A CO2 tracer-gas method for local air leakage detection and characterization

A method for local measurement of air leakage rate is presented that can be used to accurately and quickly assess leakage rates across a surface, such as around a valve or hatch in a pressurized gas tank or a window in a building. The method uses a small local enclosure with constant volume placed about a region on the structure under investigation (e.g., a window), which is depressurized and injected with a small concentration of carbon dioxide as a tracer gas. The time variation of the pressure and carbon dioxide concentration inside the enclosure are monitored and used to quantify the leakage flow rate as a function of pressure difference. This method uses a small enclosure with internal mixing so that a quasi-steady-state condition is quickly achieved. Because of the small size of the enclosure, advanced data processing techniques are necessary to reduce uncertainty in determination of the rate of change of the carbon dioxide concentration that arises from sensor variability. Results of a laboratory demonstration of the proposed leakage detection and characterization device are reported for the problem of leakage through a circular hole in a plate with prescribed pressure differences. Experimental results from the laboratory tests are found to be in excellent agreement with results of a numerical simulation of leakage flow through a hole, as well as predictions from a number of empirical equations for this problem found in the literature.     

Mechanical behavior and tensile/compressive strength asymmetry of ultrafine structured Ti–Nb–Ni–Co–Al alloys with bi-modal grain size distribution

Bulk ultrafine structured metallic materials with the bi-modal grain size distribution exhibit both high strength and good ductility. Here we show a new family of bi-modal Ti–Nb–Ni–Co–Al alloys. Their microstructure consists of an ultrafine structured eutectic matrix and relatively coarse β-Ti dendrites. Chemical modification of the parent Ti–Nb–Ni–Cu–Al system significantly affected type and volume fraction of matrix phases. In its turn, this influenced the deformation behavior. The unexpected “double yielding” behavior as well as tensile/compressive fracture strength asymmetry of the designed alloys are discussed in detail. For that, the microstructure alterations under compressive and tensile loading was in situ and ex situ analyzed by scanning electron microscopy.     

Chemical Biology Towards Precision Medicine

Organic chemistry is primed to fill a much-needed gap in our understanding of human biology and disease on the one hand and our ability to treat disease effectively on the other. The key challenge is to discover compounds having the novel mechanisms of action demanded by these new patient-derived insights.     

Mechanical properties and microstructural evolution of Al 6061 alloy processed by multidirectional forging at liquid nitrogen temperature

Al–Mg–Si alloy was subjected to multidirectional forging (MDF) at liquid nitrogen temperature (LNT), to cumulative strains of 1.8, 3.6 and 5.4. The deformed microstructures were examined by optical microscopy under polarized light and transmission electron microscopy (TEM). The deformed samples showed the formation of dislocation cells structure with high dislocation density at lower strains. Composite structure consisting of lamellar morphology at deformation bands and equiaxed grain morphology was observed. Significant differences in microstructure of the deformed samples were observed with increasing strain at LNT. At cumulative strain of 5.4, the microstructure shows nearly equiaxed subgrain structure with an average size of 250 nm with high angle grain boundaries. The mechanical properties were studied through Vickers hardness testing machine and tensile tester. The hardness value of MDFed alloy at LNT has increased from 50 Hv to 115 Hv for cumulative strain of 5.4. Tensile strength has increased from 180 MPa to 388 MPa with 4.5% percentage of elongation to failure. The improvement in hardness and tensile strength of forged alloy is attributed to the formation of equiaxed sub-grain structures and the presence of high dislocation density.     

乙烯基硅油改性苯丙乳液粘合剂的制备及应用

采用丙烯酸酯单体制备苯丙乳液粘合剂,用乙烯基硅油对其进行改性。探讨了乙烯基硅油的用量对乳液性能、胶膜性能的影响,及硅油改性粘合剂的用量对棉织物印花性能的影响。对改性粘合剂进行了红外光谱、热重分析、透射电镜等表征。结果表明,乙烯基硅油用量为9%时,乳液外观、胶膜及印花性能较好;乙烯基硅油改性粘合剂用量为6%时,印花织物的手感柔软、摩擦牢度较好。     

Biofilm formation by Salmonella Typhimurium and Staphylococcus aureus on stainless steel under either mono- or dual-species multi-strain conditions and resistance of sessile communities to sub-lethal chemical disinfection

Intercellular interactions encountered within and between different bacterial species are believed to play key roles in both biofilm formation and antimicrobial resistance. In this study, Salmonella Typhimurium and Staphylococcus aureus (3 strains per species) were left to form biofilms on stainless steel coupons incubated at 20 °C for 144 h (i.e. 6 days), in periodically renewable growth medium, under either mono- or dual-species conditions. Subsequently, the developed sessile communities were exposed for 6 min to sub-lethal concentrations of: (i) benzalkonium chloride (BC, 50 ppm), (ii) sodium hypochlorite (NaClO, 10 ppm), or (iii) peroxyacetic acid (PAA, 10 ppm). The dominance of each strain in the mono- and dual-species biofilm communities, both before and after disinfection, was monitored by pulsed field gel electrophoresis (PFGE). Results revealed that dual-species conditions led to a significant (ca. 10-fold) reduction in the number of sessile cells for both species, compared to mono-species ones, with interspecies interactions however found to not exert any significant effect on the disinfection resistance of each species as a whole. However, PFGE analysis revealed that the different strains here employed behaved differently with regard to biofilm formation and disinfection resistance, with this effect to be also strongly dependent on the culture conditions (mono-/dual-species) and the disinfectant applied. Such results expand our knowledge on multi-species biofilms formed by foodborne pathogenic bacteria and could hopefully be helpful in our efforts to develop effective elimination strategies and thus improve food safety.     

Assessment of safety margins of exposure to non-genotoxic chemical substances in food

The concept of Food Safety Margin (FSM) was introduced in microbiological risk analysis as an alternative approach to risk characterization within the informed-risk decision-making process. Its aim was to verify compliance with food safety objectives by assessing the effects of uncertainties. This paper describes the fundamentals and develop a new formulation of safety margins to verify compliance with food safety goals in relation to exposure to non-genotoxic chemical hazards. Both classical and probabilistic metrics were used to compare a given exposure to an estimated daily intake (EDI) with a given safety goal, the acceptable daily intake (ADI). The safety margins of these metrics were assessed in the exposure of peaches to organophosphorus pesticides. The pesticides considered were Azinphos-methyl, Chlorpyrifos, Diazinon, Dimethoate, Methamidophos, Parathion-methyl and Phosmet. The concentrations were obtained from the USDA pesticide database. The study period included the 11 years in which peaches were analysed from 1994 to 2014. The results show the importance of using the effect of uncertainty instead of mean values for risk characterization and that not only safety margins increased during this period but also that uncertainty was reduced. In general, large safety margins were observed in the period studied and few situations were found in which exposure was outside the safety limits.     

Experimental approaches for the estimation of uncertainty in analysis of trace inorganic contaminants in foodstuffs by ICP-MS

Total Diet Studies to estimate dietary exposure to food contaminants need to evaluate laboratory measurements data variance. In this process it is critical that data from analytical methods are reliable to correctly scrutinize and compare values over time and between countries. In Europe it is widely recognized that the evaluation of measurement uncertainty is an important parameter when assessing the sources of analytical data variability. Two approaches are considered to estimate uncertainty in analytical measurement. Arsenic, Lead, Chromium and Cadmium, content in several food matrix determined by Inductively Coupled Mass Spectrometry (ICP-MS) microwave digestion assisted, are used as examples. The aim of the present research work is to compare both approaches accepted by Eurolab and GUM: Mathematical modeling to assess uncertainty components based on a classical model (bottom up) and an empirical method (top down), based on either experimental data obtained from a single laboratory validation data or inter-laboratory data from Proficiency Testing schemes. Relative expanded uncertainty calculated by both approaches agree when U (%) <20%. These values are concordant with RSD_R reported in collaborative studies of EN 15763 (2009), which were assumed as target uncertainty. The top down approach described is simple and easy to use when compared with the mathematical modeling approach providing considerable benefits to those who assess data produced by several laboratories.     

Effect of storage time and heat processing on the volatile profile of Senegalese sole (Solea senegalensis Kaup, 1858) muscle

The effect of heat treatment and the presence or absence of fish skin on the volatile composition of Senegalese sole muscle was studied. The volatile profile of Senegalese sole at different storage periods was also evaluated. All samples were analysed by HS-SPME–GC–IT/MS and subjected to sensory evaluation. As expected, cooking enhanced the production/liberation of volatile compounds. Fish with the skin present, after cooking, had higher levels of sulphur compounds, 2-nonanone, ethyl octanoate and lower contents of hexanol and heptanol than skinned fish; moreover, the samples with the skin had a better overall sensory acceptability. During storage, changes on the volatile composition of Senegalese sole samples were found. The major differences were obtained after 2 weeks of storage. Compounds such as hexanal, heptanal, octanal, decanal, (E)-2-hexenal, (E)-2-decen-1-al, (E,Z)-2,6-nonadienal, benzaldehyde, 4-ethyl-benzaldehyde, 1-penten-3-ol, heptanol and (E)-2-octen-1-ol decreased after 2 weeks of storage, and other compounds, such as 3-methyl-1-butanal, 2-methyl-1-butanal, 2-heptanone, dimethyl trisulphide, dimethyl tetrasulphide and 2-methyltetrahydrothiophen-3-one increased. These differences were confirmed by sensory evaluation. Principal component analysis was applied to the chemical data.