12,367 research outputs found
Multilayer Graphene Synthesized by CVD Using Liquid Hexane as the Carbon Precursor
We produce multilayer graphene by the Chemical Vapor Deposition (CVD) method
at atmospheric pressure and 1000 {\deg}C, using flexible copper substrates as
catalyst and liquid hexane as the source of carbon. We designed an optical
device to measure the transmittance of the carbon films; with this information
we calculate that the approximate number of layers is 11.Comment: 6 pages, 5 figures. Accepted for publication in World Journal of
Condensed Matter Physic
Modified Newtonian Dynamics as an entropic force
Under natural assumptions on the thermodynamic properties of space and time
with the holographic principle we reproduce a MOND-like behaviour of gravity on
particular scales of mass and length, where Newtonian gravity requires a
modification or extension if no dark matter component is introduced in the
description of gravitational phenomena. The result is directly obtained with
the assumption that a fundamental constant of nature with dimensions of
acceleration needs to be introduced into gravitational interactions. This in
turn allows for modifications or extensions of the equipartion law and/or the
holographic principle. In other words, MOND-like phenomenology can be
reproduced when appropriate generalised concepts at the thermodynamical level
of space and/or at the holographic principle are introduced. Thermodynamical
modifications are reflected in extensions to the equipartition law which occur
when the temperature of the system drops below a critical value, equals to
Unruh's temperature evaluated at the acceleration constant scale introduced for
the description of the gravitational phenomena. Our calculations extend the
ones by Verlinde (2011) in which Newtonian gravity is shown to be an emergent
phenomenon, and together with it reinforces the idea that gravity at all scales
is emergent.Comment: 6 pages. Accepted for publication in Journal of Modern Physics (JMP
A direct primitive variable recovery scheme for hyperbolic conservative equations: the case of relativistic hydrodynamics
In this article we develop a Primitive Variable Recovery Scheme (PVRS) to
solve any system of coupled differential conservative equations. This method
obtains directly the primitive variables applying the chain rule to the time
term of the conservative equations. With this, a traditional finite volume
method for the flux is applied in order avoid violation of both, the entropy
and "Rankine-Hugoniot" jump conditions. The time evolution is then computed
using a forward finite difference scheme. This numerical technique evades the
recovery of the primitive vector by solving an algebraic system of equations as
it is often used and so, it generalises standard techniques to solve these kind
of coupled systems. The article is presented bearing in mind special
relativistic hydrodynamic numerical schemes with an added pedagogical view in
the appendix section in order to easily comprehend the PVRS. We present the
convergence of the method for standard shock-tube problems of special
relativistic hydrodynamics and a graphical visualisation of the errors using
the fluctuations of the numerical values with respect to exact analytic
solutions. The PVRS circumvents the sometimes arduous computation that arises
from standard numerical methods techniques, which obtain the desired primitive
vector solution through an algebraic polynomial of the charges.Comment: 19 pages, 6 figures, 2 tables. Accepted for publication in PLOS ON
International Evidence on Fiscal Solvency: Is Fiscal Policy "Responsible"?
This paper looks at fiscal solvency and public debt sustainability in both emerging market and advanced countries. Evidence of fiscal solvency, in the form of a robust positive conditional relationship between public debt and the primary fiscal balance, is established in both groups of countries, as well as in the sample as a whole. Evidence of fiscal solvency is much weaker, however, at high debt levels. The debt-primary balance relationship weakens considerably in emerging economies as debt rises above 50 percent of GDP. Moreover, the relationship vanishes in high-debt countries when the countries are split into high- and low-debt groups relative to sample means and medians, and this holds for industrial countries, emerging economies, and in the combined sample. These findings suggest that many industrial and emerging economies, including several where fiscal solvency has been the subject of recent debates, appear to conduct fiscal policy responsibly. Yet our results cannot reject the hypothesis of fiscal insolvency in groups of countries with high debt ratios, where the response of the primary balance to increases in debt is not statistically significant.
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