15,256 research outputs found
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
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