Optical Extraction Efficiency for External Cavity Quantum Cascade Lasers

In this paper, we present a simple method for calculation of optical extraction efficiency of mid-infrared quantum cascade laser coupled to external cavity. The approach is based on the three-level rate equation model describing the variation of the electron number in the states and the photon number present within the Fabry-Perot quantum cascade laser and the external cavity. The system shares the same active region and includes the dependence of the loss on external cavity parameters. We find in particular that the power coupled out through the external mirror varies linearly with current injection and depends strongly on the external cavity reflectivity. Moreover, a considerable increase in the threshold current of external cavity occurs when decreasing the values of the external cavity reflectivity and the slope efficiency decreases with decreasing external cavity reflectivity. We also derive an analytical formula for the optical extraction efficiency of external cavity and analyze the simultaneous effects of the current injection and the external cavity reflectivity on it. Results show that at laser threshold, the optical extraction efficiency is zero and it rises as the current injection increases. For high current injection, extraction efficiency of up to 11 % at Rext = 10 % can be attained. In addition, the equations allowing the determination of the optimum reflectance of external cavity and the maximum optical extraction efficiency are also derived within the premises of our model in the general case

Some entanglement features exhibited by two, three and four qubits interacting with an environment in a non-Markovian regime

We explore various aspects of the quantum entanglement dynamics of systems of two, three and four qubits interacting with an environment at zero temperature in a non-Markovian regime, as described by the paradigmatic model recently studied by Bellomo et al (2007 Phys. Rev. Lett. 99 160502). We consider important families of initial states for the alluded systems. The average, typical entanglement evolution associated with each of these families is determined, and its relation with the evolution of the global degree of mixedness of the multi-qubit system is explored. For three and four qubits we consider the family of initial states equivalent under local unitary transformations to the |GHZ〉 and |W〉 states, and compare their average behavior with the average behavior exhibited by initial maximally entangled two-qubit states. Furthermore, in the case of two qubits, the evolution of other manifestations of entanglement, related to measurable quantities, is also investigated. In particular, we consider the Mintert-Buchleitner concurrence lower bound and an entanglement indicator based upon the violation of local uncertainty relations.Fil: Hamadou Ibrahim, A.. University of Pretoria; SudáfricaFil: Plastino, Ángel Ricardo. Universidad de Granada; España. Universidad Nacional de La Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Zander, C.. University of Pretoria; Sudáfric

Essai comparatif d'efficacité des deux souches vaccinale T1/44 et T1st contre la préripneumonie contagieuse bovine

La péripneumonie est une maladie infectieuse qui touche uniquement les bovidés et connaît actuellement une recrudescence en Afrique. Dans le passé de nombreux pays ont pu contrôler la maladie, voire l'éradiquer, grâce à une prophylaxie médicale basée sur l'utilisation de deux souches vaccinales : T1/44 et sa variante streptomycino-résistante T1sr. Des échecs récents ont pu jeter un doute sur l'identité et l'efficacité de la souche T1sr. Depuis, son identité a été confirmée. Il devenait indispensable de vérifier son efficacité dans des conditions contrôlées. Les deux souches ont été utilisées en primovaccination à la dose minimum recommandée, soit 10<+>7<+> mycoplasmes par dose vaccinale. La reproduction expérimentale de la maladie a été réalisée par intubation endobronchique de 40 zébus du Nord-Cameroun qui ont servi à infecter par contact des animaux vaccinés et des animaux témoins. Tous les animaux ont fait l'objet d'un suivi clinique et sérologique. La transmission de la maladie a pleinement réussi et près de 40 p. 100 des animaux témoins ont succombé à la péripneumonie. La mortalité a été inférieure chez les animaux vaccinés mais la différence est à la limite de la signification statistique (p = 0,054). Quelle que soit la souche, la protection conférée par la vaccination, calculée sur la réduction de la mortalité, avoisine 37 p. 100 seulement. Il est difficile de comparer ces résultats avec des essais anciens qui étaient pratiquement tous réalisés avec des doses vaccinales beaucoup plus élevées et qui utilisaient une souche d'épreuve isolée en Australie. Les résultats obtenus soulignent le caractère partiel de la protection conférée par la vaccination actuellement pratiquée. Ils appellent d'une part à une meilleure définition des stratégies actuelles de lutte contre la péripneumonie et d'autre part à la mise au point de vaccins plus efficaces. (Résumé d'auteur

Trust in Crowds: probabilistic behaviour in anonymity protocols

The existing analysis of the Crowds anonymity protocol assumes that a participating member is either ‘honest’ or ‘corrupted’. This paper generalises this analysis so that each member is assumed to maliciously disclose the identity of other nodes with a probability determined by her vulnerability to corruption. Within this model, the trust in a principal is defined to be the probability that she behaves honestly. We investigate the effect of such a probabilistic behaviour on the anonymity of the principals participating in the protocol, and formulate the necessary conditions to achieve ‘probable innocence’. Using these conditions, we propose a generalised Crowds-Trust protocol which uses trust information to achieves ‘probable innocence’ for principals exhibiting probabilistic behaviour

Bioprospecting autochthonous marine microalgae strain from the Arabian Gulf Seawater, Kuwait for biofuel feedstocks

Bioprospecting programs are the key to increasing the current portfolio of indigenous microalgal strains accessible for different applications in microalgal biotechnology. In this work, nine fast-growing microalgal strains isolated from Kuwait's Arabian/Persian Gulf coastal waters were evaluated for their potential as biofuel feedstocks. 18S rRNA gene sequencing showed that the strains belong to five different genera: Chlorella, Nannochloris, Scenedesmus, Tetraselmis, and Nannochloropsis. In terms of the total lipid content, in comparison to the other strains, Tetraselmis sp. KUBS13G and Tetraselmis sp. KUBS16G displayed higher lipid contents of 29.56% dry weight (DW) and 26.13% DW, respectively, dominated by palmitic and oleic acids. Fuel properties calculated from the fatty acid methyl esters (FAMES) by empirical equations were compared with EN14214 (European) and ASTM D6751--02 (American) biodiesel standards. Multicriteria decision analysis (MCDA) methods, such as the Preference Ranking Organization Method for Enrichment Evaluation (PROMETHEE) and Graphical Analysis for Interactive Assistance (GALA), were used to select suitable microalgae for biofuel feedstock based on their biodiesel fuel properties. Overall, the results suggested that the indigenous microalgal strain Tetraselmis, particularly Tetraselmis sp. KUBS37G, and Scenedesmus sp. KUB Sl7R are the most suitable strains for biofuel feedstock owing to their improved fuel properties, such as density (rho) (0.88 g cm-3), low kinematic viscosity (3.1 mm2 s-1), high cetane number (54 and 56, respectively), high oxidation stability (14.6 hr and 14.8 hr), and cold filter plugging point (1.0 degrees C and -6.1 degrees C).info:eu-repo/semantics/publishedVersio

Biological activities and chemical composition of methanolic extracts of selected Autochthonous microalgae strains from the Red Sea

Four lipid-rich microalgal species from the Red Sea belonging to three different genera (Nannochloris, Picochlorum and Desmochloris), previously isolated as novel biodiesel feedstocks, were bioprospected for high-value, bioactive molecules. Methanol extracts were thus prepared from freeze-dried biomass and screened for different biological activities. Nannochloris sp. SBL1 and Desmochloris sp. SBL3 had the highest radical scavenging activity against 1,1-diphenyl-2-picrylhydrazyl, and the best copper and iron chelating activities. All species had potent butyrylcholinesterase inhibitory activity (>50%) and mildly inhibited tyrosinase. Picochlorum sp. SBL2 and Nannochloris sp. SBL4 extracts significantly reduced the viability of tumoral (HepG2 and HeLa) cells with lower toxicity against the non-tumoral murine stromal (S17) cells. Nannochloris sp. SBL1 significantly reduced the viability of Leishmania infantum down to 62% (250 mu g/mL). Picochlorum sp. SBL2 had the highest total phenolic content, the major phenolic compounds identified being salicylic, coumaric and gallic acids. Neoxanthin, violaxanthin, zeaxanthin, lutein and -carotene were identified in the extracts of all strains, while canthaxanthin was only identified in Picochlorum sp. SBL2. Taken together, these results strongly suggest that the microalgae included in this work could be used as sources of added-value products that could be used to upgrade the final biomass value.National Science, Technology and Innovation Program of King Abdulaziz Medical City for Science and Technology, Riyadh, Saudi Arabia [NPST, 11-ENE 1719-02]; Foundation for Science and Technology (FCT), Portugal [SFRH/BD/78062/2011]; FCT [IF/00049/2012, SFRH/BPD/86071/2012, Pest-OE/QUI/UI0612/2013]info:eu-repo/semantics/publishedVersio

Preventing Additive Attacks to Relational Database Watermarking

False ownership claims are carried on through additive and invertibility attacks and, as far as we know, current relational watermarking techniques are not always able to solve the ownership doubts raising from the latter attacks. In this paper, we focus on additive attacks. We extend a conventional image-based relational data watermarking scheme by creating a non-colluded backup of the data owner marks, the so-called secondary marks positions. The technique we propose is able to identify the data owner beyond any doubt

New features of quantum discord uncovered by q-entropies

The notion of quantum discord introduced by Ollivier and Zurek [Phys. Rev. Lett 88, 017901 (2001)] (see also Henderson and Vedral [J. Phys. A 34, 6899 (2001)]) has attracted increasing attention, in recent years, as an entropic quantifier of non-classical features pertaining to the correlations exhibited by bipartite quantum systems. Here we generalize the notion so as to encompass power-law q-entropies (that reduce to the standard Shannon entropy in the limit $q \to 1$) and study the concomitant consequences. The ensuing, new discord-like measures we advance describe aspects of non-classicality that are different from those associated with the standard quantum discord. A particular manifestation of this difference concerns a feature related to order. Let $D_1$ stand for the standard, Shannon-based discord measure and $D_q$ for the $q \ne 1$ one. If two quantum states $A$, $B$ are such that $D_1(A) > D_1(B)$, this order-relation does not remain invariant under a change from $D_1$ to $D_q$.Comment: 11 pages, 8 figure

Consequences of marine barriers for genetic diversity of the coral-specialist yellowbar angelfish from the Northwestern Indian Ocean

Ocean circulation, geological history, geographic distance, and seascape heterogeneity play an important role in phylogeography of coral‐dependent fishes. Here, we investigate potential genetic population structure within the yellowbar angelfish (Pomacanthus maculosus) across the Northwestern Indian Ocean (NIO). We then discuss our results with respect to the above abiotic features in order to understand the contemporary distribution of genetic diversity of the species. To do so, restriction site‐associated DNA sequencing (RAD‐seq) was utilized to carry out population genetic analyses on P. maculosus sampled throughout the species’ distributional range. First, genetic data were correlated to geographic and environmental distances, and tested for isolation‐by‐distance and isolation‐by‐environment, respectively, by applying the Mantel test. Secondly, we used distance‐based and model‐based methods for clustering genetic data. Our results suggest the presence of two putative barriers to dispersal; one off the southern coast of the Arabian Peninsula and the other off northern Somalia, which together create three genetic subdivisions of P. maculosus within the NIO. Around the Arabian Peninsula, one genetic cluster was associated with the Red Sea and the adjacent Gulf of Aden in the west, and another cluster was associated with the Arabian Gulf and the Sea of Oman in the east. Individuals sampled in Kenya represented a third genetic cluster. The geographic locations of genetic discontinuities observed between genetic subdivisions coincide with the presence of substantial upwelling systems, as well as habitat discontinuity. Our findings shed light on the origin and maintenance of genetic patterns in a common coral reef fish inhabiting the NIO, and reinforce the hypothesis that the evolution of marine fish species in this region has likely been shaped by multiple vicariance events.This work was conducted within the framework of the NPRP project ‘Connectivity, diversity and genetic between offshore natural coral reefs and oil platforms – NPRP No. 7‐1129‐1‐201’, funded by the Qatar National Research Fund (a member of The Qatar Foundation). The statements made herein are solely the responsibility of the authors. F.T. is supported by a CNPq/Brazil fellowship through the program Science without Borders (Proc. 232875/2014‐6). We are also grateful to Filipe Vieira (University of Copenhagen) for his advice on population genetic analyses

Novel composite materials of modified roasted date pits using ferrocyanides for the recovery of lithium ions from seawater reverse osmosis brine

In this paper, novel composite materials from modified roasted date pits using ferrocyanides were developed and investigated for the recovery of lithium ions (Li+) from seawater reverse osmosis (RO) brine. Two composite materials were prepared from roasted date pits (RDP) as supporting material, namely potassium copper hexacyanoferrate-date pits composite (RDP-FC-Cu), and potassium nickel hexacyanoferrate-date pits composite (RDP-FC-Ni). The physiochemical characterization of the RO brine revealed that it contained a variety of metals and salts such as strontium, zinc, lithium, and sodium chlorides. RDP-FC-Cu and RDP-FC-Ni exhibited enhanced chemical and physical characteristics than RDP. The optimum pH, which attained the highest adsorption removal (%) for all adsorbents, was at pH 6. In addition, the highest adsorption capacities for the adsorbents were observed at the initial lithium concentration of 100 mg/L. The BET surface area analysis confirmed the increase in the total surface area of the prepared composites from 2.518 m2/g for RDP to 4.758 m2/g for RDP-FC-Cu and 5.262 m2/g for RDP-FC-Ni. A strong sharp infrared peak appeared for the RDP-FC-Cu and RDP-FC-Ni at 2078 cm−1. This peak corresponds to the C≡N bond, which indicates the presence of potassium hexacyanoferrate, K4[Fe(CN)6]. The adsorption removal of lithium at a variety of pH ranges was the highest for RDP-FC-Cu followed by RDP-FC-Ni and RDP. The continuous increase in the adsorption capacity for lithium with increasing initial lithium concentrations was also observed. This could be mainly attributed to enhance and increased lithium mass transfer onto the available adsorption active sites on the adsorbents’ surface. The differences in the adsorption in terms of percent adsorption removal were clear and significant between the three adsorbents (P value < 0.05). All adsorbents in the study showed a high lithium desorption percentage as high as 99%. Both composites achieved full recoveries of lithium from the RO brine sample despite the presence of various other competing ions.This work was made possible by Qatar University collaborative internal grant # [QUCG-CAS-20/21-2]. The findings achieved herein are solely the responsibility of the author[s]