7,809 research outputs found
Breakdown of the Fermi-liquid regime in the 2D Hubbard model from a two-loop field-theoretical renormalization group approach
We analyze the particle-hole symmetric two-dimensional Hubbard model on a
square lattice starting from weak-to-moderate couplings by means of the
field-theoretical renormalization group (RG) approach up to two-loop order.
This method is essential in order to evaluate the effect of the
momentum-resolved anomalous dimension which arises in the
normal phase of this model on the corresponding low-energy single-particle
excitations. As a result, we find important indications pointing to the
existence of a non-Fermi liquid (NFL) regime at temperature displaying
a truncated Fermi surface (FS) for a doping range exactly in between the
well-known antiferromagnetic insulating and the -wave singlet
superconducting phases. This NFL evolves as a function of doping into a
correlated metal with a large FS before the -wave pairing
susceptibility finally produces the dominant instability in the low-energy
limit.Comment: 9 pages, 9 figures; published in Phys. Rev.
The Arecibo 430-MHz Intermediate Galactic Latitude Survey: Discovery of Nine Radio Pulsars
We have used the Arecibo Radio Telescope to search for millisecond pulsars in
two intermediate Galactic latitude regions (7 deg < | b | < 20 deg) accessible
to this telescope. For these latitudes the useful millisecond pulsar search
volume achieved by Arecibo's 430-MHz beam is predicted to be maximal. Searching
a total of 130 square degrees, we have discovered nine new pulsars and detected
four previously known objects. We compare the results of this survey with those
of other 430-MHz surveys carried out at Arecibo and of an intermediate latitude
survey made at Parkes that included part of our search area; the latter
independently found two of the nine pulsars we have discovered.
At least six of our discoveries are isolated pulsars with ages between 5 and
300 Myr; one of these, PSR J1819+1305, exhibits very marked and periodic
nulling. We have also found a recycled pulsar, PSR J2016+1948. With a
rotational period of 65 ms, this is a member of a binary system with a 635-day
orbital period. We discuss some of the the properties of this system in detail,
and indicate its potential to provide a test of the Strong Equivalence
Principle. This pulsar and PSR J0407+16, a similar system now being timed at
Arecibo, are by far the best systems known for such a test.Comment: Accepted for publication in ApJ Referee format: 22 pages, 7 figure
Proteínas de feijão caupi [Vigna unguiculata (L.) Walp]: caracterização e aplicação nutricional.
Utilização e valor protéico; Proteínas de reserva; Protéinas tóxicas.bitstream/item/35890/1/Doc44.pd
Radio Timing and Optical Photometry of the Black Widow System PSR J1953+1846A in the Globular Cluster M71
We report on the determination of the astrometric, spin and orbital
parameters for PSR J1953+1846A, a "black widow" binary millisecond pulsar in
the globular cluster M71. By using the accurate position and orbital parameters
obtained from radio timing, we identified the optical companion in ACS/Hubble
Space Telescope images. It turns out to be a faint (m_F606W>=24, m_F814W>=23)
and variable star located at only ~0.06" from the pulsar timing position. The
light curve shows a maximum at the pulsar inferior conjunction and a minimum at
the pulsar superior conjunction, thus confirming the association with the
system. The shape of the optical modulation suggests that the companion star is
heated, likely by the pulsar wind. The comparison with the X-ray light curve
possibly suggests the presence of an intra-binary shock due to the interaction
between the pulsar wind and the material released by the companion. This is the
second identification (after COM-M5C) of an optical companion to a black widow
pulsar in a globular cluster. Interestingly, the two companions show a similar
light curve and share the same position in the color magnitude diagram.Comment: Accepted for publication by ApJ; 33 Pages, 10 Figures, 3 Table
DC resistivity near a nematic quantum critical point: Effects of weak disorder and acoustic phonons
We calculate the resistivity associated with an Ising-nematic quantum
critical point in the presence of disorder and acoustic phonons in the lattice
model. We use the memory-matrix transport theory, which has a crucial advantage
compared to other methods of not relying on the existence of well-defined
quasiparticles in the low-energy effective theory. As a result, we obtain that
by including an inevitable interaction between the nematic fluctuations and the
elastic degrees of freedom of the lattice (parametrized by the nemato-elastic
coupling ), the resistivity of the system as a
function of temperature obeys a universal scaling form described by
at high temperatures, reminiscent of the paradigmatic
strange metal regime observed in many strongly correlated compounds. For a
window of temperatures comparable with
(where is the Fermi
energy of the microscopic model), the system displays another regime in which
the resistivity is consistent with a description in terms of , where the effective exponent roughly satisfies the inequality
. However, in the low-temperature limit (i.e.,
), the properties of the quantum
critical state change in an important way depending on the types of disorder
present in the system: It can either recover a conventional Fermi liquid
described by or it could exhibit yet another non-Fermi liquid
regime characterized by the scaling form . Our
results emphasize the key role played by both phonon and disorder effects in
the scenario of nematic quantum criticality and might be fundamental for
addressing recent transport experiments in some iron-based superconductors.Comment: 18 pages, 9 figure
Production, breeding and potential of cowpea crop in Brazil.
About 50 years ago cowpea was reported as a relatively minor tropical legume. However, in the last years, it has been emerging as one of the most important food legume of the 21st century (SINGH, 2010). Brazil is not out of this panorama. Brazilian agriculture is undergoing major technological changes and, in addition, globalization in agribusiness has caused impacts on the production chain of several crops, particularly those heavily dependent on the use of a large volume of agricultural inputs, mainly fertilizers and pesticides. Such crops have had a higher production cost each year. On the other hand, this situation has brought new opportunities. Business farmers have sought new alternatives for their production arrangements. In this context cowpea constitutes one of the best options.bitstream/item/85620/1/Doc-216-Production.pd
Radio timing and optical photometry of the black widow system PSR J1518+0204C in the globular cluster M5
We report on the determination of astrometric, spin and orbital parameters
for PSR J1518+0204C, a "black widow" binary millisecond pulsar in the globular
cluster M5. The accurate position and orbital parameters obtained from radio
timing allowed us to search for the optical companion. By using WFC3/HST images
we identified a very faint variable star (m_F390W > 24.8, m_F606W > 24.3,
m_F814W > 23.1) located at only 0.25" from the pulsar's timing position. Due to
its strong variability, this star is visible only in a sub-sample of images.
However, the light curve obtained folding the available data with the orbital
parameters of the pulsar shows a maximum at the pulsar inferior conjunction and
a possible minimum at the pulsar superior conjunction. Furthermore, the shape
of the optical modulation indicates a heating process possibly due to the
pulsar wind. This is the first identification of an optical companion to a
black widow pulsar in the dense stellar environment of a globular cluster.Comment: Accepted for publication by ApJ; 24 Pages, 5 Figures, 1 Tabl
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