Reducing Greenhouse Gas Emissions from U.S. Light-Duty Transport in Line with the 2 °C Target.

Making, driving, and disposing of U.S. light-duty vehicles (LDVs) account for 3% of global greenhouse gas emissions related to energy and processing. This study calculates future emissions and global temperature rises attributable to U.S. LDVs. We examine how 2021-2050 U.S. LDV cumulative emissions can be limited to 23.1 Gt CO2equiv, helping to limit global warming to less than 2 °C. We vary four vehicle life cycle parameters (transport demand, sales share of alternative fuel vehicles, vehicle material recycling rates, and vehicle lifespans) in a dynamic fleet analysis to determine annual LDV sales, scrappage, and fleet compositions. We combine these data with vehicle technology and electricity emission scenarios to calculate annual production, use, and disposal emissions attributable to U.S. LDVs. Only 3% of the 1512 modeled pathways stay within the emission limit. Cumulative emissions are most sensitive to transport demand, and the speed of fleet electrification and electricity decarbonization. Increasing production of battery electric vehicles (BEVs) to 100% of sales by 2040 (at the latest) is necessary, and early retirement of internal combustion engine vehicles is beneficial. Rapid electricity decarbonization minimizes emissions from BEV use and increasingly energy-intensive vehicle production. Deploying high fuel economy vehicles can increase emissions from the production of BEV batteries and lightweight materials. Increased recycling has a small effect on these emissions because over the time period there are few postconsumer batteries and lightweight materials available for recycling. Without aggressive actions, U.S. LDVs will likely exceed the cumulative emissions budget by 2039 and contribute a further 0.02 °C to global warming by 2050, 2.7% of the remaining global 2 °C budget.

Reducing CO2 Emissions from U.S. Steel Consumption by 70% by 2050.

The steel sector emits 25% of global industrial greenhouse gases, and the U.S. is the world's second-largest steel consumer. In this article, we determine how CO2 emissions attributable to U.S. steel consumption can be cut by 70% by 2050. We vary four key steel cycle parameters (U.S. steel stocks per capita, recycling rate, product lifespan, and manufacturing yield) in a dynamic material flow analysis to determine a range of values for annual steel demand and the scrap available for recycling. We combine these data with steelmaking technology and trade scenarios to calculate potential U.S. steel sector emissions in each year to 2050. Only 20% of the pathways we modeled for the U.S. steel sector achieved the emissions target. Emissions in 2050 are most sensitive to the CO2 released per kilogram of steel produced and the steel stocks per capita. Deployment of emerging low carbon steelmaking technology alone is insufficient to achieve the emissions cut; conversely, reducing stocks per capita from the current ∼11 tons/capita toward levels in the U.K. and France, ∼8 tons/capita, would enable the emissions cut to be achieved under a range of foreseeable steelmaking technology scenarios and steel cycle parameters. If action to reduce per capita steel stocks is delayed by more than five years, then it is likely infeasible for the U.S. steel sector to stay within its 2050 CO2 budget because of the increased demand for emissions-intensive steel made from iron ore.

On a local (de-)trapping model for highly doped Pr3+ radioluminescent and persistent luminescent nanoparticles.

Trivalent praseodymium exhibits a wide range of luminescent phenomena when doped into a variety of different materials. Herein, radioluminescent NaLuF4:20%Pr3+ nanoparticles are studied. Four different samples of this composition were prepared ranging from 400-70 nm in size. Kinetic studies of radioluminescence as a function of X-ray irradiation time revealed a decrease in the emissions originating from the 1S0 level, due to the formation or optical activation of defects during excitation, and a simultaneous increase in the visible emissions resulting from the lower optical levels. Thermoluminescence measurements elucidated that a local de-trapping mechanism was responsible for the increase in steady state emission and persistent luminescence originating from the lower optical levels. The results and mechanism described through this study serve to provide a novel nanoparticle composition with versatile luminescent properties and provides experimental evidence in favor of a local trapping model.

Optically Stimulated Nanodosimeters with High Storage Capacity.

In this work we report on the thermoluminescence (TL) and optically stimulated luminescence (OSL) properties of ß-Na(Gd,Lu)F4:Tb3+ nanophosphors prepared via a standard high-temperature coprecipitation route. Irradiating this phosphor with X-rays not only produces radioluminescence but also leads to a bright green afterglow that is detectable up to hours after excitation has stopped. The storage capacity of the phosphor was found to be (2.83 ± 0.05) × 1016 photons/gram, which is extraordinarily high for nano-sized particles and comparable to the benchmark bulk phosphor SrAl2O4:Eu2+,Dy3+. By combining TL with OSL, we show that the relatively shallow traps, which dominate the TL glow curves and are responsible for the bright afterglow, can also be emptied optically using 808 or 980 nm infrared light while the deeper traps can only be emptied thermally. This OSL at therapeutically relevant radiation doses is of high interest to the medical dosimetry community, and is demonstrated here in uniform, solution-processable nanocrystals.

Mapping the Annual Flow of Steel in the United States.

A detailed understanding of material flows is needed to target increased material efficiency and circular economy. In this article, the U.S. steel flow is modeled as a series of nodes representing processes and products. An easily updatable nonlinear least squares optimization is used to reconcile the inconsistencies across 293 collated data records on flows through and between the nodes. The data come from an integrated analysis that includes top-down estimates of steel flow from trade bodies and government statistical agencies, bottom-up estimates of the steel embedded in products based on production statistics and bills of materials, and the mass of imports and exports based on international money flow. A weighting methodology is used to consistently assign confidence scores to the data, and the optimization is used to achieve mass balance and minimize the sum of the squares of the weighted residuals. The results indicate that yield improvement efforts should focus on sheet metal forming in the car industry, which accounts for nearly half of all generated fabrication scrap. The quantity of end-of-life scrap exported and land-filled is greater than the quantity of steel products imported. Increased domestic recycling of end-of-life scrap might displace around a third of these imports.

Perspective: lanthanide-doped upconverting nanoparticles.

In this perspective, we aim to present an overview of some important physical and chemical aspects of lanthanide-doped upconverting nanoparticle research to be considered, from synthesis considerations to bioapplications. To this end, we have reviewed several practical considerations and prepared several straightforward recommendations toward improved cohesion in the field, based on observed trends over the last decade of research.

The effects of lanthanide-doped upconverting nanoparticles on cancer cell biomarkers.

Lanthanide-doped upconverting nanoparticles (Ln-UCNPs) possess optical and physicochemical properties that are promising for the design of new theranostic platforms. This applies in particular to the treatment of cancer. Towards this goal, oleate-capped-NaLuF4:Tm3+(0.5%)/Yb3+(20%)/Gd3+(30%) with an average size of 35 nm ± 2 nm were synthesized by co-precipitation. Due to their hydrophobic surface, these Ln-UCNPs produced agglomerates under cell culture conditions. To assess the cellular response to Ln-UCNPs at the molecular level, we evaluated several key aspects of tumor cell physiology. Using cancer lines of different origins, we demonstrated Ln-UCNP dependent changes of cancer cell biomarkers. Multiple cellular components that regulate tumorigenesis and cancer cell homeostasis were affected. In particular, Ln-UCNPs reduced the abundance of hsp70s, elevated DNA damage, and diminished nucleolin and B23/nucleophosmin, proteins required for the assembly of ribosomes. Treatment with Ln-UCNPs also decreased the concentration of paxillin, a focal adhesion protein that is involved in directed cell migration. Furthermore, epidermal growth factor (EGFR) levels were decreased by Ln-UCNPs for most cancer cell lines examined. Taken together, we identified several potential cancer cell targets that were affected by Ln-UCNPs. Our work thereby provides the foundation to optimize Ln-UCNPs for the targeted killing of tumor cells.

Radioluminescence studies of colloidal oleate-capped ß-Na(Gd,Lu)F4:Ln3+ nanoparticles (Ln = Ce, Eu, Tb).

We report on the synthesis, characterization, and radioluminescence quantification of several new varieties of nanoparticles with the general composition ß-NaLnF4, incorporating known luminescent activator/sensitizer pairs. Using Monte Carlo modeling to complement luminescence measurements, we have calculated the radioluminescence yields and intrinsic conversion efficiencies of colloidally-dispersed nanoparticles by comparison to an organic liquid scintillator. While five of the compositions had low to modest radioluminescence yields relative to bulk materials, colloidal ß-Na(Lu0.65Gd0.2Tb0.15)F4 displayed a strong output of 39 460 photons per MeV absorbed, comparable to some of the best non-hygroscopic bulk crystal scintillators and X-ray phosphors such as Gd2O2S:Tb. Measurements of ß-Na(Lu0.65Gd0.2Tb0.15)F4 powder samples revealed persistent luminescence as well as stable charge trapping, warranting further investigation.

Scintillation Yield Estimates of Colloidal Cerium-Doped LaF3 Nanoparticles and Potential for "Deep PDT".

A hybrid of radiotherapy and photodynamic therapy (PDT) has been proposed in previously reported studies. This approach utilizes scintillating nanoparticles to transfer energy to attached photosensitizers, thus generating singlet oxygen for local killing of malignant cells. Its effectiveness strongly depends upon the scintillation yield of the nanoparticles. Using a liquid scintillator as a reference standard, we estimated the scintillation yield of Ce0.1La0.9F3/LaF3 core/shell nanoparticles at 28.9 mg/ml in water to be 350 photons/MeV under orthovoltage X-ray irradiation. The subsequent singlet oxygen production for a 60 Gy cumulative dose to cells was estimated to be four orders of magnitude lower than the "Niedre killing dose," used as a target value for effective cell killing. Without significant improvements in the radioluminescence properties of the nanoparticles, this approach to "deep PDT" is likely to be ineffective. Additional considerations and alternatives to singlet oxygen are discussed.

Gold nanoparticles and their alternatives for radiation therapy enhancement.

Radiation therapy is one of the most commonly used treatments for cancer. The dose of delivered ionizing radiation can be amplified by the presence of high-Z materials via an enhancement of the photoelectric effect; the most widely studied material is gold (atomic number 79). However, a large amount is needed to obtain a significant dose enhancement, presenting a challenge for delivery. In order to make this technique of broader applicability, the gold must be targeted, or alternative formulations developed that do not rely solely on the photoelectric effect. One possible approach is to excite scintillating nanoparticles with ionizing radiation, and then exploit energy transfer between these particles and attached dyes in a manner analogous to photodynamic therapy (PDT). Doped rare-earth halides and semiconductor quantum dots have been investigated for this purpose. However, although the spectrum of emitted light after radiation excitation is usually similar to that seen with light excitation, the yield is not. Measurement of scintillation yields is challenging, and in many cases has been done only for bulk materials, with little understanding of how the principles translate to the nanoscale. Another alternative is to use local heating using gold or iron, followed by application of ionizing radiation. Hyperthermia pre-sensitizes the tumors, leading to an improved response. Another approach is to use chemotherapeutic drugs that can radiosensitize tumors. Drugs may be attached to high-Z nanoparticles or encapsulated. This article discusses each of these techniques, giving an overview of the current state of nanoparticle-assisted radiation therapy and future directions.

Photoluminescence of cerium fluoride and cerium-doped lanthanum fluoride nanoparticles and investigation of energy transfer to photosensitizer molecules.

CexLa1-xF3 nanoparticles have been proposed for use in nanoscintillator-photosensitizer systems, where excitation of nanoparticles by ionizing radiation would result in energy transfer to photosensitizer molecules, effectively combining the effects of radiotherapy and photodynamic therapy. Thus far, there have been few experimental investigations of such systems. This study reports novel synthesis methods for water-dispersible Ce0.1La0.9F3/LaF3 and CeF3/LaF3 core/shell nanoparticles and an investigation of energy transfer to photosensitizers. Unbound deuteroporphyrin IX 2,4-disulfonic acid was found to substantially quench the luminescence of large (>10 nm diameter) aminocaproic acid-stabilized nanoparticles at reasonable concentrations and loading amounts: up to 80% quenching at 6% w/w photosensitizer loading. Energy transfer was found to occur primarily through a cascade, with excitation of "regular" site Ce(3+) at 252 nm relayed to photosensitizer molecules at the nanoparticle surface through intermediate "perturbed" Ce(3+) sites. Smaller (<5 nm) citrate-stabilized nanoparticles were coated with the bisphosphonate alendronate, allowing covalent conjugation to chlorin e6 and resulting in static quenching of the nanoparticle luminescence: ∼50% at ∼0.44% w/w. These results provide insight into energy transfer mechanisms that may prove valuable for optimizing similar systems.

Conductance switching in the photoswitchable protein Dronpa.

Dronpa, a photoswitchable GFP-like protein, was self-assembled onto gold substrates, and its conductance was measured using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS).

Reusing steel and aluminum components at end of product life.

Reusing steel and aluminum components would reduce the need for new production, possibly creating significant savings in carbon emissions. Currently, there is no clearly defined set of strategies or barriers to enable assessment of appropriate component reuse; neither is it possible to predict future levels of reuse. This work presents a global assessment of the potential for reusing steel and aluminum components. A combination of top-down and bottom-up analyses is used to allocate the final destinations of current global steel and aluminum production to product types. A substantial catalogue has been compiled for these products characterizing key features of steel and aluminum components including design specifications, requirements in use, and current reuse patterns. To estimate the fraction of end-of-life metal components that could be reused for each product, the catalogue formed the basis of a set of semistructured interviews with industrial experts. The results suggest that approximately 30% of steel and aluminum used in current products could be reused. Barriers against reuse are examined, prompting recommendations for redesign that would facilitate future reuse.

Photosensitization of CdSe/ZnS QDs and reliability of assays for reactive oxygen species production.

CdSe/ZnS quantum dots (QDs) conjugated to biomolecules that can act as electron donors are said to be "photosensitized": that is, they are able to oxidize or reduce molecules whose redox potential lies inside their band edges, in particular molecular oxygen and water. This leads to the formation of reactive oxygen species (ROS) and phototoxicity. In this work, we quantify the generation of different forms of ROS from as-synthesized QDs in toluene; water-solubilized, unconjugated QDs; QDs conjugated to the neurotransmitter dopamine; and dopamine alone. Results of indirect fluorescent ROS assays, both in solution and inside cells, are compared with those of spin-trap electron paramagnetic resonance spectroscopy (EPR). The effect of these particles on the metabolism of mammalian cells is shown to be dependent upon light exposure and proportional to the amount of ROS generated.

Photoenhancement of lifetimes in CdSe/ZnS and CdTe quantum dot-dopamine conjugates.

The response of water-soluble, mercaptocarboxylic acid-capped fluorescent semiconductor nanoparticles, or quantum dots (QDs), to extended visible-light irradiation is variable and poorly described. Here we use time-resolved spectroscopy to investigate the photoluminescence intensities and lifetimes of CdSe/ZnS and CdTe QDs as a function of blue light illumination. Conjugates of the particles to the electron donor dopamine were also investigated, and the effect of the antioxidant beta-mercaptoethanol was explored. Both types of QD showed signs of direct electron transfer to the conjugate, but enhancement was much more pronounced in CdSe/ZnS. A model of the two different types of enhancement is proposed.

Nanotechnology for in vitro neuroscience.

Neurons in vitro are different from any other cell types in their sensitivity and complexity. Growing, differentiating, transfecting, and recording from single neurons and neuronal networks all present particular challenges. Some of the difficulties arise from the small scale of cellular structures, and have already seen substantial advances due to nanotechnology, particularly highly fluorescent semiconductor nanoparticles. Other issues have less obvious solutions, but the complex and often surprising way that novel nanomaterials react with cells have suggested some revolutionary approaches. We review some of the ways nanomaterials and nanostructures can contribute to in vitro neuroscience, with a particular focus on emphasizing techniques that are widely accessible to many laboratories and on providing references to protocols and methods. The issues of nanotoxicology of greatest interest to cultured neurons are discussed. Finally, we present some future trends and challenges in nano-neuroscience.