The cyclic ground state structure of the HF trimer revealed by far infrared jet-cooled Fourier transform spectroscopy.

International audienceThe rovibrationally resolved Fourier transform (FT) far infrared (FIR) spectra of two intermolecular librations of (HF)3, namely the in-plane ν6 and out-of-plane ν4 bending fundamentals centered, respectively, at about 494 cm(-1) and 602 cm(-1), have been recorded for the first time under jet-cooled conditions using the supersonic jet of the Jet-AILES apparatus. The simultaneous rotational analysis of 245 infrared transitions belonging to both bands enabled us to determine the ground state (GS), ν6 and ν4 rotational and centrifugal distortion constants. These results provided definite experimental answers to the structure of such a weakly bound trimer: firstly the vibrationally averaged planarity of cyclic (HF)3, also supported by the very small value of the inertia defect obtained in the GS, secondly the slight weakening of the hydrogen bond in the intermolecular excited states evidenced from the center of mass separations of the HF constituents determined in the ground, ν6 = 1 and ν4 = 1 states of (HF)3 as well as the decrease of the fitted rotational constants upon excitation. Finally, lower bounds of about 2 ns on ν6 and ν4 state lifetimes could be derived from the deconvolution of experimental linewidths. Such long lifetimes highlight the interest in probing low frequency intermolecular motions of molecular complexes to get rid of constraints related to the vibrational dynamics of coupled anharmonic vibrations at higher energy, resulting in loss of rotational information

A reduced model for shock and detonation waves. II. The reactive case

We present a mesoscopic model for reactive shock waves, which extends a previous model proposed in [G. Stoltz, Europhys. Lett. 76 (2006), 849]. A complex molecule (or a group of molecules) is replaced by a single mesoparticle, evolving according to some Dissipative Particle Dynamics. Chemical reactions can be handled in a mean way by considering an additional variable per particle describing a rate of reaction. The evolution of this rate is governed by the kinetics of a reversible exothermic reaction. Numerical results give profiles in qualitative agreement with all-atom studies

Investigating Ramp Wave Propagation inside Silica Glass with Laser Experiments and Molecular Simulations

Under elastic shock compression silica glass exhibits a very specific behaviour. A shock propagating inside a material is usually seen as the propagation of a discontinuity. However in silica glass, shocks are unstable and lead to the propagation of a ramp wave where the shock front becomes gradually larger over time. Ramp waves were already reported in the literature, however their origin remain uncertain. This work presents an original study combining laser shock-induced experiments and molecular dynamics simulation aiming to improve the understanding of the mechanisms involved. Experimental ramp waves were directly observed using shadowgraphy technique allowing for an estimation of the head and tail velocities. Molecular dynamics simulations were carried out in order to reproduce ramp waves and to gain insight into the material properties. Ramp waves were observed for both elastic and plastic shockwaves. In the latter case, the plastic waves were preceded by an elastic ramp precursor. The sound speed, related to the material compressibility, was found to decrease with increasing pressure, as observed experimentally for quasi-static hydrostatic loading, thus providing an explanation for the instabilities that lead to the propagation of ramp waves

Agri-urban patterns in Mediterranean urban regions: the case study of Pisa

Urban regions require planning tools in order to manage agricultural areas under urban pressure. The aim of our paper is to test an analytical framework that combines both the composition in urban and agricultural land covers and their spatial configuration into four general agri-urban patterns: isolated fields, urban belt fields, periurban agricultural areas and rural areas. We evaluated the spatial distribution and the changes of such patterns in the short-term (2003-2011) starting from Spot images for the case study of Pisa, Italy. The results indicate an increase of the most urban patterns despite continuing to have cash crops, a stability of periurban agricultural land patterns although highly fragmented, and a decrease of the rural agricultural land patterns. The applied methodology can help to identify new measures and actions suitable in order to strengthen the relationships between city and agriculture existing in urban regions

Superconductivity Induced by Bond Breaking in the Triangular Lattice of IrTe2

IrTe2, a layered compound with a triangular iridium lattice, exhibits a structural phase transition at approximately 250 K. This transition is characterized by the formation of Ir-Ir bonds along the b-axis. We found that the breaking of Ir-Ir bonds that occurs in Ir1-xPtxTe2 results in the appearance of a structural critical point in the T = 0 limit at xc = 0.035. Although both IrTe2 and PtTe2 are paramagnetic metals, superconductivity at Tc = 3.1 K is induced by the bond breaking in a narrow range of x > xc in Ir1-xPtxTe2. This result indicates that structural fluctuations can be involved in the emergence of superconductivity.Comment: 10 pages, 4 figure

Constant entropy sampling and release waves of shock compressions

We present several equilibrium methods that allow to compute isentropic processes, either during the compression or the release of the material. These methods are applied to compute the isentropic release of a shocked monoatomic liquid at high pressure and temperature. Moreover, equilibrium results of isentropic release are compared to the direct nonequilibrium simulation of the same process. We show that due to the viscosity of the liquid but also to nonequilibrium effects, the release of the system is not strictly isentropic

Joint PDF modelling of turbulent flow and dispersion in an urban street canyon

The joint probability density function (PDF) of turbulent velocity and concentration of a passive scalar in an urban street canyon is computed using a newly developed particle-in-cell Monte Carlo method. Compared to moment closures, the PDF methodology provides the full one-point one-time PDF of the underlying fields containing all higher moments and correlations. The small-scale mixing of the scalar released from a concentrated source at the street level is modelled by the interaction by exchange with the conditional mean (IECM) model, with a micro-mixing time scale designed for geometrically complex settings. The boundary layer along no-slip walls (building sides and tops) is fully resolved using an elliptic relaxation technique, which captures the high anisotropy and inhomogeneity of the Reynolds stress tensor in these regions. A less computationally intensive technique based on wall functions to represent boundary layers and its effect on the solution are also explored. The calculated statistics are compared to experimental data and large-eddy simulation. The present work can be considered as the first example of computation of the full joint PDF of velocity and a transported passive scalar in an urban setting. The methodology proves successful in providing high level statistical information on the turbulence and pollutant concentration fields in complex urban scenarios.Comment: Accepted in Boundary-Layer Meteorology, Feb. 19, 200

A comparative study on nine- and twelve-phase flux-switching permanent-magnet wind power generators

In this paper, two flux-switching permanent-magnet (FSPM) wind power generators with 9- and 12-phase windings are designed and comparatively analyzed. Both two generators are designed under the rated specifications of 10 kW output power and 220 V phase voltage at 500 rpm. The static characteristics and power generating performances including output voltage, power and efficiency at rated and variable load/speed conditions are predicted by finite-element (FE) analysis and validated by experimental tests based on the two FSPM prototypes. It shows that the 12-phase 24-stator-slot/22-rotor-pole FSPM generator exhibits a higher air-gap flux density, a higher torque/power density and a lower voltage regulation factor. Besides, it has a better overload capability than its 9-phase 36-stator-slot/34-rotor-pole counterpart when the load and wind speed exceed the rated levels. The comparative study reveals the benefits of the lower leakage flux and permeance from the larger stator-slot opening and longer magnetic circuit

The Burden of Progressive Fibrosing Interstitial Lung Disease: A DELPHI Approach

Introduction: The term progressive fibrosing interstitial lung disease (ILD) describes patients with fibrotic ILDs who, irrespective of the aetiology of the disease, show a progressive course of their disease despite current available (and non-licensed) treatment. Besides in idiopathic pulmonary fibrosis, little is known about management and the burden of patients with fibrotic ILD, particularly those with a progressive behaviour. Methods: Using the Delphi method, 40 European experts in ILD management delivered information on management of (progressive) fibrosing ILD and on the impact of the disease on patients’ quality of life (QoL) and healthcare resource utilisation (HCRU). Annual costs were calculated for progressive and non-/slow-progressive fibrosing ILD for diagnosis, follow-up management, exacerbation management, and end-of-life care based on the survey data. Results: Physicians reported that progression in fibrosing ILD worsens QoL in both patients and their caregivers. Progression of fibrosing ILD was associated with a greater use of HCRU for follow-up visits and maintenance treatment compared with the non-/slow progression. The number of patients who suffered at least one acute exacerbation was reported to be more than three times higher in progressive fibrosing ILD patients than in patients with non-/slow-progressive fibrosing ILD. On average, annual estimated costs of progressive fibrosing ILD per patient were 1.8 times higher than those of the non-/slow-progressive form of the disease.

The natural capital accounting opportunity: Let s really do the numbers

This work was conducted as a part of the “Accounting for U.S. Ecosystem Services at National and Subnational Scales” working group supported by the National Socio-Environmental Synthesis Center under funding received from the National Science Foundation (grant no. DBI-1052875) and the US Geological Survey John Wesley Powell Center for Analysis and Synthesis (grant no. GX16EW00ECSV00)