1,361 research outputs found
On some generalized ageing orderings
Some partial orderings which compare probability distributions with the expo-
nential distribution, are found to be very useful to understand the phenomenon
of ageing. Here, we introduce some new generalized partial orderings which de-
scribe the same kind of characterization of some generalized ageing classes. We
give some equivalent conditions for each of the orderings. Inter-relations
among the generalized orderings have also been discussed
Classical hopping in sol-gel cobalt silicate glass
The complex AC conductivity of the sol - gel-derived cobalt silicate gel-glasses is reported for the frequency range 102 - 105 Hzand temperature range 80-300 K. The experimental results were analysed in terms of theoretical models based on quantum tunnelling and classical hopping theories. It has been observed that classical hopping theory is the best model to explain the results for these glasses and that not all sites participate in the AC hopping mechanism
Superconducting properties of very high quality NbN thin films grown by high temperature chemical vapor deposition
Niobium nitride (NbN) is widely used in high-frequency superconducting
electronics circuits because it has one of the highest superconducting
transition temperatures ( 16.5 K) and largest gap among
conventional superconductors. In its thin-film form, the of NbN is very
sensitive to growth conditions and it still remains a challenge to grow NbN
thin film (below 50 nm) with high . Here, we report on the superconducting
properties of NbN thin films grown by high-temperature chemical vapor
deposition (HTCVD). Transport measurements reveal significantly lower disorder
than previously reported, characterized by a Ioffe-Regel ()
parameter of 14. Accordingly we observe 17.06 K (point of
50% of normal state resistance), the highest value reported so far for films of
thickness below 50 nm, indicating that HTCVD could be particularly useful for
growing high quality NbN thin films
Resonant enhancement of ultracold photoassociation rate by electric field induced anisotropic interaction
We study the effects of a static electric field on the photoassociation of a
heteronuclear atom-pair into a polar molecule. The interaction of permanent
dipole moment with a static electric field largely affects the ground state
continuum wave function of the atom-pair at short separations where
photoassociation transitions occur according to Franck-Condon principle.
Electric field induced anisotropic interaction between two heteronuclear ground
state atoms leads to scattering resonances at some specific electric fields.
Near such resonances the amplitude of scattering wave function at short
separation increases by several orders of magnitude. As a result,
photoaasociation rate is enhanced by several orders of magnitude near the
resonances. We discuss in detail electric field modified atom-atom scattering
properties and resonances. We calculate photoassociation rate that shows giant
enhancement due to electric field tunable anisotropic resonances. We present
selected results among which particularly important are the excitations of
higher rotational levels in ultracold photoassociation due to electric field
tunable resonances.Comment: 14 pages,9 figure
Accounting for the effect of heterogeneous plastic deformation on the formability of aluminium and steel sheets
Forming Limit Curves characterise ‘mean’ failure strains of sheet metals. Safety levels from the curves define the deterministic upper limit of the processing and part design window, which can be small for high strength, low formability materials.
Effects of heterogeneity of plastic deformation, widely accepted to occur on the microscale, are neglected. Marciniak tests were carried out on aluminium alloys (AA6111-T4, NG5754-O), dual-phase steel (DP600) and mild steel (MS3). Digital image correlation was used to measure the effect of heterogeneity on failure. Heterogeneity, based on strain variance was modelled with the 2-component Gaussian Mixture Model and a framework was proposed to 1) identify the onset of necking and to 2) re-define formability as a probability to failure.
The result were ‘forming maps’ in major-minor strain space of contours of constant probability (from probability, P=0 to P=1), which showed how failure risk increased with major strain. The contour bands indicated the unique degree of heterogeneity in each material. NG5754-O had the greatest width (0.07 strain) in plane strain and MS3 the lowest (0.03 strain). This novel characterisation will allow engineers to balance a desired forming window for a component design with the risk to failure of the material
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