12,416 research outputs found
Isospin in Reaction Dynamics. The Case of Dissipative Collisions at Fermi Energies
A key question in the physics of unstable nuclei is the knowledge of the
for asymmetric nuclear matter () away from normal conditions. We
recall that the symmetry energy at low densities has important effects on the
neutron skin structure, while the knowledge in high densities region is crucial
for supernovae dynamics and neutron star properties. The way to probe
such region of the isovector in terrestrial laboratories is through very
dissipative collisions of asymmetric (up to exotic) heavy ions from low to
relativistic energies. A general introduction to the topic is firstly
presented. We pass then to a detailed discussion on the
process as the main dissipative mechanism at the Fermi energies and to the
related isospin dynamics. From Stochastic Mean Field simulations the isospin
effects on all the phases of the reaction dynamics are thoroughly analysed,
from the fast nucleon emission to the mid-rapidity fragment formation up to the
dynamical fission of the residues. Simulations have been performed
with an increasing stiffness of the symmetry term of the .
Some differences have been noticed, especially for the fragment charge
asymmetry. New isospin effects have been revealed from the correlation of
fragment asymmetry with dynamical quantities at the freeze-out time. A series
of isospin sensitive observables to be further measured are finally listed.Comment: 16 pages, 6 figures, Contribution to the 5th Italy-Japan Symposium,
Recent Achievements and Perspectives in Nuclear Physics, Naples Nov.3-7 2004,
World Sci. in press. Latex in WorldSci/proc/styl
On vanishing theorems for Higgs bundles
We introduce the notion of Hermitian Higgs bundle as a natural generalization
of the notion of Hermitian vector bundle and we study some vanishing theorems
concerning Hermitian Higgs bundles when the base manifold is a compact complex
manifold. We show that a first vanishing result, proved for these objects when
the base manifold was K\"ahler, also holds when the manifold is compact
complex. From this fact and some basic properties of Hermitian Higgs bundles,
we conclude several results. In particular we show that, in analogy to the
classical case, there are vanishing theorems for invariant sections of tensor
products of Higgs bundles. Then, we prove that a Higgs bundle admits no nonzero
invariant sections if there is a condition of negativity on the greatest
eigenvalue of the Hitchin-Simpson mean curvature. Finally, we prove that
invariant sections of certain tensor products of a weak Hermitian-Yang-Mills
Higgs bundle are all parallel in the classical sense.Comment: 10 Pages, some typos corrected and minor change
Heavy Quark Dynamics in the QGP
We assess transport properties of heavy quarks in the Quark-Gluon Plasma
(QGP) that show a strong non-perturbative behavior. A T-matrix approach based
on a potential taken from lattice QCD hints at the presence of heavy-quark (HQ)
resonant scattering with an increasing strength as the temperature, ,
reaches the critical temperature, T_c \simeq 170 \; \MeV for deconfinement
from above. The implementation of HQ resonance scattering along with a
hadronization via quark coalescence under the conditions of the plasma created
in heavy-ion collisions has been shown to correctly describe both the nuclear
modification factor, , and the elliptic flow, , of single
electrons at RHIC and have correctly predicted the of D mesons at LHC
energy.Comment: 10 pages, 4 figures, Proceedings of EPIC@LHC Workshop, 6-8 July, Bar
Quantum Energy Expectation in Periodic Time-Dependent hamiltonians via Green Functions
Let be the Floquet operator of a time periodic hamiltonian .
For each positive and discrete observable (which we call a {\em probe
energy}), we derive a formula for the Laplace time average of its expectation
value up to time in terms of its eigenvalues and Green functions at the
circle of radius . Some simple applications are provided which support
its usefulness.Comment: 31 page
The Affine Structure of Gravitational Theories: Symplectic Groups and Geometry
We give a geometrical description of gravitational theories from the
viewpoint of symmetries and affine structure. We show how gravity, considered
as a gauge theory, can be consistently achieved by the nonlinear realization of
the conformal-affine group in an indirect manner: due the partial isomorphism
between and the centrally extended ,
we perform a nonlinear realization of the centrally extended (CE) in its semi-simple version. In particular, starting from the bundle
structure of gravity, we derive the conformal-affine Lie algebra and then, by
the non-linear realization, we define the coset field transformations, the
Cartan forms and the inverse Higgs constraints. Finally we discuss the
geometrical Lagrangians where all the information on matter fields and their
interactions can be contained.Comment: 21 pages. arXiv admin note: text overlap with arXiv:0910.2881,
arXiv:0705.460
Artemether resistance in vitro is linked to mutations in PfATP6 that also interact with mutations in PfMDR1 in travellers returning with Plasmodium falciparum infections.
BACKGROUND: Monitoring resistance phenotypes for Plasmodium falciparum, using in vitro growth assays, and relating findings to parasite genotype has proved particularly challenging for the study of resistance to artemisinins.
METHODS: Plasmodium falciparum isolates cultured from 28 returning travellers diagnosed with malaria were assessed for sensitivity to artemisinin, artemether, dihydroartemisinin and artesunate and findings related to mutations in pfatp6 and pfmdr1.
RESULTS: Resistance to artemether in vitro was significantly associated with a pfatp6 haplotype encoding two amino acid substitutions (pfatp6 A623E and S769N; (mean IC50 (95% CI) values of 8.2 (5.7 - 10.7) for A623/S769 versus 623E/769 N 13.5 (9.8 - 17.3) nM with a mean increase of 65%; p = 0.012). Increased copy number of pfmdr1 was not itself associated with increased IC50 values for artemether, but when interactions between the pfatp6 haplotype and increased copy number of pfmdr1 were examined together, a highly significant association was noted with IC50 values for artemether (mean IC50 (95% CI) values of 8.7 (5.9 - 11.6) versus 16.3 (10.7 - 21.8) nM with a mean increase of 87%; p = 0.0068). Previously described SNPs in pfmdr1 are also associated with differences in sensitivity to some artemisinins.
CONCLUSIONS: These findings were further explored in molecular modelling experiments that suggest mutations in pfatp6 are unlikely to affect differential binding of artemisinins at their proposed site, whereas there may be differences in such binding associated with mutations in pfmdr1. Implications for a hypothesis that artemisinin resistance may be exacerbated by interactions between PfATP6 and PfMDR1 and for epidemiological studies to monitor emerging resistance are discussed
Sharp Hardy inequalities in the half space with trace remainder term
In this paper we deal with a class of inequalities which interpolate the
Kato's inequality and the Hardy's inequality in the half space. Starting from
the classical Hardy's inequality in the half space \rnpiu
=\R^{n-1}\times(0,\infty), we show that, if we replace the optimal constant
with a smaller one , , then we can add an extra trace-term equals to that one that appears in the
Kato's inequality. The constant in the trace remainder term is optimal and it
tends to zero when goes to , while it is equal to the optimal
constant in the Kato's inequality when
"Magic" numbers in Smale's 7th problem
Smale's 7-th problem concerns N-point configurations on the 2-dim sphere
which minimize the logarithmic pair-energy V_0(r) = -ln r averaged over the
pairs in a configuration; here, r is the chordal distance between the points
forming a pair. More generally, V_0(r) may be replaced by the standardized
Riesz pair-energy V_s(r)= (r^{-s} -1)/s, which becomes - ln r in the limit s to
0, and the sphere may be replaced by other compact manifolds. This paper
inquires into the concavity of the map from the integers N>1 into the minimal
average standardized Riesz pair-energies v_s(N) of the N-point configurations
on the 2-sphere for various real s. It is known that v_s(N) is strictly
increasing for each real s, and for s<2 also bounded above, hence "overall
concave." It is (easily) proved that v_{-2}(N) is even locally strictly
concave, and that so is v_s(2n) for s<-2. By analyzing computer-experimental
data of putatively minimal average Riesz pair-energies v_s^x(N) for s in
{-1,0,1,2,3} and N in {2,...,200}, it is found that {v}_{-1}^x(N) is locally
strictly concave, while v_s^x(N) is not always locally strictly concave for s
in {0,1,2,3}: concavity defects occur whenever N in C^{x}_+(s) (an s-specific
empirical set of integers). It is found that the empirical map C^{x}_+(s), with
s in {-2,-1,0,1,2,3}, is set-theoretically increasing; moreover, the percentage
of odd numbers in C^{x}_+(s), s in {0,1,2,3}, is found to increase with s. The
integers in C^{x}_+(0) are few and far between, forming a curious sequence of
numbers, reminiscent of the "magic numbers" in nuclear physics. It is
conjectured that the "magic numbers" in Smale's 7-th problem are associated
with optimally symmetric optimal-energy configurations.Comment: 109 pages, of which 30 are numerical data tables. Thoroughly revised
version, to appear in J. Stat. Phys. under the different title: `Optimal N
point configurations on the sphere: "Magic" numbers and Smale's 7th problem
Temporal shifts of Bois Noir phytoplasma types infecting grapevine in South Tyrol (Northern Italy)
Research Not
- …