287 research outputs found
Successional changes in carbon storage are sustained in a temperate forest across different initiating disturbances
Managing forests for carbon (C) sequestration requires an understanding of how disturbance history shapes C pools and fluxes over successional time. At the University of Michigan Biological Station, we examined how two stand establishing disturbances influenced C pools and fluxes over 100+ years of succession, comparing these secondary forests with “legacy” late-successional stands encompassing ages and compositions that would be present in the absence of region-wide stand-replacing disturbance. Our work utilized measurements taken between 2014 and 2020 from separate experimental forest chronosequences initiated following clear-cut harvesting only or clear-cut harvesting and fire, along with three \u3e130-yr-old late successional stands comprising deciduous broadleaf, evergreen needleleaf, and mixed forest functional types. Net primary production (NPP) was relatively similar regardless of stand age and establishing disturbance, averaging 4.95 Mg C ha-1 yr-1, while heterotrophic soil respiration (Rsh) increased with age in the cut and burn chronosequence. The C pool and flux values of late successional stands varied by plant functional type, while total C pools averaged higher (271.78 Mg C ha-1) than those of chronosequence stands (140.45 Mg C ha-1). Estimates of net ecosystem balance varied depending on the approach used, with high and sometimes unrealistic Rsh values tipping net ecosystem production into C source territory, but temporally smoothed estimates of long-term C increment indicating instead that all chronosequence stands were C sinks. We conclude that late successional and old growth forests should be prioritized for protection and management, as they provide comparable C sequestration and superior storage to earlier successional forests and support a wide variety of other critical ecosystem services
Investigation of Throttleable Hybrid Rocket Engines with application to Attitude Control
The growing number of companies entering the private space sector has reignited the search for innovative propulsion techniques in an attempt to secure a position in the competitive launch vehicle industry. Hybrid Rocket Propulsion has been turned to as a cheaper and safer alternative to complex bi-propellant liquid rocket engines, appealing primarily to start-up companies in the private space sector. Previous research into Hybrid Rocket Propulsion has put focus primarily on combustion behavior and regression rate characteristics, with little literature regarding the ability to throttle such a Hybrid Rocket Engine. For Hybrid Rocket Propulsion to be more widely adopted, examination of the throttleability of Hybrid Rocket Engines must be undertaken. This research intends to examine the feasibility of throttling a Hybrid Rocket Engine through variation of oxidizer mass flow rate. The research will be focused on decreasing the engine response time (transient throttling region) through the modification of various engine components. These components primarily include injector design, fuel grain geometry, and metallic fuel grain additives. Through multiple ground test fires with varying engine component designs, an investigation into the prominent factors that dictate the transient throttling region of Hybrid Rocket Engines can be undertaken
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Artificial Light Increases Local Predator Abundance, Predation Rates, and Herbivory.
Human activity is rapidly increasing the radiance and geographic extent of artificial light at night (ALAN) leading to alterations in the development, behavior, and physiological state of many organisms. A limited number of community-scale studies investigating the effects of ALAN have allowed for spatial aggregation through positive phototaxis, the commonly observed phenomenon of arthropod movement toward light. We performed an open field study (without restricted arthropod access) to determine the effects of ALAN on local arthropod community composition, plant traits, and local herbivory and predation rates. We found strong positive phototaxis in 10 orders of arthropods, with increased (159% higher) overall arthropod abundance under ALAN compared to unlit controls. The arthropod community under ALAN was more diverse and contained a higher proportion of predaceous arthropods (15% vs 8%). Predation of immobilized flies occurred 3.6 times faster under ALAN; this effect was not observed during the day. Contrary to expectations, we also observed a 6% increase in herbivory under ALAN. Our results highlight the importance of open experimental field studies in determining community-level effects of ALAN
Evaluating Affordable Cranial Ultrasonography in East African Neonatal Intensive Care Units
Neuroimaging is a valuable diagnostic tool for the early detection of neonatal brain injury, but equipment and radiologic staff are expensive and unavailable to most hospitals in developing countries. We evaluated an affordable, portable ultrasound machine as a quantitative and qualitative diagnostic tool and to establish whether a novice sonographer could effectively operate the equipment and obtain clinically important information. Cranial ultrasonography was performed on term healthy, pre-term and term asphyxiated neonates in Rwandan and Kenyan hospitals. To evaluate the detection of ventriculomegaly and compression injuries, we measured the size of the lateral ventricles and corpus callosum. The images were also assessed for the presence of other cerebral abnormalities. Measurements were reliable across images, and cases of clinically relevant ventriculomegaly were detected. A novice sonographer had good-to-excellent agreement with an expert. This study demonstrates that affordable equipment and cranial ultrasound protocols can be used in low-resource settings to assess the newborn brain
Evaluating Affordable Cranial Ultrasonography in East African Neonatal Intensive Care Units
Neuroimaging is a valuable diagnostic tool for the early detection of neonatal brain injury, but equipment and radiologic staff are expensive and unavailable to most hospitals in developing countries. We evaluated an affordable, portable ultrasound machine as a quantitative and qualitative diagnostic tool and to establish whether a novice sonographer could effectively operate the equipment and obtain clinically important information. Cranial ultrasonography was performed on term healthy, pre-term and term asphyxiated neonates in Rwandan and Kenyan hospitals. To evaluate the detection of ventriculomegaly and compression injuries, we measured the size of the lateral ventricles and corpus callosum. The images were also assessed for the presence of other cerebral abnormalities. Measurements were reliable across images, and cases of clinically relevant ventriculomegaly were detected. A novice sonographer had good-to-excellent agreement with an expert. This study demonstrates that affordable equipment and cranial ultrasound protocols can be used in low-resource settings to assess the newborn brain
Factors Affecting the Radii of Close-in Transiting Exoplanets
The radius of an exoplanet may be affected by various factors, including
irradiation, planet mass and heavy element content. A significant number of
transiting exoplanets have now been discovered for which the mass, radius,
semi-major axis, host star metallicity and stellar effective temperature are
known. We use multivariate regression models to determine the dependence of
planetary radius on planetary equilibrium temperature T_eq, planetary mass M_p,
stellar metallicity [Fe/H], orbital semi-major axis a, and tidal heating rate
H_tidal, for 119 transiting planets in three distinct mass regimes. We
determine that heating leads to larger planet radii, as expected, increasing
mass leads to increased or decreased radii of low-mass (<0.5R_J) and high-mass
(>2.0R_J) planets, respectively (with no mass effect on Jupiter-mass planets),
and increased host-star metallicity leads to smaller planetary radii,
indicating a relationship between host-star metallicity and planet heavy
element content. For Saturn-mass planets, a good fit to the radii may be
obtained from log(R_p/R_J)=-0.077+0.450 log(M_p/M_J)-0.314[Fe/H]+0.671
log(a/AU)+0.398 log(T_eq/K). The radii of Jupiter-mass planets may be fit by
log(R_p/R_J)=-2.217+0.856 log(T_eq/K)+0.291 log(a/AU). High-mass planets' radii
are best fit by log(R_p/R_J)=-1.067+0.380 log(T_eq/K)-0.093
log(M_p/M_J)-0.057[Fe/H]+0.019 log(H_tidal/1x10^{20}). These equations produce
a very good fit to the observed radii, with a mean absolute difference between
fitted and observed radius of 0.11R_J. A clear distinction is seen between the
core-dominated Saturn-mass (0.1-0.5M_J) planets, whose radii are determined
almost exclusively by their mass and heavy element content, and the gaseous
envelope-dominated Jupiter-mass (0.5-2.0M_J) planets, whose radii increase
strongly with irradiating flux, partially offset by a power-law dependence on
orbital separation.Comment: 14 pages, 14 figures, accepted in A&
Immunoglobulin characteristics and RNAseq data of FcRL4+ B cells sorted from synovial fluid and tissue of patients with rheumatoid arthritis
Using Kuiper Belt Binaries to Constrain Neptune's Migration History
Approximately 10-20% of all Kuiper belt objects (KBOs) occupy mean-motion
resonances with Neptune. This dynamical configuration likely resulted from
resonance capture as Neptune migrated outward during the late stages of planet
formation. The details of Neptune's planetesimal-driven migration, including
its radial extent and the concurrent eccentricity evolution of the planet, are
the subject of considerable debate. Two qualitatively different proposals for
resonance capture have been proposed--migration-induced capture driven by
smooth outward evolution of Neptune's orbit and chaotic capture driven by
damping of the planet's eccentricity near its current semi-major axis. We
demonstrate that the distribution of comparable-mass, wide-separation binaries
occupying resonant orbits can differentiate between these two scenarios. If
migration-induced capture occurred, this fraction records information about the
formation locations of different populations of KBOs. Chaotic capture, in
contrast, randomizes the orbits of bodies as they are placed in resonance. In
particular, migration-induced capture produces the following signatures. The
2:1 resonance should contain a dynamically cold component, with inclinations
less than 5-10 degrees, having a binary fraction comparable to that among cold
classical KBOs. If the 3:2 resonance also hosts a cold component, its binary
fraction should be 20-30% lower than in the cold classical belt. Among cold 2:1
(and if present 3:2) KBOs, objects with eccentricities e < 0.2 should have a
binary fraction ~20% larger than those with e > 0.2. Searches for cold
components in the binary fractions of resonant KBOs are currently practical.
The additional migration-generated trends described here may be distinguished
with objects discovered by LSST. (Abstract abridged.)Comment: Accepted to ApJ, 15 pages, 4 figure
Optical and X-ray Transients from Planet-Star Mergers
We evaluate the prompt observational signatures of the merger between a
massive close-in planet (a `hot Jupiter') and its host star, events with an
estimated Galactic rate of ~0.1-1/yr. Depending on the ratio of the mean
density of the planet rho_p to that of the star rho_star, a merger results in
three possible outcomes. If rho_p/rho_star > 5, then the planet directly
plunges below the stellar atmosphere before being disrupted by tidal forces.
Dissipation of orbital energy creates a hot wake behind the planet, producing a
EUV/soft X-ray transient as the planet sinks below the stellar surface. The
peak luminosity L_X ~ 1e36 erg/s is achieved weeks-months prior to merger,
after which the stellar surface is enshrouded by an outflow. The final inspiral
is accompanied by an optical transient powered by the recombination of hydrogen
in the outflow, which peaks at L~1e37-38 erg/s on a timescale ~days. If instead
rho_planet/rho_star < 5, then Roche Lobe overflow occurs above the stellar
surface. For rho_p/rho_star < 1, mass transfer is stable, resulting the planet
being accreted on a relatively slow timescale. However, for 1 < rho_p/rho_star
< 5, mass transfer may instead be unstable, resulting in the planet being
dynamically disrupted into an accretion disk around the star. Super-Eddington
outflows from the disk power an optical transient with L~1e37-38 erg/s and
characteristic duration ~week-months. The disk itself becomes visible once the
accretion rate become sub-Eddington, resulting in a bolometric brightening and
spectral shift to the UV. Optical transients from planet merger events may
resemble classical novae, but are distinguished by lower ejecta mass and
velocity ~100s km/s, and by hard pre- and post-cursor emission, respectively.
Promising search strategies include combined optical, UV, and X-ray surveys of
nearby massive galaxies with cadences from days to months.Comment: 20 pages, 11 figures, 2 tables, submitted to MNRA
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