Compact stars with a small electric charge: the limiting radius to mass relation and the maximum mass for incompressible matter

One of the stiffest equations of state for matter in a compact star is constant energy density and this generates the interior Schwarzschild radius to mass relation and the Misner maximum mass for relativistic compact stars. If dark matter populates the interior of stars, and this matter is supersymmetric or of some other type, some of it possessing a tiny electric charge, there is the possibility that highly compact stars can trap a small but non-negligible electric charge. In this case the radius to mass relation for such compact stars should get modifications. We use an analytical scheme to investigate the limiting radius to mass relation and the maximum mass of relativistic stars made of an incompressible fluid with a small electric charge. The investigation is carried out by using the hydrostatic equilibrium equation, i.e., the Tolman-Oppenheimer-Volkoff (TOV) equation, together with the other equations of structure, with the further hypothesis that the charge distribution is proportional to the energy density. The approach relies on Volkoff and Misner's method to solve the TOV equation. For zero charge one gets the interior Schwarzschild limit, and supposing incompressible boson or fermion matter with constituents with masses of the order of the neutron mass one gets that the maximum mass is the Misner mass. For a small electric charge, our analytical approximating scheme valid in first order in the star's electric charge, shows that the maximum mass increases relatively to the uncharged case, whereas the minimum possible radius decreases, an expected effect since the new field is repulsive aiding the pressure to sustain the star against gravitational collapse.Comment: 23 pages, no figure

Emergent SU(N) symmetry in disordered SO(N) spin chains

Strongly disordered spin chains invariant under the SO(N) group are shown to display random-singlet phases with emergent SU(N) symmetry without fine tuning. The phases with emergent SU(N) symmetry are of two kinds: one has a ground state formed of randomly distributed singlets of strongly bound pairs of SO(N) spins (a `mesonic' phase), while the other has a ground state composed of singlets made out of strongly bound integer multiples of N SO(N) spins (a `baryonic' phase). The established mechanism is general and we put forward the cases of $\mathrm{N}=2,3,4$ and $6$ as prime candidates for experimental realizations in material compounds and cold-atoms systems. We display universal temperature scaling and critical exponents for susceptibilities distinguishing these phases and characterizing the enlarging of the microscopic symmetries at low energies.Comment: 5 pages, 2 figures, Contribution to the Topical Issue "Recent Advances in the Theory of Disordered Systems", edited by Ferenc Igl\'oi and Heiko Riege

Highly-symmetric random one-dimensional spin models

The interplay of disorder and interactions is a challenging topic of condensed matter physics, where correlations are crucial and exotic phases develop. In one spatial dimension, a particularly successful method to analyze such problems is the strong-disorder renormalization group (SDRG). This method, which is asymptotically exact in the limit of large disorder, has been successfully employed in the study of several phases of random magnetic chains. Here we develop an SDRG scheme capable to provide in-depth information on a large class of strongly disordered one-dimensional magnetic chains with a global invariance under a generic continuous group. Our methodology can be applied to any Lie-algebra valued spin Hamiltonian, in any representation. As examples, we focus on the physically relevant cases of SO(N) and Sp(N) magnetism, showing the existence of different randomness-dominated phases. These phases display emergent SU(N) symmetry at low energies and fall in two distinct classes, with meson-like or baryon-like characteristics. Our methodology is here explained in detail and helps to shed light on a general mechanism for symmetry emergence in disordered systems.Comment: 26 pages, 12 figure

Firm Performance and Modes of Innovation

It has been shown that firms tend to develop different modes of innovation, based on the relationship between the different types of underlying knowledge and learning processes. This paper seeks to identify different modes of business innovation, relating them to firms’ innovative and economic performance, and to analyze the relationship between the different innovation modes and the economic impact of the crisis on firms’ performance. These hypotheses are tested by regression and latent class models for the Portuguese population of firms, using a sample of 397 firms, classified according to technological intensity, firm size and region. Our results show three different modes of innovation in terms of the relationship between economic and innovative performance, with significant differences in terms of resilience in the face of the economic crisis. These findings lead to a reflection on innovation, competitiveness and regional policy.FC

Numerical modeling and optimization of an air handling unit

Concerns about the efficiency of Heating, Ventilating, and Air Conditioning systems, including Air Handling Units (AHUs), started in the last century due to the energy crisis. Thenceforth, important improvements on the AHUs performance have emerged. Among the various improvements, the control of the AHUs and the redesign of the fans are the most important ones. Although, with increasingly demanding energy efficiency requirements, other constructive solutions must be investigated. Therefore, the objective of this work is to investigate, using a computational fluid dynamics (CFD) tool, the fluid flow inside an AHU and to analyze different constructive solutions in order to improve the AHU performance. The numerical model provided a reasonable agreement with the experimental results in terms of air flow rate, despite the assumed simplifications. Regarding the constructive solution concept, the CFD results for the two different flow control units (FCUs) showed improvements in terms of fan static pressure rise. Under real conditions, improvements of 15.1% when compared with the case without the FCU were obtained. Nevertheless, it was concluded that the axial component of the air velocity, at the fan exit, can have a determinant impact on the FCU viability. Finally, an improved FCU geometry, with a new body shape, which resulted in an additional improvement of 6.1% in the fan static pressure rise.The second author would like to express his gratitude for the support given by FCT through the Grant SFRH/BD/130588/2017

Perceived overqualification and contact center workers’ burnout: are motivations mediators?

Purpose – The purpose of this paper is to test the direct effect of the perceived overqualification on the burnout syndrome and the indirect effect through the workers’ autonomous and controlled motivation. Design/methodology/approach – The hypotheses were tested with a sample of 3,256 contact center operators from one Portuguese company and data were analyzed using the software package Mplus to conduct structural equation models. Findings – The results revealed that workers’ perceived overqualification is positively related to burnout and that both autonomous and controlled motivation partially mediates this relationship. Research limitations/implications – The cross-sectional design should be regarded as a limitation. Moreover, each variable was only assessed with self-reported measures, the sample comprised call center employees from only one company and one country (Portugal), and the workers were all employed in commercial services of telecommunications, energy, banking or insurance companies, which may constrain the generalization of these results. Practical implications – Workers’ perceived overqualification should be avoided to prevent their burnout. Furthermore, an increase in workers’ skills and competencies, enhanced decision latitude, and the task variety and quality should be crucial for employees to develop more autonomous motivation to work in a contact center and the promotion of their well-being at work. More precisely, as overqualification concerns the employees’ perceptions of surplus education, experience and knowledge, from a practical perspective, enhancing the decision latitude, task variety and quality of these individuals’ work may contribute to decreasing individuals’ perception of overqualification and, therefore, contribute to increasing workers’ autonomous motivations and well-being. Originality/value – This study provides evidence concerning the mediating role of both workers’ autonomous and controlled motivation to explain the relationship between perceived overqualification and burnout. Keywords Motivation, Conditions of employment, Employees, Human resource management, Well-being, human resource planning.info:eu-repo/semantics/acceptedVersio

Insight. Transgenic solutions to increase yield and stability in wheat: shining hope or flash in the pan?

Second-generation transgenic crops have the potential to transform agriculture, but progress has been limited, and particularly so in wheat where no transgenic cultivar has yet been approved. Taking on the challenge, González et al. (2019) report that transgenic wheat lines carrying a mutated version of the sunflower transcription factor (HaHB4), belonging to the homeodomain-leucine zipper family (HD-Zip I), had increased yield and water use efficiency across a range of environments, with particular benefits under stress. It is an important step forward in an area where progress is urgently needed, though it is too early to claim that transgenic wheat will form the backbone of a second Green Revolution. To meet the growing demand for food, together with the challenges imposed by climate change, substantial improvements in yields of major crops are needed. This includes wheat, where globally the multi-year tendency for growth in yield is decreasing (Passioura, 2012) or even stagnating (Driever et al., 2017). Current and expected future relative rates of progress in yield potential and drought adaptation in wheat are a matter of real concern, and insufficient to meet the projected demand for cereals by 2050 (Hall and Richards, 2013). There are three major challenges: increasing yield potential, protecting yield potential from different types of stress, and increasing resource use efficiency to ensure sustainability (Hawkesford et al., 2013)

Rab11 is required for lysosome exocytosis through the interaction with Rab3a, Sec15 and GRAB

Funding: This study was supported by Fundaçã o para a Ciência e Tecnologia (FCT): C.E. was supported by a post-doctoral fellowship (SFRH/BPD/78491/2011), L.B.-L. by a PhD fellowship (SFRH/BD/131938/2017) and D.C.B. by the FCT Investigator Program (IF/00501/2014/CP1252/CT0001). This work was developed with the support from the research infrastructure PPBI-POCI-01-0145-FEDER-022122, co-financed by FCT (Portugal) and Lisboa2020, under the PORTUGAL2020 agreement (European Regional Development Fund). This article was supported by the LYSOCIL project. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 811087. Deposited in PMC for immediate release.Lysosomes are dynamic organelles, capable of undergoing exocytosis. This process is crucial for several cellular functions, namely plasma membrane repair. Nevertheless, the molecular machinery involved in this process is poorly understood. Here, we identify Rab11a and Rab11b as regulators of calcium-induced lysosome exocytosis. Interestingly, Rab11-positive vesicles transiently interact with lysosomes at the cell periphery, indicating that this interaction is required for the last steps of lysosome exocytosis. Additionally, we found that the silencing of the exocyst subunit Sec15, a Rab11 effector, impairs lysosome exocytosis, suggesting that Sec15 acts together with Rab11 in the regulation of lysosome exocytosis. Furthermore, we show that Rab11 binds the guanine nucleotide exchange factor for Rab3a (GRAB) and also Rab3a, which we described previously as a regulator of the positioning and exocytosis of lysosomes. Thus, our study identifies new players required for lysosome exocytosis and suggest the existence of a Rab11-Rab3a cascade involved in this process.publishersversionpublishe