Effective Energy Density Research Articles

Pneumatic Energy Sources for Autonomous and Wearable Soft Robotics

Many pneumatic energy sources are available for use in autonomous and wearable soft robotics, but it is often not obvious which options are most desirable or even how to compare them. To address this, we compare pneumatic energy sources and review their relative merits. We evaluate commercially available battery-based microcompressors (singly, in parallel, and in series) and cylinders of high-pressure fluid (air and carbon dioxide). We identify energy density (joules/gram) and flow capacity (liters/gram) normalized by the mass of the entire fuel system (versus net fuel mass) as key metrics for soft robotic power systems. We also review research projects using combustion (methane and butane) and monopropellant decomposition (hydrogen peroxide), citing theoretical and experimental values. Comparison factors including heat, effective energy density, and working pressure/flow rate are covered. We conclude by comparing the key metrics behind each technology. Battery-powered microcompressors provide relatively high capacity, but maximum pressure and flow rates are low. Cylinders of compressed fluid provide high pressures and flow rates, but their limited capacity leads to short operating times. While methane and butane possess the highest net fuel energy densities, they typically react at speeds and pressures too high for many soft robots and require extensive system-level development. Hydrogen peroxide decomposition requires not only few additional parts (no pump or ignition system) but also considerable system-level development. We anticipate that this study will provide a framework for configuring fuel systems in soft robotics.

A kinematically-enhanced relaxation scheme for the modeling of displacive phase transformations

In this contribution, a micro-mechanically motivated, energy relaxation-based constitutive model for phase transformation, martensite reorientation and twin formation in shape memory alloys is proposed. The formulation builds on an idealized parametrization of the austenite-twinned martensite microstructure through first- and second-order laminates. To estimate the effective rank-one convex energy density of the phase mixture, the concept of laminate-based energy relaxation is applied. In this context, the evolution of the energetic and dissipative internal state variables, that describe characteristic microstructural features, is computed via constrained incremental energy minimization. This work also suggests a first step towards the continuous modeling of twin formation within the framework of energy relaxation and can be viewed as a generalization of earlier models suggested by Bartel and Hackl (2009) and Bartel et al. (2011). More specifically, in the current model the orientation of martensitic variants in space is not pre-assigned. Variants are rather left free to arrange themselves relative to the martensite-martensite interface in an energy-minimizing fashion, where, however, it is assumed that they form crystallographically-twinned pairs. The formulation also eliminates the need to introduce specific expressions for the Bain strains in each of the martensitic variants, by relating them to a master variant and utilizing the information about their absolute orientation. The predictive capabilities of the proposed modeling framework are demonstrated in several representative numerical examples. In the first part of the results section, the focus is placed on purely energetic analysis, and the particular influence of the different microstructural degrees of freedom on the relaxed energy densities and the corresponding stress-strain responses is investigated in detail. In the second part, macro-homogeneous uniaxial strain and shear loading cases are analyzed for the dissipative case. It is shown, that the proposed model, which, compared to purely phenomenological macro-scale models, has the advantage of strong micro-mechanical motivation, is capable of qualitatively predicting central features of single crystal shape memory alloy behavior, such as the phase diagram in stress-temperature space, and pseudo-elastic and pseudo-plastic responses, while simultaneously providing valuable insight into the underlying micro-scale mechanisms.

Correspondence Between Einstein-Aether Gravity and Scalar Field Dark Energies

Here we briefly discuss the Einstein-Aether gravity theory by modification of Einstein-Hilbert action. We find the modified Friedmann equations and then we find the effective energy density and pressure for Einstein-Aether gravity sector. These can be treated as dark energy provided some restrictions on the free function F(K), where K is proportional to H 2. Subsequently, we study the correspondence between the effective dark energy coming from Einstein-Aether gravity with other dark energies like k-essence, tachyon, dilaton, hessence and DBI-essence dark energy and construct the scalar field and corresponding scalar potentials which describe the dynamics of the scalar fields graphically. So finally, if the Einstein-Aether gravity behaves like other dark energy models, in this situation, the scalar field increases and potential decreases.

Cu-Containing [Pt/Co] Multilayers With Low Saturation Magnetization Suitable for the Pinned Structure

We prepared [Pt/(Co, Cu)] multilayers with a very thin (i.e., 0.2 nm thick) Pt layer and a thicker (i.e., 0.4, 0.5, or 0.6 nm thick) (Co, Cu) layer and investigated the effects of the Cu content in the (Co, Cu) layer and the postannealing temperature on the magnetic properties of the multilayers. The samples in the as-deposited state and those annealed up to 500 °C for 1 h all exhibited perpendicular magnetic anisotropy (PMA). The PMA strength and saturation magnetization both decreased with increasing content of Cu in the samples. The saturation magnetization of the Cu containing multilayers annealed at 500 °C substantially decreased, probably owing to the change in the microstructure from a layered structure in the as-deposited samples to a bulk phase in the annealed ones, as supported by high resolution transmission electron microscopy images. The effective PMA energy density of the samples annealed at high temperatures, on the other hand, remained nearly unchanged and even increased slightly indicating a high postannealing stability of Cu containing multilayers. The Cu-containing multilayers may find potential application to high density magnetic random access memory as the pinned structure of magnetic tunnel junctions because the multilayers showed low saturation magnetizations in the range 164-753 emu/cm\(^{3}\) and high postannealing stability.

Topology optimization of bi-modulus structures using the concept of bone remodeling

Purpose – The purpose of this paper is to develop a heuristic method for topology optimization of a continuum with bi-modulus material which is frequently occurred in practical engineering. Design/methodology/approach – The essentials of this model are as follows: First, the original bi-modulus is replaced with two isotropic materials to simplify structural analysis. Second, the stress filed is adopted to calculate the effective strain energy densities (SED) of elements. Third, a floating reference interval of SED is defined and updated by active constraint. Fourth, the elastic modulus of an element is updated according to its principal stresses. Final, the design variables are updated by comparing the local effective SEDs and the current reference interval of SED. Findings – Numerical examples show that the ratio between the tension modulus and the compression modulus of the bi-modulus material in a structure has a significant effect on the final topology design, which is different from that in the same structure with isotropic material. In the optimal structure, it can be found that the material points with the higher modulus are reserved as much as possible. When the ratio is far more than unity, the material can be considered as tension-only material. If the ratio is far less than unity, the material can be considered as compression-only material. As a result, the topology optimization of continuum structures with tension-only or compression-only materials can also be solved by the proposed method. Originality/value – The value of this paper is twofold: the bi-modulus material layout optimization in a continuum can be solved by the method proposed in this paper, and the layout difference between the structure with bi-modulus material and the same structure but with isotropic material shows that traditional topology optimization result could not be suitable for a real bi-modulus layout design project.

Electric-field effects on magnetic anisotropy and damping constant in Ta/CoFeB/MgO investigated by ferromagnetic resonance

We investigate electric-field effects on the effective magnetic anisotropy energy density Keff and the Gilbert damping constant α in Ta/CoFeB/MgO structures with CoFeB thickness t ranging from 1.4 to 1.8 nm by ferromagnetic resonance. The electric field-induced modulation ratio of the areal energy density Kefft does not depend on the CoFeB thickness, indicating that the electric-field effect on the magnetic anisotropy originates from the modulation of CoFeB/MgO-interfacial magnetic anisotropy. A clear electric-field modulation of α is observed for the structure with t = 1.4 nm, and almost no modulation for the structures with t ≥ 1.5 nm.

An effective friction energy density approach to predict solid lubricant friction endurance: Application to fretting wear

Bonded MoS2 solid lubricant coatings are extensively used in tribology to reduce friction coefficient and wear rate. This coating strategy is particularly appreciated in aeronautical applications to limit fretting wear damage. A major question, however, concerns prediction of endurance for such palliatives (Nc: µ>µc). Focusing on a MoS2-bonded solid lubricant coating fretted against a Ti–6Al–4V counter-body, an extensive fretting wear analysis coupling a large spectrum of contact pressures, sliding amplitudes, contact sizes and contact geometries was undertaken. The study showed that different friction responses could be activated depending on contact pressure and sliding amplitude conditions. Low pressures and small sliding amplitudes induced a lubrication plateau friction response (I) whereas high pressures and large sliding amplitudes induced continuously rising friction combined with titanium transfer (II). The transition from friction response (I) to friction response (II) could be formalised using an “effective” pveff factor. Moreover, bonded-MoS2 coating endurance could be predicted by an “effective friction” energy density parameter expressed as the difference between the nominal friction energy density imputed in the interface and an energy contribution related to the titanium transfer activation. Using this φ–N chart representation, all the experimental friction endurance values followed a single endurance master curve, formalised as an inverse function of the “effective” friction energy density parameter. An equivalent “effective” Archard work density approach is also introduced. Based on a pressure work density parameter, this formulation is easier to apply but displays a wider scatter because friction fluctuations are not taken into consideration.

Entropic-force dark energy reconsidered

We reconsider the entropic-force model in which both kinds of Hubble terms, $\stackrel{\ifmmode \dot{}\else \textperiodcentered \fi{}}{H}$ and ${H}^{2}$, appear in the effective dark energy (DE) density affecting the evolution of the main cosmological functions, namely, the scale factor, deceleration parameter, matter density, and growth of linear matter perturbations. However, we find that the entropic-force model is not viable at the background and perturbation levels due to the fact that the entropic formulation does not add a constant term in the Friedmann equations. On the other hand, if on mere phenomenological grounds we replace the $\stackrel{\ifmmode \dot{}\else \textperiodcentered \fi{}}{H}$ dependence of the effective DE density with a linear term $H$ without including a constant additive term, we find that the transition from deceleration to acceleration becomes possible, but the recent structure formation data strongly disfavor this cosmological scenario. Finally, we briefly compare the entropic-force models with some related DE models (based on dynamical vacuum energy) which overcome these difficulties and are compatible with the present observations.

K-mouflage cosmology: The background evolution

We study the cosmology of K-mouflage theories at the background level. We show that the effects of the scalar field are suppressed at high matter density in the early Universe and only play a role in the late time Universe where the deviations of the Hubble rate from its $\mathrm{\ensuremath{\Lambda}}$-CDM counterpart can be of the order five percent for redshifts $1\ensuremath{\lesssim}z\ensuremath{\lesssim}5$. Similarly, we find that the equation of state can cross the phantom divide in the recent past and even diverge when the effective scalar energy density goes negative and subdominant compared to matter, preserving the positivity of the squared Hubble rate. These features are present in models for which big bang nucleosynthesis is not affected. We analyze the fate of K-mouflage when the nonlinear kinetic terms give rise to ghosts, particle excitations with negative energy. In this case, we find that the K-mouflage theories can only be considered as an effective description of the Universe at low energy below 1 keV. In the safe ghost-free models, we find that the equation of state always diverges in the past and changes significantly by a few percent since $z\ensuremath{\lesssim}1$.

Distributed SUSY breaking: dark energy, Newton’s law and the LHC

We identify the underlying symmetry mechanism that suppresses the low-energy effective 4D cosmological constant within 6D supergravity models, leading to results suppressed by powers of the KK scale relative to the much larger masses associated with particles localized on codimension-2 branes. In these models the conditions for unbroken supersymmetry can be satisfied locally everywhere within the extra dimensions, but are obstructed by global conditions like flux quantization or the mutual inconsistency of boundary conditions at the various branes. Consequently quantities forbidden by supersymmetry cannot be nonzero until wavelengths of order the KK scale are integrated out, since only such long wavelength modes see the entire space and so know that supersymmetry breaks. We verify these arguments by extending earlier rugby-ball calculations of one-loop vacuum energies to more general pairs of branes within two warped extra dimensions. The predicted effective 4D vacuum energy density can be of order C (m Mg/4 pi Mp)^4, where Mg (Mp) is the rationalized 6D (4D) Planck scale and m is the heaviest brane-localized particle. Numerically this is C (5.6 x 10^{-5} eV)^4 if we take m = 173 GeV and take Mg as small as possible (10 TeV corresponding to KK size r < 1 micron), consistent with supernova bounds. C is a constant depending on details of the bulk spectrum, which could be ~ 500 for each of hundreds of fields. The value C ~ 6 x 10^6 gives the observed Dark Energy density.

다공성 기지를 갖는 복합재의 이미지 기반 전산 모형화 및 기공 탄성 계수 산출

Poroelastic analyses of fiber-reinforced composites were performed using image-based computational models. The section image of a porous matrix was analyzed in order to investigate the porosity, number of pores, and distribution of pores. The resolution, location, and size of the section image were considered to quantify the effective elastic modulus, poroelastic parameter, and strain energy density using the image-based computational models. The poroelastic parameter was calculated from the effective elastic modulus and pore pressure-induced strain. In addition, the results of the poroelastic analyses were verified through representative volume elements by simplifying various pore configurations and arrangements. Corresponding Author, esshin@jbnu.ac.kr 2014 The Korean Society of Mechanical Engineers C

Null fluid collapse in brane world models

The brane world description of our universe entails a large extra dimension and a fundamental scale of gravity that may be lower than the Planck scale by several orders of magnitude. An interesting consequence of this scenario occurs in the nature of spherically-symmetric vacuum solutions to the brane gravitational field equations, which often have properties quite distinct from the standard black hole solutions of general relativity. In this paper, the spherically-symmetric collapse on the brane world of four types of null fluid, governed by the barotropic, polytropic, strange quark "bag" model and Hagedorn equations of state, is investigated. In each case, we solve the approximate gravitational field equations, obtained in the high density limit, determine the equation which governs the formation of apparent horizons and investigate the conditions for the formation of naked singularities. Though, naively, one would expect the increased effective energy density on the brane to favor the formation of black holes over naked singularities, we find that, for the types of fluid considered, this is not the case. However, the black hole solutions differ substantially from their general-relativistic counterparts and brane world corrections often play a role analogous to charge in general relativity. As a possible astrophysical application of this work, the possibility that energy emission from a Hagedorn fluid collapsing to form a naked singularity may be a source of GRBs in the brane world is also considered.

Enhanced Bipolar Stacked Switched Capacitor Energy Buffers

The stacked switched capacitor (SSC) energy buffer is a recently proposed architecture for buffering energy between single-phase alternating and direct current. When used with film capacitors, it can increase the life of grid-interfaced power converters by eliminating limited-life electrolytic capacitors while maintaining comparable energy density. This paper introduces an enhanced version of the bipolar SSC energy buffer that achieves higher effective energy density and round-trip efficiency while maintaining the same bus voltage ripple ratio as the original design. Furthermore, the enhanced buffer uses fewer capacitors and switches than the original design. The enhancement in performance is achieved by modifying the control and switching patterns of the buffer switches. A prototype enhanced SSC energy buffer, designed for a 320-V bus and a 135-W load, has been built and tested. The design methodology and experimental results for the enhanced SSC energy buffer are presented and compared with the original design. This paper also presents a comparison of unipolar and bipolar SSC energy buffers. It is shown that, although bipolar designs are superior in terms of effective energy density at low ripple ratios, unipolar designs can outperform bipolar designs at high ripple ratios.

Metamaterial Model of Tachyonic Dark Energy

Dark energy with negative pressure and positive energy density is believed to be responsible for the accelerated expansion of the universe. Quite a few theoretical models of dark energy are based on tachyonic fields interacting with itself and normal (bradyonic) matter. Here we propose an experimental model of tachyonic dark energy based on hyperbolic metamaterials. Wave equation describing propagation of extraordinary light inside hyperbolic metamaterials exhibits 2+1 dimensional Lorentz symmetry. The role of time in the corresponding effective 3D Minkowski spacetime is played by the spatial coordinate aligned with the optical axis of the metamaterial. Nonlinear optical Kerr effect bends this spacetime resulting in effective gravitational force between extraordinary photons. We demonstrate that this model has a self-interacting tachyonic sector having negative effective pressure and positive effective energy density. Moreover, a composite multilayer SiC-Si hyperbolic metamaterial exhibits closely separated tachyonic and bradyonic sectors in the long wavelength infrared range. This system may be used as a laboratory model of inflation and late time acceleration of the universe.

Deriving E = mc2 /22 of Einstein’s Ordinary Quantum Relativity Energy Density from the Lie Symmetry Group SO (10) of Grand Unification of All Fundamental Forces and Without Quantum Mechanics

In the present short letter we aim at deriving the cosmic ordinary effective quantum gravity energy density as well as that of dark energy from the SO (10) Lie symmetry group of grand unification. Remarkably the derivation makes no use of quantum mechanics and remains largely classical except for nonclassical geometry and topology. Finally our main conclusions and results are reinforced using a nonlocal classical elastic field theory.

Effects of Co layer thickness and annealing temperature on the magnetic properties of inverted [Pt/Co] multilayers

The effects of Co layer thickness and annealing temperature on the perpendicular magnetic anisotropy (PMA) properties of inverted [Pt (0.2 nm)/Co (tCo)]6 multilayers (where tCo indicates the thickness of the Co layer) have been investigated. The cross-sectional microstructure, as observed from the high-resolution transmission electron microscope images, shows a clear layered structure with atomically flat interfaces both in the as-deposited state as well as after annealing, indicating the interface effects for PMA. The effective PMA energy density (Keff) increases significantly with an increase in tCo from 0.2 to 0.28 nm and then becomes almost saturated with further increases in tCo, followed by a slight reduction at the highest Co thickness, tCo = 0.6 nm. In order to explain the tCo dependence on Keff, the intrinsic PMA energy density (Ki) is calculated by additionally measuring a similar set of results for the saturation magnetization. The Ki value increases nearly linearly with the increase in tCo from 0.2 to 0.5 nm, followed by saturation at a higher tCo value of 0.6 nm. Owing to a close relationship between Ki and the quality of the interfaces, these results indicate a similar tCo dependence on the quality of the interfaces. This is further supported from the magnetic measurements of the samples annealed at the highest temperature of 500 °C, where a second phase is formed, which show a similar tCo dependence on the amount of the second phase. The Ki value is nearly independent of the annealing temperature at tCo ≤ 0.4 nm, above which a substantial reduction is observed, when the annealing temperature exceeds 500 °C.

Stacked Switched Capacitor Energy Buffer Architecture

Electrolytic capacitors are often used for energy buffering applications, including buffering between single-phase ac and dc. While these capacitors have high energy density compared to film and ceramic capacitors, their life is limited. This paper presents a stacked switched capacitor (SSC) energy buffer architecture and some of its topological embodiments, which when used with longer life film capacitors overcome this limitation while achieving effective energy densities comparable to electrolytic capacitors. The architectural approach is introduced along with design and control techniques. A prototype SSC energy buffer using film capacitors, designed for a 320 V dc bus and able to support a 135 W load, has been built and tested with a power factor correction circuit. It is shown that the SSC energy buffer can successfully replace limited-life electrolytic capacitors with much longer life film capacitors, while maintaining volume and efficiency at a comparable level.

Physical effects of consistent cosmological averaging

We use cosmological perturbation theory to study the backreaction effects of a self-consistent and well-defined cosmological averaging on the dynamics and the evolution of the Universe. Working with a perturbed Friedman-Lemaitre-Robertson-Walker Einstein-de Sitter cosmological solution in a comoving volume-preserving gauge, we compute the expressions for the expansion scalar and deceleration parameter to second order, which we use to characterize the backreaction. We find that the fractional shift in the Hubble parameter with respect to the input background cosmological model is Delta~10^{-5}, which leads to an effective energy density of the order of a few times 10^{-5}. In addition, we find that an appropriate measure of the fractional shift in the deceleration parameter Q is very large.

FROM INFLATION TO DARK ENERGY THROUGH A DYNAMICAL Λ: AN ATTEMPT AT ALLEVIATING FUNDAMENTAL COSMIC PUZZLES

After decades of successful hot big-bang paradigm, cosmology still lacks a framework in which the early inflationary phase of the universe smoothly matches the radiation epoch and evolves to the present "quasi" de Sitter spacetime. No less intriguing is that the current value of the effective vacuum energy density is vastly smaller than the value that triggered inflation. In this paper, we propose a new class of cosmologies capable of overcoming, or highly alleviating, some of these acute cosmic puzzles. Powered by a decaying vacuum energy density, the spacetime emerges from a pure nonsingular de Sitter vacuum stage, "gracefully" exits from inflation to a radiation phase followed by dark matter and vacuum regimes, and, finally, evolves to a late-time de Sitter phase.

Age-Related Variations of Appetite Sensations of Fullness and Satisfaction with Different Dietary Energy Densities in a Large, Free-Living Sample of Japanese Adults

BackgroundThe effective energy density (ED) diet model for customized meal plans has not been adequately explored, and the specific differences in appetite sensation among age groups remain unclear. DesignA randomized, crossover study was conducted in 2010 to examine the effects of lunches with different dietary EDs on sensory properties across age groups. Participants/settingIn this experiment, 276 healthy Japanese subjects aged 22 to 59 years consumed packed lunches over six sessions. Using the control meal (150 g cooked rice, sautéed beef menu containing 40 g raw beef, and 240 g vegetable) as a reference, a high-meat/low-rice meal, a low-vegetable meal, a medium-fat/low-vegetable meal, a high-fat meal, and a high-fat/low-vegetable meal were served as modified test meals with varying macronutrient distribution and ED. Main outcome measuresSubjective levels of fullness and satisfaction were assessed over time by visual analogue scale ratings. Statistical analyses performedData were analyzed using analysis of variance with body mass index as a covariate followed by Bonferroni post hoc tests. ResultsMeals with high vegetable content resulted in greater fullness and satisfaction than meals with low vegetable content, regardless of the diner’s age. Particularly among the 500-kcal low-ED meals, a high-meat meal resulted in greater fullness and satisfaction than a medium-fat/low-vegetable meal among participants aged 30 to 40 years. Postprandial fullness was significantly higher with control meal than with high-meat meal among participants aged 40 to 50 years. ConclusionsThis study indicated that high vegetable content in the low-ED diet model provided sufficient fullness and satisfaction despite the low energy content and increased rice content is more effective for satiety than increased meat content for Japanese adults aged around 40 years.