硫酸在农业中的应用——作为土壤和水的改良剂

在农业生产中,越来越多地采用硫酸改良高pH值的石灰质土壤。过去20年来,尿素--硫酸肥料的产量大幅度提高并在美国西部诸州的土壤中广泛施用。将硫酸注入牛奶场湖泊,改变湖水pH值,可解决圈养牲畜过程产生的若干空气和水质问题。将硫酸施入农用土壤和水中,其主要作用是溶解钙、镁的碳酸盐和碳酸氢盐。这些钙、镁盐然后取代可交换的钠盐,钠盐随后用水浸洗除去。当碳酸盐和碳酸氢盐被分解后,硫酸与更惰性的物质反应,释放出磷、铁等植物养分。简单地降低土壤的pH值可引起许多元素溶解度的变化,提高它们对植物的效力。在高pH值的石灰质土壤上施用硫酸,可使植物更加健壮、收成增加。本文介绍硫酸在农业中的各种应用,在过去的25年里,Verdegaal Brothers公司一直致力于此项研究。     

A NONINVASIVE STUDY OF MILK CLEANING PROCESSES: CALCIUM PHOSPHATE REMOVAL

High temperature, high pH milk processing results in the formation of mineral rich deposits that are > 70% mineral and < 30% protein by weight. This research investigates the removal of P³² labeled mixtures of calcium phosphate dihydrate (brushite, CaHPO₄–2H₂O) and hydroxyapatite (Ca₅(PO₄)₃OH) from stainless steel tubes using a solid scintillation technique. Experiments were performed at pH values ranging from 2.86–7.82 and flow rates from 3.8–11.4 L/min. Previous cleaning models are reviewed and a mass transfer model is proposed which, when compared to the experimental results suggests that film removal is due to both dissolution and mechanical effects due to shear stress. A modified first order model is presented which incorporates the effects of the solvent flow rate and pH on decontamination rates. This first order model is in agreement with the experimental results over the range of pH and flow rates investigated.     

Do temperature conditions at budburst affect flower number in Vitis vinifera L. cv. Cabernet Sauvignon?

Timing of winter pruning (early July versus mid‐August) and the application of hydrogen cyanamide were used to manipulate the time of budburst in a population of spur‐pruned, 13‐year‐old Vitis vinifera L. Cabernet Sauvignon vines grown in central Victoria. Delaying pruning by six weeks delayed budburst by an average of four days. This extended the duration of budburst for the entire population, thus, exposing bursting shoots to a greater range of temperature conditions. Flowers per inflorescence and bunches per shoot were estimated by destructively sampling 300 inflorescences prior to anthesis from shoots of known bursting date. Pruning time did not significantly affect flowers per inflorescence. However, across the entire population of inflorescences sampled, flowers per inflorescence was weakly correlated with daily maximum air temperature on the day of budburst, daily mean soil temperature on the day of budburst and date of budburst (P < 0.001, Adjusted R²= 3.6%, 3.7%, 4.5% respectively). Inflorescences had fewer flowers on later‐bursting shoots and also as temperatures on the day of budburst increased. More of the variance in flowers per inflorescence was accounted for by the number of inflorescences on the shoot (P < 0.001, Adj. R²= 17.4%) and the position of the inflorescence relative to other inflorescences on the same shoot, i.e. lower of two, upper of two or sole (P < 0.001, Adj. R²= 26.1%). Average flowers per inflorescence declined in the order lower of two > upper of two > sole. The best regression model included the position of the inflorescence relative to other inflorescences on the shoot and the date of budburst (P < 0.001), but this still accounted for only 29.2% of the total variance in flowers per inflorescence. Mean flowers per inflorescence was significantly (P < 0.05) and substantially (97% for back‐transformed means) higher for inflorescences on two‐inflorescence shoots than for inflorescences on single inflorescence shoots. This suggests that conditions during the previous spring that favour the initiation of uncommitted inflorescence primordia (i.e. high temperature and adequate light) also precondition inflorescences to higher flower numbers.     

Inhibition of Listeria monocytogenes on Beef Tissue by Application of Organic Acids Immobilized in a Calcium Alginate Gel

Organic acids added to calcium alginate gels and immobilized on lean beef tissue inoculated with Listeria monocytogenes (Lm) reduced the population significantly more than did acid treatment alone. Lactic acid (1.7% v/v) immobilized in alginate reduced counts by 1.3 log₁₀ units vs 0.03 log unit decrease from the acid treatment alone. Acetic acid (2% v/v) reduced counts 1.5 and 0.25 log units, respectively. Over 7 days, Lm proliferated in samples without acid and/or alginate treatment. Differential counts on selective and non-selective agars indicated sublethal cellular injury occurred. Alginate coatings did not enhance acid inhibition on fat tissue. Immobilized agents may have potential for raw meat decontamination.     

2-(Hydroxymethyl)-N-nitrosothiazolidine-4-carboxylic Acid in Smoked Meats and Bacon and Conversion to 2-(Hydroxymethyl)-N-Nitrosothiazolidine During High-Heat Cooking

Concentrations of 2-(hydroxymethyl)-N-nitrosothiazolidine-4-carbox-ylic acid (HMNTCA) in a variety of smoked meats and bacon were determined by a newly developed method based on derivatization of HMNTCA with diazomethane and analysis by high performance liquid chromatography-thermal energy analyzer. Of samples analyzed, 4/8 raw bacon, 6/8 fried bacon, and 7/14 miscellaneous cured meat products contained 10–540 ppb of HMNTCA. Evidence suggested 2-(hydroxyrnethyl)-N-nitrosofhiazolidine in fried bacon likely originated by heat-induced decarboxylation of HMNTCA. Identity of HMNTCA in selected samples was confirmed by mass spectrometry.     

Influence of chemical etching on metal contacts to II-VI compounds: CdTe and ZnSe

The chemical nature of CdTe and ZnSe surfaces prepared by various chemical treatments has been studied by X-ray photoelectron spectroscopy. It has been found that the stoichiometry of the surfaces is very sensitive to the chemical treatments and each surface shows a similar pattern. In general bromine-containing or acid-based solutions preferentially remove the semiconductor cation, leaving a semiconductor anion-rich surface. In contrast, alkaline-based systems preferentially remove the semiconductor anion to produce a semiconductor cation-rich surface. Metal contacts fabricated on these surfaces show considerable differences in current-transport properties. The stability of these metal-semiconductor contacts has also been investigated and the microscopic interactions at these interfaces studied with Auger depth profiling and secondary-ion mass spectroscopy surface imaging techniques. The influence of microscopic interactions on the macroscopic electrical properties is presented and discussed in detail     

MOVING PORT CHROMATOGRAPHY: A METHOD OF IMPROVING PREPARATIVE CHROMATOGRAPHY

A computer study of conventional, moving feed, moving withdrawal and moving port chromatography systems was conducted. The linear ternary system of naphthalene, anthracene, and pyrene in 2-propanol with Polyclar AT as the stationary phase was studied. Moving withdrawal ports in conjunction with moving feed chromatography (moving port system) resulted in an average increased purity of 22% and an average increased throughput of 120% compared to conventional chromatography. Moving feed chromatography increased purity by 22% and throughput by 33%, and moving withdrawal chromatography increased throughput by 39% over the conventional case with no change in purity. A local equilibrium model with zone spreading was also developed and use to determine reasonable operating conditions for these chromatographic systems.     

COMPARISON OF TWO ANALYTICAL METHODS FOR THE DETERMINATION OF DIMETHYLNITROSAMINE IN BEER AND ALE, AND SOME RECENT RESULTS

The results obtained by a rapid Celite column extraction method for the determination of dimethylnitrosamine (DMN) in beer and ale were compared with those obtained by a more elaborate vacuum distillation method. The end determination in both cases was done by gas-liquid chromatography using a thermal energy analyzer (TEA) detector. The two sets of results for 28 samples of beers from various countries were highly comparable. Recent survey results for both Canadian and imported beer and ales suggest a significant decrease in the levels of DMN in these beverages from that observed 2–3 years earlier. This decrease is probably due to the improvements in the malt drying techniques instituted in Canada as well as in other countries.