Search for: All records

Abstract Background and aimsUrbanization is a stressor that can exacerbate climate change impacts. Urban ecosystems are hotter and drier than their rural counterparts, due to a lack of vegetation and an abundance of impermeable surfaces that characterize cities. Urban greening projects can reverse these trends through microclimate cooling and humidification. Vegetation and aridity gradients have the capacity to modify how neighboring plants interact with one another: plant neighbors may benefit one another through facilitation in hot and dry environments but experience more competition in cooler and more humid areas. We examined how herbaceous plants can ameliorate heat and water stress across an established urban aridity gradient in the greater Los Angeles area. MethodsWe measured 162 plants at 81 plots in 27 sites across a well-established urban-to-rural gradient. In each plot, we identified two pre-existing focal individuals: we removed the neighboring plants for one of these, and left the community intact around the other. We then measured growth of the two focal plants and placed temperature and humidity sensors near each. We also measured light above and below the canopy and total precipitation. ResultsWe found that across the urban aridity gradient, the hottest sites experienced the most vegetative microclimate amelioration. We also found that neighboring plants had positive effects on growth (facilitation), but only when neighbors also cooled microclimate temperature and decreased microclimate vapor pressure deficit (VPD). Facilitation between neighbors was also greatest at the sites with the least precipitation. ConclusionPrevious studies have shown that plants may compete for limited resources but we show that interactions can shift to be more facilitative along an urban aridity gradient. Future work should use this information to augment restoration plans in urban environments. 

This paper evaluates the behavior of a single rigid ellipsoidal particle suspended in homogeneous viscous flow with a power-law generalized Newtonian fluid rheology using a custom-built finite element analysis (FEA) simulation. The combined effects of the shear-thinning fluid rheology, the particle aspect ratio, the initial particle orientation, and the shear-extensional rate factor in various homogeneous flow regimes on the particles dynamics and surface pressure evolution are investigated. The shear-thinning fluid behavior was found to modify the particle’s trajectory and alter the particle’s kinematic response. Moreover, the pressure distribution over the particle’s surface is significantly reduced by the shear-thinning fluid rheology. The FEA model is validated by comparing results of the Newtonian case with results obtained from the well-known Jeffery’s analytical model. Furthermore, Jeffery’s model is extended to define the particle’s trajectory in a special class of homogeneous Newtonian flows with combined extension and shear rate components typically found in axisymmetric nozzle flow contractions. The findings provide an improved understanding of key transport phenomenon related to physical processes involving fluid–structure interaction such as that which occurs within the flow field developed during material extrusion–deposition additive manufacturing of fiber reinforced polymeric composites. These results provide insight into important microstructural formations within the print beads. 

White oak, a keystone species of the broadleaf forests of the North American Midwest, has a significant role in providing ecosystems services in a region experiencing warming and increasingly pluvial conditions. A one- hundred-year-old white oak stand in an arboretum, along with two second growth (~200-year-old) stands from Northeast Ohio have consistently responded positively to summer (June-July) precipitation over the past century, whereas four nearby old growth sites (>300 years old) have lost their moisture sensitivity since about the mid 1970s. This “fading drought signal,” which has been previously reported, appears to be more a result of the legacy of land use at the individual sites rather than tree age. The younger oak stands and their relative sustained drought sensitivity is also related to their history of recently attaining the canopy and similar responses associated with intervals of selective logging. All sites are strongly, negatively correlated with summer (June- July) maximum monthly temperatures and in general the maximum temperatures are negatively correlated with precipitation in those months. Future warming in the Midwest is projected to see increases in spring precipitation and likely decreases in late summer precipitation linked to a northward migration of the North American Westerly Jet. This projected decrease in summer precipitation coupled with an increase in maximum and min- imum summer temperatures in the coming decades would increase the moisture stress on these trees. Our ex- amination of these varying climate responses with respect to site characteristics and forest age can help future assessments of tree health and the forest’s ability to sequester carbon, as well as facilitate efforts to reconstruct climate by using a range of tree sites for intervals when sensitivity in old growth sites is lost. 

Many viruses eject their DNA via a nanochannel in the viral shell, driven by internal forces arising from the high-density genome packing. The speed of DNA exit is controlled by friction forces that limit the molecular mobility, but the nature of this friction is unknown. We introduce a method to probe the mobility of the tightly confined DNA by measuring DNA exit from phage phi29 capsids with optical tweezers. We measure extremely low initial exit velocity, a regime of exponentially increasing velocity, stochastic pausing that dominates the kinetics and large dynamic heterogeneity. Measurements with variable applied force provide evidence that the initial velocity is controlled by DNA–DNA sliding friction, consistent with a Frenkel–Kontorova model for nanoscale friction. We confirm several aspects of the ejection dynamics predicted by theoretical models. Features of the pausing suggest that it is connected to the phenomenon of ‘clogging’ in soft matter systems. Our results provide evidence that DNA–DNA friction and clogging control the DNA exit dynamics, but that this friction does not significantly affect DNA packaging. 

ABSTRACT Recent works have suggested that energy balance spectral energy distribution (SED) fitting codes may be of limited use for studying high-redshift galaxies for which the observed ultraviolet and far-infrared emission are offset (spatially ‘decoupled’). It has been proposed that such offsets could lead energy balance codes to miscalculate the overall energetics, preventing them from recovering such galaxies’ true properties. In this work, we test how well the SED fitting code magphys can recover the stellar mass, star formation rate (SFR), specific SFR, dust mass, and luminosity by fitting 6706 synthetic SEDs generated from four zoom-in simulations of dusty, high-redshift galaxies from the FIRE project via dust continuum radiative transfer. Comparing our panchromatic results (using wavelengths 0.4–500 μm, and spanning 1 < z < 8) with fits based on either the starlight ($$\lambda _\mathrm{eff} \le 2.2\, \mu$$m) or dust ($$\ge 100\, \mu$$m) alone, we highlight the power of considering the full range of multiwavelength data alongside an energy balance criterion. Overall, we obtain acceptable fits for 83 per cent of the synthetic SEDs, though the success rate falls rapidly beyond z ≈ 4, in part due to the sparser sampling of the priors at earlier times since SFHs must be physically plausible (i.e. shorter than the age of the universe). We use the ground truth from the simulations to show that when the quality of fit is acceptable, the fidelity of magphys estimates is independent of the degree of UV/FIR offset, with performance very similar to that previously reported for local galaxies. 

Abstract We observed a terrestrial gamma‐ray flash (TGF) shortly after the return stroke in a positive cloud‐to‐ground (+CG) flash during a 2025 winter thunderstorm in the Hokuriku region of Japan. The event was observed with multiple gamma‐ray detectors and radio antenna systems. We identify several distinctions between our event and typical +CG lightning, including: an inverted tripolar storm charge structure, a peak current (190 kA) much higher than reported averages, shorter‐than‐average leader duration between first radio source and return stroke (3.6 vs. 56 ms), and unusual symmetry in the return stroke RF waveform relating to rise and fall time. Many of these differences are consistent with disparities between usual −CG lightning and energetic compact strokes (ECSs), and may be evidence of a positive‐polarity class of ECS events. In addition, we find our TGF observation to be a distinctly short and bright event among others reported in literature.