Polycyclic aromatic hydrocarbons and molecular hydrogen in oxygen-rich planetary nebulae: the case of NGC6720

Evolved stars are primary sources for the formation of polycyclic aromatic hydrocarbons (PAHs) and dust grains. Their circumstellar chemistry is usually designated as either oxygen-rich or carbon-rich, although dual-dust chemistry objects, whose infrared spectra reveal both silicate- and carbon-dust features, are also known. The exact origin and nature of this dual-dust chemistry is not yet understood. Spitzer-IRS mid-infrared spectroscopic imaging of the nearby, oxygen-rich planetary nebula NGC6720 reveals the presence of the 11.3 micron aromatic (PAH) emission band. It is attributed to emission from neutral PAHs, since no band is observed in the 7 to 8 micron range. The spatial distribution of PAHs is found to closely follow that of the warm clumpy molecular hydrogen emission. Emission from both neutral PAHs and warm H2 is likely to arise from photo-dissociation regions associated with dense knots that are located within the main ring. The presence of PAHs together with the previously derived high abundance of free carbon (relative to CO) suggest that the local conditions in an oxygen-rich environment can also become conducive to in-situ formation of large carbonaceous molecules, such as PAHs, via a bottom-up chemical pathway. In this scenario, the same stellar source can enrich the interstellar medium with both oxygen-rich dust and large carbonaceous molecules.Comment: Accepted by MNRAS. 5 page

Multiangle static and dynamic light scattering in the intermediate scattering angle range

We describe a light scattering apparatus based on a novel optical scheme covering the scattering angle range 0.5\dg \le \theta \le 25\dg, an intermediate regime at the frontier between wide angle and small angle setups that is difficult to access by existing instruments. Our apparatus uses standard, readily available optomechanical components. Thanks to the use of a charge-coupled device detector, both static and dynamic light scattering can be performed simultaneously at several scattering angles. We demonstrate the capabilities of our apparatus by measuring the scattering profile of a variety of samples and the Brownian dynamics of a dilute colloidal suspension

Length scale dependence of dynamical heterogeneity in a colloidal fractal gel

We use time-resolved dynamic light scattering to investigate the slow dynamics of a colloidal gel. The final decay of the average intensity autocorrelation function is well described by $g\_2(q,\tau)-1 \sim \exp[-(\tau/\tau\_\mathrm{f})^p]$, with $\tau\_\mathrm{f} \sim q^{-1}$ and $p$ decreasing from 1.5 to 1 with increasing $q$. We show that the dynamics is not due to a continuous ballistic process, as proposed in previous works, but rather to rare, intermittent rearrangements. We quantify the dynamical fluctuations resulting from intermittency by means of the variance $\chi(\tau,q)$ of the instantaneous autocorrelation function, the analogous of the dynamical susceptibility $\chi\_4$ studied in glass formers. The amplitude of $\chi$ is found to grow linearly with $q$. We propose a simple --yet general-- model of intermittent dynamics that accounts for the $q$ dependence of both the average correlation functions and $\chi$.Comment: Revised and improved, to appear in Europhys. Let

Quantum limited particle sensing in optical tweezers

Particle sensing in optical tweezers systems provides information on the position, velocity and force of the specimen particles. The conventional quadrant detection scheme is applied ubiquitously in optical tweezers experiments to quantify these parameters. In this paper we show that quadrant detection is non-optimal for particle sensing in optical tweezers and propose an alternative optimal particle sensing scheme based on spatial homodyne detection. A formalism for particle sensing in terms of transverse spatial modes is developed and numerical simulations of the efficacy of both quadrant and spatial homodyne detection are shown. We demonstrate that an order of magnitude improvement in particle sensing sensitivity can be achieved using spatial homodyne over quadrant detection.Comment: Submitted to Biophys

The Rayleigh-Brillouin Spectrum in Special Relativistic Hydrodynamics

In this paper we calculate the Rayleigh-Brillouin spectrum for a relativistic simple fluid according to three different versions available for a relativistic approach to non-equilibrium thermodynamics. An outcome of these calculations is that Eckart's version predicts that such spectrum does not exist. This provides an argument to question its validity. The remaining two results, which differ one from another, do provide a finite form for such spectrum. This raises the rather intriguing question as to which of the two theories is a better candidate to be taken as a possible version of relativistic non-equilibrium thermodynamics. The answer will clearly require deeper examination of this problem.Comment: 13 pages, no figures. Accepted for publication in Phys. Rev.

Liquid Transport Due to Light Scattering

Using experiments and theory, we show that light scattering by inhomogeneities in the index of refraction of a fluid can drive a large-scale flow. The experiment uses a near-critical, phase-separated liquid, which experiences large fluctuations in its index of refraction. A laser beam traversing the liquid produces a large-scale deformation of the interface and can cause a liquid jet to form. We demonstrate that the deformation is produced by a scattering-induced flow by obtaining good agreements between the measured deformations and those calculated assuming this mechanism.Comment: 4 pages, 5 figures, submitted to Physical Review Letters v2: Edited based on comments from referee

Reconstruction of thermally-symmetrized quantum autocorrelation functions from imaginary-time data

In this paper, I propose a technique for recovering quantum dynamical information from imaginary-time data via the resolution of a one-dimensional Hamburger moment problem. It is shown that the quantum autocorrelation functions are uniquely determined by and can be reconstructed from their sequence of derivatives at origin. A general class of reconstruction algorithms is then identified, according to Theorem 3. The technique is advocated as especially effective for a certain class of quantum problems in continuum space, for which only a few moments are necessary. For such problems, it is argued that the derivatives at origin can be evaluated by Monte Carlo simulations via estimators of finite variances in the limit of an infinite number of path variables. Finally, a maximum entropy inversion algorithm for the Hamburger moment problem is utilized to compute the quantum rate of reaction for a one-dimensional symmetric Eckart barrier.Comment: 15 pages, no figures, to appear in Phys. Rev.

Quantum Monte Carlo Dynamics: the Stationary Phase Monte Carlo Path Integral Calculation of Finite Temperature Time Correlation Functions

We present a numerically exact procedure for the calculation of an important class of finite temperature quantum mechanical time correlation functions. The present approach is based around the stationary phase Monte Carlo (SPMC) method, a general mathematical tool for the calculation of high dimensional averages of oscillatory integrands. In the present context the method makes possible the direct numerical path integral calculation of real-time quantum dynamical quantities for times appreciably greater than the thermal time (βħ). Illustrative applications involving finite temperature anharmonic motion are presented. Issues of importance with respect to future applications are identified and discussed

Sagnac Interferometer Enhanced Particle Tracking in Optical Tweezers

A setup is proposed to enhance tracking of very small particles, by using optical tweezers embedded within a Sagnac interferometer. The achievable signal-to-noise ratio is shown to be enhanced over that for a standard optical tweezers setup. The enhancement factor increases asymptotically as the interferometer visibility approaches 100%, but is capped at a maximum given by the ratio of the trapping field intensity to the detector saturation threshold. For an achievable visibility of 99%, the signal-to-noise ratio is enhanced by a factor of 200, and the minimum trackable particle size is 2.4 times smaller than without the interferometer

Resolving long-range spatial correlations in jammed colloidal systems using photon correlation imaging

We introduce a new dynamic light scattering method, termed photon correlation imaging, which enables us to resolve the dynamics of soft matter in space and time. We demonstrate photon correlation imaging by investigating the slow dynamics of a quasi two-dimensional coarsening foam made of highly packed, deformable bubbles and a rigid gel network formed by dilute, attractive colloidal particles. We find the dynamics of both systems to be determined by intermittent rearrangement events. For the foam, the rearrangements extend over a few bubbles, but a small dynamical correlation is observed up to macroscopic length scales. For the gel, dynamical correlations extend up to the system size. These results indicate that dynamical correlations can be extremely long-ranged in jammed systems and point to the key role of mechanical properties in determining their nature.Comment: Published version (Phys. Rev. Lett. 102, 085702 (2009)) The Dynamical Activity Mapsprovided as Supplementary Online Material are also available on http://w3.lcvn.univ-montp2.fr/~lucacip/dam/movies.ht