Field Dependence of the Electron Spin Relaxation in Quantum Dots

Interaction of the electron spin with local elastic twists due to transverse phonons has been studied. Universal dependence of the spin relaxation rate on the strength and direction of the magnetic field has been obtained in terms of the electron gyromagnetic tensor and macroscopic elastic constants of the solid. The theory contains no unknown parameters and it can be easily tested in experiment. At high magnetic field it provides parameter-free lower bound on the electron spin relaxation in quantum dots.Comment: 4 PR pages, no figure

Magneto-elastic waves in crystals of magnetic molecules

We study magneto-elastic effects in crystals of magnetic molecules. Coupled equations of motion for spins and sound are derived and the possibility of strong resonant magneto-acoustic coupling is demonstrated. Dispersion laws for interacting linear sound and spin excitations are obtained for bulk and surface acoustic waves. We show that ultrasound can generate inverse population of spin levels. Alternatively, the decay of the inverse population of spin levels can generate ultrasound. Possibility of solitary waves of the magnetization accompanied by the elastic twists is demonstrated.Comment: 8 PR pages, 3 figure

Collective electromagnetic relaxation in crystals of molecular magnets

We study the magnetization reversal and electromagnetic radiation due to collective Landau-Zener relaxation in a crystal of molecular magnets. Analytical and numerical solutions for the time dependence of the relaxation process are obtained. The power of the radiation and the total emitted energy are computed as functions of the crystal parameters and the field sweep rate.Comment: 7 pages, 9 figure

Quantum dynamics of a nanomagnet in a rotating field

Quantum dynamics of a two-state spin system in a rotating magnetic field has been studied. Analytical and numerical results for the transition probability have been obtained along the lines of the Landau-Zener-Stueckelberg theory. The effect of various kinds of noise on the evolution of the system has been analyzed.Comment: 7 pages, 7 figure

Heat fluxes between the Guadalquivir river and the Gulf of Cádiz Continental Shelf

An 18-year time series of daily sea surface temperature of Gulf of Cadiz and an 18-month time series of temperature collected in the vicinity of the Guadalquivir estuary mouth have been analyzed to investigate the heat exchange between the estuary and the adjacent continental shelf. The first time identifies a continental shelf area where seasonal thermal oscillation signal (amplitudes and phase) changes abruptly. In order to explain this anomaly, the second data set allows a description of thermal fluctuations in a wide range of frequencies and an estimation of the upstream heat budget of the Guadalquivir estuary. Results show that high frequency thermal signal, diurnal and semidiurnal, and water flux signal through Guadalquivir mouth, mainly semidiurnal, apparently interact randomly to give a small exchange of thermal energy at high frequency. There is no trace, at the estuary's mouth, of daily heat exchanges with intertidal mudflats probably because it tends to cancel on daily time scales. Results also show that fluctuations of estimated air-sea fluxes force fluctuations of temperature in a quite homogeneous estuarine, with a delay of 20 days. The along-channel thermal energy gradient reaches magnitudes of 300-400 J m-4 near the mouth during the summer and winter and drives the estuary-shelf exchange of thermal energy at seasonal scale. Particularly, the thermal heat imported by the estuary from the shelf area during late fall-winter-early spring of 2008/2009 is balanced by the thermal heat that the estuary exports to the shelf area during late spring-summer of 2008. In summary, Guadalquivir river removes/imports excess of thermal energy towards/from the continental shelf seasonally, as a mechanism to accommodate excess of heat from one side respect to the other side.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Autoridad Portuaria de Sevilla (APS

A Taxonomy of Knowledge Spillovers for High-Tech Start-ups Development

Entrepreneurship is considered of utmost importance for national economic and industrial growth. A leading theory related to economic development is the Knowledge Spillover Theory of Entrepreneurship (KSTE), which aims to uncover the effects that economic agents have on the creation of new companies. By following the KSTE process, companies can commercialize and implement newly acquired knowledge in the market more quickly. Typically, economic growth evaluation is conducted at the country or regional level through global monitoring indexes, assessment on the generation of patents, and identification of the number of companies created. However, since knowledge is sometimes unattached to a physical document or item, it remains necessary to clarify a taxonomy and flow of knowledge spillovers at the individual level for start-ups in their first three to five years of development from the time that the company is funded. The purpose of this paper is to identify and discuss possible strategies for evaluating the effects of knowledge spillovers on start-ups in high-tech sections which, in turn, will aid the decision-making process of Chief Executive Officers (CEOs)

The Effects of Knowledge Spillovers and Accelerator Programs on the Product Innovation of High-Tech Start-Ups: A Multiple Case Study

The Knowledge Spillover Theory of Entrepreneurship (KSTE) explores the effects that new knowledge and proximity have on the exploitation of entrepreneurial opportunities and the resultant creation of start-ups. This paper aims to identify the types of knowledge spillovers that affect entrepreneurs in the early stages of start-up development. A conceptual model is proposed, using a multi-case study approach involving High-Tech start-ups that have attended accelerator and incubator programmes in Greater London, United Kingdom (UK). The research involved 32 semistructured interviews with Chief Executive Officers (CEOs) and co-founders of start-up companies. Our findings suggest that entrepreneurs are influenced by various forms of knowledge spillover which assist in determining the strategic decision of the company, in terms of formation, including partnerships or alliances, allocation of Research and Development (R&D) budgets, and engagement in product innovation. Further observations confirm that High-tech start-ups focus on a fast pace of constant product innovation to cover identified gaps in the market. One significant finding is that start-ups use various technological platforms to access knowledge spillovers which challenges the ideas of geographical proximity present in existing KSTE understanding

A Taxonomy of Knowledge Spillovers for High-Tech Start-ups Development

Entrepreneurship is considered of utmost importance for national economic and industrial growth. A leading theory related to economic development is the Knowledge Spillover Theory of Entrepreneurship (KSTE), which aims to uncover the effects that economic agents have on the creation of new companies. By following the KSTE process, companies can commercialize and implement newly acquired knowledge in the market more quickly. Typically, economic growth evaluation is conducted at the country or regional level through global monitoring indexes, assessment on the generation of patents, and identification of the number of companies created. However, since knowledge is sometimes unattached to a physical document or item, it remains necessary to clarify a taxonomy and flow of knowledge spillovers at the individual level for start-ups in their first three to five years of development from the time that the company is funded. The purpose of this paper is to identify and discuss possible strategies for evaluating the effects of knowledge spillovers on start-ups in high-tech sections which, in turn, will aid the decision-making process of Chief Executive Officers (CEOs)