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| 2. |
- Ma, Xu, et al.
(författare)
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Passive Seismic Imaging of Stress Evolution with Mining-Induced Seismicity at Hard-Rock Deep Mines
- 2020
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Ingår i: Rock Mechanics and Rock Engineering. - : Springer. - 0723-2632 .- 1434-453X. ; 53:6, s. 2789-2804
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Tidskriftsartikel (refereegranskat)abstract
- This work aims to examine the stress redistribution with evolving seismicity rates using a passive seismic tomographic tool. We compiled a total of 26,000 events from two underground mines and partitioned them into multiple clusters in a temporal sequence, each of which contains 1000 events. To image stress redistribution associated with seismicity rates, we then run the tomographic studies using each cluster to yield seismic tomograms and computed the corresponding seismicity rate. We found that high velocity anomalies grew with the increase of seismicity rates, and they switched to a shrinking tendency under low seismicity rates. Results of this study imply that seismicity rates increase with increasing stress concentration and decrease with decreasing stress concentration. This study highlights the value of utilizing passive seismic tomography for estimating stress evolution associated with the change of seismicity rates at underground mines. Our findings illuminate the applications of using mining-induced seismicity to assess stress redistribution associated with seismicity rates at hard-rock mines, providing insights into seismic hazards for deep mining.
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| 3. |
- Ossenkoppele, Rik, et al.
(författare)
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Distinct tau PET patterns in atrophy-defined subtypes of Alzheimer's disease
- 2020
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Ingår i: Alzheimer's and Dementia. - : Wiley. - 1552-5260 .- 1552-5279. ; 16:2, s. 335-344
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Differential patterns of brain atrophy on structural magnetic resonance imaging (MRI) revealed four reproducible subtypes of Alzheimer's disease (AD): (1) “typical”, (2) “limbic-predominant”, (3) “hippocampal-sparing”, and (4) “mild atrophy”. We examined the neurobiological characteristics and clinical progression of these atrophy-defined subtypes. Methods: The four subtypes were replicated using a clustering method on MRI data in 260 amyloid-β–positive patients with mild cognitive impairment or AD dementia, and we subsequently tested whether the subtypes differed on [18F]flortaucipir (tau) positron emission tomography, white matter hyperintensity burden, and rate of global cognitive decline. Results: Voxel-wise and region-of-interest analyses revealed the greatest neocortical tau load in hippocampal-sparing (frontoparietal-predominant) and typical (temporal-predominant) patients, while limbic-predominant patients showed particularly high entorhinal tau. Typical patients with AD had the most pronounced white matter hyperintensity load, and hippocampal-sparing patients showed the most rapid global cognitive decline. Discussion: Our data suggest that structural MRI can be used to identify biologically and clinically meaningful subtypes of AD.
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| 4. |
- Velickaite, Vilma, et al.
(författare)
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Visual rating versus volumetry of regional brain atrophy and longitudinal changes over a 5-year period in an elderly population.
- 2020
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Ingår i: Brain and Behavior. - : Wiley. - 2162-3279 .- 2162-3279. ; 10:7
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: The purpose of our study was to compare visual rating and volumetry of brain atrophy in an elderly population over a 5‐year period and compare findings with cognitive test results.Materials and Methods: Two hundred and one subjects were examined with magnetic resonance imaging (MRI) of the brain. Visual rating and volumetry were performed in all subjects at ages 75 and 80. Cognitive function at both time points was assessed with the Mini‐Mental State Examination (MMSE) and Trail Making Tests A and B (TMT‐A and TMT‐B). Changes in visual rating and volumetry were compared with changes in cognitive test.Results: A correlation was found between visual rating of medial temporal lobe atrophy (MTA) and hippocampal volumetry at both time points (rs = −.42 and rs = −.49, p < .001, respectively). The correlation between visual rating of posterior atrophy (PA); frontal atrophy (F‐GCA) and volumetry of these brain regions was significant only at age 80 (rs = −.16, p = .02 for PA and rpb = .19, p = .006 for F‐GCA). Visual rating showed only a minimal progression of regional atrophy at age 80, whereas volumetry showed 2%–5% decrease in volume depending on brain region. Performance in the MMSE, TMT‐A, and TMT‐B was virtually unchanged between ages 75 and 80.Conclusion: We found a mild age‐associated decrease in regional brain volumes in this healthy cohort with well‐preserved cognitive functions. Visual assessment may not be sufficient for detecting mild progression of brain atrophy due to normal aging, whereas volumetry is more sensitive to capture these subtle changes.
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| 5. |
- Ma, Xu, et al.
(författare)
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Stress Redistribution Monitoring Using Passive Seismic Tomography at a Deep Nickel Mine
- 2019
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Ingår i: Rock Mechanics and Rock Engineering. - : Springer. - 0723-2632 .- 1434-453X. ; 52:10, s. 3909-3919
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Tidskriftsartikel (refereegranskat)abstract
- High magnitude seismic events (HMSE), also called major events, triggered at underground mines can severely threaten safety and structures in mines. The aims of this work are to assess stress evolution with the occurrence of them and identify patterns in stress change. Several methods were used to help understand the stress redistribution and rock mass behavior related to two HMSE with moment magnitude greater than 1.0 in a deep nickel mine. Approximately 46,500 seismic events were compiled with 2 HMSE at this mine and used seismic tomography to obtain high-resolution images and temporal-spatial velocity changes before and after these events. This work exhibited surrounding stress evolution and geological structures. Seismic imaging results show that velocity increased in the nearby regions of HMSE before they were triggered. Stress subsequently reduced in the relaxation process after the occurrence of HMSE. Conversely, regions predominantly occupied by low-velocity anomalies increased to higher stress levels after HMSE. Overall, the stress redistributed toward an equilibrium state following HMSE. This study highlights the value of utilizing seismic tomography for estimating stress evolution associated with HMSE. The findings illuminate the applications of seismic imaging around HMSE of hard-rock mines, providing insights into seismic hazard mitigation for deep mining.
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| 6. |
- Wallert, John, et al.
(författare)
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Differentiating Patients at the Memory Clinic With Simple Reaction Time Variables : A Predictive Modeling Approach Using Support Vector Machines and Bayesian Optimization
- 2018
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Ingår i: Frontiers in Aging Neuroscience. - : Frontiers Media SA. - 1663-4365 .- 1663-4365. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Background: Mild Cognitive Impairment (MCI) and dementia differ in important ways yet share a future of increased prevalence. Separating these conditions from each other, and from Subjective Cognitive Impairment (SCI), is important for clinical prognoses and treatment, socio-legal interventions, and family adjustments. With costly clinical investigations and an aging population comes a need for more cost-efficient differential diagnostics.Methods: Using supervised machine learning, we investigated nine variables extracted from simple reaction time (SRT) data with respect to their single and conjoined ability to discriminate both MCI/dementia, and SCI/MCI/dementia, compared to—and together with—established psychometric tests. One-hundred-twenty elderly patients (age range = 65–95 years) were recruited when referred to full neuropsychological assessment at a specialized memory clinic in urban Sweden. A freely available SRT task served as index test and was administered and scored objectively by a computer before diagnosis of SCI (n = 17), MCI (n = 53), or dementia (n = 50). As reference standard, diagnosis was decided through the multidisciplinary memory clinic investigation. Bonferroni-Holm corrected P-values for constructed models against the null model are provided.Results: Algorithmic feature selection for the two final multivariable models was performed through recursive feature elimination with 3 × 10-fold cross-validation resampling. For both models, this procedure selected seven predictors of which five were SRT variables. When used as input for a soft-margin, radial-basis support vector machine model tuned via Bayesian optimization, the leave-one-out cross-validated accuracy of the final model for MCI/dementia classification was good (Accuracy = 0.806 [0.716, INS [0].877], P < 0.001) and the final model for SCI/MCI/dementia classification held some merit (Accuracy = 0.650 [0.558, 0.735], P < 0.001). These two models are implemented in a freely available application for research and educatory use.Conclusions: Simple reaction time variables hold some potential in conjunction with established psychometric tests for differentiating MCI/dementia, and SCI/MCI/dementia in these difficult-to-differentiate memory clinic patients. While external validation is needed, their implementation within diagnostic support systems is promising.
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| 7. |
- Johansson, Fredrik, et al.
(författare)
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Merkostnad för certifiering på gårdsnivå
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Lantbruksföretag har flera alternativa sätt att certifiera sin produktion. Förhoppningen hos lantbrukaren är att en certifiering ska medföra både ekonomiska mervärden och göra driften hållbar. Vid en certifiering, oavsett produktionsinriktning, förbinder sig lantbrukaren att följa de regelverk som tagits fram av berörd certifieringsorganisation. Att certifieringen medför ytterligare åtaganden som ska följas, utöver de regler som gäller för alla lantbrukare, innebär att en merkostnad för certifieringen uppstår. I denna rapport behandlas certifiering enligt IP Sigill för den konventionella produktionen och certifiering enligt EU:s gemensamma regler samt enligt KRAV:s regelverk för den ekologiska produktionen. För att erhålla merkostnaden har regelverken för de olika certifieringarna studerats och jämförts med de regler som gäller om lantbrukaren väljer att driva sin produktion utan certifiering. En större och en mindre typgård har studerats för respektive produktionsinriktning. De produktionsinriktningar som har studerats är spannmålsodling, mjölkproduktion samt nötköttsproduktion inklusive certifiering av naturbeteskött. Merkostnaden har beräknats per företag och per kilogram råvara för de olika typgårdarna. Merkostnaden som uppstår kan delas upp i tre delar: egen mertid, produktionsbegränsningar samt krav i form av pålagor. Certifieringskostnaden är genomgående högre för de mindre typgårdarna sett per kilogram producerad vara, för analyserade produktionsgrenar. Vid en certifiering av ekologisk produktion medför en certifiering enligt EU:s gemensamma regelverk en lägre merkostnad än KRAV-certifiering. Detta gäller oavsett produktionsinriktning och gårdsstorlek. Merbetalningen för sigillcertifierad vara är begränsad till naturbeteskött samt vissa spannmålsgrödor. Någon merbetalning utgår inte för sigillcertifierad mjölk. Kostnaden är inte försumbar på gårdsnivå. Typgården med 50 kor har enligt analysen dubbelt så hög merkostnad per kilo mjölk för certifieringen, jämfört med typgården med 200 kor. Rapporten visar på ett kostnadsintervall på 0,6–4,7 öre per kg spannmål som ger merbetalning. För mjölk ligger intervallet mellan 0,9–7,7 öre per kg och för nötkött mellan 0,27–3,84 kr per kilo kött som ger merbetalning.
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