bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pyroxenes as tracers of mantle water variations
Authors: Warren Jessica M. , Hauri Erik H. 
Published: March 2014

AbstractThe concentration and distribution of volatiles in the Earth's mantle influence properties such as melting temperature, conductivity, and viscosity. To constrain upper mantle water content, concentrations of H2O, P, and F were measured in olivine, orthopyroxene, and clinopyroxene in mantle peridotites by secondary ion mass spectrometry. Analyzed peridotites are xenoliths (Pali Aike, Spitsbergen, Samoa), orogenic peridotites (Josephine Peridotite), and abyssal peridotites (Gakkel Ridge, Southwest Indian Ridge, Tonga Trench). The comparison of fresh and altered peridotites demonstrates that low to moderate levels of alteration do not affect H2O concentrations, in agreement with mineral diffusion data. Olivines have diffusively lost water during emplacement, as demonstrated by disequilibrium between olivine and coexisting pyroxenes. In contrast, clinopyroxene and orthopyroxene preserve their high‐temperature water contents, and their partitioning agrees with published experiments and other xenoliths. Hence, olivine water concentrations can be determined from pyroxene concentrations using mineral‐mineral partition coefficients. Clinopyroxenes have 60–670 ppm H2O, while orthopyroxenes have 10–300 ppm, which gives calculated olivine concentrations of 8–34 ppm. The highest olivine water concentration translates to an effective viscosity of 6 × 1019 Pa s at 1250°C and ~15 km depth, compared to a dry effective viscosity of 2.5 × 1021 Pa s. Bulk rock water concentrations, calculated using mineral modes, are 20–220 ppm and correlate with peridotite indices of melt depletion. However, trace element melt modeling indicates that peridotites have too much water relative to their rare earth element concentrations, which may be explained by late‐stage melt addition, during which only hydrogen diffuses fast enough for reequilibration.
The influence of slope breaks on lava flow surface disruption
Authors: Glaze Lori S. , Baloga Stephen M. , Fagents Sarah A. , Wright Robert 
Published: March 2014

AbstractChanges in the underlying slope of a lava flow impart a significant fraction of rotational energy beyond the slope break. The eddies, circulation, and vortices caused by this rotational energy can disrupt the flow surface, having a significant impact on heat loss and thus the distance the flow can travel. A basic mechanics model is used to compute the rotational energy caused by a slope change. The gain in rotational energy is deposited into an eddy of radius R whose energy is dissipated as it travels downstream. A model of eddy friction with the ambient lava is used to compute the time‐rate of energy dissipation. The key parameter of the dissipation rate is shown to be ρR2/μ, where ρ is the lava density and μ is the viscosity, which can vary by orders of magnitude for different flows. The potential spatial disruption of the lava flow surface is investigated by introducing steady state models for the main flow beyond the steepening slope break. One model applies to slow‐moving flows with both gravity and pressure as the driving forces. The other model applies to fast‐moving, low‐viscosity, turbulent flows. These models provide the flow velocity that establishes the downstream transport distance of disrupting eddies before they dissipate. The potential influence of slope breaks is discussed in connection with field studies of lava flows from the 1801 Hualalai and 1823 Keaiwa Kilauea, Hawaii, and 2004 Etna eruptions.
Evaluation of glacier changes in high‐mountain Asia based on 10 year GRACE RL05 models
Authors: Yi Shuang , Sun Wenke 
Published: March 2014

AbstractIn this paper, 10 years of time‐variable gravity data from the Gravity Recovery and Climate Experiment Release 05 have been used to evaluate the glacier melting rate in high‐mountain Asia (HMA) using a new computing scheme, i.e., the Space Domain Inverse method. We find that in HMA area, there are three different kinds of signal sources that should be treated together. The two generally accepted sources, glacier melting and India underground water depletion, are estimated to change at the rate of −35.0 ± 5.8 Gt/yr (0.09 mm/yr sea level rising) and −30.6 ± 5.0 Gt/yr, respectively. The third source is the remarkable positive signal (+30 Gt/yr) in the inner Tibetan Plateau, which is challenging to explain. Further, we have found that there is a 5 year undulation in Pamir and Karakoram, which can explain the controversies of the previous studies on the glacier melting rate here. This 5 year signal can be explained by the influence of Arctic Oscillation and El Niño–Southern Oscillation.
Surface ozone variability and trends over the South African Highveld from 1990 to 2007
Authors: Balashov Nikolay V. , Thompson Anne M. , Piketh Stuart J. , Langerman Kristy E. 
Published: March 2014

AbstractSurface ozone is a secondary air pollutant formed from reactions between nitrogen oxides (NOx = NO + NO2) and volatile organic compounds in the presence of sunlight. In this work we examine effects of the climate pattern known as the El Niño–Southern Oscillation (ENSO) and NOx variability on surface ozone from 1990 to 2007 over the South African Highveld, a heavily populated region in South Africa with numerous industrial facilities. Over summer and autumn (December–May) on the Highveld, El Niño, as signified by positive sea surface temperature (SST) anomalies over the central Pacific Ocean, is typically associated with drier and warmer than normal conditions favoring ozone formation. Conversely, La Niña, or negative SST anomalies over the central Pacific Ocean, is typically associated with cloudier and above normal rainfall conditions, hindering ozone production. We use a generalized regression model to identify any linear dependence that the Highveld ozone, measured at five air quality monitoring stations, may have on ENSO and NOx. Our results indicate that four out of the five stations exhibit a statistically significant sensitivity to ENSO at some point over the December–May period where El Niño amplifies ozone formation and La Niña reduces ozone formation. Three out of the five stations reveal statistically significant sensitivity to NOx variability, primarily in winter and spring. Accounting for ENSO and NOx effects throughout the study period of 18 years, two stations exhibit statistically significant negative ozone trends in spring, one station displays a statistically significant positive trend in August, and two stations show no statistically significant change in surface ozone.
Laboratory simulations of acid‐sulfate weathering under volcanic hydrothermal conditions: Implications for early Mars
Authors: Marcucci Emma C. , Hynek Brian M. 
Published: March 2014

AbstractWe have completed laboratory experiments and thermochemical equilibrium models to investigate secondary mineral formation under conditions akin to volcanic, hydrothermal acid‐sulfate weathering systems. Our research used the basaltic mineralogy at Cerro Negro Volcano, Nicaragua, characterized by plagioclase, pyroxene, olivine, and volcanic glass. These individual minerals and whole‐rock field samples were reacted in the laboratory with 1 molal sulfuric acid at varying temperatures (65, 150, and 200°C), fluid:rock weight ratios (1:1, 4:1, and 10:1), and durations (1–60 days). Thermochemical equilibrium models were developed using Geochemist's Workbench. To understand the reaction products and fluids, we employed scanning electron microscopy/energy dispersive spectroscopy, X‐ray diffraction, and inductively coupled plasma‐atomic emission spectroscopy. The results of our experiments and models yielded major alteration minerals that include anhydrite, natroalunite, minor iron oxide, and amorphous Al‐Si gel. We found that variations in experimental parameters did not drastically change the suite of minerals produced; instead, abundance, size, and crystallographic shape changed. Our results also suggest that it is essential to separate phases formed during experiments from those formed during fluid evaporation to fully understand the reaction processes. Our laboratory reacted and model predicted products are consistent with the mineralogy observed at places on Mars. However, our results indicate that determination of the formation conditions requires microscopic imagery and regional context, as well as a thorough understanding of contributions from both experiment precipitation and fluid evaporation minerals.
Impact heating and coupled core cooling and mantle dynamics on Mars
Authors: Roberts James H. , Arkani‐Hamed Jafar 
Published: March 2014

AbstractSeveral giant impact basins of mid‐Noachian age have been identified on Mars, and the global magnetic field appears to have vanished at about the same time. The impacts that formed these basins delivered a large amount of heat to the planetary interior, modified the pattern of mantle convection, and suppressed core cooling, potentially contributing to the cessation of dynamo activity. Here we investigate the thermal evolution of Mars in response to the largest basin‐forming impacts, using a new method of coupling models of mantle convection with parameterized core cooling. We find that heating by a large impact generates a strong hemispheric upwelling in the mantle, which quickly spreads into a warm layer beneath the stagnant lid. The impact heating of the core leads to spherically symmetric stratification of the core; the outermost layers are strongly heated. This acts as a thermal “blanket” that prevents cooling of the interior and shuts down core convection. While the hottest part of the thermal blanket in the outermost core disappears relatively quickly, dynamo activity does not restart for ~100 Myr, and the core does not return to a fully convective state for ~1 Gyr following the impact.
Large‐scale estimation and uncertainty analysis of gross primary production in Tibetan alpine grasslands
Authors: He Honglin , Liu Min , Xiao Xiangming , Ren Xiaoli , Zhang Li , Sun Xiaomin , Yang Yuanhe , Li Yingnian , Zhao Liang , Shi Peili , Du Mingyuan , Ma Yaoming , Ma Mingguo , Zhang Yu , Yu Guirui 
Published: March 2014

AbstractGross primary production (GPP) is an important parameter for carbon cycle and climate change research. Previous estimations of GPP on the Tibetan Plateau were usually reported without quantitative uncertainty analyses. This study sought to quantify the uncertainty and its partitioning in GPP estimation across Tibetan alpine grasslands during 2003–2008 with the modified Vegetation Photosynthesis Model (VPM). Monte Carlo analysis was used to provide a quantitative assessment of the uncertainty in model simulations, and Sobol’ variance decomposition method was applied to determine the relative contribution of each source of uncertainty to the total uncertainty. The results showed that the modified VPM successfully reproduced the seasonal dynamics and magnitude of GPP of 10 flux tower sites on the plateau (R2 = 0.77 − 0.95,p < 0.001). The 6 year mean GPP in Tibetan alpine grasslands was estimated at 223.3 Tg C yr−1(312.3 g C m−2 yr−1). The mean annual GPP increased from western to eastern plateau, with the increase of annual temperature and precipitation and the decrease of elevation, while the decrease of GPP from southern to northern plateau was primarily driven by air temperature. Furthermore, the mean relative uncertainty of the annual GPP was 18.30%, with larger uncertainty occurring in regions with lower GPP. Photosynthetic active radiation, enhanced vegetation index, and the maximum light use efficiency (LUE) are the primary sources of uncertainty in GPP estimation, contributing 36.84%, 26.86%, and 21.99%, respectively. This emphasizes the importance of uncertainty in driving variables as well as that of maximum LUE in LUE model simulation.
Contrasting controls on wildland fires in Southern California during periods with and without Santa Ana winds
Authors: Jin Yufang , Randerson James T. , Faivre Nicolas , Capps Scott , Hall Alex , Goulden Michael L. 
Published: March 2014

AbstractWildland fires in Southern California can be divided into two categories: fall fires, which are typically driven by strong offshore Santa Ana winds, and summer fires, which occur with comparatively weak onshore winds and hot and dry weather. Both types of fire contribute significantly to annual burned area and economic loss. An improved understanding of the relationship between Southern California's meteorology and fire is needed to improve predictions of how fire will change in the future and to anticipate management needs. We used output from a regional climate model constrained by reanalysis observations to identify Santa Ana events and partition fires into those occurring during periods with and without Santa Ana conditions during 1959–2009. We then developed separate empirical regression models for Santa Ana and non‐Santa Ana fires to quantify the effects of meteorology on fire number and size. These models explained approximately 58% of the seasonal and interannual variation in the number of Santa Ana fires and 36% of the variation in non‐Santa Ana fires. The number of Santa Ana fires increased during years when relative humidity during Santa Ana events and fall precipitation were below average, indicating that fuel moisture is a key controller of ignition. Relative humidity strongly affected Santa Ana fire size. Cumulative precipitation during the previous three winters was significantly correlated with the number of non‐Santa Ana fires, presumably through increased fine fuel density and connectivity between infrastructure and nearby vegetation. Both relative humidity and the preceding wet season precipitation influenced non‐Santa Ana fire size. Regression models driven by meteorology explained 57% of the temporal variation in Santa Ana burned area and 22% of the variation in non‐Santa Ana burned area. The area burned by non‐Santa Ana fires has increased steadily by 1.7% year−1since 1959 (p < 0.006); the occurrence of extremely large Santa Ana fires has increased abruptly since 2003. Our results underscore the need to separately consider the fuel and meteorological controls on Santa Ana and non‐Santa Ana fires when projecting climate change impacts on regional fire.
Probabilistic prediction of cyanobacteria abundance in a Korean reservoir using a Bayesian Poisson model
Authors: Cha YoonKyung , Park Seok Soon , Kim Kyunghyun , Byeon Myeongseop , Stow Craig A. 
Published: March 2014

AbstractThere have been increasing reports of harmful algal blooms (HABs) worldwide. However, the factors that influence cyanobacteria dominance and HAB formation can be site‐specific and idiosyncratic, making prediction challenging. The drivers of cyanobacteria blooms in Lake Paldang, South Korea, the summer climate of which is strongly affected by the East Asian monsoon, may differ from those in well‐studied North American lakes. Using the observational data sampled during the growing season in 2007–2011, a Bayesian hurdle Poisson model was developed to predict cyanobacteria abundance in the lake. The model allowed cyanobacteria absence (zero count) and nonzero cyanobacteria counts to be modeled as functions of different environmental factors. The model predictions demonstrated that the principal factor that determines the success of cyanobacteria was temperature. Combined with high temperature, increased residence time indicated by low outflow rates appeared to increase the probability of cyanobacteria occurrence. A stable water column, represented by low suspended solids, and high temperature were the requirements for high abundance of cyanobacteria. Our model results had management implications; the model can be used to forecast cyanobacteria watch or alert levels probabilistically and develop mitigation strategies of cyanobacteria blooms.
Lyapunov‐based trajectory tracking controller for a fixed‐wing unmanned aerial vehicle in the presence of wind
Authors: Brezoescu A. , Lozano R. , Castillo P. 
Published: March 2014

SummaryThis paper addresses the directional control problem of autonomous air vehicles in order to obtain trajectory tracking capabilities when flying in other than calm conditions. The control strategy is designed in the framework of the Lyapunov theory, and adaptive techniques are employed for online wind identification. An application of light fixed‐wing unmanned aerial vehicles that consists in tracking straight‐line paths between geo‐referenced waypoints is first formulated, and the dynamic of the cross track error with respect to such trajectory is further obtained from the lateral airplane equations of motion. The dynamic order of the closed‐loop adaptive system is guaranteed to be minimal by choosing the proper variables so that the tuning functions method could be applied. Several simulations taking into account unknown wind have been performed to analyze the behavior and the robustness of the control scheme. Copyright © 2014 John Wiley & Sons, Ltd.
Correlates of urban children's leisure‐time physical activity and sedentary behaviors during school days
Authors: Marques Adilson , Sallis James F. , Martins João , Diniz José , Carreiro Da Costa Francisco 
Published: March 2014

ABSTRACTObjectivesUnderstanding correlates of physical activity and sedentary behaviors may contribute to fostering active lifestyles. This study aimed to identify correlates of physical activity and sedentary behaviors in leisure‐time among Portuguese urban children, during school days.MethodsA cross‐sectional survey was conducted with 802 students (416 boys), aged 10–12 years. A questionnaire was used to collect data of physical activity, sedentary behaviors, psychological and behavioral variables related to physical activity and sedentary behaviors. Analyses were run separately for boys and girls.ResultsTelevision viewing occupied the most leisure‐time of boys and girls, followed by computer usage, and video game playing. These behaviors occupied 259.7 min/day for boys and 208.6 for girls (P = 0.002). Reported moderate‐to‐vigorous physical activity was 23.7 min for boys and 12.8 min for girls (P < 0.001). Perception of competence and academic achievement were related to physical activity for the boys and girls. Computer use and playing video games with friends were only related to physical activity for the boys. On the other hand, parents' physical activity participation was related with boys' and girls' physical activity. The correlates of sedentary behavior were outdoor play for the boys, age for the girls, and playing video games with friends for both.ConclusionsThis finding suggests that interventions should be considered to replace joint video game time with joint physical activity time. Am. J. Hum. Biol. 26:407–412, 2014. © 2014 Wiley Periodicals, Inc.
Reinforcing biopolymer hydrogels with ionic‐covalent entanglement hydrogel microspheres
Authors: Kirchmajer Damian Martin , Panhuis Marc in het 
Published: March 2014

ABSTRACTMicroscopic hydrogel spheres can be used to improve the mechanical properties of conventional hydrogels. We prepared ionic‐covalent entanglement (ICE) hydrogel microspheres of calcium cross‐linked gellan gum and genipin cross‐linked gelatin using a water‐in‐oil emulsion‐based processing technique. The method was optimized to produce microspheres with number average diameter 4 ± 1 µm. These ICE microspheres were used to reinforce gelatin hydrogels and improve their compressive mechanical properties. The strongest microsphere reinforced hydrogels possessed a compressive mechanical stress at failure of 0.50 ± 0.1 MPa and a compressive secant modulus of 0.18 ± 0.02 MPa. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40557.
A different extensional viscosity prediction based on entry pressure drop
Authors: Yang Jia , Dai Yahui , Li Jigong 
Published: March 2014

ABSTRACTExtensional viscosity, an important processing parameter, can control the processing properties of polymeric products in industrial processes, such as fiber spinning, blow molding, and film casting. In this article, based on the equivalent thought, the contraction flow in the circular channel was studied without using the power laws, and the new equations of the extensional strain rate and the extensional viscosity based on entry pressure drop were proposed. The extensional viscosity of two high‐density polyethylene melts was predicted using the proposed equations, the Cogswell's equations, the Binding's equations, and the Gibson's equations. Moreover, this prediction was compared with the experimental data of the extensional viscosity. It was found that the predicted extensional viscosity of the proposed equations was close to the experimental data. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40563.
Effect of reaction conditions on grafting ratio and properties of starch nanocrystals‐g‐polystyrene
Authors: Wang Cai , Pan Zelin , Wu Meiyan , Zhao Ping 
Published: March 2014

ABSTRACTStarch nanocrystals‐g‐polystyrene (StN‐g‐PS) was synthesized by free radical emulsion copolymerization of starch nanocrystals with styrene. The effect of polymerization conditions on grafting efficiency (GE) and grafting ratio (GR) were investigated. It was found that during graft copolymerization procedure both GE and GR increase with increasing monomer concentration and reaction time. As a result the high GE and high GR can be achieved. The good linear fit of the GR with ASt/AOH (the absorption strength ratio of aromatic ring peaks and hydroxyl group peaks) confirmed that during graft copolymerization, FTIR spectra can be used as a simple method for determining GR. X‐ray diffraction showed that the crystallinity of StN‐g‐PS decreased slightly with increasing GR. Grafted polystyrene side chains can improve the interface compatibility of starch nanocrystals with the hydrophobic polymer matrix. The mechanical properties of StN‐g‐PS/rubber nanocomposites can be obviously enhanced. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40571.
Influence of microcapsule shell material on the mechanical behavior of epoxy composites for self‐healing applications
Authors: Tripathi Manorama , Rahamtullah  , Kumar D. , Rajagopal Chitra , Kumar Roy Prasun 
Published: March 2014

ABSTRACTIn this article, we have studied the effect of microcapsule shell material on the mechanical behavior of self‐healing epoxy composites. Liquid epoxy healant was encapsulated in melamine‐formaldehyde (MF) and urea‐formaldehyde (UF), using emulsion polymerization technique to prepare microcapsules of different shell walls. The core content of the microcapsules, as determined by solvent extraction technique was found to be 65 ± 4%, irrespective of the shell wall of microcapsule. Morphological investigations reveal a rough texture of the spherical microcapsules, which was attributed to the presence of protruding polymer nanoparticles on the surface. Epoxy composites containing UF and MF microcapsules (3–15% w/w) were prepared by room temperature curing and their mechanical behaviour was studied under both quasi‐static and dynamic loadings. The tensile strength, modulus, and impact resistance of the matrix was found to decrease with increasing amount of microcapsule in the formulation, irrespective of the shell wall material used for encapsulation. Interestingly, substantial improvement in the fracture toughness of the base resin was observed. Morphological investigations on the cracked surface revealed features like crack pinning, crack bowing, microcracking and crack path deflection, which were used to explain the toughened nature of microcapsule containing epoxy composites. Our studies clearly indicate that the microcapsule shell wall material does not play any significant role in defining the mechanical properties of the composites. In addition, presence of secondary amine functionalities in UF and MF shell wall do not interfere with the reaction of epoxy with triethylene tetramine hardener during the curing process. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40572.