bluuebunny/crossref_metadata_2025_split huggingface dataset:
Climatology of potential vorticity streamers and associated isentropic transport pathways across PV gradient barriers
Authors: Kunz A. , Sprenger M. , Wernli H. 
Published: April 2015

AbstractThe European Centre for Medium‐Range Weather Forecasts reanalysis product ERA‐Interim from 1979 to 2011 is used to investigate potential vorticity (PV) streamers as indicators of Rossby wave breaking (RWB) and the exchange of air masses between the tropics and the extratropics on isentropes between 350 and 500 K. The concept of the strongest isentropic gradients of PV and wind is applied to mark a dynamically relevant PV boundary on every isentrope. An Eulerian algorithm is then used to identify streamers of this PV contour and a trajectory‐based technique to study the exchange across this contour. The climatology of PV streamers reveals a seasonal cycle with a higher frequency in summer than in winter in both hemispheres on all isentropes. During winter, PV streamers are suppressed above 400 K in line with the occurrence of polar vortices. Globally, the highest frequency of PV streamers is found between 380 and 420 K over the eastern North Pacific in summer. Exchange trajectories associated with these PV streamers constitute important atmospheric transport pathways between the tropics and extratropics. In both hemispheres, PV streamers and their associated air mass exchange are controlled by the presence of monsoon anticyclones in summer and by RWB in the vicinity of jet splittings in winter. Cross‐hemispheric transport is observed between 380 and 400 K in the westerly ducts over the Pacific and Atlantic. Equatorward PV streamers are connected with a more frequent exchange than poleward PV streamers, indicating a more reversible poleward and irreversible equatorward RWB. The latter is often connected with a frequent breaking into PV cutoffs.
Drag force parameters of rigid and flexible vegetal elements
Authors: Chapman John A. , Wilson Bruce N. , Gulliver John S. 
Published: April 2015

AbstractThis paper compares parameters that characterize vegetation flexibility effects on flow resistance and drag. Drag forces have been measured in a flume for simple cylindrical obstructions of the same shape and size but with different flexibility under several flow conditions. This data set is used to fit drag parameters and to relate their value to flexibility through the Cauchy Number. A formulation is presented where the drag coefficient is evaluated as a function of a new calibration velocity parameter which is related to the elastic modulus of the obstruction. While the use of a Vogel exponent and reference velocity provides a similar response, the reference velocity when used is somewhat nebulous and appears to have a critical impact on the parameter and the drag force calculated. The proposed formulation for drag reduction is more consistently estimated for the range of flexibilities in this study.
Hydroeconomic optimization of integrated water management and transfers under stochastic surface water supply
Authors: Zhu Tingju , Marques Guilherme Fernandes , Lund Jay R. 
Published: April 2015

AbstractEfficient reallocation and conjunctive operation of existing water supplies is gaining importance as demands grow, competitions among users intensify, and new supplies become more costly. This paper analyzes the roles and benefits of conjunctive use of surface water and groundwater and market‐based water transfers in an integrated regional water system where agricultural and urban water users coordinate supply and demand management based on supply reliability and economic values of water. Agricultural users optimize land and water use for annual and perennial crops to maximize farm income, while urban users choose short‐term and long‐term water conservation actions to maintain reliability and minimize costs. The temporal order of these decisions is represented in a two‐stage optimization that maximizes the net expected benefits of crop production, urban conservation and water management including conjunctive use and water transfers. Long‐term decisions are in the first stage and short‐term decisions are in a second stage based on probabilities of water availability events. Analytical and numerical analyses are made. Results show that conjunctive use and water transfers can substantially stabilize farmer's income and reduce system costs by reducing expensive urban water conservation or construction. Water transfers can equalize marginal values of water across users, while conjunctive use minimizes water marginal value differences in time. Model results are useful for exploring the integration of different water demands and supplies through water transfers, conjunctive use, and conservation, providing valuable insights for improving system management.
A methodology for velocity field measurement in multiphase high‐pressure flow of CO2 and water in micromodels
Authors: Kazemifar Farzan , Blois Gianluca , Kyritsis Dimitrios C. , Christensen Kenneth T. 
Published: April 2015

AbstractThis paper presents a novel methodology for capturing instantaneous, temporally and spatially resolved velocity fields in an immiscible multiphase flow of liquid/supercritical CO2 and water through a porous micromodel. Of interest is quantifying pore‐scale flow processes relevant to geological CO2 sequestration and enhanced oil recovery, and in particular, at thermodynamic conditions relevant to geological reservoirs. A previously developed two‐color microscopic particle image velocimetry approach is combined with a high‐pressure apparatus, facilitating flow quantification of water interacting with supercritical CO2. This technique simultaneously resolves (in space and time) the aqueous phase velocity field as well as the dynamics of the menisci. The method and the experimental apparatus are detailed, and the results are presented to demonstrate its unique capabilities for studying pore‐scale dynamics of CO2‐water interactions. Simultaneous identification of the boundary between the two fluid phases and quantification of the instantaneous velocity field in the aqueous phase provides a step change in capability for investigating multiphase flow physics at the pore scale at reservoir‐relevant conditions.
A thermodynamic interpretation of Budyko and L'vovich formulations of annual water balance: Proportionality Hypothesis and maximum entropy production
Authors: Wang Dingbao , Zhao Jianshi , Tang Yin , Sivapalan Murugesu 
Published: April 2015

AbstractThe paper forms part of the search for a thermodynamic explanation for the empirical Budyko Curve, addressing a long‐standing research question in hydrology. Here this issue is pursued by invoking the Proportionality Hypothesis underpinning the Soil Conservation Service (SCS) curve number method widely used for estimating direct runoff at the event scale. In this case, the Proportionality Hypothesis posits that the ratio of continuing abstraction to its potential value is equal to the ratio of direct runoff to its potential value. Recently, the validity of the Proportionality Hypothesis has been extended to the partitioning of precipitation into runoff and evaporation at the annual time scale as well. In this case, the Proportionality Hypothesis dictates that the ratio of continuing evaporation to its potential value is equal to the ratio of runoff to its potential value. The Budyko Curve could then be seen as the straightforward outcome of the application of the Proportionality Hypothesis to estimate mean annual water balance. In this paper, we go further and demonstrate that the Proportionality Hypothesis itself can be seen as a result of the application of the thermodynamic principle of Maximum Entropy Production (MEP). In this way, we demonstrate a possible thermodynamic basis for the Proportionality Hypothesis, and consequently for the Budyko Curve. As a further extension, the L'vovich formulation for the two‐stage partitioning of annual precipitation is also demonstrated to be a result of MEP: one for the competition between soil wetting and fast flow during the first stage; another for the competition between evaporation and base flow during the second stage.
Toward a generalized plate motion reference frame
Authors: Becker T. W. , Schaeffer A. J. , Lebedev S. , Conrad C. P. 
Published: April 2015

AbstractAn absolute plate motion (APM) model is required to address issues such as the thermochemical evolution of Earth's mantle. All APM models have to rely on indirect inferences, including those based on hot spots and seismic anisotropy, each with their own set of uncertainties. Here, we explore a seafloor spreading‐aligned reference frame. We show that this reference frame fits azimuthal seismic anisotropy in the uppermost mantle very well. The corresponding Euler pole is close to those of hot spot reference frames, ridge motion minimizing models, and geodynamic estimates of net rotation and predicts clear trench motion patterns. We conclude that a net rotation pole guided by the spreading‐aligned model (at 64°E, 61°S, with moderate rotation of ∼ 0.2 … 0.3°/Myr) could indeed represent a standard, comprehensive reference frame for present‐day plate motions with respect to the deep mantle.
A novel sensor combination (upGPR‐GPS) to continuously and nondestructively derive snow cover properties
Authors: Schmid Lino , Koch Franziska , Heilig Achim , Prasch Monika , Eisen Olaf , Mauser Wolfram , Schweizer Jürg 
Published: April 2015

AbstractMonitoring seasonal snow cover properties is critical for properly managing natural hazards such as snow avalanches or snowmelt floods. However, measurements often cannot be conducted in difficult terrain or lack the high temporal resolution needed to account for rapid changes in the snowpack, e.g., liquid water content (LWC). To monitor essential snowpack properties, we installed an upward looking ground‐penetrating radar (upGPR) and a low‐cost GPS system below the snow cover and observed in parallel its evolution during two winter seasons. Applying external snow height (HS) information, both systems provided consistent LWC estimates in snow, based on independent approaches, namely measurements of travel time and attenuation of electromagnetic waves. By combining upGPR and GPS, we now obtain a self‐contained approach instead of having to rely on external information such as HS. This allows for the first time determining LWC, HS, and snow water equivalent (SWE) nondestructively and continuously potentially also in avalanche‐prone slopes.
Universal properties of mirror mode turbulence in the Earth's magnetosheath
Authors: Osmane A. , Dimmock A. P. , Pulkkinen T. I. 
Published: April 2015

AbstractWe use more than 7 years of Time History of Events and Macroscale Interactions during Substorms observations to quantify the non‐Gaussian properties associated with mirror mode turbulence in the Earth's magnetosheath. We find that non‐Gaussian statistics of mirror modes lead to the parabolic collapse of kurtosis as the square of the skewness (K = aS2+B with a ∼ 1.3 and b ∼− 1). The parabolic scaling is a global constraint for the magnetosheath and is dictated by kinetic processes. This parabolic scaling is qualitatively independent of the distance to the magnetopause or bow shock, which implies that, even though the bow shock is driving the mirror mode instability, the dynamical evolution of mirror structures is independent of the source region and due to local processes. The parabolic relationship and coefficients between kurtosis and skewness for mirror modes in the Earth's magnetosheath are also similar to those found in a wide range of geophysical and laboratory turbulent environments, providing further evidence that turbulent systems dominated by non‐Gaussian fluctuations hold universal statistical properties.
Bakterien und Weichtiere: Prinzipien der Biomineralisation von Eisenoxid‐Materialien
Authors: Faivre Damien , Godec Tina Ukmar 
Published: April 2015

AbstractDiverse Organismen haben ein genetisches Programm, das ihnen die kontrollierte Bildung von Mineralien ermöglicht; dieser Prozess wird Biomineralisation genannt. Die Vielfalt der verschiedenen biologischen Materialien ist enorm und beruht auf der Fähigkeit, sowohl Keimbildung als auch Wachstum der Kristalle zu kontrollieren. Die Struktur und Zusammensetzung der Biomineralien stattet die Organismen mit Eigenschaften und Fähigkeiten aus, die vergleichbare abiotisch gebildete Materialien desselben Minerals normalerweise nicht aufweisen. Daher ist es von großem interdisziplinärem Interesse, die Mechanismen der Biomineralisation und Morphogenese besser zu verstehen. In diesem Aufsatz fassen wir das momentane Wissen über die Bildung von Eisenoxiden in Bakterien und Weichtieren zusammen und konzentrieren uns dabei auf die magnetischen und mechanischen Eigenschaften. Wir beschreiben die chemischen und biologischen Prozesse, die in die Kontrolle der Mineralfällung und Morphogenese involviert sind, und zeigen, wie die Organismen es schaffen, hochkomplexe Strukturen mit primitiven physikochemischen Mitteln zu bilden.
Gezielte Optimierung von molekularen Photokatalysatoren zur Wasserstoffproduktion mit sichtbarem Licht
Authors: Pfeffer Michael G. , Kowacs Tanja , Wächtler Maria , Guthmuller Julien , Dietzek Benjamin , Vos Johannes G. , Rau Sven 
Published: April 2015

AbstractIn einem intramolekularen Photokatalysator, bestehend aus einem RuII‐Photozentrum, einem Tetrapyridophenazin‐Brückenliganden und einer PtX2‐Einheit (X=Cl oder I) als Katalysezentrum, wurde der Einfluss der Struktur des Katalysezentrums auf die katalytische Aktivität des photochemischen molekularen Systems (PMD, photochemical molecular device) untersucht. Es zeigte sich, dass der Austausch der terminalen Chloridliganden am Platinzentrum gegen Iodidliganden zu einem signifikanten Anstieg der Effizienz der Wasserstoffproduktion führt. Untersuchungen mittels Ultrakurzzeitspektroskopie belegen, dass die intramolekularen photophysikalischen Prozesse durch die strukturelle Veränderung des Katalysezentrums nicht beeinflusst werden. Zudem bleibt das grundlegende katalytische Verhalten, wie z. B. die sofortige Wasserstoffentwicklung, die konstante Umsatzfrequenz und die Stabilität des Katalysezentrums, erhalten. DFT‐Rechnungen belegen eine deutliche Erhöhung der Elektronendichte am katalytisch aktiven Platinzentrum durch den Austausch der terminalen Halogenidiganden, was als Erklärung für die signifikant erhöhte Katalyseaktivität dient.
Biomimetische Totalsynthese von Santalin Y
Authors: Strych Sebastian , Journot Guillaume , Pemberton Ryan P. , Wang Selina C. , Tantillo Dean J. , Trauner Dirk 
Published: April 2015

AbstractEine biomimetische Totalsynthese von Santalin Y, einem strukturell komplexen, jedoch racemischen Naturstoff, wird beschrieben. Ihr Schlüsselschritt ist eine (3+2)‐Cycloaddition eines Benzylstilbens an ein “vinyloges Oxidopyrylium”, gefolgt von einer intramolekularen Friedel‐Crafts‐Reaktion. Diese Kaskade erzeugt das einzigartige Oxafenestran‐Gerüst des Zielmoleküls und setzt seine fünf Stereozentren in einem einzigen Vorgang. Unsere Arbeit liefert einen schnellen Zugang zu Santalin Y und klärt dessen biosynthetische Beziehung zu anderen aus rotem Sandelholz isolierten Farbstoffen auf.
Optimization of Hydrogen‐Evolving Photochemical Molecular Devices
Authors: Pfeffer Michael G. , Kowacs Tanja , Wächtler Maria , Guthmuller Julien , Dietzek Benjamin , Vos Johannes G. , Rau Sven 
Published: April 2015

AbstractA molecular photocatalyst consisting of a RuII photocenter, a tetrapyridophenazine bridging ligand, and a PtX2 (X=Cl or I) moiety as the catalytic center functions as a stable system for light‐driven hydrogen production. The catalytic activity of this photochemical molecular device (PMD) is significantly enhanced by exchanging the terminal chlorides at the Pt center for iodide ligands. Ultrafast transient absorption spectroscopy shows that the intramolecular photophysics are not affected by this change. Additionally, the general catalytic behavior, that is, instant hydrogen formation, a constant turnover frequency, and stability are maintained. Unlike as observed for the Pd analogue, the presence of excess halide does not affect the hydrogen generation capacity of the PMD. The highly improved catalytic efficiency is explained by an increased electron density at the Pt catalytic center, this is confirmed by DFT studies.
Biochemistry students' ideas about how an enzyme interacts with a substrate
Authors: Linenberger Kimberly J. , Bretz Stacey Lowery 
Published: April 2015

AbstractEnzyme‐substrate interactions are a fundamental concept of biochemistry that is built upon throughout multiple biochemistry courses. Central to understanding enzyme‐substrate interactions is specific knowledge of exactly how an enzyme and substrate interact. Within this narrower topic, students must understand the various binding sites on an enzyme and be able to reason from simplistic lock and key or induced fit models to the more complex energetics model of transition state theory. Learning to understand these many facets of enzyme‐substrate interactions and reasoning from multiple models present challenges where students incorrectly make connections between concepts or make no connection at all. This study investigated biochemistry students' understanding of enzyme‐substrate interactions through the use of clinical interviews and a national administration (N = 707) of the Enzyme–Substrate Interactions Concept Inventory. Findings include misconceptions regarding the nature of enzyme‐substrate interactions, naïve ideas about the active site, a lack of energetically driven interactions, and an incomplete understanding of the specificity pocket. © 2015 by the International Union of Biochemistry and Molecular Biology, 43(4):213–222, 2015.
Experimental Investigation and Simulation of Organophilic Pervaporation in Laboratory and Pilot Scale
Authors: Schiffmann Patrick , Repke Jens‐Uwe 
Published: April 2015

AbstractPervaporation is a well‐established separation technology for the production of anhydrous solvents, but its distribution in the chemical industry is still limited to a few individual applications. Besides the need of high‐selective membranes, the development of membrane modules adapted to the specific requirements of this process needs more research effort. Furthermore, only few modeling tools for the pervaporation process are available. In this work, a three‐step modeling approach ranging from a shortcut to a rigorous model is developed. A hydrophobic membrane is characterized in a laboratory test cell for the separation of 2‐butanol from water in a wide temperature and concentration range. The identified performance data are used to simulate the same separation task with an industrial‐scale membrane module. The results are validated by experiments conducted with a novel membrane module in pilot scale.
Drying of Iron Chloride Solutions: Laser Heating of Levitated Single Particles
Authors: Schiemann Martin , Baer Sebastian , Esen Cemal , Ostendorf Andreas 
Published: April 2015

AbstractIron chloride solutions are a waste product from the steel industry, which has to be recovered by the so‐called spray roasting process. As this process is a complex sequence of different steps, the drying process of the droplets was separated to get deeper insight into the particle formation process from aqueous iron chloride solutions. Experiments were carried out on single droplets in an acoustic levitator. A CO2 laser was used as heat source for the drying process. Particles with different shapes were generated by various concentrations of FeCl2 and laser power. The characteristic time scales and particle size evolution are compared with literature data.
Distillation Control Structure Selection for Energy‐Efficient Operations
Authors: Osuolale Funmilayo , Zhang Jie 
Published: April 2015

AbstractFew studies have been reported concerning the energy efficiency of various distillation column control structures. The choice of an energy‐efficient control configuration by incorporating thermodynamics second law in the selection criteria is described. In addition to a relative gain array for assessing control loop interactions, a relative exergy array is used in evaluating the energy efficiency of various control structures. The preferred control structure should have both good operability and good energy efficiency as distillation columns are the major energy consumer in the chemical industry. The performance of the control structures in the dynamic mode is analyzed in detail. The proposed method is demonstrated on two binary distillation columns: methanol‐water separation and benzene‐toluene separation. Dynamic simulation results prove the efficiency of the proposed distillation control structure selection method.
Q = m c ΔT – Grundlage zur Steuerung des Stoffaustauschs von auf Verdunstung basierenden Prozessen
Authors: Feilner Roland , Werner Franz , Rehmann Dirk , Methner Frank‐Jürgen , Scheuren Hans 
Published: April 2015

AbstractThermische Trennverfahren sind in der lebensmittelverarbeitenden Industrie weit verbreitet. Oftmals werden hierbei Kochprozesse bei Atmosphären‐ oder Unterdruck eingesetzt, die aufgrund des hohen Dampfdrucks wasserreicher Lebensmittel sehr energieintensiv sind. Insbesondere bei der Auftrennung von gelösten Stoffen wie Aromen ergibt sich daher ein großes Optimierungspotenzial. Verdunstungsprozesse bieten die Möglichkeit, ohne den Einsatz zusätzlicher Primärenergie in Form von Wärme ebenfalls eine Auftrennung zu erreichen. Die bei der Verdunstung entstehende Temperaturabnahme der Flüssigkeit kann dabei als Maß für die Reduktion von (unerwünschten) flüchtigen Stoffen dienen und daher zur Regelung der Massenströme verwendet werden.
Absolute Brønsted Acidities and pH Scales in Ionic Liquids
Authors: Himmel Daniel , Goll Sascha K. , Scholz Franziska , Radtke Valentin , Leito Ivo , Krossing Ingo 
Published: April 2015

AbstractAlthough receiving large interest over the last years, some fundamental aspects of Brønsted acidity in ionic liquids (ILs) have up to now been insufficiently highlighted. In this work, standard states, activity, and activity coefficient definitions for IL solvent systems were developed from general thermodynamic considerations and then extended to a general mixed solvent standard state. By using the bromide/bromoaluminate systems as representative ILs, formulae for thermodynamically consistent pH scales for ILs with simple (Br−) and complex ([AlnBr3n+1]−) anions were derived on the basis of the chemical potential of the proton. Supported by quantum chemical [ccsd(t)/MP2/DFT/COSMO‐RS] calculations, Gibbs solvation energies of the proton were calculated, which allowed the ILs to be ranked in absolute acidity, that is, pHabs or μabs(H+, IL), and additionally allowed their acidity to be compared with molecular Brønsted acid systems. It was shown that bromoaluminate ILs are suited for reaching superacidic conditions. The complexity of autoprotolysis processes in C6MIM+[AlBr4]− (C6MIM=1‐hexyl‐3‐methylimidazolium) with or without the addition of basic (i.e. Br−) or acidic (AlBr3 and/or HBr) solutes was examined in detail by model calculations, and they indicated a large thermodynamic influence of small deviations from the exact stoichiometric composition.