9,556 research outputs found
Finite element stress analysis of polymers at high strains
A numerical analysis is presented for the problem of a flat rectangular rubber membrane with a circular rigid inclusion undergoing high strains due to the action of an axial load. The neo-hookean constitutive equations are introduced into the general purpose TITUS program by means of equivalent hookean constants and initial strains. The convergence is achieved after a few iterations. The method is not limited to any specific program. The results are in good agreement with those of a company sponsored photoelastic stress analysis. The theoretical and experimental deformed shapes also agree very closely with one another. For high strains it is demonstrated that using the conventional HOOKE law the stress concentration factor obtained is unreliable in the case of rubberlike material
Characterization of quasi-projectiles produced in symmetric collisions studied with INDRA Comparison with models
The characterization of hot quasi-projectiles produced in symmetric or
quasi-symmetric reactions (Au + Au, Xe + Sn, Ni + Ni, Ar + KCl) at di erent
incident energies are estimated by means of two di erent procedures. The
advantages and disadvantages of each method are analyzed on the basis of
simulations using events produced by two slightly di erent models: HIPSE and
ELIE.Comment: A para\^itr
Structural insights into the membrane-extracted dimeric form of the ATPase TraB from the Escherichia coli pKM101 conjugation system
Background: Type IV secretion (T4S) systems are involved in secretion of virulence factors such as toxins or transforming molecules, or bacterial conjugation. T4S systems are composed of 12 proteins named VirB1-B11 and VirD4. Among them, three ATPases are involved in the assembly of the T4S system and/or provide energy for substrate transfer, VirB4, VirB11 and VirD4. The X-ray crystal structures of VirB11 and VirD4 have already been solved but VirB4 has proven to be reluctant to any structural investigation so far. Results: Here, we have used small-angle X-ray scattering to obtain the first structural models for the membrane-extracted, dimeric form of the TraB protein, the VirB4 homolog encoded by the E. coli pKM101 plasmid, and for the monomeric soluble form of the LvhB4 protein, the VirB4 homolog of the T4S system encoded by the Legionella pneumophila lvh operon. We have obtained the low resolution structures of the full-length TraB and of its N- and C-terminal halves. From these SAXS models, we derive the internal organisation of TraB. We also show that the two TraB N- and C-terminal domains are independently involved in the dimerisation of the full-length protein. Conclusions: These models provide the first structural insights into the architecture of VirB4 proteins. In particular, our results highlight the modular arrangement and functional relevance of the dimeric-membrane-bound form of TraB
Quantitative measurement of the surface charge density
We present a method of measuring the charge density on dielectric surfaces.
Similar to electrostatic force microscopy we record the electrostatic
interaction between the probe and the sample surface, but at large tip-sample
distances. For calibration we use a pyroelectric sample which allows us to
alter the surface charge density by a known amount via a controlled temperature
change. For proof of principle we determined the surface charge density under
ambient conditions of ferroelectric lithium niobate
Quasiperiodicity and non-computability in tilings
We study tilings of the plane that combine strong properties of different
nature: combinatorial and algorithmic. We prove existence of a tile set that
accepts only quasiperiodic and non-recursive tilings. Our construction is based
on the fixed point construction; we improve this general technique and make it
enforce the property of local regularity of tilings needed for
quasiperiodicity. We prove also a stronger result: any effectively closed set
can be recursively transformed into a tile set so that the Turing degrees of
the resulted tilings consists exactly of the upper cone based on the Turing
degrees of the later.Comment: v3: the version accepted to MFCS 201
Precision measurements in nuclear {\beta}-decay with LPCTrap
The experimental achievements and the current program with the LPCTrap device
installed at the LIRAT beam line of the SPIRAL1-GANIL facility are presented.
The device is dedicated to the study of the weak interaction at low energy by
means of precise measurements of the {\beta}-{\nu} angular correlation
parameter. Technical aspects as well as the main results are reviewed. The
future program with new available beams is briefly discussed.Comment: Annalen der Physik (2013
Subshifts, MSO Logic, and Collapsing Hierarchies
We use monadic second-order logic to define two-dimensional subshifts, or
sets of colorings of the infinite plane. We present a natural family of
quantifier alternation hierarchies, and show that they all collapse to the
third level. In particular, this solves an open problem of [Jeandel & Theyssier
2013]. The results are in stark contrast with picture languages, where such
hierarchies are usually infinite.Comment: 12 pages, 5 figures. To appear in conference proceedings of TCS 2014,
published by Springe
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