bluuebunny/crossref_metadata_2025 huggingface dataset:
Computational study of filler microstructure and effective property relations in dielectric composites
Authors: Wang Yu U. , Tan Daniel Q.
Published: May 2011

Phase field modeling and computer simulation is employed to study the relations between filler microstructures and effective properties of dielectric composites. The model solves electrostatic equations in terms of polarization vector field in reciprocal space using a fast Fourier transform technique and parallel computing algorithm. Composites composed of linear constituent phases of different dielectric constants are considered. Interphase boundary conditions are automatically taken into account without explicitly tracking interphase interfaces in the composites. Various factors associated with filler microstructures are systematically investigated, including dielectric constant mismatch between fillers and matrix, particle size, shape, orientation, volume fraction, and spatial arrangement as well as directional alignment. Heterogeneous distributions of polarization, charge density, and local electric field are calculated for each composite microstructure, based on which effective dielectric constant and dielectric anisotropy of the composites are determined. It is found that electrostatic interactions among high-dielectric-constant fillers embedded in low-dielectric-constant matrix play critical roles in determining the composite properties, which sensitively depend on filler arrangement and, especially, directional alignment into fibrous microstructures (chains). Such microstructurally engineered composites, whose fillers are not randomly dispersed, exhibit strong dielectric anisotropy despite all constituent components being isotropic.
Thickness dependence of curvature, strain, and response time in ionic electroactive polymer actuators fabricated via layer-by-layer assembly
Authors: Montazami Reza , Liu Sheng , Liu Yang , Wang Dong , Zhang Qiming , Heflin James R.
Published: May 2011

Ionic electroactive polymer (IEAP) actuators containing porous conductive network composites (CNCs) and ionic liquids can result in high strain and fast response times. Incorporation of spherical gold nanoparticles in the CNC enhances conductivity and porosity, while maintaining relatively small thickness. This leads to improved mechanical strain and bending curvature of the actuators. We have employed the layer-by-layer self-assembly technique to fabricate a CNC with enhanced curvature (0.43 mm−1) and large net intrinsic strain (6.1%). The results demonstrate that curvature and net strain of IEAP actuators due to motion of the anions increase linearly with the thickness of the CNC as a result of the increased volume in which the anions can be stored. In addition, after subtracting the curvature of a bare Nafion actuator without a CNC, it is found that the net intrinsic strain of the CNC layer is independent of thickness for the range of 20–80 nm, indicating that the entire CNC volume contributes equivalently to the actuator motion. Furthermore, the response time of the actuator due to anion motion is independent of CNC thickness, suggesting that traversal through the Nafion membrane is the limiting factor in the anion motion.
A cylindrical optical black hole using graded index photonic crystals
Authors: Wang Hung-Wen , Chen Lien-Wen
Published: May 2011

The electromagnetic wave propagation of a two-dimensional optical black hole with graded index photonic crystals for transverse magnetic modes is studied. The implementation of the proposed system is validated in the metamaterial regime. The finite element method is employed in order to confirm the optical properties of the designed device. Numerical simulations show that the light incident on the device is bent toward the central area and absorbed by the inner core. As a result, the artificial optical black hole can effectively absorb the incident waves from all directions. The structure is composed of two kinds of real isotropic materials, which eases the experimental fabrication.
Innovation, Globalization, and Catch-Up of Latecomers: Cases of Chinese Telecom Firms
Authors: Fan Peilei
Published: May 2011

Through case studies of Huawei and ZTE, this paper finds that Chinese telecom firms have followed the general pathway of technological learning of latecomers, that is: they first developed mature foreign technologies; then moved on to higher level technologies in the consolidation stage in advanced countries; and finally progressed from imitation to innovation, generating emerging technologies in mobile communication and data-network fields. The study demonstrates that (1) latecomers caught up successfully by building innovation capability from the beginning, and (2) collaboration with established partners only came later when they had higher level innovation capability. In addition, R&D globalization was an important technological strategy for Huawei and ZTE. The order and pace of development indicate that their R&D globalization strategy is to tap into global resources and markets that would otherwise be unavailable to latecomers. At the beginning of catching-up, unlike Korean firms in the auto, electronics, and semiconductor industries who developed mature foreign technologies by relying on technology transfer from foreign sources, Chinese telecom firms conducted in-house R&D on switch technology, because of the high cost and unavailability of the technology, their lack of understanding of foreign markets and technology, and foreign firms' interest in China's market. Further, operating in a more dynamic technological regime and a much more integrated global economic environment, Chinese firms were able to adopt some global technology strategies such as joint collaboration, participating in industrial standards organizations, and R&D globalization at a much earlier stage of their catching up than had the Korean firms, mainly to compensate for their limited initial access to global resources.
Domestic Firm Innovation and Networking with Foreign Firms in China's ICT Industry
Authors: Sun Yifei , Du Debin
Published: May 2011

This study systematically analyzes the impacts of supplier–client and technological linkages with foreign firms on domestic firm technological innovation, based on a unique dataset that was collected through a survey of over 600 firms in China's information and communication technology industry. The results revealed that Chinese firms were engaged in extensive supplier–client relationships with foreign firms, although their technological collaborations with foreign firms were very limited. It was found that firm innovation benefited significantly from technological relationships with foreign firms. However, the results also suggest that, although export/import did contribute to domestic firm innovation, supplier–client relationships with foreign-invested enterprises in China did not show positive effects on domestic firm innovation. The analyses further suggest that such market transactions between domestic and foreign firms helped building technological linkages between domestic firms and foreign firms. These results clearly demonstrate the value of networking in enhancing firm innovation in developing countries.
The Geography of Global Corporate Networks: The Poor, the Rich, and the Happy Few Countries
Authors: Wall Ronald S , Burger Martijn J , van der Knaap G A (Bert)
Published: May 2011

The gradual integration of nations within our globalizing world is strongly related to the economic networks formed by multinational headquarters and their various subsidiaries located across the globe. Although the corporate reach of multinational corporations (MNCs) is clearly global, the geographical scope of their activities remains limited. Focusing on the network of ownership relations between the global Fortune 100 MNC headquarters and their subsidiaries, it is shown that global corporate activity remains unevenly distributed across the globe. Besides showing that richer countries are better connected within the global system than the poorer countries, the authors also reveal considerable differences in connectivity within the group of rich countries. Based on various determinants, these variations in network connectivity are explained.
Entrepreneurial Origin and the Configuration of Innovation in Rural Areas: The Case of Cumbria, North West England
Authors: Kalantaridis Christos , Bika Zografia
Published: May 2011

This paper examines the incidence of innovation and the configuration of innovation systems in rural areas, which are viewed as possessing weak knowledge-generating subsystems. Drawing on the results of a microlevel study in rural Cumbria, North West England, the paper shows that entrepreneurs were able to access nonlocal knowledge infrastructure. Thus, the emergent actor-constructed regional innovation system stretched well beyond the confines of Cumbria. This configuration can be explained, in large part, by considering entrepreneurial origin. New arrivals (especially immigrants) demonstrated the greatest propensity to innovate, using innovation systems which cut across the regional and national boundaries. Locally born and returnee entrepreneurs demonstrated a low incidence of innovation. The paper concludes that a distinction between regional innovation systems (as macrolevel analytical units with a normative dimension) and actor-constructed regional innovation systems (as microlevel descriptive units) offers scope for the advancement of research in this field of study.
Plan-Led Planning Systems in Development-Led Practices: An Empirical Analysis into the (Lack of) Institutionalisation of Planning Law
Authors: Buitelaar Edwin , Galle Maaike , Sorel Niels
Published: May 2011

Planning laws are usually made with good intentions, but do not always lead to good results—at least not when measured against their own goals. Since July 2008 the Netherlands has had a new planning act which aims for a plan-led system and a stronger role of the land-use plan in providing a framework for building permits—instead of these being granted through exemptions from the land-use plan—and in guiding spatial development. On the basis of quantitative data, we found that the land-use plan has become more important: more land-use plans have been adopted, both in absolute terms and relative to alternative measures. But functionally, these land-use plans are used primarily to follow and facilitate development instead of guiding it. Development control is still (inevitably) driven by development proposals. Although the paper looks at the Dutch case, an analysis into the relationship between planning law and its institutionalisation (or the lack thereof) at the local level is worthwhile for a wider audience. In our quest to understand the effects of changes in the law on the practice of development control, we use theories that look at the process of institutionalisation, especially of centrally designed formal institutions, such as legislation, that seek application at the local level, with its own (potentially conflicting) formal and informal institutions. We conclude the paper by arguing that changes in planning law are unsuccessful if they are not congruent with informal and formal institutions at the ‘street-level’ and if there is a lack of sufficient incentives to change the behaviour of local actors.
Discourses of Energy Infrastructure Development: A Q-Method Study of Electricity Transmission Line Siting in the UK
Authors: Cotton Matthew , Devine-Wright Patrick
Published: May 2011

The construction of new electricity-transmission infrastructure is construed in UK energy policy documents as necessary for achieving government targets to increase low-carbon electricity provision to combat climate change and ensure long-term energy security. Siting high-voltage overhead lines and substations is publicly controversial, however, due to their potential environmental, social, and economic impacts. Also controversial are issues of governance, procedural justice, and technological choice in decision making, particularly in light of recent legislative changes to the planning of nationally significant infrastructure projects in the UK. This study uses the Q-method to assess the discourses emerging from stakeholder and local community actor responses to line siting in the context of proposed transmission network upgrades in the southwest of England to support a new nuclear power station at Hinkley Point in Somerset. The analysis reveals three discourses, representing divergent positions on the adequacy of existing procedures to enable community participation, trust in network operators, the kinds of system configurations (centralised versus decentralised) required to meet the challenges of climate change and energy security, and the local impacts of overhead lines. Whilst the profile of how diverse respondents loaded upon each discourse showed expected patterns, the range of positions adopted by local residents support previous studies showing the limits of the ‘NIMBY’ conceptualisation of local protest. Whilst greater information provision and more upstream citizen participation in contexts of transmission line planning is recommended to enhance public trust, the limitations of such an approach in the absence of greater clarity at the national level regarding the configuration of future energy systems is discussed.
Shifts in Value Chain Governance and Upgrading in the European Periphery of Automotive Production: Evidence from Bursa, Turkey
Authors: Özataǧan Güldem
Published: May 2011

This paper examines shifts in value chain governance and upgrading in the automotive component production node of Bursa in Turkey. Component suppliers in Bursa have gained design and product-development competences, one result of which is that European and global firms have turned to the creation of modular value chains for the sourcing of components from these suppliers. This paper considers the implications of the insertion of Turkish suppliers into modular value chains on suppliers' upgrading, and reveals that, despite the diffusion of design and product-development competences to suppliers in Bursa, cutting-edge innovation activities such as marketing and branding continue to remain the domain of the lead firms. It is argued that although Turkish suppliers seem to be successful in upgrading to take on design and product-development tasks, this has been more due to the willingness of global lead firms to relinquish these functions than to the success of Turkish suppliers in encroaching upon these once core competences of their customers. It is concluded that power asymmetries in global automotive value chains continue to exist, and that lead firms continue to have a major influence on the type of upgrading strategies that are open to their suppliers.
The Cost of Urban Sprawl and its Potential Redistributive Effects: An Empirical Cost Assessment for Water Services in Lausanne (Switzerland)
Authors: Pflieger Géraldine , Ecoffey Florian
Published: May 2011

To what extent do costs of investment, exploitation, and maintenance of water networks vary in relation to density and dispersion? What are the redistributive effects of these cost structures and by what categories of consumer are they borne? Using as a case study the distribution of water in the Lausanne agglomeration, in Switzerland, we develop a methodology to assess the real costs of urban sprawl on water services. We will show that, while the costs of centrality for the equipment and maintenance of the network are high in absolute value, for neighbourhoods situated in the city centre, they are largely compensated for by the economies of scale related to density and the supply of a greater number of users. Moreover, the evaluation based on real costs underlines the impact of the neighbourhood location and the weight of dispersion: the proximity of already urbanised areas, the distance to water production plants, the elevation. Lastly, with the case of the Lausanne area we will show that the cost of urban sprawl could be directly paid by users thanks to high connection charges and could strongly attenuate redistributive effects.
Critical Success Factors in Urban Brownfield Regeneration: An Analysis of ‘Hardcore’ Sites in Manchester and Osaka during the Economic Recession (2009–10)
Authors: Dixon Timothy , Otsuka Noriko , Abe Hirokazu
Published: May 2011

Hardcore, or long-term derelict and vacant brownfield sites which are often contaminated, form a significant proportion of brownfield land in many cities, not only in the UK but also in other countries. The recent economic recession has placed the economic viability of such sites in jeopardy. This paper compares the approaches for bringing back hardcore brownfield sites into use in England and Japan by focusing on ten case studies in Manchester and Osaka, using an ‘agency’-based framework. The findings are set in the context of (i) national brownfield and related policy agendas; (ii) recent trends in land and property markets in both England and Japan; and (iii) city-level comparisons of brownfields in Manchester and Osaka. The research, which was conducted during 2009–10, suggests that hardcore brownfield sites have been badly affected by the recent recession in both Manchester and Osaka. Despite this, not only is there evidence that hardcore sites have been successfully regenerated in both cities, but also that the critical success factors (CSFs) operating in bringing sites back into use share a large degree of commonality. These CSFs include the presence of strong potential markets, seeing the recession as an opportunity, long-term vision, strong branding, strong partnerships, integrated development, and getting infrastructure into place. Finally, the paper outlines the policy implications of the research.
Surprise Leads to Noisier Perceptual Decisions
Authors: Garrido Marta I , Dolan Raymond J , Sahani Maneesh
Published: May 2011

Surprising events in the environment can impair task performance. This might be due to complete distraction, leading to lapses during which performance is reduced to guessing. Alternatively, unpredictability might cause a graded withdrawal of perceptual resources from the task at hand and thereby reduce sensitivity. Here we attempt to distinguish between these two mechanisms. Listeners performed a novel auditory pitch—duration discrimination, where stimulus loudness changed occasionally and incidentally to the task. Responses were slower and less accurate in the surprising condition, where loudness changed unpredictably, than in the predictable condition, where the loudness was held constant. By explicitly modelling both lapses and changes in sensitivity, we found that unpredictable changes diminished sensitivity but did not increase the rate of lapses. These findings suggest that background environmental uncertainty can disrupt goal-directed behaviour. This graded processing strategy might be adaptive in potentially threatening contexts, and reflect a flexible system for automatic allocation of perceptual resources.
The importance of social norms for uptake of catch-up human papillomavirus vaccination in young women
Authors: de Visser Richard , Waites Louisa , Parikh Chandni , Lawrie Aaron
Published: May 2011

Background Human papillomavirus (HPV) is the cause of almost all cases of cervical cancer. The current UK government immunisation program includes free routine HPV vaccination of girls aged 12–13, with a catch-up vaccination program for 13–18-year-old girls. The aim of this study was to identify correlates of intended and actual uptake of catch-up HPV vaccination. Methods: An online questionnaire was completed by 591 young women aged 16–20. Results: Of the 350 women who had been offered catch-up HPV vaccination, 90.6% had accepted. In multivariate analyses, vaccine uptake was significantly correlated with subjective norms more supportive of HPV vaccination, and greater uptake of other childhood vaccinations (χ2(3) = 39.34, P < 0.01; 91.1% correctly classified; Nagelkerke pseudo-r2 = 0.23). Among the 241 women aged 16–20 who had not been offered HPV vaccination, the average intention was 3.70 on a five-point scale. Multivariate analyses revealed four significant independent predictors of stronger intentions to accept vaccination: subjective norms more supportive of HPV vaccination, greater worry about sexually transmissible infections, greater support for young people’s sexual health services and greater support for childhood vaccination (F(4,236) = 18.67, P < 0.01; adjusted r2 = 0.23). Young women rated television advertisements, educational programs and television soaps as the most effective ways to encourage uptake of HPV vaccination. Conclusions: Uptake of HPV vaccination may be increased if interventions use appropriate media to promote social norms supportive of HPV vaccination.
Centrobin–tubulin interaction is required for centriole elongation and stability
Authors: Gudi Radhika , Zou Chaozhong , Li Jun , Gao Qingshen
Published: May 2011

Centrobin is a daughter centriole protein that is essential for centrosome duplication. However, the molecular mechanism by which centrobin functions during centriole duplication remains undefined. In this study, we show that centrobin interacts with tubulin directly, and centrobin–tubulin interaction is pivotal for the function of centrobin during centriole duplication. We found that centrobin is recruited to the centriole biogenesis site via its interaction with tubulins during the early stage of centriole biogenesis, and its recruitment is dependent on hSAS-6 but not centrosomal P4.1–associated protein (CPAP) and CP110. The function of centrobin is also required for the elongation of centrioles, which is likely mediated by its interaction with tubulin. Furthermore, disruption of centrobin–tubulin interaction led to destabilization of existing centrioles and the preformed procentriole-like structures induced by CPAP expression, indicating that centrobin–tubulin interaction is critical for the stability of centrioles. Together, our study demonstrates that centrobin facilitates the elongation and stability of centrioles via its interaction with tubulins.
HIV-1 remodels the nuclear pore complex
Authors: Monette Anne , Panté Nelly , Mouland Andrew J.
Published: May 2011

Human immunodeficiency virus type 1 (HIV-1) commandeers host cell proteins and machineries for its replication. Our earlier work showed that HIV-1 induced the cytoplasmic retention of nucleocytoplasmic shuttling and ribonucleic acid (RNA)–binding proteins. This retention is dependent on nuclear export of the viral genomic RNA and on changes in the localization and expression level of the nucleoporin (Nup) p62 (Nup62). To further characterize the extent of perturbation induced by HIV-1, we performed proteomics analyses of nuclear envelopes (NEs) isolated from infected T cells. Infection induced extensive changes in the composition of the NE and its associated proteins, including a remarkable decrease in the abundance of Nups. Immunogold electron microscopy revealed the translocation of Nups into the cytoplasm. Nup62 was identified as a component of purified virus, and small interfering RNA depletion studies revealed an important role for this Nup in virus gene expression and infectivity. This detailed analysis highlights the profound effects on NE composition induced by HIV-1 infection, providing further evidence of the magnitude of viral control over the cell biology of its host.
RhoA and RhoC have distinct roles in migration and invasion by acting through different targets
Authors: Vega Francisco M. , Fruhwirth Gilbert , Ng Tony , Ridley Anne J.
Published: May 2011

Several studies suggest that RhoA and RhoC, despite their sequence similarity, have different roles in cell migration and invasion, but the molecular basis for this is not known. Using RNAi, we show that RhoA-depleted cells became elongated and extended multiple Rac1-driven narrow protrusions in 2D and 3D environments, leading to increased invasion. These phenotypes were caused by combined but distinct effects of the Rho-regulated kinases ROCK1 and ROCK2. Depletion of ROCK2 induced multiple delocalized protrusions and reduced migratory polarity, whereas ROCK1 depletion selectively led to cell elongation and defective tail retraction. In contrast, RhoC depletion increased cell spreading and induced Rac1 activation around the periphery in broad lamellipodia, thereby inhibiting directed migration and invasion. These effects of RhoC depletion are mediated by the formin FMNL3, which we identify as a new target of RhoC but not RhoA. We propose that RhoA contributes to migratory cell polarity through ROCK2-mediated suppression of Rac1 activity in lamellipodia, whereas RhoC promotes polarized migration through FMNL3 by restricting lamellipodial broadening.
Drosophila histone locus bodies form by hierarchical recruitment of components
Authors: White Anne E. , Burch Brandon D. , Yang Xiao-cui , Gasdaska Pamela Y. , Dominski Zbigniew , Marzluff William F. , Duronio Robert J.
Published: May 2011

Nuclear bodies are protein- and RNA-containing structures that participate in a wide range of processes critical to genome function. Molecular self-organization is thought to drive nuclear body formation, but whether this occurs stochastically or via an ordered, hierarchical process is not fully understood. We addressed this question using RNAi and proteomic approaches in Drosophila melanogaster to identify and characterize novel components of the histone locus body (HLB), a nuclear body involved in the expression of replication-dependent histone genes. We identified the transcription elongation factor suppressor of Ty 6 (Spt6) and a homologue of mammalian nuclear protein of the ataxia telangiectasia–mutated locus that is encoded by the homeotic gene multisex combs (mxc) as novel HLB components. By combining genetic manipulation in both cell culture and embryos with cytological observations of Mxc, Spt6, and the known HLB components, FLICE-associated huge protein, Mute, U7 small nuclear ribonucleoprotein, and MPM-2 phosphoepitope, we demonstrated sequential recruitment and hierarchical dependency for localization of factors to HLBs during development, suggesting that ordered assembly can play a role in nuclear body formation.
Lymphatic vascular morphogenesis in development, physiology, and disease
Authors: Schulte-Merker Stefan , Sabine Amélie , Petrova Tatiana V.
Published: May 2011

The lymphatic vasculature constitutes a highly specialized part of the vascular system that is essential for the maintenance of interstitial fluid balance, uptake of dietary fat, and immune response. Recently, there has been an increased awareness of the importance of lymphatic vessels in many common pathological conditions, such as tumor cell dissemination and chronic inflammation. Studies of embryonic development and genetically engineered animal models coupled with the discovery of mutations underlying human lymphedema syndromes have contributed to our understanding of mechanisms regulating normal and pathological lymphatic morphogenesis. It is now crucial to use this knowledge for the development of novel therapies for human diseases.
The conversion of centrioles to centrosomes: essential coupling of duplication with segregation
Authors: Wang Won-Jing , Soni Rajesh Kumar , Uryu Kunihiro , Bryan Tsou Meng-Fu
Published: May 2011

Centrioles are self-reproducing organelles that form the core structure of centrosomes or microtubule-organizing centers (MTOCs). However, whether duplication and MTOC organization reflect innate activities of centrioles or activities acquired conditionally is unclear. In this paper, we show that newly formed full-length centrioles had no inherent capacity to duplicate or to organize pericentriolar material (PCM) but acquired both after mitosis through a Plk1-dependent modification that occurred in early mitosis. Modified centrioles initiated PCM recruitment in G1 and segregated equally in mitosis through association with spindle poles. Conversely, unmodified centrioles segregated randomly unless passively tethered to modified centrioles. Strikingly, duplication occurred only in centrioles that were both modified and disengaged, whereas unmodified centrioles, engaged or not, were “infertile,” indicating that engagement specifically blocks modified centrioles from reduplication. These two requirements, centriole modification and disengagement, fully exclude unlimited duplication in one cell cycle. We thus uncovered a Plk1-dependent mechanism whereby duplication and segregation are coupled to maintain centriole homeostasis.
Seed and grow: a two-step model for nuclear body biogenesis
Authors: Dundr Miroslav
Published: May 2011

Nuclear bodies are dynamic structures that form at sites of specific activities associated with gene expression and genome maintenance. A paper in this issue (White et al. 2011. J. Cell Biol. doi: 10.1083/jcb.201012077) highlights key features of nuclear body biogenesis and suggests a unifying model in which formation of nuclear bodies is driven by nonrandom, biologically determined initial seeding events followed by stochastic self-assembly.
Richard G.W. Anderson (1940–2011) and the birth of receptor-mediated endocytosis
Authors: Brown Michael S. , Goldstein Joseph L.
Published: May 2011

On March 19, 2011, the discipline of cell biology lost a creative force with the passing of Richard G.W. Anderson, Professor and Chairman of the Department of Cell Biology at the University of Texas Southwestern Medical School. An unabashed chauvinist for cell biology, Dick served for many years on the editorial board of The Journal of Cell Biology and the Council of the American Society for Cell Biology. He died of glioblastoma multiforme six days before his 71st birthday.
On the complexity of the relations of isomorphism and bi-embeddability
Authors: Ros Luca
Published: May 2011

Given an

L

ω
1

ω

\mathcal {L}_{\omega _1\omega }

-elementary class

C

\mathcal {C}

, that is, the collection of the countable models of some

L

ω
1

ω

\mathcal {L}_{\omega _1 \omega }

-sentence, denote by

≅

C

\cong _{\mathcal {C}}

and

≡

C

\equiv _{\mathcal {C}}

the analytic equivalence relations of, respectively, isomorphisms and bi-embeddability on

C

\mathcal {C}

. Generalizing some questions of A. Louveau and C. Rosendal, in a paper by S. Friedman and L. Motto  Ros they proposed the problem of determining which pairs of analytic equivalence relations

(
E
,
F
)

(E,F)

can be realized (up to Borel bireducibility) as pairs of the form

(

≅

C

,

≡

C

)

(\cong _{\mathcal {C}}, \equiv _{\mathcal {C}})

,

C

\mathcal {C}

some

L

ω
1

ω

\mathcal {L}_{\omega _1\omega }

-elementary class (together with a partial answer for some specific cases). Here we will provide an almost complete solution to such a problem: under very mild conditions on

E
E

and

F
F

, it is always possible to find such an

L

ω
1

ω

\mathcal {L}_{\omega _1\omega }

-elementary class

C

\mathcal {C}

.
Compatible intertwiners for representations of finite nilpotent groups
Authors: Kamgarpour Masoud , Thomas Teruji
Published: May 2011

We sharpen the orbit method for finite groups of small nilpotence class by associating representations to functionals on the corresponding Lie rings. This amounts to describing compatible intertwiners between representations parameterized by an additional choice of polarization. Our construction is motivated by the theory of the linearized Weil representation of the symplectic group. In particular, we provide generalizations of the Maslov index and the determinant functor to the context of finite abelian groups.
Evaluation of prosthetic-valved devices by means of numerical simulations
Authors: de Tullio M. D. , Pascazio G. , Weltert L. , De Paulis R. , Verzicco R.
Published: May 2011

The
in vivo
evaluation of prosthetic device performance is often difficult, if not impossible. In particular, in order to deal with potential problems such as thrombosis, haemolysis, etc., which could arise when a patient undergoes heart valve replacement, a thorough understanding of the blood flow dynamics inside the devices interacting with natural or composite tissues is required. Numerical simulation, combining both computational fluid and structure dynamics, could provide detailed information on such complex problems. In this work, a numerical investigation of the mechanics of two composite aortic prostheses during a cardiac cycle is presented. The numerical tool presented is able to reproduce accurately the flow and structure dynamics of the prostheses. The analysis shows that the vortical structures forming inside the two different grafts do not influence the kinematics of a bileaflet valve or the main coronary flow, whereas major differences are present for the stress status near the suture line of the coronaries to the prostheses. The results are in agreement with
in vitro
and
in vivo
observations found in literature.
Determination of the zeta potential for highly charged colloidal suspensions
Authors: Giupponi Giovanni , Pagonabarraga Ignacio
Published: May 2011

We compute the electrostatic potential at the surface, or zeta potential
ζ
, of a charged particle embedded in a colloidal suspension using a hybrid mesoscopic model. We show that, for weakly perturbing electric fields, the value of
ζ
obtained at steady state during electrophoresis is statistically indistinguishable from
ζ
in thermodynamic equilibrium. We quantify the effect of counter-ion concentration on
ζ
. We also evaluate the relevance of the lattice resolution for the calculation of
ζ
and discuss how to identify the effective electrostatic radius.
Lattice Boltzmann simulations of bubble formation in a microfluidic T-junction
Authors: Amaya-Bower Luz , Lee Taehun
Published: May 2011

A lattice Boltzmann equation method based on the Cahn–Hilliard diffuse interface theory is developed to investigate the bubble formation process in a microchannel with T-junction mixing geometry. The bubble formation process has different regimes, namely, squeezing, dripping and jetting regimes, which correspond to the primary forces acting on the system. Transition from regime to regime is generally dictated by the capillary number
Ca
, volumetric flow ratio
Q
and viscosity ratio
λ
. A systematic analysis is performed to evaluate these effects. The computations are performed in the range of 10
−4
<
Ca
<1, 1<
Q
<20 and 10
−2
<
λ
<1, with the equilibrium contact angle varying from 30
°
 to 150
°
.
Fast computation of multi-scale combustion systems
Authors: Chiavazzo Eliodoro , Asinari Pietro , Visconti Filippo
Published: May 2011

In the present work, we illustrate the process of constructing a simplified model for complex multi-scale combustion systems. To this end, reduced models of homogeneous ideal gas mixtures of methane and air are first obtained by the novel relaxation redistribution method, and thereafter used for the extraction of all the missing variables in a reactive flow simulation with a global reaction model.
Lattice Boltzmann simulation on continuously regenerating diesel filter
Authors: Yamamoto Kazuhiro , Yamauchi Kazuki , Takada Naoki , Misawa Masaki , Furutani Hirohide , Shinozaki Osamu
Published: May 2011

To reduce particulate matter (PM) including soot in diesel exhaust gas, a diesel particulate filter (DPF) has been developed. Since it is difficult to observe the phenomena in a DPF experimentally, we have conducted a lattice Boltzmann simulation. In this study, we simulated the flow in a metallic filter. An X-ray computed tomography (CT) technique was applied to obtain its inner structure. The processes of soot deposition and oxidation were included for a continuously regenerating diesel filter. By comparing experimental data, a parameter of soot deposition probability in the numerical model was determined.
Direct numerical simulation of particulate flows with heat transfer in a rotating cylindrical cavity
Authors: Schmidt Robin , Nikrityuk Petr A.
Published: May 2011

The purpose of this work was the direct numerical simulation of heat and fluid flow by granular mixing in a horizontal rotating kiln. To model particle behaviour and the heat and fluid flow in the drum, we solve the mass conservation, momentum and energy conservation equations directly on a fixed Eulerian grid for the whole domain including particles. At the same time the particle dynamics and their collisions are solved on a Lagrangian grid for each particle. To calculate the heat transfer inside the particles we use two models: the first is the direct solution of the energy conservation equation in the Lagrangian and Eulerian space, and the second is our so-called linear model that assumes homogeneous distribution of the temperature inside each particle. Numerical simulations showed that, if the thermal diffusivity of the gas phase significantly exceeds the same parameter of the particles, the linear model overpredicts the heating rate of the particles. The influence of the particle size and the angular velocity of the drum on the heating rates of particles is studied and discussed.
Numerical simulations of Rayleigh–Taylor front evolution in turbulent stratified fluids
Authors: Biferale L. , Mantovani F. , Pozzati F. , Sbragaglia M. , Scagliarini A. , Schifano F. , Toschi F. , Tripiccione R.
Published: May 2011

We present state-of-the-art numerical simulations of a two-dimensional Rayleigh–Taylor instability for a compressible stratified fluid. We describe the computational algorithm and its implementation on the QPACE supercomputer. High resolution enables the statistical properties of the evolving interface that we characterize in terms of its fractal dimension to be studied.
Shear banding from lattice kinetic models with competing interactions
Authors: Benzi Roberto , Sbragaglia Mauro , Bernaschi Massimo , Succi Sauro
Published: May 2011

We present numerical simulations based on a Boltzmann kinetic model with competing interactions, aimed at characterizing the rheological properties of soft-glassy materials. The lattice kinetic model is shown to reproduce typical signatures of driven soft-glassy flows in confined geometries, such as Herschel–Bulkley rheology, shear banding and hysteresis. This lends further credit to the present lattice kinetic model as a valuable tool for the theoretical/computational investigation of the rheology of driven soft-glassy materials under confinement.
Transverse harmonic oscillations of laminae in viscous fluids: a lattice Boltzmann study
Authors: Falcucci Giacomo , Aureli Matteo , Ubertini Stefano , Porfiri Maurizio
Published: May 2011

In this paper, we use the lattice Boltzmann method with the Bhatnagar–Gross–Krook linear collision operator to study the flow physics induced by a rigid lamina undergoing moderately large harmonic oscillations in a viscous fluid. We propose a refill procedure for the hydrodynamic quantities in the lattice sites that are in the vicinity of the oscillating lamina. The numerically estimated flow field is used to compute the complex hydrodynamic function that describes the added mass and hydrodynamic damping experienced by the lamina. Results of the numerical simulations are validated against theoretical predictions for small amplitude vibrations and experimental and numerical findings for moderately large oscillations.
Non-steady-state aerosol filtration in nanostructured fibrous media
Authors: Przekop Rafał , Gradoń Leon
Published: May 2011

The filtration of aerosol particles using composites of nano- and microsized fibrous structures is a promising method for the effective separation of nanoparticles from gases. A multi-scale physical system describing the flow pattern and particle deposition at a non-steady-state condition requires an advanced method of modelling. The combination of lattice Boltzmann and Brownian dynamics was used for analysis of the particle deposition pattern in a fibrous system. The dendritic structures of deposits for neutral and charged fibres and particles are present. The efficiency of deposition, deposit morphology, porosity and fractal dimension were calculated for a selected operational condition of the process.
Regional statistics in confined two-dimensional decaying turbulence
Authors: Házi Gábor , Tóth Gábor
Published: May 2011

Two-dimensional decaying turbulence in a square container has been simulated using the lattice Boltzmann method. The probability density function (PDF) of the vorticity and the particle distribution functions have been determined at various regions of the domain. It is shown that, after the initial stage of decay, the regional area averaged enstrophy fluctuates strongly around a mean value in time. The ratio of the regional mean and the overall enstrophies increases monotonously with increasing distance from the wall. This function shows a similar shape to the axial mean velocity profile of turbulent channel flows. The PDF of the vorticity peaks at zero and is nearly symmetric considering the statistics in the overall domain. Approaching the wall, the PDFs become skewed owing to the boundary layer.
Lattice Boltzmann simulations of incompressible liquid–gas systems on partial wetting surfaces
Authors: Shih Ching-Hsiang , Wu Cheng-Long , Chang Li-Chen , Lin Chao-An
Published: May 2011

A three-dimensional Lattice Boltzmann two-phase model capable of dealing with large liquid and gas density ratios and with a partial wetting surface is introduced. This is based on a high density ratio model combined with a partial wetting boundary method. The predicted three-dimensional droplets at different partial wetting conditions at equilibrium are in good agreement with analytical solutions. Despite the large density ratio, the spurious velocity around the interface is not substantial, and is rather insensitive to the examined liquid and gas density and viscosity ratios. The influence of the gravitational force on the droplet shape is also examined through the variations of the Bond number, where the droplet shape migrates from spherical to flattened interface in tandem with the increase of the Bond number. The predicted interfaces under constant Bond number are also validated against measurements with good agreements.
Smoothed particle hydrodynamics-based numerical investigation on sessile, oscillating droplets
Authors: Weiß Dennis , Lienemann Jan , Greiner Andreas , Kauzlarić David , G. Korvink Jan
Published: May 2011

Forced oscillations in sessile droplets can be exploited in electrowetting mixing of fluid fractions. The necessary complex flows and large shape deformations require a numerical investigation of fluid dynamics in the transient regime. We provide a means to characterize oscillations qualitatively and quantitatively with the goal to examine and to classify flow patterns occurring inside. A superposition of different harmonic excitation patterns gives the possibility to control the convective flow. In this investigation, we apply a generic and accurate multi-phase smoothed particle hydrodynamics model to a two-dimensional three-phase flow and consider an oscillating droplet sitting on a substrate and immersed in a fluidic phase. These vibrations are investigated in two ways: the analysis of a step response due to an abrupt change of the contact angle is applied to identify the resonance frequencies. Secondly, the time evolution of the shape of the droplet in terms of harmonic functions is determined. Their amplitudes are examined in the time and frequency domain. This gives the possibility to relate resonance frequencies to mode shapes and to detect a coupling between them. Our approach is successfully applied to different numerical case studies.
Tilting angle and water slippage over hydrophobic coatings
Authors: Chinappi M. , Gala F. , Zollo G. , Casciola C. M.
Published: May 2011

Hydrophobic coatings, such as octadecyltrichlorosilane or n-alkyl monolayers, enhance the slippage of liquids on solid walls. For a given alkyl chain length, the main structural parameter for homogeneous coatings is the tilt angle between coating molecules and the surface normal. In this paper,
ab initio
calculations are used to calculate the equilibrium configuration of coating molecules, showing that the tilt angle easily changes from 0
°
to 30
°
depending on the specific head group binding the solid substrate. These values are used to set up classical molecular dynamics of water slippage over the coatings using different water models (Transferable Intermolecular Potential 3 point (TIP3P), Transferable Intermolecular Potential 4 point (TIP4P) and TIP4P/2005). The slippage is found to be robust with respect to the coating tilting, while a slight dependence on the water model is observed.
Towards aeroacoustic sound generation by flow through porous media
Authors: Hasert Manuel , Bernsdorf Joerg , Roller Sabine
Published: May 2011

In this work, we present single-step aeroacoustic calculations using the Lattice Boltzmann method (LBM). Our application case consists of the prediction of an acoustic field radiating from the outlet of a porous media silencer. It has been proved that the LBM is able to simulate acoustic wave generation and propagation. Our particular aim is to validate the LBM for aeroacoustics in porous media. As a validation case, we consider a spinning vortex pair emitting sound waves as the vortices rotate around a common centre. Non-reflective boundary conditions based on characteristics have been adopted from Navier–Stokes methods and are validated using the time evolution of a Gaussian pulse. We show preliminary results of the flow through the porous medium.
Particle stress in suspensions of soft objects
Authors: Krüger T. , Varnik F. , Raabe D.
Published: May 2011

In a suspension of extended objects such as colloidal particles, capsules or vesicles, the contribution of particles to the stress is usually evaluated by first determining the stress originating from a single particle (e.g. via integrating the fluid stress over the surface of a particle) and then adding up the contributions of individual particles. While adequate for a computation of the average stress over the entire system, this approach fails to correctly reproduce the
local
stress. In this work, we propose and validate a variant of the method of planes which overcomes this problem. The method is particularly suited for many-body interactions arising from, for example, shear and bending rigidity of red blood cells.
Effects of finite mass ratio and inelastic reflection on the interaction between graphene and laminar flow
Authors: Inoue Yohei , Gotoh Toshiyuki
Published: May 2011

A modified boundary condition for the distribution function in the Lattice Boltzmann method at the interface between solid and fluid that takes into account a finite mass ratio between two phases and an inelastic reflection is proposed. The new boundary condition is built into the immersed boundary method to compute the interaction between graphene and laminar flow. Numerical simulations are carried out at a Reynolds number of 40, and drag and lift acting on the graphene and its deformation are examined by changing the mass ratio and the coefficient of restitution. It is found that the amplitude of the oscillating motion of the graphene is enhanced when compared with the case of infinite mass ratio with perfect collision.