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Giovanni Baccolo Massimiliano Clemenza Barbara Delmonte Niccolò Maffezzoli Massimiliano Nastasi Ezio Previtali Michele Prata Andrea Salvini Valter Maggi 《Analytica chimica acta》2016
Dust found in polar ice core samples present extremely low concentrations, in addition the availability of such samples is usually strictly limited. For these reasons the chemical and physical analysis of polar ice cores is an analytical challenge. In this work a new method based on low background instrumental neutron activation analysis (LB-INAA) for the multi-elemental characterization of the insoluble fraction of dust from polar ice cores is presented. Thanks to an accurate selection of the most proper materials and procedures it was possible to reach unprecedented analytical performances, suitable for ice core analyses. The method was applied to Antarctic ice core samples. Five samples of atmospheric dust (μg size) from ice sections of the Antarctic Talos Dome ice core were prepared and analyzed. A set of 37 elements was quantified, spanning from all the major elements (Na, Mg, Al, Si, K, Ca, Ti, Mn and Fe) to trace ones, including 10 (La, Ce, Nd, Sm, Eu, Tb, Ho, Tm, Yb and Lu) of the 14 natural occurring lanthanides. The detection limits are in the range of 10−13–10−6 g, improving previous results of 1–3 orders of magnitude depending on the element; uncertainties lies between 4% and 60%. 相似文献
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Edjane F. B. Silva Marcílio P. Ribeiro Luzia P. F. C. Galvão Valter J. Fernandes Antonio S. Araujo 《Journal of Thermal Analysis and Calorimetry》2011,103(2):465-469
Degradation of low density polyethylene (LDPE) was studied for the pure polymer and mixed with silicoaluminophosphate SAPO-11
catalyst. SAPO-11 was synthesized by hydrothermal method using di-isoprolpylamine as structure template, and characterized
by XRD and SEM. From X-ray diffraction, it was observed that SAPO-11 was obtained with high crystallinity. Using the model-free
kinetics, proposed by Vyazovkin, the activation energies were determined for the process of polymer degradation. It was found
that the degradation process of 90% of LDPE mixed with SAPO-11 over a period of 1 h, occurred at a temperature of 378 °C,
while for the pure LDPE, the temperature was increased to 434 °C in the same period of time and conversion, indicating that
SAPO-11 was an effective catalyst for the degradation of LDPE. The activation energy for the degradation of pure LDPE was
equivalent to 251 kJ mol−1. Also, when the SAPO-11 was mixed with the polymer, this value was decreased to 243 kJ mol−1. 相似文献
65.
Haywood NR Chang IC Ciocca V 《The Journal of the Acoustical Society of America》2011,130(3):1503-1514
Three experiments measured the perceived continuity of two pure tones "flankers" through a masker containing a silence. Experiment 1 used a 2I-2AFC procedure; one interval contained two noise bursts separated by a silent gap, and the other contained two noise bursts separated by a tone of the same duration as the silence. Discrimination between masker conditions was very accurate when the flankers were absent but was impaired substantially when the flankers were present. This was taken as evidence that illusory flanker continuity during the silent gap was heard as similar to the physical presence of a tone in the gap. In experiment 2, performance remained poor when the flankers were frequency glides aligned along a common trajectory. Performance improved significantly when the flankers were misaligned in trajectory. In experiment 3, listeners rated directly perceived flanker continuity. Strong continuity was reported in the silent gap conditions for which poor performance had been observed in experiments 1 and 2. These findings show that continuity may be heard through a masker that cannot mask a physically continuous tone but can mask the flankers' offset and onset. The results are explained in terms of the perceptual grouping of onsets and offsets of the flankers. 相似文献
66.
Alois Bonifacio Silvia Dalla Marta Riccardo Spizzo Silvia Cervo Agostino Steffan Alfonso Colombatti Valter Sergo 《Analytical and bioanalytical chemistry》2014,406(9-10):2355-2365
Surface-enhanced Raman spectroscopy (SERS) is a good candidate for the development of fast and easy-to-use diagnostic tools, possibly used on biofluids in point-of-care or screening tests. In particular, label-free SERS spectra of blood serum and plasma, two biofluids widely used in diagnostics, could be used as a metabolic fingerprinting approach for biomarker discovery. This study aims at a systematic evaluation of SERS spectra of blood serum and plasma, using various Ag and Au aqueous colloids, as SERS substrates, in combination with three excitation lasers of different wavelengths, ranging from the visible to the near-infrared. The analysis of the SERS spectra collected from 20 healthy subjects under a variety of experimental conditions revealed that intense and repeatable spectra are quickly obtained only if proteins are filtered out from samples, and an excitation in the near-infrared is used in combination with Ag colloids. Moreover, common plasma anticoagulants such as EDTA and citrate are found to interfere with SERS spectra; accordingly, filtered serum or heparin plasma are the samples of choice, having identical SERS spectra. Most bands observed in SERS spectra of these biofluids are assigned to uric acid, a metabolite whose blood concentration depends on factors such as sex, age, therapeutic treatments, and various pathological conditions, suggesting that, even when the right experimental conditions are chosen, great care must be taken in designing studies with the purpose of developing diagnostic tests. 相似文献
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68.
Marco Antonio P. Queirol Joo Tessarioli Neto Valter Arthur Frederico M. Wiendl Anna Lucia C. H. Villavicencio 《Radiation Physics and Chemistry》2002,63(3-6):341-343
After irradiating with a single dose of 50 Gy, ginger rhizomes were dipped into paraffin for coating, wrapped in a plastic film of low-density polyethylene, on perforated or non-perforated polivinyl chloride film, and compared with non-wrapping and non-irradiation as the controls. After treatments the rhizomes were maintained refrigerated at 13°C and 80% relative humidity. As a main result it could be observed that dipping into paraffin and wrapping with plastics resulted in smaller weight loss of the rhizomes. 相似文献
69.
Maša Islamčević Razboršek Darinka Brodnjak Vončina Valter Doleček Ernest Vončina 《Chromatographia》2008,67(5-6):433-440
Phytochemical investigations of different species of Lamiaceae family (rosemary-Rosmarinus officinalis L., sage-Salvia officinalis L., winter savory-Satureja montana L., clary sage-Salvia sclarea L. and sticky sage-Salvia glutinosa L.), using gas chromatography and mass spectrometry (GC-MS) were performed. The studies were focused on oleanolic, betulinic
and ursolic acid. Since oleanolic and ursolic acid are position isomers with very similar structures, the difficulties in
their separation and identification have been reported by several authors. However, both compounds can be well distinguished
by order of elution during gas chromatography and by intensities of the fragment ion signals in their mass spectra, where
the retro-Diels-Alder reaction was primarily observed. A combination of ultrasonic extraction, solid phase extraction, size
exclusion chromatography, trimethylsilylation, and GC-MS resulted in simultaneous separation, identification and quantification
of the mentioned compounds. The compounds have been identified by retention time and comparison of mass spectra with those
of pure standards. The mass spectral fragmentation behavior of all three derivatised acids was investigated. The obtained
characteristic fragment patterns are discussed in the presented work. Good linearity over the concentration range 1–50 mg
L−1 for all three compounds was confirmed. The correlation coefficients (r
2
) were in the range of 0.9980–0.9983. Quantitative analyses of different Lamiaceae extracts showed that the oleanolic acid content ranged from 0.09 to 0.9% dry weight, content of betulinic acid ranged from
traces to 0.6%, and that of ursolic acid varied from 0.09 to 1.6% dry weight. 相似文献
70.