Weak-Coupling Theory of Pair Density-Wave Instabilities in Transition Metal Dichalcogenides

The possibility of realizing pair density wave (PDW) phases, in which Cooper pairs have a finite momentum, presents an interesting challenge that has been studied in a wide variety of systems. In conventional superconductors, this is only possible when external fields lift the spin degeneracy of the Fermi surface, leading to pair formation at an incommensurate momentum. Here, we study a second possibility, potentially relevant to transition metal dichalcogenides, in which the Fermi surface consists of a pair of pockets centered at the $\pm K$ points of the Brillouin zone as well as a central pocket at the $\Gamma$ point. In the limit where these three pockets are identical, the pairing susceptibility has a logarithmic divergence at the non-zero wave-vectors $\pm \mathbf{K}$, allowing for a weak-coupling analysis of the PDW instability. We find that repulsive electronic interactions combine to yield effective attractive interactions in the singlet and triplet PDW channels, as long as the $\Gamma$ pocket is present. Because these PDW channels decouple from the uniform superconducting channel, they can become the leading unconventional pairing instability of the system. Upon solving the linearized gap equations, we find that the PDW instability is robust against small trigonal warping of the $\pm K$ pockets and small detuning between the $\Gamma$ and $\pm K$ pockets, which affect the PDW transition in a similar way as the Zeeman magnetic field affects the uniform superconducting transition. We also derive the Ginzburg-Landau free energy for the PDW gaps with momenta $\pm \mathbf{K}$, analyzing the conditions for and consequences of the emergence of FF-type and LO-type PDW ground states. Our classification of the induced orders in each ground state reveals unusual phases, including an odd-frequency charge-$2e$ superconductor in the LO-type PDW.Comment: 24 pages, 11 figure

Análise morfométrica e microevolutiva dentária através do método do polígono oclusal das cúspides

Dissertação de mestrado em Evolução e Biologia Humanas, apresentada ao Departamento de Ciências da Vida da Faculdade de Ciências da Universidade de Coimbra.Neste trabalho pretendeu-se analisar a existência de microevolução em Homo sapiens através da análise do polígono oclusal das cúspides da coroa de primeiros molares superiores num período temporal de cerca de 4300 anos que compreendia o Neolítico final e o período moderno. Dada a disponibilidade dos dados, foi também verificada a existência de variação entre populações do mesmo período. O método do polígono oclusal foi desenvolvido por Morris em 1986 e na última década foi usado em grande parte por Bailey (2004, 2006, 2008). Unindo numa fotografia os ápices das cúspides, o polígono resultante permite-nos avaliar a posição relativa das cúspides em relação à coroa do dente, assim como inferir sobre a forma deste através da observação dos ângulos formados. Para além de esta técnica poder ser utilizada para estudar a evolução da dentição humana através da comparação com hominíneos fósseis, também se demonstrou útil para períodos temporais bastante mais reduzidos. Não se observou uma evolução estatisticamente significativa do tamanho oclusal das coroas neste período microevolutivo de 4300 anos, contudo encontrou-se um aumento de 7,45% no tamanho do polígono oclusal e consequentemente da sua área relativa em 9,38%. Isto indica-nos que as cúspides se têm vindo a posicionar de forma diferente na coroa dos molares, afastando-se do centro da mesma. Os dados relativos aos ângulos entre as cúspides e à forma do dente não sugerem qualquer evolução, mas sim diferenças entre as várias populações. Duas das três populações medievais, embora baseadas num número muito reduzido de indivíduos, mostraram-se possivelmente distintas no tamanho oclusal, área poligonal relativa e em dois ângulos, apesar da proximidade geográfica. Visto se ter estudado microevolutivamente os primeiros molares superiores, procedeu-se também a uma análise da frequência da forma positiva da cúspide de Carabelli. Juntamente com os resultados obtidos por outros autores, este trabalho parece também apontar para a existência de uma variação na frequência mesmo dentro do grupo populacional Europeu. Os nossos valores enquadram-se dentro dos largos intervalos obtidos por estes autores com amostras de diferentes países.This work studied the existence of microevolution in Homo sapiens by analyzing the cusps’ occlusal polygon on the crown of first upper molars in a time period of about 4300 years. A comparative analysis of three medieval populations was also performed, given the availability of the data. The occlusal polygon method was developed by Morris in 1986 and in the last decade was largely used by Bailey (2004, 2006, 2008). By joining, in a photograph, the apexes of the cusps, the resulting polygon allows us to assess the relative position of the cusps in relation to the crown of the tooth, as well as to infer about the shape of it by observing the angles formed. Apart from using this technique to study the evolution of human dentition by comparing fossil hominins, it has also been shown useful for time periods far lower. It was not observed a statistically significant evolution of the size of the occlusal size of the crown in this microevolutionary period of 4300 years, but we found an increase of 7,45% in the size of the occlusal polygon and hence 9,38% in its relative area. This tells us that the cusps have been being positioned differently in the crown of the molars, more away from the center of it. The data for the angles between the cusps and the shape of the tooth does not suggest any evolutionary trend, but maybe differences among the various populations. Two of the three medieval populations, although based on a very small number of individuals, were found possibly different in the size of the occlusal area, occlusal polygon area and on two angles, despite their geographical proximity. Since first molares were studied microevolutionarily, we also proceeded with the analysis of the frequency of the positive form of the Carabelli’s cusp. Together with the results obtained by other authors, this work also seems to point to the existence of a variation in frequency even within the European populational group. Our results fall within the broad intervals of values obtained by those authors in samples from different countries

Radiation-Induced Error Criticality in Modern HPC Parallel Accelerators

In this paper, we evaluate the error criticality of radiation-induced errors on modern High-Performance Computing (HPC) accelerators (Intel Xeon Phi and NVIDIA K40) through a dedicated set of metrics. We show that, as long as imprecise computing is concerned, the simple mismatch detection is not sufficient to evaluate and compare the radiation sensitivity of HPC devices and algorithms. Our analysis quantifies and qualifies radiation effects on applications’ output correlating the number of corrupted elements with their spatial locality. Also, we provide the mean relative error (dataset-wise) to evaluate radiation-induced error magnitude. We apply the selected metrics to experimental results obtained in various radiation test campaigns for a total of more than 400 hours of beam time per device. The amount of data we gathered allows us to evaluate the error criticality of a representative set of algorithms from HPC suites. Additionally, based on the characteristics of the tested algorithms, we draw generic reliability conclusions for broader classes of codes. We show that arithmetic operations are less critical for the K40, while Xeon Phi is more reliable when executing particles interactions solved through Finite Difference Methods. Finally, iterative stencil operations seem the most reliable on both architectures.This work was supported by the STIC-AmSud/CAPES scientific cooperation program under the EnergySFE research project grant 99999.007556/2015-02, EU H2020 Programme, and MCTI/RNP-Brazil under the HPC4E Project, grant agreement n° 689772. Tested K40 boards were donated thanks to Steve Keckler, Timothy Tsai, and Siva Hari from NVIDIA.Postprint (author's final draft

Biosorption of Cr(VI) by an E. coli biofilm supported on GAC

The increasing concern with environmental pollution significantly motivates the investigation and development of safe remediation technologies. The retention of contaminants by a biofilm supported on granular activated carbon is one of the promising technologies. This study aims the investigation and development of an innovative process for the removal of chromium (VI) from wastewater. The effect of the initial concentration of metal was tested, the polysaccharide and polymeric net of the E.Coli biofilm were quantified and the application of this system to a real effluent was made. The industrial effluent was provided by tannery factories. The support used for the biofilm formation was granular activated carbon (GAC) from MERCK with an average particle size of 2.5 mm, characterised by N2 adsorption (77K) with an ASAP Micromeritics 2001 which indicated a Langmuir area of 1270 m2g-1 and an average pore diameter of 2 nm. The use of activated carbon as a support is justified by the fact that this material is a versatile adsorbent due to its high surface area, porous structure, high adsorption capacity and surface chemical nature. The role of the biofilm was evaluated considering that microorganisms are quite adequate for heavy metals biosorption due to their ability to sorb metal ions, suitability for natural environments and low cost. Minicolumns (internal diameter = 2 cm, ht = 30 cm) were used for open systems studies, partially filled with GAC (15 g). The metal solutions were passed in upflow through the column with a flow rate of 5 ml/min (residence time of 19 min). Samples (5 ml) were taken, centrifuged and analyzed for metals using atomic absorption spectrophotometry, AAS. The results showed uptake values of 0.19 mg/gbiosorbent, 3.60 mg/gbiosorbent and 4.61 mg/gbiosorbent, respectively for the initial concentration of 10, 50 and 100 mg/l. The quantification of polysaccharides and polymeric net reveled a value of 4.77 mg/gbiosorbent for the polysaccharides and 142 mg/gbiosorbent, for the polymeric net. The polyssacharide and polymeric net give importante informations about the capacity of biofilm formation by the microrganism. The studies made with the industrial effluent showed values of Cr uptake of 0.093 mg/gbiosorbent, for an initial concentration of 4.2 mg/l. The value obtained for the removal percentage with the most diluted solution used (10 mg/l) was of 18% (after 10 hours of experiment) and the value of removal percentage obtained with the industrial effluent was of 9%, for the same period of time. This can be explainded by the fact that another compounds present in the industrial effluent than Cr(VI) can compete for the same active sites

The effects of costumer satisfaction, service quality and perceived value on behavioural intentions in retail industry

The retail industry has in the last decades assumed a preponderant role in the Portuguese economy, similar to that of other European countries, and is definitely one of the biggest and more vibrant industries nowadays. The significance of the retail industry for the Portuguese economy, a central sector for its growth and dynamic, and the relationship between service quality and efficiency of business are the motivations for this study. In a highly competitive industry, as is the retailing sector, it is crucial that organizations have a good knowledge of the business aspects that are important to their customers. The purpose of this study is to identify the dimensions of service quality and to evaluate the interrelationships among customer satisfaction, perceived value and behavioural intentions and service quality in the modern retail industry. A multi-level and hierarchical model is used as an instrument to synthesize the effects of customer satisfaction, service quality and perceived value on behavioural intentions of customers at retail stores. The results shown that, service perceived quality significantly influences customer satisfaction. Also perceived value and quality service are the main determinants of customer satisfaction. Additionally, customer satisfaction, retail service quality and perceived value significantly affect behavioural intentions towards the act of buying.The preparation of the paper was supported by FCT - Portuguese Foundation for the Development of Science and Technology, Ministry of Science, Technology and Higher Education; “Project Code Reference UID/GES/4752/2016”info:eu-repo/semantics/publishedVersio

Tipos de tecnologias de turbinas utilizadas nas centrais mini-hidricas

De todos os elementos que constituem uma central minihídrica as turbinas e os geradores são os que mais dizem respeito à engenharia electrotécnica. Este artigo pretende apresentar os tipos de turbinas utilizadas nas centrais minihídricas. Estas podem ser classificadas por duas tecnologias distintas: turbinas de acção ou turbinas de reacção. As turbinas de acção podem ser do tipo Pelton ou Banki- Mitchell. As turbinas de reacção podem ser do tipo Francis, Kaplan ou Hélice