8,334 research outputs found
Lensing of 21-cm Fluctuations by Primordial Gravitational Waves
Weak-gravitational-lensing distortions to the intensity pattern of 21-cm radiation from the dark ages can be decomposed geometrically into curl and curl-free components. Lensing by primordial gravitational waves induces a curl component, while the contribution from lensing by density fluctuations is strongly suppressed. Angular fluctuations in the 21-cm background extend to very small angular scales, and measurements at different frequencies probe different shells in redshift space. There is thus a huge trove of information with which to reconstruct the curl component of the lensing field, allowing tensor-to-scalar ratios conceivably as small as r∼10^(-9)—far smaller than those currently accessible—to be probed
Catching Up
In lieu of an abstract, below is the essay\u27s first paragraph.
I sat down today to write some of my memoirs. I\u27m not sure why I\u27d want to do this. I really am not the type to write things down. As a matter of fact, I never liked to write, but I\u27d been thinking a lot lately, and thought it might help to ease my mind; if there are a lot of mistakes, forgive me. I don\u27t even know to whom I\u27m writing, but I have a feeling that someday someone will stumble upon this, and it will make sense to them, at least I hope it will
Review of C. S. Lewis: Twentieth Century Pilgrim
Review of Janet Hamilton, C. S. Lewis: Twentieth Century Pilgrim (Greensboro, NC, 2011). 128 pages. $28.95. ISBN: 9781599351124
Viscous Withdrawal of Miscible Liquid Layers
In viscous withdrawal, a converging flow imposed in an upper layer of viscous
liquid entrains liquid from a lower, stably stratified layer. Using the idea
that a thin tendril is entrained by a local straining flow, we propose a
scaling law for the volume flux of liquid entrained from miscible liquid
layers. A long-wavelength model including only local information about the
withdrawal flow is degenerate, with multiple tendril solutions for one
withdrawal condition. Including information about the global geometry of the
withdrawal flow removes the degeneracy while introducing only a logarithmic
dependence on the global flow parameters into the scaling law.Comment: 4 pages, 4 figure
Treasure in the Archives: A Celebration of Archival Collections
Describes the collection of the Wade Center at Wheaton College in Wheaton, Illinois, which holds extensive archives of the works of Mythlore’s three key authors—Tolkien, Lewis, and Williams—as well as fellow Inkling Owen Barfield, and writers Dorothy L. Sayers, George MacDonald, and G.K. Chesterton. Also discusses the structure and uses of archives in general
Linear spin-2 fields in most general backgrounds
We derive the full perturbative equations of motion for the most general
background solutions in ghost-free bimetric theory in its metric formulation.
Clever field redefinitions at the level of fluctuations enable us to circumvent
the problem of varying a square-root matrix appearing in the theory. This
greatly simplifies the expressions for the linear variation of the bimetric
interaction terms. We show that these field redefinitions exist and are
uniquely invertible if and only if the variation of the square-root matrix
itself has a unique solution, which is a requirement for the linearised theory
to be well-defined. As an application of our results we examine the constraint
structure of ghost-free bimetric theory at the level of linear equations of
motion for the first time. We identify a scalar combination of equations which
is responsible for the absence of the Boulware-Deser ghost mode in the theory.
The bimetric scalar constraint is in general not manifestly covariant in its
nature. However, in the massive gravity limit the constraint assumes a
covariant form when one of the interaction parameters is set to zero. For that
case our analysis provides an alternative and almost trivial proof of the
absence of the Boulware-Deser ghost. Our findings generalise previous results
in the metric formulation of massive gravity and also agree with studies of its
vielbein version.Comment: Latex, 20 pages. Matches published versio
Importance of Pelvic Floor Education and Rehabilitation Techniques for Adolescents and Young Adults: A Review
The pelvic floor is the collection of many muscles forming what is often called the pelvic girdle. Understanding the different muscles and their roles is an important part of pelvic floor education. Although both males and females have pelvic floors, there is a lack of knowledge of basic anatomy seen in adolescents and young adults. This review analyzes the importance of providing more education for students about the pelvic floor, gives examples of common pelvic disorders for young adults, and provides details on the physical therapy rehabilitation techniques offered today to treat these conditions
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