1,462 research outputs found
Condensation in disordered lasers: theory, 3D+1 simulations and experiments
The complex processes underlying the generation of a coherent-like emission
from the multiple-scattering of photons and wave-localization in the presence
of structural disorder are still mostly un-explored. Here we show that a single
nonlinear Schroedinger equation, playing the role of the Schawlow-Townes law
for standard lasers, quantitatively reproduces experimental results and
three-dimensional time-domain parallel simulations of a colloidal laser system.Comment: 4 pages, 5 figure
Internet-based Framework to Support Integration of Customer in the Design of Customizable Products
A necessary element to design and produce customer-centric products is the integration of customers in the design process. Challenges faced during customer integration into the design process include generating models of the customized product, performing analysis of these to determine feasibility, and optimizing to increase the performance. These tasks have to be performed relatively quickly, if not in real time, to provide feedback to the customer. The focus of this article is to present a framework that utilizes CAD, finite element analysis (FEA), and optimization to integrate the customer into the design process via the Internet for delivering user customized products. The design analysis, evaluation, and optimization need to be automated and enhanced to enable operation over the Internet. A product family CAD/FEA template has been developed to perform analysis, along with a general formulation to optimize the customized product. The CAD/FEA template generalizes the geometry building and analysis of each configuration developed using a product platform approach. The proposed setup is demonstrated through the use of a bicycle frame family. In this study, the focus is on the application of optimization and FEA to facilitate the design of customer-centric products.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
The precision of textural analysis in 18F-FDG-PET scans of oesophageal cancer
Objectives: Measuring tumour heterogeneity by textural analysis in 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) provides predictive and prognostic information but technical aspects of image processing can influence parameter measurements. We therefore tested effects of image smoothing, segmentation and quantisation on the precision of heterogeneity measurements.
Methods: Sixty-four 18F-FDG PET/CT images of oesophageal cancer were processed using different Gaussian smoothing levels (2.0, 2.5, 3.0, 3.5, 4.0 mm), maximum standardised uptake value (SUVmax) segmentation thresholds (45 %, 50 %, 55 %, 60 %) and quantisation (8, 16, 32, 64, 128 bin widths). Heterogeneity parameters included grey-level co-occurrence matrix (GLCM), grey-level run length matrix (GLRL), neighbourhood grey-tone difference matrix (NGTDM), grey-level size zone matrix (GLSZM) and fractal analysis methods. The concordance correlation coefficient (CCC) for the three processing variables was calculated for each heterogeneity parameter.
Results: Most parameters showed poor agreement between different bin widths (CCC median 0.08, range 0.004–0.99). Segmentation and smoothing showed smaller effects on precision (segmentation: CCC median 0.82, range 0.33–0.97; smoothing: CCC median 0.99, range 0.58–0.99). Conclusions: Smoothing and segmentation have only a small effect on the precision of heterogeneity measurements in 18F-FDG PET data. However, quantisation often has larger effects, highlighting a need for further evaluation and standardisation of parameters for multicentre studies. Key points: • Heterogeneity measurement precision in 18 F-FDG PET is influenced by image processing methods. • Quantisation shows large effects on precision of heterogeneity parameters in 18 F-FDG PET/CT. • Smoothing and segmentation show comparatively smaller effects on precision of heterogeneity parameters
A study of random laser modes in disordered photonic crystals
We studied lasing modes in a disordered photonic crystal. The scaling of the
lasing threshold with the system size depends on the strength of disorder. For
sufficiently large size, the minimum of the lasing threshold occurs at some
finite value of disorder strength. The highest random cavity quality factor was
comparable to that of an intentionally introduced single defect. At the
minimum, the lasing threshold showed a super-exponential decrease with the size
of the system. We explain it through a migration of the lasing mode frequencies
toward the photonic bandgap center, where the localization length takes the
minimum value. Random lasers with exponentially low thresholds are predicted.Comment: 4 pages, 4 figure
Modelling Li+ Ion Battery Electrode Properties
We formulated two detailed models for an electrolytic cell with particulate electrodes based on a lithium atom concentration dependent Butler-Volmer condition at the interface between electrode particles and the electrolyte. The first was based on a dilute-ion assumption for the electrolyte, while the second assumed that Li ions are present in excess.
For the first, we used the method of multiple scales to homogenize this model over the microstructure, formed by the small lithium particles in the electrodes.
For the second, we gave rigorous bounds for the effective electrochemical conductivity for a linearized case.
We expect similar results and bounds for the "full nonlinear problem" because variational results are generally not adversely affected by a sinh term.
Finally we used the asymptotic methods, based on parameters estimated from the literature, to attain a greatly simplified one-dimensional version of the original homogenized model. This simplified model accounts for the fact that diffusion of lithium atoms within individual electrode particles is relatively much faster than that of lithium ions across the whole cell so that lithium ion diffusion is what limits the performance of the battery. However, since most of the potential drop occurs across the Debye layers surrounding each electrode particle, lithium ion diffusion only significantly affects cell performance if there is more or less complete depletion of lithium ions in some region of the electrolyte which causes a break in the current flowing across the cell. This causes catastrophic failure. Providing such failure does not occur the potential drop across the cell is determined by the concentration of lithium atoms in the electrode particles. Within each electrode lithium atom concentration is, to leading order, a function of time only and not of position within the electrode. The depletion of electrode lithium atom concentration is directly proportional to the current being drawn off the cell. This leads one to expect that the potential of the cell gradually drops as current is drawn of it.
We would like to emphasize that all the homogenization methods employed in this work give a systematic approach for investigating the effect that changes in the microstructure have on the behaviour of the battery. However, due to lack of time, we have not used this method to investigate particular particle geometries
Super-reflection of light from a random amplifying medium with disorder in the complex refractive index : Statistics of fluctuations
The probability distribution of the reflection coefficient for light
reflected from a one-dimensional random amplifying medium with {\it
cross-correlated} spatial disorder in the real and the imaginary parts of the
refractive index is derived using the method of invariant imbedding. The
statistics of fluctuations have been obtained for both the correlated telegraph
noise and the Gaussian white-noise models for the disorder. In both cases, an
enhanced backscattering (super-reflection with reflection coefficient greater
than unity) results because of coherent feedback due to Anderson localization
and coherent amplification in the medium. The results show that the effect of
randomness in the imaginary part of the refractive index on localization and
super-reflection is qualitatively different.Comment: RevTex 6 pages, 3 figures in ps file
A smartphone-supported weight loss program: design of the ENGAGED randomized controlled trial
Background
Obesity remains a major public health challenge, demanding cost-effective and scalable weight management programs. Delivering key treatment components via mobile technology offers a potential way to reduce expensive in-person contact, thereby lowering the cost and burden of intensive weight loss programs. The ENGAGED study is a theory-guided, randomized controlled trial designed to examine the feasibility and efficacy of an abbreviated smartphone-supported weight loss program. Methods/design
Ninety-six obese adults (BMI 30–39.9 kg/m2) will be randomized to one of three treatment conditions: (1) standard behavioral weight loss (STND), (2) technology-supported behavioral weight loss (TECH); or (3) self-guided behavioral weight loss (SELF). All groups will aim to achieve a 7% weight loss goal by reducing calorie and fat intake and progressively increasing moderate intensity physical activity to 175 minutes/week. STND and TECH will attend 8 group sessions and receive regular coaching calls during the first 6 months of the intervention; SELF will receive the Group Lifestyle Balance Program DVD’s and will not receive coaching calls. During months 1–6, TECH will use a specially designed smartphone application to monitor dietary intake, body weight, and objectively measured physical activity (obtained from a Blue-tooth enabled accelerometer). STND and SELF will self-monitor on paper diaries. Linear mixed modeling will be used to examine group differences on weight loss at months 3, 6, and 12. Self-monitoring adherence and diet and activity goal attainment will be tested as mediators. Discussion
ENGAGED is an innovative weight loss intervention that integrates theory with emerging mobile technologies. We hypothesize that TECH, as compared to STND and SELF, will result in greater weight loss by virtue of improved behavioral adherence and goal achievement. Trial registration
NCT0105171
legumes in sustainable cropping systems
The beneficial aspects of legumes in sustainable cropping systems have long been known
and extensively documented. Although grain legumes generally contribute less fixed N
than pasture legumes, due to removal from the field of grain and stover of grain legumes,
there is increasing evidence of their positi"e contribution to N balances and increased yield
- …