77,851 research outputs found
An \u3cem\u3eIn Vitro\u3c/em\u3e Spectroscopic Analysis to Determine the Chemical Composition of the Precipitate Formed by Mixing Sodium Hypochlorite and Chlorhexidine
Introduction—The purpose of this in vitro study was to determine the chemical composition of the precipitate formed by mixing sodium hypochlorite (NaOCl) and Chlorhexidine (CHX), and relative molecular weight of the components.
Methods—Using commercially available chlorhexidine gluconate (CHXg), a 2% solution was formed and mixed in a 1:1 ratio with commercially available NaOCl producing a brown precipitate. The precipitate as well as a mixture of precipitate and pure chlorhexidine diacetate (CHXa) was then analyzed using 1D and 2D NMR spectroscopy.
Results—The 1D and 2D NMR spectra were fully assigned, in terms of chemical shifts of all proton and carbon atoms in intact CHX. This permitted identification of CHX breakdown products with and without the aliphatic linker present, including lower molecular weight components of CHX that contained a para-substituted benzene that was not para-chloroaniline (PCA).
Conclusions—Based on this in vitro study, the precipitate formed by NaOCl and CHX is composed of at least two separate molecules, all of which are smaller in size than CHX. Along with native CHX, the precipitate contains two chemical fragments derived from CHX, neither of which are PCA
The Physics of 'Now'
The world is four-dimensional according to fundamental physics, governed by
basic laws that operate in a spacetime that has no unique division into space
and time. Yet our subjective experience is divided into present, past, and
future. This paper discusses the origin of this division in terms of simple
models of information gathering and utilizing systems (IGUSes). Past, present,
and future are not properties of four-dimensional spacetime but notions
describing how individual IGUSes process information. Their origin is to be
found in how these IGUSes evolved or were constructed. The past, present, and
future of an IGUS is consistent with the four-dimensional laws of physics and
can be described in four-dimensional terms. The present, for instance, is not a
moment of time in the sense of a spacelike surface in spacetime. Rather there
is a localized notion of present at each point along an IGUS' world line. The
common present of many localized IGUSes is an approximate notion appropriate
when they are sufficiently close to each other and have relative velocities
much less than that of light. But modes of organization that are different from
present, past and future can be imagined that are consistent with the physical
laws. We speculate why the present, past, and future organization might be
favored by evolution and therefore a cognitive universal.Comment: 12 pages, 4 figures, Revtex4, minor correction
Areal Foliation and AVTD Behavior in T^2 Symmetric Spacetimes with Positive Cosmological Constant
We prove a global foliation result, using areal time, for T^2 symmetric
spacetimes with a positive cosmological constant. We then find a class of
solutions that exhibit AVTD behavior near the singularity.Comment: 15 pages, 0 figures, 2 references adde
The No-Boundary Measure of the Universe
We consider the no-boundary proposal for homogeneous isotropic closed
universes with a cosmological constant and a scalar field with a quadratic
potential. In the semi-classical limit, it predicts classical behavior at late
times if the initial scalar field is more than a certain minimum. If the
classical late time histories are extended back, they may be singular or bounce
at a finite radius. The no-boundary proposal provides a probability measure on
the classical solutions which selects inflationary histories but is heavily
biased towards small amounts of inflation. This would not be compatible with
observations. However we argue that the probability for a homogeneous universe
should be multiplied by exp(3N) where N is the number of e-foldings of slow
roll inflation to obtain the probability for what we observe in our past light
cone. This volume weighting is similar to that in eternal inflation. In a
landscape potential, it would predict that the universe would have a large
amount of inflation and that it would start in an approximately de Sitter state
near a saddle-point of the potential. The universe would then have always been
in the semi-classical regime.Comment: 4 pages, revtex4, minor corrections to accord with published versio
Vector Fields in Holographic Cosmology
We extend the holographic formulation of the semiclassical no-boundary wave
function (NBWF) to models with Maxwell vector fields. It is shown that the
familiar saddle points of the NBWF have a representation in which a regular,
Euclidean asymptotic AdS geometry smoothly joins onto a Lorentzian
asymptotically de Sitter universe through a complex transition region. The tree
level probabilities of Lorentzian histories are fully specified by the action
of the AdS region of the saddle points. The scalar and vector matter profiles
in this region are complex from an AdS viewpoint, with universal asymptotic
phases. The dual description of the semiclassical NBWF thus involves complex
deformations of Euclidean CFTs.Comment: 17 pages, 3 fig
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