Nuclear Spirals in the inner Milky Way

We use hydrodynamical simulations to construct a new coherent picture for the gas flow in the Central Molecular Zone (CMZ), the region of our Galaxy within $R\leq 500\, \mathrm{pc}$. We relate connected structures observed in $(l,b,v)$ data cubes of molecular tracers to nuclear spiral arms. These arise naturally in hydrodynamical simulations of barred galaxies, and are similar to those that can be seen in external galaxies such as NGC4303 or NGC1097. We discuss a face-on view of the CMZ including the position of several prominent molecular clouds, such as Sgr B2, the $20\,{\rm km\, s^{-1}}$ and $50\,{\rm km\, s^{-1}}$ clouds, the polar arc, Bania Clump 2 and Sgr C. Our model is also consistent with the larger scale gas flow, up to $R\simeq 3\,\rm kpc$, thus providing a consistent picture of the entire Galactic bar region.Comment: Accepted for publication in MNRAS, 12 pages, 12 figure

Periodicity makes galactic shocks unstable - I. Linear analysis

We study the dynamical stability of stationary galactic spiral shocks. The steady-state equilibrium flow contains a shock of the type derived by Roberts in the tightly wound approximation. We find that boundary conditions are critical in determining whether the solutions are stable or not. Shocks are unstable if periodic boundary conditions are imposed. For intermediate strengths of the spiral potential, the instability disappears if boundary conditions are imposed such that the upstream flow is left unperturbed as in the classic analysis of D'yakov and Kontorovich. This reconciles apparently contradictory findings of previous authors regarding the stability of spiral shocks. This also shows that the instability is distinct from the Kelvin-Helmholtz instability, confirming the findings of Kim et al. We suggest that instability is a general characteristics of periodic shocks, regardless of the presence of shear, and provide a physical picture as to why this is the case. For strong spiral potentials, high post-shock shear makes the system unstable also to parasitic Kelvin-Helmholtz instability regardless of the boundary conditions. Our analysis is performed in the context of a simplified problem that, while preserving all the important characteristics of the original problem, strips it from unnecessary complications, and assumes that the gas is isothermal, non self-gravitating, non-magnetised.Comment: Accepted for publication in MNRA

Sinopsis del género Holocompsa Burmeister, 1838 (Blattodea: Corydiidae: Holocompsinae) en América, con énfasis en México

Se presenta la información hasta la fecha del género pantropical Holocompsa Burmeister, 1838, con énfasis en México. Adicionalmente, se describe una nueva especie con base en material colectado en Yucatán, México. Se propone una guía taxonómica para las especies americanas.The information of the pantropical genus Holocompsa Burmeister is presented to date, with emphasis on Mexico. Additionally, a new species is described based on material collected in Yucatan, Mexico. A taxonomic guide for the American species is proposed

Candidate Binding Sites for Allosteric Inhibition of the SARS-CoV-2 Main Protease from the Analysis of Large-Scale Molecular Dynamics Simulations

We analyzed a 100 μs MD trajectory of the SARS-CoV-2 main protease by a non-parametric data analysis approach which allows characterizing a free energy landscape as a simultaneous function of hundreds of variables. We identified several conformations that, when visited by the dynamics, are stable for several hundred nanoseconds. We explicitly characterize and describe these metastable states. In some of these configurations, the catalytic dyad is less accessible. Stabilizing them by a suitable binder could lead to an inhibition of the enzymatic activity. In our analysis we keep track of relevant contacts between residues which are selectively broken or formed in the states. Some of these contacts are formed by residues which are far from the catalytic dyad and are accessible to the solvent. Based on this analysis we propose some relevant contact patterns and three possible binding sites which could be targeted to achieve allosteric inhibition

A theoretical explanation for the Central Molecular Zone asymmetry

It has been known for more than thirty years that the distribution of molecular gas in the innermost 300 parsecs of the Milky Way, the Central Molecular Zone, is strongly asymmetric. Indeed, approximately three quarters of molecular emission comes from positive longitudes, and only one quarter from negative longitudes. However, despite much theoretical effort, the origin of this asymmetry has remained a mystery. Here we show that the asymmetry can be neatly explained by unsteady flow of gas in a barred potential. We use high-resolution 3D hydrodynamical simulations coupled to a state-of-the-art chemical network. Despite the initial conditions and the bar potential being point-symmetric with respect to the Galactic Centre, asymmetries develop spontaneously due to the combination of a hydrodynamical instability known as the "wiggle instability" and the thermal instability. The observed asymmetry must be transient: observations made tens of megayears in the past or in the future would often show an asymmetry in the opposite sense. Fluctuations of amplitude comparable to the observed asymmetry occur for a large fraction of the time in our simulations, and suggest that the present is not an exceptional moment in the life of our Galaxy.Comment: Accepted for publication in MNRAS. Videos of the simulations are available at http://www.ita.uni-heidelberg.de/~mattia/download.htm

On the Tremaine-Weinberg method: how much can we trust gas tracers to measure pattern speeds?

Pattern speeds are a fundamental parameter of the dynamical features (e.g. bars, spiral arms) of a galaxy, setting resonance locations. Pattern speeds are not directly observable, so the Tremaine-Weinberg (TW) method has become the most common method used to measure them in galaxies. However, it has not been tested properly whether this method can straightforwardly be applied to gas tracers, despite this being widely done in the literature. When applied to observations, the TW method may return invalid results, which are difficult to diagnose due to a lack of ground truth for comparison. Although some works applying the TW method to simulated galaxies exist, only stellar populations have been tested. Therefore, here we explore the applicability of the TW method for gas gracers, by applying it to hydrodynamical simulations of galaxies, where we know the true value of the bar pattern speed. We perform some simple tests to see if the TW method has a physically reasonable output. We add different kinds of uncertainties (e.g. in position angle or flux) to the data to mock observational errors based on the magnitude of uncertainty present in the observations. Second, we test the method on 3D simulations with chemical networks. We show that in general, applying TW to observations of gas will not recover the true pattern speed. These results have implications for many "pattern speeds" reported in the literature, and based on these tests we also give some best practices for measuring pattern speeds using gas tracers going forwards.Comment: 9 pages, 8 figures, submitted to MNRA

Blood Pressure Control in Italian Essential Hypertensives Treated by General Practitioners

n/

Brain health: time matters in multiple sclerosis

publisher: Elsevier articletitle: Brain health: time matters in multiple sclerosis journaltitle: Multiple Sclerosis and Related Disorders articlelink: http://dx.doi.org/10.1016/j.msard.2016.07.003 content_type: article copyright: © 2016 Oxford PharmaGenesis Ltd. Published by Elsevier B.V

thalamic damage predicts the evolution of primary progressive multiple sclerosis at 5 years

BACKGROUND AND PURPOSE: Reliable markers to monitor PPMS are still needed. We investigated whether conventional and DTI measures of thalamic damage are predictive of long-term disability accumulation in PPMS. MATERIALS AND METHODS: Brain conventional and DTI scans were obtained at baseline and after a mean follow-up of 15 months in 54 patients with PPMS and 8 healthy controls. Patients were reassessed clinically after 5 years. At baseline and follow-up, measures of lesion load, brain atrophy, and NTV were obtained. MD and FA histograms of the NAWM, the whole GM without the thalami, and the thalami were obtained. A multivariate analysis evaluated the predictors of long-term neurologic deterioration. RESULTS: At follow-up, 35 patients showed disability worsening. At baseline, compared with healthy controls, patients with PPMS had lower NTV ( P P = .002) and higher thalamic ( P = .002) and whole GM without the thalami ( P = .005) MD. During follow-up, the change of thalamic FA was higher in PPMS versus healthy controls ( P = .01). Baseline NTV and thalamic DTI quantities differed significantly between patients with PPMS with and without thalamic lesions. Baseline thalamic quantities were significantly correlated with the extent of brain T2 lesions and the severity of NAWM damage. The multivariate model included average NAWM MD (OR = 1.46, P = .005) and FA thalamic change (OR = 0.84, P = .02) as independent predictors of EDSS score deterioration (Nagelkerke R 2 = 0.55). CONCLUSIONS: Short-term accrual of thalamic damage and the severity of NAWM involvement predict the long-term accumulation of disability in PPMS