Ground state properties and excitation spectrum of a two dimensional gas of bosonic dipoles

We present a quantum Monte Carlo study of two-dimensional dipolar Bose gases in the limit of zero temperature. The analysis is mainly focused on the anisotropy effects induced in the homogeneous gas when the polarization angle with respect to the plane is changed. We restrict our study to the regime where the dipolar interaction is strictly repulsive, although the strength of the pair repulsion depends on the vector interparticle distance. Our results show that the effect of the anisotropy in the energy per particle scales with the gas parameter at low densities as expected, and that this scaling is preserved for all polarization angles even at the largest densities considered here. We also evaluate the excitation spectrum of the dipolar Bose gas in the context of the Feynman approximation and compare the results obtained with the Bogoliubov ones. As expected, we find that these two approximations agree at very low densities, while they start to deviate from each other as the density increases. For the largest densities studied, we observe a significant influence of the anisotropy of the dipole-dipole interaction in the excitation spectrum.Comment: 6 pages, 6 figure

Single-particle vs. pair superfluidity in a bilayer system of dipolar bosons

We consider the ground state of a bilayer system of dipolar bosons, where dipoles are oriented by an external field in the direction perpendicular to the parallel planes. Quantum Monte Carlo methods are used to calculate the ground-state energy, the one-body and two-body density matrix, and the superfluid response as a function of the separation between layers. We find that by decreasing the interlayer distance for fixed value of the strength of the dipolar interaction, the system undergoes a quantum phase transition from a single-particle to a pair superfluid. The single-particle superfluid is characterized by a finite value of both the atomic condensate and the super-counterfluid density. The pair superfluid phase is found to be stable against formation of many-body cluster states and features a gap in the spectrum of elementary excitations.Comment: 4 figure

Finiteness of Ulam Polynomials

A polynomial whose coeffcients are equal to its roots is called a Ulam polynomial. In this paper we show that for a given degree n there exists a finite number of Ulam polynomials of degree n.Comment: 2 page

Towards understanding a distinct hydrogen peroxide electrocatalytic enhancement using surfactant-based coatings on silver

The detection of hydrogen peroxide has been shown to be very important in recent years due to its relevant role in many industrial applications as well as biological reactions. We are interested in it as a quantitative marker for oxidase-based biosensor applications where it is produced when substrate (e.g., glucose, cholesterol) is catalysed by its respective oxidase enzyme. Previously, a commercial silver flake-based screen-printing ink (PF-410, Acheson®), when coated with surfactant and salt (dodecylbenzenesulfonic acid (DBSA) and KCl) has shown to significantly enhance the electrochemical reduction of hydrogen peroxide - up to 80-fold over non-treated inks. In this study, the silver morphology, presence of dispersant and silver supplier is investigated for their effects on the electrocatalysis of hydrogen peroxide. In order to do this, inks loaded with silver micron-sized flakes and silver nanopowders, from various suppliers, are prepared using the binder material extracted from the Acheson® PF-410 to formulate inks

Polyaniline nanoparticles for sensing applications.

Conducting polymers are being widely employed in the manufacture of nanostructured sensors due to breakthroughs in the development of sophisticated nano-sized forms. One of the most attractive conducting polymers is polyaniline (PANI) due to its interesting electrical, electrochemical and optical properties, such as air stability and simple acid/base doping/dedoping chemistry. However, the fact that aniline is a carcinogenic monomer, its insolubility in common solvents and the acidic conditions required to the most conductive form of PANI are made its commercial application very difficult so far. The synthesis of PANI nanoparticles using dodecylbenzenesulphonic acid (DBSA) as both dopant and surfactant have allowed the use of this polymer in aqueous media, improving its processability. The additional use of ammonium persulphate (APS) as an oxidant together with DBSA during chemical PANI polymerization have led to the creation of a spherical PANI nanoparticle aqueous dispersion. Such dispersion can be deposited onto the electrodes by means of traditional methods, such as drop coating, or using more sophisticated techniques, such as inkjet printing. The application of PANI nanoparticles inkjet printed onto carbon paste screen-printed electrodes for ascorbic acid sensing is shown in the present wor

Spin reversal in Fe8 under fast pulsed magnetic fields

We report measurements on magnetization reversal in the Fe8 molecular magnet using fast pulsed magnetic fields of 1.5 kT s−1 and in the temperature range of 0.6–4.1 K. We observe and analyze the temperature dependence of the reversal process, which involves in some cases several resonances. Our experiments allow observation of resonant quantum tunneling of magnetization up to a temperature of ~4 K. We also observe shifts in the maxima of the relaxation within each resonance field with temperature that suggest the emergence of a thermal instability—a combination of spin reversal and self-heating that may result in a magnetic deflagration process. The results are mainly understood in the framework of thermally-activated quantum tunneling transitions in combination with emergence of a thermal instability

Spin reversal in Fe8 under fast pulsed magnetic fields

We report measurements on magnetization reversal in the Fe8 molecular magnet using fast pulsed magnetic fields of 1.5 kT s−1 and in the temperature range of 0.6–4.1 K. We observe and analyze the temperature dependence of the reversal process, which involves in some cases several resonances. Our experiments allow observation of resonant quantum tunneling of magnetization up to a temperature of ~4 K. We also observe shifts in the maxima of the relaxation within each resonance field with temperature that suggest the emergence of a thermal instability—a combination of spin reversal and self-heating that may result in a magnetic deflagration process. The results are mainly understood in the framework of thermally-activated quantum tunneling transitions in combination with emergence of a thermal instability