Selective Masking Research Articles

A model of selective masking in chromatic detection.

Narrowly tuned, selective noise masking of chromatic detection has been taken as evidence for the existence of a large number of color mechanisms (i.e., higher order color mechanisms). Here we replicate earlier observations of selective masking of tests in the (L,M) plane of cone space when the noise is placed near the corners of the detection contour. We used unipolar Gaussian blob tests with three different noise color directions, and we show that there are substantial asymmetries in the detection contours-asymmetries that would have been missed with bipolar tests such as Gabor patches. We develop a new chromatic detection model, which is based on probability summation of linear cone combinations, and incorporates a linear contrast energy versus noise power relationship that predicts how the sensitivity of these mechanisms changes with noise contrast and chromaticity. With only six unipolar color mechanisms (the same number as the cardinal model), the new model accounts for the threshold contours across the different noise conditions, including the asymmetries and the selective effects of the noises. The key for producing selective noise masking in the (L,M) plane is having more than two mechanisms with opposed L- and M-cone inputs, in which case selective masking can be produced without large numbers of color mechanisms.

Chemometrics-assisted cross injection analysis for simultaneous determination of phosphate and silicate

ABSTRACTThis work presents a novel method for simultaneous spectrophotometric determination of phosphate and silicate by using a cross injection analysis (CIA) coupled with the use of partial least squares (PLS) for data evaluation. The detection principle is based on the well-known ‘molybdenum blue’ method. The molybdate ions in the presence of stannous chloride in acidic medium give phosphomolybdenum blue and silicomolybdenum blue as products. In this work, all the liquids, including sample and reagents were simultaneously introduced into a CIA platform by using two peristaltic pumps for controlling the x-channel and y-channel flow which was automatically manipulated by using in-house control board. Crossflow provides sufficient mixing inside the platform prior detection of the absorption spectra of blue complexes in the wavelength of 400–900 nm. Since spectra of the blue colour product of phosphate and silicate are resemblant, these two analytes therefore reciprocally interfere with one another. This results in difficulty in simultaneous analysis of phosphate and silicate. In this work, PLS was utilised as assistor of CIA system for simultaneous analysis of phosphate and silicate using molybdenum blue reaction without using any modification of reagents and addition of selective masking agent. The calibration ranges are 0.1–6 mgP L−1 and 5–100 mgSi L−1 for phosphate and silicate, respectively. By using CIA coupled with PLS for data evaluation, the analysis of two analytes was achieved within 1.5 min with only single injection. The developed system was applied to natural water samples and the system was validated with the conventional methods. By statistical paired t-test, there was no evidence of significant difference at 95% confidence level (tstat = 2.28, tcritical = 2.31 and tstat = 0.62, tcritical = 2.31 for phosphate and silicate, respectively). This implied that the chemometrics-assisted CIA system was successfully developed for simultaneous spectrophotometric determination of phosphate and silicate.

Combination of size selective binding ability of 18-crown-6 dissolved in aqueous phase and extractive properties of an amic acid; toward enhancement of rare earths separation

The separation of La(III), Eu(III) and Er(III) ions by an amic acid, N,N-dioctyldiglycolamic acid (HL), dissolved in carbon tetrachloride has been improved in the presence of 18-crown-6 (18C6) in aqueous phase as a selective masking agent. The interaction between the studied metal ions and 18C6 resulted a shift in the extraction curve of the studied metal ions versus pH toward higher pH region. The displacement of the extraction curves was more pronounced for lanthanum ions and was varied as La(III) > Eu(III) > Er(III). This order of complexing ability of 18C6 toward the studied ions was attributed to the size adaptation of the ions and that of the crown ether cavity. The stability constants of the lanthanide–crown ether complexes in aqueous phase were evaluated. The influence of temperature on the extraction of studied metal ions from aqueous phase in the absence and the presence of 18C6 was tested in the range 298–308 K. This investigation allowed evaluating the thermodynamic parameters associated with the extraction process and those of the complexation of cations by 18C6 in the aqueous phase.

Propidium monoazide treatment to distinguish between live and dead methanogens in pure cultures and environmental samples

In clinical trials investigating human health and in the analysis of microbial communities in cultures and natural environments, it is a substantial challenge to differentiate between living, potentially active communities and dead cells. The DNA-intercalating dye propidium monoazide (PMA) enables the selective masking of DNA from dead, membrane-compromised cells immediately before DNA extraction. In the present study, we evaluated for the first time a PMA treatment for methanogenic archaea in cultures and particle-rich environmental samples. Using microscopic analyses, we confirmed the applicability of the LIVE/DEAD® BacLight™ kit to methanogenic archaea and demonstrated the maintenance of intact cell membranes of methanogens in the presence of PMA. Although strain-specific differences in the efficiency of PMA treatment to methanogenic archaea were observed, we developed an optimal procedure using 130μM PMA and 5min of photo-activation with blue LED light. The results showed that the effectiveness of the PMA treatment strongly depends on the texture of the sediment/soil: silt and clay-rich sediments represent a challenge at all concentrations, whereas successful suppression of DNA from dead cells with compromised membranes was possible for low particle loads of sandy soil (total suspended solids (TSS)≤200mgmL−1). Conclusively, we present two strategies to overcome the problem of insufficient light activation of PMA caused by the turbidity effect (shielding) in particle-rich environmental samples by (i) dilution of the particle-rich sample and (ii) detachment of the cells and the free DNA from the sediment prior to a PMA treatment. Both strategies promise to be usable options for distinguishing living cells and free DNA in complex environmental samples.

Level considerations for chimeric processing: Temporal envelope and fine structure contributions to speech intelligibility.

Chimeric processing is used to assess the respective role of the acoustic temporal envelope (ENV) and the temporal fine structure (TFS) by adding noise to either component. An acoustic analysis demonstrates that adding noise to the ENV results in noise degradation of the ENV and overall signal attenuation, whereas adding noise to the TFS results in only noise degradation of the TFS. Young normal hearing adults were then tested using a modified chimeric strategy to maintain speech levels. Results partially confirm the primary role of the ENV in determining speech intelligibility but demonstrate significant TFS contributions during selective ENV masking.

Selective noise masking of L and M cone stimuli: unipolar tests reveal theoretically significant asymmetries

Selective noise masking of L and M cone stimuli: unipolar tests reveal theoretically significant asymmetries

Reduction of dislocation densities in single crystal CVD diamond by using self-assembled metallic masks

The development of diamond-based electronic devices designed to operate at high power is strongly hampered by the lack of low dislocation single crystal material. Dislocations in Chemically Vapor Deposited (CVD) diamond are indeed generally responsible for leakage current, seriously deteriorating the performance of the devices. They can be due to defects such as polishing damage or contamination found at the substrate's surface, or they can directly originate from existing bulk defects that extend into the homoepitaxial layer. Although significant improvements have been achieved by using adapted surface treatments, dislocations found in CVD diamond grown on standard quality single crystal substrates are still typically in the range 105–106cm−2. In this work, we report on a new growth strategy aiming at preventing threading dislocations from propagating into CVD diamond layers. It is based on the selective masking of existing defects revealed at the surface of the substrates by Pt nanoparticles. The interaction of dislocations with such embedded particles has been assessed and critical remarks are given as to the use of this technique in order to reduce dislocation densities in synthetic diamond.

Experimental Validation of a Resilient Electronic Logic Design with Autonomous Fault Discrimination/Masking

This paper presents the experimental validation of a novel fault-tolerant electronic logic design conducted by an automated mixed-signal fault injection procedure. The design under evaluation relies upon a novel redundant design strategy intended to provide fault discrimination and selective fault masking embedded within a functional CMOS NAND gate. The traditional logic layout is modified to include fault detection and reporting at an extremely fine-grained design level with 2x overhead as opposed to the traditional 4x overhead. The fault injection test bench procedure requires automated fault injection, programmable fault load conditions and combined analogue/digital domain verification. The device under test is implemented using discrete n- and p-FETs arranged as a modular test board together with automated fault injection and test lines. The fault response is measured and confirms the predicted intrinsic fault rate of 25% with a successful 100% masking of suck low-faults and precise identification of stuck-high via IDDQ trigger. The test procedure is shown to be extensible towards more complex logic unit designs and for evaluation of multiple simultaneous faults.

Selective phase masking to reduce material saturation in holographic data storage systems

Emerging networks and applications require enormous data storage. Holographic techniques promise high-capacity storage, given resolution of a few remaining technical issues. In this paper, we propose a technique to overcome one such issue: mitigation of large magnitude peaks in the stored image that cause material saturation resulting in readout errors. We consider the use of ternary data symbols, with modulation in amplitude and phase, and use a phase mask during the encoding stage to reduce the probability of large peaks arising in the stored Fourier domain image. An appropriate mask is selected from a predefined set of pseudo-random masks by computing the Fourier transform of the raw data array as well as the data array multiplied by each mask. The data array or masked array with the lowest Fourier domain peak values is recorded. On readout, the recorded array is multiplied by the mask used during recording to recover the original data array. Simulations are presented that demonstrate the benefit of this approach, and provide insight into the appropriate number of phase masks to use in high capacity holographic data storage systems.

Disentangling Methodological and Biological Sources of Gene Tree Discordance on Oryza (Poaceae) Chromosome 3

We describe new methods for characterizing gene tree discordance in phylogenomic data sets, which screen for deviations from neutral expectations, summarize variation in statistical support among gene trees, and allow comparison of the patterns of discordance induced by various analysis choices. Using an exceptionally complete set of genome sequences for the short arm of chromosome 3 in Oryza (rice) species, we applied these methods to identify the causes and consequences of differing patterns of discordance in the sets of gene trees inferred using a panel of 20 distinct analysis pipelines. We found that discordance patterns were strongly affected by aspects of data selection, alignment, and alignment masking. Unusual patterns of discordance evident when using certain pipelines were reduced or eliminated by using alternative pipelines, suggesting that they were the product of methodological biases rather than evolutionary processes. In some cases, once such biases were eliminated, evolutionary processes such as introgression could be implicated. Additionally, patterns of gene tree discordance had significant downstream impacts on species tree inference. For example, inference from supermatrices was positively misleading when pipelines that led to biased gene trees were used. Several results may generalize to other data sets: we found that gene tree and species tree inference gave more reasonable results when intron sequence was included during sequence alignment and tree inference, the alignment software PRANK was used, and detectable "block-shift" alignment artifacts were removed. We discuss our findings in the context of well-established relationships in Oryza and continuing controversies regarding the domestication history of O. sativa.

Adaptation reveals automatic pitch-shift detectors

Previous work suggests that the auditory system contains automatic frequency- or pitch-shift detectors (PSDs). These hypothetical units may serve to bind successive sounds together, and appear to be tuned to optimally detect frequency shifts of about 1 semitone. The present work describes several experiments that provide more evidence for PSDs. In all experiments, listeners judged the direction (up or down) of small relevant frequency shifts whilst ignoring prior irrelevant shifts that were usually much greater in magnitude. In almost all conditions and experiments, there was a nonmonotonic relationship between sensitivity to the relevant shift (d') and the magnitude of the irrelevant shift (Δ). d' declined as a function of increasing Δ up to about 1 semitone, and further increases in Δ increased d'. The “dip” in d' could not be explained by selective attention, frequency-specific adaptation, or energetic masking. PSDs provide a convenient explanation for these results if one assumes that (a) listeners discriminate small frequency shifts using PSDs, (b) PSDs are automatically activated by irrelevant frequency shifts, causing them to adapt, and (c) maximal adaptation of PSDs occurs at around 1 semitone.

Effect of Agar Plate Volume on Accuracy of Culturable Bioaerosol Impactors

Agar plate volume in bioaerosol impactors affects collection efficiency, but it is often overlooked in practice. This study investigated the effect of agar volume (20, 35, and 50 mL) and, consequently, jet-to-plate distance on accuracy of culturable impactors. Laboratory experiments investigated sensitive Escherichia coli and hardy Bacillus atrophaeus bacteria with a BioStage impactor. Outdoors bacterial and fungal sampling assessed effects of varying agar volume in BioStage, Sampl’air Lite, and SAS Super 180 multinozzle impactors relative to a reference BioStage with 35 mL agar. The results demonstrate that agar plate volume affects not only overall collection efficiency, but also species selection and colony masking. Culturable concentrations of E. coli in laboratory were underestimated by 35% when using 20 versus 35 mL agar volume (p < 0.001). However, data indicate selection of healthier bacteria, as E. coli colonies were significantly larger on 50 versus 20 mL agar plates (p < 0.001). For outdoors, l...

Aptamer‐Guided Caging for Selective Masking of Protein Domains

Lightly unmasked: Large protein subdomains can be masked and photolytically released using aptamers with a suitable photocleavable linker. No structural knowledge of the protein site is needed. Thrombin Exosite I activity can be efficiently regulated with this approach (see scheme), allowing light-controlled activation of blood clotting.

Higher order color mechanisms: Evidence from noise-masking experiments in cone contrast space

This study addresses a fundamental question concerning the number of cortical, i.e., higher order mechanisms in color vision. The initial subcortical stages in color vision can be described by three cone mechanisms, S, M, L, and three pairs of second-stage mechanisms (achromatic L + M and -L - M, chromatic S - (L + M) and -S + (L + M), and chromatic L - M and M - L). The further mechanistic description of cortical color vision is controversial. On the one hand, numerous studies that defined their stimuli in a color-opponent Derrington-Krauskopf-Lennie (DKL) color space found evidence for higher order mechanisms. On the other hand, some studies that defined their stimuli in cone contrast (CC) space failed to find such evidence. Here we show that this failure was due to a restricted choice of stimuli. We used a noise-masking paradigm to measure discrimination thresholds for textured patterns modulated along chromatic directions in CC space. Unlike previous studies we defined noise directions in DKL space and converted them to CC space. When the noise contrast was sufficiently high we found selective masking, but this did not occur when the noise contrast was low. Selective masking indicates higher order mechanisms, since so far no alternative model has been proposed. Previous studies in CC space failed to find selective masking due to the low contrast of the noise and due to the restricted choice of perceptually highly similar noise directions that mainly stimulated the second-stage mechanisms. We conclude that cortical color vision is governed by higher order mechanisms.

Toward Thermoplastic Lignin Polymers. Part 1. Selective Masking of Phenolic Hydroxyl Groups in Kraft Lignins via Methylation and Oxypropylation Chemistries

This work offers a comprehensive understanding of the conditions required for the selective masking of the phenolic hydroxyl groups in technical kraft lignins, which is pivotal in determining their subsequent chemical and thermal reactivity. To this effect, we have examined the chemistry and developed the conditions for the facile, mild, and selective masking of the phenolic hydroxyl groups in softwood and hardwood kraft lignins. We have compared two series of methylated softwood kraft lignins synthesized using different methylation chemistries. Our data show that (when used as specified) dimethyl sulfate in aqueous NaOH selectively converts the phenolic hydroxyl groups of kraft lignin to its methylated derivatives without apparent side reactions. In contrast, methyl iodide (in the presence of excess K2CO3 in N,N-dimethylformamide) was found to be rather ineffective and unselective. Various milder methylation conditions were also examined for both softwood and hardwood kraft lignins using dimethyl sulfate, and the details of this work are documented. In addition, a series of oxypropylation reactions were also carried out using propylene oxide in aqueous NaOH. Propylene oxide was shown to selectively add (at room temperature, 0.5 M NaOH, 18 h) less than two units on average per phenolic hydroxyl group without significant additional polymerization or other side reactions.

ChemInform Abstract: Reversing the Reactivity of Carbonyl Functions with Phosphonium Salts: Enantioselective Total Synthesis of (+)‐Centrolobine.

AbstractInitial selective masking of the aldehyde function in ketoaldehydes with PPh3 and TmsOTf permits the selective reduction of the keto function or its alkylation with Grignard reagents followed by deprotection.

In vivo electrochemical recording of continuous change of magnesium in medial vestibular nucleus following vertigo induced by ice water vestibular stimulation

Vertigo is one of the most common clinical symptoms. However, the chemical processes involved in the pathological mechanism of vertigo remain to be fully understood. In this study, we investigate the dynamic changes in the magnesium (Mg2+) concentration in medial vestibular nucleus (MVN) of guinea pigs following vertigo induced by vestibular ice water stimulation with an electrochemical detection method consisting of in vivo microdialysis and on-line selective electrochemical detection. Electrochemical detection of Mg2+ was accomplished based on the current enhancement of Mg2+ towards the electrocatalytic oxidation of NADH at the electrodes modified with the polymerized film of toluidine blue O (TBO). Selectivity for the on-line electrochemical detection against Ca2+ was achieved by using ethyleneglcol-bis(2-aminoethylether) tetraacetic acid (EGTA) as the selective masking agent for Ca2+. The basal level of the extracellular Mg2+ in the MVN of guinea pigs was determined to be 759.7 ± 176.2 μM(n = 16). Upon ice water irrigation of the left external ear canal, the concentration of Mg2+ in the MVN decreases significantly, reaches 72 ± 6% (n = 8) of the basal level, and maintains for at least 1000 s. Control experiments reveal that neither warm water irrigation of the external ear canal nor ice water irrigation of the auricle induces the decrease in the concentration of Mg2+ in the MVN. These results demonstrate that the extracellular Mg2+ in the MVN decreases significantly following vertigo induced by vestibular ice water stimulation. This demonstration suggests that Mg2+ might play an important role in the pathological mechanism of vertigo.

Determination of divalent trace metals in a soil sample using electrospray ionization mass spectrometry

A novel pre-separation technique for the determination of divalent trace heavy metals in a soil sample was developed, in which deferoxamine was used as a masking agent for trivalent metal ions, Al3+ and Fe3+, and a chelate column was applied to collect target heavy metal ions and to eliminate alkali metal and alkaline earth metal ions. Deferoxamine had such a strong and selective masking effect on Al3+ and Fe3+ that divalent trace heavy metals in the soil sample were well separated from considerably greater amounts of Al3+ and Fe3+. Consequently, the determination of four trace metals (Ni, Cu, Zn, and Pb) in a certified soil reference material (JSAC-0401) was successfully performed using electrospray ionization mass spectrometry (ESIMS).

Separation of Alkaline Earth Metal Ions with a Strongly Acidic Cation Exchange Resin Using the Diazapolyoxabicyclic Ligand as an Ion Size Selective Masking Reagent

Separation of Alkaline Earth Metal Ions with a Strongly Acidic Cation Exchange Resin Using the Diazapolyoxabicyclic Ligand as an Ion Size Selective Masking Reagent

Efficiency of Neutralizing Antibodies Targeting the CD4-Binding Site: Influence of Conformational Masking by the V2 Loop in R5-Tropic Clade C Simian-Human Immunodeficiency Virus

In R5-tropic clade C simian-human immunodeficiency viruses (SHIV-Cs), we identified a 3-asparagine (3N) deletion mutation in the V2 loop stem of gp120 as the major determinant of neutralization escape of the anti-CD4-binding site (anti-CD4-bs) neutralizing monoclonal antibody (nMAb) b12. However, the more potent anti-CD4-bs nMAbs VRC01 and VRC03 were not sensitive to this mutation. Using isogenic tier 1 or tier 2 proviruses differing only in the 3N mutation, we showed that this mutation might result in selective conformational b12 epitope masking. Therefore, human immunodeficiency virus (HIV) Env immunogens targeting the CD4-bs and designed to neutralize tier 2 viruses should take conformational masking by the V2 loop into account.