Application of GaN-based ultraviolet-C light emitting diodes--UV LEDs--for water disinfection.

GaN-based ultraviolet-C (UV-C) light emitting diodes (LEDs) are of great interest for water disinfection. They offer significant advantages compared to conventional mercury lamps due to their compact form factor, low power requirements, high efficiency, non-toxicity, and overall robustness. However, despite the significant progress in the performance of semiconductor based UV LEDs that has been achieved in recent years, these devices still suffer from low emission power and relatively short lifetimes. Even the best UV LEDs exhibit external quantum efficiencies of only 1-2%. The objective of this study was to investigate the suitability of GaN-based UV LEDs for water disinfection. The investigation included the evaluation of the performance characteristics of UV LEDs at different operating conditions as well as the design of a UV LED module in view of the requirements for water treatment applications. Bioanalytical testing was conducted using Bacillus subtilis spores as test organism and UV LED modules with emission wavelengths of 269 nm and 282 nm. The results demonstrate the functionality of the developed UV LED disinfection modules. GaN-based UV LEDs effectively inactivated B. subtilis spores during static and flow-through tests applying varying water qualities. The 269 nm LEDs reached a higher level of inactivation than the 282 nm LEDs for the same applied fluence. The lower inactivation achieved by the 282 nm LEDs was compensated by their higher photon flux. First flow-through tests indicate a linear correlation between inactivation and fluence, demonstrating a well designed flow-through reactor. With improved light output and reduced costs, GaN-based UV LEDs can provide a promising alternative for decentralised and mobile water disinfection systems.

Structure investigations of nonpolar GaN layers.

The microstructure of nonpolar m-plane (1100) oriented GaN layers deposited on (100)gamma-LiAlO(2) was analysed by transmission electron microscopy. This study shows that the films contain a large number of defects. The most dominant defects in the m-plane GaN are intrinsic I(1) basal plane stacking faults (approximately 10(4) cm(-1)), threading dislocations (approximately 10(9) cm(-2)) as well as a complex defect network consisting of planar defects located on prismatic {1010} GaN and differently inclined pyramidal planes. A large number of the stacking faults nucleate at the GaN/LiAlO(2) interface. Furthermore, the inclined planar defects act as additional nucleation sites for the basal plane stacking faults. A decreasing crystal quality with an increasing layer thickness can be explained by this defect formation mechanism.

High-Q-preserving coupling between a spiral and a semicircle micro-cavity.

We present an efficient design for direct coupling between a spiral-shaped and a semicircle-shaped microcavity (micro-cavity) as an alternative to traditional evanescent wave coupling for planar integrated photonic technology. We observe the preservation of the high Q-value of the spiral oscillator when coupled to a semicircle under current injection using an AlGaAs single-quantum-well heterostructure. With slight alterations to the directly coupled micro-cavity configuration, such as coupling shape and overlap distance, the number of observed modes and output intensity are changed. AlGaAs and InGaN spiral-shaped microcavities have unidirectional emission normal to the spiral notch.

PCR detection of host and HIV-1 sequences from archival brain tissue.

Mutations in CCR5 and CCR2b have been recently shown to affect disease progression towards AIDS. A role for these host genotypes in AIDS dementia complex (ADC) has also been postulated but remains unclear. Additionally, brain-derived envelope sequences from HIV-1 have been associated with ADC but their specific contribution to pathogenesis remains uncertain. This study demonstrates the successful use of PCR techniques to isolate host CCR5 and CCR2b, and HIV-1 V3 sequences from paraffin embedded tissues from patients with and without ADC. PCR amplification from archival tissue offers a novel approach for studying the interactions between potential neuroprotective elements in the host and virulence determinants in HIV that may contribute to differences in susceptibility to ADC.

Identification, characterization and chromosomal localization of the cognate human and murine DBF4 genes.

The kinase Dbf4p/Cdc7p is required for the G1/S phase transition during the cell cycle and plays a direct role in the activation of individual origins of replication in Saccharomyces cerevisiae. Here, we report the identification and characterization of mouse and human cDNAs whose products are related in sequence to Saccharomyces cerevisiae DBF4 cDNA. Both mammalian Dbf4 proteins contain a putative site for phosphorylation by CDK, PEST protease cleavage sites, nuclear localization signals and a short-looped zinc finger-like domain. Transcription of MmDBF4 is suppressed in mouse NIH3T3 fibroblasts made quiescent by serum starvation. Upon replenishment of the medium, transcript levels increase during progression through G1, peaking as cells enter S phase. MmDbf4p interacts physically with Cdc7p and Mcm2p in vivo. Using fluorescence in situ hybridization (FISH), the human DBF4 gene was localized to chromosome 7 (q21.3), whereas FISH mapped the murine counterpart to band A2 on chromosome 5. The results of chromosome mapping indicate that in both mouse and human the gene is present as a single copy. The structural conservation between Dbf4-related proteins suggests that these proteins play a key role in the regulation of DNA replication during the cell cycle in all eukaryotes.

Human immunodeficiency virus infection, inducible nitric oxide synthase expression, and microglial activation: pathogenetic relationship to the acquired immunodeficiency syndrome dementia complex.

The regional expression of immune-mediated and neurotoxic events in the human immunodeficiency virus (HIV)-infected brain in relationship to the acquired immunodeficiency syndrome (AIDS) dementia complex (ADC) and brain pathology remains uncertain. The extent of gp41, inducible nitric oxide synthase (iNOS), and HLA-DR expression was examined in the frontal lobe and basal ganglia of 25 patients at varying stages of ADC. The expression of gp41 and iNOS was present predominantly in perivascular cells and most often in the basal ganglia. Staining for gp41 correlated significantly with iNOS in the basal ganglia, whereas the severity of staining for gp41 and iNOS in the basal ganglia and white matter was significantly greater in subjects with moderate to severe dementia compared with those with milder impairment. The degree of macrophage staining in the white matter and basal ganglia also correlated significantly with ADC severity and was more abundant than gp41 or iNOS staining, particularly in the white matter. Logistic regression analysis revealed that staining for iNOS and gp41 increased linearly with ADC severity and was significantly more abundant in the basal ganglia compared with the white matter. Double-immunolabeling studies colocalized iNOS predominantly to macrophage/microglia and to gp41-positive cells. The expression of iNOS and gp41 in the basal ganglia combined with immune activation contributes to the development and progression of the clinical syndrome.

Identification and characterization of MmORC4 and MmORC5, two subunits of the mouse origin of replication recognition complex.

Two new members of the mouse origin recognition complex (ORC) have been cloned that are closely related to Saccharomyces cerevisiae ORC4 and ORC5 as well as to their human homolog. Both MmORC4p and MmORC5p have a putative nucleotide triphosphate binding motif. Transcription of MmORC4 and MmORC5 is not suppressed in mouse NIH3T3 fibroblasts made quiescent by serum starvation. The transcription levels of both ORC genes are constantly high in all phases of the cell cycle. A screen based on the two-hybrid approach suggests that the product of the ORC4 gene interacts with the ORC2, but not with the ORC1 protein. The conservation of structure among members of the ORC4- and ORC5-related family of proteins suggests that these proteins play a key role in the initiation of DNA replication in all eukaryotes.

Separation of cis elements responsive to ethylene, fruit development, and ripening in the 5'-flanking region of the ripening-related E8 gene.

The E8 gene is expressed at a high level during fruit ripening, and is transcriptionally activated by ethylene. We have identified a 428 bp fragment of the E8 5'-flanking region, from -1528 to -1100, that makes a minimal 35S promoter responsive to ethylene. This fragment confers ethylene-responsiveness only in the 5'-to-3' orientation; in the reverse orientation it results in increased expression in unripe fruit. Interestingly, this ethylene-responsive construct does not have high levels of expression during fruit ripening, indicating that sequences required for high level expression during fruit ripening are separate from sequences required for ethylene response. The ethylene-responsive sequences of the E8 5'-flanking region interact with the same DNA-binding protein that interacts with sequences required for ethylene responsiveness of the coordinately regulated E4 gene. We also conducted experiments to test the function of a second DNA-binding protein that interacts with both E4 and E8 5'-flanking sequences, the E4/E8-binding protein (E4/E8BP). We examined the effect of an internal deletion from -1088 to -863, which includes the binding site for E4/E8BP, on gene expression. This deletion did not affect expression in ripening fruit, and did not impair ethylene responsiveness. The deletion had a negative effect on expression in unripe fruit, but resulted in increased expression in leaves. These results suggest that the E4/E8BP is not critical for high levels of expression during fruit ripening or for ethylene response, but may play a role in organ-specific gene transcription.

The Tomato E8 Gene Influences Ethylene Biosynthesis in Fruit but Not in Flowers.

We investigated the function of the tomato (Lycopersicon esculentum) E8 gene. Previous experiments in which antisense suppression of E8 was used suggested that the E8 protein has a negative effect on ethylene evolution in fruit. E8 is expressed in flowers as well as in fruit, and its expression is high in anthers. We introduced a cauliflower mosaic virus 35S-E8 gene into tomato plants and obtained plants with overexpression of E8 and plants in which E8 expression was suppressed due to co-suppression. Overexpression of E8 in unripe fruit did not affect the level of ethylene evolution during fruit ripening; however, reduction of E8 protein by cosuppression did lead to elevated levels during ripening. Levels for ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC), and ACC oxidase mRNA were increased approximately 7-fold in fruit of plants with reduced E8 protein. Levels of ACC synthase 2 mRNA were increased 2.5-fold, and ACC synthase 4 mRNA was not affected. Reduction of E8 protein in anthers did not affect the accumulation of ACC or of mRNAs encoding enzymes involved in ethylene biosynthesis. Our results suggest that the product of the E8 reaction participates in feedback regulation of ethylene biosynthesis during fruit ripening.

[Amaurosis fugax and obliteration of the carotid artery (author's transl)]. / Amaurosis fugax bei Obliterationen der A. carotis.

Obliterative processes of the carotid bifurcation can be a starting point for cerebral and especially retinal microemboli. Early diagnosis is essential in protecting such patients from a definitive insult, or a reduction of sight which can go as far as permanent blindness, whereas the amaurosis fugax being the most common ocular symptom of the internal carotid insufficiency. Due to the fact ca. 65%--75% of the patients with ocular symptoms of a carotid insufficiency show forms of amaurosis fugax or photopical sensations, this symptom complex, especially in combination with temporary contralateral hemiparalysis, has to be evaluated as a classical symptom of carotid stenosis until the contrary can be angiographically proven. Only during the last few years has it become apparent that these microemboli originate from ulcerous or verrucous beds of the carotid bifurcation. The discovery of the above connections was only made possible through the improvements in carotid angiography technique.