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"Young, David L"
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Machine landscapes : architectures of the post-anthropocene
The most significant architectural spaces in the world are now entirely empty of people. The data centres, telecommunications networks, distribution warehouses, unmanned ports and industrialised agriculture that define the very nature of who we are today are at the same time places we can never visit. Instead they are occupied by server stacks and hard drives, logistics bots and mobile shelving units, autonomous cranes and container ships, robot vacuum cleaners and internet-connected toasters, driverless tractors and taxis. This issue is an atlas of sites, architectures and infrastructures that are not built for us, but whose form, materiality and purpose is configured to anticipate the patterns of machine vision and habitation rather than our own. We are said to be living in a new geological epoch, the Anthropocene, in which humans are the dominant force shaping the planet. This collection of spaces, however, more accurately constitutes an era of the Post-Anthropocene, a period where it is technology and artificial intelligence that now computes, conditions and constructs our world. Marking the end of human-centered design, the issue turns its attention to the new typologies of the post-human, architecture without people and our endless expanse of machine landscapes.
Book
Raising the one-sun conversion efficiency of III–V/Si solar cells to 32.8% for two junctions and 35.9% for three junctions
Today’s dominant photovoltaic technologies rely on single-junction devices, which are approaching their practical efficiency limit of 25–27%. Therefore, researchers are increasingly turning to multi-junction devices, which consist of two or more stacked subcells, each absorbing a different part of the solar spectrum. Here, we show that dual-junction III–V//Sidevices with mechanically stacked, independently operated III–V and Si cells reach cumulative one-sun efficiencies up to 32.8%. Efficiencies up to 35.9% were achieved when combining a GaInP/GaAs dual-junction cell with a Si single-junction cell. These efficiencies exceed both the theoretical 29.4% efficiency limit of conventional Si technology and the efficiency of the record III–V dual-junction device (32.6%), highlighting the potential of Si-based multi-junction solar cells. However, techno-economic analysis reveals an order-of-magnitude disparity between the costs for III–V//Si tandem cells and conventional Si solar cells, which can be reduced if research advances in low-cost III–V growth techniques and new substrate materials are successful.
To improve the efficiency of photovoltaic devices while keeping the same spatial footprint, solar cells can be stacked on top of each other. Here, Essig
et al.
fabricate very efficient dual-junction and triple-junction solar cells by placing one or two III–V solar cells on top of a silicon solar cell.
Journal Article
Polycrystalline silicon passivated tunneling contacts for high efficiency silicon solar cells
We apply n- and p-type polycrystalline silicon (poly-Si) films on tunneling SiOx to form passivated contacts to n-type Si wafers. The resulting induced emitter and n+/n back surface field junctions of high carrier selectivity and low contact resistivity enable high efficiency Si solar cells. This work addresses the materials science of their performance governed by the properties of the individual layers (poly-Si, tunneling oxide) and more importantly, by the process history of the cell as a whole. Tunneling SiOx layers (<2 nm) are grown thermally or chemically, followed by a plasma enhanced chemical vapor deposition growth of p+ or n+ doped a-Si:H. The latter is thermally crystallized into poly-Si, resulting in grain nucleation and growth as well as dopant diffusion within the poly-Si and penetration through the tunneling oxide into the Si base wafer. The cell process is designed to improve the passivation of both oxide interfaces and tunneling transport through the oxide. A novel passivation technique involves coating of the passivated contact and whole cell with atomic layer deposited Al2O3 and activating them at 400 °C. The resulting excellent passivation persists after subsequent chemical removal of the Al2O3. The preceding cell process steps must be carefully tailored to avoid structural and morphological defects, as well as to maintain or improve passivation, and carrier selective transport. Furthermore, passivated contact metallization presents significant challenges, often resulting in passivation loss. Suggested remedies include improved Si cell wafer surface morphology (without micropyramids) and postdeposited a-Si:H capping layers over the poly-Si.
Journal Article
Massively Parallel Functional Analysis of BRCA1 RING Domain Variants
Interpreting variants of uncertain significance (VUS) is a central challenge in medical genetics. One approach is to experimentally measure the functional consequences of VUS, but to date this approach has been post hoc and low throughput. Here we use massively parallel assays to measure the effects of nearly 2000 missense substitutions in the RING domain of BRCA1 on its E3 ubiquitin ligase activity and its binding to the BARD1 RING domain. From the resulting scores, we generate a model to predict the capacities of full-length BRCA1 variants to support homology-directed DNA repair, the essential role of BRCA1 in tumor suppression, and show that it outperforms widely used biological-effect prediction algorithms. We envision that massively parallel functional assays may facilitate the prospective interpretation of variants observed in clinical sequencing.
Journal Article
High-resolution analysis of DNA regulatory elements by synthetic saturation mutagenesis
Patwardhan
et al
. describe a high-throughput approach for analyzing at single-nucleotide resolution the DNA regulatory sequences that control gene expression. Characterizing these sequences in a massively parallel manner will be useful for deciphering the regulatory logic of the cell and for synthetic biology.
We present a method that harnesses massively parallel DNA synthesis and sequencing for the high-throughput functional analysis of regulatory sequences at single-nucleotide resolution. As a proof of concept, we quantitatively assayed the effects of all possible single-nucleotide mutations for three bacteriophage promoters and three mammalian core promoters in a single experiment per promoter. The method may also serve as a rapid screening tool for regulatory element engineering in synthetic biology.
Journal Article
III-V-Based Optoelectronics with Low-Cost Dynamic Hydride Vapor Phase Epitaxy
Silicon is the dominant semiconductor in many semiconductor device applications for a variety of reasons, including both performance and cost. III-V materials exhibit improved performance compared to silicon, but currently, they are relegated to applications in high-value or niche markets, due to the absence of a low-cost, high-quality production technique. Here we present an advance in III-V materials synthesis, using a hydride vapor phase epitaxy process that has the potential to lower III-V semiconductor deposition costs, while maintaining the requisite optoelectronic material quality that enables III-V-based technologies to outperform Si. We demonstrate the impacts of this advance by addressing the use of III-Vs in terrestrial photovoltaics, a highly cost-constrained market.
Journal Article
Microwave Annealing for Fast and Effective Hydrogen Activation in Polycrystalline Silicon Passivating Contacts
Hydrogenation is a crucial step in the fabrication of high‐efficiency silicon solar cells. In this study, the effectiveness of hydrogen activation is demonstrated via microwave annealing of hydrogen‐rich dielectrics coated on poly‐Si passivating contacts. This method is compared with conventional hydrogenation techniques, such as annealing in N2 in the presence of a hydrogen‐rich source (such as hydrogenated aluminum oxide (AlOx:H), hydrogenated silicon nitride (SiNy:H), or a AlOx:H/SiNy:H stack). Key improvements observed include a reduction in J0 from 30 to <5 fA cm−2, an increase in iVoc from 690 to >730 mV, and an enhancement in effective lifetime (τeff) from 0.6 to ≈3.5 milliseconds on phosphorus‐doped poly‐Si/SiO2 passivating contact samples. With a very short annealing time of ≈1–2 min, the samples passivated by AlOx:H, SiNy:H, or the stack show similar performance to samples subjected to 30 min of nitrogen annealing. Photoluminescence (PL) spectra corroborate the findings regarding the hydrogenation of the poly‐Si layer and the c‐Si substrate, with an increase in PL intensity after microwave annealing. Ultimately, this work suggests that microwave annealing could be a promising addition, offering flexibility to traditional firing hydrogenation processes. Hydrogenation is a crucial step in the fabrication of high‐efficiency silicon solar cells, which is currently integrated into the fire‐through screen‐printing metallization. Truong et al. report on the use of microwave annealing as an effective decoupled method to activate hydrogen for poly‐Si passivating contacts.
Journal Article
Combining Natural Sequence Variation with High Throughput Mutational Data to Reveal Protein Interaction Sites
Many protein interactions are conserved among organisms despite changes in the amino acid sequences that comprise their contact sites, a property that has been used to infer the location of these sites from protein homology. In an inter-species complementation experiment, a sequence present in a homologue is substituted into a protein and tested for its ability to support function. Therefore, substitutions that inhibit function can identify interaction sites that changed over evolution. However, most of the sequence differences within a protein family remain unexplored because of the small-scale nature of these complementation approaches. Here we use existing high throughput mutational data on the in vivo function of the RRM2 domain of the Saccharomyces cerevisiae poly(A)-binding protein, Pab1, to analyze its sites of interaction. Of 197 single amino acid differences in 52 Pab1 homologues, 17 reduce the function of Pab1 when substituted into the yeast protein. The majority of these deleterious mutations interfere with the binding of the RRM2 domain to eIF4G1 and eIF4G2, isoforms of a translation initiation factor. A large-scale mutational analysis of the RRM2 domain in a two-hybrid assay for eIF4G1 binding supports these findings and identifies peripheral residues that make a smaller contribution to eIF4G1 binding. Three single amino acid substitutions in yeast Pab1 corresponding to residues from the human orthologue are deleterious and eliminate binding to the yeast eIF4G isoforms. We create a triple mutant that carries these substitutions and other humanizing substitutions that collectively support a switch in binding specificity of RRM2 from the yeast eIF4G1 to its human orthologue. Finally, we map other deleterious substitutions in Pab1 to inter-domain (RRM2-RRM1) or protein-RNA (RRM2-poly(A)) interaction sites. Thus, the combined approach of large-scale mutational data and evolutionary conservation can be used to characterize interaction sites at single amino acid resolution.
Journal Article
High- and ultrahigh-field magnetic resonance imaging of naïve, injured and scarred vocal fold mucosae in rats
Subepithelial changes to the vocal fold mucosa, such as fibrosis, are difficult to identify using visual assessment of the tissue surface. Moreover, without suspicion of neoplasm, mucosal biopsy is not a viable clinical option, as it carries its own risk of iatrogenic injury and scar formation. Given these challenges, we assessed the ability of high- (4.7 T) and ultrahigh-field (9.4 T) magnetic resonance imaging to resolve key vocal fold subepithelial tissue structures in the rat, an important and widely used preclinical model in vocal fold biology. We conducted serial in vivo and ex vivo imaging, evaluated an array of acquisition sequences and contrast agents, and successfully resolved key anatomic features of naïve, acutely injured, and chronically scarred vocal fold mucosae on the ex vivo scans. Naïve lamina propria was hyperintense on T1-weighted imaging with gadobenate dimeglumine contrast enhancement, whereas chronic scar was characterized by reduced lamina propria T1 signal intensity and mucosal volume. Acutely injured mucosa was hypointense on T2-weighted imaging; lesion volume steadily increased, peaked at 5 days post-injury, and then decreased – consistent with the physiology of acute, followed by subacute, hemorrhage and associated changes in the magnetic state of hemoglobin and its degradation products. Intravenous administration of superparamagnetic iron oxide conferred no T2 contrast enhancement during the acute injury period. These findings confirm that magnetic resonance imaging can resolve anatomic substructures within naïve vocal fold mucosa, qualitative and quantitative features of acute injury, and the presence of chronic scar.
Journal Article
