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A real matrix A is called sign-central if the convex hull of the columns of à contains the zero vector 0 for every matrix à with the same sign pattern as A. A sign-central matrix A is called a minimal sign-central matrix if the deletion of any of the columns of A breaks the signcentrality of A. A sign-central matrix A is called tight sign-central if the Hadamard (entrywise) product of any two c...

OBJECTIVE To evaluate whether the presence of uterorectal adhesions demonstrated by transvaginal sonography (TVS) could aid as a simple sonographic predictor for deep infiltrating endometriosis (DIE) of the rectum in patients with symptoms suggestive of endometriosis. METHODS This was a prospective multicenter study of women scheduled for laparoscopy because of symptoms suggestive of endometr...

OBJECTIVE The aim of this study was to evaluate whether or not the positivity of Abadie's sign could be an indicator of asymptomatic Achilles intratendinous changes. SUBJECTS AND METHODS A total of 18 patients (36 tendons) suffering from diabetes, with at least 1 Achilles tendon positive to Abadie's sign, were compared to matched subjects with diabetes bilaterally negative to Abadie's sign. A...

This study investigates on a quantitative basis two strategies that can be used to increase the legibility distance of retroreflective traffic signs with negative luminance contrast legend or symbols at night. The first strategy involves the increase of the letter, numeral, or symbol size associated with a corresponding increase in the stroke width (representing the visual detail) and with an i...

Sign patterns that require exponential nonnegativity are characterized. A set of conditions necessary for a sign pattern to require eventual exponential nonnegativity are established. It is shown that these conditions are also sufficient for an upper triangular sign pattern to require eventual exponential nonnegativity and it is conjectured that these conditions are both necessary and sufficien...

Results on thermodiffusion of poly~ethylene oxide! and colloidal boehmite (g-AlOOH! rods in ethanol/water mixtures are presented. Data were obtained using thermal diffusion forced Rayleigh scattering. The sign of the Soret coefficient of the boehmite rods changes from positive to negative with increasing water content, i.e., at sufficiently high water content the colloidal particles move to hig...

Sign patterns that require exponential nonnegativity are characterized. A set of conditions necessary for a sign pattern to require eventual exponential nonnegativity are established. It is shown that these conditions are also sufficient for an upper triangular sign pattern to require eventual exponential nonnegativity and it is conjectured that these conditions are both necessary and sufficien...

We show that a superlinear boundary value problem has at least three nontrivial solutions. A pair are of one sign (positive and negative, respectively), and the third solution changes sign exactly once. The critical level of the sign-changing solution is bounded below by the sum of the two lesser levels of the one-sign solutions. If nondegenerate, the one sign solutions are of Morse index 1 and...