Papers by Alejandro Eiras Varela
Journal of Immigrant and Minority Health, 2009
Journal of Cancer Education, 2010
Journal of Cancer Education, 2011
Although the profile of a patient navigator varies, navigators are often categorized as professio... more Although the profile of a patient navigator varies, navigators are often categorized as professional or paraprofessional (e.g. social workers, nurses, nurse practitioners, health educators) or lay health workers [3]. A lay health worker (LHW) has been defined as someone, paid or voluntary, who carries out functions related to health care delivery; is trained in the context of an intervention; and has no formal professional or paraprofessional
Arxiv preprint math/9911124, 1999
Let M be a von Neumann algebra, ϕ a faithful normal state and denote by Mϕ the fixed point algebr... more Let M be a von Neumann algebra, ϕ a faithful normal state and denote by Mϕ the fixed point algebra of the modular group of ϕ. Let UM and UMϕ be the unitary groups of M and Mϕ. In this paper we study the quotient Uϕ = UM /UMϕ ... Let M be a von Neumann algebra and ϕ a ...
Revista Clínica de Periodoncia, Implantología y Rehabilitación Oral, 2015
Desdentados totales; Eficiencia masticatoria; Nivel de satisfacción Resumen Se realizó un estudio... more Desdentados totales; Eficiencia masticatoria; Nivel de satisfacción Resumen Se realizó un estudio para medir y comparar el rendimiento masticatorio empleando el Test de Manly en 2 grupos de 18 individuos cada uno. El primer grupo estaba conformado por pacientes desdentados totales tratados en la Universidad Mayor en el año 2012 con prótesis totales removibles, y el segundo grupo, por pacientes con dentadura natural completa. Además, al grupo de pacientes rehabilitados con prótesis totales se le aplicó la encuesta GOHAI para conocer el nivel de satisfacción con el uso de sus prótesis. Los resultados muestran que el rendimiento masticatorio es muy superior en los individuos dentados naturales con respecto a los portadores de prótesis totales, y esta diferencia es estadísticamente significativa. Los pacientes portadores de prótesis totales señalan un bajo nivel de satisfacción con el uso de sus dentaduras completas, en especial durante la función masticatoria.
Revista Clínica de Periodoncia, Implantología y Rehabilitación Oral, 2015
Desdentados totales; Eficiencia masticatoria; Nivel de satisfacción Resumen Se realizó un estudio... more Desdentados totales; Eficiencia masticatoria; Nivel de satisfacción Resumen Se realizó un estudio para medir y comparar el rendimiento masticatorio empleando el Test de Manly en 2 grupos de 18 individuos cada uno. El primer grupo estaba conformado por pacientes desdentados totales tratados en la Universidad Mayor en el año 2012 con prótesis totales removibles, y el segundo grupo, por pacientes con dentadura natural completa. Además, al grupo de pacientes rehabilitados con prótesis totales se le aplicó la encuesta GOHAI para conocer el nivel de satisfacción con el uso de sus prótesis. Los resultados muestran que el rendimiento masticatorio es muy superior en los individuos dentados naturales con respecto a los portadores de prótesis totales, y esta diferencia es estadísticamente significativa. Los pacientes portadores de prótesis totales señalan un bajo nivel de satisfacción con el uso de sus dentaduras completas, en especial durante la función masticatoria.
Let X and Y be two n×n Hermitian matrices. In the article Proof of a conjectured exponential form... more Let X and Y be two n×n Hermitian matrices. In the article Proof of a conjectured exponential formula (Linear Multilinear Algebra 19 (1986) 187-197) R.C. Thompson proved that there exist two n×n unitary matrices U and V such that eiXeiY=eiUXU*+VYV*. In this note we consider extensions of this result to compact operators as well as to operators in an embeddable II1 factor.Facultad de Ciencias Exacta
Linear and Multilinear Algebra
For a given complex finite dimensional subspace S of C n and a fixed basis, we study the compact ... more For a given complex finite dimensional subspace S of C n and a fixed basis, we study the compact and convex subset of pRě0q n that we call the moment of S mS "convex hull`t|s| 2 P R n ě0 : s P S^}s} " 1u» tDiagpY q P M h n pCq : Y ě 0, trpY q " 1, PSY PS " Y u where |s| 2 " p|s1| 2 , |s2| 2 ,. .. , |sn| 2 q. This set is relevant in the determination of minimal hermitian matrices (M P M h n such that }M`D} ď D for every diagonal D and } } the spectral norm). We describe extremal points and curves of mS in terms of principal vectors that minimize the angle between S and the coordinate axes. We also relate mS to the joint numerical range W of n rank one nˆn matrices constructed with the orthogonal projection PS and the fixed basis used. This connection provides a new approach to the description of mS and to minimal matrices. As a consequence the intersection of two of these joint numerical ranges allow the construction or detection of a minimal matrix, a fact that is easier to corroborate than the equivalent condition for moments. It is also proved that mS is a semi-algebraic set equal to the intersection of the mentioned W with a hyperplane and whose generated positive cone coincides with that of W .
arXiv: Operator Algebras, 2019
We study the unitary orbit of a compact Hermitian diagonal operator with spectral multiplicity on... more We study the unitary orbit of a compact Hermitian diagonal operator with spectral multiplicity one under the action of the unitary group U_(K+C) of the unitization of the compact operators K(H)+C, or equivalently, the quotient U_(K+C)/ U_Diag(K+C). We relate this and the action of different unitary subgroups to describe metric geodesics (using a natural distance) which join end points. As a consequence we obtain a local Hopf-Rinow theorem. We also explore cases about the uniqueness of short curves and prove that there exist some of these that cannot be parameterized using minimal anti-Hermitian operators of K(H)+C.
Operators and Matrices, 2021
We study the elementary C *-algebra D + K which consists of sums of a diagonal plus a compact ope... more We study the elementary C *-algebra D + K which consists of sums of a diagonal plus a compact operator. We describe the structure of the unitary group, the sets of ideals, automorhisms and projections.
Demonstratio Mathematica, 2017
Given a Hermitian matrix M ∈ M3(ℂ) we describe explicitly the real diagonal matrices DM such that... more Given a Hermitian matrix M ∈ M3(ℂ) we describe explicitly the real diagonal matrices DM such that ║M + DM║ ≤ ║M + D║ for all real diagonal matrices D ∈ M3(ℂ), where ║ · ║ denotes the operator norm. Moreover, we generalize our techniques to some n × n cases.
Journal of Mathematical Analysis and Applications, 2021
Let H be a reproducing kernel Hilbert space of functions on a set X. We study the problem of find... more Let H be a reproducing kernel Hilbert space of functions on a set X. We study the problem of finding a minimal geodesic of the Grassmann manifold of H that joins two subspaces consisting of functions which vanish on given finite subsets of X. We establish a necessary and sufficient condition for existence and uniqueness of geodesics, and we then analyze it in examples. We discuss the relation of the geodesic distance with other known metrics when the mentioned finite subsets are singletons. We find estimates on the upper and lower eigenvalues of the unique self-adjoint operators which define the minimal geodesics, which can be made more precise when the underlying space is the Hardy space. Also for the Hardy space we discuss the existence of geodesics joining subspaces of functions vanishing on infinite subsets of the disk, and we investigate when the product of projections onto this type of subspaces is compact.
Linear Algebra and its Applications, 2019
We study certain pairs of subspaces V and W of C n we call supports that consist of eigenspaces o... more We study certain pairs of subspaces V and W of C n we call supports that consist of eigenspaces of the eigenvalues ± M of a minimal hermitian matrix M (M ≤ M + D for all real diagonals D). For any pair of orthogonal subspaces we define a non negative invariant δ called the adequacy to measure how close they are to form a support and to detect one. This function δ is the minimum of another map F defined in a product of spheres of hermitian matrices. We study the gradient, Hessian and critical points of F in order to approximate δ. These results allow us to prove that the set of supports has interior points in the space of flag manifolds.
Differential Geometry and its Applications, 2016
We study some examples of minimal length curves in homogeneous spaces of B(H) under a left action... more We study some examples of minimal length curves in homogeneous spaces of B(H) under a left action of a unitary group. Recent results relate these curves with the existence of minimal (with respect to a quotient norm) anti-Hermitian operators Z in the tangent space of the starting point. We show minimal curves that are not of this type but nevertheless can be approximated uniformly by those.
Studia Mathematica, 2017
Let H be a separable Hilbert space, and D(B(H) ah) the anti-Hermitian bounded diagonals in some f... more Let H be a separable Hilbert space, and D(B(H) ah) the anti-Hermitian bounded diagonals in some fixed orthonormal basis and K(H) the compact operators. We study the group of unitary operators U k,d = {u ∈ U(H) : ∃ D ∈ D (B (H)) ah such that u − e D ∈ K(H)} in order to obtain a concrete description of short curves in unitary Fredholm orbits O b = {e K be −K : K ∈ K(H) ah } of a compact selfadjoint operator b with spectral multiplicity one. We consider the rectifiable distance on O b defined as the infimum of curve lengths measured with the Finsler metric defined by means of the quotient space K(H) ah /D(K(H) ah). Then for every c ∈ O b and x ∈ T (O b) c there exist a minimal lifting Z 0 ∈ B(H) ah (in the quotient norm, not necessarily compact) such that γ(t) = e tZ0 c e −tZ0 is a short curve on O b in a certain interval.
MATHEMATICA SCANDINAVICA, 1999
Let M be a von Neumann algebra, 9 be a faithful, normal semifinite weight on M and M 9 its centra... more Let M be a von Neumann algebra, 9 be a faithful, normal semifinite weight on M and M 9 its centralizer. We characterize the conditional expectations E 9 X M 3 M 9 of finite index for a faithful normal strictly semifinite weight 9 on a semifinite von Neumann algebra M with finite dimensional center. This result is used to characterize weights 9 such that the orbit U 9 f9 Adu X u unitary in Mg can be represented as a submanifold of M 1 (=basic extension of E 9 X M 3 M 9).
Journal of Mathematical Analysis and Applications, 2015
A conjecture posed by S. Hayajneh and F. Kittaneh claims that given A, B positive matrices, 0 ≤ t... more A conjecture posed by S. Hayajneh and F. Kittaneh claims that given A, B positive matrices, 0 ≤ t ≤ 1, and any unitarily invariant norm it holds |||A t B 1−t + B t A 1−t ||| ≤ |||A t B 1−t + A 1−t B t |||. Recently, R. Bhatia proved the inequality for the case of the Frobenius norm and for t ∈ [ 1 4 ; 3 4 ]. In this paper, using complex methods we extend this result to complex values of the parameter t = z in the strip {z ∈ C : Re(z) ∈ [ 1 4 ; 3 4 ]}. We give an elementary proof of the fact that equality holds for some z in the strip if and only if A and B commute. We also show a counterexample to the general conjecture by exhibiting a pair of positive matrices such that the claim does not hold for the uniform norm. Finally, we give a counterexample for a related singular value inequality given by s j (A t B 1−t + B t A 1−t) ≤ s j (A + B), answering in the negative a question made by K. Audenaert and F. Kittaneh. 1
Journal of Geometry and Physics, 2014
Left invariant metrics induced by the p-norms of the trace in the matrix algebra are studied on t... more Left invariant metrics induced by the p-norms of the trace in the matrix algebra are studied on the general lineal group. By means of the Euler-Lagrange equations, existence and uniqueness of extremal paths for the length functional are established, and regularity properties of these extremal paths are obtained. Minimizing paths in the group are shown to have a velocity with constant singular values and multiplicity. In several special cases, these geodesic paths are computed explicitly. In particular the Riemannian geodesics, corresponding to the case p = 2, are characterized as the product of two one-parameter groups. It is also shown that geodesics are one-parameter groups if and only if the initial velocity is a normal matrix. These results are further extended to the context of compact operators with p-summable spectrum, where a differential equation for the spectral projections of the velocity vector of an extremal path is obtained. 1
We describe properties of a Hermitian matrix M ∈ M n (C) having minimal quotient norm in the foll... more We describe properties of a Hermitian matrix M ∈ M n (C) having minimal quotient norm in the following sense: M M + D for all real diagonal matrices D ∈ M n (C). Here denotes the operator norm. We show a constructive method to obtain all the minimal matrices of any size.
International Journal of Applied Geospatial Research, 2013
Dengue fever is an arboviral disease typical of the tropics that can be life-threatening and if n... more Dengue fever is an arboviral disease typical of the tropics that can be life-threatening and if not controlled properly may result in an epidemic. The absence of an effective vaccine makes strategies to prevent the virus transmission the most effective means of control. The planning of such strategies, however, is difficult due to the constant movement of individuals and mosquito host (Aedes aegypti). In this paper, the spatial and temporal relations that might exist between infected individuals during a dengue-epidemic year are explored. This research is motivated in that a deep understanding of potential transmission patterns between individuals might lead to a better design and planning of control strategies. A GIS-based Health Exploratory AnaLysis Tool (HELP) is used to compute space-time relationships by means of spatial K-function, kernel density, space-time K-function and linking pairs of cases within significant time and space intervals. Significant clustering was observed a...
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Papers by Alejandro Eiras Varela