The nuclear shell model has perhaps been the most important conceptual and computational paradigm for the understanding of the structure of atomic nuclei. While the shell model has been used ...predominantly in a phenomenological context, there have been efforts stretching back more than half a century to derive shell model parameters based on a realistic interaction between nucleons. More recently, several ab initio many-body methods-in particular, many-body perturbation theory, the no-core shell model, the in-medium similarity renormalization group, and coupled-cluster theory-have developed the capability to provide effective shell model Hamiltonians. We provide an update on the status of these methods and investigate the connections between them and their potential strengths and weaknesses, with a particular focus on the in-medium similarity renormalization group approach. Three-body forces are demonstrated to be important for understanding the modifications needed in phenomenological treatments. We then review some applications of these methods to comparisons with recent experimental measurements, and conclude with some remaining challenges in ab initio shell model theory.
While defining martial arts is not prerequisite to philosophizing about them, such a definition is desirable, helping us resolve disputes about the status of hard cases. At one extreme, Martínková ...and Parry argue that martial arts are distinguished from both close combat (as unsystematic) and combat sports (as competitive), and from warrior arts (as lethal) and martial paths (as spiritual). At the other extreme, mixed martial arts pundits and Bruce Lee speak of combat sports generally as martial arts. I argue that the fine-grained taxonomy proposed by Martínková and Parry can be usefully supplemented by a broader definition, specifically the following: martial arts are systematic fighting styles and practices as ways of embodying wisdom. A possible difficulty here is that such views face the charge of overemphasizing the “philosophical” aspect of martial arts. My definition can, however, avoid this apparent problem. If martial arts essentially aim to embody wisdom, this applies no less to the (strategic) practical wisdom of The Art of War than to the (ethical) practical wisdom of the Tao Te Ching. In an extended sense, then, any systematic fighting style, including combat sports, may count as a martial art insofar as it embodies wisdom by improving practical fighting skills.
Abstract
Heavy atomic nuclei have an excess of neutrons over protons, which leads to the formation of a neutron skin whose thickness is sensitive to details of the nuclear force. This links atomic ...nuclei to properties of neutron stars, thereby relating objects that differ in size by orders of magnitude. The nucleus
208
Pb is of particular interest because it exhibits a simple structure and is experimentally accessible. However, computing such a heavy nucleus has been out of reach for ab initio theory. By combining advances in quantum many-body methods, statistical tools and emulator technology, we make quantitative predictions for the properties of
208
Pb starting from nuclear forces that are consistent with symmetries of low-energy quantum chromodynamics. We explore 10
9
different nuclear force parameterizations via history matching, confront them with data in select light nuclei and arrive at an importance-weighted ensemble of interactions. We accurately reproduce bulk properties of
208
Pb and determine the neutron skin thickness, which is smaller and more precise than a recent extraction from parity-violating electron scattering but in agreement with other experimental probes. This work demonstrates how realistic two- and three-nucleon forces act in a heavy nucleus and allows us to make quantitative predictions across the nuclear landscape.
Ion exclusion by sub-2-nm carbon nanotube pores Fornasiero, Francesco; Park, Hyung Gyu; Holt, Jason K ...
Proceedings of the National Academy of Sciences - PNAS,
11/2008, Letnik:
105, Številka:
45
Journal Article, Conference Proceeding
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Biological pores regulate the cellular traffic of a large variety of solutes, often with high selectivity and fast flow rates. These pores share several common structural features: the inner surface ...of the pore is frequently lined with hydrophobic residues, and the selectivity filter regions often contain charged functional groups. Hydrophobic, narrow-diameter carbon nanotubes can provide a simplified model of membrane channels by reproducing these critical features in a simpler and more robust platform. Previous studies demonstrated that carbon nanotube pores can support a water flux comparable to natural aquaporin channels. Here, we investigate ion transport through these pores using a sub-2-nm, aligned carbon nanotube membrane nanofluidic platform. To mimic the charged groups at the selectivity region, we introduce negatively charged groups at the opening of the carbon nanotubes by plasma treatment. Pressure-driven filtration experiments, coupled with capillary electrophoresis analysis of the permeate and feed, are used to quantify ion exclusion in these membranes as a function of solution ionic strength, pH, and ion valence. We show that carbon nanotube membranes exhibit significant ion exclusion that can be as high as 98% under certain conditions. Our results strongly support a Donnan-type rejection mechanism, dominated by electrostatic interactions between fixed membrane charges and mobile ions, whereas steric and hydrodynamic effects appear to be less important.
We report gas and water flow measurements through microfabricated membranes in which aligned carbon nanotubes with diameters of less than 2 nanometers serve as pores. The measured gas flow exceeds ...predictions of the Knudsen diffusion model by more than an order of magnitude. The measured water flow exceeds values calculated from continuum hydrodynamics models by more than three orders of magnitude and is comparable to flow rates extrapolated from molecular dynamics simulations. The gas and water permeabilities of these nanotube-based membranes are several orders of magnitude higher than those of commercial polycarbonate membranes, despite having pore sizes an order of magnitude smaller. These membranes enable fundamental studies of mass transport in confined environments, as well as more energy-efficient nanoscale filtration.
Accurately predicting total sea-level including tides and storm surges is key to protecting and managing our coastal environment. However, dynamically forecasting sea level extremes is ...computationally expensive. Here a novel alternative based on ensembles of artificial neural networks independently trained at over 600 tide gauges around the world, is used to predict the total sea-level based on tidal harmonics and atmospheric conditions at each site. The results show globally-consistent high skill of the neural networks (NNs) to capture the sea variability at gauges around the globe. While the main atmosphere-driven dynamics can be captured with multivariate linear regressions, atmospheric-driven intensification, tide-surge and tide-tide non-linearities in complex coastal environments are only predicted with the NNs. In addition, the non-linear NN approach provides a simple and consistent framework to assess the uncertainty through a probabilistic forecast. These new and cheap methods are relatively easy to setup and could be a valuable tool combined with more expensive dynamical model in order to improve local resilience.
The modest philosophical literature on allusion focuses on descriptive issues concerning literary examples, and thus tends to neglect both allusions in other media and normative concerns about ...allusions in general. In this paper I will help fill both gaps through an analysis of three different cases of what I call casting allusions, which depend on the audience’s recognition that a certain cast member was also in the cast of a different work. These cases vary greatly in aesthetic merit, and this is best explained via two dimensions of allusive value: richness (given the medium) and dynamic engagement. All else being equal, an allusion will be more aesthetically pleasing when it relies on a wider variety of medium-relevant channels or prompts less passive, more evolving audience response. Such an account finds further support in elaborate cinematic examples, such as the tapestry of allusions to Bruce Lee in the Kill Bill films.
We review recent advances in nanoelectrode architecture for photochemical hydrogen production by water splitting. Today, solar energy is recognized as one of the most important renewable energy ...sources that humanity must harness in addressing the future energy sustainability issues. Of the different strategies for solar energy conversion, solar fuel or solar hydrogen conversion is attractive in that one can store the harvested energy in chemical bonds. Recent work in this field has focused on the use of nanoarchitecture designs that aim to increase photocatalytic activity, enable visible light harvesting, and ensure chemical stability and cost-effectiveness. In this perspective review, we focus on selected work in the following areas: (1) oxide semiconductor nanoelectrodes; (2) sensitization of semiconductor nanowire/nanotube arrays; (3) bioinorganic conjugate architectures; and (4) hybrid nanoarchitectures.
We review recent advances in nanoelectrode architecture for photochemical hydrogen production by water splitting.
Satellite cells are the chief contributor to skeletal muscle growth and regeneration. The study of mouse satellite cells has accelerated in recent years due to technical advancements in the isolation ...of these cells. The study of human satellite cells has lagged and thus little is known about how the biology of mouse and human satellite cells compare. We developed a flow cytometry-based method to prospectively isolate human skeletal muscle progenitors from the satellite cell pool using positive and negative selection markers. Results show that this pool is enriched in PAX7 expressing cells that possess robust myogenic potential including the ability to give rise to de novo muscle in vivo. We compared mouse and human satellite cells in culture and identify differences in the elaboration of the myogenic genetic program and in the sensitivity of the cells to cytokine stimulation. These results indicate that not all mechanisms regulating mouse satellite cell activation are conserved in human satellite cells and that such differences may impact the clinical translation of therapeutics validated in mouse models. Thus, the findings of this study are relevant to developing therapies to combat muscle disease.
Existing methods to predict the effects of climate change on the biomass and production of marine communities are predicated on modelling the interactions and dynamics of individual species, a very ...challenging approach when interactions and distributions are changing and little is known about the ecological mechanisms driving the responses of many species. An informative parallel approach is to develop size-based methods. These capture the properties of food webs that describe energy flux and production at a particular size, independent of species' ecology. We couple a physical–biogeochemical model with a dynamic, size-based food web model to predict the future effects of climate change on fish biomass and production in 11 large regional shelf seas, with and without fishing effects. Changes in potential fish production are shown to most strongly mirror changes in phytoplankton production. We project declines of 30–60% in potential fish production across some important areas of tropical shelf and upwelling seas, most notably in the eastern Indo-Pacific, the northern Humboldt and the North Canary Current. Conversely, in some areas of the high latitude shelf seas, the production of pelagic predators was projected to increase by 28–89%.
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