Apparent diffusion coefficient correlation with oesophageal tumour stroma and angiogenesis
Energy Technology Data Exchange (ETDEWEB)
Aoyagi, Tomoyoshi; Shuto, Kiyohiko; Okazumi, Shinichi; Hayano, Kohichi; Satoh, Asami; Saitoh, Hiroshige; Shimada, Hideaki; Nabeya, Yoshihiro; Matsubara, Hisahiro [Chiba University, Department of Frontier Surgery, Graduate School of Medicine, Chiba (Japan); Kazama, Toshiki [Chiba University, Department of Radiology, Graduate School of Medicine, Chiba (Japan)
2012-06-15
Because diffusion-weighted imaging (DWI) can predict the prognosis of patients with oesophageal squamous cell carcinoma (ESCC), we hypothesised that apparent diffusion coefficient (ADC) values might be correlated with the collagen content and tumour angiogenesis. The purpose of this study was to determine the correlation between ADC values of ESCC before treatment and oesophageal tumour stroma and angiogenesis. Seventeen patients with ESCC were enrolled. The ADC values were calculated from the DWI score. Seventeen patients who had undergone oesophagectomy were analysed for tumour stroma, vascular endothelial growth factor (VEGF) and CD34. Tissue collagen was stained with azocarmine and aniline blue to quantitatively analyse the extracellular matrix in cancer stroma. Tissues were stained with VEGF and CD34 to analyse the angiogenesis. The ADC values decreased with stromal collagen growth. We found a negative correlation between the tumour ADC and the amount of stromal collagen (r = -0.729, P = 0.001), i.e. the ADC values decreased with growth of VEGF. We also found a negative correlation between the ADC of the tumours and the amount of VEGF (r = 0.538, P = 0.026). Our results indicated that the ADC value may be a novel prognostic factor and contribute to the treatment of oesophageal cancer. circle Magnetic resonance apparent diffusion coefficient values inversely indicate tumour stromal collagen circle There is also negative correlation between ADCs and vascular endothelial growth factor circle ADC values may contribute to the treatment of oesophageal cancer. (orig.)
Apparent diffusion coefficient measurements in progressive supranuclear palsy
International Nuclear Information System (INIS)
We measured the apparent diffusion coefficient (ADC), using diffusion-weighted imaging (DWI) and signal intensity on T2-weighted MRI in the cerebral white matter of patients with progressive supranuclear palsy (PSP) and age-matched normal subjects. In PSP, ADC in the prefrontal and precentral white matter was significantly higher than in controls. There was no significant difference in signal intensity on T2-weighted images. The ADC did correlate with signal intensity. The distribution of the elevation of ADC may be the consequence of underlying pathological changes, such as neurofibrillary tangles or glial fibrillary tangles in the cortex. Our findings suggest that ADC measurement might be useful for demonstrating subtle neuropathological changes. (orig.)
Apparent diffusion coefficient measurements in progressive supranuclear palsy
Energy Technology Data Exchange (ETDEWEB)
Ohshita, T.; Oka, M.; Imon, Y.; Yamaguchi, S.; Mimori, Y.; Nakamura, S. [Hiroshima Univ. (Japan). School of Medicine
2000-09-01
We measured the apparent diffusion coefficient (ADC), using diffusion-weighted imaging (DWI) and signal intensity on T2-weighted MRI in the cerebral white matter of patients with progressive supranuclear palsy (PSP) and age-matched normal subjects. In PSP, ADC in the prefrontal and precentral white matter was significantly higher than in controls. There was no significant difference in signal intensity on T2-weighted images. The ADC did correlate with signal intensity. The distribution of the elevation of ADC may be the consequence of underlying pathological changes, such as neurofibrillary tangles or glial fibrillary tangles in the cortex. Our findings suggest that ADC measurement might be useful for demonstrating subtle neuropathological changes. (orig.)
Discrimination of paediatric brain tumours using apparent diffusion coefficient histograms
Energy Technology Data Exchange (ETDEWEB)
Bull, Jonathan G.; Clark, Christopher A. [UCL Institute of Child Health, Imaging and Biophysics Unit, London (United Kingdom); Saunders, Dawn E. [Great Ormond Street Hospital for Children NHS Trust, Department of Radiology, London (United Kingdom)
2012-02-15
To determine if histograms of apparent diffusion coefficients (ADC) can be used to differentiate paediatric brain tumours. Imaging of histologically confirmed tumours with pre-operative ADC maps were reviewed (54 cases, 32 male, mean age 6.1 years; range 0.1-15.8 years) comprising 6 groups. Whole tumour ADC histograms were calculated; normalised for volume. Stepwise logistic regression analysis was used to differentiate tumour types using histogram metrics, initially for all groups and then for specific subsets. All 6 groups (5 dysembryoplastic neuroectodermal tumours, 22 primitive neuroectodermal tumours (PNET), 5 ependymomas, 7 choroid plexus papillomas, 4 atypical teratoid rhabdoid tumours (ATRT) and 9 juvenile pilocytic astrocytomas (JPA)) were compared. 74% (40/54) were correctly classified using logistic regression of ADC histogram parameters. In the analysis of posterior fossa tumours, 80% of ependymomas, 100% of astrocytomas and 94% of PNET-medulloblastoma were classified correctly. All PNETs were discriminated from ATRTs (22 PNET and 4 supratentorial ATRTs) (100%). ADC histograms are useful in differentiating paediatric brain tumours, in particular, the common posterior fossa tumours of childhood. PNETs were differentiated from supratentorial ATRTs, in all cases, which has important implications in terms of clinical management. (orig.)
Somford, DM; Marks, MP; Thijs, VN; Tong, DC
2004-01-01
BACKGROUND AND PURPOSE: Diffusion-weighted (DW) imaging is more sensitive for early ischemia than CT, and apparent diffusion coefficient (ADC) mapping permits quantification of the severity of cytotoxic edema. We examined the relationship between early CT findings, ischemic lesion volume on DW image
International Nuclear Information System (INIS)
Objective: To evaluate the relationship between apparent diffusion coefficient (ADC) value and the local invasiveness of endometrial carcinoma. Methods and materials: The MR imaging of seventy-three patients with endometrial carcinoma proved by post-operative pathology and sixty-four patients with healthy uteri were retrospectively reviewed. All MR examinations included axial T2WI and T1WI, sagittal T2WI and diffusion-weighted sequences (b = 0 and b = 1000 s/mm2). Tumor size, mean ADC value (ADCm) and quartile ADC (ADCq) were acquired on post-processing workstation using voxel-analysis software. Differences between the ADC values among three layers of normal uterine body and endometrial carcinomas were compared by ANOVA test. Groups were divided according to pathologic type, histologic grade, depth of myometrial infiltration, presence of cervical invasion and lymphovascular space invasion, and lymph node metastasis. Tumor size and ADC values were compared and analyzed. Results: ADC values were different in three zones of uterine body (P −3 mm2/s] and highest in outer myometrium [(1.496 ± 0.196) × 10−3 mm2/s]. Mean ADC value of endometrial carcinomas [(1.011 ± 0.121) × 10−3 mm2/s] was lower than the normal uterine body. Quartile ADC and tumor size were greater in groups with more invasive pathologic factors (P < 0.05). Deep myometrial infiltration, cervical invasion, lymphovascular space invasion and lymph node metastasis were more common as quartile ADC values and tumor sizes increased. Conclusion: Mean ADC value was lower in endometrial carcinoma was lower than the normal uterus. Quartile ADC, representing the intra-tumor heterogeneity of water movement, had a profound relationship with invasiveness of endometrial carcinomas, while mean ADC value did not. ADC values may serve as a quantitative indicator to complement routine sequences.
Energy Technology Data Exchange (ETDEWEB)
Costantini, M.; Belli, P.; Rinaldi, P. [Department of Bio-Sciences and Radiological Imaging, Catholic University, Rome (Italy); Bufi, E., E-mail: reagandus@alice.i [Department of Bio-Sciences and Radiological Imaging, Catholic University, Rome (Italy); Giardina, G. [Department of Bio-Sciences and Radiological Imaging, Catholic University, Rome (Italy); Franceschini, G. [Department of Surgery, Catholic University, Rome (Italy); Petrone, G. [Department of Pathology, Catholic University, Rome (Italy); Bonomo, L. [Department of Bio-Sciences and Radiological Imaging, Catholic University, Rome (Italy)
2010-12-15
Aim: To assess the utility of diffusion-weighted imaging in diagnosing and characterizing breast malignancy. Materials and methods: From April 2006 to April 2009, all consecutive patients with breast cancer undergoing breast magnetic resonance imaging (MRI) and subsequent surgery in our hospital were enrolled in this study. MRI was performed using a 1.5 T MRI unit using a dedicated, bilateral, four-channel breast coil. The MRI protocol included a diffusion sequence acquired using b values of 0 and 1000 s/mm{sup 2}. For each malignant lesion the relationships between tumour grade and histology and the relative value of the apparent diffusion coefficient (ADC) were analysed. Results: There were 136 female patients with 162 lesions. Histology revealed 149 invasive carcinomas and 13 ductal carcinomas in situ. There were 34 grade 1, 61 grade 2, and 67 grade 3 lesions. The mean ADC value of all malignant lesions was 1.03 x 10{sup -3} mm{sup 2}/s. The mean ADC values for invasive and in situ carcinomas were 1.03 x 10{sup -3} mm{sup 2}/s and 1.05 x 10{sup -3} mm{sup 2}/s, respectively. The mean ADC values for grade 1, 2, and 3 tumours were 1.25 x 10{sup -3} mm{sup 2}/s, 1.02 x 10{sup -3} mm{sup 2}/s, and 0.92 x 10{sup -3} mm{sup 2}/s, respectively. A statistically significant (p < 0.001) inverse correlation was disclosed between the ADC value and the tumour grading. The mean ADC value of the 'less aggressive' group of disease (G1 and in situ lesions) was 1.19 x 10{sup -3} mm{sup 2}/s, whereas the mean ADC value of the 'more aggressive' group (G2-G3 invasive carcinomas) was 0.96 x 10{sup -3} mm{sup 2}/s (p < 0.001). Conclusion: The study confirms the usefulness of diffusion imaging in assessing the aggressiveness of breast tumours. ADC appears to be a promising parameter in the evaluation of the degree of malignancy of breast cancer tissue.
Directory of Open Access Journals (Sweden)
L.M. Pereira
2001-09-01
Full Text Available In this article we compare two different techniques to measure the concentration of saline solutions for the identification of the apparent mass diffusion coefficient in soils saturated with distilled water. They are the radiation measurement technique and the electrical conductivity measurement technique. These techniques are compared in terms of measured quantities, sensitivity coefficients with respect to unknown parameters and the determinant of the information matrix. The apparent mass diffusion coefficient is estimated by utilizing simulated measurements containing random errors. The Levenberg-Marquardt method of minimization of the least-squares norm is used as the parameter estimation procedure. The effects of the volume of saline solution injected into the column devised for the experiments on the accuracy of the estimated parameters are also addressed in this article.
DEFF Research Database (Denmark)
Boesen, Lars; Chabanova, Elizaveta; Løgager, Vibeke;
2015-01-01
PURPOSE: To evaluate the correlation between apparent diffusion coefficient measurements (ADCtumor and ADCratio ) and the Gleason score from radical prostatectomy specimens. MATERIALS AND METHODS: Seventy-one patients with clinically localized prostate cancer scheduled for radical prostatectomy...... were prospectively enrolled. Multiparametric magnetic resonance imaging (MRI) was performed prior to prostatectomy and mean ADC values from both cancerous (ADCtumor ) and benign (ADCbenign ) tissue were measured to calculate the ADCratio (ADCtumor divided by ADCbenign ). The ADC measurements were...
Lu, Hong; Lei, Xiaoyan
2014-01-01
After traumatic brain injury, vasogenic and cytotoxic edema appear sequentially on the involved side. Neuroimaging investigations of edema on the injured side have employed apparent diffusion coefficient measurements in diffusion tensor imaging. We investigated the changes occurring on the injured and uninjured sides using diffusion tensor imaging/apparent diffusion coefficient and histological samples in rats. We found that, on the injured side, that vasogenic edema appeared at 1 hour and in...
Apparent diffusion coefficient parametric response mapping MRI for follow-up of glioblastoma
Energy Technology Data Exchange (ETDEWEB)
Yoon, Ra Gyoung [Catholic Kwandong University International St. Mary' s Hospital, Catholic Kwandong University College of Medicine, Department of Radiology, Seo-gu, Incheon (Korea, Republic of); Kim, Ho Sung; Hong, Gil Sun; Kim, Sang Joon [Asan Medical Center, University of Ulsan College of Medicine, Department of Radiology and Research Institute of Radiology, Songpa-Gu, Seoul (Korea, Republic of); Kim, Dae Yoon [Bundang Jesaeng Hospital, Department of Radiology, Seongnam-si, Gyeonggi-do (Korea, Republic of)
2016-04-15
To determine the diagnostic superiority of parametric response mapping of apparent diffusion coefficient (ADCPR) for predicting glioblastoma treatment response, compared to single time point measurement. Fifty post-treatment glioblastoma patients were enrolled. ADCPR was calculated from serial apparent diffusion coefficient (ADC) maps acquired before and at the time of first detection of an enlarged contrast-enhancing lesion on voxel-by-voxel basis. The percentage-decrease in ADCPR and tenth percentile histogram cutoff value of ADC (ADC10) were compared at subsequent 3-month and 1-year follow-ups. The percentage-decrease in ADCPR was significantly higher in the progression group (mean = 33.2-38.3 %) than in the stable-response group (mean = 9.7 %) at 3 months follow-up (corrected p < 0.001 for both readers). ADCPR significantly improved area under the receiver operating characteristic curve from 0.67 to 0.88 (corrected p = 0.037) and from 0.70 to 0.92 (corrected p = 0.020) for both readers, respectively, compared to ADC10 at 3-month follow-up, but did not significantly improve at 1-year follow-up. The inter-reader agreement was higher for ADCPR than ADC10 (intraclass correlation coefficient, 0.93 versus 0.86). Voxel-based ADCPR appears to be a superior imaging biomarker than ADC, particularly for predicting early tumour progression in patients with glioblastoma. (orig.)
A new in-situ method to determine the apparent gas diffusion coefficient of soils
Laemmel, Thomas; Paulus, Sinikka; Schack-Kirchner, Helmer; Maier, Martin
2015-04-01
Soil aeration is an important factor for the biological activity in the soil and soil respiration. Generally, gas exchange between soil and atmosphere is assumed to be governed by diffusion and Fick's Law is used to describe the fluxes in the soil. The "apparent soil gas diffusion coefficient" represents the proportional factor between the flux and the gas concentration gradient in the soil and reflects the ability of the soil to "transport passively" gases through the soil. One common way to determine this coefficient is to take core samples in the field and determine it in the lab. Unfortunately this method is destructive and needs laborious field work and can only reflect a small fraction of the whole soil. As a consequence insecurity about the resulting effective diffusivity on the profile scale must remain. We developed a new in-situ method using new gas sampling device, tracer gas and inverse soil gas modelling. The gas sampling device contains several sampling depths and can be easily installed into vertical holes of an auger, which allows for fast installation of the system. At the lower end of the device inert tracer gas is injected continuously. The tracer gas diffuses into the surrounding soil. The resulting distribution of the tracer gas concentrations is used to deduce the diffusivity profile of the soil. For Finite Element Modeling of the gas sampling device/soil system the program COMSOL is used. We will present the results of a field campaign comparing the new in-situ method with lab measurements on soil cores. The new sampling pole has several interesting advantages: it can be used in-situ and over a long time; so it allows following modifications of diffusion coefficients in interaction with rain but also vegetation cycle and wind.
Baron, Paul; Dorrius, Monique D.; Kappert, Peter; Oudkerk, Matthijs; Sijens, Paul E.
2010-01-01
The influence of microperfusion and fat suppression technique on the apparent diffusion coefficient (ADC) values obtained with diffusion weighted imaging (DWI) of normal fibroglandular breast tissue was investigated. Seven volunteers (14 breasts) were scanned using diffusion weighting factors (b val
Energy Technology Data Exchange (ETDEWEB)
Cipolla, Valentina, E-mail: valentina.cipolla@yahoo.it [Department of Radiological Sciences, University of Rome “Sapienza”, Viale del Policlinico 155, 00161 Rome (Italy); Santucci, Domiziana; Guerrieri, Daniele; Drudi, Francesco Maria [Department of Radiological Sciences, University of Rome “Sapienza”, Viale del Policlinico 155, 00161 Rome (Italy); Meggiorini, Maria Letizia [Department of Gynaecological Sciences, University of Rome “Sapienza”, Viale del Policlinico 155, 00161 Rome (Italy); Felice, Carlo de [Department of Radiological Sciences, University of Rome “Sapienza”, Viale del Policlinico 155, 00161 Rome (Italy)
2014-12-15
Highlights: • Apparent diffusion coefficient is a quantitative parameter which reflects molecular water movement. • Grading is an independent prognostic factor which correlates with other histopathological features. • Apparent diffusion coefficient values were significantly different between G1 and G3 classes. - Abstract: Purpose: The aim of this study was to evaluate whether the apparent diffusion coefficient (ADC) provided by 3.0 T (3 T) magnetic resonance diffusion-weighted imaging (DWI) varied according to the grading of invasive breast carcinoma. Materials and methods: A total of 92 patients with 96 invasive breast cancer lesions were enrolled; all had undergone 3 T magnetic resonance imaging (MRI) for local staging. All lesions were confirmed by histological analysis, and tumor grade was established according to the Nottingham Grading System (NGS). MRI included both dynamic contrast-enhanced and DWI sequences, and ADC value was calculated for each lesion. ADC values were compared with NGS classification using the Mann–Whitney U and the Kruskal–Wallis H tests. Grading was considered as a comprehensive prognostic factor, and Rho Spearman test was performed to determine correlation between grading and tumor size, hormonal receptor status, HER2 expression and Ki67 index. Pearson's Chi square test was carried out to compare grading with the other prognostic factors. Results: ADC values were significantly higher in G1 than in G3 tumors. No significant difference was observed when G1 and G3 were compared with G2. Tumor size, hormonal receptor status, HER2 expression and Ki67 index correlated significantly with grading but there was a significant difference only between G1 and G3 related to the ER and PR status, HER2 expression and Ki67 index. There was no statistically significant difference in lesion size between the two groups. Conclusion: ADC values obtained on 3 T DWI correlated with low-grade (G1) and high-grade (G3) invasive breast carcinoma. 3
International Nuclear Information System (INIS)
To define a range of apparent diffusion coefficient values in spinal tuberculosis and to evaluate the sensitivity of diffusion-weighted magnetic resonance imaging (DW-MRI) and apparent diffusion coefficient values in patients of spinal tuberculosis. This study was conducted over a period of 20 months and included 110 patients with a total of 230 vertebral bodies. The study was performed in two parts. The first part included all patients of known tuberculosis and patients with classical features of tuberculosis. The second part included patients with spinal pathology of indeterminate etiology. All the patients underwent a routine MRI examination along with diffusion sequences. The apparent diffusion coefficient (ADC) values were calculated from all the involved vertebral bodies. The mean ADC value of affected vertebrae in first part of the study was found to be 1.4 ± 0.20 × 10−3 mm2/s. This ADC value was then applied to patients in the second part of study in order to determine its ability in predicting tuberculosis. This range of ADC values was significantly different from the mean ADC values of normal vertebrae and those with metastatic involvement. However, there was an overlap of ADC values in a few tuberculous vertebrae with the ADC values in metastatic vertebrae. We found that DW-MRI and ADC values may help in the differentiation of spinal tuberculosis from other lesions of similar appearance. However, an overlap of ADC values was noted with those of metastatic vertebrae. Therefore diffusion imaging and ADC values must always be interpreted in association with clinical history and routine MRI findings and not in isolation
Apparent diffusion coefficient and fractional anisotropy of newly diagnosed grade II gliomas†
Khayal, Inas S.; McKnight, Tracy R.; McGue, Colleen; Vandenberg, Scott; Lamborn, Kathleen R.; Chang, Susan M.; Cha, Soonmee; Nelson, Sarah J.
2013-01-01
Distinguishing between low-grade oligodendrogliomas (ODs) and astrocytomas (AC) is of interest for defining prognosis and stratifying patients to specific treatment regimens. The purpose of this study was to determine if the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) from diffusion imaging can help to differentiate between newly diagnosed grade II OD and AC subtypes and to evaluate the ADC and FA values for the mixed population of oligoastrocytomas (OA). Fifty-three patients with newly diagnosed grade II gliomas were studied using a 1.5T whole body scanner (23 ODs, 16 ACs, and 14 OAs). The imaging protocol included post-gadolinium T1-weighted images, T2-weighted images, and either three and/or six directional diffusion imaging sequence with b = 1000 s/mm2. Diffusion-weighted images were analyzed using in-house software to calculate maps of ADC and for six directional acquisitions, FA. The intensity values were normalized by values from normal appearing white matter (NAWM) to generate maps of normalized apparent diffusion coefficient (nADC) and normalized fractional anisotropy (nFA). The hyperintense region in the T2 weighted image was defined as the T2All region. A Mann–Whitney rank-sum test was performed on the 25th, median, and 75th nADC and nFA among the three subtypes. Logistic regression was performed to determine how well the nADC and nFA predict subtype. Lesions diagnosed as being OD had significantly lower nADC and significantly higher nFA, compared to AC. The nADC and nFA values individually classified the data with an accuracy of 87%. Combining the two did not enhance the classification. The patients with OA had nADC and nFA values between those of OD and AC. This suggests that ADC and FA may be helpful in directing tissue sampling to the most appropriate regions for taking biopsies in order to make a definitive diagnosis. PMID:19125391
Alipoor, Mohammad; Maier, Stephan E.; Gu, Irene Yu-Hua; Mehnert, Andrew; Kahl, Fredrik
2015-01-01
The monoexponential model is widely used in quantitative biomedical imaging. Notable applications include apparent diffusion coefficient (ADC) imaging and pharmacokinetics. The application of ADC imaging to the detection of malignant tissue has in turn prompted several studies concerning optimal experiment design for monoexponential model fitting. In this paper, we propose a new experiment design method that is based on minimizing the determinant of the covariance matrix of the estimated parameters (D-optimal design). In contrast to previous methods, D-optimal design is independent of the imaged quantities. Applying this method to ADC imaging, we demonstrate its steady performance for the whole range of input variables (imaged parameters, number of measurements, and range of b-values). Using Monte Carlo simulations we show that the D-optimal design outperforms existing experiment design methods in terms of accuracy and precision of the estimated parameters. PMID:26839880
Institute of Scientific and Technical Information of China (English)
Hong Lu; Xiaoyan Lei
2014-01-01
After traumatic brain injury, vasogenic and cytotoxic edema appear sequentially on the in-volved side. Neuroimaging investigations of edema on the injured side have employed apparent diffusion coefficient measurements in diffusion tensor imaging. We investigated the changes occurring on the injured and uninjured sides using diffusion tensor imaging/apparent diffusion coefficient and histological samples in rats. We found that, on the injured side, that vasogen-ic edema appeared at 1 hour and intracellular edema appeared at 3 hours. Mixed edema was observed at 6 hours, worsening until 12-24 hours post-injury. Simultaneously, microglial cells proliferated at the trauma site. Apparent diffusion coefficient values increased at 1 hour, decreased at 6 hours, and increased at 12 hours. The uninjured side showed no significant pathological change at 1 hour after injury. Cytotoxic edema appeared at 3 hours, and vasogen-ic edema was visible at 6 hours. Cytotoxic edema persisted, but vasogenic edema tended to decrease after 12-24 hours. Despite this complex edema pattern on the uninjured side with associated pathologic changes, no significant change in apparent diffusion coefficient values was detected over the first 24 hours. Apparent diffusion coefficient values accurately detected the changes on the injured side, but did not detect the changes on the uninjured side, giving a false-negative result.
Energy Technology Data Exchange (ETDEWEB)
Naganawa, Shinji; Sato, Chiho; Ishigaki, Takeo [Nagoya University School of Medicine, Department of Radiology, Nagoya (Japan); Kumada, Hisashi; Miura, Shunichi [Toyohashi Municipal hospital, Department of Radiology, Toyohashi, Aich (Japan); Takizawa, Osamu [Siemens-Asahi Medical Technologies Ltd, Tokyo (Japan)
2005-01-01
A relation between apparent diffusion coefficient (ADC) values and tumor cellular density has been reported. The purpose of this study was to measure the ADC values of cervical cancers in the uterus and compare them with those of normal cervical tissues, and to test whether ADC could differentiate between normal and malignant cervical tissues in the uterus. Twelve consecutive female patients with cervical cancer of the uterus and ten female patients with other pelvic abnormalities were included in this study. ADC was measured at 1.5 T with b-factors of 0, 300 and 600 s/mm{sup 2} using single-shot echo-planar diffusion-weighted imaging and a parallel imaging technique. The mean ADC value of cervical cancer lesions was 1.09{+-}0.20 x 10{sup -3} mm{sup 2}/s, and that of normal cervix tissue was 1.79{+-}0.24 x 10{sup -3} mm{sup 2}/s (P<0.0001). In nine patients treated by chemotherapy and/or radiation therapy, the mean ADC value of the cervical cancer lesion increased significantly after therapy (P<0.001). The present study showed, with a small number of patients, that ADC measurement has a potential ability to differentiate between normal and cancerous tissue in the uterine cervix. Further study is necessary to determine the accuracy of ADC measurement in monitoring the treatment response. (orig.)
Regional apparent diffusion coefficient values in 3rd trimester fetal brain
Energy Technology Data Exchange (ETDEWEB)
Hoffmann, Chen [Tel Aviv University, Department of Radiology, Sheba Medical Center, Tel Hashomer (affiliated to the Sackler School of Medicine), Tel Aviv (Israel); Sheba Medical Center, Diagnostic Imaging, 52621, Tel Hashomer (Israel); Weisz, Boaz; Lipitz, Shlomo; Katorza, Eldad [Tel Aviv University, Department of Obstetrics and Gynecology, Sheba Medical Center, Tel Hashomer (affiliated to the Sackler School of Medicine), Tel Aviv (Israel); Yaniv, Gal; Bergman, Dafi [Tel Aviv University, Department of Radiology, Sheba Medical Center, Tel Hashomer (affiliated to the Sackler School of Medicine), Tel Aviv (Israel); Biegon, Anat [Stony Brook University School of Medicine, Department of Neurology, Stony Brook, NY (United States)
2014-07-15
Apparent diffusion coefficient (ADC) values in the developing fetus can be used in the diagnosis and prognosis of prenatal brain pathologies. To this end, we measured regional ADC in a relatively large cohort of normal fetal brains in utero. Diffusion-weighted imaging (DWI) was performed in 48 non-sedated 3rd trimester fetuses with normal structural MR imaging results. ADC was measured in white matter (frontal, parietal, temporal, and occipital lobes), basal ganglia, thalamus, pons, and cerebellum. Regional ADC values were compared by one-way ANOVA with gestational age as covariate. Regression analysis was used to examine gestational age-related changes in regional ADC. Four other cases of CMV infection were also examined. Median gestational age was 32 weeks (range, 26-33 weeks). There was a highly significant effect of region on ADC, whereby ADC values were highest in white matter, with significantly lower values in basal ganglia and cerebellum and the lowest values in thalamus and pons. ADC did not significantly change with gestational age in any of the regions tested. In the four cases with fetal CMV infection, ADC value was associated with a global decrease. ADC values in normal fetal brain are relatively stable during the third trimester, show consistent regional variation, and can make an important contribution to the early diagnosis and possibly prognosis of fetal brain pathologies. (orig.)
Apparent diffusion coefficient histogram analysis of neonatal hypoxic-ischemic encephalopathy
Energy Technology Data Exchange (ETDEWEB)
Cauley, Keith A. [University of Massachusetts Medical School, Department of Radiology, Worcester, MA (United States); New York Presbyterian Hospital, Columbia University Medical Center, Department of Radiology, New York, NY (United States); Filippi, Christopher G. [New York Presbyterian Hospital, Columbia University Medical Center, Department of Radiology, New York, NY (United States)
2014-06-15
Diffusion-weighted imaging is a valuable tool in the assessment of the neonatal brain, and changes in diffusion are seen in normal development as well as in pathological states such as hypoxic-ischemic encephalopathy (HIE). Various methods of quantitative assessment of diffusion values have been reported. Global ischemic injury occurring during the time of rapid developmental changes in brain myelination can complicate the imaging diagnosis of neonatal HIE. To compare a quantitative method of histographic analysis of brain apparent coefficient (ADC) maps to the qualitative interpretation of routine brain MR imaging studies. We correlate changes in diffusion values with gestational age in radiographically normal neonates, and we investigate the sensitivity of the method as a quantitative measure of hypoxic-ischemic encephalopathy. We reviewed all brain MRI studies from the neonatal intensive care unit (NICU) at our university medical center over a 4-year period to identify cases that were radiographically normal (23 cases) and those with diffuse, global hypoxic-ischemic encephalopathy (12 cases). We histographically displayed ADC values of a single brain slice at the level of the basal ganglia and correlated peak (s-sD{sub av}) and lowest histogram values (s-sD{sub lowest}) with gestational age. Normative s-sD{sub av} values correlated significantly with gestational age and declined linearly through the neonatal period (r {sup 2} = 0.477, P < 0.01). Six of 12 cases of known HIE demonstrated significantly lower s-sD{sub av} and s-sD{sub lowest} ADC values than were reflected in the normative distribution; several cases of HIE fell within a 95% confidence interval for normative studies, and one case demonstrated higher-than-normal s-sD{sub av}. Single-slice histographic display of ADC values is a rapid and clinically feasible method of quantitative analysis of diffusion. In this study normative values derived from consecutive neonates without radiographic evidence of
International Nuclear Information System (INIS)
Objectives: to evaluate the prognostic value of apparent diffusion coefficient (ADC) values from MR diffusion-weighted imaging of unresectable hepatocellular carcinoma after chemoembolization. Methods: our study was proved by our institute and informed consent was obtained from all patients before commencement of the study. Twenty-three patients with unresectable hepatocellular carcinoma were scanned immediately before and after chemoembolization within 24 h using conventional anatomical MR imaging and diffusion-weighted imaging, from which ADC values in the lesions were measured. The changes in ADC values after chemoembolization were calculated. The relationship between the lesion ADC and the survival time was analyzed by correlation analysis. The overall cumulative survival was analyzed by the Kaplan–Meier method, and survival curves were compared by the log-rank test. Results: the mean overall survival period was (25.0 ± 8.7) months. The pre-chemoembolization lesion ADC value was (1.36 ± 0.249) ×10−3 mm2/s; the change in ADC values post-chemoembolization was (0.377 ± 0.332) ×10−3 mm2/s. There were significant linear regression relation between the survival time and pre-chemoembolization lesion ADC values (r = −0.698, P 2 = 7.339, P = 0.007) or the changes in ADC value post-chemoembolization (χ2 = 9.820, P = 0.002) significantly influenced the overall cumulative survival. Conclusion: Pre-treatment ADC values as well as changes in ADC values after treatment may provide useful information for predicting survival for patients with unresectable hepatocellular carcinoma.
Energy Technology Data Exchange (ETDEWEB)
Adachi, Yuko; Sato, Noriko; Yamashita, Fumio; Kida, Jiro; Takahashi, Tomoyuki [National Center Hospital of Neurology and Psychiatry, Department of Radiology, Kodaira, Tokyo (Japan); Okamoto, Tomoko [National Center Hospital of Neurology and Psychiatry, Department of Neurology, Kodaira, Tokyo (Japan); Sasaki, Masayuki; Komaki, Hirofumi [National Center Hospital of Neurology and Psychiatry, Department of Child Neurology, Kodaira, Tokyo (Japan); Matsuda, Hiroshi [Saitama Medial University Hospital, Department of Nuclear Medicine, Iruma-gun, Saitama (Japan)
2011-01-15
Our purpose was to clarify the magnetic resonance (MR) imaging characteristics of the brachial and lumbar plexuses in patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) using various kinds of sequences, including diffusion-weighted images (DWI). We evaluated the MR imaging findings for lumbar and/or brachial nerve plexuses in 13 CIDP patients and 11 normal volunteers. The nerve swelling was evaluated in comparison with normal controls by coronal short tau inversion recovery (STIR), and signal abnormalities were evaluated by coronal STIR, T1-weighted images, and DWIs. The degrees of contrast enhancement and apparent diffusion coefficient (ADC) values of the plexus were also assessed. In the patient group, diffuse enlargement and abnormally high signals were detected in 16 out of 24 plexuses (66.7%) on STIR, a slightly high signal was detected in 12 of 24 plexuses (50%) on T1-weighted images, and a high-intensity signal was detected in 10 of 18 plexuses (55.6%) on DWIs with high ADC values. Contrast enhancement of the plexuses was revealed in 6 of 19 plexuses (31.6%) and was mild in all cases. There were statistically significant differences between the ADC values of patients with either swelling or abnormal signals and those of both normal volunteers and patients without neither swelling nor abnormal signals. There were no relationships between MR imaging and any clinical findings. STIR is sufficient to assist clinicians in diagnosing CIDP. T1-weighted images and DWIs seemed useful for speculating about the pathological changes in swollen plexuses in CIDP patients. (orig.)
Apparent diffusion coefficient values of normal testis and variations with age
Directory of Open Access Journals (Sweden)
Athina C Tsili
2014-06-01
Full Text Available The usefulness of diffusion-weighted magnetic resonance imaging (DWI in the evaluation of scrotal pathology has recently been reported. A standard reference of normal testicular apparent diffusion coefficient (ADC values and their variations with age is necessary when interpreting normal testicular anatomy and pathology. We evaluated 147 normal testes using DWI, including 71 testes from 53 men aged 20-39 years (group 1, 67 testes from 42 men aged 40-69 years (group 2 and nine testes from six men older than 70 years (group 3. DWI was performed along the axial plane, using a single shot, multislice spin-echo planar diffusion pulse sequence and b-values of 0 and 900 s mm−2 . The mean and standard deviation of the ADC values of normal testicular parenchyma were calculated for each age group separately. Analysis of variance (ANOVA followed by post hoc analysis (Dunnett T3 was used for statistical purposes. The ADC values (× 10−3 mm 2 s−1 of normal testicular tissue were different among age groups (group 1: 1.08 ± 0.13; group 2: 1.15 ± 0.15 and group 3: 1.31 ± 0.22. ANOVA revealed differences in mean ADC among age groups (F = 11.391, P < 0.001. Post hoc analysis showed differences between groups 1 and 2 (P = 0.008 and between groups 1 and 3 (P = 0.043, but not between groups 2 and 3 (P = 0.197. Our findings suggest that ADC values of normal testicular tissue increase with advancing age.
Yang, Yunjun; Gao, Lingyun; Fu, Jun; Zhang, Jun; Li, Yuxin; Yin, Bo; Chen, Weijian; Geng, Daoying
2013-11-01
Supratentorial cerebral infarction can cause functional inhibition of remote regions such as the cerebellum, which may be relevant to diaschisis. This phenomenon is often analyzed using positron emission tomography and single photon emission CT. However, these methods are expensive and radioactive. Thus, the present study quantified the changes of infarction core and remote regions after unilateral middle cerebral artery occlusion using apparent diffusion coefficient values. Diffusion-weighted imaging showed that the area of infarction core gradually increased to involve the cerebral cortex with increasing infarction time. Diffusion weighted imaging signals were initially increased and then stabilized by 24 hours. With increasing infarction time, the apparent diffusion coefficient value in the infarction core and remote bilateral cerebellum both gradually decreased, and then slightly increased 3-24 hours after infarction. Apparent diffusion coefficient values at remote regions (cerebellum) varied along with the change of supratentorial infarction core, suggesting that the phenomenon of diaschisis existed at the remote regions. Thus, apparent diffusion coefficient values and diffusion weighted imaging can be used to detect early diaschisis. PMID:25206615
Parameterization of the Age-Dependent Whole Brain Apparent Diffusion Coefficient Histogram
Directory of Open Access Journals (Sweden)
Uwe Klose
2015-01-01
Full Text Available Purpose. The distribution of apparent diffusion coefficient (ADC values in the brain can be used to characterize age effects and pathological changes of the brain tissue. The aim of this study was the parameterization of the whole brain ADC histogram by an advanced model with influence of age considered. Methods. Whole brain ADC histograms were calculated for all data and for seven age groups between 10 and 80 years. Modeling of the histograms was performed for two parts of the histogram separately: the brain tissue part was modeled by two Gaussian curves, while the remaining part was fitted by the sum of a Gaussian curve, a biexponential decay, and a straight line. Results. A consistent fitting of the histograms of all age groups was possible with the proposed model. Conclusions. This study confirms the strong dependence of the whole brain ADC histograms on the age of the examined subjects. The proposed model can be used to characterize changes of the whole brain ADC histogram in certain diseases under consideration of age effects.
International Nuclear Information System (INIS)
Highlights: • Functional MRI in the characterization of testicular germ cell tumors was assessed. • ADC values proved useful in the characterization of testicular germ cell tumors. • Testicular germ cell tumors had similar enhancement patterns of dynamic MRI. - Abstract: Introduction: The aim of this study is to investigate the role of apparent diffusion coefficient (ADC) values and dynamic contrast enhancement (DCE) patterns in differentiating seminomas from nonseminomatous germ cell tumors (NSGCTs). Materials and methods: The MRI examinations of the scrotum of 26 men with histologically proven testicular GCTs were reviewed. DWI was performed in all patients, using a single shot, multi-slice spin-echo planar diffusion pulse sequence and b-values of 0 and 900 s/mm2. Subtraction DCE-MRI was performed in 20 cases using a 3D fast-field echo sequence after gadolinium administration. Time-signal intensity curves were created and semi-quantitative parameters (peak enhancement, time to peak, wash-in and wash-out rate) were calculated. The Student's t-test was used to compare the mean values of ADC, peak enhancement, time to peak, wash-in and wash-out rate between seminomas and NSGCTs. ROC analysis was also performed. Results: Histopathology disclosed the presence of 15 seminomas and 11 NSGCTs. The mean ± s.d. of ADC values (× 10−3 mm2/s) of seminomas (0.59 ± 0.009) were significantly lower than those of NSGCTs (0.90 ± 0.33) (P = 0.01). The optimal ADC cut-off value was 0.68 × 10−3 mm2/s. No differences between the two groups were observed for peak enhancement (P = 0.18), time to peak (P = 0.63) wash-in rate (P = 0.32) and wash-out rate (P = 0.18). Conclusions: ADC values may be used to preoperatively differentiate seminomas from NSGCTs
Energy Technology Data Exchange (ETDEWEB)
Tsili, Athina C., E-mail: a_tsili@yahoo.gr [Department of Radiology, Medical School, University of Ioannina, 45110 Ioannina (Greece); Ntorkou, Alexandra, E-mail: alexdorkou@yahoo.com [Department of Radiology, Medical School, University of Ioannina, 45110 Ioannina (Greece); Baltogiannis, Dimitrios, E-mail: Greece.dbaltog@cc.uoi.gr [Department of Urology, Medical School, University of Ioannina, 45110 Ioannina (Greece); Goussia, Anna, E-mail: agoussia@uoi.gr [Department of Pathology, Medical School, University of Ioannina, 45110 Ioannina (Greece); Astrakas, Loukas G., E-mail: astrakas@uoi.gr [Department of Medical Physics, Medical School, University of Ioannina, 45110 Ioannina (Greece); Malamou-Mitsi, Vasiliki, E-mail: vmalamou@cc.uoi.gr [Department of Pathology, Medical School, University of Ioannina, 45110 Ioannina (Greece); Sofikitis, Nikolaos, E-mail: akrosnin@hotmail.com [Department of Urology, Medical School, University of Ioannina, 45110 Ioannina (Greece); Argyropoulou, Maria I., E-mail: margyrop@cc.uoi.gr [Department of Radiology, Medical School, University of Ioannina, 45110 Ioannina (Greece)
2015-05-15
Highlights: • ADC values proved useful in the discrimination between TGCNs and normal testis. • Testicular intraepithelial neoplasia represents the precursor of most TGCNs. • ADC values cannot be used to detect testicular intraepithelial neoplasia. - Abstract: Introduction: The aim of this study is to improve detection of testicular intraepithelial neoplasia (TIN) by measurement of apparent diffusion coefficient (ADC) values. Materials and methods: Fifty-six MRI examinations of the scrotum, including 26 histologically proven testicular germ cell neoplasms were retrospectively evaluated. DWI was performed using a single shot, multi-slice spin-echo planar diffusion pulse sequence and b-values of 0 and 900 s mm{sup −2}. ADC measurements were classified into three groups according to their location: group 1 (n = 19), non-tumoral part, adjacent to testicular carcinoma, where the possible location of TIN was; group 2 (n = 26), testicular carcinoma; and group 3 (n = 60), normal testicular parenchyma. Analysis of variance (ANOVA) followed by post hoc analysis (Dunnett T3) was used for statistical purposes. Results: The mean ± s.d. of ADC values (×10{sup −3} mm{sup 2}/s) of different groups were: group 1, 1.08 ± 0.20; group 2, 0.72 ± 0.27; and group 3, 1.11 ± 0.14. ANOVA revealed differences of mean ADC between groups (F = 38.859, P < 0.001). Post hoc analysis showed differences between groups 2 and 3 (P < 0.001), groups 2 and 1 (P < 0.001), but not between groups 3 and 1 (P = 0.87). Conclusions: Based on our preliminary results, ADC values do not provide a reliable differentiation between TIN and testicular carcinoma or normal testicular parenchyma.
Energy Technology Data Exchange (ETDEWEB)
Olsen, Oe.E.; Sebire, N.J. [Great Ormond Street Hospital for Children NHS Trust, London (United Kingdom). Radiology and Histopathology Depts.
2006-03-15
Purpose: To assess the technical feasibility of apparent diffusion coefficient (ADC) mapping based on free-breathing diffusion-weighted magnetic resonance (DW-MR) outside the CNS in children. Material and Methods: Twelve children with mass lesions of varied histopathology were scanned with short-tau inversion recovery (STIR), contrast-enhanced T1-weighted (CE-T1W), and diffusion-weighted (b = 0, 500 and 1,000 s/mm{sup 2}) sequences. ADC maps were calculated. Lesion-to-background signal intensity ratios were measured and compared between STIR/CE-T1W/ADC overall (Friedman test) and between viable embryonal tumors and other lesions (Kruskal-Wallis test). Results: ADC maps clearly depicted all lesions. Lesion-to-background signal intensity ratios of STIR (median 3.7), CE-T1W (median 1.4), and ADC (median 1.6) showed no overall difference (chi-square = 3.846; P = 0.146), and there was no difference between viable embryonal tumors and other lesions within STIR/CE-T1W/ADC (chi-square 1.118/0.669/<0.001; P = 0.290/0.414/1.000, respectively). Conclusion: ADC mapping is feasible in free-breathing imaging of pediatric mass lesions outside the CNS using standard clinical equipment. Keywords: Diffusion-weighted magnetic resonance imaging; infants and children; neoplasms.
International Nuclear Information System (INIS)
Aim: To identify retrospectively potential associations between apparent diffusion coefficient (ADC) values of pancreatic adenocarcinoma and tumour grade as well as other pathological features, using histopathological assessment from the Whipple procedure as the reference standard. Materials and methods: Thirty patients with pancreatic adenocarcinoma underwent magnetic resonance imaging (MRI) including diffusion-weighted imaging with b-values of 0 and 500 s/mm2 before the Whipple procedure. Two radiologists independently recorded the ADC values of the tumour and benign pancreas for all cases. ADC values were compared with histopathological findings following the Whipple procedure. Results: The intra-class correlation coefficient was 0.689 for benign pancreas and 0.695 for tumours, indicating good inter-reader agreement for ADC values. The mean ADC value was significantly lower in tumours than in benign pancreas for both readers (reader 1: 1.74 ± 0.34 × 10−3 mm2/s versus 2.08 ± 0.48 × 10−3 mm2/s, respectively, p = 0.006; reader 2: 1.69 ± 0.41 × 10−3 mm2/s versus 2.11 ± 0.54 × 10−3 mm2/s, respectively, p −3 mm2/s versus 1.78 ± 0.33 × 10−3 mm2/s, respectively, p = 0.491; reader 2: 1.62 ± 0.33 × 10−3 mm2/s versus 1.75 ± 0.49 × 10−3 mm2/s, respectively, p = 0.405). The area under the curve (AUC) for differentiation of poorly and well/moderately differentiated tumours was 0.611 and 0.596 for readers 1 and 2, respectively, and was not significantly better than an AUC of 0.500 for either reader (p ≥ 0.306). In addition, ADC was not significantly different for either reader between tumours with stage T3 versus stage T1/T2, between tumours with and without metastatic peri-pancreatic lymph nodes, or between tumours located in the pancreatic head versus other pancreatic regions (p ≥ 0.413). Conclusion: No associations between ADC values of pancreatic adenocarcinoma and tumour grade or other adverse pathological features were observed
Energy Technology Data Exchange (ETDEWEB)
Uysal, Fatma, E-mail: afatmauysal@gmail.com [Dokuz Eylül University, Department of Pediatric Radiology, Izmir (Turkey); Çakmakçı, Handan, E-mail: handan.cakmakci@deu.edu.tr [Dokuz Eylül University, Department of Pediatric Radiology, Izmir (Turkey); Yiş, Uluç, E-mail: ulucyis@deu.edu.tr [Dokuz Eylül University, Department of Pediatric Neurology, Izmir (Turkey); Ellidokuz, Hülya, E-mail: hulyaellidokuz@deu.edu.tr [Dokuz Eylül University, Department of Medical Statistics, Izmir (Turkey); Hız, Ayşe Semra, E-mail: aysesemrahiz@deu.edu.tr [Dokuz Eylül University, Department of Pediatric Neurology, Izmir (Turkey)
2014-01-15
Objectives: To reveal the contribution of MRI and diffusion-weighted imaging (DWI) to the diagnosis of mitochondrial encephalopathy (ME) and to evaluate the parenchymal changes associated with this disease in the involved parenchymal areas using the apparent diffusion coefficient (ADC) parameter. Methods: Ten patients who had undergone MRI and DWI analysis with a pre-diagnosis of neurometabolic disease, and who were subsequently diagnosed with ME in laboratory and/or genetic studies, were included in our study. ADC values were compared with a control group composed of 20 patients of similar age with normal brains. Evaluations involved measurements made in 20 different areas determined on the ADC map. The dominance or contribution of ADC coefficient measurements to the conventional sequences was compared with the controls. Results: In the first examination, an increase in both diffusion and ADC values was detected in six cases and diffusion restriction and a decrease in ADC values in three patients. While an increase in both diffusion and ADC values was demonstrated in four cases, there was diffusion restriction and a decrease in ADC values in three cases in the control examinations. Conclusions: DWI provides information that complements conventional MRI sequences in the diagnosis of ME.
Energy Technology Data Exchange (ETDEWEB)
Toyoshima, S.; Noguchi, K.; Seto, H.; Shimizu, M.; Watanabe, N. [Toyama Medical and Pharmaceutical Univ. (Japan). Dept. of Radiology
2000-11-01
To determine the relationship between apparent diffusion coefficient (ADC) values measured by diffusion-weighted MR imaging and split renal function determined by renal scintigraphy in patients with hydronephrosis. Material and Methods: Diffusion-weighted imaging on a 1.5 T MR unit and renal scintigraphy were performed in 36 patients with hydronephrosis (45 hydronephrotic kidneys, 21 non-hydronephrotic kidneys). ADC values of the individual kidneys were measured by diffusion-weighted MR imaging. Split renal function (glomerular filtration rate (GFR)) was determined by renal scintigraphy using {sup 99m}Tc-DTPA. The relationship between ADC values and split GFR was examined in 66 kidneys. The hydronephrotic kidneys were further classified into three groups (severe renal dysfunction, GFR <10 ml/min, n=7; moderate renal dysfunction, GFR 10-25 ml/min, n=10; normal renal function, GFR >25 ml/min, n=28), and mean values for ADCs were calculated. Results: In hydronephrotic kidneys, there was a moderate positive correlation between ADC values and split GFR (R2=0.56). On the other hand, in non-hydronephrotic kidneys, poor correlation between ADC values and split GFR was observed (R2=0.08). The mean values for ADCs of the dysfunctioning hydronephrotic kidneys (severe renal dysfunction, 1.32x10{sup -3}{+-}0.18x10{sup -3} mm{sup 2}/s; moderate renal dysfunction, 1.38x10{sup -3}{+-}0.10x10{sup -3} mm2/s) were significantly lower than that of the normal functioning hydronephrotic kidneys (1.63x10{sup -3}{+-}0.12{+-}10{sup -3} mm{sup 2}/s). Conclusion: These results indicated that measurement of ADC values by diffusion-weighted MR imaging has a potential value in the evaluation of the functional status of hydronephrotic kidneys.
Energy Technology Data Exchange (ETDEWEB)
Tsili, Athina C., E-mail: a_tsili@yahoo.gr [Department of Radiology, Medical School, University of Ioannina, 45110 Ioannina (Greece); Sylakos, Anastasios, E-mail: anasylakos@yahoo.gr [Department of Urology, Medical School, University of Ioannina, 45110 Ioannina (Greece); Ntorkou, Alexandra, E-mail: alexdorkou@yahoo.com [Department of Radiology, Medical School, University of Ioannina, 45110 Ioannina (Greece); Stavrou, Sotirios, E-mail: s.sotiris@yahoo.gr [Department of Urology, Medical School, University of Ioannina, 45110 Ioannina (Greece); Astrakas, Loukas G., E-mail: astrakas@uoi.gr [Department of Medical Physics, Medical School, University of Ioannina, 45110 Ioannina (Greece); Sofikitis, Nikolaos, E-mail: akrosnin@hotmail.com [Department of Urology, Medical School, University of Ioannina, 45110 Ioannina (Greece); Argyropoulou, Maria I., E-mail: margyrop@cc.uoi.gr [Department of Radiology, Medical School, University of Ioannina, 45110 Ioannina (Greece)
2015-07-15
Highlights: • Functional MRI in the characterization of testicular germ cell tumors was assessed. • ADC values proved useful in the characterization of testicular germ cell tumors. • Testicular germ cell tumors had similar enhancement patterns of dynamic MRI. - Abstract: Introduction: The aim of this study is to investigate the role of apparent diffusion coefficient (ADC) values and dynamic contrast enhancement (DCE) patterns in differentiating seminomas from nonseminomatous germ cell tumors (NSGCTs). Materials and methods: The MRI examinations of the scrotum of 26 men with histologically proven testicular GCTs were reviewed. DWI was performed in all patients, using a single shot, multi-slice spin-echo planar diffusion pulse sequence and b-values of 0 and 900 s/mm{sup 2}. Subtraction DCE-MRI was performed in 20 cases using a 3D fast-field echo sequence after gadolinium administration. Time-signal intensity curves were created and semi-quantitative parameters (peak enhancement, time to peak, wash-in and wash-out rate) were calculated. The Student's t-test was used to compare the mean values of ADC, peak enhancement, time to peak, wash-in and wash-out rate between seminomas and NSGCTs. ROC analysis was also performed. Results: Histopathology disclosed the presence of 15 seminomas and 11 NSGCTs. The mean ± s.d. of ADC values (× 10{sup −3} mm{sup 2}/s) of seminomas (0.59 ± 0.009) were significantly lower than those of NSGCTs (0.90 ± 0.33) (P = 0.01). The optimal ADC cut-off value was 0.68 × 10{sup −3} mm{sup 2}/s. No differences between the two groups were observed for peak enhancement (P = 0.18), time to peak (P = 0.63) wash-in rate (P = 0.32) and wash-out rate (P = 0.18). Conclusions: ADC values may be used to preoperatively differentiate seminomas from NSGCTs.
DEFF Research Database (Denmark)
Diaz, Sandra; Casselbrant, Ingrid; Piitulainen, Eeva;
2008-01-01
PURPOSE: To compare apparent diffusion coefficient (ADC) measurements from hyperpolarized (HP) helium ((3)He)-magnetic resonance imaging (MRI) with quantitative data from multislice Computed Tomography (CT) (MSCT) of the whole lungs and pulmonary function tests (PFT). MATERIALS AND METHODS: Twenty...
International Nuclear Information System (INIS)
Fifteen multiple sclerosis patients were examined by diffusion tensor imaging (DTI) to determine fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in a superventricular volume of interest of 8 x 8 x 2 cm3 containing gray matter (GM) and white matter (WM) tissue. Point resolved spectroscopy 2D-chemical shift imaging of the same volume was performed without water suppression. The water contents and DTI parameters in 64 voxels of 2 cm3 were compared. The water content was increased in patients compared with controls (GM: 244±21 vs. 194±10 a.u.; WM: 245±32 vs. 190±11 a.u.), FA decreased (GM: 0.226±0.038 vs. 0.270±0.020; WM: 0.337±0.044 vs. 0.402±0.011) and ADC increased [GM: 1134±203 vs. 899±28 (x 10-6 mm2/s); WM: 901±138 vs. 751±17 (x 10-6 mm2/s)]. Correlations of water content with FA and ADC in WM were strong (r=-0.68, P<0.02; r=0.75; P<0.01, respectively); those in GM were weaker (r=-0.50, P<0.05; r=0.45, P<0.1, respectively). Likewise, FA and ADC were more strongly correlated in WM (r=-0.88; P<0.00001) than in GM (r=-0.69, P<0.01). The demonstrated relationship between DTI parameters and water content in multiple sclerosis patients suggests a potential for therapy monitoring in normal-appearing brain tissue. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Sijens, Paul E.; Irwan, Roy; Potze, Jan Hendrik; Oudkerk, Matthijs [University Medical Center Groningen and University of Groningen, Department of Radiology, Groningen (Netherlands); Mostert, Jop P.; Keyser, Jacques de [University Medical Center Groningen and University of Groningen, Department of Neurology, Groningen (Netherlands)
2006-04-15
Fifteen multiple sclerosis patients were examined by diffusion tensor imaging (DTI) to determine fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in a superventricular volume of interest of 8 x 8 x 2 cm{sup 3} containing gray matter (GM) and white matter (WM) tissue. Point resolved spectroscopy 2D-chemical shift imaging of the same volume was performed without water suppression. The water contents and DTI parameters in 64 voxels of 2 cm{sup 3} were compared. The water content was increased in patients compared with controls (GM: 244{+-}21 vs. 194{+-}10 a.u.; WM: 245{+-}32 vs. 190{+-}11 a.u.), FA decreased (GM: 0.226{+-}0.038 vs. 0.270{+-}0.020; WM: 0.337{+-}0.044 vs. 0.402{+-}0.011) and ADC increased [GM: 1134{+-}203 vs. 899{+-}28 (x 10{sup -6} mm{sup 2}/s); WM: 901{+-}138 vs. 751{+-}17 (x 10{sup -6} mm{sup 2}/s)]. Correlations of water content with FA and ADC in WM were strong (r=-0.68, P<0.02; r=0.75; P<0.01, respectively); those in GM were weaker (r=-0.50, P<0.05; r=0.45, P<0.1, respectively). Likewise, FA and ADC were more strongly correlated in WM (r=-0.88; P<0.00001) than in GM (r=-0.69, P<0.01). The demonstrated relationship between DTI parameters and water content in multiple sclerosis patients suggests a potential for therapy monitoring in normal-appearing brain tissue. (orig.)
Sijens, Paul E; Irwan, Roy; Potze, Jan Hendrik; Mostert, Jop P; De Keyser, Jacques; Oudkerk, Matthijs
2006-04-01
Fifteen multiple sclerosis patients were examined by diffusion tensor imaging (DTI) to determine fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in a superventricular volume of interest of 8 x 8 x 2 cm(3) containing gray matter (GM) and white matter (WM) tissue. Point resolved spectroscopy 2D-chemical shift imaging of the same volume was performed without water suppression. The water contents and DTI parameters in 64 voxels of 2 cm(3) were compared. The water content was increased in patients compared with controls (GM: 244+/-21 vs. 194+/-10 a.u.; WM: 245+/-32 vs. 190+/-11 a.u.), FA decreased (GM: 0.226+/-0.038 vs. 0.270+/-0.020; WM: 0.337+/-0.044 vs. 0.402+/-0.011) and ADC increased [GM: 1134+/-203 vs. 899+/-28 (x10(-6) mm(2)/s); WM: 901+/-138 vs. 751+/-17 (x10(-6) mm(2)/s)]. Correlations of water content with FA and ADC in WM were strong (r=-0.68, P<0.02; r=0.75; P<0.01, respectively); those in GM were weaker (r=-0.50, P<0.05; r=0.45, P<0.1, respectively). Likewise, FA and ADC were more strongly correlated in WM (r=-0.88; P<0.00001) than in GM (r=-0.69, P<0.01). The demonstrated relationship between DTI parameters and water content in multiple sclerosis patients suggests a potential for therapy monitoring in normal-appearing brain tissue.
Energy Technology Data Exchange (ETDEWEB)
Mahmoud, Omar M., E-mail: omarmostafa2008@yahoo.co [Department of Neurosurgery, Graduate School of Biomedical Science, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551 (Japan); Department of Radiology, South Egypt Cancer Institute, Assiut University, Assiut 71515 (Egypt); Tominaga, Atsushi, E-mail: atom@hiroshima-u.ac.j [Department of Neurosurgery, Graduate School of Biomedical Science, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551 (Japan); Amatya, Vishwa Jeet, E-mail: amatya@hiroshima-u.ac.j [Department of Pathology, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima 734-8551 (Japan); Ohtaki, Megu, E-mail: ohtaki@hiroshima-u.ac.j [Department of Environmetrics and Biometrics, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima 734-8551 (Japan); Sugiyama, Kazuhiko, E-mail: brain@hiroshima-u.ac.j [Department of Neurosurgery, Graduate School of Biomedical Science, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551 (Japan); Saito, Taiichi, E-mail: taiichi@hiroshima-u.ac.j [Department of Neurosurgery, Graduate School of Biomedical Science, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551 (Japan); Sakoguchi, Tetsuhiko, E-mail: sakog@hiroshima-u.ac.j [Department of Neurosurgery, Graduate School of Biomedical Science, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551 (Japan); Kinoshita, Yasuyuki, E-mail: d055634@hiroshima-u.ac.j [Department of Neurosurgery, Graduate School of Biomedical Science, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551 (Japan); Shrestha, Prabin, E-mail: prabinshrestha@hotmail.co [Department of Neurosurgery, Graduate School of Biomedical Science, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551 (Japan); Abe, Nobukazu, E-mail: abebe@hiroshima-u.ac.j [Dept. of Clinical Radiology, Graduate School of Biomedical Sciences, Hiroshima Univ., Hiroshima 734-8551 (Japan)
2010-06-15
Objective: To evaluate the role of the apparent diffusion coefficient (ADC) using periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) diffusion weighted imaging (DWI) in the differentiation between sellar and parasellar mass lesions. Materials and methods: The study protocol was approved by our institutional review board. We retrospectively studied 60 patients with sellar and parasellar lesions who had undergone PROPELLER DWI on a 3-T MR imager. Conventional MRI findings were expressed as the ratio of signal intensity (SI) in the lesions to the normal white matter and the degree of contrast enhancement. ADC values were calculated as the minimum (ADC-MIN), mean (ADC-MEAN), and maximum (ADC-MAX). All patients underwent surgery and all specimens were examined histologically. Logistic discriminant analysis was performed by using the SI ratios on T1- and T2-weighted images (T1-WI, T2-WI), the degree of enhancement, and absolute ADC values as independent variables. Results: ADC-MIN of hemorrhagic pituitary adenomas was lower than of the other lesions with similar appearance on conventional MRI (non-hemorrhagic pituitary adenomas, craniopharyngiomas, Rathke's cleft cysts; accuracy 100%); the useful cut-off value was 0.700 x 10{sup -3} mm{sup 2}/s. ADC-MAX of meningiomas was lower than of non-hemorrhagic pituitary adenomas (accuracy 90.3%; p < 0.01). ADC-MIN of craniopharyngiomas was lower than of Rathke's cleft cysts (accuracy 100%; p < 0.05). Conclusion: As PROPELLER DWI is less sensitive to susceptibility artifacts than single-shot echoplanar DWI, it is more useful in the examination of sellar and parasellar lesions. Calculation of the ADC values helps to differentiate between various sellar and parasellar lesions.
Energy Technology Data Exchange (ETDEWEB)
Liu, Song, E-mail: songliu532909756@gmail.com [Department of Radiology, Nanjing Drum Tower Hospital, The Affiliated Hospital of Nanjing University Medical School, Nanjing 210008 (China); Guan, Wenxian, E-mail: wenxianguan123@126.com [Department of Gastrointestinal Surgery, Nanjing Drum Tower Hospital, The Affiliated Hospital of Nanjing University Medical School, Nanjing 210008 (China); Wang, Hao, E-mail: wanghao20140525@126.com [Department of Gastrointestinal Surgery, Nanjing Drum Tower Hospital, The Affiliated Hospital of Nanjing University Medical School, Nanjing 210008 (China); Pan, Liang, E-mail: panliang2014@126.com [Department of Radiology, Nanjing Drum Tower Hospital, The Affiliated Hospital of Nanjing University Medical School, Nanjing 210008 (China); Zhou, Zhuping, E-mail: zhupingzhou@126.com [Department of Radiology, Nanjing Drum Tower Hospital, The Affiliated Hospital of Nanjing University Medical School, Nanjing 210008 (China); Yu, Haiping, E-mail: haipingyu2012@126.com [Department of Radiology, Nanjing Drum Tower Hospital, The Affiliated Hospital of Nanjing University Medical School, Nanjing 210008 (China); Liu, Tian, E-mail: tianliu2014@126.com [Radiation Oncology and Winship Cancer Institute, Emory University, Atlanta, GA 30322 (United States); Yang, Xiaofeng, E-mail: xiaofengyang2014@126.com [Radiation Oncology and Winship Cancer Institute, Emory University, Atlanta, GA 30322 (United States); He, Jian, E-mail: hjxueren@126.com [Department of Radiology, Nanjing Drum Tower Hospital, The Affiliated Hospital of Nanjing University Medical School, Nanjing 210008 (China); Zhou, Zhengyang, E-mail: zyzhou@nju.edu.cn [Department of Radiology, Nanjing Drum Tower Hospital, The Affiliated Hospital of Nanjing University Medical School, Nanjing 210008 (China)
2014-12-15
Highlights: • Gastric cancers’ ADC values were significantly lower than normal gastric wall. • Gastric adenocarcinomas with different differentiation had different ADC values. • Gastric adenocarcinomas’ ADC values correlated with histologic differentiations. • Gastric cancers’ ADC values correlated with Lauren classifications. • Mean ADC value was better than min ADC value in characterizing gastric cancers. - Abstract: Objective: The purpose of this study was to evaluate the correlations between histological differentiation and Lauren classification of gastric cancer and the apparent diffusion coefficient (ADC) value of diffusion weighted imaging (DWI). Materials and methods: Sixty-nine patients with gastric cancer lesions underwent preoperative magnetic resonance imaging (MRI) (3.0T) and surgical resection. DWI was obtained with a single-shot, echo-planar imaging sequence in the axial plane (b values: 0 and 1000 s/mm{sup 2}). Mean and minimum ADC values were obtained for each gastric cancer and normal gastric walls by two radiologists, who were blinded to the histological findings. Histological type, degree of differentiation and Lauren classification of each resected specimen were determined by one pathologist. Mean and minimum ADC values of gastric cancers with different histological types, degrees of differentiation and Lauren classifications were compared. Correlations between ADC values and histological differentiation and Lauren classification were analyzed. Results: The mean and minimum ADC values of gastric cancers, as a whole and separately, were significantly lower than those of normal gastric walls (all p values <0.001). There were significant differences in the mean and minimum ADC values among gastric cancers with different histological types, degrees of differentiation and Lauren classifications (p < 0.05). Mean and minimum ADC values correlated significantly (all p < 0.001) with histological differentiation (r = 0.564, 0.578) and
DEFF Research Database (Denmark)
Kallehauge, Jesper Folsted; Tanderup, Kari; Haack, Søren;
2010-01-01
Diffusion weighted imaging (DWI) has gained interest as an imaging modality for assessment of tumor extension and response to cancer treatment. The purpose of this study is to assess the impact of the choice of b-values on the calculation of the Apparent Diffusion Coefficient (ADC) for locally...
K. Coenegrachts; J. Delanote; L. ter Beek; M. Haspeslagh; S. Bipat; J. Stoker; L. Steyaert; H. Rigauts
2009-01-01
PURPOSE: To assess the added value of true diffusion (D), perfusion factor (f) and apparent diffusion coefficient at low b-values (ADC(low)) for differentiation between liver metastases and hemangiomas based on respiratory-triggered high-resolution Black-Blood Single-Shot SpinEcho Echo Planar Imagin
Rosenkrantz, A.B.; Oei, M.T.H.; Babb, J.S.; Niver, B.E.; Taouli, B.
2011-01-01
PURPOSE: To compare single-shot echo-planar imaging (SS EPI) diffusion-weighted MRI (DWI) of abdominal organs between 1.5 Tesla (T) and 3.0T in healthy volunteers in terms of image quality, apparent diffusion coefficient (ADC) values, and ADC reproducibility. MATERIALS AND METHODS: Eight healthy vol
Yu, Jiangsheng; Law, Michelle; Kadlecek, Stephen; Emami, Kiarash; Ishii, Masaru; Stephen, Michael; Woodburn, John M.; Vahdat, Vahid; Rizi, Rahim R.
2009-01-01
Hyperpolarized 3He (HP 3He) MRI shows promise to assess structural and functional pulmonary parameters in a sensitive, regional and non-invasive way. Structural HP 3He MRI has applied the apparent diffusion coefficient (ADC) for the detection of disease-induced lung microstructure changes at the alveolar level, and HP 3He pulmonary partial pressure of oxygen (pO2) imaging measures the oxygen transfer efficiency between the lung and blood stream. Although both parameters are affected in chroni...
Energy Technology Data Exchange (ETDEWEB)
Oh, Ji-Won, E-mail: fromentin@naver.com [Department of Radiology, Seoul St. Mary' s Hospital, College of Medicine, The Catholic University of Korea, 222 Banpo-daero, Seocho-gu, Seoul 137-701 (Korea, Republic of); Rha, Sung Eun, E-mail: serha@catholic.ac.kr [Department of Radiology, Seoul St. Mary' s Hospital, College of Medicine, The Catholic University of Korea, 222 Banpo-daero, Seocho-gu, Seoul 137-701 (Korea, Republic of); Oh, Soon Nam, E-mail: hiohsn@catholic.ac.kr [Department of Radiology, Seoul St. Mary' s Hospital, College of Medicine, The Catholic University of Korea, 222 Banpo-daero, Seocho-gu, Seoul 137-701 (Korea, Republic of); Park, Michael Yong, E-mail: digirave@kmle.com [Department of Radiology, Seoul St. Mary' s Hospital, College of Medicine, The Catholic University of Korea, 222 Banpo-daero, Seocho-gu, Seoul 137-701 (Korea, Republic of); Byun, Jae Young, E-mail: jybyun@catholic.ac.kr [Department of Radiology, Seoul St. Mary' s Hospital, College of Medicine, The Catholic University of Korea, 222 Banpo-daero, Seocho-gu, Seoul 137-701 (Korea, Republic of); Lee, Ahwon, E-mail: klee@catholic.ac.kr [Department of Hospital Pathology, Seoul St. Mary' s Hospital, College of Medicine, The Catholic University of Korea, 222 Banpo-daero, Seocho-gu, Seoul 137-701 (Korea, Republic of)
2015-04-15
Highlights: •The solid component of all invasive epithelial cancers showed high b{sub 1000} signal intensity. •ADCs can predict the histologic grade of epithelial ovarian cancer. •ADCs correlate negatively to the surgical stage of epithelial ovarian cancer. •ADCs may be useful imaging biomarkers to assess epithelial ovarian cancer. -- Abstract: Objective: The purpose of this article is to correlate the apparent diffusion coefficient (ADC) values of epithelial ovarian cancers with histologic grade and surgical stage. Materials and methods: We enrolled 43 patients with pathologically proven epithelial ovarian cancers for this retrospective study. All patients underwent preoperative pelvic magnetic resonance imaging (MRI) including diffusion-weighted images with b value of 0 and 1000 s/mm{sup 2} at 3.0-T unit. The mean ADC values of the solid portion of the tumor were measured and compared among different histologic grades and surgical stages. Results: The mean ADC values of epithelial ovarian cancers differed significantly between grade 1 (well-differentiated) and grade 2 (moderately-differentiated) (P = 0.013) as well as between grade 1 and grade 3 (poorly-differentiated) (P = 0.01); however, no statistically significant difference existed between grade 2 and grade 3 (P = 0.737). The receiver-operating characteristic analysis indicated that a cutoff ADC value of less than or equal to 1.09 × 10{sup −3} mm{sup 2}/s was associated with 94.4% sensitivity and 85.7% specificity in distinguishing grade 1 and grade 2/3 cancer. The difference in mean ADC values was statistically significant for early stage (FIGO stage I) and advanced stage (FIGO stage II-IV) cancer (P = 0.011). The interobserver agreement for the mean ADC values of epithelial ovarian cancers was excellent. Conclusion: The mean ADC values of the solid portion of epithelial ovarian cancers negatively correlated to histologic grade and surgical stage. The mean ADC values may be useful imaging
Energy Technology Data Exchange (ETDEWEB)
Mahmoud, Omar M. [Department of Neurosurgery, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551 (Japan); Department of Radiology, South Egypt Cancer Institute, Assiut University, Assiut 71515 (Egypt); Tominaga, Atsushi [Department of Neurosurgery, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551 (Japan); Amatya, Vishwa Jeet [Department of Pathology, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima 734-8551 (Japan); Ohtaki, Megu [Department of Environmetrics and Biometrics, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima 734-8551 (Japan); Sugiyama, Kazuhiko; Sakoguchi, Tetsuhiko; Kinoshita, Yasuyuki [Department of Neurosurgery, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551 (Japan); Takeshima, Yukio [Department of Pathology, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima 734-8551 (Japan); Abe, Nobukazu; Akiyama, Yuji [Department of Clinical Radiology, Hiroshima University Hospital, Hiroshima 734-8551 (Japan); El-Ghoriany, Ahmad I. [Department of Neurosurgery, Faculty of Medicine, Assiut University, Assiut 71515 (Egypt); Alla, Abdel Karim H. Abd; El-Sharkawy, Mostafa A.M. [Department of Radiology, Faculty of Medicine, Assiut University, Assiut 71515 (Egypt); Arita, Kazunori [Department of Neurosurgery, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima (Japan); Kurisu, Kaoru [Department of Neurosurgery, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551 (Japan); Yamasaki, Fumiyuki, E-mail: fyama@hiroshima-u.ac.jp [Department of Neurosurgery, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551 (Japan)
2011-11-15
Objective: The relationship between tumor consistency and apparent diffusion coefficient (ADC) values is controversial. We evaluated the role of the ADC using an advanced diffusion-weighted imaging (DWI) technique. We employed periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) DWI acquired on a 3-T magnetic resonance imaging (MRI) scanner to assess the consistency of pituitary adenomas and examined the relationship between the ADC and the hormone secretion status of the tumors and their MIB-1 labeling index (MIB-1 LI). Materials and methods: The study protocol was approved by our institutional review board. We retrospectively studied 24 operated patients with pituitary adenomas who had undergone PROPELLER DWI on a 3-T MRI scanner. Conventional MRI findings were expressed as the ratio of the signal intensity (SI) in the lesions to the SI of the normal white matter and the degree of contrast enhancement. Minimum-, mean-, and maximum ADC (ADC{sub min}, ADC{sub mean}, ADC{sub max}) values were calculated. The consistency of the tumors was determined by neurosurgeons. All surgical specimens were submitted for histological study to calculate the MIB-1 LI and the percent collagen content. Preoperative MRI-, intraoperative-, and histological findings were analyzed by a statistician. Results: Our study included 15 soft-, 5 fibrous-, and 4 hard tumors. Tumor consistency was strongly associated with the percent collagen content. However, neither the tumor consistency nor the percent collagen content was correlated with MRI findings or ADC values. The SI of growth hormone-producing adenomas on T2-WI was lower than of the other pituitary adenomas studied (p < 0.01); no other significant difference was found in the ADC or on conventional MRI between pituitary adenomas with different secretory functions. The MIB-1 LI of pituitary adenomas was not correlated with their appearance on conventional MRI or their ADC values. Conclusion: Using the
Energy Technology Data Exchange (ETDEWEB)
Fornasa, Francesca; Montemezzi, Stefania [Dept. of Radiology, San Bonifacio Hospital, Verona (Italy)], e-mail: francescafornasa@libero.it
2012-06-15
Background: Diffusion-weighted magnetic resonance imaging (DWI) is increasingly used in the diagnosis of endometrial disease. No complete knowledge, however, exists yet of the influence of physiology on the endometrial apparent diffusion coefficient (ADC) values on which DWI is based. Purpose: To establish whether the ADC values measured with DWI in the endometrium of healthy reproductive-aged women significantly vary from the early proliferative to the periovulatory phase of the menstrual cycle and between the fundus and the isthmus of the uterus. Material and Methods: In 17 women the endometrial ADC values measured on the fifth menstrual day, both at the fundus and at the isthmus of the uterus, were compared to the values obtained on the 14th day before the subsequent cycle. In 81 women (menstrual day: fifth through 21st) the endometrial ADC values measured at the fundus were compared to the values obtained at the isthmus of the uterus. All examinations were performed with a 1.5 T magnet (b values: 0 and 800 mm/s{sup 2}). The results were analyzed by means of Student's t-test per paired data. Results: The endometrial ADC values measured on the fifth day of the menstrual cycle were lower than those obtained in the periovulatory phase both at the fundus (mean 0.923 vs. 1.256 x 10{sup -}3 mm{sup 2}/s) and at the isthmus (mean 1.297 vs. 1.529 x 10{sup -}3 mm{sup 2}/s) of the uterus. The endometrial ADC values measured at the fundus of the uterus were lower than those obtained at the isthmus (mean 1.132 vs. 1.420 x 10{sup -}3 mm{sup 2}/s) through the menstrual cycle. All these differences were highly significant (P < 0.001) at statistical analysis. Conclusion: Physiological variations occurring in endometrial ADC values of healthy women should be considered by the radiologists when interpreting DWI examinations in patients with endometrial disease.
International Nuclear Information System (INIS)
Objective: The relationship between tumor consistency and apparent diffusion coefficient (ADC) values is controversial. We evaluated the role of the ADC using an advanced diffusion-weighted imaging (DWI) technique. We employed periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) DWI acquired on a 3-T magnetic resonance imaging (MRI) scanner to assess the consistency of pituitary adenomas and examined the relationship between the ADC and the hormone secretion status of the tumors and their MIB-1 labeling index (MIB-1 LI). Materials and methods: The study protocol was approved by our institutional review board. We retrospectively studied 24 operated patients with pituitary adenomas who had undergone PROPELLER DWI on a 3-T MRI scanner. Conventional MRI findings were expressed as the ratio of the signal intensity (SI) in the lesions to the SI of the normal white matter and the degree of contrast enhancement. Minimum-, mean-, and maximum ADC (ADCmin, ADCmean, ADCmax) values were calculated. The consistency of the tumors was determined by neurosurgeons. All surgical specimens were submitted for histological study to calculate the MIB-1 LI and the percent collagen content. Preoperative MRI-, intraoperative-, and histological findings were analyzed by a statistician. Results: Our study included 15 soft-, 5 fibrous-, and 4 hard tumors. Tumor consistency was strongly associated with the percent collagen content. However, neither the tumor consistency nor the percent collagen content was correlated with MRI findings or ADC values. The SI of growth hormone-producing adenomas on T2-WI was lower than of the other pituitary adenomas studied (p < 0.01); no other significant difference was found in the ADC or on conventional MRI between pituitary adenomas with different secretory functions. The MIB-1 LI of pituitary adenomas was not correlated with their appearance on conventional MRI or their ADC values. Conclusion: Using the PROPELLER DWI
Institute of Scientific and Technical Information of China (English)
Yuelang Zhang; Xingwang Sun; Guangnan Quan; Yongqian Qiang; Chenxia Li
2008-01-01
Objective:To find the value of the apparent diffusion coefficient (ADC) of diffusion weighted magnetic resonance imaging of common renal diseases. Methods: There were 30 healthy subjects and 81 patients with renal lesions (56 cases of renal carcinoma, 18 lesions of 12 cases of renal angiomyolipoma, and 21 lesions of 13 cases of renal cysts). Conventional magnetic resonance imaging and diffusion weighted magnetic resonance imaging were carded out. We measured the average ADC value of the renal lesions and normal kidneys. ADC maps from different b values were generated by a statistical package. Results: The ADC values of normal kidneys with three different motion-probing gradients(b=500, 800, 1000 sec/mm2) were 2.78±0.14×10-3mm2s-1,2.45±0.13×10-3mm2s-1, 2.13±0.14×10-3mm2s-1, respectively. The ADC values of renal cell carcinoma with three different motion-probing gradients(b=500, 800, 1008 sec/mm2) were 1.63±0.14×10-3mm2s-1, 1.31±0.18×10-3mm2s-1, 1.07±0.15-310-3mm2s-1, respectively. Among the renal cell carcinoma, the ADC value of clear cell type were 1.67±0.09×10-3mm2s-1, 1.36±0.13×10-3mm2s-1, 1.15±0.14×10-3mm2s-1,respectively; the ADC values of granular cell type were 1.59±0.19×10-3mm2s-1, 1.25±0.22×10-3mm2s-1, 0.97±0.12×10-3mm2s-1, respectively. The ADC values of renal angiomyolipoma with three different motion-probing gradients(b=500, 800, 1008 sec/mm2) were 0.88±0.08×10-3mm2s-1, 0.63±0.07×10-3mm2s-1, 0.43±0.04×10-3mm2s-1, respectively. The ADC values of renal cystic lesions with three different motion-probing gradients(b=500, 800, 1000 sec/mm2) were 3.73±0.18×10-3mm2s-1, 3.44±0.13×10-3mm2s-1, 3.09±0.21×10-3mm2s-1, respectively. Statistically significant differences exists between the ADC values of normal kidney, renal carcinomas, renal angiomyolipomas and renal cysts when the b value is the same. Among the different cell types of renal carcinomas, the ADC value of granular cell carcinoma is lower than that of clear cell
Energy Technology Data Exchange (ETDEWEB)
Giannotti, E., E-mail: ytteb84@hotmail.com [Breast Imaging Department, Ninewells Hospital and Medical School, Dundee DD1 9SY (United Kingdom); Waugh, S., E-mail: shelley.waugh@nhs.net [Department of Medical Physics, Ninewells Hospital and Medical School, Dundee DD1 9SY (United Kingdom); Department of Clinical Radiology, Ninewells Hospital and Medical School, Dundee DD1 9SY (United Kingdom); Priba, L., E-mail: lpriba@nhs.net [Department of Medical Physics, Ninewells Hospital and Medical School, Dundee DD1 9SY (United Kingdom); Davis, Z., E-mail: zoedavis@doctors.org.uk [Breast Imaging Department, Ninewells Hospital and Medical School, Dundee DD1 9SY (United Kingdom); Crowe, E., E-mail: e.crowe@nhs.net [Department of Clinical Radiology, Ninewells Hospital and Medical School, Dundee DD1 9SY (United Kingdom); Vinnicombe, S., E-mail: s.vinnicombe@dundee.ac.uk [Division of Imaging and Technology, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY (United Kingdom)
2015-09-15
Highlights: • Inter-scan errors have minimal contribution to ADC measurement variability. • Intra-observer measures of ADC values in breast cancer are excellent. • ADC measures in whole tumour are more reproducible than minimum ADC measures. • ADC measurement error is most influenced by multiple readers. - Abstract: Purpose: Apparent Diffusion Coefficient (ADC) measurements are increasingly used for assessing breast cancer response to neoadjuvant chemotherapy although little data exists on ADC measurement reproducibility. The purpose of this work was to investigate and characterise the magnitude of errors in ADC measures that may be encountered in such follow-up studies- namely scanner stability, scan–scan reproducibility, inter- and intra- observer measures and the most reproducible measurement of ADC. Methods: Institutional Review Board approval was obtained for the prospective study of healthy volunteers and written consent acquired for the retrospective study of patient images. All scanning was performed on a 3.0-T MRI scanner. Scanner stability was assessed using an ice-water phantom weekly for 12 weeks. Inter-scan repeatability was assessed across two scans of 10 healthy volunteers (26–61 years; mean: 44.7 years). Inter- and intra-reader analysis repeatability was measured in 52 carcinomas from clinical patients (29–70 years; mean: 50.0 years) by measuring the whole tumor ADC value on a single slice with maximum tumor diameter (ADC{sub S}) and the ADC value of a small region of interest (ROI) on the same slice (ADC{sub min}). Repeatability was assessed using intraclass correlation coefficients (ICC) and coefficients of repeatability (CoR). Results: Scanner stability contributed 6% error to phantom ADC measurements (0.071 × 10{sup −3} mm{sup 2}/s; mean ADC = 1.089 × 10{sup −3} mm{sup 2}/s). The measured scan-scan CoR in the volunteers was 0.122 × 10{sup −3} mm{sup 2}/s, contributing an error of 8% to the mean measured values (ADC
Energy Technology Data Exchange (ETDEWEB)
Haack, Soeren (Dept. of Clinical Engineering, Aarhus Univ. Hospital (Denmark)), E-mail: Soeren.haack@stab.rm.dk; Morre Pedersen, Erik (Dept. of Radiology, Aarhus Sygehus, Aarhus Univ. Hospital (Denmark)); Jespersen, Sune N. (Center of Functionally Integrative Neuroscience, Aarhus Univ. Hospital (Denmark)); Kallehauge, Jesper F. (Dept. of Medical Physics, Aarhus Univ. Hospital (Denmark)); Lindegaard, Jacob Christian; Tanderup, Kari (Dept. of Oncology Aarhus Univ. Hospital (Denmark))
2010-10-15
Background and purpose. T2 weighted MRI is recommended for image guided adaptive brachytherapy (IGABT) in cervical cancer. Diffusion weighted imaging (DWI) and the derived apparent diffusion coefficient (ADC) may add additional biological information on tumour cell density. The purpose of this study was to evaluate the distribution of the ADC within target volumes as recommended by GEC-ESTRO: Gross Tumour Volume at BT (GTVBT), High-Risk Clinical Tumour Volume (HR-CTV) and Intermediate-Risk Clinical Target Volume (IR-CTV) and to evaluate the change of diffusion between fractions of IGABT. Material and methods. Fifteen patients with locally advanced cervical cancer were examined by MRI before their first (BT1) and second (BT2) fraction of IGABT, resulting in a total of 30 MR examinations including both T2 weighted and DWI sequences. The Apparent Diffusion Coefficient (ADC) was calculated by use of three levels of b-values (0, 600, 1000 s/mm2). ADC maps were constructed and fused with the GEC ESTRO target contours. The mean ADC value within each target volume was calculated. Furthermore, volumes of low diffusion (ADClow) were defined based on an ADC threshold of 1.2 x 10-3 mm2/s, and overlap with target volumes was evaluated. Change of ADC level in target volumes and change of ADClow volume from BT1 to BT2 was also evaluated. Results. The mean ADC was significantly lower in GTVBT than in HR-CTV (p<0.001) which again was significantly lower than in IR-CTV (p<0.001). There was no significant change of the ADClow volume or ADC level within each target structure between BT1 and BT2 (p=0.242). All three GEC-ESTRO volumes contained volumes with low diffusion. The GTVBT contained 37.2% volume of low diffusion, HR-CTV 20.3% and IR-CTV 10.8%. Conclusion. With DWI we were able to find a significant difference in ADC-values for the three different GEC ESTRO targets. This supports the assumption that the target volumes used for dose prescription in IGABT contain tissues with
The apparent diffusion coefficient of water in gray and white matter of the infant brain
DEFF Research Database (Denmark)
Toft, P B; Leth, H; Peitersen, Birgit;
1996-01-01
at the basal ganglia level was investigated with the diffusion-encoding gradients in the slice-selection direction. RESULTS: On ADC maps, the corpus callosum and the optic radiations appeared dark before the onset of myelination, and the crus posterior of the internal capsule could be visualized...
Institute of Scientific and Technical Information of China (English)
XING Wei; SHENG Jing; CHEN Jie; TIAN Jian-ming; BI Heng-liang
2011-01-01
Background Diffusion-weighted imaging has been widely used to differentiate the character of lymphadenopathy. But there are significant differences between prior studies. The aim of the study was to compare the benefit of apparent diffusion coefficient (ADC) and rADC in the differentiation of metastatic and benign lymph nodes in a rabbit model.Methods Two observers independently measured ADCs in quadriceps of every rabbit on diffusion-weighted images with different sizes of regions of interest (ROI). The appropriate ROI for rADC was determined using the interobserver coefficient. rADC was calculated by ADClesion/ADCreference site. Receiver operating characteristics (ROC) analysis was performed to compare the diagnostic value of the ADC values and rADC values in differentiating metastatic from benign lymph nodes.Results When the ROIs included five pixels, the ICC was 0.816, indicating a good interobserver agreement. The differences of ADC and rADC values between metastatic and benign lymph nodes were both statistically significant. The area under the ROC curve was greater for the rADC than for the ADC. With the rADC criteria of 0.640, the sensitivity and specificity for differentiating metastatic from benign lymph nodes were 93％ and 90％, respectively.Conclusion As a reference site, muscles reveal a good repeatability using a small ROI and the rADC may improve diagnostic accuracy for detecting metastatic nodes in animal models.
Institute of Scientific and Technical Information of China (English)
Hui Hu; Hong Lu; Zhanping He; Xiangjun Han; Jing Chen; Rong Tu
2012-01-01
To investigate the effects of mRNA interference on aquaporin-4 expression in swollen tissue of rats with ischemic cerebral edema, and diagnose the significance of diffusion-weighted MRI, we injected 5 μL shRNA- aquaporin-4 (control group) or siRNA- aquaporin-4 solution (1:800) (RNA interference group) into the rat right basal ganglia immediately before occlusion of the middle cerebral artery. At 0.25 hours after occlusion of the middle cerebral artery, diffusion-weighted MRI displayed a high signal; within 2 hours, the relative apparent diffusion coefficient decreased markedly, aquaporin-4 expression increased rapidly, and intracellular edema was obviously aggravated; at 4 and 6 hours, the relative apparent diffusion coefficient slowly returned to control levels, aquaporin-4 expression slightly increased, and angioedema was observed. In the RNA interference group, during 0.25- 6 hours after injection of siRNA- aquaporin-4 solution, the relative apparent diffusion coefficient slightly fluctuated and aquaporin-4 expression was upregulated; during 0.5-4 hours, the relative apparent diffusion coefficient was significantly higher, while aquaporin-4 expression was significantly lower when compared with the control group, and intracellular edema was markedly reduced; at 0.25 and 6 hours, the relative apparent diffusion coefficient and aquaporin-4 expression were similar when compared with the control group; obvious angioedema remained at 6 hours. Pearson's correlation test results showed that aquaporin-4 expression was negatively correlated with the apparent diffusion coefficient (r = -0.806, P < 0.01). These findings suggest that upregulated aquaporin-4 expression is likely to be the main molecular mechanism of intracellular edema and may be the molecular basis for decreased relative apparent diffusion coefficient. Aquaporin-4 gene interference can effectively inhibit the upregulation of aquaporin-4 expression during the stage of intracellular edema with time
International Nuclear Information System (INIS)
Purpose. To determine association between apparent diffusion coefficient value on diffusion-weighted imaging and Gleason score in patients with prostate cancer. Methods. This retrospective case series was conducted at Radiology Department of Aga Khan University between June 2009 and June 2011. 28 patients with biopsy-proven prostate cancer were included who underwent ultrasound guided sextant prostate biopsy and MRI. MRI images were analyzed on diagnostic console and regions of interest were drawn. Data were entered and analyzed on SPSS 20.0. ADC values were compared with Gleason score using one-way ANOVA test. Results. In 28 patients, 168 quadrants were biopsied and 106 quadrants were positive for malignancy. 89 lesions with proven malignancy showed diffusion restriction. The mean ADC value for disease with a Gleason score of 6 was 935 mm2/s (SD = 248.4 mm2/s); Gleason score of 7 was 837 mm2/s (SD = 208.5 mm2/s); Gleason score of 8 was 614 mm2/s (SD = 108 mm2/s); and Gleason score of 9 was 571 mm2/s (SD = 82 mm2/s). Inverse relationship was observed between Gleason score and mean ADC values. Conclusion. DWI and specifically quantitative ADC values may help differentiate between low-risk (Gleason score, 6), intermediate-risk (Gleason score, 7), and high-risk (Gleason score 8 and 9) prostate cancers, indirectly determining the aggressiveness of the disease
Energy Technology Data Exchange (ETDEWEB)
Nural, Mehmet Selim, E-mail: msnural@omu.edu.tr [Department of Radiology, Medical Faculty, Ondokuz Mayis University, 55139 Samsun (Turkey); Danaci, Murat, E-mail: danacim55@yahoo.com [Department of Radiology, Medical Faculty, Ondokuz Mayis University, 55139 Samsun (Turkey); Soyucok, Ahmet, E-mail: soyucokac@hotmail.com [Department of Radiology, Medical Faculty, Ondokuz Mayis University, 55139 Samsun (Turkey); Okumus, Nilgun Ozbek, E-mail: 2121@omu.edu.tr [Department of Radiation Oncology, Medical Faculty, Ondokuz Mayis University, 55139 Samsun (Turkey)
2013-10-01
Objective: To evaluate effectiveness of apparent diffusion coefficient (ADC) values measured by diffusion-weighted magnetic resonance imaging (DW-MRI) in differentiation of colorectal tumor recurrences and posttherapeutical soft tissue changes. Methods: For this prospective study, 30 patients (22 males, 8 females; age range 30–81 years; mean age 61 ± 12 years) who underwent surgery for colorectal tumors and had a mass detected by computed tomography (CT) and/or MRI during follow-up examinations were divided into 2 groups [17 patients (Group 1) with recurrence and 13 patients (Group 2) with benign fibrosis/granulation tissue]. Final diagnoses were based on histopathological examination in 14 patients and clinical follow-up at least 6 months in the remaining 16. In the latter, the diagnosis of recurrence was made in cases in which the lesion was larger on follow-up CT and MRI; recurrence was ruled out in cases of stable or shrinking lesions without any increase in tumor markers. DW-MRI was performed in the axial plane, for two different b values (b = 0 and 800 s/mm{sup 2}). The mean apparent diffusion coefficient (ADC) values were measured by manual delineation of regions of interest on ADC maps. Results: The median ADC values were 1.07 × 10{sup −3} mm/s{sup 2} (min: 0.82, max: 2.05) and 1.91 × 10{sup −3} mm/s{sup 2} (min: 1.51, max: 2.22) in Groups 1 and 2, respectively. A statistically significant difference was detected between the two groups (P < 0.001). When the threshold value used to determine whether the lesions recurred was 1.48 × 10{sup −3} mm/s{sup 2} based on ROC analysis, the sensitivity was 82% and the specificity was 100%. There were three patients with a false-negative diagnosis, and the primary histopathological diagnosis of all was mucinous adenocarcinoma. Conclusions: Because recurrences in mucinous adenocarcinomas have high ADC values, they may show overlap with benign lesions. In the detection of the local recurrence of colorectal
Energy Technology Data Exchange (ETDEWEB)
Park, Yaewon; Kim, Man Deuk; Jung, Dae Chul; Lee, Shin Jae; Kim, Gyoungmin; Park, Sung Il; Won, Jong Yun; Lee, Do Yun [Yonsei University College of Medicine, Department of Radiology, Severance Hospital, Seoul (Korea, Republic of)
2015-05-01
To determine the usefulness of the apparent diffusion coefficient (ADC) in predicting response to uterine artery embolization (UAE) for symptomatic adenomyosis. A prospective study was performed on 25 patients who underwent diffusion-weighted (DW) magnetic resonance imaging (MRI) before UAE between June 2011 and December 2012. All patients underwent 3-month follow-up MRI after UAE using non-spherical polyvinyl alcohol (PVA) particles ranging from 150 to 500 μm. Quantitative measurement of the ADC was performed for each adenomyosis. Complete response and incomplete response were defined as ≥90 % or <90 %, respectively, of the non-perfusion area with adenomyosis at the follow-up MRI. The ADC values were compared between patients who achieved complete or incomplete response which was assessed according to the MRI findings after UAE. Nineteen patients showed complete response, and six showed incomplete response. The ADC value ranged from 0.842 to 1.346 x 10{sup -3} mm{sup 2}/s (mean 1.075 ± 0.117). The mean ADC was 1.043 ± 0.237 in the complete response group and 1.176 ± 0.429 in the incomplete response group (0.012). Using a threshold of <1.147 x 10{sup -3} mm{sup 2}/s, the sensitivity and specificity of the ADC to predict success after UAE were 83.3 % and 84.2 %. The ADC of adenomyosis may potentially predict a successful response to UAE for adenomyosis. (orig.)
Diffusion coefficient in photon diffusion theory
Graaff, R; Ten Bosch, JJ
2000-01-01
The choice of the diffusion coefficient to be used in photon diffusion theory has been a subject of discussion in recent publications on tissue optics. We compared several diffusion coefficients with the apparent diffusion coefficient from the more fundamental transport theory, D-app. Application to
Energy Technology Data Exchange (ETDEWEB)
Littooij, Annemieke S. [University Medical Centre Utrecht, Department of Radiology, Utrecht (Netherlands); Humphries, Paul D. [Great Ormond Street Hospital for Children, Department of Radiology, London (United Kingdom); University College London Hospital, Department of Radiology, London (United Kingdom); Olsen, Oeystein E. [Great Ormond Street Hospital for Children, Department of Radiology, London (United Kingdom)
2015-10-15
The apparent diffusion coefficient (ADC) is potentially useful for assessing treatment response in nephroblastoma (Wilms tumour). However the precision of ADC measurements in these heterogeneous lesions is unknown. To assess intra- and interobserver variability of whole-tumour ADC measurements in viable parts of nephroblastomas at diagnosis and after preoperative chemotherapy. We included children with histopathologically proven nephroblastoma who had undergone MRI with diffusion-weighted imaging before and after preoperative chemotherapy. Three independent observers performed whole-tumour ADC measurements of all lesions, excluding non-enhancing areas. One observer evaluated all lesions on two occasions. We performed analyses using Bland-Altman plots and concordance correlation coefficient (CCC) calculations with 95% limits of agreement for median ADC, difference between pre- and post-chemotherapy median ADC (ADC shift) and percentage of pixels with ADC values <1.0 x 10{sup -3} mm{sup 2}/s. In 22 lesions (13 pretreatment and 9 post-treatment) in 10 children the interobserver variability in median ADC and ADC shift were within the interval of approximately ±0.1 x 10{sup -3} mm{sup 2}/s (limits of agreement for median ADC ranged -0.08-0.11 x 10{sup -3} mm{sup 2}/s and for ADC-shift -0.11-0.09 x 10{sup -3} mm{sup 2}/s). The interobserver variability for percentage of low-ADC pixels was larger and also biased. The calculated CCC confirmed good intra- and interobserver agreement (ρ-c ranging from 0.968 to 0.996). Measurements of whole-tumour ADC values excluding necrotic areas seem to be sufficiently precise for detection of chemotherapy-related change. (orig.)
International Nuclear Information System (INIS)
Background: With the increased clinical use of 3-Tesla (3T) magnets, it becomes important to identify the potential applications of advanced magnetic resonance (MR) imaging techniques such as diffusion-weighted imaging in head and neck pathologies. Purpose: To establish the 3T apparent diffusion coefficient (ADC) values for normal neck structures, and to examine the utility of ADC values in distinguishing head and neck squamous cell carcinomas (HNSCC) from normal neck anatomy. Material and Methods: 3T diffusion-weighted imaging was performed on 10 normal volunteers and 10 patients with known HNSCC. In the volunteers, mean ADC was calculated in the parotid gland, submandibular gland, base of the tongue, pterygoid muscle, masseter muscle, paraspinal muscles, true vocal cord, thyroid gland, thyroid cartilage, cricoid cartilage, and lymph nodes. The mean tumor ADC value was calculated from the 10 patients with HNSCC and compared with the normal ADC values from various neck structures. Results: The mean ADC value measured in the HNSCC was 1.101 (±0.214)x10-3mm2/s. This was significantly lower than ADC values of paraspinal muscles, pterygoid muscle, masseter muscle, thyroid gland, and base of the tongue (P=0.0006, 0.0002, 0.0001, 0.001, and 0.002, respectively). The tumor ADC values were not significantly different from ADC values of parotid and submandibular glands (P=0.057 and 0.14, respectively). Conclusion: 3T ADC values show potential for distinguishing HNSCC from normal extracranial head and neck structures
Energy Technology Data Exchange (ETDEWEB)
Abdel Razek, Ahmed Abdel Khalek; Abd El-Gaber, Nahed [Mansoura Faculty of Medicine, Department of Diagnostic Radiology, Mansoura (Egypt); Abdalla, Ahmed; Fathy, Abeer [Mansoura Faculty of Medicine, Department of Pediatric, Mansoura (Egypt); Azab, Ahmed [Mansoura Faculty of Medicine, Department of Neurology, Mansoura (Egypt); Rahman, Ashraf Abdel [Radiology Unit of Pediatric Hospital, Mansoura (Egypt)
2009-11-15
The aim of this work is to assess the usefulness of apparent diffusion coefficient (ADC) value of the brain for diagnosis of patients with Gaucher's disease type II and type III. Prospective study was conducted upon 13 patients (nine boys and four girls aged 8 months-14 years: mean 6.1 years) with Gaucher's disease type II and III and for age-matched control group (n = 13). Diffusion-weighted magnetic resonance imaging using a single-shot echo-planar imaging with a diffusion-weighted factor b of 0, 500, and 1,000 s/mm{sup 2} was done for all patients and volunteers. The ADC value was calculated in ten regions of the brain parenchyma and correlated with genotyping. There was significantly lower ADC value of the cortical frontal (P = 0.003), cortical temporal (P = 0.04), frontal subcortical white matter (P = 0.02), corticospinal tract (P = 0.001), cerebellum (P = 0.001), medulla (P = 0.002), and midbrain (P = 0.02) between patients and volunteers. There was significant difference in the ADC value of the frontal and temporal gray matter (P = 0.04 and 0.05, respectively) between patients with heterozygous and homozygous gene mutation. We concluded that ADC value is a new promising quantitative imaging parameter that can be used for the detection of brain abnormalities in patients with Gaucher's disease type II and type III and has a correlation with genotyping. (orig.)
Institute of Scientific and Technical Information of China (English)
Hai-Yi Wang; Jia Wang; Ye-Huan Tang; Hui-Yi Ye; Lin Ma
2015-01-01
Background:Coronal diffusion-weighted magnetic resonance imaging (DW-MRI) and apparent diffusion coefficient (ADC) values have gradually become applied (following conventional axial DW-MRI) in the renal analysis.To explore whether data obtained using coronal DW-MRI are comparable with those derived using axial DW-MRI,this preliminary study sought to assess the agreement in renal ADC values between coronal DW-MRI and axial DW-MRI.Methods:Thirty-four healthy volunteers were enrolled in the study; written consents were obtained.All subjects underwent respiratory-triggered axial and coronal DW-MRI using a 1.5-MR system with b values of 0 and 800 s/mm2.The signal-to-noise ratios (SNRs) of the two DW-MRI sequences were measured and statistically compared using the paired t-test.The extent of agreement of ADC values of the upper pole,mid-pole,and lower pole of the kidney; the mean ADC values of the left kidney and right kidney; and the mean ADC values of the bilateral kidneys were evaluated via calculation of intraclass correlation coefficients (ICCs) or Bland-Altman method between the two DW-MRI sequences.Results:The SNR of coronal DW-MR images was statistically inferior to that of axial DW-MR images (P ＜ 0.001).The ICCs of the ADC values of each region of interest,and the mean ADC values of bilateral kidneys,between the two sequences,were greater than 0.5,and the mean ADCs of the bilateral kidneys demonstrated the highest ICC (0.869; 95％ confidence interval:0.739-0.935).In addition,94.1％ (32/34),94.1％ (32/34),and 97.1％ (31/34) of the ADC bias was inside the limits of agreement in terms of the mean ADC values of the left kidneys,right kidneys,and bilateral kidneys when coronal and axial DWI-MRI were compared.Conclusions:ADC values derived using coronal DW-MRI exhibited moderate-to-good agreement to those of axial DW-MRI,rendering the former an additional useful DW-MRI method,and causing the ADC values derived using the two types of DW-MRI to be comparable.
Energy Technology Data Exchange (ETDEWEB)
Roh, Ji Eun; Yeom, Joeng A; Kim, Young Soo; Yoon, Chang Hyo; Park, Min Gyu; Park, Kyung Pil; Baik, Seung Kug [Pusan National University Yangsan Hospital, Yangsan (Korea, Republic of)
2016-04-15
Intra-arterial revascularization therapy (IART) for acute ischemic stroke has become increasingly popular recently. However, early change in apparent diffusion coefficient (ADC) values after full recanalization in human stroke has not received much attention. The aim of this study was to evaluate ADC changes immediately after interventional full-recanalization in patients with acute ischemic stroke. ADC values of 25 lesions from 18 acute ischemic stroke patients were recorded with both pre- and post-recanalization ADC maps. Measurement was done by placing region of interests over the representative images of the lesion. For analysis, lesions were divided into territorial infarction (TI) and watershed infarction (WI). Mean ADC values of the overall 25 lesions before IART were 415.12 × 10-6 mm{sup 2}/sec, and increased to 619.08 × 10-6 mm{sup 2}/sec after the IART. Average relative ADC (rADC) value for 22 TI increased from 0.59 to 0.92 (p < 0.000), whereas, average rADC value for 3 WI did not change significantly. There was a conspicuous increase of ADC values immediately after full-recanalization in TI lesions. On the other hand, WI lesions did not show significant change in ADC values after recanalization.
Zolal, Amir; Juratli, Tareq A; Linn, Jennifer; Podlesek, Dino; Sitoci Ficici, Kerim Hakan; Kitzler, Hagen H; Schackert, Gabriele; Sobottka, Stephan B; Rieger, Bernhard; Krex, Dietmar
2016-05-01
Objective To determine the value of apparent diffusion coefficient (ADC) histogram parameters for the prediction of individual survival in patients undergoing surgery for recurrent glioblastoma (GBM) in a retrospective cohort study. Methods Thirty-one patients who underwent surgery for first recurrence of a known GBM between 2008 and 2012 were included. The following parameters were collected: age, sex, enhancing tumor size, mean ADC, median ADC, ADC skewness, ADC kurtosis and fifth percentile of the ADC histogram, initial progression free survival (PFS), extent of second resection and further adjuvant treatment. The association of these parameters with survival and PFS after second surgery was analyzed using log-rank test and Cox regression. Results Using log-rank test, ADC histogram skewness of the enhancing tumor was significantly associated with both survival (p = 0.001) and PFS after second surgery (p = 0.005). Further parameters associated with prolonged survival after second surgery were: gross total resection at second surgery (p = 0.026), tumor size (0.040) and third surgery (p = 0.003). In the multivariate Cox analysis, ADC histogram skewness was shown to be an independent prognostic factor for survival after second surgery. Conclusion ADC histogram skewness of the enhancing lesion, enhancing lesion size, third surgery, as well as gross total resection have been shown to be associated with survival following the second surgery. ADC histogram skewness was an independent prognostic factor for survival in the multivariate analysis. PMID:26830088
Directory of Open Access Journals (Sweden)
Sasaki,Takanori
2012-06-01
Full Text Available The roles of cell density, extracellular space, intracellular factors, and apoptosis induced by the molecularly targeted drug rituximab on the apparent diffusion coefficient (ADC values were investigated using bio-phantoms. In these bio-phantoms, Ramos cells (a human Burkittｾs lymphoma cell line were encapsulated in gellan gum. The ADC values decreased linearly with the increase in cell density, and declined steeply when the extracellular space became less than 4 μm. The analysis of ADC values after destruction of the cellular membrane by sonication indicated that approximately 65% of the ADC values of normal cells originate from the cell structures made of membranes and that the remaining 35% originate from intracellular components. Microparticles, defined as particles smaller than the normal cells, increased in number after rituximab treatments, migrated to the extracellular space and significantly decreased the ADC values of bio-phantoms during apoptosis. An in vitro study using bio-phantoms was conducted to quantitatively clarify the roles of cellular factors and of extracellular space in determining the ADC values yielded by tumor cells and the mechanism by which apoptosis changes those values.
Directory of Open Access Journals (Sweden)
Vijayakumar Chinnadurai
2010-05-01
Full Text Available A novel Neuro – level set algorithm is proposed and evaluated for simultaneous segmentation and grading of brain tumors. The algorithm utilizes vascular and cellular information provided by the reconstructed images of dynamic contrast susceptibility magnetic resonance images and apparent diffusion coefficient images. The reconstructed images are relative cerebral blood volume (rCBV image, time to peak (TTP image and percentage of base at peak (PBP image along with apparent diffusion coefficient (ADC maps. The proposed neural - levelset algorithm utilizes a neural block to provide the speed image for the levelset methods. In this study, two different architectures of levelset method have been implemented and their results are compared. The results show that the proposed Neuro- Levelset method performs better in differentiating the tumor, edema,necrosis in reconstructed images of dynamic contrast susceptibility magnetic resonance images and apparent diffusion coefficient MR images.
Energy Technology Data Exchange (ETDEWEB)
Rundle-Thiele, Dayle [Centre for Clinical Research, University of Queensland, Brisbane, Queensland (Australia); Day, Bryan; Stringer, Brett [Brain Cancer Research Unit, Queensland Institute of Medical Research, Brisbane, Queensland (Australia); Fay, Michael [Department of Radiation Oncology, Royal Brisbane and Women' s Hospital, Brisbane, Queensland (Australia); Martin, Jennifer [Discipline of Clinical Pharmacology, School of Medicine and Public Health, University of Newcastle, Newcastle, New South Wales (Australia); Jeffree, Rosalind L [Department of Neurosurgery, Royal Brisbane and Women' s Hospital, Brisbane, Queensland (Australia); Thomas, Paul [Queensland PET Service, Royal Brisbane and Women' s Hospital, Brisbane, Queensland (Australia); Bell, Christopher [Centre for Clinical Research, University of Queensland, Brisbane, Queensland (Australia); Salvado, Olivier [CSIRO Digital Productivity Flagship, CSIRO, Herston, Queensland (Australia); Gal, Yaniv [Centre for Medical Diagnostic Technologies in Queensland, University of Queensland, Brisbane, Queensland (Australia); Coulthard, Alan [Discipline of Medical Imaging, University of Queensland, St Lucia, Queensland (Australia); Department of Medical Imaging, Royal Brisbane and Women' s Hospital, Brisbane, Queensland (Australia); Crozier, Stuart [Centre for Medical Diagnostic Technologies in Queensland, University of Queensland, Brisbane, Queensland (Australia); Rose, Stephen, E-mail: stephen.rose@csiro.au [CSIRO Digital Productivity Flagship, CSIRO, Herston, Queensland (Australia); Centre for Clinical Research, University of Queensland, Brisbane, Queensland (Australia)
2015-06-15
Accurate knowledge of O{sup 6}-methylguanine methyltransferase (MGMT) gene promoter subtype in patients with glioblastoma (GBM) is important for treatment. However, this test is not always available. Pre-operative diffusion MRI (dMRI) can be used to probe tumour biology using the apparent diffusion coefficient (ADC); however, its ability to act as a surrogate to predict MGMT status has shown mixed results. We investigated whether this was due to variations in the method used to analyse ADC. We undertook a retrospective study of 32 patients with GBM who had MGMT status measured. Matching pre-operative MRI data were used to calculate the ADC within contrast enhancing regions of tumour. The relationship between ADC and MGMT was examined using two published ADC methods. A strong trend between a measure of ‘minimum ADC’ and methylation status was seen. An elevated minimum ADC was more likely in the methylated compared to the unmethylated MGMT group (U = 56, P = 0.0561). In contrast, utilising a two-mixture model histogram approach, a significant reduction in mean measure of the ‘low ADC’ component within the histogram was associated with an MGMT promoter methylation subtype (P < 0.0246). This study shows that within the same patient cohort, the method selected to analyse ADC measures has a significant bearing on the use of that metric as a surrogate marker of MGMT status. Thus for dMRI data to be clinically useful, consistent methods of data analysis need to be established prior to establishing any relationship with genetic or epigenetic profiling.
Directory of Open Access Journals (Sweden)
Yiqun Sun
Full Text Available OBJECTIVE: We elected to analyze the correlation between the pre-treatment apparent diffusion coefficient (ADC and the clinical, histological, and immunohistochemical status of rectal cancers. MATERIALS AND METHODS: Forty-nine rectal cancer patients who received surgical resection without neoadjuvant therapy were selected that underwent primary MRI and diffusion-weighted imaging (DWI. Tumor ADC values were determined and analyzed to identify any correlations between these values and pre-treatment CEA or CA19-9 levels, and/or the histological and immunohistochemical properties of the tumor. RESULTS: Inter-observer agreement of confidence levels from two separate observers was suitable for ADC measurement (k = 0.775. The pre-treatment ADC values of different T stage tumors were not equal (p = 0.003. The overall trend was that higher T stage values correlated with lower ADC values. ADC values were also significantly lower for the following conditions: tumors with the presence of extranodal tumor deposits (p = 0.006 and tumors with CA19-9 levels ≥ 35 g/ml (p = 0.006. There was a negative correlation between Ki-67 LI and the ADC value (r = -0.318, p = 0.026 and between the AgNOR count and the ADC value (r = -0.310, p = 0.030. CONCLUSION: Significant correlations were found between the pre-treatment ADC values and T stage, extranodal tumor deposits, CA19-9 levels, Ki-67 LI, and AgNOR counts in our study. Lower ADC values were associated with more aggressive tumor behavior. Therefore, the ADC value may represent a useful biomarker for assessing the biological features and possible relationship to the status of identified rectal cancers.
International Nuclear Information System (INIS)
Accurate knowledge of O6-methylguanine methyltransferase (MGMT) gene promoter subtype in patients with glioblastoma (GBM) is important for treatment. However, this test is not always available. Pre-operative diffusion MRI (dMRI) can be used to probe tumour biology using the apparent diffusion coefficient (ADC); however, its ability to act as a surrogate to predict MGMT status has shown mixed results. We investigated whether this was due to variations in the method used to analyse ADC. We undertook a retrospective study of 32 patients with GBM who had MGMT status measured. Matching pre-operative MRI data were used to calculate the ADC within contrast enhancing regions of tumour. The relationship between ADC and MGMT was examined using two published ADC methods. A strong trend between a measure of ‘minimum ADC’ and methylation status was seen. An elevated minimum ADC was more likely in the methylated compared to the unmethylated MGMT group (U = 56, P = 0.0561). In contrast, utilising a two-mixture model histogram approach, a significant reduction in mean measure of the ‘low ADC’ component within the histogram was associated with an MGMT promoter methylation subtype (P < 0.0246). This study shows that within the same patient cohort, the method selected to analyse ADC measures has a significant bearing on the use of that metric as a surrogate marker of MGMT status. Thus for dMRI data to be clinically useful, consistent methods of data analysis need to be established prior to establishing any relationship with genetic or epigenetic profiling
Directory of Open Access Journals (Sweden)
Daniel Paech
Full Text Available To explore the correlation between Nuclear Overhauser Enhancement (NOE-mediated signals and tumor cellularity in glioblastoma utilizing the apparent diffusion coefficient (ADC and cell density from histologic specimens. NOE is one type of chemical exchange saturation transfer (CEST that originates from mobile macromolecules such as proteins and might be associated with tumor cellularity via altered protein synthesis in proliferating cells.For 15 patients with newly diagnosed glioblastoma, NOE-mediated CEST-contrast was acquired at 7 Tesla (asymmetric magnetization transfer ratio (MTRasym at 3.3ppm, B1 = 0.7 μT. Contrast enhanced T1 (CE-T1, T2 and diffusion-weighted MRI (DWI were acquired at 3 Tesla and coregistered. The T2 edema and the CE-T1 tumor were segmented. ADC and MTRasym values within both regions of interest were correlated voxelwise yielding the correlation coefficient rSpearman (rSp. In three patients who underwent stereotactic biopsy, cell density of 12 specimens per patient was correlated with corresponding MTRasym and ADC values of the biopsy site.Eight of 15 patients showed a weak or moderate positive correlation of MTRasym and ADC within the T2 edema (0.16≤rSp≤0.53, p0.05, n = 4 or yielded rSp≈0 (p0.05, n = 6. The biopsy-analysis within CE-T1 tumor revealed a strong positive correlation between tumor cellularity and MTRasym values in two of the three patients (rSppatient3 = 0.69 and rSppatient15 = 0.87, p<0.05, while the correlation of ADC and cellularity was heterogeneous (rSppatient3 = 0.545 (p = 0.067, rSppatient4 = -0.021 (p = 0.948, rSppatient15 = -0.755 (p = 0.005.NOE-imaging is a new contrast promising insight into pathophysiologic processes in glioblastoma regarding cell density and protein content, setting itself apart from DWI. Future studies might be based on the assumption that NOE-mediated CEST visualizes cellularity more accurately than ADC, especially in the CE-T1 tumor region.
Directory of Open Access Journals (Sweden)
Jang-Zern Tsai
2014-01-01
Full Text Available Determination of the volumes of acute cerebral infarct in the magnetic resonance imaging harbors prognostic values. However, semiautomatic method of segmentation is time-consuming and with high interrater variability. Using diffusion weighted imaging and apparent diffusion coefficient map from patients with acute infarction in 10 days, we aimed to develop a fully automatic algorithm to measure infarct volume. It includes an unsupervised classification with fuzzy C-means clustering determination of the histographic distribution, defining self-adjusted intensity thresholds. The proposed method attained high agreement with the semiautomatic method, with similarity index 89.9 ± 6.5%, in detecting cerebral infarct lesions from 22 acute stroke patients. We demonstrated the accuracy of the proposed computer-assisted prompt segmentation method, which appeared promising to replace the laborious, time-consuming, and operator-dependent semiautomatic segmentation.
Energy Technology Data Exchange (ETDEWEB)
Schroeder, Paul C.; Donovan Post, M. Judith; Bruce-Gregorios, Jocelyn [University of Miami, Jackson Memorial Hospital, Miami, FL (United States); Oschatz, Elizabeth; Stadler, Alfred; Thurnher, Majda M. [Medical University of Vienna, Department of Radiology Neuroradiology Section, Vienna (Austria)
2006-10-15
Toxoplasmosis and lymphoma are common lesions of the central nervous system in patients with AIDS. It is often difficult to distinguish between these lesions both clinically and radiographically. Previous research has demonstrated restricted diffusion within cerebral lymphomas and bacterial abscesses. However, little work has been done to evaluate the diffusion characteristics of toxoplasmosis lesions. This study was designed to explore further the utility of diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) maps and values in making the distinction between toxoplasmosis and lymphoma. The magnetic resonance imaging (MRI) studies of 36 patients, including 22 with toxoplasmosis (all of whom had AIDS) and 14 with lymphoma (8 of whom had AIDS), at two institutions were reviewed retrospectively. The characteristics of the lesions on DWI were evaluated, and the ADC ratios of the lesions were calculated and compared. There was significant overlap of the ADC ratios of toxoplasma and lymphoma, most notably in the intermediate (1.0-1.6) range. There was variability in ADC ratios even among different lesions in the same patient. In only a minority of the lymphoma patients were the ADC ratios low enough to suggest the correct diagnosis. Our study showed that toxoplasmosis exhibits a wide spectrum of diffusion characteristics with ADC ratios which have significant overlap with those of lymphoma. Therefore, in the majority of patients, ADC ratios are not definitive in making the distinction between toxoplasmosis and lymphoma. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Mori, Naoko; Mugikura, Shunji; Takasawa, Chiaki; Shimauchi, Akiko; Ota, Hideki; Takase, Kei; Takahashi, Shoki [Tohoku University Graduate School of Medicine, Department of Diagnostic Radiology, Sendai (Japan); Miyashita, Minoru; Ishida, Takanori [Tohoku University Graduate School of Medicine, Department of Surgical Oncology, Sendai (Japan); Kasajima, Atsuko [Tohoku University Graduate School of Medicine, Department of Pathology, Sendai (Japan); Kodama, Tetsuya [Tohoku University Graduate School of Medicine, Department of Biomedical Engineering, Sendai (Japan)
2016-02-15
To evaluate whether visual assessment of T2-weighted imaging (T2WI) or an apparent diffusion coefficient (ADC) could predict lymphovascular invasion (LVI) status in cases with clinically node-negative invasive breast cancer. One hundred and thirty-six patients with 136 lesions underwent MRI. Visual assessment of T2WI, tumour-ADC, peritumoral maximum-ADC and the peritumour-tumour ADC ratio (the ratio between them) were compared with LVI status of surgical specimens. No significant relationship was found between LVI and T2WI. Tumour-ADC was significantly lower in the LVI-positive (n = 77, 896 ± 148 x 10{sup -6} mm{sup 2}/s) than the LVI-negative group (n = 59, 1002 ± 163 x 10{sup -6} mm{sup 2}/s; p < 0.0001). Peritumoral maximum-ADC was significantly higher in the LVI-positive (1805 ± 355 x 10{sup -6} mm{sup 2}/s) than the LVI-negative group (1625 ± 346 x 10{sup -6} mm{sup 2}/s; p = 0.0003). Peritumour-tumour ADC ratio was significantly higher in the LVI-positive (2.05 ± 0.46) than the LVI-negative group (1.65 ± 0.40; p < 0.0001). Receiver operating characteristic curve analysis revealed that the area under the curve (AUC) of the peritumour-tumour ADC ratio was the highest (0.81). The most effective threshold for the peritumour-tumour ADC ratio was 1.84, and the sensitivity, specificity, positive predictive value and negative predictive value were 77 % (59/77), 76 % (45/59), 81 % (59/73) and 71 % (45/63), respectively. We suggest that the peritumour-tumour ADC ratio can assist in predicting LVI status on preoperative imaging. (orig.)
Directory of Open Access Journals (Sweden)
Atsushi Umemura
Full Text Available BACKGROUND: It is often hard to differentiate Parkinson's disease (PD and parkinsonian variant of multiple system atrophy (MSA-P, especially in the early stages. Cardiac sympathetic denervation and putaminal rarefaction are specific findings for PD and MSA-P, respectively. PURPOSE: We investigated diagnostic accuracy of putaminal apparent diffusion coefficient (ADC test for MSA-P and (123I-metaiodobenzylguanidine (MIBG scintigram for PD, especially in early-stage patients. METHODS: The referral standard diagnosis of PD and MSA-P were the diagnostic criteria of the United Kingdom Parkinson's Disease Society Brain Bank Criteria and the second consensus criteria, respectively. Based on the referral standard criteria, diagnostic accuracy [area under the receiver-operator characteristic curve (AUC, sensitivity and specificity] of the ADC and MIBG tests was estimated retrospectively. Diagnostic accuracy of these tests performed within 3 years of symptom onset was also investigated. RESULTS: ADC and MIBG tests were performed on 138 patients (20 MSA and 118 PD. AUC was 0.95 and 0.83 for the ADC and MIBG tests, respectively. Sensitivity and specificity were 85.0% and 89.0% for MSA-P diagnosis by ADC test and 67.0% and 80.0% for PD diagnosis by MIBG test. When these tests were restricted to patients with disease duration ≤ 3 years, the sensitivity and specificity were 75.0% and 91.4% for the ADC test (MSA-P diagnosis and 47.7% and 92.3% for the MIBG test (PD diagnosis. CONCLUSIONS: Both tests were useful in differentiating between PD and MSA-P, even in the early stages. In early-stage patients, elevated putaminal ADC was a diagnostic marker for MSA-P. Despite high specificity of the MIBG test, careful neurological history and examinations were required for PD diagnosis because of possible false-negative results.
International Nuclear Information System (INIS)
Aim: To assess how the joint use of apparent diffusion coefficient (ADC) and kinetic parameters (uptake phase and delayed enhancement characteristics) from dynamic contrast-enhanced (DCE) can boost the ability to predict breast lesion malignancy. Materials and methods: Breast magnetic resonance examinations including DCE and diffusion-weighted imaging (DWI) were performed on 51 women. The association between kinetic parameters and ADC were evaluated and compared between lesion types. Models with binary outcome of malignancy were studied using generalized estimating equations (GEE), (GEE), and using kinetic parameters and ADC values as malignancy predictors. Model accuracy was assessed using the corrected maximum quasi-likelihood under the independence confidence criterion (QICC). Predicted probability of malignancy was estimated for the best model. Results: ADC values were significantly associated with kinetic parameters: medium and rapid uptake phase (p<0.001) and plateau and washout curve types (p=0.004). Comparison between lesion type showed significant differences for ADC (p=0.001), early phase (p<0.001), and curve type (p<0.001). The predicted probabilities of malignancy for the first ADC quartile (≤1.17×10−3 mm2/s) and persistent, plateau and washout curves, were 54.6%, 86.9%, and 97.8%, respectively, and for the third ADC quartile (≥1.51×10−3 mm2/s) were 3.2%, 15.5%, and 54.8%, respectively. The predicted probability of malignancy was less than 5% for 18.8% of the lesions and greater than 33% for 50.7% of the lesions (24/35 lesions, corresponding to a malignancy rate of 68.6%). Conclusion: The best malignancy predictors were low ADCs and washout curves. ADC and kinetic parameters provide differentiated information on the microenvironment of the lesion, with joint models displaying improved predictive performance. -- Highlights: •ADC and kinetic parameters provide diverse information regarding lesion environment. •The best predictors of
J.P. Hoogendam; W.M. Klerkx; G.A.P. de Kort; S. Bipat; R.P. Zweemer; D.M.D.S. Sie-Go; R.H.M. Verheijen; W.P.T.M. Mali; W.B. Veldhuis
2010-01-01
Purpose: To analyze the influence of different b-value combinations on apparent diffusion coefficient (ADC)based differentiation of known malignant and benign tissue in cervical cancer patients. Materials and Methods: A total of 35 patients with stage IB1, IB2, IIA cervical cancer underwent a 3.0T M
Directory of Open Access Journals (Sweden)
Matthew D Blackledge
Full Text Available We describe our semi-automatic segmentation of whole-body diffusion-weighted MRI (WBDWI using a Markov random field (MRF model to derive tumor total diffusion volume (tDV and associated global apparent diffusion coefficient (gADC; and demonstrate the feasibility of using these indices for assessing tumor burden and response to treatment in patients with bone metastases. WBDWI was performed on eleven patients diagnosed with bone metastases from breast and prostate cancers before and after anti-cancer therapies. Semi-automatic segmentation incorporating a MRF model was performed in all patients below the C4 vertebra by an experienced radiologist with over eight years of clinical experience in body DWI. Changes in tDV and gADC distributions were compared with overall response determined by all imaging, tumor markers and clinical findings at serial follow up. The segmentation technique was possible in all patients although erroneous volumes of interest were generated in one patient because of poor fat suppression in the pelvis, requiring manual correction. Responding patients showed a larger increase in gADC (median change = +0.18, range = -0.07 to +0.78 × 10(-3 mm2/s after treatment compared to non-responding patients (median change = -0.02, range = -0.10 to +0.05 × 10(-3 mm2/s, p = 0.05, Mann-Whitney test, whereas non-responding patients showed a significantly larger increase in tDV (median change = +26%, range = +3 to +284% compared to responding patients (median change = -50%, range = -85 to +27%, p = 0.02, Mann-Whitney test. Semi-automatic segmentation of WBDWI is feasible for metastatic bone disease in this pilot cohort of 11 patients, and could be used to quantify tumor total diffusion volume and median global ADC for assessing response to treatment.
Energy Technology Data Exchange (ETDEWEB)
Shen, Guohua; Jia, Zhiyun; Deng, Houfu [Sichuan University, Department of Nuclear Medicine, West China Hospital, Chengdu, Sichuan (China)
2016-02-15
The potential performance of apparent diffusion coefficient (ADC) values for distinguishing malignant and benign pulmonary lesions, further characterizing the subtype of lung cancer was assessed. PubMed, EMBASE, Cochrane Library, EBSCO, and three Chinese databases were searched to identify eligible studies on diffusion-weighted imaging (DWI) of focal pulmonary lesions. ADC values of malignant and benign lesions were extracted by lesion type and statistically pooled based on a linear mixed model. Further analysis for subtype of lung cancer was also performed. The methodological quality was assessed using the quality assessment of diagnostic accuracy studies tool. Thirty-four articles involving 2086 patients were included. Malignant pulmonary lesions have significantly lower ADC values than benign lesions [1.21 (95 % CI, 1.19-1.22) mm{sup 2}/s vs. 1.76 (95 % CI, 1.72-1.80) mm{sup 2}/s; P < 0.05]. There is a significant difference between ADC values of small cell lung cancer and non-small cell lung cancer (P < 0.05), while the differences were not significant among histological subtypes of lung cancer. The methodological quality was relatively high, and the data points from Begg's test indicated that there was probably no obvious publication bias. The ADC value is helpful for distinguishing malignant and benign pulmonary lesions and provides a promising method for differentiation of SCLC from NSCLC. (orig.)
International Nuclear Information System (INIS)
The potential performance of apparent diffusion coefficient (ADC) values for distinguishing malignant and benign pulmonary lesions, further characterizing the subtype of lung cancer was assessed. PubMed, EMBASE, Cochrane Library, EBSCO, and three Chinese databases were searched to identify eligible studies on diffusion-weighted imaging (DWI) of focal pulmonary lesions. ADC values of malignant and benign lesions were extracted by lesion type and statistically pooled based on a linear mixed model. Further analysis for subtype of lung cancer was also performed. The methodological quality was assessed using the quality assessment of diagnostic accuracy studies tool. Thirty-four articles involving 2086 patients were included. Malignant pulmonary lesions have significantly lower ADC values than benign lesions [1.21 (95 % CI, 1.19-1.22) mm2/s vs. 1.76 (95 % CI, 1.72-1.80) mm2/s; P < 0.05]. There is a significant difference between ADC values of small cell lung cancer and non-small cell lung cancer (P < 0.05), while the differences were not significant among histological subtypes of lung cancer. The methodological quality was relatively high, and the data points from Begg's test indicated that there was probably no obvious publication bias. The ADC value is helpful for distinguishing malignant and benign pulmonary lesions and provides a promising method for differentiation of SCLC from NSCLC. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Inchingolo, Riccardo; De Gaetano, Anna Maria; Curione, Davide; Ciresa, Marzia; Bonomo, Lorenzo [Catholic University of the Sacred Heart, Department of Bioimaging and Radiological Sciences, Institute of Radiology, ' ' Agostino Gemelli' ' Hospital, Rome (Italy); Miele, Luca; Pompili, Maurizio [Catholic University of the Sacred Heart, Department of Internal Medicine, ' ' Agostino Gemelli' ' Hospital, Rome (Italy); Vecchio, Fabio Maria [Catholic University of the Sacred Heart, Department of Anatomo-Pathology, ' ' Agostino Gemelli' ' Hospital, Rome (Italy); Giuliante, Felice [Catholic University of the Sacred Heart, Department of Surgery, ' ' Agostino Gemelli' ' Hospital, Rome (Italy)
2015-04-01
To investigate the utility of diffusion-weighted imaging (DWI), apparent diffusion coefficient (ADC) and the correlation with hepatobiliary phase (delayed phase imaging, DPI) findings in the differentiation of cirrhotic hepatocellular nodules. Forty-three patients with 53 pathology-proven nodules (29 hepatocellular carcinomas (HCCs), 13 high-grade (HGDNs) and 11 low-grade dysplastic nodules (LGDNs); mean size 2.17 cm, range 1-4 cm), who underwent liver MRI with DWI and DPI sequences, were retrospectively reviewed. Lesions were classified as hypointense, isointense, or hyperintense relative to the adjacent liver parenchyma. ADC of each nodule, of the surrounding parenchyma, and lesion-to-liver ratio were calculated. Hyperintensity versus iso/hypointensity on DWI, hypointensity versus iso/hyperintensity on DPI, and the mean lesion-to-liver ratio showed a statistically significant difference both between HCCs versus DNs and between ''HCCs + HGDNs'' versus LGDNs (p < 0.05); sensitivity, specificity, and accuracy for the diagnosis of ''HCCs + HGDNs'' were 96.8 %, 100 %, 97.4 % respectively when combining hyperintensity on DWI and hypointensity on DPI, and 90.9 %, 81.0 %, 83.6 % respectively when lesion-to-liver ratio was <0.95. Hyperintensity on DWI, especially in association with hypointensity on DPI, and low lesion-to-liver ratios should raise the suspicion of HCC, or at least of HGDN, thus helping the characterization of atypically enhancing lesions. (orig.)
International Nuclear Information System (INIS)
Diffusion-weighted imaging (DWI) has been demonstrated to be a practical method for the diagnosis of various brain diseases such as acute infarction, brain tumor, and white matter disease. In this study, we used two techniques to examine the average signal intensity (SI) and apparent diffusion coefficient (ADC) of the brains of patients who ranged in age from 10 to 60 years. Our results indicated that the average SI was the highest in amygdala (as derived from DWI), whereas that in the cerebrospinal fluid was the lowest. The average ADC was the highest in the cerebrospinal fluid, whereas the lowest measurement was derived from the pons. The average SI and ADC were higher in T2-DW-EPI than in FLAIR-DW-EPI. The higher the b-value, the smaller the average difference in both imaging techniques; the lower the b-value, the greater the average difference. Also, comparative analysis of the brains of patients who had experienced cerebral infarction showed no distinct lesion in the general MR image over time. However, there was a high SI in apparent weighted images. Analysis of other brain diseases (e.g., bleeding, acute, subacute, chronic infarction) indicated SI variance in accordance with characteristics of the two techniques. The higher the SI, the lower the ADC. Taken together, the value of SI and ADC in accordance with frequently occurring areas and various brain disease varies based on the b-value and imaging technique. Because they provide additional useful information in the diagnosis and treatment of patients with various brain diseases through signal recognition, the proper imaging technique and b-value are important for the detection and interpretation of subacute stroke and other brain diseases.
International Nuclear Information System (INIS)
Full text of publication follows: The study of the dispersion of radioactive materials in soils and in engineering barriers plays an important role in the safety analysis of nuclear waste repositories. In order to proceed with such kind of study the involved physical properties must be determined with precision, including the apparent mass diffusion coefficient, which is defined as the ratio between the effective mass diffusion coefficient and the retardation factor. Many different experimental and estimation techniques are available on the literature for the identification of the diffusion coefficient and this work describes the implementation of that developed by Pereira et al [1]. This technique is based on non-intrusive radiation measurements and the experimental setup consists of a cylindrical column filled with compacted media saturated with water. A radioactive contaminant is mixed with a portion of the media and then placed in the bottom of the column. Therefore, the contaminant will diffuse through the uncontaminated media due to the concentration gradient. A radiation detector is used to measure the number of counts, which is associated to the contaminant concentration, at several positions along the column during the experiment. Such measurements are then used to estimate the apparent diffusion coefficient of the contaminant in the porous media by inverse analysis. The inverse problem of parameter estimation is solved with the Levenberg-Marquart Method of minimization of the least-square norm. The experiment was optimized with respect to the number of measurement locations, frequency of measurements and duration of the experiment through the analysis of the sensitivity coefficients and by using a D-optimum approach. This setup is suitable for studying a great number of combinations of diverse contaminants and porous media varying in composition and compacting, with considerable easiness and reliable results, and it was chosen because that is the
Pope, WB; Qiao, XJ; Kim, HJ; Lai, A.; Nghiemphu, P; Xue, X.; Ellingson, BM; Schiff, D.; Aregawi, D; Cha, S; Puduvalli, VK; Wu, J.; Yung, WKA; Young, GS; Vredenburgh, J
2012-01-01
We have tested the predictive value of apparent diffusion coefficient (ADC) histogram analysis in stratifying progression-free survival (PFS) and overall survival (OS) in bevacizumab-treated patients with recurrent glioblastoma multiforme (GBM) from the multi-center BRAIN study. Available MRI's from patients enrolled in the BRAIN study (n = 97) were examined by generating ADC histograms from areas of enhancing tumor on T1 weighted post-contrast images fitted to a two normal distribution mixtu...
DEFF Research Database (Denmark)
Diaz, S.; Casselbrant, I.; Piitulainen, E.;
2008-01-01
PURPOSE: To measure the apparent diffusion coefficient (ADC) of hyperpolarized (HP) (3)He gas using diffusion weighted MRI in healthy volunteers and patients with emphysema and examine the reproducibility and volume dependency. MATERIALS AND METHODS: A total of eight healthy volunteers and 16...... in mean ADC with increased inhaled gas volume was observed in both groups. CONCLUSION: Mean ADC and SD of HP (3)He MRI is reproducible and discriminates well between healthy controls and patients with emphysema at the higher gas volume. This method is robust and may be useful to gain new insights...
Energy Technology Data Exchange (ETDEWEB)
Westen, D. van; Laett, J.; Englund, E.; Brockstedt, S.; Larsson, E.M. [Lund Univ. Hospital (Sweden). Depts. of Radiology, of Medical Radiation Physics and of Pathology and Cytology
2006-04-15
Purpose: To determine whether the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) can distinguish tumor-infiltrated edema in gliomas from pure edema in meningiomas and metastases. Material and Methods: Thirty patients were studied: 18 WHO grade III or IV gliomas, 7 meningiomas, and 5 metastatic lesions. ADC and FA were determined from ROIs placed in peritumoral areas with T2-signal changes, adjacent normal appearing white matter (NAWM), and corresponding areas in the contralateral healthy brain. Values and lesion-to-brain ratios from gliomas were compared to those from meningiomas and metastases. Results: Values and lesion-to-brain ratios of ADC and FA in peritumoral areas with T2-signal changes did not differ between gliomas, meningiomas, and metastases (P = 0.40, P = 0.40, P = 0.61, P 0.34). Values of ADC and FA and the lesion-to-brain ratio of FA in the adjacent NAWM did not differ between tumor types (P = 0.74, P = 0.25, and P = 0.31). The lesion-to-brain ratio of ADC in the adjacent NAWM was higher in gliomas than in meningiomas and metastases (P = 0.004), but overlapped between tumor types. Conclusion: Values and lesion-to-brain ratios of ADC and FA in areas with T2-signal changes surrounding intracranial tumors and adjacent NAWM were not helpful for distinguishing pure edema from tumor-infiltrated edema when data from gliomas, meningiomas, and metastases were compared.
International Nuclear Information System (INIS)
We wanted to evaluate the ability of the apparent diffusion coefficient (ADC) values to differentiate between benign and malignant breast lesions and the normal breast parenchyma. We used breast MRI, including DWI, to obtain images of 167 breast lesions (18 benign lesions and 149 malignant lesions) of 152 women (mean age: 48.6 years, range: 24-80 years). The mean ADC values of the malignant lesions were compared to those of the benign lesions and the normal parenchyma. We compared the ADC values of IDC, DCIS and other types of breast cancer and we also compared the ADC values with the nuclear grade of IDC. The mean ADC values of the malignant lesions were lower than those of the benign lesions and the normal parenchyma (p-3 mm2/s for discriminating between malignant and benign lesion showed a specificity of 53% and a sensitivity of 100%, and the ADC threshold value of 1.33 X 10-3 mm2/s showed a specificity of 93% and a sensitivity of 94% for discriminating between malignant and benign lesion.
Energy Technology Data Exchange (ETDEWEB)
Cavalleri, Francesca; Todeschini, Alessandra [Azienda Unita Sanitaria Locale di Modena, Neuroradiology Unit, Department of Neuroscience, Nuovo Ospedale Civile S. Agostino Estense di Modena, Modena (Italy); Lugli, Licia; Pugliese, Marisa; Della Casa, Elisa; Gallo, Claudio; Frassoldati, Rossella; Ferrari, Fabrizio [Modena University Hospital, Institute of Pediatrics and Neonatal Medicine and NICU, Modena (Italy); D' Amico, Roberto [University of Modena and Reggio Emilia, Department of Clinical and Diagnostic Medicine and Public Health, Modena (Italy)
2014-09-15
The diagnostic and prognostic assessment of newborn infants with hypoxic-ischemic encephalopathy (HIE) comprises, among other tools, diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) maps. To compare the ability of DWI and ADC maps in newborns with HIE to predict the neurodevelopmental outcome at 2 years of age. Thirty-four term newborns with HIE admitted to the Neonatal Intensive Care Unit of Modena University Hospital from 2004 to 2008 were consecutively enrolled in the study. All newborns received EEG, conventional MRI and DWI within the first week of life. DWI was analyzed by means of summation (S) score and regional ADC measurements. Neurodevelopmental outcome was assessed with a standard 1-4 scale and the Griffiths Mental Developmental Scales - Revised (GMDS-R). When the outcome was evaluated with a standard 1-4 scale, the DWI S scores showed very high area under the curve (AUC) (0.89) whereas regional ADC measurements in specific subregions had relatively modest predictive value. The lentiform nucleus was the region with the highest AUC (0.78). When GMDS-R were considered, DWI S scores were good to excellent predictors for some GMDS-R subscales. The predictive value of ADC measurements was both region- and subscale-specific. In particular, ADC measurements in some regions (basal ganglia, white matter or rolandic cortex) were excellent predictors for specific GMDS-R with AUCs up to 0.93. DWI S scores showed the highest prognostic value for the neurological outcome at 2 years of age. Regional ADC measurements in specific subregions proved to be highly prognostic for specific neurodevelopmental outcomes. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Ahn, Hye Shin; Chang, Yun Woo; Choi, Kyung Hee; Kim, Hyun Joo; Hong, Seong Suk; Hwang, Jung Hwa; Kwon, Kui Hyang [Dept.of Radiology, Soonchunhyang University Hospital, Seoul (Korea, Republic of); Kim, Yong Bae [Dept. of Preventive Medicine, Soonchunhyang University Hospital, Seoul (Korea, Republic of)
2011-04-15
We wanted to evaluate the ability of the apparent diffusion coefficient (ADC) values to differentiate between benign and malignant breast lesions and the normal breast parenchyma. We used breast MRI, including DWI, to obtain images of 167 breast lesions (18 benign lesions and 149 malignant lesions) of 152 women (mean age: 48.6 years, range: 24-80 years). The mean ADC values of the malignant lesions were compared to those of the benign lesions and the normal parenchyma. We compared the ADC values of IDC, DCIS and other types of breast cancer and we also compared the ADC values with the nuclear grade of IDC. The mean ADC values of the malignant lesions were lower than those of the benign lesions and the normal parenchyma (p<0.001, respectively). The mean ADC value of IDC was lower than those of DCIS and other breast cancers (p<0.001, respectively). The mean ADC value of mucinous carcinoma among the other breast cancer was characteristic high compared with that of the normal parenchyma. There was no significant differentiation of the ADC values between the nuclear grades of IDC (p<0.828). The ADC threshold value of 0.98 X 10{sup -3} mm{sup 2}/s for discriminating between malignant and benign lesion showed a specificity of 53% and a sensitivity of 100%, and the ADC threshold value of 1.33 X 10{sup -3} mm{sup 2}/s showed a specificity of 93% and a sensitivity of 94% for discriminating between malignant and benign lesion.
International Nuclear Information System (INIS)
The goal of our study was to evaluate the diagnostic efficacy of diffusion-weighted imaging (DWI) in the differentiation of benign and malignant breast lesions. Between June 2012 and March 2013, 60 patients with 63 lesions (age range 29-70 years, mean age 48.6 years) were included in our study. All lesions, except complicated cysts and intra-mammary lymph nodes, were confirmed histopathologically. The patients were evaluated with a 1.5 Tesla MR scanner using dedicated bilateral breast coil. DWI images were obtained by echo planar imaging sequence and 'b' values were selected as 200, 600 and 1000 s/mm2. Apparent diffusion coefficient (ADC) values of both breast lesions and the normal fibroglandular tissue of the contralateral breast were calculated and statistically compared using Shapiro-Wilk test, Student's t-test, Mann-Whitney U test, chi-square test and the receiver operating curve. Of 63 lesions, 22 were malignant and 41 were benign. In malignant lesions, the mean ADC values were 1.40 ± 0.41 × 10−3mm2/s for b = 200, 1.05 ± 0.28 × 10−3mm2/s for b = 600 and 0.91 ± 0.20 × 10−3mm2/s for b = 1000 and in benign lesions, the mean ADC values were 2.13 ± 0.85 × 10−3mm2/s for b = 200, 1.64 ± 0.47 × 10−3mm2/s for b = 600 and 1.40 ± 0.43 × 10−3mm2/s for b = 1000. The success of ADC values in differentiation of benign and malignant lesions was statistically significant (P = 0.0001). The threshold values were determined to be 1.50 × 10−3mm2/s for b = 200, 1.22 × 10−3mm2/s for b = 600 and 0.98 × 10−3mm2/s for b = 1000 (P < 0.05). DWI can be an effective radiological method in the differentiation of benign and malignant breast lesions.
Energy Technology Data Exchange (ETDEWEB)
MacKenzie, John D. [Children' s Hospital of Philadelphia, Department of Pediatric Radiology, Philadelphia, PA (United States); UCSF Benioff Children' s Hospital, Department of Radiology and Biomedical Imaging, San Francisco, CA (United States); Hernandez, Andrea; Pena, Andres; Khrichenko, Dmitry; Gonzalez, Leonardo; Jaramillo, Diego [Children' s Hospital of Philadelphia, Department of Pediatric Radiology, Philadelphia, PA (United States); Ruppert, Kai [Children' s Hospital of Philadelphia, Department of Pediatric Radiology, Philadelphia, PA (United States); University of Virginia, Department of Radiology, Charlottesville, VA (United States); Jawad, Abbas F. [Children' s Hospital of Philadelphia, Department of Pediatrics, Philadelphia, PA (United States); Wells, Lawrence [Children' s Hospital of Philadelphia, Department of Orthopedics, Philadelphia, PA (United States); Smith-Whitley, Kim [Children' s Hospital of Philadelphia, Department of Hematology, Philadelphia, PA (United States)
2012-06-15
Avascular necrosis (AVN) is a common morbidity in children with sickle cell disease (SCD) that leads to pain and joint immobility. However, the diagnosis is often uncertain or delayed. To examine the ability of apparent diffusion coefficient (ADC) measurements on diffusion-weighted imaging to detect AVN in children with SCD. ADC values were calculated at the hips of normal children (n = 19) and children with SCD who were either asymptomatic with no known previous hip disease (n = 13) or presented for the first time with clinical symptoms of hip pathology (n = 12). ADC values were compared for differences among groups with and without AVN using non-parametric statistical methods. The ADC values were elevated in the hips of children with AVN (median ADC = 1.57 x 10{sup -3} mm{sup 2}/s [95% confidence interval = 0.86-2.10]) and differed significantly in pairwise comparisons (all P < 0.05) from normal children (0.74 [0.46-0.98]), asymptomatic children with SCD (0.55 [0.25-0.85]), and SCD children who had symptoms referable to their hips but did not show findings of hip AVN on conventional MRI or radiographs (0.46 [0.18-0.72]). Children with sickle cell disease have elevated apparent diffusion coefficient values in their affected hips on initial diagnosis of avascular necrosis. (orig.)
International Nuclear Information System (INIS)
Aim: To investigate the effects of age and gender on apparent diffusion coefficient (ADC) measurements of bilateral kidneys at 3 T MRI, and compare the ADC values of left and right kidneys. Materials and methods: In all, 137 healthy participants (mean age 42.8 ± 14.7 years; age range 16–75 years) comprising 68 male and 69 female participants were enrolled. Three Tesla echo-planar diffusion-weighted imaging (DWI) of bilateral kidneys was performed and ADC values were measured in the cortex, medulla, and whole parenchyma. Pearson correlation analysis and linear regression were performed to determine the associations between the ADC values in each region and age. Effects of age and gender on ADC values were analysed using two-factor analysis of variance (ANOVA). The paired-samples t-test was established to compare the ADC values between left and right kidneys. Results: ADC values were significantly higher in the young group (≤50 years) than in the old group (>50 years), and correlated inversely with the age in all regions. Male participants had higher ADC values than female participants in all regions except left medulla. Two-factor ANOVA of age × gender showed no significant interactions between the variables age and gender were found. No significant differences in ADC values between left and right kidneys were observed. Conclusion: Renal ADC values are age- and gender-dependent, and show no significant difference between left and right kidneys. Age- and gender-related effects should be taken into consideration in future renal DWI studies when using normal ADC values from health controls. - Highlights: • Renal apparent diffusion coefficient (ADC) values decrease with ageing. • Men tend to have higher renal ADC values than women. • Bilateral kidneys seem to have no significantly different ADC values
Directory of Open Access Journals (Sweden)
Saskia Kwan
2015-01-01
Full Text Available The objective of this study was to assess the evolution of diffusion-weighted imaging (DWI and diffusion-tensor imaging (DTI over the first month of life in asphyxiated newborns treated with hypothermia and to compare it with that of healthy newborns. Asphyxiated newborns treated with hypothermia were enrolled prospectively; and the presence and extent of brain injury were scored on each MRI. Apparent diffusion coefficient (ADC and fractional anisotropy (FA values were measured in the basal ganglia, in the white matter and in the cortical grey matter. Sixty-one asphyxiated newborns treated with hypothermia had a total of 126 ADC and FA maps. Asphyxiated newborns developing brain injury eventually had significantly decreased ADC values on days 2-3 of life and decreased FA values around day 10 and 1 month of life compared with those not developing brain injury. Despite hypothermia treatment, asphyxiated newborns may develop brain injury that still can be detected with advanced neuroimaging techniques such as DWI and DTI as early as days 2-3 of life. A study of ADC and FA values over time may aid in the understanding of how brain injury develops in these newborns despite hypothermia treatment.
International Nuclear Information System (INIS)
To establish standard apparent diffusion coefficient (ADC) and the fat content as a function of age, gender and body mass index (BMI) in healthy parotid glands, and to address the influences of fat suppression on ADC measurements. A total of 100 healthy adults (gender and age evenly distributed) were prospectively recruited, with parotid fat content measured from gradient-echo images with fat-water separated using iterative decomposition with echo asymmetry and least squares (IDEAL). The ADCs were estimated using both fat-saturated and non-fat-saturated diffusion-weighted imaging via a periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) technique. Parotid fat content was larger in men than in women by about 10 percentage points (P < 0.005), and positively associated with BMI and age for both genders (mostly with P < 0.001). ADCs estimated with non-fat-saturated PROPELLER were significantly lower in men than in women (P < 0.005), but showed no gender difference if measured using fat-saturated PROPELLER (P = 0.840). The negative association between parotid ADC and age/BMI/fat (P < 0.001) showed greater regression slopes in non-fat-saturated PROPELLER than in fat-saturated data. Parotid fat content in healthy adults correlates positively with both age and BMI; the correlation with age is gender-dependent. Parotid ADC measurements are strongly influenced by fat saturation. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Chang, Hing-Chiu [National Taiwan University, Graduate Institute of Biomedical Electronics and Bioinformatics, Taipei (China); Duke University Medical Center, Brain Imaging and Analysis Center, Durham, NC (United States); GE Healthcare, Applied Science Laboratory, Taipei (China); Juan, Chun-Jung; Hsu, Hsian-He [National Defense Medical Center, Department of Radiology, Taipei (China); Tri-Service General Hospital, Department of Radiology, Taipei (China); Chiu, Hui-Chu [Tatung University, Graduate Institute of Design Science, Taipei (China); Cheng, Cheng-Chieh; Chiu, Su-Chin [National Taiwan University, Graduate Institute of Biomedical Electronics and Bioinformatics, Taipei (China); Liu, Yi-Jui [Feng Chia University, Department of Automatic Control Engineering, Taichung (China); Chung, Hsiao-Wen [National Taiwan University, Graduate Institute of Biomedical Electronics and Bioinformatics, Taipei (China); Tri-Service General Hospital, Department of Radiology, Taipei (China); National Taiwan University, MD.624, Department of Electrical Engineering, Taipei (China)
2014-09-15
To establish standard apparent diffusion coefficient (ADC) and the fat content as a function of age, gender and body mass index (BMI) in healthy parotid glands, and to address the influences of fat suppression on ADC measurements. A total of 100 healthy adults (gender and age evenly distributed) were prospectively recruited, with parotid fat content measured from gradient-echo images with fat-water separated using iterative decomposition with echo asymmetry and least squares (IDEAL). The ADCs were estimated using both fat-saturated and non-fat-saturated diffusion-weighted imaging via a periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) technique. Parotid fat content was larger in men than in women by about 10 percentage points (P < 0.005), and positively associated with BMI and age for both genders (mostly with P < 0.001). ADCs estimated with non-fat-saturated PROPELLER were significantly lower in men than in women (P < 0.005), but showed no gender difference if measured using fat-saturated PROPELLER (P = 0.840). The negative association between parotid ADC and age/BMI/fat (P < 0.001) showed greater regression slopes in non-fat-saturated PROPELLER than in fat-saturated data. Parotid fat content in healthy adults correlates positively with both age and BMI; the correlation with age is gender-dependent. Parotid ADC measurements are strongly influenced by fat saturation. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Jeong, Ju Hye [Dept. of Nuclear Medicine, Kyungpook National University Hospital, Daegu (Korea, Republic of); Cho, Ihn Ho; Chun, Kyung Ah; Kong, Eun Jung; Kwon, Sang Don; Kim, Jae Hwang [Yeungnam University Hospital, Daegu (Korea, Republic of)
2016-06-15
Fluorine-18-fluorodeoxyglucose ({sup 18}F-FDG) positron emission tomography (PET) and diffusion-weighted magnetic resonance imaging (DWI) share the same role in clinical oncology and it is feasible to obtain the standardized uptake value (SUV) and apparent diffusion coefficient (ADC) simultaneously by emerging the hybrid positron emission tomography/magnetic resonance (PET/MR). This study investigated the correlation between the ADCs of rectal cancer lesions and their SUVs derived from hybrid PET/MR. Nine patients with histologically proven rectal adenocarcinoma (5 men, 4 women; mean age, 70 ± 15.91 years) underwent torso {sup 18}F-FDG PET/CT and regional hybrid {sup 18}F-FDG PET/MR sequentially. A fixed threshold value of 40 % of maximum uptake was used to determine tumor volume of interest (VOI) on PET image; SUV{sub max}, SUV{sub peak}, and SUV{sub mean} were calculated automatically. A single freehand region of interest (ROI) was drawn on high b-value (b1000) DWI image and copied to corresponding ADC map to determine the ADCmean of rectal cancer lesion. Spearman'rank correlation coefficient (ρ) was calculated to determine the correlation between SUVs and ADC values. SUV{sub max}, SUV{sub peak}, and SUV{sub mean} derived by hybrid PET/MR were 12.35 ± 4.66 (mean ± standard deviation), 9.66 ± 3.15 and 7.41 ± 2.54, respectively. The ADCmean value of rectal cancer lesions was 1.02 ± 0.08 × 10{sup -3}mm{sup 2}/s. ADCmean was significantly and inversely correlated with SUV values (SUV{sub max}, ρ = -0.95, p < 0.001; SUV{sub peak}, ρ = -0.93, p < 0.001; SUV{sub mean}, ρ = -0.91, p = 0.001). This preliminary hybrid PET/MR study demonstrates a significant inverse correlation exists between metabolic activity on {sup 18}F-FDG PET and water diffusion on DWI in rectal cancer.
Directory of Open Access Journals (Sweden)
Martin Bulik
2015-01-01
Full Text Available Objective. To prospectively determine institutional cut-off values of apparent diffusion coefficients (ADCs and concentration of tissue metabolites measured by MR spectroscopy (MRS for early differentiation between glioblastoma (GBM relapse and treatment-related changes after standard treatment. Materials and Methods. Twenty-four GBM patients who received gross total resection and standard adjuvant therapy underwent MRI examination focusing on the enhancing region suspected of tumor recurrence. ADC maps, concentrations of N-acetylaspartate, choline, creatine, lipids, and lactate, and metabolite ratios were determined. Final diagnosis as determined by biopsy or follow-up imaging was correlated to the results of advanced MRI findings. Results. Eighteen (75% and 6 (25% patients developed tumor recurrence and pseudoprogression, respectively. Mean time to radiographic progression from the end of chemoradiotherapy was 5.8 ± 5.6 months. Significant differences in ADC and MRS data were observed between those with progression and pseudoprogression. Recurrence was characterized by N-acetylaspartate ≤ 1.5 mM, choline/N-acetylaspartate ≥ 1.4 (sensitivity 100%, specificity 91.7%, N-acetylaspartate/creatine ≤ 0.7, and ADC ≤ 1300 × 10−6 mm2/s (sensitivity 100%, specificity 100%. Conclusion. Institutional validation of cut-off values obtained from advanced MRI methods is warranted not only for diagnosis of GBM recurrence, but also as enrollment criteria in salvage clinical trials and for reporting of outcomes of initial treatment.
Knight, Michael J; McGarry, Bryony L; Rogers, Harriet J; Jokivarsi, Kimmo T; Gröhn, Olli Hj; Kauppinen, Risto A
2016-07-01
The objective of this study is to present a mathematical model which can describe the spatiotemporal progression of cerebral ischaemia and predict magnetic resonance observables including the apparent diffusion coefficient (ADC) of water and transverse relaxation time T2 This is motivated by the sensitivity of the ADC to the location of cerebral ischaemia and T2 to its time-course, and that it has thus far proven challenging to relate observations of changes in these MR parameters to stroke timing, which is of considerable importance in making treatment choices in clinics. Our mathematical model, called the cytotoxic oedema/dissociation (CED) model, is based on the transit of water from the extra- to the intra-cellular environment (cytotoxic oedema) and concomitant degradation of supramacromolecular and macromolecular structures (such as microtubules and the cytoskeleton). It explains experimental observations of ADC and T2, as well as identifying the rate of spread of effects of ischaemia through a tissue as a dominant system parameter. The model brings the direct extraction of the timing of ischaemic stroke from quantitative MRI closer to reality, as well as providing insight on ischaemia pathology by imaging in general. We anticipate that this may improve patient access to thrombolytic treatment as a future application. PMID:26661188
International Nuclear Information System (INIS)
We prospectively investigated whether the value of the apparent diffusion coefficient (ADC) of a primary lesion prior to treatment correlated with local failure of head and neck squamous cell carcinoma (HNSCC) following radiotherapy. In 17 patients who underwent radiotherapy for primary HNSCC, we compared variables considered to affect local failure, including parameters related to magnetic resonance (MR) imaging, such as ADC and its alteration ratio, between cases of local failure and controls and analyzed survival among those patients in whom the variables differed or demonstrated association with local failure. We also retrospectively analyzed variables in a validation study of 40 patients. In the prospective study, pretreatment values of ADChigh (calculated with b-values of 300, 500, 750, and 1000 s/mm2) alone showed significant association with local failure (P=0.0186). In the validation study, pretreatment values of tumor volume (P=0.0217) and ADChigh (P=0.0001) were significantly associated with local failure. Pretreatment ADChigh was superior to pretreatment tumor volume regarding association with local failure. These results suggest that pretreatment values of both ADC obtained using high b-values and tumor volume correlate with local failure of HNSCC treated with radiotherapy. (author)
Institute of Scientific and Technical Information of China (English)
LIN Fan; LEI Yi; LI Yang-bin
2009-01-01
Background The usefulness of in-phase/opposed-phase imaging and diffusion weighted imaging (DWI) in differentiating benign and neoplastic vertebral fractures has been described. In this study, we aimed to evaluate the influence of the severity of vertebral damage on the diagnostic performance of these two technologies.Methods Totally 59 patients with 68 acute benign vertebral fractures and 43 patients with 79 vertebral metastases were included in this study. The MR protocol included DWls and sagittal in-phase/opposed-phase gradient recalled sequence.The severity of vertebral damage was expressed by lesion ratio (LR, the ratio of lesion area to vertebral area on the slices of largest abnormal signal area in the T1-weighted sequence). Quantitative (signal intensity ratio (SIR) defined as signal intensity (SI) on opposed-phase gradient recalled echo (GRE) images divided by SI on in-phase; apparent diffusion coefficient (ADC) value derived from DWI analysis was performed, the relationships between LR and the measurements of these two technologies were analyzed using linear regression. The covariate-specific receiver operating characteristic (ROC) curves were also fitted to evaluate the influence of LR on the diagnostic performance of ADC and SIR. Results The difference in both SIR and ADC for vertebral metastasis and acute benign vertebral fractures was significant (P 0.05). More severe cases were associated with increased AUC for SIR.Conclusions LR is capable of affecting the diagnostic performances of chemical shift imaging. Thus, when applying these tests to make diagnoses on vertebral fractures, the severity of the vertebral damage should be taken into account.The covariate-specific ROC model is recommended because it substantially improves the ability to avoid bias when evaluating tests.
Razek, Ahmed Abdel Khalek Abdel; Nada, Nadia
2016-04-01
The aim of this study was to measure choline/creatine (Ch/Cr) levels through (1)H-MRS and apparent diffusion coefficient (ADC) values through diffusion-weighted MRI, and to correlate these values with the prognostic parameters of head and neck squamous cell carcinoma (HNSCC). The institutional review board approved this study and informed written consent was obtained from all study participants. A prospective study of 43 patients (31 men and 12 women; mean age, 65 years) with HNSCC was conducted. Single-voxel (1)H-MRS was performed at the tumor or metastatic cervical lymph node with point-resolved spectroscopy (PRESS) at TE = 135 ms. Diffusion-weighted MR images with b values of 0, 500 and 1000 s/mm(2) and contrast MRI of the head and neck were performed. The Ch/Cr levels and ADC values of HNSCC were calculated. The gross tumor volume (GTV) was also calculated. The degree of tumor differentiation was determined through pathological examination. The HNSCC Ch/Cr level was negatively correlated with the ADC value (r = -0.662, p = 0.001). There was a significant difference in the Ch/Cr and ADC values at different degrees of tumor differentiation (p = 0.003 and p = 0.001) and with different GTVs (p = 0.122 and p = 0.001). The following prognostic parameter categories were used: (i) poorly differentiated and undifferentiated versus well differentiated to moderately differentiated; and (ii) HNSCC with GTV 30 cm(3). The cut-off values for Cho/Cr and ADC for each category were 1.83, 0.95 and 1.94, 0.99, respectively, and the areas under the curve were 0.771, 0.967 and 0.726, 0.795, respectively, for each category. We conclude that the Ch/Cr levels determined using (1)H-MRS and the ADC values are well correlated with several prognostic parameters of HNSCC.
Energy Technology Data Exchange (ETDEWEB)
Karki, K; Hugo, G; Ford, J; Saraiya, S; Weiss, E [Radiation Oncology, Virginia Commonwealth University, Richmond, VA (United States); Olsen, K; Groves, R [Radiology, Virginia Commonwealth University, Richmond, VA (United States)
2014-06-15
Purpose: Diffusion-weighted MRI (DW-MRI) is increasingly being investigated for radiotherapy planning and response assessment. Selection of a limited number of b-values in DW-MRI is important to keep geometrical variations low and imaging time short. We investigated various b-value sets to determine an optimal set for obtaining monoexponential apparent diffusion coefficient (ADC) close to perfusion-insensitive intravoxel incoherent motion (IVIM) model ADC (ADC_{IVIM}) in nonsmall cell lung cancer. Methods: Seven patients had 27 DW-MRI scans before and during radiotherapy in a 1.5T scanner. Respiratory triggering was applied to the echo-planar DW-MRI with TR=4500ms approximately, TE=74ms, pixel size=1.98X1.98mm{sub 2}, slice thickness=4–6mm and 7 axial slices. Diffusion gradients were applied to all three axes producing traceweighted images with eight b-values of 0–1000μs/μm{sup 2}. Monoexponential model ADC values using various b-value sets were compared to ADC_{IVIM} using all b-values. To compare the relative noise in ADC maps, intra-scan coefficient of variation (CV) of active tumor volumes was computed. Results: ADC_{IVIM}, perfusion coefficient and perfusion fraction for tumor volumes were in the range of 880-1622 μm{sup 2}/s, 8119-33834 μm{sup 2}/s and 0.104–0.349, respectively. ADC values using sets of 250, 800 and 1000; 250, 650 and 1000; and 250–1000μs/μm{sup 2} only were not significantly different from ADC_{IVIM}(p>0.05, paired t-test). Error in ADC values for 0–1000, 50–1000, 100–1000, 250–1000, 500–1000, and three b-value sets- 250, 500 and 1000; 250, 650 and 1000; and 250, 800 and 1000μs/μm{sup 2} were 15.0, 9.4, 5.6, 1.4, 11.7, 3.7, 2.0 and 0.2% relative to the reference-standard ADC_{IVIM}, respectively. Mean intrascan CV was 20.2, 20.9, 21.9, 24.9, 32.6, 25.8, 25.4 and 24.8%, respectively, whereas that for ADC_{IVIM} was 23.3%. Conclusion: ADC values of two 3 b-value sets
Directory of Open Access Journals (Sweden)
P Brandmaier
Full Text Available Previous non-simultaneous PET/MR studies have shown heterogeneous results about the correlation between standardized uptake values (SUVs and apparent diffusion coefficients (ADCs. The aim of this study was to investigate correlations in patients with primary and recurrent tumors using a simultaneous PET/MRI system which could lead to a better understanding of tumor biology and might play a role in early response assessment.We included 31 patients with histologically confirmed primary (n = 14 or recurrent cervical cancer (n = 17 who underwent simultaneous whole-body 18F-FDG-PET/MRI comprising DWI. Image analysis was performed by a radiologist and a nuclear physician who identified tumor margins and quantified ADC and SUV. Pearson correlations were calculated to investigate the association between ADC and SUV.92 lesions were detected. We found a significant inverse correlation between SUVmax and ADCmin (r = -0.532, p = 0.05 in primary tumors as well as in primary metastases (r = -0.362, p = 0.05 and between SUVmean and ADCmin (r = -0.403, p = 0.03. In recurrent local tumors we found correlations for SUVmax and ADCmin (r = -0.747, p = 0.002 and SUVmean and ADCmin (r = -0.773, p = 0.001. Associations for recurrent metastases were not significant (p>0.05.Our study demonstrates the feasibility of fast and reliable measurement of SUV and ADC with simultaneous PET/MRI. In patients with cervical cancer we found significant inverse correlations for SUV and ADC which could play a major role for further tumor characterization and therapy decisions.
Energy Technology Data Exchange (ETDEWEB)
Ishihara, Makiko; Hayashi, Hiromitsu; Amano, Yasuo; Takagi, Ryo; Nakahara, Madoka; Kumazaki, Tatsuo [Nippon Medical School, Tokyo (Japan); Cho, Keiichi; Okada, Susumu
1998-06-01
The purpose of the present study is to evaluate diffusional anisotropy of white matter in patients with multiple lacunar infarcts using diffusion-weighted echo-planar imaging (DW-EPI), and to examine the relationship between diffusional anisotropy and global cognitive ability as assessed by the mini-mental status examination (MMSE). In particular, we focused on the parameter changes for the corpus callosum as a marker for disconnection of the associative cortices. Twenty-nine patients divided into 2 cognitive level groups (low MMSE, n=16; high MMSE, n=13) and 8 normal controls were examined with a GE 1.5 T Horizon system. Three series of DW-EPI images were obtained using the following epidw{sub g}{center_dot}psd{sup TM} sequence: TR/TE=6500/120 ms, single shot, 6.5 mm slice thickness and 1.5 mm gap transaxial sections of the whole brain, with b-factors of 0 and 710 along each x- and y-axial direction. The parametric maps for apparent diffusion coefficient (ADC) in each direction, ADC(x) and ADC(y), and their rate map (ADC rate=ADC(x)/ADC(y)) were created on a pixel-by-pixel basis. ROI data were extracted from images of the corpus callosum and bilateral optic radiata. As a result, the ADC(x) was markedly larger for corpus callosum than that for optic radiata, whereas the ADC(y) showed an inverse trend, attributable to regional differences of diffusional anisotropy. In corpus callosum, however, the ADC(y) values were observed to increase with the level of disease severity, resulting in a decrease of the ADC rate. Notably, there was a significant difference between the three groups for callosal genu, with a slight positive correlation between the ADC rate and the MMSE scores. Our study suggests that a relationship exists between the reduction of diffusional anisotropy in callosal genu and the global cognitive impairment seen in patients with multiple lacunar infarcts. (K.H.)
Kirby, Miranda; Ouriadov, Alexei; Svenningsen, Sarah; Owrangi, Amir; Wheatley, Andrew; Etemad‐Rezai, Roya; Santyr, Giles E.; McCormack, David G.; Parraga, Grace
2014-01-01
Abstract Noble gas pulmonary magnetic resonance imaging (MRI) is transitioning away from 3He to 129Xe gas, but the physiological/clinical relevance of 129Xe apparent diffusion coefficient (ADC) parenchyma measurements is not well understood. Therefore, our objective was to generate 129Xe MRI ADC for comparison with 3He ADC and with well‐established measurements of alveolar structure and function in older never‐smokers and ex‐smokers with chronic obstructive pulmonary disease (COPD). In four never‐smokers and 10 COPD ex‐smokers, 3He (b = 1.6 sec/cm2) and 129Xe (b = 12, 20, and 30 sec/cm2) ADC, computed tomography (CT) density‐threshold measurements, and the diffusing capacity for carbon monoxide (DLCO) were measured. To understand regional differences, the anterior–posterior (APG) and superior–inferior (∆SI) ADC differences were evaluated. Compared to never‐smokers, COPD ex‐smokers showed greater 3He ADC (P = 0.006), 129Xe ADCb12 (P = 0.006), and ADCb20 (P = 0.006), but not for ADCb30 (P > 0.05). Never‐smokers and COPD ex‐smokers had significantly different APG for 3He ADC (P = 0.02), 129Xe ADCb12 (P = 0.006), and ADCb20 (P = 0.01), but not for ADCb30 (P > 0.05). ∆SI for never‐ and ex‐smokers was significantly different for 3He ADC (P = 0.046), but not for 129Xe ADC (P > 0.05). There were strong correlations for DLCO with 3He ADC and 129Xe ADCb12 (both r = −0.95, P < 0.05); in a multivariate model 129Xe ADCb12 was the only significant predictor of DLCO (P = 0.049). For COPD ex‐smokers, CT relative area <−950 HU (RA950) correlated with 3He ADC (r = 0.90, P = 0.008) and 129Xe ADCb12 (r = 0.85, P = 0.03). In conclusion, while 129Xe ADCb30 may be appropriate for evaluating subclinical or mild emphysema, in this small group of never‐smokers and ex‐smokers with moderate‐to‐severe emphysema, 129Xe ADCb12 provided a physiologically appropriate estimate of gas exchange abnormalities and alveolar microstructure. PMID:25347853
Sijens, P E; Fock, J M; Meiners, L C; Potze, J H; Irwan, R; Oudkerk, M
2007-06-01
Brain magnetic resonance spectroscopy (MRS) and diffusion tensor imaging (DTI) in one patient with merosin-deficient congenital muscular dystrophy (MDCMD) revealed significant metabolite (choline, creatine, N-acetyl aspartate) level reductions, fractional anisotropy (FA) reduction and increased apparent diffusion coefficient (ADC) in the white matter (p<0.01, all). In the gray matter, the MRS properties did not differ significantly from those in controls. The ADC and FA, however, differed significantly as in the white matter, although the differences were less pronounced. This is the first quantitative MR study of the brain in a patient with MDCMD, which revealed that the concentrations of all MRS measured metabolites were decreased only in the white matter. This observation, combined with the DTI observed ADC increases and FA decrease, indicated a presence of vasogenic edema in the white matter.
Karki, Kishor; Hugo, Geoffrey D.; Ford, John C.; Olsen, Kathryn M.; Saraiya, Siddharth; Groves, Robert; Weiss, Elisabeth
2015-10-01
The purpose of this study was to determine optimal sets of b-values in diffusion-weighted MRI (DW-MRI) for obtaining monoexponential apparent diffusion coefficient (ADC) close to perfusion-insensitive intravoxel incoherent motion (IVIM) model ADC (ADCIVIM) in non-small cell lung cancer. Ten subjects had 40 DW-MRI scans before and during radiotherapy in a 1.5 T MRI scanner. Respiratory triggering was applied to the echo-planar DW-MRI with \\text{TR}≈ 4500 ms, TE = 74 ms, eight b-values of 0-1000 μs μm-2, pixel size = 1.98× 1.98 mm2, slice thickness = 6 mm, interslice gap = 1.2 mm, 7 axial slices and total acquisition time ≈6 min. One or more DW-MRI scans together covered the whole tumour volume. Monoexponential model ADC values using various b-value sets were compared to reference-standard ADCIVIM values using all eight b-values. Intra-scan coefficient of variation (CV) of active tumour volumes was computed to compare the relative noise in ADC maps. ADC values for one pre-treatment DW-MRI scan of each of the 10 subjects were computed using b-value pairs from DW-MRI images synthesized for b-values of 0-2000 μs μm-2 from the estimated IVIM parametric maps and corrupted by various Rician noise levels. The square root of mean of squared error percentage (RMSE) of the ADC value relative to the corresponding ADCIVIM for the tumour volume of the scan was computed. Monoexponential ADC values for the b-value sets of 250 and 1000; 250, 500 and 1000; 250, 650 and 1000; 250, 800 and 1000; and 250-1000 μs μm-2 were not significantly different from ADCIVIM values (p>0.05 , paired t-test). Mean error in ADC values for these sets relative to ADCIVIM were within 3.5%. Intra-scan CVs for these sets were comparable to that for ADCIVIM. The monoexponential ADC values for other sets—0-1000 50-1000 100-1000 500-1000 and 250 and 800 μs μm-2 were significantly different from the ADCIVIM values. From Rician noise simulation
Energy Technology Data Exchange (ETDEWEB)
Server, Andres, E-mail: a.s.alonso@medisin.uio.no [Section of Neuroradiology, Department of Radiology and Nuclear Medicine, Oslo University Hospital-Ullevaal and University of Oslo, Kirkeveien 166, NO-0407 Oslo (Norway); Kulle, Bettina, E-mail: b.k.andreassen@medisin.uio.no [Department of Biostatistics, University of Oslo, Oslo (Norway); Gadmar, Oystein B., E-mail: gays@uus.no [Interventional Centre, Oslo University Hospital and Institute for Hospital Medicine, University of Oslo, Oslo (Norway); Josefsen, Roger, E-mail: roos@uus.no [Department of Neurosurgery, Oslo University Hospital-Ullevaal, Oslo (Norway); Kumar, Theresa, E-mail: thku@uus.no [Department of Pathology, Oslo University Hospital-Ullevaal, Oslo (Norway); Nakstad, Per H., E-mail: pena@uus.no [Section of Neuroradiology, Department of Radiology and Nuclear Medicine, Oslo University Hospital-Ullevaal and University of Oslo, Kirkeveien 166, NO-0407 Oslo (Norway)
2011-11-15
Purpose: Tumor grading is very important both in treatment decision and evaluation of prognosis. While tissue samples are obtained as part of most therapeutic approaches, factors that may result in inaccurate grading due to sampling error (namely, heterogeneity in tissue sampling, as well as tumor-grade heterogeneity within the same tumor specimen), have led to a desire to use imaging better to ascertain tumor grade. The purpose in our study was to evaluate the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), area under the curve (AUC), and accuracy of diffusion-weighted MR imaging (DWI), proton MR spectroscopic imaging (MRSI) or both in grading primary cerebral gliomas. Materials and methods: We performed conventional MR imaging (MR), DWI, and MRSI in 74 patients with newly diagnosed brain gliomas: 59 patients had histologically verified high-grade gliomas: 37 glioblastomas multiform (GBM) and 22 anaplastic astrocytomas (AA), and 15 patients had low-grade gliomas. Apparent diffusion coefficient (ADC) values of tumor and peritumoral edema, and ADC ratios (ADC in tumor or peritumoral edema to ADC of contralateral white matter, as well as ADC in tumor to ADC in peritumoral edema) were determined from three regions of interest. The average of the mean, maximum, and minimum for ADC variables was calculated for each patient. The metabolite ratios of Cho/Cr and Cho/NAA at intermediate TE were assessed from spectral maps in the solid portion of tumor, peritumoral edema and contralateral normal-appearing white matter. Tumor grade determined with the two methods was then compared with that from histopathologic grading. Logistic regression and receiver operating characteristic (ROC) curve analysis were performed to determine optimum thresholds for tumor grading. Measures of diagnostic examination performance, such as sensitivity, specificity, PPV, NPV, AUC, and accuracy for identifying high-grade gliomas were also calculated
Energy Technology Data Exchange (ETDEWEB)
Regier, M., E-mail: mregier@uke.uni-hamburg.de [Center for Radiology and Endoscopy, Department of Diagnostic and Interventional Radiology, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg (Germany); Derlin, T. [Center for Radiology and Endoscopy, Department of Nuclear Medicine, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg (Germany); Schwarz, D.; Laqmani, A.; Henes, F.O.; Groth, M.; Buhk, J.-H. [Center for Radiology and Endoscopy, Department of Diagnostic and Interventional Radiology, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg (Germany); Kooijman, H. [Philips Healthcare, Clinical Application, Luebeckertordamm 5, 20099 Hamburg (Germany); Adam, G. [Center for Radiology and Endoscopy, Department of Diagnostic and Interventional Radiology, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg (Germany)
2012-10-15
Introduction: To investigate the potential correlation of the apparent diffusion coefficient assessed by diffusion-weighted MRI (DWI) and glucose metabolism determined by the standardized uptake value (SUV) at 18F-FDG PET/CT in non-small cell lung cancer (NSCLC). Materials and methods: 18F-FDG PET/CT and DWI (TR/TE, 2000/66 ms; b-values, 0 and 500 s/mm{sup 2}) were performed in 41 consecutive patients with histologically verified NSCLC. Analysing the PET-CT data calculation of the mean (SUV{sub mean}) and maximum (SUV{sub max}) SUV was performed. By placing a region-of-interest (ROI) encovering the entire tumor mean (ADC{sub mean}) and minimum ADC (ADC{sub min}) were determined by two independent radiologists. Results of 18F-FDG PET-CT and DWI were compared on a per-patient basis. For statistical analysis Pearson's correlation coefficient, Bland–Altman and regression analysis were assessed. Results: Data analysis revealed a significant inverse correlation of the ADC{sub min} and SUV{sub max} (r = −0.46; p = 0.032). Testing the correlation of the ADC{sub min} and SUV{sub max} for each histological subtype separately revealed that the inverse correlation was good for both adenocarcinomas (r = −0.47; p = 0.03) and squamouscell carcinomas (r = −0.71; p = 0.002), respectively. No significant correlation was found for the comparison of ADC{sub min} and SUV{sub mean} (r = −0.29; p = 0.27), ADC{sub mean} vs. SUV{sub mean} (r = −0.28; p = 0.31) or ADC{sub mean} vs. SUV{sub max} (r = −0.33; p = 0.23). The κ-value of 0.88 indicated a good agreement between both observers. Conclusion: This preliminary study is the first to verify the relation between the SUV and the ADC in NSCLC. The significant inverse correlation of these two quantitative imaging approaches points out the association of metabolic activity and tumor cellularity. Therefore, DWI with ADC measurement might represent a new prognostic marker in NSCLC.
Investigating Diffusion Coefficient Using Dynamic Light Scattering Technique
Sun, Yong
2006-01-01
In this work, the Z-average, effective, apparent diffusion coefficients and their poly-dispersity indexes were investigated for dilute poly-disperse homogeneous spherical particles in dispersion where the Rayleigh-Gans-Debye approximation is valid. The results reveal that the values of the apparent and effective diffusion coefficients at a scattering angle investigated are consistent and the difference between the effective and Z-average diffusion coefficients is a function of the mean partic...
Energy Technology Data Exchange (ETDEWEB)
Tsukamoto, Kazumichi; Kanasaki, Yoshiko; Kakite, Suguru; Fujii, Shinya; Kaminou, Toshio; Ogawa, Toshihide [Tottori University, Division of Radiology, Department of Pathophysiological and Therapeutic Science, Faculty of Medicine, Yonago, Tottori (Japan); Matsusue, Eiji [Tottori Prefectural Central Hospital, Department of Radiology, Tottori (Japan)
2012-09-15
The clinical differentiation of Parkinson's disease (PD) from multiple system atrophy (MSA) and progressive supranuclear palsy (PSP) may be challenging, especially in their early stages. The aim of this study was to evaluate the utility of apparent diffusion coefficient (ADC) measurement to distinguish among these degenerative disorders. Twenty-five MSA, 20 PSP, and 17 PD patients and 18 healthy controls were retrospectively studied. Axial diffusion-weighted and T2-weighted images were obtained using a 3-T MR system. Regions of interest (ROIs) were precisely placed in the midbrain, pons, putamen, globus pallidus, caudate nucleus, thalamus, superior cerebellar peduncle, middle cerebellar peduncle, cerebellar white matter, and cerebellar dentate nucleus, and the regional ADC (rADC) value was calculated in each ROI. In MSA, rADC values in the pons, middle cerebellar peduncle, cerebellar white matter, and cerebellar dentate nucleus were significantly higher than in PSP, PD, and controls. Furthermore, rADC values in the posterior putamen were significantly higher in MSA than in PSP and controls. In PSP, rADC values were significantly higher in the globus pallidus and midbrain than in MSA, PD, and controls. Furthermore, rADC values in the caudate nucleus and superior cerebellar peduncle were significantly higher in PSP than in MSA and controls. In PD, there were no significant differences in the rADC values compared to in MSA, PSP, and controls in all regions. Evaluation of rADC values in characteristic lesions in MSA, PSP, and PD by placing ROIs using 3-T systems can provide useful additional information for differentiating these disorders. (orig.)
Directory of Open Access Journals (Sweden)
Benedikt Michael Schaarschmidt
Full Text Available To compare the apparent diffusion coefficient (ADC in lymph node metastases of non-small cell lung cancer (NSCLC patients with standardized uptake values (SUV derived from combined 18F-fluoro-deoxy-glucose-positron emission tomography/magnetic resonance imaging (18F-FDG PET/MRI.38 patients with histopathologically proven NSCLC (mean age 60.1 ± 9.5 y received whole-body PET/CT (Siemens mCT™ 60 min after injection of a mean dose of 280 ± 50 MBq 18F-FDG and subsequent PET/MRI (mean time after tracer injection: 139 ± 26 min, Siemens Biograph mMR. During PET acquisition, simultaneous diffusion-weighted imaging (DWI, b values: 0, 500, 1000 s/mm² was performed. A maximum of 10 lymph nodes per patient suspicious for malignancy were analyzed. Regions of interest (ROI were drawn covering the entire lymph node on the attenuation-corrected PET-image and the monoexponential ADC-map. According to histopathology or radiological follow-up, lymph nodes were classified as benign or malignant. Pearson's correlation coefficients were calculated for all lymph node metastases correlating SUVmax and SUVmean with ADCmean.A total of 146 suspicious lymph nodes were found in 25 patients. One hundred lymph nodes were eligible for final analysis. Ninety-one lymph nodes were classified as malignant and 9 as benign according to the reference standard. In malignant lesions, mean SUVmax was 9.1 ± 3.8 and mean SUVmean was 6.0 ± 2.5 while mean ADCmean was 877.0 ± 128.6 x10(-5 mm²/s in PET/MRI. For all malignant lymph nodes, a weak, inverse correlation between SUVmax and ADCmean as well as SUVmean and ADCmean (r = -0.30, p<0.05 and r = -0.36, p<0.05 existed.The present data show a weak inverse correlation between increased glucose-metabolism and cellularity in lymph node metastases of NSCLC patients. 18F-FDG-PET and DWI thus may offer complementary information for the evaluation of treatment response in lymph node metastases of NSCLC.
Institute of Scientific and Technical Information of China (English)
卜春晓; 张勇; 程敬亮; 李颜良
2015-01-01
Objective To investigate the assessment value of diffusion-weighted magnetic resonance imaging (DWI)and apparent diffusion coefficient (ADC)in the differential diagnosis of common cerebellar tumors of children.Methods 45 patients with cerebel-lar tumors were retrospectively analyzed,including 23 medulloblastomas,14 astrocytomas,and 8 ependymomas .The ADCmin of parenchyma of different tumors were measured and Receiver operating characteristic (ROC)curve were delineated.The optimum ADC value for differential diagnosis of common cerebellar tumors of children was analyzed and determined.Results The mean ADC-min of medulloblastoma (0.497 ± 0.023 )× 10 -3 mm2/s was lowest,the mean ADCmin of astrocytoma (1.572 ± 0.145 )× 10 -3 mm2/s was highest,while that of ependymoma was (0.784 ± 0.037 )× 10 -3 mm2/s.The optimum ADC to distinguish ependymomas from medulloblastomas was 0.61 1 × 10 -3 mm2/s (100% sensitivity and 95.7% specificity).The optimum ADC to distinguish low-grade astrocytomas from ependymomas was 1.064×10 -3 mm2/s (92.9% sensitivity and 100% specificity).Conclu-sion ADC is very helpful with differential diagnosis of common cerebellar tumors of children.%目的：探讨扩散加权成像(DWI)和表观扩散系数(ADC)值在鉴别儿童小脑常见肿瘤中的价值。方法回顾性分析本院经手术病理证实的45例儿童小脑肿瘤患者,其中髓母细胞瘤23例,星形细胞瘤14例,室管膜瘤8例。测量不同肿瘤的实质部分的最小 ADC 值,绘制 ROC 曲线,预测儿童常见小脑肿瘤鉴别诊断的最佳 ADC 值。结果髓母细胞瘤的平均最小 ADC 值最低,为(0.497±0.023)×10-3 mm2/s；低级星形细胞瘤的平均最小 ADC 值最高,为(1.572±0.145)×10-3 mm2/s；室管膜瘤的平均最小ADC 值为(0.784±0.037)×10-3 mm2/s。髓母细胞瘤鉴别室管膜瘤的最佳 ADC 值为0.611×10-3 mm2/s,敏感度100%,特异性95.7%；室管膜瘤鉴别低级星形细胞瘤的最佳 ADC 值为1.064×10-3 mm2/s,敏感度92
Institute of Scientific and Technical Information of China (English)
陈利华; 陈永峰; 张久权; 王文伟; 夏云宝; 王健
2012-01-01
目的 探讨DWI表观扩散系数(ADC)值鉴别肺癌组织学类型的价值.方法 对58例高度怀疑肺癌患者(男39例,女19例)行胸部DWI检查,b值选择为50和1000 s/mm2,计算ADC值.采用单因素方差分析方法检测不同组织学类型肺癌ADC值的差异,并应用ROC曲线评价ADC值鉴别肺癌组织学类型的能力.结果 小细胞肺癌的平均ADC值为(1.02±0.24)×10-3 mm2/s;非小细胞肺癌的平均ADC值为(1.03±0.24)×10-3 mm2/s,其中腺癌、鳞癌的平均ADC值分别为(1.10±0.14)×10-3 mm2/s、(0.89±0.09)×10-3 mm2/s.腺癌的平均ADC值显著高于鳞癌(P＜0.001).在非小细胞肺癌中,腺癌的ROC曲线下面积为0.91±0.04.结论 腺癌的平均ADC值显著高于鳞癌；ADC值有助于鉴别肺腺癌和鳞癌.%Objective To investigate the possibility of using the apparent diffusion coefficient (ADC) value to differentiate histological subtypes of lung cancers. Methods Fifty-eight patients with suspected lung cancer (39 men, 19 women) underwent magnetic resonance diffusion-weighted imaging (DWI)of the chest with b factor of 50 and 1000 s/mm2. ADC values were calculated and correlated with histological subtypes of lung cancers. ROC analysis of ADC value was used to predict histological subtypes. Results The mean ADC value of small and non-small cell lung cancer was (1. 02±0. 24) X 10-3 mm2/s and (1. 03 ± 0. 24) X 10-3 mm2/s, respectively, while of squamous cell carcinoma and adenocarcinoma was (0. 89±0. 09)X10-3 mm2/s and (1. 10±0. 14)X10-3 mm2/s, respectively. ADC value of adenocarcinoma was significantly higher than that of squamous cell carcinoma (P<0. 001). The area under ROC curve was 0. 91±0. 04 for adenocarcinoma of non-small cell lung cancer. Conclusion The mean ADC value of lung adenocarcinoma is significantly higher than that of squamous cell carcinoma. ADC value may help to differentiate the histological subtypes of lung cancers.
Photon diffusion coefficient in an absorbing medium
Aronson, Raphael; Corngold, Noel
1999-01-01
A number of investigators have recently claimed, based on both analysis from transport theory and transport theory-based Monte Carlo calculations, that the diffusion coefficient for photon migration should be taken to be independent of absorption. We show that these analyses are flawed and that the correct way of extracting diffusion theory from transport theory gives an absorption-dependent diffusion coefficient. Experiments by two different sets of investigators give conflicting results con...
Institute of Scientific and Technical Information of China (English)
杨运俊; 郭献忠; 高凌云; 郭翔; 付军; 陈伟建
2013-01-01
Objective To investigate the variability and trends of apparent diffusion coefficient (ADC) of different brain segments in normal middle- aged and aged Han adults. Methods Thirty Han normal adult subjects aged 40~70 without positive cerebral symptoms were divided into 3 age groups (40~49, 50~59, 60~70). Plain scan and diffusion weighted imaging (DWI) were performed by 3.0T MR in al subjects. The images were transferred to ADW 4.3 workstations for post- processing. Regions of interest were placed covering grey and white matter of frontal lobe, putamen, thalamus and cerebel um. The relationship of ADC value with different ages and cerebral regions was analyzed. Results The cerebral tissues of different location had differ-ent values in the same age group. The highest ADC value was detected in gray matter of the frontal lobe, fol owed by putamen, white matter of frontal lobe and the thalamus, and the lowest one was in cerebel um. There was no significant difference in ADCs between two sides of the same cerebral parts of different regions.(P>0.05).Although there was no significant difference in ADCs between grey and white matter of frontal lobe, putamen, thalamus and cerebel um of different age groups, the ADC value of the same region tended to increase with age. The changes of ADC value in subjects aged 40~60 presented a much slower rate and an upshift tendency was observed in subjects aged>60. Conclusion The ADC value of the same region in middle- aged and elderly people tended to increase with the age, particularly in subjects aged>60 years.%目的：探讨40～70岁年龄段正常汉族人颅脑各区域磁共振表观弥散系数（ADC）变化特点，建立正常中老年人群颅脑ADC值变化趋势的基准。方法选择30例无阳性颅脑病征的正常汉族受试者，按年龄段分为3组，使用GE Medical System 3.0 T超导磁共振扫描仪进行头部平扫及弥散加权成像，测量额叶灰质、白质、壳核、丘脑及小脑感兴趣区
Institute of Scientific and Technical Information of China (English)
彭雯佳; 陆建平; 王敏杰; 金爱国; 方亮; 陈士跃; 黄挺
2013-01-01
Objective To compare the differences of parameters of diffusion weighted imaging (DWI) with both biexponential and monocxponcntial model between affected and opposite cerebral hemisphere in patients with unilateral stenosis of internal carotid artery (ICA). Methods From June to August, 2011 , patients who had no stenosis artcriostcnosis or had only unilateral stenosis of ICA which diagnosed by CTA, and had no MR imaging contraindication and signed the informed consent underwent DWI at both biexponential and monocxponcntial decay model, the b-valucs were 0, 5, 10, 20, 50, 100, 200, 400, 600, 1000, 1500, 2000, 3000 s/mm2. Then apparent diffusion coefficients (ADCs) of Monocxponcntial model, and Fast ADCs, Slow ADCs, Fraction of Fast ADCs of bi-cxponcntial model were calculated through workstation. According to the stcnotic degrees of ICA, patients were divided as following three groups: no stcnotic group, mild/moderate stcnotic group, and severe stcnotic/occlusivc group. Every parameters of both cerebral side in every groups were calculated, and compared the differences among groups by using Kruskal-Wallis statistic for Wilcoxon rank sum test. Results Fifty-two patients were enrolled in our study, among whom 10 cases in no stcnotic group, 23 cases in mild/moderate stcnotic group, and 19 cases in severe stcnotic/occlusivc group. In the patients with ICA stenosis, Monocxponcntial ADC, Fast ADC and Slow ADC on the affected sides were higher than that in the opposite sides. The differences between affected and opposite side of Monocxponcntial ADC and Slow ADC increased along with the severity of ICA stenosis, and the differences among groups had statistical significance (P = 0. 0046 and P = 0. 0054 ). The absolute different value of Fast ADC in bilateral was highest in no stcnotic group, followed by severe stcnotic/occlusivc group and mild/moderate stcnotic group, there was no of statistical significance between group ( P = 0. 0368 ). The differences of fraction of Fast
Institute of Scientific and Technical Information of China (English)
季学满; 张宗军; 卢光明; 毕俊; 袁彩云; 王俊鹏; 贾传海
2011-01-01
Objective To assess the utility of apparent diffusion coefficient ADC) for differential diagnosis of common pediatric posterior possa tumors. Materials and Methods In 43 pediatric patients with surgically and pathologically confirmed posterior possa tumors, there were 24 medulloblastomas,10 pilocytic astrocytomas,and 9 ependymomas. All pediatric patients recevied conventional MRI,DWI and contrast enhanced MRI examination, the signal intensity of tumor parenchyma was compared with that of normal cerebellar parenchymas. ADC values of tumor parenchyma were measured quantitatively. ADC values of medullohlastomas, pilocytic a8trocytomas,and ependymomas were compared by Wilcoxon rank sum test. Results On ADC map,In 24 patients with medulloblastomas, the tumors showed hypointense in 9 patients, slightly hypointense in 12 patients, and isointense in 3 patients; the average ADC value of tumor parenchymas was (0.70 ±0. II) x 10-3 mm2/s. All tumors showed hyperintense in 10 patients with pilocytic astrocytoma, the average ADC value of tumor parenchymas was (1.80 ±0.30) ×10-3 mm2/s. In 9 patients with ependymomas, the tumors showed slightly hyperintense in 5 patients, hyperintense in 4 patients; the average ADC value of tumor parenchymas was ( 1. 16 ±0.18) ×10-3 mm2/s. The ADC value of medulloblastoma was lower than that of pilocytic astrocytoma, which was statistically significant ( Z = -4. 54, P < 0.01). The ADC value of medulloblastoma was lower than that of ependymoma, which was statistically significant (Z= -4.29,P < 0.01), The ADC value of pilocytic astrocytoma was higher than that of ependymoma,which was statistically significant (Z= -3. 27,P < 0. 05). Conclusion Measurement of ADC value of cerebral tumor parenchyma is a simple and available method, which is useful for preoperative differentiation of pediatric posterior possa tumors, especially in differential diagnosis of medulloblastoma and pilocytic astrocytoma.%目的 评价MRI表观扩散系数(ADC)值在儿
Effective Diffusion Coefficients in Coal Chars
DEFF Research Database (Denmark)
Johnsson, Jan Erik; Jensen, Anker
2001-01-01
Knowledge of effective diffusion coefficients in char particles is important when interpreting experimental reactivity measurements and modeling char combustion or NO and N2O reduction. In this work, NO and N2O reaction with a bituminous coal char was studied in a fixed-bed quartz glass reactor....... Particle sizes in the range 0.05-5 mm were tested, and the effective diffusion coefficients were estimated from measured effectiveness factors using the Thiele modulus. At 1079 K the effective diffusion coefficients were 5.5 X 10(-6) m(2)/s and 6.8 X 10(-6) m(2)/s for N2O and NO, respectively....... The experimental results were compared with theoretical values calculated from the mean pore radius and the cross-linked pore model. The method of mean pore radius underestimated the effective diffusion coefficient more than an order of magnitude. Using the cross-linked pore model, the bimodal pore size...
Problems with Discontinuous Diffusion/Dispersion Coefficients
Directory of Open Access Journals (Sweden)
Stefano Ferraris
2012-01-01
accurate on smooth solutions and based on a special numerical treatment of the diffusion/dispersion coefficients that makes its application possible also when such coefficients are discontinuous. Numerical experiments confirm the convergence of the numerical approximation and show a good behavior on a set of benchmark problems in two space dimensions.
Institute of Scientific and Technical Information of China (English)
贺伟; 徐金萍; 谢汝明; 周新华; 吕岩; 宁锋钢
2014-01-01
目的 研究肺癌MR表观扩散系数(ADC)的特点,比较不同类型肺癌的ADC值差异,并探讨最佳b值的选择.方法 经临床、穿刺或手术病理证实的44例肺癌,行MRI常规T1WI、T2 WI和DWI扫描(b值为0、500、800、1000 s/mm2);对DWI序列上显示高信号的病灶分别测量并比较不同b值的ADC值,用方差分析比较其差异;采用受试者操作特征曲线(ROC)分析不同b值下ADC值对不同类型肺癌的鉴别诊断效能,选择出最佳b值;在最佳b值下分别对小细胞肺癌及非小细胞肺癌组,中心型肺癌和周围型肺癌组,各种不同类型的肺癌组的ADC值进行比较计算,符合正态分布者以t检验和方差分析进行比较.结果 本组42例肺癌显示高信号,2例腺癌未显示高信号.三种不同b值组的平均ADC值均随b值增加逐渐变小,差异有统计学意义(F=11.606,P=0.000),但b值为800和1000 s/mm2时两者未见显著差异(P =0.164,P＞0.05);8组不同类型肺癌的ROC曲线分析显示,三组不同b值下的ADC值比较均有诊断意义(曲线下面积均＜0.5),但其中7组以b取800 s/mm2时诊断效能最高,故认为b取800 s/mm2时为最佳;小细胞肺癌、类癌的ADC值高于非小细胞肺癌(P =0.046,P＜0.05;P =0.073;P＜0.1),腺癌的ADC值明显低于类癌(P=0.042,P＜0.05),腺癌的ADC值明显低于小细胞肺癌(P =0.020,P＜0.05),鳞癌与类癌略有差异(P =0.103),其他各种类型ADC值未见显著差异(P＞0.05).结论 800 s/mm2为最佳b值,ADC值对肺癌的组织学分型有一定意义.%Objective To investigate the characteristics of MR apparent diffusion coefficient (ADC) values of the pulmonary carcinomas,to compare ADC values between the different types of lung carcinomas,and to discuss the optimal b value.Methods A total of 44 patients with pathologically-proved lung cancer were enrolled in this study.Conventional MRI T1 WI and T2WI as well as DWI (b value =0,500,800 and 1000 s/mm2) was performed in all patients.ADC values
Improved Diffusion Coefficients for Stellar Plasmas
Brassard, P.; Fontaine, G.
2014-04-01
We are currently working on the fourth generation of our codes for building evolutionary and static models of hot subdwarf and white dwarf stars. One of the improvements of these codes consists in an update of all the microphysics involved in the computations. As part of our efforts, we have taken a look at possible improvements for the diffusion coefficients. Since the publication of the widely used diffusion coefficients of Paquette et al. (1986), the number-crunching power of computers has immensely increased, allowing more accurate computations of the triple collision integrals. We have thus produced new tables of diffusion coefficients with higher accuracy and higher resolution than before, of general use in stellar astrophysics.
Correlation and prediction of gaseous diffusion coefficients.
Marrero, T. R.; Mason, E. A.
1973-01-01
A new correlation method for binary gaseous diffusion coefficients from very low temperatures to 10,000 K is proposed based on an extended principle of corresponding states, and having greater range and accuracy than previous correlations. There are two correlation parameters that are related to other physical quantities and that are predictable in the absence of diffusion measurements. Quantum effects and composition dependence are included, but high-pressure effects are not. The results are directly applicable to multicomponent mixtures.
DEFF Research Database (Denmark)
Haack, Søren; Pedersen, Erik Morre; Vinding, Mads Sloth;
Diffusion weighted MRI has shown great potential in diagnostic cancer imaging and may also have value for monitoring tumor response during radiotherapy. Uncertainties due to geometric distortions caused by B0-inhomogeneity and tumor delineation are major obstacles for implementing DWI for use in ...... of advanced cervical cancer.......Diffusion weighted MRI has shown great potential in diagnostic cancer imaging and may also have value for monitoring tumor response during radiotherapy. Uncertainties due to geometric distortions caused by B0-inhomogeneity and tumor delineation are major obstacles for implementing DWI for use...
Institute of Scientific and Technical Information of China (English)
何为; 周延; 刘剑羽; 周振宇
2016-01-01
Objective To evaluate the diagnostic performance of multi ⁃ b value DWI to differentiate pancreatic adenocarcinoma from healthy pancreas using the apparent diffusion coefficient (ADC) and parameters derived from the intravoxel incoherent motion (IVIM) theory. Methods Forty⁃eight patients with histopathologically proven pancreatic adenocarcinoma and fifty patients with healthy pancreas were examined at 3.0 Tesla using a single⁃shot echo⁃planar imaging DWI pulse sequence. Eight b⁃values ranging from 0 to 1 000 s/mm2 were used. ADC, diffusion coefficient (D), perfusion⁃related diffusion (D*) and perfusion fraction (f) were compared between pancreatic adenocarcinoma and healthy pancreas, t test or Mann⁃Whitney U test was used to compare the MRI parameters, ROC was used to evaluate the diagnostic efficiency. Results In comparison to healthy pancreatic tissue, a significant reduction of the ADC, D*and f was found in pancreatic adenocarcinoma [healthy pancreatic tissue:(1.68±0.31)×10-3mm2/s, 27.10×10-3mm2/s, (36.92±12.47)%;pancreatic adenocarcinoma:(1.51±0.37)×10-3mm2/s, 13.90×10-3mm2/s, (30.06±19.84)%] (P0.05). In the ROC⁃analyses, the area under curve for D* was the largest (0.727), followed by f and ADC in order (0.680 and 0.669). Conclusion Using the IVIM DWI approach, the D*, f and ADC value are useful for differentiating pancreatic adenocarcinoma from healthy pancreatic tissue.%目的：探讨DWI单指数模型及体素内不相干运动（IVIM）模型参数诊断胰腺癌的价值。方法回顾性分析经手术病理证实为胰腺癌，且在术前1个月内行胰腺MRI检查的48例患者作为胰腺癌组；搜集同期MRI检查胰腺未见异常的50例患者作为对照组。所有受试者均行胰腺常规MRI和IVIM序列检查。对图像进行后处理，得到单指数模型参数ADC值和IVIM模型参数[包括真实扩散系数（D值）、灌注相关扩散系数（D*值）和灌注分数（f
Institute of Scientific and Technical Information of China (English)
王海屹; 王佳; 叶慧义; 张旭; 王殿军; 郭爱桃; 钟燕; 王鑫坤
2011-01-01
目的 比较肾脏病变自由呼吸扩散加权成像与屏气扩散加权成像在表观弥散系数(ADC)值及图像质量方面的异同.资料与方法 本研究纳入41例经病理结果或临床随访证实患有肾脏疾病的患者.所有患者均在1.5T磁共振扫描仪上进行自由呼吸扩散加权成像及屏气扩散加权成像.两种成像序列方面的参数除激励次数(NEX)之外均相同.两组图像的信噪比(SNR)、对比噪声比(CNR)及相对病变对比度的比较通过Wilcoxon检验进行统计学分析.两组肾实质ADC值及病变ADC值的一致性通过Pearson相关分析及信度分析方法进行分析.结果 自由呼吸扩散加权成像图像的SNR及CNR都显著高于屏气扩散加权成像图像(P＜0.01).但两组图像的病变相对对比度差异无统计学意义(P=0.459).两种扩散加权成像方法计算出的肾脏病变ADC值表现出良好的一致性(Pearson相关系数为0.888;信度分析中校正的a系数为0.949,组内相关系数为0.901).两组肾实质ADC值之间亦表现出良好的一致性(Pearson相关系数为0.871;信度分析中校正的a系数为0.931,组内相关系数为0.931).结论 自由呼吸扩散加权成像适用于肾脏病变的评价,特别适用于屏气困难的患者,而且ADC值与屏气扩散加权成像一致性良好.%Purpose To compare free-breathing and breath-hold diffusion-weighted MRI of renal lesions and to assess the coincidence of the apparent diffusion coefficient (ADC) values between the two sequences. Materials and Methods 41 patients were enrolled into this study with 41 renal masses (median diameter, 4.0cm) confirmed by pathology results or follow-up. All patients underwent both free-breathing and breath-hold diffusion-weighted MR imaging (DWI) at a 1.5 T MR system. Both sequences had identical imaging parameters except for signal averages, which were 8 in free-breathing and 2 in breath-hold sequences. Signal-to-noise ratio (SNR) of the kidney
International Nuclear Information System (INIS)
Recently, a bentonite sorption data base, comprising values taken from batch sorption data, was developed for a performance assessment study for high-level waste and spent fuel (Entsorgungsnachweis). Thus distribution coefficients (Kd) determined on dispersed systems were used to calculate apparent diffusion coefficients (Da) subsequently applied in diffusive transport calculations for the highly compacted system. Whenever such a procedure is adopted, questions invariably arise as to whether this is conservative or not. On the occasions when Kd values have been extracted from (mainly) indiffusion experiments and compared with those obtained from batch tests, apparent discrepancies have been found. In the majority of cases the batch values are larger, sometimes significantly. Hypotheses from 'surface diffusion' to 'double layer pore constrictivity effects' have been proposed to explain the inconsistencies. However, although such discrepancies have been reported periodically over the past twenty years or so, and have become generally accepted facts of life, there are surprisingly few quantitative studies directly dealing with this issue. Further, two other points are worthy of mention. The first is that a diffusion model (including the associated assumptions) is needed in order to deduce Kd values from diffusion measurements. Thus the sorption values calculated are model dependent. The second is that too little attention has been paid to the potential effects of water chemistry, i.e. a comparison between sorption values is only valid when the water chemistry in the batch tests is the same as, or very close to, the porewater chemistry in the intact material. In practice, this condition is difficult to achieve because of the uncertainties concerning the latter. This report describes a study in which Kd values for Cs(I), Ni(II), Sm(III), Am(III), Zr(IV) and Np(V) were calculated from in-diffusion data published in the open literature for a Na-bentonite (Kunigel V1) at
Energy Technology Data Exchange (ETDEWEB)
Bradbury, M.; Baeyens, B
2003-02-01
Recently, a bentonite sorption data base, comprising values taken from batch sorption data, was developed for a performance assessment study for high-level waste and spent fuel (Entsorgungsnachweis). Thus distribution coefficients (K{sub d}) determined on dispersed systems were used to calculate apparent diffusion coefficients (D{sub a}) subsequently applied in diffusive transport calculations for the highly compacted system. Whenever such a procedure is adopted, questions invariably arise as to whether this is conservative or not. On the occasions when K{sub d} values have been extracted from (mainly) indiffusion experiments and compared with those obtained from batch tests, apparent discrepancies have been found. In the majority of cases the batch values are larger, sometimes significantly. Hypotheses from 'surface diffusion' to 'double layer pore constrictivity effects' have been proposed to explain the inconsistencies. However, although such discrepancies have been reported periodically over the past twenty years or so, and have become generally accepted facts of life, there are surprisingly few quantitative studies directly dealing with this issue. Further, two other points are worthy of mention. The first is that a diffusion model (including the associated assumptions) is needed in order to deduce K{sub d} values from diffusion measurements. Thus the sorption values calculated are model dependent. The second is that too little attention has been paid to the potential effects of water chemistry, i.e. a comparison between sorption values is only valid when the water chemistry in the batch tests is the same as, or very close to, the porewater chemistry in the intact material. In practice, this condition is difficult to achieve because of the uncertainties concerning the latter. This report describes a study in which K{sub d} values for Cs(I), Ni(II), Sm(III), Am(III), Zr(IV) and Np(V) were calculated from in-diffusion data published in the
Measurements of Xe diffusion coefficient of UN
International Nuclear Information System (INIS)
Post irradiation annealing (PIA) tests were performed to obtain the Xe-133 diffusion coefficients of uranium nitride (UN). UN powder was obtained from the mixed powder of UO2 and carbon under the H2-N2 gas mixture. Porous discs (45%TD) of UN were made and used for the specimens for the PIA tests. For comparison purposes, porous discs of UO2 (47%TD) were also made. Each 300mg specimen was irradiated to a burnup of 0.1 MWd/t-U. PIA tests were performed at 1200degC, 1300degC and 1400degC for UN, and 1400degC, 1500degC and 1600degC for UO2, continuously. The oxygen potential during the annealing tests was about 440 ± 20 kJ/mol. The disc specimens of UN and UO2 were found to be cracked or broken in pieces after annealing tests. The xenon diffusion coefficient for the near stoichiometric UN turned out to be about 1,000 times higher than that of UO2 at 1400degC. And, the activation energy of diffusion in UN is about 230 kJ/mol, while that of UO2 measured to be about 393 kJ/mol. (author)
Institute of Scientific and Technical Information of China (English)
庾建英; 刘继新; 朱沂; 蒋杰
2011-01-01
Objective To explore the applied value of apparent diffusion coefficient (ADC) of diffusion weighted image (DWI) in acute posterior circulation infarction.Methods 44 patients with posterior circulation infarction were studied, which included 15 cases of occipital lobe infarction on one side, 11cases of cerebellum infarction on one side and 18 cases of brain stem infarction and were rechecked with DWI within one week after disease attack.Results Within one week after attack, the ADC of core and borderline of occipital lobe infarction and cerebellum infarction on one side decreased respectively and had significant difference from that of the other side of infarct (P＜0.01).The ADC of core of brain stem infarction decreased and had significant difference from that of infarct borderline (P＜0.05).2 weeks after infarct, the ADC of infarct core decreased and had significant difference from that of infarct borderline and other side of infarct (P＜0.05), but the ADC of infarct borderline had no significant difference from that of the other side of infarct (P ＞0.05).There were high signal realm of DWI deflated in 8 eases with occipital lobe infarction, 6 cases with cerebellum infarction and 13 cases with brain stem infarction.Conclusions ADC is a method to evaluate cerebral ischemia and quantitative analysis of ADC can help assess ischemic degree.%目的 探讨扩散加权成像(DWI)之表现扩散系数(ADC)对急性后循环梗死的应用价值.方法 对44例发病一周以内行临床及磁共振DWI检查确诊为急性后循环梗死的患者,于二周后复查磁共振DWI检查.结果 发病一周内,一侧枕叶和一侧小脑梗死的核心、梗死的边缘和其对侧镜像区ADC值比较,其差异均有统计学意义(P0.05),且一侧枕叶梗死者有8例DWI高信号范围较前缩小,小脑梗死者有6例DWI高信号范围较前缩小,脑干梗死者有13例DWI高信号范围较前缩小,结论 ADC值是一种客观的评价脑缺血的方法,其定量
Digital speckle pattern interferometric measurement of diffusion coefficients in hydrogels
Institute of Scientific and Technical Information of China (English)
周金芳; 韩雁; 章献民; 徐坚
2003-01-01
The technique of real-time digital speckle pattern interferometry is proposed to study diffusion of surfactants in hydrogel. The diffusion coefficient is simply and directly determined from the interferograms. An example of diffusion coefficient measurement of surfactant in agarose gel demonstrates the usefulness of the method. The results obtained are compared with the theoretical simulating values.
Stochastic Modelling of the Diffusion Coefficient for Concrete
DEFF Research Database (Denmark)
Thoft-Christensen, Palle
In the paper, a new stochastic modelling of the diffusion coefficient D is presented. The modelling is based on physical understanding of the diffusion process and on some recent experimental results. The diffusion coefficients D is strongly dependent on the w/c ratio and the temperature....
International Nuclear Information System (INIS)
Highlights: • Physical and osmotic properties of [HMim][TfO] in alcohols are reported. • Apparent molar properties and osmotic coefficients were obtained. • Apparent molar volumes were fitted using a Redlich–Meyer type equation. • The osmotic coefficients were modeled with the Extended Pitzer and the MNRTL models. -- Abstract: In this work, density for the binary mixtures of 1-hexyl-3-methylimidazolium trifluoromethanesulfonate in alcohols (1-propanol, or 2-propanol, or 1-butanol, or 2-butanol, or 1-pentanol) was measured at T = 323.15 K and atmospheric pressure. From this property, the corresponding apparent molar volumes were calculated and fitted to a Redlich–Meyer type equation. For these mixtures, the osmotic and activity coefficients, and vapor pressures of these binary systems were also determined at the same temperature using the vapor pressure osmometry technique. The experimental osmotic coefficients were modeled by the Extended Pitzer model of Archer. The parameters obtained in this correlation were used to calculate the mean molal activity coefficients and the excess Gibbs free energy for the studied mixtures
Invariant coefficients of diffusion in iron-chromium-nickel system
Energy Technology Data Exchange (ETDEWEB)
Mokrov, A.P.; Akimov, V.K.; Golubev, V.G.
1984-02-01
The temperature and concentration dependences of the Dsub(c) coefficients in the ..gamma..-phase of iron-chromium-nickel system are determined. It is proposed to described mutual diffusion in multicomponent systems using invariant, i.e. independent of the choice of solvent, coefficients of diffusion. The assumption that their temperature dependence follows the Arrhenius law is confirmed by the experiment.
Invariant coefficients of diffusion in iron-chromium-nickel system
International Nuclear Information System (INIS)
The temperature and concentration dependences of the Dsub(c) coefficients in the γ-phase of iron-chromium-nickel system are determined. It is proposed to described mutual diffusion in mul-- ticomponent systems using invariant, i. e. independent of the choice of solvent, coefficients of diffusion. The assumption that their temperature dependence follows the Arrhenius law is confirmed by the experiment
Measurement of carbon dioxide diffusion coefficient of concrete
Villain, G.; PAVOINE, A; Thiery, M.
2006-01-01
The carbonation of concrete is a chemical reaction, which can be at the origin of the premature degradation of reinforced concrete structures. In order to predict service life of reinforced concrete structures, many models based on gas diffusion were developed. The carbon dioxide diffusion coefficient of concrete is thus a significant input datum for these models. The objective of this article is to present a simple reliable testing method to quantify the carbon dioxide diffusion coefficient ...
Calculation of self-diffusion coefficients in iron
Baohua Zhang
2014-01-01
On the basis of available P-V-T equation of state of iron, the temperature and pressure dependence of self-diffusion coefficients in iron polymorphs (α, δ, γ and ɛ phases) have been successfully reproduced in terms of the bulk elastic and expansivity data by means of a thermodynamical model that interconnects point defects parameters with bulk properties. The calculated diffusion parameters, such as self-diffusion coefficient, activation energy and activation volume over a broad temperature r...
Determination of mutual diffusion coefficients in quaternary alloy systems
International Nuclear Information System (INIS)
Procedures of experimental study of mutual diffusion in four-component system are developed, limit ratios for diffusion coefficients are found at the transition from four component system to three-component one and experimental check of some of these ratios is carried out. Concentrational dependence of complete matrix of outer diffusion coefficients in Fe-Cr-Ni-Co system is determined. Limit correlations for this system are checked up at cobalt concentration yielding to zero
Effect of Rare Earths on Diffusion Coefficient and Transfer Coefficient of Carbon during Carburizing
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
The diffusion coefficient of carbon in surface layer of steel-20 rare earth carburized at 880 ℃ and 900 ℃ for 8 h was calculated by substituting the measured layer depths into the diffusion equation. The mathematical model of the transfer coefficient of carbon was deduced based on the kinetics of weight gain during gas carburizing. The calculated results show that the main reason why the gas carburizing process is accelerated is due to the obvious increase in the diffusion coefficient and transfer coefficient of carbon resulted from the addition of RE.
Apparent digestibility coefficients and consumption of corn silage with and without Bt gene in sheep
Camila Memari Trava; Mauro Sartori Bueno; Geraldo Balieiro
2012-01-01
Corn silage is the most important preserved food for ruminants. The transgenic corn was inserted into the genetic code Bt gene (Bacillus thuringiensis) that expresses a toxic protein to caterpillars pests of maize, reducing production costs. To evaluate the varieties of plant corn silage DKB and AG with or without the Bt gene on the voluntary intake of DM (g/day) and apparent digestibility coefficients (CDA) of nutrients in sheep, the experiment was conducted at the Institute of Animal Scienc...
Determining pitch-angle diffusion coefficients from test particle simulations
Ivascenko, A; Spanier, F; Vainio, R
2016-01-01
Transport and acceleration of charged particles in turbulent media is a topic of great interest in space physics and interstellar astrophysics. These processes are dominated by the scattering of particles off magnetic irregularities. The scattering process itself is usually described by small-angle scattering with the pitch-angle coefficient $D_{\\mu\\mu}$ playing a major role. Since the diffusion coefficient $D_{\\mu\\mu}$ can be determined analytically only for the approximation of quasi-linear theory, the determination of this coefficient from numerical simulations has, therefore, become more important. So far these simulations yield particle tracks for small-scale scattering, which can then be interpreted using the running diffusion coefficients. This method has a limited range of validity. This paper presents two new methods that allow for the calculation of the pitch-angle diffusion coefficient from numerical simulations. These methods no longer analyse particle trajectories, but the change of particle dist...
The temperature variation of hydrogen diffusion coefficients in metal alloys
Danford, M. D.
1990-01-01
Hydrogen diffusion coefficients were measured as a function of temperature for a few metal alloys using an electrochemical evolution technique. Results from these measurements are compared to those obtained by the time-lag method. In all cases, diffusion coefficients obtained by the electrochemical method are larger than those by the time-lag method by an order of magnitude or more. These differences are attributed mainly to hydrogen trapping.
Energy Technology Data Exchange (ETDEWEB)
Viehweger, Adrian; Sorge, Ina; Hirsch, Wolfgang [University Hospital Leipzig, Department of Pediatric Radiology, Leipzig (Germany); Riffert, Till; Dhital, Bibek; Knoesche, Thomas R.; Anwander, Alfred [Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig (Germany); Stepan, Holger [University Leipzig, Department of Obstetrics, Leipzig (Germany)
2014-10-15
Diffusion-weighted imaging (DWI) is important in the assessment of fetal brain development. However, it is clinically challenging and time-consuming to prepare neuromorphological examinations to assess real brain age and to detect abnormalities. To demonstrate that the Gini coefficient can be a simple, intuitive parameter for modelling fetal brain development. Postmortem fetal specimens(n = 28) were evaluated by diffusion-weighted imaging (DWI) on a 3-T MRI scanner using 60 directions, 0.7-mm isotropic voxels and b-values of 0, 150, 1,600 s/mm{sup 2}. Constrained spherical deconvolution (CSD) was used as the local diffusion model. Fractional anisotropy (FA), apparent diffusion coefficient (ADC) and complexity (CX) maps were generated. CX was defined as a novel diffusion metric. On the basis of those three parameters, the Gini coefficient was calculated. Study of fetal brain development in postmortem specimens was feasible using DWI. The Gini coefficient could be calculated for the combination of the three diffusion parameters. This multidimensional Gini coefficient correlated well with age (Adjusted R{sup 2} = 0.59) between the ages of 17 and 26 gestational weeks. We propose a new method that uses an economics concept, the Gini coefficient, to describe the whole brain with one simple and intuitive measure, which can be used to assess the brain's developmental state. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Kitajima, Kazuhiro, E-mail: kitajima@med.kobe-u.ac.jp [Department of Radiology, Kobe University Graduate School of Medicine, Kobe (Japan); Takahashi, Satoru; Ueno, Yoshiko [Department of Radiology, Kobe University Graduate School of Medicine, Kobe (Japan); Miyake, Hideaki; Fujisawa, Masato [Department of Urology, Kobe University Graduate School of Medicine, Kobe (Japan); Kawakami, Fumi [Division of Diagnostic Pathology, Kobe University Graduate School of Medicine, Kobe (Japan); Sugimura, Kazuro [Department of Radiology, Kobe University Graduate School of Medicine, Kobe (Japan)
2013-08-15
Objective: To investigate the usefulness of apparent diffusion coefficient (ADC) values in predicting true Gleason scores from radical prostatectomy specimen (tGS), compared with systematic transrectal ultrasound (TRUS)-guided biopsy GS (bGS). Materials and methods: One hundred and five patients with biopsy-proven prostate cancer underwent preoperative DWI (b-values of 0, 1000, and 2000 s/mm{sup 2}) of 3-T MRI. The mean and minimum ADCs of visible tumors were calculated for either of a pair of b-values: 0 and 1000 s/mm{sup 2} (ADC{sub 1000}), or 0 and 2000 s/mm{sup 2} (ADC{sub 2000}), and relationships between the four ADC parameters and tGS evaluated for the peripheral zone (PZ) and transition zone (TZ). For multiple tumors, the dominant tumor's GS and ADCs were estimated for cancer aggressiveness assessment by computing ROC curves. Results: Significant negative correlations were observed between tGS and mean ADC{sub 1000}, mean ADC{sub 2000}, minimum ADC{sub 1000}, and minimum ADC{sub 2000} (r = −0.41, −0.39, −0.39, and −0.37, respectively) of 100 visible PZ tumors and 66 visible TZ tumors (r = −0.40, −0.42, −0.29, and −0.21, respectively). For distinguishing high-grade from low/intermediate-grade PZ lesions, the areas under the curve (AUCs) of mean ADC{sub 1000} (0.751), mean ADC{sub 2000} (0.710), minimum ADC{sub 1000} (0.768), and minimum ADC{sub 2000} (0.752) were similar to that of the highest bGS (0.708) (p = 0.61, p = 0.98, p = 0.47, and p = 0.60, respectively). For distinguishing high-grade from low/intermediate-grade TZ lesions, AUCs of mean ADC{sub 1000} (0.779), and mean ADC{sub 2000} (0.811) were similar to that of the highest bGS (0.805) (p = 0.83 and p = 0.97). Conclusion: Tumor ADCs obtained with high b-values could predict prostate cancer aggressiveness as effectively as systematic TRUS-guided biopsy.
Methods for measuring diffusion coefficients of radon in building materials
Cozmuta, [No Value; van der Graaf, ER
2001-01-01
Two methods for determining the Rn-222 diffusion coefficient in concrete are presented. Experimentally, the flush and adsorption technique to measure radon release rates underlines both methods. Theoretically, the first method was developed fur samples of cubical geometry. The radon diffusion equati
Stationary space-periodic structures with equal diffusion coefficients
DEFF Research Database (Denmark)
Andresen, Peter Ragnar; Bache, Morten; Mosekilde, Erik;
1999-01-01
The paper investigates a chemical reaction-diffusion model in an open flow system. It is shown that such a system may, with particular boundary conditions, exhibit stationary space-periodic structures even in the case of equal diffusion coefficients. This is confirmed through numerical simulations....
Onsager coefficients for binary mixture diffusion in nanopores
R. Krishna; J.M. van Baten
2008-01-01
This paper presents a critical appraisal of current estimation methods for the Onsager coefficients L-11, L-22, and L-12 for binary mixture diffusion inside nanopores using pure component diffusivity data inputs. The appraisal is based on extensive sets of molecular dynamics (MD) simulation data on
Exploring non-linear cosmological matter diffusion coefficients
Velten, Hermano
2014-01-01
Since microscopic velocity diffusion can be incorporated into general relativity in a consistent way, we study cosmological background solutions when the diffusion phenomena takes place in an expanding universe. Our focus here relies on the nature of the diffusion coefficient $\\sigma$ which measures the magnitude of such transport phenomena. We test dynamics where $\\sigma$ has a phenomenological dependence on the scale factor, the matter density, the dark energy and the expansion rate.
Measurement and Modeling of Solute Diffusion Coefficients in Unsaturated Soils
Chou, Hsin-Yi
2010-01-01
Solute diffusion in unsaturated soils refers to the transport of dissolved constituents in liquid phase from a higher to a lower concentration point. Several empirical and conceptual models were proposed to predict the solute diffusion coefficients in unsaturated soils, but they were not systematically tested and evaluated under the same conditions using soils of different textures. Our experimental data showed that there is no perfect model that can depict the behavior of solute diffusion co...
Calculation of self-diffusion coefficients in iron
Directory of Open Access Journals (Sweden)
Baohua Zhang
2014-01-01
Full Text Available On the basis of available P-V-T equation of state of iron, the temperature and pressure dependence of self-diffusion coefficients in iron polymorphs (α, δ, γ and ɛ phases have been successfully reproduced in terms of the bulk elastic and expansivity data by means of a thermodynamical model that interconnects point defects parameters with bulk properties. The calculated diffusion parameters, such as self-diffusion coefficient, activation energy and activation volume over a broad temperature range (500-2500 K and pressure range (0-100 GPa, compare favorably well with experimental or theoretical ones when the uncertainties are considered.
Diffusion coefficient of the decay products of krypton and xenon
International Nuclear Information System (INIS)
Measurement of diffusion coefficient of the decay products of krypton and xenon e.g. sup(88,89)Rb and 138Cs is useful for evaluating the inhalation dose and also for the measurement of the concentration of noble gases by double filter method. A diffusion sampler developed by Kotrappa et al., based on Mercer's theory of diffusional deposition between the concentric circular plates was used. The deposition of decay products of krypton and xenon on the circular plates was measured using a multichannel analyser available in this division of BARC (HPGe 4K MCA). Experiments were conducted at 15 and 140 air changes per hour and at different humidities (50-100%). The diffusion coefficient for 88Rb, 89Rb, 138Cs were found to be 0.050±0.008, 0.047±0.008 and 0.047±0.006 respectively at 15 air changes per hour. The diffusion coefficients for these radionuclides were observed to be 0.061±0.005, 0.059±0.006 and 0.058±0.005 at high ventilation rate (140 air changes per hour). This study demonstrates that the diffusion coefficients increase with increasing ventilation rates. The effect of relative humidity on diffusion coefficient is less pronounced at high ventilation rate. (author). 8 refs., 1 fig., 2 tabs
Calculation of diffusion coefficients in air-metal thermal plasmas
Energy Technology Data Exchange (ETDEWEB)
Cressault, Y; Gleizes, A [Universite de Toulouse, UPS, INPT, LAPLACE (Laboratoire Plasma et Conversion d' Energie), 118 route de Narbonne, F-31062 Toulouse Cedex 9 (France)
2010-11-03
This paper presents the combined diffusion coefficients of metal vapours (silver, copper and iron) in air thermal plasmas for temperatures ranging from 300 to 30 000 K. The theory used to calculate these coefficients is remembered and validated by comparison with the literature values in several cases such as Ar-He, Ar-Cu and N{sub 2}-O{sub 2} mixtures. The results are discussed showing the influences of the metal concentration, of the vapour nature and of the pressure. The results show rather similar behaviour for the three metals. The maximum values of the combined ordinary diffusion coefficient in the evolution with temperature are obtained for temperature around 10 000 K but this peak is shifted to the highest temperatures when the metal proportion increases. Another result shows that the diffusion coefficient decreases when pressure increases.
Verifying reciprocal relations for experimental diffusion coefficients in multicomponent mixtures
DEFF Research Database (Denmark)
Medvedev, Oleg; Shapiro, Alexander
2003-01-01
The goal of the present study is to verify the agreement of the available data on diffusion in ternary mixtures with the theoretical requirement of linear non-equilibrium thermodynamics consisting in symmetry of the matrix of the phenomenological coefficients. A common set of measured diffusion...... coefficients for a three-component mixture consists of four Fickian diffusion coefficients, each being reported separately. However, the Onsager theory predicts the existence of only three independent coefficients, as one of them disappears due to the symmetry requirement. Re-calculation of the Fickian...... extended sets of experimental data and reliable thermodynamic models were available. The sensitivity of the symmetry property to different thermodynamic parameters of the models was also checked. (C) 2003 Elsevier Science B.V. All rights reserved....
Fokker-Planck Type Equations with Sobolev Diffusion Coefficients and BV Drift Coefficients
Institute of Scientific and Technical Information of China (English)
De Jun LUO
2013-01-01
Combining Le Bris and Lions' arguments with Ambrosio's commutator estimate for BV vector fields,we prove in this paper the existence and uniqueness of solutions to the Fokker-Planck type equations with Sobolev diffusion coefficients and BV drift coefficients.
Sagis, L.M.C.
2001-01-01
In this paper we developed an expression for the coefficient for plane-parallel diffusion for an arbitrarily curved fluid–fluid interface. The expression is valid for ordinary diffusion in binary mixtures, with isotropic bulk phases and an interfacial region that is isotropic in the plane parallel t
Diffusion Coefficient of Helium in Mo-Assessed by the Internal Friction Technique
Institute of Scientific and Technical Information of China (English)
WANG Weiguo; YANG Junfeng; WANG Xianping; XIE Chunyi; LI Renhong; CHEN Junling; FANG Qianfeng
2009-01-01
Diffusion behavior of helium in molybdenum was investigated by means of the in-ternal friction method. An apparent relaxation internal friction peak associated with helium long-range diffusion was observed around 475 K at a resonant frequency of 56 Hz. In terms of the Gorsky relaxation model and the shift of the peak position with the measurement frequency, the activation energy and pre-exponential factor of the diffusion coefficient of the helium atoms in molybdenum were deduced as 0.63 eV and 6.5 cm2/s, respectively.
Numerical study of the Transverse Diffusion coefficient for a one component model of a plasma
Valvo, Lorenzo
2016-01-01
We report the results of MD numerical simulations for a one component model of a plasma in the weakly coupled regime, at different values of temperature $T$ and applied magnetic field $\\vec B$, in which the diffusion coefficient $D_{\\perp}$ transverse to the field is estimated. We find that there exists a threshold in temperature, at which an inversion occurs, namely, for $T$ above the threshold the diffusion coefficient $D_{\\perp}$ starts decreasing as $T$ increases. This is at variance with the behavior predicted by the Bohm law $D_{\\perp}\\sim T/B$, which actually holds below the threshold. In addition we find that, for temperatures above such a threshold, another transition occurs, now with respect to the values of the magnetic field: for weak magnetic fields the diffusion coefficients scales as $1/B^2$, in agreement with the predictions of the standard kinetics theory, while it apparently saturates when the field strength is sufficiently increased.
Institute of Scientific and Technical Information of China (English)
张泉; 张云亭; 冯凯琳; 张敬; 张权
2011-01-01
Objective To investigate the correlation of apparent diffusion coefficient (ADC) value of hippocampus with the volume and magnetic resonance spectroscopy (MRS) of hippocampus in patients with hippocampal sclerosis (HS), and to evaluate the diagnostic value of ADC value. Methods Thirteen HS patients (HS group) of unilateral temporal lobe epilepsy (TLE) and 20 age-matched healthy subjects (control group) were studied with hippocampal ADC maps, volume measurement of hippocampus and N-acetylaspartate to choline and creatine ratios [NAA/(Cho+Cr)]. The ADC values of bilateral hippocampi and asymmetry index (AI, including AIADC, AIVOLUME and AIMRS) were measured respectively, and the correlations of ADC value with other quantitative MR measurements, age at onset and duration of epilepsy were evaluated.Results The ADC value in ipsilateral hippocampus was higher than that in contralateral side and the control group (both P ＜0. 001 ), and AIADC in patients with HS was also higher than that in the control group (P＜0. 001). Significant correlations were found between ADC value and the volume of ipsilateral hippocampus (r=-0.854, P＜0. 001), also between AIADC and AIVPLUME (r=0. 611, P＜0. 05). AIADC showed positive correlation with the duration of epilepsy in HS patients (r=0. 676, P＜0. 05). Conclusion The ADC value of hippocampus is helpful for the preoperative diagnosis of HS and has certain correlation with volume measurement and duration of epilepsy.%目的 探讨海马硬化(HS)患者的海马表观扩散系数(ADC)值与海马体积及磁共振波谱的相关性,并评价ADC值在HS诊断中的价值.方法 对13例单侧颞叶癫痫HS患者(HS组)和20名健康志愿者(正常对照组)行常规MR及磁共振扩散加权成像(DWI)检查,并对HS患者进行海马体积测量和磁共振波谱(MRS)检查,计算双侧海马的ADC值、标准化体积、N-乙酰天门冬氨酸/(胆碱+肌酸)[NAA/(Cho+Cr)]及不对称指数(AI,包括AIADC、AIVOLUME及AIMRS),评
Institute of Scientific and Technical Information of China (English)
杨晶; 敦旺欢; 马雪英; 麻少辉; 张宇辰; 刘继新; 张明
2016-01-01
目的：研究青年女性正常子宫体各结构表观扩散系数（ADC ）值在不同月经周期的变化规律，并探讨其生理机制及临床意义。方法19例健康青年女性分别于围排卵期、分泌晚期及月经期接受3次子宫体扩散加权成像（DWI）（b＝0，1000 s／mm2）扫描，后分别测量子宫内膜、结合带及子宫肌层的ADC值并分析各结构ADC值的差异及其在不同月经周期的变化规律。结果特定月经周期不同子宫结构ADC值之间均有显著统计学差异（P＜0．05），其中子宫肌层ADC值最高，子宫内膜居中，结合带最低；特定子宫结构在不同月经周期下ADC值存在显著统计学差异（F＝55．674，P＜0．05）；月经周期与子宫结构之间存在交互效应（F＝12．501，P＜0．05）。结论不同结构区及月经周期会对子宫ADC值产生影响，采用ADC值分析子宫病变时，应考虑到子宫不同结构区、不同月经周期对子宫ADC值的影响。%Objective To investigate the cyclical changes of the apparent diffusion coefficient (ADC) values of the normal uterine zonal structures and explore physiological mechanism and clinical significance of the changes .Methods Nineteen healthy young fe‐male volunteers were selected to receive DWI (b=0 and 1 000 s/mm2 ) scan during periovulatory ,late secretory and menstrual pha‐ses .The ADC values of endometrium ,junctional zone and myometrium were measured and the differences of the ADC values were analyzed .Results The ADC values among three structures were significantly different in three phases (P< 0 .05) .The ADC value of myometrium was highest and the second was endometrium and the last was junctional zone .The differences of specific uterine zonal structures in different phases were statistically significant (F=55 .674 ,P<0 .05) .There was a interaction effect between menstrual cycle and uterine structures .Conclusion The effect of zones and different phases of
Wavelet estimation of the diffusion coefficient in time dependent diffusion models
Institute of Scientific and Technical Information of China (English)
Ping; CHEN; Jin-de; WANG
2007-01-01
The estimation problem for diffusion coefficients in diffusion processes has been studied in many papers,where the diffusion coefficient function is assumed to be a 1-dimensional bounded Lipschitzian function of the state or the time only.There is no previous work for the nonparametric estimation of time-dependent diffusion models where the diffusion coefficient depends on both the state and the time.This paper introduces and studies a wavelet estimation of the time-dependent diffusion coefficient under a more general assumption that the diffusion coefficient is a linear growth Lipschitz function.Using the properties of martingale,we translate the problems in diffusion into the nonparametric regression setting and give the Lr convergence rate.A strong consistency of the estimate is established.With this result one can estimate the time-dependent diffusion coefficient using the same structure of the wavelet estimators under any equivalent probability measure.For example,in finance,the wavelet estimator is strongly consistent under the market probability measure as well as the risk neutral probability measure.
Institute of Scientific and Technical Information of China (English)
赵博; 张雪宁; 徐国萍; 孟华伟
2014-01-01
Objective Applying diffusion weighted image (DWI) and apparent diffusion coefficient (ADC) to analyze brain injury caused by hypoxic-ischemic encephalopathy (HIE) in term neonates.Methods From June 1,2010 to January 5,2011,thirty-eight full term neonates with HIE were hospitalized in the Second Hospital of Tianjin Medical University.Those with nervous system diseases were excluded.The 38 cases were divided to mild HIE group (n=24) and moderate-to-severe HIE group (n=14).The control group included 10 normal full term neonates without history of asphyxia.All babies were scanned by magnetic resonance imaging (MRI).Spin echo-echo planar imaging sequence was used for DWI images.ADC values of nine regions (frontal lobe gray matter,frontal white matter,parietal gray matter,parietal white matter,corona radiata,caudate nucleus,putamen,posterior limb of the internal capsule and thalamus) were measured.MRI and DWI images were compared.ADC values were compared by analysis of variance and Student-Newman-Keuls test.Results ADC values of the nine indicated regions (frontal lobe gray matter,frontal white matter,parietal gray matter,parietal white matter,corona radiata,caudate nucleus,putamen,posterior limb of the internal capsule and thalamus) were (1.37±0.07),(1.81±0.12),(1.35±0.10),(1.84±0.09),(1.23±0.11),(1.28±0.09),(1.18±0.08),(1.05±0.07) and (1.15±0.08) ×10-3 mm2/s in control group,(1.28±0.11),(1.60±0.15),(1.27±0.09),(1.59±0.20),(1.19±0.15),(1.19±0.13),(1.11±0.09),(0.97±0.11) and (1.06±0.12) ×10-3 mm2/s in mild HIE group,and (1.18±0.14),(1.51±0.22),(1.19±0.09),(1.56±0.19),(1.03±0.16),(1.08±0.07),(1.02±0.07),(0.87±0.09) and (0.96±0.12) × 10-3 mm2/s in moderate-to-severe HIE group.ADC values among the three groups had statistical difference (F=3.89,3.21,4.05,3.30,3.28,3.27,4.12,4.75and 4.72,all P＜0.05).ADC values of frontal lobe gray matter,frontal white matter,parietal gray matter,parietal white matter,putamen,posterior limb of the internal
Raman spectroscopic determination of concentration dependent diffusion coefficients
International Nuclear Information System (INIS)
The determination of concentration dependent diffusion coefficients D(c) is possible, if two concentration profiles in a solution at short time distances are recorded by means of the Raman spectroscopic method. D(c) is elegantly obtained by application of the Boltzmann transformation in connection with Fick's second law. (author)
Institute of Scientific and Technical Information of China (English)
杜鲲; 管生; 胡小波; 刘朝; 李明省; 陈振; 彭强
2011-01-01
目的 评估原发性肝癌介入术后完全缓解病灶磁共振表观扩散系数(ADC)值测量的可重复性和一致性,为临床应用提供参考.方法 对21个完全缓解病灶在术后第1、3、6个月时由同一名医师同一序列测量ADC值、不同医师间隔1周测量病灶的ADC 值,通过计算组内相关系数(ICC)值及绘制Bland-Altman图表确定ADC值测量的可重复性及一致性.ICC值大于0.75表示信度良好,可重复性高,75%的位点位于Bland-Altman图95%的置信区间的参考线内,其一致性高.结果 A医师术后1、3、6个月测量ICC值分别为0.928、0.878、0.934;B医师术后1、3、6个月测量ICC值分别为0.873、0.940、0.871,1周前不同时间A、B医师1、3、6个月测量ICC值分别为0.854、0.940、0.960;1周后不同时间A、B医师术后1、3、6个月测量ICC值分别为:0.788、0.945、0.858,均大于0.75,提示可信度较高,可重复性强.90%的位点Bland-Altman图95%的置信区间的参考线内,数值测量的可重复性高.结论 HCC完全缓解病灶的ADC值稳定,测量具有较高的一致性和可重复性,可以动态观察原发性肝癌介入治疗后病灶的稳定程度,可及时有效的评估巩固治疗时机.%Objective To assess the repeatability and consistency of magnetic resonance apparent diffusion coefficient (MR ADC) values of the completely remitted lesions of primary hepatocellular carcinoma (HCC) after TACE in order to provide a reference for clinical application. Methods The MR ADC values of 21 completely remitted lesions were measured at 1, 3 and 6 months after TACE by the same radiologist (radiologist A) using the same sequence, which were measured again by another radiologist (radiologist B) one week later. By calculating the intra-class correlation coefficient (ICC) value and drawing Bland-Altman graph, the repeatability and consistency of the ADC value measurement were evaluated. ICC values > 0.75 indicated good reliability and high repeatability
Temperature Dependence of the Particle Diffusion Coefficient in Dust Grains
Pechal, Radim; Richterova, Ivana; Pavlu, Jiri; Safrankova, Jana; Nemecek, Zdenek
2014-05-01
During the interaction of ions/neutrals with dust grains, some of the particles are implanted into the grain and, as a consequence, the density gradient induces their diffusion toward the grain surface. Their release can cause a transport of these particles over large distances in space. In our laboratory experiment, measurements of the diffusion coefficient of the particles implanted into the dust grain are carried out in an electrodynamic quadrupole trap. Although experimental setup does not allow an assessment of the dust grain temperature, it can be modified (e.g., by changing thermal radiation from the surrounding walls, laser irradiation, etc.). We present an upgraded laboratory set-up and the resulting temperature dependence of diffusion coefficient estimations and discuss implications for the space dust.
Jain, Preeti; Kumar, Anil
2016-01-14
This study deals with the concentration dependent apparent partition coefficients log P of the ethyl and bisulfate-based ionic liquids. It is observed that the bisulfate-based ionic liquids show different behaviour with respect to concentration as compared to ethyl sulphate-based ionic liquids. It is significant and useful analysis for the further implementation of alkyl sulfate based ionic liquids as solvents in extraction processes. The log P values of the ethyl sulphate-based ionic liquids were noted to vary linearly with the concentration of the ionic liquid, whereas a flip-flop trend with the concentration for the log P values of the bisulphate-based ionic liquids was observed due to the difference in hydrogen bond accepting basicity and possibility of aggregate formation of these anions. The π-π interactions between the imidazolium and pyridinium rings were seen to affect the log P values. The alkyl chain length of anions was also observed to influence the log P values. The hydrophobicity of ionic liquid changes with the alkyl chain in the anion in the order; [HSO4](-) < [EtSO4](-) < [BuSO4](-).
Determination of thermal diffusion coefficient of nanofluid: Fullerene-toluene
Martin, Alain; Bou-Ali, M. Mounir
2011-05-01
Thermodiffusion coefficient at fullerene mass concentrations of 0.05%, 0.1%, 0.15%, and 0.2% was established for pure fullerene (C 60) diluted in toluene solutions. For this, the thermogravitational technique has been used in planar configuration with 4 extraction points. The determination of the concentration distribution along the column in steady state is determined by the method of analysis based on density measurements. In order to determine the thermal diffusion coefficient all thermophysical properties such as density, viscosity, thermal expansion coefficient and mass expansion coefficients were determined. All these studies coincide with the importance of the knowledge of the thermophysics and transport properties of the nanofluids to develop new applications and to optimize the existing ones.
Determination of diffusion coefficient in disordered organic semiconductors
Rani, Varsha; Sharma, Akanksha; Ghosh, Subhasis
2016-05-01
Charge carrier transport in organic semiconductors is dominated by positional and energetic disorder in Gaussian density of states (GDOS) and is characterized by hopping through localized states. Due to the immobilization of charge carriers in these localized states, significant non-uniform carrier distribution exists, resulting diffusive transport. A simple, nevertheless powerful technique to determine diffusion coefficient D in disordered organic semiconductors has been presented. Diffusion coefficients of charge carriers in two technologically important organic molecular semiconductors, Pentacene and copper phthalocyanine (CuPc) have been measured from current-voltage (J-V) characteristics of Al/Pentacene/Au and Al/CuPc/Au based Schottky diodes. Ideality factor g and carrier mobility μ have been calculated from the exponential and space charge limited region respectively of J-V characteristics. Classical Einstein relation is not valid in organic semiconductors due to energetic disorders in DOS. Using generalized Einstein relation, diffusion coefficients have been obtained to be 1.31×10-6 and 1.73×10-7 cm2/s for Pentacene and CuPc respectively.
Water sorption and diffusion coefficient through an experimental dental resin.
Costella, A M; Trochmann, J L; Oliveira, W S
2010-01-01
Polymeric composites have been widely used as dental restorative materials. A fundamental knowledge and understanding of the behavior of these materials in the oral cavity is essential to improve their properties and performance. In this paper we computed the data set of water absorption through an experimental dental resin blend using specimen discs of different thicknesses to estimate the diffusion coefficient. The resins were produced using Bisphenol A glycol dimethacrylate, Bisphenol A ethoxylated dimethacrylate and Triethylene glycol dimethacrylate monomers. The water sorption test method was based on International Standard ISO 4049 "Dentistry-Polymer-based filling materials". Results show a diffusion coefficient around 6.38 x 10(-8) cm(2)/s, within a variance of 0.01%, which is in good agreement with the values reported in the literature and represents a very suitable value.
Diffusion coefficients of molecular iodine in aqueous solutions
Energy Technology Data Exchange (ETDEWEB)
Cantrel, L. [CEA Cadarache, Saint Paul lez Durance (France). Inst. de Protection et de Surete Nucleaire; Chaouche, R.; Chopin-Dumas, J. [Ecole Nationale Superieure de Syntheses, Marseille (France)
1997-01-01
In the event of a severe accident on a light water nuclear reactor (LWR), resulting in overheating of the core, the fission products would be released into the containment building. Among the fission products, iodine represents a biological hazard for the environment by reason of the {sup 131}I radioactive isotope. As iodine is a highly reactive and volatile compound, it is involved in mass transfer from the liquid phase to the gas phase of the containment vessel. In order to determine the quantity of iodine present in the gas phase, it is necessary to know the diffusion coefficient of iodine in water at several temperatures. The diffusion coefficients of iodine in 0.075 mol/dm{sup 3} sulfuric acid have been determined between 298 K and 358 K, by measuring the limiting reduction currents at a platinum rotating disk electrode. A Stokes-Einstein relation is verified over the range of temperature studied. The experimental value obtained at 298 K is compared with some available relations for the estimation of diffusion coefficients at infinite dilution. The agreement is good.
Energy Technology Data Exchange (ETDEWEB)
Takeda, M.; Hiratsuka, T.; Ito, K.; Finsterle, S.
2011-02-01
Diffusion anisotropy is a critical property in predicting migration of substances in sedimentary formations with very low permeability. The diffusion anisotropy of sedimentary rocks has been evaluated mainly from laboratory diffusion experiments, in which the directional diffusivities are separately estimated by through-diffusion experiments using different rock samples, or concurrently by in-diffusion experiments in which only the tracer profile in a rock block is measured. To estimate the diffusion anisotropy from a single rock sample, this study proposes an axisymmetric diffusion test, in which tracer diffuses between a cylindrical rock sample and a surrounding solution reservoir. The tracer diffusion between the sample and reservoir can be monitored from the reservoir tracer concentrations, and the tracer profile could also be obtained after dismantling the sample. Semi-analytical solutions are derived for tracer concentrations in both the reservoir and sample, accounting for an anisotropic diffusion tensor of rank two as well as the dilution effects from sampling and replacement of reservoir solution. The transient and steady-state analyses were examined experimentally and numerically for different experimental configurations, but without the need for tracer profiling. These experimental configurations are tested for in- and out-diffusion experiments using Koetoi and Wakkanai mudstones and Shirahama sandstone, and are scrutinized by a numerical approach to identify favorable conditions for parameter estimation. The analysis reveals the difficulty in estimating diffusion anisotropy; test configurations are proposed for enhanced identifiability of diffusion anisotropy. Moreover, it is demonstrated that the axisymmetric diffusion test is efficient in obtaining the sorption parameter from both steady-state and transient data, and in determining the effective diffusion coefficient if isotropic diffusion is assumed. Moreover, measuring reservoir concentrations in an
Institute of Scientific and Technical Information of China (English)
吴武林; 王小宜; 娄明武; 郝长胜; 廖伟华; 周高峰
2010-01-01
Objective To evaluate the apparant diffusion coefficient (ADC) values of cerebellar and the middle cerebellar peduncles in the differential diagnosis of multiple system atrophy (MSA) and Parkinson disease (PD). Methods Conventional MRI and DWI were performed in 18 clinically proved MSA patients with 7 cases of early cases (early-stage MSA group), 19 PD patients (PD group) and 18 agematched normal controls (the control group). DWI was performed using a single shot-spin echo-echo planar imaging sequences, and ADC values were measured in the ROIs (0. 16 cm2) of the bilateral cerebellum, the middle cerebellar peduncles and cerebral white matter. Then one way ANOVA test was used for statistical analysis. Results Of the 18 MSA patients, 11 had MR abnormalities, 8 had hot-cross bun sign in the pens on T2-weighted images, 11 patients had pontine, cerebellar and medulla oblongata atrophy, 10 patients had atrophy of the middle cerebellar peduncles, 2 patients had hyperintense rim of the putamen and putaminal atrophy on T2-weighted images. The ADC values in the middle cerebellar peduncles were significantly increased in the MSA group[ (0. 98 ±0. 07) × 103 mm2/s] and early-stnge MSA group [ (0. 95 ±0. 05) ×103 mm2/s] as compared to PD group [ (0. 77 ±0. 04) × 103 mm2/s] and control group[ (0. 78 ±0. 04) ×103 mm2/s]. There was statistical significant difference among them (F = 91.049,55. 301, P ＜ 0.01 ).There was no overlap in the distribution of ADC values of the middle cerebellar peduncles among the MSA group [ (0.86-1.13 ) × 103 mm2/s ], early-stage MSA group [ (0. 86-1.02 ) × 103 mm2/s ] and PD group [ (0. 68-0. 84) × 103 mm2/s] and the control group [ (0. 69-0. 82) × 103 mm2/s]. The ADC values in the cerebellum were significantly increased in the MSA group[ (0. 95 ±0. 09) × 103 mm2/s] and early-stage MSA group [ (0. 92 ±0. 07) × 103 mm2/s] as compared to PD group [ (0. 78 ±0. 05) × 103 mm2/s] and control group[ (0. 79 ± 0. 05 ) × 103 mm2/s
Rafelski, Susanne M.; Keller, Lani C.; Alberts, Jonathan B.; Marshall, Wallace F.
2011-04-01
The degree to which diffusion contributes to positioning cellular structures is an open question. Here we investigate the question of whether diffusive motion of centrin granules would allow them to interact with the mother centriole. The role of centrin granules in centriole duplication remains unclear, but some proposed functions of these granules, for example, in providing pre-assembled centriole subunits, or by acting as unstable 'pre-centrioles' that need to be captured by the mother centriole (La Terra et al 2005 J. Cell Biol. 168 713-22), require the centrin foci to reach the mother. To test whether diffusive motion could permit such interactions in the necessary time scale, we measured the motion of centrin-containing foci in living human U2OS cells. We found that these centrin foci display apparently diffusive undirected motion. Using the apparent diffusion constant obtained from these measurements, we calculated the time scale required for diffusion to capture by the mother centrioles and found that it would greatly exceed the time available in the cell cycle. We conclude that mechanisms invoking centrin foci capture by the mother, whether as a pre-centriole or as a source of components to support later assembly, would require a form of directed motility of centrin foci that has not yet been observed.
International Nuclear Information System (INIS)
The degree to which diffusion contributes to positioning cellular structures is an open question. Here we investigate the question of whether diffusive motion of centrin granules would allow them to interact with the mother centriole. The role of centrin granules in centriole duplication remains unclear, but some proposed functions of these granules, for example, in providing pre-assembled centriole subunits, or by acting as unstable 'pre-centrioles' that need to be captured by the mother centriole (La Terra et al 2005 J. Cell Biol. 168 713–22), require the centrin foci to reach the mother. To test whether diffusive motion could permit such interactions in the necessary time scale, we measured the motion of centrin-containing foci in living human U2OS cells. We found that these centrin foci display apparently diffusive undirected motion. Using the apparent diffusion constant obtained from these measurements, we calculated the time scale required for diffusion to capture by the mother centrioles and found that it would greatly exceed the time available in the cell cycle. We conclude that mechanisms invoking centrin foci capture by the mother, whether as a pre-centriole or as a source of components to support later assembly, would require a form of directed motility of centrin foci that has not yet been observed
Radon diffusion coefficients in soils of varying moisture content
Papachristodoulou, C.; Ioannides, K.; Pavlides, S.
2009-04-01
Radon is a naturally occurring radioactive gas that is generated in the Earth's crust and is free to migrate through soil and be released to the atmosphere. Due to its unique properties, soil gas radon has been established as a powerful tracer used for a variety of purposes, such as exploring uranium ores, locating geothermal resources and hydrocarbon deposits, mapping geological faults, predicting seismic activity or volcanic eruptions and testing atmospheric transport models. Much attention has also been given to the radiological health hazard posed by increased radon concentrations in the living and working environment. In order to exploit radon profiles for geophysical purposes and also to predict its entry indoors, it is necessary to study its transport through soils. Among other factors, the importance of soil moisture in such studies has been largely highlighted and it is widely accepted that any measurement of radon transport parameters should be accompanied by a measurement of the soil moisture content. In principle, validation of transport models in the field is encountered by a large number of uncontrollable and varying parameters; laboratory methods are therefore preferred, allowing for experiments to be conducted under well-specified and uniform conditions. In this work, a laboratory technique has been applied for studying the effect of soil moisture content on radon diffusion. A vertical diffusion chamber was employed, in which radon was produced from a 226Ra source, was allowed to diffuse through a soil column and was finally monitored using a silicon surface barrier detector. By solving the steady-state radon diffusion equation, diffusion coefficients (D) were determined for soil samples of varying moisture content (m), from null (m=0) to saturation (m=1). For dry soil, a D value of 4.1×10-7 m2s-1 was determined, which increased moderately by a factor of ~3 for soil with low moisture content, i.e. up to m ~0.2. At higher water fractions, a decrease
Diffusion coefficient of metal vapours into rare gases. Mercury - argon
International Nuclear Information System (INIS)
The source information is present as well as the results of analysis and integration of data on mutual diffusion coefficient (MDC) of mercury - argon mixture at Hg concentration → 0 in 300-2500 K temperature range. Reference data on MDC for metal - inert gas binary mixtures obtained on the base of complex analysis of various information, as it exemplified by Hg-Ar pair, can be used as a part of metrological support at calibration of devices for determination MDC of gas - metal vapors
Tracer diffusion coefficients in a sheared inelastic Maxwell gas
Garzó, Vicente; Trizac, Emmanuel
2016-07-01
We study the transport properties of an impurity in a sheared granular gas, in the framework of the Boltzmann equation for inelastic Maxwell models. We investigate here the impact of a nonequilibrium phase transition found in such systems, where the tracer species carries a finite fraction of the total kinetic energy (ordered phase). To this end, the diffusion coefficients are first obtained for a granular binary mixture in spatially inhomogeneous states close to the simple shear flow. In this situation, the set of coupled Boltzmann equations are solved by means of a Chapman-Enskog-like expansion around the (local) shear flow distributions for each species, thereby retaining all the hydrodynamic orders in the shear rate a. Due to the anisotropy induced by the shear flow, three tensorial quantities D ij , D p,ij , and D T,ij are required to describe the mass transport process instead of the conventional scalar coefficients. These tensors are given in terms of the solutions of a set of coupled algebraic equations, which can be exactly solved as functions of the shear rate a, the coefficients of restitution {αsr} and the parameters of the mixture (masses and composition). Once the forms of D ij , D p,ij , and D T,ij are obtained for arbitrary mole fraction {{x}1}={{n}1}/≤ft({{n}1}+{{n}2}\\right) (where n r is the number density of species r), the tracer limit ({{x}1}\\to 0 ) is carefully considered for the above three diffusion tensors. Explicit forms for these coefficients are derived showing that their shear rate dependence is significantly affected by the order-disorder transition.
Araruna, F. D.; Braz e Silva, P.; Carvalho, R. R.; Rojas-Medar, M. A.
2015-06-01
We consider the motion of a viscous incompressible fluid consisting of two components with a diffusion effect obeying Fick's law in ℝ3. We prove that there exists a small time interval where the fluid variables converge uniformly as the viscosity and the diffusion coefficient tend to zero. In the limit, we find a non-homogeneous, non-viscous, incompressible fluid governed by an Euler-like system.
Apparent digestibility coefficients and consumption of corn silage with and without Bt gene in sheep
Directory of Open Access Journals (Sweden)
Camila Memari Trava
2012-12-01
Full Text Available Corn silage is the most important preserved food for ruminants. The transgenic corn was inserted into the genetic code Bt gene (Bacillus thuringiensis that expresses a toxic protein to caterpillars pests of maize, reducing production costs. To evaluate the varieties of plant corn silage DKB and AG with or without the Bt gene on the voluntary intake of DM (g/day and apparent digestibility coefficients (CDA of nutrients in sheep, the experiment was conducted at the Institute of Animal Science Nova Odessa-SP. Were used 20 sheep and the experimental design was randomized blocks in scheme factorial type 2x2 (two varieties of plant corn to silage, with the presence or absence of Bt gene, with five animals per treatment. These animals were housed in metabolism cages, with collector and separator feces and urine for 21 days, comprising 8 days for diet adaptation and 7 days for determination of intake, followed by 6 days of collection of feces, to measure DMI (g/day, CDA DM, CP and NDF. Samples of feed offered, leftovers and feces were identified and placed in a circulating air oven maintained at 55°C to constant weight. The analyses were performed in Bromatological Analysis Laboratory of the Institute of Animal Science. To CTMS (g/day was interaction effect (p<0.05 than in the variety AG (779.36 was greater than DKB (637.52, because the DM content of the sheet AG (31.09 was superior to DKB (29.17. The AG (779.36 was higher than your counterpart isogenic without the gene (575.15 p<0.05. The DKB without the gene (637.52 did not differ (p>0.05 from your counterpart DKBBt with the gene (590.78. The lowest total DM intake in g/day was observed for varieties with Bt gene insertion (genetically modified organism - GMO and a possible explanation is the higher value of NDF in the silages of variety with the Bt gene in relation to their isogenic counterparts without the gene. The CDA, DM and NDF no had interaction effect between varieties factors and GMO (p>0
Evaluation of downwelling diffuse attenuation coefficient algorithms in the Red Sea
Tiwari, Surya Prakash
2016-05-07
Despite the importance of the optical properties such as the downwelling diffuse attenuation coefficient for characterizing the upper water column, until recently no in situ optical measurements were published for the Red Sea. Kirby et al. used observations from the Coastal Zone Color Scanner to characterize the spatial and temporal variability of the diffuse attenuation coefficient (Kd(490)) in the Red Sea. To better understand optical variability and its utility in the Red Sea, it is imperative to comprehend the diffuse attenuation coefficient and its relationship with in situ properties. Two apparent optical properties, spectral remote sensing reflectance (Rrs) and the downwelling diffuse attenuation coefficient (Kd), are calculated from vertical profile measurements of downwelling irradiance (Ed) and upwelling radiance (Lu). Kd characterizes light penetration into water column that is important for understanding both the physical and biogeochemical environment, including water quality and the health of ocean environment. Our study tests the performance of the existing Kd(490) algorithms in the Red Sea and compares them against direct in situ measurements within various subdivisions of the Red Sea. Most standard algorithms either overestimated or underestimated with the measured in situ values of Kd. Consequently, these algorithms provided poor retrieval of Kd(490) for the Red Sea. Random errors were high for all algorithms and the correlation coefficients (r2) with in situ measurements were quite low. Hence, these algorithms may not be suitable for the Red Sea. Overall, statistical analyses of the various algorithms indicated that the existing algorithms are inadequate for the Red Sea. The present study suggests that reparameterizing existing algorithms or developing new regional algorithms is required to improve retrieval of Kd(490) for the Red Sea. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is
Institute of Scientific and Technical Information of China (English)
肖吉; 陆九芳; 陈健; 李以圭
2001-01-01
Molecular dynamics simulation has been performed to determine the infinite-dilution diffusion coefficients of oxygen and nitrogen, and the diffusion coefficients of NaCl in supercritical water from 703.2- 763.2 K and 30-45 MPa.The results obtained show that the diffusion coefficients in supercritical water increase with temperature, while decreasing with pressure. Nevertheless, the diffusion coefficients in supercritical water are much larger than those in normal water.
Institute of Scientific and Technical Information of China (English)
郭翔
2014-01-01
Objective To explore the feasibility of prediction of subacute infarct lesion volumes by processing ADC maps based on ADC cut-off values in patients with acute stroke.Methods MRI was performed in 20 patients with clinically diagnosed acute infarct less than 6 h after stroke onset.The MRI included a DWI and conventional MRI.The follow-up MR examinations of all the patients
El-Shafai, S.A.A.M.; El-Gohary, F.; Verreth, J.A.J.; Schrama, J.W.; Gijzen, H.J.
2004-01-01
Dry matter (DMD), protein (PD), ash (AD), fat (FD), gross energy (ED) and phosphorus (PhD) digestibility coefficients were determined for five different iso-N fish diets fed to Nile tilapia (Oreochromis niloticus). The control diet contained fishmeal (35%), corn (29%), wheat (20%), wheat bran (10%),
Measurement of diffusion coefficient of propylene glycol in skin tissue
Genin, Vadim D.; Bashkatov, Alexey N.; Genina, Elina A.; Tuchin, Valery V.
2015-03-01
Optical clearing of the rat skin under the action of propylene glycol was studied ex vivo. It was found that collimated transmittance of skin samples increased, whereas weight and thickness of the samples decreased during propylene glycol penetration in skin tissue. A mechanism of the optical clearing under the action of propylene glycol is discussed. Diffusion coefficient of propylene glycol in skin tissue ex vivo has been estimated as (1.35±0.95)×10-7 cm2/s with the taking into account of kinetics of both weight and thickness of skin samples. The presented results can be useful for enhancement of many methods of laser therapy and optical diagnostics of skin diseases and localization of subcutaneous neoplasms.
Directory of Open Access Journals (Sweden)
Lorena Sigaut
2014-06-01
Full Text Available The gradient of Bicoid (Bcd is key for the establishment of the anterior-posterior axis in Drosophila embryos. The gradient properties are compatible with the SDD model in which Bcd is synthesized at the anterior pole and then diffuses into the embryo and is degraded with a characteristic time. Within this model, the Bcd diffusion coefficient is critical to set the timescale of gradient formation. This coefficient has been measured using two optical techniques, Fluorescence Recovery After Photobleaching (FRAP and Fluorescence Correlation Spectroscopy (FCS, obtaining estimates in which the FCS value is an order of magnitude larger than the FRAP one. This discrepancy raises the following questions: which estimate is "correct''; what is the reason for the disparity; and can the SDD model explain Bcd gradient formation within the experimentally observed times? In this paper, we use a simple biophysical model in which Bcd diffuses and interacts with binding sites to show that both the FRAP and the FCS estimates may be correct and compatible with the observed timescale of gradient formation. The discrepancy arises from the fact that FCS and FRAP report on different effective (concentration dependent diffusion coefficients, one of which describes the spreading rate of the individual Bcd molecules (the messengers and the other one that of their concentration (the message. The latter is the one that is more relevant for the gradient establishment and is compatible with its formation within the experimentally observed times.
On applicability of permanent coefficient model to diffusion description in solid state
International Nuclear Information System (INIS)
A mathematical method is assessed using the model of the constant diffusion coefficients for the solution of diffusion equations in bynary and multicomponent systems. Consideration is given to the solution of a direct problem, viz., determination of element concentration from available diffusion coefficients, and a inverse problem, viz., determination of the diffusion coefficients from known concentration curves. Errors due to using this method are estimated (particularly, in the case of the Fe-Cr-Ni ternary system)
Optimal estimation of the diffusion coefficient from non-averaged and averaged noisy magnitude data
Kristoffersen, Anders
2007-08-01
The magnitude operation changes the signal distribution in MRI images from Gaussian to Rician. This introduces a bias that must be taken into account when estimating the apparent diffusion coefficient. Several estimators are known in the literature. In the present paper, two novel schemes are proposed. Both are based on simple least squares fitting of the measured signal, either to the median (MD) or to the maximum probability (MP) value of the Probability Density Function (PDF). Fitting to the mean (MN) or a high signal-to-noise ratio approximation to the mean (HS) is also possible. Special attention is paid to the case of averaged magnitude images. The PDF, which cannot be expressed in closed form, is analyzed numerically. A scheme for performing maximum likelihood (ML) estimation from averaged magnitude images is proposed. The performance of several estimators is evaluated by Monte Carlo (MC) simulations. We focus on typical clinical situations, where the number of acquisitions is limited. For non-averaged data the optimal choice is found to be MP or HS, whereas uncorrected schemes and the power image (PI) method should be avoided. For averaged data MD and ML perform equally well, whereas uncorrected schemes and HS are inadequate. MD provides easier implementation and higher computational efficiency than ML. Unbiased estimation of the diffusion coefficient allows high resolution diffusion tensor imaging (DTI) and may therefore help solving the problem of crossing fibers encountered in white matter tractography.
Energy Technology Data Exchange (ETDEWEB)
Zerr, R. Joseph; Azmy, Yousry [The Pennsylvania State University, University Park, PA (United States); Ouisloumen, Mohamed [Westinghouse Electric Company, LLC, Monroeville, PA (United States)
2008-07-01
Studies have been performed to test for significant gains in core design computational accuracy with the added implementation of direction-dependent diffusion coefficients. The DRAGON code was employed to produce two-group homogeneous B{sub 1} diffusion coefficients and direction-dependent diffusion coefficients with the TIBERE module. A three-dimensional diffusion model of a mini-core was analyzed with the resulting cross section data sets to determine if the multiplication factor or node power was noticeably altered with the more accurate representation of neutronic behaviour in a high-void configuration. Results indicate that using direction-dependent diffusion coefficients homogenized over an entire assembly do not produce significant differences in the results compared to the B{sub 1} counterparts and are much more computationally expensive. Direction-dependent diffusion coefficients that are specific to smaller micro-regions may provide more noteworthy gains in the accuracy of core design computations. (authors)
Inner zone electron radial diffusion coefficients - An update with Van Allen Probes MagEIS data
O'Brien, Paul; Fennell, Joseph; Guild, Timothy; Mazur, Joseph; Claudepierre, Seth; Clemmons, James; Turner, Drew; Blake, Bernard; Roeder, James
2016-07-01
Using MagEIS data from NASA's recent Van Allen Probes mission, we estimate the quiet-time radial diffusion coefficients for electrons in the inner radiation belt and slot, for energies up to ~700 keV. We provide observational evidence that energy diffusion is negligible. The main dynamic processes, then, are radial diffusion and elastic pitch angle scattering. We use a coordinate system in which these two modes of diffusion are separable. Then we integrate over pitch angle to obtain a field line content whose dynamics consist of radial diffusion and loss to the atmosphere. We estimate the loss timescale from periods of exponential decay in the time series. We then estimate the radial diffusion coefficient from the temporal and radial variation of the field line content. We show that our diffusion coefficients agree well with previously determined values. Our coefficients are consistent with diffusion by electrostatic impulses, whereas outer zone radial diffusion is thought to be dominated by electromagnetic fluctuations.
The solid-phase diffusion coefficient (Dm) and material-air partition coefficient (Kma) are key parameters for characterizing the sources and transport of semivolatile organic compounds (SVOCs) in the indoor environment. In this work, a new experimental method was developed to es...
Prediction of diffusion coefficients of chlorophenols in water by computer simulation
Martins, Luís F. G.; Parreira, M. Cristina B.; Prates Ramalho, João P.; Morgado, Pedro; Filipe, Eduardo. J. M.
2015-01-01
Intra-diffusion coefficients of seven chlorophenols (2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,6-dichlorophenol, 2,4,6-dichlorophenol and pentachlorophenol) in water were determined by computer simulation (molecular dynamics) for dilute solutions at three different temperatures and the corresponding mutual diffusion coefficients estimated. The mutual diffusion coefficients of 2-chlorophenol in water agree with the available experimental results from the...
Buffie, Kaitlynn; Heesen, Volker; Shalchi, Andreas
2012-01-01
Diffusion coefficients are usually used to describe the propagation of Cosmic Rays through the Universe. Whereas such transport parameters can be obtained from experiments in the Solar System, it is difficult to determine diffusion coefficients in the Milky Way or in external galaxies. Recently a value for the perpendicular diffusion coefficient in the nearby starburst halaxy NGC 253 has been proposed. In the present paper we reproduce this value theoretically by using an advanced analytical ...
Method for quantitative determination of a small difference between diffusion coefficients
International Nuclear Information System (INIS)
Small differences between diffusion coefficients are determined by separative diffusion in the transient state. The method compares experimental results for cylindrical diffusion with computer results. As an example the isotope effect in the diffusion of uranyl nitrate in agar gel was investigated. (U.S.)
Estimation of diffusion coefficient of lanthanum ions from one-dimensional Liesegang farmation
International Nuclear Information System (INIS)
Experimental conditions for obtaining Liesegang rings in the growth of lanthanum molybdate crystals in silica gel by single diffusion technique have been discussed. The time law, spacing law and the law relating diffusion depth and width are verified. Making use of Fick's law of diffusion, a method has been devised to estimate the diffusion coefficient of lanthanum ions in silica gel and the various parameters under which the coefficient varies are investigated. (author)
LUNG DIFFUSION CAPACITY CAN PREDICT MAXIMAL EXERCISE IN APPARENTLY HEALTHY HEAVY SMOKERS
Directory of Open Access Journals (Sweden)
Alfredo Chetta
2008-06-01
Full Text Available Chronic exposure to tobacco smoking may damage lung and heart function. The aim of this study was to assess maximal exercise capacity and its relationship with lung function in apparently healthy smokers. We recruited 15 heavy smokers (age 47 years ± 7, BMI 25 kg/m2 ± 3, pack/years 32 ± 9 without any cardiovascular or pulmonary signs and symptoms. Fifteen healthy non smoking subjects were enrolled as a control group. All subjects underwent pulmonary function tests, electrocardiograms at rest and graded cycle exercise tests. In smokers and controls, resting lung and cardiac function parameters were in the normal range, apart from diffusing lung capacity (TLCO values which were significantly lower in smokers (p < 0.05. As compared to controls, smokers presented lower maximal exercise capacity with lower values at peak of exercise of oxygen uptake (peak VO2, workload, oxygen uptake/watt ratio and oxygen pulse (p < 0.05 and higher dyspnoea perception (p < 0.05. Moreover, peak VO2, maximal workload and oxygen pulse at peak exercise were related to and predicted by TLCO (p < 0. 05. Our study confirms that maximal exercise capacity is reduced in apparently healthy heavy smokers, and shows that TLCO explains some of the variance in maximal exercise
Institute of Scientific and Technical Information of China (English)
LIXiangbin; ZHAOYuechun; 等
2002-01-01
A new model,phase equilibrium-kinetics model(PEKM),for estimation of diffusion coefficient was proposed in this paper.Kinetic exeriments of phenol desorption on NKAII resin in the presence and the absence of ultrasound wree separately conducted,and diffusion coefficients of phenol within an adsorbent particle were estimated by means of proposed PEKM and classic simplified model.Results show that the use of ultrasound not only changes the phase equilibrium state of NKAII resin/phenol/water system which had been equilibrium at normal condition,but also enhances diffusion of phenol within the resin.The diffusion coefficient of phenol in the resin in the field of ultrasound increases in an order of magnitude in comparison with the diffusion coefficient determined under no ultrasound.Experimental results also indicated that the diffusion coefficients estimated by PEKM were more accurate than that estimated by the classic simplified mode.
Apparent diffusion coefifcient values of normal testis and variations with age
Institute of Scientific and Technical Information of China (English)
Athina C Tsili; Dimitrios Giannakis; Anastasios Sylakos; Alexandra Ntorkou; Loukas G Astrakas; Nikolaos Soifkitis; Maria I Argyropoulou
2014-01-01
The usefulness of diffusion-weighted magnetic resonance imaging (DWI) in the evaluation of scrotal pathology has recently been reported. A standard reference of normal testicular apparent diffusion coefifcient (ADC) values and their variations with age is necessary when interpreting normal testicular anatomy and pathology. We evaluated 147 normal testes using DWI, including 71 testes from 53 men aged 20-39 years (group 1), 67 testes from 42 men aged 40-69 years (group 2) and nine testes from six men older than 70 years (group 3). DWI was performed along the axial plane, using a single shot, multislice spin-echo planar diffusion pulse sequence and b-values of 0 and 900 s mm-2. The mean and standard deviation of the ADC values of normal testicular parenchyma were calculated for each age group separately. Analysis of variance (ANOVA) followed by post hoc analysis (Dunnett T3) was used for statistical purposes. The ADC values (× 10-3 mm2 s-1) of normal testicular tissue were different among age groups (group 1:1.08 ± 0.13;group 2:1.15 ± 0.15 and group 3:1.31 ± 0.22). ANOVA revealed differences in mean ADC among age groups (F=11.391, P<0.001). Post hoc analysis showed differences between groups 1 and 2 (P=0.008) and between groups 1 and 3 (P=0.043), but not between groups 2 and 3 (P=0.197). Our ifndings suggest that ADC values of normal testicular tissue increase with advancing age.
Zhigao Liao; Jiuping Xu; Liming Yao
2013-01-01
This paper studies the innovation diffusion problem with the affection of urbanization, proposing a dynamical innovation diffusion model with fuzzy coefficient, and uses the shifting rate of people from rural areas stepping into urban areas to show the process of urbanization. The numerical simulation shows the diffusion process for telephones in China with Genetic Algorithms and this model is effective to show the process of innovation diffusion with the condition of urbanization process.
Beijeren, H. van; Kehr, K.W.
1986-01-01
The correlation factor, defined as the ratio between the tracer diffusion coefficient in lattice gases and the diffusion coefficient for a corresponding uncorrelated random walk, is known to assume a very simple form under certain conditions. A simple derivation of this is given with the aid of the
Evaluation of diffusion coefficients in multicomponent mixtures by means of the fluctuation theory
DEFF Research Database (Denmark)
Shapiro, Alexander
2003-01-01
We derive general expressions for diffusion coefficients in multicomponent non-ideal gas or liquid mixtures. The derivation is based on the general statistical theory of fluctuations around an equilibrium state. The matrix of diffusion coefficients is expressed in terms of the equilibrium thermod...
Asymptotic Behavior of a Competition-Diffusion System with Variable Coefficients and Time Delays
Miguel Uh Zapata; Eric Avila Vales; Angel G. Estrella
2008-01-01
A class of time-delay reaction-diffusion systems with variable coefficients which arise from the model of two competing ecological species is discussed. An asymptotic global attractor is established in terms of the variable coefficients, independent of the time delays and the effect of diffusion by the upper-lower solutions and iteration method.
Fractal scaling of effective diffusion coefficient of solute in porous media
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Fractal approach is used to derive a power law relation betweeneffective diffusion coefficient of solute in porous media and the geometry parameter characterizing the media. The results are consistent with the empirical equations analogous to Archie'slaw and are expected to be applied to prediction of effective diffusion coefficient.
Institute of Scientific and Technical Information of China (English)
郭成伟; 梁长虹; 张水兴; 沈三弟; 刘再毅; 贾乾君
2011-01-01
.0 h and 48. 0 h IRI groups, they were (80±8), (181 ±34), (413 ±62), (474 ±83), (424 ±41 ),(332 ±41 )and(302 ±39) U/L for the levels of ALT,and (79 ± 10), (454 ±55), (547 ±72), (607±31 ), (649 ±79), (785 ±49) and ( 1526 ± 167) U/L for the AST respectively. The levels of AST and ALT in IRI groups were significantly higher than those in the Sham group ( P ＜ 0. 01 ). Histological findings showed diffuse hepatocytes swelling and erythrocytes depositing in the hepatic sinusoids, portal area, central venous and arterials at the initial phase. With the injury aggravated, inflammatory cell infiltration,hepatocyte nuclear condensation of apoptosis, sinusoidal dissociation and coagulation necrosis developed eventually. Conclusion 3.0 T DWI can monitor the pathological process of rabbit liver ischemia reperfusion injury dynamically, and provides a feasible imaging modality for clinical diagnosis and treatment.%目的 探讨DWI及ADC值对兔肝缺血再灌注损伤（IRI）的诊断价值及通过与肝酶、病理对照研究探讨其病理生理机制。方法 新西兰大白兔42只，用数字表法随机分成7组，每组6只。按照IRI后行MR扫描时间分为0.5、2.0、6.0、12.0、24.0和48.0 h IRI组及假手术（Sham）组。IRI组阻断肝左叶血供60 min后，恢复血供。Sham组未作缺血处理。采用3.0 T DWI，梯度因子(b)＝20、50、100、200、300、400、500、600 s/mm2，同时行T2WI、T1WI和T1WI增强扫描，并行组织病理学和肝酶学丙氨酸转氨酶(ALT)和天冬氨酸转氨酶(AST)检查。不同b值下多组ADC值、各IRI与Sham组的AST、ALT值的比较采用单因素方差分析，组间均数差异的比较采用LSD-t法。结果 ADC值的总体变化趋势是在复氧后0.5h明显下降，然后在2.0h组急剧上升，经过6.0～12.0h缓慢上升后，24.0h组再次下降，于48.0 h组ADC明显升高。B值分别为20、50、100、200、300 s/mm2时，Sham组ADC值分别为(3.47±0.53)×10-3、(3.11±0
Energy Technology Data Exchange (ETDEWEB)
Tringe, J.W., E-mail: tringe2@llnl.gov [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA (United States); Ileri, N. [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA (United States); Department of Chemical Engineering & Materials Science, University of California, Davis, CA (United States); Levie, H.W. [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA (United States); Stroeve, P.; Ustach, V.; Faller, R. [Department of Chemical Engineering & Materials Science, University of California, Davis, CA (United States); Renaud, P. [Swiss Federal Institute of Technology, Lausanne, (EPFL) (Switzerland)
2015-08-18
Highlights: • WGA proteins in nanochannels modeled by Molecular Dynamics and Monte Carlo. • Protein surface coverage characterized by atomic force microscopy. • Models indicate transport characteristics depend strongly on surface coverage. • Results resolve of a four orders of magnitude difference in diffusion coefficient values. - Abstract: We use Molecular Dynamics and Monte Carlo simulations to examine molecular transport phenomena in nanochannels, explaining four orders of magnitude difference in wheat germ agglutinin (WGA) protein diffusion rates observed by fluorescence correlation spectroscopy (FCS) and by direct imaging of fluorescently-labeled proteins. We first use the ESPResSo Molecular Dynamics code to estimate the surface transport distance for neutral and charged proteins. We then employ a Monte Carlo model to calculate the paths of protein molecules on surfaces and in the bulk liquid transport medium. Our results show that the transport characteristics depend strongly on the degree of molecular surface coverage. Atomic force microscope characterization of surfaces exposed to WGA proteins for 1000 s show large protein aggregates consistent with the predicted coverage. These calculations and experiments provide useful insight into the details of molecular motion in confined geometries.
Data set for diffusion coefficients of alloying elements in dilute Mg alloys from first-principles
Directory of Open Access Journals (Sweden)
Bi-Cheng Zhou
2015-12-01
Full Text Available Diffusion coefficients of alloying elements in Mg are critical for the development of new Mg alloys for lightweight applications. Here we present the data set of the temperature-dependent dilute tracer diffusion coefficients for 47 substitutional alloying elements in hexagonal closed packed (hcp Mg calculated from first-principles calculations based on density functional theory (DFT by combining transition state theory and an 8-frequency model. Benchmark for the DFT calculations and systematic comparison with experimental diffusion data are also presented. The data set refers to “Diffusion coefficients of alloying elements in dilute Mg alloys: A comprehensive first-principles study” by Zhou et al. [1].
Electrophoretic method for the determination of diffusion coefficients of ions in aqueous solutions
International Nuclear Information System (INIS)
The electrophoretic method was recently developed for the determination of diffusion coefficients of ions in aqueous solution. By solving the Fick's second law in the presence of unlimited media and constant quantity of diffusing species we obtain a relationship between the diffusion coefficient and the standard deviation of the distribution profile. The diffusion coefficients of Cd(II), In(III), Zr(IV), Hf(IV), Pu(VI) and [InDTPA]2- in nitric acid solution were determined as well as the effective charge of In-DTPA complex at pH 4.50. (author)
On the Diffusion Coefficient of Water in Polymer Electrolyte Membranes
DEFF Research Database (Denmark)
Olesen, Anders Christian; Berning, Torsten; Kær, Søren Knudsen
2012-01-01
generate a local maximum, if a wrong equilibrium water content relation is used. Finally, in order to study the obtained diffusivity model a parameter variation is carried out using a one-dimensional steady-state model. The effect of diffusivity model, surface roughness and water content driving force...
International Nuclear Information System (INIS)
6-gingerol and 6-shogaol are the main constituents as anti-inflammatory or bioactive compounds from zingiber officinale Roscoe. These bioactive compounds have been proven for inflammatory disease, antioxidatives and anticancer. The effect of temperature on diffusion coefficient for 6-gingerol and 6-shogaol were studied in subcritical water extraction. The diffusion coefficient was determined by Fick's second law. By neglecting external mass transfer and solid particle in spherical form, a linear portion of Ln (1-(Ct/Co)) versus time was plotted in determining the diffusion coefficient. 6-gingerol obtained the higher yield at 130°C with diffusion coefficient of 8.582x10−11 m2/s whilst for 6-shogaol, the higher yield and diffusion coefficient at 170°C and 19.417 × 10−11 m2/s.
Molecular Dynamics Simulations of Self-diffusion Coefficients ofExponential-six Fluids
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
Self-diffusion coefficients of exponential-six fluids are studied using equilibrium moleculardynamics simulation technique. Mean-square displacements and velocity autocorrelationfunctions are used to calculate self-diffusion coefficients through Einstein equation and Green-Kuboformula. It has been found that simulation results are in good agreement with experimental data for liquidargon which is taken as exponential-six fluid. The effects of density, temperature and steepness factor forrepulsive part of exponential-six potential on self-diffusion coefficients are also investigated. Thesimulation results indicate that the self-diffusion coefficient of exponential-six fluid increases astemperature increases and density decreases. In addition, the larger self-diffusion coefficients are obtainedas the steepness factor increases at the same temperature and density condition.
Ilia Anisa, Nor; Azian, Noor; Sharizan, Mohd; Iwai, Yoshio
2014-04-01
6-gingerol and 6-shogaol are the main constituents as anti-inflammatory or bioactive compounds from zingiber officinale Roscoe. These bioactive compounds have been proven for inflammatory disease, antioxidatives and anticancer. The effect of temperature on diffusion coefficient for 6-gingerol and 6-shogaol were studied in subcritical water extraction. The diffusion coefficient was determined by Fick's second law. By neglecting external mass transfer and solid particle in spherical form, a linear portion of Ln (1-(Ct/Co)) versus time was plotted in determining the diffusion coefficient. 6-gingerol obtained the higher yield at 130°C with diffusion coefficient of 8.582x10-11 m2/s whilst for 6-shogaol, the higher yield and diffusion coefficient at 170°C and 19.417 × 10-11 m2/s.
Institute of Scientific and Technical Information of China (English)
张连顺; 张春平; 王新宇; 祁胜文; 许棠; 田建国; 张光寅
2002-01-01
The applicability of diffusion theory for the determination of tissue optical properties from steady-state diffuse reflectance is investigated. Analytical expressions from diffusion theory using the two most commonly assumed boundary conditions at the air-tissue interface and the two definitions of the diffusion coefficient are compared with Monte Carlo simulations. The effects of the choice of the boundary conditions and diffusion coefficients on the accuracy of the findings for the optical parameters are quantified, and criteria for accurate curve-fitting algorithms are developed. It is shown that the error in deriving the optical coefficients is considerably smaller for the solution which uses the extrapolated boundary condition and the diffusion coefficient independence of absorption coefficient, compared to the other three solutions.
Diffusion coefficient test of {sup 237}Np in bentonite backfill materials
Energy Technology Data Exchange (ETDEWEB)
Cui Anxi; Fan Zhiwen; Zhang Jinsheng; Gu Cunli [China Inst. for Radiation Protection, Shanxi (China); Mukai, M.; Maeda, T.; Matsumoto, J.; Tanaka, T.; Ogawa, H. [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment
2002-03-01
This paper describes the work on diffusion coefficient test of Np in bentonite backfill materials. Due to its very low permeability, diffusion is the dominant migration mechanics in bentonite. The bentonite comes from Inner Mongolia of China. {sup 237}Np was used as tracer. The special apparatus for diffusion test was setup, the diffusion coefficient of Np in pure bentonite and sand-bentonite mixture were tested. The tracer was introduced between two bentonite columns. After a specific contacting period, the bentonite columns were taken out and cut to very thin slices. The radioactivity in bentonite slices was analyzed to give the nuclide concentration versus distance curves. The diffusion coefficient could be estimated. The diffusion coefficient of pure bentonite at different density was tested. When the density of pure bentonite samples varied from 1.1, 1.3, 1.5 to 1.7 g/ml, their diffusion coefficient were 1.36 x 10{sup -13} m{sup 2}/s 1.16 x 10{sup -13}m{sup 2}/s, 1.07 x 10{sup -13} m{sup 2}/s and 8.26 x 10{sup -14} m{sup 2}/s respectively. The diffusion coefficient of Np in sand-bentonite mixture sample was 4.13 x 10{sup -13} m{sup 2}/s. To estimate the distribution coefficient (K{sub d}) value of Np in mixture sample by diffusion method, the diffusion coefficient of Br was measured./ The concluded K{sub d} value was 77ml/g for the sand-bentonite mixture. The K{sub d} value obtained by batch test methods was 30ml/g. The reason is related with the error of Br diffusion coefficient and solid-liquid ratio. (author)
Response-matrix directional diffusion coefficients for application within large cavities
International Nuclear Information System (INIS)
A deterministic definition of the directional diffusion coefficient is proposed which allows diffusion theory codes to adequately reproduce the transport effects within a large cavity. The methodology has been tested satisfactorily upon the TREAT Upgrade hodoscope slot. This preliminary testing illustrates that the directional diffusion coefficients were applicable to a wide range of perturbations of the original model, thus exhibiting a high degree of versatility
Mass-dependence of self-diffusion coefficients in disparate-mass binary fluid mixtures
I. Binas; I.Mryglod
2009-01-01
Self-diffusion coefficients of a binary fluid mixture with components differing only in their particle masses are studied, in particular the case when mass ratio μ of light and heavy particles tends to zero. These coefficients were calculated within the memory function formalism, using the systematic subsequence of approximations for the relaxation times of velocity autocorrelation function. We obtained a general relation for the self-diffusion coefficients which show polynomial dependence on...
International Nuclear Information System (INIS)
Experimental determination of diffusion invariant coefficients in a four-component Fe-Cr-Ni-Co system is conducted for alloys with 16 mas.% of Cr, 13 mas.% of Ni, 2-14 mas.% of Co. Activation energies, corresponding to diffusion invariant coefficients are calculated by the least squares technique. The analysis of concentrational dependences of these coefficients has shown that under a low cobalt content the system can be characterized by the unique activation energy value
The diffusion coefficient of water in biobased hydrogels were measured utilizing a simple NMR method. This method tracks the migration of deuterium oxide through imaging data that is fit to a diffusion equation. The results show that a 5 wt% soybean oil based hydrogel gives aqueous diffusion of 1.37...
In vivo measurement of apparent diffusion coefficients of hyperpolarized 13C‐labeled metabolites
DEFF Research Database (Denmark)
Søgaard, Lise Vejby; Schilling, Franz; Janich, Martin A.;
2014-01-01
were acquired interleaved with the dw spectra and these were used to correct for signal decay during the acquisition as a result of T1 decay, pulse imperfections, flow etc. The data showed that the ADC values for [1‐13C]lactate (0.4–0.7 µm2/ms) and [1‐13C]alanine (0.4–0.9 µm2/ms) were about a factor...... was not confined inside the muscle cells but also present extracellular. Copyright © 2014 John Wiley & Sons, Ltd....
Radioisotope spectrometric method to determine diffusion coefficients in metals and alloys
International Nuclear Information System (INIS)
A brief description of the spectrometric installation to study diffusion in metals using #betta#-decay radio-isotopes is presented. Diffusion coefficients of nickel in 70% Co-5% Fe-15% Si-10% B amorphous alloy are determined according to #betta#-radiation absorption in diffusion zone. Plate samples of 10x10 mm size and about 300 μm in thickness are used. Diffusion annealing is conducted during 100 hrs. The calculation of the diffusion coefficients has been carried out by the formula I/I0= esup(μsup(2)Dtau)erfc μ √ Dtau, where I0, I is an initial and a final radiation intensity; μ- an absorption coefficient of 63Ni #betta#-ray in the given material (at calculation μ=1.3x106 m-1 was taken); tau- duration of diffusion annealing; D- diffusion coefficient at the designed temperature. The value of the diffusion coefficient of nickel in 70% Co-5% Fe-15% S-10% B amorphous alloy at the temperature of 200 deg C is turned out to be equal to 4x10-21 m2/s. It should be noted that the self-diffusion coefficient of cobalt in Co-Fe alloy, found by extrapolation from high-temperature region, is equal to 10-35 m2/s, i.e. in 14 orders lower than that of the same basis in amorphous alloy
Ha, Jiyeon; Engler, Cady R; Lee, Seung Jae
2008-07-01
Diffusion characteristics of chlorferon and diethylthiophosphate (DETP) in Ca-alginate gel beads were studied to assist in designing and operating bioreactor systems. Diffusion coefficients for chlorferon and DETP in Ca-alginate gel beads determined at conditions suitable for biodegradation studies were 2.70 x 10(-11) m(2)/s and 4.28 x 10(-11) m(2)/s, respectively. Diffusivities of chlorferon and DETP were influenced by several factors, including viscosity of the bulk solution, agitation speed, and the concentrations of diffusing substrate and immobilized cells. Diffusion coefficients increased with increasing agitation speed, probably due to poor mixing at low speed and some attrition of beads at high speeds. Diffusion coefficients also increased with decreasing substrate concentration. Increased cell concentration in the gel beads caused lower diffusivity. Theoretical models to predict diffusivities as a function of cell weight fraction overestimated the effective diffusivities for both chlorferon and DETP, but linear relations between effective diffusivity and cell weight fraction were derived from experimental data. Calcium-alginate gel beads with radii of 1.65-1.70 mm used in this study were not subject to diffusional limitations: external mass transfer resistances were negligible based on Biot number calculations and effectiveness factors indicated that internal mass transfer resistance was negligible. Therefore, the degradation rates of chlorferon and DETP inside Ca-alginate gel beads were reaction-limited. PMID:18080347
Energy Technology Data Exchange (ETDEWEB)
Zhang Yunxin, E-mail: xyz@fudan.edu.c [School of Mathematical Sciences, Fudan University, Shanghai 200433 (China); Shanghai Key Laboratory for Contemporary Applied Mathematics, Fudan University, Shanghai (China); Centre for Computational Systems Biology, Fudan University (China)
2009-07-20
In this research, diffusion of an overdamped Brownian particle in the tilted periodic potential is investigated. Using the one-dimensional hopping model, the formulations of the mean velocity V{sub N} and effective diffusion coefficient D{sub N} of the Brownian particle have been obtained [B. Derrida, J. Stat. Phys. 31 (1983) 433]. Based on the relation between the effective diffusion coefficient and the moments of the mean first passage time, the formulation of effective diffusion coefficient D{sub eff} of the Brownian particle also has been obtained [P. Reimann, et al., Phys. Rev. E 65 (2002) 031104]. In this research, we'll give another analytical expression of the effective diffusion coefficient D{sub eff} from the moments of the particle's coordinate.
Measurement of effective air diffusion coefficients for trichloroethene in undisturbed soil cores
Bartelt-Hunt, Shannon L.; Smith, James A.
2002-06-01
In this study, we measure effective diffusion coefficients for trichloroethene in undisturbed soil samples taken from Picatinny Arsenal, New Jersey. The measured effective diffusion coefficients ranged from 0.0053 to 0.0609 cm 2/s over a range of air-filled porosity of 0.23-0.49. The experimental data were compared to several previously published relations that predict diffusion coefficients as a function of air-filled porosity and porosity. A multiple linear regression analysis was developed to determine if a modification of the exponents in Millington's [Science 130 (1959) 100] relation would better fit the experimental data. The literature relations appeared to generally underpredict the effective diffusion coefficient for the soil cores studied in this work. Inclusion of a particle-size distribution parameter, d10, did not significantly improve the fit of the linear regression equation. The effective diffusion coefficient and porosity data were used to recalculate estimates of diffusive flux through the subsurface made in a previous study performed at the field site. It was determined that the method of calculation used in the previous study resulted in an underprediction of diffusive flux from the subsurface. We conclude that although Millington's [Science 130 (1959) 100] relation works well to predict effective diffusion coefficients in homogeneous soils with relatively uniform particle-size distributions, it may be inaccurate for many natural soils with heterogeneous structure and/or non-uniform particle-size distributions.
Experimental setup for evaluation of radon effective diffusion coefficient in soil
International Nuclear Information System (INIS)
Full text: It has been well recognized that radon and its decay products inhalation significantly contributes to the exposure of public. Radon is mainly generated from soil, building material and ground water. The infiltration of radon gas from soil has been identified as one of the main mechanisms influencing indoor radon levels. Therefore, radon exhalation rate from soil is one of the most important factors for the evaluation of environmental radon levels. In order to estimate the radon exhalation rate, several parameters related to soil characteristic have to be determined (i.e. effective diffusion coefficient, porosity and moisture content). In this study, an optimum experimental set-up to evaluate the radon effective diffusion coefficient was examined. This experimental setup consists of radon source (radon chamber), measuring device (scintillation cell) and diffusion column. The radon chamber calibrated by PTB (Physikalisch-Technischen Bundesanstalt, Germany) was applied as the radon source system. Also the measuring device was calibrated by the same facilities. The diffusion column was filled with glass beads instead of soil. As radon does not generate from the glass beads, therefore, it was possible to evaluate the effective diffusion coefficient precisely. Considering quality assurance of this experimental set-up, preliminary experiments as checking leakage and evaluating the radon effective diffusion coefficient in gas phase were performed. And an analytical method which evaluates the effective diffusion coefficient in a short time was discussed in this study. In general, experimental method for evaluating the effective diffusion coefficient is classified in a steady state method and a transient method. The transient method can evaluate the effective diffusion coefficient in a short time, however, it is very difficult to reach the analytical solution because two independent variables (time and position) have to be treated at the same time. In this study
Moisture in Self-levelling Flooring Compounds. Part I. Water Vapour Diffusion Coefficients
Anderberg, Anders; Wadsö, Lars
2004-01-01
Diffusion coefficients of three self-levelling flooring compounds (SLC) and water vapour resistance of a primer have been measured with the cup method. The results show that the diffusion coefficient is dependent not only on the vapour content (relative humidity), but also on the absolute moisture content, i.e., there is a hysteresis effect on moisture transport. At RH lower than approximately 90 %, SLC have higher diffusion coefficients than a standard concrete (w/c 0.7 OPC), but the opposit...
Digital Repository Service at National Institute of Oceanography (India)
Jyothi, D.; Murty, T.V.R.; Sarma, V.V.; Rao, D.P.
of Marine Sciences Vol. 29, June 2000, pp. 185-187 Short Communication Computation of diffusion coefficients for waters of Gauthami Godavari estuary using one-dimensional advection-diffusion model D Jyothi, T V Ramana Murty, V V Sarma & D P Rao National.... - Jan.) Y2(x) = 8.55283 x + 17.5469 (Jan. - April) These equations would be more useful to get diffusion coefficients for any point along the channel axis, which in turn, helps to compute the concentration of pollutant along the axis of estuary. Thus...
Optimal estimation of diffusion coefficients from single-particle trajectories
DEFF Research Database (Denmark)
Vestergaard, Christian L.; Blainey, Paul C.; Flyvbjerg, Henrik
2014-01-01
substrate, the CVE is biased by substrate motion. However, given some long time series and a substrate under some tension, an extended MLE can separate particle diffusion on the substrate from substrate motion in the laboratory frame. This provides benchmarks that allow removal of bias caused by substrate...
Tripathi, A. K.; Singhal, R. P.; Khazanov, G. V.; Avanov, L. A.
2016-04-01
Electron pitch angle (Dαα) and momentum (Dpp) diffusion coefficients have been calculated due to resonant interactions with electrostatic electron cyclotron harmonic (ECH) and whistler mode chorus waves. Calculations have been performed at two spatial locations L = 4.6 and 6.8 for electron energies ≤10 keV. Landau (n = 0) resonance and cyclotron harmonic resonances n = ±1, ±2, … ±5 have been included in the calculations. It is found that diffusion coefficient versus pitch angle (α) profiles show large dips and oscillations or banded structures. The structures are more pronounced for ECH and lower band chorus (LBC) and particularly at location 4.6. Calculations of diffusion coefficients have also been performed for individual resonances. It is noticed that the main contribution of ECH waves in pitch angle diffusion coefficient is due to resonances n = +1 and n = +2. A major contribution to momentum diffusion coefficients appears from n = +2. However, the banded structures in Dαα and Dpp coefficients appear only in the profile of diffusion coefficients for n = +2. The contribution of other resonances to diffusion coefficients is found to be, in general, quite small or even negligible. For LBC and upper band chorus waves, the banded structures appear only in Landau resonance. The Dpp diffusion coefficient for ECH waves is one to two orders smaller than Dαα coefficients. For chorus waves, Dpp coefficients are about an order of magnitude smaller than Dαα coefficients for the case n ≠ 0. In case of Landau resonance, the values of Dpp coefficient are generally larger than the values of Dαα coefficients particularly at lower energies. As an aid to the interpretation of results, we have also determined the resonant frequencies. For ECH waves, resonant frequencies have been estimated for wave normal angle 89° and harmonic resonances n = +1, +2, and +3, whereas for whistler mode waves, the frequencies have been calculated for angle 10° and Landau
Determination of the concentration dependent diffusion coefficient of nitrogen in expanded austenite
DEFF Research Database (Denmark)
Christiansen, Thomas; Somers, Marcel A. J.
2008-01-01
The concentration dependent diffusion coefficient of nitrogen in expanded austenite was determined from of the rate of retracting nitrogen from thin initially N-saturated coupons. Nitrogen saturated homogeneous foils of expanded austenite were obtained by nitriding AISI 304 and AISI 316 in pure...... in the composition range where nitrogen can be extracted by hydrogen gas at the diffusion temperature. Numerical simulation of the denitriding experiments shows that the thus determined concentration dependent diffusion coefficients are an accurate approximation of the actual diffusivity of nitrogen in expanded...
EFFECTIVE DIFFUSION AND EFFECTIVE DRAG COEFFICIENT OF A BROWNIAN PARTICLE IN A PERIODIC POTENTIAL
Institute of Scientific and Technical Information of China (English)
Hongyun Wang
2011-01-01
We study the stochastic motion of a Brownian particle driven by a constant force over a static periodic potential.We show that both the effective diffusion and the effective drag coefficient are mathematically well-defined and we derive analytic expressions for these two quantities.We then investigate the asymptotic behaviors of the effective diffusion and the effective drag coefficient,respectively,for small driving force and for large driving force.In the case of small driving force,the effective diffusion is reduced from its Brownian value by a factor that increases exponentially with the amplitude of the potential.The effective drag coefficient is increased by approximately the same factor.As a result,the Einstein relation between the diffusion coefficient and the drag coefficient is approximately valid when the driving force is small.For moderately large driving force,both the effective diffusion and the effective drag coefficient are increased from their Brownian values,and the Einstein relation breaks down. In the limit of very large driving force,both the effective diffusion and the effective drag coefficient converge to their Brownian values and the Einstein relation is once again valid.
An atmospheric electrical method to determine the eddy diffusion coefficient
Indian Academy of Sciences (India)
M N Kulkarni; A K Kamra
2010-02-01
The ion–aerosol balance equations are solved to get the profiles of atmospheric electric parameters over the ground surface in an aerosol-rich environment under the conditions of surface radioactivity. Combining the earlier results for low aerosol concentrations and the present results for high aerosol concentrations, a relation is obtained between the average value of atmospheric electric space charge in the lowest ∼2m, the surface electric field and eddy diffusivity/aerosol concentration. The values of eddy diffusivity estimated from this method using some earlier measurements of space charge and surface electric field are in reasonably good agreement with those calculated from other standard methods using meteorological or electrical variables.
Leahy-Dios, Alana; Zhuo, Lin; Firoozabadi, Abbas
2008-05-22
New thermal diffusion coefficients of binary mixtures are measured for n-decane-n-alkanes and 1-methylnaphthalene-n-alkanes with 25 and 75 wt % at 25 degrees C and 1 atm using the thermogravitational column technique. The alkanes range from n-pentane to n-eicosane. The new results confirm the recently observed nonmonotonic behavior of thermal diffusion coefficients with molecular weight for binary mixtures of n-decane- n-alkanes at the compositions studied. In this work, the mobility and disparity effects on thermal diffusion coefficients are quantified for binary mixtures. We also show for the binary mixtures studied that the thermal diffusion coefficients and mixture viscosity, both nonequilibrium properties, are closely related. PMID:18438988
Study on the Diffusion Coefficient of Sodium Chloride at Infrinite Dilution in Supercritical Water
Institute of Scientific and Technical Information of China (English)
肖吉; 陆九芳; 陈健; 李以圭
2003-01-01
The molecular dynamics(MD) was employed to simulate the diffusion coefficient of sodium chloride at infinite dilution in supercritical water from 703.2K to 763.2K and from 30 MPa to 45 MPa ,Based on the simulated data and the Patel-Teja(PT) equation of state and the Liu-Ruckenstein equation,an equation for calculating the diffusion coefficient of NaCl at infinite dilution in supercritical water is proposed,Both the agreement between the simulated and correlated data,and that between the simulated and predicted data of diffusion coefficients for NaCl in supercritical water ranging from 703.2K to 803.2K and from 25 MPa to 50MPa show that this equation is applicable for calculation of diffusion coefficients.
Diffusion Coefficient when fine Aerosol Media Propagate in a Confined Volume
Korovina N.V.; Zharova I.K.; Kudryashova O.B.; Titov S.S.
2016-01-01
An experimental estimation is reported of the value of the effective diffusion coefficient during aerosol deposition in a confined volume. Aerosol propagation regularities have experimentally been studied in a chamber of a complex configuration with different placement of aerosol generators.
Akimoto, Takuma
2016-01-01
Local diffusion coefficients in living cells are highly heterogeneous and may change over time. Such a time-dependent and spatially heterogeneous environment results in irreproducibility of single-particle-tracking measurements. Here, we provide rigorous descriptions of equilibrium and non-equilibrium diffusion processes for a heterogeneous diffusion model in living cells. We give exact solutions for the mean square displacement (MSD) and the relative standard deviation of the time-averaged MSD for equilibrium and non-equilibrium situations. We find that the time-averaged MSD grows linearly with time and that the diffusion coefficients are intrinsically random in non-equilibrium situations. Our findings pave the way for a theoretical understanding of irreproducible diffusion coefficients in cell biology.
FITTING OF THE DATA FOR DIFFUSION COEFFICIENTS IN UNSATURATED POROUS MEDIA
Energy Technology Data Exchange (ETDEWEB)
B. Bullard
1999-05-01
The purpose of this calculation is to evaluate diffusion coefficients in unsaturated porous media for use in the TSPA-VA analyses. Using experimental data, regression techniques were used to curve fit the diffusion coefficient in unsaturated porous media as a function of volumetric water content. This calculation substantiates the model fit used in Total System Performance Assessment-1995 An Evaluation of the Potential Yucca Mountain Repository (TSPA-1995), Section 6.5.4.
Diffusion Decay Coefficient for Chloride Ions of Concrete Containing Mineral Admixtures
Jae-Im Park; Kwang-Myong Lee; Soon-Oh Kwon; Su-Ho Bae; Sang-Hwa Jung; Sung-Won Yoo
2016-01-01
The diffusion coefficient for chloride ions and the diffusion decay coefficient for chloride ions are essential variables for a service life evaluation of concrete structures. They are influenced by water-binder ratio, exposure condition, curing temperature, cement type, and the type and use of mineral admixture. Mineral admixtures such as ground granulated blast furnace slag, fly ash, and silica fume have been increasingly used to improve resistance against chloride ions penetration in concr...
Diffusion coefficients for LMFBR cells calculated with MOC and Monte Carlo methods
Energy Technology Data Exchange (ETDEWEB)
Rooijen, W.F.G. van, E-mail: rooijen@u-fukui.ac.j [Research Institute of Nuclear Energy, University of Fukui, Bunkyo 3-9-1, Fukui-shi, Fukui-ken 910-8507 (Japan); Chiba, G., E-mail: chiba.go@jaea.go.j [Japan Atomic Energy Agency, 2-4 Shirakata Shirane, Tokai-mura, Naka-gun, Ibaraki-ken 319-1195 (Japan)
2011-01-15
The present work discusses the calculation of the diffusion coefficient of a lattice of hexagonal cells, with both 'sodium present' and 'sodium absent' conditions. Calculations are performed in the framework of lattice theory (also known as fundamental mode approximation). Unlike the classical approaches, our heterogeneous leakage model allows the calculation of diffusion coefficients under all conditions, even if planar voids are present in the lattice. Equations resulting from this model are solved using the method of characteristics (MOC). Independent confirmation of the MOC result comes from Monte Carlo calculations, in which the diffusion coefficient is obtained without any of the assumptions of lattice theory. It is shown by comparison to the Monte Carlo results that the MOC solution yields correct values of the diffusion coefficient under all conditions, even in cases where the classic calculation of the diffusion coefficient fails. This work is a first step in the development of a robust method to calculate the diffusion coefficient of lattice cells. Adoption into production codes will require more development and validation of the method.
Diffusion Decay Coefficient for Chloride Ions of Concrete Containing Mineral Admixtures
Directory of Open Access Journals (Sweden)
Jae-Im Park
2016-01-01
Full Text Available The diffusion coefficient for chloride ions and the diffusion decay coefficient for chloride ions are essential variables for a service life evaluation of concrete structures. They are influenced by water-binder ratio, exposure condition, curing temperature, cement type, and the type and use of mineral admixture. Mineral admixtures such as ground granulated blast furnace slag, fly ash, and silica fume have been increasingly used to improve resistance against chloride ions penetration in concrete structures built in an offshore environment. However, there is not enough measured data to identify the statistical properties of diffusion decay coefficient for chloride ions in concrete using mineral admixtures. This paper is aimed at evaluating the diffusion decay coefficient for chloride ions of concrete using ordinary Portland cement or blended cement. NT BUILD 492 method, an electrophoresis experiment, was used to measure the diffusion coefficient for chloride ions with ages. It was revealed from the test results that the diffusion decay coefficient for chloride ions was significantly influenced by W/B and the replacement ratio of mineral admixtures.
Institute of Scientific and Technical Information of China (English)
LI Pengping; SU Dagen; WANG Shengnian; FAN Zhihong
2011-01-01
The influence of binder composition and pore structure of concrete on chloride diffusion coefficient in concrete were investigated by the natural immersion test, MIP test, SEM and EDS test, respectively. The experimental results showed that the effect of binder composition on chloride diffusion coefficient was the comprehensive result of concrete pore structure and binder hydration products, and the porosity and pore size distribution were the main factors that influence the changes of diffusion coefficient. The chloride diffusion coefficient decreased with increasing the curing temperature and the relative humidity. The hydration degree were promoted by improving curing temperatures, and then the porosity of concrete decreased and the proportion of gel pore and transitional pore increased, respectively. But the water evaporation decreased with increasing the relative humidity and then decreased porosity and increased the proportion of gel pore and transitional pore. Additionally, The chloride diffusion coefficient of concrete got the lower value when the appropriate replacement of fly ash in the ranges of 10%-20%, when the double-adding fly ash and slag content was 50%. The porosity increased and the ratio of C/S in C-S-H decreased with further increasing the fly ash content, which led to increase the chloride diffusion coefficient in concrete.
Renslow, Ryan S.; Majors, Paul D.; McLean, Jeffrey S.; Jim K. Fredrickson; Ahmed, Bulbul; Beyenal, Haluk
2010-01-01
Diffusive mass transfer in biofilms is characterized by the effective diffusion coefficient. It is well-documented that the effective diffusion coefficient can vary by location in a biofilm. The current literature is dominated by effective diffusion coefficient measurements for distinct cell clusters and stratified biofilms showing this spatial variation. Regardless of whether distinct cell clusters or surface-averaging methods are used, position-dependent measurements of the effective diffus...
Institute of Scientific and Technical Information of China (English)
Wu Qiong; Li Shu-Suo; Ma Yue; Gong Sheng-Kai
2012-01-01
The diffusion coefficients of several alloying elements (Al,Mo,Co,Ta,Ru,W,Cr,Re) in Ni are directly calculated using the five-frequency model and the first principles density functional theory.The correlation factors provided by the five-frequency model are explicitly calculated.The calculated diffusion coefficients show their excellent agreement with the available experimental data.Both the diffusion pre-factor (Do) and the activation energy (Q) of impurity diffusion are obtained.The diffusion coefficients above 700 K are sorted in the following order:DAl ＞ DCr ＞ DCo ＞ DTa ＞DMo ＞ DRu ＞ DW ＞ DRe.It is found that there is a positive correlation between the atomic radius of the solute and the jump energy of Ni that results in the rotation of the solute-vacancy pair (E1).The value of E2-E1 (E2 is the solute diffusion energy) and the correlation factor each also show a positive correlation.The larger atoms in the same series have lower diffusion activation energies and faster diffusion coefficients.
International Nuclear Information System (INIS)
We discuss the role of the dynamic Oseen tensor in setting the time scales involved in the scaling of the time-dependent self-diffusion coefficient measured by diffusing wave spectroscopy. We elucidate the paradoxical short time behavior for which scaling is observed and clarify the possible discrepancies between theory and experiments
Evaluation of diffusion coefficients from composition profiles - the influence of trapping
DEFF Research Database (Denmark)
Christiansen, Thomas; Somers, Marcel A. J.
2006-01-01
The applicability of the Boltzmann-Matano method for evaluation of a diffusion coefficient and its concentration dependency by line profile analysis is tested on three different (model) systems. All systems involve interstitial diffusion. It is shown that the occurrence of trapping corrupts...
Imel, Adam; Miller, Brad; Holley, Wade; Baskaran, Durairaj; Mays, Jimmy; Dadmun, Mark
2015-03-01
The diffusion properties of nanoparticles in polymer nanocomposites are largely unknown and depend intimately on the dispersion of the nanoparticles. We examine the diffusion of soft, organic nanoparticles, which disperse in a polymer matrix due to the interpenetration of polymer chains and particles and the reduction in the depletion of entropy in the system. The impact of the presence of soft nanoparticles on the diffusion coefficient of polystyrene chains has recently been determined with neutron reflectivity. This was completed by monitoring the interdiffusion of deuterated and protonated polystyrene nanocomposite bilayers with and without the soft nanoparticles dispersed throughout both layers and extracting the diffusion coefficient from the one-dimensional solution to Fick's second law of diffusion. In this work, we extend this method to bilayer systems with only the soft nanoparticles as one of the layers and a linear deuterated polystyrene as an adjacent layer. The development of this method allows us to determine the tracer diffusion coefficient of the soft polystyrene nanoparticles for the first time by analyzing the mutual diffusion coefficient from Fick's second law and the fast and slow modes theories for diffusion.
Institute of Scientific and Technical Information of China (English)
Xin-yu Lai; Nan-rong Zhao
2013-01-01
Time-dependent diffusion coefficient and conventional diffusion constant are calculated and analyzed to study diffusion of nanoparticles in polymer melts.A generalized Langevin equation is adopted to describe the diffusion dynamics.Mode-coupling theory is employed to calculate the memory kernel of friction.For simplicity,only microscopic terms arising from binary collision and coupling to the solvent density fluctuation are included in the formalism.The equilibrium structural information functions of the polymer nanocomposites required by mode-coupling theory are calculated on the basis of polymer reference interaction site model with Percus-Yevick closure.The effect of nanoparticle size and that of the polymer size are clarified explicitly.The structural functions,the friction kernel,as well as the diffusion coefficient show a rich variety with varying nanoparticle radius and polymer chain length.We find that for small nanoparticles or short chain polymers,the characteristic short time non-Markov diffusion dynamics becomes more prominent,and the diffusion coefficient takes longer time to approach asymptotically the conventional diffusion constant.This constant due to the microscopic contributions will decrease with the increase of nanoparticle size,while increase with polymer size.Furthermore,our result of diffusion constant from modecoupling theory is compared with the value predicted from the Stokes-Einstein relation.It shows that the microscopic contributions to the diffusion constant are dominant for small nanoparticles or long chain polymers.Inversely,when nanonparticle is big,or polymer chain is short,the hydrodynamic contribution might play a significant role.
Calculation of the coefficient and dynamics of water diffusion in graphite joints
Institute of Scientific and Technical Information of China (English)
WANG Jun; LIU Wen-bin
2006-01-01
The coefficient and dynamics of water diffusion in adhesive-graphite joints were calculated insitu with energy dispersive X-ray (EDX) analysis, a method that is significantly simpler than elemental analysis. Water diffusion coefficient and dynamics of adhesive-graphite joints treated by different surface treatment methods were also investigated. Calculation results indicated that the water diffusion rate in adhesive-graphite joints treated by sandpaper was higher than that treated by chemical oxidation or by silane couple agent. Also the durability of graphite joints treated by coupling agent is superior to that treated by chemical oxidation or sandpaper burnishing.
Measurement of the Ar diffusion coefficient in graphite at high temperature by the ISOL method
Energy Technology Data Exchange (ETDEWEB)
Eleon, C. [Grand Accelerateur National d' Ions Lourds, CEA/DSM CNRS/IN2P3, 14076 Caen (France); Jardin, P. [Grand Accelerateur National d' Ions Lourds, CEA/DSM CNRS/IN2P3, 14076 Caen (France)], E-mail: Jardin@ganil.fr; Thomas, J.C.; Saint-Laurent, M.-G.; Huet-Equilbec, C.; Alves Conde, R. [Grand Accelerateur National d' Ions Lourds, CEA/DSM CNRS/IN2P3, 14076 Caen (France); Angelique, J.C. [Laboratoire de Physique Subatomique et de Cosmologie, 38026 Grenoble (France); Laboratoire de Physique Corpusculaire, ISMRA, 14050 Caen (France); Boilley, D.; Cornell, J.; Dubois, M. [Grand Accelerateur National d' Ions Lourds, CEA/DSM CNRS/IN2P3, 14076 Caen (France); Franberg, H. [Paul Scherrer Institute, 5232 Villigen PSI (Switzerland); ISOLDE, CERN, 1211 Geneve 23 (Switzerland); Gaubert, G.; Jacquot, B. [Grand Accelerateur National d' Ions Lourds, CEA/DSM CNRS/IN2P3, 14076 Caen (France); Koester, U. [ISOLDE, CERN, 1211 Geneve 23 (Switzerland); Institut Laue Langevin, 38042 Grenoble (France); Leroy, R. [Grand Accelerateur National d' Ions Lourds, CEA/DSM CNRS/IN2P3, 14076 Caen (France); Maunoury, L. [Centre Interdisciplinaire de Recherche Ion Laser, 14070 Caen (France); Orr, N. [Laboratoire de Physique Corpusculaire, ISMRA, 14050 Caen (France); Pacquet, J.Y.; Pellemoine, F.; Stodel, C. [Grand Accelerateur National d' Ions Lourds, CEA/DSM CNRS/IN2P3, 14076 Caen (France)] (and others)
2008-10-15
This work has been carried out at GANIL within the ambit of the TARGISOL European collaboration which aims to study the relevant variables governing the release of radioactive elements from targets in an ISOL system. This work shows how it has been possible to extract diffusion coefficients for {sup 35}Ar atoms diffusing out of graphite targets from release time measurements by using an analytic description of the release times. The diffusion coefficients and efficiencies are presented and compared with results obtained using a 'continuous' method.
Temperature-Dependent Diffusion Coefficients from ab initio Computations: Hydrogen in Nickel
Energy Technology Data Exchange (ETDEWEB)
E Wimmer; W Wolf; J Sticht; P Saxe; C Geller; R Najafabadi; G Young
2006-03-16
The temperature-dependent mass diffusion coefficient is computed using transition state theory. Ab initio supercell phonon calculations of the entire system provide the attempt frequency, the activation enthalpy, and the activation entropy as a function of temperature. Effects due to thermal lattice expansion are included and found to be significant. Numerical results for the case of hydrogen in nickel demonstrate a strong temperature dependence of the migration enthalpy and entropy. Trapping in local minima along the diffusion path has a pronounced effect especially at low temperatures. The computed diffusion coefficients with and without trapping bracket the available experimental values over the entire temperature range between 0 and 1400 K.
Modeling diffusion coefficients in binary mixtures of polar and non-polar compounds
DEFF Research Database (Denmark)
Medvedev, Oleg; Shapiro, Alexander
2005-01-01
The theory of transport coefficients in liquids, developed previously, is tested on a description of the diffusion coefficients in binary polar/non-polar mixtures, by applying advanced thermodynamic models. Comparison to a large set of experimental data shows good performance of the model. Only...... four temperature-independent parameters are required in order to describe the behavior of diffusion coefficients at different temperatures. The physical meaning of the parameters is analyzed. This makes it possible to reduce further their number to just two parameters for described mixtures with polar...
Dorval, Eric
2016-01-01
Neutron transport calculations by Monte Carlo methods are finding increased application in nuclear reactor simulations. In particular, a versatile approach entails the use of a 2-step pro-cedure, with Monte Carlo as a few-group cross section data generator at lattice level, followed by deterministic multi-group diffusion calculations at core level. In this thesis, the Serpent 2 Monte Carlo reactor physics burnup calculation code is used in order to test a set of diffusion coefficient model...
Directory of Open Access Journals (Sweden)
L. W. Somathilake
2005-01-01
Full Text Available We deal with a mathematical model for a four-component chemical reaction-diffusion process. The model is described by a system of strongly coupled reaction-diffusion equations with different diffusion rates. The existence of the global solution of this reaction-diffusion system in unbounded domain is proved by using semigroup theory and estimates on the growth of solutions.
Diffusion Coefficient and Electric Field Studies for HSX using Monte Carlo Methods
Gerhardt, S. P.; Talmadge, J. N.
1999-11-01
The HSX experiment has a magnetic field spectrum which closely approximates helical symmetry. Never the less, symmetry breaking terms are present which lead to asymmetric diffusion. Models for the asymmetric component of the monoenergetic diffusion coefficient are unable to account for all the terms in the HSX magnetic spectrum and the functional dependence on the radial electric field (Er). To model the diffusion coefficient as a function of Er and collisionality, Monte Carlo simulations have been made for different values of Er and background density. These results are fit to analytic models for the diffusion coefficient. Enforcing ambipolarity on these fluxes can lead to a calculation of the stellarator Er. To measure Er, we will use a spectroscopic system to measure impurity flow. A 1-meter spectrometer with a CCD detector has been purchased for this purpose; a LabVIEW control system has been implemented and collection optics designed. Details of the spectroscopic system will be presented.
Dense fluid self-diffusion coefficient calculations using perturbation theory and molecular dynamics
Directory of Open Access Journals (Sweden)
COELHO L. A. F.
1999-01-01
Full Text Available A procedure to correlate self-diffusion coefficients in dense fluids by using the perturbation theory (WCA coupled with the smooth-hard-sphere theory is presented and tested against molecular simulations and experimental data. This simple algebraic expression correlates well the self-diffusion coefficients of carbon dioxide, ethane, propane, ethylene, and sulfur hexafluoride. We have also performed canonical ensemble molecular dynamics simulations by using the Hoover-Nosé thermostat and the mean-square displacement formula to compute self-diffusion coefficients for the reference WCA intermolecular potential. The good agreement obtained from both methods, when compared with experimental data, suggests that the smooth-effective-sphere theory is a useful procedure to correlate diffusivity of pure substances.
An improved method for measuring the surface sound energy diffusion coefficient in a room
Institute of Scientific and Technical Information of China (English)
ZHANG Jiping; WU Shuoxian; LI Ningrong
2003-01-01
The partly specular reflection and partly diffusion reflection model is a convenientway to express the phenomena of surface sound energy scattering in room acoustics. Soundenergy diffusion coefficient becomes a key factor to study surface scattering. But there havebeen very few methods for determining the average sound energy diffusion coefficient. Vorlanderproposed such an easy one based on the correlation principle. However, his method ignoredthe correlation from direct sound, in which defect is present. A new approximate method forcalculating sound energy diffusion coefficient, including direct sound and first strong reflectionsis presented. Therefore, Vorlander's defect is overcome. In addition, with the aid of digitalmeasuring technology, a relevant measuring system was developed. The experiment resultshows that the method is improved than Vorlander's.
Effect of Low Diffusion Coefficient on Eutectic Instability of Al-25 wt%Sm Alloy
Institute of Scientific and Technical Information of China (English)
WANG Nan
2008-01-01
Diffusion coefficient decides the solute diffusion length and is a critical parameter in the selection of microstructure scales and in governing microstructure transitions. Al-25 wt% Sm alloy is selected to reveal the impact of low diffusion coefficient on the eutectic instability, and the results are compared with those of Al-Cu alloys.Laser remelting experiments are performed and the transition growth velocity from eutectic to α-Al dendrite is examined. Compared with Al-Cu alloys, the eutectic instability takes place at a velocity more than one order of magnitude smaller. The theoretical calculation by the Trivedi-Magnin- Kurz (TMK) model also predicts that the eutectic will become instable at smaller growth velocity for Al-Sm alloy than Al-Cu alloy, which is ascribed to the low diffusion coefficient.
Mass-dependence of self-diffusion coefficients in disparate-mass binary fluid mixtures
Directory of Open Access Journals (Sweden)
I. Binas
2009-01-01
Full Text Available Self-diffusion coefficients of a binary fluid mixture with components differing only in their particle masses are studied, in particular the case when mass ratio μ of light and heavy particles tends to zero. These coefficients were calculated within the memory function formalism, using the systematic subsequence of approximations for the relaxation times of velocity autocorrelation function. We obtained a general relation for the self-diffusion coefficients which show polynomial dependence on the mass ratio μ. The obtained expression has a correct Brownian limit. We developed the hierarchy of approximations for the self-diffusion coefficients that tends to an exact result from above and below when the order of approximations increases.
Directory of Open Access Journals (Sweden)
Franco Marinozzi
2014-01-01
Full Text Available We firstly measured the swelling of single trabeculae from human femur heads during water imbibition. Since the swelling is caused by water diffusing from external surfaces to the core of the sample, by measuring the sample swelling over time, we obtained direct information about the transport of fluids through the intimate constituents of bone, where the mineralization process takes place. We developed an apparatus to measure the free expansion of the tissue during the imbibition. In particular, we measured the swelling along three natural axes (length L, width W, and thickness T of plate-like trabeculae. For this aim, we developed a 3D analytical model of the water uptake by the sample that was performed according to Fickian transport mechanism. The results were then utilized to predict the swelling over time along the three sample directions (L, W, T and the apparent diffusion coefficients DT, DW, and DL.
DEFF Research Database (Denmark)
Jespersen, Sune Nørhøj; Lundell, Henrik; Sønderby, Casper Kaae;
2013-01-01
Pulsed field gradient diffusion sequences (PFG) with multiple diffusion encoding blocks have been indicated to offer new microstructural tissue information, such as the ability to detect nonspherical compartment shapes in macroscopically isotropic samples, i.e. samples with negligible directional...... signal dependence on diffusion gradients in standard diffusion experiments. However, current acquisition schemes are not rotationally invariant in the sense that the derived metrics depend on the orientation of the sample, and are affected by the interplay of sampling directions and compartment...... orientation dispersion when applied to macroscopically anisotropic systems. Here we propose a new framework, the d-PFG 5-design, to enable rotationally invariant estimation of double wave vector diffusion metrics (d-PFG). The method is based on the idea that an appropriate orientational average of the signal...
Determination of diffusion coefficients by quantitative evaluation of X-ray fluorescence
International Nuclear Information System (INIS)
A nondestructive method has been developed to follow changes of concentration caused by diffusion in small samples, using a micro-beam analyser. An advanced mathematical procedure was applied to evaluate directly curves of changing intensity of fluorescent radiation along the diffusion path. Experimental results of diffusion of sulphur in liquid iron served as an example. It has been proved that the experimental curves follow the shape of theoretical Gaussian curve with probabilities far exceeding the usually considered level of 0.05. The length of diffusion paths has been determined with highest possible accuracy by minimizing differences of measured and theoretical values with X2 function. Thus it was possible to apply second Fick's law for determination of diffusion coefficients of sulphur in liquid iron at temperatures from 1773 to 19230K. The proposed method can be generally applied to any diffusion systems suitable for examination under the electron beam microanalyser. The mathematical procedure given, enables to determine diffusion coefficients on very small samples and there is no need to know the absolute values of concentrations of the diffusing element along the diffusion path. The only results needed are the relative changes of concentration along the diffusion path. (author)
Albedo-adjusted fast-neutron diffusion coefficients in reactor reflectors
International Nuclear Information System (INIS)
In the newer, larger pressurized-water reactor cores, the calculated power distributions are fairly sensitive to the number of neutron groups used and to the treatment of the reflector cross sections. Comparisons between transport and diffusion calculations show that the latter substantially underpredict the reflector albedos in the fast (top) group and that the power distribution is shifted toward the core center when compared to 4-group transport theory results. When the fast-neutron diffusion coefficients are altered to make the transport- and diffusion-theory albedos agree, the power distributions are also brought into agreement. An expression for the fast-neutron diffusion coefficients in reflector regions has been derived such that the diffusion calculation reproduces the albedo obtained from a transport solution. In addition, a correction factor for mesh effects applicable to coarse mesh problems is presented. The use of the formalism gives the correct albedos and improved power distributions. (U.S.)
Rapid yet accurate measurement of mass diffusion coefficients by phase shifting interferometer
Guo Zhi Xiong; Komiya, A
1999-01-01
The technique of using a phase-shifting interferometer is applied to the study of diffusion in transparent liquid mixtures. A quick method is proposed for determining the diffusion coefficient from the measurements of the location of fringes on a grey level picture. The measurement time is very short (within 100 s) and a very small transient diffusion field can be observed and recorded accurately with a rate of 30 frames per second. The measurement can be completed using less than 0.12 cc of solutions. The influence of gravity on the measurement of the diffusion coefficient is eliminated in the present method. Results on NaCl-water diffusion systems are presented and compared with the reference data. (author)
Energy Technology Data Exchange (ETDEWEB)
Bretscher, M.M.
1984-01-01
Simple diffusion theory cannot be used to evaluate control rod worths in thermal neutron reactors because of the strongly absorbing character of the control material. However, reliable control rod worths can be obtained within the framework of diffusion theory if the control material is characterized by a set of mesh-dependent effective diffusion parameters. For thin slab absorbers the effective diffusion parameters can be expressed as functions of a suitably-defined pair of blackness coefficients. Methods for calculating these blackness coefficients in the P/sub 1/, P/sub 3/, and P/sub 5/ approximations, with and without scattering, are presented. For control elements whose geometry does not permit a thin slab treatment, other methods are needed for determining the effective diffusion parameters. One such method, based on reaction rate ratios, is discussed.
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
4 new model, phase equilibrium-kinetics model (PEKM), for estimation of diffusioncoefficient was proposed in this paper. Kinetic experiments of phenol desorption on NKAII resin inthe presence and the absence of ultrasound were separately conducted, and diffusion coefficients ofphenol within an adsorbent particle were estimated by means of proposed PEKM and classicsimplified model. Results show that the use of ultrasound not only changes the phase equilibriumstate of NKAll resin/phenol/water system which had been equilibrium at normal condition, but alsoenhances diffusion of phenol within the resin. The diffusion coefficient of phenol in the resin in thefield of ultrasound increases in an order of magnitude in comparison with the diffusion coefficientdetermined under no ultrasound Experimental results also indicated that the diffusion coefficientsestimated by PEKM were more accurate than that estimated by the classic simplified model.
RELATION BETWEEN DYNAMIC LOSS MODULUS AND DIFFUSION COEFFICIENT IN A MODIFIED PET FIBER
Institute of Scientific and Technical Information of China (English)
YU Jianming
1994-01-01
The mobility of polymer chain segments is shown to play a major role in the diffusion of disperse dyes in a copolymerization modified PET system, monoepoxy compound CH3(CH2)3OCH2CH-CH2/O modified PET.The rate of dye diffusion (diffusion coefficient D) has been related to the time-dependent mechanical property, dynamic loss modulus E", which is controlled by the mobility of chain segments. In this modified copolyester system, the variance of amount of modifier in the copolyester fibers causes the change in disperse dye diffusion coefficient to fiber, and in the dynamic loss modulus of the fibers ,but the relationship between the diffusion and the dynamic loss modulus is in agreement with the theoretical relation derived by Bell and Dumbleton. The relation obtained in this paper is:Ln D =- 2.28Ln E"+26.81
Rafelski, Susanne M.; Keller, Lani C.; Alberts, Jonathan B.; Marshall, Wallace F
2011-01-01
The degree to which diffusion contributes to positioning cellular structures is an open question. Here we investigate the question of whether diffusive motion of centrin granules would allow them to interact with the mother centriole. The role of centrin granules in centriole duplication remains unclear, but some proposed functions of these granules, for example in providing pre-assembled centriole subunits, or by acting as unstable “pre-centrioles” that need to be captured by the mother cent...
On the Diffusion Coefficient of Two-step Method for LWR analysis
Energy Technology Data Exchange (ETDEWEB)
Lee, Deokjung; Choi, Sooyoung [UNIST, Ulsan (Korea, Republic of); Smith, Kord S. [Massachusetts Institute of Technology, Cambridge (United States)
2015-10-15
The few-group constants including diffusion coefficients are generated from the assembly calculation results. Once the assembly calculation is done, the cross sections (XSs) are spatially homogenized, and a critical spectrum calculation is performed in order to take into account the neutron leakages of the lattice. The diffusion coefficient is also generated through the critical spectrum calculation. Three different methods of the critical spectrum calculation such as B1 method, P1 method, and fundamental mode (FM) calculation method are considered in this paper. The diffusion coefficients can also be affected by transport approximations for the transport XS calculation which is used in the assembly transport lattice calculation in order to account for the anisotropic scattering effects. The outflow transport approximation and the inflow transport approximation are investigated in this paper. The accuracy of the few group data especially the diffusion coefficients has been studied to optimize the combination of the transport correction methods and the critical spectrum calculation methods using the UNIST lattice physics code STREAM. The combination of the inflow transport approximation and the FM method is shown to provide the highest accuracy in the LWR core calculations. The methodologies to calculate the diffusion coefficients have been reviewed, and the performances of them have been investigated with a LWR core problem. The combination of the inflow transport approximation and the fundamental mode critical spectrum calculation shows the smallest errors in terms of assembly power distribution.
Institute of Scientific and Technical Information of China (English)
宋鲁光; 孙伟; 高建明
2015-01-01
The chloride apparent diffusion coefficients at different immersion time in slag with differ-ent curing ages were studied through natural immersion tests.The influence of the curing age on chlo-ride apparent diffusion coefficients was analyzed.And the apparent diffusion coefficient was consid-ered as the integral mean of the instantaneous diffusion coefficients during the testing period,and the obtained apparent diffusion coefficient was transferred to the instantaneous diffusion coefficients.The relationship between the curing age and the constant of time dependence of the instantaneous diffusion coefficient was derived.The experimental results show that the chloride apparent diffusion coefficient decreases with the increase of the curing age and the decrease rate slows down gradually.There is a power function relationship between the apparent diffusion coefficient and the curing age.The constant of time dependency of the instantaneous diffusion coefficient increases with the increase of the curing age and the increase rate slows down gradually.There is a square root relationship between the con-stant of time dependency of the instantaneous diffusion coefficient and the curing age.%利用自然浸泡试验，研究了不同养护龄期的矿渣混凝土在不同暴露时间下的氯离子表观扩散系数，分析了养护龄期对氯离子表观扩散系数的影响。将表观扩散系数看作暴露时间内即时扩散系数的积分平均值，将得到的表观扩散系数转换为即时扩散系数，推导出养护龄期与即时扩散系数时间依赖性常数的关系。结果表明，混凝土中氯离子表观扩散系数随着养护龄期的增加而减小，且减小幅度逐渐减缓；养护龄期与表观扩散系数成幂函数关系。即时扩散系数的时间依赖性常数随着养护龄期的增加而增加，且增加幅度逐渐减小；即时扩散系数时间依赖性常数与养护龄期符合平方根关系。
Nagy, Szilvia A; Horváth, Réka; Perlaki, Gábor; Orsi, Gergely; Barsi, Péter; John, Flóra; Horváth, Andrea; Kovács, Norbert; Bogner, Péter; Ábrahám, Hajnalka; Bóné, Beáta; Gyimesi, Csilla; Dóczi, Tamás; Janszky, József
2016-08-01
In mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS), structural abnormalities are present not only in the hippocampus but also in the white matter with ipsilateral predominance. Although the timing of epilepsy onset is commonly associated with clinical and semiological dissimilarities, limited data exist regarding white matter diffusion changes with respect to age at epilepsy onset. The aim of this study was to investigate diffusion changes in the white matter of patients with unilateral MTLE-HS with respect to clinical parameters and to compare them with an age- and sex-matched healthy control group. Apparent diffusion coefficients (ADCs) were derived using monoexponential approaches from 22 (11 early and 11 late age at onset) patients with unilateral MTLE-HS and 22 age- and sex-matched control subjects after acquiring diffusion-weighted images on a 3T MRI system. Data were analyzed using two-tailed t-tests and multiple linear regression models. In the group with early onset MTLE-HS, ADC was significantly elevated in the ipsilateral hemispheric (p=0.04) and temporal lobe white matter (p=0.01) compared with that in controls. These differences were not detectable in late onset MTLE-HS patients. Apparent diffusion coefficient of the group with early onset MTLE-HS was negatively related to age at epilepsy onset in the ipsilateral hemispheric white matter (p=0.03) and the uncinate fasciculus (p=0.03), while in patients with late onset MTLE-HS, ADC was no longer dependent on age at epilepsy onset itself but rather on the seizure frequency in the ipsilateral uncinate fasciculus (p=0.03). Such diffusivity pattern has been associated with chronic white matter degeneration, reflecting myelin loss and higher extracellular volume which are more pronounced in the frontotemporal regions and also depend on clinical features. In the group with early onset MTLE-HS, the timing of epilepsy seems to be the major cause of white matter abnormalities while in late
Tsapalov, Andrey; Gulabyants, Loren; Livshits, Mihail; Kovler, Konstantin
2014-04-01
The mathematical apparatus and the experimental installation for the rapid determination of radon diffusion coefficient in various materials are developed. The single test lasts not longer than 18 h and allows testing numerous materials, such as gaseous and liquid media, as well as soil, concrete and radon-proof membranes, in which diffusion coefficient of radon may vary in an extremely wide range, from 1·10(-12) to 5·10(-5) m(2)/s. The uncertainty of radon diffusion coefficient estimation depends on the permeability of the sample and varies from about 5% (for the most permeable materials) to 40% (for less permeable materials, such as radon-proof membranes).
Directory of Open Access Journals (Sweden)
Aleš Mráček
2010-02-01
Full Text Available The amorphous polymer film swelling in a liquid solvent below the glass transition temperature was characterized by a few kinetic parameters (especially the mutual diffusion coefficient of swelling and its mean value obtained by interference of monochromatic light in the wedge arrangement. This interferometric method allows one to determine the concentration field in the swollen surface layer and consequently to compute the concentration-dependent diffusion coefficient. A software system developed at the Department of Physics and Material Engineering at TBU in Zlin has been used for the evaluation of the main kinetic parameters of the swelling process. The software can be used for the on-line analyses of interferograms during the swelling process. The main application outputs are the computation of the concentration profile, the concentration gradient, the mutual diffusion coefficient of the swelling by the solvent and its mean value.
Field-Scale Effective Matrix Diffusion Coefficient for FracturedRock: Results From Literature Survey
Energy Technology Data Exchange (ETDEWEB)
Zhou, Quanlin; Liu, Hui Hai; Molz, Fred J.; Zhang, Yingqi; Bodvarsson, Gudmundur S.
2005-03-28
Matrix diffusion is an important mechanism for solutetransport in fractured rock. We recently conducted a literature survey onthe effective matrix diffusion coefficient, Dem, a key parameter fordescribing matrix diffusion processes at the field scale. Forty fieldtracer tests at 15 fractured geologic sites were surveyed and selectedfor study, based on data availability and quality. Field-scale Dem valueswere calculated, either directly using data reported in the literature orby reanalyzing the corresponding field tracer tests. Surveyed dataindicate that the effective-matrix-diffusion-coefficient factor FD(defined as the ratio of Dem to the lab-scale matrix diffusioncoefficient [Dem]of the same tracer) is generally larger than one,indicating that the effective matrix diffusion coefficient in the fieldis comparatively larger than the matrix diffusion coefficient at therock-core scale. This larger value could be attributed to the manymass-transfer processes at different scales in naturally heterogeneous,fractured rock systems. Furthermore, we observed a moderate trend towardsystematic increase in the emDFmDDF value with observation scale,indicating that the effective matrix diffusion coefficient is likely tobe statistically scale dependent. The FD value ranges from 1 to 10,000for observation scales from 5 to 2,000 m. At a given scale, the FD valuevaries by two orders of magnitude, reflecting the influence of differingdegrees of fractured rock heterogeneity at different sites. In addition,the surveyed data indicate that field-scale longitudinal dispersivitygenerally increases with observation scale, which is consistent withprevious studies. The scale-dependent field-scale matrix diffusioncoefficient (and dispersivity) may have significant implications forassessing long-term, large-scale radionuclide and contaminant transportevents in fractured rock, both for nuclear waste disposal and contaminantremediation.
Salazar, Agustín; Fuente, Raquel; Apiñaniz, Estibaliz; Mendioroz, Arantza; Celorrio, R.
2011-08-01
The aim of this work is to analyze the ability of modulated photothermal radiometry to retrieve the thermal diffusivity and the optical absorption coefficient of layered materials simultaneously. First, we extend the thermal quadrupole method to calculate the surface temperature of semitransparent multilayered materials. Then, this matrix method is used to evaluate the influence of heat losses by convection and radiation, the influence of the use of thin paint layers on the accuracy of thermal diffusivity measurements, and the effect of lateral heat diffusion due to the use of Gaussian laser beams. Finally, we apply the quadrupole method to retrieve (a) the thermal contact resistance in glass stacks and (b) the thermal diffusivity and optical absorption coefficient depth profiles in heterogeneous materials with continuously varying physical properties, as is the case of functionally graded materials and partially cured dental resins.
Nagai, Shingo
2013-11-01
We report estimation of the effective diffusion coefficient of moisture through a barrier coating to develop an encapsulation technology for the thin-film electronics industry. This investigation targeted a silicon oxide (SiOx) film that was deposited on a plastic substrate by a large-process-area web coater. Using the finite difference method based on diffusion theory, our estimation of the effective diffusion coefficient of a SiOx film corresponded to that of bulk glass that was previously reported. This result suggested that the low diffusivities of barrier films can be obtained on a mass-production level in the factory. In this investigation, experimental observations and mathematical confirmation revealed the limit of the water vapor transmission rate on the single barrier coating.
Nasirabadi, P. Shojaee; Jabbari, M.; Hattel, J. H.
2016-06-01
Nowadays, many electronic systems are exposed to harsh conditions of relative humidity and temperature. Mass transport properties of electronic packaging materials are needed in order to investigate the influence of moisture and temperature on reliability of electronic devices. Polycarbonate (PC) is widely used in the electronics industry. Thus, in this work the water diffusion coefficient into PC is investigated. Furthermore, numerical methods used for estimation of the diffusion coefficient and their assumptions are discussed. 1D and 3D numerical solutions are compared and based on this, it is shown how the estimated value can be different depending on the choice of dimensionality in the model.
A New Method for the Calculation of Diffusion Coefficients with Monte Carlo
Dorval, Eric
2014-06-01
This paper presents a new Monte Carlo-based method for the calculation of diffusion coefficients. One distinctive feature of this method is that it does not resort to the computation of transport cross sections directly, although their functional form is retained. Instead, a special type of tally derived from a deterministic estimate of Fick's Law is used for tallying the total cross section, which is then combined with a set of other standard Monte Carlo tallies. Some properties of this method are presented by means of numerical examples for a multi-group 1-D implementation. Calculated diffusion coefficients are in general good agreement with values obtained by other methods.
Self-diffusion coefficient of Na+ ions in Nafion-117 from radioactive tracer measurements
International Nuclear Information System (INIS)
The tracer self-diffusion coefficient of Na+ in Nafion-117 was measured using two different methodologies. The method based on the two parameters non-linear fit of experimental data with an analytical solution of Fick's second law was found to be simple and reliable. The value of tracer self-diffusion coefficient of Na+ in Nafion-117, obtained by this method (1.03 ± 0.07) x 10-6 cm2/sec, was in good agreement with other method based on Fick's first law. (author)
Quantum statistics of classical particles derived from the condition of free diffusion coefficient
Hoyuelos, Miguel
2016-01-01
We derive an equation for the current of particles in energy space; particles are subject to a mean field effective potential that may represent quantum effects. From the assumption that non-interacting particles imply a free diffusion coefficient in energy space we derive Maxwell-Boltzmann, Fermi-Dirac and Bose-Einstein statistics. Other new statistics are associated to a free diffusion coefficient; their thermodynamic properties are analyzed using the grand partition function. A negative relation between pressure and energy density for low temperatures can be derived, suggesting a possible connection with cosmological dark energy models.
Chemical diffusion coefficient of oxygen in thoria-urania mixed oxide
Matsui, Tsuneo; Naito, Keiji
1985-10-01
The chemical diffusion coefficients of oxygen ( D˜) in sintered samples of ( Th1- yUy) O2+ x ( y = 0.2 and 0.4) were measured by means of thermogravimetry in the temperature range 1282 ⩽ T ⩽ 1373 K. The defect diffusion coefficients ( Dd) were also calculated from the chemical diffusion coefficients obtained in this study. The activation energies of D˜ or Dd for the two samples ( Th1- yUy) O2+ xwithy = 0.2 and 0.4 were observed to be nearly the same, irrespective of the y value. These activation energies also nearly coincided with those of UO 2+x reported previously, suggesting the presence of a similar diffusion mechanism to that found in UO 2+x. The magnitude of both diffusion coefficients D˜ and Dd of ( Th1- yUy) O2+ x increased with increasing uranium content and approached that of UO 2+x. The increase of Dd of ( Th1- yUy) O2+ x with y value was considered to be due to the increase of both the vibrational frequency of lattice and the entropy change of migration produced by the substitution of a U ion for a Th ion.
FIELD-SCALE EFFECTIVE MATRIX DIFFUSION COEFFICIENT FOR FRACTURED ROCK:RESULTS FROM LITERATURE SURVEY
Energy Technology Data Exchange (ETDEWEB)
Q. Zhou; Hui-Hai Liu; F.J. Molz; Y. Zhang; G.S. Bodvarsson
2005-04-08
Matrix diffusion is an important mechanism for solute transport in fractured rock. We recently conducted a literature survey on the effective matrix diffusion coefficient, D{sub m}{sup e}, a key parameter for describing matrix diffusion processes at the field scale. Forty field tracer tests at 15 fractured geologic sites were surveyed and selected for the study, based on data availability and quality. Field-scale D{sub m}{sup e} values were calculated, either directly using data reported in the literature or by reanalyzing the corresponding field tracer tests. Surveyed data indicate that the effective-matrix-diffusion-coefficient factor F{sub D} (defined as the ratio of D{sub m}{sup e} to the lab-scale matrix diffusion coefficient [D{sub m}] of the same tracer) is generally larger than one, indicating that the effective matrix diffusion coefficient in the field is comparatively larger than the matrix diffusion coefficient at the rock-core scale. This larger value can be attributed to the many mass-transfer processes at different scales in naturally heterogeneous, fractured rock systems. Furthermore, we observed a moderate trend toward systematic increase in the F{sub D} value with observation scale, indicating that the effective matrix diffusion coefficient is likely to be statistically scale dependent. The F{sub D} value ranges from 1 to 10,000 for observation scales from 5 to 2,000 m. At a given scale, the F{sub D} value varies by two orders of magnitude, reflecting the influence of differing degrees of fractured rock heterogeneity at different sites. In addition, the surveyed data indicate that field-scale longitudinal dispersivity generally increases with observation scale, which is consistent with previous studies. The scale-dependent field-scale matrix diffusion coefficient (and dispersivity) may have significant implications for assessing long-term, large-scale radionuclide and contaminant transport events in fractured rock, both for nuclear waste disposal
Thermal Expansion and Diffusion Coefficients of Carbon Nanotube-Polymer Composites
Wei, Chenyu; Srivastava, Deepak; Cho, Kyeongjae
2002-01-01
Classical molecular dynamics (MD) simulations employing Brenner potential for intra-nanotube interactions and Van der Waals forces for polymer-nanotube interfaces are used to invetigate the thermal expansion and diffusion characteristics of carbon nanotube-polyethylene composites. Additions of carbon nanotubes to polymer matrix are found to increase the glass transition temperature Tg, and thermal expansion and diffusion coefficients in the composite above Tg. These findings could have implic...
Application of the Clustering Method in Molecular Dynamics Simulation of the Diffusion Coefficient
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
Using molecular dynamics (MD) simulation, the diffusion of oxygen, methane, ammonia and carbon dioxide in water was simulated in the canonical NVT ensemble, and the diffusion coefficient was analyzed by the clustering method. By comparing to the conventional method (using the Einstein model) and the differentiation-interval variation method, we found that the results obtained by the clustering method used in this study are more close to the experimental values. This method proved to be more reasonable than the other two methods.
Calculation of the effective diffusion coefficient during the drying of clay samples
Vasić Miloš; Radojević Zagorka; Grbavčić Željko
2012-01-01
The aim of this study was to calculate the effective diffusion coefficient based on experimentally recorded drying curves for two masonry clays obtained from different localities. The calculation method and two computer programs based on the mathematical calculation of the second Fick’s law and Cranck diffusion equation were developed. Masonry product shrinkage during drying was taken into consideration for the first time and the appropriate correction was entered into the calculation. ...
Directory of Open Access Journals (Sweden)
Shumanova M.V.
2015-03-01
Full Text Available The process fish salting has been studied by the method of photon correlation spectroscopy; the distribution of salt concentration in the solution and herring flesh with skin has been found, diffusion coefficients and salt concentrations used for creating a mathematical model of the salting technology have been worked out; the possibility of determination by this method the coefficient of dynamic viscosity of solutions and different media (minced meat etc. has been considered
Shumanova M.V.; Fatykhov Yu.A.; Shumanov V.A.
2015-01-01
The process fish salting has been studied by the method of photon correlation spectroscopy; the distribution of salt concentration in the solution and herring flesh with skin has been found, diffusion coefficients and salt concentrations used for creating a mathematical model of the salting technology have been worked out; the possibility of determination by this method the coefficient of dynamic viscosity of solutions and different media (minced meat etc.) has been considered
Conservation Laws and Exact Solutions for a Reaction-Diffusion Equation with a Variable Coefficient
Directory of Open Access Journals (Sweden)
Zhijie Cao
2014-01-01
Full Text Available In this paper a variable-coefficient reaction-diffusion equation is studied. We classify the equation into three kinds by different restraints imposed on the variable coefficient b(x in the process of solving the determining equations of Lie groups. Then, for each kind, the conservation laws corresponding to the symmetries obtained are considered. Finally, some exact solutions are constructed.
Energy Technology Data Exchange (ETDEWEB)
Ikonomov, Julian; Schmitz, Christoph H.; Sokolowski, Moritz [Institut fuer Physikalische und Theoretische Chemie, Universitaet Bonn, Wegelerstr. 12, 53115 Bonn (Germany)
2009-07-01
The diffusion of organic molecules on surfaces has so far been mostly investigated by molecule tracking using the video STM technique. This method requires small molecule coverages and small diffusion coefficients. Here we present a new technique suitable for higher temperatures and arbitrarily coverages based on the temporal increase in the tunneling current that occurs when a molecule diffuses under the STM tip. For our measurements, we have chosen the model system perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTCDA) on Ag(100). The PTCDA molecules form highly ordered two-dimensional islands surrounded by gas-like phase. In order to determine the diffusion coefficients, we used a continuum model to describe the diffusion of the molecules under the tip. Due to the finite size of the molecule it is even possible to obtain the spatial anisotropy of the diffusion coefficient. From the density of the peaks in the current-time spectra, one may in addition quantitatively estimate the tip-molecule interaction and the mean local coverage.
Jebaraj Johnley Muthuraj, Josiah
Cathodic protection is widely used for corrosion prevention. However, this process generates hydrogen at the protected metal surface, and diffusion of hydrogen through the metal may cause hydrogen embrittlement or hydrogen induced stress corrosion cracking. Thus the choice of a metal for use as fasteners depends upon its hydrogen uptake, permeation, diffusivity and trapping. The diffusivity of hydrogen through four high strength alloys (AISI 4340, alloy 718, alloy 686, and alloy 59) was analyzed by an electrochemical method developed by Devanathan and Stachurski. The effect of plasma nitriding and microstructure on hydrogen permeation through AISI 4340 was studied on six different specimens: as-received (AR) AISI 4340, nitrided samples with and without compound layer, samples quenched and tempered (Q&T) at 320° and 520°C, and nitrided samples Q&T 520°C. Studies on various nitrided specimens demonstrate that both the gamma'-Fe 4N rich compound surface layer and the deeper N diffusion layer that forms during plasma nitriding reduce the effective hydrogen diffusion coefficient, although the gamma'-Fe4N rich compound layer has a larger effect. Multiple permeation transients yield evidence for the presence of only reversible trap sites in as-received, Q&T 320 and 520 AISI 4340 specimens, and the presence of both reversible and irreversible trap sites in nitrided specimens. Moreover, the changes in microstructure during the quenching and tempering process result in a significant decrease in the diffusion coefficient of hydrogen compared to as-received specimens. In addition, density functional theory-based molecular dynamics simulations yield hydrogen diffusion coefficients through gamma'- Fe4N one order of magnitude lower than through α-Fe, which supports the experimental measurements of hydrogen permeation. The effect of microstructure and trapping was also studied in cold rolled, solutionized, and precipitation hardened Inconel 718 foils. The effective hydrogen
Variation of diffuse attenuation coefficient of downwelling irradiance in the Arctic Ocean
Institute of Scientific and Technical Information of China (English)
WANG Weibo; ZHAO Jinping
2014-01-01
The diffuse attenuation coefficient (Kd) for downwelling irradiance is calculated from solar irradiance data measured in the Arctic Ocean during 3rd and 4th Chinese National Arctic Research Expedition (CHINARE), including 18 stations and nine stations selected for irradiance profiles in sea water respectively. In this study, the variation of attenuation coefficient in the Arctic Ocean was studied, and the following results were ob-tained. First, the relationship between attenuation coefficient and chlorophyll concentration in the Arctic Ocean has the form of a power function. The best fit is at 443 nm, and its determination coefficient is more than 0.7. With increasing wavelength, the determination coefficient decreases abruptly. At 550 nm, it even reaches a value lower than 0.2. However, the exponent fitted is only half of that adapted in low-latitude ocean because of the lower chlorophyll-specific absorption in the Arctic Ocean. The upshot was that, in the case of the same chlorophyll concentration, the attenuation caused by phytoplankton chlorophyll in the Arctic Ocean is lower than in low-latitude ocean. Second, the spectral model, which exhibits the relationship of attenuation coefficients between 490 nm and other wavelength, was built and provided a new method to estimate the attenuation coefficient at other wavelength, if the attenuation coefficient at 490 nm was known. Third, the impact factors on attenuation coefficient, including sea ice and sea water mass, were discussed. The influence of sea ice on attenuation coefficient is indirect and is determined through the control of enter-ing solar radiation. The linear relationship between averaging sea ice concentration (ASIC, from 158 Julian day to observation day) and the depth of maximum chlorophyll is fitted by a simple linear equation. In addition, the sea water mass, such as the ACW (Alaskan Coastal Water), directly affects the amount of chlo-rophyll through taking more nutrient, and results in the
Bruining, J.; Fijnaut, H.M.
1975-01-01
We have obtained a rotational diffusion coefficient of the 70S ribosome isolated from Escherichia-coli (MRE-600), from the depolarized light scattering spectrum measured by photon correlation spectroscopy. The intensity correlation function of depolarized scattered light contains contributions due t
Fast and accurate measurement of diffusion coefficient by Taylor's dispersion analysis
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
This investigation aimed at improving the performance of Taylor's dispersion analysis for the fast and accurate measurement of diffusion coefficient of a minute solute in various solvents. The investigation was carried out on a capillary electrophoresis instrument by monitoring the UV absorption peak of a solute pulse and calculating the diffusion coefficient by peak efficiency. With L-phenylalanine as a main testing solute, some key factors were afterward disclosed including especially the capillary size, carrier flow velocity, injection volume and capillary conditioning. Peak tailing, large volume of sample injection and slow migration were found to underestimate the diffusion coefficient while very fast migration and high sample concentration caused overestimation. At a moderate flow velocity of 0.1―1 cm/s with a capillary of 72.44 μm I.D.×60 cm (50 cm effective) maintained at 25℃, the diffusion coefficient of aqueous L-phenylalanine was determined, giving a value of 7.02×10-6 cm2/s with error＜2% and relative standard deviation＜0.2% (n=3). The method was shown to be applicable to the measurement of various samples such as aqueous phenylalanine, acetone, phenol, toluene and benzene, and nonaqueous benzene (in ethanol or 1-butanol).
Energy Technology Data Exchange (ETDEWEB)
Wu, Tzi-Yi [Department of Chemistry, National Cheng Kung University, Tainan 701, Taiwan (China); Department of Polymer Materials, Kun Shan University, Tainan 71003, Taiwan (China); Su, Shyh-Gang [Department of Chemistry, National Cheng Kung University, Tainan 701, Taiwan (China); Wang, H. Paul [Department of Environmental Engineering, National Cheng Kung University, Tainan, Taiwan (China); Lin, Yuan-Chung [Institute of Environmental Engineering, National Sun Yat-Sen University, Kaohsiung 804, Taiwan (China); Gung, Shr-Tusen; Lin, Ming-Wei [Department of Chemistry, National Cheng Kung University, Tainan 701, Taiwan (China); Sun, I.-Wen, E-mail: iwsun@mail.ncku.edu.t [Department of Chemistry, National Cheng Kung University, Tainan 701, Taiwan (China)
2011-03-30
Research highlights: Cyclic ammonium-based ionic liquids with allyl substituent have high conductivity. Ionic liquids with allyl substituent have wide electrochemical window. Electrochemical and self diffusion coefficients are available for comparison. The Stokes-Einstein plots of DT{sup -1} vs. {eta}{sup -1} for redox couples in ILs are evaluated. Stokes-Einstein product of ferrocene is larger than that of cobaltocenium in ILs. - Abstract: Several cyclic ammonium-based ionic liquids (ILs) with allyl substituent are synthesized, these allyl substituent ILs have high ionic conductivity (up to 4.72 mS cm{sup -1} at 30 {sup o}C) and wide electrochemical window of 5 V. The electrochemical behaviors of two organometallic redox couples Fc/Fc{sup +} (ferrocene/ferrocenium) and Cc/Cc{sup +} (cobaltocene/cobaltocenium) have been studied in these ILs, the calculated Stokes-Einstein product (D{eta} T{sup -1}) of ferrocene in ILs is larger than that of cobaltocenium in ILs. The self-diffusion coefficients of cation and anion in these ILs are studied using pulsed gradient spin-echo NMR technique. There are very few reports where electrochemically derived diffusion coefficients and self diffusion coefficients are available for comparison, so a new key concept in electrochemistry could be developed in this paper.
Brilman, Derk W.F.; Swaaij, Wim P.M. van; Versteeg, Geert F.
2001-01-01
The diffusion coefficient and the physical solubility of isobutene and trans-2-butene in aqueous sulfuric acid solutions cannot be determined experimentally due to the occurrence of fast chemical reactions. In the present contribution these physicochemical parameters are estimated. For the solubilit
De Mezquia, D Alonso; Bou-Ali, M Mounir; Larrañaga, M; Madariaga, J A; Santamaría, C
2012-03-01
In this work we have measured the molecular diffusion coefficient of the n-alkane binary series nC(i)-nC(6), nC(i)-nC(10), and nC(i)-nC(12) at 298 K and 1 atm and a mass fraction of 0.5 by using the so-called sliding symmetric tubes technique. The results show that the diffusion coefficient at this concentration is proportional to the inverse viscosity of the mixture. In addition, we have also measured the diffusion coefficient of the systems nC(12)-nC(6), nC(12)-nC(7), and nC(12)-nC(8) as a function of concentration. From the data obtained, it is shown that the diffusion coefficient of the n-alkane binary mixtures at any concentration can be calculated from the molecular weight of the components and the dynamic viscosity of the corresponding mixture at 50% mass fraction. PMID:22263833
Spatial variation of eddy-diffusion coefficients in the turbulent plasma sheet during substorms
Directory of Open Access Journals (Sweden)
M. Stepanova
2009-04-01
Full Text Available Study of the plasma turbulence in the central plasma sheet was performed using the Interball-Tail satellite data. Fluctuations of the plasma bulk velocity in the plasma sheet were deduced from the measurements taken by the Corall instrument for different levels of geomagnetic activity and different locations inside the plasma sheet. The events that satisfied the following criteria were selected for analysis: number density 0.1–10 cm^{−3}, ion temperature T≥0.3 keV, and average bulk velocity ≤100 km/s. It was found that the plasma sheet flow generally appears to be strongly turbulent, i.e. is dominated by fluctuations that are unpredictable. Corresponding eddy-diffusion coefficients in Y- and Z-direction in the GSM coordinate system were derived using the autocorrelation time and rms velocity. Statistical studies of variation of the eddy-diffusion coefficients with the location inside the plasma sheet showed a significant increase in these coefficients in the tailward direction. During substorms this dependence shows strong increase of eddy-diffusion in the central part of the plasma sheet at the distances of 10–30 Earth's radii. This effect is much stronger for Y-components of the eddy-diffusion coefficient, which could be related to the geometry of the plasma sheet, allowing more room for development of eddies in this direction.
Calculation of the effective diffusion coefficient during the drying of clay samples
Directory of Open Access Journals (Sweden)
Vasić Miloš
2012-01-01
Full Text Available The aim of this study was to calculate the effective diffusion coefficient based on experimentally recorded drying curves for two masonry clays obtained from different localities. The calculation method and two computer programs based on the mathematical calculation of the second Fick’s law and Cranck diffusion equation were developed. Masonry product shrinkage during drying was taken into consideration for the first time and the appropriate correction was entered into the calculation. The results presented in this paper show that the values of the effective diffusion coefficient determined by the designed computer programs (with and without the correction for shrinkage have similar values to those available in the literature for the same coefficient for different clays. Based on the mathematically determined prognostic value of the effective diffusion coefficient, it was concluded that, whatever the initial mineralogical composition of the clay, there is 90% agreement of the calculated prognostic drying curves with the experimentally recorded ones. When a shrinkage correction of the masonry products is introduced into the calculation step, this agreement is even better.
Effective diffusion coefficients of gas mixture in heavy oil under constant-pressure conditions
Li, Huazhou Andy; Sun, Huijuan; Yang, Daoyong
2016-09-01
We develop a method to determine the effective diffusion coefficient for each individual component of a gas mixture in a non-volatile liquid (e.g., heavy oil) at high pressures with compositional analysis. Theoretically, a multi-component one-way diffusion model is coupled with the volume-translated Peng-Robinson equation of state to quantify the mass transfer between gas and liquid (e.g., heavy oil). Experimentally, the diffusion tests have been conducted with a PVT setup for one pure CO2-heavy oil system and one C3H8-CO2-heavy oil system under constant temperature and pressure, respectively. Both the gas-phase volume and liquid-phase swelling effect are simultaneously recorded during the measurement. As for the C3H8-CO2-heavy oil system, the gas chromatography method is employed to measure compositions of the gas phase at the beginning and end of the diffusion measurement, respectively. The effective diffusion coefficients are then determined by minimizing the discrepancy between the measured and calculated gas-phase composition at the end of diffusion measurement. The newly developed technique can quantify the contributions of each component of mixture to the bulk mass transfer from gas into liquid. The effective diffusion coefficient of C3H8 in the C3H8-CO2 mixture at 3945 ± 20 kPa and 293.85 K, i.e., 18.19 × 10^{ - 10} m^{ 2} / s, is found to be much higher than CO2 at 3950 ± 18 kPa and 293.85 K, i.e., 8.68 × 10^{ - 10} m^{ 2} / s. In comparison with pure CO2, the presence of C3H8 in the C3H8-CO2 mixture contributes to a faster diffusion of CO2 from the gas phase into heavy oil and consequently a larger swelling factor of heavy oil.
Poirier, David R.
2014-08-01
This article is a review of empirical and calculated data on density, viscosity, and diffusion coefficients in hypereutectic Al-Si liquid alloys. Many regressions of the data were effected in order to consolidate the data as functions, which can be used to calculate each property as a function of temperature and concentration of Si. The chemical diffusion coefficient in the alloys was derived based on the Sutherland model, which relates the diffusion coefficient to viscosity.
Ionization dynamics in ionic liquids probed via self-diffusion coefficient measurements
International Nuclear Information System (INIS)
Graphical abstract: - Highlights: • Exploiting non-Arrhenius nature of physiochemical properties of ionic liquids to understand ion dynamics. • Estimation of ion concentration in ionic liquids via self-diffusion coefficient measurements. • Thermodynamics of the ionization process in ionic liquids. • Thermodynamics of the self-diffusion of cations and anions through Arrhenius and Eyring equations. - Abstract: Ionic liquids contain ions and ion pairs with fast exchange between them. We propose a novel process to deduce the fraction of ions present in an ionic liquid and the equilibrium constants of ionization processes from measured ion self-diffusion coefficients using Pulsed Field Gradient (PFG) NMR. The enthalpy and entropy changes of ionization and ion self-diffusion processes are obtained for a series of ionic liquids using this method. These data were used to explain the interactions between cations and anions of ionic liquids. The interactions are also interpreted by the delocalization of the ion’s charge densities. The self-diffusion coefficients of cations and anions for measured ionic liquids are discussed
Ionization dynamics in ionic liquids probed via self-diffusion coefficient measurements
Energy Technology Data Exchange (ETDEWEB)
Mao, Yougang; Damodaran, Krishnan, E-mail: damodak@pitt.edu
2014-08-31
Graphical abstract: - Highlights: • Exploiting non-Arrhenius nature of physiochemical properties of ionic liquids to understand ion dynamics. • Estimation of ion concentration in ionic liquids via self-diffusion coefficient measurements. • Thermodynamics of the ionization process in ionic liquids. • Thermodynamics of the self-diffusion of cations and anions through Arrhenius and Eyring equations. - Abstract: Ionic liquids contain ions and ion pairs with fast exchange between them. We propose a novel process to deduce the fraction of ions present in an ionic liquid and the equilibrium constants of ionization processes from measured ion self-diffusion coefficients using Pulsed Field Gradient (PFG) NMR. The enthalpy and entropy changes of ionization and ion self-diffusion processes are obtained for a series of ionic liquids using this method. These data were used to explain the interactions between cations and anions of ionic liquids. The interactions are also interpreted by the delocalization of the ion’s charge densities. The self-diffusion coefficients of cations and anions for measured ionic liquids are discussed.
Spin--echo diffusion coefficients of water to 2380 bar and -20degreeC
International Nuclear Information System (INIS)
The self-diffusion coefficient of water has been measured by the steady-gradient spin-echo method at pressures up to 2380 bar and temperatures between 2 and -200C in the stable liquid range using both strengthened glass and beryllium--copper pressure vessels. At low temperatures and high pressures the diffusion coefficient becomes almost independent of pressure. However, a rapid increase in D/sub H/2/sub O/ with the first kilobar of applied pressure is inferred for the supercooled liquid from the relation of the new data to the 1 atm pressure diffusivity of supercooled water. The observations may be correlated with the high pressure low temperature thermodynamic properties of water in a manner consistent with the Adam--Gibbs entropy theory of liquid transport processes
International Nuclear Information System (INIS)
The diffusion coefficient is one of the parameters necessary for the obtention of the extraction exponential coefficients, that are contained within the H.T.U. (height of transfer unity) calculation expression, when operating with continuous organic phase. The organic phase used was tri-n-butyl-phosphate (TBP) and varsol in the 35% and 65% proportions respectively. After each experiment, the uranium content present in each compartment was spectrophotometrically determined and the quantities contained in the aqueous phases were determined by means of volumetric titration. It was found out that the uranyl ion diffusion coefficient is two and one half times less in organic phase, this just being attributed to the greater interactions of the uranyl ions in organic than in aqueous medium
Energy Technology Data Exchange (ETDEWEB)
Berne, P.; Brouard, C.; Pocachard, J. [CEA, FrancCEA/LITEN/LCSN, F-38054 Grenoble cedex 9 (France); Duhart-Barone, A.; Grec, D.; Le Cocguen, A. [CEA/DSN/LECD, F-13108 Cadarache (France)
2009-07-01
In water-saturated media the main mode for contaminant transport is liquid transfer, and the confinement capacity of the materials is notably characterized by the effective diffusion coefficient (EDC) of tritiated water. The major problem lies in the duration of experiments, that can exceed several years, so two methods have been explored for the development of accelerated ones. The first consists in a variation of the through-diffusion technique: a given tracer concentration, C{sub 0}, is applied on one face of the sample that has been previously impregnated with a C{sub 0/2} concentration. The duration of the essay can then be divided by 3. The second method involves accelerated migration under the influence of an electric field and direct measurement of the current density. The results are in the same range as the classical through-diffusion experiments, and obtained in about one month. In non water-saturated media, the diffusing fluid of interest is generally the gaseous phase. Two applications at various steps of the nuclear fuel cycle are presented: characterization of the migration of hydrogen in the host rock formation of a geological waste storage, and of the diffusion of tritium gas in the concrete containment structure of decommissioned UNGG nuclear power plants. In both cases the media are close to saturation and the pore water content must be precisely controlled. This paper presents a method which allows to determine the intrinsic permeability and gas diffusion coefficients of the materials. (authors)
Mueller, R; Zhang, S; Klink, M; Bäumer, M; Vasenkov, S
2015-11-01
Pulsed field gradient (PFG) NMR was applied to measure tortuosity factors for carbon dioxide diffusion in the Knudsen and gas regimes inside monoliths of a samaria-alumina aerogel catalyst, a high porosity material containing micropores in addition to meso- and macropores. The apparent tortuosity factor obtained from PFG NMR measurements for the Knudsen diffusion in the meso- and macropores of the catalyst has an unexpectedly large value of approximately 6 if carbon dioxide adsorption in the micropores and other types of surface adsorption sites of the catalyst is ignored. At the same time, the corresponding apparent tortuosity factor in the gas regime was found to be around 2. Application of a proposed model which describes fast molecular exchange between the surface adsorption sites and the main pore volume of the catalyst yields corrected tortuosity factors which depend only on the pore system geometry. Using this model, the corrected tortuosity factors were found to be around 2 for both diffusion regimes, in agreement with the expectations based on a high porosity of the studied catalyst.
Energy Technology Data Exchange (ETDEWEB)
Benoist, P. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires
1964-01-15
In an previous publication, a simple and general formulation of the diffusion coefficient, which defines the mode of weighting of the mean free paths of the various media, in introducing the collision probabilities in each medium, was established. This expression is demonstrated again here through a more direct method, and the velocity is introduced; new terms are emphasised, the existence of which implies that the representation of the diffusion area as the mean square of the straight line distance from source to absorption is not correct in a lattice. However these terms are of small enough an order of magnitude to he treated as a correction. The general expression also shows the existence, for the radial coefficient, of the series of angular correlation terms, which is seen to converge very slowly for large channels. The term by term computation which was initiated in the first work was then interrupted and a global formulation, which emphasize a resemblance with the problem of the thermal utilisation factor, was adopted. An integral method, analogous to that use for the computation of this factor, gives the possibility to establish new and simple practical formulae, which require the use of a few basic functions only. These formulae are very accurate, as seen from the results of a variational method which was studied as a reference. Various correction effects are reviewed. Expressions which allow the exact treatment of fuel rod clusters are presented. The theory is confronted with various experimental results, and a new method of measuring the radial coefficient is proposed. (author) [French] Dans une publication anterieure, on a etablie une formulation simple et generale du coefficient de diffusion, qui definit le mode de ponderation des libres parcours des differents milieux constituants en faisant apparaitre les probabilites de collision dans chaque milieu. On redemontre ici cette expression d'une maniere plus directe, tout en introduisant la variable
Worth, H; Nüsse, W; Piiper, J
1978-01-01
In order to provide data required for quantitative analysis of gas diffusion in lung airways, diffusion of He, CO, O2, CO2 and SF6 in various gases used in respiratory physiology was studied in vitro at 37 degrees C and 25 degrees C. The gases were allowed to mix by diffusion in a closed cylindrical tube (length 2 m, internal diameter 1 cm), one half of which was initially filled with 1% test gas in a second gas and the other half of which was filled with the second gas only. Kinetics of diffusional equilibration was determined by withdrawal of spot samples analyzed by gas chromatography. The binary (mutual) diffusion coefficients (D) computed there from were in most cases in good agreement with values calculated on the basis of the Chapman-Enskog theory. PMID:625611
Estimation of the eddy diffusivity coefficient in a warm monomictic tropical Lake
Directory of Open Access Journals (Sweden)
David A. Salas de León
2016-03-01
Full Text Available We used a two-year dataset (1998-1999 of monthly temperature profiles from Lake Alchichica, Mexico to estimate values of the vertical coefficient of eddy diffusivity. This lake is located in a tropical region at high altitude and shows considerable seasonal variations (i.e., rainy and dry seasons. It has an area of 2.3 km2 and a mean depth of 40.9 m. Alchichica is a warm monomictic lake, which annually becomes isothermal near the end of December or early January at the onset of the dry season and remains stratified for the rest of the year (from late March or early April to early December during the warm-rainy season. Mathematical models of the spatial and temporal variation of passive substances in lakes and oceans require a quantitative formulation of the vertical transport. Vertical mixing is generally a function of the density profile, which, in lakes, can be directly related to the temperature profile. A widely used method to estimate the vertical diffusion coefficients in lakes from temperature data is the flux-gradient method. In the present study, we applied a simple approach to calculate the eddy diffusivity coefficient (Kz based on the solution of the vertical component of the modeled temperature equation. We characterized the eddy diffusivity coefficient (Kz in Lake Alchichica as a dynamic coefficient that changes during the year, between years, and with depth, ranging from 10-10 to 10-6 m2 s-1, whereas typical values of Kz in thermally stratified lakes range from 10-9 to 10-2 m2 s-1. As expected, we found the lowest values in the deeper regions of the lake, and that the temporal variation of temperature with depth showed a quasi-bimodal shape from one year to the next. We also found a structure of alternating peaks and troughs in the vertical Kz, which indicates a response to oscillating vertical mixing. We concluded that the solution of the vertical component of the temperature equation could be a useful tool to estimate the eddy
Suzuki, S.; Itoh, H.
2016-05-01
The diffusion coefficient of the metastable excited Ne(3P2) atom in neon, the reflection coefficient of Ne(3P2) at the surface of an electrode and the rate coefficient of Ne(3P2) for collisional quenching by Ne(1S0) were determined from the gas pressure dependence of the effective lifetime of Ne(3P2). The effective lifetime of Ne(3P2) was measured from the transient current after turning off the Ultraviolet (UV) light in a Townsend discharge. The observed transient current waveform was analysed by solving the diffusion equation for the metastable excited Ne(3P2) atom using the third kind of boundary condition. The rate coefficient of Ne(3P2) for collisional quenching by Ne(1S0) and the reflection coefficient were determined by a nonspectroscopic method for the first time in neon to the best of our knowledge and were (3.2 ± 0.4) × 10‑16 cm3 s‑1 and 0.10 ± 0.04, respectively. The obtained diffusion coefficient at 1 Torr was 177 ± 17 cm2 s‑1, which is consistent with the value reported by Dixon and Grant. Moreover, the present results are compared with the results of Phelps and were found to be in good agreement. We also discuss the deexcitation rate of Ne(3P2) at pressures of up to 60 Torr in comparison with previously reported values.
International Nuclear Information System (INIS)
A Devanathan-Stachurski type diffusion cell made from a fuel cell assembly is designed to evaluate the gas transport properties of a proton exchange membrane as a function of cell temperature and gas pressure. Data obtained on this cell using the electrochemical monitoring technique (EMT) is used to estimate solubility and diffusion coefficient of oxygen (O2), carbon monoxide (CO) and hydrogen sulfide (H2S) in Nafion membranes. Membrane swelling and reverse-gas diffusion due to water flux are accounted for in the parameter estimation procedure. Permeability of all three gases was found to increase with temperature. The estimated activation energies for O2, CO and H2S diffusion in Nafion 112 are 12.58, 20 and 8.85 kJ mol-1, respectively. The estimated enthalpies of mixing for O2, CO and H2S in Nafion 112 are 5.88, 3.74 and 7.61 kJ mol-1, respectively. An extensive comparison of transport properties estimated in this study to those reported in the literature suggests good agreement. Oxygen permeability in Nafion 117 was measured as a function of gas pressures between 1 and 3 atm. Oxygen diffusion coefficient in Nafion 117 is invariant with pressure and the solubility increases with pressure and obeys Henry's law. The estimated Henry's constant is 3.5 x 103 atm.
Towards an intrinsic relationship between diffusion coefficients and microscopic feature of cements?
International Nuclear Information System (INIS)
Long-term behavior of cemented waste packages requires the knowledge of water diffusion coefficients (water is supposed to be the main degradation agent, by solubilization of some chemical compounds). A simple modeling, based on the use of hydration code CEMHYD3D is proposed and validated for pure OPC pastes (sound or degraded) at mass ratio water / cement lying between 0.25 and 0.65. The nature of the porosity available for diffusion and the role of residual anhydrous compounds are discussed. Copyright (2001) Material Research Society
Integral formula for the effective diffusion coefficient in two-dimensional channels
Kalinay, Pavol
2016-07-01
The effective one-dimensional description of diffusion in two-dimensional channels of varying cross section is revisited. The effective diffusion coefficient D (x ) , extending Fick-Jacobs equation, depending on the longitudinal coordinate x , is derived here without use of scaling of the transverse coordinates. The result of the presented method is an integral formula for D (x ) , calculating its value at x as an integral of contributions from the neighboring positions x' depending on h (x') , a function shaping the channel. Unlike the standard formulas based on the scaling, the new proposed formula also describes D (x ) correctly near the cusps, or in wider channels.
Thermal Expansion and Diffusion Coefficients of Carbon Nanotube-Polymer Composites
Wei, Chengyu; Srivastava, Deepak; Cho, Kyeongjae; Biegel, Bryan (Technical Monitor)
2001-01-01
Classical molecular dynamics (MD) simulations employing Brenner potential for intra-nanotube interactions and van der Waals forces for polymer-nanotube interface have been used to investigate thermal expansion and diffusion characteristics of carbon nanotube-polyethylene composites. Addition of carbon nanotubes to polymer matrix is found to significantly increase the glass transition temperature Tg, and thermal expansion and diffusion coefficients in the composite above Tg. The increase has been attributed to the temperature dependent increase of the excluded volume for the polymer chains, and the findings could have implications in the composite processing, coating and painting applications.
Kernel-based regression of drift and diffusion coefficients of stochastic processes
Energy Technology Data Exchange (ETDEWEB)
Lamouroux, David [Department of Epileptology, University of Bonn (Germany)] [Helmholtz-Institute for Radiation and Nuclear Physics, University of Bonn (Germany); Lehnertz, Klaus, E-mail: klaus.lehnertz@ukb.uni-bonn.d [Department of Epileptology, University of Bonn (Germany)] [Helmholtz-Institute for Radiation and Nuclear Physics, University of Bonn (Germany)] [Interdisciplinary Center for Complex Systems, University of Bonn (Germany)
2009-09-21
To improve the estimation of drift and diffusion coefficients of stochastic processes in case of a limited amount of usable data due to e.g. non-stationarity of natural systems we suggest to use kernel-based instead of histogram-based regression. We propose a method for bandwidth selection and compare it to a widely used cross-validation method. Kernel-based regression reveals an enhanced ability to estimate drift and diffusion especially for a small amount of data. This allows one to improve resolvability of changes in complex dynamical systems as evidenced by an exemplary analysis of electroencephalographic data recorded from a human epileptic brain.
Maryshev, Boris; Latrille, Christelle; Néel, Marie-Christine
2016-01-01
Tracer tests in natural porous media sometimes show abnormalities that suggest considering a fractional variant of the Advection Diffusion Equation supplemented by a time derivative of non-integer order. We are describing an inverse method for this equation: it finds the order of the fractional derivative and the coefficients that achieve minimum discrepancy between solution and tracer data. Using an adjoint equation divides the computational effort by an amount proportional to the number of freedom degrees, which becomes large when some coefficients depend on space. Method accuracy is checked on synthetical data, and applicability to actual tracer test is demonstrated.
Diffusion coefficients of Fokker-Planck equation for rotating dust grains in a fusion plasma
International Nuclear Information System (INIS)
In the fusion devices, ions, H atoms, and H2 molecules collide with dust grains and exert stochastic torques which lead to small variations in angular momentum of the grain. By considering adsorption of the colliding particles, thermal desorption of H atoms and normal H2 molecules, and desorption of the recombined H2 molecules from the surface of an oblate spheroidal grain, we obtain diffusion coefficients of the Fokker-Planck equation for the distribution function of fluctuating angular momentum. Torque coefficients corresponding to the recombination mechanism show that the nonspherical dust grains may rotate with a suprathermal angular velocity
Diffusion coefficients of Fokker-Planck equation for rotating dust grains in a fusion plasma
Bakhtiyari-Ramezani, M.; Mahmoodi, J.; Alinejad, N.
2015-11-01
In the fusion devices, ions, H atoms, and H2 molecules collide with dust grains and exert stochastic torques which lead to small variations in angular momentum of the grain. By considering adsorption of the colliding particles, thermal desorption of H atoms and normal H2 molecules, and desorption of the recombined H2 molecules from the surface of an oblate spheroidal grain, we obtain diffusion coefficients of the Fokker-Planck equation for the distribution function of fluctuating angular momentum. Torque coefficients corresponding to the recombination mechanism show that the nonspherical dust grains may rotate with a suprathermal angular velocity.
Charsooghi, Mohammad A.; Akhlaghi, Ehsan A.; Tavaddod, Sharareh; Khalesifard, H. R.
2011-02-01
We developed a graphical user interface, MATLAB based program to calculate the translational diffusion coefficients in three dimensions for a single diffusing particle, suspended inside a fluid. When the particles are not spherical, in addition to their translational motion also a rotational freedom is considered for them and in addition to the previous translational diffusion coefficients a planar rotational diffusion coefficient can be calculated in this program. Time averaging and ensemble averaging over the particle displacements are taken to calculate the mean square displacement variations in time and so the diffusion coefficients. To monitor the random motion of non-spherical particles a reference frame is used that the particle just have translational motion in it. We call it the body frame that is just like the particle rotates about the z-axis of the lab frame. Some statistical analysis, such as velocity autocorrelation function and histogram of displacements for the particle either in the lab or body frames, are available in the program. Program also calculates theoretical values of the diffusion coefficients for particles of some basic geometrical shapes; sphere, spheroid and cylinder, when other diffusion parameters like temperature and fluid viscosity coefficient can be adjusted. Program summaryProgram title: KOJA Catalogue identifier: AEHK_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEHK_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 48 021 No. of bytes in distributed program, including test data, etc.: 1 310 320 Distribution format: tar.gz Programming language: MatLab (MathWorks Inc.) version 7.6 or higher. Statistics Toolbox and Curve Fitting Toolbox required. Computer: Tested on windows and linux, but generally it would work on any
Diffusion-Coefficients of Sulfate and Methane in Marine-Sediments - Influence of Porosity
DEFF Research Database (Denmark)
IVERSEN, N.; JØRGENSEN, BB
1993-01-01
Tracer diffusion coefficients of sulfate and methane were determined in seawater (D(o)) and in sediments (D(s)). The diffusion coefficients in seawater (20 parts per thousand S) at 4-degrees-C were 0.56 +/- 0.04*10(-5) cm2 s-1 for sulfate and 0.87 +/- 0.10*10(-5) cm2 s-1 for methane. The sediment...... our data, it was possible to deduce the empirical equation theta2 = 1 + n(1 - phi), which was used to calculate D(s) from D(o):D(s) = D(o)/1 + n(1 - phi), using n = 3 for clay-silt sediments and n = 2 for sandy sediments....
Thermal diffusivity coefficient of glycerin determined on an acoustically levitated drop.
Ohsaka, K; Rednikov, A; Sadhal, S S
2002-10-01
We present a technique that can be used to determine the thermal diffusivity coefficient of undercooled liquids that exist at temperatures below their freezing points. The technique involves levitation of a small amount of liquid in the shape of a flattened drop using an acoustic levitator and heating it with a CO2 laser. The heated drop is then allowed to cool naturally by heat loss from the surface. Due to acoustic streaming, heat loss is highly non-uniform and appears to mainly occur at the drop circumference (equatorial region). This fact allows us to relate the heat loss rate with a heat transfer model to determine the thermal diffusion coefficient. We demonstrate the feasibility of the technique using glycerin drops as a model liquid. PMID:12446319
Determination of the Solute Diffusion Coefficient by the Droplet Migration Method
Energy Technology Data Exchange (ETDEWEB)
Shan Liu; Jing Teng; Jeongyun Choi
2007-07-01
Further analysis of droplet migration in a temperature gradient field indicates that different terms can be used to evaluate the solute diffusion coefficient in liquid (D{sub L}) and that there exists a characteristic curve that can describe the motion of all the droplets for a given composition and temperature gradient. Critical experiments are subsequently conducted in succinonitrile (SCN)-salol and SCN-camphor transparent alloys in order to observe dynamic migration processes of a number of droplets. The derived diffusion coefficients from different terms are the same within experimental error. For SCN-salol alloys, D{sub L} = (0.69 {+-} 0.05) x 10{sup -3} mm{sup 2}/s, and for SCN-camphor alloys, D{sub L} = (0.24 {+-} 0.02) x 10{sup -3} mm{sup 2}/s.
Kujawa, Sebastian; Weres, Jerzy; Olek, Wiesław
2016-07-01
Uncertainties in mathematical modelling of water transport in cereal grain kernels during drying and storage are mainly due to implementing unreliable values of the water diffusion coefficient and simplifying the geometry of kernels. In the present study an attempt was made to reduce the uncertainties by developing a method for computer-aided identification of the water diffusion coefficient and more accurate 3D geometry modelling for individual kernels using original inverse finite element algorithms. The approach was exemplified by identifying the water diffusion coefficient for maize kernels subjected to drying. On the basis of the developed method, values of the water diffusion coefficient were estimated, 3D geometry of a maize kernel was represented by isoparametric finite elements, and the moisture content inside maize kernels dried in a thin layer was predicted. Validation of the results against experimental data showed significantly lower error values than in the case of results obtained for the water diffusion coefficient values available in the literature.
Institute of Scientific and Technical Information of China (English)
REN Zhongqi; FEI Weiyang; Hans-Joerg Bart
2005-01-01
The Taylor dispersion method was used to measure diffusion coefficients of three-component liquid systems. An improved constrained nonlinear least-square method was used to evaluate the ternary diffusion coefficients directly by fitting the mathematical solutions of the dispersion equation to eluted solute peaks detected using a differential refractometer. Diffusion coefficients of the three-component system of acetone-benzene-CCl4, determined at 25℃, were used to test the procedure. The measured diffusion coefficients were compared with values obtained by optical interferometry and the diaphragm cell method. Ternary diffusion coefficients are also determinated for solutions of 1-hexanol-hexane-toluene and 1-propanol-water-ethylene glycol at 25℃, with an accuracy of approximately 0.05 m2·s-1.
Liu, M. K.; Li, P.; Giddings, J. C.
1993-01-01
In this study three flow field-flow fractionation (flow FFF) channels are utilized for the separation of proteins and for the simultaneous measurement of their translational diffusion coefficients, D. One channel has a traditional sample inlet, whereas the other two incorporate a frit inlet design that permits more convenient and rapid sample introduction. The dependence of retention time on D, which leads to differential elution and the opportunity to measure D for protein peaks purified by ...
Mukherjee, Arnab; Bhattacharyya, Sarika; Bagchi, Biman
2002-01-01
Extensive isothermal-isobaric (NPT) molecular dynamics simulations at many different temperatures and pressures have been carried out in the well-known Kob-Andersen binary mixture model to monitor the effect of pressure (P) and temperature (T) on the dynamic properties such as the viscosity (\\eta) and the self-diffusion (Di) coefficients of the binary system. The following results have been obtained: (i) Compared to temperature, pressure is found to have a weaker effect on the dynamical prope...
Determination of the diffusion coefficient of new insulators composed of vegetable fibers
Boulaoued I.; Mhimid A.
2012-01-01
The knowledge of the moisture transport of building materials is necessary for the performance of building structures. The control of moisture transport is essential to describe the moisture migration process through the building walls. The present work’s aim is to determine through experiment the water diffusion coefficient of different insulators in unsteady-state based on the Fick’s second law equation. This equation was solved analytically by the separation of variables method (MOD1...
International Nuclear Information System (INIS)
Diffusion coefficients of trace-level cesium in un-irradiated IG-110 graphite were determined by thin-source annealing experiments. Thus obtained values of the diffusion coefficients were larger by 3-4 orders of magnitude than in-pile values for the same brand graphite. Activation energies of the diffusion coefficients for the un-irradiated graphite were 112 and 95 kJ/mol for two series of the laboratory experiments, which are considerably lower than the in-pile value of 157 kJ/mol. An extended diffusion-trap model is proposed to explain the decreased diffusion coefficient and the increased activation energy for the in-pile diffusion, by considering the trapping effect of irradiation-induced lattice defects. (orig.)
Comparative analyses of diffusion coefficients for different extraction processes from thyme
Directory of Open Access Journals (Sweden)
Petrovic Slobodan S.
2012-01-01
Full Text Available This work was aimed to analyze kinetics and mass transfer phenomena for different extraction processes from thyme (Thymus vulgaris L. leaves. Different extraction processes with ethanol were studied: Soxhlet extraction and ultrasound-assisted batch extraction on the laboratory scale as well as pilot plant batch extraction with mixing. The extraction processes with ethanol were compared to the process of supercritical carbon dioxide extraction performed at 10 MPa and 40°C. Experimental data were analyzed by mathematical model derived from the Fick’s second law to determine and compare diffusion coefficients in the periods of constant and decreasing extraction rate. In the fast extraction period, values of diffusion coefficients were one to three orders of magnitude higher compared to those determined for the period of slow extraction. The highest diffusion coefficient was reported for the fast extraction period of supercritical fluid extraction. In the case of extraction processes with ethanol, ultrasound, stirring and extraction temperature increase enhanced mass transfer rate in the washing phase. On the other hand, ultrasound contributed the most to the increase of mass transfer rate in the period of slow extraction.
Institute of Scientific and Technical Information of China (English)
WANG Chao; WANG Zhi; WANG Jing; SU Tao
2007-01-01
To determinate the water diffusion coefficients and dynamics in adhesive/carbon fiber reinforced epoxy resin composite joints, energy dispersive X-ray spectroscopy analysis(EDX) is used to establish the content change of oxygen in the adhesive in adhesive/carbon fiber reinforced epoxy resin composite joints. As water is made up of oxygen and hydrogen, the water diffusion coefficients and dynamics in adhesive/carbon fiber reinforced epoxy resin composite joints can be obtained from the change in the content of oxygen in the adhesive during humidity aging, via EDX analysis. The authors have calculated the water diffusion coefficients and dynamics in the adhesive/carbon fiber reinforced epoxy resin composite joints with the aid of both energy dispersive X-ray spectroscopy and elemental analysis. The determined results with EDX analysis are almost the same as those determined with elemental analysis and the results also show that the durability of the adhesive/carbon fiber reinforced epoxy resin composite joints subjected to silane coupling agent treatment is better than those subjected to sand paper burnishing treatment and chemical oxidation treatment.
Energy Technology Data Exchange (ETDEWEB)
Renslow, Ryan S.; Majors, Paul D.; McLean, Jeffrey S.; Fredrickson, Jim K.; Ahmed, B.; Beyenal, Haluk
2010-08-15
Diffusive mass transfer in biofilms is characterized by the effective diffusion coefficient. It is well-documented that the effective diffusion coefficient can vary by location in a biofilm. The current literature is dominated by effective diffusion coefficient measurements for distinct cell clusters and stratified biofilms showing this spatial variation. Regardless of whether distinct cell clusters or surface-averaging methods are used, position-dependent measurements of the effective diffusion coefficient are currently: 1) invasive to the biofilm, 2) performed under unnatural conditions, 3) lethal to cells, and/or 4) spatially restricted to only certain regions of the biofilm. Invasive measurements can lead to inaccurate results and prohibit further (time dependent) measurements which are important for the mathematical modeling of biofilms. In this study our goals were to: 1) measure the effective diffusion coefficient for water in live biofilms, 2) monitor how the effective diffusion coefficient changes over time under growth conditions, and 3) correlate the effective diffusion coefficient with depth in the biofilm. We measured in situ two-dimensional effective diffusion coefficient maps within Shewanella oneidensis MR-1biofilms using pulsed-field gradient nuclear magnetic resonance methods, and used them to calculate surface-averaged relative effective diffusion coefficient (Drs) profiles. We found that 1) Drs decreased from the top of the biofilm to the bottom, 2) Drs profiles differed for biofilms of different ages, 3) Drs profiles changed over time and generally decreased with time, 4) all the biofilms showed very similar Drs profiles near the top of the biofilm, and 5) the Drs profile near the bottom of the biofilm was different for each biofilm. Practically, our results demonstrate that advanced biofilm models should use a variable effective diffusivity which changes with time and location in the biofilm.
Renslow, Ryan S.; Majors, Paul D.; McLean, Jeffrey S.; Fredrickson, Jim K.; Ahmed, Bulbul; Beyenal, Haluk
2010-01-01
Diffusive mass transfer in biofilms is characterized by the effective diffusion coefficient. It is well-documented that the effective diffusion coefficient can vary by location in a biofilm. The current literature is dominated by effective diffusion coefficient measurements for distinct cell clusters and stratified biofilms showing this spatial variation. Regardless of whether distinct cell clusters or surface-averaging methods are used, position-dependent measurements of the effective diffusion coefficient are currently: 1) invasive to the biofilm, 2) performed under unnatural conditions, 3) lethal to cells, and/or 4) spatially restricted to only certain regions of the biofilm. Invasive measurements can lead to inaccurate results and prohibit further (time-dependent) measurements which are important for the mathematical modeling of biofilms. In this study our goals were to: 1) measure the effective diffusion coefficient for water in live biofilms, 2) monitor how the effective diffusion coefficient changes over time under growth conditions, and 3) correlate the effective diffusion coefficient with depth in the biofilm. We measured in situ two-dimensional effective diffusion coefficient maps within Shewanella oneidensis MR-1 biofilms using pulsed-field gradient nuclear magnetic resonance methods, and used them to calculate surface-averaged relative effective diffusion coefficient (Drs) profiles. We found that 1) Drs decreased from the top of the biofilm to the bottom, 2) Drs profiles differed for biofilms of different ages, 3) Drs profiles changed over time and generally decreased with time, 4) all the biofilms showed very similar Drs profiles near the top of the biofilm, and 5) the Drs profile near the bottom of the biofilm was different for each biofilm. Practically, our results demonstrate that advanced biofilm models should use a variable effective diffusivity which changes with time and location in the biofilm. PMID:20589671
DIFFUSION COEFFICIENTS IN POLYMER-SOLVENT SYSTEMS FOR HIGHLY CONCENTRATED POLYMER SOLUTIONS
Directory of Open Access Journals (Sweden)
R.A. Reis
2001-12-01
Full Text Available The Vrentas/Duda proposal for the diffusion of polymer-solvent systems, which is based on the free-volume theory, was employed in correlating and predicting mutual diffusion coefficients in highly concentrated polymer solutions. It has been observed that the predictive version of the model is capable of qualitatively representing the experimental data, while the use of an adjustable parameter greatly improves the performance of the model. The systems studied were poly(vinyl acetate-toluene and Neoprene-acetone, and a comparison between experimental data and calculated values from the Vrentas/Duda model is reported. A new experimental apparatus based on the sorption technique was built to provide reliable diffusivity data on the Neoprene-acetone system.
Determination of Concentration Dependent Diffusion Coefficients of Carbon in Expanded Austenite
DEFF Research Database (Denmark)
Hummelshøj, Thomas Strabo; Christiansen, Thomas; Somers, Marcel A. J.
2008-01-01
Abstract. In the present paper various experimental procedures to experimentally determine the concentration dependent diffusion coefficient of carbon in expanded austenite are evaluated. To this end thermogravimetric carburization was simulated for various experimental conditions and the evaluated...... composition dependent diffusivity of carbon derived from the simulated experiments was compared with the input data. The most promising procedure for an accurate determination is shown to be stepwise gaseous carburizing of thin foils in a gaseous atmosphere; the finer the stepsize, the more accurate...... the approximation of the diffusivity. Thermogravimetry was applied to continuously monitor the weight change of thin foils of AISI 316 during carburizing in CO-H2 gas mixtures for one of the simulated experimental procedures....
Coefficient of Thermal Diffusivity of Insulation Brick Developed from Sawdust and Clays
Directory of Open Access Journals (Sweden)
E. Bwayo
2014-01-01
Full Text Available This paper presents an experimental result on the effect of particle size of a mixture of ball clay, kaolin, and sawdust on thermal diffusivity of ceramic bricks. A mixture of dry powders of ball clay, kaolin of the same particle size, and sawdust of different particle sizes was mixed in different proportions and then compacted to high pressures before being fired to 950°C. The thermal diffusivity was then determined by an indirect method involving measurement of thermal conductivity, density, and specific heat capacity. The study reveals that coefficient of thermal diffusivity increases with decrease in particle size of kaolin and ball clay but decreases with increase in particle size of sawdust.
Kim, Changho; Borodin, Oleg; Karniadakis, George Em
2015-12-01
We analyze two standard methods to compute the diffusion coefficient of a tracer particle in a medium from molecular dynamics (MD) simulation, the velocity autocorrelation function (VACF) method, and the mean-squared displacement (MSD) method. We show that they are equivalent in the sense that they provide the same mean values with the same level of statistical errors. We obtain analytic expressions for the level of the statistical errors present in the time-dependent diffusion coefficient as well as the VACF and the MSD. Under the assumption that the velocity of the tracer particle is a Gaussian process, all results are expressed in terms of the VACF. Hence, the standard errors of all relevant quantities are computable once the VACF is obtained from MD simulation. By using analytic models described by the Langevin equations driven by Gaussian white noise and Poissonian white shot noise, we verify our theoretical error estimates and discuss the non-Gaussianity effect in the error estimates when the Gaussian process approximation does not hold exactly. For validation, we perform MD simulations for the self-diffusion of a Lennard-Jones fluid and the diffusion of a large and massive colloid particle suspended in the fluid. Our theoretical framework is also applicable to mesoscopic simulations, e.g., Langevin dynamics and dissipative particle dynamics.
Analysis of Diffusion Coefficient using Reversed-Flow Gas Chromatography-A Review
Directory of Open Access Journals (Sweden)
Khalisanni Khalid
2011-01-01
Full Text Available Problem statement: Since the earliest publication on the technique, Reversed-Flow Gas Chromatography (RF-GC has been used to determine physicochemical properties by measuring the value of one in the presence of another. The method is precise, accurate and simple compared to other conventional techniques. Approach: The experimental setup consists of a small modification of a commercial gas chromatograph, so that it includes a four- or six-port gas sampling valve and a simple cell placed inside the chromatographic oven. Results: This cell suppresses the effects of the carrier gas flow on the physicochemical occurrence taking place in the stationary phase. These phenomena pertain to rate coefficients and diffusion coefficients. Conclusion: The RF-GC methodologies can be considered as a wise instrumental approach to study the physicochemical phenomenon of liquid pollutants. It can be used to determine the rate coefficients and diffusion coefficients values of samples at various temperatures for the studies of environmental science and physical chemistry research areas. However, the methodologies are not restricted to the current fields of research. It is also relevant in the area of food chemistry, geochemistry, material science, nanotechnology, biological science and chemical technology.
Mialdun, A; Shevtsova, V
2015-12-14
We report on the measurement of diffusion (D), Soret (S(T)), and thermodiffusion (D(T)) coefficients in toluene-cyclohexane mixture with mass fraction of toluene 0.40 onboard of the International Space Station. The coefficients were measured in the range of the mean temperatures between 20 °C and 34 °C. The Soret coefficient is negative within the investigated temperature range and its absolute value |S(T)| decreases with increasing temperature. The diffusion coefficient for this system increases with temperature rising. For comparison, the temperature dependence of diffusion coefficient was measured in ground laboratory using counter-flow cell technique and revealed a good agreement with microgravity results. A non-direct comparison of the measured onboard Soret coefficients with different systems indicated a similar trend for the temperature dependent behavior. Unexpected experimental finding is that for this system the thermodiffusion coefficient D(T) does not depend on temperature. PMID:26671399
Szyszkiewicz-Warzecha, Krzysztof; Jasielec, Jerzy J.; Fausek, Janusz; Filipek, Robert
2016-08-01
Transport properties of ions have significant impact on the possibility of rebars corrosion thus the knowledge of a diffusion coefficient is important for reinforced concrete durability. Numerous tests for the determination of diffusion coefficients have been proposed but analysis of some of these tests show that they are too simplistic or even not valid. Hence, more rigorous models to calculate the coefficients should be employed. Here we propose the Nernst-Planck and Poisson equations, which take into account the concentration and electric potential field. Based on this model a special inverse method is presented for determination of a chloride diffusion coefficient. It requires the measurement of concentration profiles or flux on the boundary and solution of the NPP model to define the goal function. Finding the global minimum is equivalent to the determination of diffusion coefficients. Typical examples of the application of the presented method are given.
Anisotropie des coefficients de diffusion dans des cristaux liquides discotiques hexagonaux
Daoud, M.; Gharbia, M.; Gharbi, A.
1994-06-01
The diffusion constants of dyes in several hexagonal discotic liquid crystals are measured and discussed. For all the liquid crystals studied, these constants are anisotropic : the diffusion in the direction parallel to the columns is faster than that in the perpendicular plane (frac{D_allel}{D_perp}>1). The effects of the length and shape of the chains bound to the triphenylene discs are shown. The effect of the dye molecular size is also described. The study of the diffusion coefficients of hexapentoxytriphenylene (C5HET) as a function of temperature has shown that the activation energies along the columns and perpendicular to the columns are comparable. The main features of dye diffusion in the hexagonal columnar liquid crystals studied are similar to those reported in nematic phases. Les mesures des constantes de diffusion de colorants dans plusieurs cristaux liquides discotiques hexagonaux sont présentées et discutées. Pour tous les cristaux liquides étudiés, ces constantes présentent une anisotropie, avec une diffusion plus rapide parallèlement aux colonnes que perpendiculairement à celles-ci (frac{D_allel}{D_perp}>1). Des effets de longueur et de forme des chaînes branchées sur les disques de triphénylène sont mis en évidence. Il en est de même pour la taille des molécules de colorants. L'étude en fonction de la température a montré que dans le cas de l'hexapentoxytriphénylène (C5HET), les énergies d'activation dans les directions parallèle et perpendiculaire aux colonnes sont comparables. Les caractéristiques de la diffusion de colorants dans les cristaux liquides colonnaires hexagonaux étudiés sont semblables à celles des nématiques.
Diffusion Coefficients and Activation Energies for Ag Transport through SiC
International Nuclear Information System (INIS)
One of the desired functions of TRISO coating is to prevent the release of fission products from inside the particle into the coolant. Among these layers, the retention of fission products is accomplished primarily by the SiC layer of the coating. These processes include oxide fuel kernel migration (via the transport of carbon from the cool to hot side); intra-layer crack formation, noble gas (Kr, Xe), Ba, Ag, Sr, Cs diffusion out of the kernel; pressure build-up due to noble gas release from the kernel and CO from released oxygen in ungettered oxide kernel; a Pd attack on SiC and noble gas, Pd, Ba, Sr, Cs, Ag, transport via bulk diffusion, grain boundaries, and cracks through the coating layers. In this paper, the measured and estimated diffusion coefficients of Ag in and/or through SiC are compared based on the following experimental methods: 1) measuring Ag diffusion through ion-implanted cubic (3C) SiC and 6H-SiC samples and annealing, 2) measuring Ag diffusion through a diffusion couple and annealing, and 3) fitting the overall integrated/fractional Ag release from a batch of TRISO fuel particle during heating after irradiation and irradiation testing. The causes of uprising Ag transport through SiC, the coating layer of TRISO fuel are complex depending on the temperature during operation or irradiation testing. Although Ag transport depends on the microstructure of SiC (such as grain boundary stoichiometry, SiC grain size and shape, the presence of free silicon, nano-cracks, etc.), neutron irradiation, irradiation temperature, Pd attack, thermal decomposition, transmutation products, layer thinning and coated particle shape, etc., Ag diffusion along the grain boundary of SiC plays a major role. Considering that the current Ag diffusion coefficient is summarized and compared from previous studies, it might also be possible that, considering the irradiation effects of SiC, the Ag retention ability of a TRISO particle somehow improves during the TRISO
Sokoletsky, Leonid; Yang, Xianping; Shen, Fang
2014-11-01
Radiative transfer modelling in atmosphere, water, and on the air-water surface was used to create an algorithm and computer code for satellite monitoring Chinese estuarine and coastal waters. The atmospheric part of the algorithm is based on the Reference Evaluation of Solar Transmittance (REST) model for calculation of optical properties of the atmosphere from the top of the atmosphere to the target; for modelling optical properties from target towards satellite's sensor, an optical reciprocity principle has been used. An algorithm uses estimates derived from three different sources: 1) the MODIS-based software; 2) radiative transfer equations, and 3) well-known empirical relationships between measured parameters and optical depths and transmittances for such atmospheric components as molecules, aerosols, ozone, nitrogen dioxide, precipitable water vapor and uniformly mixed gases. Using this model allowed us to derive a reliable relationship relating an important parameter, the diffuse-to-global solar incoming irradiance ratio, to the aerosol optical thickness, solar zenith angle and wavelength. The surface and underwater parts of the algorithm contained theoretical and semi-empirical relationships between inherent (such as absorption, scattering and backscattering coefficients) and apparent (remote-sensing reflectance and diffuse attenuation coefficient, Kd) optical properties, and suspended sediment concentration (SSC) measured in the Yangtze River Estuary and its adjacent coastal area. The first false colour maps of SSC and Kd demonstrated a well accordance with the multi-year field observations in the region, and suggest promise for use of this algorithm for the regular monitoring of Chinese and worldwide natural waters.
International Nuclear Information System (INIS)
We have fabricated parallel stripes of nanostructures in an n-type Si substrate by implanting 30 keV Ga+ ions from a focused ion beam (FIB) source. Two sets of implantation were carried out. In one case, during implantation the substrate was held at room temperature and in the other case at 400 deg. C. Photoemission electron microscopy (PEEM) was carried out on these samples. The implanted parallel stripes, each with a nominal dimension of 4000 nm x 100 nm, appear as bright regions in the PEEM image. Line scans of the intensities from the PEEM image were recorded along and across these stripes. The intensity profile at the edges of a line scan is broader for the implantation carried out at 400 deg. C compared to room temperature. From the analysis of this intensity profile, the lateral diffusion coefficient of Ga in silicon was estimated assuming that the PEEM intensity is proportional to Ga concentration. The diffusion coefficient at 400 deg. C has been estimated to be ∼1.3 x 10-15 m2/s. Across the stripes an asymmetric diffusion profile has been observed, which has been related to the sequence of implantation of these stripes and the associated defect distribution due to lateral straggling of the implanted ions.
Mongrain, Rosaire; Faik, Isam; Leask, Richard L; Rodés-Cabau, Josep; Larose, Eric; Bertrand, Olivier F
2007-10-01
In the context of drug eluting stent, we present two-dimensional numerical models of mass transport of the drug in the wall and in the lumen to study the effect of the drug diffusion coefficients in the three principal media (blood, vascular wall, and polymer coating treated as a three-compartment problem) and the impact of different strut apposition configurations (fully embedded, half embedded, and not embedded). The different conditions were analyzed in terms of their consequence on the drug concentration distribution in the arterial wall. We apply the concept of the therapeutic window to the targeted vascular wall region and derive simple metrics to assess the efficiency of the various stent configurations. Although most of the drug is dispersed in the lumen, variations in the blood flow rate within the physiological range of coronary blood flow and the diffusivity of the drug molecule in the blood were shown to have a negligible effect on the amount of drug in the wall. Our results reveal that the amount of drug cumulated in the wall depends essentially on the relative values of the diffusion coefficients in the polymer coating and in the wall. Concerning the strut apposition, it is shown that the fully embedded strut configuration would provide a better concentration distribution.
Measuring partition and diffusion coefficients for volatile organic compounds in vinyl flooring
Cox, Steven S.; Zhao, Dongye; Little, John C.
Interactions between volatile organic compounds (VOCs) and vinyl flooring (VF), a relatively homogenous, diffusion-controlled building material, were characterized. The sorption/desorption behavior of VF was investigated using single-component and binary systems of seven common VOCs ranging in molecular weight from n-butanol to n-pentadecane. The simultaneous sorption of VOCs and water vapor by VF was also investigated. Rapid determination of the material/air partition coefficient ( K) and the material-phase diffusion coefficient ( D) for each VOC was achieved by placing thin VF slabs in a dynamic microbalance and subjecting them to controlled sorption/desorption cycles. K and D are shown to be independent of concentration for all of the VOCs and water vapor. For the four alkane VOCs studied, K correlates well with vapor pressure and D correlates well with molecular weight, providing a means to estimate these parameters for other alkane VOCs. While the simultaneous sorption of a binary mixture of VOCs is non-competitive, the presence of water vapor increases the uptake of VOCs by VF. This approach can be applied to other diffusion-controlled materials and should facilitate the prediction of their source/sink behavior using physically-based models.
Ab initio calculation of oxygen self-diffusion coefficient in uranium dioxide UO2
Dorado, Boris; Garcia, Philippe; Torrent, Marc
Uranium dioxide UO2 is the most widely used nuclear fuel worldwide and its atomic transport properties are relevant to practically all engineering aspects of the material. Although transport properties have already been studied in UO2 by means of first-principles calculations, the ab initio determination of self-diffusion coefficients has up to now remained unreachable because the relevant computational tools were neither available or adapted. The present work reports our results related to the ab initio calculation of the oxygen self-diffusion coefficient in UO2. We first determine the Gibbs free energies of formation of oxygen charged defects by calculating both the electronic and vibrational (hence entropic) contributions. Then, we use the transition state theory in order to compute the effective jump frequency of the defects, which in turn provides us with the value of the pre-exponential factor. The results are compared to self-diffusion data obtained experimentally with a careful monitoring of the relevant thermodynamic conditions (oxygen partial pressure, temperature, impurity content).
The measurement of self-diffusion coefficients in liquid metals with quasielastic neutron scattering
Directory of Open Access Journals (Sweden)
Meyer Andreas
2015-01-01
Full Text Available Quasielastic incoherent neutron scattering (QENS has proven to be a versatile tool to study self diffusion of atoms in liquid metals. Here it is shown, that coherent contributions to the signal in the small q limit appear as a flat and energy independent constant to the QENS signal in single-component liquid metals even for systems with a small incoherent scattering cross section, like aluminum. Container-less processing via electromagnetic or electrostatic levitation devices, especially designed for QENS, enables the in-situ measurement on liquid metallic droplets of sizes between 5 mm to 10 mm in diameter. This gives access to the study of chemically reactive, refractory metallic melts and extends the accessible temperature range to undercoolings of several hundred Kelvin below the respective melting point. Compared to experiments using a thin-walled crucible giving hollow-cylindrical sample geometry it is shown that multiple scattering on levitated droplets is negligible for the analysis of the self-diffusion coefficient. QENS results of liquid germanium and 73germanium isotope mixtures, titanium, nickel, copper and aluminum are reviewed. The self-diffusion coefficients of these systems are best described by an Arrhenius-type temperature dependence around their respective melting points.
Evolution of the Magnetic Field Line Diffusion Coefficient and Non-Gaussian Statistics
Snodin, A. P.; Ruffolo, D.; Matthaeus, W. H.
2016-08-01
The magnetic field line random walk (FLRW) plays an important role in the transport of energy and particles in turbulent plasmas. For magnetic fluctuations that are transverse or almost transverse to a large-scale mean magnetic field, theories describing the FLRW usually predict asymptotic diffusion of magnetic field lines perpendicular to the mean field. Such theories often depend on the assumption that one can relate the Lagrangian and Eulerian statistics of the magnetic field via Corrsin’s hypothesis, and additionally take the distribution of magnetic field line displacements to be Gaussian. Here we take an ordinary differential equation (ODE) model with these underlying assumptions and test how well it describes the evolution of the magnetic field line diffusion coefficient in 2D+slab magnetic turbulence, by comparisons to computer simulations that do not involve such assumptions. In addition, we directly test the accuracy of the Corrsin approximation to the Lagrangian correlation. Over much of the studied parameter space we find that the ODE model is in fairly good agreement with computer simulations, in terms of both the evolution and asymptotic values of the diffusion coefficient. When there is poor agreement, we show that this can be largely attributed to the failure of Corrsin’s hypothesis rather than the assumption of Gaussian statistics of field line displacements. The degree of non-Gaussianity, which we measure in terms of the kurtosis, appears to be an indicator of how well Corrsin’s approximation works.
International Nuclear Information System (INIS)
The calculation of diffusion coefficients in a lattice necessitates the knowledge of a correct method of weighting the free paths of the different constituents. An unambiguous definition of this weighting method is given here, based on the calculation of leakages from a zone of a reactor. The formulation obtained, which is both simple and general, reduces the calculation of diffusion coefficients to that of collision probabilities in the different media; it reveals in the expression for the radial coefficient the series of the terms of angular correlation (cross terms) recently shown by several authors. This formulation is then used to calculate the practical case of a classical type of lattice composed of a moderator and a fuel element surrounded by an empty space. Analytical and numerical comparison of the expressions obtained with those inferred from the theory of BEHRENS shows up the importance of several new terms some of which are linked with the transparency of the fuel element. Cross terms up to the second order are evaluated. A practical formulary is given at the end of the paper. (author)
Energy Technology Data Exchange (ETDEWEB)
Lovera, P.; Ferry, C.; Poinssot, Ch. [CEA Saclay, Dept. de Physico-Chimie (DPC), 91 - Gif sur Yvette (France); Johnson, L. [Nagra, Baden (Switzerland)
2003-07-01
This document corresponds to the deliverable D2 of the Work Package 1 of the 'Spent Fuel Stability under repository conditions' (SFS) European project. It constitutes a synthesis report on relevant diffusion coefficients of fission products and helium in spent nuclear fuels at high and low temperatures. Coefficients corresponding to thermally activated diffusion were reviewed from literature data for O, U (self-diffusion coefficients), fission gases and other fission products. Data showed that thermal diffusion was irrelevant at temperatures expected in repository conditions. The occurrence of diffusion enhanced by alpha self-irradiation was studied through different theoretical approaches. A 'best estimate' value of the alpha self-irradiation diffusion coefficient, D (m{sup 2}.s{sup -1}), is proposed. It is extrapolated from enhanced diffusion under irradiation observed in reactor and would be proportional to the volume alpha activity in the spent nuclear fuel, A{sub v} (Bq.m{sup -3}) as: D/A{sub v} {approx_equal} 2.10{sup -41} (m{sup 5})The migration of stable Pb in Oklo's uraninites was studied in order to validate the proposed diffusion coefficient. The obtained value is one order of magnitude higher than the theoretical proposed value. As for He behaviour in spent nuclear fuel, a few data are today available in open literature. The document will be completed as soon as new experimental results are available. (authors)
Energy Technology Data Exchange (ETDEWEB)
Shiva, Amir Houshang; Teasdale, Peter R., E-mail: p.teasdale@griffith.edu.au; Bennett, William W.; Welsh, David T.
2015-08-12
A systematic comparison of the diffusion coefficients of cations (Al, Cd, Co, Cu, Mn, Ni, Pb, Zn) and oxyanions (Al, As, Mo, Sb, V, W) in open (ODL) and restricted (RDL) diffusive layers used by the DGT technique was undertaken. Diffusion coefficients were measured using both the diffusion cell (D{sub cell}) method at pH 4.00 and the DGT time-series (D{sub DGT}) method at pH 4.01 and 7.04 (pH 8.30 was used instead of 7.04 for Al) using the Chelex-Metsorb mixed binding layer. The performance of Chelex-Metsorb as a new DGT binding layer for Al uptake was also evaluated for the first time. Reasonable agreement was observed between D{sub cell} and D{sub DGT} measurements for both ODL and RDL, except for V and W. The ratios of D{sub cell}/D{sub DGT} for V of 0.44 and 0.39, and for W of 0.66 and 0.63 with ODL and RDL respectively, were much lower due to the formation of a high proportion of polyoxometalate species at the higher concentrations required with the D{sub cell} measurements. This is the first time that D values have been reported for several oxyanions using RDL. Except for Al at pH 8.30 with ODL, all D{sub DGT} measurements were retarded relative to diffusion coefficients in water (D{sub W}) for both diffusive hydrogels. Diffusion in RDL was further retarded compared with ODL, for all elements (0.66–0.78) with both methods. However, the degree of retardation observed changed for cations and anions at each pH. At pH 7.04 cations had a slightly higher D{sub DGT} and oxyanions had a slightly lower D{sub DGT} than at pH 4.01 for both ODL and RDL. It is proposed that this is due to partial formation of acrylic acid functional groups (pK{sub a} ≈4.5), which would be fully deprotonated at pH 7.04 (negative) and mostly protonated at pH 4.01 (neutral). As Al changes from being cationic at pH 4.01 to anionic at pH 8.30 the results were more complex. - Highlights: • Determining elemental diffusion coefficients in open and restricted diffusive gels. • The DGT
Sanford, R.F.
1982-01-01
Geological examples of binary diffusion are numerous. They are potential indicators of the duration and rates of geological processes. Analytical solutions to the diffusion equations generally do not allow for variable diffusion coefficients, changing boundary conditions, and impingement of diffusion fields. The three programs presented here are based on Crank-Nicholson finite-difference approximations, which can take into account these complicating factors. Program 1 describes the diffusion of a component into an initially homogeneous phase that has a constant surface composition. Specifically it is written for Fe-Mg exchange in olivine at oxygen fugacities appropriate for the lunar crust, but other components, phases, or fugacities may be substituted by changing the values of the diffusion coefficient. Program 2 simulates the growth of exsolution lamellae. Program 3 describes the growth of reaction rims. These two programs are written for pseudobinary Ca-(Mg, Fe) exchange in pyroxenes. In all three programs, the diffusion coefficients and boundary conditions can be varied systematically with time. To enable users to employ widely different numerical values for diffusion coefficients and diffusion distance, the grid spacing in the space dimension and the increment by which the grid spacing in the time dimension is increased at each time step are input constants that can be varied each time the programs are run to yield a solution of the desired accuracy. ?? 1982.
DEFF Research Database (Denmark)
Galliero, Guillaume; Medvedev, Oleg; Shapiro, Alexander
2005-01-01
different binary liquid mixtures of non-polar components that computed penetration lengths, for various temperatures and compositions, are consistent with those deduced from experiments in the framework of the formalism of the fluctuation theory. Moreover, the mutual diffusion coefficients obtained from a......Mutual diffusion in condensed phases is a theoretically and practically important subject of active research. One of the most rigorous and theoretically advanced approaches to the problem is a recently developed approach based on the concept of penetration lengths (Physica A 320 (2003) 211; Physica...... coupled fluctuation theory and molecular dynamics scheme exhibit consistent trends and average deviations from experimental data around 10-20%. (c) 2004 Elsevier B.V. All rights reserved....
Integral formula for the effective diffusion coefficient in two-dimensional channels.
Kalinay, Pavol
2016-07-01
The effective one-dimensional description of diffusion in two-dimensional channels of varying cross section is revisited. The effective diffusion coefficient D(x), extending Fick-Jacobs equation, depending on the longitudinal coordinate x, is derived here without use of scaling of the transverse coordinates. The result of the presented method is an integral formula for D(x), calculating its value at x as an integral of contributions from the neighboring positions x^{'} depending on h(x^{'}), a function shaping the channel. Unlike the standard formulas based on the scaling, the new proposed formula also describes D(x) correctly near the cusps, or in wider channels. PMID:27575072
SEYHAN-GÜRTAŞ, Ferda; AK, M. Mehmet; Evranuz, E. Özgül
2001-01-01
The kinetics of water absorption by chickpeas (Koçbaşı, Kuşbaşı), lentils (green Pul) and beans (Battal, Dermason, Horoz, Şeker) grown in Turkey were studied by a gravimetric method during soaking at 15, 25 and 40ºC to determine moisture diffusivity of these selected legumes. The water diffusion coefficients of the legumes were in the range 9.71x10-11 - 5.98x10-10 m2/s for the chickpeas, 3.53x10-10 - 1.33x10-9 m2/s for the lentils and 4.35x10-11 - 3.79x10-9 m2/s for the beans. An Arrhenius-t...
Wu, Yan; Duan, Guosheng; Zhao, Xiang
2015-03-01
Effects of magnetic field intensity on carbon diffusion coefficient in pure iron in the γ-Fe temperature region were investigated using carburizing technology. The carbon penetration profiles from the iron surface to interior were measured by field emission electron probe microanalyzer. The carbon diffusion coefficient in pure iron carburized with different magnetic field intensities was calculated according to the Fick's second law. It was found that the magnetic field intensity could obviously affect the carbon diffusion coefficient in pure iron in the γ-Fe temperature region, and the carbon diffusion coefficient decreased obviously with the enhancement of magnetic field intensity, when the magnetic field intensity was higher than 1 T, the carbon diffusion coefficient in field annealed specimen was less than half of that of the nonfield annealed specimen, further enhancing the magnetic field intensity, the carbon diffusion coefficient basically remains unchanged. The stiffening of lattice due to field-induced magnetic ordering was responsible for an increase in activation barrier for jumping carbon atoms. The greater the magnetic field intensity, the stronger the inhibiting effect of magnetic field on carbon diffusion.
Shear viscosity and spin-diffusion coefficient of a two-dimensional Fermi gas
DEFF Research Database (Denmark)
Bruun, Georg
2012-01-01
Using kinetic theory, we calculate the shear viscosity and the spin-diffusion coefficient as well as the associated relaxation times for a two-component Fermi gas in two dimensions, as a function of temperature, coupling strength, polarization, and mass ratio of the two components....... It is demonstrated that the minimum value of the viscosity decreases with the mass ratio, since Fermi blocking becomes less efficient. We furthermore analyze recent experimental results for the quadrupole mode of a two-dimensional gas in terms of viscous damping, obtaining a qualitative agreement using no fitting...
Shiva, Amir Houshang; Teasdale, Peter R; Bennett, William W; Welsh, David T
2015-08-12
A systematic comparison of the diffusion coefficients of cations (Al, Cd, Co, Cu, Mn, Ni, Pb, Zn) and oxyanions (Al, As, Mo, Sb, V, W) in open (ODL) and restricted (RDL) diffusive layers used by the DGT technique was undertaken. Diffusion coefficients were measured using both the diffusion cell (Dcell) method at pH 4.00 and the DGT time-series (D(DGT)) method at pH 4.01 and 7.04 (pH 8.30 was used instead of 7.04 for Al) using the Chelex-Metsorb mixed binding layer. The performance of Chelex-Metsorb as a new DGT binding layer for Al uptake was also evaluated for the first time. Reasonable agreement was observed between D(cell) and D(DGT) measurements for both ODL and RDL, except for V and W. The ratios of D(cell)/D(DGT) for V of 0.44 and 0.39, and for W of 0.66 and 0.63 with ODL and RDL respectively, were much lower due to the formation of a high proportion of polyoxometalate species at the higher concentrations required with the D(cell) measurements. This is the first time that D values have been reported for several oxyanions using RDL. Except for Al at pH 8.30 with ODL, all D(DGT) measurements were retarded relative to diffusion coefficients in water (DW) for both diffusive hydrogels. Diffusion in RDL was further retarded compared with ODL, for all elements (0.66-0.78) with both methods. However, the degree of retardation observed changed for cations and anions at each pH. At pH 7.04 cations had a slightly higher D(DGT) and oxyanions had a slightly lower D(DGT) than at pH 4.01 for both ODL and RDL. It is proposed that this is due to partial formation of acrylic acid functional groups (pKa ≈4.5), which would be fully deprotonated at pH 7.04 (negative) and mostly protonated at pH 4.01 (neutral). As Al changes from being cationic at pH 4.01 to anionic at pH 8.30 the results were more complex.
Lateral diffusivity coefficients from the dynamics of a SF6 patch in a coastal environment
Kersalé, M.; Petrenko, A. A.; Doglioli, A. M.; Nencioli, F.; Bouffard, J.; Blain, S.; Diaz, F.; Labasque, T.; Quéguiner, B.; Dekeyser, I.
2016-01-01
The dispersion of a patch of the tracer sulfur hexafluoride (SF6) is used to assess the lateral diffusivity in the coastal waters of the western part of the Gulf of Lion (GoL), northwestern Mediterranean Sea, during the Latex10 experiment (September 2010). Immediately after the release, the spreading of the patch is associated with a strong decrease of the SF6 concentrations due to the gas exchange from the ocean to the atmosphere. This has been accurately quantified, evidencing the impact of the strong wind conditions during the first days of this campaign. Few days after the release, as the atmospheric loss of SF6 decreased, lateral diffusivity coefficient at spatial scales of 10 km has been computed using two approaches. First, the evolution of the patch with time was combined with a diffusion-strain model to obtain estimates of the strain rate (γ = 2.5 10- 6 s- 1) and of the lateral diffusivity coefficient (Kh = 23.2 m2 s- 1). Second, a steady state model was applied, showing Kh values similar to the previous method after a period of adjustment between 2 and 4.5 days. This implies that after such period, our computation of Kh becomes insensitive to the inclusion of further straining of the patch. Analysis of sea surface temperature satellite imagery shows the presence of a strong front in the study area. The front clearly affected the dynamics within the region and thus the temporal evolution of the patch. Our results are consistent with previous studies in open ocean and demonstrate the success and feasibility of those methods also under small-scale, rapidly-evolving dynamics typical of coastal environments.
Nesbitt, J. A.; Heckel, R. W.
1987-01-01
Interdiffusion in Ni-rich Ni-Cr-Al alloys is investigated experimentally after annealing at 1100 and 1200 C using gamma/gamma, gamma/gamma+beta, gamma/gamma+gamma prime, and gamma/gamma+alpha diffusion couples. The amount and location of Kirkendall porosity suggests that Al diffuses more rapidly than Cr which diffuses more rapidly than Ni in the gamma phase of Ni-Cr-Al alloys. The location and extent of maxima and minima in the concentration profiles of the diffusion couples indicate that both cross-term diffusion coefficients are positive. Measurements are also presented of the ternary interdiffusion coefficients of the gamma phase in the Ni-Cr-Al system. It is shown that the interdiffusion coefficients can be accurately predicted by using a ternary finite-difference interdiffusion model.
Guilet, Jerome
2012-01-01
We investigate the radial transport of magnetic flux in a thin accretion disc, the turbulence being modelled by effective diffusion coefficients (viscosity and resistivity). Both turbulent diffusion and advection by the accretion flow contribute to flux transport, and they are likely to act in opposition. We study the consequences of the vertical variation of the diffusion coefficients, due to a varying strength of the turbulence. For this purpose, we consider three different vertical profiles of these coefficients. The first one is aimed at mimicking the turbulent stress profile observed in numerical simulations of MHD turbulence in stratified discs. This enables us to confirm the robustness of the main result of Paper I obtained for uniform diffusion coefficients that, for weak magnetic fields, the contribution of the accretion flow to the transport velocity of magnetic flux is much larger than the transport velocity of mass. We then consider the presence of a dead zone around the equatorial plane, where th...
The partition and effective diffusion coefficients of formaldehyde were measured for three materials (conventional gypsum wallboard, "green" gypsum wallboard, and "green" carpet) under three relative humidity (RH) conditions (20%, 50% and 70% RH). A dynamic dual-chamber test meth...
The partition and effective diffusion coefficients of formaldehyde were measured for three materials (conventional gypsum wallboard, "green" gypsum wallboard, and "green" carpet) under three relative humidity (RH) conditions (20%, 50% and 70% RH). A dynamic dual-chamber test meth...
Alonso de Mezquia, David; Wang, Zilin; Lapeira, Estela; Klein, Michael; Wiegand, Simone; Mounir Bou-Ali, M
2014-11-01
In this study, the thermodiffusion, molecular diffusion, and Soret coefficients of 12 binary mixtures composed of toluene, n-hexane and n-dodecane in the whole range of concentrations at atmospheric pressure and temperatures of 298.15 K and 308.15 K have been determined. The experimental measurements have been carried out using the Thermogravitational Column, the Sliding Symmetric Tubes and the Thermal Diffusion Forced Rayleigh Scattering techniques. The results obtained using the different techniques show a maximum deviation of 9% for the thermodiffusion coefficient, 8% for the molecular diffusion coefficient and 2% for the Soret coefficient. For the first time we report a decrease of the thermodiffusion coefficient with increasing ratio of the thermal expansion coefficient and viscosity for a binary mixture of an organic ring compound with a short n-alkane. This observation is discussed in terms of interactions between the different components. Additionally, the thermogravitational technique has been used to measure the thermodiffusion coefficients of four ternary mixtures consisting of toluene, n-hexane and n-dodecane at 298.15 K. In order to complete the study, the values obtained for the molecular diffusion coefficient in binary mixtures, and the thermodiffusion coefficient of binary and ternary mixtures have been compared with recently derived correlations. PMID:25376978
Directory of Open Access Journals (Sweden)
Edgar de Alencar Teixeira
2010-06-01
Full Text Available Neste trabalho, determinou-se o valor nutritivo de quatro alimentos energéticos (fubá de milho, sorgo, farelo de arroz integral e quirera de arroz para juvenis de surubim. Os coeficientes de digestibilidade aparente da matéria seca (MS, proteína bruta (PB e energia bruta (EB foram avaliados pela metodologia de substituição do alimento numa ração-referência usando-se 0,1% de óxido crômico como indicador externo. Utilizaram-se 240 alevinos com 30 g de peso médio distribuídos em tanques apropriados para coleta de fezes. O delineamento foi inteiramente casualizado com quatro dietas, cada uma com quatro repetições. O coeficiente de digestibilidade aparente da matéria seca do fubá de milho foi de 62,3%; do farelo de arroz, 59,7%; da quirera de arroz, 40,4%; e do sorgo, 38%. Os coeficientes de digestibilidade da proteína bruta, nesta ordem, foram 87,4; 83,8; 85,3; e 81,1%; e os da energia bruta, 62,4; 66,4; 46,9 e 47,8%. Entre os alimentos avaliados, o que possui maior digestibilidade da matéria seca, proteína bruta e energia bruta é o farelo de arroz e o de menor digestibilidade, o sorgo.It was determined, in this work, the nutritional value of four energetic feeds (corn meal, sorghum, whole rice bran, and ground rice for surubim juveniles. Apparent digestibility coefficients of dry matter (DM, crude protein (CP, and gross energy (GE were evaluated by food replacement methodology in a reference-feeding using 0.1% of chromic oxide as an external marker. It was used 240 fingerlings with an average weight of 30 g distributed in tanks fitted for faeces collection. A complete random design with four diets, each one with four replicates, was used. Apparent digestibility coefficient of dry matter for corn meal was 62.3%; for rice bran, 59.7%; for ground rice, 40.4%, and for sorghum, 38%. Digestibility coefficients for crude protein were, in this order, the following: 87.4, 83.8, 85.3 and 81.1% and digestibility coefficient for gross
Institute of Scientific and Technical Information of China (English)
ZHAOYechun; XIHongxia; 等
1999-01-01
The parameter identification model is proposed for determining the linear adsorption isotherms and the solid diffusion coefficients by using adsorption chromatorgaphy.Axial dispersion coefficients is firstly determined by pulse-respond experiment technique with an inert substance as tracer,then the elution curves of chromatography separating the isomer mannitol and sorbitol are determined by the chromatographic measuring technique,and pinally the adsorption isotherms and the solid diffusion coefficients of mannitol and sorbitol on Ca2+ resins are estimated by using this model.The results show that the axial dispersion coefficients increase with fluid velocity increasing,The adsorption equilibrium constants decrease with temperature rising;and the solid diffusion coefficients increase with temperature rising.The theoretical elution curves are good agreement with the experimental elution curves of the liquid adsorption chromatography separating the mannitol and the sorbitol.The model provides a simple and reliable procedure to estimate the kinetic and thermodynamic parmeters of the adsorption.
Indian Academy of Sciences (India)
BHARDWAJ S B; SINGH RAM MEHAR; SHARMA KUSHAL; MISHRA S C
2016-06-01
Attempts have been made to explore the exact periodic and solitary wave solutions of nonlinear reaction diffusion (RD) equation involving cubic–quintic nonlinearity along with timedependent convection coefficients. Effect of varying model coefficients on the physical parameters of solitary wave solutions is demonstrated. Depending upon the parametric condition, the periodic,double-kink, bell and antikink-type solutions for cubic–quintic nonlinear reaction-diffusion equation are extracted. Such solutions can be used to explain various biological and physical phenomena.
Computing the blood brain barrier (BBB) diffusion coefficient: A molecular dynamics approach
Shamloo, Amir; Pedram, Maysam Z.; Heidari, Hossein; Alasty, Aria
2016-07-01
Various physical and biological aspects of the Blood Brain Barrier (BBB) structure still remain unfolded. Therefore, among the several mechanisms of drug delivery, only a few have succeeded in breaching this barrier, one of which is the use of Magnetic Nanoparticles (MNPs). However, a quantitative characterization of the BBB permeability is desirable to find an optimal magnetic force-field. In the present study, a molecular model of the BBB is introduced that precisely represents the interactions between MNPs and the membranes of Endothelial Cells (ECs) that form the BBB. Steered Molecular Dynamics (SMD) simulations of the BBB crossing phenomenon have been carried out. Mathematical modeling of the BBB as an input-output system has been considered from a system dynamics modeling viewpoint, enabling us to analyze the BBB behavior based on a robust model. From this model, the force profile required to overcome the barrier has been extracted for a single NP from the SMD simulations at a range of velocities. Using this data a transfer function model has been obtained and the diffusion coefficient is evaluated. This study is a novel approach to bridge the gap between nanoscale models and microscale models of the BBB. The characteristic diffusion coefficient has the nano-scale molecular effects inherent, furthermore reducing the computational costs of a nano-scale simulation model and enabling much more complex studies to be conducted.
In-situ estimate of submesoscale horizontal eddy diffusion coefficients across a front
Nencioli, Francesco; d'Ovidio, Francesco; Doglioli, Andrea; Petrenko, Anne
2013-04-01
Fronts, jets and eddies are ubiquitous features of the world oceans, and play a key role in regulating energy budget, heat transfer, horizontal and vertical transport, and biogeochemical processes. Although recent advances in computational power have favored the analysis of mesoscale and submesoscale dynamics from high-resolution numerical simulations, studies from in-situ observations are still relatively scarce. The small dimensions and short duration of such structures still pose major challenges for fine-scale dedicated field experiments. As a consequence, in-situ quantitative estimates of key physical parameters for high-resolution numerical models, such as horizontal eddy diffusion coefficients, are still lacking. The Latex10 campaign (September 1-24, 2010), within the LAgrangian Transport EXperiment (LATEX), adopted an adaptive sampling strategy that included satellite data, ship-based current measurements, and iterative Lagrangian drifter releases to successfully map coherent transport structures in the western Gulf of Lion. Comparisons with AVHRR imagery evidenced that the detected structures were associated with an intense frontal feature, originated by the convergence and subsequent stirring of colder coastal waters with warmer open-sea waters. We present a method for computing horizontal eddy diffusion coefficients by combining the stirring rates estimated from the Lagrangian drifter trajectories with the shapes of the surface temperature and salinity gradient (assumed to be at the equilibrium) from the ship thermosalinograph. The average value we obtained from various sections across the front is 2.5 m2s-1, with horizontal scales (width of the front) ranging between 0.5 and 2.5 km. This is in line with the values commonly used for high-resolution numerical simulations. Further field experiment will be required to extend the results to different ocean regions and regimes, and to thoroughly test the robustness of the equilibrium hypothesis. Remote sensed
Diffusion-Exchange Weighted Imaging
Saadallah Ramadan
2009-01-01
A method has been developed whereby diffusion and exchange in micro cellular structures in the human brain are correlated to produce a new type of image contrast leading to determination of water exchange rates in vivo. The diffusion method relies on differential apparent diffusion coefficients as detectable nuclei exchange between adjacent compartments marked with different apparent diffusion coefficient values (e.g. intra- and extra-cellular compartments). A new pulse sequence was developed...
Yoshida, Ken; Matubayasi, Nobuyuki; Nakahara, Masaru
2008-12-01
The self-diffusion coefficients D for water, benzene, and cyclohexane are determined by using the pulsed-field-gradient spin echo method in high-temperature conditions along the liquid branch of the coexistence curve: 30-350 °C (1.0-0.58 g cm-3), 30-250 °C (0.87-0.56 g cm-3), and 30-250 °C (0.77-0.48 g cm-3) for water, benzene, and cyclohexane, respectively. The temperature and density effects are separated and their origins are discussed by examining the diffusion data over a wide range of thermodynamic states. The temperature dependence of the self-diffusion coefficient for water is larger than that for organic solvents due to the large contribution of the attractive hydrogen-bonding interaction in water. The density dependence is larger for organic solvents than for water. The difference is explained in terms of the van der Waals picture that the structure of nonpolar organic solvents is determined by the packing effect due to the repulsion or exclusion volumes. The dynamic solvation shell scheme [K. Yoshida et al., J. Chem. Phys. 127, 174509 (2007)] is applied for the molecular interpretation of the translational dynamics with the aid of molecular dynamics simulation. In water at high temperatures, the velocity relaxation is not completed before the relaxation of the solvation shell (mobile-shell type) as a result of the breakdown of the hydrogen-bonding network. In contrast, the velocity relaxation of benzene is rather confined within the solvation shell (in-shell type).
Energy Technology Data Exchange (ETDEWEB)
Sinha, Biswajit, E-mail: biswachem@gmail.co [Department of Chemistry, University of North Bengal, Darjeeling 734013 (India); Roy, Pran Kumar; Sarkar, Bipul Kumar; Brahman, Dhiraj [Department of Chemistry, University of North Bengal, Darjeeling 734013 (India); Roy, Mahendra Nath, E-mail: mahendraroy2002@yahoo.co.i [Department of Chemistry, University of North Bengal, Darjeeling 734013 (India)
2010-03-15
Apparent molar volumes phi{sub V} and viscosity B-coefficients for caffeine in (0.00, 0.03, 0.05, and 0.07) mol . dm{sup -3} aqueous thorium nitrate, Th(NO{sub 3}){sub 4}, solutions were determined from solution density and viscosity measurements over the temperature range (298.15 to 318.15) K as function of concentration of caffeine and the relation: phi{sub V}{sup 0}=a{sub 0}+a{sub 1}T+a{sub 2}T{sup 2}, have been used to describe the temperature dependence of the standard partial molar volumes phi{sub V}{sup 0}. These results have been used to deduce the standard volumes of transfer DELTAphi{sub V}{sup 0} and viscosity B-coefficients of transfer DELTAB for caffeine from water to aqueous Th(NO{sub 3}){sub 4} solutions for rationalizing various interactions in the ternary solutions. The structure-making or breaking ability of caffeine has been discussed in terms of the sign of (delta{sup 2}phi{sub V}{sup 0}/deltaT{sup 2}){sub P}. The Friedman-Krishnan co-sphere model was used to explain the transfer volume of caffeine with increasing Th(NO{sub 3}){sub 4} molarity. The activation parameters of viscous flow for the ternary solutions were also discussed in terms of transition state theory.
Blackness coefficients, effective diffusion parameters, and control rod worths for thermal reactors
International Nuclear Information System (INIS)
Simple diffusion theory cannot be used to evaluate control rod worths in thermal reactors because of the strongly absorbing character of the control material. However, good results can be obtained from a diffusion calculation by representing the absorber slab by means of a suitable pair of internal boundary conditions, α and β, which are ratios of neutron flux to neutron current. Methods for calculating α and β in the P1, P3, and P5 approximations, with and without scattering, are presented. By appropriately weighting the fine-group blackness coefficients, broad group values, and , are obtained. The technique is applied to the calculation of control rod worths of Cd, Ag-In-Cd, and Hf control elements. Results are found to compare very favorably with detailed Monte Carlo calculations. For control elements whose geometry does not permit a thin slab treatment, other methods are needed for determining the effective diffusion parameters. One such method is briefly discussed and applied to the calculation of control rod worths in the Ford Nuclear Reactor at the University of Michigan. Calculated and measured worths are found to be in good agreement
Blackness coefficients, effective diffusion parameters, and control rod worths for thermal reactors
Energy Technology Data Exchange (ETDEWEB)
Bretscher, M.M.
1984-09-01
Simple diffusion theory cannot be used to evaluate control rod worths in thermal reactors because of the strongly absorbing character of the control material. However, good results can be obtained from a diffusion calculation by representing the absorber slab by means of a suitable pair of internal boundary conditions, ..cap alpha.. and ..beta.., which are ratios of neutron flux to neutron current. Methods for calculating ..cap alpha.. and ..beta.. in the P/sub 1/, P/sub 3/, and P/sub 5/ approximations, with and without scattering, are presented. By appropriately weighting the fine-group blackness coefficients, broad group values, <..cap alpha..> and <..beta..>, are obtained. The technique is applied to the calculation of control rod worths of Cd, Ag-In-Cd, and Hf control elements. Results are found to compare very favorably with detailed Monte Carlo calculations. For control elements whose geometry does not permit a thin slab treatment, other methods are needed for determining the effective diffusion parameters. One such method is briefly discussed and applied to the calculation of control rod worths in the Ford Nuclear Reactor at the University of Michigan. Calculated and measured worths are found to be in good agreement.
A non-perturbative estimate of the heavy quark momentum diffusion coefficient
Francis, A; Laine, M; Neuhaus, T; Ohno, H
2015-01-01
We estimate the momentum diffusion coefficient of a heavy quark within a pure SU(3) plasma at a temperature of about 1.5Tc. Large-scale Monte Carlo simulations on a series of lattices extending up to 192^3*48 permit us to carry out a continuum extrapolation of the so-called colour-electric imaginary-time correlator. The extrapolated correlator is analyzed with the help of theoretically motivated models for the corresponding spectral function. Evidence for a non-zero transport coefficient is found and, incorporating systematic uncertainties reflecting model assumptions, we obtain kappa = (1.8 - 3.4)T^3. This implies that the "drag coefficient", characterizing the time scale at which heavy quarks adjust to hydrodynamic flow, is (1.8 - 3.4) (Tc/T)^2 (M/1.5GeV) fm/c, where M is the heavy quark kinetic mass. The results apply to bottom and, with somewhat larger systematic uncertainties, to charm quarks.
DEFF Research Database (Denmark)
Diaz, Sandra; Casselbrant, Ingrid; Piitulainen, Eeva;
2008-01-01
. Correlations between mean ADC and EI and 15th percentile were both r=0.90 and for MLD r=0.59. There was higher correlation between mean ADC and %predicted DLCO (r=0.90) than between EI and %predicted DLCO (r=0.76). CONCLUSION: HP (3)He-MRI correlates well with density measurements from MSCT and agrees better...
International Nuclear Information System (INIS)
Objective: To evaluate the correlation of ADC values on 3.0 T MR with the pathological grades in pT1b clear cell renal cell carcinoma (CCRCC). Methods: Conventional MR images, ADC values and Fuhrman pathological grading of pT1b CCRCC were performed in 30 patients. Grade Ⅰ and Ⅱ were defined as low-grade group; grade Ⅲ and Ⅳ were defined as high-grade group. The differences of ADC values among four different pathologic grades were compared with a one-way analysis of variance. The comparison of ADC values of two different grade groups was performed with t test, and the ROC curve was performed to evaluate the diagnostic efficacy of ADC value. Correlation between pathological grading and ADC values was assessed with Spearman rank correlation analysis. Results: (1) The mean ADC value of grading Ⅰ (10 patients), Ⅱ (8 patients), Ⅲ (7 patients), Ⅳ (5 patients) was (0.94 ± 0.11) ×10-3 mm2/s, (0.82 ±0.13) × 10-3 mm2/s,(0.68 ±0.09) × 10-3 mm2/s, (0.59 ±0.03) × 10-3 mm2/s, respectively. Significant differences of ADC values among the four grades were present (F=16.422, P=0.000). (2) The mean ADC value of the low-grade group was significantly higher than that of the high-grade group (t=5.738, P=0.000). Sensitivity and specificity of diagnosing the low-grade group was 88.9% and 83.3% respectively. There was a negative correlation between pathological grading and ADC value (r=-0.807, P<0.05). Conclusions: The ADC values of pT1b CCRCC have close correlation with pathological grading. They can be used to predict the degree of tumor malignancy preoperatively and guide surgical planning. (authors)
DEFF Research Database (Denmark)
Boned, C.; Allal, A.; Baylaucq, A.;
2004-01-01
In this work, a simultaneous modeling of the self-diffusion coefficient and the dynamic viscosity is presented. In the microstructural theory these two quantities are governed by the same friction coefficient related to the mobility of the molecule. A recent free-volume model, already successfully......, chlorotrifluoromethane, cyclohexane, methylcyclohexane, and tetramethylsilane. For these pure compounds we have found in the literature several data for both the self-diffusion and the dynamic viscosity in large viscosity, diffusion, temperature, and pressure intervals (up to around 500 MPa for methylcyclohexane...
Stellwagen, Earle; Stellwagen, Nancy C
2002-08-01
The free solution mobility of DNA molecules of different molecular weights, the sequence dependence of the mobility, and the diffusion coefficients of small single- and double-stranded DNA (ss- and dsDNA) molecules can be measured accurately by capillary zone electrophoresis, using coated capillaries to minimize the electroosmotic flow (EOF) of the solvent. Very small differences in mobility between various analytes can be quantified if a mobility marker is used to correct for small differences in EOF between successive experiments. Using mobility markers, the molecular weight at which the free solution mobility of dsDNA becomes independent of molecular weight is found to be approximately 170 bp in 40 mM Tris-acetate-EDTA buffer. A DNA fragment containing 170 bp has a contour length of approximately 58 nm, close to the persistence length of DNA under these buffer conditions. Hence, the approach of the free solution mobility of DNA to a plateau value may be associated with the transition from a rod-like to a coil-like conformation in solution. Markers have also been used to determine that the free solution mobilities of ss- and dsDNA oligomers are sequence-dependent. Double-stranded 20-bp oligomers containing runs of three or more adenine residues in a row (A-tracts) migrate somewhat more slowly than 20-mers without A-tracts, suggesting that somewhat larger numbers of counterions are condensed in the ion atmospheres of A-tract DNAs, decreasing their net effective charge. Single-stranded 20-mers with symmetric sequences migrate approximately 1% faster than their double-stranded counterparts, and faster than single-stranded 20-mers containing A(5)- or T(5)-tracts. Interestingly, the average mobility of two complementary single-stranded 20-mers is equal to the mobility of the double-stranded oligomer formed upon annealing. Finally, the stopped migration method has been used to measure the diffusion coefficients of single- and double-stranded oligomers. The diffusion
Hadjiev, Nicholas A; Amsden, Brian G
2015-02-10
The ability to estimate the diffusion coefficient of a solute within hydrogels has important application in the design and analysis of hydrogels used in drug delivery, tissue engineering, and regenerative medicine. A number of mathematical models have been derived for this purpose; however, they often rely on fitted parameters and so have limited predictive capability. Herein we assess the ability of the obstruction-scaling model to provide reasonable estimates of solute diffusion coefficients within hydrogels, as well as the assumption that a hydrogel can be represented as an entangled polymer solution of an equivalent concentration. Fluorescein isothiocyanate dextran solutes were loaded into sodium alginate solutions as well as hydrogels of different polymer volume fractions formed from photoinitiated cross-linking of methacrylate sodium alginate. The tracer diffusion coefficients of these solutes were measured using fluorescence recovery after photobleaching (FRAP). The measured diffusion coefficients were then compared to the values predicted by the obstruction-scaling model. The model predictions were within ±15% of the measured values, suggesting that the model can provide useful estimates of solute diffusion coefficients within hydrogels and solutions. Moreover, solutes diffusing in both sodium alginate solutions and hydrogels were demonstrated to experience the same degree of solute mobility restriction given the same effective polymer concentration, supporting the assumption that a hydrogel can be represented as an entangled polymer solution of equivalent concentration. PMID:25499554
Drabik, Dominik; Przybyło, Magda; Sikorski, Aleksander; Langner, Marek
2016-03-01
Fluorescence Correlation Spectroscopy (FCS) is a technique, which allows determination of the diffusion coefficient and concentration of fluorescent objects suspended in the solution. The measured parameter is the fluctuation of the fluorescence signal emitted by diffusing molecules. When 100 nm DOPC vesicles labeled with various fluorescent dyes (Fluorescein-PE, NBD-PE, Atto488 DOPE or βBodipy FL) were measured, different values of diffusion coefficients have been obtained. These diffusion coefficients were different from the expected values measured using the dynamic light scattering method (DLS). The FCS was initially developed for solutions containing small fluorescent molecules therefore the observed inconsistency may result from the nature of vesicle suspension itself. The duration of the fluorescence signal may depend on the following factors: the exposure time of the labeled object to the excitation beam, the photo-physical properties (e.g., stability) of a fluorophore, the theoretical model used for the calculations of the diffusion coefficient and optical properties of the vesicle suspension. The diffusion coefficients determined for differently labeled liposomes show that its dependence on vesicle size and quantity of fluorescent probed used for labeling was significant demonstrating that the fluorescence properties of the fluorophore itself (bleaching and/or blinking) were critical factors for a correct outcome of FCS experiment. The new, based on combined FCS and DLS measurements, method for the determination of the focal volume prove itself to be useful for the evaluation of a fluorescence dye with respect to its applicability for FCS experiment. PMID:26695945
Manouchehrian Fard, Manouchehr; Beiki, Hossein
2016-10-01
An experimental study was performed to measure benzoic acid diffusion coefficient in water-based γ-Al2O3 nanofluids at different temperatures. Measurements were carried out at 15, 20 and 25 °C. γ-Al2O3 nanoparticles with an average diameter of 10-20 nm were added into de-ionized water as the based fluid. Nanoparticles volume fractions used in the based fluid were 0.025, 0.05, 0.1, 0.2, 0.4 and 0.8 %. Measurements showed that the diffusion coefficients was not changed with nanoparticles concentration and no enhancement was found. Dependence of diffusion coefficients on nanoparticles concentration followed the same trend in all temperatures investigated in this work. Nano stirring and nano-obstacles could be regarded as two reasons for mass diffusivity changes in nanofluids.
DEFF Research Database (Denmark)
Christensen, Eva Arnspang; Koffman, Jennifer Skaarup; Marlar, Saw;
2014-01-01
Lateral diffusion and compartmentalization of plasma membrane proteins are tightly regulated in cells and thus, studying these processes will reveal new insights to plasma membrane protein function and regulation. Recently, k-Space Image Correlation Spectroscopy (kICS)1 was developed to enable...... available code to measure diffusion coefficients of proteins. kICS calculates a time correlation function from a fluorescence microscopy image stack after Fourier transformation of each image to reciprocal (k-) space. Subsequently, circular averaging, natural logarithm transform and linear fits...... to the correlation function yields the diffusion coefficient. This paper provides a step-by-step guide to the image analysis and measurement of diffusion coefficients via kICS. First, a high frame rate image sequence of a fluorescently labeled plasma membrane protein is acquired using a fluorescence microscope Then...
Binary Diffusion Coefficients of Platinum(II) Acetylacetonate in Supercritical Carbon Dioxide.
Kong, Chang Yi; Siratori, Tomoya; Wang, Guosheng; Sako, Takeshi; Funazukuri, Toshitaka
2013-11-14
Binary diffusion coefficients (D12) and retention factors (k) of platinum(II) acetylacetonate at infinitesimal concentration in supercritical (sc) carbon dioxide (CO2) were measured by the chromatographic impulse response method with a poly(ethylene glycol) coated capillary column at temperatures from (308.15 to 343.15) K and pressures from (8.5 to 40.0) MPa, and D12 in liquid ethanol at temperatures from (298.15 to 333.15) K and atmospheric pressure by the Taylor dispersion method. As has been seen for our previously reported data on other metal complexes measured in sc CO2 and organic solvents, the D12 data in sc CO2 and liquid ethanol were represented by a function of temperature and solvent viscosity. The D12 values for metal complexes were not related to the solute molecular weights. The k values in sc CO2 were expressed by a function of temperature and CO2 density.
Varga, Agnes; Gyetvai, Gergely; Nagy, Lívia; Nagy, Géza
2009-08-01
The diffusion coefficient of glucose in different media is an important parameter in life sciences, as well as in biotechnology and microbiology. In this work a simple, fast method is proposed that is based on the electrochemical time of flight principle. In most of the earlier time of flight experiments performed, a constant flight distance was applied. In the present work a scanning electrochemical microscope (SECM) was applied as a measuring tool. With use of the SECM, the flying distance could be changed with high precision, making measurements with several flight distances more accurate and reliable values could be obtained for solutions as well as for gels. The conventional voltammetric methods are not applicable for glucose detection. In our work electrocatalytic copper oxide coated copper microelectrodes and micro-sized amperometric enzyme sensors were used as detectors, while microdroplet-ejecting pneumatically driven micropipettes were used as a source. PMID:19517100
Dos Santos, Leslie; Laberty-Robert, Christel; Maréchal, Manuel; Perrot, Hubert; Sel, Ozlem
2015-09-15
Electrochemical Impedance Spectroscopy (EIS) was, for the first time, used to estimate the global transverse proton diffusion coefficient, D(H+)(EHM), in electrospun hybrid conducting membranes (EHMs). In contrast to conventional impedance spectroscopy, EIS measurements were performed at room temperature with a liquid interface. In this configuration, the measure of the bulk proton transport is influenced by the kinetics of the transfer of proton at the solid/liquid interface. We demonstrated that the use of additives in the process of the membrane impacts the organization of the hydrophilic domains and also the proton transport. The D(H+)(EHM) is close to 1.10(-7) cm(2) s(-1) (± 0.1.10(-7) cm(2) s(-1)) for the EHMs without additive, whereas it is 4.10(-6) cm(2) s(-1) (± 0.4.10(-6) cm(2) s(-1)) for EHMs with additives.
Variation in downwelling diffuse attenuation coefficient in the northern South China Sea
Institute of Scientific and Technical Information of China (English)
2008-01-01
The diffuse attenuation coefficient for downwelling irradiance (Kd(λ)) is an important parameter for ocean studies. Based on the optical profile data measured during three cruises in the northern South China Sea in autumn from 2003 to 2005, variations in the Kd(λ) spectra were analyzed. The variability of Kd(λ) shows much distinct features in both magnitude and spectra pattern, it is much higher in coastal waters than that of open oceanic waters; and the blue-to-green (443/555) ratio of Kd(λ) tends to increase with chlorophyll a concentration ([Chl-a]) from open ocean to coastal waters. These characteristics can be explained most by the increase of aw+p(443)/aw+p(555) with [Chl-a]. In short waveband, the relation between Kd(λ)-Kw(λ) and [Chl-a] can be well described by a power law function, indicating the large contribution of phytoplankton to the variations in Kd(λ). As for the spectral model of the diffuse attenuation coefficient, there are good linear relationships between Kd(490) and Kd(λ) in other wavelengths with own slope and intercept of a linear functions in the spectral range 412-555 nm. Kd(490) is well correlated with the spectral ratio of remote sensing reflectance; and should enough measurement data are given, this empirical algorithm would be used in the Kd(λ) retrieval from ocean color satellite data. The variation in Kd(λ) provides much useful information for us to study the bio-optical property in the northern South China Sea.
Remote sensing of the diffuse attenuation coefficient of ocean water. [coastal zone color scanner
Austin, R. W.
1981-01-01
A technique was devised which uses remotely sensed spectral radiances from the sea to assess the optical diffuse attenuation coefficient, K (lambda) of near-surface ocean water. With spectral image data from a sensor such as the coastal zone color scanner (CZCS) carried on NIMBUS-7, it is possible to rapidly compute the K (lambda) fields for large ocean areas and obtain K "images" which show synoptic, spatial distribution of this attenuation coefficient. The technique utilizes a relationship that has been determined between the value of K and the ratio of the upwelling radiances leaving the sea surface at two wavelengths. The relationship was developed to provide an algorithm for inferring K from the radiance images obtained by the CZCS, thus the wavelengths were selected from those used by this sensor, viz., 443, 520, 550 and 670 nm. The majority of the radiance arriving at the spacecraft is the result of scattering in the atmospheric and is unrelated to the radiance signal generated by the water. A necessary step in the processing of the data received by the sensor is, therefore, the effective removal of these atmospheric path radiance signals before the K algorithm is applied. Examples of the efficacy of these removal techniques are given together with examples of the spatial distributions of K in several ocean areas.
On the parametrization of the energetic-particle pitch-angle diffusion coefficient
Directory of Open Access Journals (Sweden)
Vainio Rami
2013-03-01
Full Text Available Context: Solar energetic particle (SEP events are one of the key ingredients of the near-Earth radiation environment. Pitch-angle scattering by fluctuations imposed on the large-scale magnetic field is assumed to be the basic physical process behind diffusive propagation of SEPs in the heliosphere. Various pitch-angle diffusion models have been suggested to parametrize the wave-particle interactions, based on the original results of the classical quasi-linear theory of particle scattering and improved new approaches. Aims: We investigate under which circumstances the different functional forms of the pitch-angle diffusion coefficient can lead to equivalent results. In particular, we use two forms that are commonly used in two types of numerical methods to solve the particle transport equation, i.e., finite difference methods and Monte Carlo simulations. Methods: We estimate the corresponding values of the parameters of the two scattering models by performing a least-square fitting of the functional form of one of the scattering-frequency models to the other. We also perform Monte Carlo simulations of near-relativistic solar electrons to investigate the similarity of the models in terms of observables at 1 AU. Results: Our study shows that the two forms of pitch-angle scattering frequency lead to nearly equivalent results for electron transport from the Sun to 1 AU. We give the equivalent scattering parameters of the two models as curves that can be easily used when comparing the results of the two models. Conclusions: By providing the equivalent parametrizations of two commonly used scattering models, we provide key information on how to relate the results from the two parametrizations to each other and to the theory of particle transport.
Diffusion imaging concepts for clinicians.
Neil, Jeffrey J
2008-01-01
This review covers the fundamentals of diffusion tensor imaging. It is written with the clinician in mind and assumes the reader has a passing familiarity with magnetic resonance imaging (MRI). Topics covered include comparison of diffusion MRI with conventional MRI, water apparent diffusion coefficient (ADC), diffusion anisotropy, tract tracing, and changes of water apparent diffusion in response to injury. The discussion centers primarily on applications to the central nervous system, but examples from other tissues are included. PMID:18050325
Directory of Open Access Journals (Sweden)
L.I. Gladka
2012-10-01
Full Text Available The analysis of basic and combined models for calculation of effective kinetic coefficients required to describe diffusion processes in two-phase heterogeneous environments is conducted. For a transition zone that grows between two interacting diffusion phases was built a new model of effective medium. In this model the effective kinetic coefficient depends on the kinetic coefficients in each of the phases, volumetric particle phases and additional free parameter, which generally characterizes the type of structure of a bi-phase zone. It is shown that the combined model is constructed to describe the percolation behavior of effective medium. The phenomenological approach describes the formation and development of bi-phase zones in ternary systems which including streams through both phases and the analysis of the impact of the model on the resulting effective medium diffusion zone.
Shalchi, Andreas
2016-01-01
We explore the transport of energetic particles in two-component turbulence in which the stochastic magnetic field is assumed to be a superposition of slab and two-dimensional modes. It is known that in magnetostatic slab turbulence, the motion of particles across the mean magnetic field is subdiffusive. If a two-dimensional component is added, diffusion is recovered. It was also shown before that in two-component turbulence, the slab modes do not explicitly contribute to the perpendicular diffusion coefficient. In the current paper the implicit contribution of slab modes is explored and it is shown that this contribution leads to a reduction of the perpendicular diffusion coefficient. This effect improves the agreement between simulations and analytical theory. Furthermore, the obtained results are relevant for investigations of diffusive shock acceleration.
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
The diffusion coefficients** ofl-lysine hydrochloride andl-arginine hydrochloride in their aqueous solu- tions at 25℃ were determined by the metallic diaphragm cell method which is characterized by accuracy, promptness and convenience. Meanwhile, the densities and viscosities of the solutions were also determined. Based on all these data a semi-empirical model for correlating the diffusion coefficients of solid organic salts in their aqueous solutions at 25℃ was proposed. The fitting result of this model is comparatively satisfactory. Compared to a former model, Gordon Model, this model can avoid a number of difficulties and arduous work.
Ahadi, Amirhossein; Saghir, M. Ziad
2014-08-01
In this study, a Mach-Zehnder interferometer that is equipped with two lasers of different wavelengths was used to conduct high resolution measurements of concentration profiles of a ternary mixture inside a diffusion cell. Windowed Fourier transform along with an advanced unwrapping procedure was employed to extract the phase image from fringe images. Then the phase difference was obtained for a spatial resolution of 1920×1240. According to the measured refractive index profile, concentration contours of two components (out of three) were measured. Consequently, the concentration profile of the third components was calculated. Previously, the analytical solution for binary mixtures was used to estimate only the pure diffusion coefficients. In this study, for the first time, the refractive indices measured by two lasers along with the analytical solution for the ternary system, based on Fick's law, and an evolutionary algorithm (EA) known as a genetic algorithm (GA) were employed to measure the pure and cross diffusion coefficients of a transparent ternary mixture simultaneously. The optimization method to estimate diffusion coefficients was tested against various objective functions, and the best approach was that which was proposed herein. In order to validate the proposed measurement method, the experimental results of the Selectable Optical Diagnostics Instrument-Diffusion Coefficients in Mixtures (SODI-DCMIX1 project) on board the International Space Station (ISS) were analyzed using this technique and the obtained results were compared with previous techniques.
The role of surface energy coefficients and nuclear surface diffuseness in the fusion of heavy-ions
Dutt, Ishwar; Puri, Rajeev K.
2010-01-01
We discuss the effect of surface energy coefficients as well as nuclear surface diffuseness in the proximity potential and ultimately in the fusion of heavy-ions. Here we employ different versions of surface energy coefficients. Our analysis reveals that these technical parameters can influence the fusion barriers by a significant amount. A best set of these parameters is also given that explains the experimental data nicely.
Unno, M.; Kawamoto, K.; Moldrup, P.; Komatsu, T.
2008-12-01
The soil-gas diffusion coefficient (Dp) and its dependency on air-filled porosity (ɛ) govern gas diffusion and reaction processes in soil. Accurate Dp(ɛ) prediction models for variably saturated peat soils are needed to evaluate vadose zone transport and fate of greenhouse gases such as methane in peaty wetlands. In this study, we measured Dp on undisturbed peat soil samples at different soil-water matric potentials, and developed new, linear and nonlinear expressions for describing and predicting Dp(ɛ). The new Dp(ɛ) models together with existing Dp(ɛ) models were tested against both measured data and independent data sets from literature. Twelve undisturbed 100cm3 peat soil cores were taken between the soil surface and down to 30-cm depth at Bibai wetland, Hokkaido, Japan. The soil cores were initially saturated with water, and drained at given matric potentials, pF=1.0, 1.5, 1.8, 2.0, 3.0, and 4.1 (where pF equals to log | Ψ | , Ψ: the soil-water matric potential in cm H2O), using the hanging water and pressure plate methods. At each matric potential, simultaneous measurements of volume shrinkage, soil-water retention, and Dp were conducted. Literature datasets of Dp(ɛ) for peat soil cores taken from different areas within the same wetland, specifically 12 samples from Iiyama and Hasegawa (2005) and 12 samples from Iiduka et al. (2008), were also used. A total of 191 measurements of Dp(ɛ) at pF ≤ 2.0 were applied for developing new Dp(ɛ) models for pF ≤ 2.0 where effects of shrinkage on Dp were assumed negligible. By modifying 3 existing Dp(ɛ) models, the Buckingham (1904) model, the Macroporosity-Dependent Model (MPD; Moldrup et al., 2000), and the Penman-Call model (Moldrup et al., 2005), we suggested 3 new Dp(ɛ) expressions for peat soil. In the Buckingham-based Dp(ɛ) model, a variable X(ɛ"w relationship (where X is the pore connectivity factor) derived from measurements was introduced in the Dp(ɛ) expression. In the Penman-Call-based Dp
International Nuclear Information System (INIS)
The safety and the reliability of a radioactive waste repository rely essentially on the confinement ability of the waste package and the storing structure. In the case of the low-level and intermediate level short-lived radioactive waste, the confinement property, relying on solid matrices made of cement-based materials, is assessed through a natural diffusion test, using a radioactive tracer, from which an effective diffusion coefficient is deduced. The evolution of the materials and more particularly the enhancement of the confinement properties of cement-based materials lead to test duration from a couple of months to a couple of years. The main objective of the present work involves the determination of the effective diffusion coefficient of reference chemical species, in our case the tritiated water, within a shorter time. The theoretical foundation is based on the description of ionic species mass transfer under the effects of an electrical field. With the definitions of a precise experimental protocol and of a formation factor, considered as an intrinsic topological feature of the porous network, it is possible to determine the effective diffusion coefficient of tritiated water for various types of concretes and mortars, and this within a few hours only. The comparison between the developed accelerated test, based on the application of a constant electrical field, and the normed natural diffusion test, using tritiated water, underlined two critical issues. First, omitting the impact of the radioactive decay of tritium during a natural diffusion test, leads to a non-negligible underestimation of the effective diffusion coefficient. Second, maintaining samples in high relative humidity conditions after casting is essential in order to avoid contrasted and unrelated results when performing the electrokinetic tests. Eventually, the validation of the electrokinetics technique, main objective of this work, rests on the assessment of the theoretical hypothesis
Jeong, S C; Kawakami, H
2003-01-01
We have examined, by a computer simulation, an on-line measurement of diffusion coefficients by using a short-lived alpha particle emitter, sup 8 Li (half life of 0.84s), as a radiotracer. The energy spectra of alpha particles emitted from diffusing sup 8 Li primarily implanted in the sample of LiAl ar simulated as a measure of the diffusion of sup 8 Li in the sample. As a possible time sequence for the measurement, a time cycle of 6s, i.e. the implantation of sup 8 Li for 1.5s and subsequent diffusion for 4.5s, is supposed. The sample is primarily set on a given temperature for the measurement. The time-dependent yields of alpha particles during the time cycle reveal the possibility to measure the diffusion coefficient with an accuracy of 10% if larger than 1 x 10 sup - sup 9 cm sup 2 /s, by the comparison with the experimental spectra measured at the temperature, i.e. at a certain diffusion coefficient. (author)
Directory of Open Access Journals (Sweden)
A. K. Tripathi
2011-02-01
Full Text Available Pitch-angle diffusion coefficients have been calculated for resonant interaction with electrostatic electron cyclotron harmonic (ECH waves in the magnetospheres of Earth, Jupiter, Saturn, Uranus and Neptune. Calculations have been performed at two radial distances of each planet. It is found that observed wave electric field amplitudes in the magnetospheres of Earth and Jupiter are sufficient to put electrons on strong diffusion in the energy range of less than 100 eV. However, for Saturn, Uranus and Neptune, the observed ECH wave amplitude are insufficient to put electrons on strong diffusion at any radial distance.
Hosoya, Osamu; Chono, Sumio; Saso, Yuko; Juni, Kazuhiko; Morimoto, Kazuhiro; Seki, Toshinobu
2004-12-01
The diffusion coefficient (D) of peptide and protein drugs needs to be determined to examine the permeability through biological barriers and to optimize delivery systems. In this study, the D values of fluorescein isothiocyanate (FITC)-labelled dextrans (FDs) and peptides were determined and the permeability through a porous membrane was discussed. The observed D values of FDs and peptides, except in the case of insulin, were similar to those calculated based on a relationship previously reported between the molecular weight and D of lower-molecular-weight compounds, although the molecular weight range was completely different. The observed D value of insulin was between the calculated values for the insulin monomer and hexamer. The permeability of poly-lysine and insulin through the membrane was determined and the observed values were compared with predicted values by using the relationship between molecular weight and D and an equation based on the Renkin function. The observed permeability of insulin through the membrane was between that of the predicted permeability for the insulin monomer and hexamer. For the permeation of insulin, the determination of D was useful for estimating the permeability because of the irregular relationship between molecular weight and D. The methodology used in this study will be useful for a more quantitative evaluation of the absorption of peptide and protein drugs applied to mucous membranes.
Le, Cheng-Feng; Li, Yun-Mei; Zha, Yong; Sun, De-Yong; Wang, Li-Zhen
2009-02-01
The spectral and chemical analytical data of Taihu Lake water quality in Nov. 8-22, 2007 were used to analyze the spectral characteristics of diffuse attenuation coefficient (Kd) of the water body in autumn and related affecting factors. On the basis of this analysis, the Kd at band 490 nm, Kd (490), was used as a variable to build the relationship between Kd and remote sensing reflectance. The results indicated that within the scope of visible band, the Kd of the water body at most locations of Taihu Lake presented an exponent decreasing trend with the increase of wave length. Due to the higher concentration of phytoplankton in some locations, a peak value of Kd was presented at band 675 nm. Non-organic suspended particles, because of their higher content in suspended sediment, had larger effects on Kd than organic suspended ones. There was a good correlation between Kd and remote sensing reflectance. Taking Rrs (550), Rrs (675) and Rrs (731) as independent variables and doing regression analysis with Kd (490), a good linear relationship was found between Kd (490) and Rrs (731), and multi-variate linear regression analysis using variables Rrs (550), Rrs (675) and Rrs (731) could get better effect (R2 > 0.96) than the regression analysis using variable Rrs (731). PMID:19459373
Isotopic mass-dependence of metal cation diffusion coefficients in liquid water
Energy Technology Data Exchange (ETDEWEB)
Bourg, I.C.; Richter, F.M.; Christensen, J.N.; Sposito, G.
2009-01-11
Isotope distributions in natural systems can be highly sensitive to the mass (m) dependence of solute diffusion coefficients (D) in liquid water. Isotope geochemistry studies routinely have assumed that this mass dependence either is negligible (as predicted by hydrodynamic theories) or follows a kinetic-theory-like inverse square root relationship (D {proportional_to} m{sup -0.5}). However, our recent experimental results and molecular dynamics (MD) simulations showed that the mass dependence of D is intermediate between hydrodynamic and kinetic theory predictions (D {proportional_to} m{sup -{beta}} with 0 {<=} {beta} < 0.2 for Li{sup +}, Cl{sup -}, Mg{sup 2+}, and the noble gases). In this paper, we present new MD simulations and experimental results for Na{sup +}, K{sup +}, Cs{sup +}, and Ca{sup 2+} that confirm the generality of the inverse power-law relation D {proportional_to} m{sup -{beta}}. Our new findings allow us to develop a general description of the influence of solute valence and radius on the mass dependence of D for monatomic solutes in liquid water. This mass dependence decreases with solute radius and with the magnitude of solute valence. Molecular-scale analysis of our MD simulation results reveals that these trends derive from the exponent {beta} being smallest for those solutes whose motions are most strongly coupled to solvent hydrodynamic modes.
DEFF Research Database (Denmark)
Zhelezny, Petr; Shapiro, Alexander
2006-01-01
is demonstrated. A series of such experiments was carried out. Several samples of carbonaceous and sandstone rock were investigated. The diffusion coefficients in porous media were determined by measuring the concentration of salt in different slices of a sample as a function of time. In cases where stable values...
International Nuclear Information System (INIS)
Hydrogen diffusion coefficients in a reduced activation ferritic/martensitic steel (F82H) and an oxide dispersion strengthened F82H (ODS-F82H) have been determined from depth profiles of plasma-loaded hydrogen with a tritium imaging plate technique (TIPT) in the temperature range from 298 K to 523 K. Data on hydrogen diffusion coefficients, D, in F82H, are summarized as D [m2*s-1] =1.1*10-7exp(-16[kJ mol-1]/RT). The present data indicate almost no trapping effect on hydrogen diffusion due to an excess entry of energetic hydrogen by the plasma loading, which results in saturation of the trapping sites at the surface and even in the bulk. In the case of ODS-F82H, data of hydrogen diffusion coefficients are summarized as D [m2*s-1] =2.2*10-7exp(-30[kJ mol-1]/RT) indicating a remarkable trapping effect on hydrogen diffusion caused by tiny oxide particles (Y2O3) in the bulk of F82H. Such oxide particles introduced in the bulk may play an effective role not only on enhancement of mechanical strength but also on suppression of hydrogen penetration by plasma loading
Manapova, Aigul
2016-08-01
We consider optimal control problems for second order elliptic equations with non-self-adjoint operators-convection-diffusion problems. Control processes are described by semi-linear convection-diffusion equation with discontinuous data and solutions (states) subject to the boundary interface conditions of imperfect type (i.e., problems with a jump of the coefficients and the solution on the interface; the jump of the solution is proportional to the normal component of the flux). Controls are involved in the coefficients of diffusion and convective transfer. We prove differentiability and Lipshitz continuity of the cost functional, depending on a state of the system and a control. The calculation of the gradients uses the numerical solutions of direct problems for the state and adjoint problems.
Diffusion weighted imaging in the liver
Kele, Petra G.; van der Jagt, Eric J.
2010-01-01
Diffusion weighted magnetic resonance imaging (DWI) is an imaging technique which provides tissue contrast by the measurement of diffusion properties of water molecules within tissues. Diffusion is expressed in an apparent diffusion coefficient (ADC), which reflects the diffusion properties unique t
Analysis of ligand-protein exchange by Clustering of Ligand Diffusion Coefficient Pairs (CoLD-CoP)
Snyder, David A.; Chantova, Mihaela; Chaudhry, Saadia
2015-06-01
NMR spectroscopy is a powerful tool in describing protein structures and protein activity for pharmaceutical and biochemical development. This study describes a method to determine weak binding ligands in biological systems by using hierarchic diffusion coefficient clustering of multidimensional data obtained with a 400 MHz Bruker NMR. Comparison of DOSY spectrums of ligands of the chemical library in the presence and absence of target proteins show translational diffusion rates for small molecules upon interaction with macromolecules. For weak binders such as compounds found in fragment libraries, changes in diffusion rates upon macromolecular binding are on the order of the precision of DOSY diffusion measurements, and identifying such subtle shifts in diffusion requires careful statistical analysis. The "CoLD-CoP" (Clustering of Ligand Diffusion Coefficient Pairs) method presented here uses SAHN clustering to identify protein-binders in a chemical library or even a not fully characterized metabolite mixture. We will show how DOSY NMR and the "CoLD-CoP" method complement each other in identifying the most suitable candidates for lysozyme and wheat germ acid phosphatase.
van Berkel, M; Zwart, H.J.; Hogeweij, G. M. D.; Vandersteen, G.; van den Brand, H.; M.R. de Baar; ASDEX Upgrade team
2014-01-01
In this paper, the estimation of the thermal diffusivity from perturbative experiments in fusion plasmas is discussed. The measurements used to estimate the thermal diffusivity suffer from stochastic noise. Accurate estimation of the thermal diffusivity should take this into account. It will be shown that formulas found in the literature often result in a thermal diffusivity that has a bias (a difference between the estimated value and the actual value that remains even if more measurements a...
A method for estimating the diffuse attenuation coefficient (KdPAR)from paired temperature sensors
Read, Jordan S.; Rose, Kevin C.; Winslow, Luke A.; Read, Emily Kara
2015-01-01
A new method for estimating the diffuse attenuation coefficient for photosynthetically active radiation (KdPAR) from paired temperature sensors was derived. We show that during cases where the attenuation of penetrating shortwave solar radiation is the dominant source of temperature changes, time series measurements of water temperatures at multiple depths (z1 and z2) are related to one another by a linear scaling factor (a). KdPAR can then be estimated by the simple equation KdPAR ln(a)/(z2/z1). A suggested workflow is presented that outlines procedures for calculating KdPAR according to this paired temperature sensor (PTS) method. This method is best suited for conditions when radiative temperature gains are large relative to physical noise. These conditions occur frequently on water bodies with low wind and/or high KdPARs but can be used for other types of lakes during time periods of low wind and/or where spatially redundant measurements of temperatures are available. The optimal vertical placement of temperature sensors according to a priori knowledge of KdPAR is also described. This information can be used to inform the design of future sensor deployments using the PTS method or for campaigns where characterizing sub-daily changes in temperatures is important. The PTS method provides a novel method to characterize light attenuation in aquatic ecosystems without expensive radiometric equipment or the user subjectivity inherent in Secchi depth measurements. This method also can enable the estimation of KdPAR at higher frequencies than many manual monitoring programs allow.
Berkel, van M.; Zwart, H.J.; Hogeweij, G.M.D.; Vandersteen, G.; Brand, van den H.; Baar, de M.R.
2014-01-01
In this paper, the estimation of the thermal diffusivity from perturbative experiments in fusion plasmas is discussed. The measurements used to estimate the thermal diffusivity suffer from stochastic noise. Accurate estimation of the thermal diffusivity should take this into account. It will be show
DEFF Research Database (Denmark)
Mejlbro, Leif
1996-01-01
Fick's Second Law of Diffusion with time-dependent diffusioncoefficient and surface concentration is solved. Mimicking the classicalsolution, special time-dependent surface concentration functions areconsidered. These models are used in giving estimates of the lifetimeof the structure, when the...
Lu, Yan; Li, Mingzhong
2016-01-01
The solubility and diffusion coefficient are two of the most important physicochemical properties of a drug compound. In practice, both have been measured separately, which is time consuming. This work utilizes a novel technique of UV imaging to determine the solubility and diffusion coefficients of poorly water-soluble drugs simultaneously. A 2-step optimal method is proposed to determine the solubility and diffusion coefficients of a poorly water-soluble pharmaceutical substance based on the Fick's second law of diffusion and UV imaging measurements. Experimental results demonstrate that the proposed method can be used to determine the solubility and diffusion coefficients of a drug with reasonable accuracy, indicating that UV imaging may provide a new opportunity to accurately measure the solubility and diffusion coefficients of a poorly water-soluble drug simultaneously and rapidly. PMID:26852848
Institute of Scientific and Technical Information of China (English)
SUN Guowen; SUN Wei; ZHANG Yunsheng; LIU Zhiyong
2012-01-01
N-layered spherical inclusions model was used to calculate the effective diffusion coefficient of chloride ion in cement-based materials by using multi-scale method and then to investigate the relationship between the diffusivity and the microstructure of cement-basted materials where the microstructure included the interfacial transition zone (ITZ) between the aggregates and the bulk cement pastes as well as the microstructure of the bulk cement paste itself.For the convenience of applications,the mortar and concrete were considered as a four-phase spherical model,consisting of cement continuous phase,dispersed aggregates phase,interface transition zone and their homogenized effective medium phase.A general effective medium equation was estabhshed to calculate the diffusion coefficient of the hardened cement paste by considering the microstructure.During calculation,the tortuosity (n) and eonstrictivity factors (Ds/D0) of pore in the hardened pastes are n≈3.2,Ds/D0=1.0× 10-4 respectively from the test data.The calculated results using the n-layered spherical inclusions model are in good agreement with the experimental results; The effective diffusion coefficient of ITZ is 12 times that of the bulk cement for mortar and 17 times for concrete due to the difference between particle size distribution and the volume fraction of aggregates in mortar and concrete.
Gubar, Yu. I.
2015-11-01
A radial profile of the plasma mass distribution in Jupiter's magnetosphere in the region beyond Io's orbit up to ˜15 Jupiter radii R J constructed according to the results of measurements on the Voyager 1 and Galileo spacecraft is used to determine the radial dependence and radial diffusion coefficient D LL . The initial profile is approximated by a function decreasing as L -5 ± 1. For this radial mass distribution, radial ion diffusion outside of Io's orbit caused by centrifugal forces is possible. An estimate of (1.2-6.7)10-11 L 6 ± 1 for D LL was obtained.
Montejo, Ludguier D.; Jia, Jingfei; Kim, Hyun K.; Hielscher, Andreas H.
2013-03-01
We apply the Fourier Transform to absorption and scattering coefficient images of proximal interphalangeal (PIP) joints and evaluate the performance of these coefficients as classifiers using receiver operator characteristic (ROC) curve analysis. We find 25 features that yield a Youden index over 0.7, 3 features that yield a Youden index over 0.8, and 1 feature that yields a Youden index over 0.9 (90.0% sensitivity and 100% specificity). In general, scattering coefficient images yield better one-dimensional classifiers compared to absorption coefficient images. Using features derived from scattering coefficient images we obtain an average Youden index of 0.58 +/- 0.16, and an average Youden index of 0.45 +/- 0.15 when using features from absorption coefficient images.
Cao, Fang; Fichot, Cedric G.; Hooker, Stanford B.; Miller, William L.
2014-01-01
Photochemical processes driven by high-energy ultraviolet radiation (UVR) in inshore, estuarine, and coastal waters play an important role in global bio geochemical cycles and biological systems. A key to modeling photochemical processes in these optically complex waters is an accurate description of the vertical distribution of UVR in the water column which can be obtained using the diffuse attenuation coefficients of down welling irradiance (Kd()). The Sea UV Sea UVc algorithms (Fichot et al., 2008) can accurately retrieve Kd ( 320, 340, 380,412, 443 and 490 nm) in oceanic and coastal waters using multispectral remote sensing reflectances (Rrs(), Sea WiFS bands). However, SeaUVSeaUVc algorithms are currently not optimized for use in optically complex, inshore waters, where they tend to severely underestimate Kd(). Here, a new training data set of optical properties collected in optically complex, inshore waters was used to re-parameterize the published SeaUVSeaUVc algorithms, resulting in improved Kd() retrievals for turbid, estuarine waters. Although the updated SeaUVSeaUVc algorithms perform best in optically complex waters, the published SeaUVSeaUVc models still perform well in most coastal and oceanic waters. Therefore, we propose a composite set of SeaUVSeaUVc algorithms, optimized for Kd() retrieval in almost all marine systems, ranging from oceanic to inshore waters. The composite algorithm set can retrieve Kd from ocean color with good accuracy across this wide range of water types (e.g., within 13 mean relative error for Kd(340)). A validation step using three independent, in situ data sets indicates that the composite SeaUVSeaUVc can generate accurate Kd values from 320 490 nm using satellite imagery on a global scale. Taking advantage of the inherent benefits of our statistical methods, we pooled the validation data with the training set, obtaining an optimized composite model for estimating Kd() in UV wavelengths for almost all marine waters. This
Institute of Scientific and Technical Information of China (English)
Xin Cun TANG; Tian Duo LI
2005-01-01
In this paper, the capacity titration technique (CT technique) was developed on basis of the RPG (ratio of potentio-charge capacity to galvano-charge capacity) method to continuously determine the solid diffusion coefficient D of the intercalary species within insertion-host materials with a small voltage region. The linear equations of D vs. q (value of ratio of the potentio-charge capacity to the galvano-charge capacity) were given in different range of q. By the CT technique,the Li+ solid diffusion coefficients D within LiMn2O4 at different voltages were determined. The results showed that the values of D varied from 3.447× 10-9 cm2/s to 7.60× 10-11cm2/s in the voltage range of charge from 3.3V to 4.3V as a function of voltage with "W" shape.
International Nuclear Information System (INIS)
After having presented the issue of radioactive waste storage, the concept of geological storage and its application in the Meuse/Haute-Marne underground laboratory, and described the Callovo-Oxfordian geological formation and the argillite transport properties, this research thesis aims at developing a prediction of these properties at a macroscopic scale for water and anions. A first part presents the different experimental means implemented to acquire the diffusion coefficients for the studied materials (Callovo-Oxfordian argillite and purified Puy illite), and the spatial organisation of minerals by LIBS probe-based mapping to highlight a relationship between rock microstructure and its transport macroscopic properties. The next part presents the models which have been developed at the nanometer and micrometre scale to predict the diffusion coefficients. Experimental results are then compared with computed values
Rastorguev, A S; Utkin, N D
2016-01-01
Agekyan lambda-factor that accounts for the effect of multiple distant encounters with large impact factors is used for the first time to compute the diffusion coefficients in the velocity space of a stellar system. It is shown that in this case the cumulative effect - the total contribution of distant encounters to the change in the velocity of the test star - is finite, and the logarithmic divergence inherent to the classical description disappears. At the same time, the formulas for the diffusion coefficients, as before, contain the logarithm of the ratio of two independent scale factors that fully characterize the state of the stellar system: the average interparticle distance and the impact parameter of a close encounter. However, the physical meaning of this factor is no longer associated with the classical logarithmic divergence.
Use of NMR Imaging to Determine the Diffusion Coefficient of Water in Bio-based Hydrogels
The diffusion of liquid in a hydrogel material is a fundamental property which must be controlled in order to create effective delivery systems for the agricultural and pharmaceutical industries. NMR spectroscopy has been used to determine the diffusion of water and deuterium oxide in a bio-based h...
Institute of Scientific and Technical Information of China (English)
赵长伟; 马沛生
2004-01-01
The diffusion coefficients of aqueous L-threonine solutions were determined from 298.15K to 328.15K by the metallic diaphragm cell method with accuracy, promptness and convenience. Meanwhile, the densities and viscosities of the solutions were also determined and correlated. Based on a seml-empirical model for correlating the diffusion coefficients of some amino acids in their aqueous solutions, a new semi-empirical model for correlating the diffusion coefficients involving temperature was provided, which is more comprehensive and less experiment dependent compared to the previous model. The fitting results are satisfactory. Compared to a former model for correlating the diffusion coefficients of solid organic salts in their aqueous solutions, this model provides significant improvement in correlation of diffusion coefficients with different temperatures avoiding arduous work.
Raul Bardaji; Albert-Miquel Sánchez; Carine Simon; Wernand, Marcel R.; Jaume Piera
2016-01-01
A critical parameter to assess the environmental status of water bodies is the transparency of the water, as it is strongly affected by different water quality related components (such as the presence of phytoplankton, organic matter and sediment concentrations). One parameter to assess the water transparency is the diffuse attenuation coefficient. However, the number of subsurface irradiance measurements obtained with conventional instrumentation is relatively low, due to instrument costs an...
Institute of Scientific and Technical Information of China (English)
Hamid Reza Rafiee; Mina Rastgar; Neda Heidari
2011-01-01
The accurate reduced potential energies for two binary gas mixtures including benzenemethanol and methane-tetrafluoromethane at low density have been obtained by direct inversion of the viscosity collision integral equations.The kinetic theory along with the extended principle of corresponding-states has been used to calculate the viscosity and diffusion coefficients over a wide range of temperature and composition.Good agreements between calculated and experimental data are obtained.
Ahl, J.; Liukkonen, S.
1999-01-01
The tracer diffusion coefficients of sodium-22-chloride were determined as function of magnesium chloride concentrations in aqueous solutions (10-4...1 mol dm-3) at 25°C. Closed capillary method was used in experiments. The most accurate method to calculate the tracer diffusion coefficient from an infinite series solution was further developed. The Onsager limiting law was verified to the tracer diffusion of 22NaCl in aqueous magnesium chloride in low concentration region.
Institute of Scientific and Technical Information of China (English)
WUQI－TANG; J.L.MOREL; 等
1994-01-01
The supply of cadmium from soil to plant roots mainly depends on the diffusion prooess.This work was conducted to study the effects of some soil properties on cadmium diffusion coefficient (D) in soil. Measurements were made using the Shofield and Graham-Bryce's isotopic labelling method.Cadmium diffusion coefficients varied from 10-7to 10-9 cms2-1.Higher values were observed in acid sandy soils and lower values in calcareous clay soils.Liming an acid soil resulted in a substantial decrease of D.Addition of cadmium as nitrate salt generally increased D,while addition of sewage sludge and organic matter resulted in a significant decrease of cadmium diffusion.The rhizospheric activity also induced a moderate reduction in D.The relationships between D(10-9cms2-1)on the on hand and soil pH.moisture(Mc,g kg-1) ,organic matter(OM,g kg-1),clay(Cy,gkg-1)and cadmium content(Cd,mgkg-1) on the other were obtained by the multiple regression:D=182.1-29.91pH+0.210Mc-0.303OM+0.011Cy+1.64Cd(R2=0.859,n=22).
Inoue, Gen; Yokoyama, Kouji; Ooyama, Junpei; Terao, Takeshi; Tokunaga, Tomomi; Kubo, Norio; Kawase, Motoaki
2016-09-01
The reduction of oxygen transfer resistance through porous components consisting of a gas diffusion layer (GDL), microporous layer (MPL), and catalyst layer (CL) is very important to reduce the cost and improve the performance of a PEFC system. This study involves a systematic examination of the relationship between the oxygen transfer resistance of the actual porous components and their three-dimensional structure by direct measurement with FIB-SEM and X-ray CT. Numerical simulations were carried out to model the properties of oxygen transport. Moreover, based on the model structure and theoretical equations, an approach to the design of new structures is proposed. In the case of the GDL, the binder was found to obstruct gas diffusion with a negative effect on performance. The relative diffusion coefficient of the MPL is almost equal to that of the model structure of particle packing. However, that of CL is an order of magnitude less than those of the other two components. Furthermore, an equation expressing the relative diffusion coefficient of each component can be obtained with the function of porosity. The electrical conductivity of MPL, which is lower than that of the carbon black packing, is considered to depend on the contact resistance.
Monte Carlo simulation of diffuse attenuation coefficient in presence of non uniform profiles
Digital Repository Service at National Institute of Oceanography (India)
Desa, E.S.; Desai, R.G.P.; Desa, B.A.E.
This paper presents a Monte Carlo simulation of the vertical depth structure of the downward attenuation coefficient (K sub(d)), and the irradiance reflectance (R) for a given profile of chlorophyll. The results are in quantitaive agreement...
Coefficient of Thermal Diffusivity of Insulation Brick Developed from Sawdust and Clays
Bwayo, E.; Obwoya, S. K.
2014-01-01
This paper presents an experimental result on the effect of particle size of a mixture of ball clay, kaolin, and sawdust on thermal diffusivity of ceramic bricks. A mixture of dry powders of ball clay, kaolin of the same particle size, and sawdust of different particle sizes was mixed in different proportions and then compacted to high pressures before being fired to 950°C. The thermal diffusivity was then determined by an indirect method involving measurement of thermal conductivity, density...
Inoue, Gen; Kawase, Motoaki
2016-09-01
It is important to reduce the oxygen diffusion resistance through PEFC porous electrode, because it is the key to reduce the PEFC cost. However, the gas diffusion coefficient of CL is lower than MPL in spite of framework consisted of same carbon blacks. In this study, in order to understand the reasons of the lower gas diffusion performance of CL, the relationship between a carbon black agglomerate structure and ionomer adhesion condition is evaluated by a numerical analysis with an actual reconstructed structure and a simulated structure. As a result, the gas diffusion property of CL strongly depends on the ionomer adhesion shape. In the case of adhesion shape with the same curvature of ionomer interface, each pore can not be connected enough. So the pore tortuosity increases. Moreover, in the case of existence of inefficient large pores formed by carbon black agglomerate and ununiformly coated ionomer, the gas diffusion performance decrease rapidly. As the measurement values in actual CL are almost equal to that with model structure with inefficient large pores. These characteristics can be confirmed by actual cross-section image obtained by FIB-SEM.
Estimating Tortuosity Coefficients Based on Hydraulic Conductivity.
Carey, Grant R; McBean, Edward A; Feenstra, Stan
2016-07-01
While the tortuosity coefficient is commonly estimated using an expression based on total porosity, this relationship is demonstrated to not be applicable (and thus is often misapplied) over a broad range of soil textures. The fundamental basis for a correlation between the apparent diffusion tortuosity coefficient and hydraulic conductivity is demonstrated, although such a relationship is not typically considered. An empirical regression for estimating the tortuosity coefficient based on hydraulic conductivity for saturated, unconsolidated soil is derived based on results from 14 previously reported diffusion experiments performed with a broad range of soil textures. Analyses of these experimental results confirm that total porosity is a poor predictor for the tortuosity coefficient over a large range of soil textures. The apparent diffusion tortuosity coefficient is more reliably estimated based on hydraulic conductivity. PMID:27315019
Directory of Open Access Journals (Sweden)
Yuan Hung Lo
2013-01-01
Full Text Available Little is known about how small variations in ionic currents and Ca2+ and Na+ diffusion coefficients impact action potential and Ca2+ dynamics in rabbit ventricular myocytes. We applied sensitivity analysis to quantify the sensitivity of Shannon et al. model (Biophys. J., 2004 to 5%–10% changes in currents conductance, channels distribution, and ion diffusion in rabbit ventricular cells. We found that action potential duration and Ca2+ peaks are highly sensitive to 10% increase in L-type Ca2+ current; moderately influenced by 10% increase in Na+-Ca2+ exchanger, Na+-K+ pump, rapid delayed and slow transient outward K+ currents, and Cl− background current; insensitive to 10% increases in all other ionic currents and sarcoplasmic reticulum Ca2+ fluxes. Cell electrical activity is strongly affected by 5% shift of L-type Ca2+ channels and Na+-Ca2+ exchanger in between junctional and submembrane spaces while Ca2+-activated Cl−-channel redistribution has the modest effect. Small changes in submembrane and cytosolic diffusion coefficients for Ca2+, but not in Na+ transfer, may alter notably myocyte contraction. Our studies highlight the need for more precise measurements and further extending and testing of the Shannon et al. model. Our results demonstrate usefulness of sensitivity analysis to identify specific knowledge gaps and controversies related to ventricular cell electrophysiology and Ca2+ signaling.
Institute of Scientific and Technical Information of China (English)
赵长伟; 李继定; 马沛生; 夏淑倩
2005-01-01
The diffusion coefficients of aqueous solutions ofglycine, L-alanine, L-valine and L-isoleucine at 298.15 K were determined by holographic interferometry with accuracy and promptness while without disturbance. The density and viscosity of these solutions were also determined. According to original Gordon model, a model for correlating the diffusion coefficients of amino acids in aqueous solutions was developed and applied. The results showed that this model provided significant convenience in correlation of diffusion coefficients for amino acids system.
Determination of Kubelka-Munk scattering and absorption coefficients by diffuse illumination
Molenaar, R; ten Bosch, JJ; Zijp, [No Value
1999-01-01
The Kubelka-Munk theory, although it provides an equation that relates the reflection of a sample under diffuse illumination to certain of its properties, does not take boundary reflectance into account. Boundary reflection is always present because there is always a difference between the refractiv
Determination of water diffusion coefficient by gamma radiation and thermal shock
International Nuclear Information System (INIS)
Mass transfer coefficient of water in a porous material (baked clay) is determined by gamma ray attenuation (from a Cs135 source) and thermal shock. Water content is found higher by thermal shock, difference obtained between the two methods is discussed. 7 refs
Bisetti, Fabrizio
2012-12-01
Simulations of ion and electron transport in flames routinely adopt plasma fluid models, which require transport coefficients to compute the mass flux of charged species. In this work, the mobility and diffusion coefficient of thermal electrons in atmospheric premixed methane/air flames are calculated and analyzed. The electron mobility is highest in the unburnt region, decreasing more than threefold across the flame due to mixture composition effects related to the presence of water vapor. Mobility is found to be largely independent of equivalence ratio and approximately equal to 0.4m 2V -1s -1 in the reaction zone and burnt region. The methodology and results presented enable accurate and computationally inexpensive calculations of transport properties of thermal electrons for use in numerical simulations of charged species transport in flames. © 2012 The Combustion Institute.
International Nuclear Information System (INIS)
The present paper deals with numerical simulations of complete phase change process inside porous media, based on the two-phase mixture model, using finite volume method for discretization. The investigation proposes a successful remedy in order to eliminate the occurrence of 'jump' in predicted properties, by introducing an efficient smoothing algorithm for the effective diffusion coefficient. A thorough parametric study also indicates that the adoption of proposed remedy does not alter the true or expected solution. All tested cases, covering applicable ranges of parametric variations, could be physically interpreted. The methodology is, therefore, recommended for future simulations of complete phase change processes within porous media. (authors)
Relationship between Secchi depth and the diffuse light attenuation coefficient in Danish estuaries
DEFF Research Database (Denmark)
Murray, Ciarán; Markager, Stiig
Analyis of temporal and spatial variation in the in the relationship between light attenuation and Secchi depth in Danish monitoring data There can be found timeseries of Secchi depth measurements in Danish waters which extend relatively far back in time. The Secchi depth measurement is therefore...... useful in that it allows comparison of present conditions with these older observations. An empirical inverse relationship between Secchi depth and light attenuation coefficient, Kd, has traditionally been used to estimate the light attenuation coefficient from Secchi depth measurements. However, studies...... to the present. Our study analyses the temporal and spatial variation in the in the relationship between the light attenuation and the secchi disk depth and attempts to give explanations for this variation....
Albedo and flux extinction coefficient of impure snow for diffuse shortwave radiation
Choudhury, B. J.; Mo, T.; Wang, J. R.; Chang, A. T. C.
1981-01-01
Impurities enter a snowpack as a result of fallout of scavenging by falling snow crystals. Albedo and flux extinction coefficient of soot contaminated snowcovers were studied using a two stream approximation of the radiative transfer equation. The effect of soot was calculated by two methods: independent scattering by ice grains and impurities and average refractive index for ice grains. Both methods predict a qualitatively similar effect of soot; the albedo is decreased and the extinction coefficient is increased compared to that for pure snow in the visible region; the infrared properties are largely unaffected. Quantitatively, however, the effect of soot is more pronounced in the average refractive index method. Soot contamination provides a qualitative explanation for several snow observations.
Bardaji, Raul; Sánchez, Albert-Miquel; Simon, Carine; Wernand, Marcel R; Piera, Jaume
2016-01-01
A critical parameter to assess the environmental status of water bodies is the transparency of the water, as it is strongly affected by different water quality related components (such as the presence of phytoplankton, organic matter and sediment concentrations). One parameter to assess the water transparency is the diffuse attenuation coefficient. However, the number of subsurface irradiance measurements obtained with conventional instrumentation is relatively low, due to instrument costs and the logistic requirements to provide regular and autonomous observations. In recent years, the citizen science concept has increased the number of environmental observations, both in time and space. The recent technological advances in embedded systems and sensors also enable volunteers (citizens) to create their own devices (known as Do-It-Yourself or DIY technologies). In this paper, a DIY instrument to measure irradiance at different depths and automatically calculate the diffuse attenuation Kd coefficient is presented. The instrument, named KdUINO, is based on an encapsulated low-cost photonic sensor and Arduino (an open-hardware platform for the data acquisition). The whole instrument has been successfully operated and the data validated comparing the KdUINO measurements with the commercial instruments. Workshops have been organized with high school students to validate its feasibility. PMID:26999132
Directory of Open Access Journals (Sweden)
Raul Bardaji
2016-03-01
Full Text Available A critical parameter to assess the environmental status of water bodies is the transparency of the water, as it is strongly affected by different water quality related components (such as the presence of phytoplankton, organic matter and sediment concentrations. One parameter to assess the water transparency is the diffuse attenuation coefficient. However, the number of subsurface irradiance measurements obtained with conventional instrumentation is relatively low, due to instrument costs and the logistic requirements to provide regular and autonomous observations. In recent years, the citizen science concept has increased the number of environmental observations, both in time and space. The recent technological advances in embedded systems and sensors also enable volunteers (citizens to create their own devices (known as Do-It-Yourself or DIY technologies. In this paper, a DIY instrument to measure irradiance at different depths and automatically calculate the diffuse attenuation Kd coefficient is presented. The instrument, named KdUINO, is based on an encapsulated low-cost photonic sensor and Arduino (an open-hardware platform for the data acquisition. The whole instrument has been successfully operated and the data validated comparing the KdUINO measurements with the commercial instruments. Workshops have been organized with high school students to validate its feasibility.
Institute of Scientific and Technical Information of China (English)
Ahmed Asad; Wu Jiang-Tao
2011-01-01
We use non-equilibrium molecular dynamics simulations to calculate the self-diffusion coefficient,D,of a Lennard Jones fluid over a wide density and temperature range.The change in self-diffusion coefficient with temperature decreases by increasing density.For density p* =pσ3 =0.84 we observe a peak at the value of the self-diffusion coefficient and the critical temperature T* =kT/ε =1.25.The value of the self-diffusion coefficient strongly depends on system size.The data of the self-diffusion coefficient are fitted to a simple analytic relation based on hydrodynamic arguments.This correction scales as N-α,where α is an adjustable parameter and N is the number of particles.It is observed that the values of α ＜ 1 provide quite a good correction to the simulation data.The system size dependence is very strong for lower densities,but it is not as strong for higher densities.The self-diffusion coefficient calculated with non-equilibrium molecular dynamic simulations at different temperatures and densities is in good agreement with other calculations from the literature.
Skarpalezos, Loukas; Argyrakis, Panos; Vikhrenko, Vyacheslav S.
2014-05-01
We investigate the self-intermediate scattering function (SISF) in a three-dimensional (3D) cubic lattice fluid (interacting lattice gas) with attractive nearest-neighbor interparticle interactions at a temperature slightly above the critical one by means of Monte Carlo simulations. A special representation of SISF as an exponent of the mean tracer diffusion coefficient multiplied by the geometrical factor and time is considered to highlight memory effects that are included in time and wave-vector dependence of the diffusion coefficient. An analytical expression for the diffusion coefficient is suggested to reproduce the simulation data. It is shown that the particles' mean-square displacement is equal to the time integral of the diffusion coefficient. We make a comparison with the previously considered 2D system on a square lattice. The main difference with the two-dimensional case is that the time dependence of particular characteristics of the tracer diffusion coefficient in the 3D case cannot be described by exponentially decreasing functions, but requires using stretched exponentials with rather small values of exponents, of the order of 0.2. The hydrodynamic values of the tracer diffusion coefficient (in the limit of large times and small wave vectors) defined through SIFS simulation results agree well with the results of its direct determination by the mean-square displacement of the particles in the entire range of concentrations and temperatures.
International Nuclear Information System (INIS)
The effect of soil water content and phosphate fertilization vz. phosphate diffusion on plant growth and p-uptake was studied by use of tracer technique. Two experiments were conducted using three different Egyptian soils, i.e. clay from Bahtim, loamy from Burg El-Arab and sandy loam from Abou-Zaabal. The first was a laboratory experiment and aimed to determine the self diffusion coefficient of 32P, sup(D)P, in these different soils, as affected by soil moisture content and phosphate fertilization. The second was a pot experiment conducted to further investigate the uptake and dry matter yield of corn plants under the same conditions mentioned in the first experiment. The data revealed that as the P applied was raised from 0 to 100 Kgp/Fed, the values of sup(D)P were increased with different magnitude according to the soil texture and its moisture content. The highest values for the sup(D)P were of the clay soil of Bahtim, while the lowest were of the sandy loam soil of Abou-Zaabal. The data showed the positive trends towards increasing the sup(D)P values with increasing soil moisture contents. The study of pot experiment showed that plant uptake of P is closely related to the diffusion coefficient of P in soils. The practical implication of the present study indicates that more phosphorus needs to be applied to crops during periods of moisture stress than during periods of adequate soil moisture level to provide optimum phosphorus nutrition to plants. The clay soils should show less tendency toward P deficiency during dry conditions than would sandy soils having less clay. Similarly, irrigation should help to overcome P-deficiencies, particularly on light-textured soils. (author)
Energy Technology Data Exchange (ETDEWEB)
Wang, Jinyang; Zhong, Haimin; Qiu, Wenda; Chen, Liuping, E-mail: cesclp@mail.sysu.edu.cn [KLGHEI of Environment and Energy Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Feng, Huajie [School of Chemistry and Chemical Engineering, Hainan Normal University, Haikou 571158 (China)
2014-03-14
The binary infinite dilute diffusion coefficients, D{sub 12}{sup ∞}, of some alkylbenzenes (Ph-C{sub n}, from Ph-H to Ph-C{sub 12}) from 313 K to 333 K at 15 MPa in supercritical carbon dioxide (scCO{sub 2}) have been studied by molecular dynamics (MD) simulation. The MD values agree well with the experimental ones, which indicate MD simulation technique is a powerful way to predict and obtain diffusion coefficients of solutes in supercritical fluids. Besides, the local structures of Ph-C{sub n}/CO{sub 2} fluids are further investigated by calculating radial distribution functions and coordination numbers. It qualitatively convinces that the first solvation shell of Ph-C{sub n} in scCO{sub 2} is significantly influenced by the structure of Ph-C{sub n} solute. Meanwhile, the mean end-to-end distance, the mean radius of gyration and dihedral angle distribution are calculated to gain an insight into the structural properties of Ph-C{sub n} in scCO{sub 2}. The abnormal trends of radial distribution functions and coordination numbers can be reasonably explained in term of molecular flexibility. Moreover, the computed results of dihedral angle clarify that flexibility of long-chain Ph-C{sub n} is the result of internal rotation of C-C single bond (σ{sub c-c}) in alkyl chain. It is interesting that compared with n-alkane, because of the existence of benzene ring, the flexibility of alkyl chain in Ph-C{sub n} with same carbon atom number is significantly reduced, as a result, the carbon chain dependence of diffusion behaviors for long-chain n-alkane (n ≥ 5) and long-chain Ph-C{sub n} (n ≥ 4) in scCO{sub 2} are different.
Wang, Jinyang; Zhong, Haimin; Feng, Huajie; Qiu, Wenda; Chen, Liuping
2014-03-14
The binary infinite dilute diffusion coefficients, D₁₂(∞), of some alkylbenzenes (Ph-C(n), from Ph-H to Ph-C12) from 313 K to 333 K at 15 MPa in supercritical carbon dioxide (scCO2) have been studied by molecular dynamics (MD) simulation. The MD values agree well with the experimental ones, which indicate MD simulation technique is a powerful way to predict and obtain diffusion coefficients of solutes in supercritical fluids. Besides, the local structures of Ph-C(n)/CO2 fluids are further investigated by calculating radial distribution functions and coordination numbers. It qualitatively convinces that the first solvation shell of Ph-C(n) in scCO2 is significantly influenced by the structure of Ph-C(n) solute. Meanwhile, the mean end-to-end distance, the mean radius of gyration and dihedral angle distribution are calculated to gain an insight into the structural properties of Ph-C(n) in scCO2. The abnormal trends of radial distribution functions and coordination numbers can be reasonably explained in term of molecular flexibility. Moreover, the computed results of dihedral angle clarify that flexibility of long-chain Ph-C(n) is the result of internal rotation of C-C single bond (σ(c-c)) in alkyl chain. It is interesting that compared with n-alkane, because of the existence of benzene ring, the flexibility of alkyl chain in Ph-C(n) with same carbon atom number is significantly reduced, as a result, the carbon chain dependence of diffusion behaviors for long-chain n-alkane (n ≥ 5) and long-chain Ph-C(n) (n ≥ 4) in scCO2 are different.
Baricci, Andrea; Casalegno, Andrea
2016-09-01
Limiting current density of oxygen reduction reaction in polymer electrolyte fuel cells is determined by several mass transport resistances that lower the concentration of oxygen on the catalyst active site. Among them, diffusion across porous media plays a significant role. Despite the extensive experimental activity documented in PEMFC literature, only few efforts have been dedicated to the measurement of the effective transport properties in porous layers. In the present work, a methodology for ex situ measurement of the effective diffusion coefficient and Knudsen radius of porous layers for polymer electrolyte fuel cells (gas diffusion layer, micro porous layer and catalyst layer) is described and applied to high temperature polymer fuel cells State of Art materials. Regression of the measured quantities by means of a quasi 2D physical model is performed to quantify the Knudsen effect, which is reported to account, respectively, for 30% and 50% of the mass transport resistance in micro porous layer and catalyst layer. On the other side, the model reveals that pressure gradient consequent to permeation in porous layers of high temperature polymer fuel cells has a negligible effect on oxygen concentration in relevant operating conditions.
Institute of Scientific and Technical Information of China (English)
XIANG Jiang; LI Ding; CAI Huishan
2008-01-01
In this paper, a new method to derive the Fokker-Planck coefficients defined by a non-Maxwellian velocity distribution function for the field particles is presented. The three-fold integral and the new Debye cutoff parameter, which were introduced by CHANG and LI, are applied. Therefore, divergence difficulties and the customary replacement of relative velocity g by thermal velocity νth are naturally avoided. The probability function P(ν, △ν) for non-Maxwellian scattering is derived by the method of choosing velocity transfer △ν, which is a true measure of collision intensity, as an independent variable. The method enables the difference between small-angle scattering and small-momentum-transfer collisions of the inverse-square force to be well clarified. With the help of the probability function, the Fokker-Planck coefficients are obtained by a normal original Fokker-Planck approach. The friction and diffusion coefficients of the Fokker-Planck equation are modified for non-Maxwellian scattering and are used to investigate the relaxation processes for the weakly coupled plasma. The profiles of the relaxation rates show that the slowing down and deflection processes are weakened in the conditions of non-Maxwellian scattering.
Directory of Open Access Journals (Sweden)
Jianyin Xiong
Full Text Available The diffusion coefficient (D(m and material/air partition coefficient (K are two key parameters characterizing the formaldehyde and volatile organic compounds (VOC sorption behavior in building materials. By virtue of the sorption process in airtight chamber, this paper proposes a novel method to measure the two key parameters, as well as the convective mass transfer coefficient (h(m. Compared to traditional methods, it has the following merits: (1 the K, D(m and h(m can be simultaneously obtained, thus is convenient to use; (2 it is time-saving, just one sorption process in airtight chamber is required; (3 the determination of h(m is based on the formaldehyde and VOC concentration data in the test chamber rather than the generally used empirical correlations obtained from the heat and mass transfer analogy, thus is more accurate and can be regarded as a significant improvement. The present method is applied to measure the three parameters by treating the experimental data in the literature, and good results are obtained, which validates the effectiveness of the method. Our new method also provides a potential pathway for measuring h(m of semi-volatile organic compounds (SVOC by using that of VOC.
Subdiffusion and lateral diffusion coefficient of lipid atoms and molecules in phospholipid bilayers
Flenner, Elijah; Rheinstadter, Maikel C; Kosztin, Ioan
2008-01-01
We use a long, all-atom molecular dynamics (MD) simulation combined with theoretical modeling to investigate the dynamics of selected lipid atoms and lipid molecules in a hydrated diyristoyl-phosphatidylcholine (DMPC) lipid bilayer. From the analysis of a 0.1 $\\mu$s MD trajectory we find that the time evolution of the mean square displacement, [\\delta{r}(t)]^2, of lipid atoms and molecules exhibits three well separated dynamical regions: (i) ballistic, with [\\delta{r}(t)]^2 ~ t^2 for t 30 ns. We propose a memory function approach for calculating [\\delta{r}(t)]^2 over the entire time range extending from the ballistic to the Fickian diffusion regimes. The results are in very good agreement with the ones from the MD simulations. We also examine the implications of the presence of the subdiffusive dynamics of lipids on the self-intermediate scattering function and the incoherent dynamics structure factor measured in neutron scattering experiments.
Institute of Scientific and Technical Information of China (English)
蔡文娟; 王伯涛; 王济奎
2013-01-01
目的 建立HPLC法,模拟人体皮肤环境,测定维A酸在水、正辛醇中的平衡溶解度,以及在正辛醇-缓冲液体系中的表观油水分配系数.方法 采用HPLC法测定维A酸的浓度,采用摇瓶法测定维A酸的表观油水分配系数.结果 在32℃下,pH为5.8时,测得维A酸在正辛醇中的溶解度为6.25 mg/mL,在水中的溶解度小于0.1 mg/mL,维A酸的表观油水分配系数为36 079.8(lgP=4.55).结论 本文建立的HPLC法,可用于维A酸溶解度及油水分配系数的测定,该方法简便、准确.%Objective To determine the equilibrium solubility of tretinoin in water and n-octyl alcohol, as well as to determine its apparent oil/water partition coefficient in the n-octane-water/buffer solution for establishing a high performance liquid chromatographic method by simulating the environment of human skin. Methods The concentration of tretinoin was determined by HPLC, apparent oil/water partition coefficient was measured by shaking flask method. Results The equilibrium solubility of tretinoin in n-octyl alcohol was 6.25 mg/mL and the equilibrium solubility of that in water was below 0.1 mg/mL, at 32℃, pH 5.8, and the apparent oil/water partition coefficient was 36 079.8 (lgP=4.55). Conclusion The method is accurate and reliable, which can be used in the determination the equilibrium solubility of tretinoin as well as its apparent oil/water partition coefficient.
Lu, Wanjun; Guo, Huirong; Chou, I.-Ming; Burruss, R.C.; Li, Lanlan
2013-01-01
Accurate values of diffusion coefficients for carbon dioxide in water and brine at reservoir conditions are essential to our understanding of transport behavior of carbon dioxide in subsurface pore space. However, the experimental data are limited to conditions at low temperatures and pressures. In this study, diffusive transfer of carbon dioxide in water at pressures up to 45 MPa and temperatures from 268 to 473 K was observed within an optical capillary cell via time-dependent Raman spectroscopy. Diffusion coefficients were estimated by the least-squares method for the measured variations in carbon dioxide concentration in the cell at various sample positions and time. At the constant pressure of 20 MPa, the measured diffusion coefficients of carbon dioxide in water increase with increasing temperature from 268 to 473 K. The relationship between diffusion coefficient of carbon dioxide in water [D(CO2) in m2/s] and temperature (T in K) was derived with Speedy–Angell power-law approach as: D(CO2)=D0[T/Ts-1]m where D0 = 13.942 × 10−9 m2/s, Ts = 227.0 K, and m = 1.7094. At constant temperature, diffusion coefficients of carbon dioxide in water decrease with pressure increase. However, this pressure effect is rather small (within a few percent).
Energy Technology Data Exchange (ETDEWEB)
Togrul, Inci Turk; Ispir, Ayse [Firat University, Engineering Faculty, Department of Chemical Engineering, 23279 Elazig (Turkey)
2007-10-15
This article represents the results of the variation in density and shrinkage of apricots during its osmotic dehydration. Shrinkage was investigated by means of dimensionless volume, diameter and length. Various osmotic agents such as sucrose, glucose, fructose, maltodextrin and sorbitol were used. It was found that the shrinkage of apricots could be well correlated with the moisture content of the sample during osmotic dehydration. The relationship between dimensionless parameters and moisture content was investigated by using eight non-linear models for each osmotic agent. It was find that the following proposed model can be confidently use for explaining the effect of shrinkage during osmotic dehydration of apricots.V/V{sub 0},D/D{sub 0},L/L{sub 0},{rho}/{rho}{sub 0}=a+b. exp (cX)+d. exp (e.X{sup f})In addition, the osmotic dehydration kinetics of apricots with and without shrinkage was studied. The effective diffusivities calculated from the diffusional model with and without shrinkage varied from 10.342 x 10{sup -9} m{sup 2}/s to 5.139 x 10{sup -9} and from 1.755 x 10{sup -10} and 0.767 x 10{sup -10} m{sup 2}/s, respectively. (author)
Energy Technology Data Exchange (ETDEWEB)
Hayashi, Kimio; Fukuda, Kousaku (Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan))
1990-11-01
Release of metal fission products from pyrocarbon (PyC) coated UO{sub 2} particles was studied by post-irradiation annealing at temperatures from 1600 to 2300deg C. Release of {sup 106}Ru and {sup 155}Eu was controlled by diffusion in the kernel at temperatures above 1800deg C, and their reduced diffusion coefficients in the kernel were very close to each other. The diffusion coefficient of Cs, D{sub Cs} (m{sup 2}/s), in the PyC layer was determined from the fractional release, as follows: D{sub Cs}=1.2x10{sup -3} exp(-4.12x10{sup 5} (J/mol)/RT), which was larger than that of Ce by an order of magnitude. The diffusion coefficients of fission products in the PyC layer was discussed in terms of their ionic radii and stability of their carbides. (orig.).
International Nuclear Information System (INIS)
Release of metal fission products from pyrocarbon (PyC) coated UO2 particles was studied by post-irradiation annealing at temperatures from 1600 to 2300deg C. Release of 106Ru and 155Eu was controlled by diffusion in the kernel at temperatures above 1800deg C, and their reduced diffusion coefficients in the kernel were very close to each other. The diffusion coefficient of Cs, DCs (m2/s), in the PyC layer was determined from the fractional release, as follows: DCs=1.2x10-3 exp[-4.12x105 (J/mol)/RT], which was larger than that of Ce by an order of magnitude. The diffusion coefficients of fission products in the PyC layer was discussed in terms of their ionic radii and stability of their carbides. (orig.)
Determination of diffusion coefficients of oxygen atoms in ZrO2 using first-principles calculations
International Nuclear Information System (INIS)
Density functional theory and nudged elastic band calculations were performed in order to determine the diffusion coefficient for oxygen from monoclinic ZrO2. The calculated values for monoclinic ZrO2 at 1000 K and 1500 K were 5.88 × 10-16 cm2s-1 and 2.91 × 10-11 cm2s-1, respectively, and agreed with previously determined experimental values. In addition, the results of the nudged elastic band calculations suggest that interstitial oxygen sites exist between stable oxygen sites, and if oxygen atoms occupy these sites, stable structures with values for the lattice angle β of greater than 80.53° may be obtained. (author)
Ghasemi, F; Peinke, J; Tabar, M R R; Sahimi, Muhammad
2006-01-01
We describe a method for analyzing the stochasticity in the non-stationary data for the beat-to-beat fluctuations in the heart rates of healthy subjects, as well as those with congestive heart failure. The method analyzes the returns time series of the data as a Markov process, and computes the Markov time scale, i.e., the time scale over which the data are a Markov process. We also construct an effective stochastic continuum equation for the return series. We show that the drift and diffusion coefficients, as well as the amplitude of the returns time series for healthy subjects are distinct from those with CHF. Thus, the method may potentially provide a diagnostic tool for distinguishing healthy subjects from those with congestive heart failure, as it can distinguish small differences between the data for the two classes of subjects in terms of well-defined and physically-motivated quantities.
Bahşı, Ayşe Kurt; Yalçınbaş, Salih
2016-01-01
In this study, the Fibonacci collocation method based on the Fibonacci polynomials are presented to solve for the fractional diffusion equations with variable coefficients. The fractional derivatives are described in the Caputo sense. This method is derived by expanding the approximate solution with Fibonacci polynomials. Using this method of the fractional derivative this equation can be reduced to a set of linear algebraic equations. Also, an error estimation algorithm which is based on the residual functions is presented for this method. The approximate solutions are improved by using this error estimation algorithm. If the exact solution of the problem is not known, the absolute error function of the problems can be approximately computed by using the Fibonacci polynomial solution. By using this error estimation function, we can find improved solutions which are more efficient than direct numerical solutions. Numerical examples, figures, tables are comparisons have been presented to show efficiency and usable of proposed method. PMID:27610294
Directory of Open Access Journals (Sweden)
M. J. Tang
2015-02-01
Full Text Available Diffusion of organic vapours to the surface of aerosol or cloud particles is an important step for the formation and transformation of atmospheric particles. So far, however, a database of gas phase diffusion coefficients for organic compounds of atmospheric interest has not been available. In this work we have compiled and evaluated gas phase diffusivities (pressure-independent diffusion coefficients of organic compounds reported by previous experimental studies, and we compare the measurement data to estimates obtained with Fuller's semi-empirical method. The difference between measured and estimated diffusivities are mostly Kn although their gas phase diffusivities may vary over a wide range. Knudsen numbers of gases with unknown diffusivity can be approximated by a simple function of particle diameter and pressure and can be used to characterize the influence of diffusion on gas uptake by aerosol or cloud particles. We use a kinetic multi-layer model of gas-particle interaction to illustrate the effects of gas phase diffusion on the condensation of organic compounds with different volatilities. The results show that gas-phase diffusion can play a major role in determining the growth of secondary organic aerosol particles by condensation of low-volatility organic vapours.
Ternary Isothermal Diffusion Coefficients of NaCl-MgCl2-H2O at 25 C. 7. Seawater Composition
Energy Technology Data Exchange (ETDEWEB)
Miller, D G; Lee, C M; Rard, J A
2007-02-12
The four diffusion coefficients D{sub ij} of the ternary system NaCl-MgCl{sub 2}-H{sub 2}O at the simplified seawater composition 0.48877 mol {center_dot} dm{sup -3} NaCl and 0.05110 mol {center_dot} dm{sup -3} MgCl{sub 2} have been remeasured at 25 C. The diffusion coefficients were obtained using both Gouy and Rayleigh interferometry with the highly precise Gosting diffusiometer. The results, which should be identical in principle, are essentially the same within or very close to their combined 'realistic' errors. This system has a cross-term D{sub 12} that is larger than the D{sub 22} main-term, where subscript 1 denotes NaCl and 2 denotes MgCl{sub 2}. The results are compared with earlier, less-precise measurements. Recommended values for this system are (D{sub 11}){sub V} = 1.432 x 10{sup -9} m{sup 2} {center_dot} sec{sup -1}, (D{sub 12}){sub V} = 0.750 x 10{sup -9} m{sup 2} {center_dot} sec{sup -1}, (D{sub 21}){sub V} = 0.0185 x 10{sup -9} m{sup 2} {center_dot} sec{sup -1}, and (D{sub 22}){sub V} = 0.728 x 10{sup -9} m{sup 2} {center_dot} sec{sup -1}.
Directory of Open Access Journals (Sweden)
Nazar Mohammad Ranjha
2015-06-01
Full Text Available Objective of the present work was to synthesize hydrogels of acrylic acid/polyvinyl alcohol (AA/PVA by free radical polymerization by using glutaradehyde (GA as crosslinkers. The hydrogels were evaluated for swelling, diffusion coefficient and network parameters like the average molecular weight between crosslink’s, polymer volume fraction in swollen state, number of repeating units between crosslinks and crosslinking density by using Flory-Huggins theory. It was found that the degree of swelling of AA/PVA hydrogels increases greatly within the pH range 5-7. The gel fraction and porosity increased by increasing the concentration of AA or PVA. Increase in degree of crosslinking, decreased the porosity and inverse was observed in gel fraction. Selected samples were loaded with metoprolol tartrate. Drug release was studied in USP hydrochloric acid solution of pH 1.2 and phosphate buffer solutions of pH 5.5 and 7.5. Various kinetics models like zero order, first order, Higuchi and Peppas model were used for in vitro kinetic studies. The results showed that the drug release followed concentration dependent effect (First order kinetics with non-Fickian diffusion. FTIR and SEM used to study the structure, crystallinity, compatibility, thermal stability and morphology of prepared and drug loaded hydrogels respectively.
Kozyra, J. U.; Rasmussen, C. E.; Miller, R. H.; Lyons, L. R.
1994-01-01
Protons that are convected into the inner magnetosphere in response to enhanced magnetic activity can resonate with ducted plasmaspheric hiss in the outer plasmasphere via an anomalous Doppler-shifted cyclotron resonance. Plasmaspheric hiss is a right-hand-polarized electromagnetic emission that is observed to fill the plasmasphere on a routine basis. When plasmaspheric hiss is confined within field-aligned ducts or guided along density gradients, wave normal angles remain largely below 45 deg. This allows resonant interactions with ions at typical ring current and radiation belt energies to take place. Such field-aligned ducts have been observed both within the plasmasphere and in regions outside of the plasmasphere. Wave intensities are estimated using statistical information from studies of detached plasma regions. Diffusion coefficients are presented for a range of L shells and proton energies for a fixed wave distribution. Harmonic resonances in the range N = +/-100 are considered in order to include interactions between hiss at 100 Hz to 2 kHz frequencies, and protons in the energy range between approximately 10 keV and 1000 keV. Diffusion timescales are estimated to be of the order of tens of days and comparable to or shorter than lifetimes for Coulomb decay and charge exchange losses over most of the energy and spatial ranges of interest.
International Nuclear Information System (INIS)
The diffusion of the aqueous ions of Am3+, Cm3+, Cf3+, Es3+ and for comparison, Ce3+, Eu3+, Gd3+, Tm3+, Yb3+ was investigated in aqueous LiCl-HCl solutions (pH=2.5) at 25.000C by the open-ended capillary method. The diffusion coefficients obtained in the limit of zero ionic strength are used to estimate the hydrated radius of the considered elements and, consequently, the average number h of water molecules involved. A single S-shaped curve is obtained when this number h is plotted versus the cristallographic radius of the lanthanide (III) and actinide (III) cations. A similar change is assumed, for the inner sphere hydration number, from which values can be derived for actinides. From these results ΔHsub(hyd)sup(0) values have been calculated using a general analytical expression of the hydration enthalpie developped in this work. Finally, data of the sum of ionization potentials are proposed for the transuranium elements
A program to solve a solute diffusion problem with segregation at a moving interface
Bakker, M.; Hoonhout, D.
1981-01-01
The one-dimensional transient diffusion of glucose, inulin and dextran into adult bovine knee articular cartilage was determined for transport times of 1, 5, 15 and 60 min, and 4, 12, 24 and 48 h. The apparent diffusion coefficient and apparent interface partition coefficient were calculated from th
Hagmann, P.; Jonasson, L.; Maeder, P; Thiran, Jean-Philippe; Wedeen, V.; Meuli, R
2006-01-01
The complex structural organization of the white matter of the brain can be depicted in vivo in great detail with advanced diffusion magnetic resonance (MR) imaging schemes. Diffusion MR imaging techniques are increasingly varied, from the simplest and most commonly used technique the mapping of apparent diffusion coefficient values to the more complex, such as diffusion tensor imaging, q-ball imaging, diffusion spectrum imaging, and tractography. The type of structural information obtained...
Ainscow; Aldalur; Beezer; Connor; Garbett; Mitchell; Page; Tindale; Turner; Willson
1999-05-01
Measurement of the kinetics of extraction of copper(II) by 19 different 5-alkyl-2-hydroxybenzaldoximes (alkyl is C7H15 and C9H19) from acidic (hydrogen sulfate buffer) aqueous solution in the range pH 3.4-2.0, into 20% v/v toluene in n-hexane is reported. The lowering of the interfacial tension has been measured in some cases. The solubility of the extractants in water has been measured spectrophotometrically. A modified Taylor-Aris dispersion technique has been used to measure the diffusion coefficients in n-hexane and Orfom SX7 of some of the extractants and of the copper(II) complexes which they form. At low initial bulk concentrations (<10 mol m-3) of the extractants, the rate of extraction is controlled by the rate of diffusion of the extractant from the bulk to the organic-aqueous interface. The diffusion coefficient is related to the steric bulk of the alkyl substituent. At higher initial bulk concentrations (200 mol m-3) of the extractants, when the interface is saturated, the rate of extraction is inversely related to the apparent steric bulk of the alkyl substituent. Copyright 1999 Academic Press.
Energy Technology Data Exchange (ETDEWEB)
Ainscow, T.A.; Aldalur, I.; Beezer, A.E. [Univ. of Kent, Canterbury (United Kingdom). School of Physical Sciences] [and others
1999-05-01
Measurement of the kinetics of extraction of copper(II) by 19 different 5-alkyl-2-hydroxybenzaldoximes (alkyl is C{sub 7}H{sub 15} and C{sub 9}H{sub 19}) from acidic (hydrogen sulfate buffer) aqueous solution in the range pH 3.4--2.0, into 20% v/v toluene in n-hexane is reported. The lowering of the interfacial tension has been measured in some cases. The solubility of the extractants in water has been measured spectrophotometrically. A modified Taylor-Aris dispersion technique has been used to measure the diffusion coefficients in n-hexane and Orfom SX7 of some of the extractants and of the copper(II) complexes which they form. At low initial bulk concentrations (<10 mol m{sup {minus}1}) of the extractants, the rate of extraction is controlled by the rate of diffusion of the extractant from the bulk to the organic-aqueous interface. The diffusion coefficient is related to the steric bulk of the alkyl substituent. At higher initial bulk concentrations (200 mol m{sup {minus}1}) of the extractants, when the interface is saturated, the rate of extraction is inversely related to the apparent steric bulk of the alkyl substituent.
Diffusion weighted imaging in the liver
Institute of Scientific and Technical Information of China (English)
Petra; G; Kele; Eric; J; van; der; Jagt
2010-01-01
Diffusion weighted magnetic resonance imaging (DWI) is an imaging technique which provides tissue contrast by the measurement of diffusion properties of water molecules within tissues. Diffusion is expressed in an apparent diffusion coefficient (ADC), which reflects the diffusion properties unique to each type of tissue. DWI has been originally used in neuroradiology. More recently, DWI has increasingly been used in addition to conventional unenhanced and enhanced magnetic resonance imaging (MRI) in other p...
Energy Technology Data Exchange (ETDEWEB)
Berndt, K. [Fachhochschule Magdeburg (Germany). Fachbereich Chemie; Horn, H. [Fachhochschule Magdeburg (Germany). Hydro- und Abfallchemie
1999-07-01
The diffusion coefficient of a substrate in a biofilm is an important parameter for simulating mass turnover and transport in biofilm systems. The described method permits determining the diffusion coefficients in biofilms grown under defined substrate and hydrodynamic conditions in a laboratory reactor. (orig.) [German] Der Diffusionskoeffizient des Substrats in Biofilmen ist ein wichtiger Parameter fuer die Simulation von Stoffwechsel und -transport in Biofilmsystemen. Die dargestellte Methode erlaubt die Bestimmung des Diffusionskoeffizienten in Biofilmen, die unter definierten Substrat- und hydrodynamischen Bedingungen in einem Laborreaktor gewachsen sind. (orig.)
L-抗坏血酸水溶液扩散系数的分子模拟%Molecular Simulation of Ascorbic Acid Diffusion Coefficient in Water
Institute of Scientific and Technical Information of China (English)
杨登峰; 刘清芝; 师进生
2011-01-01
Using molecular dynamics（MD） simulation,the diffusion process of ascorbic acid in water was simulated in constant（NVT） ensemble trajectory,and the diffusion coefficients were calculated.Results of the investigations showed that the simulated diffusion coefficients of ascorbic acid in water were close to the corresponding experimental value,the error were less than 4.4%.The results also showed that the diffusion coefficients decreased with the increment of ascorbic acid concentration,and at the same concentration,the diffusion coefficients increased with increasing temperature,which agreed with the experimental value.%采用分子动力学（MD）模拟的方法模拟了L-抗坏血酸在水中的扩散过程,并计算了扩散系数,计算结果与实验数据相吻合,最大误差仅为4.4%.计算结果表明,相同温度下,L-抗坏血酸在水溶液中的扩散系数随着其浓度的增加而减少,且在同一浓度下,随着温度的升高而增加,与实验现象一致.
Chanfreau, Sébastien; Cognet, Patrick; Camy, Séverine; Condoret, Jean-Stéphane
2007-01-01
Electrochemical method can be useful for the determination of diffusion coefficients in various media. For low polarity media, ultramicroelectrodes are preferably used. In this work, the electro-oxidation of ferrocene has been studied in dimethylformamide (DMF)–CO2 mixtures under various CO2 pressures, using a 100 lm diameter Pt microelectrode. Tetrabutylammonium perchlorate (TBAP) was chosen as the supporting electrolyte. Cyclic voltammetry was used in order to obtain values of diffusion coe...
Plummer, L. Neil; Sundquist, Eric T.
1982-01-01
We have calculated the total individual ion activity coefficients of carbonate and calcium, and , in seawater. Using the ratios of stoichiometric and thermodynamic constants of carbonic acid dissociation and total mean activity coefficient data measured in seawater, we have obtained values which differ significantly from those widely accepted in the literature. In seawater at 25°C and 35%. salinity the (molal) values of and are 0.038 ± 0.002 and 0.173 ± 0.010, respectively. These values of and are independent of liquid junction errors and internally consistent with the value . By defining and on a common scale (), the product is independent of the assigned value of and may be determined directly from thermodynamic measurements in seawater. Using the value and new thermodynamic equilibrium constants for calcite and aragonite, we show that the apparent constants of calcite and aragonite are consistent with the thermodynamic equilibrium constants at 25°C and 35%. salinity. The demonstrated consistency between thermodynamic and apparent constants of calcite and aragonite does not support a hypothesis of stable Mg-calcite coatings on calcite or aragonite surfaces in seawater, and suggests that the calcite critical carbonate ion curve of Broecker and Takahashi (1978,Deep-Sea Research25, 65–95) defines the calcite equilibrium boundary in the oceans, within the uncertainty of the data.
Henderson, Terry J
2010-02-01
A panel of 15 biological toxins ranging between approximately 60-28,000 g/mol was used to evaluate the feasibility of screening aqueous samples for toxin analytes based on their translational diffusion coefficients, D(t). Toxin D(t) values were measured by pulsed-field gradient (1)H NMR spectroscopy using a bipolar pulse pair, longitudinal eddy current delay pulse sequence incorporating water suppression to achieve the maximum dynamic range for toxin signals. To collect data for an effective screening protocol, reference D(t) values were determined from five independent measurements at both 25 and 37 degrees C for all toxins in the panel. In the protocol, D(t) values are measured at both temperatures for a suspected toxin target in a sample, and for assignment as a potential toxin analyte, the measurements are required to fall within +/-0.25 x 10(-6) cm(2)/s of both reference D(t) values for at least one toxin in the panel. Only solution viscosity was found to influence sample D(t) measurements appreciably; however, the measurements are easily corrected for viscosity effects by calculating the D(t) value of the suspected toxin at infinite dilution. In conclusion, the protocol provides a rapid and effective means for screening aqueous samples for all toxins in the panel, narrowing toxin identification to < or = 2 possibilities in virtually all cases.
Khlybov, Oleg A; Ryzhkov, Ilya I; Lyubimova, Tatyana P
2015-04-01
The paper is devoted to processing the data of DCMIX 1 space experiment. In this experiment, the Optical digital interferometry was used to measure the diffusion and Soret coefficients in the ternary mixture of 1,2,3,4-tetrahydronaphthalene, isobutylbenzene and n-dodecane at mass fractions of 0.8/0.1/0.1 and at 25°C. The raw interferometric images were processed to obtain the temporal and spatial evolution of refractive indices for two laser beams of different wavelengths. The method for extracting the diffusion and thermal diffusion coefficients originally developed for optical beam deflection was extended to optical digital interferometry allowing for the spatial variation of refractive index along the diffusion path. The method was validated and applied to processing the data for Soret and diffusion steps in 5 experimental runs. The obtained results for the Soret coefficients and one of the eigenvalues of diffusion matrix showed acceptable agreement within each step. The second eigenvalue was not determined with sufficient accuracy.
Khlybov, Oleg A; Ryzhkov, Ilya I; Lyubimova, Tatyana P
2015-04-01
The paper is devoted to processing the data of DCMIX 1 space experiment. In this experiment, the Optical digital interferometry was used to measure the diffusion and Soret coefficients in the ternary mixture of 1,2,3,4-tetrahydronaphthalene, isobutylbenzene and n-dodecane at mass fractions of 0.8/0.1/0.1 and at 25°C. The raw interferometric images were processed to obtain the temporal and spatial evolution of refractive indices for two laser beams of different wavelengths. The method for extracting the diffusion and thermal diffusion coefficients originally developed for optical beam deflection was extended to optical digital interferometry allowing for the spatial variation of refractive index along the diffusion path. The method was validated and applied to processing the data for Soret and diffusion steps in 5 experimental runs. The obtained results for the Soret coefficients and one of the eigenvalues of diffusion matrix showed acceptable agreement within each step. The second eigenvalue was not determined with sufficient accuracy. PMID:25916235
Diffusion length variation and proton damage coefficients for InP/In(x)Ga(1-x)As/GaAs solar cells
Jain, R. K.; Weinberg, I.; Flood, D. J.
1993-01-01
Indium phosphide solar cells are more radiation resistant than gallium arsenide and silicon solar cells, and their growth by heteroepitaxy offers additional advantages leading to the development of lighter, mechanically strong and cost-effective cells. Changes in heteroepitaxial InP cell efficiency under 0.5 and 3 MeV proton irradiations are explained by the variation in the minority-carrier diffusion length. The base diffusion length versus proton fluence is calculated by simulating the cell performance. The diffusion length damage coefficient K(L) is plotted as a function of proton fluence.
International Nuclear Information System (INIS)
Objective: Study the ADC value and the maximal diameter and their changes of breast cancer before and after neoadjuvant chemotherapy, to determine the relationship with different expression level of Ki-67. Methods: Forty eight patients with breast cancer confirmed by biopsy underwent MR DWI and enhanced scan before and after 4 cycles neoadjuvant chemotherapy. Review the MR images retrospectively. The ADC value and the maximum diameter(D)of the cancer foci were measured before and after chemotherapy, and the rate of their changes ΔADC% and ΔD% were calculated. Using different Ki-67 index level, all the foci were divided into three groups: group A with Ki-67 60%. Using nonparameter test to compare the ADC values, ΔADC%, D and ΔD% of the three groups before and after chemotherapy, determine whether there were differences. Results: Before chemotherapy, the ADC value of group A (n=15) was 1.1 × 10-3 mm2/s [(0.9 × 10-3 - 1.2 × 10-3) mm2/s], which was higher than that of group B [n=8, 0.9 × 10-3 mm2/s (0.9 × 10-3 - 1.0 × 10-3) mm2/s] and C [n=25, 0.9 × 10-3 mm2/s (0.7 × 10-3 - 1.2 × 10-3) mm2/s], and the difference was statistically significant (P-3 mm2/s [(0.2 × 10-3 - 1.4 × 10-3) mm2/s], which was higher than that of group A [1.1 × 10-3 mm2/s, (1.0 × 10-3 - 1.2 × 10-3) mm2/s] and B [1.1 × 10-3 mm2/s, (1.0 × 10-3 - 1.1 × 10-3) mm2/s], and the differences were statistically significance (P<0.01); the ADC change rate (ΔADC%) of group C was 45.5% (-12.0% - 78.6%), which was greater than group A [45.5% (-12.0% - 78.6%)] and B [45.5% (-12.0% - 78.6%)], the difference was significant (P<0.01). The maximum diameters of group A were 2.2 cm (2.0-2.4 cm) and 1.0 cm (0.0-1.4 cm) before and after chemotherapy, lower than those of group B [3.7 cm (3.6-3.9 cm) before NAC, 2.9 cm (0.0-3.1 cm) after NAC] and group C [3.4 cm (2.7-4.2 cm) before NAC, 1.9 cm (0.0-2.2 cm) after NAC], and the differences were statistically significant (P<0.05); the change rate of the maximum diameter in group B was 21.6% (-15.2% - 27.5%), which was less than group A [52.7% (-23.6% - 72.1%)] (P<0.01) and C [51.2% (-10.3% - 92.6%)] (P<0.05), and the difference was statistically significant. Conclusion: The ADC values and the maximal diameter of breast cancer differed with different expression levels of Ki-67 index before and after neoadjuvant chemotherapy, and the response to neoadjuvant chemotherapy of which varied as well. (authors)
Indian Academy of Sciences (India)
Atul Kumar; Dilip Kumar Jaiswal; Naveen Kumar
2009-10-01
Analytical solutions are obtained for one-dimensional advection –diffusion equation with variable coefficients in a longitudinal ﬁnite initially solute free domain,for two dispersion problems.In the ﬁrst one,temporally dependent solute dispersion along uniform ﬂow in homogeneous domain is studied.In the second problem the velocity is considered spatially dependent due to the inhomogeneity of the domain and the dispersion is considered proportional to the square of the velocity. The velocity is linearly interpolated to represent small increase in it along the ﬁnite domain.This analytical solution is compared with the numerical solution in case the dispersion is proportional to the same linearly interpolated velocity.The input condition is considered continuous of uniform and of increasing nature both.The analytical solutions are obtained by using Laplace transformation technique.In that process new independent space and time variables have been introduced. The effects of the dependency of dispersion with time and the inhomogeneity of the domain on the solute transport are studied separately with the help of graphs.
Diffusion Coefficients of L-arginine in Non-Newtonian Fluid%L-精氨酸在非牛顿流体中的扩散系数
Institute of Scientific and Technical Information of China (English)
朱春英; 马友光; 季喜燕
2008-01-01
L-Arginine is an important component of amino acid injection. Its diffusion in body fluid and blood is of key importance to understand drug diffusion and drug release. As a fundamental demand for study and being a considerably valuable reference for application, in this study, the diffusion coefficients of L-arginine in polyacryla-mide(PAM) aqueous solution used as non-Newtonian fluid similar to blood and body fluid were measured using a holographic interferometer. The effects of interaction among molecules and solution concentration on diffusion were analyzed and discussed, respectively. Based on the obstruction-scaling model, a novel modified model was presented for predicting diffusivity of solute in non-Newtonian fluid. Good agreement was achieved between the calculated value and the experimental data.
International Nuclear Information System (INIS)
The diffusion coefficients of hydrogen and deuterium in Zr–2.5%Nb alloy were measured in the temperature range 523 to 673 K, employing hot vacuum extraction-quadrupole mass spectrometry (HVE-QMS). One end of the Zr–2.5%Nb alloy specimens was charged electrolytically with the desired hydrogen isotope. After annealing at different temperatures for a predetermined time, the specimens were cut into thin slices, which were analyzed for their H2/D2 content using the HVE-QMS technique. The depth profile data were fitted into the equation representing the solution of Fick’s second law of diffusion. The activation energy of hydrogen/deuterium diffusion was obtained from the Arrhenius relation between the diffusion coefficient and temperature. The temperature dependent diffusion coefficient can be represented as DH = 1.41 × 10−7 exp(−36,000/RT) and DD = 6.16 × 10−8 exp(−35,262/RT) for hydrogen and deuterium, respectively
Shrivastava, Komal Chandra; Kulkarni, A. S.; Ramanjaneyulu, P. S.; Sunil, Saurav; Saxena, M. K.; Singh, R. N.; Tomar, B. S.; Ramakumar, K. L.
2015-06-01
The diffusion coefficients of hydrogen and deuterium in Zr-2.5%Nb alloy were measured in the temperature range 523 to 673 K, employing hot vacuum extraction-quadrupole mass spectrometry (HVE-QMS). One end of the Zr-2.5%Nb alloy specimens was charged electrolytically with the desired hydrogen isotope. After annealing at different temperatures for a predetermined time, the specimens were cut into thin slices, which were analyzed for their H2/D2 content using the HVE-QMS technique. The depth profile data were fitted into the equation representing the solution of Fick's second law of diffusion. The activation energy of hydrogen/deuterium diffusion was obtained from the Arrhenius relation between the diffusion coefficient and temperature. The temperature dependent diffusion coefficient can be represented as DH = 1.41 × 10-7 exp(-36,000/RT) and DD = 6.16 × 10-8 exp(-35,262/RT) for hydrogen and deuterium, respectively.
Energy Technology Data Exchange (ETDEWEB)
Shrivastava, Komal Chandra, E-mail: komal@barc.gov.in [Radioanalytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Kulkarni, A.S.; Ramanjaneyulu, P.S. [Radioanalytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Sunil, Saurav [Mechanical Metallurgy Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Saxena, M.K. [Radioanalytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Singh, R.N. [Mechanical Metallurgy Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India); Tomar, B.S.; Ramakumar, K.L. [Radioanalytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India)
2015-06-15
The diffusion coefficients of hydrogen and deuterium in Zr–2.5%Nb alloy were measured in the temperature range 523 to 673 K, employing hot vacuum extraction-quadrupole mass spectrometry (HVE-QMS). One end of the Zr–2.5%Nb alloy specimens was charged electrolytically with the desired hydrogen isotope. After annealing at different temperatures for a predetermined time, the specimens were cut into thin slices, which were analyzed for their H{sub 2}/D{sub 2} content using the HVE-QMS technique. The depth profile data were fitted into the equation representing the solution of Fick’s second law of diffusion. The activation energy of hydrogen/deuterium diffusion was obtained from the Arrhenius relation between the diffusion coefficient and temperature. The temperature dependent diffusion coefficient can be represented as D{sub H} = 1.41 × 10{sup −7} exp(−36,000/RT) and D{sub D} = 6.16 × 10{sup −8} exp(−35,262/RT) for hydrogen and deuterium, respectively.
Determination of H+ diffusion coefficient in the course of H+ response of a W/WO3 pH electrode
Institute of Scientific and Technical Information of China (English)
CHEN Dongchu; FU Zhaoyang; ZHENG Jiashen
2005-01-01
A W/WO3 pH electrode was prepared by a method of sol-gel. In order to study the H+ response dynamic mechanism, the electrochemical impedance spectroscopy (EIS) experiment was conducted. It was found that the H+ response course is controlled by the H+ diffusion from the solution to the WO3 film, based on the analysis of EIS spectra. The EIS and potential step method were used to determinate the H+ diffusion coefficient (D) in the course of H+ response of this W/WO3 electrode, and the values of D calculated by these two method correspond very well, which all are about 10-10 cm2/s.The imposed different potential steps make little effect on the calculation of H+ diffusion coefficient, and it was found that the limiting Cottrell equation of short elapsed time fits well to the current transient caused by a potential step, based on the analysis of the time constant.
Energy Technology Data Exchange (ETDEWEB)
Pawlak, M., E-mail: mpawlak@fizyka.umk.pl [Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziądzka 5/7, Toruń (Poland); Maliński, M. [Department of Electronics and Computer Science, Koszalin University of Technology, 2 Śniadeckich St., Koszalin 75-453 (Poland)
2015-01-10
Highlights: • The new method of determination of the effective infrared absorption coefficient is presented. • The method can be used for transparent samples for the excitation radiation. • The effect of aluminum foil on the PTR signal in a transmission configuration is discussed. - Abstract: In this paper we propose a new procedure of simultaneous estimation of the effective infrared optical absorption coefficient and the thermal diffusivity of solid state samples using the photothermal infrared radiometry method in the transmission configuration. The proposed procedure relies on the analysis of the frequency dependent signal obtained from the samples covered with thin aluminum foil. This method can be applied for both optically opaque and transparent samples. The proposed method is illustrated with the results of the thermal diffusivity and the effective IR absorption coefficient obtained for several Cd{sub 1−x}Mg{sub x}Se crystals.
Zhao, Lei; Yu, Yiqun; Delzanno, Gian Luca; Jordanova, Vania K.
2015-04-01
Local acceleration via whistler wave and particle interaction plays a significant role in particle dynamics in the radiation belt. In this work we explore gyroresonant wave-particle interaction and quasi-linear diffusion in different magnetic field configurations related to the 17 March 2013 storm. We consider the Earth's magnetic dipole field as a reference and compare the results against nondipole field configurations corresponding to quiet and stormy conditions. The latter are obtained with the ring current-atmosphere interactions model with a self-consistent magnetic field (RAM-SCB), a code that models the Earth's ring current and provides a realistic modeling of the Earth's magnetic field. By applying quasi-linear theory, the bounce- and Magnetic Local Time (MLT)-averaged electron pitch angle, mixed-term, and energy diffusion coefficients are calculated for each magnetic field configuration. For radiation belt (˜1 MeV) and ring current (˜100 keV) electrons, it is shown that at some MLTs the bounce-averaged diffusion coefficients become rather insensitive to the details of the magnetic field configuration, while at other MLTs storm conditions can expand the range of equatorial pitch angles where gyroresonant diffusion occurs and significantly enhance the diffusion rates. When MLT average is performed at drift shell L=4.25 (a good approximation to drift average), the diffusion coefficients become quite independent of the magnetic field configuration for relativistic electrons, while the opposite is true for lower energy electrons. These results suggest that, at least for the 17 March 2013 storm and for L≲4.25, the commonly adopted dipole approximation of the Earth's magnetic field can be safely used for radiation belt electrons, while a realistic modeling of the magnetic field configuration is necessary to describe adequately the diffusion rates of ring current electrons.
Diffusion of aroma compounds in stirred yogurts with different complex viscosities.
Déléris, Isabelle; Lauverjat, Clémentine; Tréléa, Ioan Cristian; Souchon, Isabelle
2007-10-17
To better understand aroma release in relation to yogurt structure and perception, the apparent diffusivity of aroma compounds within complex dairy gels was determined using an experimental diffusion cell. Apparent diffusion coefficients of four aroma compounds (diacetyl, ethyl acetate, ethyl hexanoate, and linalool) at 7 degrees C in yogurts (varying in composition and structure) ranged from 0.07 x 10 (-10) to 8.91 x 10 (-10) m (2) s (-1), depending on aroma compounds and on product structure. The strong effect of yogurt fat content on the apparent diffusivity of hydrophobic compounds was revealed (15-fold and 50-fold decreases in the apparent diffusion coefficient of linalool and ethyl hexanoate, respectively). Protein composition seemed to have a greater effect than that of mechanical treatment. However, variations in the apparent diffusion coefficient for the considered products remained limited and cannot completely explain differences in flavor release and in perception that were previously observed.
Institute of Scientific and Technical Information of China (English)
单进军; 狄留庆; 赵晓莉; 徐建亚
2011-01-01
OBJECTIVE To determine the equilibrium solubility of daphnetin and its partition coefficients for the n-oc-tanol-water/buffer solution systems. METHODS A high HPLC was established to detect the concentration of daphnetin in water and seven organic solvents. The partition coefficients for the n-octanol-water/buffer solution systems of daphnetin were determined by shaking flask method. RESULTS The equilibrium solubility of daphnetin was 176. 7 μg/mL in water at 25℃, a higher equilibrium solubility of daphnetin was reached at 485. 4 μg/mL in methanol, Papp of daphnetin was 2.4 (lgPapp =0.38).CONCLUSION The solubility of daphnetin was poor. It had little change in apparent partition coefficient in acidic and neutral phosphate buffer solution. Daphnetin belongs to the class II drug of Biopharmaceutics Classification System(low solubility, high permeability).%目的 测定瑞香素的平衡溶解度及表现油水分配系数.方法 采用HPLC法测定了瑞香素在水和7种有机溶剂中的平衡溶解度,摇瓶法测定瑞香素在正辛醇-水/缓冲盐溶液中的表现油水分配系数.结果 25℃下瑞香素在水中的平衡溶解度为176.7μg/mL,常用有机溶剂甲醇对瑞香素的溶解性较好,为485.4μg/mL,正辛醇/水表现分配系数Papp为2.4(lgPapp＝0.38).结论 瑞香素的水溶性差,在酸性和中性条件下,正辛醇/缓冲液分配系数受缓冲液的pH值影响不大;瑞香素属于FDA生物药剂学分类中的第二类药物(低溶解性、高渗透性).
Research on Measuring Methods and Theories of Diffusion Coefficient in Metals%金属扩散系数的测量方法与理论研究
Institute of Scientific and Technical Information of China (English)
高建新; 唐国章; 齐艳飞; 李运刚
2012-01-01
介绍了金属扩散系数的几种测量方法,包括扩散对法、毛细管-熔池法、剪切单元法、转盘法和等离子轰击技术等；以及几种自扩散系数的理论研究和液态合金的扩散、自扩散系数的理论研究方法,包括硬球模型、线性轨道假说、小步扩散理论、流体动力学模型、经验公式及慢中子散射技术,液态合金中的扩散有Darken给出的互扩散系数及互扩散系数模型.通过对比各种实验方法的优缺点,分析实验值与理论计算值之间出现偏离的原因,指出了寻求有效的示踪原子是今后的研究动向,探索离子轰击能够促进扩散的原因将成为今后的研究重点.%First, some measuring methods of diffusion coefficient in metals, including diffusion couple, capillary -melt pool, shear cell, rotary and plasma bombardment methods, are introduced; Second, the theoretical study methods of diffusion coefficient in metals, such as hard-sphere model, linear track hypothesis, step diffusion theory, fluid dynamics model, experience formula and slow neutron scattering techniques, are introduced, and the diffusion theories in liquid alloy include Darken's mutual diffusion coefficient and diffusion coefficient model. At the same time, by contrasting the advantages and defects of various experimental methods, the reasons of the deviation of measured value from theoretical value are analyzed. It is pointed out that the research trend is looking for effective tracer atom in the future, and the research is concentrated on discovering the reasons of ion bombardment promoting diffusion.
Rantakari, Miitta; Heiskanen, Jouni; Mammarella, Ivan; Tulonen, Tiina; Linnaluoma, Jessica; Kankaala, Paula; Ojala, Anne
2015-10-01
The air-water exchange of carbon dioxide (CO2) and methane (CH4) is a central process during attempts to establish carbon budgets for lakes and landscapes containing lakes. Lake-atmosphere diffusive gas exchange is dependent on the concentration gradient between air and surface water and also on the gas transfer velocity, often described with the gas transfer coefficient k. We used the floating-chamber method in connection with surface water gas concentration measurements to estimate the gas transfer velocity of CO2 (kCO2) and CH4 (kCH4) weekly throughout the entire growing season in two contrasting boreal lakes, a humic oligotrophic lake and a clear-water productive lake, in order to investigate the earlier observed differences between kCO2 and kCH4. We found that the seasonally averaged gas transfer velocity of CH4 was the same for both lakes. When the lakes were sources of CO2, the gas transfer velocity of CO2 was also similar between the two study lakes. The gas transfer velocity of CH4 was constantly higher than that of CO2 in both lakes, a result also found in other studies but for reasons not yet fully understood. We found no differences between the lakes, demonstrating that the difference between kCO2 and kCH4 is not dependent on season or the characteristics of the lake. PMID:26359720
International Nuclear Information System (INIS)
The method used to obtain the transport parameters of a Townsend discharge reported by Blevin et al. (J. Phys. D.; 9:1671, 471 and 465 (1976)) from the observation of the photon flux produced in the discharge has been extended to enable measurements of the transverse diffusion coefficient and Townsend's first ionisation to be made. The results obtained in molecular hydrogen are reported in this paper. (author)
International Nuclear Information System (INIS)
A numerical method for the calculation of the radial and axial diffusion coefficient for the hexagonal lattice of a high-temperature reactor with block elements is developed. Results for a typical lattice are given and a comparison with the formulas of Behrens and Benoist is made. A modification of Benoist's formulas for a tightly packed lattice that gives a better agreement with the numerical results is proposed. 9 refs
Estimating diffusion coefficients of gases by use of computer simulation%计算机模拟估算气体的扩散系数
Institute of Scientific and Technical Information of China (English)
晋宏营
2012-01-01
使用计算机模拟了气体分子在背景气体中的一维扩散过程,结果显示:越靠近初始位置处,分子数密度越大；扩散时间越长,分子分布的空间范围越大；模拟的分子数越多,涨落越小；分子的方均位移与扩散时间成正比.本文的模拟方法可用来估算气体的扩散系数,对1标准大气压和15℃条件下,氩气、氢气、氮气、氧气、二氧化碳和氖气的自扩散系数,以及此条件下氢气在氧气中、氢气在氮气中、氢气在二氧化碳中和氧气在氮气中的互扩散系数进行了估算,并把估算的扩散系数和相应的扩散系数实验值作了对比,二者不但数量级符合的很好,数值也比较接近,说明估算较为成功.%One-dimensional diffusion process of gas molecules in background gas is simulated by use of computer. The results show that the closer the distance between molecules and the initial position is, the larger the number density of molecules is; the longer diffusion time, the larger distribution range of molecules is; and the more the number of molecules, the less fluctuation is. The mean square displacement is proportional to the diffusion time. The simulation method can be used to estimate diffusion coefficients of gases. The self-diffusion coefficients of argon, hydrogen, nitrogen, oxygen, carbon dioxide and neon are estimated at 1 atmosphere and 15 ℃, and the mutual diffusion coefficients of hydrogen in oxygen, hydrogen in nitrogen, hydrogen in carbon dioxide and oxygen in nitrogen are estimated under the same condition. The estimative diffusion coefficients have been compared with the corresponding experimental values, and that shows not only orders of magnitude of them are in good agreement with each other, but also values are also relatively close to each other. This demonstrates that the estimation method is successful.
Energy Technology Data Exchange (ETDEWEB)
Milhau, A. [Commissariat a l' Energie Atomique, Fontenay-aux-Roses (France). Centre d' Etudes Nucleaires
1971-07-01
The vertical movement of ions in the lower atmosphere is due to two main causes: the atmospheric electrical field and turbulent diffusion. The vertical current is thus the sum of a conduction current and of a diffusion current. In order to resolve the discrepancies between the theories usually adopted (which neglect the diffusion current) and the experimental results, we propose here a theoretical model which takes into account the turbulent diffusion. This model makes it possible, if it is assumed that the conductivity is independent of the altitude in the exchange layer, to calculate the diffusivity from the three basic electrical parameters: electrical field, space charge, conductivity. The diffusivity values thus obtained have been compared to those deduced from thoron determinations made at different levels, and carried out at the same point and at the same time as the measurements of the electrical parameters. When the diffusivity is greater than 0.05 m{sup 2}s{sup -1} (this corresponding to adiabatic or super-adiabatic conditions) the values obtained are practically equal. This theoretical model thus appears to be satisfactory. (author) [French] Le mouvement vertical des ions dans la basse atmosphere est du a deux causes principales: le champ electrique atmospherique et la diffusion turbulente. Le courant vertical est donc la somme d'un courant de conduction et d'un courant de diffusion. Pour lever les contradictions entre les theories generalement admises (qui negligent le courant de diffusion) et les resultats experimentaux, nous proposons un modele theorique tenant compte de la diffusion turbulente. Celui-ci permet, en supposant la conductibilite independante de l'altitude dans la couche d'echange, de calculer la diffusivite a partir des trois parametres electriques fondamentaux: champ electrique, charge d'espace, conductibilite. Les valeurs de la diffusivite ainsi obtenues ont ete comparees a celles deduites de dosages du thoron
Alves, I. P.; Degrazia, G. A.; Buske, D.; Vilhena, M. T.; Moraes, O. L. L.; Acevedo, O. C.
2012-12-01
In this study an integral and an algebraic formulation for the eddy diffusivities in a shear driven planetary boundary layer are derived for pollutant dispersion applications. The expressions depend on the turbulence properties and on the distance from the source. They are based on the turbulent kinetic energy spectra, Taylor’s statistical diffusion theory and measured turbulent characteristics during intense wind events. The good agreement between the algebraic and the integral formulation for the eddy diffusivities corroborate the hypothesis that using an algebraic formulation as a surrogate for the eddy diffusivities in the neutral planetary boundary layer is valid. As a consequence, the vertical eddy diffusivity provided by the algebraic formulation and its asymptotic limit for large time (diffusion time much larger than the Lagrangian integral time scale), were introduced into an analytical air pollution model and validated against data from the classic Prairie Grass project. A statistical analysis, employing specific indices shows that the results are in good agreement with the observations. Furthermore, this study suggests that the inclusion of the memory effect, which is important in regions near to a continuous point source, improves the description of the turbulent transport process of atmospheric contaminants. Therefore, the major finding of this paper is the necessity of including the downwind distance-dependent eddy diffusivity for low continuous point sources in air quality modeling studies.
Directory of Open Access Journals (Sweden)
Claudete Regina Alcalde
1999-01-01
(AN and Saanen (SN goat breeds. Twelve kids, six of each breed, with average 19.8 kg LW, were used. Semipurified diets (low Mg content based on cracked rice, corn gluten meal and cellulose were supplemented with MgO to obtain the levels of .05 (without supplementation, .20 and .35% of Mg (% DM. The levels of Mg affected the coefficient of apparent absorption of Mg and Ca, with average values of 57.8, 73.9, and 73.2% for Mg and 55.7, 39.6 and 49.5% for Ca for diets with .05, .20, and .35% Mg, respectively. However, there was no effect of the dietary Mg level on the coefficient of apparent absorption of P, Na and K. An interaction between Mg level and breeds was observed for the real absorption of Mg. The mean for AN breed, on the level .05% Mg was 61.0% and for the levels 0.20 and 0.35% Mg, 77.2 and 73.2%, respectively. However, for SN breed the means were 73.3, 75.5 and 76.0%, for the same levels, without differences. The digestibility of dry matter, crude protein, and nitrogen free extract decreased with the crescent dietary Mg level. The fecal (7.0, 20.8 and 34.4 mg/kg LW0.75.d and urinary (3.9, 30.8 and 44.6 mg/kg LW0.75.d Mg excretion increased with the crescent dietary Mg level. There was also influence of the dietary Mg level on the blood serum Mg concentration (1.74, 2.23 and 2.80 mg/dL for .05, .20, and .35% Mg, respectively.
Directory of Open Access Journals (Sweden)
Marcos J. de A. Gama
2012-01-01
Full Text Available O objetivo do trabalho foi determinar a difusividade térmica aparente de sementes de cajá avaliando o efeito da variação do teor de água e da temperatura e ajustar diferentes modelos matemáticos aos valores experimentais. Sementes com a faixa de teor de água de 6,05 a 61,84% (b.u. foram submetidas a secagem e à temperatura de 40 ºC. A redução do teor de água ao longo da secagem foi acompanhada pelo método gravimétrico (perda de massa enquanto a difusividade térmica aparente da semente de cajá foi determinada pelo método de Dickerson. Concluiu-se que a difusividade térmica aparente, em temperatura acima do congelamento e em ultrabaixas temperaturas em função do teor de água (b.u, podem ser representados satisfatoriamente por um modelo de regressão linear e que o valor da difusividade térmica aparente aumenta exponencialmente com o aumento da temperatura.The aim of this study was to determine experimentally the apparent thermal diffusivity caja seeds, evaluating the effect of variation of water content and temperature and adjust different mathematical models to experimental values. Seeds with the range of water content from 6.05 to 61.84% (wb subjected to drying at a temperature of 40 ºC were studied. The reduction of water content during drying was monitored by gravimetric method (weight loss. The apparent thermal diffusivity of caja seed was determined by the method of Dickerson. It was concluded that the apparent thermal diffusivity in temperature above freezing and ultralow temperatures as a function of water content (wb, can be satisfactorily represented by a linear regression model and that value of the apparent thermal diffusivity increases exponentially with increasing temperature.
Directory of Open Access Journals (Sweden)
T.V.S.L. Satyavani
2016-03-01
Full Text Available Cathode materials in nano size improve the performance of batteries due to the increased reaction rate and short diffusion lengths. Lithium Iron Phosphate (LiFePO4 is a promising cathode material for Li-ion batteries. However, it has its own limitations such as low conductivity and low diffusion coefficient which lead to high impedance due to which its application is restricted in batteries. In the present work, increase of conductivity with decreasing particle size of LiFePO4/C is studied. Also, the dependence of conductivity and activation energy for hopping of small polaron in LiFePO4/C on variation of particle size is investigated. The micro sized cathode material is ball milled for different durations to reduce the particle size to nano level. The material is characterized for its structure and particle size. The resistivities/dc conductivities of the pellets are measured using four probe technique at different temperatures, up to 150 °C. The activation energies corresponding to different particle sizes are calculated using Arrhenius equation. CR2032 cells are fabricated and electrochemical characteristics, namely, ac impedance and diffusion coefficients, are studied.
Kushner, Joseph; Deen, William; Blankschtein, Daniel; Langer, Robert
2007-12-01
To account for the effect of branched, parallel transport pathways in the intercellular domain of the stratum corneum (SC) on the passive transdermal transport of hydrophobic permeants, we have developed, from first-principles, a new theoretical model-the Two-Tortuosity Model. This new model requires two tortuosity factors to account for: (1) the effective diffusion path length, and (2) the total volume of the branched, parallel transport pathways present in the SC intercellular domain, both of which may be evaluated from known values of the SC structure. After validating the Two-Tortuosity model with simulated SC diffusion experiments in FEMLAB (a finite element software package), the vehicle-bilayer partition coefficient, K(b), and the lipid bilayer diffusion coefficient, D(b), in untreated human SC were evaluated using this new model for two hydrophobic permeants, naphthol (K(b) = 225 +/- 42, D(b) = 1.7 x 10(-7) +/- 0.3 x 10(-7) cm(2)/s) and testosterone (K(b) = 92 +/- 29, D(b) = 1.9 x 10(-8) +/- 0.5 x 10(-8) cm(2)/s). The results presented in this paper demonstrate that this new method to evaluate K(b) and D(b) is comparable to, and simpler than, previous methods, in which SC permeation experiments were combined with octanol-water partition experiments, or with SC solute release experiments, to evaluate K(b) and D(b). PMID:17887175
Energy Technology Data Exchange (ETDEWEB)
Matsuhiro, Kenjirou [Osaka Univ., Osaka (Japan); Iwakiri, Hirotomo [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics; Hirooka, Yoshi [National Inst. for Fusion Science, Toki, Gifu (Japan); Yamamura, Yasunori [Okayama Univ. of Scinece, Okayama (Japan); Morita, Kenji [Nagoya Univ. (Japan)
2002-08-01
This report will present additional data to those included in the previous report of this series. These new data are on the hydrogen (deuterium) trapping properties of graphite materials. The units on the data on hydrogen (deuterium) diffusion and surface recombination coefficients have been updated to adopt the SI unit system. Also, the graphic representations of previously compiled data on hydrogen (deuterium) retention have been improved for better understanding. For the sake of completeness, this report will present all these data in the improved format. (author)
Institute of Scientific and Technical Information of China (English)
肖吉; 陆九芳; 陈健; 李以圭
2003-01-01
The molecular dynamics (MD) was employed to simulate the diffusion coefficient of sodium chloride at infinite dilution in supercritical water from 703.2 K to 763.2 K and from 30 MPa to 45 MPa. Based on the simulated data and the Patel-Teja(PT) equation of state and the Liu-Ruckenstein equation, an equation for calculating the diffusion coefficient of NaCl at infinite dilution in supercritical water is proposed. Both the agreement between the simulated and correlated data, and that between the simulated and predicted data of diffusion coefficients for NaCl in supercritical water ranging from 703.2 K to 803.2 K and from 25 MPa to 50 MPa show that this equation is applicable for the calculation of diffusion coefficients.
Shit, Anindita; Ghosh, Pradipta; Chattopadhyay, Sudip; Chaudhuri, Jyotipratim Ray
2011-03-01
We explore the issue of a quantum-noise-induced directed transport of an overdamped Brownian particle that is allowed to move in a spatially periodic potential. The established system-reservoir model has been employed here to study the quantum-noise-induced transport of a Brownian particle in a periodic potential, where the reservoir is being modulated externally by a Gaussian-colored noise. The mobility of the Brownian particle in the linear response regime has been calculated. Then, using Einstein's relation, the analytical expression for the diffusion rate is evaluated for any arbitrary periodic potential for the high-temperature quantum regime. PMID:21517472
Guevara-Carrion, Gabriela; Vrabec, Jadran; Hasse, Hans
2011-02-01
Density, self-diffusion coefficient, and shear viscosity of pure liquid water are predicted for temperatures between 280 and 373 K by molecular dynamics simulation and the Green-Kubo method. Four different rigid nonpolarizable water models are assessed: SPC, SPC/E, TIP4P, and TIP4P/2005. The pressure dependence of the self-diffusion coefficient and the shear viscosity for pure liquid water is also calculated and the anomalous behavior of these properties is qualitatively well predicted. Furthermore, transport properties as well as excess volume and excess enthalpy of aqueous binary mixtures containing methanol or ethanol, based on the SPC/E and TIP4P/2005 water models, are calculated. Under the tested conditions, the TIP4P/2005 model gives the best quantitative and qualitative agreement with experiments for the regarded transport properties. The deviations from experimental data are of 5% to 15% for pure liquid water and 5% to 20% for the water + alcohol mixtures. Moreover, the center of mass power spectrum of water as well as the investigated mixtures are analyzed and the hydrogen-bonding structure is discussed for different states.
Hinata, Hirofumi; Kataoka, Tomoya
2016-08-15
We propose a belt transect setting strategy for mark-recapture experiments (MREs) to evaluate the time-independent 1D diffusion coefficient (〈Dp0〉) of marine litter in the cross-shore direction that determines the backwashing flux of the litter, based on two-year MREs for plastic floats (PFs) on Wadahama Beach, Nii-jima Island, Japan. When the alongshore width of the belt transect (Lt) was of the order of, or longer than, the length scale of wave-induced nearshore current circulation (Lc), the PFs were rarely transported alongshore across the selected transects prior to being backwashed offshore. Thus, the transect residence time became longer and showed a much weaker dependence on the transect position, in contrast to when Lt was even shorter than Lc. We therefore obtained the diffusion coefficients close to the value of (〈Dp0〉) when we set Lt to the order of, or longer than, Lc. PMID:27263978
Effect of Cryogenic Treatment on Thermal Diffusion Coefficient of Cu-Al Alloy%深冷处理对Cu-Al合金热扩散系数的影响
Institute of Scientific and Technical Information of China (English)
徐红
2013-01-01
The thermal diffusion coefficient of Cu-Al alloy before and after cryogenic treatment in the heating temperature range of 25-600 ℃ was measured by thermal constant tester.The effects of cryogenic treatment on the thermal diffusion coefficient of the alloy were investigated through comparing the variation of the thermal diffusion coefficient before and after cryogenic treatment.The results show that the variation trend of the thermal diffusion coefficient of the alloy after cryogenic treatment is the same as before,cryogenic treatment can increase the thermal diffusion coefficient of Cu-Al alloy,and the maximum difference of the thermal diffusion coefficient before and after cryogenic treatment appears at 400 ℃.%采用热常数测试仪测试了深冷处理前后Cu-Al合金在25～600℃的热扩散系数,通过对比深冷处理前后Cu-Al合金热扩散系数的变化,探讨了深冷处理对Cu-Al合金热扩散系数的影响.结果表明:深冷处理前后Cu-Al合金在25～600℃的热扩散系数变化趋势一致,深冷处理能增大Cu-Al合金热扩散系数,在400℃时,两者差值最大.
Gosset, Dominique; Trocellier, Patrick; Serruys, Yves
2002-06-01
Host matrices for actinide immobilisation will undergo the formation of large helium quantities due to alpha decay. Helium diffusion rate has to be known in order to predict the long-term behaviour of the material, and particularly, the influence of helium accumulation on mechanical properties. A nuclear reaction analysis method, namely the 3He(d, p) 4He reaction, has been used to analyse the evolution of 3He profiles after ion implantations at 1 and 3 MeV in two materials, monoclinic ZrO 2 (as a test material) and Ca 9Nd(PO 4) 5(SiO 4)F 1.5(OH) 0.5 britholite (envisaged for Am and Pu long-term storage). Two data processing methods are used: the classical excitation curve (proton yields versus deuteron energy) and second, the proton energy spectrum for a given deuteron energy. The characteristics of the 3He profiles (depth, width) obtained by both methods are compared to SRIM estimations. Their evolution during subsequent annealings allows an estimation of the helium diffusion rate in the britholite: D ( cm2/ s)=(2.5±1.5)×10 -4exp(-(1.07±0.03 eV)/ kT) in the temperature range 200-400 °C, in agreement with previous results on similar materials. Moreover, the shape of the proton energy spectra suggests channeling effects in britholite.
Indian Academy of Sciences (India)
R K Sarangi; Prakash Chauhan; S R Nayak
2002-09-01
The optical classification of the different water types provides vital input for studies related to primary productivity, water clarity and determination of euphotic depth. Image data of the IRS- P3 MOS-B, for Path 90 of 27th February, 1998 was used