Resonant modes in monolithic nitride pillar microcavities

GaN-based airpost pillar microcavities are realized by focused-ion beam etching starting from an all-epitaxially grown vertical-cavity surface-emitting laser structure. Pillar diameters below 1 μm are well controllable. The sidewalls are smooth and show a damaged surface layer of a thickness less than 2 nm only. Micro-photoluminescence measurements reveal the longitudinal and transversal mode spectra of the cavities in good agreement with theoretical calculations based on a vectorial transfer-matrix method.     

Performance of slotted pores in particle manufacture using rotating membrane emulsification

This paper addresses the use of different slotted pores in rotating membrane emulsification technology.Pores of square and rectangular shapes were studied to understand the effect of aspect ratio (1-3.5) and their orientation on oil droplet formation.Increasing the membrane rotation speed decreased the droplet size,and the oil droplets produced were more uniform using slotted pores as compared to circular geometry.At a given rotation speed,the droplet size was mainly determined by the pore size and the fluid velocity of oil through the pore (pore fluid velocity).The ratio of droplet diameter to the equivalent diameter of the slotted pore increased with the pore fluid velocity.At a given pore fluid velocity and rotation speed,pore orientation significantly influences the droplet formation rate: horizontally disposed pores (with their longer side perpendicular to the membrane axis) generate droplets at double the rate of vertically disposed pores.This work indicates practical benefits in the use of slotted membranes over conventional methods.     

Photo‐Cross‐Linking of Polymethacrylates with Stilbene Chromophores in the Side Chains

Methacrylates (=2‐methylpropenoates) 5 with (E)‐stilbene (=(E)‐1,2‐diphenylethene) building blocks on tethers of variable length were prepared (Scheme 2) and polymerized (i.e., 5 → 6 ; Scheme 3) in the presence of AIBN (=2,2′‐azobis(2‐methylpropanenitrile). 4‐[(E)‐2‐Phenylethenyl]phenyl acetate ( 7 ) as model compound established the cyclodimerization as a single irreversible photoreaction. i.e., ( 7 → 8 – 11 ; Scheme 4) in the absence of oxygen. The solution photolysis of the polymers 6 provided a similar result, whereby [2π+2π] cycloadditions of stilbene units of neighboring tethers predominated. On the contrary, the desired photo‐cross‐linking of chaines occurred in the irradiation of polymer films.     

Understanding what a proof is: a classroom-based approach

Being unaware of the assumptions underlying a deductive argument is widespread among learners and is a major stumbling block to their understanding of proof. Thus, the basic idea of the present paper is that at some points in the course of secondary education there should be classroom-based interventions addressing this difficulty and making the axiomatic organization of mathematics a theme. Students should be made aware that there are axioms in mathematics, what their role is and how mathematicians come to agree about which axioms should be accepted. An axiom which is not yet accepted is simply a hypothesis. A hypothesis is evaluated by deductively drawing consequences and by investigating whether these consequences agree with experience or should be accepted for other reasons. The teaching intervention discussed in this paper exemplifies this idea by way of the example of ancient attempts at modelling the path of the sun, the so-called “anomaly of the sun”. It is investigated to what extent the teaching intervention fostered students’ understanding of the conditionality of mathematical/astronomical statements, that is, of the fact that the truth of these statements is dependent on the initial hypotheses.     

Luminescence of a semiconductor quantum dot system

A microscopic theory is used to study photoluminescence of semiconductor quantum dots under the influence of Coulomb and carrier-photon correlation effects beyond the Hartree-Fock level. We investigate the emission spectrum and the decay properties of the time-resolved luminescence from initially excited quantum dots. The influence of the correlations is included within a cluster expansion scheme up to the singlet-doublet level.     

Numerical study of influence of different parameters on mixing in a coaxial jet mixer using LES

We present a comparative numerical study about the overall mixing process in a coaxial jet mixer. The two-stream mixing problem was investigated in non-reacting single phase gas and liquid mixtures using Large-Eddy Simulations with wall functions and subgrid scale models from eddy viscosity concepts. The influence of different parameters like Reynolds number, Schmidt number, Prandtl number, density ratio and flow rate ratio on the overall mixing process was investigated. Additionally two methods of control of mixing are shown to have a significant effect on the overall mixing in a coaxial jet mixer.     

Strong field electron emission from fixed in space H(2)(+) ions

We have studied electron emission from the H(2)(+) ion by a circularly polarized laser pulse (800 nm, 6×10(14) W/cm(2)). The electron momentum distribution in the body fixed frame of the molecule is experimentally obtained by a coincident detection of electrons and protons. The data are compared to a solution of the time-dependent Schr?dinger equation in two dimensions. We find radial and angular distributions which are at odds with the quasistatic enhanced ionization model. The unexpected momentum distribution is traced back to a complex laser-driven electron dynamics inside the molecule influencing the instant of ionization and the initial momentum of the electron.     

Synthesis of Diacetylene‐Containing Peptide Building Blocks and Amphiphiles,Their Self‐Assembly and Topochemical Polymerization in Organic Solvents

A series of functional iodoacetylenes was prepared and converted into the corresponding diacetylene‐substituted amino acids and peptides via Pd/Cu‐promoted sp–sp carbon cross‐coupling reactions. The unsymmetrically substituted diacetylenes can be incorporated into oligopeptides without a change in the oligopeptide strand's directionality. Thus, a series of oligopeptide‐based, amphiphilic diacetylene model compounds was synthesized, and their self‐organization as well as their UV‐induced topochemical polymerizability was investigated in comparison to related polymer‐substituted macromonomers. Solution‐phase IR spectroscopy, gelation experiments, and UV spectroscopy helped to confirm that a minimum of five N‐H???O?C hydrogen‐bonding sites was required in order to obtain reliable aggregation into stable β‐sheet‐type secondary structures in organic solvents. Furthermore, the non‐equidistant spacing of these hydrogen‐bonding sites was proven to invariably lead to β‐sheets with a parallel β‐strand orientation, and the characteristic IR‐spectroscopic signatures of the latter in organic solution was identified. Scanning force micrographs of the organogels revealed that compounds with six hydrogen‐bonding sites gave rise to high aspect ratio nanoscopic fibrils with helical superstructures but, in contrast to the related macromonomers, did not lead to uniform supramolecular polymers. The UV‐induced topochemical polymerization within the β‐sheet aggregates was successful, proving parallel β‐strand orientation and highlighting the effect of the number and pattern of N‐H???O?C hydrogen‐bonding sites as well as the hydrophobic residue in the molecular structure on the formation of higher structures and reactivity.     

Differences in the fatty acid composition of KB-cells and gingival keratinocytes is culture medium additive dependent

The influence of culture medium additives foetal bovine serum (FBS), serum effective substitutes (SES) and human autologous serum on the fatty acid profile of KB-cells and human gingival keratinocytes was examined. The KB-cells were cultivated in RPMI medium added with FBS or SES and the gingival keratinocytes in D-MEM added with FBS or human autologous serum. Two days before the cells were prepared for gas chromatography (GC), the media were changed to serum- and antibiotic-free media. Whole fatty acids of the cells were analysed using GC and the fatty acid profiles were compared. KB-cells as well as gingival keratinocytes changed their fatty acid composition, according to the medium additive used. Significant differences were observed. In the case of KB-cells cultivated with SES the fatty acid changes suggest an increase of the membrane fluidity. Corresponding and significant differences were observed with gingival keratinocytes cultivated in medium added with human autologous serum: the membrane fluidity of the gingival keratinocytes was increased. It is supposed that an increased membrane fluidity caused by a different fatty acid spectrum of the host cell may relate to mechanisms of bacterial adhesion. Consequently, in vitro studies on invasion and adhesion of bacteria or virus are dependent on the medium used. Further analyses are necessary of the functional effects caused by differences in the content of specific FAs, especially with regard to the application of cultivated cells in the field of tissue engineering.