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Objective: Altered joint function is a hallmark of osteoarthritis (OA). Imaging techniques for joint function are limited, but [18F]sodium fluoride (NaF) PET-MRI may assess the acute joint response to loading stresses. [18F]NaF PET-MRI was used to study the acute joint response to exercise in OA knees, and compare relationships between regions of increased uptake after loading and structural OA progression two years later.Methods: In this prospective study, 10 participants with knee OA (59 ± 8 years; 8 female) were scanned twice consecutively using a PET-MR system and performed a one-legged squat exercise between scans. Changes in tracer uptake measures in 9 bone regions were compared between knees that did and did not exercise with a mixed-effects model. Areas of focally large changes in uptake between scans (ROIfocal, ΔSUVmax > 3) were identified and the presence of structural MRI features was noted. Five participants returned two years later to assess structural change on MRI.Results: There was a significant increase in [18F]NaF uptake in OA exercised knees (SUV P < 0.001, KiP = 0.002, K1P < 0.001) that differed by bone region.Conclusion: There were regional differences in the acute bone metabolic response to exercise and areas of focally large changes in the metabolic bone response that might be representative of whole-joint dysfunction. [ABSTRACT FROM AUTHOR]

In the previously published articles "Features of strong excitation control of synchronous generators in a complex power system" (Élektricheskie Stantsii, 2019, No. 7) and "Improving power system stabilization in response to grid disturbances" (Électrichestvo, 2020, No. 5), the author experimentally showed that the method conventionally used in the Unified Energy System (UES) of Russia for stabilizing the operating modes of complex power systems under external disturbances is not always efficient. This stabilization method uses signals from automatic excitation regulators (AER) based on the deviation and voltage frequency derivative on the generator terminals. In oscillating transient modes, however, these signals differ significantly in phase from the deviation and rotation frequency derivative of the generators. Instead of damping the occurring oscillations, this process can amplify their amplitude and duration. The author proposed a method for stabilizing the operating modes of power systems by the signals of deviation difference between the rotation frequency of each generator and the voltage frequency on the busbars, as well as the derivative of mismatch between them. The conducted full-scale tests confirmed the efficiency of the proposed method. Following the publication of the above articles, the efficiency of the method was confirmed in a critical discussion presented in the Élektricheskie Stantsii journal. This article discusses the physical difference between the proposed and conventional methods for stabilizing the operating modes of power systems, and explains the efficiency of the proposed method under the operating conditions of complex power systems. Experimental oscillograms of transient processes that have not been published before are presented. [ABSTRACT FROM AUTHOR]

Objective: Synovitis is hypothesized to play a role in the development and growth of osteophytes. Our objectives were to use hybrid positron emission tomography-magnetic resonance imaging (PET-MRI) to (1) determine whether synovitis adjacent to peripheral bone subregions with increased metabolic activity is greater than adjacent to regions without increased metabolic activity and (2) assess the association between subregional bone metabolic activity and adjacent synovitis.Design: We recruited 11 participants (22 knees) with a diagnosis of OA in at least one knee. Simultaneous bilateral knee PET-MRI was performed. We quantified bone metabolic activity using the radiotracer [18F]sodium fluoride ([18F]NaF) with calculation of maximum standardized uptake values (SUVmax). Synovitis was quantified using dynamic contrast-enhanced MRI with calculation of Ktrans. Bone subregions were coded as osteophyte (OP), focal increased [18F]NaF uptake without osteophyte (FIU), or normal (no osteophyte or FIU). We used robust linear mixed effects models to assess differences in adjacent Ktrans between different subregion types and to assess association between Ktrans and adjacent SUVmax.Results: 94 OPs were detected (59 MOAKS grade 1, 30 grade 2, 5 grade 3), along with 28 FIU and 18 normal subregions. Ktrans was higher adjacent to FIU (adjusted mean [95% CI] = 0.06 [0.03,0.09]) and OPs (0.08 [0.05,0.11]) when compared to normal bone subregions (0.03 [0.00,0.09]). PET SUVmax was positively associated with adjacent Ktrans (β[95% CI] = 0.018 [0.008,0.027]).Conclusions: Synovitis is more intense adjacent to peripheral bone regions with increased metabolic activity than those without, although there is some overlap. Subregional bone metabolic activity is positively associated with intensity of adjacent synovitis. [ABSTRACT FROM AUTHOR]

Objective: Molecular information derived from dynamic [18F]sodium fluoride ([18F]NaF) PET imaging holds promise as a quantitative marker of bone metabolism. The objective of this work was to evaluate physiological mechanisms of [18F]NaF uptake in subchondral bone of individuals with and without knee osteoarthritis (OA).Methods: Eleven healthy volunteers and twenty OA subjects were included. Both knees of all subjects were scanned simultaneously using a 3T hybrid PET/MRI system. MRI MOAKS assessment was performed to score the presence and size of osteophytes, bone marrow lesions, and cartilage lesions. Subchondral bone kinetic parameters of bone perfusion (K1), tracer extraction fraction, and total tracer uptake into bone (Ki) were evaluated using the Hawkins 3-compartment model. Measures were compared between structurally normal-appearing bone regions and those with structural findings.Results: Mean and maximum SUV and kinetic parameters Ki, K1, and extraction fraction were significantly different between Healthy subjects and subjects with OA. Between-group differences in metabolic parameters were observed both in regions where the OA group had degenerative changes as well as in regions that appeared structurally normal.Conclusions: Results suggest that bone metabolism is altered in OA subjects, including bone regions with and without structural findings, compared to healthy subjects. Kinetic parameters of [18F]NaF uptake in subchondral bone show potential to quantitatively evaluate the role of bone physiology in OA initiation and progression. Objective measures of bone metabolism from [18F]NaF PET imaging can complement assessments of structural abnormalities observed on MRI. [ABSTRACT FROM AUTHOR]

Epidemic malaria cases and satellite-based vegetation health (VH) indices were investigated to be used as predictors of malaria vector activities in Bangladesh. The VH indices were derived from radiances, measured by the Advanced Very High Resolution Radiometer (AVHRR) on National Oceanic and Atmospheric Administration (NOAA) afternoon polar orbiting satellites. Two indices characterizing moisture and thermal conditions were investigated using correlation and regression analysis applied to the number of malaria cases recorded in the entire Bangladesh region and three administrative divisions (Chittagong, Sylhet and Dhaka) during 1992-2001. It is shown that during the cooler months (November to March), when mosquitoes are less active, the correlation between number of malaria cases and two investigated indices was near zero. From April, when the mosquito activity season starts, the correlation increased, reaching a maximum value of 0.5-0.8 by the middle of the high season (June to July), reducing thereafter to zero by the beginning of the cool season in November. Following these results, regressional equations for the number of malaria cases as a function of VH indices were built and tested independently. They showed that, in the main malaria administrative division (Chittagong) and the entire Bangladesh region, the regressional equations can be used for early prediction of malaria development. [ABSTRACT FROM AUTHOR]

In this paper the possibility of predicting corn yield by the use of real time acquired satellite data from the Advance Very High Resolution Radiometer (AVHRR) sensor and Partial Least Squares (PLS) method was investigated. To test the methodology in practice, 23 years (1982-2004) of AVHRR data together with official corn yield statistics of Haskell County, Kansas, USA, were used for model development and validation. The AVHRR reflectances in the visible and thermal bands, extracted from the National Oceanic and Atmospheric Administration (NOAA)/NESDIS archive, were transformed into Vegetation Health (VH) Indices (Vegetation Condition Index (VCI) and Temperature Condition Index (TCI)). The PLS method was used to construct a model relating corn yield anomaly with VH indices. Independent model verification showed that the error of corn yield prediction in Haskell County, Kansas, USA, was less than 6%. For several reasons this approach could have excellent potential as a commercial application: satellite data are inexpensive, easily available and yield estimates can be known two to three months before harvest has been completed. [ABSTRACT FROM AUTHOR]

This paper shows the application of remote sensing data for estimating winter wheat yield in Kansas. An algorithm uses the Vegetation Health (VH) Indices (Vegetation Condition Index (VCI) and Temperature Condition Index (TCI)) computed for each week over a period of 23 years (1982-2004) from Advance Very High Resolution Radiometer (AVHRR) data. The weekly indices were correlated with the end of the season winter wheat (WW) yield. A strong correlation was found between winter wheat yield and VCI (characterizing moisture conditions) during the critical period of winter wheat development and productivity that occurs during April to May (weeks 16 to 23). Following the results of correlation analysis, the principal components regression (PCR) method was used to construct a model to predict yield as a function of the VCI computed for this period. The simulated results were compared with official agricultural statistics showing that the errors of the estimates of winter wheat yield are less than 8%. Remote sensing, therefore, is a valuable tool for estimating crop yields well in advance of harvest, and at a low cost. [ABSTRACT FROM AUTHOR]

Abstract: Advanced Very High Resolution Radiometer (AVHRR) -based vegetation indices are widely accepted as good indicators for providing vegetation properties and associated changes for large scale geographic regions. Also, their capability to indicate moisture conditions makes them an important data source for monitoring climate variations and droughts. The objective of this study was to test the AVHRR-vegetation conditions indices data set as indicators of the weather variability through the seasonal and interannual responses of the vegetation and the production of crops. Time-series of AVHRR vegetation condition indices during 1981–2003 were used to generate the seasonal and interannual vegetation curves for departments (administrative unites) of the Cordoba province in Argentina. Yield series of corn by departments were analyzed against AVHRR derived indices and corn yield predicting models were developed. Vegetation condition curves were able to differentiate vegetation responses associated with normal/above normal and below normal precipitation during the growing season. Corn yield models based on the vegetation condition indices explained up to 80% of the yield variation of corn, according to departments. Results from the analysis showed that the variability of the indices serves as good proxy for identifying environmental sources of variations mainly climate, and thus to provide insights for further analysis to understand the potential of the regional climate for crop production and the effects of the climate variability on vegetation and on corn yield. [Copyright &y& Elsevier]

Early drought detection and impact assessment on the amount of pasture biomass are important in Mongolia, whose economy strongly depends on livestock production. The country's large area and a lack of information on grass availability due to the sparseness of biomass-observing and/or meteorological stations make it difficult to optimize nomadic livestock output in the Mongolian dry climate. The application of a new satellite-based method for drought detection and for assessment of wild biomass in Mongolia was investigated. Measurements of biomass at an experimental station in a semi-dry steppe ecosystem during 1985-1997 were compared with the Advanced Very High Resolution Radiometer (AVHRR)-based vegetation health (VH) indices. The results showed the indices can be used as proxies for biomass production estimation (biomass anomaly, BA) applying the following equation BA=43.201+0.881 VHI ( R 2 =0.658). [ABSTRACT FROM AUTHOR]

The states of Alabama, Florida and Georgia dispute the apportioning of water from rivers that originate in Georgia and flow through the other two states. Florida and Alabama often claim that Georgia uses more than its fair share of water. In order to address such a dispute, an estimation of the total amount of water used for irrigation by different crops is required. Current estimates of irrigated areas are subject to errors because they are based entirely on survey questionnaires. In this paper, the potential of Advanced Very High Resolution Radiometer (AVHRR) on-board the National Oceanic Space Administration (NOAA) satellites is examined for estimating irrigated area. Two indices, a widely used Normalized Difference Vegetation Index (NDVI) and a newer Vegetation Health Index (VHI), were regressed against irrigated area for 1986, 1989, 1992, 1995 and 2000 for selected regions in Georgia (Baker and Mitchell counties, and Seminole and Decatur counties). The average VHI during a period from the third week of February to the end of September was better related to irrigated area than the corresponding NDVI; R 2 was above 0.80 as opposed to 0.49. It is concluded that the VHI, derived from three-channel AVHRR data, can be used to estimate irrigated area. By multiplying irrigated area with the application rate, the volume of irrigation used in a state can be determined, which can contribute to the solution of the water dispute. [ABSTRACT FROM AUTHOR]

The Advanced Very High Resolution Radiometer (AVHRR) onboard the National Oceanic and Atmospheric Administration (NOAA) series of satellites has been used for mapping vegetation cover and classification employing the Normalized Difference Vegetation Index (NDVI). Recently, this technique has been improved by converting NDVI with radiation measured in one of the thermal channels and converting brightness temperature into the Vegetation Condition Index (VCI) and Temperature Condition Index (TCI). These indices are being used for estimation of vegetation health and monitoring drought. The present study shows the application of vegetation and temperature condition indices for drought monitoring in India. [ABSTRACT FROM AUTHOR]

This study explores the potential application of NOAA/AVHRR based satellite indices to estimate the soybean yield for Brazil. NOAA AVHRR GVI (Global Vegetation Index) weekly maximum composite NDVI (Normalized Difference Vegetation Index) data sets with a resolution of 16 km for the period of 1985 to 1998 (except 1995 due to missing data) provided by NOAA/NESDIS were used in this study. Nine soybean yield models, including eight principal production states and the country, were constructed using observed yield data and NDVI and/or TCI (Temperature Condition Index) data from 1985 to 1995. The data period of 1996 to 1998 was used to evaluate the model performance. The crop yield is generally affected by technological improvements through time and by the annual weather fluctuation. The contribution of technological improvements was approximated by trend term and weather-related fluctuations of yield around the trend were estimated through AVHRR-based indices. The results showed that four states had significant technological trend contribution with slopes ranging from 0.49 to 0.86 and R2 ranging from 0.22 to 0.62. In most of the models, yield variation around the trend was sensitive to TCI (Temperature Condition Index), during the period of the grain filling stage (end of January for northern states and mid February for the southern states). For most of the models, the determination coefficient (R[sup 2]) was higher than 0.6 and the root mean square error (RMSE) was lower than 10%. The results of model validation showed that the absolute errors were lower than 10% in 21 out of 27 cases tested. It is concluded that the satellite indices are useful for crop production monitoring. In the Brazilian soybean production region, where the summer crop season coincides with the rainy season, the temperature-based index is more informative about possible fluctuation of soybean yield and production in Brazil. It is suggested that a combination use of satellite and in situ data may likely improve the yield estimate. [ABSTRACT FROM AUTHOR]

The application of satellite-derived indices for assessment of crop growth conditions in semi-arid countries is well known. In this paper the authors describe the application of these indices outside semi-arid areas, in Poland, a country with a sufficient water supply. Two indices, Vegetation Condition Index (VCI) and Temperature Condition Index (TCI), were computed for the whole country for each week for a period of 14 years. These indices were correlated with cereal yield anomalies for each of 49 regions of Poland. Two critical periods in crop development were found: early spring (14-16 weeks of the year) and early summer (22-25 weeks) when the state of crop development determines the magnitude of yield. The indices computed for these two periods were used in a yield prediction model. The results were compared with data provided by the Central Statistical Office. The average error of cereal yield estimates for 49 regions was lower than 4%. [ABSTRACT FROM AUTHOR]

The 1997-98 El Nino is one of the strongest events of the last 50 years. Its absolute magnitude, areal extent, and rapid development have raised a serious concern among decision makers because of its possible impact on global ecosystems. In this study, El Nino consequences for land ecosystem were examined using the new AVHRR-based three-channel index (VT), widely used for monitoring drought around the world. The VT index was used to identify a typical pattern of vegetation conditions in southern Africa during the recent El Nino years. Features and trends of the 1997-98 El Nino including its intensity, extent, and impact on vegetation are also discussed. [ABSTRACT FROM AUTHOR]