No spin-localization phase transition in the spin-boson model without local field

We explore the spin-boson model in a special case, i.e., with zero local field. In contrast to previous studies, we find no possibility for quantum phase transition (QPT) happening between the localized and delocalized phases, and the behavior of the model can be fully characterized by the even or odd parity as well as the parity breaking, instead of the QPT, owned by the ground state of the system. Our analytical treatment about the eigensolution of the ground state of the model presents for the first time a rigorous proof of no-degeneracy for the ground state of the model, which is independent of the bath type, the degrees of freedom of the bath and the calculation precision. We argue that the QPT mentioned previously appears due to unreasonable treatment of the ground state of the model or of the infrared divergence existing in the spectral functions for Ohmic and sub-Ohmic dissipations.Comment: 5 pages, 1 figure. Comments are welcom

Solutions to the Jaynes-Cummings model without the rotating-wave approximation

By using extended bosonic coherent states, the solution to the Jaynes-Cummings model without the rotating-wave approximation can be mapped to that of a polynomial equation with a single variable. The solutions to this polynomial equation can give all eigenvalues and eigenfunctions of this model with all values of the coupling strength and the detuning exactly, which can be readily applied to recent circuit quantum electrodynamic systems operating in the ultra-strong coupling regime.Comment: 6 pages,3 figure

Effective and Efficient Similarity Index for Link Prediction of Complex Networks

Predictions of missing links of incomplete networks like protein-protein interaction networks or very likely but not yet existent links in evolutionary networks like friendship networks in web society can be considered as a guideline for further experiments or valuable information for web users. In this paper, we introduce a local path index to estimate the likelihood of the existence of a link between two nodes. We propose a network model with controllable density and noise strength in generating links, as well as collect data of six real networks. Extensive numerical simulations on both modeled networks and real networks demonstrated the high effectiveness and efficiency of the local path index compared with two well-known and widely used indices, the common neighbors and the Katz index. Indeed, the local path index provides competitively accurate predictions as the Katz index while requires much less CPU time and memory space, which is therefore a strong candidate for potential practical applications in data mining of huge-size networks.Comment: 8 pages, 5 figures, 3 table

Optimizacija parametara taloženja za premaze α-Al2O3 tehnikom plazme dvostrukog sjaja

The parameters to prepare α-Al2O3 coatings by double glow plasma technique were optimized to obtain dense and thick α-Al2O3 coatings on 316 L stainless steel at low temperature of 580 °C. The parallel distance between the source electrode and the substrate, working pressure, source electrode voltage, and workpiece electrode voltage were designed by L9 Orthogonal array design. The thickness, microstructure, chemical composition and phase components of the sputter-deposited Al/α-Al2O3 coatings were analysed by means of 3-D non-contact surface profiler analysis, scanning electron microscopy equipped with energy dispersive X-ray spectrometry and glancing-angle X-ray diffraction, respectively. The results indicated that the parallel distance between the source electrode and the substrate played a dominant role in determining the thickness of the films. The coatings prepared at the optimum parameters exhibited a very dense, uniform, and compact microstructure without any cracks and defects. It was found that iron aluminide formed at the interface between the coatings and the substrates. The thickness of the coatings reached about 11.6 μm at the deposition rate of ~64.4 nm min–1. The oxidized coatings with the lowest porosity about 0.13 % had relative content of α-Al2O3 as high as 66.5 % when oxygen flow was 2 sccm.Za dobivanje gustih i debelih premaza α-Al2O3 na nehrđajućem čeliku 316 L pri niskoj temperaturi od 580 °C parametri za pripravu premaza α-Al2O3 optimirani su tehnikom plazme dvostrukog sjaja. Udaljenost između izvora elektrode i supstrata, radni tlak, napon izvorne elektrode i napon elektrode radnog komada dobiveni su metodom ortogonalnog niza L9. Debljina, mikrostruktura, kemijski sastav i fazne komponente pršteći pohranjenih premaza Al/α-Al2O3 analizirani su pomoću 3-D beskontaktne površinske analize, skenirajućom elektronskom mikroskopijom opremljenom spektrometrijom disperzije energije rendgenskog zračenja i difrakcijom kuta sjaja rendgenskog zračenja. Rezultati su pokazali da usporedna udaljenost između izvora elektrode i supstrata ima dominantnu ulogu u određivanju debljine filmova. Premazi pripravljeni pri optimalnim uvjetima pokazali su vrlo gustu, ujednačenu i kompaktnu mikrostrukturu bez pukotina i oštećenja. Utvrđeno je da je na granici između premaza i supstrata formiran željezov aluminid. Debljina premaza je pri stopi taloženja od ~64,4 nm min–1 dosegla oko 11,6 μm. Ako je protok kisika 2 sccm, oksidirani premazi s najmanjom poroznošću od oko 0,13 % imaju relativni udjel α-Al2O3 od oko 66,5 %