3,805 research outputs found
Bound on the multiplicity of almost complete intersections
Let be a polynomial ring over a field of characteristic zero and let be a graded ideal of height which is minimally generated by
homogeneous polynomials. If where has degree
and has height , then the multiplicity of is
bounded above by .Comment: 7 pages; to appear in Communications in Algebr
How to fill a narrow 27 KM long tube with a huge number of accelerator components?
As in large scale industrial projects, research projects, such as giant and complex particle accelerators, require intensive spatial integration studies using 3D CAD models, from the design to the installation phases. The future management of the LHC machine configuration during its operation will rely on the quality of the information, produced during these studies. This paper presents the powerful data-processing tools used in the project to ensure the spatial integration of several thousand different components in the limited space available. It describes how the documentation and information generated have been made available to a great number of users through a dedicated Web site and how installation nonconformities were handled
Lower Semi-frames, Frames, and Metric Operators
This paper deals with the possibility of transforming a weakly measurable function in a Hilbert space into a continuous frame by a metric operator, i.e., a strictly positive self-adjoint operator. A necessary condition is that the domain of the analysis operator associated with the function be dense. The study is done also with the help of the generalized frame operator associated with a weakly measurable function, which has better properties than the usual frame operator. A special attention is given to lower semi-frames: indeed, if the domain of the analysis operator is dense, then a lower semi-frame can be transformed into a Parseval frame with a (special) metric operator
Serre's "formule de masse" in prime degree
For a local field F with finite residue field of characteristic p, we
describe completely the structure of the filtered F_p[G]-module K^*/K^*p in
characteristic 0 and $K^+/\wp(K^+) in characteristic p, where K=F(\root{p-1}\of
F^*) and G=\Gal(K|F). As an application, we give an elementary proof of Serre's
mass formula in degree p. We also determine the compositum C of all degree p
separable extensions with solvable galoisian closure over an arbitrary base
field, and show that C is K(\root p\of K^*) or K(\wp^{-1}(K)) respectively, in
the case of the local field F. Our method allows us to compute the contribution
of each character G\to\F_p^* to the degree p mass formula, and, for any given
group \Gamma, the contribution of those degree p separable extensions of F
whose galoisian closure has group \Gamma.Comment: 36 pages; most of the new material has been moved to the new Section
High-order density-matrix perturbation theory
We present a simple formalism for the calculation of the derivatives of the
electronic density matrix at any order, within density functional theory. Our
approach, contrary to previous ones, is not based on the perturbative expansion
of the Kohn-Sham wavefunctions. It has the following advantages: (i) it allows
a simple derivation for the expression for the high order derivatives of the
density matrix; (ii) in extended insulators, the treatment of
uniform-electric-field perturbations and of the polarization derivatives is
straightforward.Comment: 4 page
Design of a low band gap oxide ferroelectric: BiTiO
A strategy for obtaining low band gap oxide ferroelectrics based on charge
imbalance is described and illustrated by first principles studies of the
hypothetical compound BiTiO, which is an alternate stacking of
the ferroelectric BiTiO. We find that this compound is
ferroelectric, similar to BiTiO although with a reduced
polarization. Importantly, calculations of the electronic structure with the
recently developed functional of Tran and Blaha yield a much reduced band gap
of 1.83 eV for this material compared to BiTiO. Therefore,
BiTiO is predicted to be a low band gap ferroelectric material
Geographical distribution of e-cadherin germline mutations in the context of diffuse gastric cancer: A systematic review
Hereditary diffuse gastric cancer (HDGC) is a complex and multifactorial inherited cancer predisposition syndrome caused by CDH1 germline mutations. Nevertheless, current CDH1 genetic screening recommendations disregard an unbalanced worldwide distribution of CDH1 variants, impacting testing efficacy and patient management. In this systematic review, we collected and analyzed all studies describing CDH1 variants in gastric cancer patients originating from both highand low-prevalence countries. Selected studies were categorized as family study, series study, and unknown study, according to the implementation of HDGC clinical criteria for genetic testing. Our results indicate that CDH1 mutations are more frequently identified in gastric cancer low-incidence countries, and in the family study group that encompasses cases fulfilling criteria. Considering the type of CDH1 alterations, we verified that the relative frequency of mutation types varies within study groups and geographical areas. In the series study, the missense variant frequency is higher in high-incidence areas of gastric cancer, when compared with non-missense mutations. However, application of variant scoring for putative relevance led to a strong reduction of CDH1 variants conferring increased risk of gastric cancer. Herein, we demonstrate that criteria for CDH1 genetic screening are critical for identification of individuals carrying mutations with clinical significance. Further, we propose that future guidelines for testing should consider GC incidence across geographical regions for improved surveillance programs and early diagnosis of disease.This manuscript was supported by the Italian Ministry of Health (Project Code GR‐2016‐ 02361655) and was partially supported by the Ricerca Corrente and 5 × 1000 funds, and financed by FEDER funds through the Operational Programme for Competitiveness Factors (COMPETE 2020), Programa Operacional de Competitividade e Internacionalização (POCI) and Programa Operacional Regional do Norte (Norte 2020); and by the Portuguese Foundation for Science and Technology (FCT projects PTDC/MED‐GEN/30356/2017 and PTDC/BIM‐ONC/0281/2014). We acknowledge the American Association of Patients with Hereditary Gastric Cancer “No Stomach for Cancer” for funding Figueiredo’s research
A First-Principles Approach to Insulators in Finite Electric Fields
We describe a method for computing the response of an insulator to a static,
homogeneous electric field. It consists of iteratively minimizing an electric
enthalpy functional expressed in terms of occupied Bloch-like states on a
uniform grid of k points. The functional has equivalent local minima below a
critical field E_c that depends inversely on the density of k points; the
disappearance of the minima at E_c signals the onset of Zener breakdown. We
illustrate the procedure by computing the piezoelectric and nonlinear
dielectric susceptibility tensors of III-V semiconductors.Comment: 4 pages, with 1 postscript figure embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/is_ef/index.htm
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