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Momentum and reversal effects in Brazil; Efeito momento e efeito contrário no Brasil

Improta, João Paulo de Barros
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 05/11/2012 Português
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In financial markets, momentum effect can be defined as the tendency of prices to maintain their short term movements. On the other hand, reversal effect is usually understood to be the change in direction of long term price movements. This paper examines whether momentum and reversal effects were in evidence in the Brazilian stock market between January 1999 and June 2012. After calculating 1296 trading strategies, no evidence of reversal effect is found. With regard to momentum effect, some weak evidence is presented for the very short term. Exposure to risk factors can explain returns on strategies, including returns on momentum strategies. The results are borne out with different market proxy specifications and size subsamples. When compared to previous studies, the results raise the question of whether the reversal effect is vanishing from the Brazilian stock market and whether the traces of momentum are sufficient to confirm its existence. Furthermore, evidence of seasonality is found for June in momentum strategies and for November in both reversal and momentum strategies. Subsequent tests reveal that the effects of seasonality are limited to small stocks.; Nos mercados financeiros, o efeito momento pode ser definido como a tendência dos preços em manter seus movimentos de curto prazo. Por outro lado...

Estudo de anomalias em modelos de formação de preços e o efeito sobre as empresas de diferentes classificações de risco; A study of asset pricing anomalies and the effect over companies of different credit ratings

Martins, Clarice Carneiro
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 03/09/2014 Português
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Este trabalho procura aprofundar o estudo de anomalias ao CAPM no mercado acionário brasileiro e explorar as relações destas anomalias com a característica dificuldade financeira, a qual é representada pela classificação de risco das empresas, usando estratégias de compra e venda a descoberto baseadas nas anomalias. As anomalias estudadas serão o efeito de momento, momento nos lucros, a volatilidade idiossincrática, o crescimento dos ativos, o investimento em capital e o efeito contrário. Nosso objetivo é examinar o impacto da característica dificuldade financeira sobre o retorno esperado das ações de empresas do grupo de menor classificação de risco. Para cumprir nosso objetivo, inicialmente usamos todas as ações da Bolsa de Valores de São Paulo (Bovespa) para comparar estas com a amostra de empresas que possuem classificação de crédito de longo prazo. O período estudado é de Janeiro de 2000 a Dezembro de 2012. Os métodos usados foram baseados em ordenação de carteiras e regressões univariadas e multivariadas de corte transversal. Encontramos algumas evidências de que empresas com classificação de crédito sugerem retornos anormais diferentes daqueles da amostra de todas as empresas. Este resultado foi significante...

Análise por meio da técnica FORC, do efeito da histerese a alta freqüência no fenômeno da GMI; Analysis of the hysteretic effect on the high frequency GMI phenomenon by means of FORC technique

Luis Carlos Costa Arzuza
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 15/12/2011 Português
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Este trabalho visa estudar o comportamento histerético, observado a baixos campos magnéticos, do fenômeno da magnetoimpedância gigante (GMI) em fitas amorfas a base de CoFeSiB com anisotropia magnética transversal. O fenômeno da GMI consiste na variação da impedância elétrica (aproximadamente do 100%) de uma amostra magnética mole quando submetida à aplicação de campo magnético DC externo. Apesar da importância da presença de histerese na GMI, tanto do ponto de vista básico quanto do tecnológico, existem poucos estudos na literatura que visam à explicação da origem desse efeito. Desde o ponto de vista fundamental, o completo entendimento do fenômeno poderia revelar importantes aspectos envolvidos com o processo de magnetização nos materiais considerados. De um ponto de vista prático, a presença da histerese na GMI tanto pode ser desfavorável, quando pensamos na fabricação de sensores, quanto favorável, se levamos em consideração a sua possível aplicação em sistemas de memória magnética. Por outro lado, o método denominado curva de inversão da primeira ordem (first-order reversal curve, FORC, em inglês) mostra-se uma poderosa ferramenta para o estudo e compreensão de fenômenos histeréticos...

The effect of nest aggregation on the reproductive behaviour of the peacock blenny Salaria pavo (Risso)

Barata, Eduardo N.; Saraiva, João L.; Canário, Adelino V.M.; Oliveira, Rui F.
Fonte: Universidade de Évora Publicador: Universidade de Évora
Tipo: Artigo de Revista Científica Formato: 173748 bytes; application/pdf
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The effect of nest aggregation in courtship behaviour was tested experimentally in an ecologically constrained, sex-role reversed population of the peacock blenny Salaria pavo. Mixed sex groups of eight males and eight females were tested in experimental tanks, containing eight potential nests either aggregated or dispersed. In the aggregated treatment, males spent more time inside their nests and monopolized other potential nests, causing a female-biased operational sex ratio (OSR). In the aggregated treatment, females also expressed more courtship behaviour. The results in general support the prediction that the aggregation of nests promotes male monopolization of potential nests, resulting in fewer nest-holding males and therefore a female-biased OSR that leads to the reversal o f sex roles.

Effect of curcumin on human colon cancer multidrug resistance in vitro and in vivo

Lu,Wei-Dong; Qin,Yong; Yang,Chuang; Li,Lei
Fonte: Faculdade de Medicina / USP Publicador: Faculdade de Medicina / USP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/05/2013 Português
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OBJECTIVE: To determine whether curcumin reverses the multidrug resistance of human colon cancer cells in vitro and in vivo. METHODS: In a vincristine-resistant cell line of human colon cancer, the cell viability of curcumin-treated cells was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Rhodamine123 efflux was evaluated to detect P-glycoprotein transporter activity, and expression of the multidrug resistance protein 1 and survivin genes was analyzed by reverse transcription polymerase chain reaction and western blotting. In addition, xenograft mouse tumors were grown and treated with curcumin. The morphology of the xenografts was investigated by hematoxylin-eosin staining. The in vivo expression of the multidrug resistance gene and P-glycoprotein and survivin genes and proteins was observed using reverse transcription-polymerase chain reaction and western blotting, respectively. RESULTS: Curcumin was not obviously toxic to the vincristine-resistant human colon cancer cells at concentrations less than 25 μM, but the growth of cells was significantly inhibited. At concentrations greater than 25 μM, curcumin was toxic in a concentration-dependent manner. The sensitivity of cells to vincristine...

Reversal of multidrug resistance by magnetic Fe3O4 nanoparticle copolymerizating daunorubicin and 5-bromotetrandrine in xenograft nude-mice

Chen, Baoan; Cheng, Jian; Wu, Yanan; Gao, Feng; Xu, Wenlin; Shen, Huilin; Ding, Jiahua; Gao, Chong; Sun, Qian; Sun, Xinchen; Cheng, Hongyan; Li, Guohong; Chen, Wenji; Chen, Ningna; Liu, Lijie; Li, Xiaomao; Wang, Xuemei
Fonte: Dove Medical Press Publicador: Dove Medical Press
Tipo: Artigo de Revista Científica
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In this paper we establish the xenograft leukemia model with stable multidrug resistance in nude mice and to investigate the reversal effect of 5-bromotetrandrine (5-BrTet) and magnetic nanoparticle of Fe3O4 (MNP-Fe3O4) combined with daunorubicin (DNR) in vivo. Two subclones of K562 and K562/A02 cells were inoculated subcutaneously into the back of athymic nude mice (1 × 107 cells/each) respectively to establish leukemia xenograft models. Drug-resistant and sensitive tumor-bearing nude mice were assigned randomly into five groups which were treated with normal saline; DNR; NP-Fe3O4 combined with DNR; 5-BrTet combined with DNR; 5-BrTet and MNP-Fe3O4 combined with DNR, respectively. The incidence of formation, growth characteristics, weight, and volume of tumors were observed. The histopathologic examination of tumors and organs were detected. For resistant tumors, the protein levels of Bcl-2, and BAX were detected by Western blot. Bcl-2, BAX, and caspase-3 genes were also detected. For K562/A02 cells xenograft tumors, 5-BrTet and MNP-Fe3O4 combined with DNR significantly suppressed growth of tumor. A histopathologic examination of tumors clearly showed necrosis of the tumors. Application of 5-BrTet and MNP-Fe3O4 inhibited the expression of Bcl-2 protein and upregulated the expression of BAX and caspase-3 proteins in K562/A02 cells xenograft tumor. It is concluded that 5-BrTet and MNP-Fe3O4 combined with DNR had a significant tumor-suppressing effect on a MDR leukemia cells xenograft model.

Clitocine Reversal of P-Glycoprotein Associated Multi-Drug Resistance through Down-Regulation of Transcription Factor NF-κB in R-HepG2 Cell Line

Sun, Jianguo; Yeung, Chilam Au; Co, Ngai Na; Tsang, Tsun Yee; Yau, Esmond; Luo, Kewang; Wu, Ping; Wa, Judy Chan Yuet; Fung, Kwok-Pui; Kwok, Tim-Tak; Liu, Feiyan
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 22/08/2012 Português
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Multidrug resistance(MDR)is one of the major reasons for failure in cancer chemotherapy and its suppression may increase the efficacy of therapy. The human multidrug resistance 1 (MDR1) gene encodes the plasma membrane P-glycoprotein (P-gp) that pumps various anti-cancer agents out of the cancer cell. R-HepG2 and MES-SA/Dx5 cells are doxorubicin induced P-gp over-expressed MDR sublines of human hepatocellular carcinoma HepG2 cells and human uterine carcinoma MES-SA cells respectively. Herein, we observed that clitocine, a natural compound extracted from Leucopaxillus giganteus, presented similar cytotoxicity in multidrug resistant cell lines compared with their parental cell lines and significantly suppressed the expression of P-gp in R-HepG2 and MES-SA/Dx5 cells. Further study showed that the clitocine increased the sensitivity and intracellular accumulation of doxorubicin in R-HepG2 cells accompanying down-regulated MDR1 mRNA level and promoter activity, indicating the reversal effect of MDR by clitocine. A 5′-serial truncation analysis of the MDR1 promoter defined a region from position −450 to −193 to be critical for clitocine suppression of MDR1. Mutation of a consensus NF-κB binding site in the defined region and overexpression of NF-κB p65 could offset the suppression effect of clitocine on MDR1 promoter. By immunohistochemistry...

Current Status on Marine Products with Reversal Effect on Cancer Multidrug Resistance

Abraham, Ioana; El Sayed, Khalid; Chen, Zhe-Sheng; Guo, Huiqin
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 19/10/2012 Português
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The resistance of tumor cells to a broad range of anticancer agents continues to be a problem for the success of cancer chemotherapy. Multidrug resistance (MDR) is due in part to three drug transporter proteins: ABCB1/P-glycoprotein (P-gp), ABCC1/multidrug resistance protein 1 (MRP1) and ABCG2/breast cancer resistance protein (BCRP). These transporters are part of the ATP-binding cassette (ABC) superfamily, whose members function as ATP-dependent drug-efflux pumps. Their activity can be blocked by various drugs such as verapamil (calcium channel blocker) and cyclosporin A (immunosuppressive agent), etc. These compounds are called MDR modulators or reversals. This review highlights several marine natural products with reversal effect on multidrug resistance in cancer, including agosterol A, ecteinascidin 743, sipholane triterpenoids, bryostatin 1, and welwitindolinones.

Reversal of multidrug resistance in vincristine-resistant human gastric cancer cell line SGC7901/VCR by LY980503

Wu, Da-Long; Xu, Ying; Yin, Li-Xin; Lu, Huan-Zhang
Fonte: Baishideng Publishing Group Co., Limited Publicador: Baishideng Publishing Group Co., Limited
Tipo: Artigo de Revista Científica
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AIM: To investigate the reversal effect of LY980503, a benflumetol derivative, on multidrug resistance in vincristine (VCR) -resistant human gastric carcinoma cell line SGC7901/VCR.

Methyllycaconitine- and scopolamine-induced cognitive dysfunction: differential reversal effect by cognition-enhancing drugs

Andriambeloson, Emile; Huyard, Bertrand; Poiraud, Etienne; Wagner, Stéphanie
Fonte: Blackwell Publishing Ltd Publicador: Blackwell Publishing Ltd
Tipo: Artigo de Revista Científica
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There is a growing body of evidence pointing to the pivotal role of alpha-7 nicotinic acetylcholine receptor (α7 nAchR) dysfunction in cognitive disorders such as Alzheimer’s disease or schizophrenia. This study was undertaken to establish and characterize an in vivo model for cognitive disorder secondary to the blockade of α7 nAChR by its specific antagonist, methyllycaconitine (MLA). The results show that MLA elicited cognitive dysfunction as assessed by reduced spontaneous alternation of mice in the T-maze. The maximal effect of MLA produced 25–30% reduction in the spontaneous alternation of mice, a level comparable with that induced by the muscarinic antagonism of scopolamine. Donepezil and galantamine fully reversed both MLA and scopolamine-induced cognitive dysfunction. However, the ED50 of donepezil and galantamine was significantly shifted to the left in the MLA- compared to scopolamine-treated mice (0.0005 and 0.002 mg/kg for donepezil; 0.0003 and 0.7 mg/kg for galantamine). Moreover, memantine elicited marked reversion of cognitive dysfunction (up to 70%) in MLA-treated mice while only a weak reversal effect at high dose of memantine (less than 20%) was observed in scopolamine-treated mice. The above findings indicate that MLA-induced cognitive dysfunction in the mouse is highly sensitive and more responsive to the current procognitive drugs than the traditional scopolamine-based assay. Thus...

Reversal of multidrug resistance in drug-resistant human gastric cancer cell line SGC7901/VCR by antiprogestin drug mifepristone

Li, Da-Qiang; Wang, Zhi-Biao; Bai, Jin; Zhao, Jie; Wang, Yuan; Hu, Kai; Du, Yong-Hong
Fonte: Baishideng Publishing Group Inc Publicador: Baishideng Publishing Group Inc
Tipo: Artigo de Revista Científica
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AIM: To explore the reversal effect of mifepristone on multidrug resistance (MDR) in drug-resistant human gastric cancer cell line SGC7901/VCR and its mechanisms.

Surface charge reversal method for high-resolution inkjet printing of functional water-based inks

Cobas, Raiden; Muñoz-Pérez, Susset; Cadogan, Sean; Ridgway, Mark C.; Obradors, Xavier
Fonte: Wiley-VCH Verlag Publicador: Wiley-VCH Verlag
Tipo: Artigo de Revista Científica
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Printed electronics is a rapidly growing area of research being explored for the manufacture of large-area and cost-effective electronic devices by the patterned application of functional inks. There are challenges associated with processing the inks compatible with inkjet printing technology and developing efficient methods to successfully obtain the desired features, particularly when it comes to metal and metal-organic complex inks. Here, a reliable method is developed to achieve a sophisticated microstructured pattern using the inkjet printing technique assisted by a surface charge reversal effect. In addition, a procedure is formulated to obtain good quality, stable metal-organic water-based inks compatible with salts of a variety of transition metals and rare earths, without the need for additional volatile solvents. A feasible and water-based ink formulation combined with a simple and noninvasive surface charge reversal treatment constitutes a major step toward the manufacture of high-resolution, inorganic patterned thin films on hydrophobic substrates using inkjet printing. These outcomes lead to the path of effective fusion of inorganic and organic heterointerfaces by simples designing and printing.; This work was supported by the University of New South Wales and Spanish MICINN (Consolider CSD2007-0041).

Facilitating and inhibiting learning by the spatial contiguity of text and graphic: How does cognitive load mediate the split-attention and expertise reversal effect?; Der Einfluss räumlicher Kontiguität zwischen Text und Bild auf den Wissenserwerb: Wie vermittelt kognitive Beanspruchung den Split-Attention und Expertise-Reversal Effekt?

Cierniak, Gabriele
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
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In instructional design research, which comprises also multimedia learning, two instructional design effects have gained researchers’ attention for several years that led to two design principles: First, numerous studies showed a split-attention effect, that is, students with a spatially integrated format of graphic and corresponding text had higher learning outcomes than students with a separated format of text and graphic. These findings led to the spatial contiguity principle that recommends avoiding a format that spatially separates graphic and corresponding text and suggests a spatially integrated format of text and graphic. Second, first studies showed that learners’ prior knowledge plays an important role in how successfully students learn with integrated or separated multimedia materials. According to these findings high knowledgeable students (should) benefit equally well or even more from spatially separated than integrated multimedia formats. These findings are subsumed under the term expertise reversal effect and led to the individual difference and/or prior knowledge principle. The split-attention as well as the expertise reversal effect is explained within the frameworks of Cognitive Load Theory (CLT; Sweller, van Merrienboer...

O efeito do atraso em movimentos reversos do cotovelos : comparação entre sujeitos saudaveis e portadores da doença de Parkinson; The effect of delay on the control of reversal movements of the elbow: comparison between healthy individuals and Parkinson's disease patients

Marcus Vinicius Rezende dos Santos
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 28/02/2005 Português
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Neste trabalho, foram investigados efeitos de condições especiais como o envelhecimento e a Doença de Parkinson no controle de movimentos reversos do cotovelo, realizados com um atraso variável entre a ida (Ml) e a volta (M2) do mesmo. Outro objetivo foi verificar se o ciclo de alongamento-encurtamento (CAE) age como potencializador da contração muscular nessa população. Foram recrutados 12 voluntários, sendo seis sujeitos saudáveis (três homens e três mulheres) com idades entre 51 e 71 anos (Média = 62.33 e DP = 8.95) e seis portadores da doença de Parkinson (três homens e três mulheres) com idades entre 59 e 77 anos (Média = 68.66 e DP = 7.47). Eles realizaram movimentos uni-articulares rápidos de reversão com o cotovelo, que se movia em direção à um alvo (Ml) e depois retomava à posição inicial (M2). Esses movimentos foram realizados em três diferentes distâncias (20°, 40° e 60°) e entre os dois componentes (Ml e M2) foi realizado um atraso variável (Os, 0.2s, 0.5s e ls). O deslocamento angular do cotovelo foi registrado por um sistema óptico de análise do movimento (OPTOTRAK@ 3020) e a atividade elétrica dos músculos braquiorradial (BRR) e cabeça lateral do tríceps braquial (TR) foi registrada através de um eletromiógrafo EMG DelSYS (modelo DE2.2L) com eletrodos de superficie. O envelhecimento saudável não influenciou os padrões EMG utilizados por esses indivíduos para ativar os músculos agonista e antagonista na realização de movimentos uni-articulares com reversão com diferentes atrasos. A velocidade dos movimentos executados por esses indivíduos foi mais baixa devido ao uso de um padrão semelhante aos sujeitos jovens...

Rocking ratchets in 2D Josephson networks: collective effects and current reversal

Marconi, Verónica I.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/12/2006 Português
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A detailed numerical study on the directed motion of ac-driven vortices and antivortices in 2D Josephson junction arrays (JJA) with an asymmetric periodic pinning potential is reported. Dc-voltage rectification shows a strong dependence on vortex density as well as an inversion of the vortex flow direction with ac amplitude for a wide range of vortex density around $f$=1/2 ($f$=$Ha^2 / \Phi_0$), in good agreement with recent experiments by Shal\'om and Pastoriza [Phys. Rev. Lett. {\bf 94}, 177001 (2005)]. The study of vortex structures, spatial and temporal correlations, and vortex-antivortex pairs formation gives insight into a purely collective mechanism behind the current reversal effect.; Comment: 4 pages, 5 figures. Accepted for publication in Phys. Rev. Lett

Vortex ratchet reversal in an asymmetric washboard pinning potential subject to combined dc and ac stimuli

Shklovskij, Valerij A.; Sosedkin, Vladimir V.; Dobrovolskiy, Oleksandr V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/12/2013 Português
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The mixed-state resistive response of a superconductor thin film with an asymmetric washboard pinning potential subject to superimposed dc and ac currents of arbitrary amplitudes and frequency at finite temperature is theoretically investigated. The problem is considered in the single-vortex approximation, relying upon the exact solution of the Langevin equation in terms of a matrix continued fraction. The dc voltage response and the absorbed power in ac response are analyzed as functions of dc bias, ac current amplitude and frequency, in a wide range of corresponding dimensionless parameters. Predictions are made of (i) a reversal of the rectified voltage at small dc biases and strong ac drives and (ii) a non-monotonic enhancement of the absorbed power in the nonlinear ac response at far sub-depinning frequencies. It is elucidated how and why both these effects appear due to the competition of the fixed internal and the tunable, dc bias-induced external asymmetry of the potential as the only reason. This is distinct from other scenarios used for explaining the vortex ratchet reversal effect so far.; Comment: 12 pages, 9 figures

Effect of a capping layer on the magnetic properties of island nanostructured Fe(110)

Calleja, J. F.; Contreras, M. C.; Matarranz, R.; Navarro, E.; Huttel, Yves; Cebollada, Alfonso; Armelles Reig, Gaspar
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artículo Formato: 79014 bytes; application/pdf
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We present a study on the magnetic anisotropy and magnetization reversal of Fe(110) islands grown on Al2O3 versus the island size, the island size distribution, and the magnetic interaction between islands. For small islands magnetically connected via a polarizable capping layer, the samples behave as a uniform film with an induced uniaxial in-plane anisotropy. Magnetically isotropic samples are obtained when the islands size is increased. Transverse susceptibility measurements show that the magnetic anisotropy of the particles is macroscopically averaged due to the interisland magnetic interaction. The island size distribution is correlated to the magnetic anisotropy field dispersion. When the capping layer material is Al, a superparamagnetic behavior is found due to the absence of the interisland interaction.; The Spanish Commission of Science and Technology is acknowledged for financial support. One of the authors sY.H.d thanks the “Ramón y Cajal” program.; Peer reviewed

The role of 5-HT_2C receptors in touchscreen visual reversal learning in the rat: a cross-site study

Alsi?, J.; Nilsson, S. R. O.; Gastambide, F.; Wang, R. A. H.; Dam, S. A.; Mar, A. C.; Tricklebank, M.; Robbins, T. W.
Fonte: Springer Publicador: Springer
Tipo: Article; published version
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This is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s00213-015-3963-5; Rationale Reversal learning requires associative learning and executive functioning to suppress non-adaptive responding. Reversal-learning deficits are observed in e.g. schizophrenia and obsessive-compulsive disorder and implicate neural circuitry including the orbitofrontal cortex (OFC). Serotonergic function has been strongly linked to visual reversal learning in humans and experimental animals but less is known about which receptor subtypes are involved. Objectives The objectives of the study were to test the effects of systemic and intra-OFC 5-HT_2C-receptor antagonism on visual reversal learning in rats and assess the psychological mechanisms underlying these effects within novel touchscreen paradigms. Methods In experiments 1?2, we used a novel 3-stimulus task to investigate the effects of 5-HT_2C-receptor antagonism through SB 242084 (0.1, 0.5 and 1.0 mg/kg i.p.) cross-site. Experiment 3 assessed the effects of SB 242084 in 2-choice reversal learning. In experiment 4, we validated a novel touchscreen serial visual reversal task suitable for neuropharmacological microinfusions by baclofen-/muscimol-induced OFC inactivation. In experiment 5...

Nanophotonics: Optical time reversal with graphene

Urzhumov, Yaroslav A.; Ciraci, Dr Cristian; Smith, David R.
Fonte: Nature Publishing Group / Macmillan Publishers Ltd. Publicador: Nature Publishing Group / Macmillan Publishers Ltd.
Tipo: Artigo de Revista Científica
Publicado em /07/2013 Português
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Would you ever guess that a microscopic flake of graphite could reverse the diffraction of light? An experiment that demonstrates just such an effect highlights the exciting optical applications of graphene — an atomic layer of carbon with a two-dimensional honeycomb lattice.

A Study of Solarization in the Negative Image of Reversal Films and Sensitivity and Development Rate as a Function of First Exposure

Rivera, Maximiliano
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
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This thesis has two objectives. One is to see if in reversal films solarization has begun before reaching the maximum density in the negative image. Acetone semicarbazone was added to the emulsions, so that if solarization were significant, this halogen acceptor, by elimination of the solarization, would increase the maximum density. The films tested were KODAK PLUS-X Reversal Film Type 7276, TRI-X Reversal Film Type 7278, Fine Grain Release Positive Type 5302, and PANATOMIC-X. It is concluded that solarization does not have a significant effect on the maximum density, slope near the maximum density, or density scale of the negative D Log E curve. The second objective is a study to see what happens to the development rate and the sensitivity of the residual silver-halide emulsion after first exposure, first development, and bleaching as a function of the first exposure. The sensitivity is expected to drop quite dramatically with increasing first exposure and the results show it does. For the one film tested, PLUS-X Reversal, it was found that the development rate, corrected for change in Dmax, materially decreased with increasing first exposure. There was a decrease in development rate resulting from bleaching the first image with destruction of chemical sensitization; the effect of exposure was superimposed on this. The bleached film showed a large...