The crystal structure of L-glutamine is stabilized by a three-dimensional network of intermolecular hydrogen bonds.We utilize plane-wave density functional theory lattice-dynamics calculations within the generalized-g...The crystal structure of L-glutamine is stabilized by a three-dimensional network of intermolecular hydrogen bonds.We utilize plane-wave density functional theory lattice-dynamics calculations within the generalized-gradient approximation（GGA）, Perdew–Burke–Ernzerhof（PBE）, PBE for solids（PBEsol）, PBE with Wu–Cohen exchange（WC）, and dispersion-corrected PBE, to investigate the effect of these intermolecular contacts on the absorption spectra of glutamine in the terahertz frequency range. Among these calculations, the solid-state simulated results obtained using the WC method exhibit a good agreement with the measured absorption spectra, and the absorption features are assigned with the help of WC. This indicates that the vibrational modes of glutamine were related to the combination of intramolecular and intermolecular motions, the intramolecular modes were dominated by rocking or torsion involving functional groups; the intermolecular modes mainly result from the translational motions of individual molecules, and the rocking of the hydrogenbonded functional groups.展开更多
A mathematical model based on the computational fluid dynamics method,heat and mass transfer in porous media and the unreacted shrinking core model for the oxidation reaction of an individual magnetite pellet during p...A mathematical model based on the computational fluid dynamics method,heat and mass transfer in porous media and the unreacted shrinking core model for the oxidation reaction of an individual magnetite pellet during preheating was established.The commercial software COMSOL Multiphysics was used to simulate the change in the oxidation degree of the pellet at different temperatures and oxygen concentrations,and the simulated results were compared with the exper-imental results.The model considered the influence of the exothermic heat of the reaction,and the enthalpy change was added to calculate the heat released by the oxidation.The results show that the oxidation rate on the surface of the pellet is much faster than that of the inside of the pellet.Temperature and oxygen concentration have great influence on the pellet oxidation model.Meanwhile,the exothermic calculation results show that there is a non-isothermal phenomenon inside the pellet,which leads to an increase in temperature inside the single pellet.Under the preheating condition of 873-1273 K(20%oxygen content),the heat released by the pellet oxidation reaction in a chain grate is 7.8×10^(6)-10.8×10^(6) kJ/h,which is very large and needs to be considered in the magnetite pellet oxidation modelling.展开更多
This article first generalizes the basic engineering phases of modern rapid prototyping processes, and then describes the techniques of data capture for data modeling and model making. The article also provides a brie...This article first generalizes the basic engineering phases of modern rapid prototyping processes, and then describes the techniques of data capture for data modeling and model making. The article also provides a brief overview of the photogrametric techniques of restitution of 3D objects, and highlights the difficulties and limitations of existing methods. It therefore presents a novel approach to photo-modeling for acquiring 3D model data from single 2D photorealistic images. Implementation of the approach is then described against a effectiveness of photo-modeling practice. background of rapid prototyping processes to demonstrate the展开更多
CVD growth of uniform conformal polycrystalline diamond (PCD) coatings over complex three dimensional structures is very important material processing technique. It has been found that the nucleation and subsequent gr...CVD growth of uniform conformal polycrystalline diamond (PCD) coatings over complex three dimensional structures is very important material processing technique. It has been found that the nucleation and subsequent growth period is very critical for successful development of CVD diamond based technologies. There are many methods of enhancing diamond nucleation on foreign substrates-ultrasonic treatment with diamond seed suspension being the best among them. A combination of ultrasonic seeding (US) technique with prior treatment (PT) of the substrate under CVD diamond growth conditions for brief period of time, has found to be very effective in enhancing the diamond nucleation during CVD growth—together they are known as NNP. But successive usage of the same seeding suspension up to ten cycles deteriorates the seeding efficiency. 6th seeding cycle onwards the silicon substrates are barely get covered by diamond crystallites. Five different diamond micron grits were used for seeding the silicon substrates and it is observed that US with the sub-micron particles (0.25 μm) is very effective in efficient nucleation of PCD on Si substrates. PT of the substrate somewhat negates the effect of successive use of the same seeding slurry but it is best to avoid recycling of the same seeding suspension using micron size diamond grits.展开更多
Layzer’s approximation method for investigation of two fluid interface structures associated with Rayleigh Taylor instability for arbitrary Atwood number is extended with the inclusion of second harmonic mode leaving...Layzer’s approximation method for investigation of two fluid interface structures associated with Rayleigh Taylor instability for arbitrary Atwood number is extended with the inclusion of second harmonic mode leaving out the zeroth harmonic one. The modification makes the fluid velocities vanish at infinity and leads to avoidance of the need to make the unphysical assumption of the existence of a time dependent source at infinity. The present analysis shows that for an initial interface perturbation with curvature exceeding , where A is the Atwood number there occurs an almost free fall of the spike with continuously increasing sharpening as it falls. The curvature at the tip of the spike also increases with Atwood number. Certain initial condition may also result in occurrence of finite time singularity as found in case of conformal mapping technique used earlier. However bubble growth rate is not appreciably affected.展开更多
Shock induced symmetric compression has been studied in a spherical target. The shock induced interfacial radius will shrink and would reach a minimum point during implosion situation. However, after implosion the pla...Shock induced symmetric compression has been studied in a spherical target. The shock induced interfacial radius will shrink and would reach a minimum point during implosion situation. However, after implosion the plasma tries to expand in blow off/explosion situation and as a result the interfacial radius will increase. Effects of plasma parameters like density and temperature have been studied numerically. It is seen that the density increases many times due to the mass conservation in imploding situation of a compressible shell like ICF. However, temperature will change rapidly due to change of inner density and so would be the pressure of compressible fluid following adiabatic law. Our analytical results agree qualitatively with those of simulation results in spherical geometry and also experimental observations conducted in cylindrical container.展开更多
In this paper,we used terahertz time-domain spectroscopy(THz-TDS)over a range of 0.3–2.5 THz to investigate the formation of solid-state cocrystals of amino acids,formed by grinding mixtures of two different kinds of...In this paper,we used terahertz time-domain spectroscopy(THz-TDS)over a range of 0.3–2.5 THz to investigate the formation of solid-state cocrystals of amino acids,formed by grinding mixtures of two different kinds of amino acids.For comparison,we prepared dual-layer samples,combined by pressing two single-component pellets together without grinding.In the ground-mixture samples,some extra absorption peaks appeared,different from the characteristic peaks of the pure components,but these peaks did not appear in the dual-layer samples.Thus,these extra absorption peaks in the THz range are unique features of cocrystals.From our results,we believe that THz-TDS is a promising technique to characterize cocrystals.展开更多
A fractal analysis method is proposed to investigate the wheel-rail rolling noise,in which statistics of the noise’s increments with different scales are studied.It is proven that the noise has fractality and can be ...A fractal analysis method is proposed to investigate the wheel-rail rolling noise,in which statistics of the noise’s increments with different scales are studied.It is proven that the noise has fractality and can be described by the fractional Brownian motion(FBM).On this basis,the power-law relation of the FBM regarding the variance of its wavelet coefficients and the fractal dimension is utilized to estimate the fractal dimension.Comparisons of fractal dimensions are made among noises at different speeds and the rail defect AE signals of crack propagations.It is revealed that the fractal dimension of the noise is stochastic and its estimations at different speeds distribute in a small margin below 2 with mean 1.5666.Moreover,the fractal dimension is irrelevant to the speed and is an intrinsic feature of the noise.Thus,the noises with different speeds can be modeled by an identical FBM.On the contrary,fractal dimensions of AE signals of crack propagations are all above 2 and the modeling requirement of the FBM is not met.Therefore,the fractal dimension can be taken advantage of as a distinct feature,too.The work extracts the fractal dimension of the wheel-rail rolling noise as the intrinsic feature and offers an effective analysis approach for the description of wheel-rail rolling noise and defect detection in high-speed railway.展开更多
We demonstrate a method for quickly and automatically detecting all three components of a remanent magnetic field around a shielded spin-exchange relaxation-free(SERF)atomic magnetometer(AM)using the trisection algori...We demonstrate a method for quickly and automatically detecting all three components of a remanent magnetic field around a shielded spin-exchange relaxation-free(SERF)atomic magnetometer(AM)using the trisection algorithm(TSA)for zero-field resonance(ZFR).To satisfy the measurement of AMs,a resonance light of the ^(87)Rb D1 line with a spectral width of less than 1 MHz is converted to circular polarization by a linear polarizer and a quarter-wave plate.After the light beam has passed through the alkali metal vapor cell,the residual magnetic field can be measured by searching for triaxial ZFR optical peaks.The TSA stably reduces the measurement time to 2.41 s on average and improves the measurement accuracy,significantly outpacing existing methods.The weighted averages of all measurements with corresponding uncertainties are(–15.437±0.022)nT,(6.062±0.021)nT,and(–14.158±0.052)nT on the x-,y-,and z-axes,respectively.These improvements could facilitate more extremely weak magnetic studies in real time,such as magnetoencephalography(MEG)and magnetocardiography(MCG)measurements.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61302007 and 60977065)the Fundamental Research Funds for the Central Universities of China(Grant No.FRF-SD-12-016A)the Engineering Research Center of Industrial Spectrum Imaging of Beijing,China
文摘The crystal structure of L-glutamine is stabilized by a three-dimensional network of intermolecular hydrogen bonds.We utilize plane-wave density functional theory lattice-dynamics calculations within the generalized-gradient approximation（GGA）, Perdew–Burke–Ernzerhof（PBE）, PBE for solids（PBEsol）, PBE with Wu–Cohen exchange（WC）, and dispersion-corrected PBE, to investigate the effect of these intermolecular contacts on the absorption spectra of glutamine in the terahertz frequency range. Among these calculations, the solid-state simulated results obtained using the WC method exhibit a good agreement with the measured absorption spectra, and the absorption features are assigned with the help of WC. This indicates that the vibrational modes of glutamine were related to the combination of intramolecular and intermolecular motions, the intramolecular modes were dominated by rocking or torsion involving functional groups; the intermolecular modes mainly result from the translational motions of individual molecules, and the rocking of the hydrogenbonded functional groups.
基金the National Natural Science Foundation of China(51675245).
文摘A mathematical model based on the computational fluid dynamics method,heat and mass transfer in porous media and the unreacted shrinking core model for the oxidation reaction of an individual magnetite pellet during preheating was established.The commercial software COMSOL Multiphysics was used to simulate the change in the oxidation degree of the pellet at different temperatures and oxygen concentrations,and the simulated results were compared with the exper-imental results.The model considered the influence of the exothermic heat of the reaction,and the enthalpy change was added to calculate the heat released by the oxidation.The results show that the oxidation rate on the surface of the pellet is much faster than that of the inside of the pellet.Temperature and oxygen concentration have great influence on the pellet oxidation model.Meanwhile,the exothermic calculation results show that there is a non-isothermal phenomenon inside the pellet,which leads to an increase in temperature inside the single pellet.Under the preheating condition of 873-1273 K(20%oxygen content),the heat released by the pellet oxidation reaction in a chain grate is 7.8×10^(6)-10.8×10^(6) kJ/h,which is very large and needs to be considered in the magnetite pellet oxidation modelling.
基金This work is supported by Cheung Kong Scholars Program of the People's Republic of China, in association with Southeast University, Nanjing, PRC. (No.seuzx042001)
文摘This article first generalizes the basic engineering phases of modern rapid prototyping processes, and then describes the techniques of data capture for data modeling and model making. The article also provides a brief overview of the photogrametric techniques of restitution of 3D objects, and highlights the difficulties and limitations of existing methods. It therefore presents a novel approach to photo-modeling for acquiring 3D model data from single 2D photorealistic images. Implementation of the approach is then described against a effectiveness of photo-modeling practice. background of rapid prototyping processes to demonstrate the
文摘CVD growth of uniform conformal polycrystalline diamond (PCD) coatings over complex three dimensional structures is very important material processing technique. It has been found that the nucleation and subsequent growth period is very critical for successful development of CVD diamond based technologies. There are many methods of enhancing diamond nucleation on foreign substrates-ultrasonic treatment with diamond seed suspension being the best among them. A combination of ultrasonic seeding (US) technique with prior treatment (PT) of the substrate under CVD diamond growth conditions for brief period of time, has found to be very effective in enhancing the diamond nucleation during CVD growth—together they are known as NNP. But successive usage of the same seeding suspension up to ten cycles deteriorates the seeding efficiency. 6th seeding cycle onwards the silicon substrates are barely get covered by diamond crystallites. Five different diamond micron grits were used for seeding the silicon substrates and it is observed that US with the sub-micron particles (0.25 μm) is very effective in efficient nucleation of PCD on Si substrates. PT of the substrate somewhat negates the effect of successive use of the same seeding slurry but it is best to avoid recycling of the same seeding suspension using micron size diamond grits.
文摘Layzer’s approximation method for investigation of two fluid interface structures associated with Rayleigh Taylor instability for arbitrary Atwood number is extended with the inclusion of second harmonic mode leaving out the zeroth harmonic one. The modification makes the fluid velocities vanish at infinity and leads to avoidance of the need to make the unphysical assumption of the existence of a time dependent source at infinity. The present analysis shows that for an initial interface perturbation with curvature exceeding , where A is the Atwood number there occurs an almost free fall of the spike with continuously increasing sharpening as it falls. The curvature at the tip of the spike also increases with Atwood number. Certain initial condition may also result in occurrence of finite time singularity as found in case of conformal mapping technique used earlier. However bubble growth rate is not appreciably affected.
文摘Shock induced symmetric compression has been studied in a spherical target. The shock induced interfacial radius will shrink and would reach a minimum point during implosion situation. However, after implosion the plasma tries to expand in blow off/explosion situation and as a result the interfacial radius will increase. Effects of plasma parameters like density and temperature have been studied numerically. It is seen that the density increases many times due to the mass conservation in imploding situation of a compressible shell like ICF. However, temperature will change rapidly due to change of inner density and so would be the pressure of compressible fluid following adiabatic law. Our analytical results agree qualitatively with those of simulation results in spherical geometry and also experimental observations conducted in cylindrical container.
基金supported by the National Natural Science Foundation of China (61302007 and 60977065)the Fundamental Research Funds for the Central Universities (FRF-SD12-016A)
文摘In this paper,we used terahertz time-domain spectroscopy(THz-TDS)over a range of 0.3–2.5 THz to investigate the formation of solid-state cocrystals of amino acids,formed by grinding mixtures of two different kinds of amino acids.For comparison,we prepared dual-layer samples,combined by pressing two single-component pellets together without grinding.In the ground-mixture samples,some extra absorption peaks appeared,different from the characteristic peaks of the pure components,but these peaks did not appear in the dual-layer samples.Thus,these extra absorption peaks in the THz range are unique features of cocrystals.From our results,we believe that THz-TDS is a promising technique to characterize cocrystals.
基金supported by the National Natural Science Foundation of China(61771161,61601139)the China Postdoctoral Science Foundation funded project(2017M610209)。
文摘A fractal analysis method is proposed to investigate the wheel-rail rolling noise,in which statistics of the noise’s increments with different scales are studied.It is proven that the noise has fractality and can be described by the fractional Brownian motion(FBM).On this basis,the power-law relation of the FBM regarding the variance of its wavelet coefficients and the fractal dimension is utilized to estimate the fractal dimension.Comparisons of fractal dimensions are made among noises at different speeds and the rail defect AE signals of crack propagations.It is revealed that the fractal dimension of the noise is stochastic and its estimations at different speeds distribute in a small margin below 2 with mean 1.5666.Moreover,the fractal dimension is irrelevant to the speed and is an intrinsic feature of the noise.Thus,the noises with different speeds can be modeled by an identical FBM.On the contrary,fractal dimensions of AE signals of crack propagations are all above 2 and the modeling requirement of the FBM is not met.Therefore,the fractal dimension can be taken advantage of as a distinct feature,too.The work extracts the fractal dimension of the wheel-rail rolling noise as the intrinsic feature and offers an effective analysis approach for the description of wheel-rail rolling noise and defect detection in high-speed railway.
基金This work was supported by Beijing Natural Science Foundation(Grant No.4191002)Key Research&Development Program of Zhejiang,China(Grant No.2020C01037)+1 种基金the National Key Research&Development Program of China(Grant No.2018YFB2002405)the National Natural Science Foundation of China(Grant No.62073014).
文摘We demonstrate a method for quickly and automatically detecting all three components of a remanent magnetic field around a shielded spin-exchange relaxation-free(SERF)atomic magnetometer(AM)using the trisection algorithm(TSA)for zero-field resonance(ZFR).To satisfy the measurement of AMs,a resonance light of the ^(87)Rb D1 line with a spectral width of less than 1 MHz is converted to circular polarization by a linear polarizer and a quarter-wave plate.After the light beam has passed through the alkali metal vapor cell,the residual magnetic field can be measured by searching for triaxial ZFR optical peaks.The TSA stably reduces the measurement time to 2.41 s on average and improves the measurement accuracy,significantly outpacing existing methods.The weighted averages of all measurements with corresponding uncertainties are(–15.437±0.022)nT,(6.062±0.021)nT,and(–14.158±0.052)nT on the x-,y-,and z-axes,respectively.These improvements could facilitate more extremely weak magnetic studies in real time,such as magnetoencephalography(MEG)and magnetocardiography(MCG)measurements.
