Bridge’s Overall Structural Scheme Analysis in High Seismic Risk Permafrost Regions

The mechanism of pile-soil reaction in frozen ground is not clear at present, but it is obvious that the reduction of dead weight will be beneficial to the seismic resistance of bridges. In view of the limited bridge engineering practice in high seismic risk permafrost regions, the paper addressed the structural performance of the superstructure and its effect on piles in these special regions. Four superstructures with different dead weights were compared, and bored piles were designed. Numerical simulations were implemented to investigate the refreezing time of the bored pile foundation. The concrete pile cooled rapidly in the first two days. The refreezing times of the GFRP, prestressed concrete T-girder, integrated composite girder, and MVFT girder were 15d, 37d, 39d, and 179d, respectively. The refreezing time of a pile in the same soil layer is mainly affected by the pile’s diameter, and it is significantly correlated to the square of the pile diameter. It reflects that the selection of bridge superstructures in the permafrost region is very important, which has been ignored in previous studies. The pile length and pile diameter of the lighter superstructure can be shorter and smaller to reduce the refreezing time and alleviate the thermal disturbance. Doi: 10.28991/CEJ-2022-08-07-01 Full Text: PD

Dimension-reduced FPK equation for structures excited by filtered noises

Stochastic engineering dynamic actions such as earthquakes and strong wind can be regarded as colored noise with some certain power spectral density functions. By inserting filtering equations the response of the original system could be inverted to a Markov process because most colored noises can be generated through filtering white noises, thus making it possible to adopt the method of FPK equation and other related methods. However, the large dimension of the systems lead to great challenge in the solution of related high-dimensional FPK equations. For this purpose, the present paper proposed a simplified method for the extended system by integrating the highdimensional FPK equation and establishing equivalent drift coefficients, thus resulting in a dimensionreduced FPK equation. The Kanai-Tajimi power spectral density model is used as an example. Inserting the estimated equivalent drift coefficients into the dimension-reduced FPK equation and solving it by the finite difference method leads to the PDF of response of the systems. Numerical examples are illustrated. The method established can be extended to multiplicative noises.Financial support from the National Natural Science Foundation of China (NSFC Grant Nos. 51725804, 51538010 and 11761131014) is greatly appreciated

Experimental Study on Energy Dissipation of Electrolytes in Nanopores

When a nonwetting fluid is forced to infiltrate a hydrophobic nanoporous solid, the external mechanical work is partially dissipated into thermal energy and partially converted to the liquid-solid interface energy to increase its enthalpy, resulting in a system with a superior energy absorption performance. To clarify the energy dissipation and conversion mechanisms, experimental infiltration and defiltration tests of liquid/ion solutions into nanopores of a hydrophobic ZSM-5 zeolite were conducted. The characteristics of energy dissipation were quantified by measuring the temperature variation of the immersed liquid environment and compared against that estimated from pressure-infiltration volume isotherms during infiltration and defiltration stages of the test. Both stages were observed to be endothermic, with the temperature of the liquid phase showing a steady increase with changes in liquid saturation. The confinement of the molecular-sized pore space causes the liquid molecules/ions to transit between statuses of orderly and disorderly motions, resulting in dissipation behaviors that vary with liquid infiltration/defiltration rates and the types and concentrations of additive electrolytes in the liquid—both factors of which alter the characteristics of the nanofluidic transport behavior

Transmission and reflection properties of layered left-handed materials

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2007.Includes bibliographical references (p. 179-189).This thesis is concerned with the reflection and transmission properties of layered left-handed materials (LHM). In particular, the reflection properties of (LHM) slabs are studied for the Goos-Hanchen (GH) lateral shift phenomenon. We demonstrate a unique GH lateral shift phenomenon, which shows that both positive and negative shifts can be achieved using the same LHM slab configuration. This phenomenon is different from previously established cases where the GH lateral shift can be only negative or only positive when different LHM slab configurations are used. We also show that there exist two distinct cases with this unique phenomenon. One case has two regions of incident angles where the GH lateral shift directions are different, while another case has three regions with alternated GH shift directions. A generalized analytical formulation for analyzing the GH lateral shift direction is provided, which reveals that this unique phenomenon is related to the relative amplitudes of the growing and decaying evanescent waves inside the LHM slabs. The energy flux patterns within LHM slabs are further studied to show the influence of the evanescent waves on the GH shift direction change.(cont.) Furthermore, the transmission property of LHM slabs are studied on the finite slabs' maging capability. First, the development of the numerical simulation tool - the Finite-Difference Time-Domain method (FDTD) - investigates the ability of the method to model a perfect lens made of a slab of homogeneous LHM. It is shown that because of the frequency dispersive nature of the medium and the time discretization, an inherent mismatch in the constitutive parameters exists between the slab and its surrounding medium. This mismatch in the real part of the permittivity and permeability is found to have the same order of magnitude as the losses typically used in numerical simulations. Hence, when the LHM slab is lossless, this mismatch is shown to be the main factor contributing to the image resolution loss of the slab. In addition, finite-size LHM slabs are studied both analytically and numerically since they have practical importance in the actual experiments. The analytical method is based on Huygens' principles using truncated current sheets that cover only the apertures of the slabs. It is shown that the main effects on the images' spectra due to the size of the slabs can be predicted by the proposed analytical method, which can, therefore, be used as a fast alternative to numerical simulations.(cont.) Furthermore, the property of negative energy streams at the image plane is also investigated. This unique property is found to be due to the interactions between propagating and evanescent waves and can only occur with LHM slabs, of both finite-size and infinite size. The last part of the thesis deals with multi-layered media for the application to antenna isolations. The setup is with two horn antennas located beneath the ground plane with 10 A distance apart. In order to reduce the coupling between antennas, multi-layered media placed on top of the ground plane need to be designed to suppress the fields. After the problem is simplified to the dipole antenna coupling in infinite slabs, the method to evaluate the fields inside layered media is presented. This method obtains the spectral domain Green's function first and then transforms the fields to the spatial domain using the Sommerfeld-type integration. After the method is validated using right-handed materials (RHM) from references, it is extended to include media like LHM as well as p. negative material and : negative material . The validation with these materials are done by comparing the results with CST microwave studio simulations. The first configuration for the antenna isolation design if one layer slab backed by the grounded plane. Two different approaches are used to find the optimum slab parameters for the isolation.(cont.) One approach is to use Genetic Algorithm (GA) to optimize the slab's constitutive parameters and the thickness for a minimum coupling level. The other approach is to develop an analytic asymptotic expression for the field, and then used the expression to design the slab parameters for the best isolation. We conclude that both approaches yield the same design for the given configuration. The effectiveness of the design is also validated on a grounded finite slab, which is the representation of the actual application. Finally, multi-layered media for the antenna isolation is studied. GA method is applied with an optimization scheme tailed for a five layered structure. We show that GA converges very fast to the solution and the result yields satisfactory isolation between the antennas.by Jianbing James Chen.Ph.D

Thermally Responsive Fluid Behaviors in Hydrophobic Nanopores

A fundamental understanding of the thermal effects on nanofluid behaviors is critical for developing and designing innovative thermally responsive nanodevices. Using molecular dynamics (MD) simulation and experiment, we investigate the temperature-dependent intrusion/adsorption of water molecules into hydrophobic nanopores (carbon nanotubes and nanoporous carbon) and the underlying mechanisms. The critical infiltration pressure is reduced for elevated temperature or increased pore size. The variation of wettability is related to the thermally responsive fluid characteristics, such as the surface tension and contact angle, which arise from the variations of multiple atomic variables including the confined water density, hydrogen bond, and dipole orientation. With thermal perturbation, most of these physical quantities are found to be more significantly influenced in the confined nanoenvironment than in the bulk. By utilizing the prominent thermal effect at the nanoscale, the feasibility and prospective efficiency of employing nanofluidics for energy storage, actuation, and thermal monitoring are discussed

Reliability of base-isolated structures with sliding hydromagnetic bearings considering stochastic ground motions

Stochastic seismic response analysis and reliability assessment of a base-isolated structure with sliding hydro-magnetic bearings are performed combining the probability density evolution method and the stochastic func-tion model of seismic ground motions. The reliability assessments are based on the extreme value distribution of the inter-story drifts of the base-isolated structure. Compared with the responses of the base-fixed struc-ture, the superstructure of the base-isolated structure almost behaves like a rigid body. The sliding hydromag-netic bearing is efficient in reducing the responses by one degree of seismic intensity. Finally, the dynamic re-liability of the base-isolated structure is evaluated, which provides an index for decision making in practice

Mechanical Design and Kinematic Modeling of a Cable-Driven Arm Exoskeleton Incorporating Inaccurate Human Limb Anthropomorphic Parameters

Compared with conventional exoskeletons with rigid links, cable-driven upper-limb exoskeletons are light weight and have simple structures. However, cable-driven exoskeletons rely heavily on the human skeletal system for support. Kinematic modeling and control thus becomes very challenging due to inaccurate anthropomorphic parameters and flexible attachments. In this paper, the mechanical design of a cable-driven arm rehabilitation exoskeleton is proposed to accommodate human limbs of different sizes and shapes. A novel arm cuff able to adapt to the contours of human upper limbs is designed. This has given rise to an exoskeleton which reduces the uncertainties caused by instabilities between the exoskeleton and the human arm. A kinematic model of the exoskeleton is further developed by considering the inaccuracies of human-arm skeleton kinematics and attachment errors of the exoskeleton. A parameter identification method is used to improve the accuracy of the kinematic model. The developed kinematic model is finally tested with a primary experiment with an exoskeleton prototype

ADS-Cap: A Framework for Accurate and Diverse Stylized Captioning with Unpaired Stylistic Corpora

Generating visually grounded image captions with specific linguistic styles using unpaired stylistic corpora is a challenging task, especially since we expect stylized captions with a wide variety of stylistic patterns. In this paper, we propose a novel framework to generate Accurate and Diverse Stylized Captions (ADS-Cap). Our ADS-Cap first uses a contrastive learning module to align the image and text features, which unifies paired factual and unpaired stylistic corpora during the training process. A conditional variational auto-encoder is then used to automatically memorize diverse stylistic patterns in latent space and enhance diversity through sampling. We also design a simple but effective recheck module to boost style accuracy by filtering style-specific captions. Experimental results on two widely used stylized image captioning datasets show that regarding consistency with the image, style accuracy and diversity, ADS-Cap achieves outstanding performances compared to various baselines. We finally conduct extensive analyses to understand the effectiveness of our method. Our code is available at https://github.com/njucckevin/ADS-Cap.Comment: Accepted at Natural Language Processing and Chinese Computing (NLPCC) 202

Mechanisms of water infiltration into conical hydrophobic nanopores

Fluid channels with inclined solid walls (e.g. cone- and slit-shaped pores) have wide and promising applications in micro- and nano-engineering and science. In this paper, we use molecular dynamics (MD) simulations to investigate the mechanisms of water infiltration (adsorption) into cone-shaped nanopores made of a hydrophobic graphene sheet. When the apex angle is relatively small, an external pressure is required to initiate infiltration and the pressure should keep increasing in order to further advance the water front inside the nanopore. By enlarging the apex angle, the pressure required for sustaining infiltration can be effectively lowered. When the apex angle is sufficiently large, under ambient condition water can spontaneously infiltrate to a certain depth of the nanopore, after which an external pressure is still required to infiltrate more water molecules. The unusual involvement of both spontaneous and pressure-assisted infiltration mechanisms in the case of blunt nanocones, as well as other unique nanofluid characteristics, is explained by the Young’s relation enriched with the size effects of surface tension and contact angle in the nanoscale confinement