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A modification of the growth structure of Eu-doped GaN (GaN:Eu) from a monolayer to a multilayer structure (MLS) consisting of alternating GaN and GaN:Eu, was shown to enhance the emission properties. Similarly, lowering the growth temperature of the GaN:Eu to 960°C nearly doubled the photoluminescence emission intensity, and also enhanced device performance. Hence, to design a higher power GaN:Eu red LED, a multilayer structure consisting of 40 pairs of alternating GaN and GaN:Eu was grown at 960°C. This combination resulted in the fabrication of an LED with a maximum output power of 110 μW, which is 5.8 times more output power per GaN:Eu layer thickness as compared to the best previously reported device. Moreover, it was found that the MLS sample grown at 960°C maintained a high crystal quality with low surface roughness, which enabled an increase in the number of pairs from 40 pairs to 100 pairs. An MLS-LED consisting of 100 pairs of alternating GaN/GaN:Eu layers was successfully fabricated, and had a maximum output power of 375 μW with an external quantum efficiency of 4.6%. These are the highest values reported for this system.
In this review the naturally occurring β-carbolines norharman and harman in human beings and mammals will be discussed. These β-carbolines have been recognized as aromatic alkaloids, which can be detected in very low concentrations in human plasma. Norharman and especially harman display moderate affinity to the benzodiazepine receptor. The biosynthesis of these compounds in vivo, the localization, the biological effects and the probable involvement of these compounds in the cause of psychopathologic states will be discussed. This with a special focus on alcoholism, heroin addiction, psychosis and anxiety disorders. In some of these clinical pictures the concentration of norharman is increased. Whether this is a causality or a matter of minor importance is still unknown.
Norharman is a ß-carboline, possibly of endogenous origin, although cigarette smoking and food are sources too. In brain specific binding sites have been demonstrated. In higher doses norharman binds to benzodiazepine receptors and has MAO-B inhibitory activity. From animal experiments it can be concluded that norharman induces sedation and muscle relaxation. A role in psychosis is unclear, a role in the pathogenesis in anxiety is possible, but has to be further substantiated. As current research suggests, norharman may be an important factor in addiction and withdrawal.
We report on the status of the R&D for a digital Time Projection Chamber based on Micromegas detectors using the CMOS chip TimePix as a direct readout anode protected by highly resistive a-Si:H layer. A small chamber was built as a demonstrator of the 2-D and 3-D imaging capabilities of this technique. We illustrate the new capabilities of this detector for x-ray observation with data taken from radioactive sources. This small TPC is a very useful tool both for studying gas properties thanks to its good efficiency for single electrons, and for reconstructing photoelectron direction for use as a soft x-ray polarimeter.
The presentation and management of primary brain tumors has been one of the more frustrating experiences in oncology. While good outcomes are certainly possible, the intricacy of the affected organ and the poor tolerance of therapy often spell significant debilitation for patients, dramatically affecting quality of life. Unlike most cancers in the body where metastatic disease most frequently leads to patient death, primary brain tumors rarely metastasize. Still, malignant brain tumors are rarely cured due to limitations of effectiveness and tolerance of local therapies. Even benign tumors in the brain constitute a profound threat to both a patient's quality of life and survival. As such, management strategies for primary brain tumors must be equally sensitive to quality of life issues as survival since the therapy ultimately will often fail the patient for controlling the tumor.
There are four types of glial cells that give rise to a variety of brain tumors: astrocytes, oligodendrocytes, ependyma, and microglia. Tumors arising from astrocytes are called astrocytomas including pilocytic astrocytoma (grade I), fibrillary astrocytoma (grade II), anaplastic astrocytoma (grade III) and glioblastoma multiforme (GBM, grade IV). Oligodendrocytes give rise to oligodendrogliomas, which are usually low grade but can be anaplastic. Ependymomas occur in and around the ventricles, commonly in the fourth ventricle of the posterior fossa. Although ependymomas are only occasionally malignant, they are often infiltrative at the primary site and may disseminate through the cerebrospinal fluid (CSF).
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