Application of space vector modulation in direct torque control of PMSM

The paper deals with an improvement of direct torque control method for permanent magnet synchronous motor drives. Electrical torque distortion of the machine under original direct torque control is relatively high and if proper measures are taken it can be substantially decreased. The proposed solution here is to combine direct torque control with the space vector modulation technique. Such approach can eliminate torque distortion while preserving the simplicity of the original method

ANGULAR CHLOROPHYLL INDICES ESTIMATES DERIVED FROM GROUND-BASED DIURNAL COURSE DATA AND MULTIANGULAR CHRIS-PROBA DATA: TWO CASE STUDIES

ABSTRACT At leaf and plant level chlorophyll indices have shown strong correlations with chlorophyll content and photosynthesis-related processes. However, at canopy level additional abiotic and biotic factors confound the fidelity of these indices. For instance, the Photochemical Reflectance Index (PRI) is known to be sensitive to viewing angles and canopy structure. In this paper we present case studies of two natural canopies at different scales where the influence of sun-target-sensor geometry and canopy structure is inter-compared for a range of chlorophyll indices. In the first case study, surface reflectance was measured in a montane grassland ecosystem located at the Bily Kriz experimental study site (Czech republic) using a stationary mounted AISA (Airborne Imaging Spectrometer for Applications) spectrometer. The experimental set-up resulted in a ground pixel resolution of ~2mm. The effects of changing sun angles on the indices were assessed through a diurnal sampling between 9:00 and 15:00 hrs (local time). Classes of shaded and illuminated photosynthetic (PV) and non-photosynthetic vegetation (NPV) were distinguished per image using a pixel wise classification. The relative contributions of confounding factors as well as the influence of the diurnal variability on performance of the selected chlorophyll indices were evaluated. In the second case study, surface reflectance was measured over an Alpine coniferous ecosystem in the Swiss National Park (Switzerland) using multiangular hyperspectral CHRIS-PROBA (Compact High Resolution Imaging Spectrometer onboard the Project for On-board Autonomy) satellite system with a ground pixel resolution of 17 m. The angular signature of PRI and the structure invariant pigment index (SIPI) was assessed using CHRIS data. Besides, we evaluated the influence of varying tree crown composition and varying viewing angles to the chlorophyll indices with a radiative transfer model FLIGHT. In both cases, the PRI and the green NDVI (gNDVI) responded extremely sensitively to the considered confounding factors at canopy level. The Transformed Chlorophyll Absorption in Reflectance Index normalized by the Optimized Soil-Adjusted Vegetation Index (TCARI/OSAVI), designed to be insensitive to background and LAI variations, responded more sensitively than the conventional NDVI. No certain sensitivity was found for SIPI. The pronounced sensitivity of e.g. PRI and gNDVI, on one hand, and the inconsistency between the chlorophyll indices, on the other hand, erodes the fidelity to use these spectral indices as an effective non-destructive chlorophyll detector

Wind characteristics recorded at the Czech Carbon Observation System (CzeCOS) site Rajec

The main aim of the study is to investigate general and temporal characteristics of wind speed and direction at Ecosystem station (ES) Rajec located in southern highlands of the Czech Republic which is part of Czech Carbon Observation System (CzeCOS) network. Four years (2013-16) of eddy co-variance data from mature monoculture spruce (Picea abies) forest was used to build the wind rose and analyze the wind characteristics. The prevailing wind directions at ES Rajec were South-East and North-West and general orography of region being a highland does not impact the wind flow. Seasonal variation in the wind was observed which was mainly due to general circulation. The paper also investigates the occurrence of calm wind conditions (u < 1 m s-1) which was 6% on an average for four years and the average of day-time and night-time calm conditions were observed as 8% and 4% respectively

Prospective study on non-invasive assessment of ICP in head injured patients: comparison of four methods

Elevation of intracranial pressure (ICP) may occur in many diseases and therefore the ability to measure it non-invasively would be useful. Flow velocity signals from Transcranial Doppler (TCD) have been used to estimate ICP, however the relative accuracy of these methods is unclear. This study aimed to compare 4 previously described TCD-based methods with directly measured ICP in a prospective cohort of head injured patients. Non-invasive ICP (nICP) was obtained using the following methods: I) a mathematical “black-box” model based on interaction between TCD and ABP (nICP_BB); II) based on diastolic FV (nICP_FVd); III) based on critical closing pressure (nICP_CrCP) and IV) based on TCD-derived pulsatility index (nICP_PI). In time domain, for recordings including spontaneous changes in ICP greater than 7 mmHg, nICP_PI showed the best correlation with measured ICP (R=0.61). Considering every TCD recording as an independent event, nICP_BB generally showed to be the best estimator of measured ICP (R=0.39, p0.05). nICP_PI was not related to measured ICP using any of the above statistical indicators. We also introduced a new estimator (nICP_Av) based on the average of 3 methods (nICP_BB, nICP_FVd and nICP_CrCP), which overall presented improved statistical indicators (R=0.47, p<0.05; 95% CI=9.17 mmHg; AUC= 0.73, p<0.05). nICP_PI appeared to reflect changes in ICP in time most accurately. nICP_BB was the best estimator for ICP ‘as a number’. nICP_Av demonstrated to improve the accuracy of measured ICP estimation.DC is supported by a Cambridge Commonwealth, European & International Trust Scholarship, University of Cambridge. JD is supported by a Woolf Fisher Trust Scholarship. XL is supported by a Gates Cambridge Scholarship. GVV is supported by an A. G. Leventis Foundation Scholarship, and a Charter Studentship from St Edmund’s College, Cambridge. SM and GF are supported by the Pan-American Health Organization. DC and MC are partially supported by NIHR Brain Injury Healthcare Technology Co-operative, Cambridge, UK.This is the author accepted manuscript. The final version is available from Mary Ann Liebert via http://dx.doi.org/10.1089/neu.2015.413

Morphological, biochemical and physiological traits of upper and lower canopy leaves of European beech tend to converge with increasing altitude

The present work has explored for the first time acclimation of upper versus lower canopy leaves along an altitudinal gradient. We tested the hypothesis that restrictive climatic conditions associated with high altitudes reduce within-canopy variations of leaf traits. The investigated beech (Fagus sylvatica L.) forest is located on the southern slope of the Hrubý Jeseník Mountains (Czech Republic). All measurements were taken on leaves from upper and lower parts of the canopy of mature trees (>85 years old) growing at low (400 m above sea level, a.s.l.), middle (720 m a.s.l.) and high (1100 m a.s.l.) altitudes. Compared with trees at higher altitudes, those growing at low altitudes had lower stomatal conductance, slightly lower CO2 assimilation rate (Amax) and leaf mass per area (LMA), and higher photochemical reflectance index, water-use efficiency and Rubisco content. Given similar stand densities at all altitudes, the different growth conditions result in a more open canopy and higher penetration of light into lower canopy with increasing altitude. Even though strong vertical gradients in light intensity occurred across the canopy at all altitudes, lower canopy leaves at high altitudes tended to acquire the same morphological, biochemical and physiological traits as did upper leaves. While elevation had no significant effect on nitrogen (N) and carbon (C) contents per unit leaf area, LMA, or total content of chlorophylls and epidermal flavonoids in upper leaves, these increased significantly in lower leaves at higher altitudes. The increases in N content of lower leaves were coupled with similar changes in Amax. Moreover, a high N content coincided with high Rubisco concentrations in lower but not in upper canopy leaves. Our results show that the limiting role of light in lower parts of the canopy is reduced at high altitudes. A great capacity of trees to adjust the entire canopy is thus demonstrated

Refining the prediction for OJ 287 next impact flare arrival epoch

The bright blazar OJ~287 routinely parades high brightness bremsstrahlung flares which are explained as being a result of a secondary supermassive black hole (SMBH) impacting the accretion disk of a primary SMBH in a binary system. We begin by showing that these flares occur at times predicted by a simple analytical formula, based on the Kepler equation, which explains flares since 1888. The next impact flare, namely the flare number 26, is rather peculiar as it breaks the typical pattern of two impact flares per 12 year cycle. This will be the third bremsstrahlung flare of the current cycle that follows the already observed 2015 and 2019 impact flares from OJ~287. Unfortunately, astrophysical considerations make it difficult to predict the exact arrival epoch of the flare number 26. In the second part of the paper, we describe our recent OJ~287 observations. They show that the pre-flare light curve of flare number 22, observed in 2005, exhibits similar activity as the pre-flare light curve in 2022, preceding the expected flare number 26 in our model. We argue that the pre-flare activity most likely arises in the primary jet whose activity is modulated by the transit of the secondary SMBH through the accretion disk of the primary. Observing the next impact flare of OJ~287 in October 2022 will substantiate the theory of disk impacts in binary black hole systems.Comment: 16 pages, 2 figure

Refining the 2022 OJ 287 impact flare arrival epoch

The bright blazar OJ~287 routinely parades high brightness bremsstrahlung flares, which are explained as being a result of a secondary supermassive black hole (SMBH) impacting the accretion disc of a more massive primary SMBH in a binary system. The accretion disc is not rigid but rather bends in a calculable way due to the tidal influence of the secondary. Below we refer to this phenomenon as a variable disc level. We begin by showing that these flares occur at times predicted by a simple analytical formula, based on general relativity inspired modified Kepler equation, which explains impact flares since 1888. The 2022 impact flare, namely flare number 26, is rather peculiar as it breaks the typical pattern of two impact flares per 12-year cycle. This is the third bremsstrahlung flare of the current cycle that follows the already observed 2015 and 2019 impact flares from OJ~287. It turns out that the arrival epoch of flare number 26 is sensitive to the level of primary SMBH's accretion disc relative to its mean level in our model. We incorporate these tidally induced changes in the level of the accretion disc to infer that the thermal flare should have occurred during July-August 2022, when it was not possible to observe it from the Earth. Thereafter, we explore possible observational evidence for certain pre-flare activity by employing spectral and polarimetric data from our campaigns in 2004/05 and 2021/22. We point out theoretical and observational implications of two observed mini-flares during January-February 2022.Comment: 29 pages, 6 figures, 1 table. arXiv admin note: text overlap with arXiv:2209.0836

On the need of an ultramassive black hole in OJ 287

The highly variable blazar OJ~287 is commonly discussed as an example of a binary black hole system. The 130 year long optical light curve is well explained by a model where the central body is a massive black hole of 18.35$\times$10$^9$ solar mass that supports a thin accretion disc. The secondary black hole of 0.15$\times$10$^9$ solar mass impacts the disc twice during its 12 year orbit, and causes observable flares. Recently, it has been argued that an accretion disc with a typical AGN accretion rate and above mentioned central body mass should be at least six magnitudes brighter than OJ~287's host galaxy and would therefore be observationally excluded. Based on the observations of OJ~287's radio jet, detailed in Marscher and Jorstad (2011), and up-to-date accretion disc models of Azadi et al. (2022), we show that the V-band magnitude of the accretion disc is unlikely to exceed the host galaxy brightness by more than one magnitude, and could well be fainter than the host. This is because accretion power is necessary to launch the jet as well as to create electromagnetic radiation, distributed across many wavelengths, and not concentrated especially on the optical V-band. Further, we note that the claimed V-band concentration of accretion power leads to serious problems while interpreting observations of other Active Galactic Nuclei. Therefore, we infer that the mass of the primary black hole and its accretion rate do not need to be smaller than what is determined in the standard model for OJ~287

Cortico-cerebellar functional connectivity and sequencing of movements in schizophrenia

<p>Abstract</p> <p>Background</p> <p>Abnormal execution of several movements in a sequence is a frequent finding in schizophrenia. Successful performance of such motor acts requires correct integration of cortico-subcortical processes, particularly those related to cerebellar functions. Abnormal connectivity between cortical and cerebellar regions with resulting cognitive dysmetria has been proposed as the core dysfunction behind many signs and symptoms of schizophrenia. The aim of the present study was to assess if these proposed abnormalities in connectivity are a unifying feature of schizophrenia, or, rather, reflect a specific symptom domain of a heterogeneous disease. We predicted that abnormal functional connectivity between the motor cortex and cerebellum would be linked with abnormal performance of movement sequencing.</p> <p>Methods</p> <p>We examined 24 schizophrenia patients (SCH) and 24 age-, sex-, and handedness-matched healthy controls (HC) using fMRI during a modified finger-tapping task. The ability to perform movement sequencing was tested using the Neurological Evaluation Scale (NES). The subjects were categorized into two groups, with (SQ+) and without (SQ-) movement sequencing abnormalities, according to the NES-SQ score. The effects of diagnosis and movement sequencing abnormalities on the functional connectivity parameters between the motor cortex and cerebellum (MC-CRBL) and the supplementary motor cortex and cerebellum (SMA-CRBL) activated during the motor task were analyzed.</p> <p>Results</p> <p>We found no effect of diagnosis on the functional connectivity measures. There was, however, a significant effect on the SQ group: SQ + patients showed a lower level of MC-CRBL connectivity than SQ- patients and healthy controls. Moreover, the level of MC-CRBL and SMA-CRBL negatively correlated with the magnitude of NES-SQ abnormalities, but with no other NES domain.</p> <p>Conclusions</p> <p>Abnormal cortico-cerebellar functional connectivity during the execution of a motor task is linked with movement sequencing abnormalities in schizophrenia, but not with the diagnosis of schizophrenia per se. It seems that specific patterns of inter-regional connectivity are linked with corresponding signs and symptoms of clinically heterogeneous conditions such as schizophrenia.</p