Uncountably many quasi-isometry classes of groups of type FPFP

Previously one of the authors constructed uncountable families of groups of type $FP$ and of $n$-dimensional Poincar\'e duality groups for each $n\geq 4$. We strengthen these results by showing that these groups comprise uncountably many quasi-isometry classes. We deduce that for each $n\geq 4$ there are uncountably many quasi-isometry classes of acyclic $n$-manifolds admitting free cocompact properly discontinuous discrete group actions.Comment: Version 2: minor corrections made, theorems now numbered by sectio

From a Potato Hole

Lesson

Review of: Australian Folksongs of the Land and Its People, Compiled by the Folklore Council of Australia

Book Review

Pay-as-you-go LPG: A mixed-methods pilot study in urban Rwanda

2.8 billion people still cook with biomass fuels, resulting in devastating impacts on health, gender equity and the environment. Pay-as-you-go (PAYG) liquid petroleum gas (LPG) is a new technology designed to make LPG affordable for urban biomass users by allowing customers to pay for fuel in small amounts. This mixed-methods study (N = 64) combined stove usage data, cooking diaries, household interviews and telephone surveys to examine a commercial PAYG LPG pilot in Kigali. It aimed to understand how households used PAYG LPG and its potential in accelerating access to clean cooking in urban Rwanda. PAYG LPG rapidly displaced charcoal as the primary cooking fuel for the majority of participants, resulting in a mean monthly reduction in household fuel expenditure of 3240 RWF (3.50 USD) and a mean consumption of 1.2 kg/capita/month. Participants spanning all income brackets in Kigali made use of PAYG LPG. The ability to pay in smaller amounts seemed to be critical to initial adoption and sustained use during the pilot. Follow-up activities with a small subsample of participants (N = 10) found that 70% continued to use full cylinder LPG (typically 12 kg) as their primary cooking fuel in the two months after the PAYG service was withdrawn. Throughout the pilot almost all participants continued to use charcoal, which accounted for 21% of cooking events. We identified a range of drivers of fuel stacking that encompassed both cultural and practical factors such as cylinder delivery delays and taste preferences for certain foods. We conclude that PAYG LPG could contribute to the clean cooking transition in urban Rwanda, but that larger scale pilots are needed to better understand both the supply- and demand-side viability

On the History of an Anecdote

This article explores the historical antecedents to the Russian anecdote which remarks on the reactions by various nationalities’ to finding a fly in their soup and considers the function of such anecdotes in their popular usage

Fault-Zone Waves Observed at the Southern Joshua Tree Earthquake Rupture Zone

Waveform and spectral characteristics of several aftershocks of the M 6.1 22 April 1992 Joshua Tree earthquake recorded at stations just north of the Indio Hills in the Coachella Valley can be interpreted in terms of waves propagating within narrow, low-velocity, high-attenuation, vertical zones. Evidence for our interpretation consists of: (1) emergent P arrivals prior to and opposite in polarity to the impulsive direct phase; these arrivals can be modeled as headwaves indicative of a transfault velocity contrast; (2) spectral peaks in the S wave train that can be interpreted as internally reflected, low-velocity fault-zone wave energy; and (3) spatial selectivity of event-station pairs at which these data are observed, suggesting a long, narrow geologic structure. The observed waveforms are modeled using the analytical solution of Ben-Zion and Aki (1990) for a plane-parallel layered fault-zone structure. Synthetic waveform fits to the observed data indicate the presence of NS-trending vertical fault-zone layers characterized by a thickness of 50 to 100 m, a velocity decrease of 10 to 15% relative to the surrounding rock, and a P-wave quality factor in the range 25 to 50

Observation of Interaction of Spin and Intrinsic Orbital Angular Momentum of Light

Interaction of spin and intrinsic orbital angular momentum of light is observed, as evidenced by length-dependent rotations of both spatial patterns and optical polarization in a cylindrically-symmetric isotropic optical fiber. Such rotations occur in straight few-mode fiber when superpositions of two modes with parallel and anti-parallel orientation of spin and intrinsic orbital angular momentum (IOAM=$2\hslash$) are excited, resulting from a degeneracy splitting of the propagation constants of the modes.Comment: 6 pages, 5 figures, and a detailed supplement. Version 3 corrects a typo and adds the journal referenc