Variance Reduction of Sequential Monte Carlo Approach for GNSS Phase Bias Estimation

Global navigation satellite systems (GNSS) are an important tool for positioning, navigation, and timing (PNT) services. The fast and high-precision GNSS data processing relies on reliable integer ambiguity fixing, whose performance depends on phase bias estimation. However, the mathematic model of GNSS phase bias estimation encounters the rank-deficiency problem, making bias estimation a difficult task. Combining the Monte-Carlo-based methods and GNSS data processing procedure can overcome the problem and provide fast-converging bias estimates. The variance reduction of the estimation algorithm has the potential to improve the accuracy of the estimates and is meaningful for precise and efficient PNT services. In this paper, firstly, we present the difficulty in phase bias estimation and introduce the sequential quasi-Monte Carlo (SQMC) method, then develop the SQMC-based GNSS phase bias estimation algorithm, and investigate the effects of the low-discrepancy sequence on variance reduction. Experiments with practical data show that the low-discrepancy sequence in the algorithm can significantly reduce the standard deviation of the estimates and shorten the convergence time of the filtering

Bridging and bonding social capital and their effects on internationalisation: an empirical study of international ‘take-off’ in Chinese SMEs

This paper is concerned with the role of social capital in effecting international take-off in Chinese SMEs. Social capital is posited as having different forms; a local bonding dimension and an international bridging dimension which spans structural holes between local networks and international opportunities. However, each of these forms is explored as having further constraining and enabling effects. This paper reports the results of a first phase investigation into 16 Chinese SMEs that have gone through the international take-off process. Interim findings suggest two stages in take-off, opportunity search and value proposition development. Initial findings report some previously under discussed constraining effects of international bridging social capital which include the constraint of non-exclusive international bridges, and the local peer pressure to continue to seek further international bridges, rather than focus on strengthening an initial bridge. Findings contribute to the strand of internationalisation literature positing the importance of network insidership in internationalisation and internationalisation as a by-product of entrepreneurial networking activities

Investigating Employee and Organizational Performance in a Cross-Border Acquisition : A Case of Withdrawal Behavior

Research Funding Research Development Fund (RDF-18-01-16) and Key Special Program (KSF-E-15) of Xi'an Jiaotong-Liverpool UniversityPeer reviewedPostprin

A transcription factor of the NAC family regulates nitrate-induced legume nodule senescence

17 Pags.- 7 Figs. © 2023 The AuthorsLegumes establish symbioses with rhizobia by forming nitrogen-fixing nodules. Nitrate is amajor environmental factor that affects symbiotic functioning. However, the molecularmechanism of nitrate-induced nodule senescence is poorly understood. Comparative transcriptomic analysis reveals an NAC-type transcription factor inLotus japo-nicus, LjNAC094, that acts as a positive regulator in nitrate-induced nodule senescence.Stable overexpression and mutant lines ofNAC094were constructed and used for phenotypiccharacterization. DNA-affinity purification sequencing was performed to identify NAC094targeting genes and results were confirmed by electrophoretic mobility shift and transactiva-tion assays. Overexpression ofNAC094induces premature nodule senescence. Knocking outNAC094partially relieves nitrate-induced degradation of leghemoglobins and abolishes nodule expres-sion of senescence-associated genes (SAGs) that contain a conserved binding motif forNAC094. Nitrate-triggered metabolic changes in wild-type nodules are largely affected innac094mutant nodules. Induction ofNAC094and its targetingSAGswas almost blocked inthe nitrate-insensitivenlp1,nlp4, andnlp1 nlp4mutants. We conclude that NAC094 functions downstream of NLP1 and NLP4 by regulating nitrate-induced expression ofSAGs. Our study fills in a key gap between nitrate and the execution ofnodule senescence, and provides a potential strategy to improve nitrogen fixation and stresstolerance of legumes.This work was supported by the National Natural Science Foundation of China (32000192, 31870220), the Foundation of Hubei Hongshan Laboratory (2022hszd014), Fundamental Research Funds for the Central Universities (2662020SKPY007), and MCIN/AEI/10.13039/501100011033 (grant PID2020-113985GB-I00). We also thank the BaiChuan fellowship of College of Life Science and Technology, Huazhong Agricultural University, for funding support.Peer reviewe

Heme catabolism mediated by heme oxygenase in uninfected interstitial cells enables efficient symbiotic nitrogen fixation in Lotus japonicus nodules

18 Pags.- 8 Figs. © 2023 The Authors. New Phytologist.Legume nodules produce large quantities of heme required for the synthesis of leghemoglobin (Lb) and other hemoproteins. Despite the crucial function of Lb in nitrogen fixation and the toxicity of free heme, the mechanisms of heme homeostasis remain elusive. Biochemical, cellular, and genetic approaches were used to study the role of heme oxygenases (HOs) in heme degradation in the model legume Lotus japonicus. Heme and biliverdin were quantified and localized, HOs were characterized, and knockout LORE1 and CRISPR/Cas9 mutants for LjHO1 were generated and phenotyped. We show that LjHO1, but not the LjHO2 isoform, is responsible for heme catabolism in nodules and identify biliverdin as the in vivo product of the enzyme in senescing green nodules. Spatiotemporal expression analysis revealed that LjHO1 expression and biliverdin production are restricted to the plastids of uninfected interstitial cells. The nodules of ho1 mutants showed decreased nitrogen fixation, and the development of brown, rather than green, nodules during senescence. Increased superoxide production was observed in ho1 nodules, underscoring the importance of LjHO1 in antioxidant defense. We conclude that LjHO1 plays an essential role in degradation of Lb heme, uncovering a novel function of nodule plastids and uninfected interstitial cells in nitrogen fixation.This work was supported by the Ministry of Science and Technology of the People’s Republic of China (2021YFA0910800), National Natural Science Foundation of China (31870220), the Foundation of Hubei Hongshan Laboratory (2022hszd014), HZAU-AGIS Cooperation Fund (SZYJY2022005), and MCIN/AEI/10.13039/ 501100011033 of Spain (grant PID2020-113985GB-I00).Peer reviewe

Single cell-type transcriptome profiling reveals genes that promote nitrogen fixation in the infected and uninfected cells of legume nodules

2 Pags.- 1 Fig. © 2022 The Authors. Plant Biotechnology Journal published by Society for Experimental Biology and The Association of Applied Biologists and John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use,distribution and reproduction in any medium, provided the original work is properly cited.Excessive application of nitrogen fertilizers has inevitably resultedin environmental problems. The symbiotic nitrogen fixation (SNF) that occurs in the root nodules of leguminous plants provides asustainable source of reduced nitrogen in agricultural ecosystems. More than 200 genes have been reported to regulate SNF, including rhizobial infection, nodule organogenesis and senescence (Royet al., 2020). Mature nodules consist mainly of twocell types: infected cells (IC) that contain nitrogen-fixing bac-teroids and uninfected cells (UC) that mediate active metabolismand nutrient transport. Although it is well known that SNFrequires functional specialization, the specific genes responsiblefor transcriptional regulation and carbon/nitrogen metabolismand transport in IC and UC remain largely unexplored.Single-cell transcriptomics has emerged as a powerful tech-nique for investigating spatiotemporal patterns of gene expression.This work was supported by the National Natural Science Foundation of China (31870220, 32000192), the China Post-doctoral Science Foundation (2020M680103), Fundamental Research Funds for the Central Universities 2662020SKPY007 and MCIN/AEI/10.13039/501100011033 (grant PID2020-113985GB-I00)Peer reviewe

The interplay between social capital and international opportunities: a processual study of international ‘take-off’ episodes in Chinese SMEs

The paper presents a processual analysis of international take-off episodes in Chinese SMEs. In considering the dynamics of pre-internationalization, the paper posits four temporally finer-grained, phases based on an actor’s orientation towards international opportunities. Based on a sample of twenty Chinese SMEs, the paper theorizes 12 temporally fine-grained take-off episodes, or which appear in practice as a series of tactical moves through which Chinese SMEs advance through the four phases in the longer pre-internationalisation of the process. By considering the multi-dimensional nature of social capital in international take-off, the findings contribute to a greater understanding of how forming international relationships work in the context of pre-internationalization in SMEs, also adding insights into the dynamics of internationalisation as an entrepreneurial and networked endeavour

Online-Schätzung der Interfrequenz-/Systemphasenbias in der präzisen Positionsbestimmung

Global Navigation Satellite Systems (GNSS) play an important role in precise positioning for geodesy and surveying engineering. The key to the real-time GNSS precise positioning is the instantaneous integer ambiguity resolution. However, some of the biases in carrier phase observations cannot be removed by differencing between either stations or satellites, so the integer nature of the double-differenced ambiguities is destroyed and thus the ambiguities cannot be fixed to integers. Two typical biases are the inter-frequency bias (IFB) in GLObal NAvigation Satellite System (GLONASS) data processing and the inter-system bias (ISB) in multi-GNSS integration. Hence, the main objective of this thesis is the investigation, estimation and correction of these biases in carrier phase observations to achieve better positioning accuracy, reliability and availability through the improvement of its ambiguity resolution. The estimated parameters of the carrier phase IFB and ISB are usually the IFB rate and the fractional ISB (F-ISB), respectively. Most of the current methods estimate IFB rate or F-ISB together with the float ambiguities and usually need observations of relatively long time due to their high correlation. Theoretically, the performance of the ambiguity resolution depends on the quality of the given IFB rate/F-ISB value if the observations are precisely modelled. In other words, the closer the given IFB rate/F-ISB value to the truth value is, the better the resolution will be. Therefore, the RATIO in the ambiguity fixing can be applied as the qualification factor of the IFB rate/F-ISB value. Based on this fact, a new methodology based on particle filter is developed to estimate these biases in both post-processing and real-time mode in this study. In the proposed method, the IFB/ISB is represented by its samples (i.e. particles) with the weights determined by the designed likelihood function of the related RATIO given the sample values, so that the true bias value can be estimated successfully by the particle filter approach. The integer nature of the ambiguities in the models with IFB/ISB parameters is well utilised in the ambiguity resolution with the given IFB rate/F-ISB values. Thus, the new method can significantly reduce the convergence time and increase the reliability of the estimation without a priori values. Besides, when more than one bias parameter is included in the model, the multi-dimensional particle filter approach is developed to estimate more than one bias parameter simultaneously in GNSS precise positioning. In this case, the aforementioned benefits of the method are obviously enlarged. In the GLONASS data processing with a nonzero IFB rate, the method can estimate the IFB rate from observations of a few epochs. With the estimated IFB rate, the GLONASS fixed solutions are as accurate as the GPS fixed solutions in the experiments with short baselines. In addition, the bias in the estimated IFB rate when the state noise is set to a very small value or even zero is significant, but this bias can be removed by utilising the regularized particle filter (RPF) and the precision of the estimated IFB rate is continuously improved by new observations. An approach for adapting the number of particles in the estimation of the IFB rate is also proposed to reduce the calculation burden by relating the number of particles to the standard deviation of the weighted particles. In the estimation of the F-ISB in multi-GNSS integration, the new method based on particle filter largely reduces the convergence time and improves the reliability of F-ISB estimation when satellites from each system are not sufficient for independent positioning. Due to the periodic characteristics of ISB, the F-ISB particles can be separated into different groups leading to the divergence of the filtering. This problem is solved successfully by introducing the cluster analysis method which can detect the groups automatically so that they can be shifted together into one group in the filtering. The estimation of the phase IFB rate with the new method enables the usage of GLONASS in real-time kinematic positioning even when the IFB between receivers is large. The estimation of the phase F-ISB with the new method allows the precise positioning to be carried out with fewer satellites from each system than the number of satellites required by the current methods. Therefore, the IFB rate/F-ISB estimation significantly extends the application of real-time kinematic GNSS positioning. It also proves that the developed new method is capable of estimating biases quickly and accurately, which initiates a new way of bias estimation in GNSS precise positioning.Global Navigation Satellite Systems (GNSS) spielen eine wichtige Rolle bei der präzisen Positionierung für Geodäsie und Vermessungstechnik. Der Schlüssel für die präzise GNSS Echtzeitpositionierung ist die sofortige Auflösung der ganzzahligen Mehrdeutigkeit. Jedoch können einige der Bias in Trägerphasenbeobachtungen nicht durch Differenzbildung entweder zwischen Stationen oder Satelliten entfernt werden, so dass die ganzzahlige Natur der Mehrdeutigkeit durch doppelte Differenzbildung zerstört werden kann und somit können die Mehrdeutigkeit nicht als ganze Zahlen festgelegt werden. Zwei typische Biasarten sind die Inter-Frequency-Bias (IFB) in der Prozessierung von GLObal NAvigation Satellite System (GLONASS) Daten und die Inter-System-Bias (ISB) für Integration von mehreren GNSS. Daher ist das Hauptziel dieser Arbeit die Untersuchung, Schätzung und Korrektur dieser Bias in Trägerphasenbeobachtungen um bessere Positionierungsgenauigkeit, Zuverlässigkeit und Verfügbarkeit durch die Verbesserung der Auflösung von Mehrdeutigkeiten zu erreichen. Die geschätzten Parameter der IFB und ISB von Trägerphasen sind normalerweise die IFB Rate und der bruchzahlige Teil von ISB (F-ISB). Die meisten der aktuellen Methoden schätzen die IFB Rate oder F-ISB zusammen mit den nicht-ganzzahligen Mehrdeutigkeiten und brauchen aufgrund ihrer hohen Korrelation meistens relativ lange Beobachtungszeitintervalle. Theoretisch hängt die Leistung der Auflösung von Mehrdeutigkeiten von der Qualität des gegebenen Wertes von IFB Rate/F-ISB ab, wenn die Beobachtungen präzise modelliert werden. Mit anderen Worten, je näher der gegebene Wert von IFB Rate/F-ISB an dem wahren Wert liegt, desto besser ist die Auflösung. Daher kann RATIO in der Festlegung von Mehrdeutigkeiten als Qualifizierungsfaktor des Wertes von IFB-Rate/F-ISB angewendet werden. Aufgrund dieser Tatsache wurde in dieser Arbeit eine neue auf dem Partikelfilter basierende Methode entwickelt, um diese Bias sowohl in Post-Prozessierung als auch im Echtzeit-Modus zu schätzen. Bei dem vorgeschlagenen Verfahren wird die IFB/ISB durch deren Stichproben (d.h. Partikel) repräsentiert, mit den Gewichten die durch die konstruierte Wahrscheinlichkeitsverteilung (Likelihood-Funktion) von dem dazugehörigen RATIO für die gegebenen Stichprobenwerte so festgelegt werden, dass der wahre Biaswert mit dem Partikelfilterverfahren erfolgreich geschätzt werden kann. Die ganzzahlige Natur der Mehrdeutigkeiten in den Modellen mit IFB/ISB-Parametern wird in der Auflösung von Mehrdeutigkeit mit dem gegebenen Wert von IFB Rate/F-ISB vorteilhaft verwendet. Somit kann das neue Verfahren die Konvergenzzeit erheblich verringern und die Zuverlässigkeit der Schätzung ohne a priori Werte erhöhen. Außerdem, für den Fall wenn mehr als ein Bias-Parameter in dem Modell enthalten ist, wurde der mehrdimensionale Partikelfilter-Ansatz entwickelt, um mehr als einen Bias-Parameter gleichzeitig innerhalb der präzisen GNSS-Positionierung abzuschätzen. In diesem Fall sind die oben genannten Vorteile des Verfahrens noch offensichtlicher. In der GLONASS-Datenverarbeitung mit einer Nicht-Null IFB Rate kann das Verfahren die IFB Rate aus den Beobachtungen von einigen wenigen Epochen abschätzen. Mit der geschätzten IFB Rate sind in den Experimenten mit kurzen Basislinien die GLONASS Lösungen mit festgesetzten Mehrdeutigkeiten so genau wie die dazugehörigen GPS Lösungen. Zusätzlich ist das Bias in der geschätzten IFB Rate, wenn das Zustandsrauschen als ein sehr kleiner Wert oder sogar Null festgelegt wird, signifikant, kann aber mit dem regularisierten Partikelfilter (RPF) entfernt werden und die Präzision des geschätzten IFB wird mit neuen Beobachtungen kontinuierlich verbessert. Ein Ansatz für die Anpassung der Anzahl der Teilchen in der Schätzung der IFB Rate wurde auch vorgeschlagen, um die Berechnungslast zu reduzieren, indem die Anzahl der Partikel mit der Standardabweichung der gewichteten Teilchen in Beziehung gesetzt wurde. In der Schätzung der F-ISB in der Integration von mehreren GNSS reduziert das neue auf dem Partikelfilter basierende Verfahren weitgehend die Konvergenzzeit und verbessert die Zuverlässigkeit der F-ISB Schätzung, wenn Satelliten von jedem einzelnen System zu wenige für eine unabhängige Positionierung sind. Aufgrund der periodischen Eigenschaften von ISB, können die F-ISB Partikel in verschiedene Gruppen getrennt werden, was zur Divergenz der Filterung führen kann. Dieses Problem wird durch die Einführung der Cluster-Analyse, die die Gruppen automatisch erkennen kann, so dass sie in der Filterung in eine Gruppe zusammengeführt werden können, erfolgreich gelöst. Die Schätzung der IFB Rate der Phase mit dem neuen Verfahren ermöglicht die Nutzung von GLONASS in Echtzeit für kinematische Positionierung, auch wenn das Bias zwischen den Empfängern groß ist. Die Schätzung des F-ISB der Phase mit dem neuen Verfahren erlaubt, dass die präzise Positionierung mit weniger Satelliten von jedem System durchgeführt wird, als erforderlich für gängige Methoden. Daher erweitert die Schätzung der IFB Rate/F-ISB bedeutend die Anwendung von kinematischen GNSS Echtzeitpositionierung. Es beweist auch, dass die entwickelte neue Methode Bias schnell und genau schätzen kann, und eine neue Art der Biasschätzung in der präzisen GNSS Positionierung einführt

Exploring the limits of mindfulness during the COVID-19 pandemic:qualitative evidence from African context

Abstract Purpose: This paper is one of the first studies to examine specificities, including limits of mindfulness at work in an African organisational context, whilst dealing with the ongoing COVID-19 pandemic. It specifically addresses the role of organisational and managerial support systems in restoring employee wellbeing, social connectedness and attachment to their organisations, in order to overcome the exclusion caused by the ongoing pandemic. Design/methodology/approach: The study uses a qualitative research methodology that includes interviews as the main data source. The sample comprises of 20 entrepreneurs (organisational leaders) from Ghana and Nigeria. Findings: The authors found that COVID-19-induced worries restricted the practice of mindfulness, and this was prevalent at the peak of the pandemic, particularly due to very tough economic conditions caused by reduction in salaries, and intensified by pre-existing general economic and social insecurities, and institutional voids in Africa. This aspect further resulted in lack of engagement and lack of commitment, which affected overall team performance and restricted employees’ mindfulness at work. Hence, quietness by employees even though can be linked to mindfulness was linked to larger psychological stress that they were facing. The authors also found leaders/manager’s emotional intelligence, social skills and organisational support systems to be helpful in such circumstances. However, their effectiveness varied among the cases. Originality/value: This paper is one of the first studies to establish a link between the COVID-19 pandemic and mindfulness limitations. Moreover, it is a pioneering study specifically highlighting the damaging impact of COVID-19-induced concerns on leader–member exchange (LMX) and team–member exchange (TMX) relationships, particularly in the African context. It further brings in a unique discussion on the mitigating mechanisms of such COVID-19-induced concerns in organisations and highlights the roles of manager’s/leader’s emotional intelligence, social skills and supportive intervention patterns. Finally, the authors offer an in-depth assessment of the effectiveness of organisational interventions and supportive relational systems in restoring social connectedness following a social exclusion caused by COVID-19-induced worries

Expression and information hierarchical authorization of BDS reference station observation data based on states and residual

BDS reference stations typically store and transmit raw observations directly and make them available to users, which can lead to two disadvantages:first, there is no hierarchical authorization mechanism for users. Any user can solve the precise spatial, time and atmospheric datum information of the reference station through the original observation measurement, which poses a potential threat to the safety of the reference station, second, the strong correlation between the original observation measurement leads to a large amount of data, in BDS receiver observation appears network, uninterrupted, high sampling and multi-band trend, its observation data is a massive explosion, to the data storage and transmission have brought great pressure. Therefore, this paper proposes to use state and residual to express the raw observation data of BDS reference station. Compared with the common data services based on international protocols such as RINEX, Compact RINEX and RTCM, the advantage of this method is that it cannot only provide hierarchical authorization service of datum information for users, technically guarantee the security of data services, but also significantly reduce the amount of transmission data and user-side computation. At the same time, the new expression is equivalent to the original data and does not reduce the accuracy of the final calculation results. This method can be used to establish BDS observation data storage and transmission protocol with independent intellectual property rights, and provide technical support for satellite-based broadcasting services of high-precision data