21,676 research outputs found
Rayleigh number dependence of the Archimedes number dependent large-scale flow structure formation in mixed convection
No full textWe report on experimental investigations of large-scale flow structure formation in mixed convection. We characterize the flow field by measuring the velocity fields within a rectangular model room using 2D2C PIV. The control parameters are the Reynolds number Re, the Rayleigh number Ra and the Prandtl number Pr. All parameters are linked through the Archimedes number Ar. In 6.4x10-2 ≤ Ar ≤ 1.39x101, 4.2x103 ≤ Re ≤ 6.35x104 and Ra = 3.1x107, Ra = 1.8x108 and Pr = 0.713 we found flow 3 different flow structures. While keeping Ra and Pr constant and varying Ar through Re variations, we found an Ar dependence of the largescale flow structure formation within 6.4x10-2 ≤ Ar ≤ 1.39x101. Furthermore, we found a Ra dependence of the structure formation, which shifts the transition points between the structures to higher Archimedes numbers and reduces the mean velocities within the investigated domain
3-D reconstruction of anterior mantle-field techniques in Hodgkin's disease survivors: doses to cardiac structures
No full textBACKGROUND: The long-term dose-effect relationship for specific cardiac structures in mediastinal radiotherapy has rarely been investigated. As part of an interdisciplinary project, the 3-D dose distribution within the heart was reconstructed in all long-term Hodgkin's disease survivors (n = 55) treated with mediastinal radiotherapy between 1978 and 1985. For dose reconstruction, original techniques were transferred to the CT data sets of appropriate test patients, in whom left (LV) and right ventricle (RV), left (LA) and right atrium (RA) as well as right (RCA), left anterior descending (LAD) and left circumflex (LCX) coronary arteries were contoured. Dose-volume histograms (DVHs) were generated for these heart structures and results compared between techniques. RESULTS: Predominant technique was an anterior mantle field (cobalt-60). 26 patients (47%) were treated with anterior mantle field alone (MF), 18 (33%) with anterior mantle field and monoaxial, bisegmental rotation boost (MF+ROT), 7 (13%) with anterior mantle field and dorsal boost (MF+DORS) and 4 (7%) with other techniques. Mean +/- SD total mediastinal doses for MF+ROT (41.7 +/- 3.5 Gy) and for MF+DORS (42.7 +/- 7.4) were significantly higher than for MF (36.7 +/- 5.2 Gy). DVH analysis documented relative overdosage to right heart structures with MF (median maximal dose to RV 129%, to RCA 127%) which was significantly reduced to 117% and 112%, respectively, in MF+ROT. Absolute doses in right heart structures, however, did not differ between techniques. Absolute LA doses were significantly higher in MF+ROT patients than in MF patients where large parts of LA were blocked. Median maximal doses for all techniques ranged between 48 and 52 Gy (RV), 44 and 46 Gy (LV), 47 and 49 Gy (RA), 38 and 45 Gy (LA), 46 and 50 Gy (RCA), 39 and 44 Gy (LAD) and 34 and 42 Gy (LCX). CONCLUSION: In patients irradiated with anterior mantle-field techniques, high doses to anterior heart portions were partly compensated by boost treatment from non-anterior angles. As the threshold doses for coronary artery disease, cardiomyopathy, pericarditis and valvular changes are assumed to be 30 to 40 Gy, cardiac toxicity must be anticipated in these patients. Thus, dose distributions in individual subjects should be correlated to the corresponding cardiovascular findings in these long-term survivors, e. g. by cardiovascular magnetic resonance imaging
Recommended from our members
In-field determination of ²²⁶Ra and ²²⁸Ra in the oil exploration sector
No full texttextThe presence of radioactivity in the production of oil is now a well-known phenomenon. Specifically ²²⁶Ra, ²²²Rn, ²²⁸Ra and ²¹⁰Pb and their various decay products are of environmental concern especially to the workers in the field. The Nuclear Engineering Teaching Lab at the University of Texas has been in collaboration with Enviroklean Product Development Inc. (EPDI) in Houston, an environmental restoration and chemical product company, in the clean-up of technologically enhanced naturally occurring radioactive material in the oil exploration sector. In particular radioactive scale build-up in the equipment has been an on-going concern. Unlike typical naturally occurring radioactive material (NORM) samples, ²²⁶Ra and ²³²Th, and their daughters dominate the radioactivity. As such, they are not in secular equilibrium with any of the radionuclides above the decay chain that emanate from ²³⁸U or ²³²Th. Respectively, this thesis sought to test a Cesium Iodide (CsI) detector for in-field analysis of NORM samples. Additionally, quality control procedures and an in-house reference material were created to facilitate this testing. This in-house reference material was used to thoroughly test the CsI detector against the radiation detection stalwarts of High Purity Germanium (HPGe) and Sodium Iodide (NaI). Neither the NaI nor CsI were able to detect the low energy ²¹⁰Pb photons, but ²²⁶̕²²⁸Ra were no issue for either detector. The CsI was found to be 33% more efficient than an HPGe and have twice the full-width half maximum resolution of the NaI (16 keV vs 31 keV at the 186.5 keV peak). The CsI was also able to reach detection limits of 361 +/- 20 pCi/g for ²²⁶Ra and 25 +/- 2 for pCi/g ²²⁸Ra in scale from west Texas. Additionally, the self-attenuation of the sample was evaluated and, as expected, the lower energy photons, e.g. ²¹⁰Pb, are significantly more attenuated than photons at higher energies. We found approximately a 79 % reduction in counts at 47 keV, 7% at 186 keV, and 5% at 911 keV. Self-attenuation must be factored in or there will be an underestimation of the radioactivity, especially for ²¹⁰Pb. The last issue faced while testing the CsI detector was its inability to discriminate the ²²⁸Ra peaks around 911 keV from other peaks in the vicinity. This problem was solved using an HPGe detector to find the ratio of wanted peaks to unwanted peaks around 911 keV photon. This ratio can be applied to the convoluted CsI peak around 911 keV to find the actual net counts coming from ²²⁸Ra. The detection limits, self-attenuation, and deconvolution ratio can all be used to develop software capable of accurately determining radioactivity concentrations in NORM in a field environment.Mechanical Engineerin
Patient Uncertainty Questionnaire-Rheumatology (PUQ-R): development and validation of a new patient-reported outcome instrument for systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) in a mixed methods study
No full textBackground
An in-depth qualitative exploration of uncertainty in systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) led to the development of a five-domain conceptual framework of patient uncertainty in these two conditions. The purpose of this study was to develop and evaluate a new patient-reported outcome (PRO) instrument for patient uncertainty in SLE and RA on the basis of this empirically developed conceptual framework.
Methods
Cognitive debriefing interviews were conducted to pre-test the initial items generated on the basis of the preliminary qualitative exploration of patient uncertainty in SLE and RA. Two separate field tests were conducted in five hospital sites to evaluate the measurement properties of the new instrument; the first to identify and form scales, and the second to assess measurement properties of the final version in an independent sample. Psychometric evaluation was conducted in line with the Rasch Measurement Theory (RMT), examining the extent to which sample to scale targeting was satisfactory, measurement scales were constructed effectively and the sample was measured successfully. Traditional psychometric techniques were also used to provide complementary analyses best understood by clinicians.
Results
Pre-testing supported the relevance, acceptability and comprehensibility of the initial items. Findings indicated that the Patient Uncertainty Questionnaire for Rheumatology PUQ-R instrument fulfilled the expectations of RMT to a large extent (including person separation index 0.73 – 0.91). The PUQ-R comprises 49 items across five scales; symptoms and flares (14 items), medication (11 items), trust in doctor (8 items), self-management (6 items) and impact (10 items) which further displayed excellent measurement properties as assessed against the traditional psychometric criteria (including Cronbach’s alpha 0.82 – 0.93).
Conclusion
The PUQ-R has been developed and evaluated specifically for patients with SLE and RA. By quantifying uncertainty, the PUQ-R has the potential to support evidence-based management programmes and research
Reynolds numbers near the ultimate state of turbulent Rayleigh-Bénard convection
No full textWe report on measurements of the mean-flow Reynolds number ReU and the rms fluctuation Reynolds number ReV in turbulent Rayleigh-Bénard convection as a function of the Rayleigh number Ra for 4 x 1011 < Ra < 2 1014 and Pr ' 0:8. Both can be described by the same power law with an effective exponent = 0:44, in agreement with predictions for ReU but in disagreement with predictions for ReV
Field emission enhancement by new CNT paste components and characterization of degradation in CNT tips during field emission
No full text학위논문(박사) - 한국과학기술원 : 신소재공학과, 2006.2, [ viii, 143 p. ]본 연구에서는 CNT 페이스트의 조성물을 탐색하여 최적의 전계 방출 특성을 구현할 수 있는 CNT 페이스트의 조성을 확립하고 각 조성물의 전계 방출 특성에 미치는 영향을 고찰하였다. 최적의 전계 방출 특성을 구현할 수 있는 CNT 페이스트를 개발하기 위해 CNT 페이스트의 기본 조성물인 organic binder, CNT powder, inorganic binder (frit glass, inorganic powder) 등을 각각 개발 및 다양화하여 각각의 특성을 규명하였다. 또한 FED 중 가장 그 실용화가 기대되는 CNT FE-BLU의 패널을 구현하여 구동 시 관찰되는 특성인 CNT tip의 degradation 현상을 관찰하였다. CNT cathode의 제작 시 각 공정이 전계 방출 특성에 미치는 영향도 고려하여 CNT cathode 제작 조건을 확립하였다. 개발된 CNT 페이스트를 이용하여 3.5 inch, 10 inch 백색광 패널을 제작하여 패널의 구동시 CNT cathode가 겪는 degradation에 대해서도 고찰하였다. CNT FE-BLU의 cathode가 degradation 되는 원인은 다양하다. 본 연구에서는 그 중 CNT FE-BLU에서 형광막에서 구동 중 발생 가능한 원소들이 CNT tip의 degradation에 미치는 영향은 밝혀진 바가 없으므로 실제 패널을 구현하여 구동 중 발생하는 형광체 원소들과 CNT tip의 degradation을 다양한 분석을 통해 규명하였다.
(1) CNT 페이스트 조성물
1) organic binder
일반적으로 사용되는 ethyl celullose의 높은 소성 온도에 의한 CNT의 파괴를 방지하기 위해 300 도의 저온에서 소성되는 새로운 organic binder를 개발하였다. 개발된 organic binder의 조성은 P(MMA-co-BMA) 였으며 열분석 결과 300 도에서 완전히 분해되는 안정된 저온소성 특성을 가짐을 확인하였다. 또한 소성 후 잔류물의 양도 상용 350 도 소성 binder와 비교 시 1/4 수준으로 매우 낮았다. 페이스트 형성 능력도 조절이 용이하고 스크린 프린팅 후 morphology도 상용 binder와 차이가 없는 우수한 수준임을 확인하였다. 이를 이용하여 CNT 페이스트를 제조하여 전계 방출 특성을 관찰한 결과 CNT 표면의 잔류물을 최소화 하여 전계 방출 특성을 개선하는 효과가 있음을 확인하였다.
2) Inorganic binder (frit glass, inorganic powder)
Frit glass와 inorganic powder를 사용하여 각각이 전계 방출 특성에 미치는 영향을 고찰하였다. Frit glass는 일반적으로 CNT와 기판 간의 adhesion을 도와주는 물질로서 첨가되었다. 그러나 연구 결과를 통하여 frit glass가 직접적으로 CNT를 접착시키기 보다는 inorganic powder와 기판간의 adhesion을 증가시킴을 확인하였다. Adhesion이 향상된inorganic powder들이 CNT의 사이사이에 위치하여 CNT를 분산시키고 이를 통하여 CNT와 기판의 adhesion이 얻어진다는 결론을 얻었다. 또한 frit glass와 inorganic powder가 전계 방출 특성에 미치는 영향에 대해서도 고찰하였다. 그 결과 frit glass는 adhesion agent로서의 역할에 더하여 insulator의 역할을 하여 전계 방출 특성에서 stability를 높이기도 함을 확인하였다. Inorganic powder의 가장 주요한 역할은 CNT의 dispersion agent 였으며 inorganic powder 자체가 가지고 있는 물성에 의해 전계 방출 특성을 향상 시킬 수도 있음을 확인하였다.
3) Field emission enhanced by dielectric materials
CNT 페이스트를 이용한 전계 방출 cathode의 개발에 있어 cathode의 특성을 효과적으로 개선하한국과학기술원 : 신소재공학과
Logarithmic variance profiles and the corresponding f-1 spectra of temperature fluctuations in turbulent Rayleigh-Bénard convection
No full textWe report experimental results for the temperature variance 2(z) and the corresponding frequency spectra P(f) in turbulent Rayleigh-Bénard convection (RBC) in a cylindrical sample of aspect ratioT= D/L = 1:00 (D = 1:12 m is the diameter and L = 1:12 m the height). The measurements were conducted in the Rayleigh-number range 1011 < Ra < 1:35 1014 and Pr ' 0:8. For Ra = 1:35x1014, 2(z) could be described well by a logarithmic dependence on the vertical position z in a range of z 1 < z < z 2 with z 1 ' 70 and z 2 = 0:1L. Here L=(2Nu) is the thickness of a thin thermal sublayer adjacent to the horizontal plate where the heat flux (denoted by the Nusselt number Nu) is carried mostly by thermal diffusion. In the log layer, we found that the temperature spectra had a significant frequency range over which P(f) f with close to 1. As Ra decreased, increased so that the log layer became thinner. At Ra = 2:05 1011, z 2 < z 1 and therefore there was no range for a log layer. Correspondingly, the temperature spectrum near the horizontal plate did not have the f1 scaling form either
Improvement of quality in the evaluation of radium isotopes Ra-224,Ra-226,Ra-228 in oil scale samples
No full textElevated concentrations of the radium isotopes Ra-224,Ra-226,Ra-228 exist in the scale and produced water in oil exploration. the activity concentration of Ra-226 was calculated from 186.2 keV peak with no usual spectral interference of 185.7 from U-235. the activity concentration of Ra-228 was calculated from its first daughter product Ac-228 using the 911.2 keV gamma rays since it is a pure beta emitter. the activity concentration of Ra-224 was calculated from Pb-212 using the 238.6 keV gamma-ray and the secular equilibrium equation with Ra-228. the IAEA 448 (oil contaminated field soil) reference material was used as a quality control for Ra-226,Ra-228 and but was unreliable for Ra-224 using Pb-212
- …
