Electron Capture into Quantum Wells via Scattering by Electrons, Holes, and Optical Phonons

Electron capture times due to the electron-electron (e-e), electron-hole (e-h) and electron-polar optical phonon (e-pop) interactions are calculated in the GaAs quantum well (QW) with electron and hole densities 10^11 cm^-2. The calculated capture times oscillate as a function of the QW width with the same period but with different amplitudes. The e-h capture time is two to four orders larger and the e-e capture time one to three orders larger than the e-pop capture time. The exceptions are the QW widths near resonance minima, where the e-e capture time is only 2-3 times larger and the e-h capture time 10-100 times larger. Different physical origin of the oscillatory behavior is demonstrated for the e-e and e-pop capture times. Effects of exchange and degeneracy on the e-e capture are analysed. The exchange effect increases the e-e capture time approximately two times while the degeneracy does not change the capture time except for the QW depths and widths near the resonance.Comment: 10 pages, LaTeX2.09, 8 PostScript figure

Frictional drag between quantum wells mediated by phonon exchange

We use the Kubo formalism to evaluate the contribution of acoustic phonon exchange to the frictional drag between nearby two-dimensional electron systems. In the case of free phonons, we find a divergent drag rate ($\tau_{D}^{-1}$). However, $\tau_{D}^{-1}$ becomes finite when phonon scattering from either lattice imperfections or electronic excitations is accounted for. In the case of GaAs quantum wells, we find that for a phonon mean free path $\ell_{ph}$ smaller than a critical value, imperfection scattering dominates and the drag rate varies as $ln (\ell_{ph}/d)$ over many orders of magnitude of the layer separation $d$. When $\ell_{ph}$ exceeds the critical value, the drag rate is dominated by coupling through an electron-phonon collective mode localized in the vicinity of the electron layers. We argue that the coupled electron-phonon mode may be observable for realistic parameters. Our theory is in good agreement with experimental results for the temperature, density, and $d$-dependence of the drag rate.Comment: 45 pages, LaTeX, 8 postscript file figure

Coupled operation experience at the Holifield Heavy-Ion research Facility

The 25URC Pelletron tandem electrostatic accelerator and the Oak Ridge Isochronous Cyclotron (ORIC) comprise the accelerators of the Holifield Heavy-Ion Research Facility (HHIRF). The two machines may be operated individually or coupled, with ORIC serving as an energy booster for the tandem. In the coupled dode, the ion beam enters the cyclotron through the dee stem and is directed by the inflection magnet so that it is tangent to an orbit suitable for acceleration at a higher charge state. A thin carbon foil, placed at the point of tangency, strips the ions so that a substantial fraction are in the desired higher charge state. This fraction of the beam is then accelerated and extracted in the normal fashion. Full energy performance (25 MeV/A oxygen) was demonstrated during first coupled operation in January 1981. Routine coupled operation for experiments commenced in July 1982

Finding Common Ground: relational concepts of land tenure and economy in the oil palm frontier of Papua New Guinea

In the oil palm frontier regions of West New Britain and Oro provinces, Papua New Guinea, customary land tenure arrangements are changing in response to the growing demand for land for agricultural development. This paper examines one aspect of these changes, namely the gifting and selling of customary land for oil palm development to people who have no customary birthrights to the land. By analysing how access rights are maintained over the relatively long cultivation cycle of oil palm (approximately 25 years), and in the context of the rapidly changing socio-economic and demographic environments of the oil palm frontiers, the paper demonstrates that while land transactions seemingly entail the commodification of land, land rights and security of land tenure remain embedded in social relationships. For customary landowners, the moral basis of land rights is contingent on ‘outsiders’ maintaining particular kinds of social and economic relationships with their customary landowning ‘hosts’. In exploring how these social relationships are constituted through the performance of particular kinds of exchange relationships, the paper provides insights into relational concepts of land rights and how these are able to persist in Papua New Guinea's oil palm frontier regions where resource struggles are often intense and where large migrant populations are seeking land for agricultural development

Defining Standards for Fluoroscopy in Gastrointestinal Endoscopy using a Delphi Methodology

Background and Study Aims The use of fluoroscopy in gastrointestinal endoscopy is an essential aid in advanced endoscopic interventions. However, it also raises concerns about radiation exposure. This study aimed to develop consensus-based statements for the safe and effective use of fluoroscopy in gastrointestinal endoscopy, prioritizing the safety and well-being of healthcare workers and patients. Methods A modified Delphi approach was employed to achieve consensus over three rounds of surveys. Proposed statements were generated in round 1. In the second round, panelists rated potential statements on a 5-point scale, with consensus defined as ≥80% agreement. Statements were subsequently prioritized in round 3, using a 1 (lowest priority) to 10 (highest priority) scale. Results Forty-six experts participated, consisting of 34 therapeutic endoscopists and 12 endoscopy nurses from six continents, with an overall 45.6% female representation (n=21). Forty-three item statements were generated in the first round. Out of these, 31 statements achieved consensus after the second round. These statements were categorized into General Considerations (n=6), Education (n=10), Pregnancy (n=4), Family Planning (n=2), Patient Safety (n=4), and Staff Safety (n=5). In the third round, accepted statements received mean priority scores ranging from 7.28 to 9.36, with 87.2% of statements rated as very high priority (mean score of ≥9). Conclusion This study presents consensus-based statements for the safe and effective use of fluoroscopy in gastrointestinal endoscopy, addressing the well-being of healthcare workers and patients. These consensus-based statements aim to mitigate the risks associated with radiation exposure while maintaining the benefits of fluoroscopy, ultimately promoting a culture of safety in healthcare settings

Defining standards for fluoroscopy in gastrointestinal endoscopy using Delphi methodology

Background and study aims Use of fluoroscopy in gastrointestinal endoscopy is an essential aid in advanced endoscopic interventions. However, it also raises concerns about radiation exposure. This study aimed to develop consensus-based statements for safe and effective use of fluoroscopy in gastrointestinal endoscopy, prioritizing the safety and well-being of healthcare workers and patients.Methods A modified Delphi approach was employed to achieve consensus over three rounds of surveys. Proposed statements were generated in Round 1. In the second round, panelists rated potential statements on a 5-point scale, with consensus defined as ≥80% agreement. Statements were subsequently prioritized in Round 3, using a 1 (lowest priority) to 10 (highest priority) scale.Results Forty-six experts participated, consisting of 34 therapeutic endoscopists and 12 endoscopy nurses from six continents, with an overall 45.6% female representation (n = 21). Forty-three item statements were generated in the first round. Of these, 31 statements achieved consensus after the second round. These statements were categorized into General Considerations (n = 6), Education (n = 10), Pregnancy (n = 4), Family Planning (n = 2), Patient Safety (n = 4), and Staff Safety (n = 5). In the third round, accepted statements received mean priority scores ranging from 7.28 to 9.36, with 87.2% of statements rated as very high priority (mean score ≥ 9)Conclusions This study presents consensus-based statements for safe and effective use of fluoroscopy in gastrointestinal endoscopy, addressing the well-being of healthcare workers and patients. These consensus-based statements aim to mitigate risks associated with radiation exposure while maintaining benefits of fluoroscopy, ultimately promoting a culture of safety in healthcare settings.Cellular mechanisms in basic and clinical gastroenterology and hepatolog