Existence and Vanishing of the Breathing Mode in Strongly Correlated Finite Systems

One of the fundamental eigenmodes of finite interacting systems is the mode of {\em uniform radial expansion and contraction} -- the ``breathing'' mode (BM). Here we show in a general way that this mode exists only under special conditions: i) for harmonically trapped systems with interaction potentials of the form $1/r^\gamma$ $(\gamma\in\mathbb{R}_{\neq0})$ or $\log(r)$, or ii) for some systems with special symmetry such as single shell systems forming platonic bodies. Deviations from the BM are demonstrated for two examples: clusters interacting with a Lennard-Jones potential and parabolically trapped systems with Yukawa repulsion. We also show that vanishing of the BM leads to the occurence of multiple monopole oscillations which is of importance for experiments

Alberta's Water for Life Strategy: Some early indications of its acceptance by the irrigation industry in Southern Alberta

Water is essential for sustainable agricultural development - for irrigation of crops, livestock watering, processing, and sustaining farm families. Agriculture uses 71 percent of all water diverted for consumptive use in Canada (Environment Canada, 2004), and is by far the greatest water consumer in Canada. In the absence of a Canadian national water strategy, Alberta has developed a long-term water management plan called the Water for Life Strategy. Its successful implementation will depend largely on the participation of irrigators. This study explores the reaction of irrigators to one of the strategy's main goals - a 30 percent increase in water use efficiency and productivity by 2015 over 2005 levels. The study reveals that irrigators vary significantly in their views as to the extent to which this goal can be reached, and the means by which it should be achieved within agriculture. Further, these responses reflect differences among irrigation districts relating to the extent of water stress, on-farm irrigation water efficiency and natural factors that limit crop diversity in some areas. Ultimately the government may have to revise its 30 percent target and tailor the strategy to irrigation districts as opposed to a broad-based approach.Resource /Energy Economics and Policy,

Investigation of vertical cavity surface emitting laser dynamics for neuromorphic photonic systems

We report an approach based upon vertical cavity surface emitting lasers (VCSELs) to reproduce optically different behaviors exhibited by biological neurons but on a much faster timescale. The technique proposed is based on the polarization switching and nonlinear dynamics induced in a single VCSEL under polarized optical injection. The particular attributes of VCSELs and the simple experimental configuration used in this work offer prospects of fast, reconfigurable processing elements with excellent fan-out and scaling potentials for use in future computational paradigms and artificial neural networks. © 2012 American Institute of Physics

Dust rings and filaments around the isolated young star V1331 Cygni

We characterize the small and large scale environment of the young star V1331 Cygni with high resolution HST/WFPC2 and Digitized Sky Survey images. In addition to a previously known outer dust ring (~30'' in diameter), the HST/WFPC2 scattered light image reveals an inner dust ring for the first time. This ring has a maximum radius of 6.5'' and is possibly related to a molecular envelope. Large-scale optical images show that V1331 Cyg is located at the tip of a long dust filament linking it to the dark cloud LDN 981. We discuss the origin of the observed dust morphology and analyze the object's relation to its parent dark cloud LDN 981. Finally, based on recent results from the literature, we investigate the properties of V1331 Cyg and conclude that in its current state the object does not show suffcient evidence to be characterized as an FU Ori object.Comment: 15 pages ApJ preprint style including 3 figures, accepted for publication in ApJ (Feb. 2007

Experimental Characterization of the Energetics of Low-temperature Surface Reactions

Astrochemical surface reactions are thought to be responsible for the formation of complex organic molecules, which are of potential importance for the origin of life. In a situation, when the chemical composition of dust surfaces is not precisely known, the fundamental knowledge concerning such reactions gains significance. We describe an experimental technique, which can be used to measure the energy released in reactions of a single pair of reactants. These data can be directly compared with the results of quantum chemical computations leading to unequivocal conclusions regarding the reaction pathways and the presence of energy barriers. It allows for predicting the outcomes of astrochemical surface reactions with higher accuracy compared to that achieved based on gas-phase studies. However, for the highest accuracy, some understanding of the catalytic influence of specific surfaces on the reactions is required. The new method was applied to study the reactions of C atoms with H2, O2, and C2H2. The formation of HCH, CO + O, and triplet cyclic-C3H2 products has been revealed, correspondingly

Polarization of Thermal Emission from Aligned Dust Grains Under an Anisotropic Radiation Field

If aspherical dust grains are immersed in an anisotropic radiation field, their temperature depends on the cross-sections projected in the direction of the anisotropy.It was shown that the temperature difference produces polarized thermal emission even without alignment, if the observer looks at the grains from a direction different from the anisotropic radiation. When the dust grains are aligned, the anisotropy in the radiation makes various effects on the polarization of the thermal emission, depending on the relative angle between the anisotropy and alignment directions. If the both directions are parallel, the anisotropy produces a steep increase in the polarization degree at short wavelengths. If they are perpendicular, the polarization reversal occurs at a wavelength shorter than the emission peak. The effect of the anisotropic radiation will make a change of more than a few % in the polarization degree for short wavelengths and the effect must be taken into account in the interpretation of the polarization in the thermal emission. The anisotropy in the radiation field produces a strong spectral dependence of the polarization degree and position angle, which is not seen under isotropic radiation. The dependence changes with the grain shape to a detectable level and thus it will provide a new tool to investigate the shape of dust grains. This paper presents examples of numerical calculations of the effects and demonstrates the importance of anisotropic radiation field on the polarized thermal emission.Comment: 13pages, 7figure

petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval

We present the easy-to-use, publicly available, Python package petitRADTRANS, built for the spectral characterization of exoplanet atmospheres. The code is fast, accurate, and versatile; it can calculate both transmission and emission spectra within a few seconds at low resolution ($\lambda/\Delta\lambda$ = 1000; correlated-k method) and high resolution ($\lambda/\Delta\lambda = 10^6$; line-by-line method), using only a few lines of input instruction. The somewhat slower correlated-k method is used at low resolution because it is more accurate than methods such as opacity sampling. Clouds can be included and treated using wavelength-dependent power law opacities, or by using optical constants of real condensates, specifying either the cloud particle size, or the atmospheric mixing and particle settling strength. Opacities of amorphous or crystalline, spherical or irregularly-shaped cloud particles are available. The line opacity database spans temperatures between 80 and 3000 K, allowing to model fluxes of objects such as terrestrial planets, super-Earths, Neptunes, or hot Jupiters, if their atmospheres are hydrogen-dominated. Higher temperature points and species will be added in the future, allowing to also model the class of ultra hot-Jupiters, with equilibrium temperatures $T_{\rm eq} \gtrsim 2000$ K. Radiative transfer results were tested by cross-verifying the low- and high-resolution implementation of petitRADTRANS, and benchmarked with the petitCODE, which itself is also benchmarked to the ATMO and Exo-REM codes. We successfully carried out test retrievals of synthetic JWST emission and transmission spectra (for the hot Jupiter TrES-4b, which has a $T_{\rm eq}$ of $\sim$ 1800 K). The code is publicly available at http://gitlab.com/mauricemolli/petitRADTRANS, and its documentation can be found at https://petitradtrans.readthedocs.io.Comment: 17 pages, 7 figures, published in A&

Very Low-Mass Objects in the Coronet Cluster: The Realm of the Transition Disks

We present optical and IR spectra of a set of low-mass stars and brown dwarfs in the Coronet cluster (aged ~1Myr), obtained with the multifiber spectrograph FLAMES/VLT and IRS/Spitzer. The optical spectra reveal spectral types between M1 and M7.5, confirm the youth of the objects (via Li 6708 A absorption), and show the presence of accretion (via Halpha) and shocks (via forbidden line emission). The IRS spectra, together with IR photometry from the IRAC/MIPS instruments on Spitzer and 2MASS, confirm the presence of IR excesses characteristic of disks around ~70% of the objects. Half of the disks do not exhibit any silicate emission, or present flat features characteristic of large grains. The rest of the disks show silicate emission typical of amorphous and crystalline silicate grains a few microns in size. About 50% of the objects with disks do not show near-IR excess emission, having "transitional" disks, according to their classical definition. This is a very high fraction for such a young cluster. The large number of "transitional" disks suggests lifetimes comparable to the lifetimes of typical optically thick disks. Therefore, these disks may not be in a short-lived phase, intermediate between Class II and Class III objects. The median spectral energy distribution of the disks in the Coronet cluster is also closer to a flat disk than observed for the disks around solar-type stars in regions with similar age. The differences in the disk morphology and evolution in the Coronet cluster could be related to fact that these objects have very late spectral types compared to the solar-type stars in other cluster studies. Finally, the optical spectroscopy reveals that one of the X-ray sources is produced by a Herbig Haro object in the cloud.Comment: 51 pages, 13 figures, 10 table