Extended Far-Infrared CO Emission in the Orion OMC-1 Core

We report on sensitive far-infrared observations of $^{12}$CO pure rotational transitions in the OMC-1 core of Orion. The lines were observed with the Long Wavelength Spectrometer (LWS) in the grating mode on board the Infrared Space Observatory (ISO), covering the 43-197 $\mu$m wavelength range. The transitions from $J_{up}=14$ up to $J_{up}=19$ have been identified across the whole OMC-1 core and lines up to $J_{up}= 43$ have been detected towards the central region, KL/IRc2. In addition, we have taken high-quality spectra in the Fabry-Perot mode of some of the CO lines. In KL/IRc2 the lines are satisfactorily accounted for by a three-temperature model describing the plateau and ridge emission. The fluxes detected in the high-$J$ transitions ($J_{up} > 34$) reveal the presence of a very hot and dense gas component ($T=1500-2500$ K; $\rm N(CO)$=2\times 10^{17}\cmmd$), probably originating from some of the embedded sources previously observed in the$\rm H_2$near-infrared lines. At all other positions in the OMC-1 core, we estimate kinetic temperatures$\geq 80$ K and as high as 150 K at some positions around IRc2, from a simple Large-Velocity Gradient model.Comment: 10 pages, 3 figure

Is it Worth Refining Linear Approximations to Non-Linear Rational Expectations Models?

We characterize the balanced growth path of the basic neoclassical growth economy using standard, almost linear numerical solution methods, as well as the parameterized expectations approach, which preserves the nonlinearity in the model. We also apply the same methods after adding indivisible labor to the basic model, and to a monetary version of that economy, subject to a cash-in-advance constraint. In a unified framework we tackle the question of how much of the nonlinear structure of the original problem is useful to maintain when using an “almost” linear method. We show that it is possible to find an almost linear method to solve these models as accurately as by parameterizing expectations. Our results show the importance of performing log-linear approximations, as well as the convenience of refining a linear solution method by mixing some structure of the original non-linear problem with structure of the approximated system.Linear-quadratic approximation, numerical accuracy, simulation,numerical methods.

Super-spreading Events and Contribution to Transmission of MERS, SARS, and COVID-19

There is no clear definition for the term ‘super-spreader’ or ‘super-spreading event’. The World Health Organization refers to a super-spreader as a patient (or an event) that may transmit infection to a larger number of individuals than is usual by one individual (or event). In the severe acute respiratory syndrome (SARS) situation, a super-spreading event was defined as the transmission of SARS to at ≥8 contacts, and other authors defined this as individuals infecting an unusually large number of secondary cases [ 1 , 2 ]. A super-spreading event could merely be defined as an event in which one patient infects far more people than an average patient does, which is estimated by the basic reproduction number (R0)

The first INTEGRAL-OMC catalogue of optically variable sources

The Optical Monitoring Camera (OMC) onboard INTEGRAL provides photometry in the Johnson V-band. With an aperture of 50 mm and a field of view of 5deg x 5deg, OMC is able to detect optical sources brighter than V~18, from a previously selected list of potential targets of interest. After more than nine years of observations, the OMC database contains light curves for more than 70000 sources (with more than 50 photometric points each). The objectives of this work have been to characterize the potential variability of the objects monitored by OMC, to identify periodic sources and to compute their periods, taking advantage of the stability and long monitoring time of the OMC. To detect potential variability, we have performed a chi-squared test, finding 5263 variable sources out of an initial sample of 6071 objects with good photometric quality and more than 300 data points each. We have studied the periodicity of these sources using a method based on the phase dispersion minimization technique, optimized to handle light curves with very different shapes.In this first catalogue of variable sources observed by OMC, we provide for each object the median of the visual magnitude, the magnitude at maximum and minimum brightness in the light curve during the window of observations, the period, when found, as well as the complete intrinsic and period-folded light curves, together with some additional ancillary data.Comment: Accepted by Astronomy & Astrophysics; 13 pages, 16 figures. Figures' resolution has been degraded to fit astro-ph constraint

Hierarchical nanomechanics of collagen microfibrils

Collagen constitutes one third of the human proteome, providing mechanical stability, elasticity and strength to connective tissues. Collagen is also the dominating material in the extracellular matrix (ECM) and is thus crucial for cell differentiation, growth and pathology. However, fundamental questions remain with respect to the origin of the unique mechanical properties of collagenous tissues, and in particular its stiffness, extensibility and nonlinear mechanical response. By using x-ray diffraction data of a collagen fibril reported by Orgel et al. (Proceedings of the National Academy of Sciences USA, 2006) in combination with protein structure identification methods, here we present an experimentally validated model of the nanomechanics of a collagen microfibril that incorporates the full biochemical details of the amino acid sequence of the constituting molecules. We report the analysis of its mechanical properties under different levels of stress and solvent conditions, using a full-atomistic force field including explicit water solvent. Mechanical testing of hydrated collagen microfibrils yields a Young’s modulus of ≈300 MPa at small and ≈1.2 GPa at larger deformation in excess of 10% strain, in excellent agreement with experimental data. Dehydrated, dry collagen microfibrils show a significantly increased Young’s modulus of ≈1.8 to 2.25 GPa (or ≈6.75 times the modulus in the wet state) owing to a much tighter molecular packing, in good agreement with experimental measurements (where an increase of the modulus by ≈9 times was found). Our model demonstrates that the unique mechanical properties of collagen microfibrils can be explained based on their hierarchical structure, where deformation is mediated through mechanisms that operate at different hierarchical levels. Key mechanisms involve straightening of initially disordered and helically twisted molecules at small strains, followed by axial stretching of molecules, and eventual molecular uncoiling at extreme deformation. These mechanisms explain the striking difference of the modulus of collagen fibrils compared with single molecules, which is found in the range of 4.8±2 GPa or ≈10-20 times greater. These findings corroborate the notion that collagen tissue properties are highly scale dependent and nonlinear elastic, an issue that must be considered in the development of models that describe the interaction of cells with collagen in the extracellular matrix. A key impact the atomistic model of collagen microfibril mechanics reported here is that it enables the bottom-up elucidation of structure-property relationships in the broader class of collagen materials such as tendon or bone, including studies in the context of genetic disease where the incorporation of biochemical, genetic details in material models of connective tissue is essential