DMRG study of the Bond Alternating \textbf{S}=1/2 Heisenberg ladder with Ferro-Antiferromagnetic couplings

We obtain the phase diagram in the parameter space $(J'/J, \gamma)$ and an accurate estimate of the critical line separating the different phases. We show several measuments of the magnetization, dimerization, nearest neighbours correlation, and density of energy in the different zones of the phase diagram, as well as a measurement of the string order parameter proposed as the non vanishing phase order parameter characterizing Haldane phases. All these results will be compared in the limit $J'/J\gg 1$ with the behaviour of the $\textbf{S}=1$ Bond Alternated Heisenberg Chain (BAHC). The analysis of our data supports the existence of a dimer phase separated by a critical line from a Haldane one, which has exactly the same nature as the Haldane phase in the $\textbf{S}=1$ BAHC.Comment: Version 4. 8 pages, 15 figures (12 figures in document

Structure of fish assemblages on coastal rocky shores of the Azores

Bol. Mus. Mun. Funchal, Sup. N.º 6: 127-138, 2001The structure of fish assemblages was investigated from the surface down to 25 m depth on Azorean rocky shores. A total of 57 fish species was recorded by visual censuses, most species (66%) occurring in the whole depth range studied. Fish abundance was dominated by 11 species, mainly sparids, labrids, carangids and pomacentrids, which constituted over 88% of the total number of individuals recorded. The trophic structure of the fish assemblages studied in the Azores was characterized by the dominance of benthic mesocarnivores and high proportions of herbivores and pelagic macrocarnivores.A estrutura das comunidades ictiológicas dos fundos rochosos dos Açores foi estudada desde a superfície até aos 25 m de profundidade. Um total de 57 espécies de peixes foi identificado com recurso a censos visuais. A maioria das espécies (66%) ocorreu em toda a gama de profundidades estudada. A fauna ictiológica era dominada, em termos de abundância, por 11 espécies, principalmente pertencentes às famílias Sparidae, Labridae, Carangidae e Pomacentridae, os quais constituíram mais de 88% do número total de indivíduos observados. A estrutura trófica das comunidades ictiológicas estudadas nos Açores apresentouse dominada por meso-carnívoros bentónicos e proporções elevadas de herbívoros e macro-carnívoros pelágico

Frequency up- and down-conversions in two-mode cavity quantum electrodynamics

In this letter we present a scheme for the implementation of frequency up- and down-conversion operations in two-mode cavity quantum electrodynamics (QED). This protocol for engineering bilinear two-mode interactions could enlarge perspectives for quantum information manipulation and also be employed for fundamental tests of quantum theory in cavity QED. As an application we show how to generate a two-mode squeezed state in cavity QED (the original entangled state of Einstein-Podolsky-Rosen)

Quantum-state transfer in staggered coupled-cavity arrays

We consider a coupled-cavity array, where each cavity interacts with an atom under the rotating-wave approximation. For a staggered pattern of inter-cavity couplings, a pair of field normal modes each bi-localized at the two array ends arise. A rich structure of dynamical regimes can hence be addressed depending on which resonance condition between the atom and field modes is set. We show that this can be harnessed to carry out high-fidelity quantum-state transfer (QST) of photonic, atomic or polaritonic states. Moreover, by partitioning the array into coupled modules of smaller length, the QST time can be substantially shortened without significantly affecting the fidelity.Comment: 12 pages, 8 figure

Group theory for structural analysis and lattice vibrations in phosphorene systems

Group theory analysis for two-dimensional elemental systems related to phosphorene is presented, including (i) graphene, silicene, germanene and stanene, (ii) dependence on the number of layers and (iii) two stacking arrangements. Departing from the most symmetric $D_{6h}^{1}$ graphene space group, the structures are found to have a group-subgroup relation, and analysis of the irreducible representations of their lattice vibrations makes it possible to distinguish between the different allotropes. The analysis can be used to study the effect of strain, to understand structural phase transitions, to characterize the number of layers, crystallographic orientation and nonlinear phenomena.Comment: 24 pages, 3 figure

Working from home during COVID-19 lockdown: Changing competencies and work-home life boundaries

Crisis situations often introduces drastic lifestyle changes. This study is focused on the COVID-19 pandemic and aims to shed light on an unprecedented context of forcing employees to work from home with a short notice of companies and the government. The goal is three-fold: i) to understand the extent to which employees were indeed prepared to work from home; ii) to uncover the most important competencies that enabled employees to deal better with a crisis situation, such as the COVID-19 pandemic; and iii) to discuss the real impact that working from home had in the employees’ lives during the pandemic situation and the quarantine period. Using narrative inquiry, this study explores the experiences of 18 young adult consultants working in different business areas, in Portugal. Semi-structure interviews were conducting during the third wave (12/2020 – 03/2021) and thematic analysis was used to analysis the transcripts. The analysis revealed three main themes: ‘management competencies’, ‘work-life balance’ and ‘work flexibility’. Each theme consisted of several subthemes which illustrates how the participants perceived working from home and the factors that reflect their experiences and understanding. The research findings illustrate that interpersonal communication, anxiety and stress management, time management, and e-leadership are vital skills to cause a great impact on participants’ productivity and well-being at work. Participants all appeared to notice that working from home provides a better work-life balance (e.g. saving time on daily commute) and more flexibility with regards to the work schedule and home commitments. Nonetheless, their experiences of home working depend on the personal situation, personality and the perceived management support offered during the COVID-19 lockdown. The research highlights a need to train employees on soft skills and prepare them to future crisis situations. Theoretical implications suggest that academics should expand research and interventions to include not only the work environment but also other external factors that affect employees. The limitations of the study and recommendations for future research are suggested.info:eu-repo/semantics/publishedVersio

Experimental feedback control of quantum systems using weak measurements

A goal of the emerging field of quantum control is to develop methods for quantum technologies to function robustly in the presence of noise. Central issues are the fundamental limitations on the available information about quantum systems and the disturbance they suffer in the process of measurement. In the context of a simple quantum control scenario--the stabilization of non-orthogonal states of a qubit against dephasing--we experimentally explore the use of weak measurements in feedback control. We find that, despite the intrinsic difficultly of implementing them, weak measurements allow us to control the qubit better in practice than is even theoretically possible without them. Our work shows that these more general quantum measurements can play an important role for feedback control of quantum systems.Comment: 4 pages, 3 figures. v2 Added extra citation, journal reference and DOI. Minor typographic correction

Neutral heavy lepton production at next high energy e+e−e^+e^- linear colliders

The discovery potential for detecting new heavy Majorana and Dirac neutrinos at some recently proposed high energy $e^+e^-$ colliders is discussed. These new particles are suggested by grand unified theories and superstring-inspired models. For these models the production of a single heavy neutrino is shown to be more relevant than pair production when comparing cross sections and neutrino mass ranges. The process $e^+e^- \longrightarrow {\nu} e^{\pm} W^{\mp}$ is calculated including on-shell and off-shell heavy neutrino effects. We present a detailed study of cross sections and distributions that shows a clear separation between the signal and standard model contributions, even after including hadronization effects.Comment: 4 pages including 15 figures, 1 table. RevTex. Accepted in Physical Review