4,833 research outputs found
Fluctuation superconductivity limited noise in a transition-edge sensor
In order to investigate the origin of the until now unaccounted excess noise
and to minimize the uncontrollable phenomena at the transition in X-ray
microcalorimeters we have developed superconducting transition-edge sensors
into an edgeless geometry, the so-called Corbino disk (CorTES), with
superconducting contacts in the centre and at the outer perimeter. The measured
rms current noise and its spectral density can be modeled as resistance noise
resulting from fluctuations near the equilibrium superconductor-normal metal
boundaryComment: 9 pages, 4 figures.; Corrections to text and equations; replaced the
affected figures. Added reference [12
A transmission problem across a fractal self-similar interface
We consider a transmission problem in which the interior domain has
infinitely ramified structures. Transmission between the interior and exterior
domains occurs only at the fractal component of the interface between the
interior and exterior domains. We also consider the sequence of the
transmission problems in which the interior domain is obtained by stopping the
self-similar construction after a finite number of steps; the transmission
condition is then posed on a prefractal approximation of the fractal interface.
We prove the convergence in the sense of Mosco of the energy forms associated
with these problems to the energy form of the limit problem. In particular,
this implies the convergence of the solutions of the approximated problems to
the solution of the problem with fractal interface. The proof relies in
particular on an extension property. Emphasis is put on the geometry of the
ramified domain. The convergence result is obtained when the fractal interface
has no self-contact, and in a particular geometry with self-contacts, for which
an extension result is proved
Discovery of a New Deeply Eclipsing SU UMa-Type Dwarf Nova, IY UMa (= TmzV85)
We discovered a new deeply eclipsing SU UMa-type dwarf nova, IY UMa, which
experienced a superoutburst in 2000 January. Our monitoring revealed two
distinct outbursts, which suggest a superoutburst interval of ~800 d, or its
half, and an outburst amplitude of 5.4 mag. From time-series photometry during
the superoutburst, we determined a superhump and orbital period of 0.07588 d
and 0.0739132 d, respectively.Comment: 5 pages, 3 figures, accepted by PASJ lette
Homogeneous Fermion Superfluid with Unequal Spin Populations
For decades, the conventional view is that an s-wave BCS superfluid can not
support uniform spin polarization due to a gap in the quasiparticle
excitation spectrum. We show that this is an artifact of the dismissal of
quasiparticle interactions in the conventional approach at the
outset. Such interactions can cause triplet fluctuations in the ground state
and hence non-zero spin polarization at "magnetic field" . The
resulting ground state is a pairing state of quasiparticles on the ``BCS
vacuum". For sufficiently large , the spin polarization of at unitarity
has the simple form . Our study is motivated by the recent
experiments at Rice which found evidence of a homogenous superfluid state with
uniform spin polarization.Comment: 4 pages, 3 figure
Imbalanced Superfluid Phase of a Trapped Fermi Gas in the BCS-BEC Crossover Regime
We theoretically investigate the ground state of trapped neutral fermions
with population imbalance in the BCS-BEC crossover regime. On the basis of the
single-channel Hamiltonian, we perform full numerical calculations of the
Bogoliubov-de Gennes equation coupled with the regularized gap and number
equations. The zero-temperature phase diagram in the crossover regime is
presented, where the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing state
governs the weak-coupling BCS region of a resonance. It is found that the FFLO
oscillation vanishes in the BEC side, in which the system under population
imbalance turns into a phase separation (PS) between locally binding superfluid
and fully polarized spin domains. We also demonstrate numerical calculations
with a large particle number O(10^5), comparable to that observed in recent
experiments. The resulting density profile on a resonance yields the PS, which
is in good agreement with the recent experiments, while the FFLO modulation
exists in the pairing field. It is also proposed that the most favorable
location for the detection of the FFLO oscillation is in the vicinity of the
critical population imbalance in the weak coupling BCS regime, where the
oscillation periodicity becomes much larger than the interparticle spacing.
Finally, we analyze the radio-frequency (RF) spectroscopy in the imbalanced
system. The clear difference in the RF spectroscopy between BCS and BEC sides
reveals the structure of the pairing field and local ``magnetization''.Comment: 16 pages, 13 figures, replaced by the version to appear in J. Phys.
Soc. Jp
The role of social networks in studentsâ learning experiences
The aim of this research is to investigate the role of social networks in computer science education. The Internet shows great potential for enhancing collaboration between people and the role of social software has become increasingly relevant in recent years. This research focuses on analyzing the role that social networks play in studentsâ learning experiences. The construction of studentsâ social networks, the evolution of these networks, and their effects on the studentsâ learning experience in a university environment are examined
Flow and critical velocity of an imbalanced Fermi gas through an optical potential
Optical lattices offer the possibility to investigate the superfluid
properties of both Bose condensates and Fermionic superfluid gases. When a
population imbalance is present in a Fermi mixture, this leads to frustration
of the pairing, and the superfluid properties will be affected. In this
contribution, the influence of imbalance on the flow of a Fermi superfluid
through an optical lattice is investigated. The flow through the lattice is
analysed by taking into account coupling between neighbouring layers of the
optical lattice up to second order in the interlayer tunneling amplitude for
single atoms. The critical velocity of flow through the lattice is shown to
decrease monotonically to zero as the imbalance is increased to 100%.
Closed-form analytical expressions are given for the tunneling contribution to
the action and for the critical velocity as a function of the binding energy of
pairs in the (quasi) two-dimensional Fermi superfluid and as a function of the
imbalance.Comment: 8 pages, 1 figure, contribution for the QFS 2007 conferenc
Fractional differentiability for solutions of nonlinear elliptic equations
We study nonlinear elliptic equations in divergence form
When
has linear growth in , and assuming that enjoys smoothness, local
well-posedness is found in for certain values of
and . In the particular case
, and ,
, we obtain for each
. Our main tool in the proof is a more general result, that
holds also if has growth in , , and
asserts local well-posedness in for each , provided that
satisfies a locally uniform condition
Principal-component analysis of two-particle azimuthal correlations in PbPb and pPb collisions at CMS
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