431 research outputs found
2-dimensional membrane separator modelling: Mass transfer by convection and diffusion
AbstractHydrogen selective membranes may present a technologically and economically efficient method for the separation of H2 from CO2 in pre-combustion decarbonisation of power production from fossil fuels. Accurate scale-up and performance prediction of membranes strongly depends on adequate representation of the prevailing resistances to mass transfer, especially for present-day high flux membranes. In a series of experiments, H2/N2 separation is measured as a function of feed flow and retentate pressure for a supported palladium membrane enclosed by annular channels for feed/retentante and sweep/permeate flow. Comparison of model predictions with measured data reveals that mass transfer resistances in the gas phase are significantly reduced by a radial velocity component in cases of high transmembrane flux, which can only be adequately described by a 2D model. For accurate interpretation of experiments, scale-up, and design of modules with high flux membranes, 2D modelling is required
Improving the efficiency of fibre-chip grating couplers near 1310 nm
We present our recent work on fibre-chip grating couplers operating around 1310 nm. For the first time, we demonstrated the combination of dual-etch and apodization design approaches which can offer state of the art performance. Initial tests from fabricated structures show a -2.2dB loss
Bulk Scale Factor at Very Early Universe
In this paper we propose a higher dimensional Cosmology based on FRW model
and brane-world scenario. We consider the warp factor in the brane-world
scenario as a scale factor in 5-dimensional generalized FRW metric, which is
called as bulk scale factor, and obtain the evolution of it with space-like and
time-like extra dimensions. It is then showed that, additional space-like
dimensions can produce exponentially bulk scale factor under repulsive strong
gravitational force in the empty universe at a very early stage.Comment: 7 pages, October 201
Localization of electromagnetic waves in a two dimensional random medium
Motivated by previous investigations on the radiative effects of the electric
dipoles embedded in structured cavities, localization of electromagnetic waves
in two dimensions is studied {\it ab initio} for a system consisting of many
randomly distributed two dimensional dipoles. A set of self-consistent
equations, incorporating all orders of multiple scattering of the
electromagnetic waves, is derived from first principles and then solved
numerically for the total electromagnetic field. The results show that
spatially localized electromagnetic waves are possible in such a simple but
realistic disordered system. When localization occurs, a coherent behavior
appears and is revealed as a unique property differentiating localization from
either the residual absorption or the attenuation effects
Magnetism, Critical Fluctuations and Susceptibility Renormalization in Pd
Some of the most popular ways to treat quantum critical materials, that is,
materials close to a magnetic instability, are based on the Landau functional.
The central quantity of such approaches is the average magnitude of spin
fluctuations, which is very difficult to measure experimentally or compute
directly from the first principles. We calculate the parameters of the Landau
functional for Pd and use these to connect the critical fluctuations beyond the
local-density approximation and the band structure.Comment: Replaced with the revised version accepted for publication.
References updated, errors corrected, other change
Hot Deck Multiple Imputation for Handling Missing Accelerometer Data
Missing data due to non-wear are common in accelerometer studies measuring physical activity and sedentary behavior. Accelerometer outputs are high-dimensional time-series data that are episodic and often highly skewed, presenting unique challenges for handling missing data. Common methods for missing accelerometry either are ad-hoc, require restrictive parametric assumptions, or do not appropriately impute bouts. This study developed a flexible hot-deck multiple imputation (MI; i.e., “replacing” missing data with observed values) procedure to handle missing accelerometry. For each missing segment of accelerometry, “donor pools” contained observed segments from either the same or different participants, and ten imputed segments were randomly drawn from the donor pool according to selection weights, where the donor pool and selection weight depended on variables associated with non-wear and/or accelerometer-based measures. A simulation study of 2550 women compared hot deck MI to two standard methods in the field: available case (AC) analysis (i.e., analyzing all observed accelerometry with no restriction on wear time or number of days) and complete case (CC) analysis (i.e., analyzing only participants that wore the accelerometer for ≥ 10 h for 4–7 days). This was repeated using accelerometry from the entire 24-h day and daytime (10am–8pm) only, and data were missing at random. For the entire 24-h day, MI produced less bias and better 95% confidence interval (CI) coverage than AC and CC. For the daytime only, MI produced less bias and better 95% CI coverage than AC; CC produced similar bias and 95% CI coverage, but longer 95% CIs than MI
Hawking Radiation of Black Holes in Infrared Modified Ho\v{r}ava-Lifshitz Gravity
We study the Hawking radiation of the spherically symmetric, asymptotically
flat black holes in the infrared modified Horava-Lifshitz gravity by applying
the methods of covariant anomaly cancellation and effective action, as well as
the approach of Damour-Ruffini-Sannan's. These black holes behave as the usual
Schwarzschild ones of the general relativity when the radial distance is very
large. We also extend the method of covariant anomaly cancellation to derive
the Hawking temperature of the spherically symmetric, asymptotically AdS black
holes that represent the analogues of the Schwarzschild AdS ones.Comment: no figures, 16 pages,accepted by EPJ
DAW: Duplicate-AWare Federated Query Processing over the Web of Data
Abstract. Over the last years the Web of Data has developed into a large compendium of interlinked data sets from multiple domains. Due to the decentralised architecture of this compendium, several of these datasets contain duplicated data. Yet, so far, only little attention has been paid to the effect of duplicated data on federated querying. This work presents DAW, a novel duplicate-aware approach to feder-ated querying over the Web of Data. DAW is based on a combination of min-wise independent permutations and compact data summaries. It can be directly combined with existing federated query engines in or-der to achieve the same query recall values while querying fewer data sources. We extend three well-known federated query processing engines – DARQ, SPLENDID, and FedX – with DAW and compare our exten-sions with the original approaches. The comparison shows that DAW can greatly reduce the number of queries sent to the endpoints, while keeping high query recall values. Therefore, it can significantly improve the performance of federated query processing engines. Moreover, DAW provides a source selection mechanism that maximises the query recall, when the query processing is limited to a subset of the sources
Optical Properties of GaAs Quantum Dots Fabricated by Filling of Self-Assembled Nanoholes
Experimental results of the local droplet etching technique for the self-assembled formation of nanoholes and quantum rings on semiconductor surfaces are discussed. Dependent on the sample design and the process parameters, filling of nanoholes in AlGaAs generates strain-free GaAs quantum dots with either broadband optical emission or sharp photoluminescence (PL) lines. Broadband emission is found for samples with completely filled flat holes, which have a very broad depth distribution. On the other hand, partly filling of deep holes yield highly uniform quantum dots with very sharp PL lines
- …