The Kato Square Root Problem for Mixed Boundary Conditions

We consider the negative Laplacian subject to mixed boundary conditions on a bounded domain. We prove under very general geometric assumptions that slightly above the critical exponent $\frac{1}{2}$ its fractional power domains still coincide with suitable Sobolev spaces of optimal regularity. In combination with a reduction theorem recently obtained by the authors, this solves the Kato Square Root Problem for elliptic second order operators and systems in divergence form under the same geometric assumptions.Comment: Inconsistencies in Section 6 remove

Functional hybrid rubisco enzymes with plant small subunits and algal large subunits: engineered rbcS cDNA for expression in chlamydomonas.

There has been much interest in the chloroplast-encoded large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) as a target for engineering an increase in net CO(2) fixation in photosynthesis. Improvements in the enzyme would lead to an increase in the production of food, fiber, and renewable energy. Although the large subunit contains the active site, a family of rbcS nuclear genes encodes the Rubisco small subunits, which can also influence the carboxylation catalytic efficiency and CO(2)/O(2) specificity of the enzyme. To further define the role of the small subunit in Rubisco function, small subunits from spinach, Arabidopsis, and sunflower were assembled with algal large subunits by transformation of a Chlamydomonas reinhardtii mutant that lacks the rbcS gene family. Foreign rbcS cDNAs were successfully expressed in Chlamydomonas by fusing them to a Chlamydomonas rbcS transit peptide sequence engineered to contain rbcS introns. Although plant Rubisco generally has greater CO(2)/O(2) specificity but a lower carboxylation V(max) than Chlamydomonas Rubisco, the hybrid enzymes have 3-11% increases in CO(2)/O(2) specificity and retain near normal V(max) values. Thus, small subunits may make a significant contribution to the overall catalytic performance of Rubisco. Despite having normal amounts of catalytically proficient Rubisco, the hybrid mutant strains display reduced levels of photosynthetic growth and lack chloroplast pyrenoids. It appears that small subunits contain the structural elements responsible for targeting Rubisco to the algal pyrenoid, which is the site where CO(2) is concentrated for optimal photosynthesis.This work was supported in part by Grant DE-FG02-00ER15044 from the United States Department of Energy

Holocene fluctuations of neodymium isotope ratios in eastern Fram Strait sediments - An indication for deepwater variability?

EGU2012-11739 The Fram Strait as the only deep water connection of the world’s oceans to the Arctic plays a substantial role for the heat influx to the Arctic Ocean and controls freshening of the Nordic Seas through Arctic sea ice export. Large amounts of warm and saline Atlantic Water derived from the North Atlantic Drift transport most of the heat through eastern Fram Strait to the Arctic basin, resulting in year-round ice-free conditions. Arctic sea ice and cold and fresh waters exit the western part of the strait southward along the Greenland shelf. However, little is still known about the water mass transport at intermediate and bottom water depths in the Fram Strait. High-resolution Holocene sediment sequences from the Western Svalbard margin have been investigated for its neodymium isotope ratios stored in ferromanganese oxyhydroxide coatings of the sediment to derive information on the source of bottom seawater passing the site. The radiogenic isotope data are compared to a multitude of proxy indicators for the climatic and oceanographic variability in the eastern Fram Strait during the past 8,500 years. In order to obtain a calibration of the Nd isotope compositions extracted from sediments to modern bottom water mass signatures in the area, a set of core top and water samples from different water depths in the Fram Strait was additionally investigated for its present-day Nd isotope signatures. A significantly higher inflow of deepwater produced in the Nordic Seas to the core site is inferred for the earlier periods of the Holocene. Cooler surface water conditions and increased sea ice abundances during the late Holocene coincide with more radiogenic Nd isotope ratios likely resembling the neoglacial trend of the northern North Atlantic

Late Cretaceous structural control and Alpine overprint of the high-sulfidation Cu-Au epithermal Chelopech deposit, Srednogorie belt, Bulgaria

The Chelopech epithermal high-sulfidation deposit is located in the Panagyurishte ore district in Bulgaria, which is defined by a NNW alignment of Upper Cretaceous porphyry-Cu and Cu-Au epithermal deposits, and forms part of the Eastern European Banat-Srednogorie belt. Detailed structural mapping and drillcore descriptions have been used to define the structural evolution of the Chelopech deposit from the Late Cretaceous to the present. The Chelopech deposit is characterized by three fault populations including ∼N55, ∼N110, and ∼N155-trending faults, which are also recognized in the entire Panagyurishte district. Mapping and 3-D modeling show that hydrothermal alteration and orebody geometry at Chelopech are controlled by the ∼N55-trending and ∼N110-trending faults. Moreover, the ∼N155-trending faults are parallel to the regional ore deposit alignment of the Panagyurishte ore district. It is concluded that the three fault populations are early features and Late Cretaceous in age, and that they were active during high-sulfidation ore formation at Chelopech. However, the relative fault chronology cannot be deduced anymore due to Late Cretaceous and Tertiary tectonic overprint. Structurally controlled ore formation was followed by Senonian sandstone, limestone, and flysch deposition. The entire Late Cretaceous magmatic and sedimentary rock succession underwent folding, which produced WNW-oriented folds throughout the Panagyurishte district. A subsequent tectonic stage resulted in overthrusting of older rock units along ∼NE-trending reverse faults on the Upper Cretaceous magmatic and sedimentary host rocks of the high-sulfidation epithermal deposit at Chelopech. The three fault populations contemporaneous with ore formation, i.e., the ∼N55-, ∼N110- and ∼N155-trending faults, were reactivated as thrusts or reverse faults, dextral strike-slip faults, and transfer faults, respectively, during this event. Previous studies indicate that the present-day setting is characterized by dextral transtensional strike-slip tectonics. The ∼NE-trending overthrust affecting the Chelopech deposit and the reactivation of the ore-controlling faults are compatible with dextral strike-slip tectonics, but indicate local transpression, thus revealing that the Chelopech deposit might be sited at a transpressive offset within a generally transtensional strike-slip system. The early WNW-trending folds require a roughly NNE-SSW shortening, which is incompatible with the present-day dextral strike-slip tectonic setting and the ∼NE-trending thrust formed during the tectonic overprint of the Chelopech deposit. This reveals a rotation of the principal stress axes after Late Cretaceous high-sulfidation ore formation and post-ore deposition of sedimentary rocks. The nature of the sedimentary rocks interlayered and immediately covering the Upper Cretaceous magmatic rocks hosting the Chelopech deposit indicates sedimentation and associated volcanism in an extensional setting immediately before ore formation. It is concluded that the Chelopech deposit was formed when the tectonic setting changed from extensional during Late Cretaceous basin sedimentation and magmatism, to compressional producing WNW-trending folds under a roughly NNE-SSW compression, possibly in a sinistral strike-slip system. Thus, like other world-class, high-sulfidation epithermal deposits, the Chelopech deposit was formed at the end of an extensional period or during a transient period of stress relaxation, which are particularly favorable tectonic settings for the formation of high-sulfidation epithermal deposits. The exceptional preservation of the Upper Cretaceous Chelopech epithermal deposit is explained by the combined deposition of a thick Senonian sedimentary sequence on top of the Upper Cretaceous magmatic host rocks of the deposit, and the later overthrust of older rock units on top of the deposit. Our study at Chelopech supports previous studies stating that post-ore basin sedimentation and tectonic processes provide the favorable environment to preserve old epithermal deposits from erosion. The tectonic evolution of the Chelopech deposit is similar to that of the entire Panagyurishte ore district. This coherence of the magmatic, hydrothermal, and tectonic events from north to south suggests that the ore deposits of the entire Panagyurishte ore district were formed in a similar tectonic environmen

Impact of ambient oxygen on the surface structure of α-Cr2O3(0001)

Surface x-ray diffraction has been employed to quantitatively assess the surface structure of α-Cr2O3(0001) as a function of oxygen partial pressure at room temperature. In ultrahigh vacuum, the surface is found to exhibit a partially occupied double layer of chromium atoms. At an oxygen partial pressure of 1×10−2 mbar, the surface is determined to be terminated by chromyl species (CrO), clearly demonstrating that the presence of oxygen can significantly influence the structure of α-Cr2O3(0001)