THE STRUCTURE, PERFORMANCE, AND SUSTAINABILITY OF AGRICULTURE IN THE MOUNTAIN REGION

Farmers in the Mountain Region-in both metro and nonmetro areas-face growth in population and nonfarm employment that affects land use and how farmers operate their businesses. Even in remote locations, people moving to amenity areas may result in farmers changing their operations. Sustainable agriculture, already practiced by Mountain Region farmers to some extent, may help farming to continue. Nonfarm people also have an interest in the continuation of agriculture and the adaptation of sustainable practices, in order to help preserve the amenities that make the region attractive to migrants. Growth in the region does provide some benefits to farmers, however. Growth can help keep the value of farmland up through nonfarm demand for land. In addition, the greater availability of jobs means that off-farm work is available to households operating farms. Off-farm work is particularly important, given the concentrated distribution of farm income.Production Economics,

Two-Loop Bethe Logarithms

We calculate the two-loop Bethe logarithm correction to atomic energy levels in hydrogen-like systems. The two-loop Bethe logarithm is a low-energy quantum electrodynamic (QED) effect involving multiple summations over virtual excited atomic states. Although much smaller in absolute magnitude than the well-known one-loop Bethe logarithm, the two-loop analog is quite significant when compared to the current experimental accuracy of the 1S-2S transition: it contributes -8.19 and -0.84 kHz for the 1S and the 2S state, respectively. The two-loop Bethe logarithm has been the largest unknown correction to the hydrogen Lamb shift to date. Together with the ongoing measurement of the proton charge radius at the Paul Scherrer Institute its calculation will bring theoretical and experimental accuracy for the Lamb shift in atomic hydrogen to the level of 10^(-7).Comment: 4 pages, RevTe

On the transonic aerodynamics of a compressor blade row

Linearized analyses have been carried out for the induced velocity and pressure fields within a compressor blade row operating in an infinite annulus at transonic Mach numbers of the flow relative to the blades. In addition, the relationship between the induced velocity and the shape of the mean blade surface has been determined. A computational scheme has been developed for evaluating the blade mean surface ordinates and surface pressure distributions. The separation of the effects of a specified blade thickness distribution from the effects of a specified distribution of the blade lift has been established. In this way, blade mean surface shapes that are necessary for the blades to be locally nonlifting have been computed and are presented for two examples of blades with biconvex parabolic arc sections of radially tapering thickness. Blade shapes that are required to achieve a zero thickness, uniform chordwise loading, constant work spanwise loading are also presented for two examples. In addition, corresponding surface pressure distributions are given. The flow relative to the blade tips has a high subsonic Mach number in the examples that have been computed. The results suggest that at near-sonic relative tip speeds the effective blade shape is dominated by the thickness distribution, with the lift distribution playing only a minor role

Probability Bifurcations of L\'evy Bridges

A L\'evy bridge--a stable L\'evy stochastic process conditioned to arrive at some state at some later time--can exhibit behavior differing dramatically from the more widely studied case of conditioned Brownian (Gaussian) processes. This difference stems from a structural change in the conditioned probability density at intermediate times as the arrival position varies. This structural shift gives rise to a distinction between "short" and "long" jumps. We explore the consequences of this idea for the statistics of L\'evy vs. Brownian bridges, with applications to the analysis of the boundary-crossing problem and a computationally useful representation of L\'evy bridges that does not carry over directly from the Gaussian case.Comment: 5 pages, 7 figure

Orbiter Entry Aeroheating Working Group Viscous CFD Boundary Layer Transition Trailblazer Solutions

Boundary layer transition correlations for the Shuttle Orbiter have been previously developed utilizing a two-layer boundary layer prediction technique. The particular two-layer technique that was used is limited to Mach numbers less than 20. To allow assessments at Mach numbers greater than 20, it is proposed to use viscous CFD to the predict boundary layer properties. This report addresses if the existing Orbiter entry aeroheating viscous CFD solutions, which were originally intended to be used for heat transfer rate predictions, adequately resolve boundary layer edge properties and if the existing two-layer results could be leveraged to reduce the number of needed CFD solutions. The boundary layer edge parameters from viscous CFD solutions are extracted along the wind side centerline of the Space Shuttle Orbiter at reentry conditions, and are compared with results from the two-layer boundary layer prediction technique. The differences between the viscous CFD and two-layer prediction techniques vary between Mach 6 and 18 flight conditions and Mach 6 wind tunnel conditions, and there is not a straightforward scaling between the viscous CFD and two-layer values. Therefore: it is not possible to leverage the existing two-layer Orbiter flight boundary layer data set as a substitute for a viscous CFD data set; but viscous CFD solutions at the current grid resolution are sufficient to produce a boundary layer data set suitable for applying edge-based boundary layer transition correlations

Is Pre-Kindergarten an Educational Panacea? A Systematic Review and Meta-Analysis of Scaled-Up Pre-Kindergarten in the United States

We synthesize the existing research and compute meta-analytic averages for the effects of scaled-up, publicly funded pre-kindergarten (pre-K) programs on student pre-kindergarten achievement in math and reading. Other systematic reviews of pre-K programs have focused on the effects for specific groups of students from various types of pre-K programs. We add to the literature by focusing on scaled-up pre-K often provided at the state level, which is of growing policy interest. Scaled-up programs are large state or district run programs that are available to a large portion of children before they enter kindergarten. We limit our analysis to state and districtwide pre-K programs in the United States from 2000 through 2016. In order to obtain the most accurate effect estimates, we restrict our analysis to experimental and quasi-experimental research designs with the highest internal validity. We synthesize the short-term cognitive effects of pre-K and find large positive effects of scaled-up public pre-K programs on student pre-kindergarten test scores. In particular, we find that the overall effect on math scores is over a third of a standard deviation and the overall effect on reading scores is three-fifths of a standard deviation. This review is restricted to studies focused on short term results of pre-K programs; our search uncovered only one study rigorously assessing the impacts of scaled-up pre-K programs on student achievement after kindergarten. More research is needed on the sustained effects of pre-K as policymakers debate whether to expand or adopt such programs

Significant initial results from the environmental measurements experiment on ATS-6

The Applications Technology Satellite (ATS-6), launched into synchronous orbit on 30 May 1974, carried a set of six particle detectors and a triaxial fluxgate magnetometer. The particle detectors were able to determine the ion and electron distribution functions from 1 to greater than 10 to the 8th power eV. It was found that the magnetic field is weaker and more tilted than predicted by models which neglect internal plasma and that there is a seasonal dependence to the magnitude and tilt. ATS-6 magnetic field measurements showed the effects of field-aligned currents associated with substorms, and large fluxes of field-aligned particles were observed with the particle detectors. Encounters with the plasmasphere revealed the existence of warm plasma with temperatures up to 30 eV. A variety of correlated waves in both the particles and fields were observed: pulsation continuous oscillations, seen predominantly in the plasmasphere bulge; ultralow frequency (ULF) standing waves; ring current proton ULF waves; and low frequency waves that modulate the energetic electrons. In additon, large scale waves on the energetic-ion-trapping boundary were observed, and the intensity of energetic electrons was modulated in association with the passage of sector boundaries of the interplanetary magnetic field

Upper Limits on the Continuum Emission from Geminga at 74 and 326 MHz

We report a search for radio continuum emission from the gamma-ray pulsar Geminga. We have used the VLA to image the location of the optical counterpart of Geminga at 74 and 326 MHz. We detect no radio counterpart. We derive upper limits to the pulse-averaged flux density of Geminga, taking diffractive scintillation into account. We find that diffractive scintillation is probably quenched at 74 MHz and does not influence our upper limit, S < 56 mJy (2\sigma), but that a 95% confidence level at 326 MHz is S < 5 mJy. Owing to uncertainties on the other low-frequency detections and the possibility of intrinsic variability or extrinsic variability (refractive interstellar scintillation) or both, our non-detections are nominally consistent with these previous detections.Comment: 8 pages, LaTeX2e with AASTeX 4.0, 3 figures; to be published in Ap

Uncovering Bugs in Distributed Storage Systems during Testing (not in Production!)

Testing distributed systems is challenging due to multiple sources of nondeterminism. Conventional testing techniques, such as unit, integration and stress testing, are ineffective in preventing serious but subtle bugs from reaching production. Formal techniques, such as TLA+, can only verify high-level specifications of systems at the level of logic-based models, and fall short of checking the actual executable code. In this paper, we present a new methodology for testing distributed systems. Our approach applies advanced systematic testing techniques to thoroughly check that the executable code adheres to its high-level specifications, which significantly improves coverage of important system behaviors. Our methodology has been applied to three distributed storage systems in the Microsoft Azure cloud computing platform. In the process, numerous bugs were identified, reproduced, confirmed and fixed. These bugs required a subtle combination of concurrency and failures, making them extremely difficult to find with conventional testing techniques. An important advantage of our approach is that a bug is uncovered in a small setting and witnessed by a full system trace, which dramatically increases the productivity of debugging