Green Up-Conversion Continuous-Wave Er3+Liyf4 Laser At Room-Temperature

We report room-temperature upconversion pumped continuous wave laser emission of 1% Er3+:LiYF4 at 551 nm excited by a Ti:sapphire laser at 810 nm. Output powers of up to 40 mW with output coupling of 6.6% have been obtained by using nearly concentric resonator design

Green Up-Conversion Laser-Emission In Er-Doped Crystals At Room-Temperature

We report room-temperature pulsed up-conversion laser oscillation in Er-doped LiYF4 and KYF4 at 551 and 562 nm, respectively. In both crystals laser oscillation is observed on the S-4(3/2)-I-4(15/2) ground state transition. Excitation was provided by a tunable flashlamp-pumped Ti:sapphire laser in the spectral region around 810 nm. Additional pumping with a continuous wave krypton ion laser at 647 nm was beneficial to both lasers. Laser action has also been observed in Er-doped Y3Al5O12 on the same transition

Spectroscopy And Green Up-Conversion Laser-Emission Of Er(3+)-Doped Crystals At Room-Temperature

The spectroscopic parameters of Er3+-doped crystals were determined with regard to the upconversion laser parameters of the green transition S-4(3/2) -- \u3e I-4(15/2), The influence of excited-state absorption on this laser channel was determined. Furthermore, upconversion pump mechanisms using ground-state and excited-state absorption around 810 and 970 nm were investigated by direct measurements of excited-state absorption. The spectroscopic results confirm the pulsed room-temperature laser experiments on the S-4(3/2) -- \u3e I-5(5/2) transition. The lasers based on Er:LiYF4, Er:Y3Al5O12, and Er:Lu3Al5O12 were directly excited into the upper laser level by an excimer laser pumped dye laser in the blue spectral range. In Er:LiYF4, Er:KYF4, and Er:Y3Al5O12, laser action was achieved with two-step upconversion pumping by a Ti:sapphire laser and a krypton ion laser. In the case of the fluorides, the additional pumping with the krypton ion laser was not necessary. The laser emission wavelengths were 551 nm for Er:LiYF4, 561 nm for Er:Y3Al5012 and Er:Lu3Al5O12, and 562 nm for Er:KYF4. In addition, green quasi-cw laser emission of Er:LiYF4 pumped with an argon-ion laser was realized at room temperature

Effects of finite curvature on soliton dynamics in a chain of nonlinear oscillators

We consider a curved chain of nonlinear oscillators and show that the interplay of curvature and nonlinearity leads to a number of qualitative effects. In particular, the energy of nonlinear localized excitations centered on the bending decreases when curvature increases, i.e. bending manifests itself as a trap for excitations. Moreover, the potential of this trap is double-well, thus leading to a symmetry breaking phenomenon: a symmetric stationary state may become unstable and transform into an energetically favorable asymmetric stationary state. The essentials of symmetry breaking are examined analytically for a simplified model. We also demonstrate a threshold character of the scattering process, i.e. transmission, trapping, or reflection of the moving nonlinear excitation passing through the bending.Comment: 13 pages (LaTeX) with 10 figures (EPS

The Heumann-Hotzel model for aging revisited

Since its proposition in 1995, the Heumann-Hotzel model has remained as an obscure model of biological aging. The main arguments used against it were its apparent inability to describe populations with many age intervals and its failure to prevent a population extinction when only deleterious mutations are present. We find that with a simple and minor change in the model these difficulties can be surmounted. Our numerical simulations show a plethora of interesting features: the catastrophic senescence, the Gompertz law and that postponing the reproduction increases the survival probability, as has already been experimentally confirmed for the Drosophila fly.Comment: 11 pages, 5 figures, to be published in Phys. Rev.

Trends in the incidence of AIDS-defining and non-AIDS-defining cancers in people living with AIDS: a population-based study from Sao Paulo, Brazil

People living with AIDS are at increased risk of developing certain cancers. Since the introduction of the highly active antiretroviral therapy (HAART), the incidence of AIDS-defining cancers (ADCs) has decreased in high-income countries. The objective of this study was to analyse trends in ADCs and non-AIDS-defining cancers (NADCs) in HIV-positive people with a diagnosis of AIDS, in comparison to the general population, in Sao Paulo, Brazil. A probabilistic record linkage between the 'Population-based Cancer Registry of Sao Paulo' and the AIDS notification database (SINAN) was conducted. Cancer trends were assessed by annual per cent change (APC). In people with AIDS, 2074 cancers were diagnosed. Among men with AIDS, the most frequent cancer was Kaposi's sarcoma (469;31.1%), followed by non-Hodgkin lymphoma (NHL;304;20.1%). A decline was seen for ADCs (APC = -14.1%). All NADCs have increased (APC = -7.4%/year) significantly since the mid-2000s driven by the significant upward trends of anal (APC = -24.6%/year) and lung cancers (APC = -15.9%/year). In contrast, in men from the general population, decreasing trends were observed for these cancers. For women with AIDS, the most frequent cancer was cervical (114;20.2%), followed by NHL (96;17.0%). Significant declining trends were seen for both ADCs (APC = -15.6%/ year) and all NADCs (APC = -15.8%/ year), a comparable pattern to that found for the general female population. Trends in cancers among people with AIDS in Sao Paulo showed similar patterns to those found in developed countries. Although ADCs have significantly decreased, probably due to the introduction of HAART, NADCs in men have shown an opposite upward trend

Using MODIS derived <i>f</i>PAR with ground based flux tower measurements to derive the light use efficiency for two Canadian peatlands

International audienceWe used satellite remote sensing data; fraction of photosynthetically active radiation absorbed by vegetation (fPAR) from the Moderate Resolution Imaging Spectroradiometer (MODIS) in combination with tower eddy covariance and meteorological measurements to characterise the light use efficiency parameter (?) variability and the maximum ? (?max) for two contrasting Canadian peatlands. Eight-day MODIS fPAR data were acquired for the Mer Bleue (2000 to 2003) and Western Peatland (2004). Flux tower eddy covariance and meteorological measurements were integrated to the same eight-day time stamps as the MODIS fPAR data. A light use efficiency model: GPP=? * APAR (where GPP is Gross Primary Productivity and APAR is absorbed photosynthetically active radiation) was used to calculated ?. The ?max value for each year (2000 to 2003) at the Mer Bleue bog ranged from 0.58 g C MJ?1 to 0.78 g C MJ?1 and was 0.91 g C MJ?1 in 2004, for the Western Peatland. The average growing season ? for the Mer Bleue bog for the four year period was 0.35 g C MJ?1 and for the Western Peatland in 2004 was 0.57 g C MJ?1. The average snow free period ? for the Mer Bleue bog over the four year period was 0.27 g C MJ?1 and for the Western Peatland in 2004 was 0.39 g C MJ?1. Using the light use efficiency method we calculated the ?max and the annual variability in ? for two Canadian peatlands. We determined that temperature was a growth-limiting factor at both sites Vapour Pressure Deficit (VPD) however was not. MODIS fPAR is a useful tool for the characterization of ? at flux tower sites

Exact Solution of an Evolutionary Model without Ageing

We introduce an age-structured asexual population model containing all the relevant features of evolutionary ageing theories. Beneficial as well as deleterious mutations, heredity and arbitrary fecundity are present and managed by natural selection. An exact solution without ageing is found. We show that fertility is associated with generalized forms of the Fibonacci sequence, while mutations and natural selection are merged into an integral equation which is solved by Fourier series. Average survival probabilities and Malthusian growth exponents are calculated indicating that the system may exhibit mutational meltdown. The relevance of the model in the context of fissile reproduction groups as many protozoa and coelenterates is discussed.Comment: LaTeX file, 15 pages, 2 ps figures, to appear in Phys. Rev.

540 mW of blue output power at 425 nm generated by intracavity frequency doubling an upconversion-pumped Er3+: YLiF4 laser

We report efficient room-temperature continuous-wave intracavity frequency doubling of an upconversion-pumped Er(1%):YLiF4 laser at 850 nm. A titanium-sapphire laser was used for excitation of the S-4(3/2)-- \u3e I-4(13/2) transition in erbium. The maximum laser output power at 850 nm was 1200 mW. Intracavity frequency doubling the fundamental wave utilizing lithium triborate as nonlinear crystal yielded a maximum second-harmonic output power of 540 mW at 425 nm