测定炉水二氧化硅时掩蔽剂的选用

叙述了用硅钼蓝分光光度法测定锅炉用水SiO2含量时，不同的掩蔽剂对磷酸盐掩蔽的效果。试验表明，草酸能有效掩蔽磷酸盐的干扰，酒石酸的掩蔽效果次之，但分析时适当增加酒石酸的用量也能获得满意的掩蔽效果。     

双硫腙─四氯化碳萃取光度法测定锑矿中汞

经试验，拟定了在溶矿过程中加入酒石酸掩蔽大量锑（Ｖ），用ＥＤＴＡ─柠檬酸钠掩蔽铅（Ⅱ），硫氰酸钾掩蔽银（Ⅰ），双硫腙─四氯化碳萃取，光度法测定锑矿，锑精矿，锑氧粉中汞的方法。     

双硫腙——四氯化碳萃取光度法测定锑矿中汞

经试验，拟定了在溶矿过程中加入酒石酸掩蔽大量锑（Ｖ），用ＥＤＴＡ－柠檬酸钠掩蔽铅（ＩＩ），硫氰酸钾掩蔽银（Ｉ）双硫腙－四氯化碳萃取，光度法测定锑矿，锑精矿，锑氧粉中汞的方法。     

硅钡合金中钡的测定

本文采用盐酸羟胺掩蔽Ｆｅ＾３＋，硫酸铵掩蔽Ｃａ＾２＋，同时生成沉淀硫酸钡，用重量法测定硅钡合金中的钡，方法简便，结果准确。     

铝合金中镁的快速测定

本文介绍的铝合金中镁的快速测定是不需分离，采用DDTC、盐酸羟胺、三乙醇胺联合掩蔽剂掩蔽大量的铝及铜、铁、锰离子，在PH10以铬黑T为指示剂，用EDTA滴至溶液由紫红色变为纯蓝色为终点。方法简单、快速、准确度高，适合于铝合金中各种镁含量的测定．     

铝合金中镁的快速测定

本文介绍的铝合金中镁的快速测定是不需分离，采用ＤＤＴＣ、盐酸羟胺、三乙醇胺联合掩蔽剂掩蔽大量的铝及铜，铁，锰离子，在ＰＨ１０以铬黑Ｔ为指示剂，用ＥＤＴＡ滴至溶液由紫红色变为纯蓝色为终点，方法简单，快速，准确度高，适合于铝合金中各种镁含量的测定。     

掩蔽剂在金属分析中的应用

掩蔽是建立选择性或专一性分析方法的有效途径之一,因此掩蔽剂在分析化学中的应用是极其广泛的.掩蔽剂不仅在重量法、容量法、光度法、溶剂萃取法、离子交换法、电化学分析法等方面获得了卓有成效的应用,而且在化学光谱法、原子吸收光谱法和色谱法等方面的应用也日益增多.近年来关于掩蔽和解蔽在分析化学中的应用亦有评论.本文拟讨论1978年以来有关掩蔽剂在金属分析中应用的文献;必要的也涉及个别以前的文献.     

合金中镁、镍、铅的测定—用丙酮氰醇代替氰化钾作掩蔽剂

在络合滴定中,国内许多单位多年来一直使用氰化钾作掩蔽剂,因氰化钾剧毒,长期使用很不安全.许多分析工作者也曾寻找过多种掩蔽剂来代替氰化钾,但都没有得到满意的结果.根据文献关于丙酮氰醇(文中用[Ⅰ]代表丙酮氰醇)在络合滴定中作掩蔽剂的介绍,本文对[Ⅰ]的掩蔽条件和用量进行试验.实验证明在氨性溶液中,0.5毫升[Ⅰ],可以完全掩蔽50毫克的镍、铜、锌.对一些用氰化钾作掩蔽剂的分析方法,用[Ⅰ]代替     

铝合金中镁的快速测定

该文介绍的铝合金中镁的快速测定不需分离，采用DDTC、盐酸羟胺、三乙醇胺联合掩蔽剂掩蔽大量的铝及少量的铜、铁、锰离子，在pH10条件下，以铬黑T为指标剂，用EDTA滴至溶液由紫红色变为纯蓝色为终点。方法简单、快速、准确度高，适用于铝合金中镁含量的快速测定。     

原子荧光光谱法测定金矿石中的碲及干扰抑制

准确、快速的碲元素分析方法对富碲金矿床中碲资源的综合利用和矿床成因研究均具有重要的实际意义。采用原子荧光光谱法测定金矿石中的碲,并对干扰元素进行了分析。实验结果表明,金矿石中的Au、Ag干扰碲的测定,采用硫脲作为掩蔽剂,可有效地掩蔽Au、Ag的干扰,提高测定的准确度,但不能掩蔽As、Sb和Bi,反而会加重干扰。硫脲作为掩蔽剂具有一定的局限性,As、Sb和Bi含量低的金矿石样品,可采用硫脲掩蔽剂+稀释法测定碲。     

Cortical dynamics of lateral inhibition: Metacontrast masking.

The dynamic properties of a neural network model of visual perception, called the boundary contour system, explain characteristics of metacontrast visual masking. Computer simulations of the model, with a single set of parameters, demonstrate that it accounts for 9 key properties of metacontrast masking: Metacontrast masking is strongest at positive stimulus onset asynchronies (SOAs); decreasing target luminance changes the shape of the masking curve; increasing target duration weakens masking; masking effects weaken with spatial separation; increasing mask duration leads to stronger masking at shorter SOAs; masking strength depends on the amount and distribution of contour in the mask; a second mask can disinhibit the masking of the target; such disinhibition depends on the SOA of the 2 masks; and such disinhibition depends on the spatial separation of the 2 masks. No other theory provides a unified explanation of these data sets. Additionally, the model suggests a new analysis of data related to the SOA law and makes several testable predictions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Combining simultaneous with temporal masking.

Simultaneous and temporal masking are two frequently used techniques in psychology and vision science. Although there are many studies and theories related to each masking technique, there are no systematic investigations of their mutual relationship, even though both techniques are often applied together. Here, the authors show that temporal masking can both undo and enhance the deteriorating effects of simultaneous masking depending on the stimulus onset asynchrony between the simultaneous and temporal masks. For the task and stimuli used in this study, temporal masking was largely unaffected by the properties of the simultaneous mask. In contrast, simultaneous masking seems to depend strongly on spatial grouping and was strongly affected by the properties of the temporal mask. These findings help to identify the nature of both temporal and simultaneous masking and promote understanding of the role of spatial and temporal grouping in visual perception. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective forward masking.

Assessed the effects of masking on recall accuracy in 2 experiments with a total of 28 male undergraduates. When a patterned masking stimulus was presented immediately before a centrally-fixated, tachistoscopically-presented 7-letter row (forward masking), a selective effect on recall accuracy was found, as measured by a partial-report technique. There was greater masking of the end letters than of the center letters in the displays. When the masking stimulus was presented immediately after the presentation of a letter row (backward masking), the results confirmed previous findings of greater masking of the center letters than the end letters. These different selective effects of forward and backward masking are consistent with the assumption that the processing of multiletter displays begins at the ends of the letter rows. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Remote masking generated by high-frequency two-tone complexes

Auditory masking generated by two-tone complexes centered around 7 000 Hz was measured in 10 young adults with normal hearing sensitivity as a function of the frequency separation (deltaf) and SPL of the masker's components. Remote masking (1) was evident for test signals in the frequency region corresponding to the masker's deltaf; (2) increased with masker SPL, but at a rate less than that usually observed when lower frequency bands of noise are used as maskers, and (3) was relatively constant in magnitude for a given SPL as a function of the masker's deltaf. The masking produced in low-frequency regions by high-frequency two-tone complexes adds support to the hypothesis that remote masking is primarily a result of aural distortion.     

Locus of presentation and the selective masking effect.

Obtained forward and backward masking functions for 4 adult Ss in a nonmetacontrast letter recognition paradigm for letters presented either foveally or 1.75. in the periphery with a patterned mask. Both forward and backward masking were greater for peripherally presented stimuli. Forward masking showed a greater sensitivity to locus of presentation than backward masking. Results are considered in relation to the "ends-first" processing strategy explanation of the selective masking effect proposed by P. M. Merikle, et al. (French summary) (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Auditory suppression and frequency selectivity in older and younger adults

Age differences in auditory suppression were examined by comparing auditory-filter shapes obtained with simultaneous and forward masking at 2 kHz in young and elderly normal-hearing listeners. To compensate for the decay of forward masking, growth of masking functions were used to transform thresholds obtained with a notched-noise masker to the level of a continuous noise band that would give the same threshold values. Although both age groups exhibited smaller equivalent rectangular bandwidths (ERBs) when the filters derived from transformed thresholds were obtained with forward masking, the change from simultaneous to nonsimultaneous masking was significantly greater for young adults. Measures of the low- (Pl) and high- (Pu) frequency sides of the filters for young listeners indicated that the slopes of both sides increased following a change from simultaneous to forward masking but that the high-frequency side exhibited significantly greater sharpening. Filter slopes (both upper and lower) for older adults, in contrast, did not differ between the two masking procedures. The findings from the study are discussed as reflecting possible age differences in auditory suppression. However, it is also noted that conclusions regarding differences between filter shapes derived with simultaneous and forward masking are limited to filter parameters determined with transformed (as described above) thresholds.     

The importance of information localization in scene gist recognition.

People can recognize the meaning or gist of a scene from a single glance, and a few recent studies have begun to examine the sorts of information that contribute to scene gist recognition. The authors of the present study used visual masking coupled with image manipulations (randomizing phase while maintaining the Fourier amplitude spectrum; random image structure evolution [RISE]; J. Sadr & P. Sinha, 2004) to explore whether and when unlocalized Fourier amplitude information contributes to gist perception. In 4 experiments, the authors found that differences between scene categories in the Fourier amplitude spectrum are insufficient for gist recognition or gist masking. Whereas the global 1/f spatial frequency amplitude spectra of scenes plays a role in gist masking, local phase information is necessary for gist recognition and for the strongest gist masking. Moreover, the ability to recognize the gist of a target image was influenced by mask recognizability, suggesting that conceptual masking occurs even at the earliest stages of scene processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual masking during the attentional blink: Tests of the object substitution hypothesis.

When 2 masked targets are presented in a rapid sequence, correct identification of the 1st hinders identification of the 2nd. Visual masking of the 2nd target plays a critical role during this 2nd-target deficit, or "attentional blink" (AB). The object substitution hypothesis (B. Giesbrecht and V. Di Lollo, 1998) predicts that late-stage visual processes involved in object substitution mediate masking of the 2nd target during AB, whereby stronger masking should produce a more severe deficit. Six experiments are presented, together testing this hypothesis. Although masking by object substitution was observed, it did not interact with the AB. An alternative hypothesis is proposed stating that mostly early-stage visual processes mediate the masking effects that are critical to the AB. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interaction effects in the lateral visual field: an extension of Bouma's (1970) approach

The recognizability of a letter is impaired by the presence of additional letters. This phenomenon is called lateral masking. Proceeding on the assumption of Bouma (1970) lateral masking can be described in terms of retinal eccentricity of the target letter and the distance between target and flanking stimuli. In this paper, we will address to the question if these kinds of parameters are adequate for describing lateral masking effects. For this purpose, characteristics of the string like its length and its homogenity are varied. The subject's task is to identify the central letter of a tachistoscopically presented string. The targets in the string are flanked both by only x and by different randomly selected letters. Additionally, we varied the length of the string. The data show that these variations influence the strength of the masking effect. It is concluded that a pure sensorical approach is not sufficient for an explanation of lateral masking effects.     

Suppression and the upward spread of masking

The purpose of this study is to clarify the role of suppression in the growth of masking when a signal is well above the masker in frequency (upward spread of masking). Classical psychophysical models assume that masking is primarily due to the spread of masker excitation, and that the nonlinear upward spread of masking reflects a differential growth in excitation between the masker and the signal at the signal frequency. In contrast, recent physiological studies have indicated that upward spread of masking in the auditory nerve is due to the increasing effect of suppression with increasing masker level. This study compares thresholds for signals between 2.4 and 5.6 kHz in simultaneous and nonsimultaneous masking for conditions in which the masker is either at or well below the signal frequency. Maximum differences between simultaneous and nonsimultaneous masking were small (< 6 dB) for the on-frequency conditions but larger for the off-frequency conditions (15-32 dB). The results suggest that suppression plays a major role in determining thresholds at high masker levels, when the masker is well below the signal in frequency. This is consistent with the conclusions of physiological studies. However, for signal levels higher than about 40 dB SPL, the growth of masking for signals above the masker frequency is nonlinear even in the nonsimultaneous-masking conditions, where suppression is not expected. This is consistent with an explanation based on the compressive response of the basilar membrane, and confirms that suppression is not necessary for nonlinear upward spread of masking.