989 research outputs found
En Route to European Journals of Inorganic and Organic Chemistry
In 1997 a new journal structure for the chemical literature in Europe will begin to evolve. Recueil des Travaux Chimiques
des Pays-Bas will unite with Liebigs Annalen and Chemische Berichte; furthermore, Chemistry - A European Journal will
become independent of Angewandte Chemie, its âcarrier journalâ. Recueil was founded in 1882 and is the journal of the
Royal Netherlands Chemical Society (KNCV); Chemische Berichte (1865) and Liebigs Annalen (1832) are German Chemical
Society (GDCh) journals. With these heritages in mind, we will apply the image of a âEuropean Houseâ, often used
by politicians, to scientific publishing in Europe
What is going to become of Chemische Berichte/Recueil and Liebigs Annalen/Receuil?
Although these two chemistry journals have a long tradition behind them, they have not shied away from changes!
Did you know, for example, that âBerichteâ and âAnnalenâ have published in English - no longer in German - since
1995? The two journals have also been allocated specific interest areas, and another big move took place at the beginning
of this year: the merger with the Dutch âRecueil des Travaux Chimiques des Pays-Basâ. To accommodate all these changes,
widescale reorganization had to take place. However, not only did the daily work continue, but another major and exciting
development took place in the background: the changeover to electronic manuscript processing. (For an update see
http://www.wiley-vch.de). The results of these efforts are concrete and can be seen on the pages of the journals every
month
Insecurity for compact surfaces of positive genus
A pair of points in a riemannian manifold is secure if the geodesics
between the points can be blocked by a finite number of point obstacles;
otherwise the pair of points is insecure. A manifold is secure if all pairs of
points in are secure. A manifold is insecure if there exists an insecure
point pair, and totally insecure if all point pairs are insecure.
Compact, flat manifolds are secure. A standing conjecture says that these are
the only secure, compact riemannian manifolds. We prove this for surfaces of
genus greater than zero. We also prove that a closed surface of genus greater
than one with any riemannian metric and a closed surface of genus one with
generic metric are totally insecure.Comment: 37 pages, 11 figure
A remark on an overdetermined problem in Riemannian Geometry
Let be a Riemannian manifold with a distinguished point and
assume that the geodesic distance from is an isoparametric function.
Let be a bounded domain, with , and consider
the problem in with on ,
where is the -Laplacian of . We prove that if the normal
derivative of along the boundary of is a
function of satisfying suitable conditions, then must be a
geodesic ball. In particular, our result applies to open balls of
equipped with a rotationally symmetric metric of the form
, where is the standard metric of the sphere.Comment: 8 pages. This paper has been written for possible publication in a
special volume dedicated to the conference "Geometric Properties for
Parabolic and Elliptic PDE's. 4th Italian-Japanese Workshop", organized in
Palinuro in May 201
Hopf bifurcation in a gene regulatory network model:Molecular movement causes oscillations
Gene regulatory networks, i.e. DNA segments in a cell which interact with
each other indirectly through their RNA and protein products, lie at the heart
of many important intracellular signal transduction processes. In this paper we
analyse a mathematical model of a canonical gene regulatory network consisting
of a single negative feedback loop between a protein and its mRNA (e.g. the
Hes1 transcription factor system). The model consists of two partial
differential equations describing the spatio-temporal interactions between the
protein and its mRNA in a 1-dimensional domain. Such intracellular negative
feedback systems are known to exhibit oscillatory behaviour and this is the
case for our model, shown initially via computational simulations. In order to
investigate this behaviour more deeply, we next solve our system using Green's
functions and then undertake a linearized stability analysis of the steady
states of the model. Our results show that the diffusion coefficient of the
protein/mRNA acts as a bifurcation parameter and gives rise to a Hopf
bifurcation. This shows that the spatial movement of the mRNA and protein
molecules alone is sufficient to cause the oscillations. This has implications
for transcription factors such as p53, NF-B and heat shock proteins
which are involved in regulating important cellular processes such as
inflammation, meiosis, apoptosis and the heat shock response, and are linked to
diseases such as arthritis and cancer
Global Hopf bifurcation in the ZIP regulatory system
Regulation of zinc uptake in roots of Arabidopsis thaliana has recently been
modeled by a system of ordinary differential equations based on the uptake of
zinc, expression of a transporter protein and the interaction between an
activator and inhibitor. For certain parameter choices the steady state of this
model becomes unstable upon variation in the external zinc concentration.
Numerical results show periodic orbits emerging between two critical values of
the external zinc concentration. Here we show the existence of a global Hopf
bifurcation with a continuous family of stable periodic orbits between two Hopf
bifurcation points. The stability of the orbits in a neighborhood of the
bifurcation points is analyzed by deriving the normal form, while the stability
of the orbits in the global continuation is shown by calculation of the Floquet
multipliers. From a biological point of view, stable periodic orbits lead to
potentially toxic zinc peaks in plant cells. Buffering is believed to be an
efficient way to deal with strong transient variations in zinc supply. We
extend the model by a buffer reaction and analyze the stability of the steady
state in dependence of the properties of this reaction. We find that a large
enough equilibrium constant of the buffering reaction stabilizes the steady
state and prevents the development of oscillations. Hence, our results suggest
that buffering has a key role in the dynamics of zinc homeostasis in plant
cells.Comment: 22 pages, 5 figures, uses svjour3.cl
Singular solutions of fully nonlinear elliptic equations and applications
We study the properties of solutions of fully nonlinear, positively
homogeneous elliptic equations near boundary points of Lipschitz domains at
which the solution may be singular. We show that these equations have two
positive solutions in each cone of , and the solutions are unique
in an appropriate sense. We introduce a new method for analyzing the behavior
of solutions near certain Lipschitz boundary points, which permits us to
classify isolated boundary singularities of solutions which are bounded from
either above or below. We also obtain a sharp Phragm\'en-Lindel\"of result as
well as a principle of positive singularities in certain Lipschitz domains.Comment: 41 pages, 2 figure
Variational bound on energy dissipation in plane Couette flow
We present numerical solutions to the extended Doering-Constantin variational
principle for upper bounds on the energy dissipation rate in turbulent plane
Couette flow. Using the compound matrix technique in order to reformulate this
principle's spectral constraint, we derive a system of equations that is
amenable to numerical treatment in the entire range from low to asymptotically
high Reynolds numbers. Our variational bound exhibits a minimum at intermediate
Reynolds numbers, and reproduces the Busse bound in the asymptotic regime. As a
consequence of a bifurcation of the minimizing wavenumbers, there exist two
length scales that determine the optimal upper bound: the effective width of
the variational profile's boundary segments, and the extension of their flat
interior part.Comment: 22 pages, RevTeX, 11 postscript figures are available as one
uuencoded .tar.gz file from [email protected]
Perturbative Linearization of Reaction-Diffusion Equations
We develop perturbative expansions to obtain solutions for the initial-value
problems of two important reaction-diffusion systems, viz., the Fisher equation
and the time-dependent Ginzburg-Landau (TDGL) equation. The starting point of
our expansion is the corresponding singular-perturbation solution. This
approach transforms the solution of nonlinear reaction-diffusion equations into
the solution of a hierarchy of linear equations. Our numerical results
demonstrate that this hierarchy rapidly converges to the exact solution.Comment: 13 pages, 4 figures, latex2
GALEX J201337.6+092801: The lowest gravity subdwarf B pulsator
We present the recent discovery of a new subdwarf B variable (sdBV), with an
exceptionally low surface gravity. Our spectroscopy of J20136+0928 places it at
Teff = 32100 +/- 500, log(g) = 5.15 +/- 0.10, and log(He/H) = -2.8 +/- 0.1.
With a magnitude of B = 12.0, it is the second brightest V361 Hya star ever
found. Photometry from three different observatories reveals a temporal
spectrum with eleven clearly detected periods in the range 376 to 566 s, and at
least five more close to our detection limit. These periods are unusually long
for the V361 Hya class of short-period sdBV pulsators, but not unreasonable for
p- and g-modes close to the radial fundamental, given its low surface gravity.
Of the ~50 short period sdB pulsators known to date, only a single one has been
found to have comparable spectroscopic parameters to J20136+0928. This is the
enigmatic high-amplitude pulsator V338 Ser, and we conclude that J20136+0928 is
the second example of this rare subclass of sdB pulsators located well above
the canonical extreme horizontal branch in the HR diagram.Comment: 5 pages, accepted for publication in ApJ Letter
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