Piezoelectric Phononic Plates: Retrieving the Frequency Band Structure via All-electric Experiments

We propose an experimental technique based on all-electric measurements to retrieve the frequency response of a one-dimensional piezoelectric phononic crystal plate, structured periodically with millimeter-scaled metallic strips on its two surfaces. The metallic electrodes, used for the excitation of Lamb-like guided modes in the plate, ensure at the same time control of their dispersion by means of externally loaded electric circuits that offer non-destructive tunability in the frequency response of these structures. Our results, in very good agreement with finite-element numerical predictions, reveal interesting symmetry aspects that are employed to analyze the frequency band structure of such crystals. More importantly, Lamb-like guided modes interact with electric-resonant bands induced by inductance loads on the plate, whose form and symmetry are discussed and analyzed in depth, showing unprecedented dispersion characteristics.Comment: This is the version of the article before peer review or editing, as submitted by an author to Smart Materials and Structures. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1361-665X/ab4aa

Observation of topologically protected helical edge modes in Kagome elastic plates

The investigation of topologically protected waves in classical media has opened unique opportunities to achieve exotic properties like one-way phonon transport, protection from backscattering and immunity to imperfections. Contrary to acoustic and electromagnetic domains, their observation in elastic solids has so far been elusive due to the presence of both shear and longitudinal modes and their modal conversion at interfaces and free surfaces. Here we report the experimental observation of topologically protected helical edge waves in elastic media. The considered structure consists of an elastic plate patterned according to a Kagome architecture with an accidental degeneracy of two Dirac cones induced by drilling through holes. The careful breaking of symmetries couples the corresponding elastic modes which effectively emulates spin orbital coupling in the quantum spin Hall effect. The results shed light on the topological properties of the proposed plate waveguide and opens avenues for the practical realization of compact, passive and cost-effective elastic topological waveguides

Bayesian calibration of the nitrous oxide emission module of an agro-ecosystem model

Nitrous oxide (N2O) is the main biogenic greenhouse gas contributing to the global warming potential (GWP) of agro-ecosystems. Evaluating the impact of agriculture on climate therefore requires a capacity to predict N2O emissions in relation to environmental conditions and crop management. Biophysical models simulating the dynamics of carbon and nitrogen in agro-ecosystems have a unique potential to explore these relationships, but are fraught with high uncertainties in their parameters due to their variations over time and space. Here, we used a Bayesian approach to calibrate the parameters of the N2O submodel of the agro-ecosystem model CERES-EGC. The submodel simulates N2O emissions from the nitrification and denitrification processes, which are modelled as the product of a potential rate with three dimensionless factors related to soil water content, nitrogen content and temperature. These equations involve a total set of 15 parameters, four of which are site-specific and should be measured on site, while the other 11 are considered global, i.e. invariant over time and space. We first gathered prior information on the model parameters based on the literature review, and assigned them uniform probability distributions. A Bayesian method based on the Metropolis–Hastings algorithm was subsequently developed to update the parameter distributions against a database of seven different field-sites in France. Three parallel Markov chains were run to ensure a convergence of the algorithm. This site-specific calibration significantly reduced the spread in parameter distribution, and the uncertainty in the N2O simulations. The model’s root mean square error (RMSE) was also abated by 73% across the field sites compared to the prior parameterization. The Bayesian calibration was subsequently applied simultaneously to all data sets, to obtain better global estimates for the parameters initially deemed universal. This made it possible to reduce the RMSE by 33% on average, compared to the uncalibrated model. These global parameter values may be used to obtain more realistic estimates of N2O emissions from arable soils at regional or continental scales

Interferometric imaging of the sulfur-bearing molecules H2S, SO and CS in comet C/1995 O1 (Hale-Bopp)

We present observations of rotational lines of H2S, SO and CS performed in comet C/1995 O1 (Hale-Bopp) in March 1997 with the Plateau de Bure interferometer (IRAM). The observations provide informations on the spatial and velocity distributions of these molecules. They can be used to constrain their photodissociation rate and their origin. We use a radiative transfer code which allows us to compute synthetic line profiles and interferometric maps, to be compared to the observations. Both single-dish spectra and interferometric spectral maps show a day/night asymmetry in the outgassing. From the analysis of the spectral maps, including the astrometry, we show that SO and CS present in addition a jet-like structure that may be the gaseous counterpart of the dust high-latitude jet observed in optical images. A CS rotating jet is also observed. Using the astrometry provided by continuum radio maps obtained in parallel, we conclude that there is no need to invoke of nongravitational forces acting on this comet, and provide an updated orbit. The radial extension of H2S is found to be consistent with direct release from the nucleus. SO displays an extended radial distribution. Assuming that SO2 is the parent of SO, the photodissociation rate of SO is measured to be 1.5 E-4 s-1 at 1 AU from the Sun. This is lower than most laboratory-based estimates and may suggest that SO is not solely produced by SO2 photolysis. From the observations of J(2-1) and J(5-4) CS lines, we deduce a CS photodissociation rate of 1 to 5 E-5 s-1. The photodissociation rate of CS2, the likely parent of CS, cannot be constrained due to insufficient resolution, but our data are consistent with published values. These observations illustrate the cometary science that will be performed with the future ALMA interferometer.Comment: Accepted for publication in Astronomy & Astrophysic

Hydrogen Isocyanide in Comet 73P/Schwassmann-Wachmann (Fragment B)

We present a sensitive 3-sigma upper limit of 1.1% for the HNC/HCN abundance ratio in comet 73P/Schwassmann-Wachmann (Fragment B), obtained on May 10-11, 2006 using Caltech Submillimeter Observatory (CSO). This limit is a factor of ~7 lower than the values measured previously in moderately active comets at 1 AU from the Sun. Comet 73P/Schwassmann-Wachmann was depleted in most volatile species, except of HCN. The low HNC/HCN ratio thus argues against HNC production from polymers produced from HCN. However, thermal degradation of macromolecules, or polymers, produced from ammonia and carbon compounds, such as acetylene, methane, or ethane appears a plausible explanation for the observed variations of the HNC/HCN ratio in moderately active comets, including the very low ratio in comet 73P/Schwassmann-Wachmann reported here. Similar polymers have been invoked previously to explain anomalous 14N/15N ratios measured in cometary CN.Comment: 6 pages, 5 figures, 2 table

High resolution spectroscopy of Pluto's atmosphere: detection of the 2.3 μ\mum CH4_4 bands and evidence for carbon monoxide

The goal is to determine the composition of Pluto's atmosphere and to constrain the nature of surface-atmosphere interactions. We perform high--resolution spectroscopic observations in the 2.33--2.36 $\mu$m range, using CRIRES at the VLT. We obtain (i) the first detection of gaseous methane in this spectral range, through lines of the $\nu_3$ + $\nu_4$ and $\nu_1$ + $\nu_4$ bands (ii) strong evidence (6-$\sigma$ confidence) for gaseous CO in Pluto. For an isothermal atmosphere at 90 K, the CH$_4$ and CO column densities are 0.75 and 0.07 cm-am, within factors of 2 and 3, respectively. Using a physically--based thermal structure model of Pluto's atmosphere also satisfying constraints from stellar occultations, we infer CH$_4$ and CO mixing ratios q$_{CH_4}$= 0.6$^{+0.6}_{-0.3}$% (consistent with results from the 1.66 $\mu$m range) and q$_{CO}$ = 0.5$^{+1}_{-0.25}$$\times10^{-3}$. The CO atmospheric abundance is consistent with its surface abundance. As for Triton, it is probably controlled by a thin, CO-rich, detailed balancing layer resulting from seasonal transport and/or atmospheric escape.Comment: Astronomy and Astrophysics Letters, in pres

The unusual volatile composition of the Halley-type comet 8P/Tuttle: Addressing the existence of an Inner Oort Cloud

We measured organic volatiles (CH4, CH3OH, C2H6, H2CO), CO, and water in comet 8P/Tuttle, a comet from the Oort cloud reservoir now in a short-period Halley-type orbit. We compare its composition with two other comets in Halley-type orbits, and with comets of the "organics-normal" and "organics-depleted" classes. Chemical gradients are expected in the comet-forming region of the proto-planetary disk, and an individual comet should reflect its specific heritage. If Halley-type comets came from the inner Oort cloud as proposed, we see no common characteristics that could distinguish such comets from those that were stored in the outer Oort cloud.Comment: 14 pages, including 1 figure and 2 Table

Searches for HCl and HF in comets 103P/Hartley 2 and C/2009 P1 (Garradd) with the Herschel space observatory

HCl and HF are expected to be the main reservoirs of fluorine and chlorine wherever hydrogen is predominantly molecular. They are found to be strongly depleted in dense molecular clouds, suggesting freeze-out onto grains in such cold environments. We can then expect that HCl and HF were also the major carriers of Cl and F in the gas and icy phases of the outer solar nebula, and were incorporated into comets. We aimed to measure the HCl and HF abundances in cometary ices as they can provide insights on the halogen chemistry in the early solar nebula. We searched for the J(1-0) lines of HCl and HF at 626 and 1232 GHz, respectively, using the HIFI instrument on board the Herschel Space Observatory. HCl was searched for in comets 103P/Hartley 2 and C/2009 P1 (Garradd), whereas observations of HF were conducted in comet C/2009 P1. In addition, observations of H$_2$O and H$_2^{18}$O lines were performed in C/2009 P1 to measure the H$_2$O production rate. Three lines of CH$_3$OH were serendipitously observed in the HCl receiver setting. HCl is not detected, whereas a marginal (3.6-$\sigma$) detection of HF is obtained. The upper limits for the HCl abundance relative to water are 0.011% and 0.022%, for 103P and C/2009 P1, respectively, showing that HCl is depleted with respect to the solar Cl/O abundance by a factor more than 6$^{+6}_{-3}$ in 103P, where the error is related to the uncertainty in the chlorine solar abundance. The marginal HF detection obtained in C/2009 P1 corresponds to an HF abundance relative to water of (1.8$\pm$0.5) $\times$ 10$^{-4}$, which is approximately consistent with a solar photospheric F/O abundance. The observed depletion of HCl suggests that HCl was not the main reservoir of chlorine in the regions of the solar nebula where these comets formed. HF was possibly the main fluorine compound in the gas phase of the outer solar nebula.Comment: Accepted for publication in Astronomy & Astrophysic

The Composition of Comets

This paper is the result of the International Cometary Workshop, held in Toulouse, France in April 2014, where the participants came together to assess our knowledge of comets prior to the ESA Rosetta Mission. In this paper, we look at the composition of the gas and dust from the comae of comets. With the gas, we cover the various taxonomic studies that have broken comets into groups and compare what is seen at all wavelengths. We also discuss what has been learned from mass spectrometers during flybys. A few caveats for our interpretation are discussed. With dust, much of our information comes from flybys. They include {\it in situ} analyses as well as samples returned to Earth for laboratory measurements. Remote sensing IR observations and polarimetry are also discussed. For both gas and dust, we discuss what instruments the Rosetta spacecraft and Philae lander will bring to bear to improve our understanding of comet 67P/Churyumov-Gerasimenko as "ground-truth" for our previous comprehensive studies. Finally, we summarize some of the initial Rosetta Mission findings.Comment: To appear in Space Science Review