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  • 1
    Electronic Resource
    Electronic Resource
    Coupled LO–plasmon modes in semi-insulating GaAs of ZnSe/GaAs heterojunctions (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1128-1135 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman spectroscopy is used to investigate strong band bending at the interface in semi-insulating substrates of ZnSe/GaAs heterostructures grown at high epitaxy rates. Direct evidence is given of the enhancement of polar modes strength, on the substrate side, by the electric field of the space-charge zone associated with Fermi-level pinning. The latter is qualitatively analyzed by following band flattening under illumination through the evolution of interfacial coupled LO-phonon–plasmon modes. Corresponding Raman line shapes are discussed within the phenomenological approach of D. H. Hon and W. L. Faust [Appl. Phys. 1, 241 (1973)]. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362850
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  • 2
    Electronic Resource
    Electronic Resource
    Raman study of band bending at ZnSe/GaAs interfaces (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1241-1248 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Apparent p-type conductivity in nonintentionally doped ZnSe layers, grown at high temperature on semi-insulating GaAs substrates, is investigated by Raman spectroscopy. The microprobe technique provides direct evidence for carrier location on the GaAs side of the structures, close to the interface. Line-shape analysis of the coupled LO phonon-plasmon mode for different exciting wavelengths can be achieved, within the model of Hon and Faust [Appl. Phys. 1, 241 (1973)], only when incorporating plasma inhomogeneity. Electronic band bending at the junction in GaAs is deduced from the inferred carrier-density profile. Changes in Raman spectra under strong illumination are shown to proceed from the flattening of the bands through selective carrier photoinjection. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358925
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  • 3
    Electronic Resource
    Electronic Resource
    Comment on "Observation of phonon-plasmon coupled modes at the interface between ZnSe and semi-insulating GaAs by Raman spectroscopy'' [Appl. Phys. Lett. 62, 1800 (1993)] (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 3236-3237 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110209
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  • 4
    Electronic Resource
    Electronic Resource
    Raman study of ZnxBe1−xSe alloy (100) epitaxial layers (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 519-521 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Long wavelength longitudinal optical (LO) and transverse optical (TO) phonons of BeSe and ZnxBe1−xSe layers are identified in a wide composition range by using Raman spectroscopy. A two-mode behavior is clearly evidenced. As predicted by the dielectric model of Hon and Faust, the eigenfrequencies of the BeSe- and ZnSe-like LO modes correspond to the maxima of Im〈−cursive-epsilon(ω, x)−1〉. Excellent agreement is obtained with a model where the calculations are performed by using the equations of motion and polarization derived from the modified random element isodisplacement model. Besides, the TO and LO frequencies for BeSe are determined to be 501 and 579 cm−1, respectively. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.127030
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  • 5
    Electronic Resource
    Electronic Resource
    Percolation behavior in the Raman spectra of ZnBeTe alloy (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 3081-3083 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Zone-center longitudinal (LO) and transverse (TO) optical phonons of Zn1−xBexTe epilayers are identified by Raman spectroscopy. On top of the expected BeTe- and ZnTe-like modes, which obey the modified-random-element-isodisplacement model, we observe an extra BeTe-like (TO, LO) doublet at intermediate x values. It has the same atypical characteristics as its BeSe-like counterpart in ZnBeSe alloy. Its activation validates our percolative picture for multimode description in Be–chalcogenide alloys that open the attractive class of mixed crystals with a sharp contrast in the bond stiffness. Also, the local modes of Be in ZnTe and of Zn in BeTe are identified at 411 cm−1 and 195 cm−1, respectively. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1467711
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  • 6
    Electronic Resource
    Electronic Resource
    Inhomogeneous electric field-induced Raman scattering at ZnSe/GaAs interfaces (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 2371-2376 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The activation of inhomogeneous electric field-induced Raman scattering (IEFIRS) at ZnSe/GaAs interfaces is investigated. The consideration of the inhomogeneous character of the electric field brings additional conditions on top of those predicted by the microscopic and perturbative approaches. These conditions concern the relative orientations of (i) the wave vector of the vibrational modes in the matter, (ii) the direction of the electric field at the junction, and (iii) the gradient vector of the electric field magnitude in the space charge regions. As latter vector has opposite directions in the layer and the substrate, IEFIRS is only observed from one side of the junction for a given scattering geometry. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369552
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  • 7
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    Monitoring bypass of single replication-blocking lesions by damage avoidance in the Escherichia coli chromosome (2012)
    Oxford University Press
    Details
    Publication Date: 2012-10-10
    Description: Although most deoxyribonucleic acid (DNA) lesions are accurately repaired before replication, replication across unrepaired lesions is the main source of point mutations. The lesion tolerance processes, which allow damaged DNA to be replicated, entail two branches, error-prone translesion synthesis (TLS) and error-free damage avoidance (DA). While TLS pathways are reasonably well established, DA pathways are poorly understood. The fate of a replication-blocking lesion is generally explored by means of plasmid-based assays. Although such assays represent efficient tools to analyse TLS, we show here that plasmid-borne lesions are inappropriate models to study DA pathways due to extensive replication fork uncoupling. This observation prompted us to develop a method to graft, site-specifically, a single lesion in the genome of a living cell. With this novel assay, we show that in Escherichia coli DA events massively outweigh TLS events and that in contrast to plasmid, chromosome-borne lesions partially require RecA for tolerance.
    Keywords: Repair, Replication
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
    Published by Oxford University Press
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  • 8
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    A defect in homologous recombination leads to increased translesion synthesis in E. coli (2016)
    Oxford University Press
    Details
    Publication Date: 2016-09-20
    Description: DNA damage tolerance pathways allow cells to duplicate their genomes despite the presence of replication blocking lesions. Cells possess two major tolerance strategies, namely translesion synthesis (TLS) and homology directed gap repair (HDGR). TLS pathways involve specialized DNA polymerases that are able to synthesize past DNA lesions with an intrinsic risk of causing point mutations. In contrast, HDGR pathways are essentially error-free as they rely on the recovery of missing information from the sister chromatid by RecA-mediated homologous recombination. We have investigated the genetic control of pathway choice between TLS and HDGR in vivo in Escherichia coli . In a strain with wild type RecA activity, the extent of TLS across replication blocking lesions is generally low while HDGR is used extensively. Interestingly, recA alleles that are partially impaired in D-loop formation confer a decrease in HDGR and a concomitant increase in TLS. Thus, partial defect of RecA's capacity to invade the homologous sister chromatid increases the lifetime of the ssDNA.RecA filament, i.e. the ‘SOS signal’. This increase favors TLS by increasing both the TLS polymerase concentration and the lifetime of the TLS substrate, before it becomes sequestered by homologous recombination. In conclusion, the pathway choice between error-prone TLS and error-free HDGR is controlled by the efficiency of homologous recombination.
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
    Published by Oxford University Press
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  • 9
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    Effect of low-frequency KRAS mutations on the response to anti-EGFR therapy in metastatic colorectal cancer (2013)
    Oxford University Press
    Details
    Publication Date: 2013-04-19
    Description: Background Only patients with wild-type (WT) KRAS tumors benefit from anti-epidermal growth factor receptor (EGFR) monoclonal antibodies (Mabs) in metastatic colorectal cancer (mCRC). Pyrosequencing is now widely used for the determination of KRAS mutation burden and a conservative cut-off point of 10% has been defined. Up until now, the impact of low-frequency KRAS mutations (〈10%) on the response to anti-EGFR Mabs has yet to be evaluated. Patients and methods Tumors from patients receiving anti-EGFR Mabs based on a WT genotype for KRAS , as determined using direct sequencing, have been retrospectively analyzed by pyrosequencing. Patients were categorized as WT (no KRAS mutation) or low-frequency mutation when KRAS mutation was 〈10% ( KRAS low MT). Results A total of 168 patients treated by anti-EGFR Mabs for mCRC were analyzed. According to pyrosequencing, 138 tumors remained KRAS WT, while 30 tumors were KRAS low MT. In the KRAS low MT and KRAS WT groups, the response rates were 6.7% and 37.0%, respectively, while stabilization amounted to 23.3% versus 32.6% and progression to 70% versus 29% ( P 〈 0.01). Progression-free survival (PFS) was 2.7 ± 0.5 months for KRAS low MT and was 6.0 ± 0.3 months for KRAS WT ( P 〈 0.01). Conclusions These results appear to validate consideration of low-frequency KRAS mutation tumors as positive, and justify a large-scale prospective study.
    Print ISSN: 0923-7534
    Electronic ISSN: 1569-8041
    Topics: Medicine
    Published by Oxford University Press
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  • 10
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    Attenuated Virulence and Genomic Reductive Evolution in the Entomopathogenic Bacterial Symbiont Species, Xenorhabdus poinarii (2014)
    Oxford University Press
    Details
    Publication Date: 2014-06-29
    Description: Bacteria of the genus Xenorhabdus are symbionts of soil entomopathogenic nematodes of the genus Steinernema . This symbiotic association constitutes an insecticidal complex active against a wide range of insect pests. Unlike other Xenorhabdus species, Xenorhabdus poinarii is avirulent when injected into insects in the absence of its nematode host. We sequenced the genome of the X. poinarii strain G6 and the closely related but virulent X. doucetiae strain FRM16. G6 had a smaller genome (500–700 kb smaller) than virulent Xenorhabdus strains and lacked genes encoding potential virulence factors (hemolysins, type 5 secretion systems, enzymes involved in the synthesis of secondary metabolites, and toxin–antitoxin systems). The genomes of all the X. poinarii strains analyzed here had a similar small size. We did not observe the accumulation of pseudogenes, insertion sequences or decrease in coding density usually seen as a sign of genomic erosion driven by genetic drift in host-adapted bacteria. Instead, genome reduction of X. poinarii seems to have been mediated by the excision of genomic blocks from the flexible genome, as reported for the genomes of attenuated free pathogenic bacteria and some facultative mutualistic bacteria growing exclusively within hosts. This evolutionary pathway probably reflects the adaptation of X. poinarii to specific host.
    Electronic ISSN: 1759-6653
    Topics: Biology
    Published by Oxford University Press
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