Dynamic shear deformation and failure of Ti6Al4V

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Influence of the geometry of hat-shaped specimens on the formation of adiabatic shear bands

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Experimental study of the high strain rate shear behaviour of Ti6Al4V

Three different high strain rate shear test techniques are applied on the titanium alloy Ti6Al4V. Two techniques for testing of bulk materials and one technique for sheet materials are used: torsion of thin-walled tubes, compression of hat-shaped specimens and tension of planar shear specimens. The tests are carried out on respectively torsion, compression and tensile split Hopkinson bar setups. Although shear stresses dominate the stress state in these three tests, the local stress state and its distribution and evolution are different. Therefore, the three techniques are considered to be rather complementary than equivalent tests. In this work, the value of the three test techniques for material characterization is evaluated. Where possible, digital image correlation (DIC) is used to clarify the test results. In addition, parameters difficult to assess experimentally are estimated through finite element simulations of the three tests

υ-representability of one-body density matrices

We consider low-dimensional model systems with a fixed two-body interaction and a variable (nonlocal) one-body potential. It is shown explicitly that an extended domain of allowed (N-representable) one-body density matrices cannot be generated in this way, the excluded domain depending on the two-body interaction under consideration. This stands in contrast to the behavior of the diagonal part of the density matrix

Maximum occupation number for composite boson states

One of the major differences between fermions and bosons is that fermionic states have a maximum occupation number of one, whereas the occupation number for bosonic states is in principle unlimited. For bosons that are made up of fermions, one could ask the question to what extent the Pauli principle for the constituent fermions would limit the boson occupation number. Intuitively one can expect the maximum occupation number to be proportional to the available volume for the bosons divided by the volume occupied by the fermions inside one boson, though a rigorous derivation of this result has not been given before. In this letter we show how the maximum occupation number can be calculated from the ground-state energy of a fermionic generalized pairing problem. A very accurate analytical estimate of this eigenvalue is derived. From that a general expression is obtained for the maximum occupation number of a composite boson state, based solely on the intrinsic fermionic structure of the bosons. The consequences for Bose-Einstein condensates of excitons in semiconductors and ultra cold trapped atoms are discussed.Comment: 4 pages, Revte

Изучение микробиологической стабильности геля кальция глюконата 2,5%

ГЕЛИКАЛЬЦИЯ ГЛЮКОНАТМИКРОБИОЛОГИ

Low power consumption mini rotary actuator with SMA wires

Shape memory alloys (SMAs) are smart materials widely used as actuators for their high power to weight ratio despite their well-known low energy efficiency and limited mechanical bandwidth. For robotic applications, SMAs exhibit limitations due to high power consumption and limited stroke, varying from 4% to 7% of the total length. Hysteresis, during the contraction and extension cycle, requires a complex control algorithm. On the positive side, the small size and low weight are eminently suited for the design of mini actuators for robotic platforms. This paper describes the design and construction of a light weight and low power consuming mini rotary actuator with on-board contact-less position and force sensors. The design is specifically intended to reduce (i) energy consumption, (ii) dimensions of the sensory system, and (iii) provide a simple control without any need for SMA characterisation. The torque produced is controlled by on-board force sensors. Experiments were performed to investigate the energy consumption and performance (step and sinusoidal angle profiles with a frequency varying from 0.5 to 10 Hz and maximal amplitude of 15?). We describe a transient capacitor effect related to the SMA wires during the sinusoidal profile when the active SMA wire is powered and the antagonist one switched-off, resulting in a transient current time varying from 300 to 400 ms