Electro collisions with molecular nitrogen in its ground and electronically excited states using the R-matrix method

A comprehensive study of electron collisions with the X1Σg+ ground state as well as the metastable A3Σu+ and a1Πg excited states of the N2 molecule is reported using the fixed-nucleus R-matrix method. Integral elastic scattering and electronic excitation cross sections from the X1Σg+ ground state to the eight lowest electronic states, A3Σu+, B3Πg, W3Δu, B'3Σu−, a1Πg, a'1Σu−, w1Δu and C3Πu, overall agree well with the available experimental and theoretical results although updates of some recommended values are suggested. Accurate electron impact electronic transition cross sections starting from the A3Σu+ and a1Πg metastable excited states are reported. The total summed electronic transition cross sections from the a1Πg state is dominant: an order of magnitude higher than those of the X1Σg+ ground state. The de-excitation cross sections generally show a downward trend with increasing incident electron energy, which is different from the elastic and electronic excitation cross sections which generally increase with collision energy. There is a prominent 2Πu symmetry resonance peak at 2.8 eV for electronic de-excitation scattering of a1Πg → B3Πg, which significantly contributes to the total summed cross sections from the a1Πg excited state. The present results provide a new insight which will aid understanding of electron spectra in the atmosphere of the Earth and Titan

A vibration-based damage identification technique free of structural baseline information: experimental validation in multi-component plane structure

A vibration-based method for damage identification was established based on the “weak” formulation of Pseudo-excitation (PE) technique. The method can be effectively conducted without any prior knowledge of structural baseline parameters, e.g., Young’s Modulus, and is capable of detecting multi-damage in both one- and two-dimensional structural components. Moreover, relying on point-wise examination of structural dynamic equilibrium conditions, the baseline parameters of inspected structure can be inversely estimated in a statistical way, showing promising potential in engineering practices. As a proof-of-concept investigation, multi-damage in a plane structure, containing both beam and plate components, were identified experimentally using the proposed method

SCOOTER: A compact and scalable dynamic labeling scheme for XML updates

Although dynamic labeling schemes for XML have been the focus of recent research activity, there are significant challenges still to be overcome. In particular, though there are labeling schemes that ensure a compact label representation when creating an XML document, when the document is subject to repeated and arbitrary deletions and insertions, the labels grow rapidly and consequently have a significant impact on query and update performance. We review the outstanding issues todate and in this paper we propose SCOOTER - a new dynamic labeling scheme for XML. The new labeling scheme can completely avoid relabeling existing labels. In particular, SCOOTER can handle frequently skewed insertions gracefully. Theoretical analysis and experimental results confirm the scalability, compact representation, efficient growth rate and performance of SCOOTER in comparison to existing dynamic labeling schemes

Suppressing influence of measurement noise on vibration-based damage detection involving higher-order derivatives

Author name used in this publication: Cheng, Li.2012-2013 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Scanning supersaturation condensation particle counter applied as a nano-CCN counter for size-resolved analysis of the hygroscopicity and chemical composition of nanoparticles

Knowledge about the chemical composition of aerosol particles is essential to understand their formation and evolution in the atmosphere. Due to analytical limitations, however, relatively little information is available for sub-10 nm particles. We present the design of a nano-cloud condensation nuclei counter (nano-CCNC) for measuring size-resolved hygroscopicity and inferring chemical composition of sub-10 nm aerosol particles. We extend the use of counting efficiency spectra from a water-based condensation particle counter (CPC) and link it to the analysis of CCN activation spectra, which provides a theoretical basis for the application of a scanning supersaturation CPC (SS-CPC) as a nano-CCNC. Measurement procedures and data analysis methods are demonstrated through laboratory experiments with monodisperse particles of diameter down to 2.5 nm, where sodium chloride, ammonium sulfate, sucrose and tungsten oxide can be easily discriminated by different characteristic supersaturations of water droplet formation. A near-linear relationship between hygroscopicity parameter κ and organic mass fraction is also found for sucrose-ammonium sulfate mixtures. The design is not limited to the water CPC, but also applies to CPCs with other working fluids (e.g. butanol, perfluorotributylamine). We suggest that a combination of SS-CPCs with multiple working fluids may provide further insight into the chemical composition of nanoparticles and the role of organic and inorganic compounds in the initial steps of atmospheric new particle formation and growth

Molecular dynamics simulation of the surface tension of aqueous sodium chloride: from dilute to highly supersaturated solutions and molten salt

Sodium chloride (NaCl) is one of the key components of atmospheric aerosols. The surface tension of aqueous NaCl solution (σNaCl, sol) and its concentration dependence are essential to determine the equilibrium water vapor pressure of aqueous NaCl droplets. Supersaturated NaCl solution droplets are observed in laboratory experiments and under atmospheric conditions, but the experimental data for σNaCl, sol are mostly limited up to subsaturated solutions. In this study, the surface tension of aqueous NaCl is investigated by molecular dynamics (MD) simulations and the pressure tensor method from dilute to highly supersaturated solutions. We show that the linear approximation of concentration dependence of σNaCl, sol at molality scale can be extended to the supersaturated NaCl solution until a molality of  ∼ 10.7&thinsp;mol kg−1 (i.e., solute mass fraction (xNaCl) of  ∼ 0.39). Energetic analyses show that this monotonic increase in surface tension is driven by the increase in excess surface enthalpy (ΔH) as the solution becomes concentrated. After that, the simulated σNaCl, sol remains almost unchanged until xNaCl of  ∼ 0.47 (near the concentration upon efflorescence). The existence of the inflection point at xNaCl of  ∼ 0.39 and the stable surface tension of xNaCl between  ∼ 0.39 and  ∼ 0.47 can be attributed to the nearly unchanged excess surface entropy term (T ⋅ ΔS) and the excess surface enthalpy term (ΔH). After a second inflection point at xNaCl of  ∼ 0.47, the simulated σNaCl, sol gradually regains the growing momentum with a tendency to approach the surface tension of molten NaCl ( ∼ 175.58&thinsp;mN m−1 at 298.15&thinsp;K, MD simulation-based extrapolation). This fast increase in σNaCl, sol at xNaCl &gt; 0.47 is a process driven by excess surface enthalpy and excess surface entropy. Our results reveal different regimes of concentration dependence of the surface tension of aqueous NaCl at 298.15&thinsp;K: a water-dominated regime (xNaCl from 0 to  ∼ 0.39), a transition regime (xNaCl from  ∼ 0.39 to  ∼ 0.47) and a molten NaCl-dominated regime (xNaCl from  ∼ 0.47 to 1).</p

Non-collinear magnetic structure and anisotropic magnetoelastic coupling in cobalt pyrovanadate Co2V2O7

The Co2V2O7 is recently reported to exhibit amazing magnetic field-induced magnetization plateaus and ferroelectricity, but its magnetic ground state remains ambiguous due to its structural complexity. Magnetometry measurements, and time-of-flight neutron powder diffraction (NPD) have been employed to study the structural and magnetic properties of Co2V2O7, which consists of two non-equivalent Co sites. Upon cooling below the Ne\'el temperature TN = 6.3 K, we observe magnetic Bragg peaks at 2K in NPD which indicated the formation of long range magnetic order of Co2+ moments. After symmetry analysis and magnetic structure refinement, we demonstrate that Co2V2O7 possesses a complicated non-collinear magnetic ground state with Co moments mainly located in b-c plane and forming a non-collinear spin-chain-like structure along the c-axis. The ab initio calculations demonstrate that the non-collinear magnetic structure is more stable than various ferromagnetic states at low temperature. The non-collinear magnetic structure with canted up-up-down-down spin configuration is considered as the origin of magnetoelectric coupling in Co2V2O7 because the inequivalent exchange striction induced by the spin-exchange interaction between the neighboring spins is the driving force of ferroelectricity. Besides, it is found that the deviation of lattice parameters a and b is opposite below TN, while the lattice parameter c and stay almost constant below TN, evidencing the anisotropic magnetoelastic coupling in Co2V2O7.Comment: 9 pages, 8 figure

Dirac Cosmology and the Acceleration of the Contemporary Universe

A model is suggested to unify the Einstein GR and Dirac Cosmology. There is one adjusted parameter $b_2$ in our model. After adjusting the parameter $b_2$ in the model by using the supernova data, we have calculated the gravitational constant $\bar G$ and the physical quantities of $a(t)$, $q(t)$ and $\rho_r(t)/ \rho_b(t)$ by using the present day quantities as the initial conditions and found that the equation of state parameter $w_{\theta}$ equals to -0.83, the ratio of the density of the addition creation $\Omega_{\Lambda}=0.8$ and the ratio of the density of the matter including multiplication creation, radiation and normal matter $\Omega_m =0.2$ at present. The results are self-consistent and in good agreement with present knowledge in cosmology. These results suggest that the addition creation and multiplication creation in Dirac cosmology play the role of the dark energy and dark matter.Comment: 13 pages, 8 figure