The Earliest Phases of Star formation (EPoS): Temperature, density, and kinematic structure of the star-forming core CB 17

Context: The initial conditions for the gravitational collapse of molecular cloud cores and the subsequent birth of stars are still not well constrained. The characteristic cold temperatures (about 10 K) in such regions require observations at sub-millimetre and longer wavelengths. The Herschel Space Observatory and complementary ground-based observations presented in this paper have the unprecedented potential to reveal the structure and kinematics of a prototypical core region at the onset of stellar birth. Aims: This paper aims to determine the density, temperature, and velocity structure of the star-forming Bok globule CB 17. This isolated region is known to host (at least) two sources at different evolutionary stages: a dense core, SMM1, and a Class I protostar, IRS. Methods: We modeled the cold dust emission maps from 100 micron to 1.2 mm with both a modified blackbody technique to determine the optical depth-weighted line-of-sight temperature and column density and a ray-tracing technique to determine the core temperature and volume density structure. Furthermore, we analysed the kinematics of CB17 using the high-density gas tracer N2H+. Results: From the ray-tracing analysis, we find a temperature in the centre of SMM1 of 10.6 K, a flat density profile with radius 9500 au, and a central volume density of n(H) = 2.3x10^5 cm-3. The velocity structure of the N2H+ observations reveal global rotation with a velocity gradient of 4.3 km/s/pc. Superposed on this rotation signature we find a more complex velocity field, which may be indicative of differential motions within the dense core. Conclusions: SMM is a core in an early evolutionary stage at the verge of being bound, but the question of whether it is a starless or a protostellar core remains unanswered.Comment: published in A&

The Whole is Greater than the Sum of the Parts: Optimizing the Joint Science Return from LSST, Euclid and WFIRST

The focus of this report is on the opportunities enabled by the combination of LSST, Euclid and WFIRST, the optical surveys that will be an essential part of the next decade's astronomy. The sum of these surveys has the potential to be significantly greater than the contributions of the individual parts. As is detailed in this report, the combination of these surveys should give us multi-wavelength high-resolution images of galaxies and broadband data covering much of the stellar energy spectrum. These stellar and galactic data have the potential of yielding new insights into topics ranging from the formation history of the Milky Way to the mass of the neutrino. However, enabling the astronomy community to fully exploit this multi-instrument data set is a challenging technical task: for much of the science, we will need to combine the photometry across multiple wavelengths with varying spectral and spatial resolution. We identify some of the key science enabled by the combined surveys and the key technical challenges in achieving the synergies.Comment: Whitepaper developed at June 2014 U. Penn Workshop; 28 pages, 3 figure

Reconstructing cosmic growth with kSZ observations in the era of Stage IV experiments

Future ground-based CMB experiments will generate competitive large-scale structure datasets by precisely characterizing CMB secondary anisotropies over a large fraction of the sky. We describe a method for constraining the growth rate of structure to sub-1% precision out to $z\approx 1$, using a combination of galaxy cluster peculiar velocities measured using the kinetic Sunyaev-Zel'dovich (kSZ) effect, and the velocity field reconstructed from galaxy redshift surveys. We consider only thermal SZ-selected cluster samples, which will consist of $\mathcal{O}(10^4-10^5)$ sources for Stage 3 and 4 CMB experiments respectively. Three different methods for separating the kSZ effect from the primary CMB are compared, including a novel blind "constrained realization" method that improves signal-to-noise by a factor of $\sim 2$ over a commonly-used aperture photometry technique. Measurements of the integrated tSZ $y$-parameter are used to break the kSZ velocity-optical depth degeneracy, and the effects of including CMB polarization and SZ profile uncertainties are also considered. A combination of future Stage 4 experiments should be able to measure the product of the growth and expansion rates, $\alpha\equiv f H$, to better than 1% in bins of $\Delta z = 0.1$ out to $z \approx 1$ -- competitive with contemporary redshift-space distortion constraints from galaxy surveys.Comment: 16 pages, 8 figure

Spectroscopic Confusion: Its Impact on Current and Future Extragalactic HI Surveys

We present a comprehensive model to predict the rate of spectroscopic confusion in HI surveys, and demonstrate good agreement with the observable confusion in existing surveys. Generically the action of confusion on the HI mass function was found to be a suppression of the number count of sources below the `knee', and an enhancement above it. This results in a bias, whereby the `knee' mass is increased and the faint end slope is steepened. For ALFALFA and HIPASS we find that the maximum impact this bias can have on the Schechter fit parameters is similar in magnitude to the published random errors. On the other hand, the impact of confusion on the HI mass functions of upcoming medium depth interferometric surveys, will be below the level of the random errors. In addition, we find that previous estimates of the number of detections for upcoming surveys with SKA-precursor telescopes may have been too optimistic, as the framework implemented here results in number counts between 60% and 75% of those previously predicted, while accurately reproducing the counts of existing surveys. Finally, we argue that any future single dish, wide area surveys of HI galaxies would be best suited to focus on deep observations of the local Universe (z < 0.05), as confusion may prevent them from being competitive with interferometric surveys at higher redshift, while their lower angular resolution allows their completeness to be more easily calibrated for nearby extended sources.Comment: Accepted to MNRAS, 14 pages, 9 figures, 2 table

Development and Application of Hybrid Wray-Agarwal Turbulence Model and Large-Eddy Simulation

Rapid development in computing power in past five decades along with the development and progress in building blocks of Computational Fluid Dynamics (CFD) technology has made CFD an indispensable tool for modern engineering analysis and design of fluid-based products and systems. For CFD analysis, Reynolds-Averaged Navier-Stokes (RANS) equations are currently the most widely used fluid equations in the industry. RANS methods require modeling of turbulence effect (i.e. turbulence modeling) based on empirical relations and therefore often produce low accuracy results for many flows. In recent years, the Large Eddy Simulation (LES) approach has been developed which has shown promise of achieving higher accuracy, however it is computationally very intensive and therefore has remained limited to computing relatively simple flows from low to moderate Reynolds numbers. As a result, a hybrid technique called Detached Eddy Simulation (DES) has been proposed in recent years. This technique has shown improved accuracy and computational efficiency for solution of wide variety of complex turbulent flows. The goal of this dissertation has been to develop a DES model based on a recently proposed very promising RANS model, known as the ‘Wray-Agarwal (WA)’ model and the LES. Decaying Isotropic Turbulence (DIT) case is computed to determine the coefficient in the DES model by matching its energy spectrum with the Kolmogorov spectrum. The new WA-DES model (DES model based on WA model) is applied to compute a wide variety of wall bounded separated flows to assess it accuracy and computational efficiency compared to the widely used RANS turbulence models in the industry, namely the Spalart-Allmaras (SA) and SST k-ω models. Improved Delayed-Detached Eddy Simulation (IDDES) and Elliptic Blending are also considered as further refinements of WA model to improve its accuracy

KiDS-i-800: Comparing weak gravitational lensing measurements in same-sky surveys

We present a weak gravitational lensing analysis of 815 square degree of $i$-band imaging from the Kilo-Degree Survey (KiDS-$i$-800). In contrast to the deep $r$-band observations, which take priority during excellent seeing conditions and form the primary KiDS dataset (KiDS-$r$-450), the complementary yet shallower KiDS-$i$-800 spans a wide range of observing conditions. The overlapping KiDS-$i$-800 and KiDS-$r$-450 imaging therefore provides a unique opportunity to assess the robustness of weak lensing measurements. In our analysis, we introduce two new `null' tests. The `nulled' two-point shear correlation function uses a matched catalogue to show that the calibrated KiDS-$i$-800 and KiDS-$r$-450 shear measurements agree at the level of $1 \pm 4$\%. We use five galaxy lens samples to determine a `nulled' galaxy-galaxy lensing signal from the full KiDS-$i$-800 and KiDS-$r$-450 surveys and find that the measurements agree to $7 \pm 5$\% when the KiDS-$i$-800 source redshift distribution is calibrated using either spectroscopic redshifts, or the 30-band photometric redshifts from the COSMOS survey.Comment: 24 pages, 20 figures. Submitted to MNRAS. Comments welcom

Green Energy Technology

This book, entitled “The Green Energy Technology”, covers technologies, products, equipment, and devices, as well as energy services, based on software and data protected by patents and/or trademarks. The recent trends underline the principles of a circular economy such as sustainable product design, extending the product’s lifecycle, reusability, and recycling. These are highly related to climate change and environmental impact, and limited natural resources require scientific research and novel technical solutions. This book will serve as a collection of the latest scientific and technological approaches to “green”—i.e., environmentally friendly and sustainable—technologies. While the focus is on energy and bioenergy, it also covers "green" solutions in all aspects of industrial engineering. Green Energy Technology addresses researchers, advanced students, technical consultants and decision-makers in industries and politics. This book is a comprehensive overview and in-depth technical research paper addressing recent progress in Green Energy Technology. We hope that readers will enjoy reading this book

A Definitive Survey for Lyman Limit Systems at z~3.5 with the Sloan Digital Sky Survey

We perform a semi-automated survey for tau>=2 Lyman Limit systems (LLSs) in quasar spectra from the Sloan Digital Sky Survey, Data Release 7. From a starting sample of 2473 quasars with zem=3.6-4.4, we analyze 469 spectra meeting strict seletion criteria for a total redshift path Dz=93.8 and identify 192 intervening systems at z>3.3. The incidence of tau>=2 LLSs per unit redshift, l(z), is well described by a single-power law at these redshifts: l(z) = C_LLS [(1+z)/(1+z_*)]^gamma, with z_*=3.7, C_LLS = 1.9+/-0.2, and gamma = 5.2+/-1.5 (68% c.l.). These values are systematically lower than previous estimates (especially at z<4) but are consistent with recent measurements of the mean free path to ionizing radiation. Extrapolations of this power-law to z=0 are inconsistent with previous estimations of l(z) at z<1 and suggest a break at z~2, similar to that observed for the Lya forest. Our results also indicate that the systems giving rise to LLS absorption decrease by ~50% in comoving number density and/or physical size from z=4 to 3.3, perhaps due to an enhanced extragalactic ultraviolet background. The observations place an integral constraint on the HI frequency distribution f(N_HI,X) and indicate that the power-law slope beta= dln[f(N,X)]/dln[N] is likely shallower than beta = -1 at N_HI=10^18 cm^-2. Including other constraints on f(N_HI,X) from the literature, we infer that beta is steeper than beta = -1.7 at N_HI~10^15 cm^-2, implying at least two inflections in f(N_HI,X). We also perform a survey for proximate LLSs (PLLSs) and find that l(z)_PLLS is systematically lower ~25% than intervening systems. Finally, we estimate that systematic effects impose an uncertainty of 10-20% in the l(z) measurements; these effects may limit the precision of all future surveys.Comment: 26 pages, 17 figures (most in color). Submitted to Ap