| 1. |
- Wilson, A. N., et al.
(författare)
-
Magnetic dipole bands in 190Hg : First evidence of excitations across the Z = 82 sub-shell in Hg nuclei
- 2001
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 505:1-4, s. 6-14
-
Tidskriftsartikel (refereegranskat)abstract
- An experiment aimed at studying high-spin states in 190Hg was performed with the Eurogam II array. The data have revealed the presence of cascades of magnetic dipole transitions with some unexpected properties. Unlike the MI bands previously observed in the heavier Hg isotopes, these structures have extremely large B(M1)/B(E2) ratios, The observation of a third dipole band with much lower B(M1)/B(E2) values in the same spin/excitation energy regime suggests that the bands may represent configurations occurring in different minima in the potential energy surface. Configuration-dependent Cranked Nilsson-Strutinsky calculations predict the presence of a minimum in the nuclear potential energy surface at a deformation of ε ≅ 0.2, γ ≅ -90°, occurring when a proton is excited across the Z = 82 shell-gap into an h9/2 orbital. It is suggested that the bands exhibiting anomalously large B(M1)/B(E2) ratios may be associated with this minimum.
|
|
| 2. |
- Martens, C.S., et al.
(författare)
-
Radon fluxes in tropical forest ecosystems of Brazilian Amazonia: night-time CO2 net ecosystem exchange derived from radon and eddy covariance methods.
- 2004
-
Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 10:5, s. 618-629
-
Tidskriftsartikel (refereegranskat)abstract
- Radon-222 (Rn-222) is used as a transport tracer of forest canopy–atmosphere CO2 exchange in an old-growth, tropical rain forest site near km 67 of the Tapajós National Forest, Pará, Brazil. Initial results, from month-long periods at the end of the wet season (June–July) and the end of the dry season (November–December) in 2001, demonstrate the potential of new Rn measurement instruments and methods to quantify mass transport processes between forest canopies and the atmosphere. Gas exchange rates yield mean canopy air residence times ranging from minutes during turbulent daytime hours to greater than 12 h during calm nights. Rn is an effective tracer for net ecosystem exchange of CO2 (CO2 NEE) during calm, night-time hours when eddy covariance-based NEE measurements are less certain because of low atmospheric turbulence. Rn-derived night-time CO2 NEE (9.00±0.99 μmol m−2 s−1 in the wet season, 6.39±0.59 in the dry season) was significantly higher than raw uncorrected, eddy covariance-derived CO2 NEE (5.96±0.51 wet season, 5.57±0.53 dry season), but agrees with corrected eddy covariance results (8.65±1.07 wet season, 6.56±0.73 dry season) derived by filtering out lower NEE values obtained during calm periods using independent meteorological criteria. The Rn CO2 results suggest that uncorrected eddy covariance values underestimate night-time CO2 loss at this site. If generalizable to other sites, these observations indicate that previous reports of strong net CO2 uptake in Amazonian terra firme forest may be overestimated.
|
|
| 3. |
- Gueorguieva, E., et al.
(författare)
-
High-spin states in Au-191 : Evidence for triaxial shape?
- 2003
-
Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 68:5, s. 543081-5430814
-
Tidskriftsartikel (refereegranskat)abstract
- The level scheme of Au-191 was considerably extended to high spin using gamma spectroscopy with the Eurogam-II array and internal conversion measurements with the Orsay electron spectrometer. Several bands that appear as strongly coupled were associated with low- Omega configurations in Au-191 . Using total routhian surface and cranked shell model calculations it was shown that these bands have a rotation-aligned nature and are most likely generated by the nonaxiallity of the nucleus induced by the odd proton. The predictions for the presence of such bands in Au-191 and in the oblate nuclei in the Pt-Au-Hg region found excellent agreement with the experimental data, as well as the predictions for their alignments and band-crossing frequencies in Au-191 .
|
|
| 4. |
|
|
| 5. |
- Gueorguieva, E., et al.
(författare)
-
Sets of rotation-aligned bands indicating nonaxiality in Au-190
- 2004
-
Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 69:4, s. 044320-
-
Tidskriftsartikel (refereegranskat)abstract
- The level scheme of Au-190 was extended up to high spin using gamma spectroscopy with the Eurogam-II array and internal conversion measurements with the electron- gamma spectrometer of Orsay. Several sets of rotation-aligned bands were found and associated with high- j, low- K configurations. According to the total Routhian surface and cranked shell model calculations these bands are caused by the nonaxiality of the nuclear deformation (gammaless than or equal to-70degrees). Furthermore, very good agreement was obtained between the experimental data and the theoretical predictions for the properties of these bands, such as alignments, band-crossing frequencies, and signature inversion, thus supporting the suggested nonaxial shapes.
|
|
| 6. |
- Martens, C, et al.
(författare)
-
Underdosage of the upper-airway mucosa for small fields as used in intensity-modulated radiation therapy: A comparison between radiochromic film measurements, Monte Carlo simulations, and collapsed cone convolution calculations
- 2002
-
Ingår i: Medical Physics. - : Wiley. - 0094-2405. ; 29:7, s. 1528-1535
-
Tidskriftsartikel (refereegranskat)abstract
- Head-and-neck tumors are often situated at an air-tissue interface what may result in an underdosage of part of the tumor in radiotherapy treatments using megavoltage photons. especially for small fields. In addition to effects of transient electronic disequilibrium, for these small fields, an increased lateral electron range in air will result in an important extra reduction of the central axis (lose beyond the cavity. Therefore dose calculation algorithms need to model electron transport accurately. We simulated the trachea by a 2 cm diameter cylindrical air cavity with the rin) situated 2 cm beneath the phantom surface. A 6 MV photon beam from an Elekta SLi plus linear accelerator, equipped with the standard multileaf collimator (MLC), was assessed. A 10 x 2 cm(2) and a 10 K 1 cm(2) field, both widthwise collimated by the MLC, were applied with their long side parallel to the cylinder axis. Central axis dose rebuild-up was studied. Radiochromic film measurements were performed in an in-house manufactured polystyrene phantom with the films oriented either along or perpendicular to the beam axis. Monte Carlo simulations were performed with BEAM and EGSnrc. Calculations were also performed using the pencil beam (PB) algorithm and the collapsed cone convolution (CCC) algorithm of Helax-TMS (MDS Nordion, Kanata. Canada) version 6.0.2 and using the CCC algorithm of Pinnacle (ADAC Laboratories, Milpitas. CA, USA) version 4.2. A very good agreement between the film measurements and the Monte Carlo simulations was found. The CCC algorithms were not able to predict the interface dose accurately when lateral electronic disequilibrium occurs, but were shown to be a considerable improvement compared to the PB algorithm. The CCC algorithms overestimate the dose in the rebuild-up region. The interface dose was overestimated by a maximum of 31% or 54%, depending on the implementation of the CCC algorithm. At a depth of I rum, the maximum dose overestimation was 14% or 24%.
|
|
| 7. |
- van Niel, Ed, et al.
(författare)
-
Effect of carbon dioxide and temperature on H2 producing cultures of the extreme thermophile, Caldicellulosiruptor saccharolyticus
- 2004
-
Ingår i: Proceedings of the 15th World Hydrogen Energy Conference.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Carbon dioxide could replace nitrogen gas as stripping gas for the production of H2 by the extreme thermophile, Caldicellulosiruptor saccharolyticus, provided that the pH is kept below 7.0. Above this pH, ≥77 mM sodium bicarbonate will be introduced as an extra salt burden to the culture. High concentrations of sugars and salts contribute each to the inhibition of growth and H2 production, which is most probably due to the osmolality. As a consequence, using CO2 as stripping gas might lower the maximum allowable acetate concentration in culture, and therefore the productivity of the culture at neutral pH. Although the growth rate was not affected by CO2, lower biomass and hydrogen yields were obtained. This could be due to an increased lactate production. In a thermodynamic study an estimation of the activation enthalpies was made for both hydrogen production and its thermal inactivation, being 45.9 kJ/mol and 112.3 kJ/mol, respectively. Hydrogen production showed a wider temperature range (estimated 40 - 90° C) than growth (49.6 – 85.7° C).
|
|
