Natural vibration of cantilever porous twisted plate with variable thickness in different directions

In this paper,the blade is assumed to be a rotating variable thickness cantilever twisted plate structure,and the natural vibrations of variable thickness cantilever twisted plate made of metal porous material are studied.It is assumed that the thickness of the plate changes along spanwise direction and chordwise direction,respectively,and it changes in both directions.The classical thin shell theory,the first and second fundamental forms of surface and von Karman geometric relationship are employed to derive the total potential energy and kinetic energy of the cantilever twisted plate,in which the centrifugal force potential due to high rotational speed is included.Then,according to the Rayleigh-Ritz procedure and applying the polynomial functions which satisfy the cantilever boundary conditions,the dynamic system expressed by equations of motion is reduced to an eigenvalue problem.By numerical simulation,the frequency curves and the mode shapes of the twisted plate can be obtained to reveal the internal connection between natural vibration and the parameters.A series of comparison studies are performed to verify the accuracy of the present formulation and calculations,in which compared data come from experimental,finite element method and theoretical calculation,respectively.The influence of pre-twist angle,three different forms of thickness taper ratio and rotational speed on natural vibration,mode exchange and frequency veering phenomenon of the system is discussed in detail.In addition,the approach proposed here can efficiently extract analytical expressions of mode functions for rotating variable thickness cantilever twisted plate structures.

离体年轻恒牙脱矿后再矿化及美白效果的实验研究

目的探讨牙齿美白治疗对脱矿的离体年轻恒牙再矿化及牙色变化的作用。方法选取和制作24个离体的年轻恒牙标本,用微硬度测量仪(M-400-H1,St,Joseph,MI)测定牙体标本的硬度。牙体的颜色由ShadeVision(X-Rite,Inc.,Grand-ville,MI)来测定。脱矿处理后,选取的每个标本的牙体硬度控制在170KHN(努氏硬度)左右。24个标本被随机地分成A、B、C3组(P>0.05),每组8个标本。C组用美白产品Treswhite进行7次漂白治疗,同时A、B组标本浸泡于人唾液中。然后B、C组用含氟的Crest牙膏进行再矿化处理,而A组用无氟的Crest牙膏进行再矿化处理。每个牙标本的硬度(KHN)和颜色(CIELAB)的数据分别在以下4个阶段采集:原始阶段(BL)、脱矿后(AL)、美白治疗或唾液浸泡后(AB/S)、和矿化治疗后(AR)。结果3组标本的牙硬度在BL、AL和AB/S阶段不存在显著的差异(P>0.05),在AR阶段,B组、C组标本牙硬度增高而A组牙硬度下降(P<0.001)。脱矿后阶段(AD)各组的牙颜色变化CIELAB数据ΔE接近8,在AB/S阶段与AD阶段之间,C组的ΔE值明显高于A、B组(P=0.001),经过再矿化处理,各阶段之间的ΔE值变小及每组间的ΔE值不存在显著的差异。结论美白产品Tre-swhite对脱矿的离体年轻恒牙的再矿化无不良反应,而对其牙颜色的变化无明显的影响。

离体脱矿年轻恒牙漂白与再矿化治疗的相互影响

目的探讨离体脱矿年轻恒牙漂白与再矿化治疗的相互影响。方法选取和制作16个离体的年轻恒牙标本,随机分成A组和B组,各8个标本。两组标本先进行脱矿,B组用美白产品Treswhite进行7次漂白治疗;A组标本浸泡于人唾液中,然后用含氟的Crest牙膏进行再矿化处理。测定并比较四阶段(原始阶段、脱矿后、美白治疗或唾液浸泡后和矿化治疗后)两组牙标本的硬度和颜色数据。结果两组四阶段牙齿硬度组内和组间比较差异均无显著性(﹥0.05)。B组从美白治疗或唾液浸泡后至脱矿后比色值改变最明显,值为6.01±1.94,较A组的3.18±2.44大(﹤0.05)。经再矿化处理后与美白治疗或唾液浸泡后比较,B组值大于A组,但差异无显著性(﹥0.05);经再矿化处理后与脱矿后比较,两组值比较差异无显著性(﹥0.05)。结论漂白治疗对脱矿的离体年轻恒牙的再矿化有促进作用,但其效果不明显;漂白在短期内效果明显,经过长期的再矿化后,牙体色泽的变化会变得不明显,但仍有别于漂白前。

Gyroscopic modes decoupling method in parametric instability analysis of gyroscopic systems

Traditional procedures to treat vibrations of gyroscopic continua involve direct application of perturbation methods to a system with both a strong gyroscopic term and other weakly coupled terms.In this study,a gyroscopic modes decoupling method is used to obtain an equivalent system with decoupled gyroscopic modes having only weak couplings.Taking the axially moving string as an example,the instability boundaries in the vicinity of parametric resonances are detected using both the traditional coupled gyroscopic system and our system with decoupled gyroscopic modes,and the results are compared to show the advantages and disadvantages of each method.

Time-varying nonlinear dynamics of a deploying piezoelectric laminated composite plate under aerodynamic force

Using Reddy’s high-order shear theory for laminated plates and Hamilton’s principle, a nonlinear partial differential equation for the dynamics of a deploying cantilevered piezoelectric laminated composite plate, under the combined action of aerodynamic load and piezoelectric excitation, is introduced. Two-degree of freedom(DOF)nonlinear dynamic models for the time-varying coefficients describing the transverse vibration of the deploying laminate under the combined actions of a first-order aerodynamic force and piezoelectric excitation were obtained by selecting a suitable time-dependent modal function satisfying the displacement boundary conditions and applying second-order discretization using the Galerkin method. Using a numerical method, the time history curves of the deploying laminate were obtained, and its nonlinear dynamic characteristics,including extension speed and different piezoelectric excitations, were studied. The results suggest that the piezoelectric excitation has a clear effect on the change of the nonlinear dynamic characteristics of such piezoelectric laminated composite plates. The nonlinear vibration of the deploying cantilevered laminate can be effectively suppressed by choosing a suitable voltage and polarity.

Nonlinear Transient Response of Functionally Graded Material Sandwich Doubly Curved Shallow Shell Using New Displacement Field

In this paper, the nonlinear transient dynamic response of functionally graded material （FGM） sandwich doubly curved shell with homogenous isotropic material core and functionally graded face sheet is analyzed using a new displacement field on the basis of Reddy＇s third-order shear theory for the first time. The equivalent material properties for the FGM face sheet are assumed to obey the rule of simple power law function in the thickness direction. Based on Reddy＇s theory of higher shear deformation, a new displacement field is developed by introducing the secant function into transverse displacement. Four coupled nonlinear differential equations are obtained by applying Hamilton＇s principle and Galerkin method. It is assumed that the FGM sandwich doubly curved shell is subjected to step loading, air-blast loading, triangular loading, and sinusoidal loading, respectively. On the basis of double-precision variable- coefficient ordinary differential equation solver, a new program code in FORTRAN software is developed to solve the nonlinear transient dynamics of the system. The influences of core thickness, volume fraction, core-to-face sheet thickness ratio, width-to-thickness ratio and blast type on the transient response of the shell are discussed in detail through numerical simulation.

A Global Weizsacker mass model with relativistic mean field shell correction

A relativistic Weizsacker mass model is proposed based on the single-particle levels and ground state deformations obtained in axial deformed relativistic mean field theory.The density functional of relativistic mean field theory is chosen as DD-LZ1,which can partially remove spurious shell closures.Compared with the fourth Weizsacker-Skyrme mass model,the proposed model provides shell correction energies that exhibit wide spreading,and the root-mean-square mass deviation is 1.353 MeV.Further improvement is in progress.

NONLINEAR DYNAMICS OF A FGM PLATE WITH TWO CLAMPED OPPOSITE EDGES AND TWO FREE EDGES

This paper deals with the nonlinear forced vibration of FGM rectangular plate with a boundary of two edges clamped opposite and the other two free. The plate is subjected to transversal and in-plane excitations. The present research treats the material properties of the FGM plates as temperature-dependent and graded continuously throughout the thickness direction, following the volume fraction of the constituent materials according to the power law. The temperature is assumed to be constant in the plane and varied only in the thickness direction of the plate. In the framework of geometrical nonlinearity the plate is modeled and the equations of motion are obtained on Hamilton＇s principle. With the help of Galerkin discretization, the nonlinear ordinary differential equations describing transverse vibration of the plate are proposed. By the numerical method, the nonlinear dynamical responses of the FGM plate with two clamped opposite and two free edges are analyzed.

新型辊压机成形

工程制造业在获取更大效益的驱使下，已经向净形成形、近净形成形和高精密技术发展。锻造公司，多采用完全封闭或接近完全封闭的模腔来终成形或只需要很少后续工作的终成形生产零件。对模具和工艺过程精密控制，批量生产精密锻件，只有轴对称的零件才有可能。

Improving Scientific Research Methodology in Undergraduate Medical Students: a case of team based training blended in a research project

An educational intervention targeting medical students and aiming to develop skills useful to the writing of a health science research protocol over a short period of time has been developed in the Shanghai Jiao Tong University School of Medicine. The methodology blending the principles of PBL and TBL is detailed and key issues of this implementation are discussed. Twenty-one students were enrolled in a research master degree and participated to three mandatory 180-minutes sessions. Beyond classical skills useful to solve a problem, this new intervention focused on the transformation of knowledge to create an authentic content, which is a feature of the project-based learning(PBL). The training process was designed according to team-based learning(TBL) procedure except that work sharing between groups and pooling resources and outcomes of each group allowed the construction of one final class original research project in the field of respiratory pharmacology. The combination of both learning methods allowed promoting individual and group accountability necessary to improve self-learning and the quality of the final joint project. The peer reviewing was an essential factor in creating the students' motivation and improving of team discussion. The grades individually assigned for skills and quality of the project by an external teacher suggested that key objectives of the intervention were reached. In conclusion, the educational intervention described in this paper appears as an appropriate method to develop specific skills necessary to write and discuss a research project within a research team.Further works are necessary to measure the degree of satisfaction of students and improvement of performance.

Frequency Veering of Rotating Metal Porous Twisted Plate with Cantilever Boundary Using Shell Theory

The frequency veering of a metal porous rotating cantilever twisted plate with twist angle and stagger angle is investigated.Metal porous materials may have the characteristics of gradient or uniform distribution along the thickness direction.Based on the classical shell theory,considering the influence of centrifugal force produced by high-speed rotation,the free vibration equations of a rotating cantilever twisted plate are derived.Through the polynomial function and Rayleigh-Ritz method,the natural frequencies and mode shapes of the metal porous cantilever twisted plate in both static and rotating states are derived.The accuracy of the present theory and calculation results is confirmed by a comparison between them and the results available from the literature and those obtained from Abaqus.The influences of the thickness ratio,porosity,twist angle,stagger angle and rotational velocity on the frequency veering and mode shape shift of the rotating cantilever twisted plate with porous material under three different distributions are analyzed.It should be mentioned that the frequency veering accompanied by mode shape shift occurs in both static and dynamic states.

Fundamental aspects of access control for geospatial data

In recent years,geographical information systems have been employed in a wide variety of application domains,and as a result many research efforts are being devoted to those upcoming problems.Geospatial data security,especially access control,has attracted increased research interests within the academic community.The tendency towards sharing and interoperability of geospatial data and applications makes it common to acquire and integrate geospatial data from multiple organisations to accomplish a complex task.Meanwhile,many organisations have the requirement for securing access to possessed sensitive or proprietary geospatial data.In this heterogeneous and distributed environment,consistent access control functionality is crucial to promote controlled accessibility.As an extension of general access control mechanisms in the IT domain,the mechanism for geospatial data access control has its own requirements and characteristics of granularity and geospatial logic.In this paper,we address several fundamental aspects concerning the design and implementation of an access control system for geospatial data,including the classification,requirements,authorisation models,storage structures and management approaches for authorisation rules,matching and decision-making algorithms between authorisation rules and access requests,and its policy enforcement mechanisms.This paper also presents a system framework for realising access control functionality for geospatial data,and explain access control procedures in detail.

Two-Fluid Formulation of Lower-Hybrid Drift Instabilities in Current-Sheet Equilibrium with a Guide Field

Anonlocal two-fluid formulation has been constructed for describing lowerhybrid drift instabilities in current-sheet configuration with a finite guide magnetic field in the context of magnetic reconnection.As a benchmark and verification,a class of unstable modes with multiple eigenstates are found by numerical solutions with guide field turned off.It is found that the most unstable modes are the electrostatic,short-wavelength perturbations in the lower-hybrid frequency range,with wave functions localized at the edge of the current sheet where the density gradient reaches its maximum.It is also found that there exist electrostatic modes located near the center of the current sheet where the current density is maximum.These modes are lowfrequency,long-wavelength perturbations.Attempts will bemade to compare the current results with those from kinetic theory in the near future since the validity of the fluid theory ultimately needs to be checked with the more fundamental kinetic theory.