1,446 research outputs found
Ab initio lattice results for Fermi polarons in two dimensions
We investigate the attractive Fermi polaron problem in two dimensions using
non-perturbative Monte Carlo simulations. We introduce a new Monte Carlo
algorithm called the impurity lattice Monte Carlo method. This algorithm
samples the path integral in a computationally efficient manner and has only
small sign oscillations for systems with a single impurity. As a benchmark of
the method, we calculate the universal polaron energy in three dimensions in
the scale-invariant unitarity limit and find agreement with published results.
We then present the first fully non-perturbative calculations of the polaron
energy in two dimensions and density correlations between the impurity and
majority particles in the limit of zero range interactions. We find evidence
for a smooth crossover transition from fermionic quasiparticle to molecular
state as a function of interaction strength.Comment: Includes new results on density-density correlations. Final version
as will appear in Phys. Rev. Let
Modeling and Propagation of Noisy Waveforms in Static Timing Analysis
A technique based on the sensitivity of the output to input waveform is
presented for accurate propagation of delay information through a gate for the
purpose of static timing analysis (STA) in the presence of noise. Conventional
STA tools represent a waveform by its arrival time and slope. However, this is
not an accurate way of modeling the waveform for the purpose of noise analysis.
The key contribution of our work is the development of a method that allows
efficient propagation of equivalent waveforms throughout the circuit.
Experimental results demonstrate higher accuracy of the proposed
sensitivity-based gate delay propagation technique, SGDP, compared to the best
of existing approaches. SGDP is compatible with the current level of gate
characterization in conventional ASIC cell libraries, and as a result, it can
be easily incorporated into commercial STA tools to improve their accuracy.Comment: Submitted on behalf of EDAA (http://www.edaa.com/
High-frequency Oscillations in Small Magnetic Elements Observed with Sunrise/SuFI
We characterize waves in small magnetic elements and investigate their
propagation in the lower solar atmosphere from observations at high spatial and
temporal resolution. We use the wavelet transform to analyze oscillations of
both horizontal displacement and intensity in magnetic bright points found in
the 300 nm and the Ca II H 396.8 nm passbands of the filter imager on board the
Sunrise balloon-borne solar observatory. Phase differences between the
oscillations at the two atmospheric layers corresponding to the two passbands
reveal upward propagating waves at high frequencies (up to 30 mHz). Weak
signatures of standing as well as downward propagating waves are also obtained.
Both compressible and incompressible (kink) waves are found in the small-scale
magnetic features. The two types of waves have different, though overlapping,
period distributions. Two independent estimates give a height difference of
approximately 450+-100 km between the two atmospheric layers sampled by the
employed spectral bands. This value, together with the determined short travel
times of the transverse and longitudinal waves provide us with phase speeds of
29+-2 km/s and 31+-2 km/s, respectively. We speculate that these phase speeds
may not reflect the true propagation speeds of the waves. Thus, effects such as
the refraction of fast longitudinal waves may contribute to an overestimate of
the phase speed.Comment: 14 pages, 7 figure
Use of fly-ash geopolymer incorporating ground granulated slag for stabilization of kaolin clay cured at ambient temperature
This paper focuses on stabilisation of kaolin clay at ambient temperature using fly-ash based geopolymer incorporating ground granulated blast-furnace slag (GGBFS). Comprehensive experimental programme was conducted including soil plasticity, compaction, unconfined compressive strength, durability and leaching. These tests were followed by a microstructural analysis using scanning electron microscopy (SEM) technique. An optimisation study using several combinations of geopolymer ingredients was performed, and the role of GGBFS in enhancing the geopolymer-stabilised clay was evaluated. The results indicated that introducing partial replacement of class (F) fly-ash by GGBFS assists, when synthesised in certain ratios, in achieving strength properties of geopolymer-stabilised clay comparable to those of cement stabilised clay. Although a small percentage of geopolymer can improve the soil strength, a larger amount was essential to enhance the wetting–drying durability performance. Under freezing–thawing conditions, low durability performance was detected indicating retardation in the geopolymer reaction at low temperature. For simulated water infiltration, leaching of the activator from geopolymer-stabilised clay was a minor concern in relation to the gel formation and long-term strength gain. Finally, SEM results clearly demonstrated a clay fabric modification attributed to the inter-particle contacts and the corresponding bonding due to the gel formation and hardening
A note on void ratio of fibre-reinforced soils
This technical note extends the concept of void ratio, presented traditionally in soil mechanics, for fibre-reinforced soils. Phase relationships related to the void ratio of fibre-reinforced soils are presented along with their definitions. A simple analytical model verified with experimental data for estimating the void ratio of fibre-reinforced soils is developed which can be used to express the compressibility of fibre-reinforced soils in geotechnical engineering applications. The results indicate that the void ratio of fibre-reinforced soils is dependent on the volume ratio of fibre-soil solid
Benchmark calculations for elastic fermion-dimer scattering
We present continuum and lattice calculations for elastic scattering between
a fermion and a bound dimer in the shallow binding limit. For the continuum
calculation we use the Skorniakov-Ter-Martirosian (STM) integral equation to
determine the scattering length and effective range parameter to high
precision. For the lattice calculation we use the finite-volume method of
L\"uscher. We take into account topological finite-volume corrections to the
dimer binding energy which depend on the momentum of the dimer. After
subtracting these effects, we find from the lattice calculation kappa a_fd =
1.174(9) and kappa r_fd = -0.029(13). These results agree well with the
continuum values kappa a_fd = 1.17907(1) and kappa r_fd = -0.0383(3) obtained
from the STM equation. We discuss applications to cold atomic Fermi gases,
deuteron-neutron scattering in the spin-quartet channel, and lattice
calculations of scattering for nuclei and hadronic molecules at finite volume.Comment: 16 pages, 5 figure
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