超声波信号渡越时间参数法测量空气中温度分布

超声波已成功在医疗、化工和无损探伤等领域得到广泛的应用。根据超声波在空气中的传播速度会随着温度改变而改变这一特点,本文把空气中的温度场作为研究对象,利用超声波信号在空气中的渡越时间参数TOF(Time of Flight)来对空气中的温度分布情况进行超声波CT画像的重建。     

Molecular conformation and melting behavior of alkyl/oligo(oxyethylene)/alkyl triblock position isomers: effect of the position of an oligo(oxyethylene) block

The molecular conformation and melting behavior of triblock position isomers H(CH(2))(k)(OCH(2)CH(2))(4)O(CH(2))(12)(-)(k)H (abbreviated as C(k)E(4)C(12)(-)(k)) with k = 6-11 have been studied by infrared spectroscopy and differential scanning calorimetry (DSC), with focus on the effect of the position of an oligo(oxyethylene) block in the molecule. The analysis of infrared spectra has revealed that the stable molecular form changes from a fully planar structure (gamma form) to a planar/helical/planar structure (beta form) with a change of the position of the tetrakis(oxyethylene) block from the center to the end of the molecule. The DSC measurements have shown that the melting points of the gamma-form solid decrease and the melting points of the beta-form solid increase with a shift of the tetrakis(oxyethylene) block toward the terminal of the molecule. The stabilities of the two molecular forms change over between k = 8 and 9. C(8)E(4)C(4) and C(9)E(4)C(3) exhibit contrasting conformational behavior with temperature; when the temperature is increased, the metastable beta form of C(8)E(4)C(4) transforms into the stable gamma form, while the metastable gamma form of C(9)E(4)C(3) transforms into the stable beta form. The metastable gamma form with a planar oligo(oxyethylene) block is a new finding in the present work. The experimental results of the stabilities of molecular forms are explained by the relative stabilities of partial crystal lattices formed by the alkyl and oligo(oxyethylene) blocks.     

A bovine glucuronidase for assembly of beta-D-glucuronyl-(1-3)-6-O-sulfo-beta-D-gluco- and galacto-pyranosyl linkages

Glucuronidase-catalyzed transglycosylation was examined by using 4-nitrophenyl beta-D-glucuronide (D-GlcA-O-pNP) as the glycosyl donor; when pNP 6-O-sulfo-beta-D-gluco- and D-galacto-pyranosides were used as the acceptors, a bovine enzyme was found to construct beta-D-GlcA-(1-3)-linkages with the 6-O-sulfo-sugars in both a site- and beta-selective way.     

Semi-tilting Modules and Mutation

We introduce the notion of semi-tilting modules and show that the class of basic semi-tilting modules is closed under mutation. Using this, we provide a partial answer to the Wakamatsu tilting conjecture. Also, we define a partial order on the set of equivalence classes of semi-tilting modules and show that this order is closely related to mutation for semi-tilting modules.     

Contrast analysis of Shockley partial dislocations in 4H-SiC observed by synchrotron Berg–Barrett X-ray topography

Shockley partial dislocations in 4H-SiC were observed using monochromatic synchrotron X-ray topography with a grazing-incidence Bragg-case geometry, that is, Berg–Barrett topography. The contrast of partial dislocations at the edges of Shockley-type stacking faults is discussed in terms of whether they have C- or Si-core edge components, or screw components. The dissociated state of basal-plane dislocation is discussed on a basis of the stacking sequence for basal-planes in the 4H-SiC crystal structure. It is expected that the results obtained in this study will be useful for characterizing Shockley-type stacking faults in Berg–Barrett topography.     

On Partial Tilting Complexes

Let R be a commutative noetherian ring and A a noetherian R-algebra. Let P ^? ∈ 𝒦^b(𝒫 _A ) with Hom_𝒦(Mod-A)(P ^?, P ^?[i]) = 0 for i > 0. We will provide a sufficient condition for P ^? to be a direct summand of a silting complex. Also, in case Hom_𝒦(Mod-A)(P ^?, P ^?[i]) = 0 for i ≠ 0, we will provide a sufficient condition for P ^? to be a direct summand of a tilting complex.     

Laminar–Turbulent Intermittency in Annular Couette–Poiseuille Flow: Whether a Puff Splits or Not

Direct numerical simulations were carried out with an emphasis on the intermittency and localized turbulence structure occurring within the subcritical transitional regime of a concentric annular Couette–Poiseuille flow. In the annular system, the ratio of the inner to outer cylinder radius is an important geometrical parameter affecting the large-scale nature of the intermittency. We chose a low radius ratio of 0.1 and imposed a constant pressure gradient providing practically zero shear on the inner cylinder such that the base flow was approximated to that of a circular pipe flow. Localized turbulent puffs, that is, axial uni-directional intermittencies similar to those observed in the transitional circular pipe flow, were observed in the annular Couette–Poiseuille flow. Puff splitting events were clearly observed rather far from the global critical Reynolds number, near which given puffs survived without a splitting event throughout the observation period, which was as long as 104 outer time units. The characterization as a directed-percolation universal class was also discussed.     

Force field parameters for rotation around chi torsion axis in nucleic acids

To raise the accuracy of the force field for nucleic acids, several parameters were elaborated, focusing on the rotation around chi torsion axis. The reliability of molecular dynamics (MD) simulation was significantly increased by improving the torsion parameters at C8--N9--C1'--X (X = H1', C2', O4') in A, G and those at C6--N1--C1'--X in C, T, and U. In this work, we constructed small models representing the chemical structure of A, G, C, T, and U, and estimated energy profile for chi-axis rotation by executing numerous quantum mechanical (QM) calculations. The parameters were derived by discrete Fourier transformation of the calculated QM data. A comparison in energy profile between molecular mechanical (MM) calculation and QM one shows that our presently derived parameters well reproduce the energy surface of QM calculation for all the above torsion terms. Furthermore, our parameters show a good performance in MD simulations of some nucleic acids. Hence, the present refinement of parameters will enable us to perform more accurate simulations for various types of nucleic acids.     

Average electron tunneling route of the electron transfer in protein media

We present a new theoretical method to determine and visualize the average tunneling route of the electron transfer (ET) in protein media. In this, we properly took into account the fluctuation of the tunneling currents and the quantum-interference effect. The route was correlated with the electronic factor in the case of ET by the elastic tunneling mechanism. We expanded by the interatomic tunneling currents 's. Incorporating the quantum-interference effect into the mean-square interatomic tunneling currents, denoted as , we could express as a sum of variant Planck's over 2pi(2). Drawing the distribution of on the protein structure, we obtain the map which visually represents which parts of bonds and spaces most significantly contribute to . We applied this method to the ET from the bacteriopheophytin anion to the primary quinone in the bacterial photosynthetic reaction center of Rhodobacter sphaeroides. We obtained 's by a combined method of molecular dynamics simulations and quantum chemical calculations. In calculating , we found that much destructive interference works among the interatomic tunneling currents even after taking the average. We drew the map by a pipe model where atoms a and b are connected by a pipe with width proportional to the magnitude of . We found that two groups of 's, which are mutually coupled with high correlation in each group, have broad pipes and form the average tunneling routes, called Trp route and Met route. Each of the two average tunneling routes is composed of a few major pathways in the Pathways model which are fused at considerable part to each other. We also analyzed the average tunneling route for the ET by the inelastic tunneling mechanism.     

Theoretical Modelling and Facile Synthesis of a Highly Active Boron‐Doped Palladium Catalyst for the Oxygen Reduction Reaction

A highly active alternative to Pt electrocatalysts for the oxygen reduction reaction (ORR), which is the cathode‐electrode reaction of fuel cells, is sought for higher fuel‐cell performance. Our theoretical modelling reveals that B‐doped Pd (Pd‐B) weakens the absorption of ORR intermediates with nearly optimal binding energy by lowering the barrier associated with O₂ dissociation, suggesting Pd‐B should be highly active for ORR. In fact, Pd‐B, facile synthesized by an electroless deposition process, exhibits 2.2 times and 8.8 times higher specific activity and 14 times and 35 times less costly than commercial pure Pd and Pt catalysts, respectively. Another computational result is that the surface core level of Pd is negatively shifted by B doping, as confirmed by XPS, and implies that filling the density of states related to the anti‐bonding of oxygen to Pd surfaces with excess electrons from B doping, weakens the O bonding to Pd and boosts the catalytic activity.