Reverse Doppler effect in backward spin waves scattered on acoustic waves

We report on the observation of reverse Doppler effect in backward spin waves reflected off of surface acoustic waves. The spin waves are excited in a yttrium iron garnet (YIG) film. Simultaneously, acoustic waves are also generated. The strain induced by the acoustic waves in the magnetostrictive YIG film results in the periodic modulation of the magnetic anisotropy in the film. Thus, in effect, a travelling Bragg grating for the spin waves is produced. The backward spin waves reflecting off of this grating exhibit a reverse Doppler shift: shifting down rather than up in frequency when reflecting off of an approaching acoustic wave. Similarly, the spin waves are shifted up in frequency when reflecting from receding acoustic waves.Comment: 4 pages, 3 figure

Equilibrium and off-equilibrium simulations of chiral-glass order in three-dimensional Heisenberg spin glasses

Spin-glass and chiral-glass orderings in three-dimensional Heisenberg spin glasses are studied both by equilibrium and off-equilibrium Monte Carlo simulations. Fully isotropic model is found to exhibit a finite-temperature chiral-glass transition without the conventional spin-glass order. Although chirality is an Ising-like quantity from symmetry, universality class of the chiral-glass transition appears to be different from that of the standard Ising spin glass. In the off-equilibrium simulation, while the spin autocorrelation exhibits only an interrupted aging, the chirality autocorrelation persists to exhibit a pronounced aging effect reminisecnt of the one observed in the mean-field model. Effects of random magnetic anisotropy is also studied by the off-equilibrium simulation, in which asymptotic mixing of the spin and the chirality is observed.Comment: 15 pages including 8 figures, plain Tex, to appear in Computer Simulation Studies in Condensed Matter Physics XI, Springer, 199

Two-Nucleon Scattering without partial waves using a momentum space Argonne V18 interaction

We test the operator form of the Fourier transform of the Argonne V18 potential by computing selected scattering observables and all Wolfenstein parameters for a variety of energies. These are compared to the GW-DAC database and to partial wave calculations. We represent the interaction and transition operators as expansions in a spin-momentum basis. In this representation the Lippmann-Schwinger equation becomes a six channel integral equation in two variables. Our calculations use different numbers of spin-momentum basis elements to represent the on- and off-shell transition operators. This is because different numbers of independent spin-momentum basis elements are required to expand the on- and off-shell transition operators. The choice of on and off-shell spin-momentum basis elements is made so that the coefficients of the on-shell spin-momentum basis vectors are simply related to the corresponding off-shell coefficients.Comment: 14 pages, 8 Figures, typos correcte

Repeating Routines? How transfer and inheritance to corporate spin-offs varies among gestation contexts

In economic geography literature the attention for spin‐off entrepreneurship has been steadily growing. Its main driver is that spin-off firms are said to have intrinsic advantages over other start-ups because of their embedded link to a parent company. Through this embedded link spin-off firms have a relatively ââ¬Ëeasyââ¬â¢ access to resources for production which has several interesting implications on both the firm and the regional level. At the firm level, spin-off firms seem to outperform other entrants on at least some aspects of success including employment growth and survival chances. At the regional level, they may play a key role in the development of clusters. Despite the increasing number of studies addressing the effects of spin-off processes, important issues remain unresolved. Most importantly, there is still work to be done in identifying what it is that spin-off entrepreneurs take with them from their previous employer and how this affects their innovative behavior, business strategies and performance; and ultimately their alleged contribution to regional economic development. This has been acknowledged before: ââ¬Åââ¬Â¦ we know little about how conversion [between knowledge and technology commercialization] actually occurs, even though knowledge conversion is at the core of what spin‐offs doââ¬Â¦Ã¢â¬ (Zahra et al., 2007: 570). Based on a review of recent spin-off studies, this paper draws on key inheritance mechanisms in an attempt to develop a new conceptualization of explanations of spin-off effects. Following Koster (2006), initially a distinction will be made between direct resource transfers between parent and spin‐off (providing accommodation or guaranteed turnover) and indirect transfers (spin‐off entrepreneurs capitalizing on previously gained skills). We explore the concept of indirect transfers further in differentiating between personal skills of spin-off entrepreneurs gained while working in the parent organization on the one hand, and the inheritance of specific features of the parental organization, in particular its organizational characteristics and strategies. This closely fits in with the evolutionary economics vocabulary, especially with Nelson and Wintersââ¬â¢ (1982) famous DNA metaphor: the knowledge and routines of firms (their ââ¬ËDNAââ¬â¢) are partially inherited by their spin‐offs (Boschma et al., 2002).

Suppression of Ground-State Magnetization in Finite-Sized Systems Due to Off-Diagonal Interaction Fluctuations

We study a generic model of interacting fermions in a finite-sized disordered system. We show that the off-diagonal interaction matrix elements induce density of states fluctuations which generically favor a minimum spin ground state at large interaction amplitude, $U$. This effect competes with the exchange effect which favors large magnetization at large $U$, and it suppresses this exchange magnetization in a large parameter range. When off-diagonal fluctuations dominate, the model predicts a spin gap which is larger for odd-spin ground states as for even-spin, suggesting a simple experimental signature of this off-diagonal effect in Coulomb blockade transport measurements.Comment: Final, substantially modified version of the article. Accepted for publication in Physical Review Letter

Effects of in-chain and off-chain substitutions on spin fluctuations in the spin-Peierls compound CuGeO_3

The effect of in-chain and off-chain substitutions on 1D spin fluctuations in the spin-Peierls compound CuGeO_3 has been studied using Raman scattering in order to understand the interplay between defect induced states, enhanced spin-spin correlations and the ground state of low dimensional systems. In-chain and off-chain substitutions quench the spin-Peierls state and induce 3D antiferromagnetic order at T\leq 5 K. Consequently a suppression of a 1D gap-induced mode as well as a constant intensity of a spinon continuum are observed at low temperatures. A 3D two-magnon density of states now gradually extends to higher temperatures T\leq 60K compared with pure CuGeO_3. This effect is more pronounced in the case of off-chain substitutions (Si) for which a N\'eel state occurs over a larger substitution range, starting at very low concentrations. Besides, additional low energy excitations are induced. These effects, i.e. the shift of a dimensional crossover to higher temperatures are due to an enhancement of the spin-spin correlations induced by a small amount of substitutions. The results are compared with recent Monte Carlo studies on substituted spin ladders, pointing to a similar instability of coupled, dimerized spin chains and spin ladders upon substitution.Comment: 14 pages, 6 eps figures, to be published in PR

Maximizing Spin Correlations in Top Quark Pair Production at the Tevatron

A comparison is made between the off-diagonal and helicity spin bases for top quark pair production at the FNAL Tevatron. In the off-diagonal basis, 92% of the top quark pairs are in the spin configuration up-down plus down-up, whereas in the helicity basis only 70% are left-right plus right-left. The off-diagonal basis maximizes the spin asymmetry and hence the measured angular correlations between the decay products, which are more than twice as big in this basis as compared to the helicity basis. In addition, for the process q qbar --> t tbar, we give a very simple analytic expression for the matrix element squared which includes all spin correlations between the production and subsequent decay of the top quarks.Comment: 15 pages, revtex. 4 Postscript figures (included