Multiple Wavelength InGaAs Quantum Dot Lasers Using Ion Implantation Induced Intermixing

We demonstrate multiple wavelength InGaAs quantum dot lasers using ion implantation induced intermixing. Proton implantation, followed by annealing is used to create differential interdiffusion in the active region of the devices. The characteristics (lasing-spectra, threshold currents and slope efficiencies) of the multi-wavelength devices are compared to those of as-grown devices and the differences are explained in terms of altered energy level spacing in the annealed quantum dots

Consequences of Eukaryotic Enhancer Architecture for Gene Expression Dynamics, Development, and Fitness

The regulatory logic of time- and tissue-specific gene expression has mostly been dissected in the context of the smallest DNA fragments that, when isolated, recapitulate native expression in reporter assays. It is not known if the genomic sequences surrounding such fragments, often evolutionarily conserved, have any biological function or not. Using an enhancer of the even-skipped gene of Drosophila as a model, we investigate the functional significance of the genomic sequences surrounding empirically identified enhancers. A 480 bp long “minimal stripe element” is able to drive even-skipped expression in the second of seven stripes but is embedded in a larger region of 800 bp containing evolutionarily conserved binding sites for required transcription factors. To assess the overall fitness contribution made by these binding sites in the native genomic context, we employed a gene-replacement strategy in which whole-locus transgenes, capable of rescuing even-skipped- lethality to adulthood, were substituted for the native gene. The molecular phenotypes were characterized by tagging Even-skipped with a fluorescent protein and monitoring gene expression dynamics in living embryos. We used recombineering to excise the sequences surrounding the minimal enhancer and site-specific transgenesis to create co-isogenic strains differing only in their stripe 2 sequences. Remarkably, the flanking sequences were dispensable for viability, proving the sufficiency of the minimal element for biological function under normal conditions. These sequences are required for robustness to genetic and environmental perturbation instead. The mutant enhancers had measurable sex- and dose-dependent effects on viability. At the molecular level, the mutants showed a destabilization of stripe placement and improper activation of downstream genes. Finally, we demonstrate through live measurements that the peripheral sequences are required for temperature compensation. These results imply that seemingly redundant regulatory sequences beyond the minimal enhancer are necessary for robust gene expression and that “robustness” itself must be an evolved characteristic of the wild-type enhancer

Mathematics and biology: a Kantian view on the history of pattern formation theory

Driesch’s statement, made around 1900, that the physics and chemistry of his day were unable to explain self-regulation during embryogenesis was correct and could be extended until the year 1972. The emergence of theories of self-organisation required progress in several areas including chemistry, physics, computing and cybernetics. Two parallel lines of development can be distinguished which both culminated in the early 1970s. Firstly, physicochemical theories of self-organisation arose from theoretical (Lotka 1910–1920) and experimental work (Bray 1920; Belousov 1951) on chemical oscillations. However, this research area gained broader acceptance only after thermodynamics was extended to systems far from equilibrium (1922–1967) and the mechanism of the prime example for a chemical oscillator, the Belousov–Zhabotinski reaction, was deciphered in the early 1970s. Secondly, biological theories of self-organisation were rooted in the intellectual environment of artificial intelligence and cybernetics. Turing wrote his The chemical basis of morphogenesis (1952) after working on the construction of one of the first electronic computers. Likewise, Gierer and Meinhardt’s theory of local activation and lateral inhibition (1972) was influenced by ideas from cybernetics. The Gierer–Meinhardt theory provided an explanation for the first time of both spontaneous formation of spatial order and of self-regulation that proved to be extremely successful in elucidating a wide range of patterning processes. With the advent of developmental genetics in the 1980s, detailed molecular and functional data became available for complex developmental processes, allowing a new generation of data-driven theoretical approaches. Three examples of such approaches will be discussed. The successes and limitations of mathematical pattern formation theory throughout its history suggest a picture of the organism, which has structural similarity to views of the organic world held by the philosopher Immanuel Kant at the end of the eighteenth century

Interaction of Excitons Bound to 3d Transition Metal Ions with Lattice Vibrations in II-VI Semiconductors

The analysis of an interaction of bound excitons with lattice vibrations for ZnO:Ni and ZnO:Cu is given on the basis of symmetry consideration

Fe2+\text{}^{2+} → Fe3+\text{}^{3+} Ionization Transition in ZnSe

Detailed photo-ESR study of iron and chromium impurities in ZnSe is presented. The energy level position of Fe$\text{}^{2+}\text{}^{/}\text{}^{3+}$ energy level is determined. The role of iron and chromium impurities in nonradiative recombination processes is discussed

Electronic Structure of ZnS:Co Semiconductors: X-ray and Optical Spectroscopy Studies

Experimental studies of X-ray photoelectron and Co L$\text{}_{α}$ X-ray emission spectra of the ZnS:Co semiconductor were carried out. It was established that Co ions are in a Co$\text{}^{2+}$ configuration and that the Co 3d impurity states are localized above the top of the valence band by 1.0±0.2 eV

Electronic Structure of ZnS:Co Semiconductors: X-ray and Optical Spectroscopy Studies

Experimental studies of X-ray photoelectron and Co L$\text{}_{α}$ X-ray emission spectra of the ZnS:Co semiconductor were carried out. It was established that Co ions are in a Co$\text{}^{2+}$ configuration and that the Co 3d impurity states are localized above the top of the valence band by 1.0±0.2 eV

Transition Metal Impurities and Electronic Structure of ZnSe-Based Isovalent Semiconductor Alloys

Energy level positions of the nickel 2+/1+ and cobalt 2+/3+ charge states have been used to estimate band edges for the valence and conduction bands of ZnSe-based alloys with cation (ZnCdSe) and anion (ZnSSe) substitution. Chemical trends in band offsets of heterostructures of Zn- or Mn-based II-VI compounds are analysed. Further on, the change of Ni$\text{}^{2+}$(3d$\text{}^{8}$) and Co$\text{}^{2+}$(3d$\text{}^{7}$) intra-d shell transition bands upon the alloying of host material is discussed

Excitonic Spectra of Cd1−x\text{}_{1-x}Fex\text{}_{x}Te Crystals

Strong modification of the optical spectra near the band-gap edge is observed in Cd$\text{}_{1-x}$Fe$\text{}_{x}$Te crystals as compared to the spectra of a pure compound. The evolution of the luminescence spectra at the increase in Fe concentration is represented by the change of radiative recombination channels from dominantly (A$\text{}^{0}$, x) acceptor bound exciton emission in undoped CdTe to the free exciton luminescence in Cd$\text{}_{1-x}$Fe$\text{}_{x}$Te solid solutions

Photo-ESR Studies of Ni doped ZnS and ZnSe

The results of electron spin resonance experiments are presented for nickel doped ZnS and ZnSe. Energy level position of Ni$\text{}^{1+}$ state in band gap of ZnS and ZnSe is determined. The nonradiative recombination processes of donor-acceptor pairs in Ni doped samples are discussed