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Amitsur's property for skew polynomials of derivation type
Hong, Chan Yong,Kim, Nam Kyun,Lee, Yang,Nielsen, Pace P. Rocky Mountain Mathematics Consortium 2017 The Rocky Mountain journal of mathematics Vol.47 No.7
<P>We investigate when radicals a satisfy Amitsur's property on skew polynomials of derivation type, namely, F(R[x; delta) = (F(R[x; delta) boolean AND R)[x; delta]. In particular, we give a new argument that the Brown-McCoy radical has this property. We also give a new characterization of the prime radical of R[x; delta].</P>
A direct XFEM formulation for modeling of cohesive crack growth in concrete
P. N. Poulsen,L. O. Nielsen,J. L. Asferg 한국계산역학회 2007 Computers and Concrete, An International Journal Vol.4 No.2
Applying a direct formulation for the enrichment of the displacement field an extended finite element (XFEM) scheme for modeling of cohesive crack growth is developed. Only elements cut by the crack is enriched and the scheme fits within the framework of standard FEM code. The scheme is implemented for the 3-node constant strain triangle (CST) and the 6-node linear strain triangle (LST). Modeling of standard concrete test cases such as fracture in the notched three point beam bending test (TPBT) and in the four point shear beam test (FPSB) illustrates the performance. The XFEM results show good agreement with results obtained by applying standard interface elements in FEM and with experimental results. In conjunction with criteria for crack growth local versus nonlocal computation of the crack growth direction is discussed.
Radicals in skew polynomial and skew Laurent polynomial rings
Hong, C.Y.,Kim, N.K.,Nielsen, P.P. North-Holland Pub. Co 2014 Journal of pure and applied algebra Vol.218 No.10
We provide a general procedure for characterizing radical-like functions of skew polynomial and skew Laurent polynomial rings under grading hypotheses. In particular, we are able to completely characterize the Wedderburn and Levitzki radicals of skew polynomial and skew Laurent polynomial rings in terms of ideals in the coefficient ring. We also introduce the T-nilpotent radideals, and perform similar characterizations.
Beam Dynamics in a Long-pulse Linear Induction Accelerator
Carl Ekdahl,E. O. Abeyta,P. Aragon,R. Archuleta,G. Cook,D. Dalmas,K. Esquibel,R. Gallegos,R. Garnett,J. Harrison,J. Johnson,E. Jacquez,B. Trent McCuistian,N. Montoya,S. Nath,K. Nielsen,D. Oro,C. Rose 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.61
The second axis of the Dual Axis Radiography of Hydrodynamic Testing (DARHT) facility produces up to four radiographs within an interval of 1.6 microseconds. It accomplishes this by slicing four micro-pulses out of a long 1.8-kA, 16.5-MeV electron beam pulse and focusing them onto a bremsstrahlung converter target. The long beam pulse is created by a dispenser cathode diode and accelerated by the unique DARHT Axis-II linear induction accelerator (LIA). Beam motion in the accelerator would be a problem for radiography. High frequency motion, such as from beam breakup instability, would blur the individual spots. Low frequency motion, such as produced by pulsed power variation, would produce spot to spot differences. In this article, we describe these sources of beam motion, and the measures we have taken to minimize it.
The minimal prime spectrum of rings with annihilator conditions
Hong, C.Y.,Kim, N.K.,Lee, Y.,Nielsen, P.P. North-Holland Pub. Co 2009 Journal of pure and applied algebra Vol.213 No.7
In this paper, we study rings with the annihilator condition (a.c.) and rings whose space of minimal prime ideals, Min(R), is compact. We begin by extending the definition of (a.c.) to noncommutative rings. We then show that several extensions over semiprime rings have (a.c.). Moreover, we investigate the annihilator condition under the formation of matrix rings and classical quotient rings. Finally, we prove that if R is a reduced ring then: the classical right quotient ring Q(R) is strongly regular if and only if R has a Property (A) and Min(R) is compact, if and only if R has (a.c.) and Min(R) is compact. This extends several results about commutative rings with (a.c.) to the noncommutative setting.
On σ-nil ideals of bounded index of σ-nilpotence
Hong, C.Y.,Kim, N.K.,Lee, Y.,Nielsen, P.P. Academic Press 2012 Journal of algebra Vol.371 No.-
We investigate properties of σ-nil subsets with bounded index of σ-nilpotence, beginning with a classification of many of the possible types of nilpotence available in the σ-skewed case. In the process we introduce a σ-analog of the bounded nilradical of a ring. In many situations we completely describe the bounded nilradical for skew polynomial rings in terms of the σ-bounded nilradical in the coefficient ring. We also construct an example demonstrating that the bounded nilradical for skew polynomial rings is more complicated than one might initially guess. Further extensions are explored when one assumes additional restrictions on σ.