6,314 research outputs found
Spinon-Holon binding in model
Using a phenomenological model, we discuss the consequences of spinon-holon
binding in the U(1) slave-boson approach to model. Within a small
( hole concentration) expansion, we show that spinon-holon binding produces
a pseudo-gap normal state with a segmented Fermi surface and the
superconducting state is formed by opening an "additional" d-wave gap on the
segmented Fermi surface. The d-wave gap merge with the pseudo-gap smoothly as
temperature . The quasi-particles in the superconducting state are
coupled to external electromagnetic field with a coupling constant of order
where , depending on the strength of the
effective spinon-holon binding potential.Comment: 9 pages, 3 figure
Phase transition in a spring-block model of surface fracture
A simple and robust spring-block model obeying threshold dynamics is
introduced to study surface fracture of an overlayer subject to stress induced
by adhesion to a substrate. We find a novel phase transition in the crack
morphology and fragment-size statistics when the strain and the substrate
coupling are varied. Across the transition, the cracks display in succession
short-range, power-law and long-range correlations. The study of stress release
prior to cracking yields useful information on the cracking process.Comment: RevTeX, 4 pages, 4 Postscript figures included using epsfi
Dynamical coupled-channel model of kaon-hyperon interactions
The pi N --> KY and KY --> KY reactions are studied using a dynamical
coupled-channel model of meson-baryon interactions at energies where the baryon
resonances are strongly excited. The channels included are: pi N, K \Lambda,
and K\Sigma. The resonances considered are: N^* [S_{11}(1650), P_{11}(1710),
P_{13}(1720),D_{13}(1700)]; \Delta^* [S_{31}(1900), P_{31}(1910),
P_{33}(1920)]; \Lambda ^* [S_{01}(1670), P_{01}(1810)] \Sigma^* [P_{11}(1660),
D_{13}(1670)]; and K^*(892). The basic non-resonant \pi N --> KY and KY --> KY
transition potentials are derived from effective Lagrangians using a unitary
transformation method. The dynamical coupled-channel equations are simplified
by parametrizing the pi N -->pi N amplitudes in terms of empirical pi N
partial-wave amplitudes and a phenomenological off-shell function. Two models
have been constructed. Model A is built by fixing all coupling constants and
resonance parameters using SU(3) symmetry, the Particle Data Group values, and
results from a constituent quark model. Model B is obtained by allowing most of
the parameters to vary around the values of model A in fitting the data. Good
fits to the available data for pi^- p to K^0 \Lambda, K^0 \Sigma^0 have been
achieved. The investigated kinematics region in the center-of-mass frame goes
from threshold to 2.5 GeV. The constructed models can be imbedded into
associated dynamical coupled-channel studies of kaon photo- and
electro-production reactions.Comment: 35 pages, 11 Figure
High resolution 10 mu spectrometry at different planetary latitudes. A practical Hadamard transform spectrometer for astronomical application
Infrared observations at different latitudes were studied in order to obtain spectra in the 10 micrometers region to understand differences in chemical composition or physical structure of the optical features. In order to receive such spectra of a rotating planet, simultaneous observations at different latitudes were made. A Hadamard transform spectrometer with 15 entrance slits was used to obtain 15 simultaneous spectra, at a resolution of 0.01 micrometers. The spectral band covered contained 255 spectral elements
Feedback that works: a realist review of feedback interventions for written tasks
Despite feedback being considered important to learning, its potential is rarely fully realised. Promoting learning through feedback in open-ended written tasks (e.g. essays and reports) is a complex endeavour that requires students who are motivated to identify and utilise appropriate information. We set out to understand the mechanisms that enable feedback interventions to work, for whom and in what contexts. Using a realist review research methodology, 19,065 papers mentioning feedback in undergraduate courses were screened, 375 full-text papers were assessed for rigour and relevance, resulting in 58 papers for analysis. Self-determination theory was identified as a good fit for understanding what is required of feedback interventions to mobilise students to engage with the process. Findings indicate that the design of feedback processes in open-ended tasks needs to afford opportunities for students to have a sense of relatedness to their teacher, and perceptions of competence and autonomy. In addition, the role of emotion in mediating perceptions of competence needs to be considered. This review supports the use of feedback designs which include scaffolded tasks, dialogue, action plans and sequenced tasks. These designs promote students’ perceptions of relatedness, competence and autonomy, leading to motivation to engage in feedback, and thus improved performance
Normalization Perturbation: A Simple Domain Generalization Method for Real-World Domain Shifts
Improving model's generalizability against domain shifts is crucial,especially for safety-critical applications such as autonomous driving.Real-world domain styles can vary substantially due to environment changes andsensor noises, but deep models only know the training domain style. Such domainstyle gap impedes model generalization on diverse real-world domains. Ourproposed Normalization Perturbation (NP) can effectively overcome this domainstyle overfitting problem. We observe that this problem is mainly caused by thebiased distribution of low-level features learned in shallow CNN layers. Thus,we propose to perturb the channel statistics of source domain features tosynthesize various latent styles, so that the trained deep model can perceivediverse potential domains and generalizes well even without observations oftarget domain data in training. We further explore the style-sensitive channelsfor effective style synthesis. Normalization Perturbation only relies on asingle source domain and is surprisingly effective and extremely easy toimplement. Extensive experiments verify the effectiveness of our method forgeneralizing models under real-world domain shifts.<br
Overview of Hard processes at RHIC: high-pt light hadron and charm production
An overview of the experimental results on high-pt light hadron production
and open charm production is presented. Data on particle production in
elementary collisions are compared to next-to-leading order perturbative QCD
calculations. Particle production in Au+Au collisions is then compared to this
baseline.Comment: 9 pages, 6 figures, Strange Quark Matter 200
Weak and Strong coupling regimes in plasmonic-QED
We present a quantum theory for the interaction of a two level emitter with
surface plasmon polaritons confined in single-mode waveguide resonators. Based
on the Green's function approach, we develop the conditions for the weak and
strong coupling regimes by taking into account the sources of dissipation and
decoherence: radiative and non-radiative decays, internal loss processes in the
emitter, as well as propagation and leakage losses of the plasmons in the
resonator. The theory is supported by numerical calculations for several
quantum emitters, GaAs and CdSe quantum dots and NV centers together with
different types of resonators constructed of hybrid, cylindrical or wedge
waveguides. We further study the role of temperature and resonator length.
Assuming realistic leakage rates, we find the existence of an optimal length at
which strong coupling is possible. Our calculations show that the strong
coupling regime in plasmonic resonators is accessible within current technology
when working at very low temperatures (<4K). In the weak coupling regime our
theory accounts for recent experimental results. By further optimization we
find highly enhanced spontaneous emission with Purcell factors over 1000 at
room temperature for NV-centers. We finally discuss more applications for
quantum nonlinear optics and plasmon-plasmon interactions.Comment: published as Phys. Rev. B 87, 115419 (2013
Dynamics of fermions coupling to a U(1) gauge field in the limit
We study in this paper the properties of a gas of fermions coupling to a U(1)
gauge field at wavevectors at dimensions larger than one,
where is a high momentum cutoff and is the fermi wave
vector. In particular, we shall consider the limit where charge
and current fluctuations at wave vectors are forbidden. Within a
bosonization approximation, effective actions describing the low energy physics
of the system are constructed, where we show that the system can be described
as a fermion liquid formed by chargeless quasi-particles which has vanishing
wavefunction overlap with the bare fermions in the system.Comment: 25 page
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