4,209 research outputs found
S-Lemma with Equality and Its Applications
Let and be two quadratic functions
having symmetric matrices and . The S-lemma with equality asks when the
unsolvability of the system implies the existence of a real
number such that . The
problem is much harder than the inequality version which asserts that, under
Slater condition, is unsolvable if and only if for some . In this paper, we
show that the S-lemma with equality does not hold only when the matrix has
exactly one negative eigenvalue and is a non-constant linear function
(). As an application, we can globally solve as well as the two-sided generalized trust region subproblem
without any condition. Moreover, the
convexity of the joint numerical range where is a (possibly non-convex) quadratic
function and are affine functions can be characterized
using the newly developed S-lemma with equality.Comment: 34 page
An Improved Analysis of Semidefinite Approximation Bound for Nonconvex Nonhomogeneous Quadratic Optimization with Ellipsoid Constraints
We consider the problem of approximating nonconvex quadratic optimization
with ellipsoid constraints (ECQP). We show some SDP-based approximation bounds
for special cases of (ECQP) can be improved by trivially applying the extened
Pataki's procedure. The main result of this paper is to give a new analysis on
approximating (ECQP) by the SDP relaxation, which greatly improves Tseng's
result [SIAM Journal Optimization, 14, 268-283, 2003]. As an application, we
strictly improve the approximation ratio for the assignment-polytope
constrained quadratic program.Comment: 12 page
Photoluminescence pressure coefficients of InAs/GaAs quantum dots
We have investigated the band-gap pressure coefficients of self-assembled
InAs/GaAs quantum dots by calculating 17 systems with different quantum dot
shape, size, and alloying profile using atomistic empirical pseudopotential
method within the ``strained linear combination of bulk bands'' approach. Our
results confirm the experimentally observed significant reductions of the band
gap pressure coefficients from the bulk values. We show that the nonlinear
pressure coefficients of the bulk InAs and GaAs are responsible for these
reductions. We also find a rough universal pressure coefficient versus band gap
relationship which agrees quantitatively with the experimental results. We find
linear relationships between the percentage of electron wavefunction on the
GaAs and the quantum dot band gaps and pressure coefficients. These linear
relationships can be used to get the information of the electron wavefunctions.Comment: 8 pages, 2 tables, 4 figure
The risk factors and preventive measures for the recurrence of endometrial polyps
Endometrial polyps (EPs) are a frequently encountered gynecologic disease with abnormal uterine bleeding and infertility being the two common presenting problems, and hysteroscopic polypectomy is an effective method to remove them. The postoperative polyp recurrence might result in reappearance of abnormal uterine bleeding or infertility, whereas factors influencing the postoperative recurrence potential have limited data. Endometrial polyp recurrence remains a concern with recurrence rates of 2.5% to 43.6%. As such, it is critical to identify the risk factors and the preventive measures for endometrial recurrence, especially in reproductive-age women desiring future conception, to aid in clinical counselling and decision making. The recurrence of EPs is related to estrogen stimulation and endometrial hyperplasia. The progesterone-containing drugs are currently the most commonly used method to prevent the recurrence of EPs. In this article, authors aim to discuss the high-risk factors of EPs recurrence and the preventive measures for EPs recurrence. The preventive measures will focus on the combined oral contraceptives (COCs) and the levonorgestrel-releasing intrauterine system (LNG-IUS)
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