Direct-gap gain up to 850 cm(-1) at 0.74 eV is measured and modeled in optically pumped Ge-on-Si layers for photoexcited carrier densities of 2.0 × 10(20) cm(-3). The gain spectra are correlated to carrier density via plasma-frequency determinations from reflection spectra. Despite significant gain, optical amplification cannot take place, because the carriers also generate pump-induced absorption of ≈7000 cm(-1). Parallel studies of III-V direct-gap InGaAs layers validate our spectroscopy and modeling. Our self-consistent results contradict current explanations of lasing in Ge-on-Si cavities.
The reproductive cycle of female mosquitoes is activated by ingestion of blood from vertebrate hosts. Shortly after feeding, neurohormones are released from the brain neurosecretory system and stimulate the ovaries to secrete ecdysteroids, which are necessary for vitellogenesis by the fat body. Because bombyxins, which are insulin-like peptides, stimulate ecdysteriodgenesis in silkworm larvae, we tested porcine insulin and found that it activates ecdysteroidogenesis and protein synthesis in ovaries isolated from unfed mosquitoes. To further characterize the regulation of ecdysteroidogenesis in female mosquitoes, we cloned the mosquito insulin receptor (MIR) homologue from ovarian mRNA. The sequence of the extracellular domain shows moderate homologies with vertebrate and Drosophila insulin receptor homologues, as well as with the insulin receptor-related receptor, the latter being an "orphan" receptor with an unknown function. In the intracellular domain, high homologies are observed, particularly in those subdomains that are responsible for ATP binding and kinase activity. Northern blot analysis of MIR demonstrated a highly specific expression in ovaries, and cloning experiments indicated its presence in the brain. Recombinant MIR extracts from a baculovirus expression system contained high constitutive kinase activity in the presence of manganese or magnesium. Activation was independent of a ligand. SDS-gel analysis suggested that the recombinant receptor was not post-translationally processed into an alpha- and beta-subunit as was expected from a putative cleavage signal. Enzymatic properties of the proreceptor are presented: the Km for ATP was between 15 and 50 microM in the presence of a synthetic substrate: maximal kinase activity to 100-fold over basic activity was reached in the presence of 1 mM manganese. Stimulation of key oogenic processes by porcine insulin and identification of a MIR indicate that insulin-like neurohormones may have an important regulatory role in mosquito oogenesis.
Functional microarrays are powerful tools that allow the parallel detection of multiple strains at the species level and therefore to rapidly obtain information on microbial communities in the environment. However, the design of suitable probes is prone to uncertainties, as it is based so far on in silico predictions including weighted mismatch number and Gibbs free-energy values. This study describes the experimental selection of probes targeting subsequences of the nifH gene to study the community structure of diazotrophic populations present in Damma glacier (Swiss Central Alps) forefield soils. Using the Geniom One in situ synthesis technology (Febit, Germany), 2727 in silico designed candidate probes were tested. A total of 946 specific probes were selected and validated. This probe set covered a large diversity of the NifH phylotypes (35 out of the 45) found in the forefield. Hybridization predictors were tested statistically. Gibbs free-energy value for probe-target binding gave the best prediction for hybridization efficiency, while the weighted mismatch number was not significantly associated to probe specificity. In this study, we demonstrate that extensive experimental tests of probe-hybridization behaviour against sequences present in the studied environment remain a prerequisite for meaningful probe selection.
Glacier forefield environments are exposed to extreme and fluctuating climatic and nutritional conditions. The high diversity of free-living diazotrophic communities found in these environments indicates that nitrogen fixers are able to efficiently cope with such conditions. In this study, a nifH microarray was used to monitor changes in diazotrophic populations in the field over a season, in the presence or absence of plants and in 2 glacier forefields characterized by a different bedrock type (siliceous or calcareous), as well as at different temperatures (10 °C, 15 °C) and under different nitrogen fertilization regimes (0, 10, 40 kg N·ha(-1)·year(-1)) in laboratory systems. Population structures responded highly dynamically to environmental changes. Plant presence had the strongest impact, which decreased toward the end of the season and with high amounts of nitrogen fertilization. Temperature and nitrogen fertilization increases indirectly affected diazotrophic communities through their positive impact on plant growth. These results indicate strong carbon limitation in young glacier forefield soils. Phylotypes related to the genus Methylocystis strongly responded to environmental variations. These methanotrophic microorganisms, which are able to retrieve nitrogen and carbon from the atmospheric pool, are particularly adapted to the extreme nutritional conditions found in glacier forefields.
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