6,336 research outputs found
Nature-Inspired, Computer-Assisted Optimization of Hierarchically Structured Zeolites
Zeolite catalysis is often affected by transport limitations, which significantly influence overall performance. Introducing wide pores as molecular transport highways can reduce transport limitations, control the product distribution, and mitigate effects of catalyst deactivation. Nevertheless, the importance to rationally design the meso‐ and macropore space remains underappreciated. This article reviews multiscale modelling approaches to optimize overall catalytic performance. It provides a general methodology and rules of thumb to guide catalyst synthesis with optimal pore network characteristics. Inspiration is taken from nature, such as the structure of leaves and tissues, with similar requirements and associated features. In optimal hierarchically structured zeolites, the added macro‐/mesopore volume fraction, connectivity, crystal size, and minimum wide pore size are crucial. The broad pore size distribution is secondary. No uncontrolled diffusion limitations should exist within the zeolite crystals. Surface barriers, however, can significantly affect, even dominate overall transport. Understanding their origin and ways to control them is an emergent research area. Synthesis methods to realize hierarchically structured zeolites are briefly reviewed. Significant gaps exist between laboratory synthesis methods and industrial requirements. Zeolite catalysis could benefit from computer‐assisted design of their hierarchical pore network, embracing principles used by natural transport networks for scalable efficiency, selectivity, and robustness
Real Scalar Field Scattering with Polynomial Approximation around Schwarzschild-de Sitter Black-hole
As one of the fitting methods, the polynomial approximation is effective to
process sophisticated problem. In this paper, we employ this approach to handle
the scattering of scalar field around the Schwarzschild-de Sitter black-hole.
The complex relationship between tortoise coordinate and radial coordinate is
replaced by the approximate polynomial. The Schrdinger-like equation,
the real boundary conditions and the polynomial approximation construct a full
Sturm-Liouville type problem. Then this boundary value problem can be solved
numerically according to two limiting cases: the first one is the Nariai
black-hole whose horizons are close to each other, the second one is when the
horizons are widely separated. Compared with previous results (Brevik and
Tian), the field near the event horizon and cosmological horizon can have a
better description.Comment: revtex4 source file, 11 pages, 8 figure
A framework for distributed managing uncertain data in RFID traceability networks
The ability to track and trace individual items, especially through large-scale and distributed networks, is the key to realizing many important business applications such as supply chain management, asset tracking, and counterfeit detection. Networked RFID (radio frequency identification), which uses the Internet to connect otherwise isolated RFID systems and software, is an emerging technology to support traceability applications. Despite its promising benefits, there remains many challenges to be overcome before these benefits can be realized. One significant challenge centers around dealing with uncertainty of raw RFID data. In this paper, we propose a novel framework to effectively manage the uncertainty of RFID data in large scale traceability networks. The framework consists of a global object tracking model and a local RFID data cleaning model. In particular, we propose a Markov-based model for tracking objects globally and a particle filter based approach for processing noisy, low-level RFID data locally. Our implementation validates the proposed approach and the experimental results show its effectiveness.Jiangang Ma, Quan Z. Sheng, Damith Ranasinghe, Jen Min Chuah and Yanbo W
Time-dependent density-functional theory for open systems
By introducing the self-energy density functionals for the dissipative
interactions between the reduced system and its environment, we develop a
time-dependent density-functional theory formalism based on an equation of
motion for the Kohn-Sham reduced single-electron density matrix of the reduced
system. Two approximate schemes are proposed for the self-energy density
functionals, the complete second order approximation and the wide-band limit
approximation. A numerical method based on the wide-band limit approximation is
subsequently developed and implemented to simulate the steady and transient
current through various realistic molecular devices. Simulation results are
presented and discussed.Comment: 16 pages, 12 figure
Gene Expression Differences between Enriched Normal and Chronic Myelogenous Leukemia Quiescent Stem/Progenitor Cells and Correlations with Biological Abnormalities
In comparing gene expression of normal and CML CD34+ quiescent (G0) cell, 292 genes were downregulated and 192 genes upregulated in the CML/G0 Cells. The differentially expressed genes were grouped according to their reported functions, and correlations were sought with biological differences previously observed between the same groups. The most relevant findings include the following. (i) CML G0 cells are in a more advanced stage of development and more poised to proliferate than normal G0 cells. (ii) When CML G0 cells are stimulated to proliferate, they differentiate and mature more rapidly than normal counterpart. (iii) Whereas normal G0 cells form only granulocyte/monocyte colonies when stimulated by cytokines, CML G0 cells form a combination of the above and erythroid clusters and colonies. (iv) Prominin-1 is the gene most downregulated in CML G0 cells, and this appears to be associated with the spontaneous formation of erythroid colonies by CML progenitors without EPO
Constraining Primordial Non-Gaussianity with High-Redshift Probes
We present an analysis of the constraints on the amplitude of primordial
non-Gaussianity of local type described by the dimensionless parameter . These constraints are set by the auto-correlation functions (ACFs) of two
large scale structure probes, the radio sources from NRAO VLA Sky Survey (NVSS)
and the quasar catalogue of Sloan Digital Sky Survey Release Six (SDSS DR6
QSOs), as well as by their cross-correlation functions (CCFs) with the cosmic
microwave background (CMB) temperature map (Integrated Sachs-Wolfe effect).
Several systematic effects that may affect the observational estimates of the
ACFs and of the CCFs are investigated and conservatively accounted for. Our
approach exploits the large-scale scale-dependence of the non-Gaussian halo
bias. The derived constraints on {} coming from the NVSS CCF and
from the QSO ACF and CCF are weaker than those previously obtained from the
NVSS ACF, but still consistent with them. Finally, we obtain the constraints on
() and () from
NVSS data and SDSS DR6 QSO data, respectively.Comment: 16 pages, 8 figures, 1 table, Accepted for publication on JCA
A Simple Model for Anisotropic Step Growth
We consider a simple model for the growth of isolated steps on a vicinal
crystal surface. It incorporates diffusion and drift of adatoms on the terrace,
and strong step and kink edge barriers. Using a combination of analytic methods
and Monte Carlo simulations, we study the morphology of growing steps in
detail. In particular, under typical Molecular Beam Epitaxy conditions the step
morphology is linearly unstable in the model and develops fingers separated by
deep cracks. The vertical roughness of the step grows linearly in time, while
horizontally the fingers coarsen proportional to . We develop scaling
arguments to study the saturation of the ledge morphology for a finite width
and length of the terrace.Comment: 20 pages, 12 figures; [email protected]
Electrospinning for healthcare: recent advancements
Electrospinning is a simple route to generate polymer-based fibres with diameters on the nano- to micron-scale. It has been very widely explored in biomedical science for applications including drug delivery systems, diagnostic imaging, theranostics, and tissue engineering. This extensive literature reveals that a diverse range of functional components including small molecule drugs, biologics, and nanoparticles can be incorporated into electrospun fibres, and it is possible to prepare materials with complex compartmentalised architectures. This perspective article briefly introduces the electrospinning technique before considering its potential applications in biomedicine. Particular attention is paid to the translation of electrospinning to the clinic, including the need to produce materials at large scale and the requirement to do so under Good Manufacturing Practice conditions. We finish with a summary of the key current challenges and future perspectives
The effect of monomer evaporation on a simple model of submonolayer growth
We present a model for thin film growth by particle deposition that takes
into account the possible evaporation of the particles deposited on the
surface. Our model focuses on the formation of two-dimensional structures. We
find that the presence of evaporation can dramatically affect the growth
kinetics of the film, and can give rise to regimes characterized by different
``growth'' exponents and island size distributions. Our results are obtained by
extensive computer simulations as well as through a simple scaling approach and
the analysis of rate equations describing the system. We carefully discuss the
relationship of our model with previous studies by Venables and Stoyanov of the
same physical situation, and we show that our analysis is more general.Comment: 41 pages including figures, Revtex, to be published in Physical
Review
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