Hydrolytic stability of terephthaloyl chloride and isophthaloyl chloride

The phthaloyl chloride isomers, terephthaloyl chloride (TCl) and isophthaloyl chloride (ICl), are high production volume chemicals used in polymers to impartflame resistance, chemical resistance, and temperature stability and as water scavengers. In these studies, we determined the hydrolytic stability of TCl and ICl and their hydrolysis products in aqueous solutions. Hydrolysis rates for TCl and ICl were initially determined by gas chromatography/flame ionization detection in water buffered at pH 4.0, 7.0, and 9.0 and 0 degrees C for up to 30 min. Subsequent studies determined the products from TCl and ICl hydrolysis. The parent phthaloyl chlorides (TCl and ICl), their intermediate hydrolysis products (designated as the "half-acids"), and their stable hydrolysis products (terephthalic acid (TPA) and isophthalic acid (IPA)) were determined by high-performance liquid chromatography. The half-lives (t(1/2)) of TCl and ICl ranged from an average of 1.2 to 2.2 min and from 2.2 to 4.9 min, respectively, at pH 4-9 and 0 degrees C. The observed first-order rate constants (k(obs)) ranged from an average of 530 to 1100 (x 10(5) s(-1)) for TCl and 240 to 520 (x 10(5) s(-1)) for ICl. Both phthaloyl chlorides formed their respective short-lived intermediates, in which one of the two carboxylic acid chloride functionalities reacts with water to form the carboxylic acid ("half-acid"). Subsequently, the half-acids underwent further hydrolysis so that greater than 90% of the initial phthaloyl chloride hydrolyzed in less than 60 min at 0 degrees C. The hydrolysis products TPA and IPA were hydrolytically stable, undergoing no further transformations after 20 min at pH 7 and 25 degrees C. This work demonstrated that TCl, ICl, and their respective half-acids will not be persistent in aqueous systems for a time sufficient to have a sustained toxicological effect on aquatic organisms (less than 1 h). Performing additional aquatic toxicity studies, biodegradation studies, and potentially mammalian studies on TCl and ICl are unnecessary since the existing information on TPA and IPA with the hydrolysis data presented here is sufficient to address questions on the fate and effects of these two substances in aqueous environments.     

Crop yield after 5 decades of contrasting residue management

Nutrient Cycling in Agroecosystems - The benefits of soil organic input on crop yields have long been discussed, yet details of their relationship remain controversial. This study considers the...     

机器人柔性关节前馈力/位混合控制策略研究

针对机器人关节柔性引起的轨迹跟踪误差问题和末端执行器残余振动现象,在PD反馈控制律基础上,提出一种基于柔体动力学模型的前馈力矩补偿控制算法和后置多模态自适应输入整形算法前馈力/位混合控制策略。建立六轴工业机器人柔体动力学简化模型,在不附加关节编码器和外设的情况下进行柔体动力学参数辨识,再将动力学模型改写为力矩计算方程,经计算得到前馈力矩并加入控制律中进行补偿;计算前馈力矩所用的期望轨迹需经过输入整形器处理,考虑机器人系统的时变性问题,采用后置多模态自适应输入整形算法对期望输入位移信号进行命令整形,从而抑制末端的残余振动现象。结果表明：所提出的前馈力/位混合控制策略能有效减少轨迹跟踪误差,抑制机器人末端的残余振动现象。     

Stability of composite systems with an asymptotically hyperstable subsystem

In this note, it is proved that stability of composite systems including parallel subsystems can be achieved for certain sets of initial conditions and additional stability assumptions for the non-hyperstable subsystems. It is required that at least one subsystem be asymptotically hyperstable.     

关于定量界定设备修理周期若干问题的研究

本文通过对确定设备修理周期经验公式的讨论,指出了两点不足。对此笔者提出了:在生产过程中运用单位产品维修成本与产量的量化模型,从经济效益的角度动态界定最佳修理周期的设想,以期在设备维修管理方面,为企业提供最佳经济效益。并由此得出了几点有益的启示。     

Flow imaging with pulsed Doppler ultrasound and flow phantoms

The use of a multigate profiling system with steady laminar flow in plastic tubes revealed spectral artifacts not previously described. In particular, a double or split profile was often observed. In this paper, these artifacts are related to the dual mode ultrasound propagation in the plastic tube. The propagation speeds and, therefore, refraction angles and propagation paths are different for the longitudinal and the shear wave. The power transmission can be extraordinarily sensitive to small variations in the angle of incidence, and this may combine with the existence of a range of angles of incidence within any focused ultrasound beam to produce spectral distortions. The plastic tube is thus shown equivalent to a selective filter, which diminishes some frequency components in the Doppler spectrum relative to others. The spectral artifacts are explained in terms of the relative power transmitted by each mode, and the degree of beam defocusing experienced by each. Spectral distortions persist even when the beam-to-flow orientation is well away from the critical angle. The results of this study show that it is feasible to understand the acoustic transmission behavior of a flow phantom, based on a knowledge of the material properties, and to demonstrate the usefulness of doing so.     

Determinant spreading associated with demyelination in a nonhuman primate model of multiple sclerosis

Definition of the immune process that causes demyelination in multiple sclerosis is essential to determine the feasibility of Ag-directed immunotherapy. Using the nonhuman primate, Callithrix jacchus jacchus (common marmoset), we show that immunization with myelin basic protein and proteolipid protein determinants results in clinical disease with significant demyelination. Demyelination was associated with spreading to myelin oligodendrocyte glycoprotein (MOG) determinants that generated anti-MOG serum Abs and Ig deposition in central nervous system white matter lesions. These data associate intermolecular "determinant spreading" with clinical autoimmune disease in primates and raise important issues for the pathogenesis and treatment of multiple sclerosis.     

Hypotension following acute hypovolaemia depends on the caudal midline medulla

Acute hypovolaemia evokes abrupt, life-threatening hypotension and bradycardia. Hypotension can be evoked also by excitation of the caudal midline medulla (CMM). This study investigated the possible contribution of the CMM depressor area to hypotension evoked by acute hypovolaemia. Inactivation of the CMM, with either lignocaine or cobalt chloride did not alter resting arterial pressure. However lignocaine injections blocked the fall in arterial pressure, and cobalt chloride injections delayed the onset and significantly attenuated the size of hypovolaemic-evoked hypotension. These findings suggest that the CMM is a key region triggering hypotension after blood loss, and that the brain areas mediating cardiovascular response to challenges such as acute hypovolaemia are not the same areas that regulate resting arterial pressure.     

Dynamic course of neurological syndromes in very young children with the history of intrauterine growth retardation

90 infants with intrauterine growth retardation (IGR) and 100 normal infants (control group) were followed up from 5 days till 3 years of life. In IGR infants there was a more frequent combination of several neurologic syndromes, an early manifestation of motor disorders (from the very moment of birth), a delay of neuro-psychic development (during the first year of life), a tendency to development of moderate hydrocephalus by the age of 6 months. Autonomic-visceral disorders in them were mostly characterized by the symptoms of abaissement, but not of irritation.