20,363 research outputs found
New receivers for DS-SS in time variant multipath channels based on the PN alignment concept
We present new combined blind equalization and detection schemes for a DS-SS system. The new proposed algorithms improve the bit error rate compared to traditional RAKE receivers in time-variant channels with multipath. This improvement is obtained in both simulated and a real ionospheric HF link. Its very low computational complexity makes them suitable to be implemented in real receivers.Peer ReviewedPostprint (published version
An Index to Networks Defined on a Topological Conceptualization of the Geographical Space by Threefolds: The Balance Index
DSP-based ionospheric radiolink using DS-CDMA and on-line channel estimation
In this paper, a new blind multiuser detection algorithm is presented. It can both cancel multiuser interference and estimate the multipath channel response in a blind way. The method has been specially conceived for low coherence bandwidth channels such as the ionospheric channel and exhibits very low computational requirements. Real-time measurements from a fully digital HF radio-link are presented that confirm the reliability of the method for the ionospheric channel.Peer ReviewedPostprint (published version
Ground State of the Hydrogen Atom via Dirac Equation in a Minimal Length Scenario
In this work we calculate the correction to the ground state energy of the
hydrogen atom due to contributions arising from the presence of a minimal
length. The minimal length scenario is introduced by means of modifying the
Dirac equation through a deformed Heisenberg algebra (kempf algebra). With the
introduction of the Coulomb potential in the new Dirac energy operator, we
calculate the energy shift of the ground state of the hydrogen atom in first
order of the parameter related to the minimal length via perturbation theory.Comment: 11 page
Electrically controllable magnetism in twisted bilayer graphene
Twisted graphene bilayers develop highly localised states around AA-stacked
regions for small twist angles. We show that interaction effects may induce
either an antiferromagnetic (AF) and a ferromagnetic (F) polarization of said
regions, depending on the electrical bias between layers. Remarkably,
F-polarised AA regions under bias develop spiral magnetic ordering, with a
relative misalignment between neighbouring regions due to a
frustrated antiferromagnetic exchange. This remarkable spiral magnetism emerges
naturally without the need of spin-orbit coupling, and competes with the more
conventional lattice-antiferromagnetic instability, which interestingly
develops at smaller bias under weaker interactions than in monolayer graphene,
due to Fermi velocity suppression. This rich and electrically controllable
magnetism could turn twisted bilayer graphene into an ideal system to study
frustrated magnetism in two dimensions, with interesting potential also for a
range of applications.Comment: 7 pages, 3 figures. Minor correction
Diacritical study of light, electrons, and sound scattering by particles and holes
We discuss the differences and similarities in the interaction of scalar and
vector wave-fields with particles and holes. Analytical results are provided
for the transmission of isolated and arrayed small holes as well as surface
modes in hole arrays for light, electrons, and sound. In contrast to the
optical case, small-hole arrays in perforated perfect screens cannot produce
acoustic or electronic surface-bound states. However, unlike electrons and
light, sound is transmitted through individual holes approximately in
proportion to their area, regardless their size. We discuss these issues with a
systematic analysis that allows exploring both common properties and unique
behavior in wave phenomena for different material realizations.Comment: 3 figure
Entrepreneurial intention, cognitive social capital and culture : empirical anaylisis for Spain and Taiwan
The main purpose of this paper is building a research model to integrate the socioeconomic concept of social capital within intentional models of new firm creation. Nevertheless, some researchers have found cultural differences between countries and regions to have an effect on economic development. Therefore, a second objective of this study is exploring whether those cultural differences affect entrepreneurial cognitions. Research design and methodology: Two samples of last year university students from Spain and Taiwan are studied through an Entrepreneurial Intention Questionnaire (EIQ). Structural equation models (Partial Least Squares) are used to test the hypotheses. The possible existence of differences between both sub-samples is also empirically explored through a multigroup analysis. Main outcomes and results: The proposed model explains 54.5% of the variance in entrepreneurial intention. Besides, there are some significant differences between both subsamples that could be attributed to cultural diversity. Conclusions: This paper has shown the relevance of cognitive social capital in shaping individuals' entrepreneurial intentions across different countries. Furthermore, it suggests that national culture could be shaping entrepreneurial perceptions, but not cognitive social capital. Therefore, both cognitive social capital and culture (made up essentially of values and beliefs), may act together to reinforce the entrepreneurial intention
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