Asymptotically simple spacetime manifolds

This is the published version, also available here: http://dx.doi.org/10.1063/1.1666825.Asymptotic simplicity is shown to be k‐stable (k≥3) at any Minkowski metric on R4 in both the Whitney fine Ck topology and a coarser topology (in which the Ck twice‐convariant symmetric tensors form a Banach manifold whose connected components consist of tensor field asymptotic to one another at null infinity). This result, together with a sequential method for solving the field equations previously proposed by the authors, allows a fairly straightforward proof that a well‐known result in the linearized theory holds in the full nonlinear theory as well: There are no nontrivial (i.e., non‐Minkowskian) asymptotically simple vacuum metrics on R4 whose conformal curvature tensors result from prescribing zero initial data on past null infinity

Rise in Land Values Slows to 2 Percent in 1969

The average value of farm land in Iowa rose to $382 per acre in 1969. That\u27s up$7 an acre. It\u27s the eighth year of increase, but also the smallest rise since 1962

Returns to Crop-Share Rented Land in Iowa

Landlords received a 4.2 percent to 5 percent return on crop-share rented land from 1965 through 1969, this analysis of professionally-managed farms shows. If the increase in land values is added, the return is more than 8 1/2 percent

Self-regulation for and of learning : student insights for online success in a Bachelor of Nursing Program in regional Australia

The blended online digital (BOLD) approach to teaching is popular within many universities. Despite this popularity, our understanding of the experiences of students making the transition to online learning is limited, specifically an examination of those elements associated with success. The aim of this study is to explore the experiences of students transitioning from a traditional mode of delivery to a more online approach in an inaugural BOLD Bachelor of Nursing program at a regional multi-campus institution in Victoria, Australia. Fifteen students across two regional campuses participated in one of four focus groups. This qualitative exploration of students’ experience contributes to contemporary insights into how we might begin to develop programs of study that help students develop self-regulation. A modified method of thematic analysis of phenomenological data was employed to analyse the focus group interview data to identify themes that represent the meaning of the transition experience for students. This qualitative exploration of students’ experience contributes to contemporary insights into how we might begin to develop programs of study that help students develop self-regulation

Ptychographic hyperspectral spectromicroscopy with an extreme ultraviolet high harmonic comb

We demonstrate a new scheme of spectromicroscopy in the extreme ultraviolet (EUV) spectral range, where the spectral response of the sample at different wavelengths is imaged simultaneously. It is enabled by applying ptychographical information multiplexing (PIM) to a tabletop EUV source based on high harmonic generation, where four spectrally narrow harmonics near 30 nm form a spectral comb structure. Extending PIM from previously demonstrated visible wavelengths to the EUV/X-ray wavelengths promises much higher spatial resolution and more powerful spectral contrast mechanism, making PIM an attractive spectromicroscopy method in both the microscopy and the spectroscopy aspects. Besides the sample, the multicolor EUV beam is also imaged in situ, making our method a powerful beam characterization technique. No hardware is used to separate or narrow down the wavelengths, leading to efficient use of the EUV radiation

LightBox: Full-stack Protected Stateful Middlebox at Lightning Speed

Running off-site software middleboxes at third-party service providers has been a popular practice. However, routing large volumes of raw traffic, which may carry sensitive information, to a remote site for processing raises severe security concerns. Prior solutions often abstract away important factors pertinent to real-world deployment. In particular, they overlook the significance of metadata protection and stateful processing. Unprotected traffic metadata like low-level headers, size and count, can be exploited to learn supposedly encrypted application contents. Meanwhile, tracking the states of 100,000s of flows concurrently is often indispensable in production-level middleboxes deployed at real networks. We present LightBox, the first system that can drive off-site middleboxes at near-native speed with stateful processing and the most comprehensive protection to date. Built upon commodity trusted hardware, Intel SGX, LightBox is the product of our systematic investigation of how to overcome the inherent limitations of secure enclaves using domain knowledge and customization. First, we introduce an elegant virtual network interface that allows convenient access to fully protected packets at line rate without leaving the enclave, as if from the trusted source network. Second, we provide complete flow state management for efficient stateful processing, by tailoring a set of data structures and algorithms optimized for the highly constrained enclave space. Extensive evaluations demonstrate that LightBox, with all security benefits, can achieve 10Gbps packet I/O, and that with case studies on three stateful middleboxes, it can operate at near-native speed.Comment: Accepted at ACM CCS 201

Experimental Infection of Brazilian Free-Tailed Bats (\u3ci\u3eTadarida brasiliensis\u3c/i\u3e) with Two Strains of SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is presumed to have originated from wildlife and shares homology with other bat coronaviruses. Determining the susceptibility of North American bat species to SARS-CoV-2 is of utmost importance for making decisions regarding wildlife management, public health, and conservation. In this study, Brazilian free-tailed bats (Tadarida brasiliensis) were experimentally infected with two strains of SARS-CoV-2 (parental WA01 and Delta variant), evaluated for clinical disease, sampled for viral shedding and antibody production, and analyzed for pathology. None of the bats (n = 18) developed clinical disease associated with infection, shed infectious virus, or developed histopathological lesions associated with SARS-CoV-2 infection. All bats had low levels of viral RNA in oral swabs, six bats had low levels of viral RNA present in the lungs during acute infection, and one of the four bats that were maintained until 28 days post-infection developed a neutralizing antibody response. These findings suggest that Brazilian free-tailed bats are permissive to infection by SARS-CoV-2, but they are unlikely to contribute to environmental maintenance or transmission