An efficient complex‐frequency shifted‐perfectly matched layer for second‐order acoustic wave equation

In the context of simulations of wave propagations in unbounded domain, absorbing boundary conditions are often used to truncate the simulation domain to a finite space. Perfectly matched layer (PML) has proven to be an excellent absorbing boundary conditions. However, as this technique was primarily designed for the first‐order equation system, it cannot be applied to the second‐order equation system directly. In this paper, based on a complex‐coordinate stretching technique, we developed a novel, efficient auxiliary‐differential equation form of the complex‐frequency shifted‐PML for the second‐order equation system. This facilitates the use of complex‐frequency shifted‐PML in acoustic simulations based upon wave equations of second‐order form. Compared with previous state‐of‐the‐art methods, the proposed one has the advantage of simpler implementation. It is an unsplit‐field scheme that can be extended to higher‐order discretization schemes conveniently. Numerical results from both homogeneous and heterogeneous computational domains are provided to illustrate the validity of the method. Copyright © 2013 John Wiley & Sons, Ltd.     

A BEM‐level set domain‐decomposition strategy for non‐linear and fragmented interfacial flows

A domain‐decomposition algorithm has been developed to handle two‐phase flows with large deformation, breaking and fragmentation of the interface. The strategy couples a boundary element method with a Navier–Stokes solver combined with a level‐set technique for the tracking of the interface. The former is used in the fluid region where the interface can be modelled as a smooth surface. In the rest of the domain the field solver is applied. This results in an efficient and accurate method. In this paper, the features of the used strategy are described and the challenges connected with the coupling are deeply discussed. The numerical investigation highlighted the importance of a proper rational study when CFD methods are considered. In the present case, a crucial aspect is represented by the domain‐composition step, that is when the information from one solver to the other have to be properly reconstructed and made consistent with the receiver sub‐domain. Copyright © 2006 John Wiley & Sons, Ltd.     

A study of long‐term fMRI reproducibility using data‐driven analysis methods

The reproducibility of functional magnetic resonance imaging (fMRI) is important for fMRI‐based neuroscience research and clinical applications. Previous studies show considerable variation in amplitude and spatial extent of fMRI activation across repeated sessions on individual subjects even using identical experimental paradigms and imaging conditions. Most existing fMRI reproducibility studies were typically limited by time duration and data analysis techniques. Particularly, the assessment of reproducibility is complicated by a fact that fMRI results may depend on data analysis techniques used in reproducibility studies. In this work, the long‐term fMRI reproducibility was investigated with a focus on the data analysis methods. Two spatial smoothing techniques, including a wavelet‐domain Bayesian method and the Gaussian smoothing, were evaluated in terms of their effects on the long‐term reproducibility. A multivariate support vector machine (SVM)‐based method was used to identify active voxels, and compared to a widely used general linear model (GLM)‐based method at the group level. The reproducibility study was performed using multisession fMRI data acquired from eight healthy adults over 1.5 years' period of time. Three regions‐of‐interest (ROI) related to a motor task were defined based upon which the long‐term reproducibility were examined. Experimental results indicate that different spatial smoothing techniques may lead to different reproducibility measures, and the wavelet‐based spatial smoothing and SVM‐based activation detection is a good combination for reproducibility studies. On the basis of the ROIs and multiple numerical criteria, we observed a moderate to substantial within‐subject long‐term reproducibility. A reasonable long‐term reproducibility was also observed from the inter‐subject study. It was found that the short‐term reproducibility is usually higher than the long‐term reproducibility. Furthermore, the results indicate that brain regions with high contrast‐to‐noise ratio do not necessarily exhibit high reproducibility. These findings may provide supportive information for optimal design/implementation of fMRI studies and data interpretation.     

A Fourier‐series‐based virtual fields method for the identification of 2‐D stiffness distributions

The virtual fields method (VFM) is a powerful technique for the calculation of spatial distributions of material properties from experimentally determined displacement fields. A Fourier‐series‐based extension to the VFM (the F‐VFM) is presented here, in which the unknown stiffness distribution is parameterised in the spatial frequency domain rather than in the spatial domain as used in the classical VFM. We present in this paper the theory of the F‐VFM for the case of elastic isotropic thin structures with known boundary conditions. An efficient numerical algorithm based on the two‐dimensional Fast Fourier Transform (FFT) is presented, which reduces the computation time by three to four orders of magnitude compared with a direct implementation of the F‐VFM for typical experimental dataset sizes. Artefacts specific to the F‐VFM (ringing at the highest spatial frequency near to modulus discontinuities) can be largely removed through the use of appropriate filtering strategies. Reconstruction of stiffness distributions with the F‐VFM has been validated on three stiffness distribution scenarios under varying levels of noise in the input displacement fields. Robust reconstructions are achieved even when the displacement noise is higher than in typical experimental fields.Copyright © 2014 John Wiley & Sons, Ltd.     

Extension of MITC to higher‐order beam models and shear locking analysis for compact,thin‐walled,and composite structures

A class of mixed interpolated beam elements is introduced in this paper under the framework of the Carrera Unified Formulation to eliminate the detrimental effects due to shear locking. The Mixed Interpolation of Tensorial Components (MITC) method is adopted to generate locking‐free displacement‐based beam models using general 1D finite elements. An assumed distribution of the transverse shear strains is used for the derivation of the virtual work, and the full Gauss‐Legendre quadrature is used for the numerical computation of all the components of the stiffness matrix. Linear, quadratic, and cubic beam elements are developed using the unified formulation and applied to linear static problems including compact, laminated, and thin‐walled structures. A comprehensive study of how shear locking affects general beam elements when different classical integration schemes are used is presented, evidencing the outstanding capabilities of the MITC method to overcome this numerical issue. Refined beam theories based on the expansion of pure and generalized displacement variables are implemented making use of Lagrange and Legendre polynomials over the cross‐sectional domain, allowing one to capture complex states of stress with a 3D‐like accuracy. The numerical examples are compared to analytic, numerical solutions from the literature, and commercial software solutions, whenever it is possible. The efficiency and robustness of the proposed method demonstrated throughout all the assessments, illustrating that MITC elements are the natural choice to avoid shear locking and showing an unprecedent accuracy in the computation of transverse shear stresses for beam formulations.     

An improved continued‐fraction‐based high‐order transmitting boundary for time‐domain analyses in unbounded domains

A high‐order local transmitting boundary to model the propagation of acoustic or elastic, scalar or vector‐valued waves in unbounded domains of arbitrary geometry is proposed. It is based on an improved continued‐fraction solution of the dynamic stiffness matrix of an unbounded medium. The coefficient matrices of the continued‐fraction expansion are determined recursively from the scaled boundary finite element equation in dynamic stiffness. They are normalised using a matrix‐valued scaling factor, which is chosen such that the robustness of the numerical procedure is improved. The resulting continued‐fraction solution is suitable for systems with many DOFs. It converges over the whole frequency range with increasing order of expansion and leads to numerically more robust formulations in the frequency domain and time domain for arbitrarily high orders of approximation and large‐scale systems. Introducing auxiliary variables, the continued‐fraction solution is expressed as a system of linear equations in iω in the frequency domain. In the time domain, this corresponds to an equation of motion with symmetric, banded and frequency‐independent coefficient matrices. It can be coupled seamlessly with finite elements. Standard procedures in structural dynamics are directly applicable in the frequency and time domains. Analytical and numerical examples demonstrate the superiority of the proposed method to an existing approach and its suitability for time‐domain simulations of large‐scale systems. Copyright © 2011 John Wiley & Sons, Ltd.     

Novel mixed-encoding for forecasting patent grant duration

In an age when data is regarded as the most essential commodity, organizations are racing to use it for better decision making. The quality of the patent portfolio is an important indicator of technological innovation in an organization and its analysis can reveal several indicators linked to the growth of a company. The advancement of machine learning along with the access to large amounts of patent data has led to a paradigm shift from traditional patent data analysis methodologies to novel approaches. A lot of research has been done in this direction for analysing data on patent citations, patent text, IPC class etc. However, much less has been explored regarding the forecast of patent grant duration and its significance for decision making with an even lower focus on data collected from developing countries. This work is built upon our existing study on patent grant duration prediction by devising a novel methodology of encoding the data using a combination of augmented one-hot encoding and label-encoding. Thereafter, methodologies such as Outlier Detection have been applied to this data to yield an improved result vis-à-vis our baseline results. In addition, we identify some of the important factors which impact the decision on grant duration of patent applications using the raw data from the Indian Patent Office.     

On‐Chip Magnetic Platform for Single‐Particle Manipulation with Integrated Electrical Feedback

Methods for the manipulation of single magnetic particles have become very interesting, in particular for in vitro biological studies. Most of these studies require an external microscope to provide the operator with feedback for controlling the particle motion, thus preventing the use of magnetic particles in high‐throughput experiments. In this paper, a simple and compact system with integrated electrical feedback is presented, implementing in the very same device both the manipulation and detection of the transit of single particles. The proposed platform is based on zig‐zag shaped magnetic nanostructures, where transverse magnetic domain walls are pinned at the corners and attract magnetic particles in suspension. By applying suitable external magnetic fields, the domain walls move to the nearest corner, thus causing the step by step displacement of the particles along the nanostructure. The very same structure is also employed for detecting the bead transit. Indeed, the presence of the magnetic particle in suspension over the domain wall affects the depinning field required for its displacement. This characteristic field can be monitored through anisotropic magnetoresistance measurements, thus implementing an integrated electrical feedback of the bead transit. In particular, the individual manipulation and detection of single 1‐μm sized beads is demonstrated.     

Monitoring Based on Narrow‐Band Resonance Raman for “Phase‐Shifting” π‐Conjugated Polydiacetylene Vesicles upon Host–Guest Interaction and Thermal Stimuli

The present study reports a quantified monitoring by means of in situ resonance Raman scattering that analyzes phase‐shifting characteristics of π‐systems upon interacting with target analytes. A chemo‐ and thermochromic polydiacetylene vesicular probe is evaluated with multiple‐wavelength Raman scattering modes in resonance with its phases, respectively, and thus can trace the phase‐shifts. This Raman scattering‐based analytical quantification is also successful in monitoring host–guest recognition events by utilizing much narrower bands, compared to those in conventional absorption or photoluminescence (PL) methods. As one of the outcomes, the monitoring analysis overcomes the limitations based on widely used colorimetric response (%CR) or PL that failed in the case of interaction with a surfactant, CTAB.     

Asynchronous multi‐domain variational integrators for non‐linear problems

We develop an asynchronous time integration and coupling method with domain decomposition for linear and non‐linear problems in mechanics. To ensure stability in the time integration and in coupling between domains, we use variational integrators with local Lagrange multipliers to enforce continuity at the domain interfaces. The asynchronous integrator lets each domain step with its own time step, using a smaller time step where required by stability and accuracy constraints and a larger time step where allowed. We show that in practice the time step is limited by accuracy requirements rather than by stability requirements. Copyright © 2008 John Wiley & Sons, Ltd.     

Semi‐analytical analysis for multi‐directional functionally graded plates: 3‐D elasticity solutions

Semi‐analytical 3‐D elasticity solutions are presented for orthotropic multi‐directional functionally graded plates using the differential quadrature method (DQM) based on the state‐space formalism. Material properties are assumed to vary not only through the thickness but also in the in‐plane directions following an exponential law. The graded in‐plane domain is solved numerically via the DQM, while exact solutions are sought for the thickness domain using the state‐space method. Convergence studies are performed, and the present hybrid semi‐analytical method is validated by comparing numerical results with the exact solutions for a conventional unidirectional functionally graded plate. Finally, effects of material gradient indices on the displacement and stress fields of the plates are investigated and discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Multifunctional RbxWO3 Nanorods for Simultaneous Combined Chemo‐photothermal Therapy and Photoacoustic/CT Imaging

Light‐triggered drug delivery based on near‐infrared (NIR)‐mediated photothermal nanocarriers has received tremendous attention for the construction of cooperative therapeutic systems in nanomedicine. Herein, a new paradigm of light‐responsive drug carrier that doubles as a photothermal agent is reported based on the NIR light‐absorber, Rb _x WO₃ (rubidium tungsten bronze, Rb‐TB) nanorods. With doxorubicin (DOX) payload, the DOX‐loaded Rb‐TB composite (Rb‐TB‐DOX) simultaneously provides a burst‐like drug release and intense heating effect upon 808‐nm NIR light exposure. MTT assays show the photothermally enhanced antitumor activity of Rb‐TB‐DOX to the MCF‐7 cancer cells. Most remarkably, Rb‐TB‐DOX combined with NIR irradiation also shows dramatically enhanced chemotherapeutic effect to DOX‐resistant MCF‐7 cells compared with free DOX, demonstrating the enhanced efficacy of combinational chemo‐photothermal therapy for potentially overcoming drug resistance in cancer chemotherapy. Furthermore, in vivo study of combined chemo‐photothermal therapy is also conducted and realized on pancreatic (Pance‐1) tumor‐bearing nude mice. Apart from its promise for cancer therapy, the as‐prepared Rb‐TB can also be employed as a new dual‐modal contrast agent for photoacoustic tomography and (PAT) X‐ray computed tomography (CT) imaging because of its high NIR optical absorption capability and strong X‐ray attenuation ability, respectively. The results presented in the current study suggest promise of the multifunctional Rb _x WO₃ nanorods for applications in cancer theranostics.     

Finite element analysis of time‐dependent semi‐infinite wave‐guides with high‐order boundary treatment

A new finite element (FE) scheme is proposed for the solution of time‐dependent semi‐infinite wave‐guide problems, in dispersive or non‐dispersive media. The semi‐infinite domain is truncated via an artificial boundary ??, and a high‐order non‐reflecting boundary condition (NRBC), based on the Higdon non‐reflecting operators, is developed and applied on ??. The new NRBC does not involve any high derivatives beyond second order, but its order of accuracy is as high as one desires. It involves some parameters which are chosen automatically as a pre‐process. A C⁰ semi‐discrete FE formulation incorporating this NRBC is constructed for the problem in the finite domain bounded by ??. Augmented and split versions of this FE formulation are proposed. The semi‐discrete system of equations is solved by the Newmark time‐integration scheme. Numerical examples concerning dispersive waves in a semi‐infinite wave guide are used to demonstrate the performance of the new method. Copyright © 2003 John Wiley & Sons, Ltd.     

A non-singular boundary integral formula for frequency domain analysis of the dynamic <Emphasis Type="Italic">T</Emphasis>-stress

A non-singular 2-D boundary integral equation (BIE) in the Fourier-space frequency domain for determining the dynamic T-stress (DTS) is presented in this paper. This formulation, based upon the Fourier transform of the asymptotic expansion for the stress field in the vicinity of a crack tip, can be conveniently implemented as a post-processing step in a frequency-domain boundary element analysis of cracks. The proposed BIE is accurate as it can be directly collocated at the crack tip in question. The technique is also computationally effective as it simply requires a similar computing effort as that used in determining the dynamic stress components at an interior point of a domain. Five numerical examples involving both straight and curved cracks are studied to validate the proposed technique. For the frequency domain analysis of the DTS in these examples, the exponential window method is employed to obtain its time history.     

Magnesium‐Based Micromotors: Water‐Powered Propulsion,Multifunctionality, and Biomedical and Environmental Applications

The new capabilities and functionalities of synthetic micro/nanomotors open up considerable opportunities for diverse environmental and biomedical applications. Water‐powered micromachines are particularly attractive for realizing many of these applications. Magnesium‐based motors directly use water as fuel to generate hydrogen bubbles for their propulsion, eliminating the requirement of common toxic fuels. This Review highlights the development of new Mg‐based micromotors and discusses the chemistry that makes it extremely attractive for micromotor applications. Understanding these Mg properties and its transient nature is essential for controlling the propulsion efficiency, lifetime, and overall performance. The unique and attractive behavior of Mg offers significant advantages, including efficient water‐powered movement, remarkable biocompatibility, controlled degradation, convenient functionalization, and built‐in acid neutralization ability, and has paved the way for multifunctional micromachines for diverse real‐life applications, including operation in living animals. A wide range of such Mg motor‐based applications, including the detection and destruction of environmental threats, effective in‐vivo cargo delivery, and autonomous release, have been demonstrated. In conclusion, the current challenges, future opportunities, and performance improvements of the Mg‐based micromotors are discussed. With continuous innovation and attention to key challenges, it is expected that Mg‐based motors will have a profound impact on diverse biomedical and environmental applications.     

A multi‐modal,multi‐atlas‐based approach for Alzheimer detection via machine learning

The use of biomarkers for early detection of Alzheimer's disease (AD) improves the accuracy of imaging‐based prediction of AD and its prodromal stage that is mild cognitive impairment (MCI). Brain parcellation‐based computer‐aided methods for detecting AD and MCI segregate the brain in different anatomical regions and use their features to predict AD and MCI. Brain parcellation generally is carried out based on existing anatomical atlas templates, which vary in the boundaries and number of anatomical regions. This works considers dividing the brain based on different atlases and combining the features extracted from these anatomical parcellations for a more holistic and robust representation. We collected data from the ADNI database and divided brains based on two well‐known atlases: LONI Probabilistic Brain Atlas (LPBA40) and Automated Anatomical Labeling (AAL). We used baselines images of structural magnetic resonance imaging (MRI) and ¹⁸F‐fluorodeoxyglucose positron emission tomography (FDG‐PET) to calculate average gray‐matter density and average relative cerebral metabolic rate for glucose in each region. Later, we classified AD, MCI and cognitively normal (CN) subjects using the individual features extracted from each atlas template and the combined features of both atlases. We reduced the dimensionality of individual and combined features using principal component analysis, and used support vector machines for classification. We also ranked features mostly involved in classification to determine the importance of brain regions for accurately classifying the subjects. Results demonstrated that features calculated from multiple atlases lead to improved performance compared to those extracted from one atlas only.     

A multi-frontal parallel algorithm for coupled thermo–hydro–mechanical analysis of deforming porous media

In this paper, a multi-frontal parallel algorithm is developed to solve fully coupled heat, water and gas flow in deformable porous media. The mathematical model makes use of the modified effective stress concept together with the capillary pressure relationship and takes phase change and latent heat transfer into account. The chosen macroscopic field variables are displacement, capillary pressure, gas pressure and temperature. The parallel program is developed on a cluster of workstations. The PVM (Parallel Virtual Machine) system is used to handle communications among networked workstations. The multi-frontal method has advantages such as numbering of the finite element mesh in an arbitrary manner, simple programming organization, smaller core requirements and shorter computation times. An implementation of this parallel method on workstations is discussed. The speedup and efficiency of this method is demonstrated and compared with a general domain decomposition method based on band matrix methods by numerical examples. © 1998 John Wiley & Sons, Ltd.     

Parallelized FVM algorithm for three-dimensional viscoelastic flows

 A parallel implementation for the finite volume method (FVM) for three-dimensional (3D) viscoelastic flows is developed on a distributed computing environment through Parallel Virtual Machine (PVM). The numerical procedure is based on the SIMPLEST algorithm using a staggered FVM discretization in Cartesian coordinates. The final discretized algebraic equations are solved with the TDMA method. The parallelisation of the program is implemented by a domain decomposition strategy, with a master/slave style programming paradigm, and a message passing through PVM. A load balancing strategy is proposed to reduce the communications between processors. The three-dimensional viscoelastic flow in a rectangular duct is computed with this program. The modified Phan-Thien–Tanner (MPTT) constitutive model is employed for the equation system closure. Computing results are validated on the secondary flow problem due to non-zero second normal stress difference N ₂. Three sets of meshes are used, and the effect of domain decomposition strategies on the performance is discussed. It is found that parallel efficiency is strongly dependent on the grid size and the number of processors for a given block number. The convergence rate as well as the total efficiency of domain decomposition depends upon the flow problem and the boundary conditions. The parallel efficiency increases with increasing problem size for given block number. Comparing to two-dimensional flow problems, 3D parallelized algorithm has a lower efficiency owing to largely overlapped block interfaces, but the parallel algorithm is indeed a powerful means for large scale flow simulations. Received: 2 July 2002 / Accepted: 15 November 2002 This research is supported by an A^⋆STAR Grant EMT/00/011.     

Trap Healing for High‐Performance Low‐Voltage Polymer Transistors and Solution‐Based Analog Amplifiers on Foil

Solution‐processed semiconductors such as conjugated polymers have great potential in large‐area electronics. While extremely appealing due to their low‐temperature and high‐throughput deposition methods, their integration in high‐performance circuits has been difficult. An important remaining challenge is the achievement of low‐voltage circuit operation. The present study focuses on state‐of‐the‐art polymer thin‐film transistors based on poly(indacenodithiophene‐benzothiadiazole) and shows that the general paradigm for low‐voltage operation via an enhanced gate‐to‐channel capacitive coupling is unable to deliver high‐performance device behavior. The order‐of‐magnitude longitudinal‐field reduction demanded by low‐voltage operation plays a fundamental role, enabling bulk trapping and leading to compromised contact properties. A trap‐reduction technique based on small molecule additives, however, is capable of overcoming this effect, allowing low‐voltage high‐mobility operation. This approach is readily applicable to low‐voltage circuit integration, as this work exemplifies by demonstrating high‐performance analog differential amplifiers operating at a battery‐compatible power supply voltage of 5 V with power dissipation of 11 µW, and attaining a voltage gain above 60 dB at a power supply voltage below 8 V. These findings constitute an important milestone in realizing low‐voltage polymer transistors for solution‐based analog electronics that meets performance and power‐dissipation requirements for a range of battery‐powered smart‐sensing applications.