American gas journal.

Title from cover.

Invisible CO₂ gas killing trees at Mammoth Mountain, California /

Mode of access: Internet.

Leaf gas exchange characteristics of three neotropical mangrove species in response to varying hydroperiod

We determined how different hydroperiods affected leaf gas exchange characteristics of greenhouse-grown seedlings (2002) and saplings (2003) of the mangrove species Avicennia germinans (L.) Stearn., Laguncularia racemosa (L.) Gaertn. f., and Rhizophora mangle L. Hydroperiod treatments included no flooding (unflooded), intermittent flooding (intermittent), and permanent flooding (flooded). Plants in the intermittent treatment were measured under both flooded and drained states and compared separately. In the greenhouse study, plants of all species maintained different leaf areas in the contrasting hydroperiods during both years. Assimilation-light response curves indicated that the different hydroperiods had little effect on leaf gas exchange characteristics in either seedlings or saplings. However, short-term intermittent flooding for between 6 and 22 days caused a 20% reduction in maximum leaf-level carbon assimilation rate, a 51% lower light requirement to attain 50% of maximum assimilation, and a 38% higher demand from dark respiration. Although interspecific differences were evident for nearly all measured parameters in both years, there was little consistency in ranking of the interspecific responses. Species by hydroperiod interactions were significant only for sapling leaf area. In a field study, R. mangle saplings along the Shark River in the Everglades National Park either demonstrated no significant effect or slight enhancement of carbon assimilation and water-use efficiency while flooded. We obtained little evidence that contrasting hydroperiods affect leaf gas exchange characteristics of mangrove seedlings or saplings over long time intervals; however, intermittent flooding may cause short-term depressions in leaf gas exchange. The resilience of mangrove systems to flooding, as demonstrated in the permanently flooded treatments, will likely promote photosynthetic and morphological adjustment to slight hydroperiod shifts in many settings.

THREE AMERICAN INTERNATIONAL PIANO COMPETITIONS: THE PIANO WORKS THEY COMMISSIONED BETWEEN 1962 AND 2012

Over a period of 50 years—between 1962 and 2012—three preeminent American piano competitions, the Van Cliburn International Piano Competition, the University of Maryland International Piano Competition/William Kapell International Piano Competition and the San Antonio International Piano Competition, commissioned for inclusion on their required performance lists 26 piano works, almost all by American composers. These compositions, works of sufficient artistic depth and technical sophistication to serve as rigorous benchmarks for competition finalists, constitute a unique segment of the contemporary American piano repertoire. Although a limited number of these pieces have found their way into the performance repertoire of concert artists, too many have not been performed since their premières in the final rounds of the competitions for which they were designed. Such should not be the case. Some of the composers in question are innovative titans of 20th-century American music—Samuel Barber, Aaron Copland, Leonard Bernstein, John Cage, John Corigliano, William Schuman, Joan Tower and Ned Rorem, to name just a few—and many of the pieces themselves, as historical touchstones, deserve careful examination. This study includes, in addition to an introductory overview of the three competitions, a survey of all 26 compositions and an analysis of their expressive characteristics, from the point of view of the performing pianist. Numerous musical examples support the analysis. Biographical information about the composers, along with descriptions of their overall musical styles, place these pieces in historical context. Analytical and technical comprehension of this distinctive and rarely performed corner of the modern classical piano world could be of inestimable value to professional pianists, piano pedagogues and music educators alike.

Approaching and Executing Premiere, Interpretive, and Historical Works

The spectrum of vocal music spans time, genres, styles, and is infinitely vast. New works are ever evolving and expanding, new artistic ideas are revealed from older works, and interest renewed from the tried and true. As a vocal musician in present day, I aspired to find a common thread amidst the boundless spectrum of works to be performed—whether I was hearkening back to a time of old, dissecting pieces by composers who have opened the door to personal artistry, or learning to sing a new work never performed or heard before. The Mercuriality of Song unearths more differences than commonalities in preparation, despite the fact that my voice remains the constant— differences which were expected, often surprising, but nevertheless new and rewarding in their challenges. Three performances (a world-premiere, a lieder recital, and an early music recital) comprise the basis for my investigation into comparing methods and processes of different periods via program notes, laying the foundation for initial preparation from an historical context. An amalgam of genres and stylistic differences along with performance planning culminate this exploration of vocal discovery and implementation.

TROMBONE MUSIC OF SCANDINAVIA: A STUDY OF TROMBONE SOLO AND CHAMBER WORKS FROM SWEDEN, NORWAY, AND DENMARK

This dissertation project aims to establish Scandinavian trombone solo and chamber works as a major contribution to the trombone repertoire. From the late 19th century to modern day, Scandinavian composers have produced a steady output of trombone works of substantial musical quality. Deep-rooted in the traditions of strong military wind bands, Scandinavia has also produced an unusual number of trombone virtuosos, ranging from those holding positions in leading orchestras, and internationally renowned pedagogues, to trombonists enjoying careers as soloists. In this study I propose that it is the symbiotic relationship between strong performers and traditionally nationalist composers that created the fertile environment for the large number of popular trombone solo and chamber repertoire not seen in any other region besides the Paris Conservatory and its infamous test pieces. I also interpret the selected repertoire through the prism of nationalism and influence of folk music, and convey that the allure of the mystic Nordic folk influences enhances the appeal of the Scandinavian trombone repertoire to world-wide audiences and performers. The dissertation project was realized over three solo recitals, each showcasing the music of Sweden, Norway, and Denmark respectively. For each program, I looked to choose a standard work from the trombone solo repertoire, a work written for or by a native virtuoso, and a lesser-known work that warrants the attention of other performers for its musical qualities. The recital of Swedish music presented Mandrake in the Corner by Christian Lindberg, Subadobe by Frederik Högberg, A Christian Song by Jan Sandström, and Concertino for trombone and strings by Lars-Erik Larsson. The recital of Norwegian music presented Concerto for Trombone op. 76 by Egil Hovland, Ordner Seg by Øystein Baadsvik, Elegi by Magne Amdahl, and Concerto in F major by Ole Olsen. The recital of Danish music presented Rapsodia Borealis by Søren Hyldgaard, Madrigal by Bo Gunge, Romance for trombone and piano by Axel Jørgensen, Concerto for trombone by Launy Grøndahl, and Three Swedish Tunes by Mogens Andresen. Through the performance of works from these three countries, the dissertation establishes Scandinavia as a rich source of solo trombone repertoire perpetuated by nationalist composers and virtuosos, as well as providing a brief survey of Scandinavian trombone works of various instrumentation and difficulty levels to be enjoyed by student, professional, and amateur performers and their audience.

RACHMANINOFF AND MEDTNER: SELECTED WORKS FROM THE SOLO AND COLLABORATIVE PIANO REPERTOIRE

Sergei Rachmaninoff and Nikolai Medtner occupy a special place in the history of Russian music. Both composers were exceptional pianists and left us some of the greatest works in the piano repertoire. Although these composers shared many similarities, and were often compared, their musical languages and views on composition were very different. Unfortunately, Medtner’s music, which Rachmaninoff admired greatly, has remained neglected for several generations of performers and listeners. In my dissertation I will explore the similarities and contrasts in Rachmaninoff’s and Medtner’s music. Through these performances, I hope to encourage other musicians to discover the imaginative power of Medtner’s music. Of course, no such encouragement is needed for Rachmaninoff’s extremely popular music; however, the technical and musical challenges of performing that repertoire are an invaluable part of every pianist’s education. This dissertation project was presented in three recitals which were performed in Gildenhorn Recital Hall at the Clarice Smith Performing Arts Center of the University of Maryland on May 8, 2014, December 5, 2014 and March 21, 2016. The following pieces comprised the survey of Rachmaninoff music: Vocalise Op. 34, Variations on a Theme of Corelli Op. 42, Piano Concerto No 2 Op. 18, Selected Songs Opp. 4 and 8, and two Moments Musicaux Op. 16 - Nos 3 and 4. The following pieces were included to represent Medtner: Sonata for Violin and Piano Op. 57 in E minor “Epica”, Fairy Tales for solo piano Op. 20 No 1, Op. 26 No 3 and Op. 51 No 1, and Selected Songs Op. 6 and 15. My partners in this project were Lilly Ahn, soprano, Jennifer Lee, violin and Nadezhda Christova, piano. All three recitals can be found in the Digital Repository at the University of Maryland (DRUM).

Many-body approach to the BCS-BEC crossover for an imbalanced ultra-cold Fermi gas

The aim of this thesis is the study of the normal phase of a mass imbalanced and polarized ultra-cold Fermi gas in the context of the BCS-BEC crossover, using a diagrammatic approach known as t-matrix approximation. More specifically, the calculations are implemented using the fully self-consistent t-matrix (or Luttinger- Ward) approach, which is already experimentally and numerically validated for the balanced case. An imbalance (polarization) between the two spin populations works against pairing and superfluidity. For sufficiently large polarization (and not too strong attraction) the system remains in the normal phase even at zero temperature. This phase is expected to be well described by the Landau’s Fermi liquid theory. By reducing the spin polarization, a critical imbalance is reached where a quantum phase transition towards a superfluid phase occurs and the Fermi liquid description breaks down. Depending on the strength of the interaction, the exotic superfluid phase at the quantum critical point (QCP) can be either a FFLO phase (Fulde-Ferrell-Larkin-Ovchinnikov) or a Sarma phase. In this regard, the presence of mass imbalance can strongly influence the nature of the QCP, by favouring one of these two exotic types of pairing over the other, depending on whether the majority of the two species is heavier or lighter than the minority. The analysis of the system is made by focusing on the temperature-coupling-polarization phase diagram for different mass ratios of the two components and on the study of different thermodynamic quantities at finite temperature. The evolution towards a non-Fermi liquid behavior at the QCP is investigated by calculating the fermionic quasi-particle residues, the effective masses and the self-energies at zero temperature.

Quantum Monte Carlo study of effective masses in a polarized unitary Fermi gas

Ultracold gases provide an ideal platform for quantum simulations of many-body systems. Here we are interested in a particular system which has been the focus of most experimental and theoretical works on ultracold fermionic gases: the unitary Fermi gas. In this work we study with Quantum Monte Carlo simulations a two-component gas of fermionic atoms at zero temperature in the unitary regime. Specifically, we are interested in studying how the effective masses for the quasi-particles of the two components of the Fermi liquid evolve as the polarization is progressively reduced from full to lower values. A recent theoretical work, based on alternative diagrammatic methods, has indeed suggested that such effective masses should diverge at a critical polarization. To independently verify such predictions, we perform Variational Monte Carlo (VMC) calculations of the energy based on Jastrow-Slater wavefunctions after adding or subtracting a particle with a given momentum to a full Fermi sphere. In this way, we determine the quasi-particle dispersions, from which we extract the effective masses for different polarizations. The resulting effective masses turn out to be quite close to the non-interacting values, even though some evidence of an increase for the effective mass of the minority component appears close to the predicted value for the critical polarization. Preliminary results obtained for the majority component with the Fixed-node Diffusion Monte Carlo (DMC) method seem to indicate that DMC could lead to an increase of the effective masses in comparison with the VMC results. Finally, we point out further improvements of the trial wave-function and boundary conditions that would be necessary in future simulations to draw definite conclusions on the effective masses of the polarized unitary Fermi gas.

Ihwg-μnir: A Miniaturised Near-infrared Gas Sensor Based On Substrate-integrated Hollow Waveguides Coupled To A Micro-nir-spectrophotometer.

A miniaturised gas analyser is described and evaluated based on the use of a substrate-integrated hollow waveguide (iHWG) coupled to a microsized near-infrared spectrophotometer comprising a linear variable filter and an array of InGaAs detectors. This gas sensing system was applied to analyse surrogate samples of natural fuel gas containing methane, ethane, propane and butane, quantified by using multivariate regression models based on partial least square (PLS) algorithms and Savitzky-Golay 1(st) derivative data preprocessing. The external validation of the obtained models reveals root mean square errors of prediction of 0.37, 0.36, 0.67 and 0.37% (v/v), for methane, ethane, propane and butane, respectively. The developed sensing system provides particularly rapid response times upon composition changes of the gaseous sample (approximately 2 s) due the minute volume of the iHWG-based measurement cell. The sensing system developed in this study is fully portable with a hand-held sized analyser footprint, and thus ideally suited for field analysis. Last but not least, the obtained results corroborate the potential of NIR-iHWG analysers for monitoring the quality of natural gas and petrochemical gaseous products.

Assessment Of Robustness On Analysis Using Headspace Solid-phase Microextraction And Comprehensive Two-dimensional Gas Chromatography Through Experimental Designs.

Plackett-Burman experimental design was applied for the robustness assessment of GC×GC-qMS (Comprehensive Two-Dimensional Gas Chromatography with Fast Quadrupolar Mass Spectrometric Detection) in quantitative and qualitative analysis of volatiles compounds from chocolate samples isolated by headspace solid-phase microextraction (HS-SPME). The influence of small changes around the nominal level of six factors deemed as important on peak areas (carrier gas flow rate, modulation period, temperature of ionic source, MS photomultiplier power, injector temperature and interface temperature) and of four factors considered as potentially influential on spectral quality (minimum and maximum limits of the scanned mass ranges, ions source temperature and photomultiplier power). The analytes selected for the study were 2,3,5-trimethylpyrazine, 2-octanone, octanal, 2-pentyl-furan, 2,3,5,6-tetramethylpyrazine, and 2-nonanone e nonanal. The factors pointed out as important on the robustness of the system were photomultiplier power for quantitative analysis and lower limit of mass scanning range for qualitative analysis.

Separation Of Glycosidic Catiomers By Twim-ms Using Co2 As A Drift Gas.

Traveling wave ion mobility mass spectrometry (TWIM-MS) is shown to be able to separate and characterize several isomeric forms of diterpene glycosides stevioside (Stv) and rebaudioside A (RebA) that are cationized by Na(+) and K(+) at different sites. Determination and characterization of these coexisting isomeric species, herein termed catiomers, arising from cationization at different and highly competitive coordinating sites, is particularly challenging for glycosides. To achieve this goal, the advantage of using CO2 as a more massive and polarizable drift gas, over N2 , was demonstrated. Post-TWIM-MS/MS experiments were used to confirm the separation. Optimization of the possible geometries and cross-sectional calculations for mobility peak assignments were also performed. Copyright © 2015 John Wiley & Sons, Ltd.

In Vivo Determination Of The Volatile Metabolites Of Saprotroph Fungi By Comprehensive Two-dimensional Gas Chromatography.

In this work, we discuss the use of multi-way principal component analysis combined with comprehensive two-dimensional gas chromatography to study the volatile metabolites of the saprophytic fungus Memnoniella sp. isolated in vivo by headspace solid-phase microextraction. This fungus has been identified as having the ability to induce plant resistance against pathogens, possibly through its volatile metabolites. Adequate culture media was inoculated, and its headspace was then sampled with a solid-phase microextraction fiber and chromatographed every 24 h over seven days. The raw chromatogram processing using multi-way principal component analysis allowed the determination of the inoculation period, during which the concentration of volatile metabolites was maximized, as well as the discrimination of the appropriate peaks from the complex culture media background. Several volatile metabolites not previously described in the literature on biocontrol fungi were observed, as well as sesquiterpenes and aliphatic alcohols. These results stress that, due to the complexity of multidimensional chromatographic data, multivariate tools might be mandatory even for apparently trivial tasks, such as the determination of the temporal profile of metabolite production and extinction. However, when compared with conventional gas chromatography, the complex data processing yields a considerable improvement in the information obtained from the samples. This article is protected by copyright. All rights reserved.

Measuring air pressure with a polymeric gas sensor

In this communication we describe the application of a conductive polymer gas sensor as an air pressure sensor. The device consists of a thin doped poly(4'-hexyloxy-2,5-biphenylene ethylene) (PHBPE) film deposited on an interdigitated metallic electrode. The sensor is cheap, easy to fabricate, lasts for several months, and is suitable for measuring air pressures in the range between 100 and 700 mmHg.

Gas-phase solvolysis type reactions of SiCl3+ cations

Gas-phase SiCl3+ ions undergo sequential solvolysis type reactions with water, methanol, ammonia, methylamine and propylene. Studies carried out in a Fourier Transform mass spectrometer reveal that these reactions are facile at 10-8 Torr and give rise to substituted chlorosilyl cations. Ab initio and DFT calculations reveal that these reactions proceed by addition of the silyl cation to the oxygen or nitrogen lone pair followed by a 1,3-H migration in the transition state. These transition states are calculated to lie below the energy of the reactants. By comparison, hydrolysis of gaseous CCl3+ is calculated to involve a substantial positive energy barrier.