Morphology and thermal stability of AlF3 thin films grown on Cu(100)

The growth of ultrathin epitaxial layers of aluminum fluoride on Cu(100) has been studied by a combination of surface science techniques. Deposition at room temperature results in step decoration followed by the formation of dendritic two-dimensional islands that coalesce to form porous films. Ultrathin layers (up to 2 monolayers in thickness) are morphologically unstable upon annealing; de-wetting takes place around 430 K with the formation of three-dimensional islands and leaving a large fraction of the Cu surface uncovered. Films several nanometers thick, on the contrary, are stable up to ca. 730 K where desorption in molecular form sets on. The effect of electron irradiation on the AlF₃ has also been characterized by different spectroscopic techniques; we find that even small quantities of stray electrons from rear electron beam heating can provoke significant decomposition of the aluminum fluoride, resulting in the release of molecular fluorine and the formation of deposits of metallic aluminum. These features make AlF₃ an interesting material for spintronic applications.     

New Coherent States for the BDS-Hamiltonian

In the paper we construct a new set of coherent states for a deformed Hamiltonian of the harmonic oscillator, previously introduced by Beckers, Debergh, and Szafraniec, which we have called the BDS-Hamiltonian. This Hamiltonian depends on the new creation operator a ⁺, i.e. the usual creation operator displaced with the real quantity . In order to construct the coherent states, we use a new measure in the Hilbert space of the Hamiltonian eigenstates, in fact we change the inner product. This ansatz assures that the set of eigenstates be orthonormalized and complete. In the new inner product space the BDS-Hamiltonian is self-adjoint. Using these coherent states, we construct the corresponding density operator and we find the P-distribution function of the unnormalized density operator of the BDS-Hamiltonian. Also, we calculate some thermal averages related to the BDS-oscillators system which obey the quantum canonical distribution conditions.     

The standard model on non-commutative space-time

We consider the standard model on a non-commutative space and expand the action in the non-commutativity parameter . No new particles are introduced; the structure group is . We derive the leading order action. At zeroth order the action coincides with the ordinary standard model. At leading order in we find new vertices which are absent in the standard model on commutative space-time. The most striking features are couplings between quarks, gluons and electroweak bosons and many new vertices in the charged and neutral currents. We find that parity is violated in non-commutative QCD. The Higgs mechanism can be applied. QED is not deformed in the minimal version of the NCSM to the order considered. Received: 29 November 2001 / Published online: 25 January 2002     

Lorentz invariance with an invariant energy scale

We propose a modification of special relativity in which a physical energy, which may be the Planck energy, joins the speed of light as an invariant, in spite of a complete relativity of inertial frames and agreement with Einstein's theory at low energies. This is accomplished by a nonlinear modification of the action of the Lorentz group on momentum space, generated by adding a dilatation to each boost in such a way that the Planck energy remains invariant. The associated algebra has unmodified structure constants. We also discuss the resulting modifications of field theory and suggest a modification of the equivalence principle which determines how the new theory is embedded in general relativity.     

New exact solutions of the space-time fractional cubic Schrodinger equation using the new type F-expansion method

In this study, a more general version of F-expansion method is proposed. With this offered method, more than one Jacobi elliptic functions are located in the solution function. We seek analytical solutions of the space-time fractional cubic Schrodinger equation by use of the new type of F-expansion method. Consequently, multifarious exact analytical solutions consisting of single, double, and multiple combined Jacobi elliptic functions solutions are acquired.     

Utilization of Fly Ash Nanofluids in Two-phase Closed Thermosyphon for Enhancing Heat Transfer

This study investigates how fly ash nanofluids affect the thermal performance of a two-phase closed thermosyphon at various states of operation. The utilization of nanofluids obtained from X₂O₃-type oxides, such as Al₂O₃, Fe₂O₃, or CuO, on the improvement of two-phase closed thermosyphon performance was reported in a number of studies in the literature. The present study experimentally demonstrated the effect of using a nanofluid obtained from fly ash comprised of various types of metal oxides in varying ratios on improving the performance of a two-phase closed thermosyphon. The fly ash was obtained from the flue gas that was captured in the cyclones of the Yatagan thermal power plant (Turkey). Triton X-100 (Dow Chemical Company) dispersant was used in the study to produce the 0.2% (wt) fly ash/water nanofluid via direct synthesis. A straight copper tube with an inner diameter of 13 mm, outer diameter of 15 mm, and length of 1 m was used as the two-phase closed thermosyphon. The nanofluid filled 33.3% (44.2 ml) of the volume ofthe two-phase closed thermosyphon. Three heating power levels (200, 300, and 400 W) were used in the experiments with three different flow rates of cooling water (5, 7.5, and 10 g/s) used in the condenser for cooling the system. A increase of 26.39% was achieved in the efficiency of the two-phase closed thermosyphon when 4% (wt) fly ash containing nanofluid was used to replace deionized water at a heat load of 200 W and with a cooling water flow rate of 5 g/s.     

Gravitational and electromagnetic signatures of accretion into a charged black hole

We present the derivation and the solutions to the coupled electromagnetic and gravitational perturbations with sources in a charged black hole background. We work in the so called ghost gauge and consider as source of the perturbations the infall of radial currents. In this way, we study a system in which it is provoked a response involving both, gravitational and electromagnetic waves, which allows us to analyze the dependence between them. We solve numerically the wave equations that describe both signals, characterize the waveforms and study the relation between the input parameters of the infalling matter with those of the gravitational and electromagnetic responses.     

EPR of Cu2+-doped Cs2CO3 and CsHCO3: evidence of the Jahn–Teller effect

Cu²⁺-doped Cs₂CO₃ and CsHCO₃ single crystals were investigated by electron paramagnetic resonance between 113–273 and 173–313 K, respectively. For both single crystals, two sites were observed for the Cu²⁺ at ambient temperature for arbitrary orientations of the single crystals in the magnetic field. However, when the temperature is varied, the spectra indicate the equivalence of the two sites at 225 and 240 K for the single crystals, respectively, to the above order. Below and above these temperatures two sites for Cu²⁺ appear, and below 133 and 173 K the signals do not vary and two sites were always observed. This is attributed to the transition of the dynamic Jahn–Teller effect to a static situation at lower temperatures. Cu²⁺ seems to replace Cs⁺ and the charge compensation is fulfilled by another Cs⁺. Spin-Hamiltonian parameters for both single crystals at ambient temperature are reported and discussed.