Semiconvergence and Relaxation Parameters for Projected SIRT Algorithms

We give a detailed study of the semiconvergence behavior of projected nonstationary simultaneous iterative reconstruction technique (SIRT) algorithms, including the projected Landweber algorithm. We also consider the use of a relaxation parameter strategy, proposed recently for the standard algorithms, for controlling the semiconvergence of the projected algorithms. We demonstrate the semiconvergence and the performance of our strategies by examples taken from tomographic imaging.Funding Agencies|Danish Research Council for Technology and Production Sciences|274-07-0065|</p

Lectin staining shows no evidence of involvement of glycocalyx/mucous layer carbohydrate structures in development of celiac disease

The presence of unique carbohydrate structures in the glycocalyx/mucous layer of the intestine may be involved in a susceptibility to celiac disease (CD) by serving as attachment sites for bacteria. This host-microbiota interaction may influence the development of CD and possibly other diseases with autoimmune components. We examined duodenal biopsies from a total of 30 children, of which 10 had both celiac disease (CD) and type 1 diabetes (T1D); 10 had CD alone; and 10 were suspected of having gastrointestinal disease, but had normal duodenal histology (non-CD controls). Patients with both CD and T1D were examined before and after remission following a gluten-free diet. We performed lectin histochemistry using peanut agglutinin (PNA) and Ulex europaeus agglutinin (UEA) staining for Gal-β(1,3)-GalNAc and Fucα1-2Gal-R, respectively, of the glycocalyx/mucous layer. The staining was scored based on dissemination of stained structures on a scale from 0 to 3. Evaluation of the scores revealed no difference between biopsies obtained before and after remission in the group of children with both CD and T1D. A comparison of this pre-remission group with the children who had CD alone or the non-CD controls also showed no significant differences. Based on our material, we found no indication that the presence of Gal-β(1,3)-GalNAc or Fucα1-2Gal-R is involved in the susceptibility to CD, or that the disease process affects the expression of these carbohydrates

Using ⁸⁷Sr/⁸⁶Sr Ratios to Date Fossil Methane Seep Deposits: Methodological Requirements and an Example from the Great Valley Group, California

Methane seep carbonates preserve information about the history of methane seepage and of the fauna inhabiting these ecosystems. For this information to be useful, a reliable determination of the carbonates’ stratigraphic ages is required, but this is not always available. Here we investigate the using strontium isotope stratigraphy to date fossil methane seep carbonates via detailed petrographic and geochemical investigation of the different carbonate phases in biostratigraphically well-dated seep carbonates of Paleozoic, Mesozoic, and Cenozoic age. The best results are obtained from banded, botryoidal rim cements from carbonate phases showing a weak or no cathodoluminescence signal, an oxygen isotope signature close to that of seawater, and the lowest Mn concentrations. We then applied the method to a presumably late Jurassic seep carbonate from the Great Valley Group in California. Strontium isotope ratios of the least diagenetically altered carbonate phases indicate a Tithonian (late Jurassic) age for this seep site, which is in conflict with a recent study that suggested the absence of Jurassic strata from the Great Valley Group

Biodegradability of hydrothermally altered deep-sea dissolved organic matter

Deep-sea dissolved organic matter (DOM) constitutes a huge carbon reservoir in the worlds' oceans that – despite its abundance – is virtually unused as a substrate by marine heterotrophs. Heating within hydrothermal systems induces major molecular modifications of deep-sea DOM. Here, we tested the hypothesis that hydrothermal heating of deep-sea DOM enhances bioavailability. Aliquots of DOM extracted from the deep North Pacific (North Equatorial Pacific Intermediate Water; NEqPIW) were re-dissolved in artificial seawater and subjected to temperatures of 100 and 200 °C (40 MPa) using Dickson-type reactors. In agreement with earlier findings we observed a temperature-related drop in dissolved organic carbon (DOC) concentration (−6.1% at 100 °C, −21.0% at 200 °C) that predominantly affected the solid-phase extractable (SPE-DOC) fraction (−18.2% at 100 °C, −51.4% at 200 °C). Fourier-transform ion cyclotron resonance mass spectrometric (FT-ICR-MS) analysis confirmed a temperature-related reduction of average molecular mass, O/C ratios, double bond equivalents (DBE) and a relative increase in aromaticity (AImod). This thermally altered DOM was added (25 μmol L−1 DOC) to deep-water samples from the South West Pacific (Kermadec Arc, RV Sonne / SO253, 32° 37.706′ S | 179° 38.728′ W) and incubated with the prevailing natural microbial community. After 16 days at 4 °C in the dark, prokaryotic cell counts in incubations containing the full spectrum of thermally-degraded DOM (extractable and non-extractable compounds) had increased considerably (on average 21× for DOM100°C and 27× for DOM200°C). In contrast, prokaryotic growth in incubations to which only solid-phase extractable thermally-altered DOM was added was not enhanced compared to control incubations. The experiments demonstrate that temperature-driven degradation of deep-sea recalcitrant DOM within hydrothermal systems turns fractions of it accessible to microbes. The thermally-produced DOM compounds that stimulate microbial growth are not retained on reversed-phase resins (SPE-DOM) and are likely low-molecular mass organic acids. Despite the comprehensive compositional modifications of the solid-phase extractable (SPE-DOM) fraction through heating, it remains inaccessible to microbes at the investigated concentration levels. The microbial incubation resulted in only minor and mostly insignificant overall changes in SPE-DOM molecular composition and concentration

Reduced timing Sensitivity in all-optical switching using flat-top control pulses obtained by the optical fourier transform technique

For high-speed serial data, timing tolerance is crucial for switching and regeneration. We propose a novel scheme to generate flat-top pulses, for use as gating control pulses. The scheme relies on spectral shaping by a square-shaped filter, followed by a linear transformation of the spectral shape into the time domain, referred to as the optical Fourier transform technique. A 3 ps flat-top pulse derived from a 3 nm wide square filter is obtained, and used to gate an all-optical OTDM demultiplexer, yielding an error-free timing jitter tolerance of 3 ps for 80 Gb/s and 160 Gb/s data signals.</p

Experimental evidence for the hydrothermal formation of native sulfur by synproportionation

Elemental sulfur (S0) is known to form in submarine acid-sulfate vents by disproportionation of magmatic SO2. S0 formed upon disproportionation shows δ34SS values considerably lower than the influxing magmatic SO2, which results in δ34SS values typically &lt;0‰. The peculiar occurrence of isotopically heavy sulfur in the Kemp Caldera hydrothermal system (δ34SS &gt; 5‰) and Niua North (δ34SS = 3.1‰) led to the suggestion that disproportionation is not the only sulfur forming process in submarine hydrothermal systems. We conducted hydrothermal experiments to investigate if synproportionation of SO2 and H2S can explain the occurrence and isotopic composition of S0 observed in some vent fields. Provided that SO2 and H2S are both abundant, this formation mechanism is thermodynamically conceivable, but it has not yet been demonstrated experimentally that this process actually takes place in submarine hydrothermal systems. We conducted the experiments in collapsible Ti-cells under pT-conditions (20–30 MPa, 220°C) that are relevant to S0 formation in submarine hydrothermal systems. We used starting concentrations of 10 mM sulfite and 20 mM sulfide of known isotopic composition. Under acidic conditions (pH25 °C = 1.2), S0 was the most abundant reaction product, but small amounts of sulfate were also produced. A Rayleigh fractionation model was applied to determine the isotopic composition of SO42–, SO2, H2S and S0 expected to form by SO2 disproportionation, H2S oxidation, and SO2–H2S synproportionation. The sulfur isotopic signatures of the sulfur produced in the experiments can only be explained by synproportionation of sulfite and sulfide. These results provide strong evidence that synproportionation is likely responsible for exceptionally high δ34SS values observed in S0 from some arc/back-arc hydrothermal environments, like the Kemp Caldera in the South Sandwich arc. Coeval degassing of H2S and SO2 is likely required to have this particular reaction dominate in the H–S–O reaction network and produce noticeable accumulations of isotopically heavy native sulfur at the seafloor