Helsinki University of Technology

About: Helsinki University of Technology is a based out in . It is known for research contribution in the topics: Thin film & Vortex. The organization has 8962 authors who have published 20136 publications receiving 723787 citations. The organization is also known as: TKK & Teknillinen korkeakoulu.

Cognitive Dynamics of Capability Development Paths

Abstract: Recent research on capability dynamics has increasingly turned its attention to the cognitive microfoundations of capability development. On the basis of a longitudinal case study of the evolution of three network security software firms, we find that the effects of managerial cognition can be detected at three distinct levels of capability development. At the level of operational capabilities, instrumental cognition affects the way in which capabilities are developed. At the level of a firm's capability portfolio, shifts in management's attention regarding capability development cause different evolutionary paths to emerge. Finally, at the extended enterprise level, managerial foresight influences the way in which a firm's capability constellation morphs over time. Our findings provide novel empirical evidence and contribute to an improved understanding of the role of managerial cognition in capability development.

Comparison of Full-Duplex and Half-Duplex Modes with a Fixed Amplify-and-Forward Relay

Abstract: We study the fundamental capacity trade-off between full-duplex and half-duplex transmission modes in a twohop communication system with a fixed infrastructure-based amplify-and-forward relay. First, we derive closed-form expressions for the average end-to-end capacity in the relay link. We show that it may be better to tolerate some loop interference with the full-duplex mode than to consume channel resources by allocating two orthogonal channels with the half-duplex mode. Furthermore, we evaluate the maximum loop interference power levels that still allow the full-duplex mode to achieve the same capacity as the half-duplex mode. Our results indicate that with practical signal-to-noise ratio values, the full-duplex mode is preferable in terms of capacity.

Electron and phonon transport in silicon nanowires: Atomistic approach to thermoelectric properties

Abstract: We compute both electron- and phonon transmissions in thin disordered silicon nanowires. Our atomistic approach is based on tight-binding and empirical potential descriptions of the electronic and phononic systems, respectively. Surface disorder is modeled by including surface silicon vacancies. It is shown that the average phonon- and electron transmissions through long SiNWs containing many vacancies can be accurately estimated from the scattering properties of the isolated vacancies using a recently proposed averaging method [Phys. Rev. Lett. 99, 076803 (2007)]. We apply this averaging method to surface disordered SiNWs in the diameter range 1 − 3 nm to compute the thermoelectric figure of merit, ZT. It is found that the phonon transmission is affected more by the vacancies than the electronic transmission leading to an increased thermoelectric performance of disordered wires, in qualitative agreement with recent experiments. The largest ZT > 3 is found in strongly disordered h 111i oriented wires with a diameter of 2 nm.

An intrinsic velocity-independent criterion for superfluid turbulence.

Abstract: Hydrodynamic flow in classical and quantum fluids can be either laminar or turbulent. Vorticity in turbulent flow is often modelled with vortex filaments. While this represents an idealization in classical fluids, vortices are topologically stable quantized objects in superfluids. Superfluid turbulence1 is therefore thought to be important for the understanding of turbulence more generally. The fermionic 3He superfluids are attractive systems to study because their characteristics vary widely over the experimentally accessible temperature regime. Here we report nuclear magnetic resonance measurements and numerical simulations indicating the existence of sharp transition to turbulence in the B phase of superfluid 3He. Above 0.60Tc (where Tc is the transition temperature for superfluidity) the hydrodynamics are regular, while below this temperature we see turbulent behaviour. The transition is insensitive to the fluid velocity, in striking contrast to current textbook knowledge of turbulence2. Rather, it is controlled by an intrinsic parameter of the superfluid: the mutual friction between the normal and superfluid components of the flow, which causes damping of the vortex motion.

Time-dependent cross-correlations between different stock returns: a directed network of influence.

Abstract: We study the time-dependent cross-correlations of stock returns, i.e., we measure the correlation as the function of the time shift between pairs of stock return time series using tick-by-tick data. We find a weak but significant effect showing that in many cases the maximum correlation appears at nonzero time shift, indicating directions of influence between the companies. Due to the weakness of this effect and the shortness of the characteristic time (of the order of a few minutes), our findings are compatible with market efficiency. The interaction of companies defines a directed network of influence.