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Are we overlooking the eco-geomorphic importance of wood in braided rivers?: A case study in Grand Teton National Park
No full textA decades-long body of research has hypothesized a fundamental incompatibility between braided rivers, which form due to a lack of bank cohesion and a highly-mobile channel bed, with vegetation, which stabilizes channel surfaces and hinders sediment mobilization. At the same time, many researchers have observed high densities of wood, occurring either as large jams or dense stands of mature trees, along the braid plain of multi-thread rivers worldwide. Here we seek to reconcile the perceived incompatibility of wood and braided rivers with the high densities of vegetation found along these streams using two multi-thread, gravel-bed rivers in Grand Teton National Park. In August of 2017, we completed topographic surveys along ~500 m reaches of Pacific and Pilgrim Creeks, tributaries to the Snake River in Jackson Hole. We seek to compare digital elevation models generated from these surveys with 2014 elevation data collected via airborne lidar to determine whether in-channel wood drives increases in bar density, depth variability, and in-channel habitat suitability for native salmonids. While the majority of our efforts following the August 2017 field campaign have been focused on lidar data processing and cleaning, our initial results indicate that wood is a dominant driver of bar formation in both Pilgrim and Pacific Creek, and may be the dominant driver of depth variability (e.g., pool scour) in gravel-bed braided streams in Grand Teton National Park.
Featured photo by Grand Teton on Flickr. https://flic.kr/p/MyszY
Peralta, Dan-el Padilla (2015) Undocumented: A Dominican Boy’s Odyssey from a Homeless Shelter to the Ivy League, Penguin Books, New York, Ny. Vance, J.D. (2016) Hillbilly Elegy: A Memoir of a Family and Culture in Crisis, HarperCollins, New York, Ny.
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Class and Narrative Accrual: Personal Troubles and Public Issues in Five Vignettes
No full textThis paper develops Bruner’s (1991) notion of narrative accrual, in conjunction with ‘lifestories’ and ‘event-stories’, to focus on the accumulation of experiences as a contributor to working-class identity. Situated between Mills’ (1959) personal troubles and public issues, and framed by Nouri and Helterline’s (1998) argument that identity is framed by social interaction with signification systems and other people, the author’s own experiences as an early-career academic in two different British Universities – one more research-oriented with a predominantly middle-class student body, the other more teaching-oriented with a more class diverse student body – are utilized to forward ‘personal narrative accrual’ as a way of both conceptualizing and unpacking class associations, reflecting on Warnock’s (2016) fivefold typology of alienation, cultural capital, stereotyping/microaggression, survivor guilt/impostor syndrome and middle class networking. Ultimately, this paper considers the interrelated problems of working-class identity, career development, and ‘playing the game’ through autobiographical vignettes, and suggests the potential application of personal narrative accrual in decreasing feelings of isolation in academia by working-class academics
Comparison between Laplacian--energy--like invariant and Kirchhoff index
No full textFor a simple connected graph G of order n, having Laplacian eigenvalues μ_1, μ_2, . . . ,μ_{nâ1}, μ_n = 0, the Laplacianâenergyâlike invariant (LEL) and the Kirchhoff index (Kf) are defined as LEL(G) = \sum_{i=1}^{n-1} \sqrt{μ_i} Kf(G) = \sum_{i=1}^{n-1} 1/μ_i, respectively. In this paper, LEL and Kf arecompared, and sufficient conditions for the inequality Kf(G) < LEL(G) are established
A counterexample to a question of Bapat and Sunder
No full textWe present a counterexample to a question of Bapat and Sunder
Minimal Estrada Indices of the Trees with a Perfect Matching
No full textLet be the set of the trees having a perfect matching with vertices. The ordering of the trees in according to their minimal Estrada indices is investigated. We obtain the trees with the smallest and the second smallest Estrada indices among with
Principal Pivot Transforms of Quasidefinite Matrices and Semidefinite Lagrangian Subspaces
No full textLagrangian subspaces are linear subspaces that appear naturally in control theory applications, and especially in the context of algebraic Riccati equations. We introduce a class of semidefinite Lagrangian subspaces and show that these subspaces can be represented by a subset I â {1, 2, . . . , n} and a Hermitian matrix X â C nÃn with the property that the submatrix X II is negative semidefinite and the submatrix X I c I c is positive semidefinite. A matrix X with these definiteness properties is called I-semidefinite and it is a generalization of a quasidefinite matrix. Under mild hypotheses which hold true in most applications, the Lagrangian subspace associated to the stabilizing solution of an algebraic Riccati equation is semidefinite, and in addition we show that there is a bijection between Hamiltonian and symplectic pencils and semidefinite Lagrangian subspaces; hence this structure is ubiquitous in control theory. The (symmetric) principal pivot transform (PPT) is a map used by Mehrmann and Poloni [SIAM J. Matrix Anal. Appl., 33(2012), pp. 780â805] to convert between two different pairs (I, X) and (J , X 0 ) representing the same Lagrangian subspace. For a semidefinite Lagrangian subspace, we prove that the symmetric PPT of an I-semidefinite matrix X is a J -semidefinite matrix X 0 , and we derive an implementation of the transformation X 7â X 0 that both makes use of the definiteness properties of X and guarantees the definiteness of the submatrices of X 0 in finite arithmetic. We use the resulting formulas to obtain a semidefiniteness-preserving version of an optimization algorithm introduced by Mehrmann and Poloni to compute a pair (I opt , X opt ) with M = max i,j |(X opt ) ij | as small as possible. Using semidefiniteness allows one to obtain a stronger inequality on M with respect to the general case
On the group invertibility of operators
No full textThe main topic of this paper is the group invertibility of operators in Hilbert spaces. Conditions for the existence of the group inverses of products of two operators and the group invertibility of anti-triangular block operator matrices are studied. The equivalent conditions related to the reverse order law for the group inverses of operators are obtained
