A finite difference scheme for three-dimensional steady laminar incompressible flow

A finite difference scheme for three-dimensional steady laminar incompressible flows is presented. The Navier-Stokes equations are expressed conservatively in terms of velocity and pressure increments (delta form). First order upwind differences are used for first order partial derivatives of velocity increments resulting in a diagonally dominant matrix system. Central differences are applied to all other terms for second order accuracy. The SIMPLE pressure correction algorithm is used to satisfy the continuity equation. Numerical results are presented for cubic cavity flow problems for Reynolds numbers up to 2000 and are in good agreement with other numerical results

Performance of a new stator-diffuser design for an axial-flow pump unit

In an axial-flow pump unit with conventional stator and diftllser, often considerable energy is still present in the swirl (rotation) of the liquid leaving the stator. This energy will eventually be lost from the pump system. In this experimental investigation a new design, combining the stator and diffuser together into a single component, was tested for its effectiveness in recovering this energy and thereby improving the performance of an industrysized single-stage axial-flow pump unit. Measurements of static pressure rise along the new stator-difTuser and of the swirl angle of the fluid leaving the pump unit indicate that the new design performs better than the conventional one, as a component. However, efticiency of the whole pump unit is in general slightly reduced with the new design. A number of factors were identified as contributing to this performance degradation. Most notable are the poor matching of the fluid's and vanes' angles at the component's inlet and the sudden expansion of the flow geometry at the component's outlet. It is thus expected that when these factors have been adequately addressed, the new design should improve the pump's overall performance

Secrecy outage probability of a NOMA scheme and impact imperfect channel state information in underlay cooperative cognitive networks

Security performance and the impact of imperfect channel state information (CSI) in underlay cooperative cognitive networks (UCCN) is investigated in this paper. In the proposed scheme, relay R uses non-orthogonal multiple access (NOMA) technology to transfer messages e1, e2 from the source node S to User 1 (U1) and User 2 (U2), respectively. An eavesdropper (E) is also proposed to wiretap the messages of U1 and U2. The transmission’s security performance in the proposed system was analyzed and performed over Rayleigh fading channels. Through numerical analysis, the results showed that the proposed system’s secrecy performance became more efficient when the eavesdropper node E was farther away from the source node S and the intermediate cooperative relay R. The secrecy performance of U1 was also compared to the secrecy performance of U2. Finally, the simulation results matched the Monte Carlo simulations well

The ATLAS 9.0 GHz Survey of the Extended Chandra Deep Field South: The Faint 9.0 GHz Radio Population

We present a new image of the 9.0 GHz radio emission from the extended Chandra Deep Field South. A total of 181 hours of integration with the Australia Telescope Compact Array has resulted in a 0.276 square degree image with a median sensitivity of $\sim$20 $\mu$Jy/beam rms, for a synthesised beam of 4.0 $\times$ 1.3 arcsec. We present a catalogue of the 9.0 GHz radio sources, identifying 70 source components and 55 individual radio galaxies. Source counts derived from this sample are consistent with those reported in the literature. The observed source counts are also generally consistent with the source counts from simulations of the faint radio population. Using the wealth of multiwavelength data available for this region, we classify the faint 9 GHz population and find that 91% are radio loud AGN, 7% are radio quiet AGN and 2% are star forming galaxies. The 9.0 GHz radio sources were matched to 5.5 and 1.4 GHz sources in the literature and we find a significant fraction of flat or inverted spectrum sources, with 36% of the 9 GHz sources having $\alpha_{5.5GHz}^{9.0GHz}$ $>$ -0.3 (for $S \propto \nu^\alpha$). This flat or inverted population is not well reproduced by current simulations of radio source populations.Comment: 17 pages, 12 figures. Accepted for publication in MNRA

Productivity and reallocation: evidence from ecuadorian firm-level data

Ecuador, a developing small open economy, serves as an important case study for aggregate productivity growth and input reallocation. Since little is known about the economic performance of Ecuador with its crisis and reforms between 1998 and 2007, this paper uses a comprehensive microdata set from Ecuador’s National Statistics and Census Institute to study Ecuadorian firm dynamics in that period. We find that the reallocation of factor inputs (2.6 percent) and technical efficiency growth (3.2 percent) on the intensive margin are the dominant sources of aggregate productivity growth. Net entry, as a channel of reallocation on the extensive margin, generally has minor effects (–0.1 percent) and contributes to productivity growth only in the later recovery period (2002–04)

crs: A package for nonparametric spline estimation in R

crs is a library for R written by Jeffrey S. Racine (Maintainer) and Zhenghua Nie. This add-on package provides a collection of functions for spline-based nonparametric estimation of regression functions with both continuous and categorical regressors. Currently, the crs package integrates data-driven methods for selecting the spline degree, the number of knots and the necessary bandwidths for nonparametric conditional mean, IV and quantile regression. A function for multivariate density spline estimation with mixed data is also currently in the works. As a bonus, the authors have also provided the first simple R interface to the NOMAD (‘nonsmooth mesh adaptive direct search’) optimization solver which can be applied to solve other mixed integer optimization problems that future users might find useful in other settings. Although the crs package shares some of the same functionalities as its kernel-based counterpart—the np package by the same author—it currently lacks some of the features the np package provides, such as hypothesis testing and semiparametric estimation. However, what it lacks in breadth, crs makes up in speed. A Monte Carlo experiment in this review uncovers sizable speed gains compared to its np counterpart, with a marginal loss in terms of goodness of fit. Therefore, the package will be extremely useful for applied econometricians interested in employing nonparametric techniques using large amounts of data with a small number of discrete covariates

Partner orbits and action differences on compact factors of the hyperbolic plane. Part I: Sieber-Richter pairs

Physicists have argued that periodic orbit bunching leads to universal spectral fluctuations for chaotic quantum systems. To establish a more detailed mathematical understanding of this fact, it is first necessary to look more closely at the classical side of the problem and determine orbit pairs consisting of orbits which have similar actions. In this paper we specialize to the geodesic flow on compact factors of the hyperbolic plane as a classical chaotic system. We prove the existence of a periodic partner orbit for a given periodic orbit which has a small-angle self-crossing in configuration space which is a `2-encounter'; such configurations are called `Sieber-Richter pairs' in the physics literature. Furthermore, we derive an estimate for the action difference of the partners. In the second part of this paper [13], an inductive argument is provided to deal with higher-order encounters.Comment: to appear on Nonlinearit

No Evidence for Evolution in the Far-Infrared-Radio Correlation out to z ~ 2 in the eCDFS

We investigate the 70 um Far-Infrared Radio Correlation (FRC) of star-forming galaxies in the Extended Chandra Deep Field South (ECDFS) out to z > 2. We use 70 um data from the Far-Infrared Deep Extragalactic Legacy Survey (FIDEL), which comprises the most sensitive (~0.8 mJy rms) and extensive far-infrared deep field observations using MIPS on the Spitzer Space Telescope, and 1.4 GHz radio data (~8 uJy/beam rms) from the VLA. In order to quantify the evolution of the FRC we use both survival analysis and stacking techniques which we find give similar results. We also calculate the FRC using total infrared luminosity and rest-frame radio luminosity, qTIR, and find that qTIR is constant (within 0.22) over the redshift range 0 - 2. We see no evidence for evolution in the FRC at 70 um which is surprising given the many factors that are expected to change this ratio at high redshifts.Comment: 18 pages, 13 figures. Accepted for publication in Ap