Technical Note: Characterisation of a DUALER instrument for the airborne measurement of peroxy radicals during AMMA 2006

A DUALER (dual-channel airborne peroxy radical chemical amplifier) instrument has been developed and optimised for the airborne measurement of the total sum of peroxy radicals during the AMMA (African Monsoon Multidisciplinary Analyses) measurement campaign which took place in Burkina Faso in August 2006. The innovative feature of the instrument is that both reactors are sampling simultaneously from a common pre-reactor nozzle while the whole system is kept at a constant pressure to ensure more signal stability and accuracy. <br><br> Laboratory experiments were conducted to characterise the stability of the NO<sub>2</sub> detector signal and the chain length with the pressure. The results show that airborne measurements using chemical amplification require constant pressure at the luminol detector. Wall losses of main peroxy radicals HO<sub>2</sub> and CH<sub>3</sub>O<sub>2</sub> were investigated. The chain length was experimentally determined for different ambient mixtures and compared with simulations performed by a chemical box model. <br><br> The DUALER instrument was successfully mounted within the German DLR-Falcon. The analysis of AMMA data utilises a validation procedure based on the O<sub>3</sub> mixing ratios simultaneously measured onboard. The validation and analysis procedure is illustrated by means of the data measured during the AMMA campaign. The detection limit and the accuracy of the ambient measurements are also discussed

Nearly universal crossing point of the specific heat curves of Hubbard models

A nearly universal feature of the specific heat curves C(T,U) vs. T for different U of a general class of Hubbard models is observed. That is, the value C_+ of the specific heat curves at their high-temperature crossing point T_+ is almost independent of lattice structure and spatial dimension d, with C_+/k_B \approx 0.34. This surprising feature is explained within second order perturbation theory in U by identifying two small parameters controlling the value of C_+: the integral over the deviation of the density of states N(\epsilon) from a constant value, characterized by \delta N=\int d\epsilon |N(\epsilon)-1/2|, and the inverse dimension, 1/d.Comment: Revtex, 9 pages, 6 figure

Contrasting carbonate depositional systems for Pliocene cool-water limestones cropping out in central Hawke's Bay, New Zealand

Pliocene limestone formations in central Hawke's Bay (eastern North Island, New Zealand) accumulated on and near the margins of a narrow forearc basin seaway within the convergent Australia/Pacific plate boundary zone. The active tectonic setting and varied paleogeographic features of the limestone units investigated, in association with probable glacioeustatic sea-level fluctuations, resulted in complex stratigraphic architectures and contrasting types of carbonate accumulation on either side of the seaway. Here, we recognise recurring patterns of sedimentary facies, and sequences and systems tracts bounded by key physical surfaces within the limestone sheets. The facies types range from Bioclastic (B) to Siliciclastic (S) end-members via Mixed (M) carbonate-siliciclastic deposits. Skeletal components are typical cool-water associations dominated by epifaunal calcitic bivalves, bryozoans, and especially barnacles. Siliciclastic contents vary from one formation to another, and highlight siliciclastic-rich limestone units in the western ranges versus siliciclastic-poor limestone units in the eastern coastal hills. Heterogeneities in facies types, stratal patterns, and also in diagenetic pathways between eastern and western limestone units are considered to originate in the coeval occurrence in different parts of the forearc basin of two main morphodynamic carbonate systems over time

Observations of Particulates within the North Atlantic Flight Corridor: POLINAT 2, September-October 1997

This paper discusses particulate concentration and size distribution data gathered using the University of Missouri-Rolla Mobile Aerosol Sampling System (UMR-MASS), and used to investigate the southern extent of the eastern end of the North Atlantic Flight Corridor (NAFC) during project Pollution From Aircraft Emissions in the North Atlantic Flight Corridor/Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (POLINAT 2/SONEX) from September 19 to October 23, 1997. The analysis presented in this paper focuses on the corridor effect, or enhancement of pollutants by jet aircraft combustion events. To investigate the phenomena, both vertical and horizontal profiles of the corridor, and regions immediately adjacent to the corridor, were performed. The profiles showed a time-dependent enhancement of particulates within the corridor, and a nonvolatile (with respect to thermal volatilization at 300° C) aerosol enhancement at corridor altitudes by a factor of 3.6. The southern extent of the North Atlantic Flight Corridor was established from a four flight average of the particulate data and yielded a boundary near 42.5° N during the study period. A size distribution analysis of the nonvolatile particulates revealed an enhancement in the \u3c40 nm particulates for size distributions recorded within the flight corridor

Local Dynamics and Strong Correlation Physics I: 1D and 2D Half-filled Hubbard Models

We report on a non-perturbative approach to the 1D and 2D Hubbard models that is capable of recovering both strong and weak-coupling limits. We first show that even when the on-site Coulomb repulsion, U, is much smaller than the bandwith, the Mott-Hubbard gap never closes at half-filling in both 1D and 2D. Consequently, the Hubbard model at half-filling is always in the strong-coupling non-perturbative regime. For both large and small U, we find that the population of nearest-neighbour singlet states approaches a value of order unity as $T\to 0$ as would be expected for antiferromagnetic order. We also find that the double occupancy is a smooth monotonic function of U and approaches the anticipated non-interacting limit and large U limits. Finally, in our results for the heat capacity in 1D differ by no more than 1% from the Bethe ansatz predictions. In addition, we find that in 2D, the heat capacity vs T for different values of U exhibits a universal crossing point at two characteristic temperatures as is seen experimentally in a wide range of strongly-correlated systems such as $^3He$, $UBe_3$, and $CeCu_{6-x}Al_x$. The success of this method in recovering well-established results that stem fundamentally from the Coulomb interaction suggests that local dynamics are at the heart of the physics of strongly correlated systems.Comment: 10 pages, 16 figures included in text, Final version for publication with a reference added and minor corrections. Phys. Rev. B, in pres

Isosbestic points in the spectral function of correlated electrons

We investigate the properties of the spectral function A(omega,U) of correlated electrons within the Hubbard model and dynamical mean-field theory. Curves of A(omega,U) vs. omega for different values of the interaction U are found to intersect near the band-edges of the non-interacting system. For a wide range of U the crossing points are located within a sharply confined region. The precise location of these 'isosbestic points' depends on details of the non-interacting band structure. Isosbestic points of dynamic quantities therefore provide valuable insights into microscopic energy scales of correlated systems.Comment: 16 pages, 5 figure

Lightning-produced NO_x over Brazil during TROCCINOX: Airborne measurements in tropical and subtropical thunderstorms and the importance of mesoscale convective systems

International audienceDuring the TROCCINOX field experiments in February?March 2004 and February 2005, airborne in situ measurements of NO, NOy, CO, and O3 mixing ratios and the J(NO2) photolysis rate were carried out in the anvil outflow of thunderstorms over southern Brazil. Both tropical and subtropical thunderstorms were investigated, depending on the location of the South Atlantic convergence zone. Tropical air masses were discriminated from subtropical ones according to the higher equivalent potential temperature (?e) in the lower and mid troposphere, the higher CO mixing ratio in the mid troposphere, and the lower wind velocity and proper wind direction in the upper troposphere. During thunderstorm anvil penetrations, typically at 20?40 km horizontal scales, NOx mixing ratios were on average enhanced by 0.2?1.6 nmol mol?1. This enhancement was mainly attributed to NOx production by lightning and partly due to upward transport from the NOx-richer boundary layer. In addition, CO mixing ratios were occasionally enhanced, indicating upward transport from the boundary layer. For the first time, the composition of the anvil outflow from a large, long-lived mesoscale convective system (MCS) advected from northern Argentina and Uruguay was investigated in more detail. Over a horizontal scale of about 400 km, NOx, CO and O3 mixing ratios were significantly enhanced in these air masses in the range of 0.6?1.1, 110?140 and 60?70 nmol mol?1, respectively. Analyses from trace gas correlations and a Lagrangian particle dispersion model indicate that polluted air masses, probably from the Buenos Aires urban area and from biomass burning regions, were uplifted by the MCS. Ozone was distinctly enhanced in the aged MCS outflow, due to photochemical production and entrainment of O3-rich air masses from the upper troposphere ? lower stratosphere region. The aged MCS outflow was transported to the north, ascended and circulated, driven by the Bolivian High over the Amazon basin. In the observed case, the O3-rich MCS outflow remained over the continent and did not contribute to the South Atlantic ozone maximum

Specific Heat of a Three Dimensional Metal Near a T=0 Magnetic Transition with Dynamic Exponent z=2,3,4

We derive expressions for the universal contribution to the specific heat of a three-dimensional metal near a zero-temperature phase transition with dynamic exponent $z=2,3$, or 4. The results allow a quantitative comparison of theory to data. We illustrate the application of our results by analyzing data for Ce$_{1-x}$Lu$_x$Cu$_2$Si$_2$, which has been claimed to be near a quantum critical point.Comment: 23 pages, revtex. For figures, send mail to [email protected]

Three-dimensional geometric morphometrics of thorax-pelvis covariation and its potential for predicting the thorax morphology: A case study on Kebara 2 Neandertal

The skeletal torso is a complex structure of outstanding importance in understanding human body shape evolution, but reconstruction usually entails an element of subjectivity as researchers apply their own anatomical expertise to the process. Among different fossil reconstruction methods, 3D geometric morphometric techniques have been increasingly used in the last decades. Two-block partial least squares analysis has shown great potential for predicting missing elements by exploiting the covariation between two structures (blocks) in a reference sample: one block can be predicted from the other one based on the strength of covariation between blocks. The first aim of this study is to test whether this predictive approach can be used for predicting thorax morphologies from pelvis morphologies within adult Homo sapiens reference samples with known covariation between the thorax and the pelvis. The second aim is to apply this method to Kebara 2 Neandertal (Israel, ∼60 ka) to predict its thorax morphology using two different pelvis reconstructions as predictors. We measured 134 true landmarks, 720 curve semilandmarks, and 160 surface semilandmarks on 60 3D virtual torso models segmented from CT scans. We conducted three two-block partial least squares analyses between the thorax (block 1) and the pelvis (block 2) based on the H. sapiens reference samples after performing generalized Procrustes superimposition on each block separately. Comparisons of these predictions in full shape space by means of Procrustes distances show that the male-only predictive model yields the most reliable predictions within modern humans. In addition, Kebara 2 thorax predictions based on this model concur with the thorax morphology proposed for Neandertals. The method presented here does not aim to replace other techniques, but to rather complement them through quantitative prediction of a virtual 'scaffold' to articulate the thoracic fossil elements, thus extending the potential of missing data estimation beyond the methods proposed in previous works