Anterior regions of the ventral visual stream encode substantial information about object categories. Are top-down category-level forces critical for arriving at this representation, or can this ...representation be formed purely through domain-general learning of natural image structure? Here we present a fully self-supervised model which learns to represent individual images, rather than categories, such that views of the same image are embedded nearby in a low-dimensional feature space, distinctly from other recently encountered views. We find that category information implicitly emerges in the local similarity structure of this feature space. Further, these models learn hierarchical features which capture the structure of brain responses across the human ventral visual stream, on par with category-supervised models. These results provide computational support for a domain-general framework guiding the formation of visual representation, where the proximate goal is not explicitly about category information, but is instead to learn unique, compressed descriptions of the visual world.
•Secondary dispersal is an important process in seagrass meadows.•Microtopography could affect secondary seed dispersal distances.•A theory relating secondary dispersal with the microtopography is ...formulated.•The formulation is validated with computational fluid dynamics for two seagrasses.•These results can inform seed-based restoration to assess secondary dispersal.
Motivated by observational and experimental evidence, a theoretical model is proposed to relate the secondary dispersal of seagrass seeds with the complexity of microtopography in natural environments. Complexity is encoded in terms of the Hurst exponent of a fractal description of the microtopographical geometry. The percentage of a seafloor transect where secondary dispersal of seagrass seeds occurs, is quantified in terms of the mainstream velocity, bottom complexity and properties of the seeds. Theoretical expressions are validated considering the cases of Zostera marina and Posidonia oceanica seeds and using computational fluid dynamics (CFD). A total of 200 CFD simulations with different bottom complexities and flow conditions, were done for each seagrass genus to validate the theoretical model. Numerical results agree with theoretical predictions. This finding provides a management tool to assess the degree of seed retention in seed-based restoration areas.
ABSTRACT The kinetic Sunyaev-Zel'dovich (kSZ) effect results from Thomson scattering by coherent flows in the reionized intergalactic medium. We present new results based on ray-tracing an 8 Gpc/h ...realization of reionization with resolution elements 2 Mpc/h (subtending ′ at z = 6) on a side to create a full-sky kSZ map. The realization includes, self-consistently, the effects of reionization on scales corresponding to multipoles . We separate the kSZ map into Doppler ( ), Ostriker-Vishniac ( ), patchy ( ), and third-order ( ) components, and compute explicitly all the auto- and cross-correlations (e.g., , , etc.) that contribute to the total power. We find a complex and nonmonotonic dependence on the duration of reionization at and evidence for a non-negligible (10%-30%) contribution from connected four-point correlations, , usually neglected in analytical models. We also investigate the cross-correlation of linear matter and large-scale kSZ temperature fluctuations, focusing on (1) cross-power spectra with biased tracers of the matter density and (2) cold spots from infall onto large, rare H ii regions centered on peaks in the matter distribution at redshifts that are a generic non-Gaussian feature of patchy reionization. Finally, we show that the reionization history can be reconstructed at 5 -10 significance by correlating full-sky 21 cm maps stacked in bins with with existing cosmic microwave background (CMB) temperature maps at , raising the prospects for probing reionization by correlating CMB and LSS measurements. The resulting kSZ maps have been made publicly available at www.cita.utoronto.ca/~malvarez/research/ksz-data/.
Natural gas is seen by many as the future of American energy: a fuel that can provide energy independence and reduce greenhouse gas emissions in the process. However, there has also been confusion ...about the climate implications of increased use of natural gas for electric power and transportation. We propose and illustrate the use of technology warming potentials as a robust and transparent way to compare the cumulative radiative forcing created by alternative technologies fueled by natural gas and oil or coal by using the best available estimates of greenhouse gas emissions from each fuel cycle (i.e., production, transportation and use). We find that a shift to compressed natural gas vehicles from gasoline or diesel vehicles leads to greater radiative forcing of the climate for 80 or 280 yr, respectively, before beginning to produce benefits. Compressed natural gas vehicles could produce climate benefits on all time frames if the well-to-wheels CH4 leakage were capped at a level 45–70% below current estimates. By contrast, using natural gas instead of coal for electric power plants can reduce radiative forcing immediately, and reducing CH4 losses from the production and transportation of natural gas would produce even greater benefits. There is a need for the natural gas industry and science community to help obtain better emissions data and for increased efforts to reduce methane leakage in order to minimize the climate footprint of natural gas.
•Hard clams may enhance local mixing in the presence of predators, by controlling pumping.•Enhanced mixing masks chemical cues and may prevent predatory tracking success.•A numerical model is used to ...investigate mixing from clam's pumping behavior.•Finite-time Lyapunov exponents (FTLE) are used to analyze downstream mixing.•Success to mask chemical clues depends on the exhalant jet-to-crossflow velocity ratio.
Motivated by experimental findings, a computational fluid dynamics (CFD) model was used to investigate whether the clam Mercenaria mercenaria may alter its cue downstream variability by an exhalant random pumping behavior. This behavior was hypothesized to occur in the presence of predator chemical signals in order to prevent successful tracking by the predator. Simulated downstream flow and mixing conditions derived from the random nature of the clam exhalant jet in a crossflow were analyzed by computing an intermittency factor, determining the field of finite-time Lyapunov exponents (FTLEs) and identifying the resulting Lagrangian coherent structures (LCSs). Numerical simulations illustrate that the effectiveness of a fluctuating exhalant jet to prevent downstream tracking by a crab, depends on the ratio of the exhalant jet to the crossflow. Specifically, the clam could effectively enhance the downstream dispersion to prevent tracking, but only in the range of parameters where LCSs are generated (jet-to-crossflow ratio ≥ 1). Then, the probability of detection is reduced with respect to the case of a less fluctuating exhalant jet.
Surface‐enhanced Raman scattering (SERS) is one of the most straightforward applications of the so‐called nanoplasmonics. This powerful molecular spectroscopy technique is based on the enhancement of ...the inelastic scattering from molecules located near nanostructured metallic surfaces when these are illuminated and surface plasmons are excited. The analytical applications of SERS are hindered when the Raman cross‐section of the analyte is too low, which is often the case in inorganic molecular species. This problem is even more serious when atomic species are to be identified, since these cannot display a vibrational signal. Herein we discuss the recent advancements toward the SERS detection of small inorganic compounds, including both molecular and atomic species.
SERS you right: Surface‐enhanced Raman scattering (SERS) can be used for the direct or indirect detection of inorganic molecules and even ions, in spite of their intrinsically low Raman scattering cross‐sections. Recent advances even allow ion sensing and localization within living organisms (see picture).
Emissions from natural gas production sites are characterized by skewed distributions, where a small percentage of sitescommonly labeled super-emittersaccount for a majority of emissions. A better ...characterization of super-emitters is needed to operationalize ways to identify them and reduce emissions. We designed a conceptual framework that functionally defines superemitting sites as those with the highest proportional loss rates (methane emitted relative to methane produced). Using this concept, we estimated total methane emissions from natural gas production sites in the Barnett Shale; functionally superemitting sites accounted for roughly three-fourths of total emissions. We discuss the potential to reduce emissions from these sites, under the assumption that sites with high proportional loss rates have excess emissions resulting from abnormal or otherwise avoidable operating conditions, such as malfunctioning equipment. Because the population of functionally superemitting sites is not expected to be static over time, continuous monitoring will likely be necessary to identify them and improve their operation. This work suggests that achieving and maintaining uniformly low emissions across the entire population of production sites will require mitigation steps at a large fraction of sites.
Due to the high surface: volume ratio and the extraordinary properties arising from the nanoscale (optical, electric, magnetic, etc.), nanoparticles (NPs) are excellent candidates for multiple ...applications. In this context, nanoscience is opening a wide range of modern technologies in biological and biomedical fields, among others. However, one of the main drawbacks that still delays its fast evolution and effectiveness is related to the behavior of nanomaterials in the presence of biological fluids. Unfortunately, biological fluids are characterized by high ionic strengths which usually induce NP aggregation. Besides this problem, the high content in biomacromolecules-such as lipids, sugars, nucleic acids and, especially, proteins-also affects NP stability and its viability for some applications due to, for example, the formation of the protein corona around the NPs. Here, we will review the most common strategies to achieve stable NPs dispersions in high ionic strength fluids and, also, antifouling strategies to avoid the protein adsorption.
This Perspective will examine the organization of intrastriatal circuitry, review recent findings in this area, and discuss how the pattern of connectivity between striatal neurons might give rise to ...the behaviorally observed synergism between the direct/indirect pathway neurons. The emphasis of this Perspective is on the underappreciated role of lateral inhibition between striatal projection cells in controlling neuronal firing and shaping the output of this circuit. We review some classic studies in combination with more recent anatomical and functional findings to lay out a framework for an updated model of the intrastriatal lateral inhibition, where we explore its contribution to the formation of functional units of processing and the integration and filtering of inputs to generate motor patterns and learned behaviors.
Striatum integrates cortical and limbic information to assist in the selection of appropriate behaviors. Burke et al. review recent findings implicating local striatal circuitry in this computation and hypothesize a framework wherein lateral inhibition between projection neurons facilitates action selection.
Plasmonic optical biosensors for the analysis of nucleic acids have drawn a great deal of interest in nanomedicine because of their capability to overcome major limitations of conventional methods. ...Within this realm, surface-enhanced Raman scattering (SERS)-based sensing is progressively emerging as a powerful analytical tool beyond the basic grounds of academia to viable commercial products. SERS benefits from the synergistic combination between the intrinsic structural specificity and experimental flexibility of Raman spectroscopy, the extremely high sensitivity provided by plasmonic nanomaterials, and the tremendous advances in nanofabrication techniques and spectroscopic instrumentation. SERS application to nucleic acids analysis has been largely restricted to indirect sensing approaches, where a SERS reporter and oligonucleotide ligands are typically combined onto the nanomaterials to enable extrinsic detection of the target sequences. On the other hand, the acquisition of the intrinsic SERS vibrational fingerprint of nucleic acids (direct sensing) has traditionally suffered from major limitations. However, recent years have witnessed a burst of interest in this area, largely driven by the efforts to address key reproducibility and sensitivity issues. In this tutorial review, we summarize and discuss the most recent cutting-edge research in the field of direct SERS sensing of nucleic acids by coherently organising the diverse data reported in the literature in a structurally logical fashion.
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