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Institution

University of Waterloo

EducationWaterloo, Ontario, Canada
About: University of Waterloo is a education organization based out in Waterloo, Ontario, Canada. It is known for research contribution in the topics: Population & Poison control. The organization has 36093 authors who have published 93906 publications receiving 2948139 citations. The organization is also known as: UW & uwaterloo.


Papers
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Journal ArticleDOI
TL;DR: In this article, a holographic version of the Vafa-Witten theorem was shown to hold for non-supersymmetric, four-dimensional QCDs with N c colours and N f 0, obeying the Gell-Mann-Oakes-Renner relation.
Abstract: We study N f D6-brane probes in the supergravity background dual to N c D4-branes compactified on a circle with supersymmetry-breaking boundary conditions. In the limit in which the resulting Kaluza-Klein modes decouple, the gauge theory reduces to non-supersymmetric, four-dimensional QCD with N c colours and N f 0, obeying the Gell-Mann-Oakes-Renner relation: M π 2 = −m q ψ/fπ2 . In the case 1$> N f>1 we provide a holographic version of the Vafa-Witten theorem, which states that the U(N f) flavour symmetry cannot be spontaneously broken. Further, we find N f 2−1 unexpectedly light pseudo-scalar mesons in the spectrum. We argue that these are not (pseudo-)Goldstone bosons and speculate on the string mechanism responsible for their lightness. We then study the theory at finite temperature and exhibit a phase transition associated with a discontinuity in ψ(T). D6/ pairs are also briefly discussed.

614 citations

Journal ArticleDOI
TL;DR: Several lines of evidence suggest that degradation of lipids in senescing membranes and the ensuing release of free fatty acids initiate oxidative deterioration by providing substrate for lipoxygenase, and membranes are primary targets of free radical damage.
Abstract: Reactions involving free radicals are an inherent feature of plant senescence and appear to contribute to a process of oxidative deterioration that leads ultimately to cell death. Radical species derived from molecular oxygen are the primary mediators of this oxidative damage, but non-radical excited states of oxygen, specifically singlet oxygen, may also be involved. Several lines of evidence suggest that degradation of lipids in senescing membranes and the ensuing release of free fatty acids initiate oxidative deterioration by providing substrate for lipoxygenase. In some tissues, lipoxygenase activity increases with advancing senescence in a pattern that is consistent with its putative role in promoting oxidative damage. However, there are important exceptions to this which may be explained by the fact that the timing and extent of peroxidative reactions initiated by lipoxygenase are likely to be determined more by the availability of substrate for the enzyme than by changes in its activity. There are both membranous and cytosolic forms of lipoxygenase in senescing tissues, and peroxidation of membrane lipids appears to be initiated by the membranous enzyme once the appropriate fatty acid substrates, linoleic acid and linolenic acid, become available. Since lipid peroxidation is known to form alkoxy and peroxy radicals as well as singlet oxygen, these reactions in membrane bilayers are probably a major source of activated oxygen species in senescing tissues. Further-more, there are indications that activated oxygen from the lipoxygenase reaction can become substrate for the cytosolic form of the enzyme which, in turn, may raise the titre of activated oxygen during senescence. Additional possible sources of increased free radical production in senescing tissues include peroxidase, which shows greatly increased activity with advancing age, leakage of electrons from electron transport systems to oxygen, in particular from the photosynthetic electron transport system, and decompartmentalization of iron, which would facilitate formation of the highly reactive hydroxyl radical from the less reactive superoxide anion. A variety of macromolecules can be damaged by activated oxygen. Unsaturated fatty acids are especially prone to attack, and this implies that membranes are primary targets of free radical damage. The manifestations of this damage in senescing tissues range from altered membrane fluidity and phase properties to leakiness that can be attributed to a destabilized and highly perturbed membrane bilayer. There is also a progressive breakdown of cellular protein with advancing senescence. Free radicals can inactivate proteins by reacting with specific amino acid residues, and a number of in zitro studies have indicated that such alteration renders the proteins more prone to hydrolysis by proteases. Thus, although there is no direct evidence linking enhanced proteolysis during senescence to free radical damage, there is reason to believe that this may be a contributing factor. Wounding of certain plant tissues also initiates a series of reactions that revolve around the breakdown of membrane lipids and their peroxidation. Indeed, as in the case of senescence, membrane deterioration follokving wounding appears to be facilitated by a self-perpetuating wave of free radical production emanating from peroxidation within the lipid bilayer. There is also recent evidence for activation of an O2- -producing NADPH oxidase in plant tissues following fungal infection that may be analogous to the well-characterized O2- -generating NADPH oxidase associated with the plasma membrane of polymorphonuclear leukocytes. This raises the interesting possibility that plants and animals share a common defence response to invading organisms. Contents Summary 317 I. Introduction 318 II. Species of activated oxygen 319 III. Sites of activated oxygen production 319 IV. Free radical production during senescence 323 V. Targets of free radical damage in senescing tissues 330 VI. The role of free radicals in seed ageing 336 VII. The role of free radicals in wounding 337 VIII. Concluding remarks 338 Acknowledgement 338 References 338.

612 citations

Journal ArticleDOI
TL;DR: Exposing participants to gender-stereotypic TV commercials designed to elicit the female stereotype explored whether vulnerability to stereotype threat could persuade women to avoid leadership roles in favor of nonthreatening subordinate roles.
Abstract: Exposing participants to gender-stereotypic TV commercials designed to elicit the female stereotype, the present research explored whether vulnerability to stereotype threat could persuade women to avoid leadership roles in favor of nonthreatening subordinate roles. Study 1 confirmed that exposure to the stereotypic commercials undermined women's aspirations on a subsequent leadership task. Study 2 established that varying the identity safety of the leadership task moderated whether activation of the female stereotype mediated the effect of the commercials on women's aspirations. Creating an identity-safe environment eliminated vulnerability to stereotype threat despite exposure to threatening situational cues that primed stigmatized social identities and their corresponding stereotypes.

612 citations

Journal ArticleDOI
TL;DR: In this paper, a natural formulation for a massless colored cubic scalar theory is presented, which is an integral over the space of n marked points on a sphere and has as integrand two factors: the first is a combination of Parke-Taylor-like terms dressed with U(N ) color structures while the second is a Pfaffian.
Abstract: In a recent note we presented a compact formula for the complete tree-level S-matrix of pure Yang-Mills and gravity theories in arbitrary spacetime dimension. In this paper we show that a natural formulation also exists for a massless colored cubic scalar theory. In Yang-Mills, the formula is an integral over the space of n marked points on a sphere and has as integrand two factors. The first factor is a combination of Parke-Taylor-like terms dressed with U(N ) color structures while the second is a Pfaffian. The S-matrix of a U(N ) × U(N ) cubic scalar theory is obtained by simply replacing the Pfaffian with a U(N ) version of the previous U(N ) factor. Given that gravity amplitudes are obtained by replacing the U(N ) factor in Yang-Mills by a second Pfaffian, we are led to a natural color-kinematics correspondence. An expansion of the integrand of the scalar theory leads to sums over trivalent graphs and are directly related to the KLT matrix. Combining this and the Yang-Mills formula we find a connection to the BCJ color-kinematics duality as well as a new proof of the BCJ doubling property that gives rise to gravity amplitudes. We end by considering a special kinematic point where the partial amplitude simply counts the number of color-ordered planar trivalent trees, which equals a Catalan number. The scattering equations simplify dramatically and are equivalent to a special Y-system with solutions related to roots of Chebyshev polynomials. The sum of the integrand over the solutions gives rise to a representation of Catalan numbers in terms of eigenvectors and eigenvalues of the adjacency matrix of an A-type Dynkin diagram.

611 citations

Journal ArticleDOI
TL;DR: In this paper, the surface chemistry of the following cathode materials: LiCoO 2, V 2 O 5, LiMn 2 O 4, Li Mn 0.5 O 4 and Li MmN 0.

611 citations


Authors

Showing all 36498 results

NameH-indexPapersCitations
John J.V. McMurray1781389184502
David A. Weitz1781038114182
David Taylor131246993220
Lei Zhang130231286950
Will J. Percival12947387752
Trevor Hastie124412202592
Stephen Mann12066955008
Xuan Zhang119153065398
Mark A. Tarnopolsky11564442501
Qiang Yang112111771540
Wei Zhang112118993641
Hans-Peter Seidel112121351080
Theodore S. Rappaport11249068853
Robert C. Haddon11257752712
David Zhang111102755118
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
20241
2023213
2022701
20215,359
20205,388
20195,200