187 research outputs found
The Electrostatic Ion Beam Trap : a mass spectrometer of infinite mass range
We study the ions dynamics inside an Electrostatic Ion Beam Trap (EIBT) and
show that the stability of the trapping is ruled by a Hill's equation. This
unexpectedly demonstrates that an EIBT, in the reference frame of the ions
works very similar to a quadrupole trap. The parallelism between these two
kinds of traps is illustrated by comparing experimental and theoretical
stability diagrams of the EIBT. The main difference with quadrupole traps is
that the stability depends only on the ratio of the acceleration and trapping
electrostatic potentials, not on the mass nor the charge of the ions. All kinds
of ions can be trapped simultaneously and since parametric resonances are
proportional to the square root of the charge/mass ratio the EIBT can be used
as a mass spectrometer of infinite mass range
Curved Koszul duality theory
38 pagesInternational audienceWe extend the bar-cobar adjunction to operads and properads, not necessarily augmented. Due to the default of augmentation, the objects of the dual category are endowed with a curvature. We handle the lack of augmentation by extending the category of coproperads to include objects endowed with a curvature. As usual, the bar-cobar construction gives a (large) cofibrant resolution for any properad, such as the properad encoding unital and counital Frobenius algebras, a notion which appears in 2d-TQFT. We also define a curved Koszul duality theory for operads or properads presented with quadratic, linear and constant relations, which provides the possibility for smaller relations. We apply this new theory to study the homotopy theory and the cohomology theory of unital associative algebras
Modulated Amplitude Waves and Defect Formation in the One-Dimensional Complex Ginzburg-Landau Equation
The transition from phase chaos to defect chaos in the complex
Ginzburg-Landau equation (CGLE) is related to saddle-node bifurcations of
modulated amplitude waves (MAWs). First, the spatial period P of MAWs is shown
to be limited by a maximum P_SN which depends on the CGLE coefficients;
MAW-like structures with period larger than P_SN evolve to defects. Second,
slowly evolving near-MAWs with average phase gradients and
various periods occur naturally in phase chaotic states of the CGLE. As a
measure for these periods, we study the distributions of spacings p between
neighboring peaks of the phase gradient. A systematic comparison of p and P_SN
as a function of coefficients of the CGLE shows that defects are generated at
locations where p becomes larger than P_SN. In other words, MAWs with period
P_SN represent ``critical nuclei'' for the formation of defects in phase chaos
and may trigger the transition to defect chaos. Since rare events where p
becomes sufficiently large to lead to defect formation may only occur after a
long transient, the coefficients where the transition to defect chaos seems to
occur depend on system size and integration time. We conjecture that in the
regime where the maximum period P_SN has diverged, phase chaos persists in the
thermodynamic limit.Comment: 25 pages, 18 figure
Manin products, Koszul duality, Loday algebras and Deligne conjecture
In this article we give a conceptual definition of Manin products in any
category endowed with two coherent monoidal products. This construction can be
applied to associative algebras, non-symmetric operads, operads, colored
operads, and properads presented by generators and relations. These two
products, called black and white, are dual to each other under Koszul duality
functor. We study their properties and compute several examples of black and
white products for operads. These products allow us to define natural
operations on the chain complex defining cohomology theories. With these
operations, we are able to prove that Deligne's conjecture holds for a general
class of operads and is not specific to the case of associative algebras.
Finally, we prove generalized versions of a few conjectures raised by M. Aguiar
and J.-L. Loday related to the Koszul property of operads defined by black
products. These operads provide infinitely many examples for this generalized
Deligne's conjecture.Comment: Final version, a few references adde
The homotopy theory of simplicial props
The category of (colored) props is an enhancement of the category of colored
operads, and thus of the category of small categories. In this paper, the
second in a series on "higher props," we show that the category of all small
colored simplicial props admits a cofibrantly generated model category
structure. With this model structure, the forgetful functor from props to
operads is a right Quillen functor.Comment: Final version, to appear in Israel J. Mat
Backward error analysis and the substitution law for Lie group integrators
Butcher series are combinatorial devices used in the study of numerical
methods for differential equations evolving on vector spaces. More precisely,
they are formal series developments of differential operators indexed over
rooted trees, and can be used to represent a large class of numerical methods.
The theory of backward error analysis for differential equations has a
particularly nice description when applied to methods represented by Butcher
series. For the study of differential equations evolving on more general
manifolds, a generalization of Butcher series has been introduced, called
Lie--Butcher series. This paper presents the theory of backward error analysis
for methods based on Lie--Butcher series.Comment: Minor corrections and additions. Final versio
Static and Dynamic Properties of Inhomogeneous Elastic Media on Disordered Substrate
The pinning of an inhomogeneous elastic medium by a disordered substrate is
studied analytically and numerically. The static and dynamic properties of a
-dimensional system are shown to be equivalent to those of the well known
problem of a -dimensional random manifold embedded in -dimensions.
The analogy is found to be very robust, applicable to a wide range of elastic
media, including those which are amorphous or nearly-periodic, with local or
nonlocal elasticity. Also demonstrated explicitly is the equivalence between
the dynamic depinning transition obtained at a constant driving force, and the
self-organized, near-critical behavior obtained by a (small) constant velocity
drive.Comment: 20 pages, RevTeX. Related (p)reprints also available at
http://matisse.ucsd.edu/~hwa/pub.htm
Opposite role of Bax and BCL-2 in the anti-tumoral responses of the immune system
BACKGROUND: The relative role of anti apoptotic (i.e. Bcl-2) or pro-apoptotic (e.g. Bax) proteins in tumor progression is still not completely understood. METHODS: The rat glioma cell line A15A5 was stably transfected with human Bcl-2 and Bax transgenes and the viability of theses cell lines was analyzed in vitro and in vivo. RESULTS: In vitro, the transfected cell lines (huBax A15A5 and huBcl-2 A15A5) exhibited different sensitivities toward apoptotic stimuli. huBax A15A5 cells were more sensitive and huBcl-2 A15A5 cells more resistant to apoptosis than mock-transfected A15A5 cells (pCMV A15A5). However, in vivo, in syngenic rat BDIX, these cell lines behaved differently, as no tumor growth was observed with huBax A15A5 cells while huBcl-2 A15A5 cells formed large tumors. The immune system appeared to be involved in the rejection of huBax A15A5 cells since i) huBax A15A5 cells were tumorogenic in nude mice, ii) an accumulation of CD8+ T-lymphocytes was observed at the site of injection of huBax A15A5 cells and iii) BDIX rats, which had received huBax A15A5 cells developed an immune protection against pCMV A15A5 and huBcl-2 A15A5 cells. CONCLUSIONS: We show that the expression of Bax and Bcl-2 controls the sensitivity of the cancer cells toward the immune system. This sensitization is most likely to be due to an increase in immune induced cell death and/or the amplification of an anti tumour immune respons
Disruption of Dnmt1/PCNA/UHRF1 Interactions Promotes Tumorigenesis from Human and Mice Glial Cells
Global DNA hypomethylation is a hallmark of cancer cells, but its molecular mechanisms have not been elucidated. Here, we show that the disruption of Dnmt1/PCNA/UHRF1 interactions promotes a global DNA hypomethylation in human gliomas. We then demonstrate that the Dnmt1 phosphorylations by Akt and/or PKC abrogate the interactions of Dnmt1 with PCNA and UHRF1 in cellular and acelluar studies including mass spectrometric analyses and the use of primary cultured patient-derived glioma. By using methylated DNA immunoprecipitation, methylation and CGH arrays, we show that global DNA hypomethylation is associated with genes hypomethylation, hypomethylation of DNA repeat element and chromosomal instability. Our results reveal that the disruption of Dnmt1/PCNA/UHRF1 interactions acts as an oncogenic event and that one of its signatures (i.e. the low level of mMTase activity) is a molecular biomarker associated with a poor prognosis in GBM patients. We identify the genetic and epigenetic alterations which collectively promote the acquisition of tumor/glioma traits by human astrocytes and glial progenitor cells as that promoting high proliferation and apoptosis evasion
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