Effect Of Energy Dissipation Research Articles

Time-dependent current-density-functional theory taking into consideration the effect of energy dissipation

As a microscopic theory to express the electromagnetic response of the system to the external fields, we present the time-dependent current-density-functional theory (td-CDFT), taking into account the effect of the energy dissipation from the system. In order to express such an effect, the non-Hermitian term which corresponds to the lifetime of the higher-energy component of the many-electron state is added to the Hamiltonian of the system. Specifically, the occupation number of the Bloch states, the energies of which are higher than the Fermi energy, is chosen as a basic variable in addition to the electron density and paramagnetic current density. In order to confirm its validity, the present td-CDFT is applied to the two-level system. We successfully revisit the electric susceptibility of the Drude-Lorentz model via the present theory.

Analytical and experimental studies on buckling-restrained brace with gap-supported tendon protection

This paper proposes a new brace called TP-BRB, composed of a conventional buckling-restrained brace (BRB) with a gap-supported tendon protection (TP) in parallel. The gap-supported tendon protection remains inactive before the deformation of TP-BRB reaches a threshold value, while obtaining a high axial stiffness after the threshold value is exceeded. Under strong earthquake, the TP-BRB is expected to provide structures with effective energy dissipation capacity and mitigate the risks of global collapse caused by low post-yield stiffness of the conventional BRB. As the earliest part of the research on the TP-BRB, this paper firstly presents both the stiffness characteristics of the hysteretic curve and a theoretical formula of residual deformation. Secondly, a quasi-static test is conducted, the results of which illustrate that TP-BRB shows a stable hysteretic behavior, a skeleton curve with significant tri-linear characteristic, and a smaller residual deformation than a conventional BRB. Finally, parametric studies based on numerical models show that, with the reduction of the threshold value (u0) and the increase of the ratio (γ) between the axial stiffness of BRB and gap-supported tendon protection, both the residual deformation and the equivalent damping ratio of TP-BRB decrease, but the secant stiffness of TP-BRB increases.

Optimization Research of Clustered Riverbed Structure Based on Orthogonal Experimental Design

By using the k — ε turbulence model combined with the VOF model, this paper numerically simulates the influence of the size of different baffle piers on the energy dissipation effect of the tufted riverbed structure and the water flow characteristics of the river channel on the the clustered riverbed. The results show that: 1. After changing the size of the baffle piers, it is found that the width has the greatest influence on the energy dissipation rate, followed by the length and finally the height. 2. Under the test conditions, the optimal test group is A2B3C1, which is the test plan No. 6.

Energy Transfer from Perovskite Nanocrystals to Dye Molecules Does Not Occur by FRET.

Single formamidinium lead bromide (FAPbBr3) perovskite nanocubes, approximately 10 nm in size, have extinction cross sections orders of magnitude larger than single dye molecules and can therefore be used to photoexcite one single dye molecule within their immediate vicinity by means of excitation-energy transfer (EET). The rate of photon emission by the single dye molecule is increased by 2 orders of magnitude under excitation by EET compared to direct excitation at the same laser fluence. Because the dye cannot accommodate biexcitons, NC biexcitons are filtered out by EET, giving rise to up to an order-of-magnitude improvement in the fidelity of photon antibunching. We demonstrate here that, contrary to expectation, energy transfer from the nanocrystal to dye molecules does not depend on the spectral line widths of the donor and acceptor and is therefore not governed by Förster's theory of resonance energy transfer (FRET). Two different cyanine dye acceptors with substantially different spectral overlaps with the nanocrystal donor show a similar light-harvesting capability. Cooling the sample from room temperature to 5 K reduces the average transition line widths 25-fold but has no apparent effect on the number of molecules emitting, i.e., on the spatial density of single dye molecules being photoexcited by single nanocrystals. Narrow zero-phonon lines are identified for both donor and acceptor, with an energetic separation of over 40 times the line width, implying a complete absence of spectral overlap-even though EET is evident. Both donor and acceptor exhibit spectral fluctuations, but no correlation is apparent between the jitter, which controls spectral overlap, and the overall light harvesting. We conclude that the energy transfer process is fundamentally nonresonant, implying effective energy dissipation in the perovskite donor because of strong electron-phonon coupling of the carriers comprising the exciton. The work highlights the importance of performing cryogenic spectroscopy to reveal the underlying mechanisms of energy transfer in complex donor-acceptor systems.

Homogeneous and Real Super Tough Multi-Bond Network Hydrogels Created through a Controllable Metal Ion Permeation Strategy.

Poly(acrylic acid) (PAA) hydrogels with a multi-bond network composed of sparse chemical cross-links and carboxyl-Fe3+ coordination are prepared through a controllable permeation strategy utilizing ferric citrate (FeCA). The existing strategies that directly soak PAA hydrogels in Fe3+ solutions usually induce an inhomogeneous network with densely cross-linked shells and uncertain water content of the hydrogels, which brings about ambiguity when investigating strengthening mechanisms because water content significantly affects the mechanical properties of hydrogels. Herein, the controllable permeation of Fe3+ into PAA networks based on the competition between citric acid (CA)-Fe3+ chelation and PAA-Fe3+ coordination guarantees sustained release of Fe3+, facilitating homogeneous distribution of ionic cross-links and a certain water content. The obtained hydrogels exhibit excellent and balanced mechanical properties (high tensile strength of 3.28 to 6.95 MPa with large elongations at break of 1400 to 780% when water content decreases from 80 to 50 wt %). The real robust tensile strength of this hydrogel originates from the effective energy dissipation of the homogeneous PAA-Fe3+ cross-links, and the high water content ensures a large elongation at break. Furthermore, the hydrogel also has pH-responsive and shape-memory properties.

Effects of 3d electron configurations on helium bubble formation and void swelling in concentrated solid-solution alloys

Elemental specific chemical complexity is known to play a critical role in microstructure development in single-phase concentrated solid-solution alloys (SP-CSAs), including both He bubble formation and irradiation-induced void swelling. While cavity formation and evolution under ion irradiation at elevated temperature are complex nonequilibrium processes, chemical effects are revealed at the level of electrons and atoms herein in a simplified picture, using Ni and a special set of Ni-based SP-CSAs composed of 3d transition metals as model alloys. Based on Ni and the model alloys with minimized variables (e.g., atomic mass, size, and lattice structure), we discuss the effects of chemically-biased energy dissipation, defect energetics, sluggish diffusion, and atomic transport on cavity formation and evolution under both self-ion Ni irradiation and He implantation. The observed difference in microstructure evolution is attributed to the effects of d electron interactions in their integrated ability to dissipate radiation energy. The demonstrated impact of alloying 3d transition metals with larger differences in the outermost electron counts suggests a simple design strategy for tuning defect properties to improve radiation tolerance in structural alloys.

Characterizing the Intrinsic Strength (Fatigue Threshold) of Natural Rubber/Butadiene Rubber Blends

ABSTRACT Tires require rubber compounds capable of enduring more than 108 deformation cycles without developing cracks. One strategy for evaluating candidate compounds is to measure the intrinsic strength, which is also known as the fatigue threshold or endurance limit. The intrinsic strength is the residual strength remaining in the material after the strength-enhancing effects of energy dissipation in crack tip fields are removed. If loads stay always below the intrinsic strength (taking proper account of the possibility that the intrinsic strength may degrade with aging), then cracks cannot grow. Using the cutting protocol proposed originally by Lake and Yeoh, as implemented on a commercial intrinsic strength analyzer, the intrinsic strength is determined for a series of carbon black (CB) reinforced blends of natural rubber (NR) and butadiene rubber (BR) typical of tire applications. The intrinsic strength benefits of the blends over the neat NR and BR compounds are only observed after aging at temperatures in the range from 50 to 70 °C, thus providing fresh insights into the widespread durability success of CB-filled NR/BR blends in tire sidewall compounds and commercial truck tire treads.

Characteristics of wave attenuation due to roughness of stepped obstacles

ABSTRACT In this study, we investigated the energy dissipation characteristics of stepped obstacles by using both the regular and irregular waves in a physical wave flume. The stepped obstacle used in this study is different from those of traditional stepped dikes with fixed horizontal and vertical stage surfaces; here, the angle of the stepped surface varies with the slope of the embankment surface, with various interaction angles between the incident waves and the rough stepped surfaces. The stepped embankments were composed of six types of stepped arrangements and were used to analyse the wave run-up heights and reflection coefficients; in addition, the variations in energy dissipation effects were also studied. The results identify two of the six roughness types that have better mitigation effects on the investigated the energy dissipation characteristics of stepped obstacles. The reflection coefficient is larger for a submerged dike with a rough surface than for one with a smooth surface.

Enhanced mechanical property and flame resistance of graphene oxide nanocomposite paper modified with functionalized silica nanoparticles

Graphene oxide (GO) paper with outstanding integrated multiple functionalities (good mechanical performance, thermal stability and flame resistance, etc.) is strongly needed for numerous potential applications in cutting-edge fields. In this work, we report a facile and green process to fabricate GO-based nanocomposite papers via introducing functionalized silica (f-SiO2) nanoparticles. The results reveal that addition of f-SiO2 produces simultaneous improvements in mechanical strength, stiffness and flame resistance for GO paper. With incorporation of 10 wt% f-SiO2, the tensile strength, elastic modulus and toughness of the GO/f-SiO2 nanocomposite papers can be increased by about 51%, 317%, and 69%, respectively. Various characterizations disclose that hydrogen bonds and covalent interactions between GO sheets and f-SiO2 mainly contribute to the effective load transfer and energy dissipation between them, and thus leading to the improvements of mechanical properties. Based on the structural observation and analysis, the improved flame resistance of the GO/f-SiO2 papers should be attributed to the formation of rGO/SiO2 protective char, which are derived from the decomposition and redeposition of the grafted silane molecules and inorganic SiO2 and thermal reduction of GO into rGO. Our results suggest that the mechanical and thermal properties of GO papers can be tuned by introducing inorganic/organic f-SiO2, providing a new route for the rational designing and development of mechanically flexible and flame-retardant GO-based nanocomposite paper materials.

Fabrication of PLLA with High Ductility and Transparence by Blending with Tiny Amount of PVDF and Compatibilizers

AbstractPoly(L‐lactic acid) (PLLA) with high ductility and transparence is fabricated by a blending tiny amount of polyvinylidene fluoride (PVDF) and reactive comb compatibilizers (RCC). Upon blending, the reaction between terminal carboxyl groups in PLLA and expoxy groups in RCC produces graft copolymer (PLLA‐g‐poly(methyl methacrylate) (PMMA)), which locates at the PVDF/PLLA interface due to the balanced stress on two sides. On the one hand, the PVDF domain size decreases remarkably with the help of compatibilization, accounting for the excellent transparence. On the other hand, the interface is enhanced significantly, resulting in an activated PLLA layer surrounding PVDF domains. The thickness exhibits higher magnitude because of the high molecular weight of grafted PLLA (relative to premade compatibilizers). During uniaxial tension, the activated PLLA layers (in addition to PVDF) can cause effective energy absorption and dissipation in the case of percolation of them, which is the reason for the better ductility. These results provide an efficient strategy to improve the ductility and transparence simultaneously.

Scattering and radiation force dependence on properties of empty elastic spherical shells: Low-frequency phase-shift derivation.

It is helpful to evaluate scattering and acoustic radiation forces on spheres for idealized cases in which the effects of energy dissipation are ignorable. Let x denote the product of the acoustic wave number and the sphere's radius. Previously expansions were obtained for fluid and solid spheres involving powers of x and algebraic expressions containing material properties. The present analysis concerns the case of empty elastic shells and reveals how expansion coefficients also depend on shell thickness. Incident waves considered are plane traveling and standing waves, though relevance to Bessel wave-fields is also noted. The expansions give leading-order corrections to the usual Rayleigh scattering approximation.

Investigations of the Hydraulic Characteristics of Stilling Basin with Baffle-Blocks Using an Integrated SPH Method

The stilling basin has been one of the most powerful hydraulic structures for the dissipation of the flow energy. Meshfree and particle methods have special advantages in modeling incompressible flows with free surfaces. In this paper, an integrated smoothed particle hydrodynamics (SPH) method is developed to model energy dissipation process of stilling basins. The integrated SPH includes the kernel gradient correction (KGC) technique, the dynamic solid boundary treatment, [Formula: see text]-SPH model and density reinitialization. We first conducted the simulations of dam-breaking and hydraulic jump to validate the accuracy of the present method. The present simulation results agree well with the experimental observations and numerical results from other sources. Then the discharge process of stilling basin with baffle-blocks is simulated with the integrated SPH. It is demonstrated that the detailed discharge process can be well captured by this method. The energy dissipation effect of stilling basin could be significantly improved by the baffle-blocks. The structure and position of the baffle-block directly affect the energy dissipation effect, while the height of the baffle-block has big influence on the drainage capacity.

Mechanically robust, notch-insensitive, fatigue resistant and self-recoverable hydrogels with homogeneous and viscoelastic network constructed by a novel multifunctional cross-linker

Designing a homogeneous network is an efficient way to improve the mechanical properties of hydrogels. However, the homogeneous hydrogels usually have negligible notch-insensitivity due to the lack of effective energy dissipation, limiting their practical applications in many fields. Herein, we provide a straightforward method to prepare a category of tough and notch-insensitive polyacrylamide hydrogels crosslinked by a novel cross-linker with multiple vinyl functional groups (TA). Due to the multifunctionality of TA, a relatively uniform network with the coexistence of physical cross-links is constructed by the steric effect between chain radicals on TA molecules during the polymerization. The uniform network distributes stress evenly while the physical cross-links lead to viscoelastic dissipated energy under external force. As a result, the hydrogels achieve an ultrastretchability of 2400% and a tensile toughness of 4.33 MJ/m3. Even with a notch of 10 mm, the hydrogels can still be stretched to a strain of 20, indicating an impressive notch-insensitivity. Meanwhile, the hydrogels exhibit high fatigue resistance and good self-recovery. This research offers a facile strategy for designing high-performance hydrogels and may pave the way for their practical application in emerging fields, such as oil displacement agent and artificial cartilage.

Effect of residence time and energy dissipation on drop size distribution for the dispersion of oil in water using KMS and SMX+ static mixer

The Planar Laser Induced Fluorescence technique was used to determine the drop size distribution of oil dispersed in water at the inlet and outlet of two static mixer geometries (KMS and Sulzer_SMX+) equipped with either 6 or 12 elements. A mineral oil (Lytol®), three times more viscous than the water continuous phase, was used as the dispersed phase. The oil flow rate was kept constant through all experiments forcing the drop detachment from the secondary inlet. The L–L system was very dilute (˜0.05–0.0007% v/v O/W) to avoid coalescence phenomena. The flowrate of the continuous phase (water) was altered giving values of Reynolds number from 2000 to 12,000, covering high transitional and turbulent flow regimes. Increasing the flow rate of the continuous phase, the detached oil drops from the secondary inlet decreased in size as expected. However, same drops after flowing a length of 0.4m of an empty pipe reached a constant size. To investigate a wider range of energy dissipation and residence time, the presence of static mixers has been investigated. Pressure drops, hence energy consumed, were measured to compare the different set ups and drop size distributions. The results show that by increasing the flow rate, the drop size decreased up to a critical point, beyond which oil droplet size reduction became inefficient. The collected data were then used to derive a methodology to identify the optimal flow conditions and choice of static mixer device to achieve best drop size reduction with less energy per unit mass.

Conformational manipulation of scale-up prepared single-chain polymeric nanogels for multiscale regulation of cells

Folded single chain polymeric nano-objects are the molecular level soft material with ultra-small size. Here, we report an easy and scalable method for preparing single-chain nanogels (SCNGs) with improved efficiency. We further investigate the impact of the dynamic molecular conformational change of SCNGs on cellular interactions from molecular to bulk scale. First, the supramolecular unfoldable SCNGs efficiently deliver siRNAs into stem cells as a molecular drug carrier in a conformation-dependent manner. Furthermore, the conformation changes of SCNGs enable dynamic and precise manipulation of ligand tether structure on 2D biomaterial interfaces to regulate the ligand–receptor ligation and mechanosensing of cells. Lastly, the dynamic SCNGs as the building blocks provide effective energy dissipation to bulk biomaterials such as hydrogels, thereby protecting the encapsulated stem cells from deleterious mechanical shocks in 3D matrix. Such a bottom-up molecular tailoring strategy will inspire further applications of single-chain nano-objects in the biomedical area.

CFD simulations of a full-loop CFB reactor using coarse-grained Eulerian–Lagrangian dense discrete phase model: Effects of modeling parameters

The hydrodynamics of a 3D full-loop circulating fluidized bed (CFB) reactor were investigated using a coarse-grained dense discrete phase model (DDPM). The effects of changes in key modeling parameters such as the drag force, particle number per parcel, and particle–particle/particle–wall restitution coefficients were thoroughly investigated. Previous experimental data were used as a benchmark for validating the numerical results. In terms of the drag force, the simulation results show that the effect of mesoscale structures on drag force must be considered in the DDPM approach. Regarding the number of particles per parcel, the predictions indicate parcel-independent behavior at all of the coarse-graining ratios tested (dcl/dp = 55, 95, and 125), which is further proof that parcel-independent results can be achieved when the parcel diameter is in the size range of clusters. The effect of energy dissipation from particle–particle (epp) collisions shows that better results are generated when epp is in the non-ideal range (0.1–0.9) than for the ideal case (epp = 1.0). However, the particle–wall restitution coefficient (epw) has little effect on hydrodynamic behavior in either the ideal or non-ideal collision range. In addition, the effect of the particle size distribution on the full-loop hydrodynamics was investigated. The predicted results are similar to those from mean particle diameter simulations, but the distributions for different particles in the CFB are different. This would certainly affect the heat and mass transfer and reactions, and will be further investigated in our ongoing simulations of combustion in CFBs.

A Well-defined Hierarchical Hydrogen Bonding Strategy to Polyureas with Simultaneously Improved Strength and Toughness

A well-defined quadruple hydrogen bonding strategy involving dimerization of 2-ureido-4[1H]-pyrimidone (UPy) units is innovatively designed to prepare polyureas with high overall mechanical properties. Three polyureas containing different amounts of UPy units were synthesized by replacing a portion of isophorone diisocyanate (IPDI) with a UPy-derived diisocyanate. The formation of quadruple hydrogen bonds in hard segments via UPy dimers was confirmed by nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The mechanical properties of the polyureas were evaluated by uniaxial tensile testing. Compared to the polyurea without UPy units, remarkable improvements in Young’s modulus, tensile strength, and toughness were simultaneously achieved when UPy units were incorporated. The mechanism behind the strong strengthening effect rooted in the stronger intermolecular forces among hard segments brought by the quadruple hydrogen bonds, which were stronger than the inherent bidentate and monodentate hydrogen bonds among urea groups, and the slower soft segmental dynamics reaveled by both increased Tg and relaxation time of the soft segments. The mechanism behind the strong toughening effect was ascribed to more effective energy dissipation brought by the quadruple hydrogen bonds that served as stronger sacrificial bonds upon deformation. This work may offer new insight into the design of polyurea elastomers with comprehensively improved mechanical properties.

Innovative seismic resistant structure of shield building with base isolation and tuned-mass-damping for AP1000 nuclear power plants

PurposeSeismic isolation, as an effective risk mitigation strategy of building/bridge structures, is incorporated into AP1000 nuclear power plants (NPPs) to alleviate the seismic damage that may occur to traditional structures of NPPs during their service. This is to promote the passive safety concept in the structural design of AP1000 NPPs against earthquakes.Design/methodology/approachIn conjunction with seismic isolation, tuned-mass-damping (TMD) is integrated into the seismic resistance system of AP1000 NPPs to satisfy the multi-functional purposes. The proposed base-isolation-tuned-mass-damper (BIS-TMD) is studied by comparing the seismic performance of NPPs with four different design configurations (i.e. without BIS, BIS, BIS-TMD and TMD) with the design parameters of the TMD subsystem optimized.FindingsSuch a new seismic protection system (BIS-TMD) is proved to be promising because the advantages of BIS and TMD can be fully used. The benefits of the new structure include effective energy dissipation (i.e. wide vibration absorption band and a stable damping effect), which results in the high performance of NPPs subject to earthquakes with various intensity levels and spectra features.Originality/valueParametric studies are performed to demonstrate the seismic robustness (e.g. consistent performance against the changing mass of the water in the gravity liquid tank and mechanical properties) which further ensures that seismic safety requirements of NPPs can be satisfied through the use of BIS-TMD.

Classified effects of nanofillers on DC breakdown and partial discharge resistance of polypropylene/alumina nanocomposites

The enhancement of DC breakdown strength in polypropylene/alumina nanocomposites (NCs) with low filler content (1 wt%) while the obviously increased partial discharge (PD) resistance at higher filler content (15 and 20 wt%), are observed. Possible mechanisms underlying such contrastive performance are proposed based on considering a combination of electric conductivity, traps distribution and morphology of the eroded test specimen. The DC breakdown is closely related to trap-controlled charge transport and the property is improved for NCs with low filler content. Comparatively, the PD resistance of NCs with higher filler content exhibits longer failure time and more spreading of the eroded area on specimen surface. A model of PD resistance of NCs is proposed on the basis of synergistic effects of energy dissipation by nanoparticle scattering and charge dissipation. The scattering effect on charged ions induced by nanoparticles plays an important role in energy dissipation, and faster charge dissipation along the sample surface induced by shallower traps mitigates energy concentration. Thus two aspects contribute to the improved PD resistance. It is concluded that the effects of nanofillers on short-term DC breakdown and long-term PD resistance are different. A low filler content improves short-term DC breakdown performance whereas a high filler content enhances long-term PD resistance.

Irreversibility Analysis of Hybrid Nanofluid Flow over a Thin Needle with Effects of Energy Dissipation

The flow and heat transfer analysis in the conventional nanofluid A l 2 O 3 − H 2 O and hybrid nanofluid C u − A l 2 O 3 − H 2 O was carried out in the present study. The present work also focused on the comparative analysis of entropy generation in conventional and hybrid nanofluid flow. The flows of both types of nanofluid were assumed to be over a thin needle in the presence of thermal dissipation. The temperature at the surface of the thin needle and the fluid in the free stream region were supposed to be constant. Modified Maxwell Garnet (MMG) and the Brinkman model were utilized for effective thermal conductivity and dynamic viscosity. The numerical solutions of the self-similar equations were obtained by using the Runge-Kutta Fehlberg scheme (RKFS). The Matlab in-built solver bvp4c was also used to solve the nonlinear dimensionless system of differential equations. The present numerical results were compared to the existing limiting outcomes in the literature and were found to be in excellent agreement. The analysis demonstrated that the rate of entropy generation reduced with the decreasing velocity of the thin needle as compared to the free stream velocity. The hybrid nanofluid flow with less velocity was compared to the regular nanofluid under the same circumstances. Furthermore, the enhancement in the temperature profile of the hybrid nanofluid was high as compared to the regular nanofluid. The influences of relevant physical parameters on flow, temperature distribution, and entropy generation are depicted graphically and discussed herein.