Resolutions of ideals of quasiuniform fat point subschemes of

The notion of a quasiuniform fat point subscheme is introduced and conjectures for the Hilbert function and minimal free resolution of the ideal defining are put forward. In a large range of cases, it is shown that the Hilbert function conjecture implies the resolution conjecture. In addition, the main result gives the first determination of the resolution of the th symbolic power of an ideal defining general points of when both and are large (in particular, for infinitely many for each of infinitely many , and for infinitely many for every 2$">). Resolutions in other cases, such as ``fat points with tails', are also given. Except where an explicit exception is made, all results hold for an arbitrary algebraically closed field . As an incidental result, a bound for the regularity of is given which is often a significant improvement on previously known bounds.

     

Determination of arsenic and antimony in milk by hydride generation atomic fluorescence spectrometry

A highly sensitive procedure has been developed for total arsenic and antimony determination in milk samples by hydride generation atomic fluorescence spectrometry after microwave-assisted sample digestion. The discrete introduction of 2 ml of digested sample in the automated continuous flow hydride generation system allows us to reduce drastically the sample and HCl consume and to determine several elements from a same sample digestion. The method provides detection limits of 0.006 and 0.003 ng ml⁻¹, a sensitivity of 2390 and 2840 fluorescence units per ng ml⁻¹ for As and Sb respectively, and average relative standard deviation of 2.3% for As and 4.8% for Sb. The analysis of cow milk samples, obtained from the Spanish market evidenced the presence of As at concentration levels from 3.4 to 11.6 ng g⁻¹ and Sb levels from 3.5 to 11.9 ng g⁻¹, thus in a proportion near to 1:1, which is in contrast with the 10:1 natural ratio between As and Sb and could evidence the effect of the introduction of new alloys and polymer materials in the industrial process of milk. The method was validated by the comparison of data found for commercial samples by using the proposed procedure and reference methods based on dry-ashing and AFS, and microwave-assisted digestion and inductively coupled plasma mass spectrometry determination.     

Analysis and leaching characteristics of mercury and arsenic in Chinese medicinal material

The purpose of this study is to investigate the amounts and characteristics of heavy metals (As, Hg) leachable from several Chinese medicinal materials (CMM) under conditions simulating stomach and intestine digestion and absorption. Analysis by inductively coupled plasma mass spectrometry (ICP-MS) was compared with that by hydride generation atomic fluorescence spectrometry (HG-AFS). Focused microwave assisted extraction (MAE) and Soxhlet extraction were carried out to compare with the conventional sequential extraction method. The CMM studied included two mineral drugs: realgar and cinnabar, and two formulated drugs containing the two minerals. The leachable amounts of the target elements into artificial stomach fluid, artificial intestinal fluid, and artificial intestinal fluid in 0.5% trypsin were compared. The last solvent gave the greatest amounts of leachable As (0.41%) from realgar and Hg (1×10⁻⁴%) from cinnabar, but otherwise no significant effect on the leachable amounts was observed upon changing the following parameters: temperature (37-60 °C), HCl concentration (0.5-6 M), and CMM sample particle size (74 and 250 μm). The low leaching efficiencies observed confirmed the presence of As and Hg as insoluble species (sulfides)in these mineral drugs. Sequential extraction schemes were used to determine the species of mercury and arsenic in formulated drugs containing the minerals. Trace amounts of organic forms of arsenic (0.43%) and mercury (2.9×10⁻⁴%) were observed which could be the transformation products derived from the original cinnabar or realgar minerals in drug formulation.     

氢化物发生原子荧光法测定聚氯化铝中砷含量的不确定度评定

依据JJF 1059-1999，对氢化物发生原子荧光法测定聚氯化铝中的砷含量进行不确定度评定。建立了数学模型，对各不确定度分量进行了分析和量化。计算出相对合成标准不确定度为0．0095，扩展不确定度为0．032mg／kg。砷含量测量不确定度主要来源于测量样品测试液中砷浓度产生的不确定度。     

Application of the electronegativity indices of organic molecules to tasks of chemical informatics

An efficient structure filtration method for the operation with chemical databases containing information on the structures and properties of organic molecules was proposed. The technique involves the use of electronegativity indices for generation of identification keys and for isomorphism tests of the molecular graphs corresponding to the structural formulas. The test set for the method proposed included a total of 95,000,000 molecules containing up to sixty carbon atoms. Tests revealed a high discriminating capability of the electronegativity indices and high efficiency of the method for solving both general problems (recognition of chemical structures, chemical database management systems) and specific tasks (generation of molecular graphs, etc.) in chemical informatics. Dedicated to Academician N. S. Zefirov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2166–2176, September, 2005.     

氢化物发生-冷阱捕获-色谱分离-原子吸收法测定天然水中砷的形态

研究建立了氢化物发生－冷阱捕获－色谱分离－原子吸收方法测定天然水中四种主要砷形态。测试系统自行组装，色谱住填料采用ChromosorbGAW－DMCS（粒径0．3～0．45mm），其上涂布3％OV－101。方法的检出限以砷计分别为：As（V）0．51ng，As（Ⅲ）0．43ng，MMA0．38ng，DMA067ng；12ng砷标准偏差As（Ⅴ）4．21％，As（Ⅲ）3．56％，MMA3．23％，DMA5．46％。在0～50ng砷量范围标准曲线线性关系良好。该法适用性广，已用于湖水、河水、海水和地下水等不同水样神形态测定，加标回收率93．5％～104．9％。给出了上述水样四种砷形态的分析结果。     

Speciation of antimony by differential generation of its volatile covalent hydride in aqueous and organic phase

By using the ammonium pyrrolidinedithiocarbamate (APDC) — methylisobutyl ketone (MIBK) extraction system Sb(III) is extracted into the organic phase. Sb(III) is directly determined in this organic phase by hydride generation AAS using NaBH₄/dimethylformamide solution as reducing agent. Sb(V) is determined in the aqueous phase using the same technique.     

流动注射在线离子交换预富集-氢化物发生原子荧光光谱法测定痕量碲的研究

研究了流动注射在线离子交换预富集及在线氢化物发生法与原子荧光光谱法的联用技术。设计了双柱交替正向富集和反向洗脱的在线离子交换流路系统。在采样频率为３０次／ｈ下，灵敏度较常规流动注射氢化物发生原子荧光光谱法提高１１倍。应用于环境水样中痕量碲的分析，获得了满意的结果。     

Interference-free atomic spectrometric method for the determination of trace amounts of germanium by utilizing the vaporization of germanium tetrachloride

Trace amounts of germanium can be determined by atomic spectrometry by utilizing the vaporization of germanium tetrachloride at ambient temperature. Using an intermittent or continuous flow reactor, the sample solution was mixed with concentrated hydrochloric acid to form volatile germanium tetrachloride which can subsequently be determined by atomic spectrometry. The conditions for the volatilization of germanium chloride were investigated in detail and rapid method for the determination of trace amounts of germanium in real samples was proposed. A detection limit of 0.5 ng ml⁻¹ (3σ_n−1) was obtained by using atomic fluorescence spectrometric detection and the precision found was 0.8% for a germanium concentration of l00 ng ml⁻¹. Atomic emission and absorption spectrometric methods were also tested. Owing to the high selectivity of the reaction, no interference was found in the determination. The method was applied to the determination of germanium in several standard and certified reference materials; the results obtained were in good agreement with the certified values.