"Plateau"-related summary statistics are uninformative for comparing working memory models.

Performance on visual working memory tasks decreases as more items need to be remembered. Over the past decade, a debate has unfolded between proponents of slot models and slotless models of this phenomenon (Ma, Husain, Bays (Nature Neuroscience 17, 347-356, 2014). Zhang and Luck (Nature 453, (7192), 233-235, 2008) and Anderson, Vogel, and Awh (Attention, Perception, Psychophys 74, (5), 891-910, 2011) noticed that as more items need to be remembered, "memory noise" seems to first increase and then reach a "stable plateau." They argued that three summary statistics characterizing this plateau are consistent with slot models, but not with slotless models. Here, we assess the validity of their methods. We generated synthetic data both from a leading slot model and from a recent slotless model and quantified model evidence using log Bayes factors. We found that the summary statistics provided at most 0.15 % of the expected model evidence in the raw data. In a model recovery analysis, a total of more than a million trials were required to achieve 99 % correct recovery when models were compared on the basis of summary statistics, whereas fewer than 1,000 trials were sufficient when raw data were used. Therefore, at realistic numbers of trials, plateau-related summary statistics are highly unreliable for model comparison. Applying the same analyses to subject data from Anderson et al. (Attention, Perception, Psychophys 74, (5), 891-910, 2011), we found that the evidence in the summary statistics was at most 0.12 % of the evidence in the raw data and far too weak to warrant any conclusions. The evidence in the raw data, in fact, strongly favored the slotless model. These findings call into question claims about working memory that are based on summary statistics.

Respiratory pattern of captive Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis)

Cetacean respiration usually happen in bouts. The most widely applied quantitative method used to analyze the structure of these bouts is the log(e)-survivorship analysis, based on the assumption that the respiratory intervals are distributed as negative exponentials. However, for the data collected from three captive Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis), we failed to obtain a convergent result with the application of log,survivorship analysis. However, the two-Gaussian model, which was recently proposed to analyze the feeding behavior of cows, was successfully fitted to the data. According to the fitting results, the overall respiratory pattern of the captive Yangtze finless porpoises can be described as a dive with a mean duration of around 30-40 s, followed by two or three ventilations with a mean interval of approximately 9 s. The average intra-bout intervals during both active and inactive periods are constant at 7.7-9.9 s for all individuals. However, when shifting from active to inactive states, the adult male and female decrease their mean numbers of respirations per bout and average length of inter-bout respiratory intervals, while the estimates of both parameters increase for the juvenile female. It was pointed out that the two-Gaussian model might be more adequate for cetacean respiratory-bout structure analyses than the log(e)-survivorship technique.

Nonconstant quality of auditory filters in the porpoises, Phocoena phocoena and Neophocaena phocaenoides (Cetacea, Phocoenidae)

Simultaneous tone-tone masking in conjunction with the envelope-following response (EFR) recording was used to obtain tuning curves in porpoises Phocoena phocoena and Neophocaena phocaenoides asiaeorientalis. The EFR was evoked by amplitude-modulated probes with a modulation rate of 1000 Hz and carrier frequencies from 22.5 to 140 kHz. Equivalent rectangular quality Q(ERB) of the obtained tuning curves varied from 8.3-8.6 at lower (22.5-32 kHz) probe frequencies to 44.8-47.4 at high (128-140 kHz) frequencies. The QERB dependence on probe frequency could be approximated by regression lines with a slope of 0.83 to 0.86 in log-log scale., which corresponded to almost frequency-proportional quality and almost constant bandwidth of 34 kHz. Thus, the frequency representation in the porpoise auditory system is much closer to a constant-bandwidth rather that to a constant-quality manner. (c) 2006 Acoustical Society of America.

Microcalorimetry as a possible tool for phylogenetic studies of Tetrahymena

Using isothermal microcalorimetry, the growth power-time curves of three strains of Tetrahymena were determined at 28 degrees C. Their Euclidean distances and cluster analysis diagram were obtained by using two thermokinetic parameters (r and Q(log)), which showed that T. thermophila BF1 and T. thermophila BF5 had a closer relationship. Compared with the single molecular biomarker (ITS1) method, microcalorimetry wasmaybe a simpler, more sensitive andmore economic technique in the phylogenetic studies of Tetrahymena species.

Quantitative structure-property relationships for octanol-air partition coefficients of polychlorinated naphthalenes, chlorobenzenes and p,p '-DDT

The octanol-air partition coefficient (K-OA) is a key descriptor of chemicals partitioning between the atmosphere and environmental organic phases. Quantitative structure-property relationships (QSPR) are necessary to model and predict KOA from molecular structures. Based on 12 quantum chemical descriptors computed by the PM3 Hamiltonian, using partial least squares (PLS) analysis, a QSPR model for logarithms of K-OA to base 10 (log K-OA) for polychlorinated naphthalenes (PCNs), chlorobenzenes and p,p'-DDT was obtained. The cross-validated Q(cum)(2) value of the model is 0.973, indicating a good predictive ability of the model. The main factors governing log K-OA of the PCNs, chlorobenzenes, and p,p'-DDT are, in order of decreasing importance, molecular size and molecular ability of donating/accepting electrons to participate in intermolecular interactions. The intermolecular dispersive interactions play a leading role in governing log K-OA. The more chlorines in PCN and chlorobenzene molecules, the greater the log K-OA values. Increasing E-LUMO (the energy of the lowest unoccupied molecular orbital) of the molecules leads to decreasing log K-OA values, implying possible intermolecular interactions between the molecules under study and octanol molecules. (C) 2002 Elsevier Science Ltd. All rights reserved.

Water solubility enhancement of phthalates by cetyltrimethylammonium bromide and beta-cyclodextrin

Water solubility enhancements of six phthalates (five aliphatic phthalates and one phenyl phthalate) by cetyltrimethylammonium bromide (CTAB) and beta-cyclodextrin (beta-CD) were studied at 25 degreesC. The solubilities of these plithalates are remarkably enhanced by CTAB solutions above the critical micelle concentration (cmc). Only marginal enhancement of phthalate solubility was observed in solutions containing CTAB below its cmc and beta-CD at low concentrations (less than 5 mM). The solubility enhancements of the plithalates are proportional to the added amount of CTAB and beta-CD. Partition coefficients of the plithalates between monomeric CTAB surfactant and water (K-MN) and between CTAB micelle and water K-MC) were estimated from the experimental data. The mechanisms of solubility enhancements by CTAB and beta-CD were discussed. A log-linear equation was proposed and evaluated for the solubilization by CTAB below cmc, while the previously proposed linear partitioning model was questioned. The structures of the complexes formed between plithalates and beta-CD were proposed, and the formation constants were estimated. The values of log K-MC, log K-MN, and log Kbeta-CD of the plithalates were found to correlate linearly with the log K-OW of plithalates, with the exception of the solid phenyl phthalate.

Quantitative structure-property relationships for octanol-air partition coefficients of polychlorinated biphenyls

Based on nine quantum chemical descriptors computed by PM3 Hamiltonian, using partial least squares analysis, a significant quantitative structure-property relationship for the logarithm of octanol-air partition coefficients (log K-OA) of polychlorinated biphenyls (PCBs) was obtained. The cross-validated Q(cum)(2) value of the model is 0.962, indicating a good predictive ability. The intermolecular dispersive interactions and thus the size of the PCB molecules play a key role in governing log K-OA. The greater the size of PCB molecules, the greater the log K-OA values. Increasing E-LUMO (the energy of the lowest unoccupied molecular orbital) values of the PCBs leads to decreasing log K-OA values, indicating possible interactions between PCB and octanol molecules. Increasing Q(Cl)(+) (the most positive net atomic charges on a chlorine atom) and Q(C)(-) (the largest negative net atomic charge on a carbon atom) values of PCBs results in decreasing log K-OA values, implying possible intermolecular electrostatic interactions between octanol and PCB molecules. (C) 2002 Elsevier Science Ltd. All rights reserved.

Quantitative structure-property relationships (QSPRs) on direct photolysis of PCDDs

By the use of partial least squares (PLS) method and 27 quantum chemical descriptors computed by PM3 Hamiltonian, a statistically significant QSPR were obtained for direct photolysis quantum yields (Y) of selected Polychlorinated dibenzo-p-dioxins (PCDDs). The QSPR can be used for prediction. The direct photolysis quantum yields of the PCDDs are dependent on the number of chlorine atoms bonded with the parent structures, the character of the carbon-oxygen bonds, and molecular polarity. Increasing bulkness and polarity of PCDDs lead to decrease of log Y values. Increasing the frontier molecular orbital energies (E-lumo and E-homo) and heat of formation (HOF) values leads to increase of log Y values. (C) 2001 Elsevier Science Ltd. All rights reserved.

Mobility and profiles of polychlorinated dibenzo-p-dioxins and dibenzofurans in sediment of Ya-Er Lake, China

The sediment of Ya-Er Lake had been heavily polluted by polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from the former chloralkali industry. The total amounts of PCDD/Fs and I-TEQ decreased along the water flow direction and also decreased from top to bottom layers of sediment cores. Sediment of Pond 1 was dominated by PCDF, especially TCDF. In contrast, in the other four ponds, PCDD dominated in all layers and octachlorinated dibenzo-p-dioxin (OCDD) predominated in all of the homologues. When homologue profiles from sediments and water samples were compared using principal component analysis (PCA), the first two principal components represented 95.2% of the variance in the data. The first component explained 75.9% of the variance and the second one 19.3%. Two clusters were most distinct, presenting a shift in PCDD/Fs composition from PCDF to heptachlorinated dibenzo-p-dioxin (HpCDD) and OCDD in sediments and water from Pond I to Ponds 2-5. The pattern variation between Pond 1 and Ponds 2-5 in Ya-Er Lake was most likely due to the change of process in the chemical plant after the dams between the ponds were built. The results of the present study also showed that log K-oc of PCDD/Fs calculated from data of sediment and water in the field were comparable with theoretical log K-oc. The results also implied that the concentrations of PCDD/Fs in water and sediments could be predicted from each other by log K-oc. (C) 2001 Elsevier Science Ltd. All rights reserved.

Quantitative relationship between chromatographic retentions and molecular structures of polychlorinated dibenzo-p-dioxins (PCDDs)

A new approach to study the quantitative relationships between chromatographic retentions and molecular structures of polychlorinated dibenzo-p-dioxins (PCDDs) is described. The retention equations of PCDDs log k' = A + B/T in gas chromatography (GC) are used to evaluate the properties of the regression coefficients A and B, which have been widely accepted as highly reliable chromatographic retentions. The quantitative relationships between the A, B values and the molecular structures are found. The molecular descriptors given for the first time in this article are very effective. As a result, the regression equations are derived with correlation coefficients greater than 0.9995. The A, B values of PCDDs with no standards available have been predicted according to these relationships. They are very useful in chromatographic identification. The retention times of all PCDDs can be conveniently predicted at any temperature program. Compared with the data obtained from the relevant experiments, the results of prediction are very accurate. (C) 2000 Elsevier Science Ltd. All rights reserved.

A column method for determination of soil organic partition coefficients of eight pesticides

A column method was developed to conveniently and reliably determine the soil organic partition coefficients (K-oc) of three insecticides (methiocarb, azinphos-methyl, fenthion), four fungicides (triadimenol, fuberidazole, tebuconazole, pencycuron), and one herbicide (atrazine), in which real soil acted as a stationary phase and the water solution of pesticide as an eluent. The processes of sorption equilibrium were directly shown through a breakthrough curve(BTC). The log K-oc values are 1.69, 1.95, 2.25, 2.55, 2.69, 2.67, 3.10, and 3.33 for atrazine, triadimenol, methiocarb, fuberidazole, azinphos-methyl, tebuconazole, fenthion and pencycuron, respectively.

Space-charge-limited currents in GaN Schottky diodes

Unusual dark current voltage (I-V) characteristics were observed in GaN Schottky diodes. I-V characteristics of the GaN Schottky diodes were measured down to the magnitude of 10(-14) A. Although these Schottky diodes were clearly rectifying, their I-V characteristics were non-ideal which can be judged from the non-linearity in the semi-logarithmic plots. Careful analysis of the forward bias I-V characteristics on log-log scale indicates space-charge-limited current (SCLC) conduction dominates the current transport in these GaN Schottky diodes. The concentration of the deep trapping centers was estimated to be higher than 10(15) cm(-3). In the deep level transient spectra (DLTS) measurements for the GaN Schottky diodes, deep defect levels around 0.20 eV below the bottom of the conduction band were identified, which may act as the trapping centers. The concentration of the deep centers obtained from the DLTS data is about 5 x 10(15) cm(-3). SCLC measurements may be used to probe the properties of deep levels in wide bandgap GaN-AlGaN compound semiconductors, as is the case with insulators in the presence of trapping centers. (c) 2005 Elsevier Ltd. All rights reserved.

分子间链缠结与高聚物的转变和松驰

玻璃化转变与结构松驰是高聚物的两个非常重要的现象，对高聚物的许多物理性质、使用温度范围、以及长期使用性能等都起着至关重要的决定作用。影响高聚物的玻璃化转变温度的因素有高聚物结构单元的化学结构，分子量的大小以及分布，分子链间的交联以及结晶等，而高聚物的链缠结对其玻璃化转变湿度也有着重要的影响。高聚物的链缠结概念首先是由高聚物的分子量--粘度之间的关系得出的。1940 年 Flory 首先发现对于柔性链聚合物而言，其液态的零切粘度同其分子量成正比；此后，1948 年 Fox 和 Flory 发现当聚合物链的长度超过某一临界值时，粘度与分子量的 3.4 次方成正比，而在临界值之下时粘度与他子量的 1 次方成正比。Bueche 于 1952 年首次提出了高聚物链缠结的概念，并对粘度与分子量的关系进行了成功的解释。链缠结从此之后就成为线性高聚物的一个重要特征并成为控制熔（溶）体流变和固体形变机制的关键因素。关于链缠结的理论也有许多，其中应用最为广泛的有蛇链模型（Reptation Model）和管子模型（Tube Model）等。1969年 Flory 提出聚合物的性质同其均方无扰尺寸有关，此后Doi 和 Edwards 得出了高聚物的链缠结同其无扰尺寸的关系。在通常情况下高聚物在本体状态下是以无规线团的形式彼此相互缠绕在一起的，根本无法相互区分开。而通过特殊的方法可以将在极稀溶液中保持彼此孤立的聚合物分子从溶液中分离出来，并且保持在溶液中的相互孤立状态，从而得到单链高聚物。在单链状态下高聚物分子之间是相互分离的，不存在分子间的链缠结作用，因此通过测定单链高聚物的性质，并与本体状态进行比较，就可以得出分子间链缠结对高聚物性质的影响。我们在本工作中采用了一种新的方法－－快速蒸发法来制备高聚物的单链状态样品。具体步骤就是将由沸点远低于 100 ℃ 的溶剂所制成的高分子溶液逐滴滴加到在恒温槽中保持沸腾的水中，溶剂就会在瞬间蒸发出去，而高聚物则基本上保持在溶液中的状态析出。对于几种链段僵硬性不同的高聚物在不同浓度下进行快速蒸发而得到的样品，在相同的升温速率下，用 DSC 方法测定其玻璃化转变温度，发现这些高聚物的玻璃化转变温度随制备溶液浓度的变化都有相同的变化趋势，即在其临界浓度之上时，制备样品的玻璃化转变温度基本上不随浓度的变化而改变，并且同本体状态下的样品的 Tg 温度相近。而在临界浓度以下时，样品的玻璃化温度则随制备溶液浓度的降低而明显下降，在些浓度范围内玻璃化温度与溶液浓度的对数大致成一线性关系。在我们所研究的三种高聚物中，样品的玻璃化温度受制备溶液浓度的影响程度是不一样的，对 PS 的玻璃化转变湿度的影响最大，而对于 PES-C 的影响最小。为了定量地描述制备溶液的浓度变化对样品玻璃化转变温度的影响，我们定义了一个参数 s , s 的值越大，则表明浓度的降低对玻璃化温度下降的影响越明显。对于我们所研究的三种聚合物，S_(PS)>S_(PC)>S_(PES-C)。我们在本工作中还对单链状态对高聚物的结构松弛行为的影响进行了初步的研究，发现同本体样品相比，单链样品的热焓松弛峰所处的温度也比较低，这同其玻璃化转变温度较低相对应。并且同本体样品的焓松弛峰相比，单链样品松弛峰的峰高较低，峰的面积（同松弛焓相对应）也比本体样品的要小，但松弛峰的峰宽却变宽。由 KWW 方程及 TNM 现象学模型通过曲线拟合得出了本体样品与单链样品的结构松弛参数，发现对于所研究的三种高聚物，单链样品的松弛焓相对本体而言都有显著的降低，而特征时间并没有明显的变化，这其中的原因可能是单链状态下的高聚物，发现单链状态对其松弛焓的降低的影响程度也有差异，对于 PS 的影响最为显著，而对 PES－C 的影响最小，这同单链状态对玻璃化转变温度的影响相一致。在研究 PES－C 的分子量的变化对其结构松弛行为的影响时，通过 DSC 方法测出了 PES－C 在不同升温速率下的玻璃化温度，得到了玻璃化转变温度对升温速率的变化曲线，由 1/Tg 对 logQ_h这一直线的斜率，得出了 PES－C 样品的结构松弛的活化能 Δh~*，并且发现对于不同分子量的 PES－C 样品，尽管 Δh~* 和 Tg 的值各不相同，但是 Δh~*/Tg~2 的值却近似为一常数。这样，我们只要知道 PES-C 在某一分子量下的 Tg 以及 Δh~* 值，就可以推算出其它分子量的 PES-C 样品的 Δh~* 值。对于 PES-C 在不同退火温度下的焓变 ΔH(t) 对松弛时间 ta 的曲线进行拟合，并用 KWW 方程（Kraulsch — Watts — Williams）以及结构松弛的 NM（Narayanaswamy — Moynihan）现象学模型进行解析，得出了 PES-C 的结构松弛参数，如极限焓松弛 ΔH_∞，非指数性参数 β，特征结构松弛时间 logτ_c，非线性参数 x 等。并且发现对于不同分子量的样品，其结构弛行为对分子量的大小有着很强的依赖性，在退火间隔温度（Tg — Ta）相同时，特征松弛时间 logτ_c 随着分子量的增加而增加，极限焓松弛 ΔH_∞ 则随着 PES-C 分子量的增加而降低。这些都同 PC 和 PS 有着明显的区别。我们用分子链的运动性随分子量的变化对此作了解释，同普通柔性链高聚物相比，PES－C 的分子链的中间部分所受的限制更为强烈，相对只有链端部分可以相对自由运动。链端的数目随着分子量的降低而增加，因此当分子量降低时，样品在松弛过程中更加容易重排，因此相应的极限焓松弛 ΔH_∞ 也更大。

苯乙烯辐射乳液聚合

用膨胀计连续记录法测定了St辐射乳液聚合的转化率～时间曲线，并由此得到包括在临界胶束浓度以下和在低的单体浓度下在内的各种反应条件下的聚合反应速度。发现其聚合速率与各因素之间的依赖关系，为：R_p∝l~(0.4)，R_p∝E~(0.7～0.9)。测得反应活化能为6.1 ～ 8千卡／摩尔。实验结果还表明：恒定速率部分延续到转化率70％左右，粒子数随温度的增加而减少，水与单体体积比对聚合速率以及分子量与转化率的关系都有影响。在监界胶束浓度以下进行聚合所获得的胶乳的粒子直径分布是单分散的，而聚合速率仍然符合一般情况下的聚合速率与乳化剂浓度的关系。这些实验结果在某些方面与Smith-Ewart理论相符，在某些方面不符。目前，大多数研究者都认为：St乳液聚合的成核方式是胶束成核。对于增长反应的位置有分歧。一派认为是在粒子内；另一派认为是在肥皂分子吸附层与单体一聚合物粒子表面之间为了探讨增长反应的位置究竟是在哪方。同时澄清国际上两个学派在这个问题上的争论，我们用电镜，光散射（未去单体），肥皂滴定三种测定方法同时测定了St乳液聚合恒定速率部分胶乳粒子的增长情况。测定结果表明：由于聚合物胶乳中溶胀有单体造成了用不同方法测定 将得出不同的结果。所以，两个学派仅从电镜或肥皂滴定的测定结果都不能证实增长反应发生的位置。根据我们的上述实验结果，我们设想其聚合反应机理如下：i)成核是既有水相成核又有胶束成核。ii)增长反应是在具有“核－壳“结构的单体－聚合物乳胶粒表面与肥皂分子吸附层之间进行的即在“壳“中进行的。我们从热力学和静电排斥的观点出发进行了理论分析。结果表明这种增长反应的模型是合理的。 我们所设想的反应机理能满意地解释实验结果，并在实验上得到证实。在所设想的反应机理的基础上，建立了动学模型计算公式，其第Ⅱ阶段总转化率表达式如下：X = AX_m + BX_w其中：X_m = k/2N_(mc) (t-t_(mcl)) + X_(mcl) X_w = k/2N_(wc) (t-t_(wcl)) + X_(wcl) A和B分别为胶束成核和水相成核分数用我们的动力学模型计算公式计算出的结果与实验结果相符合。这表明我们所设想的反应机理及动力学模型计算公式是合理的。根据我们所设想的反应机理，在临界胶束浓度以下只有一种成核方式。因此可以预期到利用在临界胶束浓度以下进行St辐射乳液聚合，将可以合成出用化学法无乳乳液聚合所不能获得的稳定，单分散、高固体含量、粒子直径较小的胶乳。实验结果表明，利用这种聚合方法确实可以合成出这种胶乳。用此法合成出的胶乳粒子直径一般在600A ～ 4000A范围内。通过改变聚合条件可以控制所获得的胶乳粒子直径。在实验所使用的聚合条件范围内得到一个胶乳粒子直径与聚合条件的关系式：logD = 0.28 [log ([M])/E~(2.14)I~(0.5) + 0.143T] + 2.03。我们还考察了St辐射无乳乳聚合，发现聚合速率与I成0.5次方关系，活化能为7.5千卡／摩尔，水与单体体积比对聚合速率胶乳稳定性影响很大。产物分子量在10~4 ～ 10~5范围内，聚合物胶乳的分子量分布比用化学法和有乳化剂存在下的辐射法所获得的要窄些。实验结果表明在合适的聚合条件下，可以获得单分散、干净的胶乳，其聚合规律类似于化学法的。

Cr(III)盐在Pt电极和PbO_2电极上阳极氧化为络酸盐的机理的研究

关于Cr(III)阳极氧化为Cr(VI)的过程，在工业应用方面已有许多工作，但对机理尚不清楚。本文对Pt电极和PbO_2电极上的这一过程进行了动力学的研究，首次得到了Cr(VI)在这两种电极上阳极形成的真实动力学数据，并提出了与实验基本相符的反应机理。用“分解极化曲线法”和稳态极化曲线的测量，得到了[H_2SO_4]和[SO_4~=]恒定的不同浓度Cr_2(SO_4)_3溶液中Cr(VI)在光滑Pt电极上阳极形成的真实动力学数据，可用如下方程式来表达：在较低电位下φ = a + 0.25 log i_2 - 0.23 log [Cr(III)]在较高电位下φ = a' + 0.48 log i_2 - 0.44 log [Cr(III)]同时得到了氧的阳极发生的动力学数据，Tafel线性区的斜率接近于2.303 RT/ΔF (Δ ≈ 0.5)。动力学方程式的推导与实验的比较表明，在光滑Pt电极上Cr(VI)是由Cr(II)通过“活性氧”的氧化形成的，提出了如下反应机理：H_2O → (OH)_(ad) + H~+ + e~- 2(OH)_(ad) → (O)_(ad) + H_2O 2(O)_(ad) →O_2 (OH)_(ad) + [Cr(H_2O)_6]~(3+) → (CrO_2)_(ad) + 3H~+ + 5H_2O (CrO_2)_(ad) + H_2O → (CrO_3~-)_(ad) + 2H~+ + e~- (CrO_3~-)_(ad) + H_2O → HCrO_4~- + H~+ + e~- 2HCrO_4~- <-> Cr_2O_7~(2-) + H_2O 在[H_2SO_4]和[SO_4~(2-)]恒定的不同浓度Cr_2(SO_4)_3溶液中，测得了Cr(VI)在Δ-PbO_2电极上阳极形成的动力学数据：在较低电位下φ = a + 0.28 log i_2 - 0.30 log [Cr(III)]在较高电位下φ = a' + 0.55 log i_2 - 0.51 log [Cr(III)]氧的极化曲线的Tafel线性区斜率也为2.303RT/ΔF (Δ approx= 0.5)。PbO_2电极和Pt电极上分解极化曲线的比较表明，Cr(VI)在前一电极上阳极形成的过电位远低于在后一电极上，这可能是两电极上电流效率显著差别的原因。测得了PbO_2电极上不同过电位下电极反应的有效活化能，其数值均在10 Kcal mol~(-1)以上，且随着极化的增大而减小，据此在动力学处理中可以忽略扩散的作用，交流阻抗的研究进一步证实了这一点。溶液pH的增大或[H_2SO_4]的减小会降低Cr(VI)阳极形成的过电位，使反应加速。在[H_2SO_4]和[SO_4~(2-)]恒定的不同浓度Cr_2(SO_4)_3溶液中，测得了在不同电位极化下PbO_2电极的阻抗频谱。在较高电位下阻抗谱呈现明显的两个半圆，表明电极过程包括了中间吸附物的形成。求得的吸附电容Cad比双层电容Cd大1-2个数量级；Cd比通常光滑电极表面的Cd大得多，这可能与SO_4~(2-)，HCrO_4~-, Cr_2O_7~-以及[_((SO_4))~((H_2O)_2) Cr_((SO_4))~((OH)_2) Cr_((SO_4))~((OH_2)_2)]~(2-)等阳离子的特性吸附有关。从动力学的推导与实验的比较得出，在PbO_2电极上Cr(VI)也按“活性氧”机构形成，可能的机理如下：H_2O → (OH)_(ad) + H~+ + e~- (OH)_(ad) + H_2O → (O)_(ad) + H_3O~+ + e~- 2(O)_(ad) → O_2 [Cr(H_2O)_6]~(3+) + (O)_(ad) → (CrO_3~-)_(ad) + 4H~+ + 4H_2O (CrO_3~-)_(ad) + H_2O → HCrO_4~- + H~+ +e~- 2HCrO_4~- <-> Cr_2O_7~(2-) + H_2O.