for a successful control strategy.     

Development of the Flight Hardware for the Experiment XENOPUS on the Kubik BIO4-Mission

The needs of developing aquatic animals depend on their age. For example, amphibian tadpole stages require regular food supply while embryos use their yolk as food source. Thus, life support systems have to be adapted to the different ages; an efficient control for water cleanness and steady food supply is mandatory for a safe flight in microgravity. A list of biological and technical requirements prompted the concept of the Dornier-Mini-System and the design for the Astrium SUPPLY Unit. These life support systems are connected with the Astrium miniaquarium that was used several times for the transport of small aquatic animals in space. Scientific experience from this concept was considered by Kayser Italia to design and develop a space suitable hardware. Its functionality was successfully demonstrated by the experiment XENOPUS that flew on the Soyuz TMA13/TMA12 mission in 2008. From 36 launched tadpoles, 35 returned back to Earth after the 12 days lasting space flight in physiologically stable conditions.     

Nanostructuring of NiAl-Mo eutectic alloys by selective phase dissolution

A technique for the electrochemical structuring of directionally solidified NiAl-Mo eutectic by selective phase dissolution is presented. Local matrix dissolution at 200 mV SHE in 1 M HCl of pH 1 yielded the grid of Mo nanowires spanning along the central part of the sample. On the other hand, the dissolution of the fibrous minor phase while passivating the continuous NiAl matrix resulted in continuous nanopore arrays. Initially, mechanical polishing and electropolishing were employed to thin the samples. Etching time was optimized by plotting the etch time until hole formation as a function of initial sample thickness, along with plotting sample thickness versus etching time. As a next step, an investigation into the passivation behaviour of the NiAl was performed in order to determine the optimal potential for wire dissolution. A potential scan from 0 to 2500 mV SHE on a bulk sample of pure NiAl in an electrolyte of 0.1 M acetate buffer pH 6.0 indicated that a potential of 500 mV SHE, just below the breakdown potential would provide maximum driving force for wire dissolution process. Different parameters within the electrochemical system are varied in order to optimize the wire dissolution. The extent of wire dissolution is measured both quantitatively (total charge transfer) and qualitatively (optical and SEM imaging).     

Basic properties mapping of anodic oxides in the hafnium–niobium–tantalum ternary system

A thin film combinatorial library deposited by co-sputtering of Hf, Nb and Ta was employed to characterise fundamental properties of the Hf-Nb-Ta system. Compositional mappings of microstructure and crystallography revealed similarities in alloy evolution. Distinct lattice distortion was observed upon addition of hexagonal Hf, leading to amorphisation of alloys containing more than 32 at.% Hf and less than 27 and 41 at.% Nb and Ta, respectively. Volta potential and open circuit potential mappings indicated minimal values for the highest Hf concentration. Localised anodisation of the library by scanning droplet cell microscopy revealed valve metal behaviour. Oxide formation factors above 2 nm V^?1 were identified in compositional zones with high amounts of Nb and Ta. Fitting of electrochemical impedance spectroscopy data allowed electrical permittivity and resistivity of mixed oxides to be mapped. Their compositional behaviours were attributed to characteristics of the parent metal alloys and particularities of the pure oxides. Mott–Schottky analysis suggested n-type semiconductor properties for all Hf–Nb–Ta oxides studied. Donor density and flat-band potential were mapped compositionally, and their variations were found to be related mainly to the Nb amount. Synergetic effects were identified in mappings of Hf-Nb-Ta parent metals and their anodic oxides.