95 research outputs found
Growth modes of Fe(110) revisited: a contribution of self-assembly to magnetic materials
We have revisited the epitaxial growth modes of Fe on W(110) and Mo(110), and
propose an overview or our contribution to the field. We show that the
Stranski-Krastanov growth mode, recognized for a long time in these systems, is
in fact characterized by a bimodal distribution of islands for growth
temperature in the range 250-700°C. We observe firstly compact islands
whose shape is determined by Wulff-Kaischev's theorem, secondly thin and flat
islands that display a preferred height, ie independant from nominal thickness
and deposition procedure (1.4nm for Mo, and 5.5nm for W on the average). We
used this effect to fabricate self-organized arrays of nanometers-thick stripes
by step decoration. Self-assembled nano-ties are also obtained for nucleation
of the flat islands on Mo at fairly high temperature, ie 800°C. Finally,
using interfacial layers and solid solutions we separate two effects on the
preferred height, first that of the interfacial energy, second that of the
continuously-varying lattice parameter of the growth surface.Comment: 49 pages. Invited topical review for J. Phys.: Condens. Matte
On the number of limit cycles of the Lienard equation
In this paper, we study a Lienard system of the form dot{x}=y-F(x),
dot{y}=-x, where F(x) is an odd polynomial. We introduce a method that gives a
sequence of algebraic approximations to the equation of each limit cycle of the
system. This sequence seems to converge to the exact equation of each limit
cycle. We obtain also a sequence of polynomials R_n(x) whose roots of odd
multiplicity are related to the number and location of the limit cycles of the
system.Comment: 10 pages, 5 figures. Submitted to Physical Review
Collapse of the N=28 shell closure in Si
The energies of the excited states in very neutron-rich Si and
P have been measured using in-beam -ray spectroscopy from the
fragmentation of secondary beams of S at 39 A.MeV. The low 2
energy of Si, 770(19) keV, together with the level schemes of
P provide evidence for the disappearance of the Z=14 and N=28
spherical shell closures, which is ascribed mainly to the action of
proton-neutron tensor forces. New shell model calculations indicate that
Si is best described as a well deformed oblate rotor.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev. let
Stirring Strongly Coupled Plasma
We determine the energy it takes to move a test quark along a circle of
radius L with angular frequency w through the strongly coupled plasma of N=4
supersymmetric Yang-Mills (SYM) theory. We find that for most values of L and w
the energy deposited by stirring the plasma in this way is governed either by
the drag force acting on a test quark moving through the plasma in a straight
line with speed v=Lw or by the energy radiated by a quark in circular motion in
the absence of any plasma, whichever is larger. There is a continuous crossover
from the drag-dominated regime to the radiation-dominated regime. In the
crossover regime we find evidence for significant destructive interference
between energy loss due to drag and that due to radiation as if in vacuum. The
rotating quark thus serves as a model system in which the relative strength of,
and interplay between, two different mechanisms of parton energy loss is
accessible via a controlled classical gravity calculation. We close by
speculating on the implications of our results for a quark that is moving
through the plasma in a straight line while decelerating, although in this case
the classical calculation breaks down at the same value of the deceleration at
which the radiation-dominated regime sets in.Comment: 27 pages LaTex, 5 figure
Weak Interaction Studies ith \u3csup\u3e6\u3c/sup\u3eHe
The 6He nucleus is an ideal candidate to study the weak interaction. To this end we have built a high-intensity source of 6He delivering ∼1010 atoms/s to experiments. Taking full advantage of that available intensity we have performed a high-precision measurement of the 6He half-life that directly probes the axial part of the nuclear Hamiltonian. Currently, we are preparing a measurement of the beta-neutrino angular correlation in 6He beta decay that will allow to search for new physics beyond the Standard Model in the form of tensor currents. © 2013 AIP Publishing LLC
In gas laser ionization and spectroscopy experiments at the Superconducting Separator Spectrometer (S3): Conceptual studies and preliminary design
International audienceThe results of preparatory experiments and the preliminary designs of a new in-gas laser ionization and spectroscopy setup, to be coupled to the Super Separator Spectrometer S3 of SPIRAL2-GANIL, are reported. Special attention is given to the development and tests to carry out a full implementation of the in-gas jet laser spectroscopy technique. Application of this novel technique to radioactive species will allow highsensitivity and enhanced-resolution laser spectroscopy studies of ground- and excited-state properties of exotic nuclei
Regenerative memory in time-delayed neuromorphic photonic resonators
We investigate a photonic regenerative memory based upon a neuromorphic oscillator with a delayed self-feedback (autaptic) connection. We disclose the existence of a unique temporal response characteristic of localized structures enabling an ideal support for bits in an optical buffer memory for storage and reshaping of data information. We link our experimental implementation, based upon a nanoscale nonlinear resonant tunneling diode driving a laser, to the paradigm of neuronal activity, the FitzHugh-Nagumo model with delayed feedback. This proof-of-concept photonic regenerative memory might constitute a building block for a new class of neuron-inspired photonic memories that can handle high bit-rate optical signals
Assay platform for clinically relevant metallo-beta-lactamases
Metallo-β-lactamases (MBLs) are a growing threat to the use of almost all clinically used β-lactam antibiotics. The identification of broad-spectrum MBL inhibitors is hampered by the lack of a suitable screening platform, consisting of appropriate substrates and a set of clinically relevant MBLs. We report procedures for the preparation of a set of clinically relevant metallo-β-lactamases (i.e., NDM-1 (New Delhi MBL), IMP-1 (Imipenemase), SPM-1 (São Paulo MBL), and VIM-2 (Verona integron-encoded MBL)) and the identification of suitable fluorogenic substrates (umbelliferone-derived cephalosporins). The fluorogenic substrates were compared to chromogenic substrates (CENTA, nitrocefin, and imipenem), showing improved sensitivity and kinetic parameters. The efficiency of the fluorogenic substrates was exemplified by inhibitor screening, identifying 4-chloroisoquinolinols as potential pan MBL inhibitors
In-beam spectroscopic studies of S nucleus
The structure of the S nucleus has been studied at GANIL through the
one proton knock-out reaction from a Cl secondary beam at 42
AMeV. The rays following the de-excitation of S were
detected in flight using the 70 BaF detectors of the Ch\^{a}teau de
Cristal array. An exhaustive -coincidence analysis allowed an
unambiguous construction of the level scheme up to an excitation energy of 3301
keV. The existence of the spherical 2 state is confirmed and three new
-ray transitions connecting the prolate deformed 2 level were
observed. Comparison of the experimental results to shell model calculations
further supports a prolate and spherical shape coexistence with a large mixing
of states built on the ground state band in S.Comment: 6 pages, 5 figures, accepted for publication in Physical Review
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