711 research outputs found
Two ground-state modifications of quantum-dot beryllium
Exact electronic properties of a system of four Coulomb-interacting
two-dimensional electrons in a parabolic confinement are reported. We show that
degenerate ground states of this system are characterized by qualitatively
different internal electron-electron correlations, and that the formation of
Wigner molecule in the strong-interaction regime is going on in essentially
different ways in these ground states.Comment: 5 pages, incl 5 Figures and 2 Table
Deep structure of the Baikal rift zone revealed by joint inversion of gravity and seismology
International audience[1] The question of plate boundary forces and deep versus shallow asthenospheric uplift has long been debated in intracontinental rift areas, particularly in the Baikal rift zone, Asia, which is colder than other continental rifts. As previous gravity and teleseismic studies support the dominance of opposing mechanisms in the Baikal rift, we reconsidered both data sets and jointly inverted them. This more effective approach brings insight into location of the perturbing bodies related to the extension in this region. Our new joint inversion method allows for inverting the velocity-density relationship with independent model parametrization. We obtain velocity and density models that consistently show (1) crustal heterogeneities that coincide with the main tectonic features at the surface, (2) a faster and denser cratonic mantle NW of Lake Baikal that we relate to the thermal contrast between old and depleted Archean (Siberian platform) and Paleozoic orogenic belt (Sayan-Baikal belt), (3) three-dimensional topographic variations of the crust-mantle boundary with well-located upwarpings, and (4) the lithosphere-asthenosphere boundary uplift up to 70 km depth with a NW dip. Our resulting velocity and density models support the idea of a combined influence of lithospheric extension and inherited lithospheric heterogeneities for the origin of the Baikal rift zone. INDEX TERMS: 1234 Geodesy and Gravity: Regional and global gravity anomalies and Earth structure; 7218 Seismology: Lithosphere and upper mantle; 8122 Citation: Tiberi, C., M. Diament, J. Déverchère, C. Petit-Mariani, V. Mikhailov, S. Tikhotsky, and U. Achauer, Deep structure of the Baikal rift zone revealed by joint inversion of gravity and seismology
Spin chains and string theory
Recently, an impressive agreement was found between anomalous dimensions of
certain operators in N=4 SYM and rotating strings with two angular momenta in
the bulk of AdS5xS5. A one-loop field theory computation, which involves
solving a Heisenberg chain by means of the Bethe ansatz agrees with the large
angular momentum limit of a rotating string. We point out that the Heisenberg
chain can be equally well solved by using a sigma model approach. Moreover we
also show that a certain limit, akin to the BMN limit, leads exactly to the
same sigma model for a string rotating with large angular momentum. The
agreement is then at the level of the action. As an upshot we propose that the
rotating string should be identified with a coherent, semi-classical state
built out of the eigenstates of the spin chain. The agreement is then complete.
For example we show that the mean value of the spin gives, precisely, the
position of the string in the bulk. This suggests a more precise formulation of
the AdS/CFT correspondence in the large-N limit and also indicates a way to
obtain string theory duals of other gauge theories.Comment: 16 pages. LaTeX. v2: References and some comments added. v3:
References to more recent work adde
Mass Dependent Evolution and the Light Gluino Existence
There is an intriguing discrepancy between \alpha_s(M_Z) values measured
directly at the CERN -factory and low-energy (at few GeV) measurements
transformed to by a massless QCD \alpha_s(Q) evolution relation.
There exists an attempt to reconcile this discrepancy by introducing a light
gluino \gl in the MSSM.
We study in detail the influence of heavy thresholds on \alpha_s(Q)
evolution. First, we consruct the "exact" explicit solution to the
mass-dependent two-loop RG equation for the running \alpha_s(Q). This solution
describes heavy thresholds smoothly. Second, we use this solution to
recalculate anew \alpha_s(M_Z) values corresponding to "low-energy" input data.
Our analysis demonstrates that using {\it mass-dependent RG procedure}
generally produces corrections of two types: Asymptotic correction due to
effective shift of threshold position; Local threshold correction only for the
case when input experiment lies in the close vicinity of heavy particle
threshold: .
Both effects result in the effective shift of the \asmz values of the order
of . However, the second one could be enhanced when the gluino mass is
close to a heavy quark mass. For such a case the sum effect could be important
for the discussion of the light gluino existence as it further changes the
\gl mass.Comment: 13, Late
Multiscale expansions of difference equations in the small lattice spacing regime, and a vicinity and integrability test. I
We propose an algorithmic procedure i) to study the ``distance'' between an
integrable PDE and any discretization of it, in the small lattice spacing
epsilon regime, and, at the same time, ii) to test the (asymptotic)
integrability properties of such discretization. This method should provide, in
particular, useful and concrete informations on how good is any numerical
scheme used to integrate a given integrable PDE. The procedure, illustrated on
a fairly general 10-parameter family of discretizations of the nonlinear
Schroedinger equation, consists of the following three steps: i) the
construction of the continuous multiscale expansion of a generic solution of
the discrete system at all orders in epsilon, following the Degasperis -
Manakov - Santini procedure; ii) the application, to such expansion, of the
Degasperis - Procesi (DP) integrability test, to test the asymptotic
integrability properties of the discrete system and its ``distance'' from its
continuous limit; iii) the use of the main output of the DP test to construct
infinitely many approximate symmetries and constants of motion of the discrete
system, through novel and simple formulas.Comment: 34 pages, no figur
Effect of a boron implantation on the electrical properties of epitaxial HgCdTe with different material composition
In this work the experimental results of investigations of the dynamics of accumulation and spatial distribution of electrically active radiation defects when irradiating epitaxial films of Hg1-xCdxTe (MCT) with different material composition (x). The films, grown by molecular beam epitaxy (MBE) were irradiated by B ions at room temperature in the radiation dose range 1012 -1015 ions/cm2 and with ion energy 100 keV. The results give the differences in implantation profiles, damage accumulation and electrical properties as a function of the material composition of the film
Non-linear electromagnetic response of graphene
It is shown that the massless energy spectrum of electrons and holes in
graphene leads to the strongly non-linear electromagnetic response of this
system. We predict that the graphene layer, irradiated by electromagnetic
waves, emits radiation at higher frequency harmonics and can work as a
frequency multiplier. The operating frequency of the graphene frequency
multiplier can lie in a broad range from microwaves to the infrared.Comment: 5 pages, 3 figure
Statistical Mechanics of Canonical-Dissipative Systems and Applications to Swarm Dynamics
We develop the theory of canonical-dissipative systems, based on the
assumption that both the conservative and the dissipative elements of the
dynamics are determined by invariants of motion. In this case, known solutions
for conservative systems can be used for an extension of the dynamics, which
also includes elements such as the take-up/dissipation of energy. This way, a
rather complex dynamics can be mapped to an analytically tractable model, while
still covering important features of non-equilibrium systems. In our paper,
this approach is used to derive a rather general swarm model that considers (a)
the energetic conditions of swarming, i.e. for active motion, (b) interactions
between the particles based on global couplings. We derive analytical
expressions for the non-equilibrium velocity distribution and the mean squared
displacement of the swarm. Further, we investigate the influence of different
global couplings on the overall behavior of the swarm by means of
particle-based computer simulations and compare them with the analytical
estimations.Comment: 14 pages incl. 13 figures. v2: misprints in Eq. (40) corrected, ref.
updated. For related work see also:
http://summa.physik.hu-berlin.de/~frank/active.htm
- …