力-位移分控多点成形新工艺及其回弹控制机理

目的对比研究力-位移分控多点弯曲成形的受力和变形特点,揭示力-位移分控多点成形技术改善成形质量的机理。方法首先设计制造出采用力-位移分控多点成形原理成形的实验装置,并进行圆柱面的实际成形,比较不同成形模式下所获得成形制件的差异,然后采用理论分析和数值模拟等手段,分析对比不同成形模式的受力与变形条件,探讨不同成形模式下的变形特点与规律。结果从理论上给出了力-位移分控多点成形能有效减小回弹、消除"直边效应"的力学原理,指出了力-位移分控多点成形技术减小回弹的根本原因在于法向约束力的作用,且回弹减小量与法向约束力的大小成正比,并通过数值模拟,从应力和应变分布、支反力变化等方面予以了验证。结论力-位移分控多点成形从本质上改变了板材的受力和变形条件,能有效提升成形质量。     

The Variation of “Surface” Pressure in a Nanocrystal as a Function of Temperature

The Mie-Lennard-Jones potential of interatomic interaction is used to derive an expression for “surface” pressure in a nanocrystal with free surface. The nanocrystal has the form of a parallelepiped with a square base. The number of atoms N may vary from eight to ∞. It is found that a certain “inversion temperature” T _i exists for any substance, where the temperature dependences of surface pressure for different sizes of nanocrystal intersect. When the crystal disperses in the T < T _i region, the “surface” pressure increases, and in the T > T _i region decreases, with decreasing size of nanocrystal: P _sf(N) ～ N ^?1/3. The greater the deviation of the nanocrystal shape from cubic, the stronger the dependence P _sf(N). It is demonstrated that, at some temperatures (T < T ₀), the “surface” pressure compresses the nanocrystal, and at other temperatures-stretches this nanocrystal, as its size decreases. The more clearly the quantum effects are defined in the crystal, the lower the value of the “temperature of zero surface pressure” T ₀, which depends on the nanocrystal size and shape.     

Synthesis and Superconductivity of Layered Compounds with Orthogonal [Zr<Subscript>2</Subscript>N<Subscript>2</Subscript>] Network

Layered α-form ZrNX (X: Cl and Br) compounds with high quality were prepared by chemical vapor transport. The intercalation of alkali metal A (A: Li, Na, K, Rb) was carried out to realize electron doping into the orthogonal [Zr₂N₂] layers. The Rietveld refinement analysis reveals that the [Zr₂N₂] crystalline layers in the intercalation compounds shift mutually in the ab plane when compared with the hosts. Magnetic measurements show that the intercalation compounds A _x ZrNX are changed into superconductors with transition temperature T _c of up to 12 K. Upon the cointercalation of solvent molecules such as THF, T _c decreases to as low as 6.1 K with increasing the interlayer spacing d up to 14 Å, which is similar to the d dependence of T _c recently found in electron-doped α-form TiNX series. We also succeeded in synthesizing another new polymorph of α-Zr₂N₂S by the topochemical reaction between α-form ZrNX and Na₂S. α-Zr₂N₂S (space group: Immm, a = 4.1375(1) Å, b = 3.5422(1) Å, and c = 11.5204(3) Å) has the same α-[Zr₂N₂] layers, whereas the interlayer spacing between two adjacent [Zr₂N₂] layers is effectively decreased by 1/3 when compared with the parent compounds of ZrNX.     

A diffusion criterion of the crystal-liquid phase transition

A diffusion criterion of the crystal-liquid phase transition (PT) is proposed according to which the PT begins when the E _d/k _b ratio reaches a threshold value of E _d(s)/k _b T _m, where E _d is the self-diffusion energy, k _B is the Boltzmann constant, T is the absolute temperature, and E _d(s) is the self-diffusion energy in the solid phase at the melting temperature T _m. It is shown that this criterion is a generalization of the Lindemann criterion and is applicable both to solids exhibiting normal melting and to those melting with a decrease in the specific volume. Based on the new criterion, it is possible to explain the relation T _N < T _m, where T _N, is the crystallization onset temperature. The results of calculations of the T _N/T _m ratio well coincide with experimental data.     

Facile synthesis of thermo-responsive nanogels less than 50 nm in diameter via soap- and heat-free precipitation polymerization

Owing to their highly desirable properties that combine the properties of both hydrogels and nanomaterials, smart nanogels own great potentials as active nanocarriers in medical applications. In this paper, thermo-responsive nanogels with uniform sizes less than 50 nm in diameter were synthesized using potassium persulfate (KPS)/N,N,N′,N′-tetramethylethylenediamine (TMEDA) as a initiator system via a facile surfactant-free precipitation radical polymerization of N-isopropylacrylamide (NIPAM) at room temperature. Both transmission electron microscopy and dynamic light scattering were used to characterize the morphologies and diameters of the PNIPAM nanogels. All nanogels with spherical shape exhibited a narrow size distribution, and the finest nanogels were 43 nm in diameter on average. The very fine and highly pure nanogels would be more promising for drug delivery carriers than the bulk gels or microgels.     

Field-Controllable Spin Filter Based on Parallel Quantum Dot Systems

In this paper, we investigate the spin-polarized transport through parallel N?dot (N = 1, 2, 3) systems in the strongly correlated regime. We focus our attention on the responses of the N _{t o t} = i n t e g e r states to an increasing magnetic field B, where N _{t o t} is the total charge number on the dots. We show that when the charge level ?? is chosen at the particle-hole (p-h) symmetric case, spin filtering is difficult to occur. While if ?? is beyond the p-h symmetric point, perfect spin-polarized currents could be achieved, and the spin directions can be easily manipulated by tuning external electric and/or magnetic fields, making it easy to be realized in future experiments of the ideas. To approach these problems, the celebrated numerical renormalization group (NRG) technique is implemented, the dynamical properties and the quantum fluctuations are shown.     

Magnetic structure of a spherical cluster of monodomain particles

A numerical model is proposed for simulating the magnetic properties of a system (N-cluster) comprising a finite number N of monodomain particles uniformly distributed over a spherical surface. The calculation algorithm is based on the Monte Carlo method. In the absence of an external magnetic field, the magnetic moment of any spherical N-cluster vanishes due to the formation of vortex structures, with a measure of vorticity offered by the toroid moment Q. The results of model calculations show that the value of Q in N-clusters with 4 < N < 20 amounts to about 80% of the maximum and is virtually independent of N, while exhibiting weak even-odd oscillations.     

Aerodynamic characteristics of an ogive-nose spinning projectile

This work experimentally investigates the Robins–Magnus effect on a 5-caliber spinning projectile at a low subsonic Mach number of 0.1 corresponding to a Reynolds number of 3.2 × 10⁵ based on the model length. The model configuration tested was a cylinder with spherically blunt tangent ogive nose portion. The normal, axial and side force coefficients were obtained for various angles of attack (α) ranging from 0° to 34° with non-dimensional spin rates (Ω) of 0–0.05. Results indicate that the side force coefficient increases with α up to a value of around 28° and decreases thereafter. Interestingly, in the range of spin rates considered in the present study, normal and axial force coefficients are not affected due to spin. However, the side force coefficients are seen to increase with spin rates at higher α. Flow visualization studies are demonstrated to explain the underlying mechanism behind the variation of these aerodynamic coefficients.     

Effect of restricted geometry and external pressure on the phase transitions in ammonium hydrogen sulfate confined in a nanoporous glass matrix

A study of heat capacity, thermal dilatation, susceptibility to hydrostatic pressure, permittivity and polarization loops was carried out on NH₄HSO₄–porous glass nanocomposites (AHS?+?PG) as well as empty glass matrices. The formation of dendrite clusters of AHS with a size, d_cryst, exceeding the pore size was found. An insignificant anisotropy of thermal expansion of AHS?+?PG showing statistically uniform distribution of AHS with random orientations of nanocrystallites over the matrix was observed. The effect of internal and external pressures on thermal properties and permittivity was studied. At the phase transition P-1???Pc, a strongly nonlinear decrease in the entropy ΔS₂ and volume strain (ΔV/V)_T2 was observed with decreasing d_cryst. The linear change in temperatures of both phase transitions P-1???Pc???P2₁/c under hydrostatic pressure is accompanied by the expansion of the temperature range of existence of the ferroelectric phase Pc, while this interval narrows as d_cryst decreases.     

The generation of the forming path with the springback compensation in the CNC incremental forming

Aiming at the problem of the springback in the CNC incremental forming, a method for predicting the springback and generating the compensated forming trajectory was proposed based on the explicit and implicit finite element analysis. First, the middle surface of the simulated sheet metal part was reconstructed after the springback simulation with the coordinates of all nodes obtained from the numerical simulations, and the reconstructed middle surface was compared with the middle surface of the theory model to calculate the normal deviation values. Second, the theory model was offset with the unequal distances of the deviation values to generate the compensated facet and the forming path. Once more, the finite element analysis was done until the compensatory effect met the required precision. Meanwhile, aiming at the roughness of the compensated facet caused by the multi-compensation process, the smoothing method was given to guarantee the smooth of the forming path. According to the predicted result of the numerical simulations, three times compensation meets the required precision and the normal deviation value is decreased from 0.696 mm to 0.194 mm. The forming experiments indicate that the springback of the target part in Z direction is decreased from 1.107 mm to 0.427 mm. Therefore, the predicting and compensating method of the springback proposed in the paper is available, which can improve the forming precision of the sheet metal part.     

Correlation between the electrical and luminescent properties of high-purity gallium arsenide

Epitaxial n-GaAs layers with a background impurity concentration of N_D-N_A<10¹⁵ cm^?3, grown by chloride vapor phase epitaxy in an open system, exhibit correlation between the electrical properties and the long persistence of the edge photoluminescence lines D⁰x and D⁰h related to the hole trapping centers. An increase in the concentration of such trapping centers in n-GaAs leads to a decrease in the mobility of free charge carriers.     

How much is a quantum controller controlled by the controlled system?

We consider unitary transformations on a bipartite system A × B. To what extent entails the ability to transmit information from A to B the ability to transfer information in the converse direction? We prove a dimension-dependent lower bound on the classical channel capacity C(A ← B) in terms of the capacity C(A → B) for the case that the bipartite unitary operation consists of controlled local unitaries on B conditioned on basis states on A. If the local operations are given by the regular representation of a finite group G we have C(A → B) = log |G| and C(A ← B) = log N where N is the sum over the degrees of all inequivalent representations. Hence the information deficit C(A → B) ? C(A ← B) between the forward and the backward capacity depends on the “non-abelianness” of the control group. For regular representations, the ratio between backward and forward capacities cannot be smaller than 1/2. The symmetric group S _n reaches this bound asymptotically. However, for the general case (without group structure) all bounds must depend on the dimensions since it is known that the ratio can tend to zero. Our results can be interpreted as statements on the strength of the inevitable backaction of a quantum system on its controller.     

Oscillating cylinder in viscous fluid: calculation of flow patterns and forces

Laminar and large-eddy-simulation (LES) calculations with the dynamic Smagorinsky model evaluate the flow and force on an oscillating cylinder of diameter D = 2R in otherwise calm fluid, for β = D ²/νT in the range 197–61400 and Keulegan–Carpenter number K = U _m T/D in the range 0.5–8 (ν kinematic viscosity, T oscillation period, U _m maximal velocity). Calculations resolving the streakline patterns of the Honji instability exemplify the local flow structures in the cylinder boundary layer (β ~ 197–300, K ~ 2) but show that the drag and inertia force are not affected by the instability. The present force calculations conform with the classical Stokes–Wang solution for all cases below flow separation corresponding to K < 2 (with β < 61400). The LES calculations of flow separation and vortical flow resolve the flow physics containing a large range of motion scales; it is shown that the energy in the temporal turbulent fluctuations (in fixed points) are resolved. Accurate calculation of the flow separation occurring for K > 2 has strong implication for the force on the cylinder. Present calculations of the force coefficients for K up to 4 and β = 11240 are in agreement with experiments by Otter (Appl Ocean Res 12:153–155, 1990). Drag coeffients when flow separation occurs are smaller than found in U-tube experiments. Inertia coefficients show strong decline for large K (up to 8) and moderate β = 1035 but is close to unity for K = 4 and β = 11240. The finest grid has 2.2 × 10⁶ cells, finest radial Δr/R = 0.0002, number of points along the cylinder circumference of 180, Δz/R = 0.044 and a time step of 0.0005T.     

Experimental modelling of free-surface dry granular flows under a centrifugal acceleration field

We investigate the dynamics of granular flows under the action of a centrifugal acceleration field. The granular flows consist of a monodisperse set of glass beads flowing down an inclined plane. The experiments are performed at variable slope angles \(\zeta \) and equivalent centrifugal accelerations \(a_\text {cf}\equiv Ng\). We study the effect of this parameters on the superficial flow velocity u and flow height h. Two trends are observed, by increasing \(\zeta \) and \(a_\text {cf}\), u increases proportionally, and h decreases asymptotically until a constant height. This relation is analysed in terms of the system potential and kinetic energy, leading to the estimation of equivalent impact forces one order of magnitude larger than those observed in small scale 1g laboratory experiments, with the possibility to reach higher forces by increasing N. Finally, considering the trend of u and h, our results suggest a scaling principle of inertial velocity proportional to \(\sqrt{N}\).     

Explanation of Non-linear In-Plane Resistivity and Hall Coefficient in the Normal State of Cuprates: Polaronic Approach

We present a theoretical study of the in-plane resistivity ρ _{a b} (T) and Hall coefficient R _H (T) within the polaronic model and precursor pairing scenario by considering a two-component charge carrier picture in the normal state of high-temperature superconducting cuprates (HTSC). Here, we use a Boltzmann-equation approach and extended BCS-like model to compute ρ _{a b} (T) and R _H (T) in the τ-approximation. The opening of the pseudogap (PG) in the normal state of the cuprates should affect their transport properties. We have found that the transition to the PG regime and the effective conductivity of charge carriers in the normal state are responsible for the pronounced non-linear temperature dependence of ρ _{a b} and R _H . With the two-component model analysis, we conclude that the opening of the BCS-like PG, while the non-linear temperature dependence of ρ _{a b} and R _H could be understood as a consequence of pairing fluctuations in the PG state of cuprate superconductors. The calculated results for ρ _{a b} (T) and R _H (T) were compared with the experimental data obtained for various hole-doped cuprates. For all the considered cases, a good quantitative agreement was found between theory and experimental data. We also show that the energy scales of the binding energies of charge carriers are identified by PG crossover temperature on the cuprate phase diagram.     

Rate constant of <Emphasis Type="Italic">VT</Emphasis>/<Emphasis Type="Italic">VV</Emphasis> energy exchange in the collision of di- and polyatomic molecules within the SFO model

The numerical-analytical investigation of the shock forced oscillator (SFO) model is complete. Approaches for calculating the probabilities of quantum transitions from the initial to some final state with VV energy exchange of diatomic molecules and VV and VT energy exchange of polyatomic molecules are considered. Formulas for calculating the probabilities of the \({W_{{i_1},{i_2} \to {f_1},{f_2}}}\) transition for VV energy exchange in collision of molecules AB and CD within the harmonic approximation are represented (SFHO model). It is shown that the probabilities of a quantum transition in VV and VT energy exchange of polyatomic molecules can be calculated in terms of the quantum transition probability for VT energy exchange of diatomic molecules on the assumption of “frozen” quantum transitions of polyatomic molecules. The problem of determining the dissociation rate constant is considered by the example of a nitrogen molecule (N₂) in the N₂–N₂ system for the “improved” Lennard-Jones potential in VV energy exchange. The calculated dissociation rate constant is compared with the experimental data obtained for a shock tube.     

Surface Effects on the Dynamic Behavior of Vortices in Type II Superconducting Strips with Periodic and Conformal Pinning Arrays

Using molecular dynamics techniques, we simulate the vortex behavior in a type II superconducting strip in the presence of triangular and two types of conformal pinning arrays, one with a pinning gradient perpendicular to the driving force (C1) and the other parallel (C2), at zero temperature. A transport force is applied in the infinite direction of the strip, and the magnetic field is increased until the rate between the density of vortices (n _v ) and pinning (n _p ) reaches n _v /n _p =?1.5. Our results show a monotonic increase, by steps, of the vortex density with the applied magnetic field. Besides, each pinning lattice presents a different vortex penetration delay. For the triangular pinning array, different than the case of infinite films, here the system exhibits only one pronounced depinning force peak at n _v /n _p =?1. However, the depinning force peak is present for only one value of field, in the range of fields where n _v /n _p =?1 is stable. For the case of conformal pinning arrays, in analogy to what is observed in infinite films, no commensurability depinning force peaks were found. In the present case, the C1 array is more efficient at low fields, all arrays are equivalent in the intermediate fields, and the C2 array is more efficient for high fields. We also show that for the C1 array at high fields, vortices depin following the conformal arches, from the edge to the center. For the C2 array, the depinning force is higher when compared to that of C1, because this particular conformal structure prevents the formation of easy vortex flow channels.     

Modified inelastic bouncing ball model of the Brazil nut effect and its reverse

We developed the modified inelastic bouncing ball model (mIBBM) to describe the emergence of the Brazil nut effect (BNE) and its reverse (RBNE) in a vertically-vibrated binary granular mixture. The mIBBM incorporates the container-to-grains force-transmission efficiency (transmissibility) T_r to quantify the dimensionless mean void lifetime \( \omega \langle \delta t\rangle \) that acts as the segregation phase indicator where ω is the vibration angular frequency. The mixture is represented as two non-interacting inelastic balls, Ball A and Ball B. Each ball bounces with a time-of-flight τ_A (or τ_B) that depends on transmissibility T_rA (or T_rB) and the dimensionless container acceleration Γ, i.e., τ_A?=?τ_A(Γ, T_rA) and τ_B?=?τ_B(Γ, T_rB). The ball dynamics are described by the bifurcation diagrams of the dimensionless times-of-flight, ωτ_A(Γ, T_rA) and ωτ_B(Γ, T_rB). The probability-weighted difference \( \omega \langle \delta t\rangle \) between branches of the two diagrams is computed and interpreted as follows: \( \omega \langle \delta t\rangle > 0 \) (occurrence of BNE), \( \omega \langle \delta t\rangle < 0 \) (RBNE) and \( \omega \langle \delta t\rangle \)?=?0 (no segregation). Segregation phases are revealed as varying shifts and widths of \( \omega \langle \delta t\rangle \) across the Γ axis. The phase boundaries in the \( \omega \langle \delta t\rangle \)-versus-Γ diagram are sensitive to changes in T_rA, T_rB and ΔT_r?=?(T_rA???T_rB). The mIBBM explains why the BNE is a more likely than the RBNE and predicts a segregation phase sequence that is generally consistent with related experimental results taken over a limited ω-range. Additional experiments are needed to enable a more comprehensive and precise evaluation of the mIBBM.     

Band structure of silicon carbide nanotubes

Using the linear augmented cylindrical wave method in the muffin-tin approximation, we have calculated the band structure of (n, n) and (n, 0) silicon carbide nanotubes for n = 5–10. In the range n = 7–10, (n, n) nanotubes are semiconductors, and their band gap decreases steadily with increasing n: 0.28 eV at n = 7, 0.26 eV at n = 8, 0.19 eV at n = 9, and 0.11 eV at n = 10. Nanotubes with n = 5 and 6 are metallic. At n = 7–9, (n, 0) nanotubes are semiconductors, and their band gap increases steadily with n: 0.39 eV at n = 7, 0.46 eV at n = 8, and 0.62 eV at n = 9. Nanotubes with n = 5 and 6 have metallic conductivity according to our results.