| 1. |
- Sadowski, J., et al.
(författare)
-
Structural and magnetic properties of molecular beam epitaxy grown GaMnAs layers
- 2000
-
Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 18:3, s. 1697-1700
-
Tidskriftsartikel (refereegranskat)abstract
- GaMnAs layers with Mn contents from 0.05% to 7% were grown by low temperature molecular beam epitaxy. At substrate temperatures lower than 300 degrees C and in this composition range a uniform ternary GaMnAs compound can be grown without MnAs precipitation. Reflection high energy electron diffraction intensity oscillations recorded during GaMnAs growth were used to calibrate the composition of the GaMnAs films with high accuracy (better than 0.1%). Films containing more than 1% Mn exhibit a ferromagnetic phase transition with Curie temperatures from a few up to 70 K depending on the composition and other growth parameters. In contrast to previous reports we have observed this transition also in the case of layers grown at very low substrate temperatures (below 300 degrees C).
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
- Gaist, D, et al.
(författare)
-
Stroke research in GenomEUtwin
- 2003
-
Ingår i: Twin research : the official journal of the International Society for Twin Studies. - : Cambridge University Press (CUP). - 1369-0523. ; 6:5, s. 442-447
-
Tidskriftsartikel (refereegranskat)
|
|
| 5. |
- Jensen, PS, et al.
(författare)
-
Determination of urea, glucose, and phosphate in dialysate with Fourier transform infrared spectroscopy
- 2004
-
Ingår i: Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy. - 1386-1425. ; 60:4, s. 899-905
-
Tidskriftsartikel (refereegranskat)abstract
- Individual control and quantification of phosphate removal is desirable in dialysis treatment. Currently, no on-line method exists to quantify phosphate removal. We demonstrate that a multivariate calibration model based on infrared transmission spectra is capable of predicting phosphate, urea, and glucose concentrations at clinically relevant levels. The on-line monitoring of these components by infrared spectroscopy is therefore feasible. (C) 2003 Elsevier B.V. All rights reserved.
|
|
| 6. |
- Jensen, PS, et al.
(författare)
-
Fourier transform infrared spectroscopy of aqueous solutions using optical subtraction
- 2002
-
Ingår i: OPTICAL DIAGNOSTICS AND SENSING OF BIOLOGICAL FLUIDS AND GLUCOSE AND CHOLESTEROL MONITORING II. - : SPIE. - 1996-756X .- 0277-786X. - 0819443638 ; 4624, s. 150-159
-
Konferensbidrag (refereegranskat)abstract
- For the analysis of small concentrations of organics in aqueous solutions, a novel add-on accessory for dual-beam / optical subtraction spectroscopy has been built for a commercial Fourier transform infrared spectrometer. A standard FT-IR instrument requires a sample measurement and a separate reference measurement, whereas the optical subtraction instrument directly measures the difference between sample and reference. This has a number of advantages. The time delay between the two measurements is eliminated, and the effective measurement time is improved by a factor of two. Moreover, the optical subtraction provides a large reduction in dynamic range of the measured signal, which prevents detector saturation, and enables effective use of dynamic range of the analog to digital converter in the FT-IR spectrometer. This results in an increased signal to noise ratio, compared to the standard FT-IR instrument. By changing detector and light source the instrument may be used for both near- and mid.-infrared spectroscopy. The increased sensitivity and stability of the optical subtraction instrument compared to the standard instrument is demonstrated by transmission measurements of aqueous urea solutions in the combination band region 4000 to 5000cm(-1) (2000 to 2500nm).
|
|
| 7. |
- Jensen, PS, et al.
(författare)
-
Influence of temperature on water and aqueous glucose absorption spectra in the near- and mid-infrared regions at physiologically relevant temperatures
- 2003
-
Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 57:1, s. 28-36
-
Tidskriftsartikel (refereegranskat)abstract
- Near- and mid-infrared absorption spectra of pure water and aqueous 1.0 g/dL glucose solutions in the wavenumber range 8000-950 cm(-1) were measured in the temperature range 30-42 C in steps of 2 degreesC. Measurements were carried out with an FT-IR spectrometer and a variable pathlength transmission cell controlled within 0.02 degreesC. Pathlengths of 50 mum and 0.4 mm were used in the mid- and near-infrared spectral region, respectively. Difference spectra were used to determine the effect of temperature on the water spectra quantitatively. These spectra were obtained by subtracting the 37 degreesC water spectrum from the spectra measured at other temperatures. The difference spectra reveal that the effect of temperature is highest in the vicinity of the strong absorption bands, with a number of isosbestic points with no temperature dependence and relatively flat plateaus in between. On the basis of these spectra, prospects for and limitations on data analysis for infrared diagnostic methods are discussed. As an example, the absorptive properties of glucose were studied in the same temperature range in order to determine the effect of temperature on the spectral shape of glucose. The change in water absorption associated with the addition of glucose has also been studied. An estimate of these effects is given and is related to the expected level of infrared signals from glucose in humans.
|
|
| 8. |
- Jensen, PS, et al.
(författare)
-
Online monitoring of urea concentration in dialysate with dual-beam Fourier-transform near-infrared spectroscopy
- 2004
-
Ingår i: Journal of Biomedical Optics. - : SPIE-Intl Soc Optical Eng. - 1083-3668. ; 9:3, s. 553-557
-
Tidskriftsartikel (refereegranskat)abstract
- The robustness of a dual-beam, optical null, Fourier-transform near-infrared (FTNIR) spectrometer was investigated by means of online, near-infrared measurements and predictions of urea concentrations in spent dialysate during hemodialysis treatment. Simple multivariate calibration using a few factors based on a small number of prepared samples provided stable and accurate predictions over a period of 1 month. The calibration was robust when faced with adjustment of reference cell intensity and did not require a daily measured reference spectrum. The root-mean-square error of prediction of urea was 0.4 mM based on a two-factor partial least-squares regression model. (C) 2004 Society of Photo-Optical Instrumentation Engineers.
|
|
| 9. |
- Snoer Jensen, Peter, et al.
(författare)
-
Near-infrared transmission spectroscopy of aqueous solutions: Influence of optical pathlength on signal-to-noise ratio
- 2002
-
Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 56:12, s. 1600-1606
-
Tidskriftsartikel (refereegranskat)abstract
- The optimal choice of optical pathlength, source intensity, and detector for near-infrared transmission measurements of trace components in aqueous solutions depends on the strong absorption of water. In this study we examine under which experimental circumstances one may increase the pathlength to obtain a measurement with higher signal-to-noise ratio. The noise level of measurements at eight different pathlengths from 0.2 to 2.0 mm of pure water and of 1 g/dL aqueous glucose signals were measured using a Fourier transform near-infrared spectrometer and a variable pathlength transmission cell. The measurements demonstrate that the noise level is determined by the water transmittance. The noise levels in the spectral region from 5000 to 4000 cm(-1) show that the optimal pathlength (0.4 mm) is the same for pure water and 1 g/dL aqueous glucose solutions. When detector saturation occurs it is favorable to increase the pathlength instead of attenuating the light source. The obtained results are explained by an analytical model.
|
|
