Precessing Jets and Molecular Outflows: A 3-D Numerical Study

We present 3-D numerical hydrodynamical simulations of precessing supersonic heavy jets to explore how well they serve as a model for generating molecular outflows from Young Stellar Objects. The dynamics are studied with a number of high resolution simulations on a Cartesian grid (128x128x128 zones) using a high order finite difference method. A range of cone angles and precession rates were included in the study. Two higher resolution runs (256x256x256 zones) were made for comparison in order to confirm numerical convergence of global flow characteristics. Morphological, kinematical and dynamical characteristics of precessing jets are described and compared to important properties of straight jets and also to observations of YSOs. In order to examine the robustness of precessing jets as a mean to produce molecular outflows around Young Stellar Objects, ``synthetic observations'' of the momentum distributions of the simulated precessing jets are compared to observations of molecular outflows. It is found that precessing jets match better the morphology, highly forward driven momentum and momentum distributions along the long axis of molecular outflows than do wind-driven or straight jet-driven flow models.Comment: Accepted by ApJ, 31 pages, using aasms.sty, Also available in postscript with figures via a gzipped tar file at ftp://s1.msi.umn.edu/pub/afrank/3DJet/3DJet.tar.gz . For information contact [email protected]

Chromium silicide formation by ion mixing

The formation of CrSi_2 by ion mixing was studied as a function of temperature, silicide thickness and irradiated interface. Samples were prepared by annealing evaporated couples of Cr on Si and Si on Cr at 450°C for short times to form Si/CrSi_2/Cr sandwiches. Xenon beams with energies up to 300 keV and fluences up to 8 X 10^15 cm^(-2) were used for mixing at temperatures between 20 and 300°C. Penetrating only the Cr/CrSi_2 interface at temperatures above 150°C induces further growth of the silicide as a uniform stoichiometric layer. The growth rate does not depend on the thickness of the initially formed silicide at least up to a thickness of 150 nm. The amount of growth depends linearly on the density of energy deposited at the interface. The growth is temperature dependent with an apparent activation energy of 0.2 eV. Irradiating only through the Si/CrSi_2 interface does not induce silicide growth. We conclude that the formation of CrSi_2 by ion beam mixing is an interface-limited process and that the limiting reaction occurs at the Cr/CrSi_2 interface

Stochastic Matrix Product States

The concept of stochastic matrix product states is introduced and a natural form for the states is derived. This allows to define the analogue of Schmidt coefficients for steady states of non-equilibrium stochastic processes. We discuss a new measure for correlations which is analogous to the entanglement entropy, the entropy cost $S_C$, and show that this measure quantifies the bond dimension needed to represent a steady state as a matrix product state. We illustrate these concepts on the hand of the asymmetric exclusion process

William H. Sorrell, Attorney General of Vermont, et al. v. IMS Health Inc., et al. - Amicus Brief in Support of Petitioners

On April 26, 2011, the US Supreme Court will hear oral arguments in the Vermont data mining case, Sorrell v. IMS Health Inc. Respondents claim this is the most important commercial speech case in a decade. Petitioner (the State of Vermont) argues this is the most important medical privacy case since Whalen v. Roe. The is an amicus brief supporting Vermont, written by law professors and submitted on behalf of the New England Journal of Medicin

Generation and detection of NOON states in superconducting circuits

NOON states, states between two modes of light of the form $|N,0\rangle+e^{i\phi}|0,N\rangle$ allow for super-resolution interformetry. We show how NOON states can be efficiently produced in circuit quntum electrodynamics using superconducting phase qubits and resonators. We propose a protocol where only one interaction between the two modes is required, creating all the necessary entanglement at the start of the procedure. This protocol makes active use of the first three states of the phase qubits. Additionally, we show how to efficiently verify the success of such an experiment, even for large NOON states, using randomly sampled measurements and semidefinite programming techniques.Comment: 15 pages and 3 figure

Role of soft-iron impellers on the mode selection in the VKS dynamo experiment

A crucial point for the understanding of the von-K\'arm\'an-Sodium (VKS) dynamo experiment is the influence of soft-iron impellers. We present numerical simulations of a VKS-like dynamo with a localized permeability distribution that resembles the shape of the flow driving impellers. It is shown that the presence of soft-iron material essentially determines the dynamo process in the VKS experiment. % An axisymmetric magnetic field mode can be explained by the combined action of the soft-iron disk and a rather small $\alpha$-effect parametrizing the induction effects of unresolved small scale flow fluctuations

Classical no-cloning theorem under Liouville dynamics by non-Csisz\'ar f-divergence

The Csisz\'ar f-divergence, which is a class of information distances, is known to offer a useful tool for analysing the classical counterpart of the cloning operations that are quantum mechanically impossible for the factorized and marginality classical probability distributions under Liouville dynamics. We show that a class of information distances that does not belong to this divergence class also allows for the formulation of a classical analogue of the quantum no-cloning theorem. We address a family of nonlinear Liouville-like equations, and generic distances, to obtain constraints on the corresponding functional forms, associated with the formulation of classical analogue of the no-cloning principle.Comment: 6 pages, revised, published versio

Why does wurtzite form in nanowires of III-V zinc-blende semiconductors?

We develop a nucleation-based model to explain the formation of the wurtzite (WZ) crystalline phase during the vapor-liquid-solid growth of free-standing nanowires of zinc-blende (ZB) semiconductors. We first show that, in nanowires, nucleation generally occurs at the outer edge of the solid/liquid interface (the triple phase line) rather than elsewhere at the solid/liquid interface. In the present case, this entails major differences between ZB and WZ nuclei. Depending on the pertinent interface energies, WZ nucleation is favored at high liquid supersaturation. This explains our systematic observation of ZB during the early stages of nanowire growth.Comment: 4 pages with 4 figures Submitted to Physical Review Letter

Horizon Pretracking

We introduce horizon pretracking as a method for analysing numerically generated spacetimes of merging black holes. Pretracking consists of following certain modified constant expansion surfaces during a simulation before a common apparent horizon has formed. The tracked surfaces exist at all times, and are defined so as to include the common apparent horizon if it exists. The method provides a way for finding this common apparent horizon in an efficient and reliable manner at the earliest possible time. We can distinguish inner and outer horizons by examining the distortion of the surface. Properties of the pretracking surface such as its expansion, location, shape, area, and angular momentum can also be used to predict when a common apparent horizon will appear, and its characteristics. The latter could also be used to feed back into the simulation by adapting e.g. boundary or gauge conditions even before the common apparent horizon has formed.Comment: 14 pages, 8 figures, minor change

Very-High Energy Gamma-Ray Flux Limits for Nearby Active Galactic Nuclei

Combining the results of targeted observations, H.E.S.S. has accumulated a large amount of extra-galactic exposure at TeV energies. Due to its large field of view a considerable part of the sky (0.6 sr) has been observed with high sensitivity outside the targeted observation positions. Since this exposure region contains little inherent bias, it is well suited for studies of extra-galactic source populations. Given the correlation between ultra-high energy cosmic rays and nearby extra-galactic objects recently claimed by the Auger collaboration, this unbiased sky sample by H.E.S.S. is of interest since it includes (besides the targeted sources) 63 AGN within 100 Mpc, for which very-high energy gamma-ray flux limits are derived.Comment: 4 pages, 5 figures, Submitted to Proceedings of "4th International Symposium on High Energy Gamma-Ray Astronomy 2008