25,652 research outputs found
CLONING, EXPRESSION IN ESCHERICHIA-COLI, AND CHARACTERIZATION OF CELLULOLYTIC ENZYMES OF AZOARCUS SP, A ROOT-INVADING DIAZOTROPH
The mass of asymptotically hyperbolic Riemannian manifolds
We present a set of global invariants, called "mass integrals", which can be
defined for a large class of asymptotically hyperbolic Riemannian manifolds.
When the "boundary at infinity" has spherical topology one single invariant is
obtained, called the mass; we show positivity thereof. We apply the definition
to conformally compactifiable manifolds, and show that the mass is
completion-independent. We also prove the result, closely related to the
problem at hand, that conformal completions of conformally compactifiable
manifolds are unique.Comment: 27 pages, Latex2e with several style files; various misprints
corrected, positivity theorem for black holes considerably strengthened, to
appear in Pacific Jour. of Mathematic
A Posteriori Error Estimation for the p-curl Problem
We derive a posteriori error estimates for a semi-discrete finite element
approximation of a nonlinear eddy current problem arising from applied
superconductivity, known as the -curl problem. In particular, we show the
reliability for non-conforming N\'{e}d\'{e}lec elements based on a residual
type argument and a Helmholtz-Weyl decomposition of
. As a consequence, we are also able to derive an a
posteriori error estimate for a quantity of interest called the AC loss. The
nonlinearity for this form of Maxwell's equation is an analogue of the one
found in the -Laplacian. It is handled without linearizing around the
approximate solution. The non-conformity is dealt by adapting error
decomposition techniques of Carstensen, Hu and Orlando. Geometric
non-conformities also appear because the continuous problem is defined over a
bounded domain while the discrete problem is formulated over a weaker
polyhedral domain. The semi-discrete formulation studied in this paper is often
encountered in commercial codes and is shown to be well-posed. The paper
concludes with numerical results confirming the reliability of the a posteriori
error estimate.Comment: 32 page
Local linear spatial regression
A local linear kernel estimator of the regression function x\mapsto
g(x):=E[Y_i|X_i=x], x\in R^d, of a stationary (d+1)-dimensional spatial process
{(Y_i,X_i),i\in Z^N} observed over a rectangular domain of the form
I_n:={i=(i_1,...,i_N)\in Z^N| 1\leq i_k\leq n_k,k=1,...,N}, n=(n_1,...,n_N)\in
Z^N, is proposed and investigated. Under mild regularity assumptions,
asymptotic normality of the estimators of g(x) and its derivatives is
established. Appropriate choices of the bandwidths are proposed. The spatial
process is assumed to satisfy some very general mixing conditions, generalizing
classical time-series strong mixing concepts. The size of the rectangular
domain I_n is allowed to tend to infinity at different rates depending on the
direction in Z^N.Comment: Published at http://dx.doi.org/10.1214/009053604000000850 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
A classical bounce: constraints and consequences
We perform a detailed investigation of the simplest possible cosmological
model in which a bounce can occur, namely that where the dynamics is led by a
simple massive scalar field in a general self-interacting potential and a
background spacetime with positively curved spatial sections. By means of a
phase space analysis, we give the conditions under which an initially
contracting phase can be followed by a bounce and an inflationary phase lasting
long enough (i.e., at least 60-70 e-folds) to suppress spatial curvature in
today's observable universe. We find that, quite generically, this realization
requires some amount of fine-tuning of the initial conditions. We study the
effect of this background evolution on scalar perturbations by propagating an
initial power-law power spectrum through the contracting phase, the bounce and
the inflationary phase. We find that it is drastically modified, both
spectrally (k-mode mixing) and in amplitude. It also acquires, at leading
order, an oscillatory component, which, once evolved through the radiation and
matter dominated eras, happens to be compatible with the WMAP data.Comment: Updated references, improved figure resolutio
Specialization and Regulation: The Rise of Professionals and the Emergence of Occupational Licensing Regulation
This paper explores the origins and effects of occupational licensing regulation in late nineteenth and early twentieth century America. Was licensing regulation introduced to limit competition in the market for professional services at the expense of efficiency? Or was licensing adopted to reduce informational asymmetries about professional quality? To investigate these hypotheses, we analyze the determinants of licensing legislation and the effect of licensing on entry into eleven occupations. We also examine the impact of medical licensing laws on entry into the medical profession, physician earnings, mortality rates, and the incidence of medical malpractice. We believe that, at least for the Progressive Era, the evidence is more consistent with the asymmetric information hypothesis than the industry capture hypothesis.
Gravity tests in the solar system and the Pioneer anomaly
We build up a new phenomenological framework associated with a minimal
generalization of Einsteinian gravitation theory. When linearity, stationarity
and isotropy are assumed, tests in the solar system are characterized by two
potentials which generalize respectively the Newton potential and the parameter
of parametrized post-Newtonian formalism. The new framework seems to
have the capability to account for the Pioneer anomaly besides other gravity
tests.Comment: 5 pages. Accepted version, to appear in Modern Physics Letters
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