Observation-driven models for discrete-valued time series

Statistical inference for discrete-valued time series has not been developed like traditional methods for time series generated by continuous random variables. Some relevant models exist, but the lack of a homogenous framework raises some critical issues. For instance, it is not trivial to explore whether models are nested and it is quite arduous to derive stochastic properties which simultaneously hold across different specifications. In this paper, inference for a general class of first order observation-driven models for discrete-valued processes is developed. Stochastic properties such as stationarity and ergodicity are derived under easy-to-check conditions, which can be directly applied to all the models encompassed in the class and for every distribution which satisfies mild moment conditions. Consistency and asymptotic normality of quasi-maximum likelihood estimators are established, with the focus on the exponential family. Finite sample properties and the use of information criteria for model selection are investigated throughout Monte Carlo studies. An empirical application to count data is discussed, concerning a test-bed time series on the spread of an infection

Cold gas in the Milky Way's nuclear wind

The centre of the Milky Way is the site of several high-energy processes that have strongly impacted the inner regions of our Galaxy. Activity from the super-massive black hole, Sgr A*, and/or stellar feedback from the inner molecular ring expel matter and energy from the disc in the form of a galactic wind. Multiphase gas has been observed within this outflow, from hot highly-ionized, to warm ionized and cool atomic gas. To date, however, there has been no evidence of the cold and dense molecular phase. Here we report the first detection of molecular gas outflowing from the centre of our Galaxy. This cold material is associated with atomic hydrogen clouds travelling in the nuclear wind. The morphology and the kinematics of the molecular gas, resolved on ~1 pc scale, indicate that these clouds are mixing with the warmer medium and are possibly being disrupted. The data also suggest that the mass of molecular gas driven out is not negligible and could impact the rate of star formation in the central regions. The presence of this cold, dense, high-velocity gas is puzzling, as neither Sgr A* at its current level of activity, nor star formation in the inner Galaxy seem viable sources for this material.Comment: Published in the August 19 issue of Nature. This is the authors' version before final edits. Published version is available at http://www.nature.com/articles/s41586-020-2595-

Direct observations of the atomic-molecular phase transition in the Milky Way's nuclear wind

Hundreds of high-velocity atomic gas clouds exist above and below the Galactic Centre, with some containing a molecular component. However, the origin of these clouds in the Milky Way's wind is unclear. This paper presents new high-resolution MeerKAT observations of three atomic gas clouds and studies the relationship between the atomic and molecular phases at $\sim 1$ pc scales. The clouds' atomic hydrogen column densities, $N_{\mathrm{HI}}$, are less than a \mbox{few}\times 10^{20} cm$^{-2}$, but the two clouds closest to the Galactic Centre nonetheless have detectable CO emission. This implies the presence of H$_{2}$ at levels of $N_{\mathrm{HI}}$ at least a factor of ten lower than in the typical Galactic interstellar medium. For the cloud closest to the Galactic Centre, there is little correlation between the $N_{\mathrm{HI}}$ and the probability that it will harbour detectable CO emissions. In contrast, for the intermediate cloud, detectable CO is heavily biased toward the highest values of $N_{\mathrm{HI}}$. The cloud most distant from the Galactic Centre has no detectable CO at similar $N_{\mathrm{HI}}$ values. Moreover, we find that the two clouds with detectable CO are too molecule-rich to be in chemical equilibrium, given the depths of their atomic shielding layers, which suggests a scenario whereby these clouds consist of pre-existing molecular gas from the disc that the Galactic wind has swept up, and that is dissociating into atomic hydrogen as it flows away from the Galaxy. We estimate that entrained molecular material of this type has a $\sim \mathrm{few}-10$ Myr lifetime before photodissociating.Comment: 11 pages, 6 figures, 2 tables. Submitted to MNRA

Testosterone decreases adiponectin levels in female to male transsexuals

Aim: To evaluate the effect of testosterone (T) on adiponectin serum levels in transsexual female patients. Methods: We measured adiponectin, leptin, luteinizing hormone and follicle stimulating hormone, T, estradiol, lipid profile, biochemical parameters and body composition in 16 transsexual female patients at baseline and after 6 months of T treatment (100 mg Testoviron Depot /10 days, i.m.). Results: Adiponectin levels were 16.9 ± 7.3 mg/mL at baseline and 13.5 ± 7.4 mg/mL at month 6 of T treatment (P < 0.05). Leptin and high-density lipoprotein cholesterol decreased significantly, whereas body mass index, waist circumference and lean body mass increased significantly after 6 months of T treatment. No changes in insulin or Homeostasis Model Assessment were detected. Conclusion: T can significantly reduce adiponectin serum levels in transsexual female patients

The Life Cycle of the Central Molecular Zone. II: Distribution of atomic and molecular gas tracers

We use the hydrodynamical simulation of our inner Galaxy presented in Armillotta et al. (2019) to study the gas distribution and kinematics within the CMZ. We use a resolution high enough to capture the gas emitting in dense molecular tracers such as NH3 and HCN, and simulate a time window of 50 Myr, long enough to capture phases during which the CMZ experiences both quiescent and intense star formation. We then post-process the simulated CMZ to calculate its spatially-dependent chemical and thermal state, producing synthetic emission data cubes and maps of both HI and the molecular gas tracers CO, NH3 and HCN. We show that, as viewed from Earth, gas in the CMZ is distributed mainly in two parallel and elongated features extending from positive longitudes and velocities to negative longitudes and velocities. The molecular gas emission within these two streams is not uniform, and it is mostly associated to the region where gas flowing towards the Galactic Center through the dust lanes collides with gas orbiting within the ring. Our simulated data cubes reproduce a number of features found in the observed CMZ. However, some discrepancies emerge when we use our results to interpret the position of individual molecular clouds. Finally, we show that, when the CMZ is near a period of intense star formation, the ring is mostly fragmented as a consequence of supernova feedback, and the bulk of the emission comes from star-forming molecular clouds. This correlation between morphology and star formation rate should be detectable in observations of extragalactic CMZs.Comment: 19 pages, 11 figures, accepted for publication in MNRA

Black or red phosphorus yields the same blue phosphorus film

After the discovery of graphene, many other 2D materials have been predicted theoretically and successfully prepared. In this context, single-sheet black phosphorus - phosphorene - is emerging as a viable contender in the field of (2D) semiconductors. Phosphorene offers high carrier mobility and an anisotropic structure that gives rise to a modulation of physical and chemical properties. This opens the way to many novel and fascinating applications related to field-effect transistors and optoelectronic devices. In previous studies, a single layer of blue phosphorene intermixed with Au atoms was grown using purified black phosphorus as a precursor. Starting from the observation that phosphorus vapor mainly consists of P clusters, in this work we aimed at obtaining blue phosphorus using much less expensive purified red phosphorus as an evaporant. By means of microscopy, spectroscopy and diffraction experiments, we show that black or red phosphorus deposition on Au(111) substrates yields the same blue phosphorus film