Differential stiffness effects

Differential stiffness as developed in NASTRAN is a linear change in stiffness caused by applied loads. Examples of differential stiffness are the stiffening effects of gravity forces in a pendulum, centrifugal forces in rotor blades and pressure loading of shell structures. In cases wherein this stiffness caused by a load is destabilizing, the differential stiffness concept lends itself to nonlinear structural analysis. Rigid Formats 4 (static analysis with differential stiffness) and 13 (normal modes with differential stiffness) are specifically designed to account for such stiffness changes. How pressure loading may be treated in these rigid formats is clarified. This clarification results from modal correlation of Ground Vibration Test (GVT) results from the empty and pressurized Filament Wound Case (FWC) quarter-scale Space Shuttle solid rocket booster (QSSRB). A sketch of the QSSRB cantilevered to the floor by its external tank attachments is shown

Modelling of Dynamic Strain Aging with a Dislocation-Based Isotropic Hardening Model and Investigation of Orthogonal Loading

Based on experimental results, a dislocation material model describing the dynamic strain aging\ud effect at different temperatures is presented. One and two stage loading tests were performed in\ud order to investigate the influence of the loading direction as well as the temperature influence due\ud to the hardening mechanism. Bergström’s theory of work hardening was used as a basis for the\ud model development regarding the thermal isotropic behavior as well as the Chaboche model to\ud describe the kinematic hardening. Both models were implemented in an in-house FE-Code in\ud order to simulate the real processes. The present paper discusses two hardening mechanisms,\ud where the first part deals with the pure isotropic hardening including dynamic strain aging and the\ud second part involves the influence of the loading direction regarding combined (isotropic and\ud kinematic) hardening behavior

Precoded turbo code within 0.1dB of Shannon limit

The application of the precoding technique to turbo codes is investigated, resulting in a new class of turbo-like codes named precoded turbo codes. The introduction of a precoder provides a degree of freedom for code optimisation. As a result, an optimised rate-1/2 precoded turbo code with a threshold of 0.28 dB is designed using the EXIT chart

The observation of a positive magnetoresistance and close correlation among lattice, spin and charge around TC in antipervoskite SnCMn3

The temperature dependences of magnetization, electrical transport, and thermal transport properties of antiperovskite compound SnCMn3 have been investigated systematically. A positive magnetoresistance (~11%) is observed around the ferrimagnetic-paramagnetic transition (TC ~ 280 K) in the field of 50 kOe, which can be attributed to the field-induced magnetic phase transition. The abnormalities of resistivity, Seebeck coefficient, normal Hall effect and thermal conductivity near TC are suggested to be associated with an abrupt reconstruction of electronic structure. Further, our results indicate an essential interaction among lattice, spin and charge degrees of freedom around TC. Such an interaction among various degrees of freedom associated with sudden phase transition is suggested to be characteristic of Mn-based antiperovskite compounds.Comment: 13 pages, 5 figure

Attosecond probing of instantaneous AC Stark shifts in helium atoms

Based on numerical solutions of the time-dependent Schr\"odinger equation for either one or two active electrons, we propose a method for observing instantaneous level shifts in an oscillating strong infrared (IR) field in time, using a single tunable attosecond pulse to probe excited states of the perturbed atom. The ionization probability in the combined fields depends on both, the frequency of the attosecond pulse and the time delay between both pulses, since the IR field shifts excited energy levels into and out of resonance with the attosecond probe pulse. We show that this method (i) allows the detection of instantaneous atomic energy gaps with sub-laser-cycle time resolution and (ii) can be applied as an ultrafast gate for more complex processes such as non-sequential double-ionization

Extraction of Plumes in Turbulent Thermal Convection

We present a scheme to extract information about plumes, a prominent coherent structure in turbulent thermal convection, from simultaneous local velocity and temperature measurements. Using this scheme, we study the temperature dependence of the plume velocity and understand the results using the equations of motion. We further obtain the average local heat flux in the vertical direction at the cell center. Our result shows that heat is not mainly transported through the central region but instead through the regions near the sidewalls of the convection cell.Comment: 4 pages, 4 figures, submitted to Physical Review Letter

Comparison of chemical profiles and effectiveness between Erxian decoction and mixtures of decoctions of its individual herbs : a novel approach for identification of the standard chemicals

Acknowledgements This study was partially supported by grants from the Seed Funding Programme for Basic Research (Project Number 201211159146 and 201411159213), the University of Hong Kong. We thank Mr Keith Wong and Ms Cindy Lee for their technical assistances.Peer reviewedPublisher PD