bluuebunny/crossref_metadata_2025_split huggingface dataset:
Slow shock and rotational discontinuity in MHD and Hall MHD models with anisotropic pressure
Authors: Hau L.‐N. , Wang B.‐J. 
Published: June 2016

AbstractPressure anisotropy may modify the characteristics of magnetohydrodynamic (MHD) waves, in particular, the slow mode wave and the corresponding shocks and discontinuities. In this study the formation of slow shocks (SSs) in anisotropic plasmas is examined by solving the gyrotropic MHD and Hall MHD equations numerically for one‐dimensional Riemann problem. The MHD shocks and discontinuities are generated by imposing a finite normal magnetic field on the Harris type current sheet with a guide magnetic By component. It is shown that anomalous SSs moving faster than the intermediate wave or with positive density‐magnetic field correlation may be generated in gyrotropic MHD and Hall MHD models. Moreover, for some parameter values SSs may exhibit upstream wave trains with right‐handed polarization in contrast with the earlier prediction that SSs shall possess downstream left‐hand polarized wave trains based on the isotropic Hall MHD theory. For the cases of By ≠ 0, SSs with increased density and decreased magnetic field followed by noncoplanar intermediate mode or rotational discontinuity (RD)‐like structures similar to the compound SS‐RD structures observed in space plasma environments may possibly form in symmetric and asymmetric current layers. The Walén relation of these anomalous RDs without the correction of pressure anisotropy may significantly be violated.
Subsidence rates at the southern Salton Sea consistent with reservoir depletion
Authors: Barbour Andrew J. , Evans Eileen L. , Hickman Stephen H. , Eneva Mariana 
Published: June 2016

AbstractSpace geodetic measurements from the Envisat satellite between 2003 and 2010 show that subsidence rates near the southeastern shoreline of the Salton Sea in Southern California are up to 52mmyr−1greater than the far‐field background rate. By comparing these measurements with model predictions, we find that this subsidence appears to be dominated by poroelastic contraction associated with ongoing geothermal fluid production, rather than the purely fault‐related subsidence proposed previously. Using a simple point source model, we suggest that the source of this proposed volumetric strain is at depths between 1.0 km and 2.4 km (95% confidence interval), comparable to generalized boundaries of the Salton Sea geothermal reservoir. We find that fault slip on two previously imaged tectonic structures, which are part of a larger system of faults in the Brawley Seismic Zone, is not an adequate predictor of surface velocity fields because the magnitudes of the best fitting slip rates are often greater than the full plate boundary rate and at least 2 times greater than characteristic sedimentation rates in this region. Large‐scale residual velocity anomalies indicate that spatial patterns predicted by fault slip are incompatible with the observations.
Identification of dominant source of errors in developing streamflow and groundwater projections under near‐term climate change
Authors: Seo S. B. , Sinha T. , Mahinthakumar G. , Sankarasubramanian A. , Kumar M. 
Published: June 2016

AbstractUncertainties in projecting the changes in hydroclimatic variables (i.e., temperature and precipitation) under climate change partly arises from the inability of global circulation models (GCMs) in explaining the observed changes in hydrologic variables. Apart from the unexplained changes by GCMs, the process of customizing GCM projections to watershed scale through a model chain—spatial downscaling, temporal disaggregation, and hydrologic model—also introduces errors, thereby limiting the ability to explain the observed changes in hydrologic variability. Toward this, we first propose metrics for quantifying the errors arising from different steps in the model chain in explaining the observed changes in hydrologic variables (streamflow and groundwater). The proposed metrics are then evaluated using a detailed retrospective analyses in projecting the changes in streamflow and groundwater attributes in four target basins that span across a diverse hydroclimatic regimes over the U.S. Sunbelt. Our analyses focused on quantifying the dominant sources of errors in projecting the changes in eight hydrologic variables—mean and variability of seasonal streamflow, mean and variability of 3 day peak seasonal streamflow, mean and variability of 7 day low seasonal streamflow, and mean and standard deviation of groundwater depth—over four target basins using an Penn state Integrated Hydrologic Model (PIHM) between the period 1956–1980 and 1981–2005. Retrospective analyses show that small/humid (large/arid) basins show increased (reduced) uncertainty in projecting the changes in hydrologic attributes. Further, changes in error due to GCMs primarily account for the unexplained changes in mean and variability of seasonal streamflow. On the other hand, the changes in error due to temporal disaggregation and hydrologic model account for the inability to explain the observed changes in mean and variability of seasonal extremes. Thus, the proposed metrics provide insights on how the error in explaining the observed changes being propagated through the model under different hydroclimatic regimes.
Probing ionospheric structures using the LOFAR radio telescope
Authors: Mevius M. , van der Tol S. , Pandey V. N. , Vedantham H. K. , Brentjens M. A. , de Bruyn A. G. , Abdalla F. B. , Asad K. M. B. , Bregman J. D. , Brouw W. N. , Bus S. , Chapman E. , Ciardi B. , Fernandez E. R. , Ghosh A. , Harker G. , Iliev I. T. , Jelić V. , Kazemi S. , Koopmans L. V. E. , Noordam J. E. , Offringa A. R. , Patil A. H. , van Weeren R. J. , Wijnholds S. , Yatawatta S. , Zaroubi S. 
Published: June 2016

AbstractLOFAR is the LOw‐Frequency Radio interferometer ARray located at midlatitude (52°53′N). Here we present results on ionospheric structures derived from 29 LOFAR nighttime observations during the winters of 2012/2013 and 2013/2014. We show that LOFAR is able to determine differential ionospheric total electron content values with an accuracy better than 0.001 total electron content unit = 1016m−2 over distances ranging between 1 and 100 km. For all observations the power law behavior of the phase structure function is confirmed over a long range of baseline lengths, between 1 and 80 km, with a slope that is, in general, larger than the 5/3 expected for pure Kolmogorov turbulence. The measured average slope is 1.89 with a one standard deviation spread of 0.1. The diffractive scale, i.e., the length scale where the phase variance is 1rad2, is shown to be an easily obtained single number that represents the ionospheric quality of a radio interferometric observation. A small diffractive scale is equivalent to high phase variability over the field of view as well as a short time coherence of the signal, which limits calibration and imaging quality. For the studied observations the diffractive scales at 150 MHz vary between 3.5 and 30 km. A diffractive scale above 5 km, pertinent to about 90% of the observations, is considered sufficient for the high dynamic range imaging needed for the LOFAR epoch of reionization project. For most nights the ionospheric irregularities were anisotropic, with the structures being aligned with the Earth magnetic field in about 60% of the observations.
Cellulose acetate ultrafiltration membranes reinforced by cellulose nanocrystals: Preparation and characterization
Authors: Zhou Jianjun , Chen Jin , He Ming , Yao Jianfeng 
Published: June 2016

ABSTRACTCellulose nanocrystals (CNCs) were used as a sustainable additive to improve the hydrophilicity, permeability, antifouling, and mechanical properties of blend membranes. Different CNC loadings (0–1.2 wt %) in cellulose acetate (CA) membranes were studied. The blend membranes were prepared by a phase‐inversion process, and their chemical structure and morphological properties were characterized by attenuated total reflectance–Fourier transform infrared spectroscopy, scanning electron microscopy, porosity, and mean pore size and contact angle measurement. The blend membranes became more porous and more interconnected after the addition of CNCs. The thickness of the top layer decreased and a few large holes in the porous substrate appeared with increasing CNC loading. In comparison with the pure CA membranes, the pure water flux of the blend membranes increased with increasing CNC loading. It reaches a maximum value of 76 L m−2 h−1 when the CNC loading was 0.5 wt %. The antifouling properties of the CA membrane were significantly improved after the addition of CNCs, and the flux recovery ratio value increased to 68% with the addition of 0.5 wt % CNCs. In comparison with that of the pure CA membranes, the tensile strength of the composite membranes increased by 47%. This study demonstrated the importance of using sustainable CNCs to achieve great improvements in the physical and chemical performance of CA ultrafiltration membranes and provided an efficient method for preparing high‐performance membranes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43946.
Facile UV‐curing technique to establish a 3D‐grafted poly(ethylene glycol) layer on an epoxy resin base for underwater applications
Authors: Yang Yang , Luo Huali , Yang Jinlong , Huang Daofen , Zhou Shuxue 
Published: June 2016

ABSTRACTConstruction of a highly hydrophilic polymer surface with excellent long‐term stability underwater is a great challenge. In this paper, a facile ultraviolet (UV) curing technique was employed to realize the three‐dimensional (3D) grafting of poly(ethylene glycol) diacrylate (PEGDA, molecular weight: 400, 600, and 1000 g/mol) on a bisphenol A epoxy acrylate (BEA) sheet. The cross section morphology, surface chemical composition, and wettability of the sheets were monitored using an optical microscope, an attenuated total reflectance Fourier transform infrared spectroscope, and a water contact angle analyzer, respectively. The PEGDA‐grafted epoxy sheets displayed a highly hydrophilic surface and meanwhile possessed excellent stability underwater, despite the molecular weight of PEGDA. In contrast, the PEGDA/BEA blend sheets are easily damaged underwater, due to strong swelling. In addition, the PEGDA1000‐grafted BEA sheet demonstrated good antifouling performance in a natural marine environment. Nevertheless, its long‐term antifouling is not satisfactory, being presumably due to hydrolysis or biodegradation of the PEG segments. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43972.
Covalent integration of differently structured polyester polyols improves the toughness and strength of cationically polymerized, amorphous epoxy networks
Authors: Arnebold Andre , Wellmann Stefanie , Hartwig Andreas 
Published: June 2016

ABSTRACTThe structure–property relationship of polyester polyols in cationically polymerized, amorphous epoxy‐based copolymers is investigated. An epoxy resin is polymerized in the presence of structurally different polyesters. These resulting copolymers show improved tensile strength and toughness. The optimal epoxide/polyester ratio depends on the structure of the polyesters. Poly(δ‐valerolactone) (PVL) reveals the highest ester group density of the investigated polyesters, which enhances physical interactions with the epoxide during polymerization as well as in the network. Furthermore, PVL leads to outstanding tensile strength, strain at break, and toughness. Among all polyester polyols examined, PVL leads to the highest gel fraction or, in other words, the most complete integration into the epoxy network. This work shows that polyesters that are present in the reactive system should be covalently integrated into the polymer network as completely as possible to obtain good mechanical properties of the amorphous copolymer. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43986.
Ancillary contributions of heterologous biotin protein ligase and carbonic anhydrase for CO2 incorporation into 3‐hydroxypropionate by metabolically engineered Pyrococcus furiosus
Authors: Lian Hong , Zeldes Benjamin M. , Lipscomb Gina L. , Hawkins Aaron B. , Han Yejun , Loder Andrew J. , Nishiyama Declan , Adams Michael W.W. , Kelly Robert M. 
Published: June 2016

ABSTRACTAcetyl‐Coenzyme A carboxylase (ACC), malonyl‐CoA reductase (MCR), and malonic semialdehyde reductase (MRS) convert HCO3− and acetyl‐CoA into 3‐hydroxypropionate (3HP) in the 3‐hydroxypropionate/4‐hydroxybutyrate carbon fixation cycle resident in the extremely thermoacidophilic archaeon Metallosphaera sedula. These three enzymes, when introduced into the hyperthermophilic archaeon Pyrococcus furiosus, enable production of 3HP from maltose and CO2. Sub‐optimal function of ACC was hypothesized to be limiting for production of 3HP, so accessory enzymes carbonic anhydrase (CA) and biotin protein ligase (BPL) from M. sedula were produced recombinantly in Escherichia coli to assess their function. P. furiosus lacks a native, functional CA, while the M. sedula CA (Msed_0390) has a specific activity comparable to other microbial versions of this enzyme. M. sedula BPL (Msed_2010) was shown to biotinylate the β‐subunit (biotin carboxyl carrier protein) of the ACC in vitro. Since the native BPLs in E. coli and P. furiosus may not adequately biotinylate the M. sedula ACC, the carboxylase was produced in P. furiosus by co‐expression with the M. sedula BPL. The baseline production strain, containing only the ACC, MCR, and MSR, grown in a CO2‐sparged bioreactor reached titers of approximately 40 mg/L 3HP. Strains in which either the CA or BPL accessory enzyme from M. sedula was added to the pathway resulted in improved titers, 120 or 370 mg/L, respectively. The addition of both M. sedula CA and BPL, however, yielded intermediate titers of 3HP (240 mg/L), indicating that the effects of CA and BPL on the engineered 3HP pathway were not additive, possible reasons for which are discussed. While further efforts to improve 3HP production by regulating gene dosage, improving carbon flux and optimizing bioreactor operation are needed, these results illustrate the ancillary benefits of accessory enzymes for incorporating CO2 into 3HP production in metabolically engineered P. furiosus, and hint at the important role that CA and BPL likely play in the native 3HP/4HB pathway in M. sedula. Biotechnol. Bioeng. 2016;113: 2652–2660. © 2016 Wiley Periodicals, Inc.
Production of citramalate by metabolically engineered Escherichia coli
Authors: Wu Xianghao , Eiteman Mark A. 
Published: June 2016

ABSTRACTCitramalic acid (citramalate) is a five carbon hydroxy‐dicarboxylic acid and potential precursor for the production of methacrylic acid from renewable resources. We examined citramalate production in Escherichia coli expressing the citramalate synthase gene cimA. Although, knockouts in ldhA coding lactate dehydrogenase and glcB/aceB coding malate synthase did not benefit citramalate accumulation, knockouts in gltA coding citrate synthase, and ackA coding acetate kinase significantly increased citramalate accumulation compared to the control strain. A fed‐batch process in a controlled fermenter using a glucose feed resulted in 46.5 g/L citramalate in 132 h with a yield of 0.63 g/g, over 75% of the theoretical maximum yield from glucose of 0.82 g/g. Biotechnol. Bioeng. 2016;113: 2670–2675. © 2016 Wiley Periodicals, Inc.
Molecular basis of substrate recognition and specificity revealed in family 12 glycoside hydrolases
Authors: Calzado Felipe , Prates Erica T. , Gonçalves Thiago A. , Rubio Marcelo V. , Zubieta Mariane P. , Squina Fabio M. , Skaf Munir S. , Damásio André R.L. 
Published: June 2016

ABSTRACTFungal GH12 enzymes are classified as xyloglucanases when they specifically target xyloglucans, or promiscuous endoglucanases when they exhibit catalytic activity against xyloglucan and β‐glucan chains. Several structural and functional studies involving GH12 enzymes tried to explain the main patterns of xyloglucan activity, but what really determines xyloglucanase specificity remains elusive. Here, three fungal GH12 enzymes from Aspergillus clavatus (AclaXegA), A. zonatus (AspzoGH12), and A. terreus (AtEglD) were studied to unveil the molecular basis for substrate specificity. Using functional assays, site‐directed mutagenesis, and molecular dynamics simulations, we demonstrated that three main regions are responsible for substrate selectivity: (i) the YSG group in loop 1; (ii) the SST group in loop 2; and (iii) loop A3‐B3 and neighboring residues. Functional assays and sequence alignment showed that while AclaXegA is specific to xyloglucan, AtEglD cleaves β‐glucan, and xyloglucan. However, AspzoGH12 was also shown to be promiscuous contrarily to a sequence alignment‐based prediction. We find that residues Y111 and R93 in AtEglD harbor the substrate in an adequate orientation for hydrolysis in the catalytic cleft entrance and that residues Y19 in AclaXegA and Y30 in AspzoGH12 partially compensate the absence of the YSG segment, typically found in promiscuous enzymes. The results point out the multiple structural factors underlying the substrate specificity of GH12 enzymes. Biotechnol. Bioeng. 2016;113: 2577–2586. © 2016 Wiley Periodicals, Inc.
Investigating strain dependency in the production of aromatic compounds in Saccharomyces cerevisiae
Authors: Suástegui Miguel , Guo Weihua , Feng Xueyang , Shao Zengyi 
Published: June 2016

ABSTRACTAlthough Saccharomyces cerevisiae is the most highly domesticated yeast, strain dependency in biotechnological processes still remains as a common, yet poorly understood phenomenon. To investigate this, the entrance to the aromatic amino acid biosynthetic pathway was compared in four commonly used S. cerevisiae laboratory strains. The strains were engineered to accumulate shikimate by overexpressing a mutant version of the pentafunctional ARO1 enzyme with disrupted activity in the shikimate kinase subunit. Carbon tracing and 13C metabolic flux analysis combined with quantitative PCR, revealed that precursor availability and shikimate production were dramatically different in the four equally engineered strains, which were found to be correlated with the strains’ capacity to deal with protein overexpression burden. By implementing a strain‐dependent approach, the genetic platform was reformulated, leading to an increase in yield and titer in all strains. The highest producing strain, INVSc1‐SA3, produced 358 mg L−1 of shikimate with a yield of 17.9 mg g−1glucose. These results underline the importance of strain selection in developing biological manufacturing processes, demonstrate the first case of high production of shikimate in yeast, and provide an appropriate platform for strain selection for future production of aromatic compounds. Biotechnol. Bioeng. 2016;113: 2676–2685. © 2016 Wiley Periodicals, Inc.
A comparison between data requirements and availability for calibrating predictive ecological models for lowland UK woodlands: learning new tricks from old trees
Authors: Evans Matthew R. , Moustakas Aristides 
Published: June 2016

AbstractWoodlands provide valuable ecosystem services, and it is important to understand their dynamics. To predict the way in which these might change, we need process‐based predictive ecological models, but these are necessarily very data intensive. We tested the ability of existing datasets to provide the parameters necessary to instantiate a well‐used forest model (SORTIE) for a well‐studied woodland (Wytham Woods). Only five of SORTIE's 16 equations describing different aspects of the life history and behavior of individual trees could be parameterized without additional data collection. One age class – seedlings – was completely missed as they are shorter than the height at which Diameter at Breast Height (DBH) is measured. The mensuration of trees has changed little in the last 400 years (focussing almost exclusively on DBH) despite major changes in the nature of the source of value obtained from trees over this time. This results in there being insufficient data to parameterize process‐based models in order to meet the societal demand for ecological prediction. We do not advocate ceasing the measurement of DBH, but we do recommend that those concerned with tree mensuration consider whether additional measures of trees could be added to their data collection protocols. We also see advantages in integrating techniques such as ground‐based LIDAR or remote sensing techniques with long‐term datasets to both preserve continuity with what has been performed in the past and to expand the range of measurements made.
Shifts in leaf litter breakdown along a forest–pasture–urban gradient in Andean streams
Authors: Iñiguez‐Armijos Carlos , Rausche Sirkka , Cueva Augusta , Sánchez‐Rodríguez Aminael , Espinosa Carlos , Breuer Lutz 
Published: June 2016

AbstractTropical montane ecosystems of the Andes are critically threatened by a rapid land‐use change which can potentially affect stream variables, aquatic communities, and ecosystem processes such as leaf litter breakdown. However, these effects have not been sufficiently investigated in the Andean region and at high altitude locations in general. Here, we studied the influence of land use (forest–pasture–urban) on stream physico‐chemical variables (e.g., water temperature, nutrient concentration, and pH), aquatic communities (macroinvertebrates and aquatic fungi) and leaf litter breakdown rates in Andean streams (southern Ecuador), and how variation in those stream physico‐chemical variables affect macroinvertebrates and fungi related to leaf litter breakdown. We found that pH, water temperature, and nutrient concentration increased along the land‐use gradient. Macroinvertebrate communities were significantly different between land uses. Shredder richness and abundance were lower in pasture than forest sites and totally absent in urban sites, and fungal richness and biomass were higher in forest sites than in pasture and urban sites. Leaf litter breakdown rates became slower as riparian land use changed from natural to anthropogenically disturbed conditions and were largely determined by pH, water temperature, phosphate concentration, fungal activity, and single species of leaf‐shredding invertebrates. Our findings provide evidence that leaf litter breakdown in Andean streams is sensitive to riparian land‐use change, with urban streams being the most affected. In addition, this study highlights the role of fungal biomass and shredder species (Phylloicus; Trichoptera and Anchytarsus; Coleoptera) on leaf litter breakdown in Andean streams and the contribution of aquatic fungi in supporting this ecosystem process when shredders are absent or present low abundance in streams affected by urbanization. Finally, we summarize important implications in terms of managing of native vegetation and riparian buffers to promote ecological integrity and functioning of tropical Andean stream ecosystems.