| 1. |
- Griffiths, P. C., et al.
(författare)
-
Small-angle neutron scattering, electron paramagnetic resonance, electrophoretic NMR, and time-resolved fluorescence quenching studies of sodium dodecyl sulfate and tetra(ethylene oxide) dodecyl ether mixed surfactant micelles
- 2004
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 108:4, s. 1351-1356
-
Tidskriftsartikel (refereegranskat)abstract
- Small-angle neutron scattering (SANS), time-resolved fluorescence quenching (TRFQ), electrophoretic NMR (ENMR), and electron paramagnetic resonance (EPR) have been used to study mixed micelles formed from the two dodecyl tailed surfactants, sodium dodecyl sulfate (SDS) and tetra(ethylene oxide) dodecyl ether. By combining the TRFQ and EPR techniques, one is essentially able to calculate the SANS data, lending significant weight to the micelle characteristics thus obtained. EPR reports the degree of hydration of the surfactant headgroups; TRFQ, the micelle aggregation number and inter alia the volume of the hydrophobic core. Given the physical dimensions of the surfactant, i.e., alkyl chain length, headgroup volumes, etc., it is then possible to calculate the micelle ellipticity and shell thickness. The ENMR studies provide a rather different but complementary estimate of the ionic character of the micelle. With increasing nonionic content, the aggregation number increases, the micelle becomes more elliptical, and the headgroup region of the micelle becomes less hydrated and significantly more viscous. The degree of sodium counterion dissociation shows an initial small decrease with decreasing SDS micelle mole fraction but subsequently increases, reflecting the interplay between the electrostatic character of the micelle surface and the micelle curvature.
|
|
| 2. |
|
|
| 3. |
- Fiedler, Heidelore, 1953-, et al.
(författare)
-
PCDD/PCDF, chlorinated pesticides and PAH in Chinese teas
- 2002
-
Ingår i: Chemosphere. - : Elsevier. - 0045-6535 .- 1879-1298. ; 46:9-10, s. 1429-1433
-
Tidskriftsartikel (refereegranskat)abstract
- Four samples of Chinese tea (two green teas, and two brick teas) were analyzed for their concentrations of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/PCDF), chlorinated pesticides and PAH. The infusions prepared from these teas were also analyzed for PCDD/PCDF. The levels of DDT and its metabolites in tea leaves were within the safety limit of 0.2 mg/kg. Rather high levels of total PAH were obtained in brick tea (1048-1162 mg/kg), when compared with green tea (497-517 mg/kg). In terms of PCDD/PCDF, the concentrations of green tea and brick tea differed by a factor of 16, while the concentrations of all infusions were within a factor of 2. The dioxin concentrations in green tea leaves can be explained through uptake of atmospheric PCDD/PCDF. The higher concentrations in the brick tea leaves are due the longer exposure time, and to certain extent, the use of old leaves, branches and roots when making the tea, and additional components such as soil particulates through contamination. Certain Chinese populations drinking a large amount of brick tea (>31 per day) indicated that individuals of these populations consume more tea than Europeans or North Americans result in a comparably higher intake of PCDD/PCDF. Tea consumption can attribute to up to 10% of the TDI recommended by WHO (only PCDD/PCDF considered, no PCB analyzed).
|
|
| 4. |
|
|
| 5. |
- Scherer, SW, et al.
(författare)
-
Human chromosome 7: DNA sequence and biology
- 2003
-
Ingår i: Science (New York, N.Y.). - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 300:5620, s. 767-772
-
Tidskriftsartikel (refereegranskat)abstract
- DNA sequence and annotation of the entire human chromosome 7, encompassing nearly 158 million nucleotides of DNA and 1917 gene structures, are presented. To generate a higher order description, additional structural features such as imprinted genes, fragile sites, and segmental duplications were integrated at the level of the DNA sequence with medical genetic data, including 440 chromosome rearrangement breakpoints associated with disease. This approach enabled the discovery of candidate genes for developmental diseases including autism.
|
|
| 6. |
- Yu, Kai, et al.
(författare)
-
On the tap and cluster angular spreads of indoor WLAN channels
- 2004
-
Ingår i: VTC2004-SPRING. - NEW YORK : IEEE. - 0780382552 ; , s. 218-222
-
Konferensbidrag (refereegranskat)abstract
- Herein we present results on the cluster angular spread (AS), the tap AS and its variation with different channel bandwidths for a measured large office environment. The measurements were conducted in the 5 GHz band using a virtual cross antenna array at the receiver. A frequency domain space alternating generalized expectation maximization (FD-SAGE) algorithm is employed to estimate the multipath components. The clusters of the multipaths are then manually identified. For each measured location, 4-5 clusters are identified and the processed results show that the cluster AS ranges 5.6degrees-36.5degrees. Furthermore, we investigate the tap AS for each cluster. It is found that for the channels with 100 MHz bandwidth, the instantaneous tap AS ranges 0degrees-43degrees and the average tap AS of each cluster is just few degrees less than the AS of that cluster. The difference between the average tap AS and the cluster AS becomes smaller for less channel bandwidth.
|
|
