Stable Light‐Emitting Diodes Using Phase‐Pure Ruddlesden–Popper Layered Perovskites

State‐of‐the‐art light‐emitting diodes (LEDs) are made from high‐purity alloys of III–V semiconductors, but high fabrication cost has limited their widespread use for large area solid‐state lighting. Here, efficient and stable LEDs processed from solution with tunable color enabled by using phase‐pure 2D Ruddlesden–Popper (RP) halide perovskites with a formula (CH₃(CH₂)₃NH₃)₂(CH₃NH₃)_n?1Pb_nI_3n+1 are reported. By using vertically oriented thin films that facilitate efficient charge injection and transport, efficient electroluminescence with a radiance of 35 W Sr^?1 cm^?2 at 744 nm with an ultralow turn‐on voltage of 1 V is obtained. Finally, operational stability tests suggest that phase purity is strongly correlated to stability. Phase‐pure 2D perovskites exhibit >14 h of stable operation at peak operating conditions with no droop at current densities of several Amperes cm^?2 in comparison to mixtures of 2D/3D or 3D perovskites, which degrade within minutes.     

Peptidic Ligands to Control the Three‐Dimensional Self‐Assembly of Quantum Rods in Aqueous Media

The use of peptidic ligands is validated as a generic chemical platform allowing one to finely control the organization in solid phase of semiconductor nanorods originally dispersed in an aqueous media. An original method to generate, on a macroscopic scale and with the desired geometry, three‐dimensional supracrystals composed of quantum rods is introduced. In a first step, nanorods are transferred in an aqueous phase thanks to the substitution of the original capping layer by peptidic ligands. Infrared and nuclear magnetic resonance spectroscopy data prove that the exchange is complete; fluorescence spectroscopy demonstrates that the emitter optical properties are not significantly altered; electrophoresis and dynamic light scattering experiments assess the good colloidal stability of the resulting aqueous suspension. In a second step, water evaporation in a microstructured environment yields superstructures with a chosen geometry and in which nanorods obey a smectic B arrangement, as shown by electron microscopy. Incidentally, bulk drying in a capillary tube generates a similar local order, as evidenced by small angle X‐ray scattering.     

Regulation of CD95 (Apo-1/Fas) ligand and receptor expression in squamous-cell carcinoma by interferon-gamma and cisplatin

CD95 (Apo-1/Fas) ligand (CD95L) expression has been observed in various malignancies. In human primary cell lines from a squamous cell carcinoma (SCC) of the vulva, the effect of cisplatin (CDDP) and IFNgamma on the expression of CD95L and its 2 receptor isoforms, CD95 transmembrane (CD95tm) and CD95 soluble receptor, was studied at the mRNA and protein levels. Addition of CDDP and IFNgamma increased CD95L mRNA levels in the primary cell line 6-fold and 1.7-fold, respectively. In comparison, CD95tm mRNA levels were diminished by CDDP but increased 8-fold upon IFNgamma challenge. CD95L expressed by SCC cells was functionally relevant since these cells were able to induce CD95-specific apoptosis in autologous lymphocytes from the SCC-bearing patient. Thus, CD95L expression in SCC may contribute to tumor-associated immunosuppression, which may be modulated by CDDP and IFNgamma. In tumor samples of the primary SCC, CD95L expression was enhanced in the area of the border between invasive tumor tissue and surrounding stroma cells. The locally restricted over-expression of CD95L was congruent with the arrangement of apoptotic stroma cells in the direct vicinity of invading tumor tongues, suggesting a role as invasion factor for CD95L.     

Metabolic action of neuropeptide Y in relation to its effect on feeding

Because energy homeostasis depends on a continuous balance between food intake, energy expenditure, and energy storage, it was expected that neuropeptide Y (NPY) could act not only on food intake but also on metabolic parameters. Using an original calorimetric device that allows the computation of the background metabolism (energy expenditure free from the cost of locomotor activity), we assessed the effect of a microinjection of NPY upon the quantitative (background metabolism, thermic effect of food) and qualitative (respiratory quotient) components of energy metabolism. NPY was injected into the juxtafornical hypothalamus at a dose that promotes feeding behavior (1 microg/0.5 microL) and enhances locomotor activity. Although total metabolism was increased proportionally to locomotion, no effect of NPY on background metabolism was observed when no food was available. Only following a calibrated meal given 30 min after the microinjection did NPY induce a delayed decrease in respiratory quotient whereas the postprandial background metabolism remained unaffected. In conclusion, only the new-generation calorimeters can show that the NPY-induced rise in overall metabolic rate is entirely accounted for by the unavoidable enhancement in locomotor activity and that the only metabolic effect of NPY is the delayed postprandial respiratory quotient decrease, suggesting a postabsorptive orientation toward more lipid utilization.     

High cycle fatigue life estimation of materials processed by laser powder bed fusion

The fatigue life of metal components is known to depend on the surface topography. For components made by laser powder bed fusion, the roughness of the as‐built surfaces depends on the orientation of the component surface with respect to the build plate. Surface topographies of AlSi10Mg and Inconel 718 specimens built at 0° to 90° inclination, with 15° increments, were characterised by white light interferometry. Two methods for calculating the stress concentration factor using the surface roughness data are proposed, and the results of each approach are presented and compared. Moreover, a finite element model was developed, in order to analyse the stress field when subsurface porosity is present. The fatigue lifetime estimates suggest that the lifetime of components may differ up to two orders of magnitude, depending on the build orientation.     

Theoretical and experimental studies of (In,Ga)As/GaP quantum dots

(In,Ga)As/GaP(001) quantum dots (QDs) are grown by molecular beam epitaxy and studied both theoretically and experimentally. The electronic band structure is simulated using a combination of k·p and tight-binding models. These calculations predict an indirect to direct crossover with the In content and the size of the QDs. The optical properties are then studied in a low-In-content range through photoluminescence and time-resolved photoluminescence experiments. It suggests the proximity of two optical transitions of indirect and direct types.     

On the direct solution of Dirichlet's problem in two dimensions

Computing - General methods for the solution of the two-dimensionalDirichlet problem are presented. They are general in the sense that they are independent of the numerical values of the entries of...