1,374 research outputs found
The Uncertainty in Newton's Constant and Precision Predictions of the Primordial Helium Abundance
The current uncertainty in Newton's constant, G_N, is of the order of 0.15%.
For values of the baryon to photon ratio consistent with both cosmic microwave
background observations and the primordial deuterium abundance, this
uncertainty in G_N corresponds to an uncertainty in the primordial 4He mass
fraction, Y_P, of +-1.3 x 10^{-4}. This uncertainty in Y_P is comparable to the
effect from the current uncertainty in the neutron lifetime, which is often
treated as the dominant uncertainty in calculations of Y_P. Recent measurements
of G_N seem to be converging within a smaller range; a reduction in the
estimated error on G_N by a factor of 10 would essentially eliminate it as a
source of uncertainty in the calculation of the primordial 4He abundance.Comment: 3 pages, no figures, fixed typos, to appear in Phys. Rev.
Nonlinear porous medium flow with fractional potential pressure
We study a porous medium equation, with nonlocal diffusion effects given by
an inverse fractional Laplacian operator. We pose the problem in n-dimensional
space for all t>0 with bounded and compactly supported initial data, and prove
existence of a weak and bounded solution that propagates with finite speed, a
property that is nor shared by other fractional diffusion models.Comment: 32 pages, Late
Spin, charge and orbital ordering in ferrimagnetic insulator YBaMnO
The oxygen-deficient (double) perovskite YBaMnO, containing
corner-linked MnO square pyramids, is found to exhibit ferrimagnetic
ordering in its ground state. In the present work we report
generalized-gradient-corrected, relativistic first-principles full-potential
density-functional calculations performed on YBaMnO in the nonmagnetic,
ferromagnetic and ferrimagnetic states. The charge, orbital and spin orderings
are explained with site-, angular momentum- and orbital-projected density of
states, charge-density plots, electronic structure and total energy studies.
YBaMnO is found to stabilize in a G-type ferrimagnetic state in
accordance with experimental results. The experimentally observed insulating
behavior appears only when we include ferrimagnetic ordering in our
calculation. We observed significant optical anisotropy in this material
originating from the combined effect of ferrimagnetic ordering and crystal
field splitting. In order to gain knowledge about the presence of different
valence states for Mn in YBaMnO we have calculated -edge x-ray
absorption near-edge spectra for the Mn and O atoms. The presence of the
different valence states for Mn is clearly established from the x-ray
absorption near-edge spectra, hyperfine field parameters and the magnetic
properties study. Among the experimentally proposed structures, the recently
reported description based on 4/ is found to represent the stable
structure
Bose-Einstein Correlations for Systems with Large Halo
Model-independent considerations are presented for the calculation of
Bose-Einstein correlation functions and momentum distributions which describe
boson-emitting systems containing a central part surrounded by a large halo. If
the characteristic geometrical size of the halo is sufficiently large, the
contributions of central part and the halo to the invariant momentum
distribution are shown to be separable. The momentum-dependence of the
intercept parameter of the correlation function plays a central role. Almost
all high energy reactions including lepton-lepton, lepton hadron, hadron-hadron
and nuclear reactions are shown to be interpretable as boson emitting systems
with large halo. The results are applied to certain high energy heavy ion data
at CERN SPS. New insights are obtained for the description of low transverse
momentum enhancement of pions.Comment: Z. Phys. C in press, LaTeX, ReVTeX, 20 pages + 2 ps figure
XUV digital in-line holography using high-order harmonics
A step towards a successful implementation of timeresolved digital in-line
holography with extreme ultraviolet radiation is presented. Ultrashort XUV
pulses are produced as high-order harmonics of a femtosecond laser and a
Schwarzschild objective is used to focus harmonic radiation at 38 nm and to
produce a strongly divergent reference beam for holographic recording.
Experimental holograms of thin wires are recorded and the objects
reconstructed. Descriptions of the simulation and reconstruction theory and
algorithms are also given. Spatial resolution of few hundreds of nm is
potentially achievable, and micrometer resolution range is demonstrated.Comment: 8 pages, 8 figure
Deconstructing Decoherence
The study of environmentally induced superselection and of the process of
decoherence was originally motivated by the search for the emergence of
classical behavior out of the quantum substrate, in the macroscopic limit. This
limit, and other simplifying assumptions, have allowed the derivation of
several simple results characterizing the onset of environmentally induced
superselection; but these results are increasingly often regarded as a complete
phenomenological characterization of decoherence in any regime. This is not
necessarily the case: The examples presented in this paper counteract this
impression by violating several of the simple ``rules of thumb''. This is
relevant because decoherence is now beginning to be tested experimentally, and
one may anticipate that, in at least some of the proposed applications (e.g.,
quantum computers), only the basic principle of ``monitoring by the
environment'' will survive. The phenomenology of decoherence may turn out to be
significantly different.Comment: 13 two-column pages, 3 embedded figure
Environment-Induced Decoherence and the Transition From Quantum to Classical
We study dynamics of quantum open systems, paying special attention to those
aspects of their evolution which are relevant to the transition from quantum to
classical. We begin with a discussion of the conditional dynamics of simple
systems. The resulting models are straightforward but suffice to illustrate
basic physical ideas behind quantum measurements and decoherence. To discuss
decoherence and environment-induced superselection einselection in a more
general setting, we sketch perturbative as well as exact derivations of several
master equations valid for various systems. Using these equations we study
einselection employing the general strategy of the predictability sieve.
Assumptions that are usually made in the discussion of decoherence are
critically reexamined along with the ``standard lore'' to which they lead.
Restoration of quantum-classical correspondence in systems that are classically
chaotic is discussed. The dynamical second law -it is shown- can be traced to
the same phenomena that allow for the restoration of the correspondence
principle in decohering chaotic systems (where it is otherwise lost on a very
short time-scale). Quantum error correction is discussed as an example of an
anti-decoherence strategy. Implications of decoherence and einselection for the
interpretation of quantum theory are briefly pointed out.Comment: 80 pages, 7 figures included, Lectures given by both authors at the
72nd Les Houches Summer School on "Coherent Matter Waves", July-August 199
The Green River Natural Analogue as a field laboratory to study the long-term fate of CO2 in the subsurface
Understanding the long-term response of CO2 injected into porous reservoirs is one of the most important aspects to demonstrate safe and permanent storage. In order to provide quantitative constraints on the long-term impacts of CO2-charged fluids on the integrity of reservoir-caprock systems we recovered some 300m of core from a scientific drill hole through a natural CO2 reservoir, near Green River, Utah. We obtained geomechanical, mineralogical, geochemical, petrophysical and mineralogical laboratory data along the entire length of the core and from non CO2-charged control samples. Furthermore, we performed more detailed studies through portions of low permeability layers in direct contact with CO2-charged layers. This was done to constrain the nature and penetration depths of CO2-promoted fluid-mineral reaction fronts. The major reactions identified include the dissolution of diagenetic dolomite cements and hematite grain coatings, and the precipitation of ankerite and pyrite and have been used as input for geochemical 1D reactive transport modelling, to constrain the magnitude and velocity of the mineral-fluid reaction front.
In addition, we compared geomechanical data from the CO2-exposed core and related unreacted control samples to assess the mechanical stability of reservoir and seal rocks in a CO2 storage complex following mineral dissolution and precipitation for thousands of years. The obtained mechanical parameters were coupled to mineralogy and porosity. Key aim of this work was to better quantify the effect of long-term chemical CO2/brine/rock interactions on the mechanical strength and elastic properties of the studied formations
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