Lithium–sulfur (Li–S) batteries hold great promise to serve as next‐generation energy storage devices. However, the practical performances of Li–S batteries are severely limited by the sulfur cathode ...regarding its low conductivity, huge volume change, and the polysulfide shuttle effect. The first two issues have been well addressed by introducing mesoporous carbon hosts to the sulfur cathode. Unfortunately, the nonpolar nature of carbon materials renders poor affinity to polar polysulfides, leaving the shuttling issue unaddressed. In this contribution, atomic cobalt is implanted within the skeleton of mesoporous carbon via a supramolecular self‐templating strategy, which simultaneously improves the interaction with polysulfides and maintains the mesoporous structure. Moreover, the atomic cobalt dopants serve as active sites to improve the kinetics of the sulfur redox reactions. With the atomic‐cobalt‐decorated mesoporous carbon host, a high capacity of 1130 mAh gS−1 at 0.5 C and a high stability with a retention of 74.1% after 300 cycles are realized. Implanting atomic metal in mesoporous carbon demonstrates a feasible strategy to endow nanomaterials with targeted functions for Li–S batteries and broad applications.
Atomic cobalt implantation to mesoporous carbon enhances the sulfur kinetics in Li–S batteries. Atomic cobalt dopants with high polarity endow the mesoporous carbon (represented by the apes) with high affinity with polysulfides (represented by the bananas). Therefore, the shuttle effect is eliminated and the sulfur kinetics is improved, facilitating highly stable Li–S batteries.
The first catalytic inverse hydroboration of imines with N‐heterocyclic carbene (NHC) boranes has been realized by means of cooperative organocatalysis and photocatalysis. This catalytic combination ...provides a promising platform for promoting NHC‐boryl radical chemistry under sustainable and radical‐initiator‐free conditions. The highly important functional‐group compatibility and possible application in late‐stage hydroborations represent an important step forward to an enhanced α‐amino organoboron library.
Unprecedented inversion: The first catalytic inverse hydroboration of imines with N‐heterocyclic carbene boranes has been realized by means of cooperative organocatalysis and photocatalysis. The nature of the thiol is vital for inverse hydroboration. This procedure represents an important step forward to enhancing α‐amino organoboron libraries.
Complex geometric variations of 3D models usually pose great challenges in 3D shape matching and retrieval. In this paper, we propose a novel 3D shape feature learning method to extract high-level ...shape features that are insensitive to geometric deformations of shapes. Our method uses a discriminative deep auto-encoder to learn deformation-invariant shape features. First, a multiscale shape distribution is computed and used as input to the auto-encoder. We then impose the Fisher discrimination criterion on the neurons in the hidden layer to develop a deep discriminative auto-encoder. Finally, the outputs from the hidden layers of the discriminative auto-encoders at different scales are concatenated to form the shape descriptor. The proposed method is evaluated on four benchmark datasets that contain 3D models with large geometric variations: McGill, SHREC'10 ShapeGoogle, SHREC'14 Human and SHREC'14 Large Scale Comprehensive Retrieval Track Benchmark datasets. Experimental results on the benchmark datasets demonstrate the effectiveness of the proposed method for 3D shape retrieval.
Zonal jets and inertia–gravity waves are ubiquitous on planets such as Earth, Jupiter and Saturn. Motivated by the modification of energy flux of balanced flow by inertia–gravity waves, this paper ...studies the impact of near-inertial waves (NIWs) on zonal jets on a
$\beta$
-plane. Using a two-dimensional quasi-geostrophic and NIW coupled system on a
$\beta$
-plane (Xie & Vanneste,
J. Fluid Mech.
, vol. 774, 2015, pp. 143–169), we find NIWs catalytically impact several features of zonal jets. The NIWs inhibit jet formation due to the waves’ catalytic induction of downscale mean energy flux. As the strength of NIWs increases, a critical point exists beyond which zonal jets are annihilated. The jet spacing is captured by the Rhines scale
$L\sim \sqrt {U/\beta }$
with
$U$
estimated from the upscale energy flux induced by the mean flow alone, which again shows that the NIWs’ impact is catalytic. Also, the temporal asymmetry of NIWs leads to the spatial asymmetry of jet dynamics. The jet profiles are asymmetric with a stronger shear on the left flank. And similar to the left turning of vortex dipole under the impact of NIWs, the NIW-modified jets migrate poleward. The NIWs also show a catalytic role in jet migration: the net momentum flux directly induced by NIWs is of secondary importance in the zonal mean momentum dynamics and impedes jet migration, while the advective effect of NIW-modified mean flow dominates the jet migration velocity.
Large-scale coherent structures such as jets in Rayleigh–Bénard convection and related systems are receiving increasing attention. This paper studies, both numerically and theoretically, the process ...of jet formation in two-dimensional salt-finger convection. The approach utilizes an asymptotically derived system of equations referred to as the modified Rayleigh–Bénard convection (MRBC) model, valid in the geophysically and astrophysically relevant limit in which the solute diffuses much more slowly than heat. In these equations, convection is driven by a destabilizing salinity gradient while the effects of the stabilizing temperature gradient manifest themselves as an additional anisotropic dissipation acting on large scales. The MRBC system is specified by two external parameters: the Schmidt number
$\mathit{Sc}$
(ratio of viscosity to solutal diffusivity) and the Rayleigh ratio
$\mathit{Ra}$
(ratio between the Rayleigh numbers of the destabilizing solutal stratification and the stabilizing thermal stratification). Two distinct
$\mathit{Ra}$
regimes are explored for fixed
$\mathit{Sc}=1$
. In all cases studied the system develops a horizontal jet structure that is maintained self-consistently by turbulent fluctuations, but coarsens over time. For intermediate Rayleigh ratios (e.g.
$\mathit{Ra}=6$
), the MRBC model captures the relaxation oscillations superposed on the jet structure observed at similar parameter values in direct numerical simulations of the primitive equations. For smaller Rayleigh ratios (e.g.
$\mathit{Ra}=2$
), a regime for which direct numerical simulation of the primitive equations is difficult because of the presence of fast gravity waves, the MRBC model reveals the existence of statistically steady jets whose properties are studied in detail. Three hierarchical models, the MRBC and further reductions in the form of quasilinear and single-mode approximations, are used to confirm that jets form and are sustained as a result of the interaction between fluctuations (salt fingers) and large-scale horizontally averaged horizontal flows (jets). Even though the small-scale structures exhibited by the three models exhibit clear differences, all three produce the same power-law spectrum of the mean fields at large vertical scales: in all, the spectrum of the mean streamfunction scales as
$m^{-3}$
and the mean salinity field scales as
$m^{-1}$
, with
$m$
the vertical wavenumber. A theoretical explanation of these observations based on the dominant balances in the mean and fluctuation equations is provided. As a consequence, the jets have a zigzag profile, a conclusion that is consistent with numerical simulations. Based on numerical observations, a three-component phenomenological model consisting of a linearly growing mode, a linearly damped mode and a mean mode is proposed to explain the observed transition from statistically steady jet structure to jets with superposed oscillations that takes place with increasing Rayleigh ratio.
Thermal management through personal heating and cooling is a strategy by which to expand indoor temperature setpoint range for large energy saving. We show that nanoporous polyethylene (nanoPE) is ...transparent to mid-infrared human body radiation but opaque to visible light because of the pore size distribution (50 to 1000 nanometers). We processed the material to develop a textile that promotes effective radiative cooling while still having sufficient air permeability, water-wicking rate, and mechanical strength for wearability. We developed a device to simulate skin temperature that shows temperatures 2.7° and 2.0°C lower when covered with nanoPE cloth and with processed nanoPE cloth, respectively, than when covered with cotton. Our processed nanoPE is an effective and scalable textile for personal thermal management.
Enormous efforts have been made toward the translation of nanotechnology into medical practice, including cancer management. Generally the applications have fallen into two categories: diagnosis and ...therapy. Because the targets are often the same, the development of separate approaches can miss opportunities to improve efficiency and effectiveness. The unique physical properties of nanomaterials enable them to serve as the basis for superior imaging probes to locate and report cancerous lesions and as vehicles to deliver therapeutics preferentially to those lesions. These technologies for probes and vehicles have converged in the current efforts to develop nanotheranostics, nanoplatforms with both imaging and therapeutic functionalities. These new multimodal platforms are highly versatile and valuable components of the emerging trend toward personalized medicine, which emphasizes tailoring treatments to the biology of individual patients to optimize outcomes. The close coupling of imaging and treatment within a theranostic agent and the data about the evolving course of an illness that these agents provide can facilitate informed decisions about modifications to treatment. Magnetic nanoparticles, especially superparamagnetic iron oxide nanoparticles (IONPs), have long been studied as contrast agents for magnetic resonance imaging (MRI). Owing to recent progress in synthesis and surface modification, many new avenues have opened for this class of biomaterials. Such nanoparticles are not merely tiny magnetic crystals, but potential platforms with large surface-to-volume ratios. By taking advantage of the well-developed surface chemistry of these materials, researchers can load a wide range of functionalities, such as targeting, imaging and therapeutic features, onto their surfaces. This versatility makes magnetic nanoparticles excellent scaffolds for the construction of theranostic agents, and many efforts have been launched toward this goal. In this Account, we introduce the surface engineering techniques that we and others have developed, with an emphasis on how these techniques affect the role of nanoparticles as imaging or therapeutic agents. We and others have developed a set of chemical methods to prepare magnetic nanoparticles that possess accurate sizes, shapes, compositions, magnetizations, relaxivities, and surface charges. These features, in turn, can be harnessed to adjust the toxicity and stability of the nanoparticles and, further, to load functionalities, via various mechanisms, onto the nanoparticle surfaces.
Power staple insertion is an effective means to mitigate IR drop in the advanced technology process. Previous works have shown that detailed placement refinement can greatly enhance the power staple ...insertion rate. However, with FinFET, it is necessary to consider the drain-to-drain abutment (DDA) constraints. We note that extra source node insertion for resolving DDA violations can interfere with power staple insertion. To handle DDA constraints and optimize power staple insertion at the same time, we formulate and solve a new DDA-aware placement refinement problem in this work. Given an initial nonoverlapping placement optimized for other conventional objectives, we compute a refined placement with cell shifting subject to DDA constraints such that the number of staple insertion slots can be maximized. An effective approach is proposed that supports a nonrestricted cell displacement range during placement refinement. It provides the flexibility to adjust the displacement bound of each cell dynamically in order to resolve all DDA violations. As a result, our algorithm guarantees that a placement solution with no DDA violation can always be computed without using a large displacement range for each cell which would require much longer runtime and larger average cell displacement. In addition to cell shifting, we incorporate concurrent cell flipping to reduce the required cell displacement to satisfy the DDA constraints and to facilitate power staple insertion. The experimental results showed the effectiveness of the proposed approach.
Although mixed use is an emerging strategy that has been widely accepted in urban planning for promoting neighbourhood vibrancy, there is no consensus on how to quantitatively measure the mix and the ...effects of mixed use on neighbourhood vibrancy. Shannon entropy, the most commonly used diversity measurement in assessing mixed use, has been found to be inadequate in measuring the multifaceted, multidimensional characteristics of mixed use. And lack of data also makes it difficult to find the relationship between mixed use and neighbourhood vibrancy. However, the recent availability of new sources including mobile phone data and Point of Interest (POI) data have made it possible to develop new indices of mixed use and neighbourhood vibrancy to analyse their relationships. Taking advantage of these emerging new data sources, this study used the numbers of mobile phone users in a 24-hour period as a proxy of neighbourhood vibrancy and used POIs from a navigation database to develop a series of mixed-use indicators that can better reflect the multifaceted, multidimensional characteristics of mixed-use neighbourhoods. The Hill numbers, a unified form of diversity measurement used in ecological literature that includes richness, entropy, and the Simpson index, are used to measure the degrees of mixed use. Using such fine-grained data sets and the Hill numbers allowed us to obtain better insights into the relationship between mixed use and neighbourhood vibrancy. Four models varying in POI measurements that reflect different dimensions of mixed use were presented. The results showed that either POI density or entropy can explain approximately 1% of neighbourhood vibrancy, while POI richness contributes significantly in improving neighbourhood vibrancy. The results also revealed that the entropy has limitations as a measure for representing mixed use and demonstrated the necessity of adopting a set of more appropriate measurements for mixed use. Increasing the number of POIs has limited power to improve neighbourhood vibrancy compared with encouraging the mixing of complementary POIs. These exploratory findings may be useful for adjusting mixed-use assessments and to help guide urban planning and neighbourhood design.
PDF
