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A continuum mechanics model is established for hydrogen storage in single- and multi-wall carbon nanotubes (CNTs) and the bundle of single-wall CNTs. The model accounts for the deformation of CNTs, and van der Waals interactions a...
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A continuum mechanics model is established for hydrogen storage in single- and multi-wall carbon nanotubes (CNTs) and the bundle of single-wall CNTs. The model accounts for the deformation of CNTs, and van der Waals interactions among hydrogen molecules and between hydrogen and carbon atoms. The analytical expressions of hydrogen storage (number of hydrogen molecules per unit volume) in CNTs are obtained, and are validated by atomistic simulations. CNTs are categorized as tiny, small, medium and large CNTs; tiny CNTs cannot achieve the goals of hydrogen storage (62 kg/m~3 and 6.5 wt% of hydrogen set by the US Department of Energy) without fracture; small CNTs are strained during hydrogen storage; medium CNTs can achieve the above goals without the strain and do not self collapse; and large CNTs may self collapse upon the release of hydrogen.
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Natural convection within closed cavities is of practical and theoretical interest in many nonlinear sciences and industrial applications. Using a simple lattice Boltzmann (LB) thermal model with the Boussinesq approximation, this...
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Natural convection within closed cavities is of practical and theoretical interest in many nonlinear sciences and industrial applications. Using a simple lattice Boltzmann (LB) thermal model with the Boussinesq approximation, this study investigates 2D natural convection flows with nonlinear phenomena within enclosed rectangular cavities. The simulations are performed at a constant Prandtl number of Pr = 0.71 and the reference Rayleigh numbers of Ra~*≤2 × 10~4 at the macroscopic scale (Kn = 10~(-4)) and the mesoscopic scale (Kn = 10~(-2)), respectively. In every case, an appropriate value of the characteristic velocity, i.e. V ≡ (βg_yΔTH), is chosen using a simple model based on the kinetic theory. The simulations commence to identify the convective-dominated stationary, time-independent steady flow (i.e. the primary instability condition). The spectral information of secondary instability with an oscillatory flow is then investigated using a spectrum analysis based on the fast-Fourier transform (FFT) technique. The relationship between the Nusselt number (Nu) and the reference Rayleigh number (Ra~*) is also systematically examined. In general, the simulation results show that unstable flow is generated at particular values of the Rayleigh number, Knudsen number, and cavity aspect ratio. Meanwhile, the Knudsen number and the aspect ratio play key roles in determining the evolution of oscillatory flows beyond the threshold of secondary instability.
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This paper investigates dynamic responses of a viscous fluid flow introduced under a time dependent pressure gradient in a rigid cylindrical tube that is lined with a deformable porous surface layer. With the Darcy's law and a lin...
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This paper investigates dynamic responses of a viscous fluid flow introduced under a time dependent pressure gradient in a rigid cylindrical tube that is lined with a deformable porous surface layer. With the Darcy's law and a linear elasticity assumption, we have solved the coupling effect of the fluid movement and the deformation of the porous medium in the Laplace transform space. Governing equations are deduced for the solid displacement and the fluid velocity in the porous layer. Analytical solutions in the transformed domain are derived and the time dependent variables are inverted numerically using Durbin's algorithm. Interaction between the solid and the fluid phases in the porous layer and its effects on fluid flow in tube are investigated under steady and unsteady flow conditions when the solid phase is either rigid or deformable. Examples are presented for flows driven by a Heaviside or a sinusoid pressure gradient. Significant effects of the porous surface layer on the flow in the tube are observed. The analytical solutions can be used to test more complicated numerical schemes.
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A comprehensive numerical study of the equivalent thermal conductivity of a multi-holed clay brick with the size of 240 × 115 × 90 (in mm) has been conducted, and 50 kinds of combination of holes and arrangements are examined. T...
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A comprehensive numerical study of the equivalent thermal conductivity of a multi-holed clay brick with the size of 240 × 115 × 90 (in mm) has been conducted, and 50 kinds of combination of holes and arrangements are examined. The indoor-outdoor temperature difference varies from 50 ℃ to 20 ℃. The effects of following factors are studied in details: the hole surface radiation, the width-wise and length-wise hole numbers, and the indoor-outdoor temperature difference. The major findings are as follows: (1) the radiation between hole surfaces has some effect on the equivalent thermal conductivity, thus it should be taken into account; (2) the hole number and arrangement affect the thermal conductivity in a rather complicated manner. Analysis shows that depending on the relative importance of natural convection, surface radiation and heat conduction through the clay solid, the thermal conductivity may decrease with the hole number or increase with the hole number and (3) among the 50 kinds of combination, the optimum configuration is found which has five length-wise holes, four width-wise holes and all the holes are from bottom to top in the depth direction of a brick. Its equivalent thermal conductivity is 0.419 W/(m K), which is only 53.1% of solid clay of which it is made, showing great energy-saving possibility if it is adopted in the construction of building wall.
Detailed discussion of the simulated results is conducted and flow field and temperature distributions are also provided for some typical configurations.
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Each vulnerability scanner (VS) represents, identifies and classifies vulnerabilities in its own way, thus making the different scanners difficult to study and compare. Despite numerous efforts by researchers and organisations to ...
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Each vulnerability scanner (VS) represents, identifies and classifies vulnerabilities in its own way, thus making the different scanners difficult to study and compare. Despite numerous efforts by researchers and organisations to solve the disparity in vulnerability names used in the different VSs, vulnerability categories have still not been standardised. This paper highlights the importance of having a standard vulnerability category set. It also outlines an approach towards achieving this goal by generating a standard set of vulnerability categories. A data-clustering algorithm that employs artificial intelligence is used for this purpose. The significance of this research results from having an intelligent technique that aids in the generation of standardised vulnerability categories in a relatively fast way. In addition, the technique is generic in the sense that it allows one to accommodate any VS currently known on the market to create such vulnerability categories. Another benefit is that the approach followed in this paper allows one to also compare various VSs currently available on the market. A prototype is presented to verify the concept.
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The Beasley Lake watershed (BLW), established for the Mississippi Delta Management Systems Evaluation Area project, represents the US Mississippi Delta region in the national Conservation Effects Assessment Project.The 915-ha (2,2...
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The Beasley Lake watershed (BLW), established for the Mississippi Delta Management Systems Evaluation Area project, represents the US Mississippi Delta region in the national Conservation Effects Assessment Project.The 915-ha (2,260-ac) BLW drains into an oxbow lake that has been monitored since 1995 when row crops were grown on 79% of the area, and the remaining area included a 25-ha (62-ac) lake and a 135-ha (330-ac) riparian forest. Currently, row crops account for 66.5% of the area with 12.4% enrolled in the Conservation Reserve Program. Cotton (Gossypium hirsutum L.) acreage has decreased from 63.3% to 8.9%. Historical and current research in BLW focuses on monitoring lake limnology, evaluating conservation practice effects on edge-of-field runoff, quantifying changes associated with the Conservation Reserve Program, and modeling watershed responses. Applying combinations of conservation practices can significantly reduce nonpoint source pollution. For example, converting row crops to reduced tillage and transgenic herbicide-resistant crops in BLW reduced suspended sediment (70% reduction), total phosphorus (41% reduction), and pesticide concentrations in lake water. Corresponding increases in Secchi visibility (97%) and chlorophyll a (a primary productivity indicator) likely contributed to improved fish productivity (e.g., fish weight increase comparing 1998 and 2004: Micropterus salmoides 87%, Lepomis macrochims, 65%) during this period. Additional studies should quantify effects of individual practices and improve modeling tools for making better management decisions. The utilization of the Annualized Agricultural Non-Point Source (AnnAGNPS) model and the Riparian Ecosystem Management Model (REMM) together provides additional information on the effectiveness of conservation practices within the watershed by combining technology that assesses riparian buffer effectiveness in filtering nutrients at the field scale with the watershed water quality transport capabilities of the AnnAGNPS model.
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A boundary-type meshless method named dual reciprocity hybrid boundary node method (DRHBNM) is presented. It can be applied to solve elasticity problems with body force, centrifugal load, or other similar problems. In this method,...
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A boundary-type meshless method named dual reciprocity hybrid boundary node method (DRHBNM) is presented. It can be applied to solve elasticity problems with body force, centrifugal load, or other similar problems. In this method, the solution comprises two parts, i.e., the general solution and the particular solution. The general solution is solved by the hybrid boundary node method (HBNM), and the particular one is obtained by the dual reciprocity method (DRM). This method extends the Kelvin fundamental solution for static elastic problems without body force to non-homogeneous problems with body or inertial forces. A modified variational formulation is applied to form the discrete equations of HBNM. The moving least squares (MLS) are employed to approximate the boundary variables, while the domain variables are interpolated by the classical fundamental solution. The particular solution for the body force is obtained by DRM, and the integration in the domain is interpolated by the radial basis function. The proposed method retains the characteristics of the meshless method. At the same time, it employs the fundamental solution as in the boundary element method (BEM). Therefore, this method has the advantages of both meshless method and BEM. It does not require a 'boundary element mesh', either for the purpose of interpolation of the solution variables, or for the integration of the 'energy'. The points in the domain are used only to interpolate particular solutions by the radial basis function and it is not necessary for the integration and approximation of the solution variables. Finally, the boundary solution variables are interpolated by the independent smooth segment boundary. As special treatments for corners are not required, it can obtain accurate boundary tractions for non-smooth boundaries.
Numerical examples of 2-D elasticity problems with body force are used to demonstrate the versatility of the method and its fast convergence. The computational results for unknown variables are accurate. Also, the variable parameters have little influence on the results and can be changed in wide ranges. It is shown that the present method is effective and can be widely applied to practical problems.
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Experiments are conducted here to investigate how the channel size affects the R-407C saturated flow boiling heat transfer and associated bubble characteristics in a horizontal narrow annular duct. The gap of the duct is fixed at ...
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Experiments are conducted here to investigate how the channel size affects the R-407C saturated flow boiling heat transfer and associated bubble characteristics in a horizontal narrow annular duct. The gap of the duct is fixed at 1.0 and 2.0 mm in this study. The measured data indicate that the saturated flow boiling heat transfer coefficient increases with a decrease in the duct gap. Besides, raising the imposed heat flux can cause a significant increase in the boiling heat transfer coefficients. However, the effects of the refrigerant mass flux and saturated temperature on the boiling heat transfer coefficient are milder. The results from the flow visualization show that the mean diameter of the bubbles departing from the heating surface decreases noticeably at increasing R-407C mass flux. Moreover, the bubble departure frequency increases at reducing duct size and at a high imposed heat flux many bubbles generated from the cavities in the heating surface tend to merge together to form big bubbles. Meanwhile comparison of the present heat transfer data for R-407C with R-134a in the same duct and with some existing correlations is conducted. Furthermore, correlation for the present R-407C saturated flow boiling heat transfer data is proposed. Additionally, the present data for some quantitative bubble characteristics such as the mean bubble departure diameter and frequency and the active nucleation site density are also correlated.
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In the Compact Muon Solenoid (CMS) experiment, muon detection in the forward direction is accomplished by cathode strip chambers (CSC). These detectors identify muons, provide a fast muon trigger, and give a precise measurement of...
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In the Compact Muon Solenoid (CMS) experiment, muon detection in the forward direction is accomplished by cathode strip chambers (CSC). These detectors identify muons, provide a fast muon trigger, and give a precise measurement of the muon trajectory. There are 468 six-plane CSCs in the system. The efficiency of finding muon trigger primitives (muon track segments) was studied using 36 CMS CSCs and cosmic ray muons during the Magnet Test and Cosmic Challenge (MTCC) exercise conducted by the CMS experiment in 2006. In contrast to earlier studies that used muon beams to illuminate a very small chamber area (<0.01 m~2), results presented in this paper were obtained by many installed CSCs operating in situ over an area of ≈ 23 m~2 as a part of the CMS experiment. The efficiency of finding two-dimensional trigger primitives within six-layer chambers was found to be 99.93 ± 0.03%. These segments, found by the CSC electronics within 800 ns after the passing of a muon through the chambers, are the input information for the Level-1 muon trigger and, also, are a necessary condition for chambers to be read out by the Data Acquisition System.
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A facility for studying (n,p) reactions at neutron kinetic energies of 140 approx ＜ T_n approx ＜ 300 MeV has been constructed by using the existing Large Acceptance Spectrometer at the Research Center for Nuclear Physics, Osaka ...
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A facility for studying (n,p) reactions at neutron kinetic energies of 140 approx ＜ T_n approx ＜ 300 MeV has been constructed by using the existing Large Acceptance Spectrometer at the Research Center for Nuclear Physics, Osaka University. A neutron beam produced by the ~7Li(p,n) reaction hits the (n,p) targets located in a segmented target system, which allows one to use a relatively thick target in total (～0.5g/cm~2) with a moderate energy resolution of ～1 MeV. The facility enables one to obtain spectra at 300 MeV up to an excitation energy of 70 MeV with a single setting of the spectrometer. This (n,p) facility has a large effective solid angle of 11 msr for an effective target size of 30~W × 20~H mm~2.
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