Showing papers in "Science China-physics Mechanics & Astronomy in 2010"
TL;DR: In this article, it was shown that all equations of the linearized Gurtin-Murdoch model of surface elasticity can be derived, in a straightforward way, from a simple second-order expression for the ratio of deformed surface area to initial surface area.
Abstract: It is showed that all equations of the linearized Gurtin-Murdoch model of surface elasticity can be derived, in a straightforward way, from a simple second-order expression for the ratio of deformed surface area to initial surface area. This elementary derivation offers a simple explanation for all unique features of the model and its simplified/modified versions, and helps to clarify some misunderstandings of the model already occurring in the literature. Finally, it is demonstrated that, because the Gurtin-Murdoch model is based on a hybrid formulation combining linearized deformation of bulk material with 2nd-order finite deformation of the surface, caution is needed when the original form of this model is applied to bending deformation of thin-walled elastic structures with surface stress.
212 citations
TL;DR: In this paper, the authors compare some popular dark energy models under the assumption of a flat universe by using the latest observational data including the type Ia supernovae compilation, the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey, the cosmic microwave background measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observations and the determination of H 0 from the Hubble Space Telescope.
Abstract: We compare some popular dark energy models under the assumption of a flat universe by using the latest observational data including the type Ia supernovae Constitution compilation, the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey, the cosmic microwave background measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observations and the determination of H 0 from the Hubble Space Telescope. Model comparison statistics such as the Bayesian and Akaike information criteria are applied to assess the worth of the models. These statistics favor models that give a good fit with fewer parameters. Based on this analysis, we find that the simplest cosmological constant model that has only one free parameter is still preferred by the current data. For other dynamical dark energy models, we find that some of them, such as the α dark energy, constant w, generalized Chaplygin gas, Chevalliear-Polarski-Linder parametrization, and holographic dark energy models, can provide good fits to the current data, and three of them, namely, the Ricci dark energy, agegraphic dark energy, and Dvali-Gabadadze-Porrati models, are clearly disfavored by the data.
128 citations
TL;DR: In this article, the electric enthalpy variational principle for nanosized dielectrics with the strain gradient and the polarization gradient effect, as well as the effect of the electrostatic force was established.
Abstract: The flexoelectric effect is very strong and coupled with large strain gradients for nanoscale dielectrics. At the nanoscale, the electrostatic force cannot be ignored. In this paper, we have established the electric enthalpy variational principle for nanosized dielectrics with the strain gradient and the polarization gradient effect, as well as the effect of the electrostatic force. The complete governing equations, which include the effect of the electrostatic force, are derived from this variational principle, and based on the principle the generalized electrostatic stress is obtained, the generalized electrostatic stress contains the Maxwell stress corresponding to the polarization and strain, and stress related to the polarization gradient and strain gradient. This work provides the basis for the analysis and computations for the electromechanical problems in nanosized dielectric materials.
124 citations
TL;DR: A quantum secret-sharing protocol is presented here, which mends the security loophole of the original secret- sharing protocol, and doubles the information capacity.
Abstract: A detailed analysis has showed that the quantum secret sharing protocol based on the Grover algorithm (Phys Rev A, 2003, 68: 022306) is insecure. A dishonest receiver may obtain the full information without being detected. A quantum secret-sharing protocol is presents here, which mends the security loophole of the original secret-sharing protocol, and doubles the information capacity.
84 citations
TL;DR: In this paper, the interpolating boundary element-free method (IBEFM) for two-dimensional elasticity problems is presented, and corresponding formulae of the IBEFM for 2D elasticity problem are obtained.
Abstract: The paper begins by discussing the interpolating moving least-squares (IMLS) method. Then the formulae of the IMLS method obtained by Lancaster are revised. On the basis of the boundary element-free method (BEFM), combining the boundary integral equation method with the IMLS method improved in this paper, the interpolating boundary element-free method (IBEFM) for two-dimensional elasticity problems is presented, and the corresponding formulae of the IBEFM for two-dimensional elasticity problems are obtained. In the IMLS method in this paper, the shape function satisfies the property of Kronecker δ function, and then in the IBEFM the boundary conditions can be applied directly and easily. The IBEFM is a direct meshless boundary integral equation method in which the basic unknown quantity is the real solution to the nodal variables. Thus it gives a greater computational precision. Numerical examples are presented to demonstrate the method.
72 citations
TL;DR: A quantum secure direct communication protocol with cluster states is proposed that can achieve higher intrinsic efficiency by using two-step transmission.
Abstract: A quantum secure direct communication protocol with cluster states is proposed. Compared with the deterministic secure quantum communication protocol with the cluster state proposed by Yuan and Song (Int. J. Quant. Inform., 2009, 7: 689), this protocol can achieve higher intrinsic efficiency by using two-step transmission. The implementation of this protocol is also discussed.
65 citations
TL;DR: In this article, the authors re-analyze the spectrum and the relevant wave functions of the heavy quarkonia within the framework of Bethe-Salpeter (B.S.) equation with a proper QCD-inspired kernel.
Abstract: Considering the fact that some excited states of the heavy quarkonia (charmonium and bottomonium) are still missing in experimental observations and potential applications of the relevant wave functions of the bound states, we re-analyze the spectrum and the relevant wave functions of the heavy quarkonia within the framework of Bethe-Salpeter (B.S.) equation with a proper QCD-inspired kernel. Such a kernel for the heavy quarkonia, relating to potential of the non-relativistic quark model, is instantaneous, so we call the corresponding B.S. equation as BS-In equation throughout the paper. Particularly, a new way to solve the B.S. equation, which is different from the traditional ones, is proposed here, and with it not only the known spectrum for the heavy quarkonia is re-generated, but also an important issue is brought in, i.e., the obtained solutions of the equation 'automatically' include the 'fine', 'hyperfine' splittings and the wave function mixture, such as S-D wave mixing in J (PC) = 1(--) states, P-F wave mixing in J (PC) = 2(++) states for charmonium, bottomonium etc. It is pointed out that the best place to test the wave mixture probably is at Z-factory (e (+) e (-) collider running at Z-boson pole with extremely high luminosity).
61 citations
TL;DR: The results reveal that scaling-down roughness into the micro-submicron range is a unique and elegant strategy to not only achieve superhydrophobicity but also to increase its stability against environmental disturbances.
Abstract: Thousands of plant and animal species have been observed to have superhydrophobic surfaces that lead to various novel behaviors. These observations have inspired attempts to create artificial superhydrophobic surfaces, given that such surfaces have multitudinous applications. Superhydrophobicity is an enhanced effect of surface roughness and there are known relationships that correlate surface roughness and superhydrophobicity, based on the underlying physics. However, while these examples demonstrate the level of roughness they tell us little about the independence of this effect in terms of its scale. Thus, they are not capable of explaining why such naturally occurring surfaces commonly have micron-submicron sizes. Here we report on the discovery of a new relation, its physical basis and its experimental verification. The results reveal that scaling-down roughness into the micro-submicron range is a unique and elegant strategy to not only achieve superhydrophobicity but also to increase its stability against environmental disturbances. This new relation takes into account the previously overlooked but key fact that the accumulated line energy arising from the numerous solid-water-air intersections that can be distributed over the apparent contact area, when air packets are trapped at small scales on the surface, can dramatically increase as the roughness scale shrinks. This term can in fact become the dominant contributor to the surface energy and so becomes crucial for accomplishing superhydrophobicity. These findings guide fabrication of stable super water-repellant surfaces.
58 citations
TL;DR: In this article, the effect of Young's modulus on tensile analysis of a nanorod has been investigated and it has been shown that a lower Youngs modulus (smaller stress-strain rate) indicates smaller extension.
Abstract: It has been a known fact in classical mechanics of materials that Young’s modulus is an indicator of material stiffness and materials with a higher Young’s modulus are stiffer. At the nanoscale, within the scope and under specific circumstances described in this paper, however, a nanorod (or a nanotube) with a smaller Young’s modulus (smaller stress-strain rate) is stiffer. In such a scenario, Young’s modulus is not a stiffness indicator for nanostructures. Furthermore, the nonlocal stress-strain rate is dependent on types of load, boundary conditions and location. This is likely to be one of the many possible reasons why numerous experiments in the past obtained significantly varying values of Young’s modulus for a seemingly identical nanotube, i.e. because the types of loading and/or boundary conditions in the experiments were different, as well as at which point the property was measured. Based on the nonlocal elasticity theory and within the scope of material and geometric linearity, this paper reports the strange and hitherto unrealized effect that a nanorod (or a nanotube) with a lower Young’s modulus (smaller stress-strain rate) indicates smaller extension in tensile analysis. Similarly, it is also predicted that a nanorod (or a nanotube) with a lower Young’s modulus results in smaller bending deflection, higher critical buckling load, higher free vibration frequency and higher wave propagation velocity, which are at all consequences of a stiffer nanostructure.
55 citations
TL;DR: In this paper, a scheme for determining the stable gain region of a linear vibration system under a fractional-order control was proposed, based on the idea of stability switch, and the authors showed that the linear term involving the fractional order derivative of an order between 0 and 2 always acts as a damping force.
Abstract: It begins with the study of damping representation of a linear vibration system of single degree of freedom (SDOF), from the view point of fractional calculus. By using the idea of stability switch, it shows that the linear term involving the fractional-order derivative of an order between 0 and 2 always acts as a damping force, so that the unique equilibrium is asymptotically stable. Further, based on the idea of stability switch again, the paper proposes a scheme for determining the stable gain region of a linear vibration system under a fractional-order control. It shows that unlike the classical velocity feedback which can adjust the damping force only, a fractional-order feedback can adjust not only the damping force, but also the elastic restoring force, and in addition, a fractional-order PDα control can either enlarge the stable gain region or narrow the stable gain region. For the dynamic systems described by integer-order derivatives, the asymptotical stability of an equilibrium is guaranteed if all characteristic roots stay in the open left half-plane, while for the systems with fractional-order derivatives, the asymptotical stability of an equilibrium is guaranteed if all characteristic roots stay within a sector in the complex plane. Analysis shows that the proposed method, based on the idea of stability switch, works effectively in the stability analysis of dynamical systems with fractional-order derivatives.
55 citations
TL;DR: In this article, a direct numerical simulation of the boundary layer interaction flow in a supersonic 24-degree compression ramp is conducted with the free stream Mach number 2.9, where the blow-and-suction disturbance in the upstream wall boundary is used to trigger the transition.
Abstract: A direct numerical simulation of the shock/turbulent boundary layer interaction flow in a supersonic 24-degree compression ramp is conducted with the free stream Mach number 2.9. The blow-and-suction disturbance in the upstream wall boundary is used to trigger the transition. Both the mean wall pressure and the velocity profiles agree with those of the experimental data, which validates the simulation. The turbulent kinetic energy budget in the separation region is analyzed. Results show that the turbulent production term increases fast in the separation region, while the turbulent dissipation term reaches its peak in the near-wall region. The turbulent transport term contributes to the balance of the turbulent conduction and turbulent dissipation. Based on the analysis of instantaneous pressure in the downstream region of the mean shock and that in the separation bubble, the authors suggest that the low frequency oscillation of the shock is not caused by the upstream turbulent disturbance, but rather the instability of separation bubble.
TL;DR: In this paper, the fluid mechanics of underwater supersonic gas jets were studied using a CCD camera and three kinds of measuring methods were used, i.e., pressure probe submerged in water, pressure measurements from the side and front walls of the nozzle devices respectively.
Abstract: An experimental research was carried out to study the fluid mechanics of underwater supersonic gas jets. High pressure air was injected into a water tank through converging-diverging nozzles (Laval nozzles). The jets were operated at different conditions of over-, full- and under-expansions. The jet sequences were visualized using a CCD camera. It was found that the injection of supersonic air jets into water is always accompanied by strong flow oscillation, which is related to the phenomenon of shock waves feedback in the gas phase. The shock wave feedback is different from the acoustic feedback when a supersonic gas jet discharges into open air, which causes screech tone. It is a process that the shock waves enclosed in the gas pocket induce a periodic pressure with large amplitude variation in the gas jet. Consequently, the periodic pressure causes the jet oscillation including the large amplitude expansion. Detailed pressure measurements were also conducted to verify the shock wave feedback phenomenon. Three kinds of measuring methods were used, i.e., pressure probe submerged in water, pressure measurements from the side and front walls of the nozzle devices respectively. The results measured by these methods are in a good agreement. They show that every oscillation of the jets causes a sudden increase of pressure and the average frequency of the shock wave feedback is about 5–10 Hz.
TL;DR: In this article, the results of magnetic susceptibility and electrical resistivity were reported in a temperature range of 2 to 800 K. The Kadowaki-Woods ratio was found to be 1×10−5 μΩ cm mol2 K2 mJ−2, which fits well to the universal value for correlated electron systems.
Abstract: High quality single crystal CrAs was grown by Sn flux method. The results of magnetic susceptibility and electrical resistivity are reported in a temperature range of 2 to 800 K. At low temperatures, a T2 dependence of resistivity is observed showing a Fermi-liquid behavior. The Kadowaki-Woods ratio is found to be 1×10−5 μΩ cm mol2 K2 mJ−2, which fits well to the universal value for many correlated electron systems. At about 270 K, a clear magnetic transition is observed with sharp changes of resistivity and susceptibility. Above 270 K, a linear-temperature dependence of the magnetic susceptibility is observed up to 700 K, which resembles the T-dependent magnetic susceptibility of parents of iron-pnictides superconductors.
TL;DR: This work presents a quantum secret sharing scheme between multiparty and multiparty, which takes EPR pairs in Bell states as quantum resources and concludes that this scheme approaches 100% efficiency.
Abstract: We present a quantum secret sharing scheme between multiparty (m members in Group 1) and multiparty (n members in Group 2), and analyze its security. This scheme takes EPR pairs in Bell states as quantum resources. In order to obtain the shared key, all members only need to perform Bell measurements, rather than perform any local unitary operation. The total efficiency in this scheme approaches 100% as the classical information exchanged is not necessary except for the eavesdropping checks.
TL;DR: In this paper, the effect of non-magnetic dopants in the zinc-blende SiC (3C-SiC) was investigated by first-principle calculations, where the atoms of the first 20 elements in the periodic table except inert gas are used to replace either Si or C atoms.
Abstract: Magnetism induced by the nonmagnetic dopants in the zinc-blende SiC (3C-SiC) is investigated by first-principle calculations. The atoms of the first 20 elements in the periodic table except inert gas are used to replace either Si or C atoms as dopants. We find that some nonmagnetic substitutional dopants (mainly the Group IA, Group IIA, Group IIIB, and Group VIIB elements) prefer the spin-polarized ground states with local magnetic moments. In general, the condition for obtaining the local magnetic moments and the magnetic ground state requires that the dopants are p-type and have large electronegativity difference from the neighboring host atoms. The magnetic moments can be tuned over a range between 1 µB and 3 µB by doping with the nonmagnetic elements. The nearest-neighbor exchange couplings J0 between the local magnetic moments are quite large and the codoping method is proposed to increase the dopant concentration. These imply that the nonmagnetic doping in SiC may exhibit collective magnetism. Moreover, the Group IIA Mg and Ca atoms substituting the preferred Si atoms favor the ferromagnetic ground states with the half-metallic electronic properties, which suggests that Mg or Ca substitutional doping on the Si sites in SiC could be a potential route to fabricating the diluted magnetic semiconductors.
Abstract: Glass formation, mechanical and magnetic properties of the Fe76−xC7.0Si3.3B5.0P8.7Mox (x=0, 1 at.%, 3 at.% and 5 at.%) alloys prepared using an industrial Fe-P master alloy have been studied. With the substitution of Mo for Fe, glass-forming ability (GFA) was significantly enhanced and fully amorphous rods with a diameter of up to 5 mm were produced in the alloy with 3% Mo. The Mo-containing amorphous alloys also exhibited high fracture strength of 3635–3881 MPa and excellent magnetic properties including a high saturation magnetization of 1.10–1.41 T, a high Curie temperature and a low coercive force. The unique combination of high GFA, high fracture strength and excellent magnetic properties make the newly developed bulk metallic glasses viable for practical engineering applications.
TL;DR: In this paper, the reproducing kernel particle method (RKPM) is applied to solve two-dimensional elasto-plasticity problems. But the advantage of the CVRKPM is that the correction function of a twodimensional problem is formed with one-dimensional basis function when the shape function is formed.
Abstract: On the basis of reproducing kernel particle method (RKPM), using complex variable theory, the complex variable reproducing kernel particle method (CVRKPM) is discussed in this paper. The advantage of the CVRKPM is that the correction function of a two-dimensional problem is formed with one-dimensional basis function when the shape function is formed. Then the CVRKPM is applied to solve two-dimensional elasto-plasticity problems. The Galerkin weak form is employed to obtain the discretized system equation, the penalty method is used to apply the essential boundary conditions. And then, the CVRKPM for two-dimensional elasto-plasticity problems is formed, the corresponding formulae are obtained, and the Newton-Raphson method is used in the numerical implementation. Three numerical examples are given to show that this method in this paper is effective for elasto-plasticity analysis.
TL;DR: In this article, an elastic constitutive model for frozen soil with damage is presented based on the microcosmic mechanics of composite materials, which can offer necessary constraints for engineering design and construction in permafrost regions.
Abstract: Based on the microcosmic mechanics of composite materials, an elastic constitutive model for frozen soil with damage is presented. For frozen sandy soil with a range of ice contents and under a range of temperature conditions, quantitative results determined by this constitutive model agree with practically measured stress-strain curves. After numerically simulating the coupled water, temperature and stress fields of channel frozen and frozen roadbed using a self-developed finite-element routine, more accurate and practical calculation results for the temperature field coupled with stress, displacement and strain fields are obtained; the results match predictions and tests undertaken by earlier researchers. Our results support the reliability of our routine for calculating interdependent physical quantities of frozen soil and for describing the relationships between them. Our program can offer necessary constraints for engineering design and construction in permafrost regions.
TL;DR: In this article, the properties of the glassy specimens fabricated at different cooling rates with a composition of Ti40Zr25Cu12Ni3Be20 were systematically investigated and it was confirmed that faster cooling rates caused not only a larger amount of frozen-in free volume but also a higher glass transition temperature in the bulk glassy alloy.
Abstract: Mechanical properties of the glassy specimens fabricated at different cooling rates with a composition of Ti40Zr25Cu12Ni3Be20 were systematically investigated. It was confirmed that faster cooling rates caused not only a larger amount of frozen-in free volume but also a higher glass transition temperature in the bulk glassy alloy. Increase in the free volume was found to favor plastic deformation and then to give rise to larger compressive plasticity, whilst the rise in the glass transition temperature seemed to be closely related to the higher yield strength. Moreover, the increase of yield strength and plasticity induced by fast cooling rates may also be associated with the residual stress generated during the fabrication process. Our results suggest that the deformation behavior of bulk metallic glasses is sensitive to various factors and influences from the other factors should be excluded as far as cooling-rate effects on bulk metallic glasses are considered.
TL;DR: In this article, the robustness and breakup of spiral wave in a two-dimensional lattice networks of neurons are investigated, and the effect of small-world type connection is often simplified with local regular connection and the long-range connection with certain probability.
Abstract: The robustness and breakup of spiral wave in a two-dimensional lattice networks of neurons are investigated. The effect of small-world type connection is often simplified with local regular connection and the long-range connection with certain probability. The network effect on the development of spiral wave can be better described by local regular connection and changeable long-range connection probability than fixed long-range connection probability because the long-range probability could be changeable in realistic biological system. The effect from the changeable probability for long-range connection is simplified by multiplicative noise. At first, a stable rotating spiral wave is developed by using appropriate initial values, parameters and no-flux boundary conditions, and then the effect of networks is investigated. Extensive numerical studies show that spiral wave keeps its alive and robust when the intensity of multiplicative noise is below a certain threshold, otherwise, the breakup of spiral wave occurs. A statistical factor of synchronization in two-dimensional array is defined to study the phase transition of spiral wave by checking the membrane potentials of all neurons corresponding to the critical parameters(the intensity of noise or forcing current)in the curve for factor of synchronization. The Hindmarsh-Rose model is investigated, the Hodgkin-Huxley neuron model in the presence of the channel noise is also studied to check the model independence of our conclusions. And it is found that breakup of spiral wave is easier to be induced by the multiplicative noise in presence of channel noise.
TL;DR: In this paper, a fractal model for nucleate pool boiling heat transfer of nanofluids is developed based on the fractal distribution of nanoparticles and nucleation sites on boiling surfaces.
Abstract: In this paper, a fractal model for nucleate pool boiling heat transfer of nanofluids is developed based on the fractal distribution of nanoparticles and nucleation sites on boiling surfaces. The model shows the dependences of the heat flux on nanoparticle size and the nanoparticle volume fraction of the suspension, the fractal dimension of the nanoparticle and nucleation site, temperature of nanofluids and properties of fluids. The fractal model predictions show that the natural convection stage continues relatively longer in the case of nanofluids. The addition of nanoparticles causes a decrease of the pool nucleate boiling heat transfer. The nucleate pool boiling heat transfer coefficient is decreased by increasing particle concentration. An excellent agreement between the proposed model predictions and experimental data is found. The validity of the fractal model for nucleate pool boiling heat transfer is thus verified.
TL;DR: In this article, all kinematic symmetries can be set up as the subsets of the Umov-Weyl-Fock-Hua transformations for the inertial motions.
Abstract: Based on the relativistic principle and the postulate of universal invariant constants (c, l), all kinematic symmetries can be set up as the subsets of the Umov-Weyl-Fock-Hua transformations for the inertial motions. These symmetries are connected to each other via combinations rather than via contractions and deformations.
TL;DR: In this paper, the use of graphite oxide (GO) as a gate dielectric for CNT field effect transistor (FET) has been investigated in the ambient condition and the exceptional transistor characteristics, including low operation voltage (2 V), high carrier mobility (950 cm2/V−1 s−1), and negligible gate hysteresis, suggest a potential route to the future all carbon nanoelectronics.
Abstract: Carbon nanomaterials, including the one-dimensional (1-D) carbon nanotube (CNT) and two-dimensional (2-D) graphene, are heralded as ideal candidates for next generation nanoelectronics. An essential component for the development of advanced nanoelectronics devices is processing-compatible oxide. Here, in analogy to the widespread use of silicon dioxide (SiO2) in silicon microelectronic industry, we report the proof-of-principle use of graphite oxide (GO) as a gate dielectrics for CNT field-effect transistor (FET) via a fast and simple solution-based processing in the ambient condition. The exceptional transistor characteristics, including low operation voltage (2 V), high carrier mobility (950 cm2/V−1 s−1), and the negligible gate hysteresis, suggest a potential route to the future all-carbon nanoelectronics.
TL;DR: In this article, a new nonlinear reduced order model based on the dynamically nonlinear flow equation was investigated, which can capture the limit cycle oscillation of aeroelastic system very well.
Abstract: As the amplitude of the unsteady flow oscillation is large or large changes occur in the mean background flow such as limit cycle oscillation, the traditional proper orthogonal decomposition reduced order model based on linearized time or frequency domain small disturbance solvers can not capture the main nonlinear features. A new nonlinear reduced order model based on the dynamically nonlinear flow equation was investigated. The nonlinear second order snapshot equation in the time domain for proper orthogonal decomposition basis construction was obtained from the Taylor series expansion of the flow solver. The NLR 7301 airfoil configuration and Goland+ wing/store aeroelastic model were used to validate the capability and efficiency of the new nonlinear reduced order model. The simulation results indicate that the proposed new reduced order model can capture the limit cycle oscillation of aeroelastic system very well, while the traditional proper orthogonal decomposition reduced order model will lose effectiveness.
TL;DR: In this paper, random packings of binary mixtures of spheres and spherocylinders with the same volume and the same diameter were simulated by a sphere assembly model and relaxation algorithm.
Abstract: Random packings of binary mixtures of spheres and spherocylinders with the same volume and the same diameter were simulated by a sphere assembly model and relaxation algorithm. Simulation results show that, independently of the component volume fraction, the mixture packing density increases and then decreases with the growth of the aspect ratio of spherocylinders, and the packing density reaches its maximum at the aspect ratio of 0.35. With the same volume particles, results show that the dependence of the mixture packing density on the volume fraction of spherocylinders is approximately linear. With the same diameter particles, the relationship between the mixture packing density and component volume fraction is also roughly linear for short spherocylinders, but when the aspect ratio of spherocylinders is greater than 1.6, the curves turn convex which means the packing of the mixture can be denser than either the sphere or spherocylinder packing alone. To validate the sphere assembly model and relaxation algorithm, binary mixtures of spheres and random packings of spherocylinders were also simulated. Simulation results show the packing densities of sphere mixtures agree with previous prediction models and the results of spherocylinders correspond with the simulation results in literature.
TL;DR: In this article, the influence of obstacles in a duct on the explosion flame of premixed coal gas and air was investigated using upwind WENO scheme and two-step chemical reaction model.
Abstract: In combination with experimental research, numerical simulation is performed to investigate the influence law of the obstacles in a duct on the explosion flame of premixed coal gas and air. The numerical method uses upwind WENO scheme and two-step chemical reaction model. The interaction mechanism is addressed between the compression wave from reflection on the right end of the duct and flame propagation. The reflected wave is found to result in the decrease of flame velocity. On this basis, we analyze the mechanism of the obstacles on flame as well as the law of flow field variation thus caused. The results suggest that, due to the obstacles, deflagration wave is repeatedly reflected, combustible gas mixture is fully compressed, temperature and pressure rise, chemical reaction speed increases, and hence flame intensity is strengthened. At the same time, a tripe point forms as a result of wall reflection of the deflagration wave from the obstacles and furthermore local flame speed increases. As the triple point propagates forward, the flame speed gradually decreases due to dissipation of energy. These conclusions provide a valuable theoretical foundation for the prediction of explosion field, prevention of fire and explosion and effective control of the combustion speed and flame propagation speed in detonation propulsion.
TL;DR: In this article, the thermodynamic performance of a thermal Brownian heat pump, which consists of Brownian particles moving at a periodic sawtooth potential with external forces and contacting with the alternating hot and cold reservoirs along the space coordinate, was studied.
Abstract: This paper has studied the thermodynamic performance of a thermal Brownian heat pump, which consists of Brownian particles moving at a periodic sawtooth potential with external forces and contacting with the alternating hot and cold reservoirs along the space coordinate. The heat flows driven by both potential and kinetic energies are taken into account. The analytical expressions for the heating load, coefficient of performance (COP) and power input of the Brownian heat pump are derived and the performance characteristics are obtained by numerical calculations. It is shown that due to the heat flow via the change of kinetic energy of the particles, the Brownian heat pump is always irreversible and the COP can never attain the Carnot COP. The study has also investigated the influences of the operating parameters, i.e. the external force, barrier height of the potential, asymmetry of the sawtooth potential and temperature ratio of the heat reservoirs, on the performance of the Brownian heat pump. The effective regions of external force and barrier height of the potential in which the Brownian motor can operates as a heat pump are determined. The results show that the performance of the Brownian heat pump greatly depends on the parameters; if the parameters are properly chosen, the Brownian heat pump may be controlled to operate in the optimal regimes.
TL;DR: Here a fixed-point duality quantum search algorithm is proposed that uses iteratively non-unitary operations and measurements to search an unsorted database and requires N/4 steps on average to locate the marked state.
Abstract: Here a fixed-point duality quantum search algorithm is proposed. This algorithm uses iteratively non-unitary operations and measurements to search an unsorted database. Once the marked item is found, the algorithm stops automatically. This algorithm uses a constant non-unitary operator, and requires N/4 steps on average (N is the number of data from the database) to locate the marked state. The implementation of this algorithm in a usual quantum computer is also demonstrated.
TL;DR: In this paper, the authors investigated the overall and detailed features of cosmic ray (CR) spectra in the knee region using the scenario of nuclei-photon interactions around the acceleration sources.
Abstract: The paper investigates the overall and detailed features of cosmic ray (CR) spectra in the knee region using the scenario of nuclei-photon interactions around the acceleration sources. Young supernova remnants can be the physical realities of such kind of CR acceleration sites. The results show that the model can well explain the following problems simultaneously with one set of source parameters: the knee of CR spectra and the sharpness of the knee, the detailed irregular structures of CR spectra, the so-called “component B” of Galactic CRs, and the electron/positron excesses reported by recent observations. The coherent explanation serves as evidence that at least a portion of CRs might be accelerated at the sources similar to young supernova remnants, and one set of source parameters indicates that this portion mainly comes from standard sources or from a single source.
TL;DR: In this article, a new method was developed to fabricate ultrahydrophobic surfaces with micro-nano hierarchical structures made from carbon nanotubes, which was used to measure the flow velocity in channels.
Abstract: A series of experiments have been performed to demonstrate the significant drag reduction of the laminar flow in the ultrahydrophobic channels with dual-scale micro-nano structured surfaces. However, in previous experiments, the ultrahydrophobic surfaces were fabricated with micro-structures or nano-structures and the channels were on the microscale. For the drag reduction in macro-scale channels few reports are available. Here a new method was developed to fabricate ultrahydrophobic surfaces with micro-nano hierarchical structures made from carbon nanotubes. The drag reductions up to 36.3% were observed in the macro-channels with ultrahydrophobic surfaces. The micro-PIV was used to measure the flow velocity in channels. Compared with the traditional no-slip theory at walls, a significant slip velocity was observed on the ultrahydrophobic surfaces.