Dangling-bond spin relaxation and magnetic 1/f noise from the amorphous-semiconductor/oxide interface: Theory

We propose a model for magnetic noise based on spin-flips (not electron-trapping) of paramagnetic dangling-bonds at the amorphous-semiconductor/oxide interface. A wide distribution of spin-flip times is derived from the single-phonon cross-relaxation mechanism for a dangling-bond interacting with the tunneling two-level systems of the amorphous interface. The temperature and frequency dependence is sensitive to three energy scales: The dangling-bond spin Zeeman energy delta, as well as the minimum (E_min) and maximum (E_max) values for the energy splittings of the tunneling two-level systems. We compare and fit our model parameters to a recent experiment probing spin coherence of antimony donors implanted in nuclear-spin-free silicon [T. Schenkel {\it et al.}, Appl. Phys. Lett. 88, 112101 (2006)], and conclude that a dangling-bond area density of the order of 10^{14}cm^{-2} is consistent with the data. This enables the prediction of single spin qubit coherence times as a function of the distance from the interface and the dangling-bond area density in a real device structure. We apply our theory to calculations of magnetic flux noise affecting SQUID devices due to their Si/SiO_2 substrate. Our explicit estimates of flux noise in SQUIDs lead to a noise spectral density of the order of 10^{-12}Phi_{0}^{2} {Hz}^{-1} at f=1Hz. This value might explain the origin of flux noise in some SQUID devices. Finally, we consider the suppression of these effects using surface passivation with hydrogen, and the residual nuclear-spin noise resulting from a perfect silicon-hydride surface.Comment: Final published versio

A Growth model for DNA evolution

A simple growth model for DNA evolution is introduced which is analytically solvable and reproduces the observed statistical behavior of real sequences.Comment: To be published in Europhysics Letter

Of the significance of business relationships

The Industrial Network Theory aims to describe and explain the business relationships and networks in which the focal firm is deeply embedded. One of its major propositions is that business relationships somehow influence, to different extents and over time, the focal firm’s survival. This pertains to the diverse and time-varying significance of business relationships for the focal firm. It has often been implicitly sustained that such significance is strongly related to the role played by business relationships and consequently the relationship outcomes accruing to the focal firm. The logic underlying the relationship significance proposition is outwardly oriented, somewhat overlooking the focal firm’s inside and in particular the conspicuous influence of business relationships on what the focal firm does competently both within and across its vertical boundaries. Arguably, the (predominantly ‘functional’) network-based arguments currently advanced represent a necessary but not sufficient condition for relationship significance. This conceptual paper tentatively suggests that there may be missing a supplementary (essentially internal) explanation supported by Competence-based Theories of the Firm.Industrial Network Theory; relationship significance proposition

The strategic relevance of business relationships: a preliminary assessment

The ubiquitous contention within the Industrial Networks literature - that business relationships are one of the firm´s most important resources - has not been, in our viewpoint, thoroughly explored. Hence we argue that the ‘Resource-based View of the Firm’ (‘RBV’) may complement the network-based reasoning on the strategic relevance of business relationships. A theoretical framework is proposed – a competence-based view of the firm – which solves RBV´s terminological and inconsistency problems and, more importantly, assures compatibility with the network perspective´s assumptions. The possibility of cross-fertilizing the Industrial Networks and RBV theories seems not only real, but also conceptually profitable for both theoretical fields.Business Relationships, Industrial Networks, Resource-Based View of the Firm, Competence-Based View of the Firm