Extra Energy Dissipation Research Articles

Friedmann equations from nonequilibrium thermodynamics of the Universe: A unified formulation for modified gravity

Inspired by the Wald-Kodama entropy $S=A/(4G_{\text{eff}})$ where $A$ is the horizon area and $G_{\text{eff}}$ is the effective gravitational coupling strength in modified gravity with field equation $R_{\mu\nu}-Rg_{\mu\nu}/2=$ $8\pi G_{\text{eff}} T_{\mu\nu}^{\text{(eff)}}$, we develop a unified and compact formulation in which the Friedmann equations can be derived from thermodynamics of the Universe. The Hawking and Misner-Sharp masses are generalized by replacing Newton's constant $G$ with $G_{\text{eff}}$, and the unified first law of equilibrium thermodynamics is supplemented by a nonequilibrium energy dissipation term $\mathcal{E}$ which arises from the revised continuity equation of the perfect-fluid effective matter content and is related to the evolution of $G_{\text{eff}}$. By identifying the mass as the total internal energy, the unified first law for the interior and its smooth transit to the apparent horizon yield both Friedmann equations, while the nonequilibrium Clausius relation with entropy production for an isochoric process provides an alternative derivation on the horizon. We also analyze the equilibrium situation $G_{\text{eff}}=G=\text{constant}$, provide a viability test of the generalized geometric masses, and discuss the continuity/conservation equation. Finally, the general formulation is applied to the FRW cosmology of minimally coupled $f(R)$, generalized Brans-Dicke, scalar-tensor-chameleon, quadratic, $f(R,\mathcal{G})$ generalized Gauss-Bonnet and dynamical Chern-Simons gravity. In these theories we also analyze the $f(R)$-Brans-Dicke equivalence, find that the chameleon effect causes extra energy dissipation and entropy production, geometrically reconstruct the mass $\rho_m V$ for the physical matter content, and show the self-inconsistency of $f(R,\mathcal{G})$ gravity in problems involving $G_{\text{eff}}$.

Wave-driven stellar expansion and binary interaction in pre-supernova outbursts

We suggest that the main outcome of energy leakage carried by waves from the core to the envelope of pre-collapse massive stars is envelope expansion rather than major mass ejection. We show that the propagating waves add to the pressure in the envelope at radii smaller than the radius where the convection driven by the waves becomes supersonic, the driven radius. The extra wave pressure and wave energy dissipation lead to envelope expansion. Using the numerical code MESA we show that the envelope expansion absorbs most of the energy carried by the waves. A possible conclusion from our results is that pre-explosion outbursts (PEOs) result from a binary companion accreting mass from the extended envelope and releasing a huge amount of energy. The accreting companion is likely to expel mass in a bipolar morphology, e.g., jets and an equatorial ring.

Inclusion of additional energy dissipation due to plunging breakers in parametric type wave models

One of the most critical issues in coastal engineering problems is to accurately predict the wave height profile across the surfzone. Parametric wave models are broadly used in modelling the wave energy dissipation in this regard. Three parametric wave models based on the bore energy dissipation model were evaluated against new field measurements under various conditions from mild to stormy. The results indicate that a discrepancy between models and data occurred near the break point for cases where the wave breaking was of the plunging type but after the breakpoint the wave height decay rates compared well. In order to improve this model shortcoming, comprehensive new laboratory tests were conducted to quantify the additional energy dissipation due to plunging breakers. Based on the data, new empirical equations were derived and incorporated into the most recent bore dissipation parametric wave model. The inclusion of the extra energy dissipation due to plunging breakers results in significant improvement in the prediction of the wave height profile.

A 200 mV low leakage current subthreshold SRAM bitcell in a 130 nm CMOS process

A low leakage current subthreshold SRAM in 130 nm CMOS technology is proposed for ultra low voltage (200 mV) applications. Almost all of the previous subthreshold works ignore the leakage current in both active and standby modes. To minimize leakage, a self-adaptive leakage cut off scheme is adopted in the proposed design without any extra dynamic energy dissipation or performance penalty. Combined with buffering circuit and reconfigurable operation, the proposed design ensures both read and standby stability without deteriorating writability in the subthreshold region. Compared to the referenced subthreshold SRAM bitcell, the proposed bitcell shows: (1) a better critical state noise margin, and (2) smaller leakage current in both active and standby modes. Measurement results show that the proposed SRAM functions well at a 200 mV supply voltage with 0.13 μW power consumption at 138 kHz frequency.

Viscoelastic and Mechanical Behavior of Hydrophobically Modified Hydrogels

The viscoelastic and mechanical behaviors of physically cross-linked copolymer hydrogels synthesized from N,N-dimethylacrylamide (DMA) and 2-(N-ethylperfluorooctane sulfonamido)ethyl acrylate (FOSA) with varying FOSA concentration were studied by rheological and static tensile tests. The strong hydrophobic association of the FOSA moieties in an aqueous environment produced core–shell nanodomains that provided the physical cross-links. These PDMA–FOSA hydrogels exhibited excellent mechanical properties, including a modulus of ∼130–190 kPa, elongation at break of 1000–1600%, and ∼500 kPa tensile strength, depending on the FOSA concentration. The physical gels were more viscous than comparable chemical gels and were much more efficient at dissipating stress. The latter characteristic produced relatively high tensile toughness, ∼4–6 MPa, because of the extra energy dissipation mechanism provided by the reversible, hydrophobic cross-links. The PDMA–FOSA hydrogel exhibited peculiar dynamic behavior which was gr...

Probable Observation of Quantized Vortex Lines Through Solid He Under DC Rotation

We report how one can detect quantized vortices in superfluids contained in cylindrical vessels in well-designed torsional oscillator (TO) experiments under DC rotation. We show the case of an artificial 3D superfluid (Fukuda et al. in Phys. Rev. B 71:212502, 2005) which is made of Kosterlits-Thouless 2D He film condensed on a porous glass substrate with a 3D connected surface of well-controlled pore size. We understand the TO experimental results with an extra energy dissipation peak under DC rotation by considering the circular quantized superflow around each of the vortex lines and interaction with thermally excited 2D vortices as discussed in Fukuda et al. (Phys. Rev. B 71:212502, 2005) and in Nemirovskii and Sonin (Phys. Rev. B 76: 224507, 2007). We discuss here the case of hcp solid 4He (see for ex. Balibar and Caupin in J. Phys., Condens. Matter 20:173201-1-19, 2008) and show the evidence of observation of the vortex lines penetration below a supersolid transition temperature (Kubota et al. in J. Low Temp. Phys. 158:572, 2010), Tc, where macroscopic phase coherence is realized. It is found at exactly the same temperature Tc, below which the hysteresis occurrs (Shimizu et ail. in arXiv:0903.1326, 2009). For hcp solid 4He we have reported the vortex fluid (VF) state onset temperature (Penzev et al. in Phys. Rev. Lett. 101:065301, 2008) To=∼500 mK, by detailed drive velocity, Vac dependence study using TO technique. The TO response of the hcp 4He is characterized by the energy dissipation peaked at Tp near 100 mK similar to the behavior in a KT transition. The real supersolid (SS) state occurs at Tc below Tp and much lower than To. Our observation of the evidence of vortex lines penetration just below Tc together with the VF state properties gives support for the idea that hcp 4He shares some features with the “new type of superconductors”, where the vortex state, involving the VF as well as various vortex solid states, has been commonly discussed (Fisher et al. in Phys. Rev. B 43(1):130, 1991; Leggett in Quantum Liquids, Oxford University Press, London, 2006).

A Study of Energy Dissipation in Exfoliated Polyurethane/Organoclay Nanocomposites

Exfoliated polyurethane (PU)/organoclay nanocomposites were prepared by in situ polymerization of polyol/organoclay mixture, chain extender and diisocyanate. The effect of organoclay on energy dissipation in the exfoliated PU/organoclay nanocomposites during cyclic deformation at strain ratios of 50%, 100% and 200% was investigated experimentally and by molecular dynamics (MD) simulation. The addition of organoclay resulted in extra energy loss in the PU nanocomposites and greater energy dissipation in the exfoliated nanocomposites compared with intercalated ones containing the same percentage of organoclay. With the help of MD simulation, understanding of the energy dissipation arising from the addition of organoclay to the exfoliated PU nanocomposites is now clearer. The nanoplatelets exhibited reversible orientation behaviour at a low strain ratio of 50%, suggesting that the additional energy dissipation may be due to the frictional sliding at the interface between polymer chains and the surfaces of organoclay layers. However, when the sample was subjected to large strain, the orientation of nanoplatelets revealed more irreversible behaviour indicating that the extra energy dissipation is due to both the frictional sliding at the interface and the orientation of the nanoplatelets. The additional energy dissipation was also influenced by the strength of interactions between polymer chains and clay platelets: the stronger interactions, the greater the energy dissipation.

Identification of material stiffness and damping in vibrating plates using full-field measurements

This study concerns the identification of complex stiffness components (ie, stiffness and damping) on isotropic vibrating plates. One of the main difficulties in damping measurements comes from the connection of the specimen to its environment (joints, clamps etc...) causing extra energy dissipation. The present procedure based on full field slope measurements from a deflectometry set up together with an inverse identification technique called the Virtual Fields Method is capable of identifying the material damping regardless of the dissipation coming from the specimen boundary conditions. This paper will present some experimental results confirming this statement.

Verification and validation study of some polydisperse kinetic theories

The predictions of several polydisperse kinetic theories are presented in this study for the simple shear flow of a binary mixture of powders with varying sizes in a vacuum under zero gravity. These results are compared to published numerical data obtained using discrete molecular dynamics technique. The theory showing the most accurate results is modified so that the sum of the kinetic stresses of two or more identical solid phases adds to that of a monodisperse system with the same properties. Simulation results obtained in a three-dimensional riser for the flow of air and a binary mixture of glass beads are compared with available experimental data for each solid-phase velocity, concentration, and granular temperature. The predictions of the theory compare reasonably well with experimental data when the value of the linear particle–particle restitution coefficient is lowered to take into account the extra energy dissipation due to collisions between pairs of slightly frictional particles.

The Hot Inner Disk of FU Orionis

We have constructed a detailed radiative transfer disk model which reproduces the main features of the spectrum of the outbursting young stellar object FU Orionis from ~4000 A to ~8 μm. Using an estimated visual extinction AV ~ 1.5, a steady disk model with a central star mass ~0.3 M☉, and a mass accretion rate ~2 × 10-4 M☉ yr-1, we can reproduce the SED of FU Ori quite well. Higher values of extinction used in previous analysis (AV ~ 2.1) result in SEDs which are less well fitted by a steady disk model, but might be explained by extra energy dissipation of the boundary layer in the inner disk. With the mid-infrared spectrum obtained by the IRS on board the Spitzer Space Telescope, we estimate that the outer radius of the hot, rapidly accreting inner disk is ~1 AU, using disk models truncated at this outer radius. Inclusion of radiation from a cooler irradiated outer disk might reduce the outer limit of the hot inner disk to ~0.5 AU. In either case, the radius is inconsistent with a pure thermal instability model for the outburst. Our radiative transfer model implies that the central disk temperature Tc ≥ 1000 K out to ~0.5-1 AU, suggesting that the magnetorotational instability can be supported out to that distance. Assuming that the ~100 yr decay timescale in brightness of FU Ori represents the viscous timescale of the hot inner disk, we estimate the viscosity parameter to be α ~ 0.2-0.02 in the outburst state, consistent with numerical simulations of the magnetorotational instability in disks. The radial extent of the high- region is inconsistent with the model of Bell & Lin, but may be consistent with theories incorporating both gravitational and magnetorotational instabilities.

Energy reduction through crosstalk avoidance coding in networks on chip

Commercial designs are currently integrating from 10 to 100 embedded processors in a single system on chip (SoC) and the number is likely to increase significantly in the near future. With this ever increasing degree of integration, design of communication architectures for large, multi-core SoCs is a challenge. Traditional bus-based systems will no longer be able to meet the clock cycle requirements of these big SoCs. Instead, the communication requirements of these large multi processor SoCs (MP-SoCs) are convened by the emerging network-on-chip (NoC) paradigm. Crosstalk between adjacent wires is an important signal integrity issue in NoC communication fabrics and it can cause timing violations and extra energy dissipation. Crosstalk avoidance codes (CACs) can be used to improve the signal integrity by reducing the effective coupling capacitance, lowering the energy dissipation of wire segments. As NoCs are built on packet-switching, it is advantageous to modify data packets by including coded bits to protect against the negative effects of crosstalk. By incorporating crosstalk avoidance coding in NoC data streams and organizing the CAC-encoded data packets in an efficient manner, so that total number of encoding/decoding operations can be reduced over the communication channel, we are able to achieve lower communication energy, which in turn will help to decrease the overall energy dissipation.

Impact of reinforcing filler on the dynamic moduli of elastomer compounds under shear deformation in relation to wet sliding friction

In pursuit of a better understanding of the relationship between wet sliding friction and bulk viscoelastic properties of elastomer compounds, especially the contribution from different reinforcing fillers, the linear thermorheological behavior, the nonlinear dynamic moduli under shear deformation (for strain up to about 140%), and the wet sliding friction have been characterized in detail for crosslinked compounds of low-cis polybutadiene filled with different reinforcing fillers including carbon black, graphitized carbon black, and precipitated silica. We examine the scenario of possible extra energy dissipation via higher harmonic excitation in rubber compounds coupled with dynamic deformation consisting of components at many frequencies during sliding of rubber on a rough surface. While no straightforward explanation is identified relating the observed difference in wet sliding friction arising from different fillers to the bulk viscoelastic properties, some unexpected viscoelastic features arising from the compounds are observed.

Materials removal and energy dissipation during sawing of polycarbonate and glass

A series of experiments on sawing plastic (PC) and glass (TaFD5) samples was conducted to verify the validity of the French–Preston law and also to study the environmental (air, water, decanol and cyclohexanol) effects on the sawing energy. Linear relations between cutting rate and sawing power were found using any liquid coolant, as predicted by the French–Preston law. The normal load and tangential force in sawing had a linear relation, as suggested by the law of kinetic friction, independent of speed or temperature in the ranges studied. However, air is not a good coolant for sawing PC although it is good for sawing glass. By blowing air on the PC sample at the cutting interface and extrapolating to infinite air pressure, the French–Preston law was found to be obeyed. Using a coolant in sawing may cause extra energy dissipation, namely, the energy required to shear the fluid. The investigation shows that the extra energy dissipation is proportional to the viscosity of the coolant so the sawing power required for PC was in the order of air, water, decanol and cyclohexanol. However, for sawing glass the cutting efficiency (cutting rate per sawing power) is the highest in decanol, next in water and the lowest in air, just the opposite to the case of sawing PC. In order to understand the difference between PC and glass the fracture toughness of TaFD5 was measured by the indentation method and the lowest fracture toughness was found in decanol, next in water and the highest in air based on the lengths of indentation cracks. So it appears that the material removal rate increases with decreasing of fracture toughness, but not exactly inversely proportional to it, as proposed by Buijs and Houten. Since the glass removal rate is strongly dependent on the fracture toughness, it suggests that sawing of glass takes place by a process of microscopic fracture. On the other hand, the mechanism for sawing PC appears to be plastic deformation or ductile tearing.

Analysis of the indentation size effect on the apparent hardness for ceramics

Based on a reasonable assumption that Meyer's law gives an accurate description for the variation of the apparent hardness with indentation size for ceramics, the empirical equation proposed originally by Bückle: P= a 0+ a 1 d+ a 2 d 2, is proved sufficiently suitable for representing the original data from the conventional hardness testing. The physical meanings of the parameters included in this equation are discussed in detail. It is shown that the energy–balance relationship can be evaluated completely with this equation, in which the extra energy dissipation and the experimental errors are considered properly. Further analysis reveals that the origin of the indentation size effect on the apparent hardness of ceramics lies in the fact that the traditional definition of hardness, i.e., the ratio of the applied load to the resulting indentation area, is an incomplete description for the energy–balance relationship during indentation.

Dynamics of phase-separated fluids under external fields

Phase separation in external fields has attracted much attention recently. The reason is twofold. Since kinetics of phase separation and morphology of growing domains can be controlled by external fields, it is of technological importance. The other is that existence of mesoscale domains causes curious dynamical properties in fields, which provides us with a fundamental statistical dynamic problem. One example is a phase separation of binary fluids under shear flow. Phase-separated domains are deformed under the field, which causes burst, fusion, and reconnection of domains so that extra energy dissipation occurs in these processes. Because of this large deformation of domains, the system exhibits quite unusual rheological behavior. The kinetics of phase separation of binary fluids is also influenced by an external electric field when the new phases have different dielectric constants. Deformation and interaction of domains in an electric field are investigated by means of an interfacial approach.

An inclusion model for crack arrest in a composite reinforced by sliding fibers

The inclusion model of Mori and Mura for crack arrest in fiber reinforced materials is extended. The analysis is restricted to short fibers. The sliding of fibers is allowed along fiber-matrix interfaces. Analytical expressions for energy release rate and extra energy dissipation during crack extension are obtained. Sliding fibers result in a larger energy release rate than non-sliding and perfectly bridging fibers. However, the energy dissipation accompanied by sliding offers additional resistance to the extension of a crack. Fibers of smaller radius decrease the energy release rate and raise the energy dissipation more efficiently.

Energy dissipation in stretching filled rubbers

Energy expended irreversibly in stretching filled rubbers is calculated for a simple two-phase series model: a soft phase resembling the corresponding unfilled rubber and a hard phase in series with the soft phase. It is assumed that the rubber is initially wholly in the hard state and that it changes progressively into the softened state on stretching, as proposed by Mullins and Tobin. For a wide range of model parameters, the dissipation of mechanical energy is predicted to rise to about 40% of the input energy at large strains. This predicted behavior is in reasonably good agreement with observations of extra energy dissipation in carbon black-filled rubbers, in comparison with corresponding unfilled rubbers, suggesting that the proposed mechanism of hysteresis by phase transformation is valid. A method of combining energy losses from two simultaneous dissipative processes is also proposed.