1,042 research outputs found
Coupled thermomechanical dynamics of phase transitions in shape memory alloys and related hysteresis phenomena
In this paper the nonlinear dynamics of shape memory alloy phase transformations is studied with thermomechanical models based on coupled systems of partial differential equations by using computer algebra tools. The reduction procedures of the original model to a system of differential-algebraic equations and its solution are based on the general methodology developed by the authors for the analysis of phase transformations in shape memory materials with low dimensional approximations derived from center manifold theory. Results of computational experiments revealing the martensitic-austenitic phase transition mechanism in a shape-memory-alloy rod are presented. Several groups of computational experiments are reported. They include results on stress- and temperature-induced phase transformations as well as the analysis of the hysteresis phenomenon. All computational experiments are presented for Cu-based structures
Surface plasmon peak intensity dependence on the oxygen coverage at metal surfaces
The dependence of the surface plasmon peak intensity on a submonolayer coverage of oxygen in the reflection electron energy loss spectra has been investigated for non-monocrystalline aluminium, magnesium, and indium surfaces. It will be shown that the decrease of the surface plasmon peaks can be related to a modification of the surface plasmons dispersion relation. A simple model for this modification introduced by changes of the surface electron density profile is proposed. Parameters of this model will be determined from experimental data
Oscillation of solar radio emission at coronal acoustic cut-off frequency
Recent SECCHI COR2 observations on board STEREO-A spacecraft have detected
density structures at a distance of 2.5--15~R propagating with periodicity of
about 90~minutes. The observations show that the density structures probably
formed in the lower corona. We used the large Ukrainian radio telescope URAN-2
to observe type IV radio bursts in the frequency range of 8--32~MHz during the
time interval of 08:15--11:00~UT on August 1, 2011. Radio emission in this
frequency range originated at the distance of 1.5--2.5 R according to the
Baumbach-Allen density model of the solar corona. Morlet wavelet analysis
showed the periodicity of 80~min in radio emission intensity at all
frequencies, which demonstrates that there are quasi-periodic variations of
coronal density at all heights. The observed periodicity corresponds to the
acoustic cut-off frequency of stratified corona at a temperature of 1~MK. We
suggest that continuous perturbations of the coronal base in the form of
jets/explosive events generate acoustic pulses, which propagate upwards and
leave the wake behind oscillating at the coronal cut-off frequency. This wake
may transform into recurrent shocks due to the density decrease with height,
which leads to the observed periodicity in the radio emission. The recurrent
shocks may trigger quasi-periodic magnetic reconnection in helmet streamers,
where the opposite field lines merge and consequently may generate periodic
density structures observed in the solar wind.Comment: 10 pages, 6 figures, accepted in A&
Chromatography-mass spectrometry studies on the metabolism of synthetic cannabinoids JWH-018 and JWH-073, psychoactive components of smoking mixtures
The lack or low content of their native compounds in urine requires detailed identification of their metabolites, which are excreted with urine and are present in blood. Using gas and liquid chromatography-mass spectrometry, we identified a series of metabolites in urine samples from humans and ratsyesBelgorod State Universit
- …