The Effect of Projection on Derived Mass-Size and Linewidth-Size Relationships

Power law mass-size and linewidth-size correlations, two of "Larson's laws," are often studied to assess the dynamical state of clumps within molecular clouds. Using the result of a hydrodynamic simulation of a molecular cloud, we investigate how geometric projection may affect the derived Larson relationships. We find that large scale structures in the column density map have similar masses and sizes to those in the 3D simulation (PPP). Smaller scale clumps in the column density map are measured to be more massive than the PPP clumps, due to the projection of all emitting gas along lines of sight. Further, due to projection effects, structures in a synthetic spectral observation (PPV) may not necessarily correlate with physical structures in the simulation. In considering the turbulent velocities only, the linewidth-size relationship in the PPV cube is appreciably different from that measured from the simulation. Including thermal pressure in the simulated linewidths imposes a minimum linewidth, which results in a better agreement in the slopes of the linewidth-size relationships, though there are still discrepancies in the offsets, as well as considerable scatter. Employing commonly used assumptions in a virial analysis, we find similarities in the computed virial parameters of the structures in the PPV and PPP cubes. However, due to the discrepancies in the linewidth- and mass- size relationships in the PPP and PPV cubes, we caution that applying a virial analysis to observed clouds may be misleading due to geometric projection effects. We speculate that consideration of physical processes beyond kinetic and gravitational pressure would be required for accurately assessing whether complex clouds, such as those with highly filamentary structure, are bound.Comment: 25 pages, including 7 Figures; Accepted for publication in Ap

The manifold rheology of fluidized granular media

Fluidized granular media have a rich rheology: measuring shear stress $\sigma$ as a function of shear rate $\dot\gamma$, they exhibit Newtonian behavior $\sigma\sim\dot\gamma$ for low densities and shear rates, develop a yield stress for intermediate shear rates and densities approaching the granular glass transition, and finally, cross over to shear-thickening Bagnold scaling, $\sigma\sim\dot\gamma^2$. This wealth of flow-behaviors makes fluidized beds a fascinating material, but also one that is challenging to encompass into a global theory, despite its relevance for optimizing industrial processes and predicting natural hazards. We provide careful measurements spanning eight orders of magnitude in shear rate, and show that all these rheological regimes can be described qualitatively and quantitatively using the granular integration through transient formalism, a theory for glassy dynamics under shear adapted to granular fluids

Hoeffding Tree Algorithms for Anomaly Detection in Streaming Datasets: A Survey

This survey aims to deliver an extensive and well-constructed overview of using machine learning for the problem of detecting anomalies in streaming datasets. The objective is to provide the effectiveness of using Hoeffding Trees as a machine learning algorithm solution for the problem of detecting anomalies in streaming cyber datasets. In this survey we categorize the existing research works of Hoeffding Trees which can be feasible for this type of study into the following: surveying distributed Hoeffding Trees, surveying ensembles of Hoeffding Trees and surveying existing techniques using Hoeffding Trees for anomaly detection. These categories are referred to as compositions within this paper and were selected based on their relation to streaming data and the flexibility of their techniques for use within different domains of streaming data. We discuss the relevance of how combining the techniques of the proposed research works within these compositions can be used to address the anomaly detection problem in streaming cyber datasets. The goal is to show how a combination of techniques from different compositions can solve a prominent problem, anomaly detection

Heavy Residue Isoscaling as a Probe of the Symmetry Energy of Hot Fragments

The isoscaling properties of isotopically resolved projectile residues from peripheral collisions of 86Kr (25 MeV/nucleon), 64Ni (25 MeV/nucleon) and 136Xe (20 MeV/nucleon) beams on various target pairs are employed to probe the symmetry energy coefficient of the nuclear binding energy. The present study focuses on heavy projectile fragments produced in peripheral and semiperipheral collisions near the onset of multifragment emission E*/A = 2-3 MeV). For these fragments, the measured average velocities are used to extract excitation energies. The excitation energies, in turn, are used to estimate the temperatures of the fragmenting quasiprojectiles in the framework the Fermi gas model. The isoscaling analysis of the fragment yields provided the isoscaling parameters "alpha" which, in combination with temperatures and isospin asymmetries provided the symmetry energy coefficient of the nuclear binding energy of the hot fragmenting quasiprojectiles. The extracted values of the symmetry energy coefficient at this excitation energy range (2-3 MeV/nucleon) are lower than the typical liquid-drop model value ~25 MeV corresponding to ground-state nuclei and show a monotonic decrease with increasing excitation energy. This result is of importance in the formation of hot nuclei in heavy-ion reactions and in hot stellar environments such as supernova.Comment: 11 pages, 9 figures, submitted to Phys. Rev.

Trigonometric Parallaxes of Massive Star Forming Regions: III. G59.7+0.1 and W 51 IRS2

We report trigonometric parallaxes for G59.7+0.1 and W 51 IRS2, corresponding to distances of 2.16^{+0.10}_{-0.09} kpc and 5.1^{+2.9}_{-1.4} kpc, respectively. The distance to G59.7+0.1 is smaller than its near kinematic distance and places it between the Carina-Sagittarius and Perseus spiral arms, probably in the Local (Orion) spur. The distance to W 51 IRS2, while subject to significant uncertainty, is close to its kinematic distance and places it near the tangent point of the Carina-Sagittarius arm. It also agrees well with a recent estimate based on O-type star spectro/photometry. Combining the distances and proper motions with observed radial velocities gives the full space motions of the star forming regions. We find modest deviations of 5 to 10 km/s from circular Galactic orbits for these sources, both counter to Galactic rotation and toward the Galactic center.Comment: 16 pages, 6 figures; to appear in the Astrophysical Journa

Preliminary Experience with Digital Subtraction Angiography in Cardiac Evaluation

iVe report our initial experience using digital subtraction angiography (DSA) techniques for cardiac evaluation. DSA of the heart may be performed with intravenous or right atrial injection of contrast medium (IVDSA) and with left ventricular or aortic root contrast injection (lADSA). The right ventricle and the atria are best demonstrated by IVDSA, while the left ventricle and coronary arteries are best demonstrated by lADSA. The advantages and disadvantages of DSA ofthe bean are discussed. Present equipment limitations restrict the routine use of cardiac DSA, but these should be overcome with advances in technology

Symmetry energy and the isoscaling properties of the fragments produced in 40^{40}Ar, 40^{40}Ca + 58^{58}Fe, 58^{58}Ni reactions at 25 −- 53 MeV/nucleon

The symmetry energy and the isoscaling properties of the fragments produced in the multifragmentation of $^{40}$Ar, $^{40}$Ca + $^{58}$Fe, $^{58}$Ni reactions at 25 - 53 MeV/nucleon were investigated within the framework of statistical multifragmentation model. The isoscaling parameters $\alpha$, from the primary (hot) and secondary (cold) fragment yield distributions, were studied as a function of excitation energy, isospin (neutron-to-proton asymmetry) and fragment symmetry energy. It is observed that the isoscaling parameter $\alpha$ decreases with increasing excitation energy and decreasing symmetry energy. The parameter $\alpha$ is also observed to increase with increasing difference in the isospin of the fragmenting system. The sequential decay of the primary fragments into secondary fragments, when studied as a function of excitation energy and isospin of the fragmenting system, show very little influence on the isoscaling parameter. The symmetry energy however, has a strong influence on the isospin properties of the hot fragments. The experimentally observed scaling parameters can be explained by symmetry energy that is significantly lower than that for the ground state nuclei near saturation density. The results indicate that the properties of hot nuclei at excitation energies, densities and isospin away from the normal ground state nuclei could be significantly different.Comment: 14 pages, 15 figure