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The electron effective mass, me, has been determined by magnetophotoluminescence in as-grown and hydrogenated Ga As1-x Nx samples for a wide range of nitrogen concentrations (from x

The effective gyromagnetic factor of electrons, ge*, has been determined by Zeeman splitting measurements in a large number of Ga As1-x Nx GaAs (x

GaN x As 1-x and Ga 1-y In y N x As 1-x are the most prominent members of a novel class of non-amalgamation type semiconductor alloys where a fraction x of the anions of the host (e.g., GaAs or Ga 1-y In y As) is replaced by N isovalent impurity atoms. The localized N-states in GaN x As 1-x and Ga 1-y In y N x As 1-x form a series of discrete energy levels (e.g., isolated N-state, N-pairs and higher order N-cluster states) resonant with the conduction band of the host. The effect of the alloying with nitrogen on the bandstructure of GaN x As 1-x and Ga 1-y In y N x As 1-x can be well parameterized using a band-anticrossing (BAC) model, namely, assuming a level repulsion between an effective N-state and the conduction band-edge state. The dependence of several physical properties on nitrogen incorporation can be predicted qualitatively in the framework of this model, e.g., a tremendous increase of the electron effective mass in GaN x As x with increasing x, a huge cross section for scattering of electrons by N impurities in electronic transport, etc. Most of these predictions can be tested and verified by performing hydrostatic pressure experiments which, within the picture of the BAC model, allow one to tune continuously the energy difference between the host-like conduction band edge and the effective N-level within one and the same specimen. Several examples of this kind will be discussed. Furthermore, we will demonstrate the limitations of the BAC model in the case of GaN x P 1-x and also of GaN x As 1-x . In particular, we will show several examples where the description by a single effective N-state fails and that the multiplicity of the N-states needs to be taken into account. Again hydrostatic pressure experiments prove to be a useful and suitable tool for revealing the effects due to N-cluster states.

The project FULLSPECTRUM - an Integrated Project (IP) in the terminology of the European Commission - pursues a better exploitation of the FULL solar SPECTRUM by (1) further developing concepts already scientifically proven but not yet developed and (2) by trying to prove new ones in the search for a breakthrough in photovoltaic (PV) technology. More specific objectives are the development of. (a) III-V multijunction cells (MJC), (b) solar thermo-photovoltaic (TPV) converters, (c) intermediate band (IB) materials and cells (IBC), (d) molecular-based concepts (MBC) for full PV utilisation of the solar spectrum and (e) manufacturing technologies (MFG) for novel concepts including assembling. MJC technology towards 40% efficiency will be developed using lower cost substrates and high light concentration (up or above 1000 suns). TPV is a concept with a theoretically high efficiency limit because the entire energy of all the photons is used in the heating process and because the non-used photons can be fed back to the emitter, therefore helping in keeping it hot. In the IBC approach, sub-bandgap photons are exploited by means of an IB. Specific IB materials will be sought by direct synthesis suggested by material-band calculations and using nanotechnology in quantum dot (QD) IBCs. In the development of the MBC, topics such as the development of two-photon dye cells and the development of a static global (direct and diffuse) light concentrator by means of luminescent multicolour dyes and QDs, with the radiation confined by photonic crystals, will be particularly addressed. MFG include optoelectronic assembling techniques and coupling of light to cells with new-optic miniconcentrators. (c) 2004 Elsevier B.V. All rights reserved. 87 1-4 467 479 PT: J CT: International Conference on Physics, Chemistry and Engineering of Solar Cells CY: MAY 13-15, 2004 CL: Univ Extremadura, Sch Ind Engn, Badajoz, SPAIN TC: 30 J9: SOL ENERG MAT SOL C SI: SI

Using RNA arbitrarily primed PCR, the authors selected for transcripts with cell cycle-related differential expression in cultured human melanocytes. Among the partial cDNAs cloned, a novel cDNA was identified, which showed 54% identity to the recently cloned cDNA of the retinoblastoma binding protein-2 (RBP2). The 6.5-kB full-length cDNA of this RBP2-related gene, termed RBP2 homolog 1 (RBP2-H1), was obtained from a human teratocarcinoma cDNA library. Two independent libraries from human malignant melanomas were negative. A computerized sequence analysis revealed highly conserved motifs with possible functional meaning: two domains that, in the RBP2 homolog, mediate the binding and interaction with the proteins encoded by the retinoblastoma susceptibility gene, the TATA-binding protein, and the oncoprotein rhombotin 2; in addition, two DNA-binding zinc finger/leukemia-associated protein motifs were detected. Because a functional role in cell-cycle control and transcriptional activation can be envisioned, we investigated the expression of this novel transcript in normal fetal and adult tissues, as well as tissues of benign and malignant melanocytic tumors. By conducting multiple Northern blot, RT-PCR, and in situ hybridization analyses, the authors showed that the corresponding mRNA is expressed in virtually all normal tissues. Accordingly, they found RBP2-H1 expression in microdissected tissue samples from benign melanocytic nevi (n = 10). In contrast, the transcript is significantly down-regulated or even lost in tissue samples from human malignant melanomas (n = 13), melanoma metastases (n = 10), and melanoma cell lines (n = 7). The authors concluded that the loss or down-regulation of RBP2-H1 expression could be a useful molecular marker for a transformed phenotype in the human melanocytic system.

The Lerks, ligands of eph-related receptor tyrosine kinases, are a rapidly expanding family of genes thought to play an important role in the development and oncogenesis of various tissues. However, very little experimental evidence supports this hypothesis. Using RNA fingerprinting, we detected increased expression of Lerk-5 mRNA in human melanocytes as a response to the tumor-promoting drug 12-O-tetradecanoylphorbol-13-acetate, which suggests a possible role of the Lerks in melanoma tumorigenesis and progression. Therefore, we studied Lerk-5 mRNA expression in various melanoma cell lines and tissues of melanocytic tumors by semiquantitative reverse transcription-PCR. Modest expression of Lerk-5 mRNA was found in two melanoma cell lines derived from early primary tumors (WM35 and WM1645B); two metastatic cell lines tested showed a 3.9-fold increased transcript abundance when compared to the primary cell lines (RPMI-7951 and SK-Mel5). Progeny of a melanoma cell line with very low Lerk-5 mRNA abundance (WM35) showed a 5-fold increase in Lerk-5 mRNA expression when it was selected for higher tumorigenicity and multicytokine resistance by passaging in nude mice or repeated high-dose UVB irradiation. Consistent with these experimental data, we found high levels of Lerk-5 mRNA expression in advanced primary malignant melanomas and metastases (n = 22) but significantly lower or undetectable mRNA expression in benign melanocytic nevi (n = 9; P0.001). We conclude that increased Lerk-5 expression possibly reflects or induces an increased potential of growth, tumorigenicity, and metastatic abilities in human melanomas. This makes the yet to be elucidated eph-related receptor tyrosine kinase/Lerk signaling system a potential new source for molecular markers as well as a target for new therapies.

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