Bottom-up Method Research Articles

Synthesis of the land carbon fluxes of the Amazon region between 2010 and 2020

The Amazon is the largest continuous tropical forest in the world and plays a key role in the global carbon cycle. Human-induced disturbances and climate change have impacted the Amazon carbon balance. Here we conduct a comprehensive synthesis of existing state-of-the-art estimates of the contemporary land carbon fluxes in the Amazon using a set of bottom-up methods (i.e., dynamic vegetation models and bookkeeping models) and a top-down inversion (atmospheric inversion model) over the Brazilian Amazon and the whole Biogeographical Amazon domain. Over the whole biogeographical Amazon region bottom-up methodologies suggest a small average carbon sink over 2010-2020, in contrast to a small carbon source simulated by top-down inversion (2010-2018). However, these estimates are not significantly different from one another when accounting for their large individual uncertainties, highlighting remaining knowledge gaps, and the urgent need to reduce such uncertainties. Nevertheless, both methodologies agreed that the Brazilian Amazon has been a net carbon source during recent climate extremes and that the south-eastern Amazon was a net land carbon source over the whole study period (2010-2020). Overall, our results point to increasing human-induced disturbances (deforestation and forest degradation by wildfires) and reduction in the old-growth forest sink during drought.

Photothermal metasurface with polarization and wavelength multiplexing.

Controlling temperature distribution at the micro/nano-scale brings new applications in many fields such as physics, chemistry and biology. This paper proposes a photothermal metasurface that employs polarization and wavelength multiplexing to regulate various temperature distributions at the micro/nano-scale. Such a photothermal metasurface is numerically validated by the finite element method. Firstly, the inversion algorithm is used to calculate the thermal power density distribution, which is decided by a given temperature distribution. Then, based on the bottom-up design method, (a) the library of absorption cross sections of gold nanoparticles is established by resizing nanoparticles; (b) the single pixel is constructed for wavelength and polarization multiplexing; (c) the overall structure of a photothermal metasurface is optimized and established. Finally, four given temperature distributions, combining the multiplexing of two orthogonal polarizations and two wavelengths, are achieved in the same area. The simulation results well confirm the feasibility of photothermal multiplexing. Such photothermal metasurface provides solutions for flexible control of temperature distribution at the micro/nano-scale.

Enhanced Broadband Manipulation of Acoustic Vortex Beams Using 3-bit Coding Metasurfaces through Topological Optimization.

The acoustic coding metasurfaces (ACMs) have the ability to manipulate complex acoustic behavior by reconstructing the coding sequence. In particular, the design of broadband coding enhances the versatility of ACMs. ACMs offer significant advantages over traditional metasurfaces, including a limited number of units and flexible wave control performance. The unit quantity is determined by 2n, with 1-bit utilizing 2 units, 2-bit using 4 units, and 3-bit employing 8 units. Utilizing multiple bits allows for precise control over the phase of sound waves and enables the realization of more intricate acoustic functions. To address the requirements of broadband multi-bit applications, this paper presents the development of novel 3-bit broadband reflected acoustic coding metasurfaces (BACMs) with eight coding units. These metasurfaces are systematically designed using the bottom-up topology optimization method. A constant phase difference of 45° can be achieved across all eight coding units within a broad frequency range. Additionally, the spiral distribution of phase differences enables the construction of an acoustic vortex metasurface. Moreover, by combining the convolution method, the strategies are outlined for constructing vortex-focusing metasurfaces and vortex beam manipulation metasurfaces. These 3-bit coding metasurfaces possess significant potential in the fields of acoustic particle suspension and acoustic communication.

Economic burden of chronic obstructive pulmonary disease in Morocco: a cost of illness study.

Chronic obstructive pulmonary disease (COPD) carries an important economic burden worldwide. However, the cost of this disease in Morocco is not well explored. This study aimed to estimate the economic cost associated with COPD in Morocco and identify its determinants. A cost of illness, prevalence-based study using a bottom-up approach method, including COPD patients, was carried out in 2021-2022. The cost was estimated from a societal perspective, and the time horizon was 1 year. Data collection was performed using a questionnaire including socio-demographic, clinical data, and utilization of health care resources in 2019: hospitalization, medical tests, medications, and medical visits. Direct health cost (DHC) was estimated by multiplying the use of health services by the official prices (unit costs) published by the National Agency for Health Insurance. The indirect cost (IC) represented by labor productivity losses was calculated using the human capital method. Costs were compared according to different socio-demographic and clinical factors. We included 159 patients; 82.4% were men, 80.4% were current or former smokers, and 78.7% were categorized as "high-risk" groups (grades C-D). The DHC was estimated at $1816.6 per patient per year. Pharmaceutical and hospitalization costs represented the highest part of the total DHC (42.5% and 22.1%, respectively). The IC was estimated at $709.5±1081.3 per patient per year. DHC increased with increasing disease severity and with the number of severe exacerbations (p<0.001). Current and former smokers were more costly to the healthcare system than nonsmokers (p=0.029). IC also increased with the number of severe exacerbations (p=0.003). In this study, we showed that COPD in Morocco generates important costs for the health system, mainly related to smoking and the severity of the disease. It is therefore important to strengthen tobacco control measures in our country.

Expanding single-trace YMS amplitudes with gauge-invariant coefficients

In this note, we use the new bottom-up method based on soft theorems to recursively construct the expansion of single-trace Yang–Mills-scalar amplitudes. The resulting expansion manifests the gauge invariance for any polarization carried by external gluons, as well as the permutation symmetry among external gluons. Our result is equivalent to that found by Clifford Cheung and James Mangan via the so-called covariant color–kinematics duality approach.

Review of: "multi-layered nanographene is made by placing individual carbon atoms together, which is also called the bottom-up method."

Review of: "multi-layered nanographene is made by placing individual carbon atoms together, which is also called the bottom-up method."

Distilling coarse-grained representations of molecular electronic structure with continuously gated message passing.

Bottom-up methods for coarse-grained (CG) molecular modeling are critically needed to establish rigorous links between atomistic reference data and reduced molecular representations. For a target molecule, the ideal reduced CG representation is a function of both the conformational ensemble of the system and the target physical observable(s) to be reproduced at the CG resolution. However, there is an absence of algorithms for selecting CG representations of molecules from which complex properties, including molecular electronic structure, can be accurately modeled. We introduce continuously gated message passing (CGMP), a graph neural network (GNN) method for atomically decomposing molecular electronic structure sampled over conformational ensembles. CGMP integrates 3D-invariant GNNs and a novel gated message passing system to continuously reduce the atomic degrees of freedom accessible for electronic predictions, resulting in a one-shot importance ranking of atoms contributing to a target molecular property. Moreover, CGMP provides the first approach by which to quantify the degeneracy of "good" CG representations conditioned on specific prediction targets, facilitating the development of more transferable CG representations. We further show how CGMP can be used to highlight multiatom correlations, illuminating a path to developing CG electronic Hamiltonians in terms of interpretable collective variables for arbitrarily complex molecules.

A Review of Advances in Graphene Quantum Dots: From Preparation and Modification Methods to Application

Graphene quantum dot (GQD) is a new type of carbon nanometer material. In addition to the excellent properties of graphene, it is superior due to the quantum limit effect and edge effect. Because of its advantages such as water solution, strong fluorescent, small size, and low biological toxicity, it has important application potential in various fields, especially in sensors and biomedical areas, which are mainly used as optical electrical sensors as well as in biological imaging and tumor therapy. In addition, GQDs have very important characteristics, such as optical and electrical properties. There are many preparation methods, divided into top-down and bottom-up methods, which have different advantages and disadvantages, respectively. In addition, the modification methods include heterogeneous doping, surface heterogeneity, etc. There are still many challenges in developing GQDs. For example, the synthesis steps are still hard to conduct, but as the inquiry continues to deepen, GQDs will be revolutionary materials in the future. In this work, the literature concerning research progress on GQDs has been reviewed and summarized, while the key challenges of their application have been pointed out, which may bring new insights to the application of GQDs.

Spatial-temporal characteristics of methane emission in shandong, China, based on an updated comprehensive methane emission inventory in 2020

As methane (CH4) is a powerful greenhouse gas (GHG) responsible for global warming, a refined CH4 emission inventory is crucial for formulating targeted mitigation policies and achieving carbon neutrality. However, provincial comprehensive CH4 emission inventories are rare due to data deficiency and fail to reflect the spatial and temporal characteristics of CH4 emission. Owing to its large population and rapid economic growth, Shandong Province has become the largest GHG emitter in China. Combining bottom-up and top-down methods, a high-spatial-resolution (0.03° × 0.03°) natural and anthropogenic CH4 emission inventory across Shandong Province in 2020 was established based on detailed activity data and updated source-specific emission factors. The total CH4 emission of Shandong was 1711.31 Gg in 2020, of which anthropogenic sources were responsible for 89.96% emission. The top three contributors, namely energy activities, agricultural activities, and waste treatment accounted for 52.86%, 21.25% and 12.70% emission, respectively, followed by vegetation (5.40%), wetland (4.64%), biomass burning (3.14%). Owing to the emission structure, spatial distribution of CH4 emission varied significantly. Jining was the largest contributor (488.92 Gg; 28.57% provincial CH4 emission) owing to the high coal production, followed by Heze (149.17 Gg; 8.72% provincial CH4 emission) and Dongying (138.28 Gg; 8.08% provincial CH4 emission) owing to coal and oil production. The monthly variation of CH4 emission from different sources are different, and the maximum emissions occurred in August. This study reports a set of methods for creating a CH4 emission inventory in China and provides detailed data for air quality simulations and various emission control policies.

Assessment of the correlation between optical properties and CQD preparation approaches

Various production procedures, for carbon quantum dots (CQDs), are still being extensively researched to understand the nature of CQD luminescence. This study compares and examines the impact of chemical as well as green methods on the structural and optical properties of CQDs. We present a straightforward, cost-effective bottom-up method for producing fluorescent CQDs from lemon peels (L-CQDs), orange juice (O-CQDs), and citric acid (C-CQDs) without having to deal with time-consuming or ineffective post-processing processes. The proposed green synthesis has no toxic by-products, and the residual resources utilized promote the large-scale production of CQDs. X-ray diffraction, high-resolution transmission electron microscopy, FTIR, Raman, DLS, and UV–Vis spectroscopy are utilized to investigate the structure and optical characteristics of the prepared CQDs. The as-prepared CQDS possess small particle sizes of 5.6 nm, 6.2 nm, and 1.1 nm for L-CQDs, O-CQDs, and C-CQDs samples, respectively. FTIR results reveal the coexistence of carboxylic and hydroxyl groups on the surface of the CQDs, as also supported by zeta-potential values. Maximal fluorescence intensity was reached at excitation wavelengths of 365, 250, and 280 nm with an emission color of blue, indigo, and light blue for L-CQDs, O-CQDs, and C-CQDs, respectively. The presented approaches show a high quantum yield of 88% for O-CQDs, 49% for L-CQDs, and 37% for C-CQDs. Due to their minuscule particle size, perfect water solubility, high stability, and tunable luminescence properties, the prepared CQDs are preferred for potential applications in multicolor imaging, metal ion sensing, and wastewater technologies.

Programmable inverse-designed acoustic coding metasurfaces for multifunctional broadband reflection

In this paper, we develop tunable reflection-type broadband acoustic coding metasurfaces (BACMs) using a bottom-up topology optimization method. These metasurfaces enable flexible configuration switching between the antiphase coding units of “0” and “1” across a wide frequency range through electromagnetic regulation. By introducing a customized dispersion design, the optimized structure exhibits broadband properties. The optimized coding units consist of irregular air channels and connected air cavities. The coding bits of “0” and “1” show a constant opposite phase difference over a wide frequency range through the coupling resonances. By adjusting the electromagnets, arbitrary coding sequences in the BACMs can be rapidly reconstructed. We numerically and experimentally demonstrate the acoustic focusing and splitting properties within the frequency range of 2.2 kHz–4.4 kHz.

Integrating Photoactive Ligands into Crystalline Ultrathin 2D Metal-Organic Framework Nanosheets for Efficient Photoinduced Energy Transfer.

3D metal-organic frameworks (MOFs) have gained attention as heterogeneous photocatalysts due to their porosity and unique host-guest interactions. Despite their potential, MOFs face challenges, such as inefficient mass transport and limited light penetration in photoinduced energy transfer processes. Recent advancements in organic photocatalysis have uncovered a variety of photoactive cores, while their heterogenization remains an underexplored area with great potential to build MOFs. This gap is bridged by incorporating photoactive cores into 2D MOF nanosheets, a process that merges the realms of small-molecule photochemistry and MOF chemistry. This approach results in recyclable heterogeneous photocatalysts that exhibit an improved mass transfer efficiency. This research demonstrates a bottom-up synthetic method for embedding photoactive cores into 2D MOF nanosheets, successfully producing variants such as PCN-641-NS, PCN-643-NS, and PCN-644-NS. The synthetic conditions were systematically studied to optimize the crystallinity and morphology of these 2D MOF nanosheets. Enhanced host-guest interactions in these 2D structures were confirmed through various techniques, particularly solid-state NMR studies. Additionally, the efficiency of photoinduced energy transfer in these nanosheets was evidenced through photoborylation reactions and the generation of reactive oxygen species (ROS).

Crystal Self-Assembly under Confinement: Bridging Nanomaterials to Integrated Devices.

ConspectusSelf-assembly, a spontaneous process that organizes disordered constituents into ordered structures, has revolutionized our fundamental understanding of living matter, nanotechnology, and molecular science. From the perspective of nanomaterials, self-assembly serves as a bottom-up method for creating long-range-ordered materials. This is accomplished by tailoring the geometry, chemistry, and interactions of the components, thereby facilitating the efficient fabrication of high-quality materials and high-performance functional devices. Over the past few decades, we have seen controllable organization and diverse phases in self-assembled materials, such as organic crystals, biomolecular structures, and colloidal nanoparticle supercrystals. However, most self-assembled ordered materials and their assembly mechanisms are derived from constituents in a liquid bulk medium, where the effects of boundaries and interfaces are negligible. In the context of nanostructure patterning, self-assembly occurs in confined spaces, with feature sizes ranging from a few to hundreds of nanometers. In such settings, ubiquitous boundaries and interfaces can trap the system in a kinetically favored but metastable state, devoid of long-range order. This makes it extremely difficult to achieve ordered structures in micro/nano-patterning techniques that rely on sessile microdroplets, such as inkjet printing, dip-pen lithography, and contact printing.In stark contrast to sessile droplets, capillary bridges─formed by liquids confined between two solid surfaces─provide unique opportunities for understanding the long-range-ordered self-assembly of crystalline materials under spatial confinement. Because capillary bridges are stabilized by Laplace pressure, which is inversely proportional to the feature size, the confinement and manipulation of solutions or suspensions of functional materials at the nanoscale become accessible through the rational design of surface chemistry and geometry. Although global thermodynamic equilibrium is unattainable in evaporative systems, ordered nucleation and packing of constituent components can be locally realized at the contact line of capillary bridges. This enables the unprecedented fabrication of long-range-ordered micro/nanostructures with deterministic patterns.In this Account, we review the advancements in long-range-ordered self-assembly of crystalline micro/nanostructures under confinement. First, we briefly introduce crystalline materials characterized by strong intramolecular interactions and relatively weak intermolecular forces, analyzing both the opportunities and challenges inherent to self-assembled nanomaterials. Next, we delve into the construction and manipulation of confined liquids, focusing especially on capillary bridges controlled by engineered chemistry and geometry to regulate Laplace pressure. Through this approach, we have achieved capillary bridges with thicknesses on the order of a few nanometers and wafer-scale homogeneity, facilitating the self-assembly of ordered structures. Supported by factors such as local free-volume entropy, electrostatic interactions, curvilinear geometry, directional microfluidics, and nanoconfinement, we have achieved long-range-ordered, deterministic patterning of organic semiconductors, metal-halide perovskites, and colloidal nanocrystal superlattices using this capillary-bridge platform. These long-range microstructures serve as a bridge between nanomaterials and integrated devices, enabling emergent functionalities like intrinsic stretchability, giant photoconductivity, propagating and interacting exciton polaritons, and spin-valley-locked lasing, which are otherwise unattainable in disordered materials. Finally, we discuss potential directions for both the fundamental understanding and practical applications of confined self-assembly.

Hybrid NVH modeling approach: How numerical and experimental methods complement each other

The ever-increasing demand for shorter development times and cost savings means that important design decisions must be made at an early stage of the development process. This goal of saving time and reducing costs leads to an increased use of virtual prototypes. However, by combining the methods of simulation and testing, the idea of saving time and reducing costs can be extended even further. In addition, in some cases the accuracy of the results can be increased compared to the approach based solely on numerical models or experimental results. Depending on the task and the availability of data (to build virtual prototypes), methods (to model certain physical phenomena) and physical prototypes, the optimal approach must be chosen. In a connected world, where development processes are distributed across different companies, the availability of data and physical prototypes becomes even more critical: companies need to share product features to create system models, but may not want to share development knowledge or product design details. In the proposed talk, a combined method of measurement and numerical simulation to predict and analyze the NVH properties of an e-bike is demonstrated. In this specific case, the electric drive unit of an e-bike that is already in series production is installed virtually in a numerical model of a new e-bike prototype. The excitation and structural dynamics of the electric drive unit are derived from experiment using the method of in-situ blocked forces. This kind of source description is known from the experimental transfer path analysis. In parallel, the numerical model of the e-bike prototype is built using a bottom-up method. The vibrations of the carbon frame induced by the virtually mounted electric drive unit are analyzed. The validity of the approach is shown using experimental data. The model presented can be used for further investigation of the airborne noise excited by the electric drive unit and radiated by the frame, which will be shown in following publications.

Superhydrophobic fluorinated metal–organic framework (MOF) devices for high-efficiency oil–water separation

A series of fluorinated UiO-66 was prepared using the bottom-up method. The composites of 2CF3-UiO-66 and cotton show excellent oil–water separation efficiency (up to 99.66%).

Least Squares-based Optimal Reconciliation Method for Hierarchical Forecasts of Wind Power Generation

Wind power generation is hierarchically organized and can be aggregated/disaggregated based on geography and electrical network structure. Forecasts are required at all levels of such a hierarchy for different operational requirements, which are also known as “hierarchical forecasts”. In this paper, we propose a new method to produce hierarchical wind power forecasts which performs better than the conventional top-down or bottom-up method. At first, wind power generation at all levels of the hierarchy is independently forecasted using state-of-the-art techniques. Then, a least squares regression model is used to optimally reconcile these base forecasts. Adjusted forecasts are as close as possible to base forecasts but also satisfy the requirement of the aggregate consistency (i.e., the lower-level forecasts add up exactly to the higher-level forecasts). Case studies validate the effectiveness of the proposed approach for very short-term wind power forecasts. The accuracy improvement of reconciled forecasts over benchmarks is confirmed at all levels of the hierarchy, regardless of forecast horizons and hierarchical structures.

Exploring borderline SN1-SN2 mechanisms: the role of explicit solvation protocols in the DFT investigation of isopropyl chloride.

Nucleophilic substitution at saturated carbon is a crucial class of organic reactions, playing a pivotal role in various chemical transformations that yield valuable compounds for society. Despite the well-established SN1 and SN2 mechanisms, secondary substrates, particularly in solvolysis reactions, often exhibit a borderline pathway. A molecular-level understanding of these processes is fundamental for developing more efficient chemical transformations. Typically, quantum-chemical simulations of the solvent medium combine explicit and implicit solvation methods. The configuration of explicit molecules can be defined through top-down approaches, such as Monte Carlo (MC) calculations for generating initial configurations, and bottom-up methods that involve user-dependent protocols to add solvent molecules around the substrate. Herein, we investigated the borderline mechanism of the hydrolysis of a secondary substrate, isopropyl chloride (iPrCl), at DFT-M06-2X/aug-cc-pVDZ level, employing explicit and explicit + implicit protocols. Top-down and bottom-up approaches were employed to generate substrate-solvent complexes of varying number (n = 1, 3, 5, 7, 9, and 12) and configurations of H2O molecules. Our findings consistently reveal that regardless of the solvation approach, the hydrolysis of iPrCl follows a loose-SN2-like mechanism with nucleophilic solvent assistance. Increasing the water cluster around the substrate in most cases led to reaction barriers of ΔH‡ ≈ 21 kcal mol-1, with nine water molecules from MC configurations sufficient to describe the reaction. The More O'Ferrall-Jencks plot demonstrates an SN1-like character for all transition state structures, showing a clear merged profile. The fragmentation activation strain analyses indicate that energy barriers are predominantly controlled by solvent-substrate interactions, supported by the leaving group stabilization assessed through CHELPG atomic charges.

Economic burden due to COVID-19 in a Colombian Caribbean state, 2020 and 2021.

To estimate the economic burden associated with COVID-19 in Córdoba, Colombia, 2020 and 2021. Economic burden study. Direct costs were analyzed from the third-party payer perspective using healthcare administrative databases and interviews from a cohort of confirmed COVID-19 cases from Córdoba. Costing aggregation was performed by the bottom-up method. Indirect costs were estimated using the productivity loss approach. Contrast tests and statistical models were estimated at 5% significance. We studied 1,800 COVID-19 cases. The average economic cost of COVID-19 per episode was estimated at US$ 2,519 (95%CI 1,980;3,047). The direct medical cost component accounted for 92.9% of the total; out-of-pocket and indirect costs accounted for 2% and 5.1%, respectively. COVID-19 economic cost was mainly due to direct medical costs. This study provided evidence of the economic burden faced by households due to COVID-19, with the most vulnerable households bearing much of the burden on their income.

High solid-state photoluminescence quantum yield of carbon-dot-derived molecular fluorophores for light-emitting devices.

Several recent studies of carbon dots (CDs) synthesized by bottom-up methods under mild conditions have reported the presence of organic molecular fluorophores in CD dispersions. These fluorophores have a tendency to aggregate, and their properties strongly depend on whether they are present in the form of discrete molecules or aggregates. The aggregation becomes more prominent in the solid state, which motivates the study of the properties of the fluorophores associated with CDs in the solid state. Here, we report the solid-state characterization of N4,N11-dimethyldibenzo[a,h]phenazine-4,11-diamine (BPD) - a molecular fluorophore that forms CDs. Discrete BPD molecules show excitation-wavelength-independent photoluminescence (PL) emission in the green wavelength region at ∼520 nm. However, additional blue PL is also observed due to aggregation, making the PL emission significantly broad. For detailed studies, BPD is mixed in different solid matrices, and it is observed that the PL quantum yield (PLQY) of BPD films strongly depends on the concentration of BPD in the solid matrices. Increasing the concentration of BPD results in a considerable decrease in the PLQY. The PLQY of the films with an optimum concentration of BPD is 75.9% and 40.2% in polymethyl methacrylate and polystyrene, respectively. At higher concentrations, these PLQY values decrease to ∼11%. The significant decrease in the PLQY is ascribed to reabsorption and nonradiative exciton decay that is facilitated by BPD aggregation at higher concentrations. Finally, light-emitting devices (LEDs) were fabricated with almost pure white emission color, having CIE (International Commission on Illumination) coordinates of (0.35, 0.37) using BPD in the color-converting layer of blue-pumped LEDs. The device shows a luminous efficiency 3.8 lm W-1 and luminance of 43 331 cd m-2.

ADOR zeolite with 12 × 8 × 8-ring pores derived from IWR germanosilicate.

Zeolites have been well known for decades as catalytic materials and adsorbents and are traditionally prepared using the bottom-up synthesis method. Although it was productive for more than 250 zeolite frameworks, the conventional solvothermal synthesis approach provided limited control over the structural characteristics of the formed materials. In turn, the discovery and development of the Assembly-Disassembly-Organization-Reassembly (ADOR) strategy for the regioselective manipulation of germanosilicates enabled the synthesis of previously unattainable zeolites with predefined structures. To date, the family tree of ADOR materials has included the topological branches of UTL, UOV, IWW, *CTH, and IWV zeolites. Herein, we report on the expansion of ADOR zeolites with a new branch related to the IWR topology, which is yet unattainable experimentally but theoretically predicted as highly promising adsorbents for CO2 separation applications. The optimization of not only the chemical composition but also the dimensions of the crystalline domain in the parent IWR zeolite in the Assembly step was found to be the key to the success of its ADOR transformation into previously unknown IPC-17 zeolite with an intersecting 12 × 8 × 8-ring pore system. The structure of the as-prepared IPC-17 zeolite was verified by a combination of microscopic and diffraction techniques, while the results on the epichlorohydrin ring-opening with alcohols of variable sizes proved the molecular sieving ability of IPC-17 with potential application in heterogeneous catalysis. The proposed synthesis strategy may facilitate the discovery of zeolite materials that are difficult or yet impossible to achieve using a traditional bottom-up synthesis approach.