An investigation of current sheet structure in a cylindrical Z-pinch

Structure of propagating current sheet in large radius cylindrical pinch discharg

Linearisation instability of gravity waves?

Gravity waves in irrotational dust spacetimes are characterised by nonzero magnetic Weyl tensor $H_{ab}$. In the linearised theory, the divergence of $H_{ab}$ is set to zero. Recently Lesame et al. [Phys. Rev. D {\bf 53}, 738 (1996)] presented an argument to show that, in the exact nonlinear theory, $div H=0$ forces $H_{ab}=0$, thus implying a linearisation instability for gravity waves interacting with matter. However a sign error in the equations invalidates their conclusion. Bianchi type V spacetimes are shown to include examples with $div H=0\neq H_{ab}$. An improved covariant formalism is used to show that in a generic irrotational dust spacetime, the covariant constraint equations are preserved under evolution. It is shown elsewhere that \mbox{div} H=0 does not generate further conditions.Comment: 8 pages Revtex; to appear Phys. Rev.

Direction Judgement Errors in Perspective Displays

Spatial information transfer characteristics of perspective situation displays were investigated by having eight subjects judge the directions of displayed targets relative to a fixed position in the center of computer generated perspective scenes. Their errors in judging azimuth angles varied sinusoidally with the azimuth of the targets. Errors alternated between clockwise and counterclock wise from one direction quadrant to the next. As the perspective geometry was varied between telephoto lens and wide angle lens views, the direction of error gradually reversed in all quadrants. The results can be explained by systematic differences between the three-dimensional stimulus angles and the perspective projections of those angles onto the display screen

Numerical evaluation of one-loop QCD amplitudes

We present the publicly available program NGluon allowing the numerical evaluation of primitive amplitudes at one-loop order in massless QCD. The program allows the computation of one-loop amplitudes for an arbitrary number of gluons. The focus of the present article is the extension to one-loop amplitudes including an arbitrary number of massless quark pairs. We discuss in detail the algorithmic differences to the pure gluonic case and present cross checks to validate our implementation. The numerical accuracy is investigated in detail.Comment: Talk given at ACAT 2011 conference in London, 5-9 Septembe

Discrete Newtonian Cosmology

In this paper we lay down the foundations for a purely Newtonian theory of cosmology, valid at scales small compared with the Hubble radius, using only Newtonian point particles acted on by gravity and a possible cosmological term. We describe the cosmological background which is given by an exact solution of the equations of motion in which the particles expand homothetically with their comoving positions constituting a central configuration. We point out, using previous work, that an important class of central configurations are homogeneous and isotropic, thus justifying the usual assumptions of elementary treatments. The scale factor is shown to satisfy the standard Raychaudhuri and Friedmann equations without making any fluid dynamic or continuum approximations. Since we make no commitment as to the identity of the point particles, our results are valid for cold dark matter, galaxies, or clusters of galaxies. In future publications we plan to discuss perturbations of our cosmological background from the point particle viewpoint laid down in this paper and show consistency with much standard theory usually obtained by more complicated and conceptually less clear continuum methods. Apart from its potential use in large scale structure studies, we believe that out approach has great pedagogic advantages over existing elementary treatments of the expanding universe, since it requires no use of general relativity or continuum mechanics but concentrates on the basic physics: Newton's laws for gravitationally interacting particles.Comment: 33 pages; typos fixed, references added, some clarification

Liquidity creation without a lender of last resort: clearinghouse loan certificates in the Banking Panic of 1907

We employ a new data set comprised of disaggregate figures on clearinghouse loan certificate issues in New York City to document how the dominant national banks were crucial providers of temporary liquidity during the Panic of 1907. Clearinghouse loan certificates were essentially "bridge loans" arranged between clearinghouse members that enabled and were issued in anticipation of monetary gold imports, which took a few weeks to arrive. The large New York City national banks acted as private liquidity providers by requesting (and the New York clearinghouse issuing) a volume of clearinghouse loan certificates beyond their own immediate liquidity needs. While loan certificates were a temporary solution at best to the liquidity crisis in 1907, their issuance allowed the New York banks to serve their role as central reserve city banks in the national banking system.

Why didn't the United States establish a central bank until after the panic of 1907?

Monetary historians conventionally trace the establishment of the Federal Reserve System in 1913 to the turbulence of the Panic of 1907. But why did the successful movement for creating a U.S. central bank follow the Panic of 1907 and not any earlier National Banking Era panic? The 1907 panic displayed a less severe output contraction than other national banking era panics, and national bank deposit and loan data suggest only a limited impairment to intermediation through these institutions. ; We argue that the Panic of 1907 was substantially different from earlier National Banking Era panics. The 1907 financial crisis focused on New York City trust companies, a relatively unregulated intermediary outside the control of the New York Clearinghouse. Yet trusts comprised a large proportion of New York City intermediary assets in 1907. Prior panics struck primarily national banks that were within the influence of the clearinghouses, and the private clearinghouses provided liquidity to member institutions that were perceived as solvent. Absent timely information on trusts, the New York Clearinghouse offered insufficient liquidity to the trust companies to quell the panic quickly. ; In the aftermath of the 1907 panic, New York bankers saw heightened danger to the financial system arising from "riskier" institutions outside of their clearinghouse and beyond their direct influence. The reform proposals from New York banking interests advocated universal membership in a centralized reserve system to overcome the risk of financial panic arising from the observed isolation of some intermediaries. Serious consideration of federal legislation to reform the banking system took place because New York bankers changed in their attitude toward a system of reserves beyond their control.Banks and banking - History ; Banks and banking, Central

Dynamics of Inflationary Universes with Positive Spatial Curvature

If the spatial curvature of the universe is positive, then the curvature term will always dominate at early enough times in a slow-rolling inflationary epoch. This enhances inflationary effects and hence puts limits on the possible number of e-foldings that can have occurred, independently of what happened before inflation began and in particular without regard for what may have happened in the Planck era. We use a simple multi-stage model to examine this limit as a function of the present density parameter $\Omega_0$ and the epoch when inflation ends.Comment: 9 Pages RevTex4. Revised and update

Liquidity creation without a lender of last resort: clearing house loan certificates in the Banking Panic of 1907

We employ a new data set comprised of disaggregate figures on clearing house loan certificate issues in New York City to document how the dominant national banks were crucial providers of temporary liquidity during the Panic of 1907. Clearing house loan certificates were essentially “bridge loans” arranged between clearing house members. They enabled and were issued in anticipation of gold imports, which took a few weeks to arrive. The large, New York City national banks acted as private liquidity providers by requesting (and the New York Clearing House issuing) a volume of clearing house loan certificates beyond their own immediate liquidity needs, in accord with their role as central reserve city banks in the national banking system.Financial crises - United States ; Lenders of last resort