Expansion Point Research Articles

A view on coupled cluster perturbation theory using a bivariational Lagrangian formulation.

We consider two distinct coupled cluster (CC) perturbation series that both expand the difference between the energies of the CCSD (CC with single and double excitations) and CCSDT (CC with single, double, and triple excitations) models in orders of the Møller-Plesset fluctuation potential. We initially introduce the E-CCSD(T-n) series, in which the CCSD amplitude equations are satisfied at the expansion point, and compare it to the recently developed CCSD(T-n) series [J. J. Eriksen et al., J. Chem. Phys. 140, 064108 (2014)], in which not only the CCSD amplitude, but also the CCSD multiplier equations are satisfied at the expansion point. The computational scaling is similar for the two series, and both are term-wise size extensive with a formal convergence towards the CCSDT target energy. However, the two series are different, and the CCSD(T-n) series is found to exhibit a more rapid convergence up through the series, which we trace back to the fact that more information at the expansion point is utilized than for the E-CCSD(T-n) series. The present analysis can be generalized to any perturbation expansion representing the difference between a parent CC model and a higher-level target CC model. In general, we demonstrate that, whenever the parent parameters depend upon the perturbation operator, a perturbation expansion of the CC energy (where only parent amplitudes are used) differs from a perturbation expansion of the CC Lagrangian (where both parent amplitudes and parent multipliers are used). For the latter case, the bivariational Lagrangian formulation becomes more than a convenient mathematical tool, since it facilitates a different and faster convergent perturbation series than the simpler energy-based expansion.

Two Degree of Freedom Controller Design by AGTM\\AGMP Matching Method for Time Delay Systems

This paper proposes the design of a general Two Degree Of Freedom (2-DOF) controller for time delay systems using a novel method which combines model order reduction, approximate model matching concepts as well as optimization techniques. The desired spectrum is embodied in the form of a transfer function which can be constructed from a set of time domain specifications. The problem of finding the parameters of the 2-DOF controller is formulated as that of obtaining the solution of a set of non-homogeneous linear equations. These set of non-homogeneous linear equations is obtained by using Approximate Generalized Time Moments (AGTM) matching concept, where closed loop response at certain frequency points in s-plane is matched with that of the desired model response. Using genetic algorithm optimum selection of frequency points (expansion points) in s-plane are obtained, which results in an optimum solution of controller parameters. This leads to a high degree of matching of the closed loop response with that of the desired model. The proposed method not only ensures the stability of the closed loop system with a 2-DOF controller but also satisfies the required performance criteria. The developed method does not pose any restriction on either the order of the model or on the structure/order of the controller transfer function. Moreover, this method is computationally simple and easy to implement. Simulation results demonstrate the effectiveness of the proposed method.

Cellular environmental stimuli-responsive hyaluronan nanocapsules for delivery of anticancer drugs

Event Abstract Back to Event Cellular environmental stimuli-responsive hyaluronan nanocapsules for delivery of anticancer drugs Qiangying Yi1, Jin Ma1 and Zhongwei Gu1 1 Sichuan University, National Engineering Research Center for Biomaterials, China Introduction: Owing to the widely existence in extracellular matrix and specific binding affinity for cancer cell over-expressed HA receptor CD 44, hyaluronan (HA) has been extensively studied for potential applications in drug delivery. In this work we propose using of this biocompatible polymer to build up novel anti-cancer drug DOX (Doxorubicin) delivery system possessing environmental stimuli responsive properties. In general, folic acid (FA) terminated hydrophilic zwitterionic tentacles was designed for “stealthy” transportation and targeted delivery of the carriers; specific tumor environmental signals were applied as triggering stimuli to achieve rapid swell up and burst of the carriers, and thereby to realize fast release of encapsulated anti-cancer drugs. For cellular activation, chemical modification is conducted to functionalize the hyaluronan, GSH sensitive crosslinking sites and pH sensitive expansion points are introduced specifically. When the DOX encapsulated nanocapsules arriving at tumor sites, cellular environmental signals would activate exploding of these nanocapsules, generate pulsatile release of the payloads. This drug release pattern could greatly overcome drug resistance of tumor cells and promisingly achieve a better tumor inhibitory effect. Materials and Methods: Photoinitiator 2,2-dimethoxy-2-phenylaceto-phenone (DPAP) was used to initiate free radical thiol-ene coupling reaction of the thiolated HA and Di-ipr-galactopyranose-ene. Poly(carboxybetaine methacrylate) (pCBMA) was introduced to the side chain of thiolated HA via ATRP reaction. Encapsulation of anticancer drug DOX was carried out using the oil-in-water emulsion approach, and formed HA nanocapsules were simultaneously stabilized through ultrasound-mediated thiol to disulfide bond transition. External stimuli activated size change and DOX release from HA nanocapsules were investigated in aqueous buffer solutions with varied pH values and GSH concentrations. The anticancer activity of the DOX-encapsulated HA nanocapules (DOX/HA-NCs) was evaluated both in vitro and in vivo. Results and Discussion: Anticancer drug was successful encapsulated into HA nanocapsules with the DOX content of 6.5% (w/w). Prepared DOX/HA-NCs were observed as shrunk black dots in TEM (~100 nm), while their hydrodynamic diameter of was determined to be 195±53 nm in water. Significant different pH and GSH conditions between tumor and adjacent normal tissue were applied to trigger HA nanocapsule disassembly and thus to promote drug release. In the buffer mimicking tumor cellular environments (pH 5, GSH 10 mM), HA nanocapsules exhibited a 10-fold size swelling in 2 hours and nearly disassembly within 24 hours, whereas these nanocapsules in PBS (pH 7.4, GSH 0) and tumor microenvironment (pH 6.8, GSH 2.8 μM) showed quite better stability. Drug release profiles revealed that release of the encapsulated DOX molecules could be accelerated remarkably (6~10 times) in tumor cellular environment than that in tumor microenvironments and PBS, indicating great potential to fast release vast majority of drugs in tumor tissue. In vivo evaluation showed that zwitterionic tentacles could help the carriers’ safe transportation in circulation and large accumulation in liver tumor sites; DOX-encapsulated nanocapsules exhibited comparable antitumor efficiency and greatly reduced side effect as compared with the free drug DOX. Conclusions: We fabricated HA nanocapsules for delivery of anticancer drug DOX. Prepared nanocapsules demonstrated good stability in storage and also body circulation. Tumor cellular environmental stimuli (pH and GSH) could be applied to stimulate nanocapsule disassembly and drug release. DOX encapsulated HA nanocapsules performed high inhibition efficiency against HepG2 cells. More importantly, in vivo study revealed their comparable antitumor activity and reduced side effect of free DOX. National Natural Science Foundation of China (81471775); Fundamental Research Funds for the Central Universities (2015SCU04A31)

A Fully Adaptive Scheme for Model Order Reduction Based on Moment Matching

A fully adaptive model order reduction scheme based on moment matching is proposed to derive the reduced-order models of linear time-invariant (LTI) systems. According to the given error tolerance, the order of the reduced-order model as well as the expansion points for the transfer function is automatically determined on the fly during the process of model reduction. In this sense, the reduced-order model is automatically obtained without assigning the number of moments and expansion points in a priori , which is a prerequisite for the standard implementation of model reduction based on moment matching. The proposed adaptive scheme is found to be efficient when it is tested on various LTI systems.

LIQUID LEAD-BISMUTH EUTECTIC AS A COOLANT IN GENERATION IV NUCLEAR REACTORS AND IN HIGH TEMPERATURE SOLAR CONCENTRATOR APPLICATIONS: CHARACTERISTICS, CHALLENGES, ISSUES

Heavy liquid metals have found a wide range of application in energy conversion systems, due to their beneficial thermal properties, especially their low melting points and their capability of operating at higher temperatures without boiling. In addition, the neutronic properties of various liquid metals make them attractive for fusion as well as in Generation IV nuclear reactors. Lately, concentrated solar power (CSP) systems have developed an interest in this technology, calling for temperatures up to 800 o C. The main challenge in realizing engineering scale units is to find proper structural materials that can withstand the corrosion and provide mechanical strength at operation conditions. Lead-Bismuth Eutectic (LBE) is one of the main candidate coolants for liquid metal cooled reactors and solar thermal power applications due to its physical properties such as good thermal conduction, low thermal expansion and melting point, non-violent reactivity to water and low neutron absorption. However, the key limiting factor for LBE usage is the fact of its high corrosiveness to steels and other structural materials. In this work, the results of our systematic materials study in liquid LBE and its alternatives are presented. Various potential structural materials were exposed to LBE, Rose’s metal (Pb-Bi-Sn) and Pb-Bi-Zn eutectic, in static corrosion tests. Post corrosion characterization was conducted by micro-structural analysis (SEM/EDS, X-ray diffraction, Raman spectroscopy) and preferential corrosion mechanisms were evaluated.

Time dependent semiclassical tunneling through one dimensional barriers using only real valued trajectories.

The time independent semiclassical treatment of barrier tunneling has been understood for a very long time. Several semiclassical approaches to time dependent tunneling through barriers have also been presented. These typically involve trajectories for which the position variable is a complex function of time. In this paper, a method is presented that uses only real valued trajectories, thus avoiding the complications that can arise when complex trajectories are employed. This is accomplished by expressing the time dependent wave packet as an integration over momentum. The action function in the exponent in this expression is expanded to second order in the momentum. The expansion is around the momentum, p0(*) , at which the derivative of the real part of the action is zero. The resulting Gaussian integral is then taken. The stationary phase approximation requires that the derivative of the full action is zero at the expansion point, and this leads to a complex initial momentum and complex tunneling trajectories. The "pseudo-stationary phase" approximation employed in this work results in real values for the initial momentum and real valued trajectories. The transmission probabilities obtained are found to be in good agreement with exact quantum results.

Elastodynamic analysis of mode III multiple cracks in a functionally graded orthotropic half-plane

This paper presents a set of dynamic analyses of multiple parallel or perpendicular cracks to the boundary in a functionally graded orthotropic half-plane subjected to anti-plane shear stresses. The material properties are assumed to vary based on an exponential law. Integral transformations (Laplace and Fourier) and Green’s function method are applied to elastodynamic equations. The displacement discontinuous distribution method is used to model the crack problems which are solved by using a set of appropriate boundary conditions. As a result, a set of stress equations with both hypersingular and logarithm singular terms is obtained. Using Chebyshev series expansion and collocation points in Laplace domain, the solution of hypersingular integral equation for multiple cracks is achieved. Finally, different algorithms of numerical Laplace inversion are presented and the dynamic stress intensity factors (DSIFs) are obtained. The presented results are compared with the available published data and a very good agreement is observed. Moreover, it is also demonstrated that the present theoretical study is capable of modeling multiple cracks with different arrangements and variety of FG Orthotropic material properties. Furthermore, influence of FGM constant and shear modulus ratio on the dynamic overshoot of stress intensity is investigated.

Bio-based thermosetting resins composed of aliphatic polyol-derived polymaleimides and allyleugenol

Bio-based bismaleimide (2MPD), trismaleimide (3MGC) and tetramaleimide (4MDG) were synthesized by reactions of 4-isocyanatophenylmaleimide with 1,3-propanediol, glycerol and α,α′-diglycerol, respectively. Although 2MPD did not melt until the temperature where thermal decomposition starts, 3MGC and 4MDG exhibited broad melting temperatures with onset points at 165°C and 124°C, respectively. 3MGC and 4MDG were homogeneously prepolymerized at 170°C with 2,4-diallyl-6-methoxyphenol (rAEG) which was prepared by the Claisen rearrangement of allyl-etherified eugenol (AEG). The prepolymers were compression-molded at 250°C to produce cured rAEG/3MGC (A3Mxy) and rAEG/4MDG (A4Mxy) with the allyl/maleimide ratio of x/y=1/1, 1/2 or 1/3. The FT-IR analysis revealed that the ene reaction of allyl and maleimide groups and subsequent addition copolymerization occurred for the cured resins. The thermal and mechanical properties of the cured resins were compared with those of the cured rAEG/4,4′-bismaleimidodiphenylmethane (BMI) (ABMxy) with the same allyl/maleimide ratio. A3M13 and A4M13 showed no inflection point of thermal expansion due to glass transition until 300°C, which is a little lower than the thermo-degradation temperature. Flexural strengths and flexural strains at break for A3Ms and A4Ms increased with the polymaleimide contents, and those of A3M13 and A4M13 were much higher than those of ABM13.

A fully adaptive rational global Arnoldi method for the model-order reduction of second-order MIMO systems with proportional damping

The model order reduction of second-order dynamical multi-input and multi-output (MIMO) systems with proportional damping arising in the numerical simulation of mechanical structures is discussed. Based on finite element modelling the systems describing the mechanical structures are large and sparse, either undamped or proportionally damped. This work concentrates on a new model reduction algorithm for such second order MIMO systems which automatically generates a reduced system approximating the transfer function in the lower range of frequencies. The method is based on the rational global Arnoldi method. It determines the expansion points iteratively. The reduced order and the number of moments matched per expansion point are determined adaptively using a heuristic based on some error estimation. Numerical examples comparing our results to modal reduction and reduction via the rational block Arnoldi method are presented.

Model Order Reduction for Problems With Dispersive Surface Boundary Conditions

This letter proposes a new scheme for reduced-order finite-element modeling of electromagnetic structures with nonlinear, dispersive surface boundary conditions, which optimally exploits the numerically stable and efficient MOR framework for second-order systems provided by SAPOR method. The presented results of numerical experiments for an example of a waveguide filter demonstrate the superior accuracy of the resulting reduced models both locally, around the expansion point, and over a wide frequency band, as compared to other commonly used methods for approximating the dispersive boundary conditions.

Distributed pedagogy of difference: Reimagining immigrant training and education

In order to integrate into the host labour market, immigrants are often expected and indeed trained to minimize sociocultural differences. This paper problematizes the deficit/dismissive approach towards difference. It stresses instead that, in the context of globalization and immigration, encounters of difference have afforded a potentially productive and permeable space of living, learning, teaching, working and change vis-à-vis the hegemony of western-centric culture and practices. It then advances a distributed pedagogy of difference. The pedagogical proposals made include: 1) turning differences into strength based curriculum; 2) engaging differences to advance knowledge and practices; and 3) experimenting with sociocultural and sociomaterial power and order. Central to these pedagogical proposals is to mark differences as a space of learning and teaching for all, and a point of expansion for sociocultural and sociomaterial practices. This distributed pedagogy incorporates and extends the scholarship of critical pedagogies, and benefits from the practice-based ontology of learning.

Mechanical and thermal properties of calcium–magnesium aluminosilicate (CMAS) glass

Thermal stability of a synthetic sand composition, which was developed as a simulant for calcium–magnesium aluminosilicate (CMAS) turbine deposits, was characterized using thermogravimetric and differential thermal analysis (TG/DTA). The sand was melted into CMAS glass, which had a composition of 23.3CaO–6.4MgO–3.1Al2O3–62.5SiO2–4.1Na2O–0.5K2O–0.04Fe2O3 (mol.%), determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Bulk density of the glass was measured to be 2.63g/cm3, and the Young's and shear moduli were 84.3GPa and 33.6GPa, respectively, along with a Poisson's ratio of 0.26. Vickers microhardness and indentation fracture toughness were determined to be 6.14±0.1GPa and 0.70±0.05MPam1/2, respectively. Glass transition temperature, softening point and coefficient of thermal expansion of the glass were measured by dilatometry. Glass viscosities were estimated over a temperature range of 600–1500°C using dilatometric reference points of the glass and from composition-based methods. Times required for infiltration of molten CMAS glass into thermal or environmental barrier coatings were also estimated.

A New Method for Accurate and Efficient Residual Computation in Adaptive Model-Order Reduction

Projection-based model-order reduction is a powerful methodology for solving parameter-dependent linear systems of equations. The efficient computation of the residual norm is of paramount importance in adaptive model reduction schemes because it is heavily used in error indicators and a posteriori error bounds. These guide the adaptive selection of expansion points in multi-point methods and serve as stopping criteria for subspace enrichment. This paper demonstrates that the standard algorithm for fast residual norm computation leads to premature stagnation, and it presents a new approach of improved accuracy.

Gauge-invariant calculation of static and dynamical magnetic properties from the current density.

In this work we solve two problems related to the calculation of static and dynamical magnetic properties with abinitio theories. First, we show that the dependence of the dynamical magnetic dipole moment on the reference point of the multipole expansion and on the gauge origin of the vector potential have a clear physical significance. They are due to a dynamical electric dipole moment and an electric field, respectively. Both are fully determined by the experimental setup and do not pose any fundamental problem, contrary to what is commonly assumed. Second, in the static case, any dependence on the gauge origin is an artifact of the computational method. We show that the artificial dependence on the gauge origin can be removed in an elegant way by the introduction of a sum rule that puts the diamagnetic and paramagnetic contributions on equal footing. Our approach can be applied to calculate any magnetic observable that can be derived from the current density, and can be used in combination with any abinitio theory from which it can be obtained. To illustrate our method we apply it here to time-dependent current-density-functional theory for the calculation of static and dynamical magnetizabilities of molecules.

A Lagrange series approach to the spectrum of the Kite

A Lagrange series around adjustable expansion points to compute the eigenvalues of graphs, whose characteristic polynomial is analytically known, is presented. The computations for the kite graph P_nK_m, whose largest eigenvalue was studied by Stevanovic and Hansen [D. Stevanovic and P. Hansen. The minimum spectral radius of graphs with a given clique number. Electronic Journal of Linear Algebra, 17:110–117, 2008.], are illustrated. It is found that the first term in the Lagrange series already leads to a better approximation than previously published bounds.

LIQUID LEAD-BISMUTH EUTECTIC AS A COOLANT IN GENERATION IV NUCLEAR REACTORS AND IN HIGH TEMPERATURE SOLAR CONCENTRATOR APPLICATIONS: CHARACTERISTICS, CHALLENGES, ISSUES

Heavy liquid metals have found a wide range of application in energy conversion systems, due to their beneficial thermal properties, especially their low melting points and their capability of operating at higher temperatures without boiling. In addition, the neutronic properties of various liquid metals make them attractive for fusion as well as in Generation IV nuclear reactors. Lately, concentrated solar power (CSP) systems have developed an interest in this technology, calling for temperatures up to 800 oC. The main challenge in realizing engineering scale units is to find proper structural materials that can withstand the corrosion and provide mechanical strength at operation conditions. Lead-Bismuth Eutectic (LBE) is one of the main candidate coolants for liquid metal cooled reactors and solar thermal power applications due to its physical properties such as good thermal conduction, low thermal expansion and melting point, non-violent reactivity to water and low neutron absorption. However, the key limiting factor for LBE usage is the fact of its high corrosiveness to steels and other structural materials. In this work, the results of our systematic materials study in liquid LBE and its alternatives are presented. Various potential structural materials were exposed to LBE, Rose’s metal (Pb-Bi-Sn) and Pb-Bi-Zn eutectic, in static corrosion tests. Post corrosion characterization was conducted by micro-structural analysis (SEM/EDS, X-ray diffraction, Raman spectroscopy) and preferential corrosion mechanisms were evaluated.

Improvement of Krylov-Subspace-Reduced Models by Iterative Mode-Truncation

Model order reduction techniques are well established in control theory and likewise in structural mechanics, e.g. when dealing with Elastic Multi-Body-Systems. Apart from the reduction method used, the objective lies in finding a minimal reliable model dimension with desired quality. Extensive research has been conducted concerning Krylov-subspace methods. Rational Krylov-subspace methods based on the second-order Arnoldi-algorithm (SOAR) turned out to give promising results. Current investigations are about generating an optimal reduced model by iteratively choosing the expansion points based on a predefined model dimension. Still, the sufficient choice of this initial dimension is uncertain.The novel approach consists of a two-stage strategy and starts with a fairly large reduced model based on a fixed number and distribution of expansion points. By an iterative posttreatment, the dispensable Krylov-modes are truncated. For an efficient and fast calculation, a special reordering scheme for the Krylov-modes is introduced. Numerical experiments at different mechanical models show, that the novel technique is comparatively fast and confidently generates reliable models with a minimal dimension.

Simultaneous expander and deep inferior epigastric perforator reconstruction: indications and alloderm sling technique for protecting the anastomosis

Aim: Autologous tissue is considered the gold standard for breast reconstruction today. However, little is known about deep inferior epigastric perforator (DIEP) flap reconstruction in combination with tissue expander (TE)/implant. The authors describe a series of combined DIEP flap/TE reconstruction, including its indications and technique to ensure protection of the pedicle during the expansion process. Methods: Between January 2009 and December 2012, patients undergoing immediate DIEP with TE reconstruction were retrospectively reviewed. Oncologic, comorbid conditions, intraoperative, postoperative expansion, complications, and technique data points were collected. Photographs were taken postoperatively and patient's satisfaction surveys were obtained to assess overall satisfaction. Results: Five patients underwent immediate DIEP flap/TE reconstruction utilizing our alloderm sling technique. There were no complications to the pedicle, flap, expander, or mastectomy skin perioperatively or postoperatively. All patients describe being very satisfied, often with improved breast volume and projection as compared to their preoperative appearance. Conclusion: The results of this study suggest that DIEP flap/TE reconstruction is safe, in particular when utilizing the alloderm sling technique, and should be considered in patients who lack sufficient abdominal tissue, have existing breast asymmetries, or do not desire the scar deformity of latissimus dorsi.

Treading the Boards: the Significance of Walking on the Stage

In this article Kris Darby examines the significance of walking on the theatre stage, responding to the growth of pedestrian performance as an area of research. He seeks to provide a point of expansion for a field that is still largely concerned with site-specific works where audiences walk during the performance. Beginning with a discussion of the possible reasons for the neglect of walking on stage, the author addresses the prominence of walking and the journey as a rehearsal tool employed by a wealth of practitioners. As further justification for the inclusion of the stage in pedestrian performance research, a series of historical case studies is presented which spans over a century of theatrical history, and includes an examination of the audience's pilgrimage to Richard Wagner's Parsifal (1882) and the ‘epic flow“ of Erwin Piscator's treadmill in Good Soldier Schwejk (1927). The significance of walking in Samuel Beckett's life is also explored through the ‘inward walking’ of Footfalls (1976), and the proscenium staging of Matthew Earnest's Wanderlust (2010) is made significant through its critique of supermodernity. The author concludes by arguing that an immobile audience can kinaesthetically empathize with the performers, embarking on their own internalized journey within the theatre. Kris Darby is a Post-Doctoral Teaching Fellow in Drama at Liverpool Hope, whose research interests concern the relationship between walking and performance.

미세기포 생성을 위한 벤츄리 시스템 개발

본 연구는 벤츄리 시스템을 미세기포 생성을 위한 공기공급 장치로 개발하는데 그 목표를 두고 수행하였다. 이를 위해 상용유동해석 프로그램인 ANSYS CFX-15를 사용한 전산 유동해석을 통해 기하학적 형상변화가 벤츄리 관 내 유동특성들에 미치는 영향을 규명하였다 그리고 공급공기를 공급하는 공기 공급관의 위치, 크기, 개수 등을 변수로 2-유체 유동 해석을 수행하여 이들 설계 값들이 공기 공급특성에 미치는 효과를 규명하였다. 최종적으로 직경 비  =0.75의 벤츄리 확대관이 시작되는 위치에 공기 공급 구멍을 설치할 경우 가장 많은 공기가 벤츄리 관으로 유입되는 것을 확인할 수 있었으며, 유입공기 공급구멍 개수 및 직경과 벤츄리 관 내 공급되는 공기량 사이에는 선형적인 관계가 성립됨을 확인하였다.