| 1. |
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Artursson, Tom, et al.
(författare)
-
Drift correction for gas sensors using multivariate methods
- 2000
-
Ingår i: Journal of Chemometrics. - 0886-9383 .- 1099-128X. ; 14:5-6, s. 711-723
-
Tidskriftsartikel (refereegranskat)abstract
- Drift is one of the most serious impairments afflicting gas sensors. It can be seen as a gradual change in the sensor response over a long period of time when the external conditions an constant. This paper presents a new simple drift counteraction method based on PCA and PLS. The basic idea is to remove the drift direction component from the measurements. The direction of the drift, p, is calculated from measurements for a reference gas. Projecting the sample gas measurements on this vector gives the score vector t. The drift component tp(T) can then he removed from the sample gas data, which we call component correction (CC). The method is tested on a data set based on a reduced factorial design with four gases and a concentration gradient of hydrogen. It is found that the method works efficiently for both cases. Copyright (C) 2000 John Wiley & Sons, Ltd.
|
|
| 9. |
- Artursson, Tom, et al.
(författare)
-
Study of Preprocessing Methods for the Determination of Crystalline Phases in Binary Mixtures of Drug Substances by X-ray Powder Diffraction and Multivariate Calibration
- 2000
-
Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 54:8, s. 272A-301A
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, various preprocessing methods were tested on data generated by X-ray powder diffraction (XRPD) in order to enhance the partial least-squares (PLS) regression modeling performance. The preprocessing methods examined were 22 different discrete wavelet transforms, Fourier transform, Savitzky-Golay, orthogonal signal correction (OSC), and combinations of wavelet transform and OSC, and Fourier transform and OSC. Root mean square error of prediction (RMSEP) of an independent test set was used to measure the performance of the various preprocessing methods. The best PLS model was obtained with a wavelet transform (Symmlet 8), which at the same time compressed the data set by a factor of 9.5. With the use of wavelet and X-ray powder diffraction, concentrations of less than 10% of one crystal from could be detected in a binary mixture. The linear range was found to be in the range 10-70% of the crystalline form of phenacetin, although semiquantitative work could be carried out down to a level of approximately 2%. Furthermore, the wavelet-pretreated models were able to handle admixtures and deliberately added noise.
|
|
| 10. |
|
|
| 11. |
|
|
| 12. |
|
|
| 13. |
|
|
| 14. |
- Köping-Hoggard, M, et al.
(författare)
-
Relationship between the physical shape and the efficiency of oligomeric chitosan as a gene delivery system in vitro and in vivo
- 2003
-
Ingår i: Journal of Gene Medicine. - : Wiley. - 1521-2254 .- 1099-498X. ; 5:2, s. 130-141
-
Tidskriftsartikel (refereegranskat)abstract
- Background Chitosans of high molecular weights have emerged as efficient. nonviral gene delivery systems, but the properties and efficiency of well-defined low molecular weight chitosans ((.) 5 kDa) have not been studied. We therefore characterized DNA complexes Of Such low molecular weight chitosans and related their physical shape and stability to their efficiency as gene delivery systems in vitro and in vivo.Methods Individual complexes between six different chitosan oligomers (6-, 8-, 10-, 12-, 14- and 24-mers) and fluorescence-labeled T4 DNA were visualized and classified into six physical shapes using video-enhanced fluorescence microscopy. The effects of chitosan chain length, charge ratio (+/-) and solvent properties (pH and ionic strength) on the stability and structure of the complexes were studied. Gene expression in vitro and in vivo were studied using a luciferas reporter gene.Results Free DNA appeared as extended coils. Chitosan complexes had, a variety of physical shapes depending on the experimental conditions. in general, the fraction of complexes that had nonaggregated, globular structures increased with increasing chain length of the chitosan oligomer, increasing charge ratio and reduction of pH (from 6.5 to 3.5). A further increase in charge ratio for globular complexes or a further reduction in pH (to 2.5) increased the fraction of aggregates, indicating a window where pharmaceutically desirable globules are obtained. Gene transfection efficiencies in vitro and in vivo were related to the physical shape and stability of the complexes. Only the 24-mer formed stable complexes that gave a high level of gene expression comparable to that of high molecular weight ultrapure chitosan (UPC) in vitro and in vivo.Conclusions Chitosan oligomers form complexes with DNA in a structure-dependent manner. We conclude that the 24-mer, which has more desirable physical prope ties than UPC, is more attractive as a gene delivery system than the conventional high molecular weight chitosans. Copyright (C) 2002 John Wiley Sons, Ltd.
|
|
| 15. |
|
|
| 16. |
|
|
| 17. |
|
|
| 18. |
|
|
| 19. |
|
|
| 20. |
|
|
| 21. |
|
|
| 22. |
|
|
| 23. |
|
|
