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Search Results: 1 - 10 of 403269 matches for " S. Liu "
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Using Multiple Imputation for Vote Choice Data: A Comparison across Multiple Imputation Tools  [PDF]
Frank C. S. Liu
Open Journal of Political Science (OJPS) , 2014, DOI: 10.4236/ojps.2014.42006

One commonly acknowledged challenge in polls or surveys is item non-response, i.e., a significant proportion of respondents conceal their preferences about particular questions. This paper applies the multiple imputation (MI) method to reconstruct the distribution of vote choice in the sample. Vote choice is one of most important dependent variables in political science studies. This paper shows how the MI procedure in general facilitates the work of reconstructing the distribution of a targeted variable. Particularly, it shows how MI can be applied to point-estimation in descriptive statistics. The three packages of R, AmeliaII, MICE, and mi, are employed for this project. The findings, based on a Taiwan Election and Democratization Study (TEDS) samples collected after the 2012 presidential election (N = 1826) suggest the following: First, there is little adjustment done given the MI methods; Second, the three tools based on two algorithms lead to similar results, while Amelia II and MICE perform better. Although the results are not striking, the implications of these findings are worthy of discussion.

Do Credit Rating Agencies Sacrifice Timeliness by Pursuing Rating Stability? Evidence from Equity Market Reactions to CreditWatch Events  [PDF]
Jenny Gu, Jeffrey S. Jones, Pu Liu
Theoretical Economics Letters (TEL) , 2014, DOI: 10.4236/tel.2014.45042

In this paper we examine how well CreditWatch is used by credit rating agencies to balance two conflicting goals: rating timeliness and rating stability. Examining equity market reactions around CreditWatch events in 2002-2005, we find evidence that while CreditWatch has improved rating timeliness, its intended purpose has not been completely achieved. Equity prices start to change days before companies are listed on CreditWatch and abnormal equity returns of firms prior to being listed on CreditWatch are effective predictors of the ultimate change in ratings. The findings in the study suggest that in the pursuit of rating stability, rating agencies may have sacrificed rating timeliness.

Evaluation of High-Speed Track Quality Using Dynamic Simulation of Vehicle-Track Interaction  [PDF]
D. Liu, B. Lechner, S. Freudenstein
Journal of Transportation Technologies (JTTs) , 2016, DOI: 10.4236/jtts.2016.61002
Abstract: Track quality is a determinant factor for evaluating the overall performance of vehicle track interaction with respect to safety, ride quality and maintenance. Important parameters specifying the general quality of the track include track geometry (undamped) and track stiffness (damped), which can be evaluated by measurements taken along with track sections. A new co-simulation model based on Finite Element Method (FEM) and Multi Body Simulation (MBS) is built for the detailed description of track quality and its contribution to vehicle track interaction without simplifying the track structure as interconnected single elements. The simulation models and tools have been validated with the help of measured track geometry, track stiffness and dynamic wheel rail forces along the track sections of high speed lines. A comparative study between high speed lines using conventional ballasted track and ballastless track showed a significantly better quality in ballastless track sections. The dynamic forces which were determined by simulations and verified by measurements along the ballastless track section were comparatively less than the specified limits by German regulations for ballastless track design. Lower levels of dynamic forces can be utilized for optimization of track design and installation procedures with respect to lower initial costs.
Analysis of Road Embankment Slope Stability  [PDF]
Chunyuan Liu, Ulysse Sèho F. Hounsa
Open Journal of Civil Engineering (OJCE) , 2018, DOI: 10.4236/ojce.2018.82010
Abstract: The stability of earthworks (cuttings, embankments, dikes) and natural slopes is a?problem that is of concern to geotechnicians, both practitioners and researchers. The disorders generated by breaking the slopes are usually spectacular, often destructive and sometimes murderers. Many methods of calculating stability have been proposed. These are differentiated?by the assumptions accepted by their authors (methods of calculation in equilibrium limit, methods of calculation at break, deformation calculation methods) and the ease of their implementation (calculations using charts, automatic calculations using software), but they all agree to define an overall factor of safety according to which the stability?of?the studied slope is considered to be insured or compromised, or by safety factor spartial effects on the one hand, applied stresses and, on the other hand, the mechanical properties soil. Various embankment strengthening techniques have been developed. They are differentiated by the process of their realization, their cost and their durability. The main objective of this study is to present the problems of both natural and artificial slope stability on construction projects. In this regard, special emphasis?is given to the sensitivity of the calculation model input parameters (soil, load),?which should contribute to raising awareness about this issue, as a prerequisite to make the right decisions and optimal technical solutions in this area.
Stability of nonlinear systems under constantly acting perturbations
Xinzhi Liu,S. Sivasundaram
International Journal of Mathematics and Mathematical Sciences , 1995, DOI: 10.1155/s0161171295000330
Abstract: In this paper, we investigate total stability, attractivity and uniform stability in terms of two measures of nonlinear differential systems under constant perturbations. Some sufficient conditions are obtained using Lyapunov's direct method. An example is also worked out.
Study of singular radius and surface boundary constraints in refractive beam shaper design
C. Liu,S. Zhang
Physics , 2008, DOI: 10.1364/OE.16.006675
Abstract: This paper presents analysis of important issues associated with the design of refractive laser beam shaping systems. The concept of singular radius is introduced along with solutions to minimize its adverse effect on shaper performance. In addition, the surface boundary constraint is discussed in detail. This study provides useful guidelines to circumvent possible design errors that would degrade the shaper quality or add undesired complication to the system.
Signature of a Pairing Transition in the Heat Capacity of Finite Nuclei
S. Liu,Y. Alhassid
Physics , 2000, DOI: 10.1103/PhysRevLett.87.022501
Abstract: The heat capacity of iron isotopes is calculated within the interacting shell model using the complete $(pf+0g_{9/2})$-shell. We identify a signature of the pairing transition in the heat capacity that is correlated with the suppression of the number of spin-zero neutron pairs as the temperature increases. Our results are obtained by a novel method that significantly reduces the statistical errors in the heat capacity calculated by the shell model Monte Carlo approach. The Monte Carlo results are compared with finite-temperature Fermi gas and BCS calculations.
Impurity effect as a probe of the paring symmetry in BiS_{2} based superconductors
S. L. Liu
Physics , 2012, DOI: 10.1007/s10948-013-2237-x
Abstract: The impurity effects are studied for the BiS_{2}- layered superconductors based on a two orbital model with the Bogoliubov-de-Gennes technique. The superconducting critical temperature (T_{c}) as a function of the mpurity concentration is calculated. Significant reduction of T_{c} is found for spin singlet nearest-neighboring paring d-wave state and the spin triplet next-nearest-neighboring (NNN) paring p-wave state, while no depression of T_{c} for isotropic s-wave state. The single impurity effects for various paring states are also explored. The impurity resonance peak in the local density of states spectrum is found only for the d-wave state. For the spin triplet NNN paring p-wave state, two in-gap peaks occur in the case of positive impurity potential; and a single in-gap peak is found for the negative impurity potential, which shifts towards to lower energy with decreasing the potential strength. These results can be used to detect the paring symmetry of the BiS_{2}- based superconductors.
Self-organization behavior in a constrained minority game
C. Liu,S. S. Liaw
Physics , 2006,
Abstract: In the standard minority game, every agent switches to his best strategy in hand at each time step. If only a small number of agents are allowed to switch their strategies at each time step, the population variance of the system plunges. The variance reaches a low value and remains steady for a period of time. Then without any sign it starts to rise abruptly to a high value and then decreases smoothly to the previous low value again. The process of an abrupt rise followed by a gentle decrease repeats again and again but without obvious characteristic length as time goes on. The phenomenon is similar to the collapse of a sand pile with sands being added continuously from the top. We define the scale of collapse of the population variance by the difference of the variance before and after an abrupt rise. We then find that the logarithmic plot of the frequency versus scale of the collapses follows a power law.
Accurate determination of thermal neutron fluence for fission track dating
S. S. Liu,S. H. Sun
Chinese Science Bulletin , 1998, DOI: 10.1007/BF02891506
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