Cell Cycle Kinetics Following UVA Irradiation in Comparison to UVB and UVC Irradiation

Abstract— There is limited information about the carcinogenic effect of longwave ultraviolet radiation (UVA: 315-400 nm). In particular very little is known about the relevant genotoxic damage caused by physiological doses of UVA radiation. A general response of cells to DNA damage is a delay or arrest of the cell cycle. Conversely, such cellular responses after UVA irradiation would indicate significant genotoxic damage. The aim of this study is to compare cell cycle kinetics of human fibroblasts after UVC (190-280 nm radiation), UVB (280-315 nm radiation) and UVA irradiation. Changes in the cell cycle kinetics were assessed by bivariate flow cytometric analysis of DNA synthesis and of DNA content. After UVC, UVB or UVA irradiation of human fibroblasts a suppression was seen of bromodeoxyuridine (BrdU) incorporation at all stages of S phase. The magnitude of this suppression appeared dose dependent. Maximum suppression was reached at 5-7 h after UVB exposure and directly after UVA exposure, and normal levels were reached 25 h after UVB and 7 h after UVA exposure. The lowered BrdU uptake corresponded with a lengthening of the S phase. No dramatic changes in percentages of cells in G₁, S and G₂/M were seen after the various UV irradiations. Apparently, UVA irradiation, like UVB and UVC irradiation, can temporarily inhibit DNA synthesis, which is indicative of genotoxic damage.     

The study of prompt and delayed muon induced fission

Mass yield and total kinetic energy release (TKE) distributions of fragments from prompt and delayed muon induced fission, separately, have been measured for the isotopes²³⁵U,²³⁸U,²³⁷Np and²⁴²Pu. The distributions from prompt muon induced fission are compared with the corresponding distributions from hadronic reactions and from spontaneous fission (s.f.). The distributions from the delayed muonic fission processes are compared to the distributions for neutron and proton-induced fission. No mass distributions measured in the prompt muonic fission process show any signature, which can be attributed to the presence of the muon. Differences observed between the TKE distributions of prompt muon induced and hadron induced fission can be explained by the screening effect of the negative charge of the muon bound in the orbit of one of the fission fragments. The observed yield of symmetric muon induced fission was found to be defined merely by the value of the excitation energy.     

Radiationless transition probabilities in muonic208Pb,232Th,and238U

The probabilities for non-radiative (n.r.) excitationsP _n.r. in the muonic nuclides²⁰⁸Pb,²³²Th, and²³⁸U have been determined from (μ^?,γγ)-measurements by comparing the intensities of muonic X-ray transitions in single and coincidence spectra. The value ofP _n.r. (3p→1s), measured for the first time, is about 90% for the actinides²³²Th and²³⁸U, but only about 8% for²⁰⁸Pb. The value ofP _n.r. (3d→1s) is found to be 10 % for²³³Th, 13% for²³⁸U, and about 4% for²⁰⁸Pb. For²⁰⁸Pb a vanishing strength of the n.r. decay of the 2p-level is found, while for²³²Th and for²³⁸U n.r. strengths of about 20% and 26%, respectively, are observed. By regarding two subcomplexes of the 2p→1s transitions leading to different mean excitation energies the n.r. transition probabilities were found to be different for²³⁸U only, 21.6% and 31.1.%, respectively.     

Laser sintering of perovskite-oxide and metal coatings by the sol gel process

This paper presents a novel laser technique for the formation of metal Ag and perovskite-oxide La_xSr_1-xCoO₃ coatings. Metallic Ag and La_xSr_1-xCoO₃ are conductive materials with applications as resistors and as electrodes in the microelectronics area. Suitable precursors in the form of sol gels are placed on substrates and are subsequently sintered by high-power laser irradiation. The Ag precursor is an aqueous sol of nanosized particles, while for the La_0.8Sr_0.2CoO₃, a sol gel type precursor is used. Substrates (e.g., fused silica) are coated with the precursor solutions by spinning and are dried to stable solid layers. The coatings are cured and sintered to a defined pattern by means of a 3-kW CO₂ laser beam scanned over the whole substrate surface. The microstructure of the coatings was examined by the use of scanning electron microscopy and X-ray diffraction, and the electrical properties were measured by the four-point resistivity method. The La_0.8Sr_0.2CoO₃ coatings had a perovskite cubic structure with a lattice constant of 0.383 nm. The resistivity of the coatings was 30 mQ cm, and the temperature dependence of the resistivity was 1.8 mQ cm/°C. Metallic Ag coatings with a thickness of 100-170 nm were obtained with a resistivity of 20 7Q cm. This new technology is promising for the growth of three-dimensional (3-D) structures and multilayers, especially because it can be introduced in industrial scale production.     

k-Point semidefinite programming bounds for equiangular lines

Mathematical Programming - We propose a hierarchy of k-point bounds extending the Delsarte–Goethals–Seidel linear programming 2-point bound and the Bachoc–Vallentin semidefinite...     

Novel poly(vinyl ether) block copolymers: Synthesis and colloidal stabilization of α-Fe2O3 in water and organic solvents

 Novel poly(vinyl-methylether)-b-poly(vinyloxy-4-butyric acid) diblock copolymers were made for the purpose of colloidal stabilization of particles in liquids. The synthesis via cationic polymerization with HI/I₂ initiation and the characterization of such novel diblock copolymers is described. A set of polymers was prepared including block copolymers with different block length ratios and the two separate homopolymers having the chemical composition of one of the blocks. Colloidal stabilization of α-Fe₂O₃ particles in water could be realized with all polymers except with the (vinylmethylether) homopolymer. One of the block copolymers was used for evaluation of the stabilizing abilities in organic solvents. Stable α-Fe₂O₃ dispersions could be prepared in solvents with very different polarities, ranging from methanol to toluene. In addition, it is shown that particles stabilized with these block copolymers can be easily transferred from water to an organic liquid. Received: 15 May 1997 Accepted: 13 October 1997     

Bounds on entanglement dimensions and quantum graph parameters via noncommutative polynomial optimization

This paper studies the matrix completion problem under arbitrary sampling schemes. We propose a new estimator incorporating both max-norm and nuclear-norm regularization, based on which we can conduct efficient low-rank matrix recovery using a random subset of entries observed with additive noise under general non-uniform and unknown sampling distributions. This method significantly relaxes the uniform sampling assumption imposed for the widely used nuclear-norm penalized approach, and makes low-rank matrix recovery feasible in more practical settings. Theoretically, we prove that the proposed estimator achieves fast rates of convergence under different settings. Computationally, we propose an alternating direction method of multipliers algorithm to efficiently compute the estimator, which bridges a gap between theory and practice of machine learning methods with max-norm regularization. Further, we provide thorough numerical studies to evaluate the proposed method using both simulated and real datasets.     

Cell Cycle Effects and Concomitant p53 Expression in Hairless Murine Skin after Longwave UVA (365 nm) Irradiation: A Comparison with UVB Irradiation

Abstract— Ultraviolet A (UVA,315–400 nm) radiation is known to be a complete carcinogen, but in contrast to UVB (280-315 nm) radiation, much of the cell damage is oxygen dependent (mediated through reactive oxygen species), and the dominant premutational DNA lesion(s) remains to be identified. To investigate further the basic differences in UVA and UVB carcinogenesis, we compared in vivo cellular responses, viz. cell cycle progression and transient p53 expression in the epidermis, after UVA1 (340-400 nm) exposure with those after broadband UVB exposure of hairless mice. Using flow cytometry we found a temporary suppression of bromodeoxyuridine (BrdU) uptake in S-phase cells both after UVB and UVA1 irradiation, which only in the case of UVB is followed by an increase to well over control levels. With equally erythemogenic doses (1-2 MED), the modulation of BrdU uptake was more profound after UVB than after UVA1 irradiation. Also, a marked transient increase in the percentage of S-phase cells occurred both after UVB and after UVA1 irradiation, but this increase evolved more rapidly after UVA1 irradiation. Further, p53 expression increased both after UVB and UVA1 irradiations, with peak expression already occurring from 12 to 24 h after UVA1 exposure and around 24 h after UVB exposure. Overall, UVA1 radiation appears to have less of an impact on the cell cycle than UVB radiation, as measured by the magnitude and duration of changes in DNA synthesis and cells in S phase. These differences are likely to reflect basic differences between UVB and UVA1 in genotoxicity and carcinogenic action.