Demonstration of nanoimprinted hyperlens array for high-throughput sub-diffraction imaging

11124Nsciescopu

Electrochemical Investigation of Exchange Current Density of Uranium and Rare-earths Couples (M3+/M0) in LiCl-KCl Eutectic Electrolyte

The objective of this work is to use electrochemical techniques to quantify the electrode reaction rate of some rare-earth elements and uranium in a LiCl-KCl eutectic electrolyte at 500oC. The exchange current densities of the oxidation-reduction couples of M3+/M0 (La3+/La0, Ce3+/Ce0, Pr3+/Pr0, Nd3+/Nd0,Gd3+/Gd0, Y3+/Y0, U3+/U0) on a tungsten electrode were measured by applying a linear polarization resistance technique. A region of linear dependence of potential on applied current could be found to describe the reaction rate of oxidation-reduction system. From these measurements, the estimated exchange current density was 0.38 mA/cm2 for uranium, and was within the range of 0.27 to 0.38mA/cm2 for rare-earth elements.open0

Successive spin-flop transitions of a Neel-type antiferromagnet Li2MnO3 single crystal with a honeycomb lattice

We have carried out high magnetic field studies of single-crystalline Li2MnO3, a honeycomb lattice antiferromagnet. Its magnetic phase diagram was mapped out using magnetization measurements at applied fields up to 35 T. Our results show that it undergoes two successive meta-magnetic transitions around 9 T fields applied perpendicular to the ab plane (along the c* axis). These phase transitions are completely absent in the magnetization measured with the field applied along the ab plane. In order to understand this magnetic phase diagram, we developed a mean-field model starting from the correct Neel-type magnetic structure, consistent with our single crystal neutron diffraction data at zero field. Our model calculations succeeded in explaining the two meta-magnetic transitions that arise when Li2MnO3 enters two different spin-flop phases from the zero field Neel phase.open1187Nsciescopu

Multiscale architectured materials with composition and grain size gradients manufactured using high-pressure torsion

The concept of multiscale architectured materials is established using composition and grain size gradients. Composition-gradient nanostructured materials are produced from coarse grained interstitial free steels via carburization and high-pressure torsion. Quantitative analyses of the dislocation density using X-ray diffraction and microstructural studies clearly demonstrate the gradients of the dislocation density and grain size. The mechanical properties of the gradient materials are compared with homogeneous nanostructured carbon steel without a composition gradient in an effort to investigate the gradient effect. Based on the above observations, the potential of multiscale architecturing to open a new material property is discussed.111010Ysciescopu

Thermodynamic analysis of the Quantum Critical behavior of Ce-lattice compounds

A systematic analysis of low temperature magnetic phase diagrams of Ce compounds is performed in order to recognize the thermodynamic conditions to be fulfilled by those systems to reach a quantum critical regime and, alternatively, to identify other kinds of low temperature behaviors. Based on specific heat ($C_m$) and entropy ($S_m$) results, three different types of phase diagrams are recognized: i) with the entropy involved into the ordered phase ($S_{MO}$) decreasing proportionally to the ordering temperature ($T_{MO}$), ii) those showing a transference of degrees of freedom from the ordered phase to a non-magnetic component, with their $C_m(T_{MO})$ jump ($\Delta C_m$) vanishing at finite temperature, and iii) those ending in a critical point at finite temperature because their $\Delta C_m$ do not decrease with $T_{MO}$ producing an entropy accumulation at low temperature. Only those systems belonging to the first case, i.e. with $S_{MO}\to 0$ as $T_{MO}\to 0$, can be regarded as candidates for quantum critical behavior. Their magnetic phase boundaries deviate from the classical negative curvature below $T\approx 2.5$\,K, denouncing frequent misleading extrapolations down to T=0. Different characteristic concentrations are recognized and analyzed for Ce-ligand alloyed systems. Particularly, a pre-critical region is identified, where the nature of the magnetic transition undergoes significant modifications, with its $\partial C_m/\partial T$ discontinuity strongly affected by magnetic field and showing an increasing remnant entropy at $T\to 0$. Physical constraints arising from the third law at $T\to 0$ are discussed and recognized from experimental results

Influence of prohexadione-calcium, trinexapac-ethyl and hexaconazole on lodging characteristic and gibberellin biosynthesis of rice (Oryza sativa L.)

We investigated the influence of prohexadione-calcium (Pro-Ca), trinexapac-ethyl (TNE) and hexaconazole (HX) on lodging and gibberellin (GA) biosynthesis pathway of rice cultivar, Hwayeongbyeo. It was observed that these novel synthetic growth retardants suppressed lodging of rice under field conditions through blocking GA biosynthesis pathway. These growth retarding chemicals were applied at basic (20 uM) and elevated (40 uM) rates either 10 days before heading (10 DBH) or 5 days before heading (5 DBH). We found that Pro-Ca, TNE and their combined application (Pro-Ca + TNE) were most effective in decreasing rice length and lodging index, when applied at 10 DBH. Similarly, the endogenous bioactive GA1 contents of rice significantly declined with application of Pro-Ca, TNE and Pro-Ca + TNE, while they were less effected by basic and elevated rates of HX as compared to the control. The growth retardants were more effective in decreasing rice lodging and blocking GA biosynthesis when applied in elevated rates. The levels of the endogenous gibberellins in rice shoots were measured by GC/MS-SIM using 2H2-labeled gibberellins as internal standards. Effect of these synthetic chemicals on growth and GA inhibition were stronger initially but eroded rapidly under field conditions. It was thus concluded that Pro-Ca and TNE were most effective in reducing plant length and suppressing lodging of rice crop under field conditions, where lodging is a major constraint to higher productivity.Key words: Growth retardants, plant growth, gibberellin biosynthesis, lodging index, rice

Characteristics of biochemical markers and quality parameters using whole wheat flours in Korean wheat cultivars and lines

Tese de doutoramento em Ciências e Tecnologias da Informação, apresentada ao Departamento de Engenharia Informática da Faculdade de Ciências e Tecnologia da Universidade de CoimbraO espectro rádio tem vindo a ser regulado de um modo estático. Ou seja, este encontra-se essencialmente dividido em bandas de frequência licenciadas, com utilização restringida a um número limitado de utilizadores autorizados, e em algumas bandas de frequência não licenciadas para utilização livre. Devido à falta de flexibilidade resultante desta abordagem, partes significativas do espectro rádio encontram-se subutilizadas. Em simultâneo, outras bandas de frequência estão a ficar cada vez mais saturadas, nomeadamente as não licenciadas em áreas densamente povoadas. O Rádio Cognitivo é um paradigma recente cujo objetivo é melhorar o nível de eficiência na utilização do espectro rádio. Os seus princípios gerais consistem em permitir que dispositivos sem fios não licenciados (os denominados Utilizadores Secundários) possam aceder às bandas de frequência licenciadas desde que estes não interferiram de forma prejudicial com os utilizadores licenciados (os denominados Utilizadores Primários). A abordagem preponderante na área de Rádio Cognitivo consiste em ter utilizadores secundários com capacidade para, de um modo dinâmico, detetar e aceder a oportunidades espectrais, ou seja, bandas de frequência que não estão a ser acedidas pelos respetivos utilizadores primários num determinado momento numa determinada localização. Neste contexto, os utilizadores secundários devem ser capazes de analisar o espectro rádio com precisão e, de preferência, possuírem mecanismos de aprendizagem baseados em observação local e experiência passada. Apesar da área de Rádio Cognitivo ter implicações na totalidade das camadas das pilhas protocolares de comunicação, os seus problemas fundamentais localizam-se nos níveis físico (PHY) e de controlo de acesso ao meio (MAC). Em particular, os protocolos de controlo de acesso ao meio desempenham um papel fundamental no âmbito de operações de controlo de acesso ao espectro rádio e de suporte à cooperação entre utilizadores secundários. Os utilizadores primários, quanto a eles, devem manter-se abstraídos das operações de Rádio Cognitivo e, em consequência, não estarem sujeitos a qualquer tipo de alteração em cenários de Rádio Cognitivo. Esta tese apresenta cinco contribuições, essencialmente relacionadas com o nível do controlo de acesso ao meio, com o objetivo de incrementar os níveis de proteção dos utilizadores primários e de desempenho dos utilizadores secundários em redes de Rádio Cognitivo distribuídas, especialmente quando os utilizadores secundários não têm antecipadamente acesso a qualquer tipo de informação, tal como a localização de utilizadores primários. Neste tipo de cenário, não existe qualquer entidade central responsável por recolher e processar dados de origem diversa ou tomar decisões de acesso ao espectro rádio. Ou seja, as soluções propostas adequam-se a utilizadores secundários que operam de um modo autónomo e cooperativo. Estes tomam as suas decisões baseando-se, essencialmente, em observações locais, em eventuais resultados de aprendizagem e em dados trocados entre si. A primeira contribuição desta tese consiste numa descrição da área de Rádio Cognitivo através de um estado da arte detalhado. A segunda contribuição resulta na definição de um protocolo de controlo de acesso ao meio apoiado num mecanismo inovador, designado COSBET (Cooperative Sense-Before-Transmit), que oferece um nível superior de proteção dos utilizadores primários em cenários de Rádio Cognitivo distribuídos sujeitos ao problema do utilizador primário oculto. Este tipo de anomalia ocorre quando um utilizador secundário é incapaz de detetar as atividades de um determinado utilizador primário apesar de poder provocar interferências na respetiva área de abrangência. Tal como já foi referido, na área de Rádio Cognitivo, é considerado desejável os utilizadores secundários terem capacidades de aprendizagem baseadas em observação local e experiência passada. No entanto, em cenários distribuídos, o problema do utilizador primário oculto afeta negativamente a qualidade dos resultados de aprendizagem obtidos e, em consequência, o nível efetivamente alcançado em termos de proteção dos utilizadores primários. Sendo assim, esta tese também analisa esta questão e propõe uma solução destinada a tratá-la, estando esta terceira contribuição baseada num conceito chave designado FIBASC (Filtering Based on Suspicious Channels). A troca de informação de controlo em redes de Rádio Cognitivo distribuídas é frequentemente suportada por um canal partilhado e acessível à globalidade dos utilizadores secundários. Este é o designado canal de controlo comum (CCC), sendo igualmente esta a abordagem seguida pelo protocolo COSBET-MAC proposto. No entanto, os CCC estão sujeitos a problemas de saturação. A ocorrência deste tipo de problema impede os utilizadores secundários de tirarem pleno proveito das potencialidades oferecidas pelo Rádio Cognitivo, acabando por limitar os níveis de desempenho de comunicação alcançáveis. Sendo assim, nesta tese também analisamos esta questão e propomos uma solução destinada a abordá-la, correspondendo esta à nossa quarta contribuição. A solução proposta, designada CORHYS (Cognitive Radio Hybrid Signalling), baseia-se num esquema de sinalização híbrido que recorre simultaneamente a um CCC e aos canais de dados que vão sendo alocados de forma dinâmica. A quinta e última contribuição desta tese consiste na definição de uma estratégia adicional, igualmente localizada no nível do controlo de acesso ao meio, destinada a melhorar o desempenho dos utilizadores secundários em cenários de Rádio Cognitivo distribuídos em que se recorre a um CCC. Fazem parte das suas linhas orientadoras a otimização da reutilização espacial do espectro rádio e a redução do tráfego de controlo gerado entre utilizadores secundários. As soluções de Rádio Cognitivo propostas no âmbito desta tese foram avaliadas em ambiente de simulação, sendo esta uma prática comum, nomeadamente devido a limitações de tempo e de outros tipos de recursos. Para o efeito, recorreu-se ao OMNET++ (Objective Modular Network Testbed in C++), um simulador baseado em eventos discretos e de código aberto. A totalidade das contribuições da presente tese podem ser aplicadas em conjunto. A integração destas deu origem a uma solução única e otimizada de controlo de acesso ao meio destinada a cenários de Rádio Cognitivo distribuídos. Esta aborda as duas principais preocupações existentes em cenários de Rádio Cognitivo: proteger os utilizadores primários de qualquer tipo de interferência prejudicial; e melhorar o desempenho de comunicação dos utilizadores secundários. Tanto quanto sabemos, as várias soluções propostas e o nível de completude que a utilização conjunta destas permite não são oferecidos por qualquer outra proposta de controlo de acesso ao meio existente para cenários de Rádio Cognitivo distribuídos. As contribuições desta tese também apontam direções que podem ser seguidas no âmbito de outros protocolos de controlo de acesso ao meio, especialmente aqueles que se destinam a redes de Rádio Cognitivo distribuídas.The radio spectrum has been statically regulated, i.e., essentially partitioned into licensed frequency bands, which are accessed exclusively by authorized users, and unlicensed frequency bands that can be freely accessed. Due to this inflexible policy, large portions of the entire radio spectrum remain unused independently of time and location in the world, while some frequency bands suffer from increasing levels of saturation, particularly the unlicensed ones in densely populated areas. Cognitive Radio (CR) is a recent paradigm that aims at improving efficiency regarding spectrum utilization. Its principles consist in allowing unlicensed wireless devices (i.e., secondary users) to access licensed frequency bands provided that the respective incumbent users (i.e., primary users) do not suffer any harmful interference. The most preponderant CR approach consists in having a secondary user (SU) dynamically locating and accessing spectrum opportunities, i.e., frequency bands that are not being accessed by any primary user (PU) at a given time and location. Consequently, sensing the spectrum and learning through local observation and past experience, which enables proactive spectrum decision, are key CR issues. Despite CR has implications in all the layers of the communication protocol stack, its fundamentals are mainly related to the physical (PHY) and medium access control (MAC) levels. In fact, CR MAC protocols are at the heart of spectrum access control and cooperation between SUs. PUs are expected to be unware of CR operations and, consequently, should not suffer any modification under CR scenarios. This thesis provides five contributions, essentially related to the MAC level, with the aim of improving the protection of PUs and the communication performance of SUs in cooperative distributed CR networks, particularly when there is no access to any a priori known information, such as the locations of primary transmitters. In this type of scenario, there are no central entities that collect and fuse data, or take spectrum decisions. That is, the proposed solutions fit into totally autonomous and cooperating SUs, i.e., SUs that take their own decisions based on local observation, on learning outcomes if any is available, and on data they exchange with each other. The first contribution of this thesis consists in a description of the CR area through an indepth state of the art. The second contribution lies in the definition of a CR MAC protocol that follows a novel approach, named Cooperative Sense-Before-Transmit (COSBET), which provides a higher protection of PUs in distributed CR scenarios that suffer from the hidden PU problem. This issue occurs when a SU cannot sense the activities of a given PU despite it can cause harmful interference to its coverage area. As already mentioned, CR considers that the SUs might have learning capabilities based on local observation and past experience. However, in distributed scenarios, the hidden PU problem affects the accuracy of learning and, therefore, the effectiveness of PU protection. For that reason, in this thesis we also discuss this issue and propose a novel solution that addresses it. This solution is based on a key concept named FIBASC (Filtering Based on Suspicious Channels). Utilizing a common control channel (CCC), i.e., a channel that is available to all the SUs in a CR network, for signalling purposes is a frequent practice concerning existing distributed CR MAC solutions. It is also the solution adopted by COSBET-MAC. However, a CCC is susceptible to saturation and can, therefore, become a performance bottleneck that inhibits the SUs from taking full advantage of CR potentialities. Consequently, the fourth contribution of this thesis consists in analysing this issue and addressing it through a novel solution, which we named CORHYS (Cognitive Radio Hybrid Signalling). CORHYS is based on a hybrid signalling approach that performs signalling over the CCC and over the allocated data channels simultaneously. The fifth and last contribution of this thesis consists in a MAC-level strategy that aims at further improving the performance of SUs in distributed CR scenarios that are based on a CCC. The key guidelines for this strategy are optimizing the spatial reuse of the radio spectrum and reducing control traffic. The CR solutions that resulted from this thesis were evaluated through simulation, which is a common practice, particularly due to time and other resource restrictions. For this purpose, we used OMNET++ (Objective Modular Network Testbed in C++), an open source discrete event simulator. The contributions of this thesis can be applied jointly and were successfully integrated with each other, which resulted in an optimized CR MAC solution that addresses the two main concerns in distributed CR scenarios: protecting the PUs from harmful interference; and improving the communication performance of the SUs. To the best of our knowledge, the proposed solutions and the level of completeness that they jointly achieve are not found in any other existing distributed CR MAC proposal. We also note that they define directions that can be followed by other CR MAC protocols, particularly those that target distributed CR networks

Two-dimensional universal conductance fluctuations and the electron-phonon interaction of topological surface states in Bi2Te2Se nanoribbons

The universal conductance fluctuations (UCFs), one of the most important manifestations of mesoscopic electronic interference, have not yet been demonstrated for the two-dimensional surface state of topological insulators (TIs). Even if one delicately suppresses the bulk conductance by improving the quality of TI crystals, the fluctuation of the bulk conductance still keeps competitive and difficult to be separated from the desired UCFs of surface carriers. Here we report on the experimental evidence of the UCFs of the two-dimensional surface state in the bulk insulating Bi2Te2Se nanoribbons. The solely-B\perp-dependent UCF is achieved and its temperature dependence is investigated. The surface transport is further revealed by weak antilocalizations. Such survived UCFs of the topological surface states result from the limited dephasing length of the bulk carriers in ternary crystals. The electron-phonon interaction is addressed as a secondary source of the surface state dephasing based on the temperature-dependent scaling behavior

Active immunization with myelin-derived altered peptide ligand reduces mechanical pain hypersensitivity following peripheral nerve injury

BACKGROUND: T cells have been implicated in neuropathic pain that is caused by peripheral nerve injury. Immunogenic myelin basic protein (MBP) peptides have been shown to initiate mechanical allodynia in a T cell-dependent manner. Antagonistic altered peptide ligands (APLs) are peptides with substitutions in amino acid residues at T cell receptor contact sites and can inhibit T cell function and modulate inflammatory responses. In the present study, we studied the effects of immunization with MBP-derived APL on pain behavior and neuroinflammation in an animal model of peripheral nerve injury. METHODS: Lewis rats were immunized subcutaneously at the base of the tail with either a weakly encephalitogenic peptide of MBP (cyclo-MBP(87-99)) or APL (cyclo-(87-99)[A(91),A(96)]MBP(87-99)) in complete Freund’s adjuvant (CFA) or CFA only (control), following chronic constriction injury (CCI) of the left sciatic nerve. Pain hypersensitivity was tested by measurements of paw withdrawal threshold to mechanical stimuli, regulatory T cells in spleen and lymph nodes were analyzed by flow cytometry, and immune cell infiltration into the nervous system was assessed by immunohistochemistry (days 10 and 30 post-CCI). Cytokines were measured in serum and nervous tissue of nerve-injured rats (day 10 post-CCI). RESULTS: Rats immunized with the APL cyclo-(87-99)[A(91),A(96)]MBP(87-99) had significantly reduced mechanical pain hypersensitivity in the ipsilateral hindpaw compared to cyclo-MBP(87-99)-treated and control rats. This was associated with significantly decreased infiltration of T cells and ED1+ macrophages in the injured nerve of APL-treated animals. The percentage of anti-inflammatory (M2) macrophages was significantly upregulated in the APL-treated rats on day 30 post-CCI. Compared to the control rats, microglial activation in the ipsilateral lumbar spinal cord was significantly increased in the MBP-treated rats, but was not altered in the rats immunized with the MBP-derived APL. In addition, immunization with the APL significantly increased splenic regulatory T cells. Several cytokines were significantly altered after CCI, but no significant difference was observed between the APL-treated and control rats. CONCLUSIONS: These results suggest that immune deviation by active immunization with a non-encephalitogenic MBP-derived APL mediates an analgesic effect in animals with peripheral nerve injury. Thus, T cell immunomodulation warrants further investigation as a possible therapeutic strategy for the treatment of peripheral neuropathic pain