610 research outputs found
Estimativas dos coeficientes de repetibilidade para caracteres do fruto do bacurizeiro (Platonia insignis Mart.).
Publicado também: FRAZÃO, D. A. C.; HOMMA, A. K. O; VIÉGAS, I. de J. M. (Ed.). Contribuição ao desenvolvimento da fruticultura na Amazônia. Belém, PA: Embrapa Amazônia Oriental, 2006. p. 137-142
Germinação de sementes de araticum-do-brejo (Annona glabra L.) submetidas à pré-embebição em ácido giberélico.
Publicado também: FRAZÃO, D. A. C.; HOMMA, A. K. O; VIÉGAS, I. de J. M. (Ed.). Contribuição ao desenvolvimento da fruticultura na Amazônia. Belém, PA: Embrapa Amazônia Oriental, 2006. p. 129-134
Superconducting phase coherence in striped cuprates
We study the problem of phase coherence in doped striped cuprates. We assume
the stripes to form a network of one-dimensional Luttinger liquids which are
dominated by superconducting fluctuations and pinned by impurities. The problem
of phase coherence is discussed. We study the dynamics of the superconducting
phase using a model of resistively shunted junctions which leads to a
Kosterlitz-Thouless transition. We show that our results are consistent with
recent experiments in Zn-doped cuprates. We also explain the scaling of the
superconducting critical temperature with the incommensurability as seen
in recent neutron scattering experiments and predict the behavior of
in the underdoped region.Comment: Final version to appear in Physical Review Letters with a new
reference to an earlier work of F.Guinea and G.Zymanyi on Luttinger network
Local Defect in Metallic Quantum Critical Systems
We present a theory of a single point, line or plane defect coupling to the
square of the order parameter in a metallic system near a quantum critical
point at or above its upper critical dimension. At criticality, a spin droplet
is nucleated around the defect with droplet core size determined by the
strength of the defect potential. Outside the core a universal slowly decaying
tail of the droplet is found, leading to many dissipative channels coupling to
the droplet and to a complete suppression of quantum tunneling. We propose an
NMR experiment to measure the impurity-induced changes in the local spin
susceptibility.Comment: 2 figures; 5 page
Single to Double Hump Transition in the Equilibrium Distribution Function of Relativistic Particles
We unveil a transition from single peaked to bimodal velocity distribution in
a relativistic fluid under increasing temperature, in contrast with a
non-relativistic gas, where only a monotonic broadening of the bell-shaped
distribution is observed. Such transition results from the interplay between
the raise in thermal energy and the constraint of maximum velocity imposed by
the speed of light. We study the Bose-Einstein, the Fermi-Dirac, and the
Maxwell-J\"uttner distributions, all exhibiting the same qualitative behavior.
We characterize the nature of the transition in the framework of critical
phenomena and show that it is either continuous or discontinuous, depending on
the group velocity. We analyze the transition in one, two, and three
dimensions, with special emphasis on two-dimensions, for which a possible
experiment in graphene, based on the measurement of the Johnson-Nyquist noise,
is proposed.Comment: 5 pages, 5 figure
Bosonization for Wigner-Jordan-like Transformation : Backscattering and Umklapp-processes on Fictitious Lattice
We analyze the asymptotic behavior of the exponential form in the fermionic
density operators as the function of ruling parameter Q. In the particular case
Q=\pi this exponential associates with the Wigner-Jordan transformation for XY
spin chain model. We compare the bosonization approach and the evaluation via
the Toeplitz determinant. The use of Szego-Kac theorem suggests that at Q>\pi/3
the divergent series for intrinsic logarithm provides a bosonized solution and
faster decaying one, found as the logarithm's value on another sheet of the
complex plane. The second solution is revealed as umklapp-process on the
fictitious lattice while originates from backscattering terms in bosonized
density. Our finding preserves in a wide range of fermion filling ratios.Comment: 8 pages, REVTEX, 3 eps figures, accepted to Phys.Rev.
Condensed matter and AdS/CFT
I review two classes of strong coupling problems in condensed matter physics,
and describe insights gained by application of the AdS/CFT correspondence. The
first class concerns non-zero temperature dynamics and transport in the
vicinity of quantum critical points described by relativistic field theories. I
describe how relativistic structures arise in models of physical interest,
present results for their quantum critical crossover functions and
magneto-thermoelectric hydrodynamics. The second class concerns symmetry
breaking transitions of two-dimensional systems in the presence of gapless
electronic excitations at isolated points or along lines (i.e. Fermi surfaces)
in the Brillouin zone. I describe the scaling structure of a recent theory of
the Ising-nematic transition in metals, and discuss its possible connection to
theories of Fermi surfaces obtained from simple AdS duals.Comment: 39 pages, 12 figures; Lectures at the 5th Aegean summer school, "From
gravity to thermal gauge theories: the AdS/CFT correspondence", and the De
Sitter Lecture Series in Theoretical Physics 2009, University of Groninge
In vitro culture with gemcitabine augments death receptor and NKG2D ligand expression on tumour cells
Much effort has been made to try to understand the relationship between chemotherapeutic treatment of cancer and the immune system. Whereas much of that focus has been on the direct effect of chemotherapy drugs on immune cells and the release of antigens and danger signals by malignant cells killed by chemotherapy, the effect of chemotherapy on cells surviving treatment has often been overlooked. In the present study, tumour cell lines: A549 (lung), HCT116 (colon) and MCF-7 (breast), were treated with various concentrations of the chemotherapeutic drugs cyclophosphamide, gemcitabine (GEM) and oxaliplatin (OXP) for 24 hours in vitro. In line with other reports, GEM and OXP upregulated expression of the death receptor CD95 (fas) on live cells even at sub-cytotoxic concentrations. Further investigation revealed that the increase in CD95 in response to GEM sensitised the cells to fas ligand treatment, was associated with increased phosphorylation of stress activated protein kinase/c-Jun N-terminal kinase and that other death receptors and activatory immune receptors were co-ordinately upregulated with CD95 in certain cell lines. The upregulation of death receptors and NKG2D ligands together on cells after chemotherapy suggest that although the cells have survived preliminary treatment with chemotherapy they may now be more susceptible to immune cell-mediated challenge. This re-enforces the idea that chemotherapy-immunotherapy combinations may be useful clinically and has implications for the make-up and scheduling of such treatments
Supersymmetry and Integrability in Planar Mechanical Systems
We present an N=2-supersymmetric mechanical system whose bosonic sector, with
two degrees of freedom, stems from the reduction of an SU(2) Yang-Mills theory
with the assumption of spatially homogeneous field configurations and a
particular ansatz imposed on the gauge potentials in the dimensional reduction
procedure. The Painleve test is adopted to discuss integrability and we focus
on the role of supersymmetry and parity invariance in two space dimensions for
the attainment of integrable or chaotic models. Our conclusion is that the
relationships among the parameters imposed by supersymmetry seem to drastically
reduce the number of possibilities for integrable interaction potentials of the
mechanical system under consideration.Comment: 20 pages, 3 figure
Study of the Mg waiting point relevant for x-ray burst nucleosynthesis via the Mg(,)Al reaction
The Mg(,)Al reaction rate has been identified as a
major source of uncertainty for understanding the nucleosynthesis flow in
Type-I x-ray bursts (XRBs). We report a direct measurement of the energy- and
angle-integrated cross sections of this reaction in a 3.3-6.9 MeV
center-of-mass energy range using the MUlti-Sampling Ionization Chamber
(MUSIC). The new Mg(,)Al reaction rate is a factor of
4 higher than the previous direct measurement of this reaction within
temperatures relevant for XRBs, resulting in the Mg waiting point of
x-ray burst nucleosynthesis flow to be significantly bypassed via the
() reactionComment: 6 pages, 3 figures, 1 tabl
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