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Nanostructured materials offer the possibility to tailor light-matter interaction at scales below the wavelength. Metallic nanostructures benefit from the excitation of surface plasmons that permit light concentration at ultrasmal...
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Nanostructured materials offer the possibility to tailor light-matter interaction at scales below the wavelength. Metallic nanostructures benefit from the excitation of surface plasmons that permit light concentration at ultrasmall length scales and ultrafast time scales. The local density of states (LDOS) is a central concept that drives basic processes of light-matter interaction such as spontaneous emission, thermal emission and absorption. We introduce theoretically the concept of LDOS, emphasizing the specificities of plasmonics. We connect the LDOS to real observables in nanophotonics, and show how the concept can be generalized to account for spatial coherence. We describe recent methods developed to probe or map the LDOS in complex nanostructures ranging from nanoantennas to disordered metal surfaces, based on dynamic fluorescence measurements or on the detection of thermal radiation.
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Elastic recovery is a measure of the extent to which a rubber specimen regains its original dimensions after release of an imposed strain. A recoverable strain and rate of recovery after prolonged aging under compression in the en...
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Elastic recovery is a measure of the extent to which a rubber specimen regains its original dimensions after release of an imposed strain. A recoverable strain and rate of recovery after prolonged aging under compression in the environment of intended use are important factors in characterizing rubber performance characteristics. So far the recoverable strain and its rate at very short time intervals have not been studied. Therefore, the present study describes an instrument and reliable method for measuring elastic recovery after release of compressive strain within time periods from 0.007 to 0.1 s. Significant differences are observed in both recoverable strains and their rates measured within these short time periods for the different rubber vulcanizates after aging. Data obtained for various rubbers aged in different environments are fitted to power law and Williams-Watts equations relating elastic strain with time after release of stress. The intercept in the power law equation and characteristic time in Williams-Watts equation are found to be very sensitive to changes in the elastic recovery of various rubbers during aging. The designed testing procedures will make possible the ability to discriminate different rubber materials intended for use in sealing applications, especially those used in dynamic seals. A comparison between novel and traditional measurements is also given.
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The properties of three different pitch-interconnected hydro-pneumatic suspensions are systematically explored. The vertical and pitch mode properties of the proposed suspensions are derived through formulation and analysis of a g...
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The properties of three different pitch-interconnected hydro-pneumatic suspensions are systematically explored. The vertical and pitch mode properties of the proposed suspensions are derived through formulation and analysis of a generalised pitch plane model. The results suggest that the pitch-connected suspensions offer superior flexibility for enhancing the pitch mode properties, without affecting the bounce mode properties. The dynamic characteristics of the proposed pitch-connected suspensions are further evaluated for a two-axle heavy vehicle under braking and road inputs. The results demonstrate that the proposed pitch-connected suspensions could offer significant benefits in improving both the handling and ride qualities of heavy vehicles.
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Existing nonisothermal thin-filament melt spinning models treat temperature as a one-dimensional (1D) quantity, varying only with axial distance. Such models accurately simulate processes in which the melt has high thermal conduct...
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Existing nonisothermal thin-filament melt spinning models treat temperature as a one-dimensional (1D) quantity, varying only with axial distance. Such models accurately simulate processes in which the melt has high thermal conductivity relative to the surface heat loss (i.e., small Biot number), or the ambient air temperature is near the melt temperature. However, in industrial melt spinning processes, where neither of these characteristics is true, a leading-order transverse temperature variation exists, no matter how slender the filament. Alternative models implement a hybrid 1D mass and momentum, 2D energy computation. Here we extend existing 1D models to include radial as well as axial resolution of temperature, thereby also providing a 2D resolution of stress, while retaining the computational advantages of 1D models. The model's predictions depend on the thermal conductivity of the melt, a property absent from existing 1D models. In addition to demonstrating the 2D resolution afforded by the new model, we also demonstrate significant differences between the new model and existing 1D models in predictions of fundamentally 1D quantities such as average axial stress, the quantity from which performance properties of the spun fiber are typically inferred.
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When a production lot is split into alternative routes, the production run in each route will be shortened. Merging sub-lots from different alternative routes to one selected route will result in a longer production run in the sel...
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When a production lot is split into alternative routes, the production run in each route will be shortened. Merging sub-lots from different alternative routes to one selected route will result in a longer production run in the selected route. Such variation in product run length could have impacts on product quality. The paper formulates a mathematical programming model for optimal lot splitting into alternative routes to account for the impact of production run length on product quality in a cellular manufacturing environment. A genetic algorithm is developed to solve the proposed model efficiently. Numerical examples are presented to demonstrate the features of the proposed model and computational efficiency of the solution method. It further proposes extensions of the developed model and solution procedure to consider cell formation decisions when the impact of splitting production lots into alternative routes on product quality is considered.
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Laser-direct drive (LDD), along with laser indirect (X-ray) drive (LID) and magnetic drive with pulsed power, is one of the three viable inertial confinement fusion approaches to achieving fusion ignition and gain in the laborator...
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Laser-direct drive (LDD), along with laser indirect (X-ray) drive (LID) and magnetic drive with pulsed power, is one of the three viable inertial confinement fusion approaches to achieving fusion ignition and gain in the laboratory. The LDD programme is primarily being executed at both the Omega Laser Facility at the Laboratory for Laser Energetics and at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory. LDD research at Omega includes cryogenic implosions, fundamental physics including material properties, hydrodynamics and laser-plasma interaction physics. LDD research on the NIF is focused on energy coupling and laser-plasma interactions physics at ignition-scale plasmas. Limited implosions on the NIF in the 'polardrive' configuration, where the irradiation geometry is configured for LID, are also a feature of LDD research. The ability to conduct research over a large range of energy, power and scale size using both Omega and the NIF is a major positive aspect of LDD research that reduces the risk in scaling from OMEGA to megajoule-class lasers. The paper will summarize the present status of LDD research and plans for the future with the goal of ultimately achieving a burning plasma in the laboratory. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.
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A twin-gas-chamber hydropneumatic suspension strut concept is proposed to achieve enhanced bounce and pitch ride, and pitch attitude control. The response characteristics of the twin-gas-chamber strut suspension are compared with ...
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A twin-gas-chamber hydropneumatic suspension strut concept is proposed to achieve enhanced bounce and pitch ride, and pitch attitude control. The response characteristics of the twin-gas-chamber strut suspension are compared with those of a single-gas-chamber strut suspension to demonstrate not only superior performance potentials but also the added design flexibility offered by the twin-gas-chamber struts. The relative responses of both strut suspensions are evaluated through analysis of a pitch plane vehicle model, subject to straight-line braking inputs and excitations arising from randomly distributed road elevations. A generalized formulation for the strut forces is presented to derive the bounce and pitch rates of the proposed strut suspensions. The results reveal that the twin-gas-chamber strut suspension exhibits a slightly lower pitch stiffness in the vicinity of design ride height, but progressively hardening effects with increasing pitch deflections. Moreover, the twin-gas-chamber strut suspension exhibits considerably fewer hardening-softening effects in suspension rate compared with the suspension involving the single-gas-chamber struts. The results attained from the parametric studies are also discussed to demonstrate superior design flexibility of the twin-gas-chamber struts for tuning of the suspension bounce and pitch stiffness properties. The dynamic responses of the vehicle model with different suspensions are assessed subject to random road roughness excitations as well as braking torque inputs. The results demonstrate that the twin-gas-chamber strut suspension offers considerable potential for enhancing bounce and pitch ride, pitch attitude control, and suspension travel responses under braking, while the influence on the ride and road-holding responses under random road inputs is insignificant. The results also suggest that a relatively soft front suspension design could provide further enhancement of pitch ride and pitch deflection responses under random road roughness excitations.
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A hydro-pneumatic strut comprising two gas chambers is proposed to realise nearly symmetric vertical stiffness properties in compression and rebound, and progressively hardening roll stiffness. The fundamental properties of the pr...
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A hydro-pneumatic strut comprising two gas chambers is proposed to realise nearly symmetric vertical stiffness properties in compression and rebound, and progressively hardening roll stiffness. The fundamental properties of the proposed struts are derived in terms of suspension rate and roll stiffness through formulations of strut forces in the roll plane of a vehicle. Dynamic responses are investigated under excitations arising from vehicle-road interactions and a steady centrifugal acceleration. The results demonstrate that the suspension with proposed struts could reduce ride height drift, and improve suspension topping, tyre deflection and roll response characteristics, with negligible influence on vertical and roll ride.
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We present a detailed extended x-ray absorption fine structure (EXAFS) analysis of the thermoelectric clathrates Eu_8Ga_(16)Ge_(30) and Sr_8Ga_(16)Ge_(30), both of which have an unusually low thermal conductivity attributed to a "...
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We present a detailed extended x-ray absorption fine structure (EXAFS) analysis of the thermoelectric clathrates Eu_8Ga_(16)Ge_(30) and Sr_8Ga_(16)Ge_(30), both of which have an unusually low thermal conductivity attributed to a "rattler" motion of the filler atoms Eu and Sr. The EXAFS results show that the Ga/Ge lattice is quite stiff with a high correlated Debye temperature ～400 K. Eu is on-center in the site 1 cage but off-center (0.445+-0.020 A) in the large cage called the Eu2 site. The results for Sr are similar, but ～75% are off-center 0.40+-0.05 A and ～25% are on-center in the Sr2 site. Both results are in reasonable agreement with diffraction results. The temperature dependence of the nearest neighbor pair distribution widths yield low Einstein temperatures (80+-10 and 100+-10 K for Eul and Sr1, respectively, and 95+-10 and 125+-10 K for the shortest Eu2-Ga/Ge and Sr2-Ga/Ge pairs). In contrast, the more distant Eu2/Sr2-Ga/Ge pair distributions within the Eu2/Sr2 cage are strongly disordered even at low T, indicating considerable local disorder. This indicates that the off-center Eu or Sr atom is bonded to the side of the site 2 cage. This has two important implications for the thermal conductivity: it increases the coupling between the "rattler" vibrations and the lattice phonons and it introduces a symmetry-breaking large mass defect.
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In cellular manufacturing environments, manufacturing cells are generally formed based on deterministic product demands. In this paper, we consider a system configuration problem with product demands expressed in a number of proba...
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In cellular manufacturing environments, manufacturing cells are generally formed based on deterministic product demands. In this paper, we consider a system configuration problem with product demands expressed in a number of probabilistic scenarios. An optimization model integrating cell formation and part allocation is developed to generate a robust system configuration to minimize machine cost and expected inter-cell material handling cost. A two-stage Tabu search based heuristic algorithm is developed to find the optimal or near optimal solutions to the NP-hard problem. Numerical examples show that this model leads to an appropriate compromise between system configuration costs and expected material handling costs to meet thevarying product demands. These example problems also show that the proposed algorithm is effective and computationally efficient for small or medium size problems.
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