Estimated Energy Density Research Articles

P2-Type Na2/3Fe1/3Mn1/3Co1/3O2 As a New Positive Electrode for Na-Ion Batteries

Introduction A number of P2-type layered cathode materials have been synthesized as possible candidates for Na-ion battery application. These include Na2/3CoO2 [1], Na2/3Fe1/2Mn1/2O2 [2], Na2/3Co2/3Mn1/3O2 [3] among others. Each of these systems each have a unique set of promising characteristics. We have found another promising candidate for a practical Na-ion cathode material. Na2/3Mn1/3Fe1/3Co1/3O2was synthesized and was found to have high energy density, good cycling stability and low polarization. Experimental Phase pure samples were prepared by conventional solid state reaction at 950 °C in O2 from stoichiometric amounts of Na2O2, MnO2, Fe3O4 and Co3O4. X-ray diffraction (XRD) patterns were measured under Ar gas in a gas-tight sample holder. Electrodes were prepared from a slurry with 80% by weight active material, 12% Super-P carbon black and 8% PVDF binder dissolved in NMP. The slurry was then coated on Al foil using a coating bar with a 0.006" gap and dried in air for several hours at 120 °C. 2325 coin-type cells were constructed using 1M NaClO4(98% purity) dissolved in PC electrolyte with 2% by volume FEC. Two Celgard 3501 separators, one blown microfiber separator (3M Company) and a sodium foil counter electrode (Aldrich) were used. Cells were cycled with constant 10 mA/g current in indicated voltage ranges. Results and Discussion Figure 1 shows an XRD pattern of Na2/3Mn1/3Co1/3Fe1/3O2. The pattern shows no noticeable impurities. The pattern was fit using a Rietveld refinement with the P63/mmc space group. Lattice parameters of a = 2.89 Å and c = 11.1 Å were obtained, corresponding to a bulk density of 4.30 g/mL at 2/3 sodiation.Figure 2 shows the first cycle voltage profile for Na2/3Mn1/3Co1/3Fe1/3O2 when charged to different voltages. It was found that substitution of Co into NaxFe1/2Mn1/2O2causes an increase in average voltage [2, 4]. Upon sodiation from 4.5 V, an average voltage of 3.00 V is achieved with 173 Ah/kg / 745 Ah/L of reversible capacity, yielding an estimated energy density of ~ 520 Wh/kg / 2240 Wh/L. When cycled to 4.0 V, average voltage is 2.77 V but the energy density is reduced to ~ 350 Wh/kg (1510 Wh/L), resulting from less access of the high voltage plateau.Figure 2 also shows some of the consequences of accessing voltages above 4.1V using the current electrolyte formulation. Increasing use of the plateau increases voltage hysteresis and reduces reversibility, as evidenced by the decreasing negative capacity of the subsequent sodiation half-cycle. Ex-situ Mössbauer studies and the electrochemical performance of P2-type Na2/3Fe1/3Mn1/3Co1/3O2will be presented. Figure captions Figure 1 Rietveld refinement of the P2-Na2/3Fe1/3Mn1/3Co1/3O2XRD pattern. Figure 2 First cycle voltage profile of P2-Na2/3Fe1/3Mn1/3Co1/3O2at different cutoff voltages.

An advanced lithium-ion battery based on a graphene anode and a lithium iron phosphate cathode.

We report an advanced lithium-ion battery based on a graphene ink anode and a lithium iron phosphate cathode. By carefully balancing the cell composition and suppressing the initial irreversible capacity of the anode in the round of few cycles, we demonstrate an optimal battery performance in terms of specific capacity, that is, 165 mAhg(-1), of an estimated energy density of about 190 Wh kg(-1) and a stable operation for over 80 charge-discharge cycles. The components of the battery are low cost and potentially scalable. To the best of our knowledge, complete, graphene-based, lithium ion batteries having performances comparable with those offered by the present technology are rarely reported; hence, we believe that the results disclosed in this work may open up new opportunities for exploiting graphene in the lithium-ion battery science and development.

Correlated noise in networks of gravitational-wave detectors: Subtraction and mitigation

One of the key science goals of advanced gravitational-wave detectors is to observe a stochastic gravitational-wave background. However, recent work demonstrates that correlated magnetic fields from Schumann resonances can produce correlated strain noise over global distances, potentially limiting the sensitivity of stochastic background searches with advanced detectors. In this paper, we estimate the correlated noise budget for the worldwide advanced detector network and conclude that correlated noise may affect upcoming measurements. We investigate the possibility of a Wiener filtering scheme to subtract correlated noise from Advanced LIGO searches, and estimate the required specifications. We also consider the possibility that residual correlated noise remains following subtraction, and we devise an optimal strategy for measuring astronomical parameters in the presence of correlated noise. Using this new formalism, we estimate the loss of sensitivity for a broadband, isotropic stochastic background search using 1 yr of LIGO data at design sensitivity. Given our current noise budget, the uncertainty with which LIGO can estimate energy density will likely increase by a factor of $\ensuremath{\approx}12$---if it is impossible to achieve significant subtraction. Additionally, narrow band cross-correlation searches may be severely affected at low frequencies $f\ensuremath{\lesssim}70\text{ }\text{ }\mathrm{Hz}$ without effective subtraction.

Estimates of relativistic electron and proton energy densities in starburst galactic nuclei from radio measurements

The energy density of energetic protons, U_p, in several nearby starburst nuclei (SBNs) has been directly deduced from gamma-ray measurements of the radiative decay of neutral pions produced in interactions with ambient protons. Lack of sufficient sensitivity and spatial resolution makes this direct deduction unrealistic in the foreseeable future for even moderately distant SBNs. A more viable indirect method for determining U_p in star-forming galaxies is to use its theoretically based scaling to the energy density of energetic electrons, U_e, which can be directly deduced from radio synchrotron and possibly also nonthermal hard X-ray emission. In order to improve the quantitative basis and diagnostic power of this leptonic method we reformulate and clarify its main aspects. Doing so we obtain a basic expression for the ratio U_p/U_e in terms of the proton and electron masses and the power-law indices that characterize the particle spectral distributions in regions where the total particle energy density is at equipartition with that of the mean magnetic field. We also express the field strength and the particle energy density in the equipartition region in terms of the region's size, mean gas density, IR and radio fluxes, and distance from the observer, and determine values of U_p in a sample of nine nearby and local SBNs.

P2-Type Na2/3Ni1/3Mn2/3- x Ti x O2 as a 3.7 V Class Positive Electrode for Na-Ion Batteries

IntroductionLayered Na x MeO2 (Me = transition metal) compounds have been intensively studied as electrode materials for Na-ion batteries. Among them, P2-Na2/3Fe1/2Mn1/2O2 and O3-NaFe0.5Co0.5O2 can deliver 200 and 160 mAh g-1 of reversible capacity with relatively good capacity retention, respectively.1, 2 However, average operating potential of Na x MeO2 is usually lower than that of Li x MeO2, resulting in lower energy density of Na-ion cell. To increase the operating voltage of Na-ion batteries, we focus on P2-Na2/3Ni1/3Mn2/3O2 showing relatively high operating voltage based on a Ni2+/Ni4+ redox couple.3 The discharge capacity of Na//Na2/3Ni1/3Mn2/3O2 cell is, however, limited to only 80 mAh g-1 because of rapid capacity decay during cycles by charge to 4.5 V.4 In this study, we present synthesis and improved electrode performance of titanium substituted Na2/3Ni1/3Mn2/3-x Ti x O2 as positive electrode materials.ExperimentalNa2/3Ni1/3Mn2/3-x Ti x O2 (x = 0, 1/6, 1/3, 2/3) samples were prepared by solid-state reaction from starting materials of Na2CO3, NiO, TiO2, and Mn2O3. The mixture was pelletized and heated at 900-950 °C for 12 h in air. Crystal structures and morphology of the samples were examined by using powder X-ray diffraction (XRD) measurement and scanning electron microscopy (SEM). Electrochemical properties were tested using a coin-type cell. Positive electrodes consisted of the active material, acetylene black and polyvinylidenefluoride(PVdF) with a gravimetric ratio of 80:10:10. Metallic sodium was used as a negative electrode. The electrolyte used was 1.0 mol dm-3 NaPF6 / PC.Results and discussionAll diffraction lines in XRD patterns of synthesized Na2/3Ni1/3Mn2/3-x Ti x O2 (x = 0, 1/6, 1/3, 2/3) samples can be assigned into the P2-type layered structure with space group P63/mmc without any impurities. The calculated lattice parameters linearly increase by the substitution of Ti for Mn, and its increase obeys Vegard’s law with the consideration of larger ionic size of Ti4+ than Mn4+, suggesting that a solid solution is successfully synthesized in the range of 0 ≤ x ≤ 2/3 in Na2/3Ni1/3Mn2/3-x Ti x O2 samples. The substitution of titanium effectively improves capacity retention even though reversible capacity decreases with the titanium substitution. Figure 1 shows charge/discharge curves of a Na//Na2/3Ni1/3Mn1/2Ti1/6O2 cell. Among the substituted samples, the Na2/3Ni1/3Mn1/2Ti1/6O2 particularly delivers 127 mAh g-1 of reversible capacity with ca. 3.7 V of average discharge voltage for the initial cycle with relatively good capacity retention. Ex-situ XRD results reveal that volume shrinkage of the fully charged state is effectively reduced from 23% for Ti-free to 12-13% for Ti-substituted ones, which probably leads to the improved cycle stability. Estimated energy density of a Na//Na2/3Ni1/3Mn1/2Ti1/6O2 cell reaches 470 Wh kg-1 and that of a hard-carbon//Na2/3Ni1/3Mn1/2Ti1/6O2 full cell achieves 300 Wh kg-1, corresponding to approximately 80% of energy density for the graphite//LiCoO2 system. Na2/3Ni1/3Mn1/2Ti1/6O2 is one of the higher energy density materials for Na-ion batteries with good cyclability among layered oxides reported so far. Influence of the titanium substitution on structural changes during charge and electrochemical properties will be further discussed.

Thermal Energy Harvesting Using Bulk Lead‐Free Ferroelectric Ceramics

This article demonstrates the energy harvesting capabilities of bulk lead‐free ferroelectric materials using Olsen cycle. Lead‐free compositions K[(Nb0.90Ta0.10)0.99Mn0.01]O3 (KNTM) and 0.5Ba(Zr0.2Ti0.8)O3‐0.5(Ba0.7Ca0.3)TiO3 (BZT‐50BCT) have been explored for their energy harvesting capabilities. Further, we studied the variation in energy density over wide range of applied temperature and electric field. The maximum harness‐able energy density for KNTM and BZT‐50BCT compositions are found to be 629 J/L (629 kJ/m3) and 87 J/L (87 kJ/m3), respectively. This estimated energy density, obtained for the bulk samples, is comparable with the highest energy density reported to‐date (888 J/L for lanthanum‐doped lead zirconate titanate (8/65/35 PLZT) thick films).

Fall-grown oat to extend the fall grazing season for replacement dairy heifers

Our objective was to assess the pasture productivity and forage characteristics of 2 fall-grown oat (Avena sativa L.) cultivars, specifically for extending the grazing season and reducing reliance on harvested forages by replacement dairy heifers. A total of 160 gravid Holstein heifers (80 heifers/yr) were stratified by weight, and assigned to 1 of 10 identical research pens (8 heifers/pen). Initial body weights were 480±43.5kg in 2011 and 509±39.4kg in 2012. During both years of the trial, four 1.0-ha pasture replicates were seeded in August with Ogle oat (Schumitsch Seed Inc., Antigo, WI), and 4 separate, but similarly configured, pasture replicates were seeded with Forage Plus oat (Kratz Farms, Slinger, WI). Heifer groups were maintained as units, assigned to specific pastures, and then allowed to graze fall-oat pastures for 6h daily before returning to the barn, where they were offered a forage-based basal total mixed ration. Two heifer groups were retained in confinement (without grazing) as controls and offered the identical total mixed ration as pasture groups. During 2011, available forage mass increased with strong linear and quadratic effects for both cultivars, peaking at almost 9Mg/ha on October 31. In contrast, forage mass was not affected by evaluation date in 2012, remaining ≤2,639kg/ha across all dates because of droughty climatic conditions. During 2012, Ogle exhibited greater forage mass than Forage Plus across all sampling dates (2,678 vs. 1,856kg/ha), largely because of its more rapid maturation rate and greater canopy height. Estimates of energy density for oat forage ranged from 59.6 to 69.1% during 2011, and ranged narrowly from 68.4 to 70.4% during 2012. For 2011, responses for both cultivars had strong quadratic character, in which the most energy-dense forages occurred in mid November, largely due to accumulation of water-soluble carbohydrates that reached maximum concentrations of 18.2 and 15.1% for Forage Plus and Ogle, respectively. Across the 2-yr trial, average daily gain for grazing heifer groups tended to be greater than heifers remaining in confinement (0.85 vs. 0.74kg/d), but both management strategies produced weight gains within reasonable proximity to normal targets for heifers in this weight range. Fall-grown oat should be managed as stockpiled forage for deferred grazing, and good utilization of fall-oat forage can be accomplished by a one-time removal of standing forage, facilitated by a single lead wire advanced daily to prevent waste.

An analysis of lead-free (Bi0.5Na0.5)0.915-(Bi0.5K0.5)0.05Ba0.02Sr0.015TiO3 ceramic for efficient refrigeration and thermal energy harvesting

This article demonstrates the colossal energy harvesting capability of a lead-free (Bi0.5Na0.5)0.915-(Bi0.5K0.5)0.05Ba0.02Sr0.015TiO3 ceramic using the Olsen cycle. The maximum harvestable energy density estimated for this system is found to be 1523 J/L (1523 kJ/m3) where the results are presented for extreme ambient conditions of 20–160 °C and electric fields of 0.1–4 MV/m. This estimated energy density is 1.7 times higher than the maximum reported to date for the lanthanum-doped lead zirconate titanate (thin film) system. Moreover, this study introduces a generalized and effective solid state refrigeration cycle in contrast to the ferroelectric Ericson refrigeration cycle. The cycle is based on a temperature induced polarization change on application of an unipolar electric field to ferroelectric ceramics.

Monolithic Ceramic Redox Materials for Thermochemical Heat Storage Applications in CSP Plants

The present work relates to the investigation of cobalt and manganese oxide based compositions as candidate materials for the storage of surplus energy, available in the form of heat, generated from high temperature concentrated solar power plants (e.g. solar tower, solar dish) via a two-step thermochemical cyclic redox process under air flow. Emphasis is given on the utilization of small structured monolithic bodies (flow-through pellets) made entirely from the two aforementioned oxides. As compared to the respective powders, and in addition to the natural advantage of substantially lower pressure drop that monolithic structures can offer, this study demonstrated that structured bodies can also improve redox kinetics to a measurable extent. Cobalt oxide was found to be superior to manganese oxide both from an estimated energy density and from a redox reactions kinetics point-of-view. Among the redox conditions studied, the optimum reduction-oxidation operating window for the former oxide was determined to be in the range of 1000-800°C, while for the latter material no clear conclusion was drawn with reduction reaching its maximum extent at 1000°C and oxidation occurring in the range of 500-650°C. In both cases, no significant degradation of redox performance was observed upon cyclic operation (up to 10 cycles), however manganese oxide showed notably slower oxidation kinetics.

Na2CoPO4F as a High-voltage Electrode Material for Na-ion Batteries

A sodium-containing layered cobalt fluorophosphate, Na2CoPO4F, is prepared by a solid-state method. Electrode performance of the Na2CoPO4F is first examined as a positive electrode material for non-aqueous Na batteries. The carbon-modified Na2CoPO4F delivers 100 mAh g−1 of initial discharge capacity with a nearly flat voltage plateau at approximately 4.3 V vs. Na metal. The estimated energy density as a positive electrode material reaches 407 Wh kg−1 based on metallic sodium. Na2CoPO4F exhibits the highest operating voltage in a series of Na2MePO4F (Me = Fe, Co, and Mn).

Application of graphite–solid electrolyte composite anode in all-solid-state lithium secondary battery with Li2S positive electrode

Abstract Graphite–solid electrolyte (SE) composite anode, prepared by spark-plasma-sintering (SPS) process, was applied to all-solid-state lithium secondary batteries with lithium sulfide (Li 2 S) positive electrode. The electrochemical tests demonstrated that the graphite–SE/Li 2 S cells showed the discharge capacity of ca . 750 mAh·g − 1 -Li 2 S with the average voltage of ca . 1.98 V. Although the discharge capacity was lower than that of the In/Li 2 S cells ( ca . 920 mAh·g − 1 -Li 2 S), the estimated energy density was higher than that ( ca . 1490 and 1220 mWh·g − 1 -Li 2 S for graphite–SE/Li 2 S and In/Li 2 S cells, respectively), due mainly to its higher average voltage. The graphite–SE/Li 2 S cells showed improved rate capability as compared with the cells with the graphite + SE blended powder, which was attributable mainly to the reduced interfacial resistance between the graphite and SE particles caused by the SPS process.

Property optimization of BST-based composite glass ceramics for energy-storage applications

Abstract A series of Ba 0.4 Sr 0.6 TiO 3 (BST)-based glass ceramics with different content of BST additive was prepared via sintering and crystallization route, and the subsequent phase evolution, microstructure and dielectric properties were investigated. Results showed that the BST additive obviously improved the dielectric constant of the BST-based glass ceramics. In addition, BST additive can modify the microstructure and reduce the activation energy of grain boundary, which led to an improvement in the dielectric breakdown strengths. The estimated energy density of BST-based glass ceramics with optimized composition reached up to 2.81 J/cm 3 , which was improved by 8.5 times as compared with that of the pure glass ceramics (0.33 J/cm 3 ).

Synchrotron and inverse-Compton emission from radio galaxies with non-uniform magnetic field and electron distributions

I investigate the effect of non-uniform magnetic fields in the extended structures of radio galaxies on the observed synchrotron and inverse-Compton emission. On the assumption of an isotropic field, with a given power spectrum and a Gaussian distribution of the Cartesian components of the magnetic field strength, I derive a simple integral that can be used numerically to calculate the synchrotron emissivity from any electron population. In the case of power-law spectra, I show that it is possible to estimate the difference between the synchrotron emissivity from a region with such a field and that from the commonly assumed arrangement where $B$ is constant everywhere, though fully tangled, and that this difference is small, though it increases if the electron energy density scales with the field. An aged electron spectrum in such a field produces a characteristic curved synchrotron spectrum which differs significantly from the classical Jaffe-Perola spectrum, and I discuss some effects that this might have on standard spectral age fitting. Finally, I show that inverse-Compton scattering of the cosmic microwave background is only moderately affected by such a field structure, with the effects becoming more important if the electrons follow the field. Magnetic-field estimates in the literature from combined synchrotron and inverse-Compton modelling will give reasonable estimates of the mean magnetic field energy density if the field is non-uniform but isotropic.

Multifunctional Structural Supercapacitor Composites Based on Carbon Aerogel Modified High Performance Carbon Fiber Fabric

A novel multifunctional material has been designed to provide excellent mechanical properties while possessing a high electrochemical surface area suitable for electrochemical energy storage: structural carbon fiber fabrics are embedded in a continuous network of carbon aerogel (CAG) to form a coherent but porous monolith. The CAG-modification process was found to be scalable and to be compatible with a range of carbon fiber fabrics with different surface properties. The incorporation of CAG significantly increased the surface area of carbon fiber fabrics, and hence the electrochemical performance, by around 100-fold, resulting in a CAG-normalized specific electrode capacitance of around 62 F g(-1), determined by cyclic voltammetry in an aqueous electrolyte. Using an ionic liquid (IL) electrolyte, the estimated energy density increased from 0.003 to 1 Wh kg(-1), after introducing the CAG into the carbon fiber fabric. 'Proof-of-concept' multifunctional structural supercapacitor devices were fabricated using an IL-modified solid-state polymer electrolyte as a multifunctional matrix to provide both ionic transport and physical support for the primary fibers. Two CAG-impregnated carbon fabrics were sandwiched around an insulating separator to form a functioning structural electrochemical double layer capacitor composite. The CAG-modification not only improved the electrochemical surface area, but also reinforced the polymer matrix surrounding the primary fibers, leading to dramatic improvements in the matrix-dominated composite properties. Increases in in-plane shear strength and modulus, of up to 4.5-fold, were observed, demonstrating that CAG-modified structural carbon fiber fabrics have promise in both pure structural and multifunctional energy storage applications.

Effect of post-deposition annealing on the growth of nanocrystalline TiO2 thin films and elastic anisotropy of rutile phase at different temperatures

Abstract In this work, predominant anatase and rutile nanocrystalline TiO 2 thin films deposited by DC reactive magnetron sputtering are annealed at different temperatures. Raman spectroscopy and XRD experiments suggest phase transformations to rutile at elevated temperatures. A sharp increase of rutile content of the films confirms rutile phase stability above 650 °C. The variations in unit cell parameters are attributed to the changes in microstrain and macrostrain present in the films. The Miller indices dependence of Young’s modulus of rutile nanocrystals is estimated on the basis of the Reuss approximation for polycrystalline aggregates. Young’s modulus shows strong anisotropy. The elastic anisotropy is introduced in the Williamson–Hall (WH) method for the estimation of isotropic stress and uniform deformation energy density. Microstrain decreases with increasing annealing temperature. Lattice microstrain of nanocrystalline rutile is anisotropic. Along a particular crystallographic direction, rutile transformed from anatase rich films exhibit lower microstrain.

Microfabrication of High-Performance Thick Co80Pt20 Permanent Magnets for Microsystems Applications

The fabrication, via aqueous electrodeposition, of 8 - 30 µm-thick photolithographically-patterned Co80Pt20 films for microsystems applications is reported in this paper. The dependence of their magnetic properties on film thickness has also been studied. Results show that a deposition rate of ~12 µm per hour is achievable via a bath pre-conditioning step without significantly sacrificing the magnetic properties of the film. Maximum out-of-plane intrinsic coercivity (Hci) of 330 kA/m and squareness (Mr/Ms) of 0.9 were obtained for films 15 - 18 µm thick, corresponding to an estimated energy density (BHmax) of 130 kJ/m3. A 23% decrease in coercivity is observed with increase in thickness to 30 µm.

Cosmic ray modulation of infra-red radiation in the atmosphere

Cosmic rays produce molecular cluster ions as they pass through the lower atmosphere. Neutral molecular clusters such as dimers and complexes are expected to make a small contribution to the radiative balance, but atmospheric absorption by charged clusters has not hitherto been observed. In an atmospheric experiment, a narrowband thermopile filter radiometer centred on 9.15 μm, an absorption band previously associated with infra-red absorption of molecular cluster ions, was used to monitor changes following events identified by a cosmic ray telescope sensitive to high-energy (>400 MeV) particles, principally muons. The average change in longwave radiation in this absorption band due to molecular cluster ions is 7 mWm−2. The integrated atmospheric energy density for each event is 2 Jm−2, representing an amplification factor of 1012 compared to the estimated energy density of a typical air shower. This absorption is expected to occur continuously and globally, but calculations suggest that it has only a small effect on climate.

Tidal Current Energy Resources off the South and West Coasts of Korea: Preliminary Observation-Derived Estimates

In this study we estimate the prospective tidal current energy resources off the south and west coasts of Korea and explore the influence of modeling tidal current energies based on 15-day versus month-long data records for regimes with pronounced perigean/apogean influences. The tidal current energy resources off southern and western Korea were calculated using 29-day in situ observation data from 264 stations. The resultant annual energy densities found at each station were categorized into six groups, with a greater percentage of sites falling into the lower-energy groups: 1.1% for >10 MWh·m−2; 2.7% for 5 to 10 MWh·m−2; 6.8% for 3 to 5 MWh·m−2; 9.1% for 2 to 3 MWh·m−2 and 80.3% for <2 MWh·m−2. Analysis shows that the greatest concentration of high annual energy densities occurs in the Jeonnam Province coastal region on the western tip of southwest Korea: 23 MWh·m−2 at Uldolmok, 15 MWh·m−2 at Maenggol Sudo, 9.2 MWh·m−2 at Geocha Sudo and 8.8 MWh·m−2 at Jaingjuk Sudo. The second highest annual energy density concentration, with 16 MWh·m−2, was found in Gyudong Suro, in Gyeonggi Province’s Gyeonggi Bay. We then used data from the 264 stations to examine the effect of perigean and apogean influences on tidal current energy density evaluations. Compared to derivations using month-long records, mean annual energy densities derived using 15-day perigean spring-neap current records alone overestimate the annual mean energy by around 10% whereas those derived using only the apogean records underestimate energy by around 12%. In particular, accuracy of the S2 contribution to the energy density calculations is significantly affected by use of the 15-day data sets, compared to the M2 component, which is relatively consistent. Further, annual energy density estimates derived from 29-day records but excluding the N2 constituent underestimate the potential resource by about 5.4%. Results indicate that one month of data is required to accurately estimate tidal current energy in regimes showing pronounced perigean and apogean differences in spring-neap tidal current patterns and that inclusion of the N2 constituent in calculations is preferable. This finding has widespread applicability for green energy resource assessments, for example, in regions of the Unites States Atlantic coast and in New Zealand.

Influence of Al2O3 additive on the dielectric behavior and energy density of Ba0.5Sr0.5TiO3 ceramics

High dense Ba0.5Sr0.5TiO3 ceramics with Al2O3 additives have been prepared by a method combined the sol–gel process and the solid state reaction. Phase compositions, microstructure and dielectric behaviors are investigated systematically. Our experiment results reveal that the Al2O3 additives reduce the dielectric constant slightly and increase the breakdown strength greatly due to the refined microstructure and the formation of the second phases. The estimated energy density of Ba0.5Sr0.5TiO3 ceramics with optimized Al2O3 additives is improved by 1.5 times as compared with that of pure Ba0.5Sr0.5TiO3 ceramics.

Extension of the statistical modal energy distribution analysis for estimating energy density in coupled subsystems

The present article deals with an extension of the Statistical modal Energy distribution Analysis (SmEdA) method to estimate kinetic and potential energy density in coupled subsystems. The SmEdA method uses the modal bases of uncoupled subsystems and focuses on the modal energies rather than the global energies of subsystems such as SEA (Statistical Energy Analysis). This method permits extending SEA to subsystems with low modal overlap or to localized excitations as it does not assume the existence of modal energy equipartition. We demonstrate that by using the modal energies of subsystems computed by SmEdA, it is possible to estimate energy distribution in subsystems. This approach has the same advantages of standard SEA, as it uses very short calculations to analyze damping effects. The estimation of energy distribution from SmEdA is applied to an academic case and an industrial example.