Forest Water Use is Increasingly Decoupled from Water Availability Even During Severe Drought

Context: Key to understanding forest water balances is the role of tree species regulating evapotranspiration (ET), but the synergistic impact of forest species composition, topography, and water availability on ET and how this shapes drought sensitivity across the landscape remains unclear.Objectives: Our aims were to quantify (1) the effect of forest composition and topography including elevation and hillslope gradients on the relationship between ET and water availability, and (2) whether the relationship has changed over time. Methods: We used remotely sensed Landsat and MODIS ET to quantify forest ET across the Blue Ridge ecoregion of the southeastern USA. Then quantified metrics describing ET responses to water availability and trends in responses over time and assessed how these metrics varied across elevation, hillslope, and forest composition gradients. Results: We demonstrated forest ET is becoming less constrained by water availability at the expense of lateral flow. Drought impacts on ET diverged along elevation and hillslope gradients, and that divergence was more pronounced with increasingly severe drought, indicating high elevation and drier, upslope regions tend to maintain ET rates even during extreme drought. We identified a decoupling of ET from water availability over time, and found this process was accelerated at higher elevations and in areas with more diffuse-porous trees. Conclusions: Given the large proportion of forests on the landscape distributed across high elevation and upslope positions, reductions in downslope water availability could be widespread, amplifying vulnerability of runoff, the health of downslope vegetation, and aquatic biodiversity.

How the interplay of molecular and colloidal scales controls drying of microgel dispersions

Bringing an aqueous dispersion or solution into open air leads to water evaporation. The resulting drying process initiates the buildup of spatial heterogeneities, as nonvolatile solutes and colloids concentrate. Such composition gradients associate with mesostructure gradients, which, in turn, impact flows within these multicomponent systems. In this work, we investigate the drying of microgel dispersions in respect to two reference systems, a colloidal dispersion and a polymer solution, which, respectively, involve colloidal and molecular length scales. We evidence an intermediate behavior in which a film forms at the air/liquid interface and is clearly separated from bulk by a sharp drying front. However, complex composition and mesostructure gradients develop throughout the drying film, as evidenced by Raman and small-angle X-ray scattering mapping. We show that this results from the soft colloidal structure of microgel, which allows them to interpenetrate, deform, and deswell. As a result, water activity and water transport are drastically decreased in the vicinity of the air/liquid interface. This notably leads to diffusional drying kinetics that are nearly independent on the air relative humidity. The interplay between water fraction, water activity, and mesostructure on water transport is generic and, thus, shown to be pivotal in order to master evaporation in drying complex fluids.

Fabrication, Microstructure and Properties of Nickel/Epoxy Resin Functionally Graded Materials With Magnetic-Field-Driving Method

Functionally graded materials are attracting more attentions because of the continuously varying properties in different locations. How to design and fabricate FGMs has become a key and difficult point. In this paper, a magnetic-field-driving method is developed to prepare Ni/epoxy resin FGMs by moving a narrow magnetic field from one end of the sample to the other end with the moving direction perpendicular to the field direction. Ni follows the moving of the magnetic field, and a gradient distribution is obtained. The composition gradients are influenced by Ni content, moving velocity, and also cycle times. The results illustrate that this magnetic-field-driving method is an effective way to prepare FGMs, which is very promising into scientific and technological applications.

Emerging Capabilities for the High-Throughput Characterization of Structural Materials

Structural materials have lagged behind other classes in the use of combinatorial and high-throughput (CHT) methods for rapid screening and alloy development. The dual complexities of composition and microstructure are responsible for this, along with the need to produce bulk-like, defect-free materials libraries. This review evaluates recent progress in CHT evaluations for structural materials. High-throughput computations can augment or replace experiments and accelerate data analysis. New synthesis methods, including additive manufacturing, can rapidly produce composition gradients or arrays of discrete alloys-on-demand in bulk form, and new experimental methods have been validated for nearly all essential structural materials properties. The remaining gaps are CHT measurement of bulk tensile strength, ductility, and melting temperature and production of microstructural libraries. A search strategy designed for structural materials gains efficiency by performing two layers of evaluations before addressing microstructure, and this review closes with a future vision of the autonomous, closed-loop CHT exploration of structural materials. Expected final online publication date for the Annual Review of Materials Science, Volume 51 is August 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The promise and limitations of improved-accuracy gravity field measurements for Uranus and Neptune

<p>Uranus and Neptune present unique challenges to planetary modelers. The<br>composition of the so-called ice giants is very uncertain, even more so than the<br>composition of the gas giants. For instance, it is far from clear that either<br>planet's composition is dominated by water. Instead, the composition of Uranus and<br>Neptune likely includes water and other refractory elements in large quantities as<br>well as a substantial H/He envelope. Furthermore, formation models also predict<br>that composition gradients are likely in the interiors of these planets, rather<br>than a neat differentiation into layers of homogeneous composition. (See Helled<br>and Fortney 2020 and references within.)</p><p>A key question that impacts the science case for a potential orbiting mission to<br>Uranus or Neptune is how will more precise measurements of the gravitational field<br>better constrain either planet's interior density profile and composition.<br>Surprisingly, there is yet no published answer to this question.  Here, we present<br>new work that explores this issue, using a Bayesian framework that allows<br>exploration of a wide range of interior density profiles.</p><p>Our approach, which builds off our previous work for Saturn (Movshovitz et al.,<br>2020) and that of others  (e.g. Marley et al., 1995, Helled et al., 2011) takes a<br>relatively unbiased view of the interior structure by employing so-called<br>empirical density profiles. A parameterization is applied to the density profiles<br>directly (via mathematical base functions) instead of to an assumed layered<br>composition (H/He, water, rocks). While some of these empirical density profiles<br>may imply unrealistic compositions, they can also probe solutions that would be<br>missed by the standard layered-composition approach.</p><p>Here we will present models of Uranus and Neptune constructed with this approach,<br>and ask two questions: 1) How large is the space of possible solutions today? 2)<br>How much will it be reduced should a future mission to Uranus and Neptune improve<br>the precision on their gravity field measurements by several orders of magnitude,<br>to the level now available for Jupiter and Saturn?</p>

Saturn's Diffuse Core from Ring Seismology

<p>Gravity field measurements only weakly constrain the deep interiors of Jupiter and Saturn, stymieing efforts to measure the mass and compactness of these planets' cores, crucial properties for understanding their formation pathways and evolution. However, studies of Saturn's rings by Cassini have revealed waves driven by pulsation modes within Saturn, offering independent seismic probes of Saturn's interior. The observations reveal gravity mode (g mode) pulsations that indicate that a part of Saturn's interior is stably stratified by composition gradients, and the g mode frequencies directly probe the buoyancy frequency within the planet.</p><p>We compare structure models with gravity and new seismic measurements from Cassini to show that the data can only be explained by a diffuse, stably stratified core-envelope transition region in Saturn extending to approximately 60% of the planet's radius. This predominantly stable interior imposes significant constraints on Saturn's intrinsic magnetic field generation. The gradual distribution of heavy elements required by the seismology constrains mixing processes at work in Saturn, and it may reflect the planet's primordial structure and accretion history.</p>