238 resultados para fast scan voltammetric determinations
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Purpose: To compare two fast threshold strategies of visual field assessment; SITA Fast (HSF) and Tendency Orientated Perimetry (TOP), in detecting visual field loss in patients with glaucoma. Methods: Seventy-six glaucoma, ocular hypertensive and normal patients had HSF and TOP performed in random order. Quantitative comparisons for the global visual field indices - mean deviation and defect (MD) for HSF and TOP, and pattern standard deviation (PSD) for HSF and loss variance (LV) for TOP - were made using correlation coefficients. Humphrey global parameters were converted to Octopus equivalents, and method comparison analysis was used to determine agreement between the two strategies. Test duration times were compared using t-test. Sensitivity and specificity for these two algorithms were determined according to predetermined criteria. Results: High correlation coefficient values were obtained for MD measurements between HSF and TOP (r=-0.89, P
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High power femtosecond laser pulses have unique properties that could lead to their application as ionization or activation sources in mass spectrometry. By concentrating many photons into pulse lengths approaching the timescales associated with atomic motion, very strong electric field strengths are generated, which can efficiently ionize and fragment molecules without the need for resonant absorption. However, the complex interaction between these pulses and biomolecular species is not well understood. To address this issue, we have studied the interaction of intense, femtosecond pulses with a number of amino acids and small peptides. Unlike previous studies, we have used neutral forms of these molecular targets, which allowed us to investigate dissociation of radical cations without the spectra being complicated by the action of mobile protons. We found fragmentation was dominated by fast, radical-initiated dissociation close to the charge site generated by the initial ionization or from subsequent ultrafast migration of this charge. Fragments with lower yields, which are useful for structural determinations, were also observed and attributed to radical migration caused by hydrogen atom transfer within the molecule.
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The electrochemical reduction of benzoic acid in the presence and absence of hydrogen (H-2) has been investigated using a 10 mu m diameter platinum microelectrode in four different room temperature ionic liquids (RTILs), namely [C(4)mim][NTf2], [C(4)mpyrr][NTf2], [C(4)mim][OTf] and [C(4)mim][BF4], versus Ag/Ag+. In all cases, reductive voltammetry is observed, and is suggested to occur via a CE mechanism in which dissociation of benzoic acid is followed by electron transfer to H+ ultimately forming adsorbed hydrogen. Furthermore, the adsorbed H atoms, formed from the reduction of benzoic acid, could be used to achieve the rapid hydrogenolysis of the organic compound (bis(benzyloxycarbonyl)-L-lysine) on the timescale of the voltammetric technique under moderate conditions (25 degrees C).
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The H-2-assisted hydrocarbon selective catalytic reduction (HC-SCR) of NO, was investigated using fast transient kinetic analysis coupled with isotopically labelled (NO)-N-15. This allowed monitoring of the evolution of products and reactants during switches of H-2 in and out of the SCR reaction mix. The results obtained with a time resolution of less than 1 s showed that the effect on the reaction of the removal or addition of H-2 was essentially instantaneous. This is consistent with the view that H-2 has a direct chemical effect on the reaction mechanism rather than a secondary one through the formation of "active" Ag clusters. The effect of H-2 partial pressure was investigated at 245 degrees C, it was found that increasing partial pressure of H-2 resulted in increasing conversion of NO and octane. It was also found that the addition of H-2 at 245 degrees C had different effects on the product distribution depending on its partial pressure. The change of the nitrogen balance over time during switches in and out of hydrogen showed that significant quantities of N-containing species were stored when hydrogen was introduced to the system. The positive nitrogen balance on removal of H-2 from the gas phase showed that these stored species continued to react after removal of hydrogen to form N-2. (c) 2006 Elsevier Inc. All rights reserved.
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Recently, two fast selective encryption methods for context-adaptive variable length coding and context-adaptive binary arithmetic coding in H.264/AVC were proposed by Shahid et al. In this paper, it was demonstrated that these two methods are not as efficient as only encrypting the sign bits of nonzero coefficients. Experimental results showed that without encrypting the sign bits of nonzero coefficients, these two methods can not provide a perceptual scrambling effect. If a much stronger scrambling effect is required, intra prediction modes, and the sign bits of motion vectors can be encrypted together with the sign bits of nonzero coefficients. For practical applications, the required encryption scheme should be customized according to a user's specified requirement on the perceptual scrambling effect and the computational cost. Thus, a tunable encryption scheme combining these three methods is proposed for H.264/AVC. To simplify its implementation and reduce the computational cost, a simple control mechanism is proposed to adjust the control factors. Experimental results show that this scheme can provide different scrambling levels by adjusting three control factors with no or very little impact on the compression performance. The proposed scheme can run in real-time and its computational cost is minimal. The security of the proposed scheme is also discussed. It is secure against the replacement attack when all three control factors are set to one.
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Human listeners seem to have an impressive ability to recognize a wide variety of natural sounds. However, there is surprisingly little quantitative evidence to characterize this fundamental ability. Here the speed and accuracy of musical-sound recognition were measured psychophysically with a rich but acoustically balanced stimulus set. The set comprised recordings of notes from musical instruments and sung vowels. In a first experiment, reaction times were collected for three target categories: voice, percussion, and strings. In a go/no-go task, listeners reacted as quickly as possible to members of a target category while withholding responses to distractors (a diverse set of musical instruments). Results showed near-perfect accuracy and fast reaction times, particularly for voices. In a second experiment, voices were recognized among strings and vice-versa. Again, reaction times to voices were faster. In a third experiment, auditory chimeras were created to retain only spectral or temporal features of the voice. Chimeras were recognized accurately, but not as quickly as natural voices. Altogether, the data suggest rapid and accurate neural mechanisms for musical-sound recognition based on selectivity to complex spectro-temporal signatures of sound sources.
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There has been much debate in the literature over the past 60 years regarding an appropriate oven-drying temperature for water content determinations in peat and other organic soils. For inorganic soils, the water content is usually based on the equilibrium dry mass corresponding to drying temperatures in the range 100-110°C. However, for peat and other organic soils, several researchers have recommended lower drying temperatures in the range 60-90°C in an attempt to prevent possible charring, oxidation, and/or vaporization of substances other than pore water. However, all of the relevant water is not fully evaporated at too low a temperature, and because specimen dry mass is a function of drying temperature, the resulting water content values are lower than those determined for the temperature range 100-110°C. Experimental data reported in this article show that oven drying of peat and other organic soils at 100-110°C using either gravity-convection or forced-draft ovens is acceptable for routine water content determinations. Because a standardized oven temperature is desirable when correlating water content with other material properties, it is recommended that oven drying of peat and other organic soils be performed over temperature ranges of either 105-110°C or 105 ± 5°C, in line with standardized ranges for inorganic soils. © 2014 Copyright Taylor & Francis Group, LLC.
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No bioadhesive patch-based system is currently marketed. This is despite an extensive number of literature reports on such systems detailing their advantages over conventional pressure sensitive adhesive-based patches in wet environments and describing successful delivery of a diverse array of drug substances. This lack of proprietary bioadhesive patches is largely due to the fact that such systems are exclusively water-based, meaning drying is difficult. In this paper we describe, for the first time, a novel multiple lamination method for production of bioadhesive patches. In contrast to patches produced using a conventional casting approach, which took 48 hours to dry, bioadhesive films prepared using the novel multiple lamination method were dried in 15?min and were folded into formed patches in a further 10?min. Patches prepared by both methods had comparable physicochemical properties. The multiple lamination method allowed supersaturation of 5-aminolevulinic acid to be achieved in formed patch matrices. However, drug release studies were unable to show an advantage for supersaturation with this particular drug, due to its water high solubility. The multiple lamination method allowed greater than 90% of incorporated nicotine to remain within formed patches, in contrast to the 48% achieved for patches prepared using a conventional casting approach. The procedure described here could readily be adapted for automation by industry. Due to the reduced time, energy and ensuing finance now required, this could lead to bioadhesive patch-based drug delivery systems becoming commercially viable. This would, in turn, mean that pathological conditions occurring in wet or moist areas of the body could now be routinely treated by prolonged site-specific drug delivery, as mediated by a commercially produced bioadhesive patch.
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This paper proposes a fast moving window algorithm for QR and Cholesky decompositions by simultaneously applying data updating and downdating. The developed procedure is based on inner products and entails a similar downdating to that of the Chambers’ approach. For adding and deleting one row of data from the original matrix, a detailed analysis shows that the proposed algorithm outperforms existing ones in terms or computational efficiency, if the number of columns exceeds 7. For a large number of columns, the proposed algorithm is numerically superior compared to the traditional sequential technique.
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Schizophrenia is a common disorder with high heritability and a 10-fold increase in risk to siblings of probands. Replication has been inconsistent for reports of significant genetic linkage. To assess evidence for linkage across studies, rank-based genome scan meta-analysis (GSMA) was applied to data from 20 schizophrenia genome scans. Each marker for each scan was assigned to 1 of 120 30-cM bins, with the bins ranked by linkage scores (1 = most significant) and the ranks averaged across studies (R(avg)) and then weighted for sample size (N(sqrt)[affected casess]). A permutation test was used to compute the probability of observing, by chance, each bin's average rank (P(AvgRnk)) or of observing it for a bin with the same place (first, second, etc.) in the order of average ranks in each permutation (P(ord)). The GSMA produced significant genomewide evidence for linkage on chromosome 2q (PAvgRnk
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ULTRACAM is a high-speed three-colour CCD camera designed to provide imaging photometry at high temporal resolutions. The instrument is highly portable and will be used at a number of large telescopes around the world. ULTRACAM was successfully commissioned on the 4.2-m William Herschel Telescope on La Palma on 16 May 2002 over 3 months ahead of schedule and within budget. The instrument was funded by PPARC and designed and built by a consortium involving the Universities of Sheffield Southampton and the UKATC Edinburgh. We present an overview of the design and performance characteristics of ULTRACAM and highlight some of its most recent scientific results.
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Hemispherical electron plasma waves generated from ultraintense laser interacting with a solid target having a subcritical preplasma is studied using particle-in-cell simulation. As the laser pulse propagates inside the preplasma, it becomes self-focused due to the response of the plasma electrons to the ponderomotive force. The electrons are mainly heated via betatron resonance absorption and their thermal energy can become higher than the ponderomotive energy. The hot electrons easily penetrate through the thin solid target and appear behind it as periodic hemispherical shell-like layers separated by the laser wavelength.