Generation of femtosecond light pulses in the near infrared around λ = 850 nm

Femtosecond light pulses tunable between 840 nm and 880 nm are generated in a synchronously pumped ring dye laser. The laser emits nearly bandwidth-limited pulses (Δv tp = 0.45) with pulse durations down to 65 fs. At a pumping power of 450 mW of a mode-locked Ar-ion laser (λ = 514 nm) the infrared femtosecond dye laser has an output of up to 15 mW

Systems and Methods for Providing Energy to Support Missions in Near Earth Space

A system has a plurality of spacecraft in orbit around the earth for collecting energy from the Sun in space, using stimulated emission to configure that energy as well defined states of the optical field and delivering that energy efficiently throughout the region of space surrounding Earth

Direct and Indirect Effects of Dissolved Organic Matter Source and Concentration on Denitrification in Northern Florida Rivers

Using a natural gradient of dissolved organic carbon (DOC) source and concentration in rivers of northern Florida, we investigated how terrestrially-derived DOC affects denitrification rates in river sediments. Specifically, we examined if the higher concentrations of DOC in blackwater rivers stimulate denitrification, or whether such terrestrially-derived DOC supports lower denitrification rates because (1) it is less labile than DOC from aquatic primary production; whether (2) terrestrial DOC directly inhibits denitrification via biochemical mechanisms; and/or whether (3) terrestrial DOC indirectly inhibits denitrification via reduced light availability to-and thus DOC exudation by-aquatic primary producers. We differentiated among these mechanisms using laboratory denitrification assays that subjected river sediments to factorial amendments of NO3- and dextrose, humic acid dosing, and cross-incubations of sediments and water from different river sources. DOC from terrestrial sources neither depressed nor stimulated denitrification rates, indicating low lability of this DOC but no direct inhibition; humic acid additions similarly did not affect denitrification rates. However, responses to addition of labile C increased with long-term average DOC concentration, which supports the hypothesis that terrestrial DOC indirectly inhibits denitrification via decreased autochthonous production. Observed and future changes in DOC concentration may therefore reduce the ability of inland waterways to remove reactive nitrogen. © 2013 Springer Science+Business Media New York

Die Transporter SLC22A7 (OAT2) und SLC22A13: Substratsuche, Lokalisation, Entdeckung eines Orotsäure-Transporters

Die Solute Carrier SLC22A7 (OAT2, "Organic Anion Transporter 2") und SLC22A13 liegen in mehreren Mammalia-Spezies konserviert vor. OAT2 wird im Mensch primär in der Leber exprimiert, wohingegen SLC22A13 hauptsächlich in den Nieren vorzufinden ist. Ihre physiologische Bedeutung ist jedoch unklar. Da Transporter im Wesentlichen durch ihre Substrate definiert werden, wurden Substrate für diese beiden verwandten Proteine, mittels LC-MS- (Liquid Chromatography - Mass Spectrometry) Differenz Abtönung, aufgespürt. Über diese Methode konnten Guanidiniumsuccinat (GSA) für SLC22A13h (human) und Trigonellin (Trig) für OAT2h als Substrate identifiziert werden. Darüber hinaus konnten die organischen Anionen a-Ketoglutarat, Glutarat, Glycocholat, Guanidiniumglutarat (GGA), Nikotinat, para-Aminohippurat, Pantothenat (PA), Orotat und Urat sowie die Zwitterionen Glycylprolin (GP), Prolylglycin (PG) und Kreatin als Substrate für SLC22A13h gefunden werden. Die höchste Transporteffizienz (TE) von 15 ul min-1 mg Protein-1 wurde hierbei mit dem Nikotinat erzielt. Auf Grund eines verminderten intrazellulären Gehalts von GSA, GGA, GP, PG und PA bei Expression von SLC22A13h in HEK293-Zellen sowie trans-Stimulations Experimente, ließ die Schlussfolgerung zu, dass SLC22A13h als Austaucher operiert. Neben dem Aufspüren von Substraten wurde die Lokalisation von SLC22A13 durch eine Antikörperfärbung untersucht. So konnte erstmalig gezeigt werden, dass der Transporter in der basolateralen Membran von Schaltzellen im Sammelrohr der Rattenniere lokalisiert ist. Aufgrund dieser Tatsache, wurde die Hypothese aufgestellt, dass SLC22A13 für die Exkretion und/oder Resorption von organischen Anionen, im Zusammenspiel mit dem in Schaltzellen apikal lokalisierten SLC22A9 eine Rolle spielt. Für OAT2 konnte festgestellt werden, dass Trig ein spezifisches Substrat für den humanen und den orthologen Rattentransporter (OAT2r) (TE = 4 ul min-1 mg Protein-1, Km = 409 uM) ist. Die Glutaminsäure an Position 441 im humanen Protein ist am Trig-Transport involviert. Mit Trig als Leitstruktur wurden strukturähnliche Verbindungen auf einen Transport untersucht. Nikotinat-Ribosid wurde hierbei als ein weiteres Substrat nachgewiesen (TE für OAT2r 7 ul min-1 mg Protein1). Des Weiteren wurde erstmalig aufgedeckt, dass OAT2r das Pyrimidin-Derivat Orotsäure bzw. das Salz Orotat effizient transportiert (TE = 74-99 ul min-1 mg Protein-1, Km = 234 uM), wohingegen OAT2h Orotat nicht als Substrat akzeptierte. Aufgrund der hier gewonnenen Erkenntnisse, kann die anatomische und physiologische Veränderung der Rattenleber (Steatosis hepatis (Fettleber)) durch vermehrte Orotsäure-Aufnahme mit der Nahrung auf OAT2r zurückgeführt werden. Mit OAT2r wurde zum ersten mal ein Orotsäure-Transporter in Eukaryonten identifiziert

Ion-implanted lanthanum fluoride waveguides

The effects of He+ and H+ implantation into LaF3 substrates have been investigated at both room temperature and 77 K. At room temperature the surface of the samples becomes black, possibly due to chemical reduction effects, but at low temperature the crystals remain clear and a refractive index change is observed which produces a surface waveguide. The dark mode spectra of these guides have been recorded using the prism coupling technique, and their refractive index profiles have been deduced from the spacing of these modes. The ion implantation produces a thin optical barrier layer of low refractive index at the end of the ion range. This paper discusses the use of multiple-energy implantation to produce a broad optical barrier in order to reduce the tunnelling losses of the guides, and subsequent thermal annealing to reduce absorption and scattering losses caused by colour centre formation in the electronic stopping surface region of the guides. It is concluded that either single- or multiple-energy He+ implants can be ideally used to form waveguides, for applications in the blue/UV or red/IR wavelength regions, respectively, with losses of a few dB/cm

Multilayer Dielectric Transmissive Optical Phase Modulator

A multilayer dielectric device has been fabricated as a prototype of a low-loss, low-distortion, transmissive optical phase modulator that would provide as much as a full cycle of phase change for all frequency components of a transmitted optical pulse over a frequency band as wide as 6.3 THz. Arrays of devices like this one could be an alternative to the arrays of mechanically actuated phase-control optics (adaptive optics) that have heretofore been used to correct for wave-front distortions in highly precise optical systems. Potential applications for these high-speed wave-front-control arrays of devices include agile beam steering, optical communications, optical metrology, optical tracking and targeting, directional optical ranging, and interferometric astronomy. The device concept is based on the same principle as that of band-pass interference filters made of multiple dielectric layers with fractional-wavelength thicknesses, except that here there is an additional focus on obtaining the desired spectral phase profile in addition to the device s spectral transmission profile. The device includes a GaAs substrate, on which there is deposited a stack of GaAs layers alternating with AlAs layers, amounting to a total of 91 layers. The design thicknesses of the layers range from 10 nm to greater than 1 micrometer. The number of layers and the thickness of each layer were chosen in a computational optimization process in which the wavelength dependences of the indices of refraction of GaAs and AlAs were taken into account as the design was iterated to maximize the transmission and minimize the group-velocity dispersion for a wavelength band wide enough to include all significant spectral components of the pulsed optical signal to be phase modulated

Microresonator and associated method for producing and controlling photonic signals with a photonic bandgap delay apparatus

By applying a photonic signal to a microresonator that includes a photonic bandgap delay apparatus having a photonic band edge transmission resonance at the frequency of the photonic signal, the microresonator imparts a predetermined delay to the photonic signal. The photonic bandgap delay apparatus also preferably has a photonic band edge transmission resonance bandwidth which is at least as wide as the bandwidth of the photonic signal such that a uniform delay is imparted over the entire bandwidth of the photonic signal. The microresonator also includes a microresonator cavity, typically defined by a pair of switchable mirrors, within which the photonic bandgap delay apparatus is disposed. By requiring the photonic signal to oscillate within the microresonator cavity so as to pass through the photonic bandgap delay apparatus several times, the microresonator can controllably impart an adjustable delay to the photonic signal

Denitrification and inference of nitrogen sources in the karstic Floridan Aquifer

Aquifer denitrification is among the most poorly constrained fluxes in global and regional nitrogen budgets. The few direct measurements of denitrification in groundwaters provide limited information about its spatial and temporal variability, particularly at the scale of whole aquifers. Uncertainty in estimates of denitrification may also lead to underestimates of its effect on isotopic signatures of inorganic N, and thereby confound the inference of N source from these data. In this study, our objectives are to quantify the magnitude and variability of denitrification in the Upper Floridan Aquifer (UFA) and evaluate its effect on N isotopic signatures at the regional scale. Using dual noble gas tracers (Ne, Ar) to generate physical predictions of N2 gas concentrations for 112 observations from 61 UFA springs, we show that excess (i.e. denitrification-derived) N2 is highly variable in space and inversely correlated with dissolved oxygen (O2). Negative relationships between O2 and δ15N NO3 across a larger dataset of 113 springs, well-constrained isotopic fractionation coefficients, and strong 15N:18O covariation further support inferences of denitrification in this uniquely organic-matter-poor system. Despite relatively low average rates, denitrification accounted for 32 % of estimated aquifer N inputs across all sampled UFA springs. Back-calculations of source δ15N NO3 based on denitrification progression suggest that isotopically-enriched nitrate (NO3-) in many springs of the UFA reflects groundwater denitrification rather than urban- or animal-derived inputs. © Author(s) 2012