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Increasing photosensitizer concentration has been considered as an effective approach to improve the performance of holographic material. In this paper, we report on new method for increasing the saturated dissolvability of photosensitizer PQ within polymeric media by introducing copolymerization monomer into the PQ/PMMA. The photosensitizer concentration of PQ was increased from 0.7wt% to 1.3wt%, compared with the typical PQ/PMMA sample. Besides, we investigated performance of polarization holographic recordings in typical PQ/PMMA and copolymerization monomer-containing PQ/PMMA with the orthogonally polarized signal and reference waves. And the doping of THFMA component resulted in a significant improvement of diffraction intensity and photosensitivity. In addition, high-quality holographic image reconstruction was realized in our home-made material.

Recurrence is frequently associated with the acquisition of radioresistance by tumors and resulting failures in radiotherapy. We report, in this study, that long-term fractionated radiation (FR) exposures conferred radioresistance to the human tumor cells, HepG2 and HeLa with cyclin D1 overexpression. A positive feedback loop was responsible for the cyclin D1 overexpression in which constitutively active AKT was involved. AKT is known to inactivate glycogen synthase kinase-3beta (GSK3beta), which is essential for the proteasomal degradation of cyclin D1. The resulting cyclin D1 overexpression led to the forced progression of S-phase with the induction of DNA double strand breaks. Cyclin D1-dependent DNA damage activated DNA-dependent protein kinase (DNA-PK), which in turn activated AKT and inactivated GSK3beta, thus completing a positive feedback loop of cyclin D1 overproduction. Cyclin D1 overexpression led to the activation of DNA damage response (DDR) consisted of ataxia telangiectasia mutated (ATM)- and Chk1-dependent DNA damage checkpoint and homologous recombination repair (HRR). Long-term FR cells repaired radiation-induced DNA damage faster than non-FR cells. Thus, acquired radioresistance of long-term FR cells was the result of alterations in DDR mediated by cyclin D1 overexpression. Inhibition of the AKT/GSK3beta/cyclin D1/Cdk4 pathway by the AKT inhibitor, Cdk4 inhibitor or cyclin D1 targeting small interfering RNA (siRNA) suppressed the radioresistance. Present observations give a mechanistic insight for acquired radioresistance of tumor cells by cyclin D1 overexpression, and provide novel therapeutic targets for recurrent radioresistant tumors.

Holographic reconstruction with polychromatic light was investigated in terms of the multiplexing capability in a volume holographic memory. The broadband spectrum of the probe beam considerably degrades the angular selectivity and causes a serious deterioration of the multiplexing capability, but this can be overcome if an additional suitable optical component is used in the imaging system. We could selectively detect the signal image alone even though the angular separation between holograms was insufficient to suppress the diffraction from other holograms. We theoretically derived the minimum angular separation for multiplexing and experimentally demonstrated the effectiveness of this selective detection method. 2010 Optical Society of America.

We succeeded to develop a reference light source in the range of very low luminance using a double integrating sphere system, and calibrated a commercial spectrophotometer below 1 × 10-5cd/m2 levels, which is 1/100 lower than the specified limit for measurement. And we improved measurements in the ultra low luminance range of displays using the calibrated commercial spectrophotometer and a dark sphere to suppress the influence of the surround.

The properties of a light-induced absorption and two-color recording were investigated in three kinds of Ru and Fe codoped LiNbO3 crystals with different Fe concentrations. A nonvolatile hologram could be recorded at a wavelength of 633 nm when blue light was simultaneously incident on the crystal. The characteristic feature of these crystals is a high persistence factor , i.e., small loss of the hologram strength at the beginning of the readout process. The sensitivity and the dynamic range increased with increasing Fe concentration, and a high sensitivity of 0.12 cm/J and a large dynamic range of 0.53 were obtained in a 0.5 mm-thick crystal. The recording model of the nonvolatile hologram is discussed from the results of light-induced absorption measurements. 2009 Elsevier B.V. All rights reserved.

We experimentally demonstrate engineerable compression of two-colored pulses in a linearly-chirped quasi-phase-matching grating. Quadratic solitons generated from fundamental input are reshaped through cascaded parametric processes of second-harmonic generation (SHG) and the back-conversion. We use type-I (e: o + o) SHG geometry in a 50-mm-long aperiodically-poled MgO:LiNbO 3 device to satisfy the group-velocity matching condition. Simultaneously compressed fundamental and SH pulses of about 55-fs duration with small pedestal are generated from the fundamental input pulses of 95-fs duration.

We studied the sorting of micro-scale objects by use of an optically induced asymmetric double-well potential. Migration events, driven by Brownian motion, were experimentally investigated for various particle sizes, inter-well distances, and optical intensities. Temporal evolution of the measured sorting efficiency qualitatively agreed well with theoretical predictions. We found that the sorting performance was improved by introducing temporal modulation on the potential landscape.

The biological functions of nuclear topoisomerase I (Top1) have been difficult to study because knocking out TOP1 is lethal in metazoans. To reveal the functions of human Top1, we have generated stable Top1 small interfering RNA (siRNA) cell lines from colon and breast carcinomas (HCT116-siTop1 and MCF-7-siTop1, respectively). In those clones, Top1 is reduced ∼5-fold and Top2α compensates for Top1 deficiency. A prominent feature of the siTop1 cells is genomic instability, with chromosomal aberrations and histone γ-H2AX foci associated with replication defects. siTop1 cells also show rDNA and nucleolar alterations and increased nuclear volume. Genome-wide transcription profiling revealed 55 genes with consistent changes in siTop1 cells. Among them, asparagine synthetase (ASNS) expression was reduced in siTop1 cells and in cells with transient Top1 down-regulation. Conversely, Top1 complementation increased ASNS, indicating a causal link between Top1 and ASNS expression. Correspondingly, pharmacologic profiling showed l-asparaginase hypersensitivity in the siTop1 cells. Resistance to camptothecin, indenoisoquinoline, aphidicolin, hydroxyurea, and staurosporine and hypersensitivity to etoposide and actinomycin D show that Top1, in addition to being the target of camptothecins, also regulates DNA replication, rDNA stability, and apoptosis. Overall, our studies show the pleiotropic nature of human Top1 activities. In addition to its classic DNA nicking-closing functions, Top1 plays critical nonclassic roles in genomic stability, gene-specific transcription, and response to various anticancer agents. The reported cell lines and approaches described in this article provide new tools to perform detailed functional analyses related to Top1 function. [Cancer Res 2007;67(18):8752–61]

The early stage embryogenesis of higher eukaryotes lacks some of the damage response pathways such as G1/S checkpoint, G2/M checkpoint and apoptosis. We examined here the damage response of preimplantation stage embryos after fertilization with 6 Gy irradiated sperm. Sperm-irradiated embryos developed normally for the first 2.5 days, but started to exhibit a developmental delay at day 3.5. p21 was activated in the delayed embryos, which carried numerous micronuclei owing to delayed chromosome instability. Apoptosis was observed predominantly in the inner cell mass of the day 4.0 embryos. Sperm-irradiated p21-/- embryos lacked the delay, but chromosome instability and apoptosis were more pronounced than the corresponding p21 wild-type embryos. We conclude from the result that damage responses come in a stage-specific manner during preimplantation stage development; p53-dependent S checkpoint at the zygote stage, p21-mediated cell cycle arrest at the morula/blastocyst stages and apoptosis after the blastocyst stage in the inner cell mass.

Summary Cells that suffer substantial inhibition of DNA replication halt their cell cycle via a checkpoint response mediated by the PI3 kinases ATM and ATR. It is unclear how cells cope with milder replication insults, which are under the threshold for ATM and ATR activation. A third PI3 kinase, DNA-dependent protein kinase (DNA-PK), is also activated following replication inhibition, but the role DNA-PK might play in response to perturbed replication is unclear since this kinase does not activate the signaling cascades involved in the S-phase checkpoint. Here we report that mild, transient drug-induced perturbation of DNA replication rapidly induced DNA breaks that promptly disappeared in cells that contained a functional DNA-PK whereas such breaks persisted in cells that were deficient in DNA-PK activity. After the initial transient burst of DNA breaks, cells with a functional DNA-PK did not halt replication and continued to synthesize DNA at a slow pace in the presence of replication inhibitors. In contrast, DNA-PK deficient cells subject to low levels of replication inhibition halted cell cycle progression via an ATR-mediated S-phase checkpoint. The ATM kinase was dispensable for the induction of the initial DNA breaks. These observations suggest that DNA-PK is involved in setting a high threshold for the ATR-Chk1-mediated S-phase checkpoint by promptly repairing DNA breaks that appear immediately following inhibition of DNA replication.

Within minutes of the induction of DNA double-strand breaks in somatic cells, histone H2AX becomes phosphorylated in the serine 139 residue at the damage site. The phosphorylated H2AX, designated as γ-H2AX, is visible as nuclear foci in the irradiated cells which are thought to serve as a platform for the assembly of proteins involved in checkpoint response and DNA repair. It is known that early stage mammalian embryos are highly sensitive to radiation but the mechanism of radiosensitivity is not well understood. Thus, we investigated the damage response of the preimplantation stage development by analyzing focus formation of γ-H2AX in mouse embryos γ-irradiatedin utero. Our analysis revealed that although H2AX is present in early preimplantation embryos, its phosphorylation after 3 Gy γ-irradiation is hindered up to the two cell stage of development. When leftin uterofor another 24–64 h, however, these irradiated embryos showed delayed phosphorylation of H2AX. In contrast, phosphorylation of H2AX was readily induced by radiation in post-compaction stage embryos. It is possible that phosphorylation of H2AX is inefficient in early stage embryos. It is also possible that the phosphorylated H2AX exists in the dispersed chromatin structure of early stage embryonic pronuclei, so that it cannot readily be detected by conventional immunostaining method. In either case, this phenomenon is likely to correlate with the lack of cell cycle arrest, apoptosis and high radiosensitivity of these developmental stages.

// Tsutomu Shimura 1 , Megumi Sasatani 2 , Kenji Kamiya 2 , Hidehiko Kawai 3 , Yohei Inaba 1 , Naoki Kunugita 1 1 Department of Environmental Health, National Institute of Public Health, Saitama, Japan 2 Department of Experimental Oncology, Research Institute for Radiation Biology and Medicine (RIRBM), Hiroshima University, Hiroshima, Japan 3 Department of Molecular Radiobiology, Research Center for Radiation Genome Medicine, Research Institute for Radiation Biology and Medicine (RIRBM), Hiroshima University, Hiroshima, Japan Correspondence to: Tsutomu Shimura, e-mail: tsimura@niph.go.jp Keywords: mitochondria, ROS, cyclin D1, low-dose radiation, AKT Received: August 20, 2015 Accepted: November 21, 2015 Published: December 09, 2015 ABSTRACT Here we investigated the cellular response of normal human fibroblasts to repeated exposure to low-dose radiation. In contrast to acute single radiation, low-dose fractionated radiation (FR) with 0.01 Gy/fraction or 0.05 Gy/fraction for 31 days increased in mitochondrial mass, decreased cellular levels of the antioxidant glutathione and caused persistent accumulation of mitochondrial reactive oxygen species (ROS). Excess ROS promoted oxidative inactivation of protein phosphatase PP2A which in turn led to disruption of normal negative feed-back control of AKT/cyclin D1 signaling in cells treated with long-term FR. The resulting abnormal nuclear accumulation of cyclin D1 causes growth retardation, cellular senescence and genome instability in low-dose irradiated cells. Thus, loss of redox control and subsequently elevated levels of ROS perturb signal transduction as a result of oxidative stress. Our study highlights a specific role of mitochondrial ROS in perturbation of AKT/cyclin D1 cell cycle signaling after low-dose long-term FR. The antioxidants N-acetyl-L-cysteine, TEMPO and mitochondrial-targeted antioxidant Mito-TEMPO provided protection against the harmful cell cycle perturbations induced by low-dose long-term FR.

Introduction: As one of the detailed surveys in the Fukushima Health Survey, thyroid ultrasound examinations is covering roughly 360,000 residents aged 0 to 18 years at the time of the nuclear acci...

The xeroderma pigmentosum group C (XPC) protein complex is a key factor that detects DNA damage and initiates nucleotide excision repair (NER) in mammalian cells. Although biochemical and structural studies have elucidated the interaction of XPC with damaged DNA, the mechanism of its regulation in vivo remains to be understood in more details. Here, we show that the XPC protein undergoes modification by small ubiquitin-related modifier (SUMO) proteins and the lack of this modification compromises the repair of UV-induced DNA photolesions. In the absence of SUMOylation, XPC is normally recruited to the sites with photolesions, but then immobilized profoundly by the UV-damaged DNA-binding protein (UV-DDB) complex. Since the absence of UV-DDB alleviates the NER defect caused by impaired SUMOylation of XPC, we propose that this modification is critical for functional interactions of XPC with UV-DDB, which facilitate the efficient damage handover between the two damage recognition factors and subsequent initiation of NER.

The Mus81 endonuclease resolves recombination intermediates and mediates cellular responses to exogenous replicative stress. Here, we show that Mus81 also regulates the rate of DNA replication during normal growth by promoting replication fork progression while reducing the frequency of replication initiation events. In the absence of Mus81 endonuclease activity, DNA synthesis is slowed and replication initiation events are more frequent. In addition, Mus81 deficient cells fail to recover from exposure to low doses of replication inhibitors and cell viability is dependent on the XPF endonuclease. Despite an increase in replication initiation frequency, cells lacking Mus81 use the same pool of replication origins as Mus81-expressing cells. Therefore, decelerated DNA replication in Mus81 deficient cells does not initiate from cryptic or latent origins not used during normal growth. These results indicate that Mus81 plays a key role in determining the rate of DNA replication without activating a novel group of replication origins.

The ubiquitin ligase RAD18 is involved in post replication repair pathways via its recruitment to stalled replication forks, and its role in the ubiquitylation of proliferating cell nuclear antigen (PCNA). Recently, it has been reported that RAD18 is also recruited to DNA double strand break (DSB) sites, where it plays novel functions in the DNA damage response induced by ionizing radiation (IR). This new role is independent of PCNA ubiquitylation, but little is known about how RAD18 functions after IR exposure. Here, we describe a role for RAD18 in the IR-induced DNA damage signaling pathway at G2/M phase in the cell cycle. Depleting cells of RAD18 reduced the recruitment of the DNA damage signaling factors ATM, γH2AX, and 53BP1 to foci in cells at the G2/M phase after IR exposure, and attenuated activation of the G2/M checkpoint. Furthermore, depletion of RAD18 increased micronuclei formation and cell death following IR exposure, both in vitro and in vivo. Our data suggest that RAD18 can function as a mediator for DNA damage response signals to activate the G2/M checkpoint in order to maintain genome integrity and cell survival after IR exposure.

Cell cycle arrest in response to DNA damage is important for the maintenance of genomic integrity in higher eukaryotes. We have previously reported the novel p53-dependent S-phase checkpoint operating in mouse zygotes fertilized with irradiated sperm. In the present study, we analysed the detail of the p53 function required for this S-phase checkpoint in mouse zygotes. The results indicate that ATM kinase is likely to be indispensable for the p53-dependent S-phase checkpoint since the suppression was abrogated by inhibitors such as caffeine and wortmannin. However, ATM phosphorylation site mutant proteins were still capable of suppressing DNA synthesis when microinjected into sperm-irradiated zygotes lacking the functional p53, suggesting that the target of the phosphorylation is not p53. In addition, the suppression was not affected by alpha-amanitin, and p53 protein mutated at the transcriptional activation domain was also functional in the suppression of DNA synthesis. However, p53 proteins mutated at the DNA-binding domain were devoid of the suppressing activity. Taken together, the transcription-independent function of p53 associated with the DNA-binding domain is involved in the S-phase checkpoint in collaboration with yet another unidentified target protein(s).

International audience; A new method to determine complex amplitudes of index and absorption gratings in photorefractive multiple quantum wells is presented. In usual method to evaluate these parameters, spectral measurement of absorption change due to the applied field over a wide wavelength range is required and the index change is calculated through the Kramers-Krönig's relationship. In our method, only a set of measured data for photorefractive two-wave mixing set-up with small sinusoidal phase modulation for fixed wavelength is needed. This is thus well adapted to insitu characterization of systems that operate at a given wavelength. Real and imaginary part of the gains owing to the index and the absorption gratings are calculated from the output signals of the system. We apply this method to our photorefractive multiple quantum devices operating at 1064 nm, and obtain consistent results

We have investigated photo-induced absorption changes for In 0.10 Ga 0.90 N multiple quantum wells and a thin film induced by a continuous-wave (cw) beam and a femtosecond pulse in the violet region. For the thin-film sample, nearly the same absorption changes were observed in cw pumping and pulse pumping measurements. Screening of the piezoelectric field in InGaN heterostructures causes absorption changes around the band edge. This screening results from spatial separation of electron-hole pairs to the opposite sides of the InGaN epilayer. These spatially separated carriers are trapped in deep levels and maintain the absorption changes. The trapped charges are considered to be thermally excited to the conduction band and diffuse to attain the equilibrium state. This process takes on the order of 100 ps and such a long decay time of absorption changes allows us to have large absorption changes even by low-intensity cw pumping.

Cascaded processes of energy exchanges between optical beams via second-order nonlinearities lead to various phenomena, including Kerr-like nonlinear phase shifts and optical solitons. The cascading nonlinearity, combined with the developments in quasi-phase-matching devices, is becoming more promising for all-optical signal processing and ultrashort pulse generation. Here we review the basic properties of the cascading nonlinearity and present our recent experiments on femtosecond cascading with quasi-phase-matching devices.

We studied the electric-field-induced birefringence, the photoconductivity and the photorefractive properties of photorefractive polymer composites based on N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine (TPD). Photorefractive response rate is improved in TPD-based photorefractive polymer, composed of TPD, polystyrene (PS), 4-butoxy-3-propyl-1-(4'-nitrophenylazo)benzene (m3p4) and C 6 0 . We obtained the photorefractive response time of as fast as 3.2 ms (@I = 837 mW/cm 2 , E = 40 V/μm). The photoconductivity of TPD-based photorefractive polymer is found to be greater than that of the PVK-based one.

Nondegenerate femtosecond pump and probe spectroscopy was performed in In0.10Ga0.90N/In0.03Ga0.97N multiple quantum wells and epilayers at room temperature. The structural dependence of the photoinduced differential absorption (Δα) spectrum was studied on four In0.10Ga0.90N layers of different thickness (5.5, 17, 34, and 66 nm). A single bulge was clearly observed in Δα spectra except for the 5.5 nm thick sample. The bulges are sharper in thicker In0.10Ga0.90N layer samples. These spectrum changes are caused by excitonic absorption quenching and screening of internal piezoelectric fields by photoinduced carriers. Both rapid and slow temporal behaviors were observed in transient absorption spectra. The results of time-resolved photoluminescence measurements and existence of saturation pump fluences indicate that trapped carriers in potential minima originate from In-rich regions and/or midgap carrier traps are responsible for the observed lasting screening of the internal electric field.

Carrier dynamics in In0.10Ga0.90N/In0.03Ga0.97N multiple quantum wells and epilayers were studied by nondegenerate femtosecond pump and probe spectroscopy and by using monochromatic continuous wave light at room temperature. Structurally dependent transient absorption spectra were observed after pump pulse excitation. These spectral changes are caused by excitonic absorption quenching and screening of internal piezoelectric fields by photoinduced carriers. Both rapid (∼400 ps) and slow (∼90 μs) temporal behavior was observed in the transient absorption spectra. The results of time-resolved photoluminescence measurements and the existence of saturation pump fluences indicate that trapped carriers in potential minima originating from In-rich regions and/or midgap carrier traps are responsible for the lasting screening of the internal electric field.

The adaptive measurement of nanometre-scale vibrations of diffuse surfaces using the polarization self-modulation effect in a photorefractive GaP crystal is described. The sensitivity is investigated as a function of the applied electric field, the intensity of the incident light, and the mean size of the speckles. Numerical estimation of the sensitivity dependence on the mean size of the speckles shows a good agreement with experimental results.

Cascaded quadratic nonlinearities in periodically poled lithium tantalate are studied with femtosecond pulses by using the spectrally resolved two-beam coupling technique. The nonlinear phase shifts show obvious dependence on the phase mismatch conditions. Relatively large intrinsic nonlinear refraction and its anisotropy are also measured.

Photorefractive response rate in a polymer composite of poly(N-vinylcarbazole)/2,4,7-trinitro-9-fluorenone, doped with 2,5-dimethyl-4-(4'-nitrophenylazo)anisole (DMNPAA) is improved by modifying the structure of DMNPAA. We found that four kinds of modified DMNPAA with alkyl substituents have fast orientational response to an external electric field and keep large anisotropy in polarizability. Among them, 4-butoxy-3-propyl-1-(4'-nitorophenylazo)benzene has the shortest reorientation time constant of 19 ms (E=54 V/µm) and photorefractive time constant of 80 ms (I=2 W/cm2, E=54 V/µm) that are 2,300 times and 63 times faster than those of the DMNPAA composite. The mechanism of the fast reorientation in new polymer composites is investigated. The fast reorientational response is achieved by the improvement of the dispersivity in the polymer composites and the decrease of the glass transition temperature.

Faithful reconstruction, the polarization state of the diffraction wave being identical to that of the signal wave, is the primary target in polarization holography. With the large crossing angle between signal and reference wave, namely, nonparaxial approximation, attaining a balance between intensity and polarization grating is generally known as a prerequisite for faithful reconstruction. However, obtaining such a balance point within polarization-sensitive material has long been known as a challenging job, due to its extremely strict exposure condition. In this paper, we report on a smart method with the well-designed reference and reading wave to faithfully reconstruct the signal wave at an arbitrary exposure energy. Moreover, when the signal is circularly polarized, the diffraction efficiency can be precisely manipulated by changing the reading wave’s polarization state, which is favorable for optical storage and functional diffractive optical elements.

Semiconductor photorefractive quantum well (PR-QW) devices have high sensitivity and fast response because of large excitonic electrooptic effects and large carrier mobilities. Taking advantages of these attractive features, interesting applications using PR-QW devices as dynamic holographic media have been demonstrated. Here basic features of PR-QW devices, materials, and device configurations are reviewed. In addition, two important applications of PR-QW devices, adaptive vibration measurement and optical imaging through scattering media, are also discussed.

We report on dual-channel recording within polarization holography written by orthogonal linear polarization waves. The null reconstruction effect (NRE) of linear polarization holography was experimentally achieved at a large cross-angle of π/2 inside the polarization-sensitive media. Based on the NRE, two polarization encoded holograms were recorded in a dual-channel recording system with negligible inter-channel crosstalk. The two polarization multiplexed holograms could then be sequentially or simultaneously readout by shifting the polarization state of reference wave with the best signal-to-noise of 18:1 obtained within the experiment.

Unidirectional control of optically induced spin waves in a rare-earth iron garnet crystal is demonstrated. We observed the interference of two spin-wave packets with different initial phases generated by circularly polarized light pulses. This interference results in unidirectional propagation if the spin-wave sources are spaced apart at 1/4 of the wavelength of the spin waves and the initial phase difference is set to pi/2. The propagating direction of the spin wave is switched by the polarization helicity of the light pulses. Moreover, in a numerical simulation, applying more than two spin-wave sources with a suitable polarization and spot shape, arbitrary manipulation of the spin wave by the phased array method was replicated.

In experiment and theory, we resolve the mechanism of ultrafast optical magnon excitation in antiferromagnetic NiO. We employ time-resolved optical two-color pump-probe measurements to study the coherent non-thermal spin dynamics. Optical pumping and probing with linearly and circularly polarized light along the optic axis of the NiO crystal scrutinizes the mechanism behind the ultrafast optical magnon excitation. A phenomenological symmetry-based theory links these experimental results to expressions for the optically induced magnetization via the inverse Faraday effect and the inverse Cotton-Mouton effect. We obtain striking agreement between experiment and theory that, furthermore, allows us to extract information about the spin domain distribution. We also find that in NiO the energy transfer into the magnon mode via the inverse Cotton-Mouton effect is about three orders of magnitude more efficient than via the inverse Faraday effect., Comment: 11 pages, 5 figures

Tritium is used as fuel for nuclear fusion reactions and has cancer risk for workers in nuclear fusion plant by its exposure during routine operation or accidents. Tritium exists as tritiated water...

Direct measurements of carrier recombination dynamics in In0.1Ga0.9N/In0.03Ga0.97N multiple quantum well (QW) structures with different well thickness (d = 5.5, 17, 34 nm) are presented. The measurements by light-induced picosecond transient grating and time-resolved photoluminescence techniques revealed three contributing carrier recombination mechanisms at high carrier injections (“efficiency droop” conditions): stimulated emission (SE), bimolecular, and Shockley-Read-Hall. The study indicates on absence of Auger recombination rate with quadratic dependence, 1/τ ∝ N2, which was not observed up to ∼5x1019 cm-3 excess carrier density (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Time- and space-resolved spin wave excitation by circularly polarized pulses was investigated in a garnet ferrite. Propagation of the spin wave was con-trolled by spatially shaping of the light pulses.

Cyclin D1 is a mitogenic sensor that responds to growth signals from the extracellular environment and regulates the G 1-to-S cell cycle transition. When cells are acutely irradiated with a single dose of 10 Gy, cyclin D1 is degraded, causing cell cycle arrest at the G 1/S checkpoint. In contrast, cyclin D1 accumulates in human tumor cells that are exposed to long-term fractionated radiation (0.5 Gy/fraction of X-rays). In this study we investigated the effect of fractionated low-dose radiation exposure on cyclin D1 localization in 3 strains of normal human fibroblasts. To specifically examine the nuclear accumulation of cyclin D1, cells were treated with a hypotonic buffer containing detergent to remove cytoplasmic cyclin D1. Proliferating cell nuclear antigen (PCNA) immunofluorescence was used to identify cells in S phase. With this approach, we observed S-phase nuclear retention of cyclin D1 following low-dose fractionated exposures, and found that cyclin D1 nuclear retention increased with exposure time. Cells that retained nuclear cyclin D1 were more likely to have micronuclei than non-retaining cells, indicating that the accumulation of nuclear cyclin D1 was associated with genomic instability. Moreover, inhibition of the v-akt murine thymoma viral oncogene homolog (AKT) pathway facilitated cyclin D1 degradation and eliminated cyclin D1 nuclear retention in cells exposed to fractionated radiation. Thus, cyclin D1 may represent a useful marker for monitoring long-term effects associated with exposure to low levels of radiation.

We fabricate semi-insulating InGaAs/GaAs multiple quantum wells and observe the excitonic enhancement of the photorefractivity in the Franz–Keldysh geometry at wavelengths of 0.92–0.94 μm. A maximum two-wave mixing gain of 138 cm−1 and a maximum diffraction efficiency of 1.5×10−4 are obtained. The saturation intensity and the spatial resolution are also measured by four-wave mixing. The diffraction efficiency is saturated at a high external electric field. The dominant cause of this saturation is the deviation of the excitonic electroabsorption from its quadratic law.

We have demonstrated photorefractive InGaAs/GaAs multiple-quantum-well devices in the quantum confined Stark geometry. A four-wave-mixing diffraction efficiency up to 0.3% is obtained at a wavelength of 949 nm. Proton implantation strongly reduces the maximum diffraction efficiency although it saturates the diffraction efficiency at smaller grating period comparing to as-grown device. We have also observed higher order diffractions. It is found that the space-charge field changes its pattern temporally from a sinusoidal pattern to a rectangular one with decreasing its modulation depth.

「狭小箱桁」は従来の箱桁に比べ, ウェブ間隔を狭小化することにより縦リブ・リブを幅に削減し, 併せて床版を強化することで縦桁も省略した構造である. 本構造は上記の特徴から床版支間長がきくなるという点では, 2主桁などの少数主桁橋と同様に長支間床版の革新的な技術が要求されるが, 主桁のねじり剛性などの性能が異なるため, 設計上の多くの点で2主桁橋に比べて優れていると考えた. そこで全体挙動の把握と, 桁の省略・簡素化を一つの到達点としたさらなる構造の合理化を目指して, 立体FEM解析を用いた検討を行った. さらに, 床版の長支間化によって床版および床版と主桁の接合部に生じる作用力について, 2主桁との比較を交えながら構造上の安定性を検証した.

The experimental study of the in-plain vibration of the speckle pattern in photorefractive GaP and BTO crystals using the polarization self-modulation effect are presented. The simple model based on the propagation of the Gaussian beam through the crystal with recorded space-charge field is proposed to explain main features of the experiment. It is shown that these results allow designing a linear sensor of the speckle-pattern displacement in an effective way. The optical system is very simple and does not include any reference or readout beam. The sensitivity of this system is the same as that of an interferometer.

A broad-area laser is injection-locked by another broad-area laser that is also injection-locked by a single-mode diode laser. Two double-phase conjugate mirrors of photorefractive BaTaO3 are used to couple the master laser beams to the first slave laser, and the first slave laser output to the second slave laser. One of the double-phase conjugate mirrors is built up with the beams from two broad-area lasers. Two slave lasers are oscillating in single longitudinal mode at 808.5 nm and the spectral width is the same as that of the master laser. Final single-mode output power from the second slave broad-area laser is 840 mW, which is limited by the power of the injection beam. This work verifies the possibility of the multi-stage cascaded injection locking of high-power diode lasers with phase-conjugate injection.

Injection locking of a 1-W broad-area diode laser was achieved using a double phase-conjugate mirror (DPCM). The DPCM was build up for the first time using the broad-area laser beam and it coupled an elliptical-shaped beam of a single-mode master laser efficiently into a broad-area laser's slit-shaped output facet. Single longitudinal mode operation up to 550 mW output was achieved by an injection beam power of no more than 0.6% of the whole output. The lateral beam pattern was also improved and the measured M 2 value of the locked beam greatly decreased compared with that of the free-running beam. M 2 =8 for low-power operation and M 2 =28 for high-power operation were achieved.