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51.
52.
Vaclav Synek 《Accreditation and quality assurance》2001,6(8):360-367
Linear regression of calibration lines passing through the origin was investigated for three models of y-direction random errors: normally distributed errors with an invariable standard deviation (SD) and log normally and normally
distributed errors with an invariable relative standard deviation (RSD). The weighted (weighting factor is x
2
i
), geometric and arithmetic means of the ratios y
i
/x
i
estimate the calibration slope for these models, respectively. Regression of the calibration lines with errors in both directions
was also studied. The x-direction errors were assumed to be normally distributed random errors with either an invariable SD or invariable RSD, both
combined with a constant relative systematic error. The random errors disperse the true, unknown x-values about the plotted, demanded x-values, which are shifted by the constant relative systematic error. The systematic error biases the slope estimate while
the random errors do not. They only increase automatically the slope estimate uncertainty, in which the uncertainty component
reflecting the range of the possible values of the systematic error must be additionally included.
Received: 9 May 2000 Accepted: 7 March 2001 相似文献
53.
Bedrˇich Kosˇata Václav Kozmik Jirˇí Svoboda Vladimíra Novotná Prˇemysl Vaneˇk Milada Glogarová 《Liquid crystals》2013,40(5):603-610
Four series of new [1]benzothieno[3,2- b][1]benzothiophene derivatives have been synthesized. In the non-chiral series a SmA phase occurs, while the chiral series exhibits a rather wide antiferroelectric SmCA* phase just below the SmA phase. The SmA-SmCA* phase transition has been studied using DSC and dielectric spectroscopy. In the SmCA* phase the spontaneous quantities have been measured. The tilt angle shows a typical temperature dependence and the values of spontaneous polarization are rather moderate. The length of the helical pitch increases on increasing the length of the non-chiral alkyl chain. 相似文献
54.
An interaction of the free turbulent shear flow and the steady temperature field, which develops to the homogeneity, was studied. The temperature field was generated by parallel thin heated wires. The isotropic grid turbulence is supposed. Heated wire generates large cross temperature gradients and development of the temperature field was investigated experimentally. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
55.
Sylvie Skalickova Ondrej Zitka Lukas Nejdl Sona Krizkova Jiri Sochor Libor Janu Marketa Ryvolova David Hynek Jarmila Zidkova Vaclav Zidek Vojtech Adam Rene Kizek 《Chromatographia》2013,76(7-8):345-353
Quantum dots (QDs) belong to a new class of fluorescent agent for biochemical, medicinal or other purposes. However, QDs based on cadmium or other metals can be risky for an organism. As one of the mechanism how to detoxify cadmium-based QDs expression of metallothioneins (MT) can be considered. Due to high affinity of metallothionein to cadmium(II) ions, we attempted to develop an approach for studying of possible interaction with QDs. We prepared QDs with CdTe core and studied the interaction with MT, which we isolated from livers of Cd-administered rabbits. To study the interaction, we used the mixture of both components MT (3.6 μM): CdTe QDs (0, 0.34, 0.68, 1.02, 1.36, 1.7, 2.04 and 2.47 μM). The mixtures were studied by spectrophotometry within the range from 200 to 750 nm with detected maxima at 260 and 505 nm. Same mixtures were also analysed by differential pulse voltammetry Brdicka reaction, which supported data from spectrophotometry. Subsequently, we used fast protein liquid chromatography for purification of protein–quantum dot conjugates. We obtained the different chromatograms for (1) Apo MT, (2) CdTe QDs and (3) MT–QD complex. We also collected the fractions and subsequently analysed them on the content of Cd and MT, which confirmed the formation of CdTe QDs–MT complex. 相似文献
56.
A recently discovered anion receptor is jointed by three related macrocycles differing in the number of glycoluril units and type of substitution. The synthesis is carried out in nonpolar solvents compared to aqueous media used in the case of the original macrocycle. The size of macrocycle is controlled by a template. A hexameric macrocycle with benzyl substitution binds halide anions with an affinity exceeding 10(9) M(-1) while a tetrameric analog does not bind any of the investigated anions. 相似文献
57.
Alena Reznickova Zdenka Kolska Vladimir Hnatowicz Vaclav Svorcik 《Journal of nanoparticle research》2011,13(7):2929-2938
Properties of pristine, plasma modified, and etched (by water and methanol) polytetrafluoroethylene (PTFE) were studied. Gold
nanolayers sputtered on this modified PTFE have been also investigated. Contact angle, measured by goniometry, was studied
as a function of plasma exposure and post-exposure aging times. Degradation of polymer chains was examined by etching of plasma
modified PTFE in water or methanol. The amount of ablated and etched layer was measured by gravimetry. In the next step the
pristine, plasma modified, and etched PTFE was sputtered with gold. Changes in surface morphology were observed using atomic
force microscopy. Chemical structure of modified polymers was characterized by X-ray photoelectron spectroscopy (XPS). Surface
chemistry of the samples was investigated by electrokinetic analysis. Sheet resistance of the gold layers was measured by
two-point technique. The contact angle of the plasma modified PTFE decreases with increasing exposure time. The PTFE amount,
ablated by the plasma treatment, increases with the plasma exposure time. XPS measurements proved that during the plasma treatment
the PTFE macromolecular chains are degraded and oxidized and new –C–O–C–, –C=O, and –O–C=O groups are created in modified
surface layer. Surface of the plasma modified PTFE is weakly soluble in methanol and intensively soluble in water. Zeta potential
and XPS shown dramatic changes in PTFE surface chemistry after the plasma exposure, water etching, and gold deposition. When
continuous gold layer is formed a rapid decrease of the sheet resistance of the gold layer is observed. 相似文献
58.
In ultrasonic non-destructive testing of materials with a coarse-grained structure the scattering from the grains causes backscattering noise, which masks flaw echoes in the measured signal. Several filtering methods have been proposed for improving the signal-to-noise ratio. In this paper we present a comparative study of methods based on the wavelet transform. Experiments with stationary, discrete and wavelet packet de-noising are evaluated by means of signal-to-noise ratio enhancement. Measured and simulated ultrasonic signals are used to verify the proposed de-noising methods. For comparison, we use signal-to-noise ratio enhancement related to fault echo amplitudes and filtering efficiency specific for ultrasonic signals. The best results in our setup were achieved with the wavelet packet de-noising method. 相似文献
59.
Jing B Janout V Herold BC Klotman ME Heald T Regen SL 《Journal of the American Chemical Society》2004,126(49):15930-15931
A series of persulfated molecular umbrellas have been synthesized from putrescine, spermidine, spermine, lysine, and cholic acid (1a, 2a, 3a, 4a, and 5a) and their anti-HIV and anti-HSV activities determined. Despite it size, the most active of these conjugates (5a) was able to cross phospholipid bilayers made from 1-palmitoyl-2-oleyol-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (POPG). The unique combination of anti-viral activity, an ability to cross hydrophobic barriers, a lack of cytotoxicity, and a simple three-step synthesis from biogenic starting material suggests that 5a and related conjugates may be exploitable as a novel class of anti-viral agents for systemic and topical applications. 相似文献
60.
Dr. Mirza Arfan Yawer Vaclav Havel Prof. Vladimir Sindelar 《Angewandte Chemie (International ed. in English)》2015,54(1):276-279
Synthetic receptors that function in water are important for the qualitative and quantitative detection of anions, which may act as pollutants in the environment or play important roles in biological processes. Neutral receptors are particularly appealing because they are often more selective than positively charged receptors; however, their affinity towards anions in pure water is only in range of 1–103 L mol?1. The anion‐templated synthesis of a water‐soluble bambusuril derivative is shown to be an outstanding receptor for various inorganic anions in pure water, with association constants of up to 107 L mol?1. Furthermore, the macrocycle discriminates between anions with unprecedented selectivity (up to 500 000‐fold). We anticipate that the combination of remarkable affinity and selectivity of this macrocycle will enable the efficient detection and isolation of diverse anions in aqueous solutions, which is not possible with current supramolecular systems. 相似文献