Thermodynamics of open networks: Ordering and entropy in NaAlSiO4 glass,liquid, and polymorphs     

Pascal Richet  Richard A. Robie  Jacques Rogez  Bruce S. Hemingway  Philippe Courtial  Christophe Téqui 《Physics and Chemistry of Minerals》1990,17(5):385-394

The thermodynamic properties of carnegieite and NaAlSiO₄ glass and liquid have been investigated through C _p determinations from 10 to 1800 K and solution-calorimetry measurements. The relative entropies S ₂₉₈-S₀ of carnegieite and NaAlSiO₄ glass are 118.7 and 124.8 J/mol K, respectively. The low-high carnegieite transition has been observed at 966 K with an enthalpy of transition of 8.1±0.3 kJ/mol, and the enthalpy of fusion of carnegieite at the congruent melting point of 1799 K is 21.7±3 kJ/mol. These results are consistent with the reported temperature of the nepheline-carnegieite transition and available thermodynamic data for nepheline. The entropy of quenched NaAlSiO₄ glass at 0 K is 9.7±2 J/mol K and indicates considerable ordering among AlO₄ and SiO₄ tetrahedra. In the liquid state, progressive, temperature-induced Si, Al disordering could account for the high configurational heat capacity. Finally, the differences between the entropies and heat capacities of nepheline and carnegieite do not seem to conform to current polyhedral modeling of these properties  相似文献   

Study on the cross-correlation of GNSS signals and typical approximations     

Myriam Foucras  Jérôme Leclère  Cyril Botteron  Olivier Julien  Christophe Macabiau  Pierre-André Farine  Bertrand Ekambi 《GPS Solutions》2017,21(2):293-306

In global navigation satellite system (GNSS) receivers, the first signal processing stage is the acquisition, which consists of detecting the received GNSS signals and determining the associated code delay and Doppler frequency by means of correlations with a code and carrier replicas. These codes, as part of the GNSS signal, were chosen to have very good correlation properties without considering the effect of a potential received Doppler frequency. In the literature, it is often admitted that the maximum GPS L1 C/A code cross-correlation is about ?24 dB. We show that this maximum can be as high as ?19.2 dB when considering a Doppler frequency in a typical range of [?5, 5] kHz. We also show the positive impact of the coherent integration time on the cross-correlation and that even a satellite with Doppler outside the frequency search space of a receiver impacts the cross-correlation. In addition, the expression of the correlation is often provided in the continuous time domain, while its implementation is typically made in the discrete domain. It is then legitimate to ask the validity of this approximation. Therefore, the purpose of this research is twofold: First, we discuss typical approximations and evaluate their regions of validity, and second, we provide characteristic values such as maximums and quantiles of the auto- and cross-correlation of the GPS L1 C/A and Galileo E1 OS codes in the presence of Doppler, for frequency ranges up to 50 kHz and for different integration times.  相似文献   

The high temperature reaction zone of the Oman ophiolite: new field data,microthermometry of fluid inclusions,PIXE analyses and oxygen isotopic ratios     

Juteau  Thierry  Manac'h  Gilles  Moreau  Olivier  Lécuyer  Christophe  Ramboz  Claire 《Marine Geophysical Researches》2000,21(3-4):351-385

Marine Geophysical Research - The present study is focused on the so-called High Temprature Reaction Zone of the Oman ophiolite, a thin zone located between the roots of the sheeted dyke complex...  相似文献   

Influence of spatial scales of observation on temporal change in diversity and trophic structure of fine-sand communities from the English Channel and the southern North Sea   总被引：2，自引：0，他引：2  

Ghertsos  Konstantinos; Luczak  Christophe; Dewarumez  Jean-Marie; Dauvin  Jean-Claude 《ICES Journal of Marine Science》2000,57(5):1481-1487

  相似文献   

Photoacclimation of the invasive alga Caulerpa racemosa var. cylindracea to depth and daylight patterns and a putative new role for siphonaxanthin     

Raffaella Raniello  Maurizio Lorenti  Christophe Brunet  & Maria Cristina Buia 《Marine Ecology》2006,27(1):20-30

The introduced green alga Caulerpa racemosa var. cylindracea grows along a broad depth range (from very shallow to 60 m depth) in the Mediterranean basin. In the present work, the photoacclimation capacity of this invasive variety was investigated in summer, the season of its maximum spread. Natural populations from the Gulf of Naples (Italy) were analyzed for photoresponse on two scales of light variability: a spatial scale (at three stations along a depth gradient, from 0.3 to 20 m depth) and a temporal scale (on the shallowest meadow, from sunrise to sunset). These responses were studied through pigment analysis (with HPLC), and in situ measurements of photosynthetic parameters (with a Diving‐PAM fluorometer). Electron transport rate (ETR)–irradiance curve parameters showed acclimation along environmental gradients dominated by variation in irradiance. In the shallowest plants, the lack of a midday depression in both the maximum relative ETRs and the photosynthetic efficiency at sub‐saturating irradiance (α) pointed to a maintenance of energy conversion levels despite the protective lowering of light‐harvesting efficiency revealed by the trend in F_v/F_m. On the other side, variation of photosynthetic efficiency occurred with depth and buffered the effect of decreasing light on maximum photosynthetic rates. A previously undescribed xanthophyll cycle centred on lutein‐siphonaxanthin interconversion appeared to operate in the shallowest populations in addition to the violaxanthin/antheraxanthin/zeaxanthin cycle commonly occurring in Chlorophyta; this would further enhance phototolerance of the alga. A further role of siphonaxanthin is in the acclimation to low light of deep environments as indicated by its stronger increase from the surface to the deepest station with respect to siphonein and chlorophyll b.  相似文献   

Estimating rockfall release frequency from blocks deposited in protection barriers,growth disturbances in trees,and trajectory simulations     

Farvacque  Manon  Corona  Christophe  Lopez-Saez  J&#;r&#;me  Mainieri  Robin  Stoffel  Markus  Bourrier  Franck  Eckert  Nicolas  Toe  David 《Landslides》2022,19(1):7-18

Landslides - The spatial and temporal quantification of rockfall frequency remains a major challenge in mountain environments, especially also in terms of rockfall management. Approaches that have...  相似文献   

Microbial deposits in the aftermath of the end‐Permian mass extinction: A diverging case from the Mineral Mountains (Utah,USA)          下载免费PDF全文

Emmanuelle Vennin  Nicolas Olivier  Arnaud Brayard  Ivan Bour  Christophe Thomazo  Gilles Escarguel  Emmanuel Fara  Kevin G. Bylund  James F. Jenks  Daniel A. Stephen  Richard Hofmann 《Sedimentology》2015,62(3):753-792

The Lower Triassic Mineral Mountains area (Utah, USA) preserves diversified Smithian and Spathian reefs and bioaccumulations that contain fenestral‐microbialites and various benthic and pelagic organisms. Ecological and environmental changes during the Early Triassic are commonly assumed to be associated with numerous perturbations (productivity changes, acidifica‐tion, redox changes, hypercapnia, eustatism and temperature changes) post‐dating the Permian–Triassic mass extinction. New data acquired in the Mineral Mountains sediments provide evidence to decipher the relationships between depositional environments and the growth and distribution of microbial structures. These data also help to understand better the controlling factors acting upon sedimentation and community turnovers through the Smithian–early Spathian. The studied section records a large‐scale depositional sequence during the Dienerian(?)–Spathian interval. During the transgression, depositional environments evolved from a coastal bay with continental deposits to intertidal fenestral–microbial limestones, shallow subtidal marine sponge–microbial reefs to deep subtidal mud‐dominated limestones. Storm‐induced deposits, microbialite–sponge reefs and shallow subtidal deposits indicate the regression. Three microbialite associations occur in ascending order: (i) a red beds microbialite association deposited in low‐energy hypersaline supratidal conditions where microbialites consist of microbial mats and poorly preserved microbially induced sedimentary structure; (ii) a Smithian microbialite association formed in moderate to high‐energy, tidal conditions where microbialites include stromatolites and associated carbonate grains (oncoids, ooids and peloids); and (iii) a Spathian microbialite association developed in low‐energy offshore conditions that is preserved as multiple decimetre thick isolated domes and coalescent domes. Data indicate that the morphologies of the three microbialite associations are controlled primarily by accommodation, hydrodynamics, bathymetry and grain supply. This study suggests that microbial constructions are controlled by changes between trapping and binding versus precipitation processes in variable hydrodynamic conditions. Due to the presence of numerous metazoans associated with microbialites throughout the Smithian increase in accommodation and Spathian decrease in accommodation, the commonly assumed anachronistic character of the Early Triassic microbialites and the traditional view of prolonged deleterious conditions during the Early Triassic time interval is questioned.  相似文献   

Error analysis of a new planar electrostatic gravity gradiometer for airborne surveys   总被引：1，自引：1，他引：0  

Karim Douch  Isabelle Panet  Gwendoline Pajot-Métivier  Bruno Christophe  Bernard Foulon  Marie-Françoise Lequentrec-Lalancette  Michel Diament 《Journal of Geodesy》2015,89(12):1217-1231

  相似文献   

Determination of Mercury in One Hundred and Sixteen Geological and Environmental Reference Materials Using a Direct Mercury Analyser          下载免费PDF全文

Barbara Marie  Luc Marin  Pierre‐Yves Martin  Tioga Gulon  Christophe Cloquet 《Geostandards and Geoanalytical Research》2015,39(1):71-86

The mercury content of 116 reference materials (RMs) from ten international organisations was determined in this study, which focused on variability within and between batches of RMs. Direct mercury analysis (DMA) was applied to RMs having Hg contents between 1 and 6300 ng g^?1 and provided good precision and accuracy. Accuracy was demonstrated by the agreement of our results with certified values, while replicates were made to establish the precision. Low within‐batch variability was noted, with precision from 0.1 to 23% (n = 3–5) apparently depending on Hg content and homogeneity, whereas systematic offsets were detected among several batches. Thanks to the analysis of different batches; the homogeneity or heterogeneity of several RMs was shown, and thus, suitable RMs for quality control for Hg determinations could be recommended.  相似文献   

Cyclic and creep combination effects on the long-term undrained behavior of overconsolidated clay     

Han  Jian  Yin  Zhen-Yu  Dano  Christophe  Hicher  Pierre-Yves 《Acta Geotechnica》2021,16(4):1027-1041

Acta Geotechnica - Soft soil subjected to cyclic loading typically exhibits an increase in excess pore pressure under undrained condition which brings the soil to an overconsolidated state. Then,...  相似文献