26,992 research outputs found
Yule-Walker Equations for singular AR systems
No full textIn dieser Arbeit behandeln wir Yule-Walker Gleichungen bei singulären AR Systemen. Im Gegensatz zum in der Literatur üblichen Fall der regulären AR Systeme besteht der Fehlerprozess νt aus linear abhängigen Komponenten. Durch diese Abhängigkeit ist die Toeplitz-Kovarianzmatrix Γp möglicherweise singulär und die Yule-Walker Gleichungen sind nicht eindeutig lösbar.Im ersten Kapitel betrachten wir generalisierte dynamische Faktormodelle und beschreiben Umstände, unter denen singuläre AR Systeme auftreten können.Im zweiten Kapitel geht es um die Yule-Walker Gleichungen im singulären Fall. Für eine Lösung der Yule-Walker Gleichungen suchen wir einen stationären Prozess, der diese Differennzengleichung erfüllt. Ein derartiger Prozess besteht aus einer regulären und einer singulären Komponente. Wir können zeigen, dass die partikuläre Lösung der Differenzengleichung, die reguläre Komponente, ein Moving Average Prozess ist, der für alle Lösungen der Yule-Walker Gleichungen eindeutig ist, während die homogene Lösung, die singuläre Komponente, ein harmonischer Prozess ist.Weiters beschreiben wir die Lösungsmenge aller stationären AR(p) Prozesse, die die vorgegebenen Kovarianzdaten erfüllen. Darüber hinaus betrachten wir die Stabilität der Lösungen der Yule-Walker Gleichungen.Wir geben eine spezielle Lösung an, die Minimumnormlösung, die unter allen Lösungen der Yule-Walker Gleichungen diejenige mit den meisten stabilen Nullstellen ist.Im dritten Kapitel wenden wir uns dem Schätzen zu. Zuerst geben wir eine Prozedur an, die im Falle, dass Populationskovarianzdaten vorliegen, ein AR System und einen Prozess liefert, sodass die vorgegebenen Kovarianzdaten realisiert werden.Bei echten Stichprobendaten gelingt es uns auch, einen Prozess anzugeben, der die Kovarianzdaten realisiert, jedoch finden wir kein einheitliches AR System für reguläre und singuläre Komponente
Interview of Richard Walker
No full textRobinson interviews Walker on his experiences in the mission field in Germany. The interview was conducted in Searcy, AR
"I don’t really like tedious, monotonous work": working-class young women, service sector employment and social mobility in contemporary Russia
No full textThis article contributes a global perspective to the emerging literature on girlhood in western contexts by examining the changing shape of transitions to adulthood amongst working-class young women in St. Petersburg, Russia. As in many western countries, new forms of service sector employment and an increasingly accessible higher education system appear to offer young women new prospects for social mobility. In contrast to the increasingly impoverished and denigrated traditional pathways into work, the young women in the study derive significant value from these new opportunities, constructing narratives of self-actualisation and approximating notions of respectable femininity. Nevertheless, actual social mobility is elusive, as familiar patterns of classed and gendered stratification limit their prospects. Despite its specificity, the case thus further illustrates the limited nature of the transformations available to young women through the new forms of education and work characteristic of global neoliberal contexts
A recursive algorithm for solving the spatial Yule-Walker equations of causal spatial AR models
No full textA recursive algorithm is proposed to solve the spatial Yule-Walker equations for causal spatial AR models.Spatial AR process Yule-Walker equations Recursive algorithm Order determination
Solutions of Yule-Walker Equations for Singular AR Processes
No full textA study is presented on solutions of the Yule-Walker equations for singular AR processes that are stationary outputs of a given AR system. If the Yule-Walker equations admit more than one solution and the order of the AR system is no less than two, the solution set includes solutions which define unstable AR systems. The solution set also includes one solution, the minimal norm solution, which defines an AR system whose characteristic polynomial has either only stable zeros (implying that only one stationary output exists for this system and it is linearly regular) or has stable zeros as well as zeros of unit modulus, (implying that stationary solutions of this system are a sum of a linearly regular process and a linearly singular process). The numbers of stable and unit circle zeros of the characteristic polynomial of the defined AR system can be characterized in terms of the ranks of certain matrices, and the characteristic polynomial of the AR system defined by the minimal norm solution has the least number of unit circle zeros and the most number of stable zeros over all possible solutions
Tumor growth characteristics of the Walker 256 AR tumor, a regressive variant of the rat Walker 256 A tumor
No full textThe present study aimed at characterizing the subcutaneous development of the Walker 256 (W256) AR tumor, a regressive variant of the rat W256 A tumor. Wistar rats were injected subcutaneously with 4x10(6) W256 A or W256 AR tumor cells. The development of tumors was evaluated daily by percutaneous measurements. None of the W256 A tumors (n=20) regressed, but 62% of the W256 AR tumor-bearing rats (n=21) underwent complete tumor regression within 35 days. Continuous growth of AR tumors was characterized by an increase of the tumor growth rate from day 12, which reached values above 1.0 g/day, and were significantly higher (pO objetivo neste estudo foi caracterizar o desenvolvimento subcutâneo do tumor de Walker 256 (W256) AR, uma variante regressiva do tumor de W256 A de rato. Ratos Wistar foram injetados com 4x10(6) células tumorais de W256 A ou W256 AR. O desenvolvimento tumoral foi avaliado diariamente. Nenhum dos tumores W256 A (n=20) regrediu, mas 62% dos ratos com tumor W256 AR apresentaram regressão completa dos tumores em até 35 dias. O crescimento contínuo dos tumores AR foi caracterizado pelo aumento da taxa de crescimento tumoral a partir do dia 12, alcançando valores maiores que 1,0g/dia, que foram significativamente superiores (p<0,05) aos valores de taxa de crescimento dos tumores regressivos AR. A imunossupressão por irradiação precedendo a injeção das células tumorais AR eliminou completamente a regressão tumoral e favoreceu disseminação metastática severa. Este estudo caracterizou o desenvolvimento do tumor de W256 AR em condições específicas, documentando a regressão espontânea deste tumor após a injeção subcutânea de altas doses de células tumorais em ratos Wistar. A avaliação diária da taxa de crescimento tumoral permite discriminar precocemente os tumores com crescimento continuo daqueles que são regressivos. A taxa de crescimento tumoral é um parâmetro útil para a avaliação dos animais experimentais, particularmente no período que precede a regressão dos tumores
A Case of Marden-Walker Syndrome With Dandy-Walker Malformation
No full textA 5-month-old girl with Marden-Walker syndrome is presented. This is a rare autosomal recessive syndrome. So far, approximately 20 cases have been described in the literature. The patient was hospitalized because of difficulty in feeding and slow spontaneous movements. Her parents were first cousins. She was diagnosed with clinical findings of growth and motor retardation, typical facial appearance, congenital heart disease, arachnodactyly, joint contractures, and a Dandy-Walker malformation on magnetic resonance imaging
Ittijahat Abi Dhu'ayb Al-Hudhali fi Qasidatihi Ar-Ritsa’
No full textThis article aims to know Ittijahat of Abu Dhu’ayb Al-Hudhali in his poem of Ritsa’. Ittijahat in this study is a description of the poet's tendency to divide Ar-Ritsa', namely Nadb and Ta'ziyah. Ar-Ritsa 'is one of the various forms of Arabic poetry. To analyze the discussion problem, the author uses descriptive analysis method, because this method is very appropriate to find out the picture and state of a thing by describing it in as much detail as possible based on the facts found in the data in question. The results obtained are: In the beginning of the poem, he tends to mourn (Nadb) their five children. He describes in it that he does not stop crying and has trouble sleeping until he becomes weak emaciated due to the intensity of the grief, pain and worries that dominated in his pysche. As for the middle of the poem to the end, the poet turns to the consolation (Ta’ziyah) of his children’s death, as he reflects on the reality of life and death, the poet declares that death is inevitable for every human being that he must accept it and let it go, which the poet portrayed in the exciting narrative style. The story is divided into three stories: the zebra, the bull of the beast, and the two knights.</jats:p
Cytokine Gene Expression In Walker 256: A Comparison Of Variants A (aggressive) And Ar (regressive).
No full textTwo variants of this Walker 256 tumor have been previously reported as Walker 256 A and variant AR. The variant A has more aggressive property than variant AR and can induce systemic effects such as anorexia, sodium and water retention, followed by weight loss and death. The mechanisms involved in enhancing tumor regression and progression in this model are still incompletely understood. In the present study, serum and spleen mononuclear cells and tumor cells from animals inoculated with variants A and AR, were isolated to investigate the TGF-beta, IL-12, IFN-gamma and TNF-alpha and relationship with anemia, weight of animals, weight of spleen, volume of tumor and osmotic fragility compared with controls inoculated with Ringer Lactate. Results demonstrate that the group inoculated with variant A, compared to variant AR, shows high levels of TGF-beta gene expression in both tumor tissue and spleen cells, no expression of IFN-gamma and a progressive and higher levels of IL-12 in tumor tissue without inflammatory infiltrate visualized by optical microscopy. These results suggest that the aggressively of variant A is relate to cytokine modulation, facilitating the growth and escape of tumor cells. Furthermore, IL-12 seems to be constitutively expressed in both tumor lineage A and AR.36123-3
Finite-Sample Bias Propagation in Autoregressive Estimation With the Yule–Walker Method
No full textThe Yule-Walker (YW) method for autoregressive (AR) estimation uses lagged-product (LP) autocorrelation estimates to compute an AR parametric spectral model. The LP estimates only have a small triangular bias in the estimated autocorrelation function and are asymptotically unbiased. However, using them in finite samples with the YW method for AR estimation can give a strong distortion in the weak parts of the power spectral density. The distortion is shown to be influential in an example without strong spectral peaks. The true biased AR model, which is computed by applying the triangular bias to the true autocorrelation function, has an infinite order. A new objective measure is introduced to determine the smallest sample size for which the unbiased asymptotic theory can be considered as a fair approximation.Multi-Scale PhysicsApplied Science
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