1,030 research outputs found
On the smallest scale for the incompressible Navier-Stokes equations
It is proven that for solutions to the two- and three-dimensional incompressible Navier-Stokes equations the minimum scale is inversely proportional to the square root of the Reynolds number based on the kinematic viscosity and the maximum of the velocity gradients. The bounds on the velocity gradients can be obtained for two-dimensional flows, but have to be assumed to be three-dimensional. Numerical results in two dimensions are given which illustrate and substantiate the features of the proof. Implications of the minimum scale result to the decay rate of the energy spectrum are discussed
The Effect of Photoactivated TMP on \u3cem\u3eBurkholderia cepacia\u3c/em\u3e Biofilms
Burkholderia cepacia is an opportunistic pathogen that causes infections in immunocompromised individuals such as cystic fibrosis patients. B. cepacia infections are typically characterized by the formation of complex communities of cells known as biofilms. Because B. cepacia biofilms are difficult to eradicate using antibiotics, it is important to pursue alternative treatment methods. Photodynamic therapy (PDT) is a type of therapy that uses light, a photosensitizer, and oxygen to elicit cell death through the production of reactive oxygen species. PDT has been shown in previous studies to be successful in killing both Pseudomonas aeruginosa and Staphylococcus aureus. In this study, we examined the effect of a cationic porphyrin on B. cepacia biofilms by exposing static biofilms to 5,10,15,20-tetrakis(1-methyl-pyridino)-21H,23H-porphine, tetra-p-tosylate salt (TMP) followed by irradiation. Standard plate counts of cells recovered from attached biofilms revealed a 0.7-log10 reduction (80.2%) in cell viability in the presence of 225µM of TMP and light. In addition, there was a 2.74-log(10) reduction in cell viability when biofilms were treated with TMP and ciprofloxacin in comparison to a 1.96-log(10) reduction when biofilms were treated with ciprofloxacin alone. Because surface motility is involved in biofilm formation, we also examined the effects of TMP on swarming motility in B. cepacia and P. aeruginosa. In the presence of TMP in the dark, there was a substantial increase in swarming motility of both B. cepacia and P. aeruginosa. These results suggest that photoactivated TMP not only kills biofilm-associated cells, but may promote biofilm disruption through pre-dispersion behavior in the absence of light
Chaotic motion of space charge wavefronts in semiconductors under time-independent voltage bias
A standard drift-diffusion model of space charge wave propagation in
semiconductors has been studied numerically and analytically under dc voltage
bias. For sufficiently long samples, appropriate contact resistivity and
applied voltage - such that the sample is biased in a regime of negative
differential resistance - we find chaos in the propagation of nonlinear fronts
(charge monopoles of alternating sign) of electric field. The chaos is always
low-dimensional, but has a complex spatial structure; this behavior can be
interpreted using a finite dimensional asymptotic model in which the front
(charge monopole) positions and the electrical current are the only dynamical
variables.Comment: 12 pages, 8 figure
Stationary solutions of driven fourth- and sixth-order Cahn-Hilliard type equations
New types of stationary solutions of a one-dimensional driven sixth-order
Cahn-Hilliard type equation that arises as a model for epitaxially growing
nano-structures such as quantum dots, are derived by an extension of the method
of matched asymptotic expansions that retains exponentially small terms. This
method yields analytical expressions for far-field behavior as well as the
widths of the humps of these spatially non-monotone solutions in the limit of
small driving force strength which is the deposition rate in case of epitaxial
growth. These solutions extend the family of the monotone kink and antikink
solutions. The hump spacing is related to solutions of the Lambert
function. Using phase space analysis for the corresponding fifth-order
dynamical system, we use a numerical technique that enables the efficient and
accurate tracking of the solution branches, where the asymptotic solutions are
used as initial input. Additionally, our approach is first demonstrated for the
related but simpler driven fourth-order Cahn-Hilliard equation, also known as
the convective Cahn-Hilliard equation
Analytic and geometric properties of photoinduced effects in noncentrosymmetric crystals: photovoltaic current and optical rectification
An original dispersion relation between the stationary coherent nonlinear
optical responses by current and polarisation is obtained. The dispersion
relation provides a new complimentary tool that can be employed to study
light-induced charge transport models and facilitate experimental data
analysis. It is shown that the origin of the coherent current and the
dc-polarisation induced in a noncentrosymmetric crystal under illumination is
related to the theory of the Berry phase and can be represented in terms of the
renormalised geometric potentials. This renormalisation originates from the
extra phase difference acquired by a carrier in the light field on the quantum
transition between the electronic bands. The gauge invariance of the
corresponding expressions for the current and the polarisation is demonstrated.Comment: 7 page
Challenges and Lessons Learned in Applying Sensitivity Analysis to Building Stock Energy Models
Uncertainty Analysis (UA) and Sensitivity Analysis (SA) offer essential tools to determine the limits of inference of a model and explore the factors which have the most effect on the model outputs. However, despite a wellestablished body of work applying UA and SA to models of individual buildings, a review of the literature relating to energy models for larger groups of buildings undertaken by Fennell et al. (2019) highlighted very limited application at larger scales. This contribution describes the efforts undertaken by a group of research teams in the context of IEA-EBC Annex 70 working with a diverse set of Building Stock Models (BSMs) to apply global sensitivity analysis methods and compare their results. Since BSMs are a class of model defined by their output and coverage rather than their structure and inputs, they represent a diverse set of modelling approaches. Key challenges for the application of SA are identified and explored, including the influence of model form, input data types and model outputs. This study combines results from 7 different modelling teams, each using different models across a range of urban areas to explore these challenges and begin the process of developing standardised workflows for SA of BSMs
Experimental constraints on a dark matter origin for the DAMA annual modulation effect
A claim for evidence of dark matter interactions in the DAMA experiment has
been recently reinforced. We employ a new type of germanium detector to
conclusively rule out a standard isothermal galactic halo of Weakly Interacting
Massive Particles (WIMPs) as the explanation for the annual modulation effect
leading to the claim. Bounds are similarly imposed on a suggestion that dark
pseudoscalars mightlead to the effect. We describe the sensitivity to light
dark matter particles achievable with our device, in particular to
Next-to-Minimal Supersymmetric Model candidates.Comment: v4: introduces recent results from arXiv:0807.3279 and
arXiv:0807.2926. Sensitivity to pseudoscalars is revised in light of the
first. Discussion on the subject adde
Results from a Search for Light-Mass Dark Matter with a P-type Point Contact Germanium Detector
We report on several features present in the energy spectrum from an ultra
low-noise germanium detector operated at 2,100 m.w.e. By implementing a new
technique able to reject surface events, a number of cosmogenic peaks can be
observed for the first time. We discuss several possible causes for an
irreducible excess of bulk-like events below 3 keVee, including a dark matter
candidate common to the DAMA/LIBRA annual modulation effect, the hint of a
signal in CDMS, and phenomenological predictions. Improved constraints are
placed on a cosmological origin for the DAMA/LIBRA effect.Comment: 4 pages, 4 figures. v2: submitted version. Minimal changes in
wording, one reference adde
Androgen receptor gene polymorphism influence fat accumulation: a longitudinal study from adolescence to adult age.
To determine the influence of androgen receptor CAG and GGN repeat polymorphisms on fat mass and maximal fat oxidation (MFO), CAG and GGN repeat lengths were measured in 128 young boys, from which longitudinal data were obtained in 45 of them [mean?±?SD: 12.8?±?3.6 years old at recruitment, and 27.0?±?4.8 years old at adult age]. Subjects were grouped as CAG short (CAGS ) if harboring repeat lengths ?21, the rest as CAG long (CAGL ); and GGN short (GGNS ) if GGN repeat lengths ?23, or long if >?23 (GGNL ). CAGS and GGNS were associated with lower adiposity than CAGL or GGNL (P?<?0.05). There was an association between the logarithm of CAG repeats polymorphism and the changes of body mass (r?=?0.34, P?=?0.03). At adult age, CAGS men showed lower accumulation of total body and trunk fat mass, and lower resting metabolic rate (RMR) and MFO per kg of total lean mass compared with CAGL (P?<?0.05). GGNS men also showed lower percentage of body fat (P?<?0.05). In summary, androgen receptor CAG and GGN repeat polymorphisms are associated with RMR, MFO, fat mass, and its regional distribution in healthy male adolescents, influencing fat accumulation from adolescence to adult age
- …