温度测量系统对ADC的要求

为具体应用选择适当的温度传感器取决于待测温度范围和所需的精度.系统精度取决于温度传感器的精度和对传感器的输出数字化的模数转换器(ADC)的性能.     

Ferroelectric Materials: Probing Local and Global Ferroelectric Phase Stability and Polarization Switching in Ordered Macroporous PZT (Adv. Funct. Mater. 5/2011)

We describe the characterization, ferroelectric phase stability and polarization switching in strain‐free assemblies of PbZr_0.3Ti_0.7O₃ (PZT) nanostructures. The 3‐dimensionally ordered macroporous structures present uniquely large areas and volumes of PZT where the microstructure is spatially modulated and the composition is homogeneous. Variable temperature powder X‐ray diffraction (XRD) studies show that the global structure is crystalline and tetragonal at room temperature and undergoes a reversible tetragonal to cubic phase transition on heating/cooling. The measured phase‐transition temperature is 50–60 °C lower than bulk PZT of the same composition. The local ferroelectric properties were assessed using piezoresponse force spectroscopy that reveal an enhanced piezoresponse from the nanostructured films and demonstrate that the switching polarization can be spatially mapped across these structures. An enhanced piezoresponse is observed in the nanostructured films which we attribute to the formation of strain free films, thus for the first time we are able to assess the effects of crystallite‐size independently of internal stress. Corresponding polarization distributions have been calculated for the bulk and nanostructured materials using a direct variational method and Landau‐Ginzburg‐Devonshire (LGD) theory. By correlating local and global characterization techniques we have for the first time unambiguously demonstrated the formation of tetragonal and ferroelectric PZT in large volume nanostructured architectures. With the wide range of materials available that can be formed into such controlled architectures we conclude that this study opens a pathway for the effective studies of nanoscale ferroelectrics in uniquely large volumes.     

Non‐Covalent Functionalization of Graphene Using Self‐Assembly of Alkane‐Amines

A simple, versatile method for non‐covalent functionalization of graphene based on solution‐phase assembly of alkane‐amine layers is presented. Second‐order Møller–Plesset (MP2) perturbation theory on a cluster model (methylamine on pyrene) yields a binding energy of ≈220 meV for the amine–graphene interaction, which is strong enough to enable formation of a stable aminodecane layer at room temperature. Atomistic molecular dynamics simulations on an assembly of 1‐aminodecane molecules indicate that a self‐assembled monolayer can form, with the alkane chains oriented perpendicular to the graphene basal plane. The calculated monolayer height (≈1.7 nm) is in good agreement with atomic force microscopy data acquired for graphene functionalized with 1‐aminodecane, which yield a continuous layer with mean thickness ≈1.7 nm, albeit with some island defects. Raman data also confirm that self‐assembly of alkane‐amines is a non‐covalent process, i.e., it does not perturb the sp² hybridization of the graphene. Passivation and adsorbate n‐doping of graphene field‐effect devices using 1‐aminodecane, as well as high‐density binding of plasmonic metal nanoparticles and seeded atomic layer deposition of inorganic dielectrics using 1,10‐diaminodecane are also reported.     

A review of current challenges and legal advances in the global management of plastic waste

Clean Technologies and Environmental Policy - Plastic waste is an ever-growing global challenge, perhaps second only to climate change in its scope and impact. Unmanaged plastic waste can be found...     

Extraction and on-line concentration of flavonoids in Brassica oleracea by capillary electrophoresis using large volume sample stacking

Flavonoids are bioactive compounds found in plants. Studies indicate consumption of food containing these compounds may reduce the incidences of cancer and cardiovascular diseases. In broccoli, the flavonoids are present at variable concentrations and so far have mainly been determined using high performance liquid chromatography (HPLC). This paper describes a rapid capillary electrophoresis method, involving large volume sample stacking (LVSS), suitable for the analysis of flavonoids in broccoli. Following acid hydrolysis, the two key flavonoids (kaempferol and quercetin) in a broccoli extract were concentrated on-line by LVSS prior to separation by capillary zone electrophoresis (CZE). Using an optimised method, the extract was injected for 50 s into a 50 μm (internal diameter) × 85 cm (total length) capillary followed by stacking/matrix removal at −5 kV for 83 s. The two analytes were then separated in less than 8 min by CZE using a 10 mM sodium borate buffer (pH 8.40) and a separation voltage of +30 kV at 30 °C. A linear relationship in the range 1–20 ppm was observed for the method (r² = 0.9991–0.9995) with detection limits of 0.9 and 0.6 mg/kg of broccoli for kaempferol and quercetin, respectively. This method demonstrated good repeatability for the standard and extract with relative standard deviations of less than 5% for both peak area and migration time measured over five different days (n = 5). The method was successfully applied to quantitatively determine kaempferol and quercetin contents in a commercial broccoli sample as 11.8 and 14.6 mg/kg fresh weight, respectively. This result was validated by HPLC analysis and is within the ranges reported in the literature.     

Reformation of casein particles from alkaline-disrupted casein micelles

In this study, the properties of casein particles reformed from alkaline disrupted casein micelles were studied. For this purpose, micelles were disrupted completely by increasing milk pH to 10.0, and subsequently reformed by decreasing milk pH to 6.6. Reformed casein particles were smaller than native micelles and had a slightly lower zeta-potential. Levels of ionic and serum calcium, as well as rennet coagulation time did not differ between milk containing native micelles or reformed casein particles. Ethanol stability and heat stability, >pH 7.0, were lower for reformed casein particles than native micelles. Differences in heat stability, ethanol stability and zeta-potential can be explained in terms of the influence of increased concentrations of sodium and chloride ions in milk containing reformed casein particles. Hence, these results indicate that, if performed in a controlled manner, casein particles with properties closely similar to those of native micelles can be reformed from alkaline disrupted casein micelles.     

Consumer assessment of safety and date labeling statements on ready-to-eat meat and poultry products designed to minimize risk of listeriosis

Point-of-purchase safety-based labeling guidance on the proper storage and handling of refrigerated ready-to-eat (RTE) meat and poultry products could help reduce the risk of listeriosis. Seniors and pregnant women are two population groups at increased risk of listeriosis due to suppressed or compromised immune systems. We conducted 11 focus groups with senior-aged women and women of childbearing age in Colorado and Ohio to assess consumer awareness of Listeria, storage practices of RTE meat products, perceptions regarding the acceptability and usefulness of common date and potential food safety labeling statements on RTE meat and poultry products, and food safety information needs. Storage times for opened and unopened RTE products varied widely, with opened products often being stored longer than recommended. Women in both age groups paid attention to date labels on packages but varied highly in their interpretation of the statements. "Use by" statements were considered clearer and more helpful than "Sell by" or "Best if used by" labels. Proposed food safety-based labeling statements listing "antilisterial" agents used in RTE products were not well received. However, labels giving consumers instructions on how long they could keep RTE products and when to discard them after opening were considered helpful and well received. Participants indicated the need for further information about Listeria and its control. Educational information at point-of-purchase and where seniors and pregnant women congregate are suggested. Manufacturers are encouraged to provide more complete information on the safe storage and use of ready-to-eat meat and poultry products on package labels.     

Study on the effects of humic and fulvic acids on quantum dot nanoparticles using capillary electrophoresis with laser-induced fluorescence detection

The increasing production and use of quantum dot (QD) nanoparticles have caused concerns on the possibility of contaminating the aquatic and terrestrial ecosystems with wastes that may contain QDs. Therefore, studies on the behavior of QDs upon interaction with components of the natural environment have become of interest. This study investigated the fluorescence and electrophoretic mobility of carboxylic or amine polyethylene glycol (PEG)-functionalized CdSe/ZnS QDs in the presence of two aquatic humic substances (HS), Suwannee River humic and fulvic acids, using capillary electrophoresis with laser-induced fluorescence detection. Results showed initial enhancement in fluorescence of QDs at the onset of the interaction with HS, followed by fluorescence quenching at longer exposure with HS (>30 min). It was also observed that the electrophoretic mobility of QDs increases with increasing concentration of HS, suggesting an increase in the ratio in charge to hydrodynamic size of the nanoparticles. To determine if the QDs degraded upon interaction with HS, the QD-HS mixtures were dialyzed to separate free Cd2+ from intact QDs, followed by analysis of the solutions using inductively coupled plasma-mass spectrometry. Results suggested that degradation of QDs in the presence of HS did not occur within the period of incubation.     

Inhibition of verocytotoxigenic Escherichia coli by antimicrobial peptides caseicin A and B and the factors affecting their antimicrobial activities

The antimic robial activities of caseicin A and B antimicrobial peptides (AMPs) were assessed against a selection of verocytotoxigenic Escherichia coli (VTEC) strains (n = 11), other bacterial pathogenic and spoilage bacteria (n = 7), using a model broth system. The ability of the AMPs to retain their antimicrobial activities against a strain of E. coli O157:H7 380-94 under various test conditions (pH, temperature, water activity, sodium chloride concentrations, inoculum size and the presence of competitive microflora) was assessed and the minimum inhibitory concentrations (MIC) and number of surviving E. coli O157:H7 calculated. The mean number of VTEC surviving after exposure to 2 mg/ml caseicin A and B was reduced by 4.96 and 4.19 log₁₀ cfu/ml compared to the respective controls. The susceptibility of E. coli O157:H7 to the caseicin AMPs decreased as temperature, pH, water activity and inoculum size were reduced. The presence of sodium chloride (0.5-2.5%) did not affect the activity of caseicin A (p > 0.05), however it did inhibit the activity of caseicin B. The presence of a competitive microflora cocktail did not significantly (p > 0.05) affect the activities of the AMPs for the majority of the concentrations tested. Using a quantitative PCR assay, the levels of verotoxins (vt1 and vt2) expressed by E. coli O157:H7 following exposure to a sub-inhibitory concentration (0.5 mg/ml) of caseicin A showed that the verotoxin levels did not differ from the levels produced by the control cultures. The antimicrobial activity of caseicin A against E. coli O157:H7 was also tested in a model rumen system, however concentrations of ≥ 2 mg/ml did not significantly (p > 0.05) reduce E. coli O157:H7 numbers in the model system over a 24 h period. The application of caseicin AMPs in food and/or animal production may be valuable in combination with other antimicrobials although further research is required.