Transfer measurements for the Ti+Ni systems at near barrier energies

Large enhancements have been observed in the sub-barrier fusion cross sections for Ti+Ni systems in our previous studies. Coupled channel calculations incorporating couplings to 2⁺ and 3⁻ states failed to explain these enhancements completely. A possibilty of transfer channels contributing to the residual enhancements had been suggested. In order to investigate the role of relevant transfer channels, measurements of one- and two-nucleon transfer were carried out for ^46,48Ti+⁶¹Ni systems. The present paper gives the results of these studies.     

Laser fluorescence on radio-active isotopes produced in very low yield

East particle-photon coincidence techniques, developed at Daresbury with strontium isotopes, allow ultrasensitive laser fluorescence spectroscopy of beams of radio-active isotopes which can only be produced in very low yields. The technique has now been applied to neutron-deficient barium isotopes down to¹²⁰Ba. From measured hyperfine splittings and isotope shifts, nuclear moments and changes in mean square radii have been determined. The work has revealed an abrupt increase in the mean square radius for¹²¹Ba large enough to disrupt the systematic staggering of nuclear size seen for the series. In a recent experiment an isomeric state of¹²⁷Ba with a half-life of about 2 seconds has been produced in a very low yield; nevertheless we have succeeded in obtaining a fluorescence spectrum.     

Dynamics of coherent and incoherent spin polarizations in ensembles of quantum dots

The temperature dependence of spin coherence in InGaAs quantum dots is obtained from quantum beats observed in polarization-resolved pump-probe experiments. Within the same sample we clearly distinguish between coherent spin dynamics leading to quantum beats and incoherent long-lived spin-memory effects. Analysis of the coherent data using a theoretical model reveals approximately 10 times greater stability of the spin coherence at high temperature compared to that found previously for exciton states in four-wave-mixing experiments by Borri et al. [Phys. Rev. Lett. 87, 157401 (2001)]]. The data on incoherent polarization reveal a new form of spin memory based on charged quantum dots.     

Electron spin lifetimes in Hg0.78Cd0.22 Te and InSb

We have made direct pump–probe measurements of spin lifetimes in long wavelength narrow-gap semiconductors at wavelengths between 4 and 10 μm and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes, τ_s300 ps, even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that τ_s is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of τ_s in non-degenerate lightly n-type Hg_0.78Cd_0.22Te of approximately the same band gap as InSb, and find that τ_s varies from 356 ps at 150 K to 24 ps at 300 K. Our results, both in magnitude and temperature dependence of τ_s, imply that the Elliott–Yafet model dominates in these materials.     

Breakup modes of a laminar hollow water jet

Graphical Abstract  

     

Theoretical modeling of bifunctional multilayer systems

Crystalline multilayer systems with structure ABABA... offer the possibility of combining functional properties of two distinctly different materials, and of exploiting the interfaces to couple functionality of one component to the other. The multilayer environment permits the amplification of interface properties as would be important for device applications. The manipulation of ferroelectric, ferromagnetic, and/or ferroelastic properties in so-called ferroic materials through growth of thin films, multilayers, and graded composition structures has received considerable experimental and theoretical attention in recent years. We survey the current status of atomic-scale modeling of multilayer systems which could exhibit ferroic behavior; i.e., spontaneous order below a critical temperature and hysteresis in stimulus-response behavior. The roles of interfacial strain, chemical variability at the interface, and film thickness are explored, taking as a primary example the classic BaTiO₃?∣∣Fe₃O₄ ferroelectric∣∣ferrimagnetic interactions. First principles band structure calculations are used to determine relaxed interface structures and residual stresses, as well as the underlying electronic distributions. Embedded cluster methods are then used to extract local chemical bonding characteristics and hyperfine properties.     

A comparative first-principles study of the adsorption of a carbon atom on copper and nickel surfaces

The adsorption energies of a carbon atom at the most stable adsorption sites on the Cu and Ni(100), (110) and (111) surfaces have been studied by first-principles calculations. The preference order of the adsorption sites for both Cu and Ni surfaces is the same. The (100) hollow site is the most stable one. The diffusion barriers for a C atom on the three surfaces have also been obtained, with the highest mobility on the (111) surface of both metals. Our investigation shows that the adsorption energies of the C atom on Ni are significantly higher in magnitude than those on Cu for all the three surfaces. This phenomenon is mainly due to the interaction and hybridization between C p-orbits and partially filed d-shell of Ni, which forms a stronger binding.