Evidence for Variable, Correlated X-ray and Optical/IR Extinction toward the Nearby, Pre-main Sequence Binary TWA 30

We present contemporaneous XMM-Newton X-ray and ground-based optical/near-IR spectroscopic observations of the nearby ($D \approx 42$ pc), low-mass (mid-M) binary system TWA 30A and 30B. The components of this wide (separation $\sim$3400 AU) binary are notable for their nearly edge-on disk viewing geometries, high levels of variability, and evidence for collimated stellar outflows. We obtained XMM-Newton X-ray observations of TWA 30A and 30B in 2011 June and July, accompanied (respectively) by IRTF SpeX (near-IR) and VLT XSHOOTER (visible/near-IR) spectroscopy obtained within $\sim$20 hours of the X-ray observations. TWA 30A was detected in both XMM-Newton observations at relatively faint intrinsic X-ray luminosities ($L_{X}$$\sim$$8\times10^{27}$ $erg$ $s^{-1}$) compared to stars of similar mass and age . The intrinsic (0.15-2.0 keV) X-ray luminosities measured in 2011 had decreased by a factor 20-100 relative to a 1990 (ROSAT) X-ray detection. TWA 30B was not detected, and we infer an upper limit of ($L_{X}$ $\lesssim$ 3.0 $\times$ $10^{27}$ erg s$^{-1}$). We measured a large change in visual extinction toward TWA 30A (from $A_V \approx 14.9$ to $A_V \approx 4.7$) between the two 2011 observing epochs, and we find evidence for a corresponding significant decrease in X-ray absorbing column ($N_H$). The apparent correlated change in $A_V$ and $N_H$ is suggestive of variable obscuration of the stellar photosphere by disk material composed of both gas and dust. However, in both observations, the inferred $N_{H}$ to $A_{V}$ ratio is lower than that typical of the ISM, suggesting that the disk is either depleted of gas or is deficient in metals in the gas phase.Comment: 10 pages, 7 figures, Accepted for publication in MNRA

The Multiple Young Stellar Objects of HBC 515: An X-ray and Millimeter-wave Imaging Study in (Pre-main Sequence) Diversity

We present Chandra X-ray Observatory and Submillimeter Array (SMA) imaging of HBC 515, a system consisting of multiple young stellar objects (YSOs). The five members of HBC 515 represent a remarkably diverse array of YSOs, ranging from the low-mass Class I/II protostar HBC 515B, through Class II and transition disk objects (HBC 515D and C, respectively), to the "diskless", intermediate- mass, pre-main sequence binary HBC 515A. Our Chandra/ACIS imaging establishes that all five components are X-ray sources, with HBC 515A - a subarcsecond-separation binary that is partially resolved by Chandra - being the dominant X-ray source. We detect an X-ray flare associated with HBC 515B. In the SMA imaging, HBC 515B is detected as a strong 1.3 mm continuum emission source; a second, weaker mm continuum source is coincident with the position of the transition disk object HBC 515C. These results strongly support the protostellar nature of HBC 515B, and firmly establish HBC 515A as a member of the rare class of relatively massive, X-ray luminous "weak-lined T Tauri stars" that are binaries and have shed their disks at very early stages of pre-MS evolution. The coexistence of two such disparate objects within a single, presumably coeval multiple YSO system highlights the influence of pre- MS star mass, binarity, and X-ray luminosity in regulating the lifetimes of circumstellar, planet-forming disks and the timescales of star-disk interactions.Comment: Accepted for publication in A&A; 11 pages, 5 figure

A ring in a shell: the large-scale 6D structure of the Vela OB2 complex

The Vela OB2 association is a group of 10 Myr stars exhibiting a complex spatial and kinematic substructure. The all-sky Gaia DR2 catalogue contains proper motions, parallaxes (a proxy for distance) and photometry that allow us to separate the various components of Vela OB2. We characterise the distribution of the Vela OB2 stars on a large spatial scale, and study its internal kinematics and dynamic history. We make use of Gaia DR2 astrometry and published Gaia-ESO Survey data. We apply an unsupervised classification algorithm to determine groups of stars with common proper motions and parallaxes. We find that the association is made up of a number of small groups, with a total current mass over 2330 Msun. The three-dimensional distribution of these young stars trace the edge of the gas and dust structure known as the IRAS Vela Shell across 180 pc and shows clear signs of expansion. We propose a common history for Vela OB2 and the IRAS Vela Shell. The event that caused the expansion of the shell happened before the Vela OB2 stars formed, imprinted the expansion in the gas the stars formed from, and most likely triggered star formation.Comment: Accepted by A&A (02 November 2018), 13 pages, 9+2 figure

Stochastic wind-load model for building vibration estimation using large-eddy cfd simulation and random turbulenc flow generation algorithms

The application of computer fluid dynamics to the estimation of a stochastic wind loading model for vibration analysis of flexible buildings is studied in this paper. Large-Eddy-Simulation with random turbulence field as inflow boundary condition is used for estimating along the wind forces, across the wind forces and torsional moments along the height of the building. The stochastic turbulence of the inlet flow is modeled using techniques proposed in the literature and variations suggested by the authors, and along the wind and along the wind forces and torsional moments applied along the building height are estimated with sampled random processes resulting from the CFD analyses. The application of this numerical technique during the design stage of a concrete-wall 36-storey building with a parallelogram-shape plan is described. This structure is prone to high floor accelerations due to wind loading, compromising occupant comfort. The construction of random loading models for this building considering time and space correlation of forces and torsional moments is discussed and the use of the random loading to the design process of supplemental damping devices for the building is described.Publicado en: Mecánica Computacional vol. XXXV, no. 12Facultad de Ingenierí

Stochastic wind-load model for building vibration estimation using large-eddy cfd simulation and random turbulenc flow generation algorithms

The application of computer fluid dynamics to the estimation of a stochastic wind loading model for vibration analysis of flexible buildings is studied in this paper. Large-Eddy-Simulation with random turbulence field as inflow boundary condition is used for estimating along the wind forces, across the wind forces and torsional moments along the height of the building. The stochastic turbulence of the inlet flow is modeled using techniques proposed in the literature and variations suggested by the authors, and along the wind and along the wind forces and torsional moments applied along the building height are estimated with sampled random processes resulting from the CFD analyses. The application of this numerical technique during the design stage of a concrete-wall 36-storey building with a parallelogram-shape plan is described. This structure is prone to high floor accelerations due to wind loading, compromising occupant comfort. The construction of random loading models for this building considering time and space correlation of forces and torsional moments is discussed and the use of the random loading to the design process of supplemental damping devices for the building is described.Publicado en: Mecánica Computacional vol. XXXV, no. 12Facultad de Ingenierí

Stochastic wind-load model for building vibration estimation using large-eddy cfd simulation and random turbulenc flow generation algorithms

The application of computer fluid dynamics to the estimation of a stochastic wind loading model for vibration analysis of flexible buildings is studied in this paper. Large-Eddy-Simulation with random turbulence field as inflow boundary condition is used for estimating along the wind forces, across the wind forces and torsional moments along the height of the building. The stochastic turbulence of the inlet flow is modeled using techniques proposed in the literature and variations suggested by the authors, and along the wind and along the wind forces and torsional moments applied along the building height are estimated with sampled random processes resulting from the CFD analyses. The application of this numerical technique during the design stage of a concrete-wall 36-storey building with a parallelogram-shape plan is described. This structure is prone to high floor accelerations due to wind loading, compromising occupant comfort. The construction of random loading models for this building considering time and space correlation of forces and torsional moments is discussed and the use of the random loading to the design process of supplemental damping devices for the building is described.Publicado en: Mecánica Computacional vol. XXXV, no. 12Facultad de Ingenierí

High resolution nuclear magnetic resonance spectroscopy (NMR) studies on meat components: potentialities and prospects

In recent years, increasing application of nuclear magnetic resonance (NMR) spectroscopy in the study of the agricultur- al food products has been remarked, thanks to the advantages of this technique over other conventional analytical tech- niques. This preliminary work presents, for the first time, the application of an innovative NMR technique, the proton high resolution magic angle spinning (1H HR-MAS), for studying meat features. It stresses that this method makes it pos- sible to acquire qualitative and quantitative information about chemical composition, both quickly and without any par- ticular preparation of the sample to be analysed. Finally, the study highlights the potentiality of this method in defining the origin of meat and the possibility of identifying meat adulteration

Search for periodicities near 59 s in the COS-B gamma-ray data of 2CG195+04 (Geminga)

The COS-B data relating to five observations in the general direction of Geminga, spanning 6.7 years, were searched for pulsation near 59 s. The SAS-2 indication is not confirmed. An indication of a 59 s pulsation in the gamma ray emission from 2CG195+04 (Geminga) was reported. Early analysis of COS-B data supported the result while later improved statistics did not confirm it. Subsequently, detection of a 59 s pulsation in the emission from the direction of Geminga at ultra high gamma and X-rays was reported. Geminga was identified with the X-ray source 1E0630+128. The final COS-B data on Geminga which was observed five times for a total of 214 days are reported

Ultrasensitive Piezoresistive and Piezocapacitive Cellulose-Based Ionic Hydrogels for Wearable Multifunctional Sensing

Tactile sensors, namely, flexible devices that sense physical stimuli, have received much attention in the last few decades due to their applicability in a wide range of fields like the world of wearables, soft robotics, prosthetics, and e-skin. Nevertheless, achieving a trade-off among stretchability, good sensitivity, easy manufacturability, and multisensing ability is still a challenge. Herein, an extremely flexible strain sensor composed of a cellulose-based hydrogel is presented. A natural biocompatible carboxymethylcellulose (CMC) hydrogel endowed with ionic conductivity by sodium chloride (NaCl) was used as the sensitive part. Both the sensible layer and electrodes were investigated with an innovative approach for wearable sensor applications based on electrochemical impedance spectroscopy to find the best device configuration. The sensor, exploitable both as a piezoresistor and as a piezocapacitor, presents high sensitivity to external stimuli, together with an extreme stretchability of up to 600%, showing the best strain and temperature sensitivity among the ionic conductive hydrogel-based devices presented in the literature. The very high strain sensitivity enables the hydrogel to be implemented in wearable strain sensors to monitor different human motions and physiological signals, representing a valid solution for the realization of transparent, easily manufacturable, and low-environmental-impact devices