Spin diffusion of the t-J model

The spin-diffusion constant of the 2D $t-J$ model is calculated for the first time using an analytical approach at high temperatures and a recently-developed numerical method based on the Lanczos technique combined with random sampling in the intermediate temperature regime. A simple relation, $\sigma = D_s\chi$, between spin conductivity and spin diffusion is established and used to calculate the latter. In the high-temperature and low-doping limit the calculated diffusion constant agrees with known results for the Heisenberg model. At small hole doping, $D_s$ increases approximately linearly with doping, which leads us to an important conclusion that hopping processes enhance spin diffusion at high temperatures. At modest hole doping, $\delta\sim 0.25$, diffusion exhibits a nonmonotonic temperature dependence, which indicates anomalous spin dynamics at small frequencies.Comment: 12 pages with figure

Productivity growth and functional upgrading in foreign subsidiaries in the Slovenian manufacturing sector

The paper discusses the determinants of productivity growth in manufacturing foreign subsidiaries in Slovenia. Special attention is given to the impact of control pattern. Using the standard growth accounting approach we show that productivity growth is significantly and positively correlated with the level of foreign parent companies' control of marketing and strategic business functions. Larger subsidiaries and subsidiaries with higher exports to sales ratio also experience higher changes in the productivity level. Subsidiaries in high technology intensity sectors exhibit significantly lower change in productivity than subsidiaries in other sectors

Optical conductivity in doped manganites with planar x2^2-y2^2 orbital order

We investigate a planar model for the ferromagnetic (FM) phase of manganites, which develops orbital order of $e_g$ electrons with x$^2$-y$^2$-symmetry at low temperature. The dynamic structure factor of orbital excitations and the optical conductivity $\sigma(\omega)$ are studied with help of a finite-temperature diagonalization method. Our calculations provide a theoretical prediction for $\sigma(\omega)$ for the 2D FM state and are of possible relevance for the recently found A-type phase of manganites at high doping which consists of FM layers coupled antiferromagnetically. In the x$^2$-y$^2$ ordered regime $\sigma(\omega)$ shows both a Drude peak and a gapped incoherent absorption due to a gap in the orbital excitations.Comment: 5 pages, 5 figures, to appear in Phys. Rev. Let

Anomalous Spin Dynamics in Doped Quantum Antiferromagnets

Finite-temperature spin dynamics in planar t-J model is studied using the method based on the Lanczos diagonalization of small systems. Dynamical spin structure factor at moderate dopings shows the coexistence of free-fermion-like and spin-fluctuation timescales. At T<J, the low-frequency and static susceptibility show pronounced T dependence, supporting a scenario, related to the marginal Fermi-liquid one, for the explanation of neutron-scattering and NMR-relaxation experiments in cuprates. Calculated NMR relaxation rates reasonably reproduce experimental ones.Comment: 10 pages + 4 figures, Postscript in uuencoded compressed tar file, IJS-TP-94/2

From local to nonlocal Fermi liquid in doped antiferromagnets

The variation of single-particle spectral functions with doping is studied numerically within the t-J model. It is shown that corresponding self energies change from local ones at the intermediate doping to strongly nonlocal ones for a weakly doped antiferromagnet. The nonlocality shows up most clearly in the pseudogap emerging in the density of states, due to the onset of short-range antiferromagnetic correlations.Comment: 4 pages, 3 Postscript figures, revtex, submitted to Phys.Rev.Let

Charge Dynamics in the Planar t-J Model

The finite-temperature optical conductivity $\sigma(\omega)$ in the planar $t-J$ model is analysed using recently introduced numerical method based on the Lanczos diagonalization of small systems (up to 20 sites), as well as by analytical approaches, including the method of frequency moments and the retraceable-path approximation. Results for a dynamical mobility of a single hole at elevated temperatures $T>t$ reveal a Gaussian-like $\mu(\omega)$ spectra, however with a nonanalytical behavior at low $\omega$. In the single hole response a difference between the ferromagnetic (J=0) and the antiferromagnetic ($J>0$) polaron shows up at $T<J$. At larger dopings numerical results in studied systems are consistent with the thermodynamical behavior for $T>T^*\ge 0.1~t$. $\sigma(\omega)$ spectra show a non-Drude falloff at large frequencies. In particular for `optimum' doping $n_h \sim 0.2$ we obtain in the low-$\omega,T$ regime the relaxation rate $\tau^{-1} \sim 0.6 (\omega+\xi T)$ with $\xi \sim 3$, being consistent with the marginal Fermi liquid concept and experiments. Within the same regime we reproduce the nearly linear variation of dc resistivity $\rho$ with $T$. This behavior is weakly dependent on $J$, provided that $J<t$.Comment: 21 pages of text plus 17 figures, postscrip

Korelacija između sadržaja titana u čeliku i elektromagnetskih svojstava neorijentiranih elektrolimova

In this study the correlation between the titanium content of steel and the core loss of non-oriented electrical steel sheets was determined. The core loss and titanium content of steel have a weak, but positive, correlation. The core loss was found to increase with an increasing titanium content. The study included a statistical analysis of an industrial data set and a metallographic analysis of the titanium inclusions. The analyzed titanium inclusions in the electrical steel sheets containing 0,006 mas.% Ti and 0,008 mas.% Ti were complex oxycarbonitrides, complex TiC and complex Ti(C,N).U radu se opisuje korelacija između sadržaja titana u čeliku i elektromagnetskih svojstava neorijentiranih elektrolimova. Postoji relativno niski stupanj pozitivne korelacije između magnetskih gubitaka i sadržajem titana. Magnetski gubici rastu sa sadržajem titana u čeliku. Izvedena je statistička analiza podataka za limove industrijske proizvodnje i metalografska analiza titanovih uključaka. Analizirani uključci u elektrolimovima sa 0,006 mas.% Ti i 0,008 mas.% Ti bili su kompleksni oksikarbonitridi, kompleksni TiC i kompleksni Ti(C,N)

Korelacija između sadržaja titana u čeliku i elektromagnetskih svojstava neorijentiranih elektrolimova

In this study the correlation between the titanium content of steel and the core loss of non-oriented electrical steel sheets was determined. The core loss and titanium content of steel have a weak, but positive, correlation. The core loss was found to increase with an increasing titanium content. The study included a statistical analysis of an industrial data set and a metallographic analysis of the titanium inclusions. The analyzed titanium inclusions in the electrical steel sheets containing 0,006 mas.% Ti and 0,008 mas.% Ti were complex oxycarbonitrides, complex TiC and complex Ti(C,N).U radu se opisuje korelacija između sadržaja titana u čeliku i elektromagnetskih svojstava neorijentiranih elektrolimova. Postoji relativno niski stupanj pozitivne korelacije između magnetskih gubitaka i sadržajem titana. Magnetski gubici rastu sa sadržajem titana u čeliku. Izvedena je statistička analiza podataka za limove industrijske proizvodnje i metalografska analiza titanovih uključaka. Analizirani uključci u elektrolimovima sa 0,006 mas.% Ti i 0,008 mas.% Ti bili su kompleksni oksikarbonitridi, kompleksni TiC i kompleksni Ti(C,N)

Antecedents and determinants of high-tech SMEs’ commercialisation enablers: opening the black box of open innovation practices

Innovation activities have become globalised and open in ways that were unimaginable 20 years ago. These changes have brought new insight into research on innovation activities and specific innovation practices in organisations, including that previous research largely ignored small and medium-sized enterprises (SMEs). This paper tests a variance-based structural equation model (SEM) for selected antecedents and determinants of commercialisation enablers on a sample of 105 SMEs from Slovenia – a small, open, post-transition economy with a dominant SME sector. The main contribution of the paper lies in testing how two specific open innovation practices (open innovation information exchange and open innovation collaboration) impact the commercialisation enablers of high-tech SMEs through their innovation activities (antecedent) and their innovativeness (determinant). Both open innovation practices show statistically significant effect on high-tech SMEs’ innovativeness, thus supporting the idea that both collaboration and information exchange lead to more innovativeness in high-tech SMEs. They also show a high impact of internal (organisational) factors on innovation activities of and a high impact of innovativeness on the commercialisation enablers of high-tech SMEs

Magnetic properties of cuprate perovskites in the normal state

Normal-state magnetic properties of cuprate high-T_c superconductors are interpreted based on the self-consistent solution of the t-J model of Cu-O planes. The solution method retains the rotation symmetry of spin components in the paramagnetic state and has no preset magnetic ordering. The obtained solution is homogeneous. The calculated temperature and concentration dependencies of the magnetic susceptibility are close to those observed in experiment. These results offer explanations for the observed scaling of the static uniform susceptibility and for the changes in the spin correlation length, spin-lattice and spin-echo decay rates in terms of the temperature and doping variations in the spin excitation spectrum.Comment: 9 pages, 5 figure