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Nasel, Christian [Division of Neuroradiology, Department of Radiology, Medical University of Vienna, Waehringerguertel 18-20, A-1090 Vienna (Austria)]. E-mail: christian.nasel@perfusion.at
2005-08-01
Fluid-attenuated inversion recovery imaging (=flair imaging) is widely used as primary screening sequence in various investigation protocols, due to its high lesion contrast and sensitivity in detection of parenchymatous and leptomeningeal disease. An additional increase of sensitivity for detection of lesions may be achieved by contrast-enhanced flair imaging. Based on flair imaging a dual-echo inversion recovery imaging sequence (=proton echo usage [=protoneus] - sequence) was developed, which could significantly extend the possibilities of conventional flair imaging.
Fast spine echo and fast fluid attenuated inversion recovery sequences in multiple sclerosis
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Fast spin echo (FSE) and fast fluid attenuated inversion recovery (fast-FLAIR) sequences, were compared with conventional spin echo (CSE) in quantitating multiple sclerosis (MS) lesion burden. For each sequence, the total number and volume of MS lesions were calculated in 38 remitting multiple sclerosis patients using a semiautomated lesion detection program. Conventional spin echo, fast spin echo, and fast fluid attenuated inversion recovery image were reported on randomly and at different times by two expert observers. Interobserver differences, the time needed to quantitative multiple sclerosis lesions and lesion signal intensity (contrast-to-noise ratio and overall contrast) were considered. The lesions were classified by site into infratentorial, white matter and cortical/subcortical. A total of 2970 lesions with a volume of 961.7 cm3 was calculated on conventional spin echo images. Fast spin echo images depicted fewer (16.6%; p < .005) and smaller (24.9%; p < .0001) lesions and the differences were statistically significant. Despite an overall nonsignificant reduction for fast-FLAIR images (-5% and 4.8% for lesion number and volume, respectively), significantly lower values (lesion number: p < 0.1; volume: p < .04)were observed for infratentorial lesions, while significantly higher values were seen for cortical/subcortical lesions (lesion number: p < .01; volume: p < .02). A higher lesion/white matter contrast (p < .002), a significant time saving for lesion burden quantitation (p < .05) and very low interobserver variability were found in favor of fast-FLAIR. Our data suggest that, despite the limitations regarding infratentorial lesions, fast-FLAIR sequences are indicated in R studies because of their good identification of cortical/subcortical lesions, almost complete interobserver agreement, higher contrast-to-noise ratio and limited time needed for semiautomated quantitation
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Postcontrast fluid-attenuated inversion recovery (FLAIR) imaging effectively depicts parenchymal and leptomeningeal metastases. as reported. We compared postcontrast T1-weighted (T1W) and FLAIR imaging in a group of 50 patients, and to compare our results with published ones regarding the so-called effect of 'late enhancement' as well. Fifty patients with known malignancy and suspected cranial metastases underwent axial FLAIR and spin-echo T1W imaging without and with intravenous gadopentetate dimeglumine (GD). Postcontrast images were compared for lesion conspicuity and enhancement, number of parenchymal metastases, and extension of leptomeningeal-cisternal metastases. All postcontrast FLAIR sequences were obtained after the postcontrast T1W sequences. Parenchymal metastases were demonstrated in 30 patients. Regarding all established criteria postcontrast FLAIR imaging was superior in two patients, equal in five, and inferior in 23. FLAIR imaging was performed as the second postcontrast sequence. Five patients had leptomeningeal-cisternal metastases; lesion conspicuity, extension, and enhancement were superior on postcontrast FLAIR images in all five patients. FLAIR imaging was performed as the second postcontrast sequence. Nine patients had cranial-nerve metastases; in eight, postcontrast FLAIR imaging was superior for lesion conspicuity and extension. In all patients, FLAIR imaging was the second postcontrast sequence. Postcontrast FLAIR imaging is a valuable adjunct to post-contrast T1W imaging. Precontrast and postcontrast FLAIR imaging effectively delineates parenchymal metastases, particularly leptomeningeal-cisternal and cranial-nerve metastases
Sodium imaging of the human knee using soft inversion recovery fluid attenuation
Feldman, Rebecca E.; Stobbe, Robert; Watts, Alexander; Beaulieu, Christian
2013-09-01
Sodium signal strength in MRI is low when compared with 1H. Thus, image voxel volumes must be relatively large in order to produce a sufficient signal-to-noise ratio (SNR). The measurement of sodium in cartilage is hindered by conflation with signal from the adjacent fluid spaces. Inversion recovery can be used to null signal from fluid, but reduces SNR. The purpose of this work was to optimize inversion recovery sodium MRI to enhance cartilage SNR while nulling fluid. Sodium relaxation was first measured for knee cartilage (T1 = 21 ± 1 ms, T2 fast∗=0.8±0.2 ms, T2 slow∗=19.7±0.5 ms) and fluid (T1 = 48 ± 3 ms, T2∗=47±4 ms) in nine healthy subjects at 4.7 T. The rapid relaxation of cartilage in relation to fluid permits the use of a lengthened inversion pulse to preferentially invert the fluid components. Simulations of inversion pulse length were performed to yield a cartilage SNR enhancing combination of parameters that nulled fluid. The simulations were validated in a phantom and then invivo. B0 inhomogeneity was measured and the effect of off-resonance during the soft inversion pulse was assessed with simulation. Soft inversion recovery yielded twice the SNR and much improved sodium images of cartilage in human knee with little confounding signal from fluid.
Contrast-enhanced fast fluid-attenuated inversion recovery MR imaging in patients with brain tumors
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Kim, Chan Kyo; Na, Dong Gyu; Ryoo, Wook Jae; Byun Hong Sik; Yoon, Hye Kyung; Kim, Jong hyun [Samsung Medical Center, School of Medicine, Sungkyunkwan University, Seoul (Korea, Republic of)
2000-09-01
To assess the feasibility of contrast-enhanced fast fluid-attenuated inversion recovery (fast FLAIR) MR imaging in patients with brain tumors. This study involved 31 patients with pathologically proven brain tumors and nine with clinically diagnosed metastases. In all patients, T2-weighted, fast FLAIR, images were visual contrast-enhanced T1-weighted MR images were obtained. Contrast-enhanced fast FLAIR images were visually compared with other MR sequences in terms of tumor conspicuity. In order to distinguish tumor and surrounding edema, contrast-enhanced fast FLAIR images were compared with fast FLAIR and T2-weighted images. The tumor-to- white matter contrast-to-noise ratios (CNRs), as demonstrated by T2-weighted, fast FLAIR, contrast-enhanced fast FLAIR and contrast-enhanced T1-weighted imaging, were quantitatively assessed and compared. For the visual assessment of tumor conspicuity, contrast-enhanced fast FLAIR image imaging superior to fast FLAIR in 60% of cases (24/40), and superior to T2-weighted in 70% (28/40). Contrast-enhanced fast FLAIR imaging was inferior to contrast-enhanced T1-weighted in 58% of cases (23/40). For distinguishing between tumor and surrounding edema, contrast-enhanced fast FLAIR imaging was superior to fast FLAIR or T2-weighted in 22 of 27 tumors with peritumoral edema (81%). Quantitatively, CNR was the highest on contrast-enhanced fast FLAIR image and the lowest on fast FLAIR. For the detection of leptomeningeal metastases, contrast-enhanced fast FLAIR was partially superior to contrast-enhanced T1-weighted imaging in two of three high-grade gliomas. Although contrast-enhanced fast FLAIR imaging should not be seen as a replacement for conventional modalities, it provides additional informaton for assessment of the extent of glial cell tumors and leptomeningeal metastases in patients with brain tumors. (author)
Contrast-enhanced fast fluid-attenuated inversion recovery MR imaging in patients with brain tumors
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To assess the feasibility of contrast-enhanced fast fluid-attenuated inversion recovery (fast FLAIR) MR imaging in patients with brain tumors. This study involved 31 patients with pathologically proven brain tumors and nine with clinically diagnosed metastases. In all patients, T2-weighted, fast FLAIR, images were visual contrast-enhanced T1-weighted MR images were obtained. Contrast-enhanced fast FLAIR images were visually compared with other MR sequences in terms of tumor conspicuity. In order to distinguish tumor and surrounding edema, contrast-enhanced fast FLAIR images were compared with fast FLAIR and T2-weighted images. The tumor-to- white matter contrast-to-noise ratios (CNRs), as demonstrated by T2-weighted, fast FLAIR, contrast-enhanced fast FLAIR and contrast-enhanced T1-weighted imaging, were quantitatively assessed and compared. For the visual assessment of tumor conspicuity, contrast-enhanced fast FLAIR image imaging superior to fast FLAIR in 60% of cases (24/40), and superior to T2-weighted in 70% (28/40). Contrast-enhanced fast FLAIR imaging was inferior to contrast-enhanced T1-weighted in 58% of cases (23/40). For distinguishing between tumor and surrounding edema, contrast-enhanced fast FLAIR imaging was superior to fast FLAIR or T2-weighted in 22 of 27 tumors with peritumoral edema (81%). Quantitatively, CNR was the highest on contrast-enhanced fast FLAIR image and the lowest on fast FLAIR. For the detection of leptomeningeal metastases, contrast-enhanced fast FLAIR was partially superior to contrast-enhanced T1-weighted imaging in two of three high-grade gliomas. Although contrast-enhanced fast FLAIR imaging should not be seen as a replacement for conventional modalities, it provides additional informaton for assessment of the extent of glial cell tumors and leptomeningeal metastases in patients with brain tumors. (author)
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Soo Chin Kim
Full Text Available PURPOSE: To evaluate whether adding a contrast-enhanced fluid-attenuated inversion recovery (FLAIR sequence to routine magnetic resonance imaging (MRI can detect additional abnormalities in the brains of symptomatic patients with mild traumatic brain injury. MATERIALS AND METHODS: Fifty-four patients with persistent symptoms following mild closed head injury were included in our retrospective study (M ∶ F = 32 ∶ 22, mean age: 59.8 ± 16.4, age range: 26-84 years. All MRI examinations were obtained within 14 days after head trauma (mean: 3.2 ± 4.1 days, range: 0.2-14 days. Two neuroradiologists recorded (1 the presence of traumatic brain lesions on MR images with and without contrast-enhanced FLAIR images and (2 the pattern and location of meningeal enhancement depicted on contrast-enhanced FLAIR images. The number of additional traumatic brain lesions diagnosed with contrast-enhanced FLAIR was recorded. Correlations between meningeal enhancement and clinical findings were also evaluated. RESULTS: Traumatic brain lesions were detected on routine image sequences in 25 patients. Three additional cases of brain abnormality were detected with the contrast-enhanced FLAIR images. Meningeal enhancement was identified on contrast-enhanced FLAIR images in 9 cases while the other routine image sequences showed no findings of traumatic brain injury. Overall, the additional contrast-enhanced FLAIR images revealed more extensive abnormalities than routine imaging in 37 cases (p<0.001. In multivariate logistic regression analysis, subdural hematoma and posttraumatic loss of consciousness showed a significant association with meningeal enhancement on contrast-enhanced FLAIR images, with odds ratios 13.068 (95% confidence interval 2.037 to 83.852, and 15.487 (95% confidence interval 2.545 to 94.228, respectively. CONCLUSION: Meningeal enhancement on contrast-enhanced FLAIR images can help detect traumatic brain lesions as well as additional abnormalities
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Fluid-attenuated inversion recovery (FLAIR) imaging of hepatic hemangiomas (10 patients, 16 lesions) and hepatic cysts (8 patients, 10 lesions) was performed. All hemangiomas were hypointense on T1-weighted images and hyperintense on T2-weighted images. With Gd-DTPA (O.1 mmol/kg), all hemangiomas were enhanced but not all cysts. It was necessary to perform contrast enhanced imaging to differentiate hepatic hemangiomas from hepatic cysts. However, on FLAIR imaging, hepatic hemangiomas were strongly hyperintense and 9 of the 10 hepatic cysts were isointense. One of the hepatic cysts was slightly hyperintense. FLAIR images were useful in differential diagnosis of hepatic hemangiomas and hepatic cysts without using Gd-DTPA. (author)
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White matter hyperintensities (WMHs) are regions of abnormally high intensity on T2-weighted or fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI). Accurate and reproducible automatic segmentation of WMHs is important since WMHs are often seen in the elderly and are associated with various geriatric and psychiatric disorders. We developed a fully automated monospectral segmentation method for WMHs using FLAIR MRIs. Through this method, we introduce an optimal threshold intensity (IO) for segmenting WMHs, which varies with WMHs volume (VWMH), and we establish the IO -VWMH relationship. Our method showed accurate validations in volumetric and spatial agreements of automatically segmented WMHs compared with manually segmented WMHs for 32 confirmatory images. Bland-Altman values of volumetric agreement were 0.96 ± 8.311 ml (bias and 95 % confidence interval), and the similarity index of spatial agreement was 0.762 ± 0.127 (mean ± standard deviation). Furthermore, similar validation accuracies were obtained in the images acquired from different scanners. The proposed segmentation method uses only FLAIR MRIs, has the potential to be accurate with images obtained from different scanners, and can be implemented with a fully automated procedure. In our study, validation results were obtained with FLAIR MRIs from only two scanner types. The design of the method may allow its use in large multicenter studies with correct efficiency. (orig.)
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Kwag, Eujean; Lim, Soo Mee; Park, Ji Eun; Chae, In Hye [Ewha Womans University School of Medicine, Department of Radiology, Mokdong Hospital, Seoul (Korea, Republic of)
2014-09-15
To evaluate the utility of BLADE fluid-attenuated inversion recovery images (FLAIR) magnetic resonance (MR) imaging compared to conventional FLAIR for the detection of arterial hyperintensity (AH) in hyperacute territorial infarction. We retrospectively analysed MR images of patients with hyperacute (<6 h) territorial infarction over a 9-month study period. Special attention was paid to the presence or absence of AH in the frontal, parietal and temporal lobes and the number of AHs in the sylvian fissure. We also evaluated the presence of three kinds of artefacts on BLADE FLAIR and conventional FLAIR images. AH was seen in 41 (91 %) patients with conventional FLAIR and 45 (100 %) patients with BLADE FLAIR images. More instances of AH were detected in the frontal, parietal and temporal lobes and within the sylvian fissure using BLADE FLAIR. Motion artefacts, pulsation artefacts from the sigmoid sinus and incomplete cerebrospinal fluid (CSF) nulling that reduced image quality were observed more frequently on conventional FLAIR images than on BLADE FLAIR images. BLADE FLAIR sequences are more sensitive than conventional FLAIR for the detection of AH in hyperacute territorial infarctions and provide better image quality by reducing artefacts. They may be used in place of conventional FLAIR for patients with hyperacute stroke. (orig.)
Fast fluid-attenuated inversion-recovery imaging: first experience with a 3D version in epilepsy
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We developed a 3D version of fast fluid-attenuated inversion-recovery imaging (FLAIR) which provides images with a slice thickness of 1.5 mm. We present our initial experience with 3D fast FLAIR in patients with epilepsy. We compared 3D fast FLAIR (slice thickness 1.5 mm), 2D fast FLAIR (slice thickness 5 mm) and a 3D spoiled GRASS (IRSPGR) sequence (slice thickness 1.5 mm) in 10 patients with lesional epilepsy (head injury 1, hippocampal sclerosis 2, low-grade glioma 2, dysembryoplastic neuroepithelial tumour 2, polymicrogyria 1, perinatal infarct 1 and presumed thrombosed aneurysm 1). Both 2D and 3D fast FLAIR sequences yielded higher conspicuity for lesions than the T1-weighted IRSPGR sequence, except in the patient with polymicrogyria. The extent of the lesion, in particular that of low-grade tumours, was best assessed on 3D fast FLAIR images. 3D fast FLAIR may be a useful additional tool especially for imaging low-grade tumours. (orig.)
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Yoo, Byung Il; Han, Ji Won; Oh, San Yeo Wool; Kim, Tae Hui [Seoul National University Bundang Hospital, Department of Neuropsychiatry, Seongnam, Gyeonggi-do (Korea, Republic of); Lee, Jung Jae; Lee, Eun Young [Kyungbook National University Chilgok Hospital, Department of Psychiatry, Buk-gu, Daegu (Korea, Republic of); MacFall, James R. [Duke University Medical Center, Neuropsychiatric Imaging Research Laboratory, Durham, NC (United States); Duke University Medical Center, Department of Radiology, Durham, NC (United States); Payne, Martha E. [Duke University Medical Center, Neuropsychiatric Imaging Research Laboratory, Durham, NC (United States); Duke University Medical Center, Department of Psychiatry and Behavioral Sciences, Durham, NC (United States); Kim, Jae Hyoung [Seoul National University Bundang Hospital, Department of Radiology, Seongnam, Gyeonggi-do (Korea, Republic of); Seoul National University College of Medicine, Department of Radiology, Jongno-gu, Seoul (Korea, Republic of); Kim, Ki Woong [Seoul National University Bundang Hospital, Department of Neuropsychiatry, Seongnam, Gyeonggi-do (Korea, Republic of); Seoul National University College of Medicine, Department of Psychiatry, Jongno-gu, Seoul (Korea, Republic of); Seoul National University College of Natural Sciences, Department of Brain and Cognitive Science, Gwanak-gu, Seoul (Korea, Republic of)
2014-04-15
White matter hyperintensities (WMHs) are regions of abnormally high intensity on T2-weighted or fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI). Accurate and reproducible automatic segmentation of WMHs is important since WMHs are often seen in the elderly and are associated with various geriatric and psychiatric disorders. We developed a fully automated monospectral segmentation method for WMHs using FLAIR MRIs. Through this method, we introduce an optimal threshold intensity (I{sub O}) for segmenting WMHs, which varies with WMHs volume (V{sub WMH}), and we establish the I{sub O} -V{sub WMH} relationship. Our method showed accurate validations in volumetric and spatial agreements of automatically segmented WMHs compared with manually segmented WMHs for 32 confirmatory images. Bland-Altman values of volumetric agreement were 0.96 ± 8.311 ml (bias and 95 % confidence interval), and the similarity index of spatial agreement was 0.762 ± 0.127 (mean ± standard deviation). Furthermore, similar validation accuracies were obtained in the images acquired from different scanners. The proposed segmentation method uses only FLAIR MRIs, has the potential to be accurate with images obtained from different scanners, and can be implemented with a fully automated procedure. In our study, validation results were obtained with FLAIR MRIs from only two scanner types. The design of the method may allow its use in large multicenter studies with correct efficiency. (orig.)
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Background and purpose: The application of a fluid-attenuated inversion-recovery pulse with a conventional diffusion-weighted MRI sequence (FLAIR DWI) decreases the partial volume effects from cerebrospinal fluid on apparent diffusion coefficient (ADC) measurements. For this reason, FLAIR DWI may be more useful in the evaluation of ischemic stroke, but few studies have looked at the effect of FLAIR on ADC measurements in this setting. This study quantitatively compares FLAIR DWI and conventional DWI in ischemic stroke of varying ages to assess the potential advantages of this technique. Methods: We respectively analyzed 139 DWI studies in patients with ischemic stroke with and without FLAIR at varying time points ranging from hyperacute to chronic. ADC values were measured in each lesion, as well as in the contralateral normal side. Comparisons were made between the ADC values obtained from the DWI sequences with and without FLAIR for both the lesion and the normal contralateral side. Results: The ADC measurements within the ischemic lesion were very similar on FLAIR DWI and conventional DWI for lesions less than 14 days old (p > 0.05), but were significantly decreased on FLAIR DWI for lesions between 15 and 30 days old and in lesions >31 days old (chronic stage) (p < 0.01). The contralateral ADC values were all significantly decreased on the FLAIR DWI sequence compared with conventional DWI (p < 0.01). Conclusions: The application of an inversion pulse does not significantly affect the ADC values for early stage ischemic stroke (less than 14 days from symptom onset), but results in a more accurate relative ADC measurement by reducing the cerebrospinal fluid partial volume effects of the normal contralateral side. In addition, combined with the conventional DWI, FLAIR DWI may be helpful in determining the age of ischemic lesions.
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The purpose of this study was to evaluate the usefulness of FLAIR(Fluid Attenuated Inversion Recovery) MR imaging in childhood adrenoleukodystrophy by comparing with those of T2-weighted FSE imaging, and to correlate MRI findings with clinical manifestations. Axial FLAIR images(TR/TE/TI=10004/123/2200) and T2-weighted FSE images(TR/TE=4000/104) of brain in six male patients(age range : 6-17 years, mean age : 10.2 years) with biochemically confirmed adrenoleukodystrophy were compared visually by two radiologists for detection, conspicuity, and the extent of lesion. Quantitatively, we compared lesion/CSF contrast, lesion/CSF contrast to noise ratio(CNR), lesion/white matter(WM) contrast, and lesion/WM CNR between FLAIR and T2 weighted image. We correlated MR findings with clinical manifestations of neurologic symptoms and evaluated whether MRI could detect white matter lesions in neurologically asymptomatic patients. Visual detection of lesions was better with FLAIR images in 2 of the 6 cases and it was equal in the remainders. Visual conspicuity and detection of the extent of lesion were superior on FLAIR images than T2-weighted images in all 6 cases. In the quantitative assessment of lesions, FLAIR was superior to T2-weighted image for lesion/CSF contrast and lesion/CSF CNR, but was inferior to T2 weighted image for lesion/WM contrast and lesion/WM CNR. In one case, FLAIR images distinguished the portion of encephalomalacic change from lesions. MR findings of adrenoleukodystrophy were correlated with clinical manifestations in symptomatic 4 cases, and also detected white matter lesions in asymptomatic 2 cases. MR imaging with FLAIR sequence provided images that were equal or superior to T2-weighted images in the evaluation of childhood adrenoleukodystrophy. MRI findings were well correlated with clinical manifestations and could detect white matter lesions in neurologically asymptomatic adrenoleukodystrophy patients
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Fujiwara, Hirokazu [Department of Diagnostic Radiology, School of Medicine, Keio University, Tokyo 1608582 (Japan)]. E-mail: hirokazu_fujiwara@ybb.ne.jp; Momoshima, Suketaka [Department of Diagnostic Radiology, School of Medicine, Keio University, Tokyo 1608582 (Japan); Kuribayashi, Sachio [Department of Diagnostic Radiology, School of Medicine, Keio University, Tokyo 1608582 (Japan)
2005-08-01
Purpose: There are a few reports on leptomeningeal high signal intensity (LMHI: ivy sign) on fluid-attenuated inversion-recovery (FLAIR) images in moyamoya disease, but the feature of this finding has not been completely understood. The purpose of this study was to characterize LMHI on FLAIR images in moyamoya disease and to assess usefulness of this finding in the diagnosis of moyamoya disease in conventional MR imaging. Material and methods: MR imaging of 28 patients with moyamoya disease was retrospectively reviewed. The grade of LMHI on FLAIR images was classified as 'absent,' 'minimal,' 'moderate' and 'marked.' Fifty-four hemispheres of 28 patients (2 patients had unilateral disease) were assessed for the frequency of visualization and distribution of LMHI. The correlations between LMHI on FLAIR images, moyamoya vessels on T1- and T2-weighted images and MR angiography findings were also analyzed. Results: Moderate and marked LMHI was seen in 31 out of 54 hemispheres (57%). LMHI was seen more prominently in the frontal and parietal lobes than in the temporal and occipital lobes. Although there was a tendency for LMHI on FLAIR images to be prominent in groups with moderate and marked moyamoya vessels on T1- and T2-weighted images, there was no significant correlation. More prominent LMHI was observed in the hemispheres in which cortical branches of the middle cerebral arteries were poorly visualized on MR angiography. Conclusion: Leptomeningeal high signal intensity (ivy sign) on FLAIR images is predominantly seen in the frontal and parietal lobes. Because this sign can be seen in patients with unremarkable moyamoya vessels, LMHI is a useful sign in conventional MR imaging for the diagnosis of moyamoya disease.
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Objective: To evaluate contrast-enhanced fluid-attenuated inversion recovery (FLAIR) imaging in the detection of leptomeningeal lesions. Methods: Seventeen patients with a variety of leptomeningeal lesions were analyzed. The MRI protocol included un-enhanced and contrast-enhanced FLAIR images and contrast-enhanced T1WI. Comparisons between contrast-enhanced FLAIR images and T1WI and between un-enhanced and contrast-enhanced FLAIR images were made to determine which sequence better depicted the lesions. Results: Leptomeningeal lesions showed as either diffusely or locally abnormal hyper-intensity along sulci or cistern on three sequences. Comparison between contrast-enhanced FLAIR and T1WI showed that only contrast-enhanced FLAIR revealed the abnormalities in 7, both revealed the abnormalities but the former was superior in 2, and both were conspicuous in 7. In 1 patient of tuberculous meningitis, diffuse abnormalities of sulci were shown only on contrast-enhanced FLAIR, abnormalities of cisterns were shown on both sequences but the former was superior. Comparison between un- enhanced and contrast-enhanced FLAIR showed that only contrast-enhanced FLAIR revealed the abnormalities in 9, both revealed the abnormalities but the former was superior in 3, and both were conspicuous in 4. In 1 patient of tuberculous meningitis, abnormalities of cisterns were shown only on contrast-enhanced FLAIR, diffuseabnormalities of sulci were shown on both sequences but the former was superior. Conclusions: Contrast-enhanced FLAIR images were superior to un-enhanced FLAIR images and contrast-enhanced T1WI in the detection of leptomeningeal lesions. Contrast-enhanced FLAIR images are helpful and should be considered when findings on un-enhanced FLAIR images and/or contrast-enhanced T1WI are inconclusive. (authors)
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Purpose: There are a few reports on leptomeningeal high signal intensity (LMHI: ivy sign) on fluid-attenuated inversion-recovery (FLAIR) images in moyamoya disease, but the feature of this finding has not been completely understood. The purpose of this study was to characterize LMHI on FLAIR images in moyamoya disease and to assess usefulness of this finding in the diagnosis of moyamoya disease in conventional MR imaging. Material and methods: MR imaging of 28 patients with moyamoya disease was retrospectively reviewed. The grade of LMHI on FLAIR images was classified as 'absent,' 'minimal,' 'moderate' and 'marked.' Fifty-four hemispheres of 28 patients (2 patients had unilateral disease) were assessed for the frequency of visualization and distribution of LMHI. The correlations between LMHI on FLAIR images, moyamoya vessels on T1- and T2-weighted images and MR angiography findings were also analyzed. Results: Moderate and marked LMHI was seen in 31 out of 54 hemispheres (57%). LMHI was seen more prominently in the frontal and parietal lobes than in the temporal and occipital lobes. Although there was a tendency for LMHI on FLAIR images to be prominent in groups with moderate and marked moyamoya vessels on T1- and T2-weighted images, there was no significant correlation. More prominent LMHI was observed in the hemispheres in which cortical branches of the middle cerebral arteries were poorly visualized on MR angiography. Conclusion: Leptomeningeal high signal intensity (ivy sign) on FLAIR images is predominantly seen in the frontal and parietal lobes. Because this sign can be seen in patients with unremarkable moyamoya vessels, LMHI is a useful sign in conventional MR imaging for the diagnosis of moyamoya disease
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Hyperintense acute reperfusion marker (HARM) without diffusion abnormalities is occasionally found in patients with an acute stroke. This study was to determine the prevalence and clinical implications of HARM without diffusion abnormalities. There was a retrospective review of magnetic resonance images 578 patients with acute strokes and identified those who did not have acute infarction lesions, as mapped by diffusion-weighted imaging (DWI). These patients were classified into an imaging-negative stroke and HARM without diffusion abnormalities groups, based on the DWI findings and postcontrast fluid attenuated inversion recovery images. The National Institutes of Health Stroke Scale (NIHSS) scores at admission, 1 day, and 7 days after the event, as well as clinical data and risk factors, were compared between the imaging-negative stroke and HARM without diffusion abnormalities groups. Seventy-seven acute stroke patients without any DWI abnormalities were found. There were 63 patients with an imaging-negative stroke (accounting for 10.9% of 578) and 13 patients with HARM without diffusion abnormalities (accounting for 2.4% of 578). The NIHSS scores at admission were higher in HARM without diffusion abnormalities group than in the imaging-negative stroke group (median, 4.5 vs. 1.0; p < 0.001), but the scores at 7 days after the event were not significantly different between the two groups (median, 0 vs. 0; p = 1). The patients with HARM without diffusion abnormalities were significantly older, compared with patients with an imaging-negative stroke (mean, 73.1 years vs. 55.9 years; p < 0.001). Patients with HARM without diffusion abnormalities are older and have similarly favorable short-term neurological outcomes, compared with the patients with imaging-negative stroke
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Lee, Hyuk Joon; Kim, Eun Hee; Lee, Kyung Mi; Kim, Jae Hyoung; Bae, Yun Jung; Choi, Byoung Se; Jung, Cheol Kyu [Dept. of Radiology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam (Korea, Republic of)
2015-08-15
Hyperintense acute reperfusion marker (HARM) without diffusion abnormalities is occasionally found in patients with an acute stroke. This study was to determine the prevalence and clinical implications of HARM without diffusion abnormalities. There was a retrospective review of magnetic resonance images 578 patients with acute strokes and identified those who did not have acute infarction lesions, as mapped by diffusion-weighted imaging (DWI). These patients were classified into an imaging-negative stroke and HARM without diffusion abnormalities groups, based on the DWI findings and postcontrast fluid attenuated inversion recovery images. The National Institutes of Health Stroke Scale (NIHSS) scores at admission, 1 day, and 7 days after the event, as well as clinical data and risk factors, were compared between the imaging-negative stroke and HARM without diffusion abnormalities groups. Seventy-seven acute stroke patients without any DWI abnormalities were found. There were 63 patients with an imaging-negative stroke (accounting for 10.9% of 578) and 13 patients with HARM without diffusion abnormalities (accounting for 2.4% of 578). The NIHSS scores at admission were higher in HARM without diffusion abnormalities group than in the imaging-negative stroke group (median, 4.5 vs. 1.0; p < 0.001), but the scores at 7 days after the event were not significantly different between the two groups (median, 0 vs. 0; p = 1). The patients with HARM without diffusion abnormalities were significantly older, compared with patients with an imaging-negative stroke (mean, 73.1 years vs. 55.9 years; p < 0.001). Patients with HARM without diffusion abnormalities are older and have similarly favorable short-term neurological outcomes, compared with the patients with imaging-negative stroke.
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The aim of our study was to assess the usefulness of fluid-attenuated inversion recovery (FLAIR) sequences in comparison with conventional spin-echo and inversion MR imaging in neonates for evaluation of myelination and for detection of hypoxic-ischemic brain injury. We reviewed early MR scans of 18 neonates with suspected hypoxic-ischemic brain damage. Myelination could be evaluated with confidence using conventional MR imaging in all but 2 infants; however, the presence of myelin was very difficult to assess on FLAIR images. Overall, 53 lesions or groups of lesions were identified. The FLAIR technique was more sensitive in 11 of the lesions; especially (pre)cystic lesions could be identified much better and more cysts were found. Conventional MR imaging failed to identify 2 of the lesions and was more sensitive in 14 of the lesions; especially punctate hemorrhages and lesions in basal ganglia or thalami could be better determined. The FLAIR technique missed 3 of these lesions. In the remaining 28 lesions conventional MR and FLAIR images were equally diagnostic. The FLAIR technique and conventional MR imaging are complementary in detecting early sequelae of hypoxic-ischemic brain injury in neonates. The FLAIR technique is not suitable for assessing myelination of the neonatal brain; therefore, FLAIR cannot replace conventional MR imaging. (orig.)
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Sie, L.T.L.; Knaap, M.S. van der [Vrije Univ. Hospital, Amsterdam (Netherlands). Dept. of Neurology; Barkhof, F.; Valk, J. [Amsterdam Univ. (Netherlands). Dept. of Diagnostic Radiology, Pathology and Gastroenterology; Lafeber, H.N. [Univ. Hospital ' Vrije Universiteit' , Amsterdam (Netherlands). Dept. of Neonatology
2000-10-01
The aim of our study was to assess the usefulness of fluid-attenuated inversion recovery (FLAIR) sequences in comparison with conventional spin-echo and inversion MR imaging in neonates for evaluation of myelination and for detection of hypoxic-ischemic brain injury. We reviewed early MR scans of 18 neonates with suspected hypoxic-ischemic brain damage. Myelination could be evaluated with confidence using conventional MR imaging in all but 2 infants; however, the presence of myelin was very difficult to assess on FLAIR images. Overall, 53 lesions or groups of lesions were identified. The FLAIR technique was more sensitive in 11 of the lesions; especially (pre)cystic lesions could be identified much better and more cysts were found. Conventional MR imaging failed to identify 2 of the lesions and was more sensitive in 14 of the lesions; especially punctate hemorrhages and lesions in basal ganglia or thalami could be better determined. The FLAIR technique missed 3 of these lesions. In the remaining 28 lesions conventional MR and FLAIR images were equally diagnostic. The FLAIR technique and conventional MR imaging are complementary in detecting early sequelae of hypoxic-ischemic brain injury in neonates. The FLAIR technique is not suitable for assessing myelination of the neonatal brain; therefore, FLAIR cannot replace conventional MR imaging. (orig.)
Sahu, Indra Dev; Shrestha, Shanta Lal; Ghimire, Ram Kumar
2009-01-01
Twenty cases of different brain pathology have been studied via MRI using an open resistive magnet with magnetic field strength of 0.2 Tesla. The relative signal intensity with respect to the repetition time (TR) at fixed echo time (TE) 0.117 sec. has been studied. It was found that the signal intensity saturates for most lesions beyond a certain TR~6 sec in the T2 - weighted image. The signal intensity differs with respect to the inversion time (TI) for fat and cerebrospinal fluid (CSF). It was found that the intensity is nulled for CSF at TI ~1.5 sec. and for Fat at TI~0.10 sec in the FLAIR imaging sequence. Thus the intensity of the lesions is qualitatively different for the two sequences. From the radiological diagnostic point of view, it was concluded that the FLAIR sequence is more useful for the detection of lesions compared to T2 sequences.
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Maeda, M.; Sakuma, H.; Takeda, K. [Dept. of Radiology, Mie Univ. School of Medicine, Mie (Japan); Yagishita, A. [Dept. of Neuroradiology, Tokyo Metropolitan Neurological Hospital, Tokyo (Japan); Yamamoto, T. [Dept. of Radiology, Obama Municipal Hospital, Fukui (Japan)
2003-12-01
A variety of central nervous system (CNS) diseases are associated with abnormal hyperintensity within the subarachnoid space (SAS) by fluid-attenuated inversion-recovery (FLAIR) MR imaging. Careful attention to the SAS can provide additional useful information that may not be available with conventional MR sequences. The purpose of this article is to provide a pictorial essay about CNS diseases and FLAIR images with abnormal hyperintensity within the SAS. We present several CNS diseases including subarachnoid hemorrhage, meningitis, leptomeningeal metastases, acute infarction, and severe arterial occlusive diseases such as moya-moya disease. We also review miscellaneous diseases or normal conditions that may exhibit cerebrospinal fluid hyperintensity on FLAIR images. Although the detection of abnormal hyperintensity suggests the underlying CNS diseases and narrows differential diagnoses, FLAIR imaging sometimes presents artifactual hyperintensity within the SAS that can cause the misinterpretation of normal SAS as pathologic conditions; therefore, radiologists should be familiar with such artifactual conditions as well as pathologic conditions shown as hyperintensity by FLAIR images. This knowledge is helpful in establishing the correct diagnosis. (orig.)
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Objective: To determine the frequency and regional involvement of temporal pole signal abnormality (TPA) in patients with hippocampal sclerosis (HS) using fluid-attenuated inversion-recovery (FLAIR) MR imaging, and to correlate this feature with history. Method: Coronal FLAIR images of the temporal pole were assessed in 120 patients with HS and in 30 normal subjects, to evaluate gray-white matter demarcation. Results: Ninety (75%) of 120 patients had associated TPA. The HS side made difference regarding the presence of TPA, with a left side prevalence (p=0.04, χ2 test). The anteromedial zone of temporal pole was affected in 27 (30%) out of 90 patients. In 63 (70%) patients the lateral zone were also affected. Patients with TPA were younger at seizure onset (p=0.018), but without association with duration of epilepsy. Conclusion: Our FLAIR study show temporal pole signal abnormality in 3/4 of patients with HS, mainly seen on the anteromedial region, with a larger prevalence when the left hippocampus was involved. (author)
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A follow-up study was performed to assess the correlation among the incidence of periventricular low intensities (PVLI) on MRI (magnetic resonance imaging) FLAIR (fluid attenuated inversion recovery) imaging, clinical evidence of perinatal insults that may cause white matter damage, and the outcome of the infants. We evaluated periventricular white matter lesions of 329 neonates whose MRI were obtained before two months corrected age. The detective rate of periventricular abnormalities on FLAIR imaging was significantly higher than that of T1-T2 weighted imaging. The most typical lesion detected on FLAIR imaging was periventricular low intensities (PVLI), frequently observed in the neonates with a history of preterm labour, very low birth weight, birth asphyxia and severe respiratory failure. Although we could not characterize the risk factors of PVLI, the incidence of PVLI had a strong correlation with the scores of motor and developmental tests at 12 and 36-months corrected age. In conclusion, FLAIR imaging, detecting the border zone damage of white matter, would be a strong tool to pick out neonates at high risk of neurological disturbances from those without clinical evidence of neurological insults in the neonatal period. (author)
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Heo, Young Jin [University of Ulsan College of Medicine, Asan Medical Center, Department of Radiology, Research Institute of Radiology, Seoul (Korea, Republic of); Inje University, Department of Radiology, Busan Paik Hospital, Busan (Korea, Republic of); Kim, Sang Joon; Kim, Ho Sung; Choi, Choong Gon; Jung, Seung Chai [University of Ulsan College of Medicine, Asan Medical Center, Department of Radiology, Research Institute of Radiology, Seoul (Korea, Republic of); Lee, Jung Kyo [University of Ulsan College of Medicine, Asan Medical Center, Department of Neurosurgery, Seoul (Korea, Republic of); Lee, Chong Sik; Chung, Sun J. [University of Ulsan College of Medicine, Asan Medical Center, Department of Neurology, Seoul (Korea, Republic of); Cho, So Hyun [Department of Radiology, Busan (Korea, Republic of); Lee, Gyoung Ro [Philips HealthCare Korea, Seoul (Korea, Republic of)
2015-09-15
Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an accepted treatment for advanced Parkinson's disease (PD). However, targeting the STN is difficult due to its relatively small size and variable location. The purpose of this study was to assess which of the following sequences obtained with the 3.0 T MR system can accurately delineate the STN: coronal 3D fluid-attenuated inversion recovery (FLAIR), 2D T2*-weighted fast-field echo (T2*-FFE) and 2D T2-weighted turbo spin-echo (TSE) sequences. We included 20 consecutive patients with PD who underwent 3.0 T MR for DBS targeting. 3D FLAIR, 2D T2*-FFE and T2-TSE images were obtained for all study patients. Image quality and demarcation of the STN were analysed using 4-point scales, and contrast ratio (CR) of the STN and normal white matter was calculated. The Friedman test was used to compare the three sequences. In qualitative analysis, the 2D T2*-FFE image showed more artefacts than 3D FLAIR or 2D T2-TSE, but the difference did not reach statistical significance. 3D FLAIR images showed significantly superior demarcation of the STN compared with 2D T2*-FFE and T2-TSE images (P < 0.001, respectively). The CR of 3D FLAIR was significantly higher than that of 2D T2*-FFE or T2-TSE images in multiple comparison correction (P < 0.001), but there was no significant difference in the CR between 2D T2*-FFE and T2-TSE images. Coronal 3D FLAIR images showed the most accurate demarcation of the STN for DBS targeting among coronal 3D FLAIR, 2D T2*-FFE and T2-TSE images. (orig.)
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Moon, Won Jin; Roh, Hong Gee; Choi, Jin Woo [Dept. of Radiology, Konkuk University Medical Center, Konkuk University School of Medicine, Seoul (Korea, Republic of); Kim, Hee Jin [Dept. of Neurology, Hanyang University Medical Center, Hanyang University School of Medicine, Seoul (Korea, Republic of); Han, Seol Heui [Center for Geriatric Neuroscience Research, Konkuk University School of Medicine, Seoul (Korea, Republic of)
2012-11-15
We hypothesized that prominent pulvinar hypointensity in brain MRI represents the disease process due to iron accumulation in Alzheimer disease (AD). We aimed to determine whether or not the pulvinar signal intensity (SI) on the fluid-attenuated inversion recovery (FLAIR) sequences at 3.0T MRI differs between AD patients and normal subjects, and also whether the pulvinar SI is correlated with the T2 map, an imaging marker for tissue iron, and a cognitive scale. Twenty one consecutive patients with AD and 21 age-matched control subjects were prospectively included in this study. The pulvinar SI was assessed on the FLAIR image. We measured the relative SI ratio of the pulvinar to the corpus callosum. The T2 values were calculated from the T2 relaxometry map. The differences between the two groups were analyzed, by using a Student t test. The correlation between the measurements was assessed by the Pearson's correlation test. As compared to the normal white matter, the FLAIR signal intensity of the pulvinar nucleus was significantly more hypointense in the AD patients than in the control subjects (p < 0.01). The pulvinar T2 was shorter in the AD patients than in the control subjects (51.5 {+-} 4.95 ms vs. 56.5 {+-} 5.49 ms, respectively, p = 0.003). The pulvinar SI ratio was strongly correlated with the pulvinar T2 (r = 0.745, p < 0.001). When controlling for age, only the pulvinar-to-CC SI ratio was positively correlated with that of the Mini-Mental State Examination (MMSE) score (r = 0.303, p < 0.050). Conversely, the pulvinar T2 was not correlated with the MMSE score (r = 0.277, p = 0.080). The FLAIR hypointensity of the pulvinar nucleus represents an abnormal iron accumulation in AD and may be used as an adjunctive finding for evaluating AD.
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We hypothesized that prominent pulvinar hypointensity in brain MRI represents the disease process due to iron accumulation in Alzheimer disease (AD). We aimed to determine whether or not the pulvinar signal intensity (SI) on the fluid-attenuated inversion recovery (FLAIR) sequences at 3.0T MRI differs between AD patients and normal subjects, and also whether the pulvinar SI is correlated with the T2 map, an imaging marker for tissue iron, and a cognitive scale. Twenty one consecutive patients with AD and 21 age-matched control subjects were prospectively included in this study. The pulvinar SI was assessed on the FLAIR image. We measured the relative SI ratio of the pulvinar to the corpus callosum. The T2 values were calculated from the T2 relaxometry map. The differences between the two groups were analyzed, by using a Student t test. The correlation between the measurements was assessed by the Pearson's correlation test. As compared to the normal white matter, the FLAIR signal intensity of the pulvinar nucleus was significantly more hypointense in the AD patients than in the control subjects (p < 0.01). The pulvinar T2 was shorter in the AD patients than in the control subjects (51.5 ± 4.95 ms vs. 56.5 ± 5.49 ms, respectively, p = 0.003). The pulvinar SI ratio was strongly correlated with the pulvinar T2 (r = 0.745, p < 0.001). When controlling for age, only the pulvinar-to-CC SI ratio was positively correlated with that of the Mini-Mental State Examination (MMSE) score (r = 0.303, p < 0.050). Conversely, the pulvinar T2 was not correlated with the MMSE score (r = 0.277, p = 0.080). The FLAIR hypointensity of the pulvinar nucleus represents an abnormal iron accumulation in AD and may be used as an adjunctive finding for evaluating AD.
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Objective: After intratympanic gadolinium administration through the tympanic membrane, three-dimensional fluid-attenuated inversion recovery magnetic resonance imaging (3D-FLAIR MRI) was performed to evaluate endolymphatic visualization and its diagnostic value in Meniere's disease. Methods: Twenty-four hours after intratympanic gadolinium administration through the tympanic membrane, 19 patients with unilateral Meniere's disease diagnosed clinically underwent 3D-FLAIR and 3D-Balance-FFE imaging at 3.0 T MR scanner. The enhanced imaging of perilymphatic space in bilateral cochlea, vestibular and (or) canal were observed. Scala tympani and scala vestibule of bilateral cochlear basal turn were scored respectively. The enhanced range of bilateral vestibule and the signal intensity ratio (SIR) between the vestibule and the brain stem were measured. Wilcoxon tests and paired t tests were used. Results: The gadolinium appeared in almost all parts of the perilymph in cochlea,vestibular and (or) canal, so the endolymphatic space was clearly visualized on 3D-FLAIR imaging. The score of scala vestibuli between the affected side (3 cases scored 2, 9 cases scored 1, 7 cases scored 0) and the healthy side (15 cases scored 2, 2 cases scored 1, 2 cases scored 0) were significantly different (U=3.090, P<0.05). The area of enhanced vestibular were (5.77 ± 2.33) mm2 and (8.11 ± 3.32) mm2 for the affected side and the healthy side, which were significantly different (U=3.090, P<0.05 and t=2.638, P<0.05). Conclusions: According to 3D-Balance-FFE MRI and the enhancement of perilymphatic space, 3D-FLAIR MRI with intratympanic gadolinium injection through the tympanic membrane can be used to show the border between the perilymph and the endolymph and confirm endolymphatic hydrops, thus providing radiographic evidence for the diagnosis of Meniere's disease. (authors)
Directory of Open Access Journals (Sweden)
Xinyang Liu
2014-09-01
Full Text Available Background: Accumulation of amyloid beta (Aβ may occur during healthy aging and is a risk factor for Alzheimer Disease (AD. While individual Aβ-accumulation can be measured non-invasively using Pittsburgh compound-B positron-emission-tomography (PiB-PET, Fluid-Attenuated Inversion Recovery (FLAIR is a Magnetic Resonance Imaging (MRI sequence, capable of indicating heterogeneous age-related brain pathologies associated with tissue-edema. In the current study cognitively normal elderly subjects were investigated for regional correlation of PiB- and FLAIR- intensity. Methods: 14 healthy elderly subjects without known history of cognitive impairment received 11C-PiB-PET for estimation of regional Aβ-load. In addition, whole brain T1-MPRAGE and FLAIR-MRI sequences were acquired at high field strength of 7 Tesla (7T. Volume-normalized intensities of brain regions were assessed by applying an automated subcortical segmentation algorithm for spatial definition of brain structures. Statistical dependence between FLAIR- and PiB-PET intensities was tested using Spearman's rank correlation coefficient (rho, followed by Holm-Bonferroni correction for multiple testing. Results: Neuropsychological testing revealed normal cognitive performance levels in all participants. Mean regional PiB-PET and FLAIR intensities were normally distributed and independent. Significant correlation between volume-normalized PiB-PET signals and FLAIR intensities resulted for Hippocampus (right:rho=0.86; left:rho=0.84, Brainstem (rho=0.85 and left Basal Ganglia vessel region (rho=0.82. Conclusions: Our finding of a significant relationship between PiB- and FLAIR-intensity mainly observable in the Hippocampus and Brainstem, indicates regional Aβ associated tissue-edema in cognitively normal elderly subjects. Further studies including clinical populations are necessary to clarify the relevance of our findings for estimating individual risk for age-related neurodegenerative
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Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an accepted treatment for advanced Parkinson's disease (PD). However, targeting the STN is difficult due to its relatively small size and variable location. The purpose of this study was to assess which of the following sequences obtained with the 3.0 T MR system can accurately delineate the STN: coronal 3D fluid-attenuated inversion recovery (FLAIR), 2D T2*-weighted fast-field echo (T2*-FFE) and 2D T2-weighted turbo spin-echo (TSE) sequences. We included 20 consecutive patients with PD who underwent 3.0 T MR for DBS targeting. 3D FLAIR, 2D T2*-FFE and T2-TSE images were obtained for all study patients. Image quality and demarcation of the STN were analysed using 4-point scales, and contrast ratio (CR) of the STN and normal white matter was calculated. The Friedman test was used to compare the three sequences. In qualitative analysis, the 2D T2*-FFE image showed more artefacts than 3D FLAIR or 2D T2-TSE, but the difference did not reach statistical significance. 3D FLAIR images showed significantly superior demarcation of the STN compared with 2D T2*-FFE and T2-TSE images (P < 0.001, respectively). The CR of 3D FLAIR was significantly higher than that of 2D T2*-FFE or T2-TSE images in multiple comparison correction (P < 0.001), but there was no significant difference in the CR between 2D T2*-FFE and T2-TSE images. Coronal 3D FLAIR images showed the most accurate demarcation of the STN for DBS targeting among coronal 3D FLAIR, 2D T2*-FFE and T2-TSE images. (orig.)
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Lavdas, Eleftherios; Vlychou, Marianna; Arikidis, Nikos; Kapsalaki, Eftychia; Roka, Violetta; Fezoulidis, Ioannis V. (Dept. of Radiology, Univ. Hospital of Larissa, Medical School of Thessaly, Mezourlo (Greece)), e-mail: mvlychou@med.uth.gr
2010-04-15
Background: T1-weighted fluid-attenuated inversion recovery (FLAIR) sequence has been reported to provide improved contrast between lesions and normal anatomical structures compared to T1-weighted fast spin-echo (FSE) imaging at 1.5T regarding imaging of the lumbar spine. Purpose: To compare T1-weighted FSE and fast T1-weighted FLAIR imaging in normal anatomic structures and degenerative and metastatic lesions of the lumbar spine at 3.0T. Material and Methods: Thirty-two consecutive patients (19 females, 13 males; mean age 44 years, range 30-67 years) with lesions of the lumbar spine were prospectively evaluated. Sagittal images of the lumbar spine were obtained using T1-weighted FSE and fast T1-weighted FLAIR sequences. Both qualitative and quantitative analyses measuring the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and relative contrast (ReCon) between degenerative and metastatic lesions and normal anatomic structures were conducted, comparing these sequences. Results: On quantitative evaluation, SNRs of cerebrospinal fluid (CSF), nerve root, and fat around the root of fast T1-weighted FLAIR imaging were significantly lower than those of T1-weighted FSE images (P<0.001). CNRs of normal spinal cord/CSF and disc herniation/ CSF for fast T1-weighted FLAIR images were significantly higher than those for T1-weighted FSE images (P<0.001). ReCon of normal spinal cord/CSF, disc herniation/CSF, and vertebral lesions/CSF for fast T1-weighted FLAIR images were significantly higher than those for T1-weighted FSE images (P<0.001). On qualitative evaluation, it was found that CSF nulling and contrast at the spinal cord (cauda equina)/CSF interface for T1-weighted FLAIR images were significantly superior compared to those for T1-weighted FSE images (P<0.001), and the disc/spinal cord (cauda equina) interface was better for T1-weighted FLAIR images (P<0.05). Conclusion: The T1-weighted FLAIR sequence may be considered as the preferred lumbar spine imaging
An Inversion Recovery NMR Kinetics Experiment
Williams, Travis J.; Kershaw, Allan D.; Li, Vincent; Wu, Xinping
2011-01-01
A convenient laboratory experiment is described in which NMR magnetization transfer by inversion recovery is used to measure the kinetics and thermochemistry of amide bond rotation. The experiment utilizes Varian spectrometers with the VNMRJ 2.3 software, but can be easily adapted to any NMR platform. The procedures and sample data sets in this article will enable instructors to use inversion recovery as a laboratory activity in applied NMR classes and provide research students with a conveni...
An Inversion Recovery NMR Kinetics Experiment
Williams, Travis J.; Kershaw, Allan D.; Li, Vincent; Wu, Xinping
2011-01-01
A convenient laboratory experiment is described in which NMR magnetization transfer by inversion recovery is used to measure the kinetics and thermochemistry of amide bond rotation. The experiment utilizes Varian spectrometers with the VNMRJ 2.3 software, but can be easily adapted to any NMR platform. The procedures and sample data sets in this…
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The purpose of this study was to evaluate the signal intensity (SI) change of the labyrinth in patients with vestibular schwannoma on isotropic 3D fluid-attenuated inversion recovery (FLAIR) imaging at 3 T. Thirty-four patients with surgically confirmed or radiologically diagnosed vestibular schwannoma were included in this study. Retrospectively, we visually and quantitatively compared the SIs of the cochlea and vestibule on the affected side with those on the unaffected side. We also investigated whether there was correlation between the SI ratios (SIRs) of the labyrinth and the audiometric findings. On 3D FLAIR images, the SI of the cochlea and vestibule on the affected side was significantly increased in 97% (33/34) and 91% (31/34), respectively. While the SI of the cochlea was diffusely increased, that of the vestibule was only partially increased. Quantitative study also revealed statistically significantly higher SIRs of the cochlea (0.99 ± 0.29) and vestibule (0.73 ± 0.31) on the affected side, compared with the cochlea (0.47 ± 0.20) and vestibule (0.19 ± 0.10) on the unaffected side. There was no significant correlation of the SIRs of the labyrinth with the degree of hearing loss. In patients with vestibular schwannoma, isotropic 3D FLAIR imaging is a useful method for the evaluation of the SI changes of the labyrinth. (orig.)
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Lee, In Ho; Kim, Hyung-Jin; Kim, Eunhee; Moon, Jung Won; Kim, Sung Tae; Kim, Keon Ha; Jeon, Pyoung; Byun, Hong Sik [Sungkyunkwan University School of Medicine, Department of Radiology, Samsung Medical Center, Seoul (Korea); Chung, Won Ho [Sungkyunkwan University School of Medicine, Department of Otorhinolaryngology-Head and Neck Surgery, Samsung Medical Center, Seoul (Korea)
2010-04-15
The purpose of this study was to evaluate the signal intensity (SI) change of the labyrinth in patients with vestibular schwannoma on isotropic 3D fluid-attenuated inversion recovery (FLAIR) imaging at 3 T. Thirty-four patients with surgically confirmed or radiologically diagnosed vestibular schwannoma were included in this study. Retrospectively, we visually and quantitatively compared the SIs of the cochlea and vestibule on the affected side with those on the unaffected side. We also investigated whether there was correlation between the SI ratios (SIRs) of the labyrinth and the audiometric findings. On 3D FLAIR images, the SI of the cochlea and vestibule on the affected side was significantly increased in 97% (33/34) and 91% (31/34), respectively. While the SI of the cochlea was diffusely increased, that of the vestibule was only partially increased. Quantitative study also revealed statistically significantly higher SIRs of the cochlea (0.99 {+-} 0.29) and vestibule (0.73 {+-} 0.31) on the affected side, compared with the cochlea (0.47 {+-} 0.20) and vestibule (0.19 {+-} 0.10) on the unaffected side. There was no significant correlation of the SIRs of the labyrinth with the degree of hearing loss. In patients with vestibular schwannoma, isotropic 3D FLAIR imaging is a useful method for the evaluation of the SI changes of the labyrinth. (orig.)
Seismic Attenuation Inversion with t* Using tstarTomog.
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Preston, Leiph
2014-09-01
Seismic attenuation is defined as the loss of the seismic wave amplitude as the wave propagates excluding losses strictly due to geometric spreading. Information gleaned from seismic waves can be utilized to solve for the attenuation properties of the earth. One method of solving for earth attenuation properties is called t*. This report will start by introducing the basic theory behind t* and delve into inverse theory as it pertains to how the algorithm called tstarTomog inverts for attenuation properties using t* observations. This report also describes how to use the tstarTomog package to go from observed data to a 3-D model of attenuation structure in the earth.
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Saini, Jitender; Kesavadas, Chandrasekharan; Thomas, Bejoy (Dept. of Imaging Sciences and Interventional Radiology, Sree Chitra Tirunal Inst. for Medical Sciences and Technology, Trivandrum, Kerala (India)), e-mail: chandkesav@yahoo.com; Singh, Atampreet; Rathore, Chathurbhuj; Radhakrishnan, Ashalatha (Dept. of Neurology, Sree Chitra Tirunal Inst. for Medical Sciences and Technology, Trivandrum, Kerala (India)); Radhakrishnan, Kurupath; Bahuleyan, Biji (Dept. of Neurosurgery, Sree Chitra Tirunal Inst. for Medical Sciences and Technology, Trivandrum, Kerala (India))
2010-03-15
Background: Focal cortical dysplasia (FCD) is often associated with epilepsy. Identification of FCD can be difficult due to subtle magnetic resonance imaging (MRI) changes. Though fluid-attenuated inversion recovery (FLAIR) sequence detects the majority of these lesions, smaller lesions may go unnoticed while larger lesions may be poorly delineated. Purpose: To determine the ability of a specialized epilepsy protocol in visualizing and delineating the extent of FCD. Material and Methods: We compared the imaging findings in nine patients with cortical malformation who underwent routine epilepsy MR imaging as well as a specialized epilepsy protocol. All imaging was done on a 1.5T MR unit. The specialized epilepsy protocol included 3D FLAIR in the sagittal plane as well as proton density (PD) and high-resolution T2-weighted (T2W) images in the transverse plane. Results: In all nine patients, the specialized protocol identified lesion anatomy better. In three patients in whom routine MRI was normal, the specialized epilepsy protocol including 3D FLAIR helped in identifying the lesions. One of these patients underwent surgery, and histo-pathology revealed a cortical dysplasia. In one patient, lesion characterization was improved, while in the remaining patients the extent of the FCD was more clearly demonstrated in the 3D FLAIR and PD images. Statistical analysis of images for cortical thickness, cortical signal intensity, adjacent white matter abnormalities, and gray-white matter junction showed significant statistical difference in the ability of 3D FLAIR to assess these aspects over conventional images. PD images were also found superior to the routine epilepsy protocol in assessment of cortical signal, adjacent white matter, and gray-white matter junction. Conclusion: Specialized MRI sequences and techniques should be performed whenever there is a high suspicion of cortical dysplasia, especially when they remain occult on conventional MR protocols. These techniques
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Background: Focal cortical dysplasia (FCD) is often associated with epilepsy. Identification of FCD can be difficult due to subtle magnetic resonance imaging (MRI) changes. Though fluid-attenuated inversion recovery (FLAIR) sequence detects the majority of these lesions, smaller lesions may go unnoticed while larger lesions may be poorly delineated. Purpose: To determine the ability of a specialized epilepsy protocol in visualizing and delineating the extent of FCD. Material and Methods: We compared the imaging findings in nine patients with cortical malformation who underwent routine epilepsy MR imaging as well as a specialized epilepsy protocol. All imaging was done on a 1.5T MR unit. The specialized epilepsy protocol included 3D FLAIR in the sagittal plane as well as proton density (PD) and high-resolution T2-weighted (T2W) images in the transverse plane. Results: In all nine patients, the specialized protocol identified lesion anatomy better. In three patients in whom routine MRI was normal, the specialized epilepsy protocol including 3D FLAIR helped in identifying the lesions. One of these patients underwent surgery, and histo-pathology revealed a cortical dysplasia. In one patient, lesion characterization was improved, while in the remaining patients the extent of the FCD was more clearly demonstrated in the 3D FLAIR and PD images. Statistical analysis of images for cortical thickness, cortical signal intensity, adjacent white matter abnormalities, and gray-white matter junction showed significant statistical difference in the ability of 3D FLAIR to assess these aspects over conventional images. PD images were also found superior to the routine epilepsy protocol in assessment of cortical signal, adjacent white matter, and gray-white matter junction. Conclusion: Specialized MRI sequences and techniques should be performed whenever there is a high suspicion of cortical dysplasia, especially when they remain occult on conventional MR protocols. These techniques
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Erdem, L. Oktay [Department of Radiology, Zonguldak Karaelmas University, School of Medicine, 6700 Kozlu, Zonguldak (Turkey)]. E-mail: sunarerdem@yahoo.com; Erdem, C. Zuhal [Department of Radiology, Zonguldak Karaelmas University, School of Medicine, 6700 Kozlu, Zonguldak (Turkey); Acikgoz, Bektas [Department of Neurosurgery, Zonguldak Karaelmas University, School of Medicine, Zonguldak (Turkey); Gundogdu, Sadi [Department of Radiology, Zonguldak Karaelmas University, School of Medicine, 6700 Kozlu, Zonguldak (Turkey)
2005-08-01
Objective: To compare fast T1-weighted fluid-attenuated inversion recovery (FLAIR) and T1-weighted turbo spin-echo (TSE) imaging of the degenerative disc disease of the lumbar spine. Materials and methods: Thirty-five consecutive patients (19 females, 16 males; mean age 41 years, range 31-67 years) with suspected degenerative disc disease of the lumbar spine were prospectively evaluated. Sagittal images of the lumbar spine were obtained using T1-weighted TSE and fast T1-weighted FLAIR sequences. Two radiologists compared these sequences both qualitatively and quantitatively. Results: On qualitative evaluation, CSF nulling, contrast at the disc-CSF interface, the disc-spinal cord (cauda equina) interface, and the spinal cord (cauda equina)-CSF interface of fast T1-weighted FLAIR images were significantly higher than those for T1-weighted TSE images (P < 0.001). On quantitative evaluation of the first 15 patients, signal-to-noise ratios of cerebrospinal fluid of fast T1-weighted FLAIR imaging were significantly lower than those for T1-weighted TSE images (P < 0.05). Contrast-to-noise ratios of spinal cord/CSF and normal bone marrow/disc for fast T1-weighted FLAIR images were significantly higher than those for T1-weighted TSE images (P < 0.05). Conclusion: Results in our study have shown that fast T1-weighted FLAIR imaging may be a valuable imaging modality in the armamentarium of lumbar spinal T1-weighted MR imaging, because the former technique has definite superior advantages such as CSF nulling, conspicuousness of the normal anatomic structures and changes in the lumbar spinal discogenic disease and image contrast and also almost equally acquisition times.
Simultaneous inversion for velocity and attenuation by waveform tomography
Gao, Fengxia; Wang, Yanghua
2016-08-01
Seismic waveform tomography can invert for the velocity and attenuation (Q- 1) variations simultaneously. For this simultaneous inversion, we propose two strategies for waveform tomography. First, we analyze the contributions of the real part and the imaginary part of the gradients, associated with the velocity and attenuation parameters respectively, and determine that the combination of the real part of the gradient subvector for the velocity parameter and the imaginary part of the gradient subvector for the attenuation parameter would produce an optimal inversion result. Second, we attempt to balance the sensitivities of the objective function to the velocity and the attenuation parameters. Considering the magnitude differences between these two-type parameters in the simultaneous inversion, we apply preliminarily a normalization to both the velocity model and the attenuation model. However, for balancing their sensitivities, we further adjust the corresponding model updates using a tuning factor. We determine this tuning parameter adaptively, based on the sensitivities of these two parameters, at each iteration. Numerical tests demonstrate the feasibility and reliability of these two strategies in full waveform inversion.
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
Background Contrast-enhanced fluid-attenuated inversion-recovery (FLAIR) magnetic resonance imaging (MRI) has been reported to have higher sensitivity for detecting leptomeningeal disease compared with contrast- enhanced T1-weighted MRI (CE T1WI). However, currently there are no studies showing the potential value of clinical applications of contrast-enhanced FLAIR (CE FLAIR) sequence in diagnosing intracranial tumors in a larger group of patients. The purpose of this study was to evaluate the diagnostic value of CE FLAIR in comparison with CE T1WI for intracranial tumors and to provide more information for clinical diagnosis and therapy.Methods One hundred and four consecutive cases of intracranial tumors referred for CE brain MRI were analyzed with regard to FLAIR and T1WI pre- and post-administration of Gd-DTPA. The CE FLAIR and CE T1WI were evaluated independently by two radiologists for the number of examinations with one or more enhanced lesions, the number and location of enhanced lesions per examination, signal-to-noise ratio (SNR) and contrast-enhancement ratio (CER) of lesions, as well as the size and extent of the enhanced lesions. Results In 98 of 104 cases, enhanced lesions were seen both on the FLAIR and T1W images. More lesions were seen on CE T1WI (n=120) than those on CE FLAIR sequence (n=117), but no differences of statistical significance were found between the two sequences (P>0.05). Four lesions were revealed only on the CE FLAIR images whereas 7 lesions were only found on CE T1WI. Enhanced lesions located in the cerebral hemisphere or the forth ventricle were revealed much more on CE T1WI than on CE FLAIR images. However, CE FLAIR images may be useful in showing superficial abnormalities and those located in the sulcus or lateral ventricle. The CER and contrast-to-noise ratio (CNR) on CE T1WI was significantly higher (t=7.10,P=0.00;t=9.67,P=0.00, respectively), but grey matter/white matter contrast was lower (t=2.46,P=0.02) than those on CE
Inverse problems of ultrasound tomography in models with attenuation
International Nuclear Information System (INIS)
We develop efficient methods for solving inverse problems of ultrasound tomography in models with attenuation. We treat the inverse problem as a coefficient inverse problem for unknown coordinate-dependent functions that characterize both the speed cross section and the coefficients of the wave equation describing attenuation in the diagnosed region. We derive exact formulas for the gradient of the residual functional in models with attenuation, and develop efficient algorithms for minimizing the gradient of the residual by solving the conjugate problem. These algorithms are easy to parallelize when implemented on supercomputers, allowing the computation time to be reduced by a factor of several hundred compared to a PC. The numerical analysis of model problems shows that it is possible to reconstruct not only the speed cross section, but also the properties of the attenuating medium. We investigate the choice of the initial approximation for iterative algorithms used to solve inverse problems. The algorithms considered are primarily meant for the development of ultrasound tomographs for differential diagnosis of breast cancer. (paper)
Multi-resolution inversion algorithm for the attenuated radon transform
Barbano, Paolo Emilio
2011-09-01
We present a FAST implementation of the Inverse Attenuated Radon Transform which incorporates accurate collimator response, as well as artifact rejection due to statistical noise and data corruption. This new reconstruction procedure is performed by combining a memory-efficient implementation of the analytical inversion formula (AIF [1], [2]) with a wavelet-based version of a recently discovered regularization technique [3]. The paper introduces all the main aspects of the new AIF, as well numerical experiments on real and simulated data. Those display a substantial improvement in reconstruction quality when compared to linear or iterative algorithms. © 2011 IEEE.
Henrique Carrete Junior; Nitamar Abdala; Kátia Lin; Luís Otávio Caboclo; Ricardo Silva Centeno; Américo Ceiki Sakamoto; Jacob Szjenfeld; Roberto Gomes Nogueira; Elza Márcia Targas Yacubian
2007-01-01
OBJECTIVE: To determine the frequency and regional involvement of temporal pole signal abnormality (TPA) in patients with hippocampal sclerosis (HS) using fluid-attenuated inversion-recovery (FLAIR) MR imaging, and to correlate this feature with history. METHOD: Coronal FLAIR images of the temporal pole were assessed in 120 patients with HS and in 30 normal subjects, to evaluate gray-white matter demarcation. RESULTS: Ninety (75%) of 120 patients had associated TPA. The HS side made differenc...
Forward- vs. Inverse Problems in Modeling Seismic Attenuation
Morozov, I. B.
2015-12-01
Seismic attenuation is an important property of wave propagation used in numerous applications. However, the attenuation is also a complex phenomenon, and it is important to differentiate between its two typical uses: 1) in forward problems, to model the amplitudes and spectral contents of waves required for hazard assessment and geotechnical engineering, and 2) in inverse problems, to determine the physical properties of the subsurface. In the forward-problem sense, the attenuation is successfully characterized in terms of empirical parameters of geometric spreading, radiation patterns, scattering amplitudes, t-star, alpha, kappa, or Q. Arguably, the predicted energy losses can be correct even if the underlying attenuation model is phenomenological and not sufficiently based on physics. An example of such phenomenological model is the viscoelasticity based on the correspondence principle and the Q-factor assigned to the material. By contrast, when used to invert for in situ material properties, models addressing the specific physics are required. In many studies (including in this session), a Q-factor is interpreted as a property of a point within the subsurface; however this property is only phenomenological and may be physically insufficient or inconsistent. For example, the bulk or shear Q at the same point can be different when evaluated from different wave modes. The cases of frequency-dependent Q are particularly prone of ambiguities such as trade-off with the assumed background geometric spreading. To rigorously characterize the in situ material properties responsible for seismic-wave attenuation, it is insufficient to only focus on the seismic energy loss. Mechanical models of the material need to be considered. Such models can be constructed by using Lagrangian mechanics. These models should likely contain no Q but will be based on parameters of microstructure such as heterogeneity, fractures, or fluids. I illustrate several such models based on viscosity
International Nuclear Information System (INIS)
Eleven cases of retrobulbar neuritis were evaluated with MRI using short inversion time inversion recovery (STIR) sequences, which demonstrated the edematous and demyelinated lesions as hyperintense areas. Five of 6 cases in the acute phase showed hyperintense areas in the affected optic nerves. Three cases of multiple sclerosis in remission still demonstrated the hyperintense areas. MRI using STIR sequences provides very useful images for the diagnosis, pathogenesis, and evaluation of retrobulbar neuritis therapy. (author)
Energy Technology Data Exchange (ETDEWEB)
Carrete Junior, Henrique; Abdala, Nitamar; Szjenfeld, Jacob; Nogueira, Roberto Gomes [Universidade Federal de Sao Paulo (UNIFESP-EPM), Sao Paulo, SP (Brazil). Dept. de Diagnostico por Imagem; Lin, Katia; Caboclo, Luis Otavio; Centeno, Ricardo Silva; Sakamoto, Americo Ceiki; Yacubian, Elza Marcia Targas [Universidade Federal de Sao Paulo (UNIFESP-EPM), Sao Paulo, SP (Brazil). Dept. de Neurologia e Neurocirurgia
2007-09-15
Objective: To determine the frequency and regional involvement of temporal pole signal abnormality (TPA) in patients with hippocampal sclerosis (HS) using fluid-attenuated inversion-recovery (FLAIR) MR imaging, and to correlate this feature with history. Method: Coronal FLAIR images of the temporal pole were assessed in 120 patients with HS and in 30 normal subjects, to evaluate gray-white matter demarcation. Results: Ninety (75%) of 120 patients had associated TPA. The HS side made difference regarding the presence of TPA, with a left side prevalence (p=0.04, {chi}{sup 2} test). The anteromedial zone of temporal pole was affected in 27 (30%) out of 90 patients. In 63 (70%) patients the lateral zone were also affected. Patients with TPA were younger at seizure onset (p=0.018), but without association with duration of epilepsy. Conclusion: Our FLAIR study show temporal pole signal abnormality in 3/4 of patients with HS, mainly seen on the anteromedial region, with a larger prevalence when the left hippocampus was involved. (author)
A linear model approach for ultrasonic inverse problems with attenuation and dispersion
Carcreff, Ewen; Bourguignon, Sébastien; Idier, Jérôme; Simon, Laurent
2014-01-01
Ultrasonic inverse problems such as spike train deconvolution, synthetic aperture focusing or tomography aim to reconstruct spatial properties of an object (discontinuities, delaminations, flaws, \\textit{etc.}) from noisy and incomplete measurements. They require an accurate description of the data acquisition process. Dealing with frequency-dependent attenuation and dispersion is therefore crucial since both phenomena modify the wave shape as the travel distance increases. In an inversion co...
A linear model approach for ultrasonic inverse problems with attenuation and dispersion.
Carcreff, Ewen; Bourguignon, Sébastien; Idier, Jérôme; Simon, Laurent
2014-07-01
Ultrasonic inverse problems such as spike train deconvolution, synthetic aperture focusing, or tomography attempt to reconstruct spatial properties of an object (discontinuities, delaminations, flaws, etc.) from noisy and incomplete measurements. They require an accurate description of the data acquisition process. Dealing with frequency-dependent attenuation and dispersion is therefore crucial because both phenomena modify the wave shape as the travel distance increases. In an inversion context, this paper proposes to exploit a linear model of ultrasonic data taking into account attenuation and dispersion. The propagation distance is discretized to build a finite set of radiation impulse responses. Attenuation is modeled with a frequency power law and then dispersion is computed to yield physically consistent responses. Using experimental data acquired from attenuative materials, this model outperforms the standard attenuation-free model and other models of the literature. Because of model linearity, robust estimation methods can be implemented. When matched filtering is employed for single echo detection, the model that we propose yields precise estimation of the attenuation coefficient and of the sound velocity. A thickness estimation problem is also addressed through spike deconvolution, for which the proposed model also achieves accurate results. PMID:24960708
An inversion of site response and Lg attenuation using Lg waveform
Institute of Scientific and Technical Information of China (English)
ZHU Xin-yun; CHEN Yun-tai
2007-01-01
Based on spectral ratio method, a joint inversion method was used to obtain parameters of Lg wave attenuation and site response. The inversion method allows simple and direct (two-parameter) determination of Lg wave attenuation and site response from sparse spectral data, which are not affected by radiation pattern factor and different response of same instrument after geometrical spreading. The method was used successfully for estimating site response of stations of Zhejiang Seismic Network and measuring Lg wave attenuation. The study is based on 20 earthquakes occurred in northeast of Taiwan with magnitude Ms5.0～6.7 and 960 seismic wave records from 16 stations in Zhejiang area from 2002 to 2005. The parameters of site response and Lg attenuation were calculated with a frequency interval of 0.2 Hz in the range of 0.5 Hz to 10 Hz. Lg wave attenuation coefficient corresponding to U-D,E-W and N-S components are γ(f)=0.00175f0.43485, γ(f)=0.00145f0.48467 and γ(f)=0.0021f0.41241, respectively.It is found that the site response is component-independent. It is also found that the site response of QIY station is significant above the frequency of 1.5 Hz, and that the site response of NIB station is low for most frequency
Inversion of the broken ray transform in the case of energy-dependent attenuation
Krylov, R.; Katsevich, A.
2015-06-01
Broken Ray transform (BRT) arises when one considers a narrow x-ray beam propagating through medium under the assumption of single scattering. Previous algorithms for inverting the BRT assumed that the medium is characterized by a single attenuation coefficient μ. However x-rays lose their energy after Compton scattering and the energy loss depends on the scattering angle. Since the attenuation coefficient depends on energy, the μ’s before and after scattering are different. When there are three or more detectors one should distinguish not only between μ’s that are ‘seen’ by x-rays before and after scattering, but also between μ’s that are ‘seen’ by x-rays traveling towards different detectors. The main thrust of this paper is inversion of the BRT with N ⩾ 3 detectors under the assumption that the attenuation coefficient can be accurately approximated by a linear function of energy within the window of relevant energies. When the number of detectors is four or greater, we derive a family of inversion formulas. If N > 4, we find the optimal formula, which provides the best stability with respect to noise in the data. If N = 4, the family collapses into a single formula and no optimization is possible. If μ is independent of energy, N = 3 is sufficient for inversion. We also develop iterative reconstruction algorithms that can use global and local data. The results of testing the algorithms are presented.
Sequential inversion of modal data for sound attenuation in sediment at the New Jersey Shelf.
Duan, Rui; Chapman, N Ross; Yang, Kunde; Ma, Yuanliang
2016-01-01
This paper presents a method for estimating bottom geoacoustic properties especially the sediment attenuation from information contained in normal modes of a broadband signal. Propagating modes are resolved using the time-warping technique applied to signals from light bulb sound sources deployed at ranges of 5 and 7 km in the Shallow Water '06 experiment. A sequential inversion approach is designed that uses specific features of the acoustic data that are highly sensitive to specific geoacoustic model parameters. The first feature is the modal group speed, which is inverted for seabed sound speed, density, and sediment thickness. The second feature is the modal depth function for inverting receiver depths. The third feature is related to the modal coefficient spectra, and this is inverted for source depth and sediment attenuation. In each subsequent stage, estimates from the previous stage(s) are used as known values. The sequential inversion is stable and generates estimates for the geoacoustic model parameters that agree very well with results from other experiments carried out in the same region. Notably, the inversion obtains an estimated attenuation of 0.078 dB/λ in the band 120-180 Hz for the de-watered marine sediment characteristic of the continental shelf at the site. PMID:26827006
Institute of Scientific and Technical Information of China (English)
HE Gui-chun; NI Wen
2006-01-01
Based on various ultrasonic loss mechanisms, the formula of the cumulative mass percentage of minerals with different particle sizes was given, with which the particle size distribution was integrated into an ultrasonic attenuation model. And then the correlations between the ultrasonic attenuation and the pulp density, and the particle size were obtained. The derived model was combined with the experiment and the analysis of experimental data to determine the inverse model relating ultrasonic attenuation coefficient with size distribution. Finally, an optimization method of inverse parameter, genetic algorithm was applied for particle size distribution. The results of inverse calculation show that the precision of measurement was high.
3D inversion of full gravity gradient tensor data using SL0 sparse recovery
Meng, Zhaohai
2016-04-01
We present a new method dedicated to the interpretation of full gravity gradient tensor data, based on SL0 sparse recovery inversion. The SL0 sparse recovery method aims to find out the minimum value of the objective function to fit the data function and to solve the non-zero solution to the objective function. Based on continuous iteration, we can easily obtain the final global minimum (namely the property and space attribute of the inversion target). We consider which type of tensor data combination produces the best inversion results based on the inversion results of different full gravity gradient tensor data combinations (separate tensor data and combined tensor data). We compare the recovered models obtained by inverting the different combinations of different gravity gradient tensor components to understand how different component combinations contribute to the resolution of the recovered model. Based on the comparison between the SL0 sparse recovery inversion results and the smoothest and focusing inversion results of the full gravity gradient tensor data, we show that SL0 sparse recovery inversion can obtain more stable and efficient inversion results with relatively sharp edge information, and that this method can also produce a stable solution of the inverse problem for complex geological structures. This new method to resolve very large full gravity gradient tensor datasets has the considerable advantage of being highly efficient; the full gravity gradient tensor inversion requires very little time. This new method is very effective in explaining the full gravity tensor which is very sensitive to small changes in local anomaly. The numerical simulation and inversion results of the compositional model indicates that including multiple components for inversion increases the resolution of the recovered density model and improves the structure delineation. We apply our inversion method to invert the gravity gradient tensor survey data from the Vinton salt
Detection and characterization with short TI inversion recovery MR imaging
Energy Technology Data Exchange (ETDEWEB)
Komata, Kaori (Nippon Medical School, Tokyo (Japan))
1994-10-01
Short TI inversion recovery magnetic resonance imaging (STIR-MRI) with spin echo (SE) T1- and T2-weighted images of the pelvis was investigated to evaluate its usefulness in detecting and characterizing endometriosis. Thirty-one women suspected of having the disease were studied in detail. MR findings with and without STIR-MRI were correlated with the results of laparotomy (27 women) and laparoscopy (4 women). Surgery revealed endometriosis in 29 women (17 ovarian chocolate cysts, 22 intestinal adhesions, 14 cul-de-sac obliterations and 12 adenomyosis). The other two women did not have endometriosis (uterine prolapse in one and submucosal leiomyoma in one). An ovarian chocolate cyst was diagnosed when a T1-elongated lesion showed shading, loculus or a low intensity rim on SE MR images, and a low intensity rim on STIR-MRI. Only 12 of the 17 chocolate cysts and neither of the two hemorrhagic corpus lutein cysts were correctly diagnosed on SE MR images, whereas 18 of these 19 cysts were correctly diagnosed because of the low intensity rim on STIR-MRI. In the pathological analysis, the rim was found to be a fibrous capsule and there were many macrophages which phagocytized hemosiderin. For the assessment of ovarian chocolate cysts, accuracy improved from 63.2% to 94.7%. As for the adhesion between the intestine and the uterus, specificity improved from 61.9% to 90.5% and accuracy improved from 67.7% to 93.5% when STRI-MRI was used. For the assessment of the cul-de-sac obliteration, accuracy improved from 67.7% to 83.8% although [chi][sup 2] analysis showed no significance. The major factors for the improved accuracy with STIR-MRI are the decrease of the motion artifact owing to the suppression of the fat signal, decreased chemical shift artifact and accurate differentiation of fat from hemorrhagic component. Therefore, STIR-MRI is a useful and reliable procedure and should be used together with SE T1-, T2-weighted images for the assessment of endometriosis. (author).
Detection and characterization with short TI inversion recovery MR imaging
International Nuclear Information System (INIS)
Short TI inversion recovery magnetic resonance imaging (STIR-MRI) with spin echo (SE) T1- and T2-weighted images of the pelvis was investigated to evaluate its usefulness in detecting and characterizing endometriosis. Thirty-one women suspected of having the disease were studied in detail. MR findings with and without STIR-MRI were correlated with the results of laparotomy (27 women) and laparoscopy (4 women). Surgery revealed endometriosis in 29 women (17 ovarian chocolate cysts, 22 intestinal adhesions, 14 cul-de-sac obliterations and 12 adenomyosis). The other two women did not have endometriosis (uterine prolapse in one and submucosal leiomyoma in one). An ovarian chocolate cyst was diagnosed when a T1-elongated lesion showed shading, loculus or a low intensity rim on SE MR images, and a low intensity rim on STIR-MRI. Only 12 of the 17 chocolate cysts and neither of the two hemorrhagic corpus lutein cysts were correctly diagnosed on SE MR images, whereas 18 of these 19 cysts were correctly diagnosed because of the low intensity rim on STIR-MRI. In the pathological analysis, the rim was found to be a fibrous capsule and there were many macrophages which phagocytized hemosiderin. For the assessment of ovarian chocolate cysts, accuracy improved from 63.2% to 94.7%. As for the adhesion between the intestine and the uterus, specificity improved from 61.9% to 90.5% and accuracy improved from 67.7% to 93.5% when STRI-MRI was used. For the assessment of the cul-de-sac obliteration, accuracy improved from 67.7% to 83.8% although χ2 analysis showed no significance. The major factors for the improved accuracy with STIR-MRI are the decrease of the motion artifact owing to the suppression of the fat signal, decreased chemical shift artifact and accurate differentiation of fat from hemorrhagic component. Therefore, STIR-MRI is a useful and reliable procedure and should be used together with SE T1-, T2-weighted images for the assessment of endometriosis. (author)
Inversion of the broken ray transform in the case of energy-dependent attenuation
International Nuclear Information System (INIS)
Broken Ray transform (BRT) arises when one considers a narrow x-ray beam propagating through medium under the assumption of single scattering. Previous algorithms for inverting the BRT assumed that the medium is characterized by a single attenuation coefficient μ. However x-rays lose their energy after Compton scattering and the energy loss depends on the scattering angle. Since the attenuation coefficient depends on energy, the μ’s before and after scattering are different. When there are three or more detectors one should distinguish not only between μ’s that are ‘seen’ by x-rays before and after scattering, but also between μ’s that are ‘seen’ by x-rays traveling towards different detectors.The main thrust of this paper is inversion of the BRT with N ⩾ 3 detectors under the assumption that the attenuation coefficient can be accurately approximated by a linear function of energy within the window of relevant energies. When the number of detectors is four or greater, we derive a family of inversion formulas. If N > 4, we find the optimal formula, which provides the best stability with respect to noise in the data. If N = 4, the family collapses into a single formula and no optimization is possible. If μ is independent of energy, N = 3 is sufficient for inversion. We also develop iterative reconstruction algorithms that can use global and local data. The results of testing the algorithms are presented. (paper)
Malezan, A.; Tomal, A.; Antoniassi, M.; Watanabe, P. C. A.; Albino, L. D.; Poletti, M. E.
2015-11-01
In this work, a spectral reconstruction methodology for diagnostic X-ray, using Laplace inverse transform of the attenuation, was successfully applied to dental X-ray equipments. The attenuation curves of 8 commercially available dental X-ray equipment, from 3 different manufactures (Siemens, Gnatus and Dabi Atlante), were obtained by using an ionization chamber and high purity aluminium filters, while the kVp was obtained with a specific meter. A computational routine was implemented in order to adjust a model function, whose inverse Laplace transform is analytically known, to the attenuation curve. This methodology was validated by comparing the reconstructed and the measured (using semiconductor detector of cadmium telluride) spectra of a given dental X-ray unit. The spectral reconstruction showed the Dabi Atlante equipments generating similar shape spectra. This is a desirable feature from clinic standpoint because it produces similar levels of image quality and dose. We observed that equipments from Siemens and Gnatus generate significantly different spectra, suggesting that, for a given operating protocol, these units will present different levels of image quality and dose. This fact claims for the necessity of individualized operating protocols that maximize image quality and dose. The proposed methodology is suitable to perform a spectral reconstruction of dental X-ray equipments from the simple measurements of attenuation curve and kVp. The simplified experimental apparatus and the low level of technical difficulty make this methodology accessible to a broad range of users. The knowledge of the spectral distribution can help in the development of operating protocols that maximize image quality and dose.
Magnetization transfer using inversion recovery during off-resonance irradiation.
Mangia, Silvia; De Martino, Federico; Liimatainen, Timo; Garwood, Michael; Michaeli, Shalom
2011-12-01
Estimation of magnetization transfer (MT) parameters in vivo can be compromised by an inability to drive the magnetization to a steady state using allowable levels of radiofrequency (RF) irradiation, due to safety concerns (tissue heating and specific absorption rate (SAR)). Rather than increasing the RF duration or amplitude, here we propose to circumvent the SAR limitation by sampling the formation of the steady state in separate measurements made with the magnetization initially along the -z and +z axis of the laboratory frame, i.e. with or without an on-resonance inversion pulse prior to the off-resonance irradiation. Results from human brain imaging demonstrate that this choice provides a tremendous benefit in the fitting procedure used to estimate MT parameters. The resulting parametric maps are characterized by notably increased tissue specificity as compared to those obtained with the standard MT acquisition in which magnetization is initially along the +z axis only. PMID:21601405
International Nuclear Information System (INIS)
To investigate the impact of a higher magnetic field strength of 3 Tesla (T) on the detection rate of cortical lesions in multiple sclerosis (MS) patients, in particular using a dedicated double inversion recovery (DIR) pulse sequence. Thirty-four patients with clinically isolated syndromes or definite MS were included. All patients underwent magnetic resonance imaging (MRI) at 1.5 T and 3 T, including T2-weighted turbo spin echo (TSE), fluid-attenuated inversion recovery (FLAIR) and DIR sequences. All images were analysed for focal lesions categorised according to their anatomical location. The total number of detected lesions was higher at 3 T across all pulse sequences. We observed significantly higher numbers of lesions involving the cortex at 3 T using a DIR sequence. DIR at 3 T showed 192% more pure intracortical (p < 0.001) and 30% more mixed grey matter-white matter lesions (p = 0.008). No significant increase in cortical lesions could be detected on the FLAIR and T2-weighted images. Using the T2-weighted and FLAIR sequences, significantly more lesions could be detected at 3 T in the infratentorial, periventricular and juxtacortical white matter. DIR brain MR imaging at 3 T substantially improves the sensitivity of the detection of cortical lesions compared with the standard magnetic field strength of 1.5 T. (orig.)
Consensus recommendations for MS cortical lesion scoring using double inversion recovery MRI
DEFF Research Database (Denmark)
Geurts, J J G; Roosendaal, S D; Calabrese, M;
2011-01-01
Different double inversion recovery (DIR) sequences are currently used in multiple sclerosis (MS) research centers to visualize cortical lesions, making it difficult to compare published data. This study aimed to formulate consensus recommendations for scoring cortical lesions in patients with MS...
Directory of Open Access Journals (Sweden)
Henrique Carrete Junior
2007-09-01
Full Text Available OBJECTIVE: To determine the frequency and regional involvement of temporal pole signal abnormality (TPA in patients with hippocampal sclerosis (HS using fluid-attenuated inversion-recovery (FLAIR MR imaging, and to correlate this feature with history. METHOD: Coronal FLAIR images of the temporal pole were assessed in 120 patients with HS and in 30 normal subjects, to evaluate gray-white matter demarcation. RESULTS: Ninety (75% of 120 patients had associated TPA. The HS side made difference regarding the presence of TPA, with a left side prevalence (p=0.04, chi2 test. The anteromedial zone of temporal pole was affected in 27 (30% out of 90 patients. In 63 (70% patients the lateral zone were also affected. Patients with TPA were younger at seizure onset (p=0.018, but without association with duration of epilepsy. CONCLUSION: Our FLAIR study show temporal pole signal abnormality in 3/4 of patients with HS, mainly seen on the anteromedial region, with a larger prevalence when the left hippocampus was involved.OBJETIVO: Determinar a freqüência e o envolvimento regional da anormalidade de sinal do pólo temporal (APT em pacientes com esclerose hipocampal (EH utilizando seqüência inversão recuperação com supressão da água (FLAIR por RM, e correlacioná-la com a história. MÉTODO: Foram analisadas as imagens coronais FLAIR dos pólos temporais de 120 pacientes com EH e de 30 indivíduos normais, para avaliar a demarcação entre substâncias branca e cinzenta. RESULTADOS: Noventa (75% dos 120 pacientes tinham APT associada. Houve prevalência do lado esquerdo (p=0.04, chi2 teste na relação entre APT e o lado da EH. A zona ântero-medial estava acometida em 27 (30% destes pacientes. Em 63 (70% pacientes também a zona lateral estava acometida. Pacientes com APT apresentaram início da epilepsia quando mais jovens (p=0.018, porém sem associação com a sua duração. CONCLUSÃO: A seqüência FLAIR mostra haver ATP em 3/4 dos pacientes com EH
Energy Technology Data Exchange (ETDEWEB)
Hodel, Jerome; Bocher, Anne-Laure; Pruvo, Jean-Pierre; Leclerc, Xavier [Hopital Roger Salengro, Department of Neuroradiology, Lille (France); Outteryck, Olivier; Zephir, Helene; Vermersch, Patrick [Hopital Roger Salengro, Department of Neurology, Lille (France); Lambert, Oriane [Fondation Ophtalmologique Rothschild, Department of Neuroradiology, Paris (France); Benadjaoud, Mohamed Amine [Radiation Epidemiology Team, Inserm, CESP Centre for Research in Epidemiology and Population Health, U1018, Villejuif (France); Chechin, David [Philips Medical Systems, Suresnes (France)
2014-12-15
We compared the three-dimensional (3D) double inversion recovery (DIR) magnetic resonance imaging (MRI) sequence with the coronal two-dimensional (2D) short tau inversion recovery (STIR) fluid-attenuated inversion recovery (FLAIR) for the detection of optic nerve signal abnormality in patients with optic neuritis (ON). The study group consisted of 31 patients with ON (44 pathological nerves) confirmed by visual-evoked potentials used as the reference. MRI examinations included 2D coronal STIR FLAIR and 3D DIR with 3-mm coronal reformats to match with STIR FLAIR. Image artefacts were graded for each portion of the optic nerves. Each set of MR images (2D STIR FLAIR, DIR reformats and multiplanar 3D DIR) was examined independently and separately for the detection of signal abnormality. Cisternal portion of optic nerves was better delineated with DIR (p < 0.001), while artefacts impaired analysis in four patients with STIR FLAIR. Inter-observer agreement was significantly improved (p < 0.001) on 3D DIR (κ = 0.96) compared with STIR FLAIR images (κ = 0.60). Multiplanar DIR images reached the best performance for the diagnosis of ON (95 % sensitive and 94 % specific). Our study showed a high sensitivity and specificity of 3D DIR compared with STIR FLAIR for the detection of ON. These findings suggest that the 3D DIR sequence may be more useful in patients suspected of ON. (orig.)
h-Ici Darach O; Ridgway John P; Kuehne Titus; Berger Felix; Plein Sven; Sivananthan Mohan; Messroghli Daniel R
2012-01-01
Abstract Background The short inversion time inversion recovery (STIR) black-blood technique has been used to visualize myocardial edema, and thus to differentiate acute from chronic myocardial lesions. However, some cardiovascular magnetic resonance (CMR) groups have reported variable image quality, and hence the diagnostic value of STIR in routine clinical practice has been put into question. The aim of our study was to analyze image quality and diagnostic performance of STIR using a set of...
Ginn, John S
2014-01-01
Long pulse durations necessary in selective inversion recovery (SIR) experiments along with radiation damping (RD) introduce difficulties in quantitative nuclear magnetic resonance measurements, such as those that allow for the determination of a sample's characteristics, including the rates that govern magnetization transfer. Because of these influences, the assumption of perfect inversion is invalid. In this work, we present data that demonstrates that long pulse durations as well as RD cause difficulties in SIR experiments performed on simple one-spin systems, indicating that they will be problematic for multiple-spin systems as well. These results emphasize the importance of understanding the evolution of magnetization for all time points throughout an experiment used in quantitative NMR measurements. Furthermore, experimental parameters must be chosen carefully and understood completely.
Prediction of heat recovery steam generator (HRSG) noise attenuation using scale model testing
Energy Technology Data Exchange (ETDEWEB)
Bracken, M.; Barman, M.; Gambino, V. [Aercoustics Engineering Limited, Toronto, ON (Canada)
1996-08-01
An investigation was undertaken to determine whether scale modelling was effective for the study of (1) reactive attenuation on the gas flow path of heat recovery steam generators (HRSGs), (2) attenuation due to diffusion and scattering of sound, and (3) propagation loss due to flow resistivity of the tube bundles. MIDAS, a state-of-the-art measurement system, suitable for use with small models, and a microphone capable of ultrasonic measurement, were used. The noise source used was supplied by a high voltage spark source. The methodology used in the study, and some of the initial results of the scale model testing were described. A review of the initial results showed that it will be possible to model reactive effects, viscous loss and diffusion and scattering. 2 refs., 1 fig.
Energy Technology Data Exchange (ETDEWEB)
Saberi Fathi, S M, E-mail: majid.saberi@u-cergy.f [Universite de Cergy-Pontoise, Laboratoire de Physique Theorique et Modelisation, 95302 Cergy-Pontoise (France)
2010-08-20
In this paper, we present a new derivation of the inverse of the non-uniformly attenuated x-ray transform in three dimensions, based on quaternion analysis. An explicit formula is obtained using a set of three-dimensional x-ray projection data. The result without attenuation is recovered as a special case.
Sodium inversion recovery MRI on the knee joint at 7 T with an optimal control pulse
Lee, Jae-Seung; Xia, Ding; Madelin, Guillaume; Regatte, Ravinder R.
2016-01-01
In the field of sodium magnetic resonance imaging (MRI), inversion recovery (IR) is a convenient and popular method to select sodium in different environments. For the knee joint, IR has been used to suppress the signal from synovial fluids, which improves the correlation between the sodium signal and the concentration of glycosaminoglycans (GAGs) in cartilage tissues. For the better inversion of the magnetization vector under the spatial variations of the B0 and B1 fields, the IR sequence usually employ adiabatic pulses as the inversion pulse. On the other hand, it has been shown that RF shapes robust against the variations of the B0 and B1 fields can be generated by numerical optimization based on optimal control theory. In this work, we compare the performance of fluid-suppressed sodium MRI on the knee joint in vivo, between one implemented with an adiabatic pulse in the IR sequence and the other with the adiabatic pulse replaced by an optimal-control shaped pulse. While the optimal-control pulse reduces the RF power deposited to the body by 58%, the quality of fluid suppression and the signal level of sodium within cartilage are similar between two implementations.
International Nuclear Information System (INIS)
We assessed the feasibility of utilizing three-dimensional (3D) phase sensitive inversion recovery (IR) images for preoperatively determining deep brain stimulator position. We measured geometric distortion with a grid phantom and evaluated images of 3 volunteers to determine optimum imaging parameters for 3D phase sensitive IR. Geometric distortion measured less than 1.0%. Respective inversion and recovery times, which provided high T1 contrast between the subthalamic nucleus and adjacent tissue, were 200 and 4000 ms. In studies of 3 volunteers and 2 patients, the subthalamic nucleus was clearly depicted in 3D phase sensitive IR images. The measured coordinates of the subthalamic nucleus agreed well with those calculated by conventional estimation from midpoint of the anterior and posterior commissure. Three-dimensional phase sensitive inversion recovery was useful in visualizing the subthalamic nucleus for effective deep brain stimulation. (author)
Multi-criterion Optimization Approach to Ill-posed Inverse Problem with Visual Feature’s Recovery
Weihui Dai
2010-01-01
Ill-posed inverse problem is commonly existed in signal processing such as image reconstruction from projection, parameter estimation on electromagnetic field, and path optimization in IP network. Usually, the solution of an inverse problem is unstable, not unique or does not exit. Traditional approach to solve this problem is to estimate the solution by optimizing a regularized objective function. In some cases, recovery of visual features is most emphasized in that solution; thereof the dis...
Lumbar spinal nerve roots imaging using balanced sequence with inversion recovery (IR) pulse
International Nuclear Information System (INIS)
We devised a method for visualizing the distal portion of lumbar spinal nerve roots in the direction of the long axis using a three-dimensional balanced sequence with inversion recovery pulse, and we established the imaging parameters. This pulse sequence was used with the following parameters: 260 mm field of view, 4.8 ms repetition time, 2.4 ms echo time, 90 degree flip angle, 1.5 mm slice thickness (0.75 mm overlap), and low-high radial k-space profile order. We assessed the signal intensity and contrast for the phantom and healthy volunteer images with different inversion times (TI). Moreover, we evaluated this method by using the optimal TI in clinical cases. The optimal TI obtained from the phantom and human studies was 600 ms. In clinical cases, this method with 600 ms of TI provided the best definition in images of abnormal pathway and compression of the lumbar spinal nerve roots. Our imaging method makes it possible to clearly and noninvasively visualize the lumbar spinal nerve roots. (author)
Tissue Border Enhancement by inversion recovery MRI at 7.0 Tesla
International Nuclear Information System (INIS)
This contribution presents a magnetic resonance imaging (MRI) acquisition technique named Tissue Border Enhancement (TBE), whose purpose is to produce images with enhanced visualization of borders between two tissues of interest without any post-processing. The technique is based on an inversion recovery sequence that employs an appropriate inversion time to produce images where the interface between two tissues of interest is hypo-intense; therefore, tissue borders are clearly represented by dark lines. This effect is achieved by setting imaging parameters such that two neighboring tissues of interest have magnetization with equal magnitude but opposite sign; therefore, the voxels containing a mixture of each tissue (that is, the tissue interface) possess minimal net signal. The technique was implemented on a 7.0 T MRI system. This approach can assist the definition of tissue borders, such as that between cortical gray matter and white matter; therefore, it could facilitate segmentation procedures, which are often challenging on ultra-high-field systems due to inhomogeneous radiofrequency distribution. TBE allows delineating the contours of structural abnormalities, and its capabilities were demonstrated with patients with focal cortical dysplasia, gray matter heterotopia, and polymicrogyria. This technique provides a new type of image contrast and has several possible applications in basic neuroscience, neurogenetic research, and clinical practice, as it could improve the detection power of MRI in the characterization of cortical malformations, enhance the contour of small anatomical structures of interest, and facilitate cortical segmentation. (orig.)
Short TI inversion-recovery MR imaging of chest wall malignancies
International Nuclear Information System (INIS)
Short-T1 inversion-recovery (STIR) sequences have greater constant, less motion sensitivity, and require shorter imaging times than conventional T2-weighted spin-echo (SE) sequences and are therefore particularly useful for staging chest wall malignancies. MR studies of 49 patients with possible chest wall malignancies were reviewed. Images were produced at 0.15 T with a variety of SE sequences. Forty-five also had STIR (repetition time, 1,400 - 2,100; echo time, 36 or 40; inversion time, 100 or 125). MR studies indicated chest wall involvement in 39 of 49 patients; 12 had obvious rib encasement, the most definitive finding. IN 13, lesions detected on STIR were either not visible or seen only in retrospect on T1 SE images. In five of five, STIR was clearly superior to T2 SE for delineation of tumor margins. The authors have discontinued using T2 SE sequences for chest neoplasms in favor of the higher contrast and sensitivity of STIR
Tissue Border Enhancement by inversion recovery MRI at 7.0 Tesla
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Costagli, Mauro; Tiberi, Gianluigi [Imago7 Foundation, Pisa (Italy); IRCCS Stella Maris, Pisa (Italy); Kelley, Douglas A.C. [GE Healthcare Technologies, San Francisco, CA (United States); Symms, Mark R. [GE Applied Science Laboratory, Pisa (Italy); Biagi, Laura; Tosetti, Michela [IRCCS Stella Maris, Pisa (Italy); Stara, Riccardo; Cosottini, Mirco [Imago7 Foundation, Pisa (Italy); University of Pisa, Pisa (Italy); Maggioni, Eleonora [IRCCS Scientific Institute E. Medea, Bosisio Parini, Lecco (Italy); Politecnico di Milano, Milan (Italy); Barba, Carmen [Children' s Hospital A. Meyer - University of Florence, Neuroscience Department, Florence (Italy); Guerrini, Renzo [IRCCS Stella Maris, Pisa (Italy); Children' s Hospital A. Meyer - University of Florence, Neuroscience Department, Florence (Italy)
2014-07-15
This contribution presents a magnetic resonance imaging (MRI) acquisition technique named Tissue Border Enhancement (TBE), whose purpose is to produce images with enhanced visualization of borders between two tissues of interest without any post-processing. The technique is based on an inversion recovery sequence that employs an appropriate inversion time to produce images where the interface between two tissues of interest is hypo-intense; therefore, tissue borders are clearly represented by dark lines. This effect is achieved by setting imaging parameters such that two neighboring tissues of interest have magnetization with equal magnitude but opposite sign; therefore, the voxels containing a mixture of each tissue (that is, the tissue interface) possess minimal net signal. The technique was implemented on a 7.0 T MRI system. This approach can assist the definition of tissue borders, such as that between cortical gray matter and white matter; therefore, it could facilitate segmentation procedures, which are often challenging on ultra-high-field systems due to inhomogeneous radiofrequency distribution. TBE allows delineating the contours of structural abnormalities, and its capabilities were demonstrated with patients with focal cortical dysplasia, gray matter heterotopia, and polymicrogyria. This technique provides a new type of image contrast and has several possible applications in basic neuroscience, neurogenetic research, and clinical practice, as it could improve the detection power of MRI in the characterization of cortical malformations, enhance the contour of small anatomical structures of interest, and facilitate cortical segmentation. (orig.)
Rapid T1 quantification based on 3D phase sensitive inversion recovery
International Nuclear Information System (INIS)
In Contrast Enhanced Magnetic Resonance Imaging fibrotic myocardium can be distinguished from healthy tissue using the difference in the longitudinal T1 relaxation after administration of Gadolinium, the so-called Late Gd Enhancement. The purpose of this work was to measure the myocardial absolute T1 post-Gd from a single breath-hold 3D Phase Sensitivity Inversion Recovery sequence (PSIR). Equations were derived to take the acquisition and saturation effects on the magnetization into account. The accuracy of the method was investigated on phantoms and using simulations. The method was applied to a group of patients with suspected myocardial infarction where the absolute difference in relaxation of healthy and fibrotic myocardium was measured at about 15 minutes post-contrast. The evolution of the absolute R1 relaxation rate (1/T1) over time after contrast injection was followed for one patient and compared to T1 mapping using Look-Locker. Based on the T1 maps synthetic LGE images were reconstructed and compared to the conventional LGE images. The fitting algorithm is robust against variation in acquisition flip angle, the inversion delay time and cardiac arrhythmia. The observed relaxation rate of the myocardium is 1.2 s-1, increasing to 6 - 7 s-1 after contrast injection and decreasing to 2 - 2.5 s-1 for healthy myocardium and to 3.5 - 4 s-1 for fibrotic myocardium. Synthesized images based on the T1 maps correspond very well to actual LGE images. The method provides a robust quantification of post-Gd T1 relaxation for a complete cardiac volume within a single breath-hold
de Lima Stebbins, Daniela; Docs, Jon; Lowe, Paula; Cohen, Jason; Lei, Hongxia
2016-05-18
The hormones listed in the screening survey list 2 of the Unregulated Contaminant Monitoring Rule 3 (estrone, 17-β-estradiol, 17-α-ethynylestradiol, 16-α-hydroxyestradiol (estriol), equilin, testosterone and 4-androstene-3,17-dione) were analyzed by liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). Two analytical methods were compared: EPA method 539 and the isotope dilution method. EPA method 539 was successfully utilized in river and drinking water matrices with fortified recoveries of 98.9 to 108.5%. Samples from the Hillsborough River reflected levels below the method detection limit (MDL) for the majority of the analytes, except estrone (E1), which was detected at very low concentrations (aquifer storage and recovery (ASR) water samples as a result of strong matrix/solid phase extraction (SPE) losses observed in these more complex matrices. Most of the compounds were not detected or found at relatively low concentrations in the ASR samples. Attenuation of 50 to 99.1% was observed as a result of the ASR recharge/recovery cycles for most of the hormones, except for estriol (E3). Relatively stable concentrations of E3 were found, with only 10% attenuation at one of the sites and no measureable attenuation at another location. These results have substantiated that while EPA method 539 works well for most environmental samples, the isotope dilution method is more robust when dealing with complex matrices such as reclaimed and ASR samples. PMID:27146029
Takezako, Takanobu; Unal, Hamiyet; Karnik, Sadashiva S; Node, Koichi
2015-09-01
Ligand-independent signaling by the angiotensin II type 1 receptor (AT1R) can be activated in clinical settings by mechanical stretch and autoantibodies as well as receptor mutations. Transition of the AT1R to the activated state is known to lower inverse agonistic efficacy of clinically used AT1R blockers (ARBs). The structure-function basis for reduced efficacy of inverse agonists is a fundamental aspect that has been understudied not only in relation to the AT1R but also regarding other homologous receptors. Here, we demonstrate that the active-state transition in the AT1R indeed attenuates an inverse agonistic effect of four biphenyl-tetrazole ARBs through changes in specific ligand-receptor interactions. In the ground state, tight interactions of four ARBs with a set of residues (Ser109(TM3), Phe182(ECL2), Gln257(TM6), Tyr292(TM7), and Asn295(TM7)) results in potent inverse agonism. In the activated state, the ARB-AT1R interactions shift to a different set of residues (Val108(TM3), Ser109(TM3), Ala163(TM4), Phe182(ECL2), Lys199(TM5), Tyr292(TM7), and Asn295(TM7)), resulting in attenuated inverse agonism. Interestingly, V108I, A163T, N295A, and F182A mutations in the activated state of the AT1R shift the functional response to the ARB binding toward agonism, but in the ground state the same mutations cause inverse agonism. Our data show that the second extracellular loop is an important regulator of the functional states of the AT1R. Our findings suggest that the quest for discovering novel ARBs, and improving current ARBs, fundamentally depends on the knowledge of the unique sets of residues that mediate inverse agonistic potency in the two states of the AT1R. PMID:26121982
Laymon, Charles M; Bowsher, James E.
2013-01-01
In dual modality PET/CT, CT data are used to generate the attenuation correction applied in the reconstruction of the PET emission image. This requires converting the CT image into a 511-keV attenuation map. Algorithms for making this transformation require assumptions about the makeup of material within the patient. Anomalous material such as contrast agent administered to enhance the CT scan confounds conversion algorithms and has been observed to result in inaccuracies, i.e., inconsistenci...
Recovery of material parameters of soft hyperelastic tissue by an inverse spectral technique
Gou, Kun
2012-07-01
An inverse spectral method is developed for recovering a spatially inhomogeneous shear modulus for soft tissue. The study is motivated by a novel use of the intravascular ultrasound technique to image arteries. The arterial wall is idealized as a nonlinear isotropic cylindrical hyperelastic body. A boundary value problem is formulated for the response of the arterial wall within a specific class of quasistatic deformations reflective of the response due to imposed blood pressure. Subsequently, a boundary value problem is developed via an asymptotic construction modeling intravascular ultrasound interrogation which generates small amplitude, high frequency time harmonic vibrations superimposed on the static finite deformation. This leads to a system of second order ordinary Sturm-Liouville boundary value problems that are then employed to reconstruct the shear modulus through a nonlinear inverse spectral technique. Numerical examples are demonstrated to show the viability of the method. © 2012 Elsevier Ltd. All rights reserved.
Uniqueness result for an inverse conductivity recovery problem with application to EEG
Clerc, Maureen; Leblond, Juliette; Marmorat, Jean-Paul; Papageorgakis, Christos
2016-01-01
Considering a geometry made of three concentric spherical nested layers, each with constant homogeneous conductivity, we establish a uniqueness result in inverse conductivity estimation, from partial boundary data in presence of a known source term. We make use of spherical harmonics and linear algebra computations, that also provide us with stability results and a robust reconstruction algorithm. As an application to electroencephalography (EEG), in a spherical 3-layer head model (brain, sku...
High intensity and reduced volume training attenuates stress and recovery levels in elite swimmers
DEFF Research Database (Denmark)
Elbe, Anne-Marie; Rasmussen, Camilla P; Nielsen, Glen;
2016-01-01
This study investigated the effect of increased high-intensity interval training (HIT) at the expense of total training volume on the stress and recovery levels of elite swimmers. Forty-one elite swimmers participated in the study and were randomly assigned to either a HIT or a control group (CON......). Eleven swimmers did not complete the questionnaires. For 12 weeks both groups trained ~12 h per week. The amount of HIT was ~5 h vs. 1 h, and total distance was ~17 km vs. ~35 km per week for HIT and CON, respectively. HIT was performed as 6-10 × 10-30 s maximal effort interspersed by 2-4 min of rest...... adjusting for baseline values. No significant effects could be observed in sports-specific stress or sports-specific recovery. The results indicate that increasing training intensity and reducing training volume for 12 weeks can reduce general stress and increase general recovery levels in competitive...
Three Dimensional T1, T2, and Proton Density Mapping with Inversion Recovery Balanced SSFP
Newbould, Rexford D.; Skare, Stefan T.; Alley, Marcus T; Gold, Garry E; Bammer, Roland
2010-01-01
By combining a bSSFP readout with an initial inversion pulse, all three contrast parameters, T1, T2, and proton density (M0), may be rapidly calculated from the signal progression in time. However, here it is shown that this technique is quite sensitive to variation in the applied transmit RF (B1) field, leading to pronounced errors in calculated values. 2D acquisitions are taxed to accurately quantify the relaxation, as the short RF pulses required by SSFP's rapid TR contain a broad spectrum...
Inverse Estimation of Temperature Profiles in Landfills Using Heat Recovery Fluids Measurements
V. G. Dovi'; Reverberi, A.P.; A. Del Borghi; C. Solisio
2012-01-01
In addition to leachate and gas emission analysis, temperature variations in municipal solid waste landfills are routinely monitored for safety and health reasons, such as the increased production of biogas or the danger of spontaneous combustion phenomena if the temperature exceeds 70–75°C. The increasing constraints on greenhouse gas emissions and the convenience of fuel and heat recovery have helped develop a global approach to landfills' operation and maintenance, generally referred to as...
On an inverse source problem for enhanced oil recovery by wave motion maximization in reservoirs
Karve, Pranav M.
2014-12-28
© 2014, Springer International Publishing Switzerland. We discuss an optimization methodology for focusing wave energy to subterranean formations using strong motion actuators placed on the ground surface. The motivation stems from the desire to increase the mobility of otherwise entrapped oil. The goal is to arrive at the spatial and temporal description of surface sources that are capable of maximizing mobility in the target reservoir. The focusing problem is posed as an inverse source problem. The underlying wave propagation problems are abstracted in two spatial dimensions, and the semi-infinite extent of the physical domain is negotiated by a buffer of perfectly-matched-layers (PMLs) placed at the domain’s truncation boundary. We discuss two possible numerical implementations: Their utility for deciding the tempo-spatial characteristics of optimal wave sources is shown via numerical experiments. Overall, the simulations demonstrate the inverse source method’s ability to simultaneously optimize load locations and time signals leading to the maximization of energy delivery to a target formation.
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Shiono, Takahiro [Dokkyo Univ., Saitama (Japan). Koshigaya Hospital
1997-11-01
The purpose of this study was to evaluate the single breath-hold fast inversion recovery sequence (FIR) for depicting the biliary tract. A prospective study was performed in 40 patients with suspected diseases in the biliary tract. MRCP (magnetic resonance cholangiopancreatography) including cholecystograms of diagnostic quality was carried out in 35 patients. Impacted common duct stones were able to be distinguished from malignancies because of their characteristic shapes of obstruction in four of five cases. FIR with thick slices can provide a shorter acquisition time and fewer artifacts with better signal to noise ratio and contrast to noise ratio than MIP images obtained by means of gradient echo methods. MRCP with FIR was a useful adjunctive tool for non-invasive evaluation of patients with obstructive jaundice. (author)
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h-Ici Darach O
2012-03-01
Full Text Available Abstract Background The short inversion time inversion recovery (STIR black-blood technique has been used to visualize myocardial edema, and thus to differentiate acute from chronic myocardial lesions. However, some cardiovascular magnetic resonance (CMR groups have reported variable image quality, and hence the diagnostic value of STIR in routine clinical practice has been put into question. The aim of our study was to analyze image quality and diagnostic performance of STIR using a set of pulse sequence parameters dedicated to edema detection, and to discuss possible factors that influence image quality. We hypothesized that STIR imaging is an accurate and robust way of detecting myocardial edema in non-selected patients with acute myocardial infarction. Methods Forty-six consecutive patients with acute myocardial infarction underwent CMR (day 4.5, +/- 1.6 including STIR for the assessment of myocardial edema and late gadolinium enhancement (LGE for quantification of myocardial necrosis. Thirty of these patients underwent a follow-up CMR at approximately six months (195 +/- 39 days. Both STIR and LGE images were evaluated separately on a segmental basis for image quality as well as for presence and extent of myocardial hyper-intensity, with both visual and semi-quantitative (threshold-based analysis. LGE was used as a reference standard for localization and extent of myocardial necrosis (acute or scar (chronic. Results Image quality of STIR images was rated as diagnostic in 99.5% of cases. At the acute stage, the sensitivity and specificity of STIR to detect infarcted segments on visual assessment was 95% and 78% respectively, and on semi-quantitative assessment was 99% and 83%, respectively. STIR differentiated acutely from chronically infarcted segments with a sensitivity of 95% by both methods and with a specificity of 99% by visual assessment and 97% by semi-quantitative assessment. The extent of hyper-intense areas on acute STIR images
Singh, D. D.
The fundamental-mode Love and Rayleigh waves generated by 57 earthquakes which occurred in the north and central Indian Ocean (extending to 40°S) and recorded at Indian seismograph and other WWSSN stations such as HOW, SHL, VIS, MDR, HYB, KOD, CHG, TRD, POO, BOM, GOA, NDI, NIL and QUE are analysed. Love and Rayleigh wave attenuation coefficients are estimated at periods of 15-100 s using the spectral amplitude of these waves for 98 different paths across the Bay of Bengal Fan, the Arabian Fan, and the north and central Indian Ocean. The large standard deviations observed in the surface wave attenuation coefficients may be a result of regional variation of the attenuative properties of the crust and upper mantle beneath these regions. Love wave attenuation coefficients are found to vary from 0.000 03 to 0.000 45 km -1 for the Bay of Bengal Fan; from 0.000 03 to 0.000 85 km -1 for the Arabian Fan; and from 0.000 03 to 0.000 35 km -1 for the north and central Indian Ocean. Similarly, Rayleigh wave attenuation coefficients vary from 0.000 03 to 0.0004 km -1 for the Bay of Bengal Fan; from 0.000 06 to 0.0007 km -1 for the Arabian Fan; and from 0.000 03 to 0.0007 km -1 for the north and central Indian Ocean. Backus and Gilbert inversion theory is applied to these surface wave attenuation data to obtain average Q-1 models for the crust and upper mantle beneath the Bay of Bengal, the Arabian Fan, and the north and central Indian Ocean. Inversion of Love and Rayleigh wave attenuation data shows a high-attenuation zone centred at a depth of > 120 km ( Qβ ≈ 125) for the Bay of Bengal Fan. Similarly, a high-attenuation zone ( Qβ ≈ 40-70) occurs at a depth of 60-160 km for the Arabian Fan at 100-160 km ( Qβ ≈ 115) for the Indian Ocean off Ninetyeast Ridge, and at 80-160 km ( Qβ ≈ 80) for the Indian Ocean across the Ninetyeast Ridge. The Qβ-1 models show a lithosphere thickness of 120 km beneath the Bay of Bengal Fan. Similarly, lithosphere thickness of 70, 100 and
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Morimoto, Emiko; Kanagaki, Mitsunori; Okada, Tomohisa; Yamamoto, Akira; Togashi, Kaori [Kyoto University Graduate School of Medicine, Department of Diagnostic Imaging and Nuclear Medicine, Kyoto (Japan); Mori, Nobuyuki [Tenri Hospital, Department of Radiology, Tenri, Nara (Japan); Matsumoto, Riki; Ikeda, Akio; Takahashi, Ryosuke [Kyoto University Graduate School of Medicine, Department of Neurology, Kyoto (Japan); Mikuni, Nobuhiro [Sapporo Medical University, Department of Neurosurgery, Sapporo, Hokkaido (Japan); Kunieda, Takeharu; Miyamoto, Susumu [Kyoto University Graduate School of Medicine, Department of Neurosurgery, Kyoto (Japan); Paul, Dominik [Siemens AG Healthcare Sector, Erlangen (Germany)
2013-01-15
To investigate the diagnostic capability of anterior temporal lobe white matter abnormal signal (ATLAS) for determining seizure focus laterality in temporal lobe epilepsy (TLE) by comparing different MR sequences. This prospective study was approved by the institutional review board and written informed consent was obtained. Three 3D sequences (double inversion recovery (DIR), fluid-attenuated inversion recovery (FLAIR) and T2-weighted imaging (T2WI)) and two 2D sequences (FLAIR and T2WI) were acquired at 3 T. Signal changes in the anterior temporal white matter of 21 normal volunteers were evaluated. ATLAS laterality was evaluated in 21 TLE patients. Agreement of independent evaluations by two neuroradiologists was assessed using {kappa} statistics. Differences in concordance between ATLAS laterality and clinically defined seizure focus laterality were analysed using McNemar's test with multiple comparisons. Pre-amygdala high signals (PAHS) were detected in all volunteers only on 3D-DIR. Inter-evaluator agreement was moderate to almost perfect for each sequence. Correct diagnosis of seizure laterality was significantly more frequent on 3D-DIR than on any other sequences (P {<=} 0.031 for each evaluator). The most sensitive sequence for detecting ATLAS laterality was 3D-DIR. ATLAS laterality on 3D-DIR can be a good indicator for determining seizure focus localization in TLE. (orig.)
International Nuclear Information System (INIS)
To investigate the diagnostic capability of anterior temporal lobe white matter abnormal signal (ATLAS) for determining seizure focus laterality in temporal lobe epilepsy (TLE) by comparing different MR sequences. This prospective study was approved by the institutional review board and written informed consent was obtained. Three 3D sequences (double inversion recovery (DIR), fluid-attenuated inversion recovery (FLAIR) and T2-weighted imaging (T2WI)) and two 2D sequences (FLAIR and T2WI) were acquired at 3 T. Signal changes in the anterior temporal white matter of 21 normal volunteers were evaluated. ATLAS laterality was evaluated in 21 TLE patients. Agreement of independent evaluations by two neuroradiologists was assessed using κ statistics. Differences in concordance between ATLAS laterality and clinically defined seizure focus laterality were analysed using McNemar's test with multiple comparisons. Pre-amygdala high signals (PAHS) were detected in all volunteers only on 3D-DIR. Inter-evaluator agreement was moderate to almost perfect for each sequence. Correct diagnosis of seizure laterality was significantly more frequent on 3D-DIR than on any other sequences (P ≤ 0.031 for each evaluator). The most sensitive sequence for detecting ATLAS laterality was 3D-DIR. ATLAS laterality on 3D-DIR can be a good indicator for determining seizure focus localization in TLE. (orig.)
Magnetic resonance imaging of hepatic masses, especially using short T1 inversion recovery sequences
International Nuclear Information System (INIS)
Seventy-four patients with hepatic masses were examined with magnetic resonance imaging (MRI) and X-ray computed tomography (CT). Thirty-eight patients had hepatocellular carcinoma (HCC), 15 had hemangioma (HA), 8 had metastatic tumors, 8 had liver cysts, one had intrahepatic cholangiocarcinoma, 2 had regenerated nodules of liver cirrhosis, one had focal nodular hyperplasia, and one had fatty cysts. Magnetic resonance imaging was the most sensitive for the detection of HA. It was inferior to CT in detecting HCC 3 cm or more, although the two imagings were of similar sensitivity in detecting HCC less than 3 cm. Hepatic masses could be classified based on signal intensity of MRI, thus allowing the qualitative diagnosis. Hepatocellular carcinoma and HA had significantly different T1 and T2 relaxation times (p < 0.001), suggesting the postential use of MRI in the differential diagnosis. Short T1 inversion revovery sequences afforded higher contrast between the liver and tumors than conventional pulse sequences. (Namekawa, K.)
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Kido, Tomoyuki, E-mail: tomozo0421@gmail.com [Department of Radiology, Ehime University Graduate School of Medicine (Japan); Kido, Teruhito; Nakamura, Masashi; Kawaguchi, Naoto; Nishiyama, Yoshiko [Department of Radiology, Ehime University Graduate School of Medicine (Japan); Ogimoto, Akiyoshi [Department of Cardiovascular Internal Medicine, Ehime University Graduate School of Medicine (Japan); Miyagawa, Masao; Mochizuki, Teruhito [Department of Radiology, Ehime University Graduate School of Medicine (Japan)
2014-12-15
Highlights: • We evaluate 3D PSIR compared with 3D IR for the detection of myocardial scars. • In image quality, there was no significant difference between IR and PSIR. • A quantitative analysis of LGE volume shows a strong correlation between PSIR and IR. • PSIR detected greater LGE volume in non-ischemic cardiomyopathy patients than IR. • PSIR may have a specific role in scar evaluation of non-ischemic cardiomyopathy. - Abstract: Background: Late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) is a useful technique for detecting myocardial fibrosis. LGE images are typically acquired using the inversion recovery (IR) method. Recently, phase-sensitive inversion recovery (PSIR) technology has been developed. The purpose of this study was to evaluate free-breathing 3D PSIR sequencing in comparison with breath-held 3D IR sequencing for the detection of myocardial fibrosis. Methods: One hundred twenty-three patients with suspected ischemic cardiac disease (n = 27) or non-ischemic cardiomyopathy (hypertrophic cardiomyopathy, n = 29; dilated cardiomyopathy, n = 22; sarcoidosis, n = 21; arrhythmia, n = 9; myocarditis, n = 4; amyloidosis, n = 3; and others, n = 8) were evaluated by LGE–MRI, which was performed first with the IR sequence and then with the PSIR sequence, using a 3 T MRI scanner. Image quality was scored by two independent readers using a four-point scale. The 3D LGE volume was analyzed quantitatively and compared between both sequencing methods. Results: There was no significant difference in overall image quality (p = 0.19). LGE was detected in 73 patients, who were evaluated visually. Ultimately, 58 patients with acceptable image quality were enrolled in further quantitative analyses (volume assessment). Although quantification of LGE volume revealed a strong correlation between both methods, larger LGE volumes were detected with PSIR compared to IR in patients suspected of non-ischemic cardiomyopathy (39.5 ± 25.9 cm{sup 3} for
International Nuclear Information System (INIS)
Highlights: • We evaluate 3D PSIR compared with 3D IR for the detection of myocardial scars. • In image quality, there was no significant difference between IR and PSIR. • A quantitative analysis of LGE volume shows a strong correlation between PSIR and IR. • PSIR detected greater LGE volume in non-ischemic cardiomyopathy patients than IR. • PSIR may have a specific role in scar evaluation of non-ischemic cardiomyopathy. - Abstract: Background: Late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) is a useful technique for detecting myocardial fibrosis. LGE images are typically acquired using the inversion recovery (IR) method. Recently, phase-sensitive inversion recovery (PSIR) technology has been developed. The purpose of this study was to evaluate free-breathing 3D PSIR sequencing in comparison with breath-held 3D IR sequencing for the detection of myocardial fibrosis. Methods: One hundred twenty-three patients with suspected ischemic cardiac disease (n = 27) or non-ischemic cardiomyopathy (hypertrophic cardiomyopathy, n = 29; dilated cardiomyopathy, n = 22; sarcoidosis, n = 21; arrhythmia, n = 9; myocarditis, n = 4; amyloidosis, n = 3; and others, n = 8) were evaluated by LGE–MRI, which was performed first with the IR sequence and then with the PSIR sequence, using a 3 T MRI scanner. Image quality was scored by two independent readers using a four-point scale. The 3D LGE volume was analyzed quantitatively and compared between both sequencing methods. Results: There was no significant difference in overall image quality (p = 0.19). LGE was detected in 73 patients, who were evaluated visually. Ultimately, 58 patients with acceptable image quality were enrolled in further quantitative analyses (volume assessment). Although quantification of LGE volume revealed a strong correlation between both methods, larger LGE volumes were detected with PSIR compared to IR in patients suspected of non-ischemic cardiomyopathy (39.5 ± 25.9 cm3 for PSIR
International Nuclear Information System (INIS)
For oil recovery or CO2 storage, 'reservoirs' are commonly used to designate geological structures where oil can be found or CO2 can be stored. All reservoirs present a heterogeneity in terms of rock type and properties (such as porosity and permeability). In addition, some of these reservoirs present fractures and faults. Fractured reservoirs are an important part of the oil reserves in the world (Middle East, Gulf of Mexico, etc.) and some of them are important reservoirs in terms of oil volume and productivity in spite of the fractures. In addition, studies of reservoirs for geologic storage of CO2 have shown the existence of diffuse fractures and faults and their strong impacts on flow. A key point in fractured reservoirs is to understand the geometry and hydraulic conductivity of the network formed by the fractures. This requires the construction of a reservoir model that integrates all available conceptual knowledge and quantitative data. The topic of the present paper deals with a new methodology able to perform the history matching of a fractured reservoir model by adapting the sub-seismic fault properties and positions. The main difficulty of this work is to generate a sub-seismic fault network whose fault positions can be easily modified while respecting the statistical fault model. The sub-seismic fault model we have chosen allows us to obtain a sub-seismic fault network that is consistent with the seismic fault network and that succeeds in capturing the specific spatial organization of the faults. In a first step, the geometry of the seismic fault network is characterized using fractal methods. Sub-seismic faults are then generated according to a stochastic algorithm. Finally, the geometry of this discrete fracture network is optimized in order to match the hydrodynamic data about the reservoir. The optimization algorithm modifies the sub-seismic fault positions, leading to the history matching of the reservoir model. Fractal properties are preserved
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Tortora, Fabio; Belfiore, Maria Paola; Romano, Francesco; Cappabianca, Salvatore; Cirillo, Sossio [' ' F. Magrassi-A. Lanzara' ' Second University, Naples (Italy). Dept. of Clinical and Experimental Medicine and Surgery; Prudente, Mariaevelina [Second University, Naples (Italy). Medicine Dept.; Vita Salute San Raffaele Univ., Milan (Italy). Dept. of Neuroradiology; Cirillo, Mario [Second University, Naples (Italy). Neuroradiological Services; Elefante, Andrea [Federic II Univ., Naples (Italy). Neuroradilogical Dept.; Carella, Carlo [Polidiagnostic Center Check-Up, Salerno (Italy)
2014-05-15
In Graves' Ophthalmopathy, it is important to distinguish active inflammatory phase, responsive to immunosuppressive treatment, from fibrotic unresponsive inactive one. The purpose of this study is, first, to identify the relevant orbital magnetic resonance imaging signal intensities before treatment, so to classify patients according to their clinical activity score (CAS), discriminating inactive (CAS < 3) from active Graves' Ophthalmopathy (GO) (CAS > 3) subjects and, second, to follow post-steroid treatment disease. An observational study was executed on 32 GO consecutive patients in different phases of disease, based on clinical and orbital Magnetic Resonance Imaging parameters, compared to 32 healthy volunteers. Orbital Magnetic Resonance Imaging was performed on a 1.5 tesla Magnetic Resonance Unit by an experienced neuroradiologist blinded to the clinical examinations. In pre-therapy patients, compared to controls, a medial rectus muscle statistically significant signal intensity ratio (SIR) in short-time inversion recovery (STIR) (long TR/TE) sequence was found, as well as when comparing patients before and after treatment, both medial and inferior rectus muscle SIR resulted significantly statistically different in STIR. These increased outcomes explain the inflammation oedematous phase of disease, moreover after steroid administration, compared to controls; patients presented lack of that statistically significant difference, thus suggesting treatment effectiveness. In our study, we proved STIR signal intensities increase in inflammation oedematous phase, confirming STIR sequence to define active phase of disease with more sensibility and reproducibility than CAS alone and to evaluate post-therapy involvement. (orig.)
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In Graves' Ophthalmopathy, it is important to distinguish active inflammatory phase, responsive to immunosuppressive treatment, from fibrotic unresponsive inactive one. The purpose of this study is, first, to identify the relevant orbital magnetic resonance imaging signal intensities before treatment, so to classify patients according to their clinical activity score (CAS), discriminating inactive (CAS 3) subjects and, second, to follow post-steroid treatment disease. An observational study was executed on 32 GO consecutive patients in different phases of disease, based on clinical and orbital Magnetic Resonance Imaging parameters, compared to 32 healthy volunteers. Orbital Magnetic Resonance Imaging was performed on a 1.5 tesla Magnetic Resonance Unit by an experienced neuroradiologist blinded to the clinical examinations. In pre-therapy patients, compared to controls, a medial rectus muscle statistically significant signal intensity ratio (SIR) in short-time inversion recovery (STIR) (long TR/TE) sequence was found, as well as when comparing patients before and after treatment, both medial and inferior rectus muscle SIR resulted significantly statistically different in STIR. These increased outcomes explain the inflammation oedematous phase of disease, moreover after steroid administration, compared to controls; patients presented lack of that statistically significant difference, thus suggesting treatment effectiveness. In our study, we proved STIR signal intensities increase in inflammation oedematous phase, confirming STIR sequence to define active phase of disease with more sensibility and reproducibility than CAS alone and to evaluate post-therapy involvement. (orig.)
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The aim of this study was to compare a dual-inversion-recovery black-blood (BB) magnetic resonance imaging (MRI) sequence with steady-state free precession (SSFP) for the assessment of left ventricular parameters. The improved endocardial border definition seen with SSFP was not observed at the epicardial border. Improvements in segmentation at the left ventricular epicardial border have been observed with this black-blood sequence. Left ventricular (LV) mass and LV end-diastolic volume (EDV) measurements as well as inter-observer and intra-observer variability were compared between images acquired with a dual inversion BB and SSFP sequence. The mean±1 standard deviation (SD) for LV EDV was 178.3±52.7 ml measured with SSFP and 158.8±62.2 ml with BB. This difference was not statistically significant (p=0.22). For SSFP, the mean value of LV mass was 124.0±27.0 g and 147.5±37.4 g for BB, a statistically significant difference (p<0.0001). The dual-inversion-recovery BB imaging showed improved reproducibility for LV mass measurements compared with SSFP and improved spatial resolution. For studies requiring LV mass measurements, the dual-inversion-recovery BB sequence offers improved spatial resolution and improved reproducibility to SSFP. (orig.)
Castro, Marcelo A.; Williford, Joshua P.; Cota, Martin R.; MacLaren, Judy M.; Dardzinski, Bernard J.; Latour, Lawrence L.; Pham, Dzung L.; Butman, John A.
2016-03-01
Traumatic meningeal injury is a novel imaging marker of traumatic brain injury, which appears as enhancement of the dura on post-contrast T2-weighted FLAIR images, and is likely associated with inflammation of the meninges. Dynamic Contrast Enhanced MRI provides a better discrimination of abnormally perfused regions. A method to properly identify those regions is presented. Images of seventeen patients scanned within 96 hours of head injury with positive traumatic meningeal injury were normalized and aligned. The difference between the pre- and last post-contrast acquisitions was segmented and voxels in the higher class were spatially clustered. Spatial and morphological descriptors were used to identify the regions of enhancement: a) centroid; b) distance to the brain mask from external voxels; c) distance from internal voxels; d) size; e) shape. The method properly identified thirteen regions among all patients. The method failed in one case due to the presence of a large brain lesion that altered the mask boundaries. Most false detections were correctly rejected resulting in a sensitivity and specificity of 92.9% and 93.6%, respectively.
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Background: Magnetic resonance imaging (MRI) is highly useful for detecting diseases of the bone marrow. The sensitivity for detecting compression fracture is very high, but specificity is low for differential diagnosis between malignant and benign cases. Purpose: To evaluate the usefulness of in-phase/opposed-phase and short TI inversion recovery (STIR) magnetic resonance imaging (MRI) of bone marrow for differentiation between benign and malignant vertebral compression fractures. Material and Methods: A retrospective review of 66 patients with 70 vertebral compression fractures was performed. The signal intensity ratio (SIR) defined as SIR (opposed/in) was calculated from in-phase/opposed-phase MR images, and the signal intensity ratio as SIR (STIR) was calculated from STIR MR images. The relationships between values of SIR (opposed/in) and SIR (STIR) and the differential diagnosis of malignant vs. benign fractures were considered. Results: When SIR (opposed/in) was less than 1.0, bone marrow was benign. The bone marrow was malignant when both SIR (opposed/in) was greater than 1.0 and SIR (STIR) was less than 2.0. Conclusion: In cases of acute compression fracture, malignant bone marrow showed SIR(STIR) values less than 2.0 and SIR (in/opposed) greater than 1.0. In contrast, benign bone marrow showed SIR (STIR) values greater than 2.5. For chronic compression fracture, malignant bone marrow showed SIR (in/opposed) greater than 1.0. Bone marrow was benign in all cases with SIR (in/opposed) less than 1.0
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Ogura, Akio; Hayakawa, Katsumi; Maeda, Fumie; Saeki, Fumito; Syukutani, Ai; Shibutani, Sachiko; Kuroda, Emi (Dept. of Radiology, Kyoto City Hospital, Kyoto (Japan)), email: a-ogura@mbox.kyoto-inet.or.jp
2012-05-15
Background: Magnetic resonance imaging (MRI) is highly useful for detecting diseases of the bone marrow. The sensitivity for detecting compression fracture is very high, but specificity is low for differential diagnosis between malignant and benign cases. Purpose: To evaluate the usefulness of in-phase/opposed-phase and short TI inversion recovery (STIR) magnetic resonance imaging (MRI) of bone marrow for differentiation between benign and malignant vertebral compression fractures. Material and Methods: A retrospective review of 66 patients with 70 vertebral compression fractures was performed. The signal intensity ratio (SIR) defined as SIR (opposed/in) was calculated from in-phase/opposed-phase MR images, and the signal intensity ratio as SIR (STIR) was calculated from STIR MR images. The relationships between values of SIR (opposed/in) and SIR (STIR) and the differential diagnosis of malignant vs. benign fractures were considered. Results: When SIR (opposed/in) was less than 1.0, bone marrow was benign. The bone marrow was malignant when both SIR (opposed/in) was greater than 1.0 and SIR (STIR) was less than 2.0. Conclusion: In cases of acute compression fracture, malignant bone marrow showed SIR(STIR) values less than 2.0 and SIR (in/opposed) greater than 1.0. In contrast, benign bone marrow showed SIR (STIR) values greater than 2.5. For chronic compression fracture, malignant bone marrow showed SIR (in/opposed) greater than 1.0. Bone marrow was benign in all cases with SIR (in/opposed) less than 1.0
MRI of fat necrosis of the breast: The “black hole” sign at short tau inversion recovery
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Objective: To describe MRI features of fat necrosis of the breast. Materials and methods: Twenty-five lesions in 16 patients were retrospectively analyzed. MRI was performed due to equivocal findings at conventional imaging after surgical treatment of cancer (n = 14) or during anticoagulant therapy (n = 1), after focal mastitis treated with ductal resection (n = 1). In the 15 patients with previous surgery MRI was performed after a median interval of 24 months, using short tau inversion recovery (STIR) and contrast-enhanced dynamic T1-weighted sequences. Signal-to-noise ratio (SNR) inside the lesion and surrounding healthy fat was calculated on both STIR and unenhanced T1-weighted images. Maximal lesion diameter was measured on STIR images. All lesions had final clinical and imaging assessment in favor of fat necrosis and negative clinical and imaging follow-up (21–40 months; median 24 months). Results: At STIR sequence, fat necrosis appeared as a “black hole”, being markedly hypointense (median SNR = 29) compared with surrounding fat (median SNR = 95) (P < 0.001), while no significant difference was found at unenhanced T1-weighted sequence. No significant correlation with time from treatment was found. Of 25 lesions, 15 showed ring enhancement, with continuous increase (n = 10), plateau (n = 2), or wash-out curve (n = 3). The 11 enhancing lesions in the 8 patients with previous radiation therapy showed an initial enhancement higher than that of the 4 enhancing lesions in the 2 patients who did not, although the difference was not significant (P = 0.104). Conclusion: Fat necrosis of the breast exhibits a “black hole” sign on STIR images, allowing for an easier diagnosis in clinical practice.
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The aim of this study was to characterize the optimal reconstruction parameters for ordered-subset expectation maximization (OSEM) with attenuation correction, scatter correction, and depth-dependent resolution recovery (OSEMACSCRR). We assessed the optimal parameters for OSEMACSCRR in an anthropomorphic torso phantom study, and evaluated the validity of the reconstruction parameters in the groups of normal volunteers and patients with abnormal perfusion. Images of the anthropomorphic torso phantom, 9 normal volunteers and 7 patients undergoing myocardial perfusion single photon emission computed tomography (SPECT) were acquired with a SPECT/CT scanner. SPECT data comprised a 64 x 64 matrix with an acquisition pixel size of 6.6 mm. A normalized mean square error (NMSE) of the phantom image was calculated to determine both optimal OSEM update and a full width at half maximum (FWHM) of Gaussian filter. We validated the myocardial count, contrast and noise characteristic for clinical subjects derived from OSEMACSCRR processing. OSEM with depth-dependent resolution recovery (OSEMRR) and filtered back projection (FBP) were simultaneously performed to compare OSEMACSCRR. The combination of OSEMACSCRR with 90-120 OSEM updates and Gaussian filter with 13.2-14.85 mm FWHM yielded low NMSE value in the phantom study. When we used OSEMACSCRR with 120 updates and Gaussian filter with 13.2 mm FWHM in the normal volunteers, myocardial contrast showed significantly higher value than that derived from 120 updates and 14.85 mm FWHM. OSEMACSCRR with the combination of 90-120 OSEM updates and 14.85 mm FWHM produced lowest % root mean square (RMS) noise. Regarding the defect contrast of patients with abnormal perfusion, OSEMACSCRR with the combination of 90-120 OSEM updates and 13.2 mm FWHM produced significantly higher value than that derived from 90-120 OSEM updates and 14.85 mm FWHM. OSEMACSCRR was superior to FBP for the % RMS noise (8.52±1.08 vs. 9.55±1.71, P=0.02) and defect
Liu, Qing; Yan, Bryan P; Yu, Cheuk-Man; Zhang, Yuan-Ting; Poon, Carmen C Y
2014-02-01
Pulse transit time (PTT) is a cardiovascular parameter of emerging interest due to its potential to estimate blood pressure (BP) continuously and without a cuff. Both linear and nonlinear equations have been used in the estimation of BP based on PTT. This study, however, demonstrates that there is a hysteresis phenomenon between BP and PTT during and after dynamic exercise. A total of 46 subjects including 16 healthy subjects, 13 subjects with one or more cardiovascular risk factors, and 17 patients with cardiovascular disease underwent graded exercise stress test. PTT was measured from electrocardiogram and photoplethysmogram of the left index finger of the subject, i.e., a pathway that includes predominately aorta, brachial, and radial arteries. The results of this study showed that, for the same systolic BP (SBP), PTT measured during exercise was significantly larger than PTT measured during recovery for all subject groups. This hysteresis was further quantified as both normalized area bounded by the SBP-PTT relationship (AreaN) and SBP difference at PTT during peak exercise plus 20 ms (ΔSBP20). Significant attenuation of both AreaN (p <; 0.05) and ΔSBP20 (p <; 0.01) is observed in cardiovascular patients compared with healthy subjects, independent of resting BP. Since the SBP-PTT relationship are determined by the mechanical properties of arterial wall, which is predominately mediated by the sympathetic nervous system through altered vascular smooth muscle (VSM) tone during exercise, results of this study are consistent with the previous findings of autonomic nervous dysfunction in cardiovascular patients. We further conclude that VSM tone has a nonnegligible influence on the BP-PTT relationship and thus should be considered in the PTT-based BP estimation. PMID:24158470
Escobales, Nelson; Nuñez, Rebeca E; Jang, Sehwan; Parodi-Rullan, Rebecca; Ayala-Peña, Sylvette; Sacher, Joshua R; Skoda, Erin M; Wipf, Peter; Frontera, Walter; Javadov, Sabzali
2014-12-01
Mitochondria-generated reactive oxygen species (ROS) play a crucial role in the pathogenesis of aging and age-associated diseases. In this study, we evaluated the effects of XJB-5-131 (XJB), a mitochondria-targeted ROS and electron scavenger, on cardiac resistance to ischemia-reperfusion (IR)-induced oxidative stress in aged rats. Male adult (5-month old, n=17) and aged (29-month old, n=19) Fischer Brown Norway (F344/BN) rats were randomly assigned to the following groups: adult (A), adult+XJB (AX), aged (O), and aged+XJB (OX). XJB was administered 3 times per week (3mg/kg body weight, IP) for four weeks. At the end of the treatment period, cardiac function was continuously monitored in excised hearts using the Langendorff technique for 30 min, followed by 20 min of global ischemia, and 60-min reperfusion. XJB improved post-ischemic recovery of aged hearts, as evidenced by greater left ventricular developed-pressures and rate-pressure products than the untreated, aged-matched group. The state 3 respiration rates at complexes I, II and IV of mitochondria isolated from XJB-treated aged hearts were 57% (P<0.05), 25% (P<0.05) and 28% (P<0.05), respectively, higher than controls. Ca(2+)-induced swelling, an indicator of permeability transition pore opening, was reduced in the mitochondria of XJB-treated aged rats. In addition, XJB significantly attenuated the H2O2-induced depolarization of the mitochondrial inner membrane as well as the total and mitochondrial ROS levels in cultured cardiomyocytes. This study underlines the importance of mitochondrial ROS in aging-induced cardiac dysfunction and suggests that targeting mitochondrial ROS may be an effective therapeutic approach to protect the aged heart against IR injury. PMID:25451170
McInnis, Natalie H; Journeay, W Shane; Jay, Ollie; Leclair, Emily; Kenny, Glen P
2006-09-01
The following study examined the effect of 15 degrees head-down tilt (HDT) on postexercise heat loss and hemodynamic responses. We tested the hypothesis that recovery from dynamic exercise in the HDT position would attenuate the reduction in the heat loss responses of cutaneous vascular conductance (CVC) and sweating relative to upright seated (URS) recovery in association with an augmented hemodynamic response and an increased rate of core temperature decay. Seven male subjects performed the following three experimental protocols: 1) 60 min in the URS posture followed by 60 min in the 15 degrees HDT position; 2) 15 min of cycle ergometry at 75% of their predetermined V(O2 peak) followed by 60 min of recovery in the URS posture; or 3) 15 min of cycle ergometry at 75% of their predetermined V(O2 peak) followed by 60 min of recovery in the 15 degrees HDT position. Mean skin temperature, esophageal temperature (T(es)), skin blood flow, sweat rate, cardiac output (CO), stroke volume (SV), heart rate (HR), total peripheral resistance, and mean arterial pressure (MAP) were recorded at baseline, end exercise, 2, 5, 8, 12, 15, and 20 min, and every 5 min until end of recovery (60 min). Without preceding exercise, HDT decreased HR and increased SV (P < or = 0.05). During recovery after exercise, a significantly greater MAP, SV, CVC, and sweat rate and a significantly lower HR were found with HDT compared with URS posture (P < or = 0.05). Subsequently, a significantly lower T(es) was observed with HDT after 15 min of recovery onward (P < or = 0.05). At the end of 60 min of recovery, T(es) remained significantly elevated above baseline with URS (P < or = 0.05); however, T(es) returned to baseline with HDT. In conclusion, extended recovery from dynamic exercise in the 15 degrees HDT position attenuates the reduction in CVC and sweating, thereby significantly increasing the rate of T(es) decay compared with recovery in the URS posture. PMID:16741261
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Hausenloy Derek J
2011-09-01
Full Text Available Abstract Background Myocardial infarction (MI can be readily assessed using late gadolinium enhancement (LGE cardiovascular magnetic resonance (CMR. Inversion recovery (IR sequences provide the highest contrast between enhanced infarct areas and healthy myocardium. Applying such methods to small animals is challenging due to rapid respiratory and cardiac rates relative to T1 relaxation. Methods Here we present a fast and robust protocol for assessing LGE in small animals using a multi-slice IR gradient echo sequence for efficient assessment of LGE. An additional Look-Locker sequence was used to assess the optimum inversion point on an individual basis and to determine most appropriate gating points for both rat and mouse. The technique was applied to two preclinical scenarios: i an acute (2 hour reperfused model of MI in rats and ii mice 2 days following non-reperfused MI. Results LGE images from all animals revealed clear areas of enhancement allowing for easy volume segmentation. Typical inversion times required to null healthy myocardium in rats were between 300-450 ms equivalent to 2-3 R-waves and ~330 ms in mice, typically 3 R-waves following inversion. Data from rats was also validated against triphenyltetrazolium chloride staining and revealed close agreement for infarct size. Conclusion The LGE protocol presented provides a reliable method for acquiring images of high contrast and quality without excessive scan times, enabling higher throughput in experimental studies requiring reliable assessment of MI.
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Marianito R. Rodrigo
2007-10-01
Full Text Available We show that the problem of recovering the time-dependent parameters of an equation of Black-Scholes type can be formulated as an inverse Stieltjes moment problem. An application to the problem of implied volatility calculation in the case when the model parameters are time varying is provided and results of numerical simulations are presented.
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The goal of elastography is to image the shear stiffness of tissue for cancer diagnosis and the focus of this paper is on single frequency elastographic data. Assuming that the measured displacement of the propagating shear wave satisfies the acoustic wave equation, the shear modulus μ can be recovered by solving a first-order partial differential equation in the inverse problem. To capture possible exponential growth and decay of the targeted parameter μ numerically in a stable manner, we propose a log-elastographic nonlinear scheme and a linear finite difference based elliptic scheme. Both methods are shown to be convergent at first order and their performances are compared with the performances of a semi-implicit upwind scheme and the direct inversion model previously investigated (see [23]). We present shear modulus reconstructions from synthetic data with and without noise
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Greiser Andreas
2010-11-01
Full Text Available Abstract Background T1 mapping allows direct in-vivo quantitation of microscopic changes in the myocardium, providing new diagnostic insights into cardiac disease. Existing methods require long breath holds that are demanding for many cardiac patients. In this work we propose and validate a novel, clinically applicable, pulse sequence for myocardial T1-mapping that is compatible with typical limits for end-expiration breath-holding in patients. Materials and methods The Shortened MOdified Look-Locker Inversion recovery (ShMOLLI method uses sequential inversion recovery measurements within a single short breath-hold. Full recovery of the longitudinal magnetisation between sequential inversion pulses is not achieved, but conditional interpretation of samples for reconstruction of T1-maps is used to yield accurate measurements, and this algorithm is implemented directly on the scanner. We performed computer simulations for 100 msIn-vivo myocardial T1-mapping using this method and the previous gold-standard (MOLLI was performed in 10 healthy volunteers at 1.5T and 3T, 4 volunteers with contrast injection at 1.5T, and 4 patients with recent myocardial infarction (MI at 3T. Results We found good agreement between the average ShMOLLI and MOLLI estimates for T1 In-vivo, ShMOLLI measurements required 9.0 ± 1.1 s (MOLLI = 17.6 ± 2.9 s. Average healthy myocardial T1 s by ShMOLLI at 1.5T were 966 ± 48 ms (mean ± SD and 1166 ± 60 ms at 3T. In MI patients, the T1 in unaffected myocardium (1216 ± 42 ms was similar to controls at 3T. Ischemically injured myocardium showed increased T1 = 1432 ± 33 ms (p in-vivo variability within ShMOLLI T1-maps was only 14% (1.5T or 18% (3T higher than the MOLLI maps, but the MOLLI acquisitions were twice longer than ShMOLLI acquisitions. Conclusion ShMOLLI is an efficient method that generates immediate, high-resolution myocardial T1-maps in a short breath-hold with high precision. This technique provides a valuable
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Dietemann, J.L.; Thibaut-Menard, A.; Neugroschl, C.; Gillis, C.; Abu Eid, M.; Bogorin, A. [Service de Radiologie, Hopital de Hautepierre, Hopitaux Universitaires, Strasbourg (France); Warter, J.M.; Tranchant, C. [Department of Neurology, University Hospital of Strasbourg (France)
2000-11-01
We compared the sensitivity of T2-weighted spin-echo (FSE) and fast short-tau inversion-recovery (fSTIR) sequences in detection of multiple sclerosis of the spinal cord in 100 consecutive patients with clinically confirmed multiple sclerosis (MS); 86 patients underwent also brain MRI. In all, 310 focal lesions were detected on fSTIR and 212 on T2-weighted FSE, spinal cord lesions were seen better on fSTIR images, with a higher contrast between the lesion and the normal spinal cord. In 24 patients in whom cord plaques were shown with both sequences, the cranial study was normal or inconclusive. Assessment of spinal plaques can be particularly important when MRI of the brain is inconclusive, and in there situations fSTIR can be helpful. (orig.)
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We compared the sensitivity of T2-weighted spin-echo (FSE) and fast short-tau inversion-recovery (fSTIR) sequences in detection of multiple sclerosis of the spinal cord in 100 consecutive patients with clinically confirmed multiple sclerosis (MS); 86 patients underwent also brain MRI. In all, 310 focal lesions were detected on fSTIR and 212 on T2-weighted FSE, spinal cord lesions were seen better on fSTIR images, with a higher contrast between the lesion and the normal spinal cord. In 24 patients in whom cord plaques were shown with both sequences, the cranial study was normal or inconclusive. Assessment of spinal plaques can be particularly important when MRI of the brain is inconclusive, and in there situations fSTIR can be helpful. (orig.)
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Herlihy Amy H
2008-01-01
Full Text Available Abstract Purpose To demonstrate the feasibility of using an inversion recovery pulse sequence and to define the optimal inversion time (TI to assess myocardial infarction in mice by late gadolinium enhancement (LGE MRI at 9.4T, and to obtain the maximal contrast between the infarcted and the viable myocardium. Methods MRI was performed at 9.4T in mice, two days after induction of myocardial infarction (n = 4. For cardiovascular MR imaging, a segmented magnetization-prepared fast low angle shot (MP-FLASH sequence was used with varied TIs ranging from 40 to 420 ms following administration of gadolinium-DTPA at 0.6 mmol/kg. Contrast-to-noise (CNR and signal-to-noise ratio (SNR were measured and compared for each myocardial region of interest (ROI. Results The optimal TI, which corresponded to a minimum SNR in the normal myocardium, was 268 ms ± 27.3. The SNR in the viable myocardium was significantly different from that found in the infarcted myocardium (17.2 ± 2.4 vs 82.1 ± 10.8; p = 0.006 leading to a maximal relative SI (Signal Intensity between those two areas (344.9 ± 60.4. Conclusion Despite the rapid heart rate in mice, our study demonstrates that LGE MRI can be performed at 9.4T using a protocol similar to the one used for clinical MR diagnosis of myocardial infarction.
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Accurate longitudinal relaxation time (T1) of arterial blood is important in evaluating blood flow in tissue by arterial spin labeling magnetic resonance (MR) imaging. Few studies have reported the T1 of human arterial blood in vivo, especially using 3-tesla MR imaging. T1 values of human venous blood in vivo have been reported, but they differ from those measured in vitro. We aimed to evaluate the accurate T1 of human arterial blood in vivo. We measured T1 values of blood in 10 healthy volunteers in vivo using an inversion-recovery fast gradient-echo sequence and 3-tesla MR imaging unit. We also measured hematocrit (Hct) values of venous blood samples. After nonselective application of the inversion pulse using a body coil, we obtained MR imaging signals of arterial blood in the abdominal aorta. Similarly, we measured the signals of venous blood in the internal jugular vein. Inversion times varied between 200 and 5000 ms for imaging of the abdominal aorta and 200 and 2500 ms for imaging of the jugular vein. We also acquired signals without the inversion pulse. We estimated T1 values from the data by nonlinear least squares fitting of a 3-parameter model. The T1 value (mean±standard deviation) of arterial blood was 1779±80 ms and of venous blood, 1694±77 ms. The average Hct value was 0.47. The R1 (=1/T1) of arterial blood was related to the Hct value as: R1 =(0.59±0.16)Hct + (0.29±0.07) (mean±standard error) s-1. For the venous blood, R1 =(0.70±0.11)Hct + (0.27±0.05) s-1. We observed a T1 of human arterial blood in vivo of 1779±80 ms at a mean hematocrit value of 0.47 as determined by 3T MR imaging; an even longer T1 value is expected with a hematocrit value less than 0.47. (author)
Park, Jin-Hyung; Chung, Paul D. H.; Jeon, Chan-Uk; Cho, Han Ku; Pang, Linyong; Peng, Danping; Tolani, Vikram; Cecil, Tom; Kim, David; Baik, KiHo
2009-10-01
At the most advanced technology nodes, such as 32nm and 22nm, aggressive OPC and Sub-Resolution Assist Features (SRAFs) are required. However, their use results in significantly increased mask complexity, making mask defect disposition more challenging than ever. This paper describes how mask patterns can first be recovered from the inspection images by applying patented algorithms using Level Set Methods. The mask pattern recovery step is then followed by aerial/wafer image simulation, the results of which can be plugged into an automated mask defect disposition system based on aerial/wafer image. The disposition criteria are primarily based on wafer-plane CD variance. The system also connects to a post-OPC lithography verification tool that can provide gauges and CD specs, thereby enabling them to be used in mask defect disposition as well. Results on both programmed defects and production defects collected at Samsung mask shop are presented to show the accuracy and consistency of using the Level Set Methods and aerial/wafer image based automated mask disposition.
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Tove Lekva
Full Text Available Somatostatin analogs (SA have been established as the first line medical treatment for acromegaly, but following long-term treatment, SA normalizes GH and IGF-I levels in only 40-60% of patients. The epithelial marker E-cadherin plays a crucial role in the epithelial mesenchymal transition (EMT and is associated with a poor response to SA treatment. We hypothesized that the characterization of transcripts regulated by SA in somatotroph adenomas with high and low E-cadherin expression may identify signaling pathways and mediators that can explain the poor response to SA treatment. We performed a microarray analysis of sixteen adenomas with different levels of E-cadherin and SA treatment to identify regulated transcripts. Candidate transcripts were further explored in vivo in sixty-five adenomas, and interactions between SA treatment and EMT progression on mRNA expression profiles and associations with clinical recovery were assessed. Finally, the effects of SA treatment on adenoma cells in vitro from acromegalic patients were determined. Microarray analysis of selected adenomas with differential E-cadherin expression, as a marker of EMT progression, identified 172 genes that displayed differential expression that was dependent on SA treatment. The validation of selected candidates in the entire cohort identified 9 transcripts that showed an interaction between E-cadherin expression and SA treatment. Further analysis of the impact of these genes suggests that attenuated RORC expression in somatotroph adenomas is associated with increased tumor size and a blunted clinical response. Our study indicates that attenuated RORC may be involved in the poor clinical response to SA treatment in patients with acromegaly.
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Klang, Eyal; Aharoni, Dvora; Rimon, Uri; Eshed, Iris [Tel Aviv University, Department of Diagnostic Imaging, Sheba Medical Center, Tel Aviv (Israel); Hermann, Kay-Geert [Department of Radiology, Charite University Hospital, Berlin (Germany); Herman, Amir [Sheba Medical Center, Department of Orthopedic Surgery, Tel-Hashomer (Israel); Tel Aviv University, The Sackler School of Medicine, Tel Aviv (Israel); Shazar, Nachshon [Sheba Medical Center, Department of Orthopedic Surgery, Tel-Hashomer (Israel)
2014-04-15
To assess the contribution of contrast material in detecting and evaluating enthesitis of pelvic entheses by MRI. Sixty-seven hip or pelvic 1.5-T MRIs (30:37 male:female, mean age: 53 years) were retrospectively evaluated for the presence of hamstring and gluteus medius (GM) enthesitis by two readers (a resident and an experienced radiologist). Short tau inversion recovery (STIR) and T1-weighted pre- and post-contrast (T1+Gd) images were evaluated by each reader at two sessions. A consensus reading of two senior radiologists was regarded as the gold standard. Clinical data was retrieved from patients' referral form and medical files. Cohen's kappa was used for intra- and inter-observer agreement calculation. Diagnostic properties were calculated against the gold standard reading. A total of 228 entheses were evaluated. Gold standard analysis diagnosed 83 (36 %) enthesitis lesions. Intra-reader reliability for the experienced reader was significantly (p = 0.0001) higher in the T1+Gd images compared to the STIR images (hamstring: k = 0.84/0.45, GM: k = 0.84/0.47). Sensitivity and specificity increased from 0.74/0.8 to 0.87/0.9 in the STIR images and T1+Gd sequences. Intra-reader reliability for the inexperienced reader was lower (p > 0.05). Evidence showing that contrast material improves the reliability, sensitivity, and specificity of detecting enthesitis supports its use in this setting. (orig.)
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Sensory neuronopathy (SNN) is a distinctive subtype of peripheral neuropathies, specifically targeting dorsal root ganglion (DRG). We utilized MRI to demonstrate the imaging characteristics of DRG, spinal cord (SC), and brachial plexus at C7 level in SNN. We attempted multiple-echo data image combination (MEDIC) and turbo inversion recovery magnitude (TIRM) methods in nine patients with sensory neuronopathy and compared with those in 16 disease controls and 20 healthy volunteers. All participants underwent MRI for the measurement of DRG, posterior column (PC), lateral column, and spinal cord area (SCA) at C7 level. DRG diameters were obtained through its largest cross section, standardized by dividing sagittal diameter of mid-C7 vertebral canal. We also made comparisons of standardized anteroposterior diameter (APD) and left-right diameters of SC and PC in these groups. Signal intensity and diameter of C7 spinal nerve were assessed on TIRM. Compared to control groups, signal intensities of DRG and PC were higher in SNN patients when using MEDIC, but the standardized diameters were shorter in either DRG or PC. Abnormal PC signal intensities were identified in eight out of nine SNN patients (89 %) with MEDIC and five out of nine (56 %) with T2-weighted images. SCA, assessed with MEDIC, was smaller in SNN patients than in the other groups, with significant reduction of its standardized APD. C7 nerve root diameters, assessed with TIRM, were decreased in SNN patients. MEDIC and TIRM sequences demonstrate increased signal intensities and decreased area of DRG and PC, and decreased diameter of nerve roots in patients with SNN, which can play a significant role in early diagnosis. (orig.)
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Yoon, Jeong Hee [Seoul National University Hospital, Department of Radiology, Seoul (Korea, Republic of); Lee, Jeong Min; Han, Joon Koo; Choi, Byung Ihn [Seoul National University Hospital, Department of Radiology, Seoul (Korea, Republic of); Seoul National University College of Medicine, Institute of Radiation Medicine, Jongno-gu, Seoul (Korea, Republic of); Paek, Munyoung [Siemens Healthcare, Seoul (Korea, Republic of)
2016-06-15
To determine whether multislice T1 mapping of the liver using a modified look-locker inversion recovery (MOLLI) sequence on gadoxetic acid-enhanced magnetic resonance imaging (MRI) can be used as a quantitative tool to estimate liver function and predict the presence of oesophageal or gastric varices. Phantoms filled with gadoxetic acid were scanned three times using MOLLI sequence to test repeatability. Patients with chronic liver disease or liver cirrhosis who underwent gadoxetic acid-enhanced liver MRI including MOLLI sequence at 3 T were included (n = 343). Pre- and postcontrast T1 relaxation times of the liver (T1liver), changes between pre- and postcontrast T1liver (ΔT1liver), and adjusted postcontrast T1liver (postcontrast T1liver-T1spleen/T1spleen) were compared among Child-Pugh classes. In 62 patients who underwent endoscopy, all T1 parameters and spleen sizes were correlated with varices. Phantom study showed excellent repeatability of MOLLI sequence. As Child-Pugh scores increased, pre- and postcontrast T1liver were significantly prolonged (P < 0.001), and ΔT1liver and adjusted postcontrast T1liver decreased (P< 0.001). Adjusted postcontrast T1liver and spleen size were independently associated with varices (R{sup 2} = 0.29, P < 0.001). T1 mapping of the liver using MOLLI sequence on gadoxetic acid-enhanced MRI demonstrated potential in quantitatively estimating liver function, and adjusted postcontrast T1liver was significantly associated with varices. (orig.)
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Bao, Yi-Fang; Tang, Wei-Jun; Li, Yu-Xin; Geng, Dao-Ying [Fudan University, Department of Radiology, Huashan Hospital, Shanghai (China); Zhu, Dong-Qing; Chen, Xiang-Jun [Fudan University, Department of Neurology, Huashan Hospital, Shanghai (China); Zee, Chi-Shing [University of Southern California Keck School of Medicine, Department of Radiology, Los Angeles, CA (United States)
2013-01-15
Sensory neuronopathy (SNN) is a distinctive subtype of peripheral neuropathies, specifically targeting dorsal root ganglion (DRG). We utilized MRI to demonstrate the imaging characteristics of DRG, spinal cord (SC), and brachial plexus at C7 level in SNN. We attempted multiple-echo data image combination (MEDIC) and turbo inversion recovery magnitude (TIRM) methods in nine patients with sensory neuronopathy and compared with those in 16 disease controls and 20 healthy volunteers. All participants underwent MRI for the measurement of DRG, posterior column (PC), lateral column, and spinal cord area (SCA) at C7 level. DRG diameters were obtained through its largest cross section, standardized by dividing sagittal diameter of mid-C7 vertebral canal. We also made comparisons of standardized anteroposterior diameter (APD) and left-right diameters of SC and PC in these groups. Signal intensity and diameter of C7 spinal nerve were assessed on TIRM. Compared to control groups, signal intensities of DRG and PC were higher in SNN patients when using MEDIC, but the standardized diameters were shorter in either DRG or PC. Abnormal PC signal intensities were identified in eight out of nine SNN patients (89 %) with MEDIC and five out of nine (56 %) with T2-weighted images. SCA, assessed with MEDIC, was smaller in SNN patients than in the other groups, with significant reduction of its standardized APD. C7 nerve root diameters, assessed with TIRM, were decreased in SNN patients. MEDIC and TIRM sequences demonstrate increased signal intensities and decreased area of DRG and PC, and decreased diameter of nerve roots in patients with SNN, which can play a significant role in early diagnosis. (orig.)
Ye, Fan; Mathur, Sunita; Liu, Min; Borst, Stephen E; Walter, Glenn A; Sweeney, H Lee; Vandenborne, Krista
2013-05-01
Skeletal muscle is a highly dynamic tissue that responds to endogenous and external stimuli, including alterations in mechanical loading and growth factors. In particular, the antigravity soleus muscle experiences significant muscle atrophy during disuse and extensive muscle damage upon reloading. Given that insulin-like growth factor-1 (IGF-1) has been implicated as a central regulator of muscle repair and modulation of muscle size, we examined the effect of virally mediated overexpression of IGF-1 on the soleus muscle following hindlimb cast immobilization and upon reloading. Recombinant IGF-1 cDNA virus was injected into one of the posterior hindlimbs of the mice, while the contralateral limb was injected with saline (control). At 20 weeks of age, both hindlimbs were immobilized for 2 weeks to induce muscle atrophy in the soleus and ankle plantarflexor muscle group. Subsequently, the mice were allowed to reambulate, and muscle damage and recovery were monitored over a period of 2-21 days. The primary finding of this study was that IGF-1 overexpression attenuated reloading-induced muscle damage in the soleus muscle, and accelerated muscle regeneration and force recovery. Muscle T2 assessed by magnetic resonance imaging, a non-specific marker of muscle damage, was significantly lower in IGF-1-injected compared with contralateral soleus muscles at 2 and 5 days reambulation (P<0.05). The reduced prevalence of muscle damage in IGF-1-injected soleus muscles was confirmed on histology, with a lower fractional area of abnormal muscle tissue in IGF-1-injected muscles at 2 days reambulation (33.2±3.3 versus 54.1±3.6%, P<0.05). Evidence of the effect of IGF-1 on muscle regeneration included timely increases in the number of central nuclei (21% at 5 days reambulation), paired-box transcription factor 7 (36% at 5 days), embryonic myosin (37% at 10 days) and elevated MyoD mRNA (7-fold at 2 days) in IGF-1-injected limbs (P<0.05). These findings demonstrate a potential role
Courdurier, M.; Monard, F.; Osses, A.; Romero, F.
2015-09-01
In medical single-photon emission computed tomography (SPECT) imaging, we seek to simultaneously obtain the internal radioactive sources and the attenuation map using not only ballistic measurements but also first-order scattering measurements and assuming a very specific scattering regime. The problem is modeled using the radiative transfer equation by means of an explicit non-linear operator that gives the ballistic and scattering measurements as a function of the radioactive source and attenuation distributions. First, by differentiating this non-linear operator we obtain a linearized inverse problem. Then, under regularity hypothesis for the source distribution and attenuation map and considering small attenuations, we rigorously prove that the linear operator is invertible and we compute its inverse explicitly. This allows proof of local uniqueness for the non-linear inverse problem. Finally, using the previous inversion result for the linear operator, we propose a new type of iterative algorithm for simultaneous source and attenuation recovery for SPECT based on the Neumann series and a Newton-Raphson algorithm.
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Pal A
2013-06-01
Full Text Available Ajay Pal,1 Anand Singh,2 Tapas C Nag,3 Parthaprasad Chattopadhyay,2 Rashmi Mathur,1 Suman Jain1 1Department of Physiology, 2Department of Biochemistry, 3Department of Anatomy, All India Institute of Medical Sciences, New Delhi, India Background: Iron oxide nanoparticles (IONPs can attenuate oxidative stress in a neutral pH environment in vitro. In combination with an external electromagnetic field, they can also facilitate axon regeneration. The present study demonstrates the in vivo potential of IONPs to recover functional deficits in rats with complete spinal cord injury. Methods: The spinal cord was completely transected at the T11 vertebra in male albino Wistar rats. Iron oxide nanoparticle solution (25 µg/mL embedded in 3% agarose gel was implanted at the site of transection, which was subsequently exposed to an electromagnetic field (50 Hz, 17.96 µT for two hours daily for five weeks. Results: Locomotor and sensorimotor assessment as well as histological analysis demonstrated significant functional recovery and a reduction in lesion volume in rats with IONP implantation and exposure to an electromagnetic field. No collagenous scar was observed and IONPs were localized intracellularly in the immediate vicinity of the lesion. Further, in vitro experiments to explore the cytotoxic effects of IONPs showed no effect on cell survival. However, a significant decrease in H2O2-mediated oxidative stress was evident in the medium containing IONPs, indicating their free radical scavenging properties. Conclusion: These novel findings indicate a therapeutic role for IONPs in spinal cord injury and other neurodegenerative disorders mediated by reactive oxygen species. Keywords: secondary damage, oxidative stress, electromagnetic field, cytotoxicity, neurodegeneration, pain
International Nuclear Information System (INIS)
A pipeline transporting crude-oil broke in a nature reserve in 2009 and spilled 5100 m3 of oil that partly reached the aquifer and formed progressively a floating oil lens. Groundwater monitoring started immediately after the spill and crude-oil recovery by dual pump-and-skim technology was operated after oil lens formation. This study aimed at documenting the implementation of redox-specific natural attenuation processes in the saturated zone and at assessing whether dissolved compounds were degraded. Seven targeted water sampling campaigns were done during four years in addition to a routine monitoring of hydrocarbon concentrations. Liquid oil reached the aquifer within 2.5 months, and anaerobic processes, from denitrification to reduction of sulfate, were observable after 8 months. Methanogenesis appeared on site after 28 months. Stable carbon isotope analyses after 16 months showed maximum shifts in δ13C of + 4.9 ± 0.22‰ for toluene, + 2.4 ± 0.19‰ for benzene and + 0.9 ± 0.51‰ for ethylbenzene, suggesting anaerobic degradation of these compounds in the source zone. Estimations of fluxes of inorganic carbon produced by biodegradation revealed that, in average, 60% of inorganic carbon production was attributable to sulfate reduction. This percentage tended to decrease with time while the production of carbon attributable to methanogenesis was increasing. Within the investigation time frame, mass balance estimations showed that biodegradation is a more efficient process for control of dissolved concentrations compared to pumping and filtration on an activated charcoal filter. - Highlights: • One of the world largest terrestrial oil spills is studied for 4 years. • Initially pristine aerobic groundwater turns anoxic in 8 months. • Sulfate reduction is the most important redox process thereafter. • Biologically enhanced dissolution of toluene and benzene is evidenced. • Stable carbon isotopes prove the degradation of benzene and ethylbenzene
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Ponsin, Violaine [Aix-Marseille Université-CNRS, Laboratoire Chimie Environnement FRE, 3416 Marseille (France); French Environment and Energy Management Agency, 20 avenue de Grésillé, BP 90406 Angers Cedex 01 (France); Maier, Joachim; Guelorget, Yves [ICF Environnement, 14/30 rue Alexandre Bâtiment C F, 92635 Gennevilliers (France); Hunkeler, Daniel; Bouchard, Daniel; Villavicencio, Hakeline [Centre for Hydrogeology, University of Neuchâtel, Rue Emile-Argand 11, CH-2000 Neuchâtel (Switzerland); Höhener, Patrick, E-mail: patrick.hohener@univ-amu.fr [Aix-Marseille Université-CNRS, Laboratoire Chimie Environnement FRE, 3416 Marseille (France)
2015-04-15
A pipeline transporting crude-oil broke in a nature reserve in 2009 and spilled 5100 m{sup 3} of oil that partly reached the aquifer and formed progressively a floating oil lens. Groundwater monitoring started immediately after the spill and crude-oil recovery by dual pump-and-skim technology was operated after oil lens formation. This study aimed at documenting the implementation of redox-specific natural attenuation processes in the saturated zone and at assessing whether dissolved compounds were degraded. Seven targeted water sampling campaigns were done during four years in addition to a routine monitoring of hydrocarbon concentrations. Liquid oil reached the aquifer within 2.5 months, and anaerobic processes, from denitrification to reduction of sulfate, were observable after 8 months. Methanogenesis appeared on site after 28 months. Stable carbon isotope analyses after 16 months showed maximum shifts in δ{sup 13}C of + 4.9 ± 0.22‰ for toluene, + 2.4 ± 0.19‰ for benzene and + 0.9 ± 0.51‰ for ethylbenzene, suggesting anaerobic degradation of these compounds in the source zone. Estimations of fluxes of inorganic carbon produced by biodegradation revealed that, in average, 60% of inorganic carbon production was attributable to sulfate reduction. This percentage tended to decrease with time while the production of carbon attributable to methanogenesis was increasing. Within the investigation time frame, mass balance estimations showed that biodegradation is a more efficient process for control of dissolved concentrations compared to pumping and filtration on an activated charcoal filter. - Highlights: • One of the world largest terrestrial oil spills is studied for 4 years. • Initially pristine aerobic groundwater turns anoxic in 8 months. • Sulfate reduction is the most important redox process thereafter. • Biologically enhanced dissolution of toluene and benzene is evidenced. • Stable carbon isotopes prove the degradation of benzene and
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Witkowski, Grzegorz; Sienkiewicz-Jarosz, Halina [Institute of Psychiatry and Neurology, 1st Department of Neurology, Warsaw (Poland); Piliszek, Agnieszka; Ryglewicz, Danuta [Central Clinical Hospital of the Ministry of Interior, Department of Radiology, Warsaw (Poland); Skierczynska, Agnieszka; Poniatowska, Renata [Institute of Psychiatry and Neurology, Department of Radiology, Warsaw (Poland); Dorobek, Malgorzata; Filipek-Gliszczynska, Anna [Central Clinical Hospital of the Ministry of Interior, Department of Neurology, Warsaw (Poland); Walecki, Jerzy [Polish Academy of Science, Mossakowski Medical Research Centre, Warsaw (Poland)
2014-10-15
The DWI/FLAIR mismatch is a potential radiological marker for the timing of stroke onset. The aim of the study was to assess if the DWI/FLAIR mismatch can help to identify patients with both lacunar and nonlacunar acute ischemic stroke within 4.5 h of onset. A retrospective study was performed in which the authors analysed data from 86 ischemic lacunar and nonlacunar stroke patients with a known time of symptom onset, imaged within the first 24 h from stroke onset (36 patients <4.5 h, 14 patients 4.5-6 h, 15 patients 6-12 h, and 21 patients 12-24 h). Patients underwent the admission CT and MR scan. The presence of lesions was assessed in correlation with the duration of the stroke. The time from stroke onset to neuroimaging was significantly shorter in patients with an ischemic lesion visible only in the DWI (mean 2.78 h, n = 24) as compared to patients with signs of ischemia also in other modalities (mean 8.6 h, n = 62) (p = 0.0001, Kruskal-Wallis ANOVA). The DWI/FLAIR mismatch was characterised by a global sensitivity of 58 %, specificity 94 %, PPV 87.5 %, and NPV 76 % in identifying patients in the 4.5 h thrombolysis time window. For lacunar strokes (n = 20), these parameters were as follows: sensitivity 50 %, specificity 92.8 %, PPV 75 %, and NPV 81.2 %. The presence of acute ischemic lesions only in DWI can help to identify both lacunar and nonlacunar stroke patients who are in the 4.5 h time window for intravenous thrombolysis with high specificity. (orig.)
International Nuclear Information System (INIS)
The DWI/FLAIR mismatch is a potential radiological marker for the timing of stroke onset. The aim of the study was to assess if the DWI/FLAIR mismatch can help to identify patients with both lacunar and nonlacunar acute ischemic stroke within 4.5 h of onset. A retrospective study was performed in which the authors analysed data from 86 ischemic lacunar and nonlacunar stroke patients with a known time of symptom onset, imaged within the first 24 h from stroke onset (36 patients <4.5 h, 14 patients 4.5-6 h, 15 patients 6-12 h, and 21 patients 12-24 h). Patients underwent the admission CT and MR scan. The presence of lesions was assessed in correlation with the duration of the stroke. The time from stroke onset to neuroimaging was significantly shorter in patients with an ischemic lesion visible only in the DWI (mean 2.78 h, n = 24) as compared to patients with signs of ischemia also in other modalities (mean 8.6 h, n = 62) (p = 0.0001, Kruskal-Wallis ANOVA). The DWI/FLAIR mismatch was characterised by a global sensitivity of 58 %, specificity 94 %, PPV 87.5 %, and NPV 76 % in identifying patients in the 4.5 h thrombolysis time window. For lacunar strokes (n = 20), these parameters were as follows: sensitivity 50 %, specificity 92.8 %, PPV 75 %, and NPV 81.2 %. The presence of acute ischemic lesions only in DWI can help to identify both lacunar and nonlacunar stroke patients who are in the 4.5 h time window for intravenous thrombolysis with high specificity. (orig.)
International Nuclear Information System (INIS)
The incidence of missed diagnoses of acute cardiac ischemia in the emergency department could be reduced by a new imaging modality. In the present study, the clinical significance of 99mTc-pyrophosphate (PYP), 123I-β-methyl-p-iodophenyl-pentadecanoic acid (BMIPP), 201TlCl scintigraphy (imaging) and T2-weighted inversion-recovery magnetic resonance imaging (MRI) for the detection of culprit lesion in patients with acute coronary syndromes (ACS) was compared. The study group comprised 18 patients with ACS: 12 patients with acute myocardial infarction (AMI) (11 males; mean age, 63±11 years) and 6 patients with unstable angina (UA) (3 males, mean age, 67±5 years). Of the 12 patients with AMI, 10 underwent 201TlCl and PYP single photon emission computed tomography (SPECT) studies as a dual-energy acquisition (201TlCl/PYP) and 8 underwent 201TlCl SPECT within 1 week of the BMIPP study. All 18 patients underwent BMIPP SPECT and MRI. The MRI pulse sequence was black blood turbo short-inversion-time inversion recovery (STIR) (breath-hold T2-weighted studies). The T2-weighted inversion-recovery MRI showed higher sensitivity and negative predictive value than PYP and 201TlCl, and higher specificity and positive predictive value than BMIPP and 201TlCl. The area under the receiver-operating characteristic curve for PYP, BMIPP, 201TlCl and MRI was 0.787, 0.725, 0.731 and 0.878, respectively. The difference between the areas of MRI and BMIPP was significant (p<0.05). Accurate detection of culprit lesion is improved by using MRI rather than BMIPP, particularly for patients with ACS. (author)
Stability of the Gauge Equivalent Classes in Inverse Stationary Transport in Refractive Media
McDowall, Stephen; Tamasan, Alex
2010-01-01
In the inverse stationary transport problem through anisotropic attenuating, scattering, and refractive media, the albedo operator stably determines the gauge equivalent class of the attenuation and scattering coefficients.
Muksin, Umar; Haberland, Christian; Bauer, Klaus; Weber, Michael
2013-12-01
The geothermal potential in Tarutung is controlled by both the Sumatra Fault system and young arc volcanism. In this study we use the spatial distribution of seismic attenuation, calculated from local earthquake recordings, to image the 3-D seismic attenuation of the area and relate it with the temperature anomalies and the fluid distribution of the subsurface. A temporary seismic network of 42 stations was deployed around Tarutung and Sarulla (south of Tarutung) for a period of 10 months starting in 2011 May. Within this period, the network recorded 2586 local events. A high-quality subset of 229 events recorded by at least 10 stations was used for the attenuation inversion (tomography). Path-average attenuation (tp^{*}) was calculated by using a spectral inversion method. The spread function, the contour lines of the model resolution matrix and the recovery test results show that our 3-D attenuation model (Qp) has good resolution around the Tarutung Basin and along the Sarulla graben. High attenuation (low Qp) related to the geothermal system is found in the northeast of the Tarutung Basin suggesting fluid pathways from below the Sumatra Fault. The upper part of the studied geothermal system in the Tarutung district seems to be mainly controlled by the fault structure rather than by magmatic activities. In the southwest of the Tarutung Basin, the high attenuation zone is associated with the Martimbang volcano. In the Sarulla region, a low-Qp anomaly is found along the graben within the vicinity of the Hopong caldera.
International Nuclear Information System (INIS)
This technical note demonstrates the relevance of the isotropic 3D T2 turbo-spin-echo (TSE) sequence with short-term inversion recovery (STIR) and variable flip angle RF excitations (SPACE: Sampling Perfection with Application optimized Contrasts using different flip angle Evolutions) for high-resolution brachial plexus imaging. The sequence was used in 11 patients in the diagnosis of brachial plexus pathologies involving primary and secondary tumors, and in six volunteers. We show that 3D STIR imaging is not only a reliable alternative to 2D STIR imaging, but it also better evaluates the anatomy, nerve site compression and pathology of the plexus, especially to depict space-occupying tumors along its course. Finally, due to its appropriate contrast we describe how 3D-STIR can be used as a high-resolution mask to be fused with fraction of anisotropy (FA) maps calculated from diffusion tensor imaging (DTI) data of the plexus. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Viallon, M.; Vargas, M.I.; Jlassi, H.; Loevblad, K.O.; Delavelle, J. [University Hospital of Geneva, Department of Radiology, Geneva (Switzerland)
2008-05-15
This technical note demonstrates the relevance of the isotropic 3D T2 turbo-spin-echo (TSE) sequence with short-term inversion recovery (STIR) and variable flip angle RF excitations (SPACE: Sampling Perfection with Application optimized Contrasts using different flip angle Evolutions) for high-resolution brachial plexus imaging. The sequence was used in 11 patients in the diagnosis of brachial plexus pathologies involving primary and secondary tumors, and in six volunteers. We show that 3D STIR imaging is not only a reliable alternative to 2D STIR imaging, but it also better evaluates the anatomy, nerve site compression and pathology of the plexus, especially to depict space-occupying tumors along its course. Finally, due to its appropriate contrast we describe how 3D-STIR can be used as a high-resolution mask to be fused with fraction of anisotropy (FA) maps calculated from diffusion tensor imaging (DTI) data of the plexus. (orig.)
Theory of standing spin-wave attenuation
International Nuclear Information System (INIS)
Exchange attenuation of standing spin waves is calculated for an ultrathin magnetic of the order of exchange length thick. Because of the boundary conditions the wave vectors of spin waves in such films high values that are proportional to the inverse film thickness. The exchange attenuation at such wave vectors becomes dominant and can result in smearing of the standing spin wave spectrum
Robins-Steele, Sherri; Nguyen, Dung Hoang; Fehlings, Michael G
2012-05-20
Spinal cord injury (SCI) is a devastating condition that currently lacks clinically-relevant and effective neuroprotective therapeutic options. Optimal therapeutic agents for clinical translation should show efficacy in a cervical compression/contusion model using a clinically-relevant post-injury therapeutic time window. To date, few compounds have met that rigorous standard. The objective of this work was to evaluate the efficacy of delayed post-injury administration of soluble Fas receptor (sFasR) via intrathecal catheter following acute cervical SCI in a clinically-relevant contusion/compression model. Female Wistar rats were given a C7-T1 moderately severe clip compression injury, followed by either 8-h or 24-h delayed treatment initiation. Long-term neurobehavioral analysis of motor recovery and neuropathic pain development was undertaken. The extent of oligodendrocyte and neuron survival was assessed in peri-lesional cord sections 8 weeks post-SCI. This was complemented by an evaluation of the level of tissue preservation at and adjacent to the site of injury. In animals treated with sFasR delayed 8 h post-injury, significant behavioral effects were observed, coinciding with enhanced cell survival, peri-lesional tissue sparing, and enhanced integrity of descending fiber tracts compared to control treatments. Animals treated with sFasR delayed by 24 h showed more modest improvements in behavioral recovery, and had consistent improvements in cell survival and tissue preservation. This work has shown for the first time that the Fas-mediated apoptotic pathway can be therapeutically targeted in a clinically-relevant time window post-SCI. PMID:22260324
2007-01-01
This media offers the student a chance to review how to exploit differential flatness of the system and emply inverse dynamics in the virtual domain to compute the states and controls that were not approximated with the reference functions. Last modified: 5/18/2009
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Hauer, M.P.; Uhl, M.; Allmann, K.H.; Laubenberger, J.; Langer, M. [Freiburg Univ. (Germany). Radiologische Universitaetsklinik; Zimmerhackl, L.B. [Kinderklinik der Albert-Ludwigs-Univ. Freiburg (Germany)
1998-11-01
Objective. To compare turbo inversion recovery magnitude (TIRM) with standard T1-weighted (T1-W) and T2-weighted (T2-W) MR sequences in the very early detection of acute osteomyelitis in children. Materials and methods. In 15 children with osteomyelitis, 15 sets of T1-W spin-echo (SE) (TR/TE, 400-640/12-17), T2-W turbo spin-echo (TSE) (TR/TE/ETL, 3290-4465/112-120/11), and TIRM (TR/TE/TI, 4000-6120/60/160) images were acquired with a 1.0-T magnet. Contrast-to-noise (C/N) ratios and percentage of signal between lesion and normal bone marrow were analysed with a computer-assisted image analysing system in a region of interest (ROI). Results. In 13 of 15 patients, the absolute signal enhancement in a ROI on the TIRM images was better than on the T1-W SE and T2-W TSE images and in 14 of 15 cases, C/N ratios were also better on the TIRM images than on the other sequences. In the other cases, the TIRM signal was diagnostically equivalent. On the TIRM images, the signal difference between normal and pathological tissue was increased to 43-281 % (mean 124 %). On the T2-W TSE images, this signal difference was 4-79 % (mean 36 %) and on the T1-W SE images 6-77 % (mean 37 %). Conclusion. The TIRM sequence is highly sensitive for detecting bone marrow oedema in the very early stage of acute osteomyelitis in children. MRI utilising the TIRM sequence allowed for an early diagnosis. With scan time of less than 4 minutes, this sequence is superior to T1-W SE and T2-W TSE images for detecting early osteomyelitis-associated bone marrow oedema. (orig.) With 3 figs., 2 tabs., 15 refs.
International Nuclear Information System (INIS)
Objective. To compare turbo inversion recovery magnitude (TIRM) with standard T1-weighted (T1-W) and T2-weighted (T2-W) MR sequences in the very early detection of acute osteomyelitis in children. Materials and methods. In 15 children with osteomyelitis, 15 sets of T1-W spin-echo (SE) (TR/TE, 400-640/12-17), T2-W turbo spin-echo (TSE) (TR/TE/ETL, 3290-4465/112-120/11), and TIRM (TR/TE/TI, 4000-6120/60/160) images were acquired with a 1.0-T magnet. Contrast-to-noise (C/N) ratios and percentage of signal between lesion and normal bone marrow were analysed with a computer-assisted image analysing system in a region of interest (ROI). Results. In 13 of 15 patients, the absolute signal enhancement in a ROI on the TIRM images was better than on the T1-W SE and T2-W TSE images and in 14 of 15 cases, C/N ratios were also better on the TIRM images than on the other sequences. In the other cases, the TIRM signal was diagnostically equivalent. On the TIRM images, the signal difference between normal and pathological tissue was increased to 43-281 % (mean 124 %). On the T2-W TSE images, this signal difference was 4-79 % (mean 36 %) and on the T1-W SE images 6-77 % (mean 37 %). Conclusion. The TIRM sequence is highly sensitive for detecting bone marrow oedema in the very early stage of acute osteomyelitis in children. MRI utilising the TIRM sequence allowed for an early diagnosis. With scan time of less than 4 minutes, this sequence is superior to T1-W SE and T2-W TSE images for detecting early osteomyelitis-associated bone marrow oedema. (orig.)
Multiscale full waveform inversion
Fichtner, Andreas; Trampert, Jeannot; Cupillard, Paul; Saygin, Erdinc; Taymaz, Tuncay; Capdeville, Yann; Villaseñor, Antonio
2013-07-01
We develop and apply a full waveform inversion method that incorporates seismic data on a wide range of spatio-temporal scales, thereby constraining the details of both crustal and upper-mantle structure. This is intended to further our understanding of crust-mantle interactions that shape the nature of plate tectonics, and to be a step towards improved tomographic models of strongly scale-dependent earth properties, such as attenuation and anisotropy. The inversion for detailed regional earth structure consistently embedded within a large-scale model requires locally refined numerical meshes that allow us to (1) model regional wave propagation at high frequencies, and (2) capture the inferred fine-scale heterogeneities. The smallest local grid spacing sets the upper bound of the largest possible time step used to iteratively advance the seismic wave field. This limitation leads to extreme computational costs in the presence of fine-scale structure, and it inhibits the construction of full waveform tomographic models that describe earth structure on multiple scales. To reduce computational requirements to a feasible level, we design a multigrid approach based on the decomposition of a multiscale earth model with widely varying grid spacings into a family of single-scale models where the grid spacing is approximately uniform. Each of the single-scale models contains a tractable number of grid points, which ensures computational efficiency. The multi-to-single-scale decomposition is the foundation of iterative, gradient-based optimization schemes that simultaneously and consistently invert data on all scales for one multi-scale model. We demonstrate the applicability of our method in a full waveform inversion for Eurasia, with a special focus on Anatolia where coverage is particularly dense. Continental-scale structure is constrained by complete seismic waveforms in the 30-200 s period range. In addition to the well-known structural elements of the Eurasian mantle
Dickinson, R. M.; Hardy, J. C.
1969-01-01
Radio frequency attenuator, having negligible insertion loss at minimum attenuation, can be used for making precise antenna gain measurements. It is small in size compared to a rotary-vane attenuator.
Cortical edema in moderate fluid percussion brain injury is attenuated by vagus nerve stimulation.
Clough, R W; Neese, S L; Sherill, L K; Tan, A A; Duke, A; Roosevelt, R W; Browning, R A; Smith, D C
2007-06-29
Development of cerebral edema (intracellular and/or extracellular water accumulation) following traumatic brain injury contributes to mortality and morbidity that accompanies brain injury. Chronic intermittent vagus nerve stimulation (VNS) initiated at either 2 h or 24 h (VNS: 30 s train of 0.5 mA, 20 Hz, biphasic pulses every 30 min) following traumatic brain injury enhances recovery of motor and cognitive function in rats in the weeks following brain injury; however, the mechanisms of facilitated recovery are unknown. The present study examines the effects of VNS on development of acute cerebral edema following unilateral fluid percussion brain injury (FPI) in rats, concomitant with assessment of their behavioral recovery. Two hours following FPI, VNS was initiated. Behavioral testing, using both beam walk and locomotor placing tasks, was conducted at 1 and 2 days following FPI. Edema was measured 48 h post-FPI by the customary method of region-specific brain weights before and after complete dehydration. Results of this study replicated that VNS initiated at 2 h after FPI: 1) effectively facilitated the recovery of vestibulomotor function at 2 days after FPI assessed by beam walk performance (P<0.01); and 2) tended to improve locomotor placing performance at the same time point (P=0.18). Most interestingly, results of this study showed that development of edema within the cerebral cortex ipsilateral to FPI was significantly attenuated at 48 h in FPI rats receiving VNS compared with non-VNS FPI rats (P<0.04). Finally, a correlation analysis between beam walk performance and cerebral edema following FPI revealed a significant inverse correlation between behavior performance and cerebral edema. Together, these results suggest that VNS facilitation of motor recovery following experimental brain injury in rats is associated with VNS-mediated attenuation of cerebral edema. PMID:17543463
Zhang, D. L.
2013-01-01
To increase the illumination of the subsurface and to eliminate the dependency of FWI on the source wavelet, we propose multiples waveform inversion (MWI) that transforms each hydrophone into a virtual point source with a time history equal to that of the recorded data. These virtual sources are used to numerically generate downgoing wavefields that are correlated with the backprojected surface-related multiples to give the migration image. Since the recorded data are treated as the virtual sources, knowledge of the source wavelet is not required, and the subsurface illumination is greatly enhanced because the entire free surface acts as an extended source compared to the radiation pattern of a traditional point source. Numerical tests on the Marmousi2 model show that the convergence rate and the spatial resolution of MWI is, respectively, faster and more accurate then FWI. The potential pitfall with this method is that the multiples undergo more than one roundtrip to the surface, which increases attenuation and reduces spatial resolution. This can lead to less resolved tomograms compared to conventional FWI. The possible solution is to combine both FWI and MWI in inverting for the subsurface velocity distribution.
Inverse problems of geophysics
International Nuclear Information System (INIS)
This report gives an overview and the mathematical formulation of geophysical inverse problems. General principles of statistical estimation are explained. The maximum likelihood and least square fit methods, the Backus-Gilbert method and general approaches for solving inverse problems are discussed. General formulations of linearized inverse problems, singular value decomposition and properties of pseudo-inverse solutions are given
Fat Attenuation at CT in Anorexia Nervosa.
Gill, Corey M; Torriani, Martin; Murphy, Rachel; Harris, Tamara B; Miller, Karen K; Klibanski, Anne; Bredella, Miriam A
2016-04-01
Purpose To investigate the composition, cross-sectional area (CSA), and hormonal correlates of different fat depots in women with anorexia nervosa (AN) and control subjects with normal weights to find out whether patients with AN have lower fat CSA but higher attenuation than did control subjects and whether these changes may be mediated by gonadal steroids, cortisol, and thyroid hormones. Materials and Methods This study was institutional review board approved and HIPAA compliant. Written informed consent was obtained. Forty premenopausal women with AN and 40 normal-weight women of comparable age (mean age ± standard deviation, 26 years ± 5) were studied. All individuals underwent computed tomography of the abdomen and thigh with a calibration phantom. Abdominal subcutaneous adipose tissue (SAT), visceral adipose tissue (VAT), thigh SAT, and thigh intermuscular adipose tissue CSA and attenuation were quantified. Serum estradiol, thyroid hormones, and urinary free cortisol levels were assessed. Variables were compared by using analysis of variance. Associations were examined by using linear regression analysis. Results Women with AN had higher fat attenuation than did control subjects (-100.1 to -46.7 HU vs -117.6 to -61.8 HU, P < .0001), despite lower fat CSA (2.0-62.8 cm(2) vs 5.5-185.9 cm(2), P < .0001). VAT attenuation but not CSA was inversely associated with lowest prior lifetime body mass index in AN (r = -0.71, P = .006). Serum estradiol levels were inversely associated with fat attenuation (r = -0.34 to -0.61, P = .03 to <.0001) and were positively associated with fat CSA of all compartments (r = 0.42-0.64, P = .007 to <.0001). Thyroxine levels and urinary free cortisol levels were positively associated with thigh SAT attenuation (r = 0.64 [P = .006] and r = 0.68 [P = .0004], respectively) and were inversely associated with abdominal SAT and VAT CSA (r = -0.44 to -0.58, P = .04 to .02). Conclusion Women with AN have differences in fat composition, with
Hargrove, Douglas L.
2004-09-14
A portable, hand-held meter used to measure direct current (DC) attenuation in low impedance electrical signal cables and signal attenuators. A DC voltage is applied to the signal input of the cable and feedback to the control circuit through the signal cable and attenuators. The control circuit adjusts the applied voltage to the cable until the feedback voltage equals the reference voltage. The "units" of applied voltage required at the cable input is the system attenuation value of the cable and attenuators, which makes this meter unique. The meter may be used to calibrate data signal cables, attenuators, and cable-attenuator assemblies.
Attenuation Tomography of the Upper Mantle
Adenis, A.; Debayle, E.; Ricard, Y. R.
2014-12-01
We present a 3-D model of surface wave attenuation in the upper mantle. The model is constrained by a large data set of fundamental and higher Rayleigh mode observations. This data set consists of about 1,800,000 attenuation curves measured in the period range 50-300s by Debayle and Ricard (2012). A careful selection allows us to reject data for which measurements are likely biased by the poor knowledge of the scalar seismic moment or by a ray propagation too close to a node of the source radiation pattern. For each epicenter-station path, elastic focusing effects due to seismic heterogeneities are corrected using DR2012 and the data are turned into log(1/Q). The selected data are then combined in a tomographic inversion using the non-linear least square formalism of Tarantola and Valette (1982). The obtained attenuation maps are in agreement with the surface tectonic for periods and modes sensitive to the top 200km of the upper mantle. Low attenuation regions correlate with continental shields while high attenuation regions are located beneath young oceanic regions. The attenuation pattern becomes more homogeneous at depths greater than 200 km and the maps are dominated by a high quality factor signature beneath slabs. We will discuss the similarities and differences between the tomographies of seismic velocities and of attenuations.
Importance of Attenuation Correction (AC for Small Animal PET Imaging
Directory of Open Access Journals (Sweden)
Henrik H. El Ali
2012-10-01
Full Text Available The purpose of this study was to investigate whether a correction for annihilation photon attenuation in small objects such as mice is necessary. The attenuation recovery for specific organs and subcutaneous tumors was investigated. A comparison between different attenuation correction methods was performed. Methods: Ten NMRI nude mice with subcutaneous implantation of human breast cancer cells (MCF-7 were scanned consecutively in small animal PET and CT scanners (MicroPETTM Focus 120 and ImTek’s MicroCATTM II. CT-based AC, PET-based AC and uniform AC methods were compared. Results: The activity concentration in the same organ with and without AC revealed an overall attenuation recovery of 9–21% for MAP reconstructed images, i.e., SUV without AC could underestimate the true activity at this level. For subcutaneous tumors, the attenuation was 13 ± 4% (9–17%, for kidneys 20 ± 1% (19–21%, and for bladder 18 ± 3% (15–21%. The FBP reconstructed images showed almost the same attenuation levels as the MAP reconstructed images for all organs. Conclusions: The annihilation photons are suffering attenuation even in small subjects. Both PET-based and CT-based are adequate as AC methods. The amplitude of the AC recovery could be overestimated using the uniform map. Therefore, application of a global attenuation factor on PET data might not be accurate for attenuation correction.
Institute of Scientific and Technical Information of China (English)
邢栋; 查云飞; 刘昌盛; 王克军; 龚威; 闫力永
2014-01-01
目的 探讨反转时间(TI)对流动敏感性交互反转恢复(FAIR)序列脊柱骨髓灌注成像的影响,并评价该技术测量脊柱骨髓血流量(BF)的可重复性.方法 前瞻性收集24名经临床和腰椎MRI检查除外全身疾病和腰椎病变的健康志愿者进行观察.前14名志愿者行脊柱骨髓FAIR序列TI值优化研究,后10名志愿者行脊柱骨髓BF的可重复性研究.14名健康志愿者从L1～ L5椎体内选取2个相邻椎体行横断而FAIR扫描,TI值分别为800、1 000、1 200、1 400、1 600 ms,计算不同TI时椎体骨髓灌注的信号强度变化值(△M)和信噪比(SNR).10名健康志愿者选取L4或L5椎体行2次FAIR序列扫描,参数相同(TI值为1 200 ms),测量同一椎体前后2次FAIR扫描生成的BF值,并采用配对t检验及重复性分析评价2次测量的可重复性.结果 14名志愿者采用FAIR序列共扫描28个椎体,TI值分别为800、1 000、1 200、1 400、1 600 ms时,△M值分别为20.8±9.0、29.0± 10.9、36.4± 12.5、26.2±10.2和23.8±11.5,SNR分别为2.0±1.0、2.3±0.8、2.4±1.0、2.3±0.8和2.0±0.7,脊柱骨髓灌注△M值及SNR值,随TI值升高而呈现先升高后下降的趋势,TI为1 200 ms时达到高峰.10名志愿者前后2次扫描所得的椎体骨髓灌注的血流量BF值分别为(108.9±4.6)和(109.2±4.6)ml·10Og-1·min-1,差异无统计学意义(t=-0.157,P=0.879).前后2次扫描间个体间变异系数wCV为3.28％(3.57/109.06),可重复性良好.结论 TI值为1 200 ms时,脊柱椎体骨髓△M最大,灌注图像SNR最高,测量脊柱骨髓BF的可重复性好.%Objective To investigate the effect of inversion time (TI) on flow-sensitive alternating inversion recovery (FAIR) perfusion imaging of spinal bone marrow (SBM),and evaluate the reproducibility of blood flow (BF) measurements using this technique.Methods Twenty four healthy volunteers without lumbar and other disease with clinical and MR studies were prospectively included.The first 14 healthy
Particle size characterization by ultrasonic attenuation spectra
Institute of Scientific and Technical Information of China (English)
Mingxu Su; Minghua Xue; Xiaoshu Cai; Zhitao Shang; Feng Xu
2008-01-01
This paper contributes to extracting information from signals of broadband ultrasonic attenuation spectrum for effective utilization in particle size characterization. The single particle scattering model and the coupled-phase model are formulated simultaneously, the relationship between particle size distribution and ultrasonic spectrum is established, and a convergence criterion for calculation is quantified. Demonsa'ation inversion by the optimum regularization factor method is carded out to yield typical numerical results for discussion. With the experimental set-up developed by the Institute of Particle and Two-Phase Flow Measurement (IPTFM) at the University of Shanghai for Science and Technology, sand sediment particle size is measured by attenuation spectrum and analyzed using the above inversion algorithm and theoretical models. To validate the proposed ultrasonic spectrum particle sizing method, results are compared with those obtained by microscopy.
Christie, Alan M.; Snyder, Kurt I.
1985-01-01
A pressure surge attenuation system for pipes having a fluted region opposite crushable metal foam. As adapted for nuclear reactor vessels and heads, crushable metal foam is disposed to attenuate pressure surges.
International Nuclear Information System (INIS)
AIM: The aim of this study was to compare the performance of three fluid attenuated inversion recovery (FLAIR) pulse sequences for control of cerebrospinal fluid (CSF) and blood flow artifacts in imaging of the brain. The first of these sequences had an initial sinc inversion pulse which was followed by conventional k-space mapping. The second had an initial sinc inversion pulse followed by k-space re-ordered by inversion time at each slice position (KRISP) and the third had an adiabatic initial inversion pulse followed by KRISP. MATERIALS AND METHODS: Ten patients with established disease were studied with all three pulse sequences. Seven were also studied with the adiabatic KRISP sequence after contrast enhancement. Their images were evaluated for patient motion artifact, CSF and blood flow artifact as well as conspicuity of the cortex, meninges, ventricular system, brainstem and cerebellum. The conspicuity of lesions and the degree of enhancement were also evaluated. RESULTS: Both the sinc and adiabatic KRISP FLAIR sequences showed better control of CSF and blood flow artifacts than the conventional FLAIR sequence. In addition the adiabatic KRISP FLAIR sequence showed better control of CSF artifact at the inferior aspect of the posterior fossa. The lesion conspicuity was similar for each of the FLAIR sequences as was the degree of contrast enhancement to that shown with a T1weighted spin echo sequence. CONCLUSION: The KRISP FLAIR sequence controls high signal artifacts from CSF flow and blood flow and the adiabatic pulse controls high signal artifacts due to inadequate inversion of the CSF magnetization at the periphery of the head transmitter coil. The KRISP FLAIR sequence also improves cortical and meningeal definition as a result of an edge enhancement effect. The effects are synergistic and can be usefully combined in a single pulse sequence. Curati, W.L. et al. (2001)
Photonic Crystal Fiber Attenuator
Institute of Scientific and Technical Information of China (English)
Joo Beom Eom; Hokyung Kim; Jinchae Kim; Un-Chul Paek; Byeong Ha Lee
2003-01-01
We propose a novel fiber attenuator based on photonic crystal fibers. The difference in the modal field diameters of a conventional single mode fiber and a photonic crystal fiber was used. A variable optical attenuator was also achieved by applying macro-bending on the PCF part of the proposed attenuator
A NEW INVERSION METHOD OF TIME-LAPSE SEISMIC
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
Time-Lapse Seismic improves oil recovery ratio by dynamic reservoir monitoring. Because of the large number of seismic explorations in the process of time-lapse seismic inversion, traditional methods need plenty of inversion calculations which cost high computational works. The method is therefore inefficient. In this paper, in order to reduce the repeating computations in traditional, a new time-lapse seismic inversion method is put forward. Firstly a homotopy-regularization method is proposed for the first time inversion. Secondly, with the first time inversion results as the initial value of following model, a model of the second time inversion is rebuilt by analyzing the characters of time-lapse seismic and localized inversion method is designed by using the model. Finally, through simulation, the comparison between traditional method and the new scheme is given. Our simulation results show that the new scheme could save the algorithm computations greatly.
Research on Nanosecond Pulse Corona Discharge Attenuation
International Nuclear Information System (INIS)
A line-to-plate reactor was set-up in the experimental study on the application of nanosecond pulsed corona discharge plasma technology in environmental pollution control. Investigation on the attenuation and distortion of the amplitude of the pulse wave front and the discharge image as well as the waveform along the corona wire was conducted. The results show that the wave front decreases sharply during the corona discharge along the corona wire. The higher the amplitude of the applied pulse is, the more the amplitude of the wave front decreased. The wave attenuation responds in a lower corona discharge inversely. To get a higher efficiency of the line-to-plate reactor a sharp attenuation of the corona has to be considered in practical design
Research on Nanosecond Pulse Corona Discharge Attenuation
Institute of Scientific and Technical Information of China (English)
HE Zheng-hao; XU Huai-li; BAI Jing; YU Fu-sheng; HU Feng; LI Jin
2007-01-01
A line-to-plate reactor was set-up in the experimental study on the application of nanosecond pulsed corona discharge plasma technology in environmental pollution control.Investigation on the attenuation and distortion of the amplitude of the pulse wave front and the discharge image as well as the waveform along the corona wire was conducted.The results show that the wave front decreases sharply during the corona discharge along the corona wire.The higher the amplitude of the applied pulse is,the more the amplitude of the wave front decreased.The wave attenuation responds in a lower corona discharge inversely.To get a higher efficiency of the line-to-plate reactor a sharp attenuation of the corona has to be considered in practical design.
Attenuated radon transform: theory and application in medicine and biology
Energy Technology Data Exchange (ETDEWEB)
Gullberg, G.T.
1979-06-01
A detailed analysis is given of the properties of the attenuated Radon transform and of how increases in photon attenuation influence the numerical accuracy and computation efficiency of iterative and convolution algorithms used to determine its inversion. The practical applications for this work involve quantitative assessment of the distribution of injected radiopharmaceuticals and radionuclides in man and animals for basic physiological and biochemical studies as well as clinical studies in nuclear medicine. A mathematical structure is developed using function theory and the theory of linear operators on Hilbert spaces which lends itself to better understanding the spectral properties of the attenuated Radon transform. The continuous attenuated Radon transform reduces to a matrix operator for discrete angular and lateral sampling, and the reconstruction problem reduces to a system of linear equations. For the situation of variable attenuation coefficient frequently found in nuclear medicine applications of imaging the heart and chest, the procedure developed in this thesis involves iterative techniques of performing the generalized inverse. For constant attenuation coefficient less than 0.15 cm/sup -1/, convolution methods can reliably reconstruct a 30 cm object with 0.5 cm resolution. However, for high attenuation coefficients or for the situation where there is variable attenuation such as reconstruction of distribution of isotopes in the heart, iterative techniques developed in this thesis give the best results. (ERB)
Inverse Quadratic Transportation Problem
Jalilzadeh, Afrooz; Hamedani, Erfan Yazdandoost
2014-01-01
Many research has been conducted about quadratic programming and inverse optimization. In this paper we present the combination aspect of these subjects, applying on transportation problem. First, we obtain the inverse form of quadratic tranportation problem under $L_1$ norm by using duality as well as introducing the optimal value. Then, we do the same process for inverse quadratic transportation problem (IQTP) under $L_\\infty$ norm.
Acute puerperal uterine inversion
International Nuclear Information System (INIS)
Objective: To determine the frequency, causes, clinical presentations, management and maternal mortality associated with acute puerperal inversion of the uterus. Materials and Methods: All the patients who developed acute puerperal inversion of the uterus either in or outside the JPMC were included in the study. Patients of chronic uterine inversion were not included in the present study. Abdominal and vaginal examination was done to confirm and classify inversion into first, second or third degrees. Results: 57036 deliveries and 36 acute uterine inversions occurred during the study period, so the frequency of uterine inversion was 1 in 1584 deliveries. Mismanagement of third stage of labour was responsible for uterine inversion in 75% of patients. Majority of the patients presented with shock, either hypovolemic (69%) or neurogenic (13%) in origin. Manual replacement of the uterus under general anaesthesia with 2% halothane was successfully done in 35 patients (97.5%). Abdominal hysterectomy was done in only one patient. There were three maternal deaths due to inversion. Conclusion: Proper education and training regarding placental delivery, diagnosis and management of uterine inversion must be imparted to the maternity care providers especially to traditional birth attendants and family physicians to prevent this potentially life-threatening condition. (author)
Inverse agonism and its therapeutic significance
Directory of Open Access Journals (Sweden)
Gurudas Khilnani
2011-01-01
2A inverse agonist, attenuates psychosis in patients with Parkinson′s disease with psychosis and is devoid of extrapyramidal side effects. This dissociation is also evident from the development of anxioselective benzodiazepines devoid of habit-forming potential. Hemopressin is a peptide ligand that acts as an antagonist as well as inverse agonist. This agent acts as an antinociceptive agent in different in vivo models of pain. Treatment of obesity by drugs having inverse agonist activity at CB 1/2 receptors is also underway. An exciting development is evaluation of β-blockers in chronic bronchial asthma-a condition akin to congestive heart failure where β-blockade has become the standard mode of therapy. Synthesis and evaluation of selective agents is underway. Therefore, inverse agonism is an important aspect of drug-receptor interaction and has immense untapped therapeutic potential.
Foltyn, Stephen R.
1988-01-01
The disclosure relates to low loss, high power variable attenuators comprng one or more transmissive and/or reflective multilayer dielectric filters. The attenuator is particularly suitable to use with unpolarized lasers such as excimer lasers. Beam attenuation is a function of beam polarization and the angle of incidence between the beam and the filter and is controlled by adjusting the angle of incidence the beam makes to the filter or filters. Filters are selected in accordance with beam wavelength.
INVERSE SCATTERING PROBLEMS BY SINGULAR SOURCE METHODS
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
The inverse scattering problems are to detect the property of obstacles from the measurements outside the obstacles. One of important research areas in this topic is the recovery of boundary property for impenetrable obstacles. In this paper, we would like to give a brief review about the recently developed singular source methods. There are three different methods in this category, namely, linear sampling method, pointsource method and probe method. We also present some recent new results about the probe method.
Inverse osmotic process for radioactive laundry waste
International Nuclear Information System (INIS)
Purpose: To effectively recover the processing amount reduced in a continuous treatment. Method: Laundry waste containing radioactive substances discharged from a nuclear power plant is processed in an inverse osmotic process while adding starch digesting enzymes such as amylase and takadiastase, as well as soft spherical bodies such as sponge balls of a particle diameter capable of flowing in the flow of the liquid wastes along the inverse osmotic membrane pipe and having such a softness and roundness as not to damage the inverse osmotic membrane. This process can remove the floating materials such as thread dusts or hairs deposited on the membrane surface by the action of the soft elastic balls and remove paste or the like through decomposition by the digesting enzymes. Consequently, effective recovery can be attained for the reduced processing amount. (Furukawa, Y.)
Gladwell, Graham ML
2011-01-01
The papers in this volume present an overview of the general aspects and practical applications of dynamic inverse methods, through the interaction of several topics, ranging from classical and advanced inverse problems in vibration, isospectral systems, dynamic methods for structural identification, active vibration control and damage detection, imaging shear stiffness in biological tissues, wave propagation, to computational and experimental aspects relevant for engineering problems.
Labouze, Xavier
2013-01-01
The Inverse 3-SAT problem is known to be coNP Complete. This article shows a new interesting way to solve directly the problem by using closure under resolution and partial assignment properties. An algorithm is proposed which lets solve the (co)Inverse 3-SAT problem.
Inverse Kinematics using Quaternions
DEFF Research Database (Denmark)
Henriksen, Knud; Erleben, Kenny; Engell-Nørregård, Morten
In this project I describe the status of inverse kinematics research, with the focus firmly on the methods that solve the core problem. An overview of the different methods are presented Three common methods used in inverse kinematics computation have been chosen as subject for closer inspection....
0-Semidistributive Inverse Semigroups
Institute of Scientific and Technical Information of China (English)
田振际
2004-01-01
@@ For an inverse semigroup S, the set L(S) of all inverse subsemigroups (including the empty set) of S forms a lattice with respect to intersection denoted as usual by ∩ and union, where the union is the inverse subsemigroup generated by inverse subsemigroups A, B of S. The set LF(S) of all full inverse subsemigroups of S forms a complete sublattice of L(S), with Es as zero element (Es is the set of all idempotent of S)(see [3,5,6]). Note, that if S a group, then LF(S)=L(S), its lattice of all subgroups of S. If S = G0 is a group with adjoined zero, then clearly LF(S) ≌ L(G).
A quaternionic approach to x-ray transform inversion in R{sup 3}
Energy Technology Data Exchange (ETDEWEB)
Fathi, S M Saberi; Truong, T T [Laboratoire de Physique Theorique et Modelisation, Universite de Cergy-Pontoise, 95302 Cergy-Pontoise (France); Nguyen, M K [Equipes Traitement de l' Image et Systemes, Universite de Cergy-Pontoise, 95302 Cergy-Pontoise (France)], E-mail: majid.saberi@u-cergy.fr, E-mail: truong@u-cergy.fr, E-mail: nguyen@ensea.fr
2009-10-16
A new derivation of the inverse of the x-ray transform is presented based on quaternion analysis. As pointed out by practitioners, a direct inversion formula offers more efficient reconstruction algorithms than tomographic inversion. It is shown that the new inverse formula is equivalent to the existing one. The advantage of this approach is that it paves the way for a potential inversion of the x-ray transform with a non-uniform attenuation map in three dimensions, which models single photon emission imaging in nuclear medicine.
Institute of Scientific and Technical Information of China (English)
张韶辉; 秦林娣; 陆钦池
2014-01-01
Objective:To investigate the imaging feature and diagnostic value of double invesion recov-ery (DIR) MR imaging in intractable epilepsy.Method: The clinical data,EEG and imaging manifestation of 7 cases with intractable epilepsy were retrospectively analyzed on the signal intensity on DIR sequence . Result:Abnormal DIR signal intensities of the DIR images were observed in 6 patients with complex partial seizure , none of abnormal DIR signal intensities of the DIR images was observed in 1 patient with generalized tonic clonic seizure .Conclusion: DIR can show superior delineation of gray matter and white matter .DIR MR imaging can be valuable for characterizing epileptic foci and may contribute to presurgical evaluation in the intractable epilepsy patients .%目的：探讨 MR双反转恢复（ DIR）序列在难治性癫痫定位诊断中的价值。分析DIR显示难治性癫痫患者灰质、白质结构的改变。方法：回顾性分析7例难治性癫痫患者的临床、脑电图和影像学资料，观察患者在DIR上的表现。结果：6例复杂部分发作的患者在DIR上发现异常信号，1例全面性发作的癫痫患者在影像学上未发现异常。结论：DIR序列能突出显示灰质和白质结构，灰白质对比度高，对难治性癫痫术前定位诊断具有一定的价值。
Preston, W
2009-01-01
Packed with practical, freely available backup and recovery solutions for Unix, Linux, Windows, and Mac OS X systems -- as well as various databases -- this new guide is a complete overhaul of Unix Backup & Recovery by the same author, now revised and expanded with over 75% new material.
Clark, John R.
2007-01-01
Since the founding of Alcoholics Anonymous (AA) in 1935, programs offering opportunity for recovery from alcoholism and other addictions have undergone vast changes. The Internet has created nearly limitless opportunities for recovering people and those seeking recovery to find both meetings and places where they can gather virtually and discuss…
Multi-level, Multi-frequency, compressed Full Waveform Inversion
Faucher, Florian; V. de Hoop, Maarten; Calandra, Henri; Qiu, Lingyun; Rivera, Christian
2013-01-01
We study the inverse boundary value problem for the wave equation and recovery of the wavespeedupon taking a time-Fourier transform of the data. We design a hierarchical compressed reconstruction in a multi-level scheme for the inverse boundary value problem associated with the Helmholtz equation using the Dirichlet-to-Neumann map, or the single-layer potential operator, at selected frequencies as the data. The compression isbased on a domain partitioning of the subsurface, while the hierarch...
Inversion flachseismischer Wellenfeldspektren
Forbriger, Thomas
2001-01-01
In dieser Arbeit stelle ich ein neues Verfahren zur Inversion flachseismischer Wellenfelder vor. Die Inversion erfolgt in zwei Schritten. Zunächst wird ein Phasenslowness-Frequenz-Spektrum (omega,p-Spektrum) der Seismogramme bestimmt. In einem zweiten Schritt werden dieses Spektrum und die Laufzeiten der Ersteinsätze gemeinsam zu einem rein Tiefen-abhängigen Modell der seismischen Geschwindigkeiten und der Diskontinuitäten des untersuchten Mediums invertiert. Typische flachseismische Messunge...
Landing gear noise attenuation
Moe, Jeffrey W. (Inventor); Whitmire, Julia (Inventor); Kwan, Hwa-Wan (Inventor); Abeysinghe, Amal (Inventor)
2011-01-01
A landing gear noise attenuator mitigates noise generated by airframe deployable landing gear. The noise attenuator can have a first position when the landing gear is in its deployed or down position, and a second position when the landing gear is in its up or stowed position. The noise attenuator may be an inflatable fairing that does not compromise limited space constraints associated with landing gear retraction and stowage. A truck fairing mounted under a truck beam can have a compliant edge to allow for non-destructive impingement of a deflected fire during certain conditions.
Giordano, S.
1963-11-12
A high peak power level r-f attenuator that is readily and easily insertable along a coaxial cable having an inner conductor and an outer annular conductor without breaking the ends thereof is presented. Spaced first and second flares in the outer conductor face each other with a slidable cylindrical outer conductor portion therebetween. Dielectric means, such as water, contact the cable between the flares to attenuate the radio-frequency energy received thereby. The cylindrical outer conductor portion is slidable to adjust the voltage standing wave ratio to a low level, and one of the flares is slidable to adjust the attenuation level. An integral dielectric container is also provided. (AFC)
Anderson, Gene R.; Armendariz, Marcelino G.; Carson, Richard F.; Bryan, Robert P.; Duckett, III, Edwin B.; Kemme, Shanalyn Adair; McCormick, Frederick B.; Peterson, David W.
2006-04-04
An apparatus and method of attenuating and/or conditioning optical energy for an optical transmitter, receiver or transceiver module is disclosed. An apparatus for attenuating the optical output of an optoelectronic connector including: a mounting surface; an array of optoelectronic devices having at least a first end; an array of optical elements having at least a first end; the first end of the array of optical elements optically aligned with the first end of the array of optoelectronic devices; an optical path extending from the first end of the array of optoelectronic devices and ending at a second end of the array of optical elements; and an attenuator in the optical path for attenuating the optical energy emitted from the array of optoelectronic devices. Alternatively, a conditioner may be adapted in the optical path for conditioning the optical energy emitted from the array of optoelectronic devices.
Sharp spatially constrained inversion
DEFF Research Database (Denmark)
Vignoli, Giulio G.; Fiandaca, Gianluca G.; Christiansen, Anders Vest C A.V.C.; Kirkegaard, Casper C.; Auken, Esben
We present sharp reconstruction of multi-layer models using a spatially constrained inversion with minimum gradient support regularization. In particular, its application to airborne electromagnetic data is discussed. Airborne surveys produce extremely large datasets, traditionally inverted by...... using smoothly varying 1D models. Smoothness is a result of the regularization constraints applied to address the inversion ill-posedness. The standard Occam-type regularized multi-layer inversion produces results where boundaries between layers are smeared. The sharp regularization overcomes this by......, the results are compatible with the data and, at the same time, favor sharp transitions. The focusing strategy can also be used to constrain the 1D solutions laterally, guaranteeing that lateral sharp transitions are retrieved without losing resolution. By means of real and synthetic datasets, sharp...
Directory of Open Access Journals (Sweden)
Verscheure M.
2012-06-01
Full Text Available For oil recovery or CO2 storage, “reservoirs” are commonly used to designate geological structures where oil can be found or CO2 can be stored. All reservoirs present a heterogeneity in terms of rock type and properties (such as porosity and permeability. In addition, some of these reservoirs present fractures and faults. Fractured reservoirs are an important part of the oil reserves in the world (Middle East, Gulf of Mexico, etc. and some of them are important reservoirs in terms of oil volume and productivity in spite of the fractures. In addition, studies of reservoirs for geologic storage of CO2 have shown the existence of diffuse fractures and faults and their strong impacts on flow. A key point in fractured reservoirs is to understand the geometry and hydraulic conductivity of the network formed by the fractures. This requires the construction of a reservoir model that integrates all available conceptual knowledge and quantitative data. The topic of the present paper deals with a new methodology able to perform the history matching of a fractured reservoir model by adapting the sub-seismic fault properties and positions. The main difficulty of this work is to generate a sub-seismic fault network whose fault positions can be easily modified while respecting the statistical fault model. The sub-seismic fault model we have chosen allows us to obtain a sub-seismic fault network that is consistent with the seismic fault network and that succeeds in capturing the specific spatial organization of the faults. In a first step, the geometry of the seismic fault network is characterized using fractal methods. Sub-seismic faults are then generated according to a stochastic algorithm. Finally, the geometry of this discrete fracture network is optimized in order to match the hydrodynamic data about the reservoir. The optimization algorithm modifies the sub-seismic fault positions, leading to the history matching of the reservoir model. Fractal
DEFF Research Database (Denmark)
Mosegaard, Klaus
For non-linear inverse problems, the mathematical structure of the mapping from model parameters to data is usually unknown or partly unknown. Absence of information about the mathematical structure of this function prevents us from presenting an analytical solution, so our solution depends on ou...
Calculation of the inverse data space via sparse inversion
Saragiotis, Christos
2011-01-01
The inverse data space provides a natural separation of primaries and surface-related multiples, as the surface multiples map onto the area around the origin while the primaries map elsewhere. However, the calculation of the inverse data is far from trivial as theory requires infinite time and offset recording. Furthermore regularization issues arise during inversion. We perform the inversion by minimizing the least-squares norm of the misfit function by constraining the $ell_1$ norm of the solution, being the inverse data space. In this way a sparse inversion approach is obtained. We show results on field data with an application to surface multiple removal.
Bayesian seismic AVO inversion
Energy Technology Data Exchange (ETDEWEB)
Buland, Arild
2002-07-01
A new linearized AVO inversion technique is developed in a Bayesian framework. The objective is to obtain posterior distributions for P-wave velocity, S-wave velocity and density. Distributions for other elastic parameters can also be assessed, for example acoustic impedance, shear impedance and P-wave to S-wave velocity ratio. The inversion algorithm is based on the convolutional model and a linearized weak contrast approximation of the Zoeppritz equation. The solution is represented by a Gaussian posterior distribution with explicit expressions for the posterior expectation and covariance, hence exact prediction intervals for the inverted parameters can be computed under the specified model. The explicit analytical form of the posterior distribution provides a computationally fast inversion method. Tests on synthetic data show that all inverted parameters were almost perfectly retrieved when the noise approached zero. With realistic noise levels, acoustic impedance was the best determined parameter, while the inversion provided practically no information about the density. The inversion algorithm has also been tested on a real 3-D dataset from the Sleipner Field. The results show good agreement with well logs but the uncertainty is high. The stochastic model includes uncertainties of both the elastic parameters, the wavelet and the seismic and well log data. The posterior distribution is explored by Markov chain Monte Carlo simulation using the Gibbs sampler algorithm. The inversion algorithm has been tested on a seismic line from the Heidrun Field with two wells located on the line. The uncertainty of the estimated wavelet is low. In the Heidrun examples the effect of including uncertainty of the wavelet and the noise level was marginal with respect to the AVO inversion results. We have developed a 3-D linearized AVO inversion method with spatially coupled model parameters where the objective is to obtain posterior distributions for P-wave velocity, S
Radiofrequency attenuator and method
Warner, Benjamin P.; McCleskey, T. Mark; Burrell, Anthony K.; Agrawal, Anoop; Hall, Simon B.
2009-11-10
Radiofrequency attenuator and method. The attenuator includes a pair of transparent windows. A chamber between the windows is filled with molten salt. Preferred molten salts include quarternary ammonium cations and fluorine-containing anions such as tetrafluoroborate (BF.sub.4.sup.-), hexafluorophosphate (PF.sub.6.sup.-), hexafluoroarsenate (AsF.sub.6.sup.-), trifluoromethylsulfonate (CF.sub.3SO.sub.3.sup.-), bis(trifluoromethylsulfonyl)imide ((CF.sub.3SO.sub.2).sub.2N.sup.-), bis(perfluoroethylsulfonyl)imide ((CF.sub.3CF.sub.2SO.sub.2).sub.2N.sup.-) and tris(trifluoromethylsulfonyl)methide ((CF.sub.3SO.sub.2).sub.3 C.sup.-). Radicals or radical cations may be added to or electrochemically generated in the molten salt to enhance the RF attenuation.
Directory of Open Access Journals (Sweden)
Ernest Kurtz
2015-01-01
Full Text Available There is growing interest in Alcoholics Anonymous (A.A. and other secular, spiritual, and religious frameworks of long-term addiction recovery. The present paper explores the varieties of spiritual experience within A.A., with particular reference to the growth of a wing of recovery spirituality promoted within A.A. It is suggested that the essence of secular spirituality is reflected in the experience of beyond (horizontal and vertical transcendence and between (connection and mutuality and in six facets of spirituality (Release, Gratitude, Humility, Tolerance, Forgiveness, and a Sense of Being-at-home shared across religious, spiritual, and secular pathways of addiction recovery. The growing varieties of A.A. spirituality (spanning the “Christianizers” and “Seculizers” reflect A.A.’s adaptation to the larger diversification of religious experience and the growing secularization of spirituality across the cultural contexts within which A.A. is nested.
Importance of Attenuation Correction (AC) for Small Animal PET Imaging
DEFF Research Database (Denmark)
El Ali, Henrik H.; Bodholdt, Rasmus Poul; Jørgensen, Jesper Tranekjær;
2012-01-01
performed. Methods: Ten NMRI nude mice with subcutaneous implantation of human breast cancer cells (MCF-7) were scanned consecutively in small animal PET and CT scanners (MicroPETTM Focus 120 and ImTek’s MicroCATTM II). CT-based AC, PET-based AC and uniform AC methods were compared. Results: The activity...... bladder 18 ± 3% (15–21%). The FBP reconstructed images showed almost the same attenuation levels as the MAP reconstructed images for all organs. Conclusions: The annihilation photons are suffering attenuation even in small subjects. Both PET-based and CT-based are adequate as AC methods. The amplitude of...... the AC recovery could be overestimated using the uniform map. Therefore, application of a global attenuation factor on PET data might not be accurate for attenuation correction....
International Nuclear Information System (INIS)
A pressure surge attenuation arrangement comprises crushable metal foam disposed adjacent regions adapted to be expanded by a pressure surge. In a pipe system such region consists of a thin walled inner pipe surrounded by a housing with crushable metal foam disposed in the space between the housing and the inner pipe. (author)
Tritium Attenuation by Distillation
International Nuclear Information System (INIS)
The objective of this study was to determine how a 100 Area distillation system could be used to reduce to a satisfactory low value the tritium content of the dilute moderator produced in the 100 Area stills, and whether such a tritium attenuator would have sufficient capacity to process all this material before it is sent to the 400 Area for reprocessing
Natural attenuation of herbicides
DEFF Research Database (Denmark)
Tuxen, Nina; Højberg, Anker Lajer; Broholm, Mette Martina;
2002-01-01
A field injection experiment in a sandy, aerobic aquifer showed that two phenoxy acids MCPP (mecoprop) and dichlorprop were degraded within I in downgradient of the injection wells after an apparent lag period. The plume development and microbial measurements indicated that microbial growth gover...... observations may be important for application of natural attenuation as a remedy in field scale systems....
Intersections, ideals, and inversion
Energy Technology Data Exchange (ETDEWEB)
Vasco, D.W.
1998-10-01
Techniques from computational algebra provide a framework for treating large classes of inverse problems. In particular, the discretization of many types of integral equations and of partial differential equations with undetermined coefficients lead to systems of polynomial equations. The structure of the solution set of such equations may be examined using algebraic techniques.. For example, the existence and dimensionality of the solution set may be determined. Furthermore, it is possible to bound the total number of solutions. The approach is illustrated by a numerical application to the inverse problem associated with the Helmholtz equation. The algebraic methods are used in the inversion of a set of transverse electric (TE) mode magnetotelluric data from Antarctica. The existence of solutions is demonstrated and the number of solutions is found to be finite, bounded from above at 50. The best fitting structure is dominantly onedimensional with a low crustal resistivity of about 2 ohm-m. Such a low value is compatible with studies suggesting lower surface wave velocities than found in typical stable cratons.
Intersections, ideals, and inversion
International Nuclear Information System (INIS)
Techniques from computational algebra provide a framework for treating large classes of inverse problems. In particular, the discretization of many types of integral equations and of partial differential equations with undetermined coefficients lead to systems of polynomial equations. The structure of the solution set of such equations may be examined using algebraic techniques.. For example, the existence and dimensionality of the solution set may be determined. Furthermore, it is possible to bound the total number of solutions. The approach is illustrated by a numerical application to the inverse problem associated with the Helmholtz equation. The algebraic methods are used in the inversion of a set of transverse electric (TE) mode magnetotelluric data from Antarctica. The existence of solutions is demonstrated and the number of solutions is found to be finite, bounded from above at 50. The best fitting structure is dominantly one dimensional with a low crustal resistivity of about 2 ohm-m. Such a low value is compatible with studies suggesting lower surface wave velocities than found in typical stable cratons
A compact rotary vane attenuator
Nixon, D. L.; Otosh, T. Y.; Stelzried, C. T.
1969-01-01
Rotary vane attenuator, when used as a front end attenuator, introduces an insertion loss that is proportional to the angle of rotation. New technique allows the construction of a shortened compact unit suitable for most installations.
Photon attenuation by intensifying screens
International Nuclear Information System (INIS)
The photon attenuation by intensifying screens of different chemical composition has been determined. The attenuation of photons between 20 keV and 120 keV was measured by use of a multi-channel analyzer and a broad bremsstrahlung distribution. The attenuation by the intensifying screens was hereby determined simultaneously at many different monoenergetic photon energies. Experimentally determined attenuations were found to agree well with attenuation calculated from mass attenuation coefficients. The attenuation by the screens was also determined at various bremsstrahlung distributions, simulating those occurring behind the patient in various diagnostic X-ray examinations. The high attenuation in some of the intensifying screens form the basis for an analysis of the construction of asymmetric screen pairs. Single screen systems are suggested as a favourable alternative to thick screen pair systems. (Author)
Ford, Sean R.; Phillips, William S.; Walter, William R.; Pasyanos, Michael E.; Mayeda, Kevin; Dreger, Douglas S.
2010-01-01
We invert for regional attenuation of the crustal phase Lg in the Yellow Sea/Korean Peninsula (YSKP) using three different amplitude attenuation tomography methods. The first method solves for source, site, and path attenuation. The second method uses a scaling relationship to set the initial source amplitude and interpret the source term after inversion. The third method implements a coda-derived source spectral correction. By comparing methods with slightly different assumptions we are able...
Frequency-domain waveform inversion using the phase derivative
Choi, Yun Seok
2013-09-26
Phase wrapping in the frequency domain or cycle skipping in the time domain is the major cause of the local minima problem in the waveform inversion when the starting model is far from the true model. Since the phase derivative does not suffer from the wrapping effect, its inversion has the potential of providing a robust and reliable inversion result. We propose a new waveform inversion algorithm using the phase derivative in the frequency domain along with the exponential damping term to attenuate reflections. We estimate the phase derivative, or what we refer to as the instantaneous traveltime, by taking the derivative of the Fourier-transformed wavefield with respect to the angular frequency, dividing it by the wavefield itself and taking the imaginary part. The objective function is constructed using the phase derivative and the gradient of the objective function is computed using the back-propagation algorithm. Numerical examples show that our inversion algorithm with a strong damping generates a tomographic result even for a high ‘single’ frequency, which can be a good initial model for full waveform inversion and migration.
Lateral Variations Of Macroseismic Intensity Attenuation In Italy
Carletti, F.; Gasperini, P.
Using the Italian unified intensity database, a tomographic type study of the attenua- tion of macroseismic intensity on the Italian territory has been carried out on the basis of a bilinear model recently proposed by Gasperini (2001). The spatial variations of the attenuation coefficients on meshes with sides of 50 and 25 km have been computed. By checkerboard and restore tests, with a realistic standard error of one intensity de- gree, we verified that our dataset of about 20000 paths is able to well reproduce the imposed patterns. The comparison of inversion results with crustal and upper mantle seismic wave tomography of the Italian area show a fairly good agreement between high attenuation and low velocity areas (Northern and central Apennines) and between low attenuation and high velocity ones (Po valley and Adriatic coast). The resulting attenuation pattern also agrees with a set of Nonparametric Attenuation Functions (NAF) describing the attenuation of crustal phases in different regions of Italy and shows a rather strong correspondence with heat-flow data. This study also furnished a compilation of average local residuals that have been correlated with the geological, geotechnical and morphological characteristics of sites.
Correct averaging in transmission radiography: Analysis of the inverse problem
Wagner, Michael; Hampel, Uwe; Bieberle, Martina
2016-05-01
Transmission radiometry is frequently used in industrial measurement processes as a means to assess the thickness or composition of a material. A common problem encountered in such applications is the so-called dynamic bias error, which results from averaging beam intensities over time while the material distribution changes. We recently reported on a method to overcome the associated measurement error by solving an inverse problem, which in principle restores the exact average attenuation by considering the Poisson statistics of the underlying particle or photon emission process. In this paper we present a detailed analysis of the inverse problem and its optimal regularized numerical solution. As a result we derive an optimal parameter configuration for the inverse problem.
Applications of elliptic Carleman inequalities to Cauchy and inverse problems
Choulli, Mourad
2016-01-01
This book presents a unified approach to studying the stability of both elliptic Cauchy problems and selected inverse problems. Based on elementary Carleman inequalities, it establishes three-ball inequalities, which are the key to deriving logarithmic stability estimates for elliptic Cauchy problems and are also useful in proving stability estimates for certain elliptic inverse problems. The book presents three inverse problems, the first of which consists in determining the surface impedance of an obstacle from the far field pattern. The second problem investigates the detection of corrosion by electric measurement, while the third concerns the determination of an attenuation coefficient from internal data, which is motivated by a problem encountered in biomedical imaging.
Downhole pressure attenuation apparatus
International Nuclear Information System (INIS)
This patent describes a process for preventing damage to tool strings and other downhole equipment in a well caused by pressures produced during detonation of one or more downhole explosive devices. It comprises adding to a tool string at least one pressure attenuating apparatus for attenuating the peak pressure wave and quasi-static pressure pulse produced by the explosive devices, the pressure attenuating apparatus including an initially closed relief vent including tubing means supporting a plurality of charge port assemblies each including an explosive filled shaped charge and a prestressed disc, the shaped charges interconnected by a detonating cord, the amount of explosive in each shaped charge being sufficient to rupture its associated disc without damaging surrounding tubular bodies in the well, and a vent chamber defined by the tubing means and providing a liquid free volume, and opening the relief vent substantially contemporaneously with downhole explosive device detonation by detonating the shaped charges to rupture the discs of the charge port assemblies
Inverse Degree and Connectivity
Institute of Scientific and Technical Information of China (English)
MA Xiao-ling; TIAN Ying-zhi
2013-01-01
Let G be a connected graph with vertex set V(G),order n =丨V(G)丨,minimum degree δ(G) and connectivity κ(G).The graph G is called maximally connected if κ(G) =δ(G).Define the inverse degree of G with no isolated vertices as R(G) =Σv∈V(G)1/d(v),where d(v) denotes the degree of the vertex v.We show that G is maximally connected if R(G) ＜ 1 + 2/δ + n-2δ+1/(n-1)(n-3).
Directory of Open Access Journals (Sweden)
Jingyun Yang
2011-01-01
Full Text Available Cohen's kappa and weighted kappa statistics are the conventional methods used frequently in measuring agreement for categorical responses. In this paper, through the perspective of a generalized inverse, we propose an alternative general framework of the fixed-effects modeling of Cohen's weighted kappa, proposed by Yang and Chinchilli (2011. Properties of the proposed method are provided. Small sample performance is investigated through bootstrap simulation studies, which demonstrate good performance of the proposed method. When there are only two categories, the proposed method reduces to Cohen's kappa.
DEFF Research Database (Denmark)
Mosegaard, Klaus
2012-01-01
For non-linear inverse problems, the mathematical structure of the mapping from model parameters to data is usually unknown or partly unknown. Absence of information about the mathematical structure of this function prevents us from presenting an analytical solution, so our solution depends on our...... ability to produce efficient search algorithms. Such algorithms may be completely problem-independent (which is the case for the so-called 'meta-heuristics' or 'blind-search' algorithms), or they may be designed with the structure of the concrete problem in mind. We show that pure meta-heuristics are...
Control algorithms for dynamic attenuators
Energy Technology Data Exchange (ETDEWEB)
Hsieh, Scott S., E-mail: sshsieh@stanford.edu [Department of Radiology, Stanford University, Stanford, California 94305 and Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States); Pelc, Norbert J. [Department of Radiology, Stanford University, Stanford California 94305 and Department of Bioengineering, Stanford University, Stanford, California 94305 (United States)
2014-06-15
Purpose: The authors describe algorithms to control dynamic attenuators in CT and compare their performance using simulated scans. Dynamic attenuators are prepatient beam shaping filters that modulate the distribution of x-ray fluence incident on the patient on a view-by-view basis. These attenuators can reduce dose while improving key image quality metrics such as peak or mean variance. In each view, the attenuator presents several degrees of freedom which may be individually adjusted. The total number of degrees of freedom across all views is very large, making many optimization techniques impractical. The authors develop a theory for optimally controlling these attenuators. Special attention is paid to a theoretically perfect attenuator which controls the fluence for each ray individually, but the authors also investigate and compare three other, practical attenuator designs which have been previously proposed: the piecewise-linear attenuator, the translating attenuator, and the double wedge attenuator. Methods: The authors pose and solve the optimization problems of minimizing the mean and peak variance subject to a fixed dose limit. For a perfect attenuator and mean variance minimization, this problem can be solved in simple, closed form. For other attenuator designs, the problem can be decomposed into separate problems for each view to greatly reduce the computational complexity. Peak variance minimization can be approximately solved using iterated, weighted mean variance (WMV) minimization. Also, the authors develop heuristics for the perfect and piecewise-linear attenuators which do not requirea priori knowledge of the patient anatomy. The authors compare these control algorithms on different types of dynamic attenuators using simulated raw data from forward projected DICOM files of a thorax and an abdomen. Results: The translating and double wedge attenuators reduce dose by an average of 30% relative to current techniques (bowtie filter with tube current
Flexible graphene based microwave attenuators.
Byun, Kisik; Ju Park, Yong; Ahn, Jong-Hyun; Min, Byung-Wook
2015-02-01
We demonstrate flexible 3 dB and 6 dB microwave attenuators using multilayer graphene grown by the chemical vapor deposition method. On the basis of the characterized results of multilayer graphene and graphene-Au ohmic contacts, the graphene attenuators are designed and measured. The flexible graphene-based attenuators have 3 dB and 6 dB attenuation with a return loss of less than -15 dB at higher than 5 GHz. The devices have shown durability in a bending cycling test of 100 times. The circuit model of the attenuator based on the characterized results matches the experimental results well. PMID:25590144
Flexible graphene based microwave attenuators
International Nuclear Information System (INIS)
We demonstrate flexible 3 dB and 6 dB microwave attenuators using multilayer graphene grown by the chemical vapor deposition method. On the basis of the characterized results of multilayer graphene and graphene–Au ohmic contacts, the graphene attenuators are designed and measured. The flexible graphene-based attenuators have 3 dB and 6 dB attenuation with a return loss of less than −15 dB at higher than 5 GHz. The devices have shown durability in a bending cycling test of 100 times. The circuit model of the attenuator based on the characterized results matches the experimental results well. (paper)
International Nuclear Information System (INIS)
Aim: To compare T1-weighted (W) fat–water separation (Dixon's technique) with T1W fat-saturation (FS) and T2W Dixon with short-tau inversion recovery (STIR) images for fat suppression in a short-bore MRI machine. Materials and methods: Thirteen patients with lumbar disease were studied on using 1.5 T MRI machine. The protocol included T1 FS (with contrast medium administration) and/or STIR and T1W and/or T2W Dixon, for comparison. Three neuroradiologists scored the images from the two-pairs of techniques for fat suppression uniformity and lesion conspicuity. Clinical usefulness of fat-only images was also evaluated. Results: Regarding uniformity of fat suppression, mean scores were 2.28 (±0.49), 3.06 (±0.49), 2.39 (±0.49), and 3.15 (±0.35) for T1W FS, T1W Dixon, STIR, and T2W Dixon sequences, respectively. For the same pulse sequences, lesion conspicuity scores were 2.78 (±0.50), 2.78 (±0.27), 2.76 (±0.47), and 2.91 (±0.4), respectively. Both T1W and T2W Dixon sequences showed more homogeneous fat-suppression when compared to T1W FS (p = 0.026) and STIR (p = 0.008) techniques, but no significant difference was found for lesion conspicuity. Mean scores for the diagnostic utility of fat-only maps were, respectively, 1.72 (±0.39) and 2.48 (±0.50) for T1W and T2W Dixon. Conclusion: Fat suppression quality was superior with Dixon when compared to the conventional sequences, but not lesion conspicuity, suggesting that both techniques are reliable for diagnosis. Dixon may be advantageous in cases where inhomogeneity artefacts are an issue. Water-only maps appear to be useful in the clinical setting
An analysis of seismic attenuation in random porous media
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
The attenuation of seismic wave in rocks has been one of the interesting research topics, but till now no poroelasticity models can thoroughly explain the strong attenuation of wave in rocks. In this paper, a random porous medium model is designed to study the law of wave propagation in complex rocks based on the theory of Biot poroelasticity and the general theory of stochastic process. This model sets the density of grain, porosity, permeability and modulus of frame as random parameters in space, and only one fluid infiltrates in rocks for the sake of better simulation effect in line with real rocks in earth strata. Numerical simulations are implemented. Two different inverse quality factors of fast P-wave are obtained by different methods to assess attenuation through records of virtual detectors in wave field (One is amplitude decay method in time domain and the other is spectral ratio method in frequency domain). Comparing the attenuation results of random porous medium with those of homogeneous porous medium, we conclude that the attenuation of seismic wave of homogeneous porous medium is far weaker than that of random porous medium. In random porous media, the higher heterogeneous level is, the stronger the attenuation becomes, and when heterogeneity σ = 0.15 in simulation, the attenuation result is consistent with that by actual observation. Since the central frequency (50 Hz) of source in numerical simulation is in earthquake band, the numerical results prove that heterogeneous porous structure is one of the important factors causing strong attenuation in real stratum at intermediate and low frequency.
Statistical Inversion of Seismic Noise Inversion statistique du bruit sismique
Directory of Open Access Journals (Sweden)
Adler P. M.
2006-11-01
Full Text Available A systematic investigation of wave propagation in random media is presented. Spectral analysis, inversion of codas and attenuation of the direct wave front are studied for synthetic data obtained in isotropic or anisotropic, 2D or 3D media. A coda inversion process is developed and checked on two sets of real data. In both cases, it is possible to compare the correlation lengths obtained by inversion to characteristic lengths measured on seismic logs, for the full scale seismic survey, or on a thin section, for the laboratory experiment. These two experiments prove the feasibility and the efficiency of the statistical inversion of codas. Correct characteristic lengths can be obtained which cannot be determined by another method. Le problème de la géophysique est la recherche d'informations concernant le sous-sol, dans des signaux sismiques enregistrés en surface ou dans des puits. Ces informations sont habituellement recherchées sous forme déterministe, c'est-à-dire sous la forme de la donnée en chaque point d'une valeur du paramètre étudié. Notre point de vue est différent puisque notre objectif est de déduire certaines propriétés statistiques du milieu, supposé hétérogène, à partir des sismogrammes enregistrés après propagation. Il apparaît alors deux moyens de remplir l'objectif fixé. Le premier est l'analyse spectrale des codas ; cette analyse permet de déterminer les tailles moyennes des hétérogénéités du sous-sol. La deuxième possibilité est l'étude de l'atténuation du front direct de l'onde, qui conduit aussi à la connaissance des longueurs caractéristiques du sous-sol ; contrairement à la première méthode, elle ne semble pas pouvoir être transposée efficacement à des cas réels. Dans la première partie, on teste numériquement la proportionnalité entre le facteur de rétrodiffraction, relié aux propriétés statistiques du milieu, et le spectre des codas. Les distributions de vitesse, à valeur
Three-dimensional attenuation and velocity structure of the Cocos subduction zone in Mexico
Chen, T.; Clayton, R. W.
2010-12-01
The 3D P-wave attenuation and velocity structure of the Cocos subduction zone in Mexico is imaged using about 700 local events recorded by the MASE (100 seismometers running across central Mexico, 2005-2007) and VEOX (47 seismometers running across southern Mexico, 2007-2009) arrays, supplemented by stations from the National Seismic Network in Mexico (SSN). Using a spectral-decay method, we obtain a path attenuation operator t* for each seismogram in the frequency band 1 to 30 Hz, depending on the signal quality. These measurements are then inverted for 3D spatial variations in attenuation. Direct P wave arrivals are used for velocity inversion. Inversion results show low attenuation associated with the Cocos slab, and show the slab dip angle increases from central to southern Mexico. High attenuation is imaged in the mantle wedge and the crust above. The highest attenuation is found in the crust near the active Los Tuxtlas volcanic field, probably related to the dehydration and melting process. Cocos slab is also traced as high-velocity strucuture from velocity inversion. Low velocity is imaged in the mantle wedge and crust above. Anomalous high velocity structure is found near the Isthmus of Tehuantepec in southern Mexico dipping south from the Gulf of Mexico. This structure is also seen in receiver function images, and may be related to the collision between the Yucatan Block and Mexico in the Miocene.
Directory of Open Access Journals (Sweden)
Markus Spiliotis
Full Text Available Inverse fusion PCR cloning (IFPC is an easy, PCR based three-step cloning method that allows the seamless and directional insertion of PCR products into virtually all plasmids, this with a free choice of the insertion site. The PCR-derived inserts contain a vector-complementary 5'-end that allows a fusion with the vector by an overlap extension PCR, and the resulting amplified insert-vector fusions are then circularized by ligation prior transformation. A minimal amount of starting material is needed and experimental steps are reduced. Untreated circular plasmid, or alternatively bacteria containing the plasmid, can be used as templates for the insertion, and clean-up of the insert fragment is not urgently required. The whole cloning procedure can be performed within a minimal hands-on time and results in the generation of hundreds to ten-thousands of positive colonies, with a minimal background.
Inversion amalgam chronopotentiometry
International Nuclear Information System (INIS)
The review deals with the theoretical principles of the method of inversion amalgam chronopotentiometry. The transition times and the potential-time relations for the electrochemical dissolution of amalgams under galvanostatic conditions are analysed and the applications of the method in electroanalytical practise, in the study of the kinetics of electrode processes and adsorption, in the determination of the numbers of electrons involved in the reaction and diffusion coefficients, and in the study of complex formation, corrosion of amalgams, etc. are examined in detail. The fundamentals of the theory of electrode processes complicated by preceding, subsequent, and simultaneous chemical reactions are described. The possibilities and advantages of the method of amalgam chronopotentiometry in relation to other electrochemical procedures are indicated
Ahriche, Amine; Nasri, Salah
2016-01-01
We present a minimal model that simultaneously accounts for neutrino masses and the origin of dark matter (DM) and where the electroweak phase transition is strong enough to allow for electroweak baryogenesis. The Standard Model is enlarged with a Majorana fermion, three generations of chiral fermion pairs, and a single complex scalar that plays a central role in DM production and phenomenology, neutrino masses, and the strength of the phase transition. All the new fields are singlets under the SM gauge group. Neutrino masses are generated via a new variant of radiative inverse seesaw where the required small mass term is generated via loops involving DM and no large hierarchy is assumed among the mass scales. The model offers all the advantage of low-scale neutrino mass models as well as a viable dark matter candidate that is testable with direct detection experiments.
Wavelet Sparse Approximate Inverse Preconditioners
Chan, Tony F.; Tang, W.-P.; Wan, W. L.
1996-01-01
There is an increasing interest in using sparse approximate inverses as preconditioners for Krylov subspace iterative methods. Recent studies of Grote and Huckle and Chow and Saad also show that sparse approximate inverse preconditioner can be effective for a variety of matrices, e.g. Harwell-Boeing collections. Nonetheless a drawback is that it requires rapid decay of the inverse entries so that sparse approximate inverse is possible. However, for the class of matrices that, come from elliptic PDE problems, this assumption may not necessarily hold. Our main idea is to look for a basis, other than the standard one, such that a sparse representation of the inverse is feasible. A crucial observation is that the kind of matrices we are interested in typically have a piecewise smooth inverse. We exploit this fact, by applying wavelet techniques to construct a better sparse approximate inverse in the wavelet basis. We shall justify theoretically and numerically that our approach is effective for matrices with smooth inverse. We emphasize that in this paper we have only presented the idea of wavelet approximate inverses and demonstrated its potential but have not yet developed a highly refined and efficient algorithm.
Holocaust inversion and contemporary antisemitism.
Klaff, Lesley D
2014-01-01
One of the cruellest aspects of the new antisemitism is its perverse use of the Holocaust as a stick to beat 'the Jews'. This article explains the phenomenon of 'Holocaust Inversion', which involves an 'inversion of reality' (the Israelis are cast as the 'new' Nazis and the Palestinians as the 'new' Jews) and an 'inversion of morality' (the Holocaust is presented as a moral lesson for, or even a moral indictment of, 'the Jews'). Holocaust inversion is a form of soft-core Holocaust denial, yet...
International Nuclear Information System (INIS)
Parameters of stochastic point-source ground motion model were inverted based on extensive digital records from dense seismic networks for small-to-moderate earthquakes in and around the Korea. Modified Levenberg-Marquardt's nonlinear inversion method was employed for stable inversion which considers the second derivatives of the Hessian matrix. After trying various cases with regard to seismic source types, frequency dependency of crustal attenuation, and crustal amplification, the best estimates for earthquake simulation are determined to be 348f0.53 for crustal attenuation, 20∼30 bars for stress drop, 0.02 for site anelastic attenuation (kappa), and 50 km for crossover distance. In addition, detailed features of crustal attenuation such as anisotropy and localized Q were evaluated, which contributes to providing scientific bases for developing site-specific ground motion attenuation relations and interpreting the geological and geophysical characteristics of the Korean Peninsula. In the region where strong ground motion data are scarce such as in Korea, it becomes engineering practice to employ well-founded, validated, and simple stochastic point-source ground motion earthquake model to predict strong ground motion. The parameters for stochastic point-source ground motion model are stress drop for sources, frequency dependent quality factor (Q) for crustal attenuation, and kappa (K) for site effects. In this study, these model parameters were inverted based on extensive earthquake dataset at the first step and more detailed features of crustal attenuation were investigated at the second step. For stable inversion of these parameters under various cases, conventional Levenberg-Marquardt's nonlinear inversion method is simply modified by taking into account the second derivatives of the Hessian matrix
Information fusion in regularized inversion of tomographic pumping tests
Bohling, G.C.
2008-01-01
In this chapter we investigate a simple approach to incorporating geophysical information into the analysis of tomographic pumping tests for characterization of the hydraulic conductivity (K) field in an aquifer. A number of authors have suggested a tomographic approach to the analysis of hydraulic tests in aquifers - essentially simultaneous analysis of multiple tests or stresses on the flow system - in order to improve the resolution of the estimated parameter fields. However, even with a large amount of hydraulic data in hand, the inverse problem is still plagued by non-uniqueness and ill-conditioning and the parameter space for the inversion needs to be constrained in some sensible fashion in order to obtain plausible estimates of aquifer properties. For seismic and radar tomography problems, the parameter space is often constrained through the application of regularization terms that impose penalties on deviations of the estimated parameters from a prior or background model, with the tradeoff between data fit and model norm explored through systematic analysis of results for different levels of weighting on the regularization terms. In this study we apply systematic regularized inversion to analysis of tomographic pumping tests in an alluvial aquifer, taking advantage of the steady-shape flow regime exhibited in these tests to expedite the inversion process. In addition, we explore the possibility of incorporating geophysical information into the inversion through a regularization term relating the estimated K distribution to ground penetrating radar velocity and attenuation distributions through a smoothing spline model. ?? 2008 Springer-Verlag Berlin Heidelberg.
Generating Generalized Inverse Gaussian Random Variates by Fast Inversion
Leydold, Josef; Hörmann, Wolfgang
2009-01-01
We demonstrate that for the fast numerical inversion of the (generalized) inverse Gaussian distribution two algorithms based on polynomial interpolation are well-suited. Their precision is close to machine precision and they are much faster than the bisection method recently proposed by Y. Lai. (author´s abstract)
Ultrasonic Attenuation in Zircaloy-4
International Nuclear Information System (INIS)
In this work the relationship between Zircaloy-4 grain size and ultrasonic attenuation behavior was studied for longitudinal waves in the frequency range of 10-90 MHz. The attenuation was analyzed as a function of frequency for samples with different mechanical and heat treatments having recrystallized and Widmanstatten structures with different grain size. The attenuation behavior was analyzed by different scattering models, depending on grain size, wavelength and frequency
Chopping-Wheel Optical Attenuator
Leviton, Douglas B.
1988-01-01
Star-shaped rotating chopping wheel provides adjustable time-averaged attenuation of narrow beam of light without changing length of optical path or spectral distribution of light. Duty cycle or attenuation factor of chopped beam controlled by adjusting radius at which beam intersects wheel. Attenuation factor independent of wavelength. Useful in systems in which chopping frequency above frequency-response limits of photodetectors receiving chopped light. Used in systems using synchronous detection with lock-in amplifiers.
Wilds, R.B.; Ames, J.R.
1957-09-24
The line-above-ground attenuator provides a continuously variable microwave attenuator for a coaxial line that is capable of high attenuation and low insertion loss. The device consists of a short section of the line-above- ground plane type transmission lime, a pair of identical rectangular slabs of lossy material like polytron, whose longitudinal axes are parallel to and indentically spaced away from either side of the line, and a geared mechanism to adjust amd maintain this spaced relationship. This device permits optimum fineness and accuracy of attenuator control which heretofore has been difficult to achieve.
Energy Technology Data Exchange (ETDEWEB)
Pelle, L.
2003-12-01
The removal of multiple reflections remains a real problem in seismic imaging. Many preprocessing methods have been developed to attenuate multiples in seismic data but none of them is satisfactory in 3D. The objective of this thesis is to develop a new method to remove multiples, extensible in 3D. Contrary to the existing methods, our approach is not a preprocessing step: we directly include the multiple removal in the imaging process by means of a simultaneous inversion of primaries and multiples. We then propose to improve the standard linearized inversion so as to make it insensitive to the presence of multiples in the data. We exploit kinematics differences between primaries and multiples. We propose to pick in the data the kinematics of the multiples we want to remove. The wave field is decomposed into primaries and multiples. Primaries are modeled by the Ray+Born operator from perturbations of the logarithm of impedance, given the velocity field. Multiples are modeled by the Transport operator from an initial trace, given the picking. The inverse problem simultaneously fits primaries and multiples to the data. To solve this problem with two unknowns, we take advantage of the isometric nature of the Transport operator, which allows to drastically reduce the CPU time: this simultaneous inversion is this almost as fast as the standard linearized inversion. This gain of time opens the way to different applications to multiple removal and in particular, allows to foresee the straightforward 3D extension. (author)
Interlaboratory comparison of radiation-induced attenuation in optical fibers
International Nuclear Information System (INIS)
A comparison of the losses induced in step index multimode, graded index multimode and single mode fibers by pulsed radiation exposure has been made among 12 laboratories over a period of 5 years. The recoveries of the incremental attenuations from 10-9 to 101 s are reported. Although a standard set of measurement parameters was attempted, differences between the laboratories are evident; possible origins for these are discussed. 18 refs., 18 figs., 7 tabs
Enhancing comprehensive inversions using the Swarm constellation
DEFF Research Database (Denmark)
Sabaka, T.J.; Olsen, Nils
2006-01-01
signals, as well as information about mantle conductivity structure, can be met. The recovery method used in this paper is known as comprehensive inversion (CI) and involves the parameterization of all major fields followed by a co-estimation of these parameters in a least-squares sense in order to...... structure, a more complicated magnetospheric field, and an induced field reflecting a 3-D conductivity model. These data also included realistic magnetic noise from spacecraft and payload. Though the parameterization for the CI is based upon that of CM4, modifications have been made to accommodate these new...... magnetospheric and induced fields, in particular with orthogonality constraints defined so as to avoid covariance between slowly varying induced fields and SV. The use of these constraints is made feasible through an efficient numerical implementation. Constellations of 4, 3, 2, and 1 satellites were considered...
The R3 exponential x-ray transform inversion in quaternion analysis
International Nuclear Information System (INIS)
In this paper, we present a new derivation of the inverse of the exponential x-ray transform in the three dimensions, based on quaternion analysis. An explicit formula is obtained using a set of three-dimensional x-ray projection data. The result without attenuation is recovered as a special case.
The R{sup 3} exponential x-ray transform inversion in quaternion analysis
Energy Technology Data Exchange (ETDEWEB)
Fathi, S M Saberi, E-mail: majid.saberi@u-cergy.f [Laboratoire de Physique Theorique et Modelisation, Universite de Cergy-Pontoise, 95302 Cergy-Pontoise (France)
2010-07-23
In this paper, we present a new derivation of the inverse of the exponential x-ray transform in the three dimensions, based on quaternion analysis. An explicit formula is obtained using a set of three-dimensional x-ray projection data. The result without attenuation is recovered as a special case.
Buzzetti, Mike F. (Inventor)
1994-01-01
A fiber optic attenuator of the invention is a mandrel structure through which a bundle of optical fibers is wrapped around in a complete circle. The mandrel structure includes a flexible cylindrical sheath through which the bundle passes. A set screw on the mandrel structure impacts one side of the sheath against two posts on the opposite side of the sheath. By rotating the screw, the sheath is deformed to extend partially between the two posts, bending the fiber optic bundle to a small radius controlled by rotating the set screw. Bending the fiber optic bundle to a small radius causes light in each optical fiber to be lost in the cladding, the amount depending upon the radius about which the bundle is bent.
Inverse problem in hydrogeology
Carrera, Jesús; Alcolea, Andrés; Medina, Agustín; Hidalgo, Juan; Slooten, Luit J.
2005-03-01
The state of the groundwater inverse problem is synthesized. Emphasis is placed on aquifer characterization, where modelers have to deal with conceptual model uncertainty (notably spatial and temporal variability), scale dependence, many types of unknown parameters (transmissivity, recharge, boundary conditions, etc.), nonlinearity, and often low sensitivity of state variables (typically heads and concentrations) to aquifer properties. Because of these difficulties, calibration cannot be separated from the modeling process, as it is sometimes done in other fields. Instead, it should be viewed as one step in the process of understanding aquifer behavior. In fact, it is shown that actual parameter estimation methods do not differ from each other in the essence, though they may differ in the computational details. It is argued that there is ample room for improvement in groundwater inversion: development of user-friendly codes, accommodation of variability through geostatistics, incorporation of geological information and different types of data (temperature, occurrence and concentration of isotopes, age, etc.), proper accounting of uncertainty, etc. Despite this, even with existing codes, automatic calibration facilitates enormously the task of modeling. Therefore, it is contended that its use should become standard practice. L'état du problème inverse des eaux souterraines est synthétisé. L'accent est placé sur la caractérisation de l'aquifère, où les modélisateurs doivent jouer avec l'incertitude des modèles conceptuels (notamment la variabilité spatiale et temporelle), les facteurs d'échelle, plusieurs inconnues sur différents paramètres (transmissivité, recharge, conditions aux limites, etc.), la non linéarité, et souvent la sensibilité de plusieurs variables d'état (charges hydrauliques, concentrations) des propriétés de l'aquifère. A cause de ces difficultés, le calibrage ne peut êtreséparé du processus de modélisation, comme c'est le
Inverse fracture network modelling
International Nuclear Information System (INIS)
The basic problem in analyzing flow and transport in fractured rock is that the flow may be largely governed by a poorly connected network of fractures. Flow in such a system cannot be modeled with traditional modelling techniques. Fracture network models also have a limitation, in that they are based on geological data on fracture geometry even though it is known that only a small portion of fractures observed is hydraulically active. This paper discusses a new technique developed for treating the problem as well as presents a modelling example carried out to apply it. The approach is developed in Lawrence Berkeley Laboratory and it treats the fracture zone as an 'equivalent discontinuum'. The discontinuous nature of the problem is represented through flow on a partially filled lattice. An equivalent discontinuum model is constructed by adding and removing conductive elements through a statistical inverse technique called 'simulated annealing'. The fracture network model is 'annealed' until the modified systems behaves like the observed. The further development of the approach continues at LBL and in a joint LBL/VTT collaboration project the possibilities to apply the technique in Finnish conditions are investigated
Inverse Problems of Thermoelectricity
Anatychuk, L. I.; Luste, O. J.; Kuz, R. V.; Strutinsky, M. N.
2011-05-01
Classical thermoelectricity is based on the use of the Seebeck and Thomson effects that occur in the near-contact areas between n- and p-type materials. A conceptually different approach to thermoelectric power converter design that is based on the law of thermoelectric induction of currents is also known. The efficiency of this approach has already been demonstrated by its first applications. More than 10 basically new types of thermoelements were discovered with properties that cannot be achieved by thermocouple power converters. Therefore, further development of this concept is of practical interest. This paper provides a classification and theory for solving the inverse problems of thermoelectricity that form the basis for devising new thermoelement types. Computer methods for their solution for anisotropic and inhomogeneous media are elaborated. Regularities related to thermoelectric current excitation in anisotropic and inhomogeneous media are established. The possibility of obtaining eddy currents of a particular configuration through control of the temperature field and material parameters for the creation of new thermo- element types is demonstrated for three-dimensional (3D) models of anisotropic and inhomogeneous media.
Multiscale Modelling and Inverse Problems
Nolen, J; Stuart, A M
2010-01-01
The need to blend observational data and mathematical models arises in many applications and leads naturally to inverse problems. Parameters appearing in the model, such as constitutive tensors, initial conditions, boundary conditions, and forcing can be estimated on the basis of observed data. The resulting inverse problems are often ill-posed and some form of regularization is required. These notes discuss parameter estimation in situations where the unknown parameters vary across multiple scales. We illustrate the main ideas using a simple model for groundwater flow. We will highlight various approaches to regularization for inverse problems, including Tikhonov and Bayesian methods. We illustrate three ideas that arise when considering inverse problems in the multiscale context. The first idea is that the choice of space or set in which to seek the solution to the inverse problem is intimately related to whether a homogenized or full multiscale solution is required. This is a choice of regularization. The ...
Energy Technology Data Exchange (ETDEWEB)
Syracuse, Ellen Marie [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Maceira, Monica [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Phillips, William Scott [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Begnaud, Michael Lee [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Nippress, Stuart [Atomic Weapons Establishment (AWE) Blacknest, Brimpton (United Kingdom); Bergman, Eric [Global Seismological Services (GSS), Golden, CO (United States); Zhang, Haijiang [Univ. of Science and Technology of China, Hefei (China)
2016-07-19
These are slides which show many graphs and datasets for the above-mentioned topic and then concludes with the following: Joint inversion of multiple geophysical datasets improves recovery of velocity structures, particularly in Vs and in shallow parts of the model, in comparison to travel-time only models. Resulting fits to travel time data are minimally degraded by joint inversions. Correspondingly, fits to independent estimates of ground-truth locations are minimally affected by joint inversions.
Adjustable Optical-Fiber Attenuator
Buzzetti, Mike F.
1994-01-01
Adjustable fiber-optic attenuator utilizes bending loss to reduce strength of light transmitted along it. Attenuator functions without introducing measurable back-reflection or insertion loss. Relatively insensitive to vibration and changes in temperature. Potential applications include cable television, telephone networks, other signal-distribution networks, and laboratory instrumentation.
... Pressure High Blood Pressure Tools & Resources Stroke More Heart Attack Recovery FAQs Updated:Aug 24,2016 Most people ... recovery. View an animation of a heart attack . Heart Attack Recovery Questions and Answers What treatments will I ...
Multidimensional NMR Inversion without Kronecker Products: Multilinear Inversion
Medellín, David; Torres-Verdín, Carlos
2016-01-01
Multidimensional NMR inversion using Kronecker products poses several challenges. First, kernel compression is only possible when the kernel matrices are separable, and in recent years, there has been an increasing interest in NMR sequences with non-separable kernels. Second, in three or more dimensions, the singular value decomposition is not unique; therefore kernel compression is not well-defined for higher dimensions. Without kernel compression, the Kronecker product yields matrices that require large amounts of memory, making the inversion intractable for personal computers. Finally, incorporating arbitrary regularization terms is not possible using the Lawson-Hanson (LH) or the Butler-Reeds-Dawson (BRD) algorithms. We develop a minimization-based inversion method that circumvents the above problems by using multilinear forms to perform multidimensional NMR inversion without using kernel compression or Kronecker products. The new method is memory efficient, requiring less than 0.1% of the memory required...
Localized recovery of complex networks against failure.
Shang, Yilun
2016-01-01
Resilience of complex networks to failure has been an important issue in network research for decades, and recent studies have begun to focus on the inverse recovery of network functionality through strategically healing missing nodes or edges. However, the effect of network recovery is far from fully understood, and a general theory is still missing. Here we propose and study a general model of localized recovery, where a group of neighboring nodes are restored in an invasive way from a seed node. We develop a theoretical framework to compare the effect of random recovery (RR) and localized recovery (LR) in complex networks including Erdős-Rényi networks, random regular networks, and scale-free networks. We find detailed phase diagrams for the subnetwork of occupied nodes and the "complement network" of failed nodes under RR and LR. By identifying the two competitive forces behind LR, we present an analytical and numerical approach to guide us in choosing the appropriate recovery strategy and provide estimation on its effect by using the degree distribution of the original network as the only input. Our work therefore provides insight for quantitatively understanding recovery process and its implications in infrastructure protection in various complex systems. PMID:27456202
Localized recovery of complex networks against failure
Shang, Yilun
2016-07-01
Resilience of complex networks to failure has been an important issue in network research for decades, and recent studies have begun to focus on the inverse recovery of network functionality through strategically healing missing nodes or edges. However, the effect of network recovery is far from fully understood, and a general theory is still missing. Here we propose and study a general model of localized recovery, where a group of neighboring nodes are restored in an invasive way from a seed node. We develop a theoretical framework to compare the effect of random recovery (RR) and localized recovery (LR) in complex networks including Erdős-Rényi networks, random regular networks, and scale-free networks. We find detailed phase diagrams for the subnetwork of occupied nodes and the “complement network” of failed nodes under RR and LR. By identifying the two competitive forces behind LR, we present an analytical and numerical approach to guide us in choosing the appropriate recovery strategy and provide estimation on its effect by using the degree distribution of the original network as the only input. Our work therefore provides insight for quantitatively understanding recovery process and its implications in infrastructure protection in various complex systems.
Parameter estimation and inverse problems
Aster, Richard C; Thurber, Clifford H
2011-01-01
Parameter Estimation and Inverse Problems, 2e provides geoscience students and professionals with answers to common questions like how one can derive a physical model from a finite set of observations containing errors, and how one may determine the quality of such a model. This book takes on these fundamental and challenging problems, introducing students and professionals to the broad range of approaches that lie in the realm of inverse theory. The authors present both the underlying theory and practical algorithms for solving inverse problems. The authors' treatment is approp
Inverse Doppler Effects in Flute
Zhao, Xiao P; Liu, Song; Shen, Fang L; Li, Lin L; Luo, Chun R
2015-01-01
Here we report the observation of the inverse Doppler effects in a flute. It is experimentally verified that, when there is a relative movement between the source and the observer, the inverse Doppler effect could be detected for all seven pitches of a musical scale produced by a flute. Higher tone is associated with a greater shift in frequency. The effect of the inverse frequency shift may provide new insights into why the flute, with its euphonious tone, has been popular for thousands of years in Asia and Europe.
Saita, H.; Nakajima, J.; Shiina, T.
2014-12-01
The Philippine Sea (PHS) plate is subducting beneath Kyusyu and a clear volcanic front is formed through the middle of the arc. However, there is a volcanic gap in the central part of Kyushu, between Aso and Kirishima volcanoes. Many studies have discussed arc magmatism in Kyushu in terms of 3D seismic velocity structure, but little is known on seismic attenuation structure. Seismic attenuation structure provides additional insights into subduction-zone dynamics, because higher-temperature environments or the existence of fluids may have different effects on seismic attenuation from on seismic velocity. Therefore the estimate of seismic attenuation is very important to understand arc magmatism and mantle dynamics in subduction zone. This study estimates seismic attenuation structure beneath Kyushu using a large number of high-quality waveform data. We applied the method of Nakajima et al. (2013, JGR) to waveform data derived from 3052 earthquakes that occurred from April 2003 to May 2014. We determined the corner frequency of earthquakes by the spectral ratio method of S-coda waves. Then, we determined a whole-path attenuation term (t*), site-amplification factors and spectrum level simultaneously by a joint inversion. Finally, the t* values (N= 62290) were inverted to obtain three-dimensional attenuation structure. The obtained results show several interesting features. First, the subducting PHS slab is imaged as a low attenuation zone. Second, high-attenuation zone exists in the fore-arc mantle. This high-attenuation zone corresponds spatially to a high Poisson's ratio area, suggesting that the mantle is serpentinized as a result of fluids released by dehydration in the subducting crust. Third, an inclined high-attenuation zone that is interpreted as a mantle upwelling flow is observed in the back-arc mantle. However, the inclined high-attenuation zone is less developed in the volcanic gap between Aso and Kirishima volcanoes. This observation suggests the
Seismic attenuation in fractured media
International Nuclear Information System (INIS)
The prime objective of this paper is to quantitatively estimate seismic attenuation caused by fractures with different physical parameters. In seismic wave simulation, the fractured media are treated as the anisotropic media and fractures are represented by frequency-dependent elastic constants. Based on numerical experiments with three different parameters, namely viscosity, porosity and the Lamé parameters, this paper has the following observations. First, seismic attenuation is not affected by the viscosity within fractures, although it increases with the increase of porosity and decreases with the increase of the Lamé parameters within fractures. Among the latter two parameters, seismic attenuation is more sensitive to the Lamé parameters than to the porosity. Second, for the attenuation anisotropy, low frequencies have more anisotropic effect than high frequencies. For example, a 50 Hz wavefield has the strongest anisotropy effect if compared to 100 and 150 Hz wavefields. The attenuation anisotropy for low frequency (say 50 Hz) is more sensitive to the viscosity than the porosity and the Lamé parameters have the weakest effect among these three parameters. These observations suggest that low-frequency seismic attenuation, and especially the attenuation anisotropy in low frequency, would have great potential for fluid discrimination within fractured media. (paper)
Uterine Inversion; A case report.
Bouchikhi, C; Saadi, H; Fakhir, B; Chaara, H; Bouguern, H; Banani, A; Melhouf, Ma
2008-01-01
The puerperal uterine inversion is a rare and severe complication occurring in the third stage of labour. The mechanisms are not completely known. However, extrinsic factors such as oxytocic arrests after a prolonged labour, umbilical cord traction or abdominal expression are pointed. Other intrinsic factors such as primiparity, uterine hypotonia, various placental localizations, fundic myoma or short umbilical cord were also reported. The diagnosis of the uterine inversion is mainly supported by clinical symptoms. It is based on three elements: haemorrhage, shock and a strong pelvic pain. The immediate treatment of the uterine inversion is required. It is based on a medical reanimation associated with firstly a manual reduction then surgical treatment using various techniques. We report an observation of a 25 years old grand multiparous patient with a subacute uterine inversion after delivery at home. PMID:21516244
Statistical perspectives on inverse problems
DEFF Research Database (Denmark)
Andersen, Kim Emil
interior of an object from electrical boundary measurements. One part of this thesis concerns statistical approaches for solving, possibly non-linear, inverse problems. Thus inverse problems are recasted in a form suitable for statistical inference. In particular, a Bayesian approach for regularisation is...... obtained by assuming that the a priori beliefs about the solution before having observed any data can be described by a prior distribution. The solution to the statistical inverse problem is then given by the posterior distribution obtained by Bayes' formula. Hence the solution of an ill-posed inverse...... problem is given in terms of probability distributions. Posterior inference is obtained by Markov chain Monte Carlo methods and new, powerful simulation techniques based on e.g. coupled Markov chains and simulated tempering is developed to improve the computational efficiency of the overall simulation...
Testing earthquake source inversion methodologies
Page, Morgan T.
2011-01-01
Source Inversion Validation Workshop; Palm Springs, California, 11-12 September 2010; Nowadays earthquake source inversions are routinely performed after large earthquakes and represent a key connection between recorded seismic and geodetic data and the complex rupture process at depth. The resulting earthquake source models quantify the spatiotemporal evolution of ruptures. They are also used to provide a rapid assessment of the severity of an earthquake and to estimate losses. However, because of uncertainties in the data, assumed fault geometry and velocity structure, and chosen rupture parameterization, it is not clear which features of these source models are robust. Improved understanding of the uncertainty and reliability of earthquake source inversions will allow the scientific community to use the robust features of kinematic inversions to more thoroughly investigate the complexity of the rupture process and to better constrain other earthquakerelated computations, such as ground motion simulations and static stress change calculations.
Parameter estimation and inverse problems
Aster, Richard C; Thurber, Clifford H
2005-01-01
Parameter Estimation and Inverse Problems primarily serves as a textbook for advanced undergraduate and introductory graduate courses. Class notes have been developed and reside on the World Wide Web for faciliting use and feedback by teaching colleagues. The authors'' treatment promotes an understanding of fundamental and practical issus associated with parameter fitting and inverse problems including basic theory of inverse problems, statistical issues, computational issues, and an understanding of how to analyze the success and limitations of solutions to these probles. The text is also a practical resource for general students and professional researchers, where techniques and concepts can be readily picked up on a chapter-by-chapter basis.Parameter Estimation and Inverse Problems is structured around a course at New Mexico Tech and is designed to be accessible to typical graduate students in the physical sciences who may not have an extensive mathematical background. It is accompanied by a Web site that...
Reconstruction from Uniformly Attenuated SPECT Projection Data Using the DBH Method
Energy Technology Data Exchange (ETDEWEB)
Huang, Qiu; You, Jiangsheng; Zeng, Gengsheng L.; Gullberg, Grant T.
2008-03-20
An algorithm was developed for the two-dimensional (2D) reconstruction of truncated and non-truncated uniformly attenuated data acquired from single photon emission computed tomography (SPECT). The algorithm is able to reconstruct data from half-scan (180o) and short-scan (180?+fan angle) acquisitions for parallel- and fan-beam geometries, respectively, as well as data from full-scan (360o) acquisitions. The algorithm is a derivative, backprojection, and Hilbert transform (DBH) method, which involves the backprojection of differentiated projection data followed by an inversion of the finite weighted Hilbert transform. The kernel of the inverse weighted Hilbert transform is solved numerically using matrix inversion. Numerical simulations confirm that the DBH method provides accurate reconstructions from half-scan and short-scan data, even when there is truncation. However, as the attenuation increases, finer data sampling is required.
Uterine Inversion; A case report
C, Bouchikhi; H, Saadi; B, Fakhir; H, Chaara; H, Bouguern; A, Banani; Melhouf MA
2008-01-01
The puerperal uterine inversion is a rare and severe complication occurring in the third stage of labour. The mechanisms are not completely known. However, extrinsic factors such as oxytocic arrests after a prolonged labour, umbilical cord traction or abdominal expression are pointed. Other intrinsic factors such as primiparity, uterine hypotonia, various placental localizations, fundic myoma or short umbilical cord were also reported. The diagnosis of the uterine inversion is mainly supporte...
-Colour Self-Inverse Compositions
Indian Academy of Sciences (India)
Geetika Narang; A K Agarwal
2006-08-01
MacMahon’s definition of self-inverse composition is extended to -colour self-inverse composition. This introduces four new sequences which satisfy the same recurrence relation with different initial conditions like the famous Fibonacci and Lucas sequences. For these new sequences explicit formulas, recurrence relations, generating functions and a summation formula are obtained. Two new binomial identities with combinatorial meaning are also given.
Thermal measurements and inverse techniques
Orlande, Helcio RB; Maillet, Denis; Cotta, Renato M
2011-01-01
With its uncommon presentation of instructional material regarding mathematical modeling, measurements, and solution of inverse problems, Thermal Measurements and Inverse Techniques is a one-stop reference for those dealing with various aspects of heat transfer. Progress in mathematical modeling of complex industrial and environmental systems has enabled numerical simulations of most physical phenomena. In addition, recent advances in thermal instrumentation and heat transfer modeling have improved experimental procedures and indirect measurements for heat transfer research of both natural phe
Chromatid Painting for Chromosomal Inversion Detection Project
National Aeronautics and Space Administration — We propose a novel approach to the detection of chromosomal inversions. Transmissible chromosome aberrations (translocations and inversions) have profound genetic...
Directory of Open Access Journals (Sweden)
Frank Joseph
2011-08-01
Full Text Available Abstract Background and Purpose Both endothelial progenitor cells (EPC and markers of neuroinflammation are candidate biomarkers for stroke severity and outcome prediction. A relationship between EPC and neuroinflammatory markers in early stroke is not fully elucidated. The objectives were to investigate correlations between EPC and neuroinflammation markers (adhesion molecules ICAM-1, VCAM-1, E-selectin, tumor necrosis factor (TNF-α, interleukin (IL-6, endothelin (ET-1, markers of tissue injury (matrix metalloproteinases (MMP-9 and tissue inhibitor of matrix metalloproteinases (TIMP-1 in early stroke patients. Methods We prospectively recruited symptomatic patients with ischemic cerebrovascular disease. We assessed stroke severity by using of acute (diffusion-weighted imaging (DWI and final lesion volumes (fluid attenuated inversion recovery (FLAIR. We measured serum soluble ICAM-1, VCAM-1, E-selectin, MMP-9, TIMP-1 and plasma TNF-α, IL-6, ET-1 by ELISA, and quantified EPC in mononuclear fraction of peripheral blood on days 1 and 3 in 17 patients (mean(SD age 62(14, with admission National Institutes of Health Stroke Scale (NIHSS 10(8 selected from 175 patients with imaging confirmed ischemic stroke. Non-parametric statistics, univariate and multivariate analysis were used. Results Only ICAM-1 inversely correlated with EPC subset CD133+CD34+ on day 1 (Spearman r = -0.6, p Conclusion Our study showed that high ICAM-1 is associated with low CD133+CD34+subset of EPC. Biomarkers of neuroinflammation may predict tissue injury and stroke severity in early ischemia.
Multidimensional NMR inversion without Kronecker products: Multilinear inversion
Medellín, David; Ravi, Vivek R.; Torres-Verdín, Carlos
2016-08-01
Multidimensional NMR inversion using Kronecker products poses several challenges. First, kernel compression is only possible when the kernel matrices are separable, and in recent years, there has been an increasing interest in NMR sequences with non-separable kernels. Second, in three or more dimensions, the singular value decomposition is not unique; therefore kernel compression is not well-defined for higher dimensions. Without kernel compression, the Kronecker product yields matrices that require large amounts of memory, making the inversion intractable for personal computers. Finally, incorporating arbitrary regularization terms is not possible using the Lawson-Hanson (LH) or the Butler-Reeds-Dawson (BRD) algorithms. We develop a minimization-based inversion method that circumvents the above problems by using multilinear forms to perform multidimensional NMR inversion without using kernel compression or Kronecker products. The new method is memory efficient, requiring less than 0.1% of the memory required by the LH or BRD methods. It can also be extended to arbitrary dimensions and adapted to include non-separable kernels, linear constraints, and arbitrary regularization terms. Additionally, it is easy to implement because only a cost function and its first derivative are required to perform the inversion.
Global inversion for anisotropy during full-waveform inversion
Debens, H. A.; Warner, M.; Umpleby, A.
2015-12-01
Full-waveform inversion (FWI) is a powerful tool for quantitative estimation of high-resolution high-fidelity models of subsurface seismic parameters, typically P-wave velocity. The solution to FWI's posed nonlinear inverse problem is obtained via an iterative series of linearized local updates to a start model, assuming this model lies within the basin of attraction to the global minimum. Thanks to many successful published applications to three-dimensional (3D) field datasets, its advance has been rapid and driven in large-part by the oil and gas industry. The consideration of seismic anisotropy during FWI is of vital importance, as it holds influence over both the kinematics and dynamics of seismic waveforms. If not appropriately taken into account then inadequacies in the anisotropy model are likely to manifest as significant error in the recovered velocity model. Conventionally, anisotropic FWI employs either an a priori anisotropy model, held fixed during FWI, or it uses a multi-parameter local inversion scheme to recover the anisotropy as part of the FWI; both of these methods can be problematic. Constructing an anisotropy model prior to FWI often involves intensive (and hence expensive) iterative procedures, such as travel-time tomography or moveout velocity analysis. On the other hand, introducing multiple parameters to FWI itself increases the complexity of what is already an underdetermined inverse problem. We propose that global rather than local FWI can be used to recover the long-wavelength acoustic anisotropy model, and that this can then be followed by more-conventional local FWI to recover the detailed model. We validate this approach using a full 3D field dataset, demonstrating that it avoids problems associated to crosstalk that can bedevil local inversion schemes, and reconciles well with in situ borehole measurements. Although our approach includes a global inversion for anisotropy, it is nonetheless affordable and practical for 3D field data.
Institute of Scientific and Technical Information of China (English)
白万晶; 宁刚; 李学胜
2015-01-01
目的：探讨磁共振成像(MRI)采用 T1加权反转恢复(T1WIR)序列在评价婴儿颅脑发育中的应用。方法选择2014年3月~6月在四川大学华西第二医院行颅脑 MRI 检查的28例婴儿为研究对象,对其采用 T1WIR 序列和 T1加权自旋回波(T1WSE)序列进行颅脑轴位扫描(横断层扫描),评价婴儿颅脑发育情况。由2位放射科医师独立对所有 MRI 图像进行髓鞘形成清晰显示情况评分(0~3分),3分为能清晰显示髓鞘形成者。对评分结果进行一致性检验,计算 Kappa 值,并对评分结果进行秩和检验；计算2种序列灰白质对比率(CR)及相对于 T1WSE 序列的 T1WIR 序列灰、白质信号降低率；分别对2种序列 CR 及灰、白质信号降低率进行配对 t 检验。结果①2位放射科医师对 MRI 图像的髓鞘形成清晰显示情况评分结果存在一致性(u=7.887,P =0.000),并且具有相当满意的一致程度(Kappa 值=0.792)；本组28例婴儿采用 T1WIR 序列 MRI 图像的髓鞘形成清晰显示情况评分结果高于 T1WSE 序列,且差异有统计学意义(3分 vs 2分,Z =-3.64,P =0.000)。②T1WIR 序列灰白质 CR 较 T1WSE 序列灰白质 CR 高,且差异有统计学意义[(0.26±0.06)vs (0.05±0.02),t =16.544,P =0.000]；对 T1WSE 序列而言, T1WIR 序列的灰质信号降低率较白质信号降低率低,且 差 异 有 统 计 学意义[(2.03±0.83)vs (2.25±1.26),t=-2.616,P =0.014]。结论采用 T1WIR 序列可取代常规 T1WSE 序列进行 MRI 成像,用于评价婴儿颅脑发育。%Objective To explore the application of Magnetic Resonance Imaging(MRI)T1 weighted inversion recovery(T1WIR)sequence in evaluation of brain development in infants.Methods A total of 28 infants who accepted MRI examination of brain in West China Second University Hospital,Sichuan University from March to June 2014 were chosen as study subjects.Every infant was underwent both T1WIR and T1 weighted spin echo (T1WSE)sequence in brain transverse
Relationship between comfort and attenuation measurements for two types of earplugs
Directory of Open Access Journals (Sweden)
David C Byrne
2011-01-01
Full Text Available Noise-induced hearing loss is almost always preventable if properly fitted hearing protectors are worn to reduce exposure. Many individuals choose not to wear hearing protection because it may interfere with effective communication in the workplace or it may be uncomfortable. Hearing protector comfort has not received the same amount of attention as noise reduction capability. The present study was conducted to evaluate the comfort level of two different types of insert earplugs as well as the attenuation levels achieved by the earplugs. Attenuation levels were obtained with a commercially available earplug fit-test system, and the comfort ratings were obtained by questionnaire. The primary research objective was to determine whether hearing protector comfort was related to measured attenuation values. A linear mixed effects model provided evidence for an inverse relationship between comfort and attenuation.
Layered material characterization using ultrasonic transmission. An inverse estimation methodology.
Messineo, María G; Rus, Guillermo; Eliçabe, Guillermo E; Frontini, Gloria L
2016-02-01
This paper presents an inverse methodology with the aim to characterize a layered material through the identification of acoustical and mechanical properties of its layers. The framework to accomplish this objective is provided by the Inverse Problems (IPs) theory. Material characterization refers to the detection and localization of discontinuities, as well as to the identification of physical properties, in order to predict the material behaviour. In this particular case, the IP is solved in the form of a parameter estimation problem, in which the goal is the estimation of the characteristic acoustic impedance, transit time, and attenuation of each layer. These parameters are directly related to relevant material properties, such as the speed of sound, density, elastic modulus and elastic energy dissipation constants. The IP solution is obtained by minimizing a cost functional formulated as the least squares error between the waveform calculated using an equivalent model, and the measured waveform obtained from ultrasonic transmission tests. The applied methodology allowed the accurate estimation of the desired parameters in materials composed of up to three layers. As a second contribution, a power law frequency dependence of the wave attenuation was identified for several homogeneous materials, based on the same ultrasonic transmission experiments. PMID:26456278
Eulenfeld, Tom; Wegler, Ulrich
2016-05-01
We developed an improved method for the separation of intrinsic and scattering attenuation of seismic shear waves by envelope inversion called Qopen. The method optimizes the fit between Green's functions for the acoustic, isotropic radiative transfer theory and observed energy densities of earthquakes. The inversion allows the determination of scattering and intrinsic attenuation, site corrections and spectral source energies for the investigated frequency bands. Source displacement spectrum and the seismic moment of the analysed events can be estimated from the obtained spectral source energies. We report intrinsic and scattering attenuation coefficients of shear waves near three geothermal reservoirs in Germany for frequencies between 1 and 70 Hz. The geothermal reservoirs are located in Insheim, Landau (both Upper Rhine Graben) and Unterhaching (Molasse basin). We compare these three sedimentary sites to two sites located in crystalline rock with respect to scattering and intrinsic attenuation. The inverse quality factor for intrinsic attenuation is constant in sediments for frequencies smaller than 10 Hz and decreasing for higher frequencies. For crystalline rock, it is on a lower level and strictly monotonic decreasing with frequency. Intrinsic attenuation dominates scattering except for the Upper Rhine Graben, where scattering is dominant for frequencies below 10 Hz. Observed source displacement spectra show a high-frequency fall-off greater than or equal to 3.
Optimization and geophysical inverse problems
Energy Technology Data Exchange (ETDEWEB)
Barhen, J.; Berryman, J.G.; Borcea, L.; Dennis, J.; de Groot-Hedlin, C.; Gilbert, F.; Gill, P.; Heinkenschloss, M.; Johnson, L.; McEvilly, T.; More, J.; Newman, G.; Oldenburg, D.; Parker, P.; Porto, B.; Sen, M.; Torczon, V.; Vasco, D.; Woodward, N.B.
2000-10-01
A fundamental part of geophysics is to make inferences about the interior of the earth on the basis of data collected at or near the surface of the earth. In almost all cases these measured data are only indirectly related to the properties of the earth that are of interest, so an inverse problem must be solved in order to obtain estimates of the physical properties within the earth. In February of 1999 the U.S. Department of Energy sponsored a workshop that was intended to examine the methods currently being used to solve geophysical inverse problems and to consider what new approaches should be explored in the future. The interdisciplinary area between inverse problems in geophysics and optimization methods in mathematics was specifically targeted as one where an interchange of ideas was likely to be fruitful. Thus about half of the participants were actively involved in solving geophysical inverse problems and about half were actively involved in research on general optimization methods. This report presents some of the topics that were explored at the workshop and the conclusions that were reached. In general, the objective of a geophysical inverse problem is to find an earth model, described by a set of physical parameters, that is consistent with the observational data. It is usually assumed that the forward problem, that of calculating simulated data for an earth model, is well enough understood so that reasonably accurate synthetic data can be generated for an arbitrary model. The inverse problem is then posed as an optimization problem, where the function to be optimized is variously called the objective function, misfit function, or fitness function. The objective function is typically some measure of the difference between observational data and synthetic data calculated for a trial model. However, because of incomplete and inaccurate data, the objective function often incorporates some additional form of regularization, such as a measure of smoothness
Optimization for nonlinear inverse problem
International Nuclear Information System (INIS)
The nonlinear inversion of geophysical data in general does not yield a unique solution, but a single model, representing the investigated field, is preferred for an easy geological interpretation of the observations. The analyzed region is constituted by a number of sub-regions where the multi-valued nonlinear inversion is applied, which leads to a multi-valued solution. Therefore, combining the values of the solution in each sub-region, many acceptable models are obtained for the entire region and this complicates the geological interpretation of geophysical investigations. In this paper are presented new methodologies, capable to select one model, among all acceptable ones, that satisfies different criteria of smoothness in the explored space of solutions. In this work we focus on the non-linear inversion of surface waves dispersion curves, which gives structural models of shear-wave velocity versus depth, but the basic concepts have a general validity. (author)
DEFF Research Database (Denmark)
Petersen, Kirsten Schultz; Friis, Vivi Soegaard; Haxholm, Birthe Lodahl;
2015-01-01
Mental health services strive to implement a recovery-oriented approach to rehabilitation. Little is known about service users' perception of the recovery approach. The aim is to explore the service user's perspectives on facilitators and barriers associated with recovery. Twelve residents living....... Stigmatization and social barriers occurred. Social relations to peer residents and staff were reported as potentially having a positive and negative impact on recovery. Studies have explored the user's perspectives on recovery but this study contributes with knowledge on how recovery-oriented services have an...
Advanced space recovery systems
Wailes, William K.
1989-01-01
The design evolution of a space recovery system designed by a NASA-contracted study is described, with particular attention given to the design of a recovery system for a propulsion/avionics module (P/AM), which weighs 60,000 lb at the recovery initiation and achieves subsonic terminal descent at or above 50,000 ft msl. The components of the recovery system concept are described together with the operational sequences of the recovery. The recovery system concept offers low cost, low weight, good performance, a potential for pinpoint landing, and an operational flexibility.
Estimation of Water Vapour Attenuation And Rain Attenuation
Directory of Open Access Journals (Sweden)
K.Kalyana Srinivas
2015-04-01
Full Text Available Attenuation due to and water vapour and rain can severely degrade the radio wave propagation at centimeter or millimeter wavelengths. It restricts the path length of radio communication systems and limits the use of higher frequencies for line-of-sight microwave links and satellite communications. The attenuation will pose a greater problem to communication as the frequency of occurrence of heavy rain increases.In a tropical region, like Malaysia, where excessive rainfall is a common phenomenon throughout the year, the knowledge of the rain attenuation at the frequency of operation is extremely required for the design of a reliable terrestrial and earth space communication link at a particular location.
The Transmuted Inverse Exponential Distribution
Directory of Open Access Journals (Sweden)
Pelumi Oguntunde
2014-12-01
Full Text Available This article introduces a two-parameter probability model which represents another generalization of the Inverse Exponential distribution by using the quadratic rank transmuted map. The proposed model is named Transmuted Inverse Exponential (TIE distribution and its statistical properties are systematically studied. We provide explicit expressions for its moments, moment generating function, quantile function, reliability function and hazard function. We estimate the parameters of the TIE distribution using the method of maximum likelihood estimation (MLE. The hazard function of the model has an inverted bathtub shape and we propose the usefulness of the TIE distribution in modeling breast cancer and bladder cancer data sets.
Inverse Interval Matrix: A Survey
Czech Academy of Sciences Publication Activity Database
Rohn, Jiří; Farhadsefat, R.
2011-01-01
Roč. 22, - (2011), s. 704-719. E-ISSN 1081-3810 R&D Projects: GA ČR GA201/09/1957; GA ČR GC201/08/J020 Institutional research plan: CEZ:AV0Z10300504 Keywords : interval matrix * inverse interval matrix * NP-hardness * enclosure * unit midpoint * inverse sign stability * nonnegative invertibility * absolute value equation * algorithm Subject RIV: BA - General Math ematics Impact factor: 0.808, year: 2010 http://www. math .technion.ac.il/iic/ela/ela-articles/articles/vol22_pp704-719.pdf
-Dimensional Fractional Lagrange's Inversion Theorem
Directory of Open Access Journals (Sweden)
F. A. Abd El-Salam
2013-01-01
Full Text Available Using Riemann-Liouville fractional differential operator, a fractional extension of the Lagrange inversion theorem and related formulas are developed. The required basic definitions, lemmas, and theorems in the fractional calculus are presented. A fractional form of Lagrange's expansion for one implicitly defined independent variable is obtained. Then, a fractional version of Lagrange's expansion in more than one unknown function is generalized. For extending the treatment in higher dimensions, some relevant vectors and tensors definitions and notations are presented. A fractional Taylor expansion of a function of -dimensional polyadics is derived. A fractional -dimensional Lagrange inversion theorem is proved.
Inverse problems Tikhonov theory and algorithms
Ito, Kazufumi
2014-01-01
Inverse problems arise in practical applications whenever one needs to deduce unknowns from observables. This monograph is a valuable contribution to the highly topical field of computational inverse problems. Both mathematical theory and numerical algorithms for model-based inverse problems are discussed in detail. The mathematical theory focuses on nonsmooth Tikhonov regularization for linear and nonlinear inverse problems. The computational methods include nonsmooth optimization algorithms, direct inversion methods and uncertainty quantification via Bayesian inference. The book offers a c
The attenuation and the attenuators: strategies and tactics
Directory of Open Access Journals (Sweden)
Antonio Briz
2013-12-01
Full Text Available This work is inscribed in a research project (ES.POR.ATENUAÇÃO that seeks to analyze and explain the attenuator activity in different regional varieties of Spanish and Portuguese, in order to perform, subsequently, different contrastive intralinguistic and interlinguistic studies. In this article, we explain some of the theoretical and methodological principles on which are based the qualitative and quantitative analysis. And especially, we will refer to the concept of attenuation (Briz 1995, 2002, 2003, 2005, 2007a, 2012.
Three-dimensional attenuation structure beneath North Island, New Zealand
Satake, Kenji; Hashida, Toshihiko
1989-03-01
Three-dimensional attenuation structure beneath North Island, New Zealand is determined by inversion of seismic intensity data. The method developed by Hashida and Shimazaki is used; the seismic intensity is converted to the maximum acceleration of the S-wave to obtain the acceleration at a point source and the attenuation structure. Because seismic intensity data have been accumulated on a uniform scale in New Zealand since the 1950's, we were able to use more than 2000 seismic intensity data from 26 earthquakes. The results show a remarkable contrast in the attenuation structure. In the top crustal layer, a low-Q area corresponding to the Central Volcanic Region is found. This low-Q area becomes wider to the northeast of North Island, suggesting that the Central Volcanic Region continues to the Havre Trough, a young back-arc basin. The southeastern part of the upper mantle beneath North Island shows high Q while the northwestern part shows low Q. The cross section shows that the high-Q region is dipping to the northwest, with a large amount of dip in the northeast and a smaller dip in the southwestern part of North Island. A comparison of the attenuation structure with microearthquake distribution indicates that this high-Q zone is the obliquely subducting Pacific plate. A zone of abnormally low Q which has cut the high-Q slab is found at a depth range of 130 to 230 km beneath the active volcanoes in the Taupo Volcanic Zone. A tear in the Pacific plate is suggested by this discontinuity in the attenuation structure. (1984).
Liu, Xin; Ben-Zion, Yehuda; Zigone, Dimitri
2015-11-01
We develop and apply an algorithm for deriving interstation seismic attenuation from cross-correlations of ambient noise recorded by linear arrays. Theoretical results on amplitude decay due to attenuation are used to form a linear least-square inversion for interstation QR values of Rayleigh surface waves propagating along linear arrays having three or more stations. The noise wave field is assumed stationary within each day and the interstation distances should be greater than the employed wavelength. The inversion uses differences of logarithmic amplitude decay curves measured at different stations from cross-correlation functions within a given frequency band. The background attenuation between noise sources and receivers is effectively cancelled with this method. The site amplification factors are assumed constant (or following similar patterns) in the frequency band of interest. The inversion scheme is validated with synthetic tests using ambient noise generated by ray-theory-based calculations with heterogeneous attenuation and homogenous velocity structure. The interstation attenuation and phase velocity dispersion curves are inverted from cross-correlations of the synthetic data. The method is then applied to triplets of stations from the regional southern California seismic network crossing the Mojave section of the San Andreas fault, and a dense linear array crossing the southern San Jacinto Fault zone. Bootstrap technique is used to derive empirical mean and confidence interval for the obtained inverse Q values. The results for the regional stations yield QR values around 25 for a frequency band 0.2-0.36 Hz. The results for the San Jacinto fault zone array give QR values of about 6-30 for frequencies in the range 15-25 Hz.
U.S. Environmental Protection Agency — The EPA Recovery Mapper is an Internet interactive mapping application that allows users to discover information about every American Recovery and Reinvestment Act...
The effect of frequency on Young's modulus and seismic wave attenuation
International Nuclear Information System (INIS)
Laboratory experiments were performed to measure the effect of frequency, water-saturation, and strain amplitude on Young's modulus and seismic wave attenuation on rock cores recovered on or near the site of a potential nuclear waste repository at Yucca Mountain, Nevada. The purpose of this investigation is to perform the measurements using four techniques: cyclic loading, waveform inversion, resonant bar, and ultrasonic velocity. The measurements ranged in frequency between 10-2 and 106 Hz. For the dry specimens Young's modulus and attenuation were independent of frequency; that is, all four techniques yielded nearly the same values for modulus and attenuation. For saturated specimens, a frequency dependence for both Young's modulus and attenuation was observed. In general, saturation reduced Young's modulus and increased seismic wave attenuation. The effect of strain amplitude on Young's modulus and attenuation was measured using the cyclic loading technique at a frequency of 10-1 Hz. The effect of strain amplitude in all cases was small. For some rocks, such as the potential repository horizon of the Topopah Spring Member tuff (TSw2), the effect of strain amplitude on both attenuation and modulus was minimal
Ouyang, Wei; Mao, Weijian; Li, Xuelei; Li, Wuqun
2014-08-01
Sound velocity inversion problem based on scattering theory is formulated in terms of a nonlinear integral equation associated with scattered field. Because of its nonlinearity, in practice, linearization algorisms (Born/single scattering approximation) are widely used to obtain an approximate inversion solution. However, the linearized strategy is not congruent with seismic wave propagation mechanics in strong perturbation (heterogeneous) medium. In order to partially dispense with the weak perturbation assumption of the Born approximation, we present a new approach from the following two steps: firstly, to handle the forward scattering by taking into account the second-order Born approximation, which is related to generalized Radon transform (GRT) about quadratic scattering potential; then to derive a nonlinear quadratic inversion formula by resorting to inverse GRT. In our formulation, there is a significant quadratic term regarding scattering potential, and it can provide an amplitude correction for inversion results beyond standard linear inversion. The numerical experiments demonstrate that the linear single scattering inversion is only good in amplitude for relative velocity perturbation () of background media up to 10 %, and its inversion errors are unacceptable for the perturbation beyond 10 %. In contrast, the quadratic inversion can give more accurate amplitude-preserved recovery for the perturbation up to 40 %. Our inversion scheme is able to manage double scattering effects by estimating a transmission factor from an integral over a small area, and therefore, only a small portion of computational time is added to the original linear migration/inversion process.
Sound attenuation in magnetorheological fluids
Rodríguez-López, J.; Elvira, L.; Resa, P.; Montero de Espinosa, F.
2013-02-01
In this work, the attenuation of ultrasonic elastic waves propagating through magnetorheological (MR) fluids is analysed as a function of the particle volume fraction and the magnetic field intensity. Non-commercial MR fluids made with iron ferromagnetic particles and two different solvents (an olive oil based solution and an Araldite-epoxy) were used. Particle volume fractions of up to 0.25 were analysed. It is shown that the attenuation of sound depends strongly on the solvent used and the volume fraction. The influence of a magnetic field up to 212 mT was studied and it was found that the sound attenuation increases with the magnetic intensity until saturation is reached. A hysteretic effect is evident once the magnetic field is removed.
The inverse electro-oculogram.
Doft, B H; Burns, S A; Elsner, A.
1982-01-01
An electro-oculogram ratio of less than one was found to be caused by limited ocular excursions under photopic conditions in a patient with a rod-cone dystrophy. Because this inverse electro-oculogram ratio was not caused by a decrease in standing potential under photopic conditions, it should be considered an artefact.
Exponential family and inverse problems
Czech Academy of Sciences Publication Activity Database
Gottvald, Aleš
Dordrecht: Kluwer Academic Publishers, 2003 - (Rudnicki, M.; Wiak, S.), s. - ISBN 1-4020-1506-2 R&D Projects: GA MŠk ME 526 Institutional research plan: CEZ:AV0Z2065902 Keywords : exponential family * inverse problems * Bayes' theorem Subject RIV: BD - Theory of Information
Topological evolution and inverse problems
Czech Academy of Sciences Publication Activity Database
Gottvald, Aleš
Dordrecht: Kluwer Academic Publishers, 2003 - (Rudnicki, M.; Wiak, S.), s. - ISBN 1-4020-1506-2 R&D Projects: GA MŠk ME 526 Institutional research plan: CEZ:AV0Z2065902 Keywords : topological evolution * inverse problems * Cartan's exterior calculus Subject RIV: BD - Theory of Information
Topological evolution and inverse problems
Czech Academy of Sciences Publication Activity Database
Gottvald, Aleš
Lodz: IMET, 2002, s. 12. [OIPE. LODZ (PL), 12.09.2002-14.09.2002] R&D Projects: GA MŠk ME 526 Grant ostatní: AIP(XC) KONTAKT 57/2000 Institutional research plan: CEZ:AV0Z2065902 Keywords : topological evolution * inverse problems Subject RIV: BD - Theory of Information
On Inverse Methodologies of ECT
Czech Academy of Sciences Publication Activity Database
Gottvald, Aleš
Brno: Institute of Scientific Instruments of the Academy of Sciences of the Czech Republic, 1996. s. 29. [Optimization and Inverse Problems in Electromagnetism /4./. 19.06.1996-21.06.1996, Brno] R&D Projects: GA ČR GA102/95/0282
Exponential family and inverse problems
Czech Academy of Sciences Publication Activity Database
Gottvald, Aleš
Lodz: IMET, 2002, s. 13. [OIPE. LODZ (PL), 12.09.2002-14.09.2002] R&D Projects: GA MŠk ME 526 Grant ostatní: AIP(XC) KONTAKT 57/2000 Institutional research plan: CEZ:AV0Z2065902 Keywords : exponential family * inverse problems Subject RIV: BD - Theory of Information
Inverse Problems in Data Analysis
Czech Academy of Sciences Publication Activity Database
Kůrková, Věra
2006-01-01
Roč. 82, č. 4 (2006), s. 41-48. ISSN 0033-2097 R&D Projects: GA AV ČR 1ET100300419 Institutional research plan: CEZ:AV0Z10300504 Keywords : learning from data * inverse problem * regularization * reproducing kernel Hilbert spaces Subject RIV: IN - Informatics, Computer Science
International Nuclear Information System (INIS)
This Engineering Task Plan (ETP) describes the tasks, i.e., tests, studies, external support and modifications planned to increase the recovery of the recovery of the waste tank contents using combinations of improved techniques, equipment, knowledge, experience and testing to better the recovery rates presently being experienced
de Miranda, John; Williams, Greg
2011-01-01
Young people are entering long-term recovery probably in greater numbers than ever before. A key word here is "probably" because we know precious little about the phenomenon of young people who recover from alcohol and drug addition. This article is a preliminary exploration of youth in recovery. It reviews several types of recovery support…
Inverse Kinematic Control of Humanoids Under Joint Constraints
Directory of Open Access Journals (Sweden)
Inhyeok Kim
2013-01-01
Full Text Available We propose an inverse kinematic control framework for a position controlled humanoid robot with bounded joint range, velocity, and acceleration limits. The proposed framework comprises two components, an inverse kinematics algorithm and a damping controller. The proposed IKTC (Inverse Kinematics with Task Corrections algorithm is based on the second order task‐ priority method in order to ensure the velocity‐continuity of the solution. When the minimum norm solution exceeds the joint bounds, the problem is treated as a quadratic optimization problem with box constraints; an optimal task correction that lets the solution satisfy the constraints is found. In order to express the three kinds of joint constraints as a second order box constraint, a novel method is also proposed. The joint stiffness of a position controlled humanoid robot necessitates a damping controller to attenuate jolts caused by repeated contacts. We design a damping controller by using an inverted pendulum model with a compliant joint that takes into account the compliance around the foot. By using ZMP [20] measurement, the proposed damping controller is applicable not only in SSP (Single Support Phase but also in DSP (Double Support Phase. The validity of the proposed methods is shown by imitating a captured whole‐body human motion with a position controlled humanoid robot.
Multidimensional guided wave dispersion recovery for locating defects in composite materials
Harley, Joel B.; De Marchi, Luca
2016-02-01
This paper provides a framework for characterizing anisotropic guided waves to locate damage in composite structures. Composite guided wave structural health monitoring is a significant challenge due to anisotropy. Wave velocities and attenuation vary as a function of propagation direction. Traditional localization algorithms, such as triangulation and delay-and-sum beamforming, fail for composite monitoring because they rely on isotropic velocity assumptions. Estimating the anisotropic velocities is also challenging because the inverse problem is inherently ill-posed. We cannot solve for an infinite number of directions with a finite number of measurements. This paper addresses these challenges by deriving a physics-based model for unidirectional anisotropy and integrating it with sparse recovery tools and matched field processing to characterize composite guided waves and locate an acoustic source. We validate our approach with experimental laser doppler vibrometry measurements from a glass fiber reinforced composite panel. We achieve localization accuracies of more than 290 and 49 times better, respectively, than delay-and-sum and matched field processing with isotropic assumptions.
Menin, O H; Martinez, A S; Costa, A M
2016-05-01
A generalized simulated annealing algorithm, combined with a suitable smoothing regularization function is used to solve the inverse problem of X-ray spectrum reconstruction from attenuation data. The approach is to set the initial acceptance and visitation temperatures and to standardize the terms of objective function to automate the algorithm to accommodate different spectra ranges. Experiments with both numerical and measured attenuation data are presented. Results show that the algorithm reconstructs spectra shapes accurately. It should be noted that in this algorithm, the regularization function was formulated to guarantee a smooth spectrum, thus, the presented technique does not apply to X-ray spectrum where characteristic radiation are present. PMID:26943902
Seismic full waveform inversion from compressive measurements
Ramirez, Ana; Arce, Gonzalo R.
2015-05-01
Traditional methods in seismic acquisition require sources and geophones that are uniformly located along a spatial line, using the Nyquist sampling rate. Depending on the area to be explored, it can be necessary to use seismic surveys with large offsets, or decrease the separation between adjacent geophones to improve the resolution, which generates very high volumes of data. It makes the exploration process more difficult and particularly expensive. This work presents the reconstruction of a compressive set of seismic traces acquired using the compressive sensing paradigm where the pair of sources and geophones are randomly located along the spatial line. The recovery of the wavefield from compressive measurements is feasible due to the capabilities of Curvelets on representing wave propagators with only a small set of coefficients. The method first uses the compressive samples to find a sparse vector representation of each pixel in a 2-D Curvelet dictionary. The sparse vector representation is estimated by solving a sparsity constrained optimization problem using the Gradient Projection for Sparse Reconstruction (GPSR) method. The estimated vector is then used to compute the seismic velocity profiles via acoustic Full Waveform Inversion (FWI). Simulations of the reconstructed image gathers and the resulting seismic velocity profiles illustrate the performance of the method. An improvement in the resulting images is obtained in comparison with traditional F-K filtering used in seismic data processing when traces are missing.
3-D joint inversion of the magnetotelluric phase tensor and vertical magnetic transfer functions
Tietze, Kristina; Ritter, Oliver; Egbert, Gary D.
2015-11-01
With advancing computational resources, 3-D inversion techniques have become feasible in recent years and are now a more widely used tool for magnetotelluric (MT) data interpretation. Galvanic distortion caused by small-scale near-surface inhomogeneities remains an obstacle for 3-D MT inversion which so far has experienced little attention. If not considered properly, the effect on 3-D inversion can be immense and result in erroneous subsurface models and interpretations. To tackle the problem we implemented inversion of the distortion-free phase tensor into the ModEM inversion package. The dimensionless phase tensor components describe only variations of the conductivity structure. When inverting these data, particular care has to be taken of the conductivity structure in the a priori model, which provides the reference frame when transferring the information from phase tensors into absolute conductivity values. Our results obtained with synthetic data show that phase tensor inversion can recover the regional conductivity structure in presence of galvanic distortion if the a priori model provides a reasonable assumption for the regional resistivity average. Joint inversion of phase tensor data and vertical magnetic transfer functions improves recovery of the absolute resistivity structure and is less dependent on the prior model. We also used phase tensor inversion for a data set of more than 250 MT sites from the central San Andreas fault, California, where a number of sites showed significant galvanic distortion. We find the regional structure of the phase tensor inversion results compatible with previously obtained models from impedance inversion. In the vicinity of distorted sites, phase tensor inversion models exhibit more homogeneous/smoother conductivity structures.
Attenuation (1/Q) estimation in reflection seismic records
Raji, Wasiu; Rietbrock, Andreas
2013-08-01
Despite its numerous potential applications, the lack of a reliable method for determining attenuation (1/Q) in seismic data is an issue when utilizing attenuation for hydrocarbon exploration. In this paper, a new method for measuring attenuation in reflection seismic data is presented. The inversion process involves two key stages: computation of the centroid frequency for the individual signal using a variable window length and fast Fourier transform; and estimation of the difference in the centroid frequency and travel time for paired incident and transmitted signals. The new method introduces a shape factor and a constant which allows several spectral shapes to be used to represent a real seismic signal without altering the mathematical model. Application of the new method to synthetic data shows that it can provide reliable estimates of Q using any of the spectral shapes commonly assumed for real seismic signals. Tested against two published methods of Q measurement, the new method shows less sensitivity to interference from noise and change of frequency bandwidth. The method is also applied to a 3D data set from the Gullfaks field, North Sea, Norway. The trace length is divided into four intervals: AB, BC, CD, and DE. Results show that interval AB has the lowest 1/Q value, and that interval BC has the highest 1/Q value. The values of 1/Q measured in the CDP stack using the new method are consistent with those measured using the classical spectral ratio method.
An adaptive noise attenuation method for edge and amplitude preservation
Institute of Scientific and Technical Information of China (English)
Cai Han-Peng; He Zhen-Hua; Li Ya-Lin; He Guang-Ming; Zou Wen; Zhang Dong-Jun; Liu Pu
2014-01-01
Noise intensity distributed in seismic data varies with different frequencies or frequency bands; thus, noise attenuation on the full-frequency band affects the dynamic properties of the seismic reflection signal and the subsequent seismic data interpretation, reservoir description, hydrocarbon detection, etc. Hence, we propose an adaptive noise attenuation method for edge and amplitude preservation, wherein the wavelet packet transform is used to decompose the full-band seismic signal into multiband data and then process these data using nonlinear anisotropic dip-oriented edge-preservingfi ltering. In the fi ltering, the calculated diffusion tensor from the structure tensor can be exploited to establish the direction of smoothing. In addition, the fault confidence measure and discontinuity operator can be used to preserve the structural and stratigraphic discontinuities and edges, and the decorrelation criteria can be used to establish the number of iterations. These parameters can minimize the intervention and subjectivity of the interpreter, and simplify the application of the proposed method. We applied the proposed method to synthetic and real 3D marine seismic data. We found that the proposed method could be used to attenuate noise in seismic data while preserving the effective discontinuity information and amplitude characteristics in seismic refl ection waves, providing high-quality data for interpretation and analysis such as high-resolution processing, attribute analysis, and inversion.
Josephson tunnel junction microwave attenuator
DEFF Research Database (Denmark)
Koshelets, V. P.; Shitov, S. V.; Shchukin, A. V.;
1993-01-01
A new element for superconducting electronic circuitry-a variable attenuator-has been proposed, designed, and successfully tested. The principle of operation is based on the change in the microwave impedance of a superconductor-insulator-superconductor (SIS) Josephson tunnel junction when dc biased...
Compact plasmonic variable optical attenuator
DEFF Research Database (Denmark)
Leosson, Kristjan; Rosenzveig, Tiberiu; Hermannsson, Pétur Gordon;
2008-01-01
We demonstrate plasmonic nanowire-based thermo-optic variable optical attenuators operating in the 1525-1625 nm wavelength range. The devices have a footprint as low as 1 mm, extinction ratio exceeding 40 dB, driving voltage below 3 V, and full modulation bandwidth of 1 kHz. The polarization...
Attenuation of Vrancea events revisited
International Nuclear Information System (INIS)
New aspects of the frequency-dependent attenuation of the seismic waves traveling from Vrancea subcrustal sources toward NW (Transylvanian Basin) and SE (Romanian Plain) are evidenced by the recent experimental data made available by the CALIXTO'99 tomography experiment. The observations validate the previous theoretical computations performed for the assessment, by means of a deterministic approach, of the seismic hazard in Romania. They reveal an essential aspect of the seismic ground motion attenuation, that has important implications on the probabilistic assessment of seismic hazard from Vrancea intermediate-depth earthquakes. The attenuation toward NW is shown to be a much stronger frequency-dependent effect than the attenuation toward SE and the seismic hazard computed by the deterministic approach fits satisfactorily well the observed ground motion distribution in the low-frequency band (< 1 Hz). The apparent contradiction with the historically-based intensity maps arises mainly from a systematic difference in the vulnerability (buildings eigenperiod) of the buildings in the intra- and extra-Carpathians regions. (author)
Battleground Energy Recovery Project
Energy Technology Data Exchange (ETDEWEB)
Bullock, Daniel [USDOE Gulf Coast Clean Energy Application Center, Woodlands, TX (United States)
2011-12-31
In October 2009, the project partners began a 36-month effort to develop an innovative, commercial-scale demonstration project incorporating state-of-the-art waste heat recovery technology at Clean Harbors, Inc., a large hazardous waste incinerator site located in Deer Park, Texas. With financial support provided by the U.S. Department of Energy, the Battleground Energy Recovery Project was launched to advance waste heat recovery solutions into the hazardous waste incineration market, an area that has seen little adoption of heat recovery in the United States. The goal of the project was to accelerate the use of energy-efficient, waste heat recovery technology as an alternative means to produce steam for industrial processes. The project had three main engineering and business objectives: Prove Feasibility of Waste Heat Recovery Technology at a Hazardous Waste Incinerator Complex; Provide Low-cost Steam to a Major Polypropylene Plant Using Waste Heat; and Create a Showcase Waste Heat Recovery Demonstration Project.
Energy Technology Data Exchange (ETDEWEB)
Erlangga, Mokhammad Puput [Geophysical Engineering, Institut Teknologi Bandung, Ganesha Street no.10 Basic Science B Buliding fl.2-3 Bandung, 40132, West Java Indonesia puput.erlangga@gmail.com (Indonesia)
2015-04-16
Separation between signal and noise, incoherent or coherent, is important in seismic data processing. Although we have processed the seismic data, the coherent noise is still mixing with the primary signal. Multiple reflections are a kind of coherent noise. In this research, we processed seismic data to attenuate multiple reflections in the both synthetic and real seismic data of Mentawai. There are several methods to attenuate multiple reflection, one of them is Radon filter method that discriminates between primary reflection and multiple reflection in the τ-p domain based on move out difference between primary reflection and multiple reflection. However, in case where the move out difference is too small, the Radon filter method is not enough to attenuate the multiple reflections. The Radon filter also produces the artifacts on the gathers data. Except the Radon filter method, we also use the Wave Equation Multiple Elimination (WEMR) method to attenuate the long period multiple reflection. The WEMR method can attenuate the long period multiple reflection based on wave equation inversion. Refer to the inversion of wave equation and the magnitude of the seismic wave amplitude that observed on the free surface, we get the water bottom reflectivity which is used to eliminate the multiple reflections. The WEMR method does not depend on the move out difference to attenuate the long period multiple reflection. Therefore, the WEMR method can be applied to the seismic data which has small move out difference as the Mentawai seismic data. The small move out difference on the Mentawai seismic data is caused by the restrictiveness of far offset, which is only 705 meter. We compared the real free multiple stacking data after processing with Radon filter and WEMR process. The conclusion is the WEMR method can more attenuate the long period multiple reflection than the Radon filter method on the real (Mentawai) seismic data.
Stormwater Attenuation by Green Roofs
Sims, A.; O'Carroll, D. M.; Robinson, C. E.; Smart, C. C.
2014-12-01
Innovative municipal stormwater management technologies are urgently required in urban centers. Inadequate stormwater management can lead to excessive flooding, channel erosion, decreased stream baseflows, and degraded water quality. A major source of urban stormwater is unused roof space. Green roofs can be used as a stormwater management tool to reduce roof generated stormwater and generally improve the quality of runoff. With recent legislation in some North American cities, including Toronto, requiring the installation of green roofs on large buildings, research on the effectiveness of green roofs for stormwater management is important. This study aims to assess the hydrologic response of an extensive sedum green roof in London, Ontario, with emphasis on the response to large precipitation events that stress municipal stormwater infrastructure. A green roof rapidly reaches field capacity during large storm events and can show significantly different behavior before and after field capacity. At field capacity a green roof has no capillary storage left for retention of stormwater, but may still be an effective tool to attenuate peak runoff rates by transport through the green roof substrate. The attenuation of green roofs after field capacity is linked to gravity storage, where gravity storage is the water that is temporarily stored and can drain freely over time after field capacity has been established. Stormwater attenuation of a modular experimental green roof is determined from water balance calculations at 1-minute intervals. Data is used to evaluate green roof attenuation and the impact of field capacity on peak flow rates and gravity storage. In addition, a numerical model is used to simulate event based stormwater attenuation. This model is based off of the Richards equation and supporting theory of multiphase flow through porous media.
Hedland, D. A.; Degonia, P. K.
1974-01-01
The RAE-1 spacecraft inversion performed October 31, 1972 is described based upon the in-orbit dynamical data in conjunction with results obtained from previously developed computer simulation models. The computer simulations used are predictive of the satellite dynamics, including boom flexing, and are applicable during boom deployment and retraction, inter-phase coast periods, and post-deployment operations. Attitude data, as well as boom tip data, were analyzed in order to obtain a detailed description of the dynamical behavior of the spacecraft during and after the inversion. Runs were made using the computer model and the results were analyzed and compared with the real time data. Close agreement between the actual recorded spacecraft attitude and the computer simulation results was obtained.
Novel approach to Abel inversion
International Nuclear Information System (INIS)
Simple yet versatile, physically valid emissivity functions for peaked and hollow profiles with only two determinable parameters are proposed for performing Abel inversion. The advantages of the proposed functions have been explored. The inversion is very fast, accurate, convenient, and viable, in contrast to the existing methods. The validation of these functions has been confirmed by using simulated data under various conditions. The error in the process has been computed and found to depend on the functional form of the model emissivity. A comprehensive comparison has been drawn with the existing method and it has been found to offer a definite advantage over the existing technique in some respects, especially for real time applications. Limitation of this technique has also been discussed. The soft x-ray and visible light emissivity profile of SINP tokamak has been successfully obtained by using this method
Southern California Adjoint Source Inversions
Tromp, J.; Kim, Y.
2007-12-01
Southern California Centroid-Moment Tensor (CMT) solutions with 9 components (6 moment tensor elements, latitude, longitude, and depth) are sought to minimize a misfit function computed from waveform differences. The gradient of a misfit function is obtained based upon two numerical simulations for each earthquake: one forward calculation for the southern California model, and an adjoint calculation that uses time-reversed signals at the receivers. Conjugate gradient and square-root variable metric methods are used to iteratively improve the earthquake source model while reducing the misfit function. The square-root variable metric algorithm has the advantage of providing a direct approximation to the posterior covariance operator. We test the inversion procedure by perturbing each component of the CMT solution, and see how the algorithm converges. Finally, we demonstrate full inversion capabilities using data for real Southern California earthquakes.
Tiling Spaces are Inverse Limits
Sadun, Lorenzo
2002-01-01
Let M be an arbitrary Riemannian homogeneous space, and let Omega be a space of tilings of M, with finite local complexity (relative to some symmetry group Gamma) and closed in the natural topology. Then Omega is the inverse limit of a sequence of compact finite-dimensional branched manifolds. The branched manifolds are (finite) unions of cells, constructed from the tiles themselves and the group Gamma. This result extends previous results of Anderson and Putnam, of Ormes, Radin and Sadun, of...
On the Inverse Radon Transform
Czech Academy of Sciences Publication Activity Database
Chvála, František
Praha : Humusoft, 2007, s. 1-6. ISBN 978-80-7080-658-6. [Annual Conference Proceedings - Technical Computing Prague 2007 /15./. Prague (CZ), 14.11.2007] R&D Projects: GA ČR(CZ) GA202/05/0728 Institutional research plan: CEZ:AV0Z20570509 Keywords : inverse Radon transform * Radon transform Subject RIV: BA - General Mathematics www.humusoft.cz/akce/matlab07
ISIR: Independent Sliced Inverse Regression
Li, Kevin
2013-01-01
International audience In this paper we consider a semiparametric regression model involving a $p$-dimensional explanatory variable ${\\mathbf{x}}$ and including a dimension reduction of ${\\mathbf{x}}$ via an index $B'{\\mathbf{x}}$. In this model, the main goal is to estimate $B$ and to predict the real response variable $Y$ conditionally to ${\\mathbf{x}}$. A standard approach is based on sliced inverse regression (SIR). We propose a new version of this method: the independent sliced invers...
Inverse Design of Electron Lens
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
The inverae design of electron lens is reelized by two different methods in this paper. One isdamped leastsquare method and the other is the artificial neural network method. Their merits and defects are discussed accordingto our calculation results in the psper. In the condition of selecting the learning samples properly, the artificial neuralnetwork has obvious advantages in the inverse design of electron lens. It is an effective method to solve the inversedesign problem in the electron optic system.
Reconstruction of bremsstrahlung spectra from attenuation data using generalized simulated annealing
Menin, Olavo Henrique; da Costa, Alessandro Martins
2014-01-01
The throughout knowledge of a X-ray beam spectrum is mandatory to assess the quality of its source device. Since the techniques to directly measurement such spectra are expensive and laborious, the X-ray spectrum reconstruction using attenuation data has been a promising alternative. However, such reconstruction corresponds mathematically to an inverse, nonlinear and ill-posed problem. Therefore, to solve it the use of powerful optimization algorithms and good regularization functions is required. Here, we present a generalized simulated annealing algorithm combined with a suitable smoothing regularization function to solve the X-ray spectrum reconstruction inverse problem. We also propose an approach to set the initial acceptance and visitation temperatures and a standardization of the objective function terms to automatize the algorithm to address with different spectra range. Numerical tests considering three different reference spectra with its attenuation curve are presented. Results show that the algori...
Ferrite attenuator modulation improves antenna performance
Hooks, J. C.; Larson, S. G.; Shorkley, F. H.; Williams, B. T.
1970-01-01
Ferrite attenuator inserted into appropriate waveguide reduces the gain of the antenna element which is causing interference. Modulating the ferrite attenuator to change the antenna gain at the receive frequency permits ground tracking until the antenna is no longer needed.
Generalized Inverses of Matrices over Rings
Institute of Scientific and Technical Information of China (English)
韩瑞珠; 陈建龙
1992-01-01
Let R be a ring,*be an involutory function of the set of all finite matrices over R. In this pa-per,necessary and sufficient conditions are given for a matrix to have a (1,3)-inverse,(1,4)-inverse,or Morre-Penrose inverse,relative to *.Some results about generalized inverses of matrices over division rings are generalized and improved.
An elegant 3-basis for inverse semigroups
Araujo, Joao
2010-01-01
It is well known that in every inverse semigroup the binary operation and the unary operation of inversion satisfy the following three identities: \\[ \\quad x=(xx')x \\qquad \\quad (xx')(y'y)=(y'y)(xx') \\qquad \\quad (xy)z=x(yz'')\\,. \\] The goal of this note is to prove the converse, that is, we prove that every unary semigroup satisfying these three identities is an inverse semigroup and the unary operation coincides with the usual inversion on such semigroups.
From time inversion to nonlinear QED
Jin, Wei Min
2000-01-01
In Minkowski flat space-time, it is perceived that time inversion is unitary rather than antiunitary, with energy being a time vector changing sign under time inversion. The Dirac equation, in the case of electromagnetic interaction, is not invariant under unitary time inversion, giving rise to a ``Klein paradox''. To render unitary time inversion invariance, a nonlinear wave equation is constructed, in which the ``Klein paradox'' disappears. In the case of Coulomb interaction, the revised no...
An elegant 3-basis for inverse semigroups
Araujo, Joao; Kinyon, Michael
2010-01-01
It is well known that in every inverse semigroup the binary operation and the unary operation of inversion satisfy the following three identities: [\\quad x=(xx')x \\qquad \\quad (xx')(y'y)=(y'y)(xx') \\qquad \\quad (xy)z=x(yz"). ] The goal of this note is to prove the converse, that is, we prove that an algebra of type $$ satisfying these three identities is an inverse semigroup and the unary operation coincides with the usual inversion on such semigroups.
-Colour even Self-Inverse Compositions
Indian Academy of Sciences (India)
Yu-hong Guo
2010-02-01
An -colour even self-inverse composition is defined as an -colour self-inverse composition with even parts. In this paper, we get generating functions, explicit formulas and recurrence formulas for -colour even self-inverse compositions. One new binomial identity is also obtained.
Inverse Computation and the Universal Resolving Algorithm
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
We survey fundamental concepts for inverse programming and thenpresent the Uni v ersal Resolving Algorithm, an algorithm for inverse computation in a first-orde r , functional programming language. We discuss the key concepts of the algorithm, including a three-step approach based on the notion of a perfect process tree, and demonstrate our implementation with several examples of inverse computation.
ENHANCEMENTS TO NATURAL ATTENUATION: SELECTED CASE STUDIES
Energy Technology Data Exchange (ETDEWEB)
Vangelas, K; W. H. Albright, W; E. S. Becvar, E; C. H. Benson, C; T. O. Early, T; E. Hood, E; P. M. Jardine, P; M. Lorah, M; E. Majche, E; D. Major, D; W. J. Waugh, W; G. Wein, G; O. R. West, O
2007-05-15
In 2003 the US Department of Energy (DOE) embarked on a project to explore an innovative approach to remediation of subsurface contaminant plumes that focused on introducing mechanisms for augmenting natural attenuation to achieve site closure. Termed enhanced attenuation (EA), this approach has drawn its inspiration from the concept of monitored natural attenuation (MNA).
Dutta, Gaurav
2014-10-01
Strong subsurface attenuation leads to distortion of amplitudes and phases of seismic waves propagating inside the earth. Conventional acoustic reverse time migration (RTM) and least-squares reverse time migration (LSRTM) do not account for this distortion, which can lead to defocusing of migration images in highly attenuative geologic environments. To correct for this distortion, we used a linearized inversion method, denoted as Qp-LSRTM. During the leastsquares iterations, we used a linearized viscoacoustic modeling operator for forward modeling. The adjoint equations were derived using the adjoint-state method for back propagating the residual wavefields. The merit of this approach compared with conventional RTM and LSRTM was that Qp-LSRTM compensated for the amplitude loss due to attenuation and could produce images with better balanced amplitudes and more resolution below highly attenuative layers. Numerical tests on synthetic and field data illustrated the advantages of Qp-LSRTM over RTM and LSRTM when the recorded data had strong attenuation effects. Similar to standard LSRTM, the sensitivity tests for background velocity and Qp errors revealed that the liability of this method is the requirement for smooth and accurate migration velocity and attenuation models.
Jiang, Quan; Zhang, Zheng Gang; Chopp, Michael
2009-01-01
MRI is a vital tool for the measurement of acute stroke and has been used to visualize changes in activation patterns during stroke recovery. There is emerging interest on using MRI to monitor the structural substrates of spontaneous recovery and neurorestorative treatment of stroke. In this review, we describe the use of MRI and its associated challenges to measure vascular and neuronal remodeling in response to spontaneous and therapy-induced stroke recovery. We demonstrate that MRI methodo...
Hussain, Zaib-un-nisa
1999-01-01
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University. The development of techniques for the removal and recovery of metals from industrial effluent taking account of the consequences of the definition of waste in the Basel Convention on transfrontier shipment of waste is reported. The use of fluidised bed cell electrolysis in the recovery of metals from dilute solutions is investigated, and the conditions for recovery optimised. For the first...
DEFF Research Database (Denmark)
Jørgensen, Christoffer C; Kehlet, Henrik
2014-01-01
We read with great interest the special article by Smart and Daniels discussing several important topics of perioperative care, especially regarding lack of consensus on the definition of "postoperative recovery", and need for further understanding of the pathogenic mechanisms. However, we disagree...... that a "new, clearly defined standard of what "recovery" actually is", demands "a look beyond enhanced recovery"(1) for several reasons. This article is protected by copyright. All rights reserved....
Simultaneous time-lapse electrical resistivity inversion
Hayley, Kevin; Pidlisecky, A.; Bentley, L. R.
2011-10-01
Time-lapse monitoring is a powerful tool for observing dynamic changes in the subsurface. In particular it offers the potential for achieving inversion results with increased fidelity through the inclusion of complementary information from multiple time-steps. This inclusion of complementary information can reduce the need for spatial smoothing, without adding inversion artifacts to the resulting images. Commonly used time-lapse inversion methods include the ratio method, cascaded time-lapse inversion, difference inversion and differencing independent inversions. We introduce two additional methods in which both time-lapse data sets are inverted simultaneously. In the first, called temporally constrained time-lapse inversion, inversion of both datasets is done under a single optimization procedure and constraints are added to the regularization to ensure that the changes from one time to another are smooth. In the second method, called simultaneous time-lapse inversion, the inversions at time 1 and time 2 are performed simultaneously and constraints of smoothness and closeness to a reference model are applied to the difference image produced at each iteration, and subsequently, the constraints are updated at each iteration. Through both a numerical and a field example we compare the results of common time-lapse inversion methods as well as the introduced approaches. We found that of the commonly used time-lapse inversion methods the difference inversion method produced the best resolution of time-lapse changes and was the most robust in the presence of noise. However, we found that the alternative approach of simultaneous time-lapse inversion produced the best reconstruction of modeled EC changes in the numerical example and easily interpretable high resolution difference images in the field example. Moreover, there was less tailoring of regularization parameters with our simultaneous time-lapse approach, suggesting that it will lend itself well to an automated
Stierle, Eva; Vavryčuk, Václav; Kwiatek, Grzegorz; Charalampidou, Elli-Maria; Bohnhoff, Marco
2016-04-01
Seismic moment tensors can provide information on the size and orientation of fractures producing acoustic emissions (AEs) and on the stress conditions in the sample. The moment tensor inversion of AEs is, however, a demanding procedure requiring carefully calibrated sensors and accurate knowledge of the velocity model. In field observations, the velocity model is usually isotropic and time independent. In laboratory experiments, the velocity is often anisotropic and time dependent and attenuation might be significant due to opening or closure of microcracks in the sample during loading. In this paper, we study the sensitivity of the moment tensor inversion to anisotropy of P-wave velocities and attenuation. We show that retrieved moment tensors critically depend on anisotropy and attenuation and their neglect can lead to misinterpretations of the source mechanisms. The accuracy of the inversion also depends on the fracturing mode of AEs: tensile events are more sensitive to P-wave anisotropy and attenuation than shear events. We show that geometry of faulting in anisotropic rocks should be studied using the source tensors, since the P- and T-axes of the moment tensors are affected by velocity anisotropy and deviate from the true orientation of faulting. The stronger the anisotropy is, the larger the deviations are. Finally, we prove that the moment tensor inversion applied to a large dataset of AEs can be utilized to provide information on the attenuation parameters of the rock sample. The method is capable of measuring anisotropic attenuation in the sample and allows for detection of dilatant cracking according to the stress regime.
International Nuclear Information System (INIS)
The Tertiary Oil Recovery Project is sponsored by the State of Kansas to introduce Kansas producers to the economic potential of enhanced recovery methods for Kansas fields. Specific objectives include estimation of the state-wide tertiary oil resource, identification and evaluation of the most applicable processes, dissemination of technical information to producers, occasional collaboration on recovery projects, laboratory studies on Kansas applicable processes, and training of students and operators in tertiary oil recovery methods. Papers have been processed separately for inclusion on the data base
Early arrival waveform inversion of shallow seismic land data
Hanafy, Sherif M.
2013-09-22
We estimate the near-surface velocity distribution over Wadi Qudaid in Saudi Arabia by applying early arrival waveform inversion (EWI) to shallow seismic land data collected with source-receiver offsets no longer than 232 m. The main purpose is to characterize the shallow subsurface for its water storage and reuse potential. To enhance the accuracy of EWI, we extracted a natural source wavelet from the data, and also corrected for the attenuation effects with an estimated factor Q. Results suggest that, compared to traveltime tomography, EWI can generate a highly resolved velocity tomogram from shallow seismic data. The more accurate EWI tomogram can make an economically important difference in assessing the storage potential of this wadi; in this case we find an increase of 18% of storage potential in the EWI tomogram relative to the traveltime tomogram. This approach suggests that FWI might be a more accurate means for economically characterizing the water storage potential for wadis’ throughout the world.
Wettability Modulated Charge Inversion and Ionic Transport in Nanofuidic Channels
Shaik, Vaseem Akram; Hossain, Syed Sahil; Chakraborty, Suman
2015-01-01
We unveil the role of substrate wettability on the reversal in the sign of the interfacial charge distribution in a nanochannel in presence of multivalent ions. In sharp contrast to the prevailing notion that hydrophobic interactions may trivially augment the effective surface charge, we demonstrate that the interplay between surface hydrophobicity and interfacial electrostatics may result in a decrease in the effective interfacial potential, and a consequent charge inversion over regimes of low surface charges. We also show that this phenomenon, in tandem with the interfacial hydrodynamics may non-trivially lead to either augmentation or attenuation or even reversal of the net streaming current, depending on the relevant physical scales involved. These results, supported by Molecular Dynamics simulations and experimental data, may bear far ranging consequences in understanding complex biophysical processes and designing nanofluidic devices and systems involving multivalent counterions.
Pore-scale modeling of pore structure effects on P-wave scattering attenuation in dry rocks.
Directory of Open Access Journals (Sweden)
Zizhen Wang
Full Text Available Underground rocks usually have complex pore system with a variety of pore types and a wide range of pore size. The effects of pore structure on elastic wave attenuation cannot be neglected. We investigated the pore structure effects on P-wave scattering attenuation in dry rocks by pore-scale modeling based on the wave theory and the similarity principle. Our modeling results indicate that pore size, pore shape (such as aspect ratio, and pore density are important factors influencing P-wave scattering attenuation in porous rocks, and can explain the variation of scattering attenuation at the same porosity. From the perspective of scattering attenuation, porous rocks can safely suit to the long wavelength assumption when the ratio of wavelength to pore size is larger than 15. Under the long wavelength condition, the scattering attenuation coefficient increases as a power function as the pore density increases, and it increases exponentially with the increase in aspect ratio. For a certain porosity, rocks with smaller aspect ratio and/or larger pore size have stronger scattering attenuation. When the pore aspect ratio is larger than 0.5, the variation of scattering attenuation at the same porosity is dominantly caused by pore size and almost independent of the pore aspect ratio. These results lay a foundation for pore structure inversion from elastic wave responses in porous rocks.
International Nuclear Information System (INIS)
Using the monthly hydrogeochemical data of ChangLe River system from 2004 to 2008, total nitrogen (TN) export load (Sn) from nonpoint sources (NPS) to stream and in-stream attenuation load (AL) was estimated by the inverse and forward format of an existing in-stream nutrient transport equation, respectively. Estimated Sn contributed 96 ± 2% of TN entering the river system, while AL reduced the input TN by 23 ± 14% in average. In-stream TN attenuation efficiency in high flow periods (10 ± 5% in average for the entire river system) was much lower than that in low flow periods (39 ± 17%). TN attenuation efficiency in tributaries (28 ± 16% in average) was much higher than that in mainstream (11 ± 8%). Hydrological conditions are important in determining the spatio-temporal distributions of NPS TN export, stream attenuation and discharge. Increasing the water residence time might be a practical method for mitigating stream TN. - Highlights: → We examine variations of catchment TN export, stream attenuation and discharge. → Hydrological condition determines the spatio-temporal variation of NPS pollution. → High flow rate brings high N export from catchment but low attenuation efficiency. → TN attenuation efficiency in tributaries is much higher than that in mainstream. → Increasing the stream water residence time will mitigate stream N discharge. - High flow rate brings large catchment nitrogen export but low in-stream attenuation efficiency, and then enhances stream nitrogen discharge.
Inversion of GPS meteorology data
Directory of Open Access Journals (Sweden)
K. Hocke
Full Text Available The GPS meteorology (GPS/MET experiment, led by the Universities Corporation for Atmospheric Research (UCAR, consists of a GPS receiver aboard a low earth orbit (LEO satellite which was launched on 3 April 1995. During a radio occultation the LEO satellite rises or sets relative to one of the 24 GPS satellites at the Earth's horizon. Thereby the atmospheric layers are successively sounded by radio waves which propagate from the GPS satellite to the LEO satellite. From the observed phase path increases, which are due to refraction of the radio waves by the ionosphere and the neutral atmosphere, the atmospheric parameter refractivity, density, pressure and temperature are calculated with high accuracy and resolution (0.5–1.5 km. In the present study, practical aspects of the GPS/MET data analysis are discussed. The retrieval is based on the Abelian integral inversion of the atmospheric bending angle profile into the refractivity index profile. The problem of the upper boundary condition of the Abelian integral is described by examples. The statistical optimization approach which is applied to the data above 40 km and the use of topside bending angle profiles from model atmospheres stabilize the inversion. The retrieved temperature profiles are compared with corresponding profiles which have already been calculated by scientists of UCAR and Jet Propulsion Laboratory (JPL, using Abelian integral inversion too. The comparison shows that in some cases large differences occur (5 K and more. This is probably due to different treatment of the upper boundary condition, data runaways and noise. Several temperature profiles with wavelike structures at tropospheric and stratospheric heights are shown. While the periodic structures at upper stratospheric heights could be caused by residual errors of the ionospheric correction method, the periodic temperature fluctuations at heights below 30 km are most likely caused by atmospheric waves (vertically
The continuation inverse problem revisited
Huestis, Stephen P.
1998-06-01
The non-uniqueness of the continuation of a finite collection of harmonic potential field data to a level surface in the source-free region forces its treatment as an inverse problem. A formalism is proposed for the construction of continuation functions which are extremal by various measures. The problem is cast in such a form that the inverse problem solution is the potential function on the lowest horizontal surface above all sources, serving as the boundary function for the Dirichlet problem in the upper half-plane. The desired continuation, at the higher level of interest, must then be in the range of the upward continuation operator acting on this boundary function, rather than being allowed the full freedom of itself being part of a Dirichlet problem boundary function. Extremal solutions minimize non-linear functionals of the continuation function, which are re-expressed as different functionals of the boundary function. A crux of the method is that there is no essential distinction between the upward and downward continuation inverse problems to levels above or below data locations. Casting the optimization as a Lagrange multiplier problem leads to an integral equation for the boundary function, which is readily solved in the Fourier domain for a certain class of functionals. The desired extremal continuation is then given by upward continuation. It is found that for some functionals, application of the Lagrange multiplier theorem requires a further restriction on the set of allowable boundary functions: bandlimitedness is a natural choice for the continuation problem. With this imposition, the theory is developed in detail for semi-norm functionals penalizing departure from a constant potential, in the 2-norm and Sobelev norm senses, and illustrated by application for a small synthetic Deep Tow magnetic field data set.
Zabotin, N A; Kovalenko, E S; Frolov, V L; Komrakov, G P; Mityakov, N A; Sergeev, E N
2001-01-01
Multiple scattering from artificial random irregularities HF-induced in the ionosphere F region causes significant attenuation of both ordinary and extraordinary radio waves together with the conventional anomalous absorption of ordinary waves due to their conversion into the plasma waves. To study in detail features of this effect, purposeful measurements of the attenuation of weak probing waves of the extraordinary polarization have been performed at the Sura heating facility. Characteristic scale lengths of the involved irregularities are ~0.1-1 km across the geomagnetic field lines. To determine the spectral characteristics of these irregularities from the extraordinary probing wave attenuation measurements, a simple procedure of the inverse problem solving has been implemented and some conclusions about the artificial irregularity features have been drawn. Theory and details of experiments have been stated earlier. This paper reports results of two experimental campaigns carried out in August 2000 and Ju...
High resolution 3D nonlinear integrated inversion
Institute of Scientific and Technical Information of China (English)
Li Yong; Wang Xuben; Li Zhirong; Li Qiong; Li Zhengwen
2009-01-01
The high resolution 3D nonlinear integrated inversion method is based on nonlinear theory. Under layer control, the log data from several wells (or all wells) in the study area and seismic trace data adjacent to the wells are input to a network with multiple inputs and outputs and are integratedly trained to obtain an adaptive weight function of the entire study area. Integrated nonlinear mapping relationships are built and updated by the lateral and vertical geologic variations of the reservoirs. Therefore, the inversion process and its inversion results can be constrained and controlled and a stable seismic inversion section with high resolution with velocity inversion, impedance inversion, and density inversion sections, can be gained. Good geologic effects have been obtained in model computation tests and real data processing, which verified that this method has high precision, good practicality, and can be used for quantitative reservoir analysis.
Spray formation: an inverse cascade
Ling, Yue; Tryggvason, Gretar; zaleski, Stephane
2015-01-01
We present a study of droplet formation in a gas-liquid mixing layer using direct numerical simulation. It is seen that two mechanisms compete to generate the droplets: fingering at the tip of the waves and hole formation in the thin liquid sheet. The three dimensional liquid structures are much shorter than the longitudinal wavelength of the instability at the first instant of their formation. As time evolves, the structures evolves to larger and larger scales, in a way similar to the inverse cascade of length scales in droplet impact and impact crown formation.
Inverse strategies for molecular design
International Nuclear Information System (INIS)
An 'inverse' molecular design strategy is described to assist in the development of new molecules with optimized properties. This approach is based on a molecular orbital view and can be used to tailor ground state or excited state properties subject to particular constrains. In this scheme, wave functions are sought that optimize a chemical or electronic property, and then a Hamiltonian is constructed that generates these optimized wave functions. Analysis of the chemical properties in the optimized systems may suggest new synthetic targets. Examples are presented that optimize the transition dipole moment in some simple structures. 15 refs., 6 figs
Inverse Problems in Structural Mechanics
Li, Jing
2005-01-01
This dissertation deals with the solution of three inverse problems in structural mechanics. The first one is load updating for finite element models (FEMs). A least squares fitting is used to identify the load parameters. The basic studies are made for geometrically linear and nonlinear FEMs of beams or frames by using a four-noded curved beam element, which, for a given precision, may significantly solve the ill-posed problem by reducing the overall number of degrees of freedom (DOF) of t...
High dimensional linear inverse modelling
Cooper, Fenwick C
2015-01-01
We introduce and demonstrate two linear inverse modelling methods for systems of stochastic ODE's with accuracy that is independent of the dimensionality (number of elements) of the state vector representing the system in question. Truncation of the state space is not required. Instead we rely on the principle that perturbations decay with distance or the fact that for many systems, the state of each data point is only determined at an instant by itself and its neighbours. We further show that all necessary calculations, as well as numerical integration of the resulting linear stochastic system, require computational time and memory proportional to the dimensionality of the state vector.
MIT inverse Compton source concept
Graves, William S.; Brown, W.; Kaertner, Franz X.; Moncton, David E.
2009-01-01
A compact X-ray source based on inverse Compton scattering of a high-power laser on a high-brightness linac beam is described. The facility can operate in two modes: at high (MHz) repetition rate with flux and brilliance similar to that of a beamline at a large 2nd generation synchrotron, but with short ∼1 ps pulses, or as a 10 Hz high flux-per-pulse single-shot machine. It has a small footprint and low cost appropriate for university or industry laboratories. The key enabling technologies ar...
Direct inversion of shallow-water bathymetry from EO-1 hyperspectral remote sensing data
Institute of Scientific and Technical Information of China (English)
Zhishen Liu; Yan Zhou
2011-01-01
@@ Using the US National Aeronautics and space Administration (NASA) Earth Observing-1 Mission (EO-1)hyperion hyperspectral remote sensing data, we study the shallow-water bathymetry inversion in Smith Island Bay.The fast line-of-sight atmospheric analysis of spectral hypercubes module is applied for atmospheric correction, and principal component analysis method combined with scatter diagram and maximum likelihood classification is used for seabed classification.The diffuse attenuation coefficient Kd is derived using quasi-analytical algorithm (QAA), which performs well in optically deep water.Kd obtained from QAA requires correction, particularly those derived in some coastal areas with optically shallow water and calculated by direct inversion based on radiative transfer theory to obtain the bathymetry.The direct inversion method derives the water depth quickly, and matches the results from optimized algorithm.%Using the US National Aeronautics and space Administration (NASA) Earth Observing-1 Mission (EO-1) hyperion hyperspectral remote sensing data, we study the shallow-water bathymetry inversion in Smith Island Bay.The fast line-of-sight atmospheric analysis of spectral hypercubes module is applied for atmospheric correction, and principal component analysis method combined with scatter diagram and maximum likelihood classification is used for seabed classification.The diffuse attenuation coefficient Kd is derived using quasi-analytical algorithm (QAA), which performs well in optically deep water Kd obtained from QAA requires correction, particularly those derived in some coastal areas with optically shallow water and calculated by direct inversion based on radiative transfer theory to obtain the bathymetry.The direct inversion method derives the water depth quickly, and matches the results from optimized algorithm.
Attenuation in silica-based optical fibers
DEFF Research Database (Denmark)
Wandel, Marie Emilie
2006-01-01
absorption peaks in order to investigate the cause of an unusual high attenuation in a series of transmission fibers. Strong indications point to Ni2+ in octahedral coordination as being the cause of the high attenuation. The attenuation of fibers having a high core refractive index is analyzed and the cause...... well as the viscosity profile a lower attenuation of high index fibers can be obtained. The design of dispersion compensating fibers using the super mode approach is described, the object being to design dispersion compensating fibers for dispersion compensating fiber modules having a low attenuation......, described by a high figure of merit. The major trade offs encountered when designing dispersion compensating fibers with high figure of merit are to obtain a very negative dispersion, low attenuation and low micro bend loss at the same time. The model for predicting the attenuation of high index fibers is...
LHC Report: 2 inverse femtobarns!
Mike Lamont for the LHC Team
2011-01-01
The LHC is enjoying a confluence of twos. This morning (Friday 5 August) we passed 2 inverse femtobarns delivered in 2011; the peak luminosity is now just over 2 x1033 cm-2s-1; and recently fill 2000 was in for nearly 22 hours and delivered around 90 inverse picobarns, almost twice 2010's total. In order to increase the luminosity we can increase of number of bunches, increase the number of particles per bunch, or decrease the transverse beam size at the interaction point. The beam size can be tackled in two ways: either reduce the size of the injected bunches or squeeze harder with the quadrupole magnets situated on either side of the experiments. Having increased the number of bunches to 1380, the maximum possible with a 50 ns bunch spacing, a one day meeting in Crozet decided to explore the other possibilities. The size of the beams coming from the injectors has been reduced to the minimum possible. This has brought an increase in the peak luminosity of about 50% and the 2 x 1033 cm...
MOSES Inversions using Multiresolution SMART
Rust, Thomas; Fox, Lewis; Kankelborg, Charles; Courrier, Hans; Plovanic, Jacob
2014-06-01
We present improvements to the SMART inversion algorithm for the MOSES imaging spectrograph. MOSES, the Multi-Order Solar EUV Spectrograph, is a slitless extreme ultraviolet spectrograph designed to measure cotemporal narrowband spectra over a wide field of view via tomographic inversion of images taken at three orders of a concave diffraction grating. SMART, the Smooth Multiplicative Algebraic Reconstruction Technique, relies on a global chi squared goodness of fit criterion, which enables overfit and underfit regions to "balance out" when judging fit quality. "Good" reconstructions show poor fits at some positions and length scales. Here we take a multiresolution approach to SMART, applying corrections to the reconstruction at positions and scales where correction is warranted based on the noise. The result is improved fit residuals that more closely resemble the expected noise in the images. Within the multiresolution framework it is also easy to include a regularized deconvolution of the instrument point spread functions, which we do. Different point spread functions among MOSES spectral orders results in spurious doppler shifts in the reconstructions, most notable near bright compact emission. We estimate the point spread funtions from the data. Deconvolution is done using the Richardson-Lucy method, which is algorithmically similar to SMART. Regularization results from only correcting the reconstruction at positions and scales where correction is warranted based on the noise. We expect the point spread function deconvolution to increase signal to noise and reduce systematic error in MOSES reconstructions.
Instrument developments for inverse photoemission
International Nuclear Information System (INIS)
Experimental developments principally concerning electron sources for inverse photoemission are presented. The specifications of the electron beam are derived from experiment requirements, taking into account the limitations encountered (space charge divergence). For a wave vector resolution of 0.2 A-1, the maximum current is 25 microA at 20 eV. The design of a gun providing such a beam in the range 5 to 50 eV is presented. Angle-resolved inverse photoemission experiments show angular effects at 30 eV. For an energy of 10 eV, angular effects should be stronger, but the low efficiency of the spectrometer in this range makes the experiments difficult. The total energy resolution of 0.3 eV is the result mainly of electron energy spread, as expected. The electron sources are based on field effect electron emission from a cathode consisting of a large number of microtips. The emission arises from a few atomic cells for each tip. The ultimate theoretical energy spread is 0.1 eV. This value is not attained because of an interface resistance problem. A partial solution of this problem allows measurement of an energy spread of 0.9 eV for a current of 100 microA emitted at 60 eV. These cathodes have a further advantage in that emission can occur at a low temperature
The seismic reflection inverse problem
International Nuclear Information System (INIS)
The seismic reflection method seeks to extract maps of the Earth's sedimentary crust from transient near-surface recording of echoes, stimulated by explosions or other controlled sound sources positioned near the surface. Reasonably accurate models of seismic energy propagation take the form of hyperbolic systems of partial differential equations, in which the coefficients represent the spatial distribution of various mechanical characteristics of rock (density, stiffness, etc). Thus the fundamental problem of reflection seismology is an inverse problem in partial differential equations: to find the coefficients (or at least some of their properties) of a linear hyperbolic system, given the values of a family of solutions in some part of their domains. The exploration geophysics community has developed various methods for estimating the Earth's structure from seismic data and is also well aware of the inverse point of view. This article reviews mathematical developments in this subject over the last 25 years, to show how the mathematics has both illuminated innovations of practitioners and led to new directions in practice. Two themes naturally emerge: the importance of single scattering dominance and compensation for spectral incompleteness by spatial redundancy. (topical review)
Inverse problems in systems biology
International Nuclear Information System (INIS)
Systems biology is a new discipline built upon the premise that an understanding of how cells and organisms carry out their functions cannot be gained by looking at cellular components in isolation. Instead, consideration of the interplay between the parts of systems is indispensable for analyzing, modeling, and predicting systems' behavior. Studying biological processes under this premise, systems biology combines experimental techniques and computational methods in order to construct predictive models. Both in building and utilizing models of biological systems, inverse problems arise at several occasions, for example, (i) when experimental time series and steady state data are used to construct biochemical reaction networks, (ii) when model parameters are identified that capture underlying mechanisms or (iii) when desired qualitative behavior such as bistability or limit cycle oscillations is engineered by proper choices of parameter combinations. In this paper we review principles of the modeling process in systems biology and illustrate the ill-posedness and regularization of parameter identification problems in that context. Furthermore, we discuss the methodology of qualitative inverse problems and demonstrate how sparsity enforcing regularization allows the determination of key reaction mechanisms underlying the qualitative behavior. (topical review)
Solution for Ill-Posed Inverse Kinematics of Robot Arm by Network Inversion
Directory of Open Access Journals (Sweden)
Takehiko Ogawa
2010-01-01
Full Text Available In the context of controlling a robot arm with multiple joints, the method of estimating the joint angles from the given end-effector coordinates is called inverse kinematics, which is a type of inverse problems. Network inversion has been proposed as a method for solving inverse problems by using a multilayer neural network. In this paper, network inversion is introduced as a method to solve the inverse kinematics problem of a robot arm with multiple joints, where the joint angles are estimated from the given end-effector coordinates. In general, inverse problems are affected by ill-posedness, which implies that the existence, uniqueness, and stability of their solutions are not guaranteed. In this paper, we show the effectiveness of applying network inversion with regularization, by which ill-posedness can be reduced, to the ill-posed inverse kinematics of an actual robot arm with multiple joints.
Imaging Rayleigh wave attenuation with USArray
Bao, Xueyang; Dalton, Colleen A.; Jin, Ge; Gaherty, James B.; Shen, Yang
2016-07-01
The EarthScope USArray provides an opportunity to obtain detailed images of the continental upper mantle at an unprecedented scale. The majority of mantle models derived from USArray data to date contain spatial variations in seismic-wave speed; however, in many cases these data sets do not by themselves allow a non-unique interpretation. Joint interpretation of seismic attenuation and velocity models can improve upon the interpretations based only on velocity and provide important constraints on the temperature, composition, melt content, and volatile content of the mantle. The surface wave amplitudes that constrain upper-mantle attenuation are sensitive to factors in addition to attenuation, including the earthquake source excitation, focusing and defocusing by elastic structure, and local site amplification. Because of the difficulty of isolating attenuation from these other factors, little is known about the attenuation structure of the North American upper mantle. In this study, Rayleigh wave traveltime and amplitude in the period range 25-100 s are measured using an interstation cross-correlation technique, which takes advantage of waveform similarity at nearby stations. Several estimates of Rayleigh wave attenuation and site amplification are generated at each period, using different approaches to separate the effects of attenuation and local site amplification on amplitude. It is assumed that focusing and defocusing effects can be described by the Laplacian of the traveltime field. All approaches identify the same large-scale patterns in attenuation, including areas where the attenuation values are likely contaminated by unmodelled focusing and defocusing effects. Regionally averaged attenuation maps are constructed after removal of the contaminated attenuation values, and the variations in intrinsic shear attenuation that are suggested by these Rayleigh wave attenuation maps are explored.
Optimization and inverse problems in electromagnetism
Wiak, Sławomir
2003-01-01
From 12 to 14 September 2002, the Academy of Humanities and Economics (AHE) hosted the workshop "Optimization and Inverse Problems in Electromagnetism". After this bi-annual event, a large number of papers were assembled and combined in this book. During the workshop recent developments and applications in optimization and inverse methodologies for electromagnetic fields were discussed. The contributions selected for the present volume cover a wide spectrum of inverse and optimal electromagnetic methodologies, ranging from theoretical to practical applications. A number of new optimal and inverse methodologies were proposed. There are contributions related to dedicated software. Optimization and Inverse Problems in Electromagnetism consists of three thematic chapters, covering: -General papers (survey of specific aspects of optimization and inverse problems in electromagnetism), -Methodologies, -Industrial Applications. The book can be useful to students of electrical and electronics engineering, computer sci...
Inverse Magnetic/Shear Catalysis
McInnes, Brett
2015-01-01
It is well known that very large magnetic fields are generated when the Quark-Gluon Plasma is formed during peripheral heavy-ion collisions. Lattice, holographic, and other studies strongly suggest that these fields may, for observationally relevant field values, induce ``inverse magnetic catalysis'', signalled by a lowering of the critical temperature for the chiral/deconfinement transition. The theoretical basis of this effect has recently attracted much attention; yet so far these investigations have not included another, equally dramatic consequence of the peripheral collision geometry: the QGP acquires a large angular momentum vector, parallel to the magnetic field. Here we use holographic techniques to argue that the angular momentum can also, independently, have an effect on transition temperatures, and we obtain a rough estimate of the relative effects of the presence of both a magnetic field and an angular momentum density. We find that the shearing angular momentum reinforces the effect of the magne...
Inverse diffusion theory of photoacoustics
International Nuclear Information System (INIS)
This paper analyzes the reconstruction of diffusion and absorption parameters in an elliptic equation from knowledge of internal data. In the application of photoacoustics, the internal data are the amount of thermal energy deposited by high frequency radiation propagating inside a domain of interest. These data are obtained by solving an inverse wave equation, which is well studied in the literature. We show that knowledge of two internal data based on well-chosen boundary conditions uniquely determines two constitutive parameters in diffusion and Schrödinger equations. Stability of the reconstruction is guaranteed under additional geometric constraints of strict convexity. No geometric constraints are necessary when 2n internal data for well-chosen boundary conditions are available, where n is spatial dimension. The set of well-chosen boundary conditions is characterized in terms of appropriate complex geometrical optics solutions
Bayesian multitask inverse reinforcement learning
Dimitrakakis, Christos
2011-01-01
We generalise the problem of inverse reinforcement learning to multiple tasks, from a set of demonstrations. Each demonstration may represent one expert trying to solve a different task. Alternatively, one may see each demonstration as given by a different expert trying to solve the same task. Our main technical contribution is to solve the problem by formalising it as statistical preference elicitation, via a number of structured priors, whose form captures our biases about the relatedness of different tasks or expert policies. We show that our methodology allows us not only to learn to efficiently from multiple experts but to also effectively differentiate between the goals of each. Possible applications include analysing the intrinsic motivations of subjects in behavioural experiments and imitation learning from multiple teachers.
Inverse approach to design magnets
International Nuclear Information System (INIS)
An inverse approach is always better to design an optimised magnet, where the field profile is known, rather than tuning the geometry of the magnet till the desired profile is achieved. We have developed an optimizer based on standard multi dimensional Newton-Raphson technique. The optimum geometry of a magnet is obtained by a combination of analytical and numerical methods. This code is versatile and can be used to design various magnets used in different applications. Here we present two different cases to show the efficiency of the code. First, we present the design of a solenoid magnet for a.c. susceptibility set up. Second, we describe the design of two pairs of Helmholtz coils for ion beam deflection. (author)
Energy Technology Data Exchange (ETDEWEB)
Paffhausen, M.W.; Smith, D.L.; Ugaki, S.N.
1990-09-01
This report describes Phase I of the Solvent Recycle/Recovery Task of the DOE Chlorinated Solvent Substitution Program for the US Air Force by the Idaho National Engineering Laboratory, EG G Idaho, Inc., through the US Department of Energy, Idaho Operations Office. The purpose of the task is to identify and test recovery and recycling technologies for proposed substitution solvents identified by the Biodegradable Solvent Substitution Program and the Alternative Solvents/Technologies for Paint Stripping Program with the overall objective of minimizing hazardous wastes. A literature search to identify recycle/recovery technologies and initial distillation studies has been conducted. 4 refs.
Graph inverse semigroups: their characterization and completion
David G Jones; Lawson, Mark V
2011-01-01
Graph inverse semigroups generalize the polycyclic inverse monoids and play an important role in the theory of C*-algebras. This paper has two main goals: first, to provide an abstract characterization of graph inverse semigroups; and second, to show how they may be completed, under suitable conditions, to form what we call the Cuntz-Krieger semigroup of the graph. This semigroup is the ample semigroup of a topological groupoid associated with the graph, and the semigroup analogue of the Leav...
Lectures on the inverse scattering method
International Nuclear Information System (INIS)
In a series of six lectures an elementary introduction to the theory of inverse scattering is given. The first four lectures contain a detailed theory of solitons in the framework of the KdV equation, together with the inverse scattering theory of the one-dimensional Schroedinger equation. In the fifth lecture the dressing method is described, while the sixth lecture gives a brief review of the equations soluble by the inverse scattering method. (author)
STRUCTURES OF CIRCULANT INVERSE M-MATRICES
Institute of Scientific and Technical Information of China (English)
Yurui Lin; Linzhang Lu
2007-01-01
In this paper,we present a useful result on the structures of circulant inverse Mis not a positive matrix and not equal to c0I,then A is an inverse M-matrix if and only if there exists a positive integer k,which is a proper factor of n,such that cjk＞0 for The result is then extended to the so-called generalized circulant inverse M-matrices.
NICOLE: NLTE Stokes Synthesis/Inversion Code
Socas-Navarro, H.
2015-08-01
NICOLE, written in Fortran 90, seeks the model atmosphere that provides the best fit to the Stokes profiles (in a least-squares sense) of an arbitrary number of simultaneously-observes spectral lines from solar/stellar atmospheres. The inversion core used for the development of NICOLE is the LORIEN engine (the Lovely Reusable Inversion ENgine), which combines the SVD technique with the Levenberg-Marquardt minimization method to solve the inverse problem.
Forward model nonlinearity versus inverse model nonlinearity
Mehl, S.
2007-01-01
The issue of concern is the impact of forward model nonlinearity on the nonlinearity of the inverse model. The question posed is, "Does increased nonlinearity in the head solution (forward model) always result in increased nonlinearity in the inverse solution (estimation of hydraulic conductivity)?" It is shown that the two nonlinearities are separate, and it is not universally true that increased forward model nonlinearity increases inverse model nonlinearity. ?? 2007 National Ground Water Association.
Supersymmetry and the Moebius inversion function
International Nuclear Information System (INIS)
We show that the Moebius inversion function of number theory can be interpreted as the operator (-1)F in quantum field theory. Consequently, we are able to provide physical interpretations for various properties of the Moebius inversion function. These include a physical understanding of the Moebius Inversion Formula and of a result that is equivalent to the prime number theorem. Supersymmetry and the Witten index play a central role in these constructions. (orig.)
SEISMIC ATTENUATION FOR RESERVOIR CHARACTERIZATION
Energy Technology Data Exchange (ETDEWEB)
Joel Walls; M.T. Taner; Naum Derzhi; Gary Mavko; Jack Dvorkin
2003-12-01
We have developed and tested technology for a new type of direct hydrocarbon detection. The method uses inelastic rock properties to greatly enhance the sensitivity of surface seismic methods to the presence of oil and gas saturation. These methods include use of energy absorption, dispersion, and attenuation (Q) along with traditional seismic attributes like velocity, impedance, and AVO. Our approach is to combine three elements: (1) a synthesis of the latest rock physics understanding of how rock inelasticity is related to rock type, pore fluid types, and pore microstructure, (2) synthetic seismic modeling that will help identify the relative contributions of scattering and intrinsic inelasticity to apparent Q attributes, and (3) robust algorithms that extract relative wave attenuation attributes from seismic data. This project provides: (1) Additional petrophysical insight from acquired data; (2) Increased understanding of rock and fluid properties; (3) New techniques to measure reservoir properties that are not currently available; and (4) Provide tools to more accurately describe the reservoir and predict oil location and volumes. These methodologies will improve the industry's ability to predict and quantify oil and gas saturation distribution, and to apply this information through geologic models to enhance reservoir simulation. We have applied for two separate patents relating to work that was completed as part of this project.
Inverse diffraction for the Atmospheric Imaging Assembly in the Solar Dynamics Observatory
Torre, Gabriele; Benvenuto, Federico; Massone, Anna Maria; Piana, Michele
2015-01-01
The Atmospheric Imaging Assembly in the Solar Dynamics Observatory provides full Sun images every 1 seconds in each of 7 Extreme Ultraviolet passbands. However, for a significant amount of these images, saturation affects their most intense core, preventing scientists from a full exploitation of their physical meaning. In this paper we describe a mathematical and automatic procedure for the recovery of information in the primary saturation region based on a correlation/inversion analysis of the diffraction pattern associated to the telescope observations. Further, we suggest an interpolation-based method for determining the image background that allows the recovery of information also in the region of secondary saturation (blooming).
Interactive inverse kinematics for human motion estimation
DEFF Research Database (Denmark)
Engell-Nørregård, Morten Pol; Hauberg, Søren; Lapuyade, Jerome; Erleben, Kenny; Pedersen, Kim Steenstrup
We present an application of a fast interactive inverse kinematics method as a dimensionality reduction for monocular human motion estimation. The inverse kinematics solver deals efficiently and robustly with box constraints and does not suffer from shaking artifacts. The presented motion...... estimation system uses a single camera to estimate the motion of a human. The results show that inverse kinematics can significantly speed up the estimation process, while retaining a quality comparable to a full pose motion estimation system. Our novelty lies primarily in use of inverse kinematics to...
Signature Inversion in Odd-odd Nuclei
Institute of Scientific and Technical Information of China (English)
LIU Min-liang; ZHANG Yu-hu; ZHOU Xiao-hong; GUO Ying-xiang; LEI Xiang-guo; GUO Wen-tao
2009-01-01
Signature inversion in odd-odd nuclei is investigated by using a proton and a neutron coupling to the coherent state of the core.Two parameters are employed in the Hamiltonian to set the energy scales of rotation,neutron-proton coupling and their competition.Typical level staggering is extracted from the calculated level energies.The calculation can approximately reproduce experimental signature inversion.Signature inversion is attributed to the rotational motion and neutronproton residual interaction having reversed signature splitting rules.It is found signature inversion can appear at axially symmetric shape and high-K band.
Perspective: Inverse methods for material design
Jain, Avni; Bollinger, Jonathan A.; Truskett, Thomas M.
2014-01-01
In this Perspective, we highlight several recent studies that illustrate how inverse strategies using appropriate physical models and computational methods can address complex materials design questions.
Inverse Kinematics of a Serial Robot
Directory of Open Access Journals (Sweden)
Amici Cinzia
2016-01-01
Full Text Available This work describes a technique to treat the inverse kinematics of a serial manipulator. The inverse kinematics is obtained through the numerical inversion of the Jacobian matrix, that represents the equation of motion of the manipulator. The inversion is affected by numerical errors and, in different conditions, due to the numerical nature of the solver, it does not converge to a reasonable solution. Thus a soft computing approach is adopted to mix different traditional methods to obtain an increment of algorithmic convergence.
Adaptation through chromosomal inversions in Anopheles
Directory of Open Access Journals (Sweden)
Diego eAyala
2014-05-01
Full Text Available Chromosomal inversions have been repeatedly involved in local adaptation in a large number of animals and plants. The ecological and behavioral plasticity of Anopheles species - human malaria vectors - is mirrored by high amounts of polymorphic inversions. The adaptive significance of chromosomal inversions has been consistently attested by strong and significant correlations between their frequencies and a number of phenotypic traits. Here, we provide an extensive literature review of the different adaptive traits associated with chromosomal inversions in the genus Anopheles. Traits having important consequences for the success of present and future vector control measures, such as insecticide resistance and behavioral changes, are discussed.
Analysis of nonlinear channel friction inverse problem
Institute of Scientific and Technical Information of China (English)
CHENG Weiping; LIU Guohua
2007-01-01
Based on the Backus-Gilbert inverse theory, the singular value decomposition (SVD) for general inverse matrices and the optimization algorithm are used to solve the channel friction inverse problem. The resolution and covari- ance friction inverse model in matrix form is developed to examine the reliability of solutions. Theoretical analyses demonstrate that the convergence rate of the general Newton optimization algorithm is in the second-order. The Wiggins method is also incorporated into the algorithm. Using the method, noise can be suppressed effectively, and the results are close to accurate solutions with proper control parameters. Also, the numerical stability can be improved.
Chromatid Painting for Chromosomal Inversion Detection Project
National Aeronautics and Space Administration — We propose the continued development of a novel approach to the detection of chromosomal inversions. Transmissible chromosome aberrations (translocations and...
The structure of (L)*-inverse semigroups
Institute of Scientific and Technical Information of China (English)
REN Xueming; SHUM Karping
2006-01-01
The concepts of (L)*-inverse semigroups and left wreath products of semigroups are introduced. It is shown that the (L)*-inverse semigroup can be described as the left wreath product of a type A semigroup Γ and a left regular band B together with a mapping which maps the semigroup Γ into the endomorphism semigroup End(B). This result generalizes the structure theorem of Yamada for the left inverse semigroups in the class of regular semigroups.We shall also provide a constructed example for the (L)*-inverse semigroups by using the left wreath products.
Acoustic 2D full waveform inversion to solve gas cloud challenges
Directory of Open Access Journals (Sweden)
Srichand Prajapati
2015-09-01
Full Text Available The existing conventional inversion algorithm does not provide satisfactory results due to the complexity of propagated wavefield though the gas cloud. Acoustic full waveform inversion has been developed and applied to a realistic synthetic offshore shallow gas cloud feature with Student-t approach, with and without simultaneous sources encoding. As a modeling operator, we implemented the grid based finite-difference method in frequency domain using second order elastic wave equation. Jacobin operator and its adjoint provide a necessary platform for solving full waveform inversion problem in a reduced Hessian matrix. We invert gas cloud model in 5 frequency band selected from 1 to 12 Hz, each band contains 3 frequencies. The inversion results are highly sensitive to the misfit. The model allows better convergence and recovery of amplitude losses. This approach gives better resolution then the existing least-squares approach. In this paper, we implement the full waveform inversion for low frequency model with minimum number of iteration providing a better resolution of inversion results.
Choi, Yun Seok
2012-05-02
Conventional multi-source waveform inversion using an objective function based on the least-square misfit cannot be applied to marine streamer acquisition data because of inconsistent acquisition geometries between observed and modelled data. To apply the multi-source waveform inversion to marine streamer data, we use the global correlation between observed and modelled data as an alternative objective function. The new residual seismogram derived from the global correlation norm attenuates modelled data not supported by the configuration of observed data and thus, can be applied to multi-source waveform inversion of marine streamer data. We also show that the global correlation norm is theoretically the same as the least-square norm of the normalized wavefield. To efficiently calculate the gradient, our method employs a back-propagation algorithm similar to reverse-time migration based on the adjoint-state of the wave equation. In numerical examples, the multi-source waveform inversion using the global correlation norm results in better inversion results for marine streamer acquisition data than the conventional approach. © 2012 European Association of Geoscientists & Engineers.
Impact of incorrect tissue classification in Dixon-based MR-AC: fat-water tissue inversion
Ladefoged, Claes Nøhr; Hansen, Adam Espe; Keller, Sune Høgild; Holm, Søren; Law, Ian; Beyer, Thomas; Højgaard, Liselotte; Kjær, Andreas; Andersen, Flemming Littrup
2014-01-01
Background The current MR-based attenuation correction (AC) used in combined PET/MR systems computes a Dixon attenuation map (MR-ACDixon) based on fat and water images derived from in- and opposed-phase MRI. We observed an occasional fat/water inversion in MR-ACDixon. The aim of our study was to estimate the prevalence of this phenomenon in a large patient cohort and assess the possible bias on PET data. Methods PET/MRI was performed on a Siemens Biograph mMR (Siemens AG, Erlangen, Germany). ...
U.S. Department of Health & Human Services — The Recovery Audit Programs mission is to identify and correct Medicare improper payments through the efficient detection and collection of overpayments made on...
FEMA Disaster Recovery Centers
Department of Homeland Security — This is a search site for FEMA's Disaster Recovery Centers (DRC). A DRC is a readily accessible facility or mobile office set up by FEMA where applicants may go for...
Spatially Dispersed Employee Recovery
DEFF Research Database (Denmark)
Hvass, Kristian Anders; Torfadóttir, Embla
2014-01-01
Employee recovery addresses either employee well-being or management's practices in aiding employees in recovering themselves following a service failure. This paper surveys the cabin crew at a small, European, low-cost carrier and investigates employees' perceptions of management practices to aid...... personnel achieve service recovery. Employee recovery within service research often focuses on front-line employees that work in a fixed location, however a contribution to the field is made by investigating the recovery of spatially dispersed personnel, such as operational personnel in the transport sector......, who have a work place away from a fixed or central location and have minimal management contact. Results suggest that the support employees receive from management, such as recognition, information sharing, training, and strategic awareness are all important for spatially dispersed front...
National Oceanic and Atmospheric Administration, Department of Commerce — The Recovery Action Mapping Tool is a web map that allows users to visually interact with and query actions that were developed to recover species listed under the...
Grummitt, W.E.; Hardwick, W.H.
1961-01-01
A process is given for the recovery of ruthenium from its aqueous solutions by oxidizing the ruthenium to the octavalent state and subsequently extracting the ruthenium into a halogen-substituted liquid paraffin.
Disaster Debris Recovery Database
U.S. Environmental Protection Agency — The US EPA Region 5 Disaster Debris Recovery Database includes public datasets of over 3,500 composting facilities, demolition contractors, haulers, transfer...
Fabrizio Saccomanni
2013-01-01
Italy has a potential to reverse the negative cycle of the last years and to continue its action in budgetary reforms for recovery. Institutions, companies, banks must work together with a common strategy for revitalizing productive investments, technological innovation, education
DEFF Research Database (Denmark)
EFSA Scientific Committee (Scientific Committee); Topping, Christopher John
2016-01-01
recognises the importance of more integrated ERAs considering both the local and landscape scales, as well as the possible co-occurrence of multiple potential stressors that fall under the remit of EFSA, which are important when addressing ecological recovery. In this scientific opinion, the Scientific...... Committee gathered scientific knowledge on the potential for the recovery of non-target organisms for the further development of ERA. Current EFSA guidance documents and opinions were reviewed on how ecological recovery is addressed in ERA schemes. In addition, this scientific opinion is based on expert...... ecological recovery for any assessed products, and invasive alien species that are harmful for plant health. This framework proposes an integrative approach based on well-defined specific protection goals, scientific knowledge derived by means of experimentation, modelling and monitoring, and the selection...
Ford, Sean R.; Phillips, William S.; Walter, William R.; Pasyanos, Michael E.; Mayeda, Kevin; Dreger, Douglas S.
2010-10-01
We invert for regional attenuation of the crustal phase Lg in the Yellow Sea/Korean Peninsula (YSKP) using three different amplitude attenuation tomography methods. The first method solves for source, site, and path attenuation. The second method uses a scaling relationship to set the initial source amplitude and interpret the source term after inversion. The third method implements a coda-derived source spectral correction. By comparing methods with slightly different assumptions we are able to make a more realistic assessment of the uncertainties in the resulting attenuation maps than is obtainable through formal error analysis alone. We compare the site, source and path-terms produced by each method and comment on attenuation, which correlates well with tectonic and topographic features in the region. Source terms correlate well with each other and with magnitude. Site terms are similar except for two stations that are located in a region that has the greatest difference in path term, which demonstrates the site/path trade-off. Another region of path term difference has the fewest crossing paths, where the tomography method employing the coda-derived spectral correction may perform more accurately since it is not as susceptible to the source/path trade-off. The Bohai Bay basin, an area of extension, is a region of high attenuation, and regions of low attenuation occur along topographic highs located in the Da-xin-an-ling and Changbai Mountains and Mount Taishan.
Differential dust attenuation in CALIFA galaxies
Vale Asari, N.; Cid Fernandes, R.; Amorim, A. L.; Lacerda, E. A. D.; Schlickmann, M.; Wild, V.; Kennicutt, R. C.
2016-06-01
Dust attenuation has long been treated as a simple parameter in SED fitting. Real galaxies are, however, much more complicated: The measured dust attenuation is not a simple function of the dust optical depth, but depends strongly on galaxy inclination and the relative distribution of stars and dust. We study the nebular and stellar dust attenuation in CALIFA galaxies, and propose some empirical recipes to make the dust treatment more realistic in spectral synthesis codes. By adding optical recombination emission lines, we find better constraints for differential attenuation. Those recipes can be applied to unresolved galaxy spectra, and lead to better recovered star formation rates.
Laterally constrained inversion for CSAMT data interpretation
Wang, Ruo; Yin, Changchun; Wang, Miaoyue; Di, Qingyun
2015-10-01
Laterally constrained inversion (LCI) has been successfully applied to the inversion of dc resistivity, TEM and airborne EM data. However, it hasn't been yet applied to the interpretation of controlled-source audio-frequency magnetotelluric (CSAMT) data. In this paper, we apply the LCI method for CSAMT data inversion by preconditioning the Jacobian matrix. We apply a weighting matrix to Jacobian to balance the sensitivity of model parameters, so that the resolution with respect to different model parameters becomes more uniform. Numerical experiments confirm that this can improve the convergence of the inversion. We first invert a synthetic dataset with and without noise to investigate the effect of LCI applications to CSAMT data, for the noise free data, the results show that the LCI method can recover the true model better compared to the traditional single-station inversion; and for the noisy data, the true model is recovered even with a noise level of 8%, indicating that LCI inversions are to some extent noise insensitive. Then, we re-invert two CSAMT datasets collected respectively in a watershed and a coal mine area in Northern China and compare our results with those from previous inversions. The comparison with the previous inversion in a coal mine shows that LCI method delivers smoother layer interfaces that well correlate to seismic data, while comparison with a global searching algorithm of simulated annealing (SA) in a watershed shows that though both methods deliver very similar good results, however, LCI algorithm presented in this paper runs much faster. The inversion results for the coal mine CSAMT survey show that a conductive water-bearing zone that was not revealed by the previous inversions has been identified by the LCI. This further demonstrates that the method presented in this paper works for CSAMT data inversion.
Nielsen, O. F.; Ploug, C.; Mendoza, J. A.; Martínez, K.
2009-05-01
The need for increaseding accuracy and reduced ambiguities in the inversion results has resulted in focus on the development of more advanced inversion methods of geophysical data. Over the past few years more advanced inversion techniques have been developed to improve the results. Real 3D-inversion is time consuming and therefore often not the best solution in a cost-efficient perspective. This has motivated the development of 3D constrained inversions, where 1D-models are constrained in 3D, also known as a Spatial Constrained Inversion (SCI). Moreover, inversion of several different data types in one inversion has been developed, known as Mutually Constrained Inversion (MCI). In this paper a presentation of a Spatial Mutually Constrained Inversion method (SMCI) is given. This method allows 1D-inversion applied to different geophysical datasets and geological information constrained in 3D. Application of two or more types of geophysical methods in the inversion has proved to reduce the equivalence problem and to increase the resolution in the inversion results. The use of geological information from borehole data or digital geological models can be integrated in the inversion. In the SMCI, a 1D inversion code is used to model soundings that are constrained in three dimensions according to their relative position in space. This solution enhances the accuracy of the inversion and produces distinct layers thicknesses and resistivities. It is very efficient in the mapping of a layered geology but still also capable of mapping layer discontinuities that are, in many cases, related to fracturing and faulting or due to valley fills. Geological information may be included in the inversion directly or used only to form a starting model for the individual soundings in the inversion. In order to show the effectiveness of the method, examples are presented from both synthetic data and real data. The examples include DC-soundings as well as land-based and airborne TEM
E. Lalov; N. Linde; J.A. Vrugt
2012-01-01
Time-lapse geophysical measurements are widely used to monitor the movement of water and solutes through the subsurface. Yet commonly used deterministic least squares inversions typically suffer from relatively poor mass recovery, spread overestimation, and limited ability to appropriately estimate
Hosseini Fouladi, Mohammad; Mohd. Nor, Mohd. Jailani; Kamal Ariffin, Ahmad; Abdullah, Shahrir
2009-11-01
Exposure to vibration has various physiological effects on vehicle passengers. Engine is one of the main sources of vehicle vibration. The major causes of engine vibration are combustion forces transmitted through the pistons and connection rods. Evaluation of sources is the first step to attenuate this vibration. Assessment of these sources is not an easy task because internal parts of machinery are not accessible. Often, instrumentation for such systems is costly, time consuming and some modifications would be necessary. Aim of the first part of this paper was to validate an inverse technique and carry out mobility analysis on a vehicle crankshaft to achieve matrix of Frequency Response Functions (FRFs). Outcomes were implemented to reconstruct the applied force for single and multiple-input systems. In the second part, the validated inverse technique and FRFs were used to estimate piston forces of an operating engine. Bearings of crankshaft were chosen as nearest accessible parts to piston connecting rods. Accelerometers were connected to the bearings for response measurement during an ideal engine operation. These responses together with FRFs, which were estimated in the previous part, were utilised in the inverse technique. Tikhonov regularization was used to solve the ill-conditioned inverse system. Two methods, namely L-curve criterion and Generalized Cross Validation (GCV), were employed to find the regularization parameter for the Tikhonov method. The inverse problem was solved and piston forces applied to crankpins were estimated. Results were validated by pressure measurement inside a cylinder and estimating the corresponding combustion force. This validation showed that inverse technique and measurement outcomes were roughly in agreement. In presence of various noise, L-curve criterion conduces to more robust results compared to the GCV method. But in the absence of high correlation between sources ( f>600 HzHz), the GCV technique leads to more accurate
Bottazzi, F.; Mantica, S.; Jha, Birendra; Wojcik, Rafal; Coccia, Martina; Bechor Ben Dov, Noah; McLaughlin, Dennis; Herring, Thomas A.; Hager, Bradford H.; Juanes, Ruben
2015-01-01
Characterization of reservoir properties like porosity and permeability in reservoir models typically relies on history matching of production data, well pressure data, and possibly other fluid-dynamical data. Calibrated (history-matched) reservoir models are then used for forecasting production and designing effective strategies for improved oil and gas recovery. Here, we perform assimilation of both flow and deformation data for joint inversion of reservoir properties. Given the coupled nat...
Inverse diffraction for the Atmospheric Imaging Assembly in the Solar Dynamics Observatory
Torre, Gabriele; Schwartz, Richard A.; Benvenuto, Federico; Massone, Anna Maria; Piana, Michele
2015-01-01
The Atmospheric Imaging Assembly in the Solar Dynamics Observatory provides full Sun images every 1 seconds in each of 7 Extreme Ultraviolet passbands. However, for a significant amount of these images, saturation affects their most intense core, preventing scientists from a full exploitation of their physical meaning. In this paper we describe a mathematical and automatic procedure for the recovery of information in the primary saturation region based on a correlation/inversion analysis of t...
Ultrasonic attenuation in cuprate superconductors
Indian Academy of Sciences (India)
T Gupta; D M Gaitonde
2002-05-01
We calculate the longitudinal ultrasonic attenuation rate (UAR) in clean d-wave superconductors in the Meissner and the mixed phases. In the Meissner phase we calculate the contribution of previously ignored processes involving the excitation of a pair of quasi-holes or quasi-particles. There is a contribution ∝ in the regime B ≪ F ≪ 0 and a contribution ∝ 1/ in the regime F ≪ B ≪ 0. We ﬁnd that these contributions to the UAR are large and cannot be ignored. In the mixed phase, using a semi-classical description, we calculate the electronic quasi-particle contribution to the UAR which at very low , has a independent term proportional to $\\sqrt{H}$.
Attenuation characteristics of gypsum wallboard
International Nuclear Information System (INIS)
Increased cost of lead is promoting enhanced usage of common building materials for shielding in diagnostic medical and dental facilities where only a few half-value layers (HVLs) are needed. Attenuation of primary beam X-ray photons in gypsum wallboard as a function of kVp, filtration, and wallboard thickness have been measured. Findings, obtained using a Victoreen 555 with an 0.1 DAS probe in poor geometry, are substantially in agreement with the sparse data in the literature but extend to thicker wall configurations and different kVp and filtration parameters. These findings are of value in maximizing the benefit/cost ratio for diagnostic shielding, and strengthen the conviction that, where used for shielding purposes, common building materials must be installed carefully and HVL-depth dependence considered thoroughly. (author)
A Construction of Weakly Inverse Semigroups
Institute of Scientific and Technical Information of China (English)
Bing Jun YU; Yan LI
2009-01-01
Let S° be an inverse semigroup with semilattice biordered set E° of idempotents and E a weakly inverse biordered set with a subsemilattice Ep = { e ∈ E |(V) f ∈ E, S(f , e)(C) w(e) } isomorphic to E° by θ:Ep→E°. In this paper, it is proved that if(V)f, g∈E, f ←→ ,g(→) f°θ (ζ)s° g°θand there exists a mapping φ from Ep into the symmetric weakly inverse semigroup (ζξ)(E ∪S°) satisfying six appropriate conditions, then a weakly inverse semigroup ∑ can be constructed in (ζξ)(S°), called the weakly inverse hull of a weakly inverse system (S°, E, θ, φ) with I(∑) ≌ S°, E(∑) (≌) E. Conversely,every weakly inverse semigroup can be constructed in this way. Furthermore, a sufficient and necessary condition for two weakly inverse hulls to be isomorphic is also given.
An inversion algorithm for general tridiagonal matrix
Institute of Scientific and Technical Information of China (English)
Rui-sheng RAN; Ting-zhu HUANG; Xing-ping LIU; Tong-xiang GU
2009-01-01
An algorithm for the inverse of a general tridiagonal matrix is presented. For a tridiagonal matrix having the Doolittle factorization, an inversion algorithm is established.The algorithm is then generalized to deal with a general tridiagonal matrix without any restriction. Comparison with other methods is provided, indicating low computational complexity of the proposed algorithm, and its applicability to general tridiagonal matrices.
Third Harmonic Imaging using a Pulse Inversion
DEFF Research Database (Denmark)
Rasmussen, Joachim; Du, Yigang; Jensen, Jørgen Arendt
The pulse inversion (PI) technique can be utilized to separate and enhance harmonic components of a waveform for tissue harmonic imaging. While most ultrasound systems can perform pulse inversion, only few image the 3rd harmonic component. PI pulse subtraction can isolate and enhance the 3rd...
Approximation of the Inverse -Frame Operator
Indian Academy of Sciences (India)
M R Abdollahpour; A Najati
2011-05-01
In this paper, we introduce the concept of (strong) projection method for -frames which works for all conditional -Riesz frames. We also derive a method for approximation of the inverse -frame operator which is efficient for all -frames. We show how the inverse of -frame operator can be approximated as close as we like using finite-dimensional linear algebra.
On the general inversion problem
International Nuclear Information System (INIS)
We consider the problem of direct and inverse scattering for the Schroedinger operator Hυ=-Δ+υ(x) in odd space dimensions with a short range potential. It will be shown that the wave operators are built up from a family of operators Aθ, θelement ofSn-1, which satisfy the equation HυAθ=AθH0. The corresponding operator kernels are supported in the set where ≥0, and they can be described in detail. By introducing polar coordinates for y-x one finds also that these kernels have several properties in common with their one-dimensional analogues. The potential can be easily computed from a special trace of Aθ*Aθ, and this operator in turn is given from a factorization of the scattering matrix into upper and lower triangular parts with respect to the direction θ. Finally we give some remarks on the so called miracle, which was introduced by R.G. Newton. (orig.)
Inverse magnetic/shear catalysis
McInnes, Brett
2016-05-01
It is well known that very large magnetic fields are generated when the Quark-Gluon Plasma is formed during peripheral heavy-ion collisions. Lattice, holographic, and other studies strongly suggest that these fields may, for observationally relevant field values, induce "inverse magnetic catalysis", signalled by a lowering of the critical temperature for the chiral/deconfinement transition. The theoretical basis of this effect has recently attracted much attention; yet so far these investigations have not included another, equally dramatic consequence of the peripheral collision geometry: the QGP acquires a large angular momentum vector, parallel to the magnetic field. Here we use holographic techniques to argue that the angular momentum can also, independently, have an effect on transition temperatures, and we obtain a rough estimate of the relative effects of the presence of both a magnetic field and an angular momentum density. We find that the shearing angular momentum reinforces the effect of the magnetic field at low values of the baryonic chemical potential, but that it can actually decrease that effect at high chemical potentials.
Inversion based on computational simulations
International Nuclear Information System (INIS)
A standard approach to solving inversion problems that involve many parameters uses gradient-based optimization to find the parameters that best match the data. The authors discuss enabling techniques that facilitate application of this approach to large-scale computational simulations, which are the only way to investigate many complex physical phenomena. Such simulations may not seem to lend themselves to calculation of the gradient with respect to numerous parameters. However, adjoint differentiation allows one to efficiently compute the gradient of an objective function with respect to all the variables of a simulation. When combined with advanced gradient-based optimization algorithms, adjoint differentiation permits one to solve very large problems of optimization or parameter estimation. These techniques will be illustrated through the simulation of the time-dependent diffusion of infrared light through tissue, which has been used to perform optical tomography. The techniques discussed have a wide range of applicability to modeling including the optimization of models to achieve a desired design goal
MIT inverse Compton source concept
Energy Technology Data Exchange (ETDEWEB)
Graves, W.S. [Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)], E-mail: wsgraves@MIT.EDU; Brown, W. [MIT Lincoln Laboratory, 244 Wood Street, Lexington, MA 02420 (United States); Kaertner, F.X.; Moncton, D.E. [Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)
2009-09-01
A compact X-ray source based on inverse Compton scattering of a high-power laser on a high-brightness linac beam is described. The facility can operate in two modes: at high (MHz) repetition rate with flux and brilliance similar to that of a beamline at a large 2nd generation synchrotron, but with short {approx}1 ps pulses, or as a 10 Hz high flux-per-pulse single-shot machine. It has a small footprint and low cost appropriate for university or industry laboratories. The key enabling technologies are a high average power laser and a superconducting accelerator. The cryo-cooled Yb:YAG laser amplifier generates {approx}1 kW average power at 1 {mu}m wavelength that pumps a coherent cavity up to 1 MW stored power. The high-brightness electron beam is produced by a superconducting RF photoinjector and linac operating in CW mode with up to 1 mA current. The photocathode laser produces electron pulses at either 100 MHz with 10 pc per bunch, or at 10 Hz with 1 nC per bunch in the two operating modes. The design of the facility is presented, including optimization of the laser and electron beams, major technical choices, and the resulting X-ray performance with a focus on the 100 MHz mode.
MIT inverse Compton source concept
International Nuclear Information System (INIS)
A compact X-ray source based on inverse Compton scattering of a high-power laser on a high-brightness linac beam is described. The facility can operate in two modes: at high (MHz) repetition rate with flux and brilliance similar to that of a beamline at a large 2nd generation synchrotron, but with short ∼1 ps pulses, or as a 10 Hz high flux-per-pulse single-shot machine. It has a small footprint and low cost appropriate for university or industry laboratories. The key enabling technologies are a high average power laser and a superconducting accelerator. The cryo-cooled Yb:YAG laser amplifier generates ∼1 kW average power at 1 μm wavelength that pumps a coherent cavity up to 1 MW stored power. The high-brightness electron beam is produced by a superconducting RF photoinjector and linac operating in CW mode with up to 1 mA current. The photocathode laser produces electron pulses at either 100 MHz with 10 pc per bunch, or at 10 Hz with 1 nC per bunch in the two operating modes. The design of the facility is presented, including optimization of the laser and electron beams, major technical choices, and the resulting X-ray performance with a focus on the 100 MHz mode.
Fast wavelet based sparse approximate inverse preconditioner
Energy Technology Data Exchange (ETDEWEB)
Wan, W.L. [Univ. of California, Los Angeles, CA (United States)
1996-12-31
Incomplete LU factorization is a robust preconditioner for both general and PDE problems but unfortunately not easy to parallelize. Recent study of Huckle and Grote and Chow and Saad showed that sparse approximate inverse could be a potential alternative while readily parallelizable. However, for special class of matrix A that comes from elliptic PDE problems, their preconditioners are not optimal in the sense that independent of mesh size. A reason may be that no good sparse approximate inverse exists for the dense inverse matrix. Our observation is that for this kind of matrices, its inverse entries typically have piecewise smooth changes. We can take advantage of this fact and use wavelet compression techniques to construct a better sparse approximate inverse preconditioner. We shall show numerically that our approach is effective for this kind of matrices.
Forward modeling. Route to electromagnetic inversion
Energy Technology Data Exchange (ETDEWEB)
Groom, R.; Walker, P. [PetRos EiKon Incorporated, Ontario (Canada)
1996-05-01
Inversion of electromagnetic data is a topical subject in the literature, and much time has been devoted to understanding the convergence properties of various inverse methods. The relative lack of success of electromagnetic inversion techniques is partly attributable to the difficulties in the kernel forward modeling software. These difficulties come in two broad classes: (1) Completeness and robustness, and (2) convergence, execution time and model simplicity. If such problems exist in the forward modeling kernel, it was demonstrated that inversion can fail to generate reasonable results. It was suggested that classical inversion techniques, which are based on minimizing a norm of the error between data and the simulated data, will only be successful when these difficulties in forward modeling kernels are properly dealt with. 4 refs., 5 figs.
Inverse m-matrices and ultrametric matrices
Dellacherie, Claude; San Martin, Jaime
2014-01-01
The study of M-matrices, their inverses and discrete potential theory is now a well-established part of linear algebra and the theory of Markov chains. The main focus of this monograph is the so-called inverse M-matrix problem, which asks for a characterization of nonnegative matrices whose inverses are M-matrices. We present an answer in terms of discrete potential theory based on the Choquet-Deny Theorem. A distinguished subclass of inverse M-matrices is ultrametric matrices, which are important in applications such as taxonomy. Ultrametricity is revealed to be a relevant concept in linear algebra and discrete potential theory because of its relation with trees in graph theory and mean expected value matrices in probability theory. Remarkable properties of Hadamard functions and products for the class of inverse M-matrices are developed and probabilistic insights are provided throughout the monograph.
An Introduction to Inverse Problems with Applications
Moura Neto, Francisco Duarte
2013-01-01
Computational engineering/science uses a blend of applications, mathematical models and computations. Mathematical models require accurate approximations of their parameters, which are often viewed as solutions to inverse problems. Thus, the study of inverse problems is an integral part of computational engineering/science. This book presents several aspects of inverse problems along with needed prerequisite topics in numerical analysis and matrix algebra. If the reader has previously studied these prerequisites, then one can rapidly move to the inverse problems in chapters 4-8 on image restoration, thermal radiation, thermal characterization and heat transfer. “This text does provide a comprehensive introduction to inverse problems and fills a void in the literature”. Robert E White, Professor of Mathematics, North Carolina State University
Phase inversion emulsification: Current understanding and applications.
Perazzo, A; Preziosi, V; Guido, S
2015-08-01
This review is addressed to the phase inversion process, which is not only a common, low-energy route to make stable emulsions for a variety of industrial products spanning from food to pharmaceuticals, but can also be an undesired effect in some applications, such as crude oil transportation in pipelines. Two main ways to induce phase inversion are described in the literature, i.e., phase inversion composition (PIC or catastrophic) and phase inversion temperature (PIT or transitional). In the former, starting from one phase (oil or water) with surfactants, the other phase is more or less gradually added until it reverts to the continuous phase. In PIT, phase inversion is driven by a temperature change without varying system composition. Given its industrial relevance and scientific challenge, phase inversion has been the subject of a number of papers in the literature, including extensive reviews. Due to the variety of applications and the complexity of the problem, most of the publications have been focused either on the phase behavior or the interfacial properties or the mixing process of the two phases. Although all these aspects are quite important in studying phase inversion and much progress has been done on this topic, a comprehensive picture is still lacking. In particular, the general mechanisms governing the inversion phenomenon have not been completely elucidated and quantitative predictions of the phase inversion point are limited to specific systems and experimental conditions. Here, we review the different approaches on phase inversion and highlight some related applications, including future and emerging perspectives. PMID:25632889
Simple parameterization of nuclear attenuation data
Akopov, N; Akopov, Z
2007-01-01
Based on the nuclear attenuation data obtained by the HERMES experiment on nitrogen and krypton nuclei, it is shown that the nuclear attenuation $R_M^{h}$ can be parametrised in a form of a linear polynomial $P_1=a_{11}$ + $\\tau a_{12}$, where $\\tau$ is the formation time, which depends on the energy of the virtual photon $\
Docking-mechanism attenuator with electromechanical damper
Syromyatnikov, V. S.
1971-01-01
Theoretical and practical problems involved in the application of electromechanical damping for spacecraft docking-mechanism attenuation are discussed. Some drawbacks of hydraulic dampers used for the purpose are pointed out. The basic scheme of the attenuator with the electromechanical damper is given.
Precision Model for Microwave Rotary Vane Attenuator
DEFF Research Database (Denmark)
Guldbrandsen, Tom
1979-01-01
A model for a rotary vane attenuator is developed to describe the attenuator reflection and transmission coefficients in detail. All the parameters of the model can be measured in situ, i.e., without diassembling any part. The tranmission errors caused by internal reflections are calculated from...
Determination of transient fluid temperature using the inverse method
Directory of Open Access Journals (Sweden)
Jaremkiewicz Magdalena
2014-03-01
Full Text Available This paper proposes an inverse method to obtain accurate measurements of the transient temperature of fluid. A method for unit step and linear rise of temperature is presented. For this purpose, the thermometer housing is modelled as a full cylindrical element (with no inner hole, divided into four control volumes. Using the control volume method, the heat balance equations can be written for each of the nodes for each of the control volumes. Thus, for a known temperature in the middle of the cylindrical element, the distribution of temperature in three nodes and heat flux at the outer surface were obtained. For a known value of the heat transfer coefficient the temperature of the fluid can be calculated using the boundary condition. Additionally, results of experimental research are presented. The research was carried out during the start-up of an experimental installation, which comprises: a steam generator unit, an installation for boiler feed water treatment, a tray-type deaerator, a blow down flashvessel for heat recovery, a steam pressure reduction station, a boiler control system and a steam header made of martensitic high alloy P91 steel. Based on temperature measurements made in the steam header using the inverse method, accurate measurements of the transient temperature of the steam were obtained. The results of the calculations are compared with the real temperature of the steam, which can be determined for a known pressure and enthalpy.
Determination of transient fluid temperature using the inverse method
Jaremkiewicz, Magdalena
2014-03-01
This paper proposes an inverse method to obtain accurate measurements of the transient temperature of fluid. A method for unit step and linear rise of temperature is presented. For this purpose, the thermometer housing is modelled as a full cylindrical element (with no inner hole), divided into four control volumes. Using the control volume method, the heat balance equations can be written for each of the nodes for each of the control volumes. Thus, for a known temperature in the middle of the cylindrical element, the distribution of temperature in three nodes and heat flux at the outer surface were obtained. For a known value of the heat transfer coefficient the temperature of the fluid can be calculated using the boundary condition. Additionally, results of experimental research are presented. The research was carried out during the start-up of an experimental installation, which comprises: a steam generator unit, an installation for boiler feed water treatment, a tray-type deaerator, a blow down flashvessel for heat recovery, a steam pressure reduction station, a boiler control system and a steam header made of martensitic high alloy P91 steel. Based on temperature measurements made in the steam header using the inverse method, accurate measurements of the transient temperature of the steam were obtained. The results of the calculations are compared with the real temperature of the steam, which can be determined for a known pressure and enthalpy.
Particle sizing in dense two-phase droplet systems by ultrasonic attenuation and velocity spectra
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
Size and size distribution of particles in particulate two-phase flow play an important role in a wide variety of industrial areas,while their measurement still remains a hard task till now.Ultrasonic wave as a mechanical vibration contains plenty of information about medium when it passes through.Thus the size distribution could be extracted from the measured ultrasonic attenuation and velocity spectra by means of well established models and data processing techniques.This paper contributes to the extraction of information of droplet size of a two-phase fat emulsion simultaneously from signals of broad-band ultrasonic attenuation and velocity spectra.According to the formulated single particle scattering model,the relationship between particle size distribution and ultrasonic spectrum is estab-lished.The sensitivities of ultrasonic spectra to the variation of particle size are illustrated.Distin-guishing features for attenuation and velocity spectra are summarized.Demonstration calculations of inversion by optimum regularization factor method are carried out to yield the typical numerical results for discussion.Based on the proposed inversion algorithm and theoretical model,a fat emulsion sam-ple with a volume fraction up to 20% is measured and analyzed.To validate the proposed ultrasonic spectrum particle sizing method,the results are compared to those obtained from optical measure-ment.
Particle sizing in dense two-phase droplet systems by ultrasonic attenuation and velocity spectra
Institute of Scientific and Technical Information of China (English)
SU MingXu; CAI XiaoShu; XUE MingHua; DONG LiLi; XU Feng
2009-01-01
Size and size distribution of particles in particulate two-phase flow play an important role in a wide va-riety of industrial areas, while their measurement still remains a hard task till now. Ultrasonic wave as a mechanical vibration contains plenty of information about medium when it passes through. Thus the size distribution could be extracted from the measured ultrasonic attenuation and velocity spectra by means of well established models and data processing techniques. This paper contributes to the ex-traction of information of droplet size of a two-phase fat emulsion simultaneously from signals of broad-band ultrasonic attenuation and velocity spectra. According to the formulated single particle scattering model, the relationship between particle size distribution and ultrasonic spectrum is estab-lished. The sensitivilles of ultrasonic spectra to the variation of particle size are illustrated. Distin-guishing features for attenuation and velocity spectra are summarized. Demonstration calculations of inversion by optimum regularization factor method are carried out to yield the typical numerical results for discussion. Based on the proposed inversion algorithm and theoretical model, a fat emulsion sam-ple with a volume fraction up to 20% is measured and analyzed. To validate the proposed ultrasonic spectrum particle sizing method, the results are compared to those obtained from optical measure-ment.
Ultrasound fields in an attenuating medium
DEFF Research Database (Denmark)
Jensen, Jørgen Arendt; Gandhi,, D; O'Brien,, W.D., Jr.
Ultrasound fields propagating in tissue will undergo changes in shape not only due to diffraction, but also due to the frequency dependent attenuation. Linear fields can be fairly well predicted for a non-attenuating medium like water by using the Tupholme-Stepanishen method for calculating the...... spatial impulse response, whereas the field cannot readily be found for an attenuating medium. In this paper we present a simulation program capable of calculating the field in a homogeneous attenuating medium. The program splits the aperture into rectangles and uses a far-field approximation for each of...... the rectangles and sums all contributions to arrive at the spatial impulse response for the aperture and field point. This approach makes it possible to model all transducer apertures, and the program can readily calculate the emitted, pulse-echo and continuous wave field. Attenuation is included by...
Marrow fat and preadipocyte factor-1 levels decrease with recovery in women with anorexia nervosa
Fazeli, Pouneh K.; Bredella, Miriam A.; Freedman, Lauren; Thomas, Bijoy J.; Breggia, Anne; Meenaghan, Erinne; Rosen, Clifford J; Klibanski, Anne
2012-01-01
Women with anorexia nervosa (AN) have elevated marrow fat mass despite low visceral and subcutaneous fat depots, which is inversely associated with bone mineral density (BMD). Whether marrow fat mass remains persistently elevated or decreases with recovery from AN is currently unknown. In this study, we investigated changes in marrow fat with recovery from AN and the relationship between preadipocyte factor (Pref)-1 -- a member of the EGF-like family of proteins and regulator of adipocyte and...
DEFF Research Database (Denmark)
Kellman, Peter; Bandettini, W Patricia; Mancini, Christine;
2015-01-01
or within the myocardium in the case of lipomatous metaplasia of replacement fibrosis, which is commonly seen in chronic myocardial infarction. The presence of fat leads to a bias in T1 measurement. The mechanism for this artifact for widely used T1 mapping protocols using balanced steady state free...... imaging protocols using balanced steady state free precession are considered. In-vivo imaging with T1-mapping, water/fat separated imaging, and late enhancement imaging was performed on subjects with chronic myocardial infarction. RESULTS: In n = 17 subjects with chronic myocardial infarction, lipomatous...... agreement with simulation of the specific imaging protocols. CONCLUSIONS: Measurement of the myocardial T1 by widely used balanced steady state free precession mapping methods is subject to bias when there is a mixture of water and fat in the myocardium. Intramyocardial fat is frequently present in...
Inverse cascades of angular momentum
International Nuclear Information System (INIS)
Most theoretical and computational studies of turbulence in Navier-Stokes fluids and/or guiding-centre plasmas have been carried out in the presence of spatially periodic boundary conditions. In view of the frequently reproduced result that two-dimensional and/or MHD decaying turbulence leads to structures comparable in length scae to a box dimension, it is natural to ask if periodic boundary conditions are an adequate representation of any physical situation. Here, we study, computationally, the decay of two-dimensional turbulence in a Navier-Stokes fluid or guiding-centre plasma in the presence of circular no-slip rigid walls. The method is wholly spectral, and relies on a Galerkin approximation by a set of functions that obey two boundary conditions at the wall radius (analogues of the Chandrasekhar-Reid functions). It is possible to explore Reynolds numbers up to the order of 1250, based on an RMS velocity and a box radius. It is found that decaying turbulence is altered significantly by the no-slip boundaries. First, strong boundary layers serve as sources of vorticity and enstrophy and enhance the early-time energy decay rate, for a given Reynolds number, well above the periodic boundary condition values. More importantly, angular momentum turns out to be an even more slowly decaying ideal invariant than energy, and to a considerable extent governs the dynamics of the decay. Angular momentum must be taken into account, for example, in order to achieve quantitative agreement with the prediction of maximum entropy, or 'most probable', states. These are predictions of conditions that are established after several eddy turnover times but before the energy has decayed away. Angular momentum will cascade to lower azimuthal mode numbers, even if absent there initially, and the angular momentum modal spectrum is eventually dominated by the lowest mode available. When no initial angular momentum is present, no behaviour that suggests the likelihood of inverse cascades
Support minimized inversion of acoustic and elastic wave scattering
International Nuclear Information System (INIS)
This report discusses the following topics on support minimized inversion of acoustic and elastic wave scattering: Minimum support inversion; forward modelling of elastodynamic wave scattering; minimum support linearized acoustic inversion; support minimized nonlinear acoustic inversion without absolute phase; and support minimized nonlinear elastic inversion
Psychosocial Recovery and Rehabilitation.
Antai-Otong, Deborah
2016-06-01
This article discusses a psychosocial recovery and rehabilitation recovery model that uses an intensive case management approach. The approach offers an interdisciplinary model that integrates pharmacotherapy, social skills training, cognitive remediation, family involvement, and community integration. This evidence-based plan of care instills hope and nurtures one's capacity to learn and improve function and quality of life. It is cost-effective and offers psychiatric nurses opportunities to facilitate symptomatic remission, facilitate self-efficacy, and improve communication and social cognition skills. Nurses in diverse practice settings must be willing to plan and implement innovative treatment models that provide seamless mental health care across the treatment continuum. PMID:27229282
International Nuclear Information System (INIS)
Hurricane Isabel, originally a Category 5 storm, arrived at Jefferson Lab on September 18, 2003 with winds of only 75 mph, creating little direct damage to the infrastructure. However, electric power was lost for four days allowing the superconducting cryomodules to warm up and causing a total loss of the liquid helium. The subsequent recovery of the cryomodules and the impact of the considerable amount of opportunistic preventive maintenance provides important lessons for all accelerator complexes, not only those with superconducting elements. The details of how the recovery process was structured and the resulting improvement in accelerator availability will be discussed in detail
Carbon capture and storage reservoir properties from poroelastic inversion: A numerical evaluation
Lepore, Simone; Ghose, Ranajit
2015-11-01
We investigate the prospect of estimating carbon capture and storage (CCS) reservoir properties from P-wave intrinsic attenuation and velocity dispersion. Numerical analogues for two CCS reservoirs are examined: the Utsira saline formation at Sleipner (Norway) and the coal-bed methane basin at Atzbach-Schwanestadt (Austria). P-wave intrinsic dispersion curves in the field-seismic frequency band, obtained from theoretical studies based on simulation of oscillatory compressibility and shear tests upon representative rock samples, are considered as observed data. We carry out forward modelling using poroelasticity theories, making use of previously established empirical relations, pertinent to CCS reservoirs, to link pressure, temperature and CO2 saturation to other properties. To derive the reservoir properties, poroelastic inversions are performed through a global multiparameter optimization using simulated annealing. We find that the combination of attenuation and velocity dispersion in the error function helps significantly in eliminating the local minima and obtaining a stable result in inversion. This is because of the presence of convexity in the solution space when an integrated error function is minimized, which is governed by the underlying physics. The results show that, even in the presence of fairly large model discrepancies, the inversion provides reliable values for the reservoir properties, with the error being less than 10% for most of them. The estimated values of velocity and attenuation and their sensitivity to effective stress and CO2 saturation generally agree with the earlier experimental observation. Although developed and tested for numerical analogues of CCS reservoirs, the approach presented here can be adapted in order to predict key properties in a fluid-bearing porous reservoir, in general.
Regularizing priors for linear inverse problems
Florens, Jean-Pierre; De Simoni, Anna
2010-01-01
We consider statistical linear inverse problems in Hilbert spaces of the type ˆ Y = Kx + U where we want to estimate the function x from indirect noisy functional observations ˆY . In several applications the operator K has an inverse that is not continuous on the whole space of reference; this phenomenon is known as ill-posedness of the inverse problem. We use a Bayesian approach and a conjugate-Gaussian model. For a very general specification of the probability model the posterior distribut...
3rd Annual Workshop on Inverse Problem
2015-01-01
This proceeding volume is based on papers presented on the Third Annual Workshop on Inverse Problems which was organized by the Department of Mathematical Sciences, Chalmers University of Technology and University of Gothenburg, and took place in May 2013 in Stockholm. The purpose of this workshop was to present new analytical developments and numerical techniques for solution of inverse problems for a wide range of applications in acoustics, electromagnetics, optical fibers, medical imaging, geophysics, etc. The contributions in this volume reflect these themes and will be beneficial to researchers who are working in the area of applied inverse problems.
Parallel Algorithm in Surface Wave Waveform Inversion
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
In Surface wave waveform inversion, we want to reconstruct 3Dshear wav e velocity structure, which calculation beyond the capability of the powerful pr esent day personal computer or even workstation. So we designed a high parallele d algorithm and carried out the inversion on Parallel computer based on the part itioned waveform inversion (PWI). It partitions the large scale optimization pro blem into a number of independent small scale problems and reduces the computati onal effort by several orders of magnitude. We adopted surface waveform inversio n with a equal block(2°×2°) discretization.
Inverse problems in the Bayesian framework
International Nuclear Information System (INIS)
The history of Bayesian methods dates back to the original works of Reverend Thomas Bayes and Pierre-Simon Laplace: the former laid down some of the basic principles on inverse probability in his classic article ‘An essay towards solving a problem in the doctrine of chances’ that was read posthumously in the Royal Society in 1763. Laplace, on the other hand, in his ‘Memoirs on inverse probability’ of 1774 developed the idea of updating beliefs and wrote down the celebrated Bayes’ formula in the form we know today. Although not identified yet as a framework for investigating inverse problems, Laplace used the formalism very much in the spirit it is used today in the context of inverse problems, e.g., in his study of the distribution of comets. With the evolution of computational tools, Bayesian methods have become increasingly popular in all fields of human knowledge in which conclusions need to be drawn based on incomplete and noisy data. Needless to say, inverse problems, almost by definition, fall into this category. Systematic work for developing a Bayesian inverse problem framework can arguably be traced back to the 1980s, (the original first edition being published by Elsevier in 1987), although articles on Bayesian methodology applied to inverse problems, in particular in geophysics, had appeared much earlier. Today, as testified by the articles in this special issue, the Bayesian methodology as a framework for considering inverse problems has gained a lot of popularity, and it has integrated very successfully with many traditional inverse problems ideas and techniques, providing novel ways to interpret and implement traditional procedures in numerical analysis, computational statistics, signal analysis and data assimilation. The range of applications where the Bayesian framework has been fundamental goes from geophysics, engineering and imaging to astronomy, life sciences and economy, and continues to grow. There is no question that Bayesian
Inverse Raman effect: applications and detection techniques
International Nuclear Information System (INIS)
The processes underlying the inverse Raman effect are qualitatively described by comparing it to the more familiar phenomena of conventional and stimulated Raman scattering. An experession is derived for the inverse Raman absorption coefficient, and its relationship to the stimulated Raman gain is obtained. The power requirements of the two fields are examined qualitatively and quantitatively. The assumption that the inverse Raman absorption coefficient is constant over the interaction length is examined. Advantages of the technique are discussed and a brief survey of reported studies is presented
Inversion symmetry protected topological insulators and superconductors
Lee, Dung-Hai; Lu, Yuan-Ming
2015-03-01
Three dimensional topological insulator represents a class of novel quantum phases hosting robust gapless boundary excitations, which is protected by global symmetries such as time reversal, charge conservation and spin rotational symmetry. In this work we systematically study another class of topological phases of weakly interacting electrons protected by spatial inversion symmetry, which generally don't support stable gapless boundary states. We classify these inversion-symmetric topological insulators and superconductors in the framework of K-theory, and construct their lattice models. We also discuss quantized response functions of these inversion-protected topological phases, which serve as their experimental signatures.
New recursive algorithm for matrix inversion
Institute of Scientific and Technical Information of China (English)
Cao Jianshu; Wang Xuegang
2008-01-01
To reduce the computational complexity of matrix inversion, which is the majority of processing in many practical applications, two numerically efficient recursive algorithms (called algorithms Ⅰ and Ⅱ, respectively)are presented. Algorithm Ⅰ is used to calculate the inverse of such a matrix, whose leading principal minors are all nonzero. Algorithm Ⅱ, whereby, the inverse of an arbitrary nonsingular matrix can be evaluated is derived via improving the algorithm Ⅰ. The implementation, for algorithm Ⅱ or Ⅰ, involves matrix-vector multiplications and vector outer products. These operations are computationally fast and highly parallelizable. MATLAB simulations show that both recursive algorithms are valid.
Plasmodium falciparum: attenuation by irradiation
Energy Technology Data Exchange (ETDEWEB)
Waki, S.; Yonome, I.; Suzuki, M.
1983-12-01
The effect of irradiation on the in vitro growth of Plasmodium falciparum was investigated. The cultured malarial parasites at selected stages of development were exposed to gamma rays and the sensitivity of each stage was determined. The stages most sensitive to irradiation were the ring forms and the early trophozoites; late trophozoites were relatively insensitive. The greatest resistance was shown when parasites were irradiated at a time of transition from the late trophozoite and schizont stages to young ring forms. The characteristics of radiosensitive variation in the parasite cycle resembled that of mammalian cells. Growth curves of parasites exposed to doses of irradiation upto 150 gray had the same slope as nonirradiated controls but parasites which were exposed to 200 gray exhibited a growth curve which was less steep than that for parasites in other groups. Less than 10 organisms survived from the 10(6) parasites exposed to this high dose of irradiation; the possibility exists of obtaining radiation-attenuated P. falciparum.
Beta attenuation transmission system (BATS)
International Nuclear Information System (INIS)
The beta attenuation transmission system (BATS) is an automated radiation gauge designed for quantitative measurement of component thickness in explosive detonators. The BATS was designed and built by Group M-1, the Nondestructive Testing Group, of the Los Alamos Scientific Laboratory to measure the areal thickness, in mg/cm2, of a cylinder of high explosive (HE) enclosed within a plastic holder. The problem is to determine the density of the HE. A 90Sr source is collimated by a 0.25 x 1.59-mm slit, and the transmitted beta-particle flux is detected by a plastic scintillator, coupled to a photomultiplier tube. The detonator is transported through the radiation beam by a leadscrew, ballnut, stepping-motor combination. Continuous analog position data are available, derived from the output from a linear-actuated potentiometer attached to the scanner. A linear electrometer amplifies the detected signal, which is then integrated for a preselected time, to obtain the desired statistical accuracy. A microprocessor (μP) is used to control the scanner position and to make the data readings at the assigned positions. The data are stored, and, at the completion of the scan, are processed into the desired format. The final answer is displayed to the operator or output to a peripheral device for permanent record. The characteristics of the radiation source, the collimator, the signal detection and conditioning, and the final results are described in detail. The scanner and the microprocessor control system are briefly outlined
Beta attenuation transmission system (BATS)
Energy Technology Data Exchange (ETDEWEB)
Hagan, R.C.; Fullbright, H.J.
1977-01-01
The beta attenuation transmission system (BATS) is an automated radiation gauge designed for quantitative measurement of component thickness in explosive detonators. The BATS was designed and built by Group M-1, the Nondestructive Testing Group, of the Los Alamos Scientific Laboratory to measure the areal thickness, in mg/cm/sup 2/, of a cylinder of high explosive (HE) enclosed within a plastic holder. The problem is to determine the density of the HE. A /sup 90/Sr source is collimated by a 0.25 x 1.59-mm slit, and the transmitted beta-particle flux is detected by a plastic scintillator, coupled to a photomultiplier tube. The detonator is transported through the radiation beam by a leadscrew, ballnut, stepping-motor combination. Continuous analog position data are available, derived from the output from a linear-actuated potentiometer attached to the scanner. A linear electrometer amplifies the detected signal, which is then integrated for a preselected time, to obtain the desired statistical accuracy. A microprocessor (..mu..P) is used to control the scanner position and to make the data readings at the assigned positions. The data are stored, and, at the completion of the scan, are processed into the desired format. The final answer is displayed to the operator or output to a peripheral device for permanent record. The characteristics of the radiation source, the collimator, the signal detection and conditioning, and the final results are described in detail. The scanner and the microprocessor control system are briefly outlined.
BOOK REVIEW: Inverse Problems. Activities for Undergraduates
Yamamoto, Masahiro
2003-06-01
This book is a valuable introduction to inverse problems. In particular, from the educational point of view, the author addresses the questions of what constitutes an inverse problem and how and why we should study them. Such an approach has been eagerly awaited for a long time. Professor Groetsch, of the University of Cincinnati, is a world-renowned specialist in inverse problems, in particular the theory of regularization. Moreover, he has made a remarkable contribution to educational activities in the field of inverse problems, which was the subject of his previous book (Groetsch C W 1993 Inverse Problems in the Mathematical Sciences (Braunschweig: Vieweg)). For this reason, he is one of the most qualified to write an introductory book on inverse problems. Without question, inverse problems are important, necessary and appear in various aspects. So it is crucial to introduce students to exercises in inverse problems. However, there are not many introductory books which are directly accessible by students in the first two undergraduate years. As a consequence, students often encounter diverse concrete inverse problems before becoming aware of their general principles. The main purpose of this book is to present activities to allow first-year undergraduates to learn inverse theory. To my knowledge, this book is a rare attempt to do this and, in my opinion, a great success. The author emphasizes that it is very important to teach inverse theory in the early years. He writes; `If students consider only the direct problem, they are not looking at the problem from all sides .... The habit of always looking at problems from the direct point of view is intellectually limiting ...' (page 21). The book is very carefully organized so that teachers will be able to use it as a textbook. After an introduction in chapter 1, sucessive chapters deal with inverse problems in precalculus, calculus, differential equations and linear algebra. In order to let one gain some insight
Analysis of Temperature Distributions in Nighttime Inversions
Telyak, Oksana; Krasouski, Aliaksandr; Svetashev, Alexander; Turishev, Leonid; Barodka, Siarhei
2015-04-01
Adequate prediction of temperature inversion in the atmospheric boundary layer is one of prerequisites for successful forecasting of meteorological parameters and severe weather events. Examples include surface air temperature and precipitation forecasting as well as prediction of fog, frosts and smog with hazardous levels of atmospheric pollution. At the same time, reliable forecasting of temperature inversions remains an unsolved problem. For prediction of nighttime inversions over some specific territory, it is important to study characteristic features of local circulation cells formation and to properly take local factors into account to develop custom modeling techniques for operational use. The present study aims to investigate and analyze vertical temperature distributions in tropospheric inversions (isotherms) over the territory of Belarus. We study several specific cases of formation, evolution and decay of deep nighttime temperature inversions in Belarus by means of mesoscale numerical simulations with WRF model, considering basic mechanisms of isothermal and inverse temperature layers formation in the troposphere and impact of these layers on local circulation cells. Our primary goal is to assess the feasibility of advance prediction of inversions formation with WRF. Modeling results reveal that all cases under consideration have characteristic features of radiative inversions (e.g., their formation times, development phases, inversion intensities, etc). Regions of "blocking" layers formation are extensive and often spread over the entire territory of Belarus. Inversions decay starts from the lowermost (near surface) layer (altitudes of 5 to 50 m). In all cases, one can observe formation of temperature gradients that substantially differ from the basic inversion gradient, i.e. the layer splits into smaller layers, each having a different temperature stratification (isothermal, adiabatic, etc). As opposed to various empirical techniques as well as
International Nuclear Information System (INIS)
The attrition of Schistosoma mansoni challenge worms was studied in irradiation-attenuated cercaria-immunized mice as a function of site and time. The peak recovery of schistosomula from the lungs of immunized mice was delayed 2 days in comparison with non-immunized controls. The difference between the peak recoveries of control and immunized mice accounted for about half of the final attrition observed at the 7-week adult worm stge. Hepatic-mesenteric vein worm recoveries obtained 10 to 42 days after challenge were reduced in most cases at least as much as the 49-day counts. Somewhat higher reductions were observed at 14 to 28 days than at 49 days, confirming the evidence of delayed migration obtained at the lung phase. These findings, coupled with histologic observations, indicate that at least half of the worm elimination attributable to immunization occurs 8 or more days after the challenge infection
Maximum likelihood estimation of the attenuated ultrasound pulse
DEFF Research Database (Denmark)
Rasmussen, Klaus Bolding
1994-01-01
The attenuated ultrasound pulse is divided into two parts: a stationary basic pulse and a nonstationary attenuation pulse. A standard ARMA model is used for the basic pulse, and a nonstandard ARMA model is derived for the attenuation pulse. The maximum likelihood estimator of the attenuated...... ultrasound pulse, which includes a maximum likelihood attenuation estimator, is derived. The results of this correspondence are of great importance for deconvolution and attenuation imaging in medical ultrasound...
DEFF Research Database (Denmark)
Wilting, Andreas; Courtiol, Alexandre; Christiansen, Per;
2015-01-01
approaches to plan tiger recovery are partly impeded by the lack of a consensus on the number of tiger subspecies or management units, because a comprehensive analysis of tiger variation is lacking. We analyzed variation among all nine putative tiger subspecies, using extensive data sets of several traits...
Cost Recovery Through Depreciation.
Forrester, Robert T.; Wesolowski, Leonard V.
1983-01-01
The approach of adopting depreciation rather than use allowance in order to recover more accurately the cost of college buildings and equipment used on federal projects is considered. It is suggested that depreciation will offer most colleges and universities a higher annual recovery rate, and an opportunity for better facilities planning. For…
Anatomically Correct Surface Recovery
DEFF Research Database (Denmark)
Jensen, Rasmus Ramsbøl; Nielsen, Jannik Boll; Larsen, Rasmus;
2015-01-01
We present a method for 3D surface recovery in partial surface scans. The method is based on an Active Shape Model, which is used to predict missing data. The model is constructed using a bootstrap framework, where an initially small collection of hand-annotated samples is used to fit to and...
Disaster Recovery: Courting Disaster
O'Hanlon, Charlene
2007-01-01
An inadequate or nonexistent disaster recovery plan can have dire results. Fire, power outage, and severe weather all can brin down the best of networks in an instant. This article draws on the experiences of the Charlotte County Public Schools (Port Charlotte, Florida), which were able to lessen the damage caused by Hurricane Charley when it hit…
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
As robust as the economic recovery in East Asia has been in recent months,attention must now be turned to managing emerging risks challenging macroeconomic stability,said World Bank’s latest East Asia and Pacific Economic Update released on October 19.Edited excerpts follow
Adrenal adenomas: relationship between histologic lipid-rich cells and CT attenuation number
International Nuclear Information System (INIS)
Objective: To evaluate the relationship between lipid-rich cells of the adrenal adenoma and precontrast computed tomographic (CT) attenuation numbers in three clinical groups. Materials and Methods: Thirty-five surgically resected adrenal adenomas were used. The clinical diagnoses of the patients included 13 cases of primary aldosteronism, 15 cases of Cushing's syndrome, and 7 non-functioning tumors. The number of lipid-rich clear cells was counted using a microscopic eyepiece grid that contained 100 squares. The results were expressed as the percentages of lipid-rich areas. Results: There was a strong inverse linear relationship between the percentage of lipid-rich cells and the precontrast CT attenuation number (R2=0.724, P<0.0001). There were significantly more lipid-rich cells in the primary aldosteronism and non-functioning tumor cases compared to cases of Cushing's syndrome (P=0.007 and 0.015, respectively). The CT attenuation numbers of the primary aldosteronism cases were significantly lower than those of Cushing's syndrome (P=0.0052). Furthermore, the CT attenuation numbers of the non-functioning tumor cases were lower than those of Cushing's syndrome cases. Conclusion: We showed that adrenal adenomas in primary aldosteronism and non-functioning tumors contain significantly more lipid-rich cells than those in Cushing's syndrome. They also showed significantly lower attenuation than that in Cushing's syndrome on CT scans. Our results suggest that precontrast CT attenuation numbers may be helpful in the differentiation of adenomas from non-adenomatous lesions, which include malignancies
Adrenal adenomas: relationship between histologic lipid-rich cells and CT attenuation number
Energy Technology Data Exchange (ETDEWEB)
Yamada, Takayuki E-mail: yamataka@rad.med.tohoku.ac.jp; Ishibashi, Tadashi; Saito, Haruo; Matsuhashi, Toshio; Majima, Kazuhiro; Tsuda, Masashi; Takahashi, Shoki; Moriya, Takuya
2003-11-01
Objective: To evaluate the relationship between lipid-rich cells of the adrenal adenoma and precontrast computed tomographic (CT) attenuation numbers in three clinical groups. Materials and Methods: Thirty-five surgically resected adrenal adenomas were used. The clinical diagnoses of the patients included 13 cases of primary aldosteronism, 15 cases of Cushing's syndrome, and 7 non-functioning tumors. The number of lipid-rich clear cells was counted using a microscopic eyepiece grid that contained 100 squares. The results were expressed as the percentages of lipid-rich areas. Results: There was a strong inverse linear relationship between the percentage of lipid-rich cells and the precontrast CT attenuation number (R{sup 2}=0.724, P<0.0001). There were significantly more lipid-rich cells in the primary aldosteronism and non-functioning tumor cases compared to cases of Cushing's syndrome (P=0.007 and 0.015, respectively). The CT attenuation numbers of the primary aldosteronism cases were significantly lower than those of Cushing's syndrome (P=0.0052). Furthermore, the CT attenuation numbers of the non-functioning tumor cases were lower than those of Cushing's syndrome cases. Conclusion: We showed that adrenal adenomas in primary aldosteronism and non-functioning tumors contain significantly more lipid-rich cells than those in Cushing's syndrome. They also showed significantly lower attenuation than that in Cushing's syndrome on CT scans. Our results suggest that precontrast CT attenuation numbers may be helpful in the differentiation of adenomas from non-adenomatous lesions, which include malignancies.
Graphene-based Electronically Tuneable Microstrip Attenuator
Directory of Open Access Journals (Sweden)
L. Pierantoni
2014-06-01
Full Text Available This paper presents the design of a graphene- based electronically tuneable microstrip attenuator operating at a frequency of 5 GHz. The use of graphene as a variable resistor is discussed and the modelling of its electromagnetic properties at microwave frequencies is fully addressed. The design of the graphene-based attenuator is described. The structure integrates a patch of graphene, whose characteristics can range from being a fairly good conductor to a highly lossy material, depending on the applied voltage. By applying the proper voltage through two high-impedance bias lines, the surface resistivity of graphene can be modified, thereby changing the insertion loss of the microstrip attenuator.
Zinc oxide inverse opal enzymatic biosensor
You, Xueqiu; Pikul, James H.; King, William P.; Pak, James J.
2013-06-01
We report ZnO inverse opal- and nanowire (NW)-based enzymatic glucose biosensors with extended linear detection ranges. The ZnO inverse opal sensors have 0.01-18 mM linear detection range, which is 2.5 times greater than that of ZnO NW sensors and 1.5 times greater than that of other reported ZnO sensors. This larger range is because of reduced glucose diffusivity through the inverse opal geometry. The ZnO inverse opal sensors have an average sensitivity of 22.5 μA/(mM cm2), which diminished by 10% after 35 days, are more stable than ZnO NW sensors whose sensitivity decreased by 10% after 7 days.
Inversion of hysteresis and creep operators
Energy Technology Data Exchange (ETDEWEB)
Krejci, Pavel, E-mail: krejci@math.cas.cz [Institute of Mathematics, Academy of Sciences of the Czech Republic, Zitna 25, CZ-11567 Praha 1 (Czech Republic); Al Janaideh, Mohammad, E-mail: aljanaideh@gmail.com [Department of Mechatronics Engineering, The University of Jordan, Amman (Jordan); Deasy, Fergal, E-mail: deasy@math.cas.cz [Institute of Mathematics, Academy of Sciences of the Czech Republic, Zitna 25, CZ-11567 Praha 1 (Czech Republic)
2012-05-01
The explicit inversion formula for rate dependent Prandtl-Ishlinskii operators is extended to cases without the threshold dilation condition. This solves a problem in hysteresis and creep modeling of magnetostrictive behavior.
The Transmuted Generalized Inverse Weibull Distribution
Directory of Open Access Journals (Sweden)
Faton Merovci
2014-05-01
Full Text Available A generalization of the generalized inverse Weibull distribution the so-called transmuted generalized inverse Weibull distribution is proposed and studied. We will use the quadratic rank transmutation map (QRTM in order to generate a flexible family of probability distributions taking the generalized inverseWeibull distribution as the base value distribution by introducing a new parameter that would offer more distributional flexibility. Various structural properties including explicit expressions for the moments, quantiles, and moment generating function of the new distribution are derived. We propose the method of maximum likelihood for estimating the model parameters and obtain the observed information matrix. A real data set are used to compare the flexibility of the transmuted version versus the generalized inverse Weibull distribution.
Inverse Doppler Effects in Broadband Acoustic Metamaterials.
Zhai, S L; Zhao, X P; Liu, S; Shen, F L; Li, L L; Luo, C R
2016-01-01
The Doppler effect refers to the change in frequency of a wave source as a consequence of the relative motion between the source and an observer. Veselago theoretically predicted that materials with negative refractions can induce inverse Doppler effects. With the development of metamaterials, inverse Doppler effects have been extensively investigated. However, the ideal material parameters prescribed by these metamaterial design approaches are complex and also challenging to obtain experimentally. Here, we demonstrated a method of designing and experimentally characterising arbitrary broadband acoustic metamaterials. These omni-directional, double-negative, acoustic metamaterials are constructed with 'flute-like' acoustic meta-cluster sets with seven double meta-molecules; these metamaterials also overcome the limitations of broadband negative bulk modulus and mass density to provide a region of negative refraction and inverse Doppler effects. It was also shown that inverse Doppler effects can be detected in a flute, which has been popular for thousands of years in Asia and Europe. PMID:27578317
Attenuation caused by infrequently updated covariates in survival analysis
DEFF Research Database (Denmark)
Andersen, Per Kragh; Liestøl, Knut
Attenuation; Cox regression model; Measurement errors; Survival analysis; Time-dependent covariates......Attenuation; Cox regression model; Measurement errors; Survival analysis; Time-dependent covariates...
A fluorophosphate-based inverse Keggin structure
Energy Technology Data Exchange (ETDEWEB)
Fielden, John; Quasdorf, Kyle; Cronin, Leroy; Kogerler, Paul
2012-07-17
An unusual PFO(3)(2-)-templated "inverse Keggin" polyanion, [Mo(12)O(46)(PF)(4)](4-), has been isolated from the degradation reaction of an {Mo(132)}-type Keplerate to [PMo(12)O(40)](3-) by [Cu(MeCN)(4)](PF(6)) in acetonitrile. (31)P-NMR studies suggest a structure-directing role for [Cu(MeCN)(4)](+) in the formation of the highly unusual all-inorganic inverse Keggin structure.
On some nonlinear inverse problems in elasticity
Andrieux S.; Bui H.D.
2011-01-01
In this paper, we make a review of some inverse problems in elasticity, in statics and dynamics, in acoustics, thermoelasticity and viscoelasticity. Crack inverse problems have been solved in closed form, by considering a nonlinear variational equation provided by the reciprocity gap functional. This equation involves the unknown geometry of the crack and the boundary data. It results from the symmetry lost between current fields and adjoint fields which is related to their support. The...
Chris Lorenz's idea of conceptual inversion
Domanska, Ewa
2013-01-01
The text deals with Chris Lorenz’s idea of conceptual inversion, understood as an epistemological blockade that stands as a barrier to the development of a proper theory of humanities and social sciences. According to Lorenz, the methodological and theoretical views of scientific programmes embody negations (i.e. inversions) of the views being criticized by them. Because of this process of “turning upside down”, many of the conceptual problems connected with the criticized positions survive. ...
Notions of M\\"obius inversion
Leinster, Tom
2012-01-01
M\\"obius inversion, originally a tool in number theory, was generalized to posets for use in group theory and combinatorics. It was later generalized to categories in two different ways, both of which are useful. We provide a unifying abstract framework. This allows us to compare and contrast the two theories of M\\"obius inversion for categories, and advance each of them. Among several side benefits is an improved understanding of the following fact: the Euler characteristic of the classifyin...
Leinster, Tom
2012-01-01
Möbius inversion, originally a tool in number theory, was generalized to posets for use in group theory and combinatorics. It was later generalized to categories in two different ways, both of which are useful. We provide a unifying abstract framework. This allows us to compare and contrast the two theories of Möbius inversion for categories, and advance each of them. Among several side benefits is an improved understanding of the following fact: the Euler characteristic ...
Handcrafted Inversions Made Operational on Operational Semantics
Monin, Jean-François; Shi, Xiaomu
2013-01-01
When reasoning on formulas involving large-size inductively defined relations, such as the semantics of a real programming language, many steps require the inversion of a hypothesis. The built-in "inversion" tactic of Coq can then be used, but it suffers from severe controllability, maintenance and efficiency issues, which makes it unusable in practice in large applications. To circumvent this issue, we propose a proof technique based on the combination of an antidiagonal argument and the imp...
SVD Analysis of Full Wave Inversion
F Watson and WRB Lionheart
2014-01-01
Full-wave inversion (FWI) is an imaging approach in which we find thequantitative subsurface parameters (such as the dielectric permittivity) whichwould best fit the recorded GPR data. This optimisation problem isnonlinear and ill-posed, and there have been numerous successes inapplying FWI to GPR data. The dominant propertiesof the FWI inversion process can be observed in the Jacobian matrix ofpartial derivatives of the forward map for each acquisition system. Here, weuse singular value d...
Linear inverse problems the maximum entropy connection
Gzyl, Henryk
2011-01-01
This book describes a useful tool for solving linear inverse problems subject to convex constraints. The method of maximum entropy in the mean automatically takes care of the constraints. It consists of a technique for transforming a large dimensional inverse problem into a small dimensional non-linear variational problem. A variety of mathematical aspects of the maximum entropy method are explored as well. Supplementary materials are not included with eBook edition (CD-ROM)
Study on inelastic attenuation coefficient, site response and source parameters in Shanxi region
Institute of Scientific and Technical Information of China (English)
啜永清; 苏燕; 贾建喜; 黄金刚
2004-01-01
Based on 310 horizontal-component digital seismograms recorded at 14 seismic stations in Shanxi Digital Seismograph Network, the inelastic attenuation coefficient in Shanxi region is studied. By the methods of Atkinson and Moya, the site response of each station and several source parameters are obtained and the inversion results from both methods are compared and analyzed. The frequency-dependent inelastic attenuation coefficient Q is estimated as Q( f )=323.2 f 0.506. The site responses of 14 seismic stations do not show significant amplification, which is consistent with their basement on rock. We also found the dependence of corner frequency on seismic moment, seismic moment on stress drop, source radius on stress drop.
Materials analysis using x-ray linear attenuation coefficient measurements at four photon energies
International Nuclear Information System (INIS)
The analytical properties of an accurate parameterization scheme for the x-ray linear attenuation coefficient are examined. The parameterization utilizes an additive combination of N compositional- and energy-dependent coefficients. The former were derived from a parameterization of elemental cross-sections using a polynomial in atomic number. The compositional-dependent coefficients are referred to as the mixture parameters, representing the electron density and higher order statistical moments describing elemental distribution. Additivity is an important property of the parameterization, allowing measured x-ray linear attenuation coefficients to be written as linear simultaneous equations, and then solved for the unknown coefficients. The energy-dependent coefficients can be determined by calibration from measurements with materials of known composition. The inverse problem may be utilized for materials analysis, whereby the simultaneous equations represent multi-energy linear attenuation coefficient measurements, and are solved for the mixture parameters. For in vivo studies, the choice of measurement energies is restricted to the diagnostic region (approximately 20 keV to 150 keV), where the parameterization requires N ≥ 4 energies. We identify a mathematical pathology that must be overcome in order to solve the inverse problem in this energy regime. An iterative inversion strategy is presented for materials analysis using four or more measurements, and then tested against real data obtained at energies 32 keV to 66 keV. The results demonstrate that it is possible to recover the electron density to within ±4% and fourth mixture parameter. It is also a key finding that the second and third mixture parameters cannot be recovered, as they are of minor importance in the parameterization at diagnostic x-ray energies
Davies-Colley, Robert J; Ballantine, Deborah J; Elliott, Sandy H; Swales, Andrew; Hughes, Andrew O; Gall, Mark P
2014-01-01
Fine sediment continues to be a major diffuse pollution concern with its multiple effects on aquatic ecosystems. Mass concentrations (and loads) of fine sediment are usually measured and modelled, apparently with the assumption that environmental effects of sediment are predictable from mass concentrations. However, some severe impacts of fine sediment may not correlate well with mass concentration, notably those related to light attenuation by suspended particles. Light attenuation per unit mass concentration of suspended particulate matter in waters varies widely with particle size, shape and composition. Data for suspended sediment concentration, turbidity and visual clarity (which is inversely proportional to light beam attenuation) from 77 diverse New Zealand rivers provide valuable insights into the mutual relationships of these quantities. Our analysis of these relationships, both across multiple rivers and within individual rivers, supports the proposition that light attenuation by fine sediment is a more generally meaningful basis for environmental management than sediment mass. Furthermore, optical measurements are considerably more practical, being much cheaper (by about four-fold) to measure than mass concentrations, and amenable to continuous measurement. Mass concentration can be estimated with sufficient precision for many purposes from optical surrogates locally calibrated for particular rivers. PMID:24804661
Bow Ties in the Sky I: The Angular Structure of Inverse Compton Gamma-ray Halos in the Fermi Sky
Broderick, Avery E; Shalaby, Mohamad; Pfrommer, Christoph; Puchwein, Ewald; Chang, Philip; Lamberts, Astrid
2016-01-01
Extended inverse Compton halos are generally anticipated around extragalactic sources of gamma rays with energies above 100 GeV. These result from inverse Compton scattered cosmic microwave background photons by a population of high-energy electron/positron pairs produced by the annihilation of the high-energy gamma rays on the infrared background. Despite the observed attenuation of the high-energy gamma rays, the halo emission has yet to be directly detected. Here, we demonstrate that in most cases these halos are expected to be highly anisotropic, distributing the up-scattered gamma rays along axes defined either by the radio jets of the sources or oriented perpendicular to a global magnetic field. We present a pedagogical derivation of the angular structure in the inverse Compton halo and provide an analytic formalism that facilitates the generation of mock images. We discuss exploiting this fact for the purpose of detecting gamma-ray halos in a set of companion papers.
An application of sparse inversion on the calculation of the inverse data space of geophysical data
Saragiotis, Christos
2011-07-01
Multiple reflections as observed in seismic reflection measurements often hide arrivals from the deeper target reflectors and need to be removed. The inverse data space provides a natural separation of primaries and surface-related multiples, as the surface multiples map onto the area around the origin while the primaries map elsewhere. However, the calculation of the inverse data is far from trivial as theory requires infinite time and offset recording. Furthermore regularization issues arise during inversion. We perform the inversion by minimizing the least-squares norm of the misfit function and by constraining the 1 norm of the solution, being the inverse data space. In this way a sparse inversion approach is obtained. We show results on field data with an application to surface multiple removal. © 2011 IEEE.
Inverse feasibility problems of the inverse maximum ﬂow problems
Indian Academy of Sciences (India)
Adrian Deaconu; Eleonor Ciurea
2013-04-01
A linear time method to decide if any inverse maximum ﬂow (denoted General Inverse Maximum Flow problems (IMFG)) problem has solution is deduced. If IMFG does not have solution, methods to transform IMFG into a feasible problem are presented. The methods consist of modifying as little as possible the restrictions to the variation of the bounds of the ﬂow. New inverse combinatorial optimization problems are introduced and solved.
Application of the least-squares inversion method: Fourier series versus waveform inversion
Min, Dong-Joo; Shin, Jungkyun; Shin, Changsoo
2015-11-01
We describe an implicit link between waveform inversion and Fourier series based on inversion methods such as gradient, Gauss-Newton, and full Newton methods. Fourier series have been widely used as a basic concept in studies on seismic data interpretation, and their coefficients are obtained in the classical Fourier analysis. We show that Fourier coefficients can also be obtained by inversion algorithms, and compare the method to seismic waveform inversion algorithms. In that case, Fourier coefficients correspond to model parameters (velocities, density or elastic constants), whereas cosine and sine functions correspond to components of the Jacobian matrix, that is, partial derivative wavefields in seismic inversion. In the classical Fourier analysis, optimal coefficients are determined by the sensitivity of a given function to sine and cosine functions. In the inversion method for Fourier series, Fourier coefficients are obtained by measuring the sensitivity of residuals between given functions and test functions (defined as the sum of weighted cosine and sine functions) to cosine and sine functions. The orthogonal property of cosine and sine functions makes the full or approximate Hessian matrix become a diagonal matrix in the inversion for Fourier series. In seismic waveform inversion, the Hessian matrix may or may not be a diagonal matrix, because partial derivative wavefields correlate with each other to some extent, making them semi-orthogonal. At the high-frequency limits, however, the Hessian matrix can be approximated by either a diagonal matrix or a diagonally-dominant matrix. Since we usually deal with relatively low frequencies in seismic waveform inversion, it is not diagonally dominant and thus it is prohibitively expensive to compute the full or approximate Hessian matrix. By interpreting Fourier series with the inversion algorithms, we note that the Fourier series can be computed at an iteration step using any inversion algorithms such as the
Radiation-attenuated vaccine for lungworm disease
International Nuclear Information System (INIS)
The work done at the Indian Veternary Research Institute, Izatnagar, on the development of a vaccine for lungworm diseases is reported. Research work done includes: (1) studies on the epidemiology and the incidence of the lungworm infections, (ii) studies on the radiation-attenuated lungworm Dictyocaulus filaria vaccine, (iii) studies on other parasites using ionizing radiation, (iv) incidence of lungworm infection in sheep in Jammu and Kashmir State, (v) suitable dose of gamma radiation for attenuation, (vi) laboratory studies with radiation-attenuated D. filaria vaccine, (vii) serology of D. filaria infection, (viii) field trials with the radiation-attenuated vaccine, (ix) immune response of previously exposed lambs to vaccination, (x) comparative susceptibility of sheep and goats to infection with D. filaria, (xi) quantitative studies of D. filaria in lambs and (xii) production and supply of lungworm vaccine. (A.K.)
Attenuation layer for magnetostatic wave (MSW) absorbers
Glass, H. L.; Adkins, L. R.; Stearns, F. S.
1984-09-01
A new technique has been developed for the suppression of MSW end reflections which give rise to passband ripple. The basic idea is to provide a thin film of highly attenuating epitaxial material at the ends of a MSW delay line while preserving high quality YIG in the active region of the device. The GGG wafer preparation is a three step process which involves: (1) the growth of the attenuation layer, (2) the removal of this layer from the central region of the wafer and (3) the growth of high quality YIG on the remaining structure. Delay lines using the attenuation layer for end terminations have been evaluated experimentally and compared to devices utilizing other termination methods. The results indicate that the attenuation layer method produces ripple suppression characteristics which are the equal of those obtained with other termination techniques. The advantage of this new method lies in its suitability for large quantity fabrication requirements.
Cyclic Compressive Loading Facilitates Recovery after Eccentric Exercise
BUTTERFIELD, TIMOTHY A.; ZHAO, YI; AGARWAL, SUDHA; HAQ, FURQAN; BEST, THOMAS M.
2016-01-01
Purpose To assess the biologic basis of massage therapies, we developed an experimental approach to mimic Swedish massage and evaluate this approach on recovery from eccentric exercise-induced muscle damage using a well-controlled animal model. Methods Tibialis anterior muscles of six New Zealand White rabbits were subjected to one bout of damaging, eccentric contractions. One muscle was immediately subjected to cyclic compressive loads, and the contralateral served as the exercised control. Results We found that commencing 30 min of cyclic compressive loading to the muscle, immediately after a bout of eccentric exercise, facilitated recovery of function and attenuated leukocyte infiltration. In addition, fiber necrosis and wet weight of the tissue were also reduced by compressive loading. Conclusion We conclude that subjecting muscle to compressive loads immediately after exercise leads to an enhanced recovery of muscle function and attenuation of the damaging effects of inflammation in the rabbit model. Although these observations suggest that skeletal muscle responds to cyclic compressive forces similar to those generated by clinical approaches, such as therapeutic massage, further research is needed to assess the translational efficacy of these findings. PMID:18580410
Post-Retrieval Extinction Attenuates Cocaine Memories
Sartor, Gregory C.; Aston-Jones, Gary
2013-01-01
Recent studies have shown that post-retrieval extinction training attenuates fear and reward-related memories in both humans and rodents. This noninvasive, behavioral approach has the potential to be used in clinical settings to treat maladaptive memories that underlie several psychiatric disorders, including drug addiction. However, few studies to date have used a post-retrieval extinction approach to attenuate addiction-related memories. In the current study, we attempted to disrupt cocaine...
Brucellosis: The Case for Live, Attenuated Vaccines
Ficht, Thomas A.; Kahl-McDonagh, Melissa M.; Arenas-Gamboa, Angela M.; Rice-Ficht, Allison C.
2009-01-01
The successful control of animal brucellosis and associated reduction in human exposure has limited the development of human brucellosis vaccines. However, the potential use of Brucella in bioterrorism or biowarfare suggests that direct intervention strategies are warranted. Although the dominant approach has explored the use of live attenuated vaccines, side-effects associated with their use has prevented widespread use in humans. Development of live, attenuated Brucella vaccines that are sa...
Investigation of photon attenuation coefficients for marble
International Nuclear Information System (INIS)
The total linear attenuation coefficients μ (cm-1) have been obtained using the XCOM program at photon energies of 1 keV to 1 GeV for six different natural marbles produced in different places in Turkey. The individual contribution of photon interaction processes to the total linear attenuation coefficients for marble has been investigated. The calculated results were also compared with the measurements. The results obtained for marble were also compared with concrete. (note)
Electron Effective-Attenuation-Length Database
SRD 82 NIST Electron Effective-Attenuation-Length Database (PC database, no charge) This database provides values of electron effective attenuation lengths (EALs) in solid elements and compounds at selected electron energies between 50 eV and 2,000 eV. The database was designed mainly to provide EALs (to account for effects of elastic-eletron scattering) for applications in surface analysis by Auger-electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS).
ATTENUATION AND FLANKING TRANSMISSION IN LIGHTWEIGHT STRUCTURES
DEFF Research Database (Denmark)
Brunskog, Jonas; Lhomond, Alice; Ohlrich, Mogens
2007-01-01
In this paper the attenuation and flanking transmissions of impact noise in lightweight building structures is studied using a modal approach. The structural field is mainly analysed, putting the main attention to the parts being important in the modelling. The amount of attenuation produced by the...... periodically reinforcing beams used in lightweight building structures is analysed. The consequence of these factors in modelling flanking transmission is also discussed....
Karner Blue Butterfly Recovery Plan
US Fish and Wildlife Service, Department of the Interior — This recovery plan has been prepared by the Karner Blue Butterfly Recovery Team under the leadership of Dr. David Andow, University of Minnesota-St. Paul. Dr. John...
Sampling of finite elements for sparse recovery in large scale 3D electrical impedance tomography
International Nuclear Information System (INIS)
This study proposes a method to improve performance of sparse recovery inverse solvers in 3D electrical impedance tomography (3D EIT), especially when the volume under study contains small-sized inclusions, e.g. 3D imaging of breast tumours. Initially, a quadratic regularized inverse solver is applied in a fast manner with a stopping threshold much greater than the optimum. Based on assuming a fixed level of sparsity for the conductivity field, finite elements are then sampled via applying a compressive sensing (CS) algorithm to the rough blurred estimation previously made by the quadratic solver. Finally, a sparse inverse solver is applied solely to the sampled finite elements, with the solution to the CS as its initial guess. The results show the great potential of the proposed CS-based sparse recovery in improving accuracy of sparse solution to the large-size 3D EIT. (paper)
Bellefleur, G.; Riedel, M.; Brent, T.
2007-05-01
Wave attenuation is an important physical property of hydrate-bearing sediments that is rarely taken into account in site characterization with seismic data. We present a field example showing improved images of hydrate- bearing sediments on seismic data after compensation of attenuation effects. Compressional quality factors (Q) are estimated from zero-offset Vertical Seismic Profiling data acquired at Mallik, Northwest Territories, Canada. During the last 10 years, two internationally-partnered research drilling programs have intersected three major intervals of sub-permafrost gas hydrates at Mallik, and have successfully extracted core samples containing significant amount of gas hydrates. Individual gas hydrate intervals are up to 40m in thickness and are characterized by high in situ gas hydrate saturation, sometimes exceeding 80% of pore volume of unconsolidated clastic sediments having average porosities ranging from 25% to 40%. The Q-factors obtained from the VSP data demonstrate significant wave attenuation for permafrost and hydrate- bearing sediments. These results are in agreement with previous attenuation estimates from sonic logs and crosshole data at different frequency intervals. The Q-factors obtained from VSP data were used to compensate attenuation effects on surface 3D seismic data acquired over the Mallik gas hydrate research wells. Intervals of gas hydrate on surface seismic data are characterized by strong reflectivity and effects from attenuation are not perceptible from a simple visual inspection of the data. However, the application of an inverse Q-filter increases the resolution of the data and improves correlation with log data, particularly for the shallowest gas hydrate interval. Compensation of the attenuation effects of the permafrost likely explains most of the improvements for the shallow gas hydrate zone. Our results show that characterization of the Mallik gas hydrates with seismic data not corrected for attenuation would tend to
Ventilation with heat recovery
DEFF Research Database (Denmark)
Tommerup, Henrik M.; Svendsen, Svend
2005-01-01
This paper presents the experiences from the use of ventilation with heat recovery in several experimental single-family houses developed and built within the last four years to meet the new Danish energy requirements of 2005. Included are descriptions of the ventilation system components...... and the main functional demands as well as measurements of the thermal efficiency, electricity consumptions and building air tightness. The paper addresses the aspects of minimizing the heat loss from the duct system and the heat recovery unit (when placed in an unheated attic space) in order to obtain...... an acceptable efficiency. Furthermore, solutions to secure the air tightness of the building envelope are suggested. The paper does not address problems with condensate of water in the exchanger that may freeze in cold climate conditions. This complex of problem is dealt with in a separate paper....
DEFF Research Database (Denmark)
Gundlach, Carsten
2006-01-01
growth curves are represented as strings. To identify the strings a combination of a 5D connected component type algorithm and multi-peak fitting was found to be superior. The first use of the method was a study of recovery of a deformed aluminium alloy (AA1050). The aluminium alloy was deformed by cold......In the present thesis the development of a unique experimental method for volume characterisation of individual embedded crystallites down to a radius of 150 nm is presented. This method is applied to in-situ studies of recovery in aluminium. The method is an extension of 3DXRD microscopy, an X......-ray diffraction technique for studies of the evolution of grains within polycrystalline materials. The much smaller volume of the crystallites of interest here in comparison to grains implies that the existing method is not applicable due to overlap of diffraction spots. In this work this obstacle is overcome by...
Tamponnet, C; Savage, C J; Amblard, P; Lasserre, J C; Personne, J C; Germain, J C
1999-03-01
In the absence of recycling, water represents over 90% of the life-support consumables for a manned spacecraft. In addition, over 90% of the waste water generated can be classified as moderately or slightly contaminated (e.g. shower water, condensate from the air-conditioning system, etc.). The ability to recover potable water from moderately contaminated waste water hence enables significant savings to be made in resupply costs. A development model of such a water-recovery system, based on membrane technology has been produced and tested using "real waste water" based on used shower water Results indicate some 95% recovery of potable water meeting ESA standards, with total elimination of microbial contaminants such as bacteria, spores and viruses. PMID:11725802
Mechanisms of geometrical seismic attenuation
Directory of Open Access Journals (Sweden)
Igor B. Morozov
2011-07-01
Full Text Available In several recent reports, we have explained the frequency dependence of the apparent seismic quality-factor (Q observed in many studies according to the effects of geometrical attenuation, which was defined as the zero-frequency limit of the temporal attenuation coefficient. In particular, geometrical attenuation was found to be positive for most waves traveling within the lithosphere. Here, we present three theoretical models that illustrate the origin of this geometrical attenuation, and we investigate the causes of its preferential positive values. In addition, we discuss the physical basis and limitations of both the conventional and new attenuation models. For waves in media with slowly varying properties, geometrical attenuation is caused by variations in the wavefront curvature, which can be both positive (for defocusing and negative (for focusing. In media with velocity/density contrasts, incoherent reflectivity leads to geometrical-attenuation coefficients which are proportional to the mean squared reflectivity and are always positive. For «coherent» reflectivity, the geometrical attenuation is approximately zero, and the attenuation process can be described according to the concept of «scattering Q». However, the true meaning of this parameter is in describing the mean reflectivity within the medium, and not that of the traditional resonator quality factor known in mechanics. The general conclusion from these models is that non-zero and often positive levels of geometrical attenuation are common in realistic, heterogeneous media, both observationally and theoretically. When transformed into the conventional Q-factor form, this positive geometrical attenuation leads to Q values that quickly increase with frequency. These predictions show that the positive frequency-dependent Q observed in many datasets might represent artifacts of the transformations of the attenuation coefficients into Q.
Inversion for seismic anisotropy using genetic algorithms
Energy Technology Data Exchange (ETDEWEB)
Horne, S. (British Geological Survey, Edinburgh (United Kingdom) Univ. of Edinburgh (United Kingdom). Dept. of Geology and Geophysics); MacBeth, C. (Univ. of Edinburgh (United Kingdom). Dept. of Geology and Geophysics)
1994-11-01
A general inversion scheme based on a genetic algorithm is developed to invert seismic observations for anisotropic parameters. The technique is applied to the inversion of shear-wave observations from two azimuthal VSP data sets from the Conoco test site in Oklahoma. Horizontal polarizations and time-delays are inverted for hexagonal and orthorhombic symmetries. The model solutions are consistent with previous studies using trial and error matching of full waveform synthetics. The shear-wave splitting observations suggest the presence of a shear-wave line singularity and are consistent with a dipping fracture system which is known to exist at the test site. Application of the inversion scheme prior to full waveform modeling demonstrates that a considerable saving in time is possible while retaining the same degree of accuracy.
Inversion of Stokes Profiles with Systematic Effects
Ramos, A Asensio; Gonzalez, M J Martinez; Yabar, A Pastor
2016-01-01
Quantitative thermodynamical, dynamical and magnetic properties of the solar and stellar plasmas are obtained by interpreting their emergent non-polarized and polarized spectrum. This inference requires the selection of a set of spectral lines particularly sensitive to the physical conditions in the plasma and a suitable parametric model of the solar/stellar atmosphere. Nonlinear inversion codes are then used to fit the model to the observations. However, the presence of systematic effects like nearby or blended spectral lines, telluric absorption or incorrect correction of the continuum, among others, can strongly affect the results. We present an extension to current inversion codes that can deal with these effects in a transparent way. The resulting algorithm is very simple and can be applied to any existing inversion code with the addition of a few lines of code as an extra step in each iteration.
Probabilistic inversion for chicken processing lines
Energy Technology Data Exchange (ETDEWEB)
Cooke, Roger M. [Department of Mathematics, Delft University of Technology, Delft (Netherlands)]. E-mail: r.m.cooke@ewi.tudelft.nl; Nauta, Maarten [Microbiological Laboratory for Health Protection RIVM, Bilthoven (Netherlands); Havelaar, Arie H. [Microbiological Laboratory for Health Protection RIVM, Bilthoven (Netherlands); Fels, Ine van der [Microbiological Laboratory for Health Protection RIVM, Bilthoven (Netherlands)
2006-10-15
We discuss an application of probabilistic inversion techniques to a model of campylobacter transmission in chicken processing lines. Such techniques are indicated when we wish to quantify a model which is new and perhaps unfamiliar to the expert community. In this case there are no measurements for estimating model parameters, and experts are typically unable to give a considered judgment. In such cases, experts are asked to quantify their uncertainty regarding variables which can be predicted by the model. The experts' distributions (after combination) are then pulled back onto the parameter space of the model, a process termed 'probabilistic inversion'. This study illustrates two such techniques, iterative proportional fitting (IPF) and PARmeter fitting for uncertain models (PARFUM). In addition, we illustrate how expert judgement on predicted observable quantities in combination with probabilistic inversion may be used for model validation and/or model criticism.
Tabu optimization for matched field inversion
Michalopoulou, Zoi-Heleni; Ghosh-Dastidar, Urmi
2002-11-01
Matched field processing is a powerful tool for source localization and geoacoustic inversion. Because of significant environmental and geometry uncertainties, however, matched field processing usually involves multiparameter searches. To facilitate these searches, global optimization techniques such as genetic algorithms and simulated annealing have been successfully employed. In this work, a different approach, tabu, is implemented for optimization in matched field inversion. Tabu is a technique relying on the use of memory; it searches for the global maximum of the objective function through a navigation process that avoids already revisited models, also making use of aspiration criteria and diversification for faster convergence. The tabu performance in localization and geoacoustic inversion is demonstrated through experimentation with both synthetic and real (SWellEX 96) data. The approach is shown to provide reliable estimates in an efficient manner. [Work supported by ONR.
Inverse Folding of RNA Pseudoknot Structures
Gao, James Z M; Reidys, Christian M
2010-01-01
Background: RNA exhibits a variety of structural configurations. Here we consider a structure to be tantamount to the noncrossing Watson-Crick and \\pairGU-base pairings (secondary structure) and additional cross-serial base pairs. These interactions are called pseudoknots and are observed across the whole spectrum of RNA functionalities. In the context of studying natural RNA structures, searching for new ribozymes and designing artificial RNA, it is of interest to find RNA sequences folding into a specific structure and to analyze their induced neutral networks. Since the established inverse folding algorithms, {\\tt RNAinverse}, {\\tt RNA-SSD} as well as {\\tt INFO-RNA} are limited to RNA secondary structures, we present in this paper the inverse folding algorithm {\\tt Inv} which can deal with 3-noncrossing, canonical pseudoknot structures. Results: In this paper we present the inverse folding algorithm {\\tt Inv}. We give a detailed analysis of {\\tt Inv}, including pseudocodes. We show that {\\tt Inv} allows to...
Inverse Scattering Approach to Improving Pattern Recognition
Energy Technology Data Exchange (ETDEWEB)
Chapline, G; Fu, C
2005-02-15
The Helmholtz machine provides what may be the best existing model for how the mammalian brain recognizes patterns. Based on the observation that the ''wake-sleep'' algorithm for training a Helmholtz machine is similar to the problem of finding the potential for a multi-channel Schrodinger equation, we propose that the construction of a Schrodinger potential using inverse scattering methods can serve as a model for how the mammalian brain learns to extract essential information from sensory data. In particular, inverse scattering theory provides a conceptual framework for imagining how one might use EEG and MEG observations of brain-waves together with sensory feedback to improve human learning and pattern recognition. Longer term, implementation of inverse scattering algorithms on a digital or optical computer could be a step towards mimicking the seamless information fusion of the mammalian brain.
Optimization and Inverse Design of Pump Impeller
International Nuclear Information System (INIS)
As for pump impellers, the meridional flow channel and blade-to-blade flow channel, which are relatively independent of each other but greatly affect performance, are designed in parallel. And the optimization design is used for the former and the inverse design is used for the latter. To verify this new design method, a mixed-flow impeller was made. Next, we use Tani's inverse design method for the blade loading of inverse design. It is useful enough to change a deceleration rate freely and greatly. And it can integrally express the rear blade loading of various methods by NACA, Zangeneh and Stratford. We controlled the deceleration rate by shape parameter m, and its value became almost same with Tani's recommended value of the laminar airfoil.
Geometric theory of inversion and seismic imaging
Lau, August
2015-01-01
The goal of inversion is to estimate the model which generates the data of observations with a specific modeling equation. One general approach to inversion is to use optimization methods which are algebraic in nature to define an objective function. This is the case for objective functions like minimizing RMS of amplitude, residual traveltime error in tomography, cross correlation and sometimes mixing different norms (e.g. L1 of model + L2 of RMS error). Algebraic objective function assumes that the optimal solution will come up with the correct geometry. It is sometimes difficult to understand how one number (error of the fit) could miraculously come up with the detail geometry of the earth model. If one models the earth as binary rock parameters (only two values for velocity variation), one could see that the geometry of the rugose boundaries of the geobodies might not be solvable by inversion using algebraic objective function.
Optimization and Inverse Design of Pump Impeller
Miyauchi, S.; Zhu, B.; Luo, X.; Piao, B.; Matsumoto, H.; Sano, M.; Kassai, N.
2012-11-01
As for pump impellers, the meridional flow channel and blade-to-blade flow channel, which are relatively independent of each other but greatly affect performance, are designed in parallel. And the optimization design is used for the former and the inverse design is used for the latter. To verify this new design method, a mixed-flow impeller was made. Next, we use Tani's inverse design method for the blade loading of inverse design. It is useful enough to change a deceleration rate freely and greatly. And it can integrally express the rear blade loading of various methods by NACA, Zangeneh and Stratford. We controlled the deceleration rate by shape parameter m, and its value became almost same with Tani's recommended value of the laminar airfoil.
Physical mechanism of seismic attenuation in a two-phase medium%双相介质中地震波衰减的物理机制
Institute of Scientific and Technical Information of China (English)
李子顺
2008-01-01
High-frequency seismic attenuation is conventionally attributed to anelastic absorption. In this paper, I present three studies on high-frequency seismic attenuation and propose that the physical mechanism results from the interference of elastic microscopic multiple scattering waves. First, I propose a new theory on wave propagation in a two-phase medium which is based on the concept that the basic unit for wave propagation is a nano-mass point. As a result of the elasticity variations of pore fluid and rock framework, micro multiple scattering waves would emerge at the wavelength of the seismic waves passing through the two-phase medium and their interference and overlap would generate high-frequency seismic attenuation. Second, I present a study of the frequency response of seismic transmitted waves by modeling thin-layers with thicknesses no larger than pore diameters. Results indicate that high-frequency seismic waves attenuate slightly in a near-surface water zone but decay significantly in a near-surface gas zone. Third, I analyze the seismic attenuation characteristics in near-surface water and gas zones using dual-well shots in the Songliao Basin, and demonstrate that the high-frequency seismic waves attenuate slightly in water zones but in gas zones the 160-1600 Hz propagating waves decay significantly. The seismic attenuation characteristics from field observations coincide with the modeling results. Conclusions drawn from these studies theoretically support seismic attenuation recovery.
New Modified Band Limited Impedance (BLIMP) Inversion Method Using Envelope Attribute
Maulana, Z. L.; Saputro, O. D.; Latief, F. D. E.
2016-01-01
Earth attenuates high frequencies from seismic wavelet. Low frequency seismics cannot be obtained by low quality geophone. The low frequencies (0-10 Hz) that are not present in seismic data are important to obtain a good result in acoustic impedance (AI) inversion. AI is important to determine reservoir quality by converting AI to reservoir properties like porosity, permeability and water saturation. The low frequencies can be supplied from impedance log (AI logs), velocity analysis, and from the combination of both data. In this study, we propose that the low frequencies could be obtained from the envelope seismic attribute. This new proposed method is essentially a modified BLIMP (Band Limited Impedance) inversion method, in which the AI logs for BLIMP substituted with the envelope attribute. In low frequency domain (0-10 Hz), the envelope attribute produces high amplitude. This low frequency from the envelope attribute is utilized to replace low frequency from AI logs in BLIMP. Linear trend in this method is acquired from the AI logs. In this study, the method is applied on synthetic seismograms created from impedance log from well ‘X’. The mean squared error from the modified BLIMP inversion is 2-4% for each trace (variation in error is caused by different normalization constant), lower than the conventional BLIMP inversion which produces error of 8%. The new method is also applied on Marmousi2 dataset and show promising result. The modified BLIMP inversion result from Marmousi2 by using one log AI is better than the one produced from the conventional method.
Joshi, A.; Mohanty, M.; Bansal, A. R.; Dimri, V. P.; Chadha, R. K.
2010-04-01
Three-dimensional attenuation structures are related to the subsurface heterogeneities present in the earth crust. An algorithm for estimation of three-dimensional attenuation structure in the part of Garhwal Himalaya, India has been presented by Joshi (Curr Sci 90:581-585, 2006b; Nat Hazards 43:129-146, 2007). In continuation of our earlier approach, we have presented a method in which strong motion data have been used to estimate frequency-dependent three-dimensional attenuation structure of the region. The border district of Pithoragarh in the Higher Himalaya, India, lies in the central seismic gap region of Himalaya. This region falls in the seismic zones IV and V of the seismic zoning map of India. A dense network consisting of eight accelerographs has been installed in this region. This network has recorded several local events. An algorithm based on inversion of strong motion digital data is developed in this paper to estimate attenuation structure at different frequencies using the data recorded by this network. Twenty strong motion records observed at five stations have been used to estimate the site amplification factors using inversion algorithm defined in this paper. Site effects obtained from inversion has been compared with that obtained using Nakamura (1988) and Lermo et al. (Bull Seis Soc Am 83:1574-1594, 1993) approach. The obtained site amplification term has been used for correcting spectral acceleration data at different stations. The corrected spectral acceleration data have been used as an input to the developed algorithm to avoid effect of near-site soil amplification term. The attenuation structure is estimated by dividing the entire area in several three-dimensional block of different frequency-dependent shear wave quality factor Q β ( f). The input to this algorithm is the spectral acceleration of S phase of the corrected accelerogram. The outcome of the algorithm is given in terms of attenuation coefficient and source acceleration
Ensemble Kalman methods for inverse problems
International Nuclear Information System (INIS)
The ensemble Kalman filter (EnKF) was introduced by Evensen in 1994 (Evensen 1994 J. Geophys. Res. 99 10143–62) as a novel method for data assimilation: state estimation for noisily observed time-dependent problems. Since that time it has had enormous impact in many application domains because of its robustness and ease of implementation, and numerical evidence of its accuracy. In this paper we propose the application of an iterative ensemble Kalman method for the solution of a wide class of inverse problems. In this context we show that the estimate of the unknown function that we obtain with the ensemble Kalman method lies in a subspace A spanned by the initial ensemble. Hence the resulting error may be bounded above by the error found from the best approximation in this subspace. We provide numerical experiments which compare the error incurred by the ensemble Kalman method for inverse problems with the error of the best approximation in A, and with variants on traditional least-squares approaches, restricted to the subspace A. In so doing we demonstrate that the ensemble Kalman method for inverse problems provides a derivative-free optimization method with comparable accuracy to that achieved by traditional least-squares approaches. Furthermore, we also demonstrate that the accuracy is of the same order of magnitude as that achieved by the best approximation. Three examples are used to demonstrate these assertions: inversion of a compact linear operator; inversion of piezometric head to determine hydraulic conductivity in a Darcy model of groundwater flow; and inversion of Eulerian velocity measurements at positive times to determine the initial condition in an incompressible fluid. (paper)
Mesoscale inversion of carbon sources and sinks
International Nuclear Information System (INIS)
Inverse methods at large scales are used to infer the spatial variability of carbon sources and sinks over the continents but their uncertainties remain large. Atmospheric concentrations integrate the surface flux variability but atmospheric transport models at low resolution are not able to simulate properly the local atmospheric dynamics at the measurement sites. However, the inverse estimates are more representative of the large spatial heterogeneity of the ecosystems compared to direct flux measurements. Top-down and bottom-up methods that aim at quantifying the carbon exchanges between the surface and the atmosphere correspond to different scales and are not easily comparable. During this phD, a mesoscale inverse system was developed to correct carbon fluxes at 8 km resolution. The high resolution transport model MesoNH was used to simulate accurately the variability of the atmospheric concentrations, which allowed us to reduce the uncertainty of the retrieved fluxes. All the measurements used here were observed during the intensive regional campaign CERES of May and June 2005, during which several instrumented towers measured CO2 concentrations and fluxes in the South West of France. Airborne measurements allowed us to observe concentrations at high altitude but also CO2 surface fluxes over large parts of the domain. First, the capacity of the inverse system to correct the CO2 fluxes was estimated using pseudo-data experiments. The largest fraction of the concentration variability was attributed to regional surface fluxes over an area of about 300 km around the site locations depending on the meteorological conditions. Second, an ensemble of simulations allowed us to define the spatial and temporal structures of the transport errors. Finally, the inverse fluxes at 8 km resolution were compared to direct flux measurements. The inverse system has been validated in space and time and showed an improvement of the first guess fluxes from a vegetation model
Trimming and procrastination as inversion techniques
Backus, George E.
1996-12-01
By examining the processes of truncating and approximating the model space (trimming it), and by committing to neither the objectivist nor the subjectivist interpretation of probability (procrastinating), we construct a formal scheme for solving linear and non-linear geophysical inverse problems. The necessary prior information about the correct model xE can be either a collection of inequalities or a probability measure describing where xE was likely to be in the model space X before the data vector y0 was measured. The results of the inversion are (1) a vector z0 that estimates some numerical properties zE of xE; (2) an estimate of the error δz = z0 - zE. As y0 is finite dimensional, so is z0, and hence in principle inversion cannot describe all of xE. The error δz is studied under successively more specialized assumptions about the inverse problem, culminating in a complete analysis of the linear inverse problem with a prior quadratic bound on xE. Our formalism appears to encompass and provide error estimates for many of the inversion schemes current in geomagnetism, and would be equally applicable in geodesy and seismology if adequate prior information were available there. As an idealized example we study the magnetic field at the core-mantle boundary, using satellite measurements of field elements at sites assumed to be almost uniformly distributed on a single spherical surface. Magnetospheric currents are neglected and the crustal field is idealized as a random process with rotationally invariant statistics. We find that an appropriate data compression diagonalizes the variance matrix of the crustal signal and permits an analytic trimming of the idealized problem.
Cine CT for Attenuation Correction in Cardiac PET/CT
Alessio, Adam M.; Kohlmyer, Steve; Branch, Kelley; Chen, Grace; Caldwell, James; Kinahan, Paul
2007-01-01
In dual-modality PET/CT systems, the CT scan provides the attenuation map for PET attenuation correction. The current clinical practice of obtaining a single helical CT scan provides only a snapshot of the respiratory cycle, whereas PET occurs over multiple respiratory cycles. Misalignment of the attenuation map and emission image because of respiratory motion causes errors in the attenuation correction factors and artifacts in the attenuation-corrected PET image. To rectify this problem, we ...
Enabling photon counting detectors with dynamic attenuators
Hsieh, Scott S.; Pelc, Norbert J.
2014-03-01
Photon-counting x-ray detectors (PCXDs) are being investigated as a replacement for conventional x-ray detectors because they promise several advantages, including better dose efficiency, higher resolution and spectral imaging. However, many of these advantages disappear when the x-ray flux incident on the detector is too high. We recently proposed a dynamic, piecewise-linear attenuator (or beam shaping filter) that can control the flux incident on the detector. This can restrict the operating range of the PCXD to keep the incident count rate below a given limit. We simulated a system with the piecewise-linear attenuator and a PCXD using raw data generated from forward projected DICOM files. We investigated the classic paralyzable and nonparalyzable PCXD as well as a weighted average of the two, with the weights chosen to mimic an existing PCXD (Taguchi et al, Med Phys 2011). The dynamic attenuator has small synergistic benefits with the nonparalyzable detector and large synergistic benefits with the paralyzable detector. Real PCXDs operate somewhere between these models, and the weighted average model still shows large benefits from the dynamic attenuator. We conclude that dynamic attenuators can reduce the count rate performance necessary for adopting PCXDs.
Dispersion analysis with inverse dielectric function modelling.
Mayerhöfer, Thomas G; Ivanovski, Vladimir; Popp, Jürgen
2016-11-01
We investigate how dispersion analysis can profit from the use of a Lorentz-type description of the inverse dielectric function. In particular at higher angles of incidence, reflectance spectra using p-polarized light are dominated by bands from modes that have their transition moments perpendicular to the surface. Accordingly, the spectra increasingly resemble inverse dielectric functions. A corresponding description can therefore eliminate the complex dependencies of the dispersion parameters, allow their determination and facilitate a more accurate description of the optical properties of single crystals. PMID:27294550
Inverse problem for axial-deformed potentials
International Nuclear Information System (INIS)
In the literature about Inverse Problems there are no tractable methods for construction of nonspherical potentials from the asymptotic wave function. This problem turned out to be solved in special cases. The methods of reconstruction from scattering data are given for the class of potentials admitting the separation of variables in spheroidal coordinates. This is the first case when the agorithms of the inverse problem solution for spherically-nonsymmetrical local potentials can practically be realised. The modifications of the formalisms of Regge-Newton-Sabatier and finite-difference approximation of Hooshyar-Rasavy are considered
APPROXIMATE AMENABILITY OF CERTAIN INVERSE SEMIGROUP ALGEBRAS
Institute of Scientific and Technical Information of China (English)
Mehdi ROSTAMI; Abdolrasoul POURABBAS; Morteza ESSMAILI
2013-01-01
In this article,the approximate amenability of semigroup algebra e1(S) is investigated,where S is a uniformly locally finite inverse semigroup.Indeed,we show that for a uniformly locally finite inverse semigroup S,the notions of amenability,approximate amenability and bounded approximate amenability of e1 (S) are equivalent.We use this to give a direct proof of the approximate amenability of e1(S) for a Brandt semigroup S.Moreover,we characterize the approximate amenability of e1(S),where S is a uniformly locally finite band semigroup.