13,088 research outputs found
Berry phases and zero-modes in toroidal topological insulator
An effective Hamiltonian describing the surface states of a toroidal
topological insulator is obtained, and it is shown to support both bound-states
and charged zero-modes. Actually, the spin connection induced by the toroidal
curvature can be viewed as an position-dependent effective vector potential,
which ultimately yields the zero-modes whose wave-functions harmonically
oscillate around the toroidal surface. In addition, two distinct Berry phases
are predicted to take place by the virtue of the toroidal topology.Comment: New version, accepted for publication in EPJB, 6 pages, 1 figur
Fermi-Fermi Mixtures in the Strong Attraction Limit
The phase diagrams of low density Fermi-Fermi mixtures with equal or unequal
masses and equal or unequal populations are described at zero and finite
temperatures in the strong attraction limit. In this limit, the Fermi-Fermi
mixture can be described by a weakly interacting Bose-Fermi mixture, where the
bosons correspond to Feshbach molecules and the fermions correspond to excess
atoms. First, we discuss the three and four fermion scattering processes, and
use the exact boson-fermion and boson-boson scattering lengths to generate the
phase diagrams in terms of the underlying fermion-fermion scattering length. In
three dimensions, in addition to the normal and uniform superfluid phases, we
find two stable non-uniform states corresponding to (1) phase separation
between pure unpaired (excess) and pure paired fermions (molecular bosons); and
(2) phase separation between pure excess fermions and a mixture of excess
fermions and molecular bosons. Lastly, we also discuss the effects of the
trapping potential in the density profiles of condensed and non-condensed
molecular bosons, and excess fermions at zero and finite temperatures, and
discuss possible implications of our findings to experiments involving mixtures
of ultracold fermions.Comment: 12 Pages, 6 Figures and 1 Tabl
Vortex-Antivortex Lattice in Ultra-Cold Fermi Gases
We discuss ultra-cold Fermi gases in two dimensions, which could be realized
in a strongly confining one-dimensional optical lattice. We obtain the
temperature versus effective interaction phase diagram for an s-wave superfluid
and show that, below a certain critical temperature T_c, spontaneous
vortex-antivortex pairs appear for all coupling strengths. In addition, we show
that the evolution from weak to strong coupling is smooth, and that the system
forms a square vortex-antivortex lattice at a lower critical temperature T_M.Comment: Submitted to Physical Review Letter
Superfluid and Mott Insulating shells of bosons in harmonically confined optical lattices
Weakly interacting atomic or molecular bosons in quantum degenerate regime
and trapped in harmonically confined optical lattices, exhibit a wedding cake
structure consisting of insulating (Mott) shells. It is shown that superfluid
regions emerge between Mott shells as a result of fluctuations due to finite
hopping. It is found that the order parameter equation in the superfluid
regions is not of the Gross-Pitaeviskii type except near the insulator to
superfluid boundaries. The excitation spectra in the Mott and superfluid
regions are obtained, and it is shown that the superfluid shells posses low
energy sound modes with spatially dependent sound velocity described by a local
index of refraction directly related to the local superfluid density. Lastly,
the Berezinskii-Kosterlitz-Thouless transition and vortex-antivortex pairs are
discussed in thin (wide) superfluid shells (rings) limited by three (two)
dimensional Mott regions.Comment: 11 pages, 9 figures
Influence of dissolved oxygen on the nitrification kinetics in a circulating bed biofilm reactor
The influence of dissolved oxygen concentration
on the nitrification kinetics was studied in the circulating
bed reactor (CBR). The study was partly performed at
laboratory scale with synthetic water, and partly at pilot
scale with secondary effluent as feed water. The nitrifi-
cation kinetics of the laboratory CBR as a function of the
oxygen concentration can be described according to the
half order and zero order rate equations of the diffusion-reaction
model applied to porous catalysts. When oxygen
was the rate limiting substrate, the nitrification rate was
close to a half order function of the oxygen concentration.
The average oxygen diffusion coefficient estimated by fitting
the diffusion-reaction model to the experimental results
was around 66% of the respective value in water. The
experimental results showed that either the ammonia or
the oxygen concentration could be limiting for the nitri
fication kinetics. The latter occurred for an oxygen to
ammonia concentration ratio below 1.5-2 gO2/gN-NH4+
for both laboratory and pilot scale reactors. The volumetric
oxygen mass transfer coefficient (kLa) determined
in the laboratory scale reactor was 0.017 sˉ¹ for a superficial air velocity of 0.02 m sˉ¹, and the one determined in
the pilot scale reactor was 0.040 sˉ¹ for a superficial air
velocity of 0.031 m sˉ¹. The kLa for the pilot scale reactor
did not change significantly after biofilm development,
compared to the value measured without biofilm.Fundação para a Ciência e a Tecnologia (FCT) - PRAXIS XXI, project 2/2.1/Bio/37/94.INTERREG
Exactly Solvable Models of Interacting Spin-s Particles in one-dimension
We consider the exact solution of a many-body problem of spin- particles
interacting through an arbitrary U(1) invariant factorizable -matrix. The
solution is based on a unified formulation of the quantum inverse scattering
method for an arbitrary -dimensional monodromy matrix. The respective
eigenstates are shown to be given in terms of creation fields by a general
new recurrence relation. This allows us to derive the spectrum and the
respective Bethe ansatz equations.Comment: 10 pages, plain late
Phase Fluctuations and Vortex Lattice Melting in Triplet Quasi-One-Dimensional Superconductors at High Magnetic Fields
Assuming that the order parameter corresponds to an equal spin triplet
pairing symmetry state, we calculate the effect of phase fluctuations in
quasi-one-dimensional superconductors at high magnetic fields applied along the
y (b') axis. We show that phase fluctuations can destroy the theoretically
predicted triplet reentrant superconducting state, and that they are
responsible for melting the magnetic field induced Josephson vortex lattice
above a magnetic field dependent melting temperature Tm.Comment: 4 pages (double column), 1 eps figur
Caracterização do sistema produtivo da mangabeira no municÃpio de Itaporanga D'Ajuda, Sergipe.
bitstream/CPATC-2010/21506/1/bp-48.pd
Intervention of the Occupational Therapist in the Changes of the Occupational Performance of Newborn Pre-Term in Intensive Neonatal Therapy Unit
Poster apresentado no Annual Meeting 2020, Escola de Saúde de Coimbra.A newborn born less than 37 weeks gestational is considered a preterm newborn. In this sense, the occupational therapist who exhibits a holistic view about it, intends to enhance their occupational performance and improve their quality of life. To describe the performance of Occupational Therapy (OT) with the preterm newborn in Neonatal Intensive Care Units (NICUs), responding to the scarcity of information on the subject at the national level, and the need for occupational therapists in this context.The study uses as a method of data collection a semi-structured interview conducted to an occupational therapist that participates in a NICU in mainland Portugal and as a method of data analysis WebQDA software. It has a qualitative approach, it is a descriptive and exploratory study, taking into account the general objective, and it is assumed as a case study, by the technical procedures used. When identifying and analyzing the information related to the research question, we can affirm that during the interview the occupational therapist emphasized the intervention of OT in Sensory Modulation and Guidance to Caregivers of the Preterm Newborn.In order to optimize the whole intervention, and as a main conclusion, the importance of the caregivers participation in the OT intervention process is emphasized, which is done under the guidance of the therapist, making the approach of this professional indirect.info:eu-repo/semantics/acceptedVersio
Averaging out magnetic forces with fast rf-sweeps in an optical trap for metastable chromium atoms
We introduce a novel type of time-averaged trap, in which the internal state
of the atoms is rapidly modulated to modify magnetic trapping potentials. In
our experiment, fast radiofrequency (rf) linear sweeps flip the spin of atoms
at a fast rate, which averages out magnetic forces. We use this procedure to
optimize the accumulation of metastable chomium atoms into an optical dipole
trap from a magneto-optical trap. The potential experienced by the metastable
atoms is identical to the bare optical dipole potential, so that this procedure
allows for trapping all magnetic sublevels, hence increasing by up to 80
percent the final number of accumulated atoms.Comment: 4 pages, 4 figure
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