Phytochrome‐Based Extracellular Matrix with Reversibly Tunable Mechanical Properties

Interrogation and control of cellular fate and function using optogenetics is providing revolutionary insights into biology. Optogenetic control of cells is achieved by coupling genetically encoded photoreceptors to cellular effectors and enables unprecedented spatiotemporal control of signaling processes. Here, a fast and reversibly switchable photoreceptor is used to tune the mechanical properties of polymer materials in a fully reversible, wavelength‐specific, and dose‐ and space‐controlled manner. By integrating engineered cyanobacterial phytochrome 1 into a poly(ethylene glycol) matrix, hydrogel materials responsive to light in the cell‐compatible red/far‐red spectrum are synthesized. These materials are applied to study in human mesenchymal stem cells how different mechanosignaling pathways respond to changing mechanical environments and to control the migration of primary immune cells in 3D. This optogenetics‐inspired matrix allows fundamental questions of how cells react to dynamic mechanical environments to be addressed. Further, remote control of such matrices can create new opportunities for tissue engineering or provide a basis for optically stimulated drug depots.     

Residual analysis for ARCH(p)-time series

In this paper we provide consistency and distributional convergence results for functions of residuals from an ARCH(p)-time series. An application to a goodness-of-fit problem is also discussed.     

The benefits of incorporating utility dependencies in finite mixture probit models

OR Spectrum - We propose an application of a new finite mixture multinomial conditional probit (FM-MNCP) model that accommodates preference heterogeneity and explicitly accounts for utility...     

Thin films in photovoltaics: Technologies and perspectives

Thin Film technologies based on physical vapour and plasma enhanced chemical vapour deposition (PVD and PECVD) have been developed for a number of high-tech industries over the last decades. Prominent examples are the semiconductor and display industry as well as large area architectural glass and flexible substrates deposition. Inherently linked with this development was the well known price experience curve for products in the respective industries. Analysing the price experience curves for PV crystalline silicon modules over the last 30 years and those of other Thin Film based industries, it will become evident that cost efficient PV Thin Film technologies or Thin Films in conjunction with wafer based c-Si are a prerequisite to meet the anticipated cost and price goals for the upcoming decade. As PV will demonstrate to become one of the major energy provider in the future by contributing significantly to meet the goal of 100% end energy by only renewable technologies beyond 2050 we will see a huge increase of appropriate Thin Film technologies in the years to come.     

Chemistry effects on the crack susceptibility of structural steels during continuous casting

This work is a review of research results, which have been determined in recent years in order to reveal the effects of the chemical compositions on the high temperature properties of structural steels. Special emphasis has been laid on the solidification structure, phase reactions and precipitates. For this comparison exemplary different structural steel grades have been chosen. The effect of the chemical composition on the solidification structure is shown by increasing Ni mass contents up to 10 %, the influence on the phase transformation is illustrated on the basis of a steel with a Mn mass content of 1.6 % and varying carbon contents. The influence of precipitates has been investigated both on the basis of the Mn/S‐ratio and by microalloyed structural steels with different Nb, V and Ti additions. For all these steel grades the laboratory testing conditions were the same. The high temperature properties of steels can be investigated by high temperature tensile tests; the range of good ductility is determined by the measurement of the reduction of area, e.g. RoA > 50 % or >70 %. The upper limit of the ductility range is the temperature of zero ductility, T_ZD%. The lower limit of the good ductility range is marked by the transition to the ductility minimum II. The experiments for a series of different structural steels show that the hot ductility properties are affected by the metallurgical phenomena mentioned before.     

Development of Al-Ti-C grain refiners containing TiC

Cast Al-Ti-C grain refiners were synthesized by reacting up to 2 pct graphite particles of 20 micron average size with stirred Al-(5 to 10) pct Ti alloy melts, which generated submicron-sized TiC particles within the melts, and their solidified structures showed preferential segregation of the carbide phase in the grain or cell boundary regions and occasional presence of free carbon whose amount exceeded equilibrium values. At the usual melt temperatures of below 1273 K, though, TiC formed first, but was subsequently found to react with the melt forming a sheathing of A1₄C₃ and Ti₃AlC which resulted into poisoning of the TiC particles. However, it was possible to reverse these reactions in order to regain the virgin TiC particles by superheating the melts in the temperature region where TiC particles are thermodynamically stable. Grain refining tests using the TiC master alloys produced fine equiaxed grains of cast aluminum whose sizes were comparable to that obtainable with the standard TiB₂ commercial grain refiner. TiC particles introducedvia the master alloys were found to occur in the grain centers, thereby confirming that they nucleated aluminum crystals. On leave from Regional Research Laboratory (CSIR), Bhopal, is Research Associate.     

Technological application of the martensitic transformation of some austenitic stainless steels

The final heat treatment of austenitic stainless steels of types X 5 CrNi 18 9 (1.4301) and X 2 CrNi 18 10 (1.4306) normally is annealing at 1050°C and subsequent water quenching. The resulting structure is of a metastable fcc-type. Plastic deformation, especially at low temperatures, causes martensitic transformation of these metastable structures. The transformation is accompanied by a substantial flow stress increase. This strengthening mechanism should be used in practice, e.g. to save weight. The deformed structure consists of tetragonal α′-martensite, austenite and hcp ε-martensite. Whereas α′-martensite increases continuously with deformation, the content of ε-martensite reaches a maximum value at about 5% plastic strain at 77 K. The hcp phase is only detectable by means of X-ray analysis, whilst α′-martensite can be determined quantitatively by saturation magnetisation measurement. The flow stress increase during low temperature deformation of metastable austenitic stainless steels is based on normal work-hardening by dislocation accumulation, in addition to a distinct amount of work-hardening due to martensitic transformation. Analysis of the work-hardening behaviour in the range of stable deformation (T > M_D) can be used to predict the amount of normal work-hardening when deformation is performed in the instable temperature regime. Separation of the flow stress contributions according to the procedure described above enables the possible savings in weight to be predicted when using cryogenically stretched instable austenitic steels in comparison with stable grades deformed under the same conditions.     

Characterization of laser-beam surface treated cold and hot working steels

In order to increase the wear resistance of metal forming tools, four different cold and hot working steels were laser-beam surface melted and alloyed with titanium carbide and vanadium carbide. The layers were investigated concerning chemical composition, microstructure, hardness profiles, wear behaviour measured by pin-on-disk-tests with different counterbodies and plastic behaviour of the surface by a new developed repeated impact testing machine. It turned out to be more useful to take a substrate which is already quenched and tempered prior to the laser-beam surface treatment than to carry out the tool hardening heat treatment afterwards. A tempering step after the laser-beam alloying offers the advantage of carbide precipitates in the layer connected with an increase in the hardness and a reduction of residual stresses. By means of laser-beam surface alloying the wear protection of the layer can be increased while the alloying content of the substrate is reduced with respect to the core fracture toughness. The optimal alloying addition depends on the demands of the envisaged application.