scholarly journals A statistical analysis of the nulling pulsar population

2021 ◽  
Vol 502 (4) ◽  
pp. 4669-4679
Author(s):  
Sofia Z Sheikh ◽  
Mariah G MacDonald
Keyword(s):  
Statistical Analysis ◽  
Pulse Width ◽  
Local Minimum ◽  
Broad Band ◽  
Selection Effects ◽  
Clustering Methods ◽  
Pulsar Emission ◽  
Spin Period ◽  
Null State ◽  
Linear Correlations

ABSTRACT Approximately 8 per cent of the ∼2800 known pulsars exhibit ‘nulling,’ a temporary broad-band cessation of normal pulsar emission. Nulling behaviour can be coarsely quantified by the nulling fraction, which describes the percentage of time a given pulsar will be found in a null state. In this paper, we perform the most thorough statistical analysis thus far of the properties of 141 known nulling pulsars. We find weak, non-linear correlations between nulling fraction and pulse width, as well as nulling fraction and spin period which could be attributed to selection effects. We also further investigate a recently hypothesized gap at 40 per cent nulling fraction. While a local minimum does exist in the distribution, we cannot confirm a consistent and unique break in the distribution when we investigate with univariate and multivariate clustering methods, nor can we prove the existence of two statistically distinct populations about this minimum. Using the same methods, we find that nulling pulsars are a statistically different population from normal, radio, non-nulling pulsars, which has never been quantitatively verified. In addition, we summarize the findings of the prior nulling pulsar statistics literature, which are notoriously contradictory. This study, in context, furthers the idea that nulling fraction alone does not contain enough information to describe the behaviour of a nulling pulsar and that other parameters such as null lengths and null randomness, in addition to a better understanding of selection effects, are required to fully understand this phenomenon.

scholarly journals A Determination of Pulsar Emission Geometry from Polarization Observations

1992 ◽  
Vol 128 ◽  
pp. 400-403
Author(s):  
Xinji Wu ◽  
Wen Xu
Keyword(s):  
Inclination Angle ◽  
Pulse Width ◽  
Rotation Axis ◽  
Geometrical Model ◽  
Polarization Angle ◽  
Radiation Beam ◽  
Pulsar Emission ◽  
Magnetic Inclination ◽  
Large Pulse

AbstractOne of the important problems in pulsar studies is to determine the magnetic inclination angle α, the intrinsic width of the radiation beam (2ρ) and the angle (α + β) between the observer's direction and the rotation axis. In this paper we solve this problem for individual pulses by using the observed pulse width (2Δ𝜙), the swing of polarization angle (2Δψ), and its central gradient (dψ/d𝜙)max.From the polar cap model we establish three basic geometrical relations, a complete set of equations from which explicit solutions can be obtained using the observed data. This is the first time that the orientation of pulsar emission is solved analytically solely on the basis of a geometrical model. However, the results are shown to be sensitively connected to the polarization-angle swing (2Δψ), which is not well measured for most pulsars. So the number of pulsars to which our method can be applied is limited. The importance of the measurement of Δψ is seen from our method. To ensure the credibility of our results, we have discussed the conditions to be satisfied by all reliable pulsar measurements. Our method is shown to be more favorable for pulsars with large pulse width 2Δ𝜙, large central gradient (dψ/d𝜙)max and large magnetic inclination angle α. Out of 120 pulsars (from Lyne and Manchester 1988), 40 are solvable, and 7 are believed to be reliable. We discuss our method for the determination of pulsar geometry in comparison with other methods.

scholarly journals THEORETICAL ANALYSIS OF PICTURE FUZZY CLUSTERING: CONVERGENCE AND PROPERTY

2018 ◽  
Vol 34 (1) ◽  
pp. 17-32 ◽  
Author(s):  
Pham Thi Minh Phuong ◽  
Pham Huy Thong ◽  
Le Hoang Son
Keyword(s):  
Pattern Recognition ◽  
Theoretical Analysis ◽  
Fuzzy Clustering ◽  
Computational Intelligence ◽  
Local Minimum ◽  
Clustering Algorithm ◽  
Clustering Methods ◽  
Mathematical Properties ◽  
Fuzzy Clustering Algorithm ◽  
Similarities And Differences

Recently, picture fuzzy clustering (FC-PFS) has been introduced as a new computational intelligence tool for various problems in knowledge discovery and pattern recognition. However, an important question that was lacked in the related researches is examination of mathematical properties behind the picture fuzzy clustering algorithm such as the convergence, the boundary or the convergence rate, etc. In this paper, we will prove that FC-PFS converges to at least one local minimum. The similarities and differences between this algorithm and other clustering methods are compared. Analysis on the loss function is also considered.

Comparison of multivariate pattering methods in group/cluster identification regarding the science of educational research: Implicative Statistical Analysis vs. L’ Analysee Factorielle des Correspondances

2019 ◽  
Vol 6 (1) ◽  
pp. 238-245
Author(s):  
Sofia D Anastasiadou
Keyword(s):  
Statistical Analysis ◽  
Principal Components Analysis ◽  
Educational Research ◽  
Principal Components ◽  
Quantitative Research ◽  
Self Control ◽  
Clustering Methods ◽  
Technological Education ◽  
Cluster Identification ◽  
Components Analysis

Nowadays, there is a substantial improvement and utilisation of pattering methods in the science of educational research, a comparison of multivariate methods in group/cluster identification in the scientific domain of quantitative research has not been carried out. This study analyses two different statistical techniques: i.e., the principal components analysis (PCA) and the implicative statistical analysis (ASI). A survey was carried out using a structured questionnaire for a sample of 135 nurses which studied in the School of Pedagogical and Technological Education in order to be qualified in respect The study focuses on the presentation of the two main types of clustering methods, της ASI and L’ Analysee Factorielle des Correspondances (AFC). AFC’s results made it evident that Emotionality, Self-control, Sociability, General items of EI constructs are shaped attitudes and reveal the latent dimension of respondents psychological attributes related to EI conceptual constructs. Keywords: L’ Analysee Factorielle des Correspondances, principal components analysis, implicative statistical analysis, research.

Pooling samples within microarray studies: a comparative analysis of rat liver transcription response to prototypical toxicants

2005 ◽  
Vol 22 (3) ◽  
pp. 346-355 ◽  
Author(s):  
Robert A. Jolly ◽  
Keith M. Goldstein ◽  
Tao Wei ◽  
Hong Gao ◽  
Peining Chen ◽  
...  
Keyword(s):  
Statistical Analysis ◽  
Time Course ◽  
Molecular Mechanisms ◽  
Pooled Analysis ◽  
Transcript Expression ◽  
Individual Animal ◽  
Clustering Methods ◽  
Individual Analysis ◽  
Transcript Profiles ◽  
The Individual

Combining or pooling individual samples when carrying out transcript profiling using microarrays is a fairly common means to reduce both the cost and complexity of data analysis. However, pooling does not allow for statistical comparison of changes between samples and can result in a loss of information. Because a rigorous comparison of the identified expression changes from the two approaches has not been reported, we compared the results for hepatic transcript profiles from pooled vs. individual samples. Hepatic transcript profiles from a single-dose time-course rat study in response to the prototypical toxicants clofibrate, diethylhexylphthalate, and valproic acid were evaluated. Approximately 50% more transcript expression changes were observed in the individual (statistical) analysis compared with the pooled analysis. While the majority of these changes were less than twofold in magnitude (∼80%), a substantial number were greater than twofold (∼20%). Transcript changes unique to the individual analysis were confirmed by quantitative RT-PCR, while all the changes unique to the pooled analysis did not confirm. The individual analysis identified more hits per biological pathway than the pooled approach. Many of the transcripts identified by the individual analysis were novel findings and may contribute to a better understanding of molecular mechanisms of these compounds. Furthermore, having individual animal data provided the opportunity to correlate changes in transcript expression to phenotypes (i.e., histology) observed in toxicology studies. The two approaches were similar when clustering methods were used despite the large difference in the absolute number of transcripts changed. In summary, pooling reduced resource requirements substantially, but the individual approach enabled statistical analysis that identified more gene expression changes to evaluate mechanisms of toxicity. An individual animal approach becomes more valuable when the overall expression response is subtle and/or when associating expression data to variable phenotypic responses.

The Hidden Hand of Economic Coercion

2003 ◽  
Vol 57 (3) ◽  
pp. 643-659 ◽  
Author(s):  
Daniel W. Drezner
Keyword(s):  
Statistical Analysis ◽  
International Relations ◽  
Success Rate ◽  
Recent Literature ◽  
Economic Sanctions ◽  
Selection Effects ◽  
Economic Coercion ◽  
Theoretic Argument ◽  
Game Theoretic ◽  
The Cost

Why do policymakers consistently employ economic sanctions even though scholars consider them an ineffective tool of statecraft? Game-theoretic models of economic coercion suggest the success rate may be understated because of selection effects. When the targeted country prefers conceding to incurring the cost of sanctions, it has an incentive to acquiesce before the imposition of sanctions. The bulk of successful coercion episodes should therefore end with sanctions threatened but not imposed. This contradicts the recent literature on sanctions, which assumes that sanctions rarely, if ever, work at generating significant concessions from the targeted country and are imposed for domestic or symbolic political reasons. If the game-theoretic argument is correct, the crucial cases to study are those in which coercion is threatened but not implemented. A statistical analysis of data on sanctions in pursuit of economic or regulatory goals strongly supports the gametheoretic argument. These results suggest that the significance of economic coercion has been undervalued in the study of statecraft and international relations more generally.

The Secret Success of Nonproliferation Sanctions

2014 ◽  
Vol 68 (4) ◽  
pp. 913-944 ◽  
Author(s):  
Nicholas L. Miller
Keyword(s):  
United States ◽  
Statistical Analysis ◽  
Qualitative Analysis ◽  
Nuclear Weapons ◽  
Selection Effect ◽  
Original Data ◽  
The United States ◽  
Selection Effects ◽  
Data Set ◽  
South Korean

AbstractBuilding on the rationalist literature on sanctions, this article argues that economic and political sanctions are a successful tool of nonproliferation policy, but that selection effects have rendered this success largely hidden. Since the late 1970s—when the United States made the threat of sanctions credible through congressional legislation and began regularly employing sanctions against proliferating states—sanctions have been ineffective in halting ongoing nuclear weapons programs, but they have succeeded in deterring states from starting nuclear weapons programs in the first place and have thus contributed to a decline in the rate of nuclear pursuit. The logic of the argument is simple: rational leaders assess the risk of sanctions before initiating a nuclear weapons program, which produces a selection effect whereby states highly vulnerable to sanctions are deterred from starting nuclear weapons programs in the first place, so long as the threat is credible. Vulnerability is a function of a state's level of economic and security dependence on the United States—states with greater dependence have more to lose from US sanctions and are more likely to be sensitive to US-sponsored norms. The end result of this selection effect is that since the late 1970s, only insulated, inward-looking regimes have pursued nuclear weapons and become the target of imposed sanctions, thus rendering the observed success rate of nonproliferation sanctions low. I find support for the argument based on statistical analysis of a global sample of countries from 1950 to 2000, an original data set of US nonproliferation sanctions episodes, and qualitative analysis of the South Korean and Taiwanese nuclear weapons programs.

Modeling and Statistical Analysis of DPPH Scavenging Activity of Phenolics

2007 ◽  
Vol 72 (11) ◽  
pp. 1461-1471 ◽  
Author(s):  
Zhivko A. Velkov ◽  
Mikhail K. Kolev ◽  
Alia V. Tadjer
Keyword(s):  
Antioxidant Activity ◽  
Statistical Analysis ◽  
Living Cells ◽  
Basis Set ◽  
Scavenging Activity ◽  
B3lyp Level ◽  
Cellular Environment ◽  
Dpph Scavenging Activity ◽  
Dpph Scavenging ◽  
Linear Correlations

Investigations addressing correlation between antioxidant activity and theoretical descriptors are plentiful in the literature. This task is quite ambitious, bearing in mind the rather complicated interactions in living cells. In this study we have tried to simplify the problem by looking for direct correlations between calculated characteristics and scavenging activity, neglecting the specificity of cellular environment. To address the problem of antioxidant activity, a set of 20 phenolic compounds and their phenoxyl radicals were investigated at the unrestricted B3LYP level of theory using the 6-31+G(d,p) basis set. Three important descriptors of the considered compounds were related to the results of the DPPH scavenging activity. Significant linear correlations were obtained in several cases.

scholarly journals Polarization sounding of the pulsar magnetosphere

2012 ◽  
Vol 8 (S291) ◽  
pp. 530-532 ◽  
Author(s):  
O. M. Ulyanov ◽  
A. I. Shevtsova ◽  
A. A. Seredkina
Keyword(s):  
Broad Band ◽  
Probe Signal ◽  
Pulsar Magnetosphere ◽  
Free Electrons ◽  
Pulsar Emission ◽  
Pulsar Radio ◽  
Decameter Wavelength ◽  
Propagation Medium ◽  
Pulsar Radio Emission ◽  
Stratified Model

AbstractThe possibility of a polarization sounding of the pulsar magnetosphere is examined, using intrinsic pulsar emission as a probe signal, for modern radio telescopes operating in the meter and decameter wavelength range. Different models of the pulsar magnetosphere at altitudes higher than a radius of critical polarization are used. The propagation medium besides magnetosphere is described by the stratified model, in which each layer has its own density of free electrons and vector of magnetic induction, as well as the spatial and temporal fluctuation scales of these parameters.The frequency dependence of the polarization parameters of the pulsar radio emission, obtained in the broad band for a selected pulse phase, will enable a sounding deep into the pulsar magnetosphere.

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