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65 results

Page 1 of 4

  • Southern Alps equilibrium line altitudes: four decades of observations show coherent glacier–climate responses and a rising snowline trend

  • Andrew M. Lorrey, Lauren Vargo, Heather Purdie, Brian Anderson, Nicolas J. Cullen, Pascal Sirguey, Andrew Mackintosh, Andrew Willsman, Gregor Macara, Warren Chinn
  • Journal:
    Journal of Glaciology / Volume 68 / Issue 272 / December 2022
    Published online by Cambridge University Press:
    12 April 2022, pp. 1127-1140
    • Article
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  • An end of summer snowline (EOSS) photographic dataset for Aotearoa New Zealand contains over four decades of equilibrium line altitude (ELA) observations for more than 50 index glaciers. This dataset provides an opportunity to create a climatological ELA reference series that has several applications. Our work screened out EOSS sites that had low temporal coverage and also removed limited observations when the official survey did not take place. Snowline data from 41 of 50 glaciers in the EOSS dataset were retained and included in a normalised master snowline series that spans 1977–2020. Application of the regionally representative normalised master snowline series in monthly and seasonally resolved climate response function analyses showed consistently strong relationships with austral warm-season temperatures for land-based stations west of the Southern Alps and the central Tasman Sea. There is a trend towards higher regional snowlines since the 1990s that has been steepening in recent decades. If contemporary decadal normalised master snowline series trends are maintained, the average Southern Alps snowline elevation will be displaced at least 200 m higher than normal by the 2025–2034 decade. More frequent extremely high snowlines are expected to drive more extreme cumulative mass-balance losses that will reduce the glacierised area of Aotearoa New Zealand.

  • 4 - Covariate Analysis in Clinical Anaesthesia

  • from Section 1 - Basic Principles
  • Edited by Pedro L. Gambús, Jan F. A. Hendrickx
  • Book:
    Personalized Anaesthesia
    Published online:
    03 December 2019
    Print publication:
    06 February 2020, pp 40-62

  • Summary

    The goal of pharmacological treatment is a desired response, known as the target effect (e.g. bispectral index of 50). An understanding of the concentration–response relationship (i.e. pharmacodynamics (PD)) can be used to predict the target concentration (e.g. propofol 4 mg/L) required to achieve this target effect in a typical individual [1]. Pharmacokinetic (PK) knowledge (e.g. clearance, volume) then determines the dose that will achieve the target concentration. Each individual, however, is somewhat different and there is variability associated with all parameters used in PK and PD equations (known as models). Covariate information (e.g. weight, age, pathology, drug interactions, pharmacogenomics) can be used to help predict the dose in a specific patient. The Holy Grail of clinical pharmacology is prediction of drug PK and PD in the individual patient (Fig. 4.1) and this requires knowledge of the covariates that contribute to variability [2].

  • Diagnostic stewardship of C. difficile testing: a quasi-experimental antimicrobial stewardship study

  • Alyssa B. Christensen, Viktorija O. Barr, David W. Martin, Morgan M. Anderson, Amanda K. Gibson, Brian M. Hoff, Sarah H. Sutton, Valerie Widmaier, Asra A. Salim, Christina Silkaitis, Chao Qi, Teresa R. Zembower, Michael J. Postelnick, Nathaniel J. Rhodes
  • Journal:
    Infection Control & Hospital Epidemiology / Volume 40 / Issue 3 / March 2019
    Published online by Cambridge University Press:
    21 February 2019, pp. 269-275
    Print publication:
    March 2019
  • Objective:

    We evaluated whether a diagnostic stewardship initiative consisting of ASP preauthorization paired with education could reduce false-positive hospital-onset (HO) Clostridioides difficile infection (CDI).

    Design:

    Single center, quasi-experimental study.

    Setting:

    Tertiary academic medical center in Chicago, Illinois.

    Patients:

    Adult inpatients were included in the intervention if they were admitted between October 1, 2016, and April 30, 2018, and were eligible for C. difficile preauthorization review. Patients admitted to the stem cell transplant (SCT) unit were not included in the intervention and were therefore considered a contemporaneous noninterventional control group.

    Intervention:

    The intervention consisted of requiring prescriber attestation that diarrhea has met CDI clinical criteria, ASP preauthorization, and verbal clinician feedback. Data were compared 33 months before and 19 months after implementation. Facility-wide HO-CDI incidence rates (IR) per 10,000 patient days (PD) and standardized infection ratios (SIR) were extracted from hospital infection prevention reports.

    Results:

    During the entire 52 month period, the mean facility-wide HO-CDI-IR was 7.8 per 10,000 PD and the SIR was 0.9 overall. The mean ± SD HO-CDI-IR (8.5 ± 2.0 vs 6.5 ± 2.3; P < .001) and SIR (0.97 ± 0.23 vs 0.78 ± 0.26; P = .015) decreased from baseline during the intervention. Segmented regression models identified significant decreases in HO-CDI-IR (Pstep = .06; Ptrend = .008) and SIR (Pstep = .1; Ptrend = .017) trends concurrent with decreases in oral vancomycin (Pstep < .001; Ptrend < .001). HO-CDI-IR within a noninterventional control unit did not change (Pstep = .125; Ptrend = .115).

    Conclusions:

    A multidisciplinary, multifaceted intervention leveraging clinician education and feedback reduced the HO-CDI-IR and the SIR in select populations. Institutions may consider interventions like ours to reduce false-positive C. difficile NAAT tests.

  • 3 - Mercury’s Crust and Lithosphere: Structure and Mechanics

  • Edited by Sean C. Solomon, Larry R. Nittler, Carnegie Institution of Washington, Washington DC, Brian J. Anderson
  • Book:
    Mercury
    Published online:
    10 December 2018
    Print publication:
    20 December 2018, pp 52-84

  • Summary

    The outermost “crust” and an underlying, compositionally distinct, and denser layer, the “mantle,” constitute the silicate portion of a terrestrial planet. The “lithosphere” is the planet’s high-strength outer shell. The crust records the history of shallow magmatism, which along with temporal changes in lithospheric thickness, provides information on a planet’s thermal evolution. We focus on the basic structure and mechanics of Mercury’s crust and lithosphere as determined primarily from gravity and topography data acquired by the MESSENGER mission. We first describe these datasets: how they were acquired, how the data are represented on a sphere, and the limitations of the data imparted by MESSENGER’s highly eccentric orbit.  We review different crustal thickness models obtained by parsing the observed gravity signal into contributions from topography, relief on the crust–mantle boundary, and density anomalies that drive viscous flow in the mantle. Estimates of lithospheric thickness from gravity–topography analyses are at odds with predictions from thermal models, thus challenging our understanding of Mercury’s geodynamics. We show that, like those of the Moon, Mercury's ellipsoidal shape and geoid are far from hydrostatic equilibrium, possibly the result of Mercury's peculiar surface temperature distribution and associated buoyancy anomalies and thermoelastic stresses in the interior.  

  • 9 - Impact Cratering of Mercury

  • Edited by Sean C. Solomon, Larry R. Nittler, Carnegie Institution of Washington, Washington DC, Brian J. Anderson
  • Book:
    Mercury
    Published online:
    10 December 2018
    Print publication:
    20 December 2018, pp 217-248

  • Summary

    Impact craters are the dominant landform on Mercury and range from the largest basins to the smallest young craters.  Peak-ring basins are especially prevalent on Mercury, although basins of all forms are far undersaturated, probably the result of the extensive volcanic emplacement of intercrater plains and younger smooth plains between about 4.1 and 3.5 Ga.  This chapter describes the geology of the two largest well-preserved basins, Caloris and Rembrandt, and the three smaller Raditladi, Rachmaninoff, and Mozart basins.  We describe analyses of crater size–frequency distributions and relate them to populations of asteroid impactors (Late Heavy Bombardment in early epochs and the near-Earth asteroid population observable today during most of Mercury’s history), to secondary cratering, and to exogenic and endogenic processes that degrade and erase craters.  Secondary cratering is more important on Mercury than on other solar system bodies and shaped much of the surface on kilometer and smaller scales, compromising our ability to use craters for relative and absolute age-dating of smaller geological units.  Failure to find “vulcanoids” and satellites of Mercury suggests that such bodies played a negligible role in cratering Mercury.  We describe an absolute cratering chronology for Mercury’s geological evolution as well as its uncertainties. 

  • 16 - Structure and Configuration of Mercury’s Magnetosphere

  • Edited by Sean C. Solomon, Larry R. Nittler, Carnegie Institution of Washington, Washington DC, Brian J. Anderson
  • Book:
    Mercury
    Published online:
    10 December 2018
    Print publication:
    20 December 2018, pp 430-460

  • Summary

    Mercury is the only terrestrial planet other than Earth that possesses a global magnetic field, and the unique solar wind environment of the inner heliosphere has profound consequences for both the structure and dynamics of its magnetosphere. The first in situ observations of Mercury and its space environment made four decades ago by the Mariner 10 spacecraft revealed a magnetic field that is sufficiently strong to stand off the solar wind and form a magnetosphere. Many new insights into Mercury’s magnetosphere were enabled by data returned by the MESSENGER spacecraft. The extensive magnetic field and particle observations allowed detailed characterization of the magnetospheric structure and configuration. MESSENGER magnetic field observations definitively determined the orientation, moment, and location of the internal planetary magnetic dipole field. Furthermore, these observations established the configuration of the magnetopause, bow shock, and magnetospheric current systems. Plasma observations revealed the distribution and composition of plasma in the magnetosphere. We review the geometry and dominant physical processes of Mercury’s unique magnetosphere inferred from MESSENGER data, including the solar wind environment, the shape and location of magnetospheric boundaries, and the fundamental regions and configuration of the magnetosphere and transport and heating of plasma therein. 

  • 15 - Understanding Mercury’s Exosphere: Models Derived from MESSENGER Observations

  • Edited by Sean C. Solomon, Larry R. Nittler, Carnegie Institution of Washington, Washington DC, Brian J. Anderson
  • Book:
    Mercury
    Published online:
    10 December 2018
    Print publication:
    20 December 2018, pp 407-429

  • Summary

    Mercury is surrounded by a tenuous exosphere in which particles travel on ballistic trajectories under the influence of a combination of gravity and solar radiation pressure. The densities are so small that the surface forms the exobase, and particles in the exosphere are more likely to collide with it rather than with each other. During the three flybys of Mercury by the Mariner 10 spacecraft in 1974–1975, the probe's Ultraviolet Spectrometer made measurements of hydrogen and helium and a tentative detection of oxygen. These observations were followed a decade later by discoveries with Earth-based telescopes of exospheric sodium and potassium, and still later of calcium, aluminum, and iron. In addition to characterizing sodium, calcium, and hydrogen in Mercury’s exosphere, the Mercury Atmospheric and Surface Composition Spectrometer instrument on the MESSENGER spacecraft detected magnesium, ionized calcium, aluminum, and manganese. Thus, the total inventory of confirmed exospheric neutral species now includes H, He, Na, K, Ca, Mg, Al, Fe, and Mn. This chapter summarizes both ground-based and space-based observations of Mercury’s exosphere that have been made from its discovery by Mariner 10 through the four Earth years of nearly continuous orbital observations by the MESSENGER spacecraft.

  • 6 - The Geologic History of Mercury

  • Edited by Sean C. Solomon, Larry R. Nittler, Carnegie Institution of Washington, Washington DC, Brian J. Anderson
  • Book:
    Mercury
    Published online:
    10 December 2018
    Print publication:
    20 December 2018, pp 144-175

  • Summary

    We assess Mercury’s geologic history, focusing on the distribution and origin of terrain types and an overview of Mercury’s evolution from the pre-Tolstojan through the Kuiperian Period. We review evidence for the nature of Mercury’s early crust, including the possibility that a substantial portion formed by the global eruption of lavas generated by partial melting during and after overturn of the crystalline products of magma ocean cooling, whereas a much smaller fraction of the crust may have been derived from crystal flotation in such a magma ocean. The early history of Mercury may thus have been similar to that of the other terrestrial planets, with much of the crust formed through volcanism, in contrast to the flotation-dominated crust of the Moon. Small portions of Mercury’s early crust may still be exposed in a heavily modified and brecciated form; the majority of the surface is dominated by intercrater plains (Pre-Tolstojan and Tolstojan in age) and smooth plains (Tolstojan and Calorian) that formed through a combination of volcanism and impact events. As effusive volcanism waned in the Calorian, explosive volcanism continued at least through the Mansurian Period; the Kuiperian Period was dominated by impact events and the formation of hollows. 

  • 1 - The MESSENGER Mission: Science and Implementation Overview

  • Edited by Sean C. Solomon, Larry R. Nittler, Carnegie Institution of Washington, Washington DC, Brian J. Anderson
  • Book:
    Mercury
    Published online:
    10 December 2018
    Print publication:
    20 December 2018, pp 1-29

  • Summary

    MESSENGER was the first spacecraft to visit the planet Mercury in more than three decades and the first to orbit the solar system’s innermost planet, and it provided the first global observations of Mercury’s surface, interior, exosphere, magnetosphere, and heliospheric environment. This chapter begins with summaries of the objectives for the MESSENGER mission and the design of the spacecraft, payload instruments, and orbit selected to achieve those objectives. We then describe the procedures adopted to optimize the scientific return from the complex series of orbital data acquisition operations that MESSENGER followed. An overview is given next of the primary MESSENGER mission, including the three Mercury flybys prior to orbit insertion and the first year of Mercury orbital observations. We then outline the rationale for and accomplishments of MESSENGER’s first extended mission, conducted over the second year of orbital operations, and MESSENGER’s second extended mission, conducted over the final two years of orbital operations. The second extended mission included a distinctive low-altitude campaign completed at the culmination of the mission. A concluding section briefly introduces the other chapters of this book.

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