•The question of the linkages between food security and conflict has been widely and inconclusively debated for many years.•Increasing availability of fine-grained, high-quality data combined with ...new econometric approaches has led to new findings.•Causal and substantive links exist between food security and violent conflict, spanning the individual up to global levels.•For policy makers, closing data gaps will be essential for producing effective food security and peacebuilding policies.
During the previous decade, there has been an increased focus on the role of food security in processes of armed conflict, both in the academic and policy communities. While the policy community has pushed forward with new programs, the academic debate about the causal linkages between food security and conflict remains contested. This article examines the endogeneity that characterizes the coupling between food (in)security and conflict and makes three contributions. First, we define conflict and food security using the Uppsala Conflict Data Program and the FAO databases, and illustrate how intervening factors influence the relationship between conflict and food security at the micro and macro levels. Second, we provide a comprehensive review of the literature on the linkages between food security and conflict, focusing on findings that account for endogeneity issues and have a causal interpretation. Third, we highlight key data issues related to conflict and food security, and chart ways forward to collect new and better data that can help to fill existing academic gaps and support policymaking.
Context
The ecological literature is filled with studies highlighting the importance of both habitat loss and fragmentation on biodiversity. The patch concept has been central to these findings, ...being also at the heart of many ecological theories. Recently, the habitat amount hypothesis has been proposed as an alternative, where the patch concept is put to a rest, and both patch size and patch isolation effects on species richness are reduced to a single gradient: habitat loss in the landscape.
Objectives
As this theory stated clear predictions that could be experimentally tested, many formal tests of the hypothesis have been published recently and this study aims at synthesizing their results.
Methods
A meta-analysis of 13 tests of the habitat amount hypothesis was conducted, to produce a single combined test of the theory.
Results
The 13 tests combined suggest that effects of patch size and isolation, while controlling for habitat amounts, do exist although their overall effect is weak (r = 0.158).
Conclusions
Literal interpretations of the habitat amount hypothesis, where patch size and isolation have absolutely no effect on species richness, are probably oversimplifications of the processes at work. Still, the theory could prove useful as a baseline of the effects of habitat loss, against which patch size and isolation effects must be contrasted.
This book presents a state-of-the-art, robust, and adaptable process, the Theory of Being, that offers strategies for working across Difference, and for embarking on constructive dialogue around the ...issues that drive us apart, both individually and collectively. Whether around racial, gender, and/or social class inequity, core beliefs, uses of power or other points of cultural conflict, this book offers a research-validated approach, developed and refined over twenty years, to engage in difficult dialogues. "The Theory of Being" includes personal, relational, and community practices that support individuals and communities to better work through the difficult dialogues necessary to transform systems of structural inequity. It describes and offers applications of Being to help the reader understand and apply principles and practices that invite openness to controversy through facilitating deep reflection and shifting the focus of conflict from individuals to centering the issue of contention as a Third Thing about which participants can more safely express experiences and emotions. Via cases and narratives, the editors and contributors demonstrate how, through productively situating feelings of vulnerability and anger, individuals, organizations, and communities can work together to continuously evolve responsive, inclusive, and equitable practices that value social and cultural differences. This book focuses on strategies for the "how" we interact, demonstrating an orientation to process rather than prioritizing outcomes. A process-orientation can increase the quality of interaction between individuals, and the likelihood of traversing problems associated with controversial social difference in ways that result in sustainable strategies to disrupt systems of oppression. A range of applications exemplify this approach throughout the text. The primary audience is higher education leaders and leaders-in-training including student affairs professional staff, campus administrators, higher education and student affairs faculty, and undergraduate and graduate students. However, the approach has broad implications for any persons who want to productively engage across Difference in their personal and/or professional lives. Foreword written by Parker J. Palmer.
Globally, rising temperatures have resulted in numerous examples of poleward shifts in species distribution patterns with accompanying changes in community structure and ecosystem processes. In the ...Gulf of Mexico, higher mean temperatures and less frequent winter freezes have led to the expansion of tropics-associated marine organisms. Our objectives were to quantify changing environmental conditions and the poleward expansion of the common snook Centropomus undecimalis into the Cedar Keys area of Florida, USA (29 deg N). The snook is an economically and recreationally important sport fish found from southern Brazil to south Florida. Cedar Key and the Lower Suwannee River are north of the snook's historically documented range, likely due to lethal water temperatures during winter. Using data from a long-term monitoring program, we report an increase in catches of snook in this area since 2007. The spatial and temporal expansion of the species began with adult fish in 2007. By 2018, snook of all sizes were found in the region, and we found strong evidence of local reproduction during 2016-2018. The locations of nursery habitat and winter thermal refuges (e.g., freshwater springs) need to be identified and have implications for land-use policy and minimum-flow regulations for rivers. The arrival of the snook in the northern Gulf of Mexico could affect food web ecology and habitat interactions among estuarine predators, and future studies should evaluate snook's food habits and competitive interactions with resident fishes in this expanded range. Our study provides an example of how species range expansions due to changing temperatures should result in new research priorities to evaluate impacts of climate change on coastal systems.
Abstract
In many applications, one works with neural network models trained by someone else. For such pretrained models, one may not have access to training data or test data. Moreover, one may not ...know details about the model, e.g., the specifics of the training data, the loss function, the hyperparameter values, etc. Given one or many pretrained models, it is a challenge to say anything about the expected performance or quality of the models. Here, we address this challenge by providing a detailed meta-analysis of hundreds of publicly available pretrained models. We examine norm-based capacity control metrics as well as power law based metrics from the recently-developed Theory of Heavy-Tailed Self Regularization. We find that norm based metrics correlate well with reported test accuracies for well-trained models, but that they often cannot distinguish well-trained versus poorly trained models. We also find that power law based metrics can do much better—quantitatively better at discriminating among series of well-trained models with a given architecture; and qualitatively better at discriminating well-trained versus poorly trained models. These methods can be used to identify when a pretrained neural network has problems that cannot be detected simply by examining training/test accuracies.
Electroosmotic flow (EOF) is used to pump solutions through microfluidic devices and capillary electrophoresis columns. We describe here an EOF pump based on membrane EOF rectification, an ...electrokinetic phenomenon we recently described. EOF rectification requires membranes with asymmetrically shaped pores, and conical pores in a polymeric membrane were used here. We show here that solution flow through the membrane can be achieved by applying a symmetrical sinusoidal voltage waveform across the membrane. This is possible because the alternating current (AC) carried by ions through the pore is rectified, and we previously showed that rectified currents yield EOF rectification. We have investigated the effect of both the magnitude and frequency of the voltage waveform on flow rate through the membrane, and we have measured the maximum operating pressure. Finally, we show that operating in AC mode offers potential advantages relative to conventional DC-mode EOF pumps.
Ion current rectification (ICR) refers to the asymmetric potential-dependent rate of the passage of solution ions through a nanopore, giving rise to electrical current–voltage characteristics that ...mimic those of a solid-state electrical diode. Since the discovery of ICR in quartz nanopipettes two decades ago, synthetic nanopores and nanochannels of various geometries, fabricated in membranes and on wafers, have been extensively investigated to understand fundamental aspects of ion transport in highly confined geometries. It is now generally accepted that ICR requires an asymmetric electrical double layer within the nanopore, producing an accumulation or depletion of charge-carrying ions at opposite voltage polarities. Our research groups have recently explored how the voltage-dependent ion distributions and ICR within nanopores can induce novel nanoscale flow phenomena that have applications in understanding ionics in porous materials used in energy storage devices, chemical sensing, and low-cost electrical pumping of fluids. In this Account, we review our most recent investigations on this topic, based on experiments using conical nanopores (10–300 nm tip opening) fabricated in thin glass, mica, and polymer membranes. Measurable fluid flow in nanopores can be induced either using external pressure forces, electrically via electroosmotic forces, or by a combination of these two forces. We demonstrate that pressure-driven flow can greatly alter the electrical properties of nanopores and, vice versa, that the nonlinear electrical properties of conical nanopores can impart novel and useful flow phenomena. Electroosmotic flow (EOF), which depends on the magnitude of the ion fluxes within the double layer of the nanopore, is strongly coupled to the accumulation/depletion of ions. Thus, the same underlying cause of ICR also leads to EOF rectification, i.e., unequal flows occurring for the same voltage but opposite polarities. EOF rectification can be used to electrically pump fluids with very precise control across membranes containing conical pores via the application of a symmetric sinusoidal voltage. The combination of pressure and asymmetric EOF can also provide a means to generate new nanopore electrical behaviors, including negative differential resistance (NDR), in which the current through a conical pore decreases with increasing driving force (applied voltage), similar to solid-state tunnel diodes. NDR results from a positive feedback mechanism between the ion distributions and EOF, yielding a true bistability in both fluid flow and electrical current at a critical applied voltage. Nanopore-based NDR is extremely sensitive to the surface charge near the nanopore opening, suggesting possible applications in chemical sensing.
Template synthesis represents an important class of nanofabrication methods. Herein, recent advances in nanomaterial preparation by extrusion through nanoporous membranes that preserve the template ...membrane without sacrificing it, which is termed as “non‐sacrificing template synthesis,” are reviewed. First, the types of nanoporous membranes used in nanoporous membrane extrusion applications are introduced. Next, four common nanoporous membrane extrusion strategies: vesicle extrusion, membrane emulsification, precipitation extrusion, and biological membrane extrusion, are examined. These methods have been utilized to prepare a wide range of nanomaterials, including liposomes, emulsions, nanoparticles, nanofibers, and nanotubes. The principle and historical context of each specific technology are discussed, presenting prominent examples and evaluating their positive and negative features. Finally, the current challenges and future opportunities of nanoporous membrane extrusion methods are discussed.
This article systematically reviews recent advances in nanomaterial preparation by extrusion through nanoporous membranes. It introduces four common nanoporous membrane extrusion strategies: vesicle extrusion, membrane emulsification, precipitation extrusion, and biological membrane extrusion, representing a greener and more economical nanofabrication process than conventional template synthesis methods.
The ecological literature reports little empirical evidence from biodiversity– ecosystem functioning (BEF) experiments in wetland systems, even though wetlands are widely known for their water ...filtering capacity. Experiments comparing the effect of plant monocultures and mixtures on water quality to improve pollutant removal efficiency in treatment wetlands share the characteristics of classical BEF experiments, and so could provide insights for wetland management. To add to our understanding of BEF relationships in wetlands, we evaluated plant diversity effects on water purification through a meta-analysis of freshwater experimental wetlands comparing monocultures to mixtures. We found 28 studies that matched our criteria for BEF analysis, for a total of 561 diversity effects on pollutant removal. Overall, the meta-analysis shows no significant effect of plant richness on removal of total suspended solids, but a positive effect on chemical oxygen demand and total nitrogen removal, and a marginal effect on phosphorus removal. Thus, the results of this meta-analysis are consistent with reports of an overall positive biodiversity effect on ecosystem properties. An analysis of moderator variables shows that the experimental context (size of the experimental units, nutrient load, duration of the experiment) does not explain much of the residual variance. For pollutants that benefit from a positive plant richness effects on removal, mixtures do not perform better than the best monoculture. We found no evidence that plant richness effects are due to functional complementarity among species rather than to the presence of particularly efficient species. Complementarity effects may be less prevalent in highly productive, nutrient-rich wetlands, compared to nutrient-limited environments such as natural grasslands. Although findings must be confirmed by long-term field experiments under natural conditions, result from experimental wetland systems may contribute to a better understanding of biodiversity effect on ecosystem functions in wetlands, in addition to guide practices in natural wetland restoration and the use of constructed wetlands for water treatment.
The salinity gradient of estuaries plays a unique and fundamental role in structuring spatial patterns of physical properties, biota, and biogeochemical processes. We use variability along the ...salinity gradient of San Francisco Bay to illustrate some lessons about the diversity of spatial structures in estuaries and their variability over time. Spatial patterns of dissolved constituents (e.g., silicate) can be linear or nonlinear, depending on the relative importance of river-ocean mixing and internal sinks (diatom uptake). Particles have different spatial patterns because they accumulate in estuarine turbidity maxima formed by the combination of sinking and estuarine circulation. Some constituents have weak or no mean spatial structure along the salinity gradient, reflecting spatially distributed sources along the estuary (nitrate) or atmospheric exchanges that buffer spatial variability of ecosystem metabolism (dissolved oxygen). The density difference between freshwater and seawater establishes stratification in estuaries stronger than the thermal stratification of lakes and oceans. Stratification is strongest around the center of the salinity gradient and when river discharge is high. Spatial distributions of motile organisms are shaped by species-specific adaptations to different salinity ranges (shrimp) and by behavioral responses to environmental variability (northern anchovy). Estuarine spatial patterns change over time scales of events (intrusions of upwelled ocean water), seasons (river inflow), years (annual weather anomalies), and between eras separated by ecosystem disturbances (a species introduction). Each of these lessons is a piece in the puzzle of how estuarine ecosystems are structured and how they differ from the river and ocean ecosystems they bridge.
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