Recovery of semivolatile organic compounds during sample preparation: implications for characterization of airborne particulate matter

Semivolatile compounds present special analytical challenges not met by conventional methods for analysis of ambient particulate matter (PM). Accurate quantification of PM-associated organic compounds requires validation of the laboratory procedures for recovery over a wide volatility and polarity range. To meet these challenges, solutions of n-alkanes (nC12-nC40) and polycyclic aromatic hydrocarbons PAHs (naphthalene to benzo[ghi]perylene) were reduced in volume from a solvent mixture (equal volumes of hexane, dichloromethane and methanol), to examine recovery after reduction in volume. When the extract solution volume reached 0.5 mL the solvent was entirely methanol, and the recovery averaged 60% for n-alkanes nC12-nC25 and PAHs from naphthalene to chrysene. Recovery of higher MW compounds decreased with MW, because of their insolubility in methanol. When the walls of the flasks were washed with 1 mL of equal parts hexane and dichloromethane (to reconstruct the original solvent composition), the recovery of nC18 and higher MW compounds increased dramatically, up to 100% for nC22-nC32 and then slowly decreasing with MW due to insolubility. To examine recovery during extraction of the components of the High Capacity Integrated Gas and Particle Sampler, the same standards were used to spike its denuders and filters. For XAD-4 coated denuders and filters, normalized recovery was >95% after two extractions. Recovery from spiked quartz filters matched the recovery from the coated surfaces for alkanes nC18 and larger and for fluoranthene and larger PAHs. Lower MW compounds evaporated from the quartz filter with the spiking solvent. This careful approach allowed quantification of organics by correcting for volatility- and solubility-related sample preparation losses. This method is illustrated for an ambient sample collected with this sampler during the Texas Air Quality Study 2000.     

Fermentation patterns of gramicidin S formation by Bacillus brevis ATCC 9999 in high-yielding synthetic medium

Addition of the gramicidin S (GS)-constituent amino acids, other than the limiting precursor L -phenylalanine, to the high-yielding chemically defined F3/6 and G3/6 media, enhanced growth and volumetric GS-production by Bacillus brevis ATCC 9999 considerably, but did not yield a higher specific GS-production level. L -Leucine alone could duplicate this stimulatory effect in G3/6 medium. Replacing the fructose component of F3/6 medium by these four amino acids yielded a high specific GS-production level, but resulted in poor growth and low volumetric antibiotic production. Nutrient-utilisation patterns in F3/6 medium revealed that B. brevis initially grew at the expense of L -glutamine and L -arginine. After a diauxic lag period, D -fructose was consumed together with L -histidine. L -Proline was mainly used during the stationary phase. L -Methionine was broken down gradually throughout the whole fermentation cycle. L -Phenylalanine was metabolised only after GS formation started, and its disappearance was proportional to the amount of GS produced. Lowering the aeration rate caused an acidification of the medium, resulting in a slower and incomplete, although similar, nutrient-utilisation pattern. At a controlled pH of 7.3, under lowered aeration, utilisation patterns were again comparable with those of a fully aerated fermentation, but GS levels were enhanced considerably (0.220 mg of GS mg^?1 dry cell wt). Depending on environmental culture conditions, B. brevis also excreted different amino acids (L -lysine, L -alanine, L -valine, L -serine), which were in turn metabolised during late growth and differentiation stages. The onset of GS synthesis occurred on depletion of L -glutamine and L -arginine. Soluble GS synthetase 1 and 2 peaks coincided with ‘diauxic’ lag phases; this supported the idea that a high growth rate is incompatible with GS synthetase formation.     

Sheep milk kefir sweetened with different sugars: Sensory acceptance and consumer emotion profiling

The objective of this study was to determine the sensory acceptance and emotional profile of sheep milk kefir sweetened with different sugars (demerara sugar, brown sugar, fructose, coconut sugar, and honey, 100 g/L). Consumers (n = 100) assessed sensory acceptance (appearance, aroma, taste, texture, and overall impression), and expressed their emotions (satisfied, active, loving, calm, comfortable, energetic, happy, healthy, refreshing, disgusted, worried, and upset). The emotions “satisfied,” “active,” “comfortable,” “energetic,” “healthy,” and “refreshing” were found between moderate and very high levels, indicating that they are important emotions for the characterization and sensory acceptance of kefir samples. The use of different sugars had no influence on the intensity of the emotions “calm,” “comfortable,” “happy,” or “disgusted,” and resulted in a greater sense of satisfaction. The use of demerara sugar or fructose did not alter the acceptance of the products or the intensity of emotions. The use of brown sugar decreased acceptance (taste, texture, and overall impression) and the intensity of the emotions “active,” “loving,” “energetic,” “healthy,” and “refreshing.” The use of coconut sugar decreased acceptance (appearance, aroma, and taste) and the intensity of the emotions “refreshing” and “upset.” The use of honey improved acceptance in appearance and aroma but reduced the intensity of the emotions “active,” “loving,” “energetic,” and “healthy.” Based on sensory data, it is recommended to use demerara sugar or fructose as a substitute for sucrose. In conclusion, the study of emotions can be used as an additional tool for obtaining data related to the sensory acceptance of products.     

Woven graphite fiber structures for use in ultra-light weight heat exchangers

Lightweight, robust woven graphite-fiber structures were developed for heat exchangers which provide high conductivity paths along the direction of the graphite fibers. These structures were produced and characterized for air permeability/pressure drop and thermal (heat transfer) performance. Results indicate that the materials are suitable for use in ultra-light weight heat exchanger applications such as vehicle radiators or other areas where light weight, compact, conformable heat transfer devices are needed.     

An integrated high voltage digital-to-analog converter for a reconfigurable antenna array

This paper presents an integrated high voltage digital-to-analog converter, which is fabricated in a 0.35 \({\upmu }\) m high voltage CMOS technology (AMS H35), and can be applied in high voltage applications up to 115 V. The high voltage output is controlled by 8-bit digital input code. In order to improve the accuracy and decrease the required area, it is implemented by a low voltage DAC and a high voltage amplifier for boosting the controllable output voltage. Since the current consumption from the high voltage power supply is only 80 \({\upmu }\) A, it can be powered by a charge pump which generates 115 V from a battery with 3.7 V DC. Combining with a 8*8 external high voltage switch array, the proposed high voltage digital-to-analog converter can drive up to 64 individual channels of antenna array with a voltage from 0 to 115 V. It will greatly reduce the complexity and cost of mobile applications which use tunable microwave devices and require high voltages. The feasibility is proved by post-simulation result and experimental test result. The proposed concept of the high voltage ASIC is also proved by a demonstrator.     

无组合检波采集方法的三维地震波数值模拟研究

采用传统的检波器组合地震采集技术在中国西部一些复杂山地地区的效果不理想。能否仍采用无组合检波地震采集方法呢?本文采用非均匀介质三维一阶压力一速度标量波动方程交错网格高阶有限差分法进行了三维正弦形山地模型声波模拟，并通过对模拟记录进行室内不同组合和叠加处理，结果表明该法不但可以灵活、方便地实现检波道组合，有效地压制干扰波，而且可以得到最佳的叠加剖面。无组合检波地震采集技术有可能是解决复杂山地地震采集难题的一条有效途径。     

Probiotics in Goat Milk Products: Delivery Capacity and Ability to Improve Sensory Attributes

Dairy foods, particularly those of bovine origin, are the predominant vehicles for delivery of probiotic bacteria. Caprine (goat) milk also possesses potential for successful delivery of probiotics, and despite its less appealing flavor in some products, the use of goat milk as a probiotic carrier has rapidly increased over the last decade. This review reports on the diversity, applicability, and potential of using probiotics to enhance the sensory properties of goat milk and goat milk‐based products. A brief conceptual introduction to probiotic microorganisms is followed by an account of the unique physicochemical, nutritive, and beneficial aspects of goat milk, emphasizing its advantages as a probiotic carrier. The sensory properties of probiotic‐enriched goat milk products are also discussed. The maintenance of probiotic viability and desirable physicochemical characteristics in goat milk products over shelf life is possible. However, the unpleasant sensory features of some goat milk products remain a major disadvantage that hinder its wider utilization. Nevertheless, certain measures such as fortification with selected probiotic strains, inclusion of fruit pulps and popular flavor compounds, and production of commonly consumed tailor‐made goat milk‐based products have potential to overcome this limitation. In particular, certain probiotic bacteria release volatile compounds as a result of their metabolism, which are known to play a major role in the aroma profile and sensory aspects of the final products.     

Safety assessment of dairy microorganisms: the Lactococcus genus

The Lactococcus genus includes 5 species. Lactococcus lactis subsp. lactis is the most common in dairy product but L. garviae has been also isolated. Their biotope is animal skin and plants. Owing to its biochemical characteristics, strains of L. lactis are widely used in dairy fermented products processing. Cases of human infections due to lactococci are very seldom reported even if Lactococcus garviae can be involved in fish diseases. Then L. lactis can be considered as safe and it is most commonly considered as Generally Recognized as Safe.