12,399 research outputs found
ADS modules
We study the class of ADS rings and modules introduced by Fuchs. We give some
connections between this notion and classical notions such as injectivity and
quasi-continuity. A simple ring R such that R is ADS as a right R-module must
be either right self-injective or indecomposable as a right R-module. Under
certain conditions we can construct a unique ADS hull up to isomorphism. We
introduce the concept of completely ADS modules and characterize completely ADS
semiperfect right modules as direct sum of semisimple and local modules.Comment: 7 page
The success factors for SMEs: Empirical evidence
This paper empirically analyzes the success factors for SMEs. Particularly, the paper intends to analyze if firm age, human resource costs, debt, venture capital funding, investment in innovation and productivity are success factors for SMEs. The effects were tested using static and dynamic panel data, on a data set of 200 Portuguese SMEs. The use of dynamic panel data is important in order to control for: endogeneity; time-invariant characteristics; possible collinearity between independent variables; effects from possible omission of independent variables; elimination of non-observable individual effects; and, the correct estimation of the relationship between the dependent variable in the previous and current periods. Our results reveal a positive impact on success of: human resource costs; investments in innovation; productivity; and, venture capital funding. We also confirm the negative impact of firm age and debt. Also, the results show evidence of persistence in success for the case of one of the success proxies used
Design Issues for Generalized Linear Models: A Review
Generalized linear models (GLMs) have been used quite effectively in the
modeling of a mean response under nonstandard conditions, where discrete as
well as continuous data distributions can be accommodated. The choice of design
for a GLM is a very important task in the development and building of an
adequate model. However, one major problem that handicaps the construction of a
GLM design is its dependence on the unknown parameters of the fitted model.
Several approaches have been proposed in the past 25 years to solve this
problem. These approaches, however, have provided only partial solutions that
apply in only some special cases, and the problem, in general, remains largely
unresolved. The purpose of this article is to focus attention on the
aforementioned dependence problem. We provide a survey of various existing
techniques dealing with the dependence problem. This survey includes
discussions concerning locally optimal designs, sequential designs, Bayesian
designs and the quantile dispersion graph approach for comparing designs for
GLMs.Comment: Published at http://dx.doi.org/10.1214/088342306000000105 in the
Statistical Science (http://www.imstat.org/sts/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Double-phase transition and giant positive magnetoresistance in the quasi-skutterudite GdIrSn
The magnetic, thermodynamic and electrical/thermal transport properties of
the caged-structure quasi-skutterudite GdIrSn are
re-investigated. The magnetization , specific heat and the
resistivity reveal a double-phase transition -- at 10~K
and at 8.8~K -- which was not observed in the previous report on
this compound. The antiferromagnetic transition is also visible in the thermal
transport data, thereby suggesting a close connection between the electronic
and lattice degrees of freedom in this Sn-based quasi-skutterudite. The
temperature dependence of is analyzed in terms of a power-law for
resistivity pertinent to Fermi liquid picture. Giant, positive
magnetoresistance (MR) 80 is observed in GdIrSn at
2~K with the application of 9~T. The giant MR and the double magnetic
transition can be attributed to the quasi-cages and layered antiferromagnetic
structure of GdIrSn vulnerable to structural distortions and/or
dipolar or spin-reorientation effects. The giant value of MR observed in this
class of 3:4:13 type alloys, especially in a Gd-compound, is the highlight of
this work.Comment: 20 pages single column, 7 figures, 1 table; Accepted to J. Appl.
Phys., 201
Bound states in two spatial dimensions in the non-central case
We derive a bound on the total number of negative energy bound states in a
potential in two spatial dimensions by using an adaptation of the Schwinger
method to derive the Birman-Schwinger bound in three dimensions. Specifically,
counting the number of bound states in a potential gV for g=1 is replaced by
counting the number of g_i's for which zero energy bound states exist, and then
the kernel of the integral equation for the zero-energy wave functon is
symmetrized. One of the keys of the solution is the replacement of an
inhomogeneous integral equation by a homogeneous integral equation.Comment: Work supported in part by the U.S. Department of Energy under Grant
No. DE-FG02-84-ER4015
Continuous Opinions and Discrete Actions in Opinion Dynamics Problems
A model where agents show discrete behavior regarding their actions, but have
continuous opinions that are updated by interacting with other agents is
presented. This new updating rule is applied to both the voter and Sznajd
models for interaction between neighbors and its consequences are discussed.
The appearance of extremists is naturally observed and it seems to be a
characteristic of this model.Comment: 10 pages, 4 figures, minor changes for improved clarit
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