Minimum-delay schedules in layered networks

Summary In this paper, we consider the following problem: given a layered network including a set of messages, each of which must be transmitted from a source to a sink node, what is the sequence of moves from one node to another which minimizes the total completion time? We first show that the general problem is NP-complete for both fixed and variable path routing (thus the scheduling problem for more realistic networks with cycles must be considered computationally intractable). We then consider several restrictions which admit polynomia time algorithms.Most of this work was done while this author was at the Department of Mathematics, University of Rome La Sapienza     

反渗透/电去离子：食品和饮料实验室首选净水技术

目前,人们对食品饮料的分析检验的要求越来越严格.随着分析灵敏度的提高,人们对食品饮料分析中用水的质量提出了更高的要求.许多实验室仍然采用蒸馏的方法来生产纯水,但是采用能够提供更高水质的反渗透和电去离子系统更经济.     

Detection of frozen salt in pipes using gamma-ray spectrometry of potassium self-activity

Solar plants that use molten salts as heat transfer fluid need careful control to avoid the freezing of the salt in the pipes; if such a problem occurs, a diagnostic instrument to localize where is the frozen salt plug and to determine its length is useful. If the salt contains potassium (as is the case of the most common mixture used in solar plants, NaNO₃/KNO₃ 60/40% by weight), the gamma decay of the natural unstable isotope ⁴⁰K can be exploited to detect the frozen salt in a non-invasive way. Simulations and experimental results regarding the detectability of such plugs with different masses/lengths are presented.     

Determination of nitroaromatic compounds in air samples at femtogram level using C18 membrane sampling and on-line extraction with LC-MS

This paper explores the use of C18 solid-phase extraction membranes for sampling very low concentrations of nitroaromatic compounds in the atmosphere. After sampling, analytes trapped in the membrane are desorbed on-line directly by a chromatographic mobile phase. The analytes are then separated onto a porous graphitic carbon (PGC) HPLC column. Finally, they are analyzed by an LC-MS/MS detector equipped with an atmospheric pressure chemical ionization (APCI) interface. The method was validated by controlled exposure of the membranes to standard gaseous mixtures of 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (2,4-DNT). The developed method was fully characterized, and no breakthrough was observed when sampling volumes up to 9.2 m3. Analyses of membranes following medium- and long-term storage demonstrated that samples could be stored on the C18 membranes without degradation or losses. In addition, the results obtained with this technique were compared with those obtained by a gas chromatographic method in which analytes were collected on Tenax TA and thermally desorbed. The developed method allows sampling at flow rates of 15 L/min and has method detection limits in the femtogram/liter range, with a relative standard deviation lower than 10%. An additional advantage of this method is that it separates most of the TNT and DNT isomers, as demonstrated by applying the method to the analysis of headspace over military-grade TNT explosives.     

Fibers coated with molecularly imprinted polymers for solid-phase microextraction

The simplicity and flexibility of solid-phase microextraction have been combined with the selectivity of molecularly imprinted polymers (MIPs). Silica fibers were coated reproducible with a 75-microm layer of methacrylate polymer either nonimprinted or imprinted with clenbuterol to compare their extraction characteristics under various conditions. Although the template molecule could be removed effectively from the imprinted polymer, structural analogues of clenbuterol were used for evaluation. The influence of pH on the extractability of brombuterol was investigated. Extraction yields up to approximately 80% were obtained when both types of fibers were used to extract brombuterol from phosphate buffer (pH 7.0). In contrast, yields of about 75 and <5% were obtained when extraction was performed from acetonitrile with imprinted and nonimprinted polymers, respectively, which demonstrates the selectivity of the MIP-coated fiber. Time sorption profiles were measured for the extraction of brombuterol from buffer and acetonitrile at the 10 and 100 ng/mL level with both types of fibers in order to compare extraction characteristics. Equilibrium times of about 30 and 90 min were found for the extraction of brombuterol from acetonitrile and buffer, respectively. The MIP-coated fibers were capable of extracting five structural analogues of clenbuterol from both buffer and acetonitrile, which suggests that the amine alcohol part of these molecules is responsible for interaction with the imprinted polymer. To achieve selective extraction of brombuterol from human urine, MIP-coated fibers were washed with acetonitrile after the extraction. Clean extracts and yields of approximately 45% were obtained, demonstrating the suitability of MIP-coated fibers for the analysis of biological samples.     

Guar gum methyl ethers. Part I. Synthesis and macromolecular characterization

Guar gum (GG) has been partially methyl-etherified under heterogeneous reaction conditions. The resulting products, (methyl ether guar: MG) with different degrees of substitution, have been characterized by means of viscosity, ¹H NMR, and FTIR measurements. The introduction of methoxyl groups along the polysaccharidic chains reduces the hydrogen bonding sites on the guar backbone reducing primarely the extent of hydrogen bonding between guar macromolecules, hence their aggregation tendency. A comparative analysis of Mark–Houwink–Sakurada parameters and of the characteristic ratio (C_∞) of GG and MG samples in aqueous solution has been carried out using the Burchard–Stockmayer–Fixman method for flexible and semiflexible chains. The MG chains exhibit more flexibility than those of native guar gum which is traceable to a disruption of intrachain hydrogen bonds.     

Morphological changes in a hyperfunctioning thyroid adenoma after percutaneous ethanol injection: histological, enzymatic and sub-microscopical alterations

Autonomic nervous dysfunction has recently been considered to be an etiological factor in syncope and sudden death in cases of hypertrophic cardiomyopathy. However, the precise mechanism is still unknown. A 73-year-old woman with obstructive hypertrophic cardiomyopathy was hospitalized with complaints of impaired consciousness; faintness 3 to 4 h after meals, lightheadedness while walking, and syncope during and after defecation and micturition. Faintness was induced by alimentary hypoglycemia related to gastrectomy performed 5 years previously. Lightheadedness and syncope were accounted for by autonomic nervous failure combined with an impairment of alpha 1-adrenoceptor in vasoconstriction and the carotid sinus hypersensitivity which accompanied preceding events such as abdominal pain, defecation and micturition, which could enhance the vagally-mediated baroreceptor reflex.     

Wt-p53 action in human leukaemia cell lines corresponding to different stages of differentiation

Recent studies support the potential application of the wt-p53 gene in cancer therapy. Expression of exogenous wt-p53 suppresses a variety of leukaemia phenotypes by acting on cell survival, proliferation and/or differentiation. As for tumour gene therapy, the final fate of the neoplastic cells is one of the most relevant points. We examined the effects of exogenous wt-p53 gene expression in several leukaemia cell lines to identify p53-responsive leukaemia. The temperature-sensitive p53Val135 mutant or the human wt-p53 cDNA was transduced in leukaemia cell lines representative of different acute leukaemia FAB subtypes, including M1 (KG1), M2 (HL-60), M3 (NB4), M5 (U937) and M6 (HEL 92.1.7), as well as blast crisis of chronic myelogenous leukaemia (BC-CML: K562, BV173) showing diverse differentiation features. By morphological, molecular and biochemical analyses, we have shown that exogenous wt-p53 gene expression induces apoptosis only in cells corresponding to M1, M2 and M3 of the FAB classification and in BC-CML showing morphological and cytochemical features of undifferentiated blast cells. In contrast, it promotes differentiation in the others. Interestingly, cell responsiveness was independent of the vector used and the status of the endogenous p53 gene.