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排序方式: 共有105条查询结果,搜索用时 187 毫秒
1.
Pirita Rämänen Paavo A. Penttilä Kirsi Svedström Sirkka Liisa Maunu Ritva Serimaa 《Cellulose (London, England)》2012,19(3):901-912
Cellulose whiskers were prepared from wood- and cotton-based microcrystalline cellulose and dried by two methods: freeze-drying
or air-drying. The effect of drying method on the properties and structure of the whiskers were studied. Furthermore, the
influence of the source of cellulose on the nanoscale structure was investigated. Drying method was observed to slightly influence
the thermal stability of cellulose whiskers, whereas the char residue varied significantly depending on the drying process
performed. Small- and wide-angle X-ray scattering and solid state nuclear magnetic resonance spectroscopy were used to examine
the crystallinity and nanoscale structure of the dried whiskers. It was observed that the crystal structure and crystallinity
of cellulose whiskers remained during all treatments, whereas their nanoscale structure was significantly influenced by drying
method, neutralization, and source of cellulose. Relationships between thermal behavior and nanoscale structure were reported
and discussed. 相似文献
2.
Nikolaos Pahimanolis Arto Salminen Paavo A. Penttilä Juuso T. Korhonen Leena-Sisko Johansson Janne Ruokolainen Ritva Serimaa Jukka Seppälä 《Cellulose (London, England)》2013,20(3):1459-1468
In this paper, nanofibrillated cellulose/carboxymethyl cellulose (CMC) composite films were prepared using tape casting. The obtained transparent films showed shear induced partial alignment of fibrils along the casting direction, resulting in birefringence in cross polarized light. The carboxyl groups of CMC could be further utilized to create ionic crosslinking by treatment with glycidyl trimethyl ammonium chloride (GTMA). The GTMA treated composite films had improved mechanical properties both in wet and dry state. The chemical composition and morphologies of composites were analyzed with X-ray photoelectron spectroscopy, elemental analysis, scanning electron microscopy and wide-angle X-ray scattering. 相似文献
3.
Paavo Salminen 《Probability Theory and Related Fields》1990,85(1):43-56
Summary In this note stochastic calculus is used to characterise multiplicative excessive functions of a binary branching Brownian motion with a constant creation rate. Some properties of the martingales given by invariant functions are studied. In particular, it is seen that these positive and unbounded martingales tend a.s. to 0 and are not square integrable. Informally speaking, they exhibit a clustering phenomenon in the underlying supercritical branching Brownian motion.This work was done while the author was visiting the University of British Columbia, Mathematical Department, and was partly supported by a NSERC grant. AMS 1980 subject classifications: primary 60J80, 60J65 secondary 60J60 相似文献
4.
SUMMARY: The aim of this study was to investigate how different acoustic parameters, extracted both from speech pressure waveforms and glottal flows, can be used in measuring vocal loading in modern working environments and how these parameters reflect the possible changes in the vocal function during a working day. In addition, correlations between objective acoustic parameters and subjective voice symptoms were addressed. The subjects were 24 female and 8 male customer-service advisors, who mainly use telephone during their working hours. Speech samples were recorded from continuous speech four times during a working day and voice symptom questionnaires were completed simultaneously. Among the various objective parameters, only F0 resulted in a statistically significant increase for both genders. No correlations between the changes in objective and subjective parameters appeared. However, the results encourage researchers within the field of occupational voice use to apply versatile measurement techniques in studying occupational voice loading. 相似文献
5.
Pekka V?h?oja Ilkka V?lim?ki Katri Heino Paavo Per?m?ki Toivo Kuokkanen 《Analytical sciences》2005,21(11):1365-1369
Certain wear metals (Fe, Cr, Ni, Cu and Zn) of various lubrication oils were determined by means of ICP-OES and FAAS. The kerosene dilution method, which is used widely together with ICP-OES, was applied with both methods here. Calibration standards were made from a commercial organo-metallic standard. Our aim was to clarify the possibility of using the quick kerosene dilution method together with FAAS for a rapid check for certain indicator metals. Metal determinations with FAAS were accurate enough for quantitative work in machine condition diagnostics and waste oil characterization, when compared with those with ICP-OES. 相似文献
6.
In this paper we introduce a storage process with singular continuous input. The input process is defined as the local time of a stationary reflecting Brownian motion with drift. Many basic charateristics of the process are computed explicitly, e.g., stationary distribution, distributions of the starting and ending time of on-going busy and idle periods. We also consider the multifractal spectrum of the input process and observe that it is independent of system parameters. 相似文献
7.
The 13C NMR spectra of C-10 epimeric chlorophylls a and a′, pheophytins a and a′, pyrochlorophyll a and pyropheophytin a have been recorded and assigned by chemical shift comparison, by long-range selective 1H decoupling experiments and by the examination of the fully coupled spectra. Various factors influencing the 13C chemical shifts of the chlorophyll derivatives, e.g. the coordination of magnesium to the chlorin nucleus, the effect of solvent and the steric strain at the periphery of the macrocycle, have been examined. The 13C NMR spectra of chlorophyll a measured in acetone-d6 and tetrahydrofuran-d8 (THF) were compared, and remarkable solvent effects on the 13C chemical shifts were observed. These effects were interpreted mostly in terms of specific chlorophyll-solvent interactions. Different electron donor and steric properties of acetone and THF were considered to cause conformational alterations in the macrocycle, induced by the ligation of the solvent molecule(s) to the axial position(s) of the central magnesium atom of chlorophyll a. These results show that 13C NMR spectroscopy is a method of high information value for investigations of the unique electron donor acceptor (EDA) properties of the chlorophylls. The structural differences between the C-10 epimeric chlorophylls and pheophytins were examined in terms of the substituent chemical shift (SCS) parameters for the C-10 methoxycarbonyl group. The analysis showed that the change from the (10R) to the 10(S) configuration induces conformational alterations in the whole macrocycle which are, however, most prominent in rings IV and V. Owing to the increased steric interaction (repulsion) between the bulky substituents at C-7 and C-10, the peripheral strain is larger in the (10S) form, and is relieved by more pronounced deviations of rings IV and V from the macrocyclic plane compared with the (10R) form. The examination of the SCS parameters also showed that the peripheral steric strain is dissipated to a larger extent over the entire macrocycle in the Mg-free derivatives. These results confirm the previous conclusions based on 1H NMR and CD data. The possible function of chlorophyll a′ in photosynthesis is briefly discussed. 相似文献
8.
Pyropheophytin a, which is an unsymmetric porphyrin, has been titrated with trifluoroacetic acid (TFA) in tetrahydrofuran, the protonation reaction being followed by 13C NMR spectroscopy. TFA was added in small increments to a 0.28 M solution of pyropheophytin a in tetrahydrofuran, and the chemical shift changes of the macrocyclic carbons were determined as a function of the TFA increments. On the addition of TFA the signals of the α-carbons of ring II experienced a large upfield change, whereas the signals of all other macrocyclic carbons moved only slightly downfield or remained constant. These observations were interpreted as indicating the formation of a monocation in which the proton is attached to the nitrogen of ring II. The 13C protonation shifts of pyropheophytin a were compared with those previously reported for symmetric porphyrins. On the basis of this comparison, the basicity of the macrocyclic nitrogen atoms, the N–H tautomerism and the electron delocalization in structurally different porphyrin macrocycles are discussed. 相似文献
9.
Eira Jansson-Verkasalo Timo Ruusuvirta Minna Huotilainen Paavo Alku Elena Kushnerenko Kalervo Suominen Seppo Rytky Mirja Luotonen Tuula Kaukola Uolevi Tolonen Mikko Hallman 《BMC neuroscience》2010,11(1):1-7
Background
Protein aggregation plays important roles in several neurodegenerative disorders. For instance, insoluble aggregates of phosphorylated tau and of Aβ peptides are cornerstones in the pathology of Alzheimer's disease. Soluble protein aggregates are therefore potential diagnostic and prognostic biomarkers for their cognate disorders. Detection of the aggregated species requires sensitive tools that efficiently discriminate them from monomers of the same proteins. Here we have established a proximity ligation assay (PLA) for specific and sensitive detection of Aβ protofibrils via simultaneous recognition of three identical determinants present in the aggregates. PLA is a versatile technology in which the requirement for multiple target recognitions is combined with the ability to translate signals from detected target molecules to amplifiable DNA strands, providing very high specificity and sensitivity.Results
For specific detection of Aβ protofibrils we have used a monoclonal antibody, mAb158, selective for Aβ protofibrils in a modified PLA, where the same monoclonal antibody was used for the three classes of affinity reagents required in the assay. These reagents were used for detection of soluble Aβ aggregates in solid-phase reactions, allowing detection of just 0.1 pg/ml Aβ protofibrils, and with a dynamic range greater than six orders of magnitude. Compared to a sandwich ELISA setup of the same antibody the PLA increases the sensitivity of the Aβ protofibril detection by up to 25-fold. The assay was used to measure soluble Aβ aggregates in brain homogenates from mice transgenic for a human allele predisposing to Aβ aggregation.Conclusions
The proximity ligation assay is a versatile analytical technology for proteins, which can provide highly sensitive and specific detection of Aβ aggregates - and by implication other protein aggregates of relevance in Alzheimer's disease and other neurodegenerative disorders. 相似文献10.
Yrttiaho S Tiitinen H May PJ Leino S Alku P 《The Journal of the Acoustical Society of America》2008,123(4):2191-2199
Previous non-invasive brain research has reported auditory cortical sensitivity to periodicity as reflected by larger and more anterior responses to periodic than to aperiodic vowels. The current study investigated whether there is a lower fundamental frequency (F0) limit for this effect. Auditory evoked fields (AEFs) elicited by natural-sounding 400 ms periodic and aperiodic vowel stimuli were measured with magnetoencephalography. Vowel F0 ranged from normal male speech (113 Hz) to exceptionally low values (9 Hz). Both the auditory N1m and sustained fields were larger in amplitude for periodic than for aperiodic vowels. The AEF sources for periodic vowels were also anterior to those for the aperiodic vowels. Importantly, the AEF amplitudes and locations were unaffected by the F0 decrement of the periodic vowels. However, the N1m latency increased monotonically as F0 was decreased down to 19 Hz, below which this trend broke down. Also, a cascade of transient N1m-like responses was observed in the lowest F0 condition. Thus, the auditory system seems capable of extracting the periodicity even from very low F0 vowels. The behavior of the N1m latency and the emergence of a response cascade at very low F0 values may reflect the lower limit of pitch perception. 相似文献