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Using wet-chemical self-assembly, we demonstrate that standard surface reactions can be markedly altered. Although HF etching of Si surfaces is known to produce H-terminated surfaces, we show that up to ∼30% of a monolayer of stable Si–F bonds can be formed on atomically smooth Si(111) surfaces on HF reaction, when chemically isolated Si atoms are the target of the reaction. Similarly, ∼30% Si–OH termination can be achieved by immersion of the partially covered F–Si(111) surface in water without oxidation of the underlying Si substrate. Such reactions are possible when H-terminated (111)-oriented Si surfaces are initially uniformly patterned with methoxy groups. These findings are contrary to the knowledge built over the past twenty years and highlight the importance of steric interactions at surfaces and the possibility to stabilize products at surfaces that cannot be obtained on chemically homogeneous surfaces. The ability to control the surface chemistry of silicon is important for microelectronic applications. Chemical species can now be stabilized on Si(111) surfaces using a partially alkoxylated surface as a nanopatterning template.

As spin-based quantum processors grow in size and complexity, maintaining high fidelities and minimizing crosstalk will be essential for the successful implementation of quantum algorithms and error-correction protocols. In particular, recent experiments have highlighted pernicious transient qubit frequency shifts associated with microwave qubit driving. Work-arounds for small devices, including prepulsing with an off-resonant microwave burst to bring a device to a steady state, wait times prior to measurement, and qubit-specific calibrations all bode ill for device scalability. Here, we make substantial progress in understanding and overcoming this effect. We report a surprising nonmonotonic relation between mixing chamber temperature and spin Larmor frequency which is consistent with observed frequency shifts induced by microwave and baseband control signals. We find that purposefully operating the device at 200 mK greatly suppresses the adverse heating effect while not compromising qubit coherence or single-qubit fidelity benchmarks. Furthermore, systematic non-Markovian crosstalk is greatly reduced. Our results provide a straightforward means of improving the quality of multispin control while simplifying calibration procedures for future spin-based quantum processors.

Reducing the delay of backend interconnects is critical in delivering improved performance in next generation computer chips. One option is to implement interlayer dielectric (ILD) materials with increasingly lower dielectric constant (k) values. Despite industry need, there has been a recent decrease in study and production of these materials in academia and business communities. We have generated a backbone and porogen system that allows us to control porosity from 0 to 60% volume, achieve k-values from 3.4 to 1.6, maintain high chemical stability to various wet cleans, and deliver uniquely high mechanical strength at a given porosity. Finite element modeling and experimental results demonstrate that further improvements can be achieved through control of the pore volume into an ordered network. With hopes to spur more materials development, this paper discusses some molecular design and nanoscale hierarchical principles relevant to making next generation low-k ILD materials.

As spin-based quantum processors grow in size and complexity, maintaining high fidelities and minimizing crosstalk will be essential for the successful implementation of quantum algorithms and error-correction protocols. In particular, recent experiments have highlighted pernicious transient qubit frequency shifts associated with microwave qubit driving. Workarounds for small devices, including prepulsing with an off-resonant microwave burst to bring a device to a steady-state, wait times prior to measurement, and qubit-specific calibrations all bode ill for device scalability. Here, we make substantial progress in understanding and overcoming this effect. We report a surprising non-monotonic relation between mixing chamber temperature and spin Larmor frequency which is consistent with observed frequency shifts induced by microwave and baseband control signals. We find that purposefully operating the device at 200 mK greatly suppresses the adverse heating effect while not compromising qubit coherence or single-qubit fidelity benchmarks. Furthermore, systematic non-Markovian crosstalk is greatly reduced. Our results provide a straightforward means of improving the quality of multi-spin control while simplifying calibration procedures for future spin-based quantum processors.

Low interfacial electron-hole recombination rates are essential for low-noise electronic devices and high-efficiency solar energy converters. This recombination rate is dependent on both the surface electrical trap state density, NT,s, and the surface concentrations of electrons, ns, and holes, ps. A reduction in NT,s is often accomplished through surface chemistry, and lower recombination rates, through lower N T,s values, have been demonstrated in this work for surfaces chemically treated to produce methoxylated, Si-O-CH3, overlayers. The H-Si(111) surfaces can react with methanol quickly in the presence of an oxidant or slowly in neat anhydrous methanol. Mechanisms have been proposed for both reactions. Low recombination rates can also be achieved through control of the surface physics; a large ns or ps can lower recombination rates. To date, low recombination rates have often been attributed only to a reduction in NT,s, without a direct measurement of ns and p s, partly because the importance of ns and ps has not been fully recognized and partly because an accurate evaluation of ns and ps can be very difficult. Surface recombination rates of silicon immersed in liquids containing various redox species ( e.g., Fc+/0, I2, Me10Fc +/0, or CoCp2+/0) were studied using an rf photoconductivity decay apparatus and compared with ns and ps values obtained from Mott-Schottky and other analysis techniques. The results demonstrate that the observed recombination rates can only be correlated with NT,s values when ns ≈ ps. In all other cases, the recombination rate was low due to a large n s or ps even for surfaces with large NT,s values. The full impact of this work was further realized through a study of the recombination rates of H-Si immersed in solutions of 48% HF, 40% NH 4F, and buffered HF (BHF), because such measurements are often performed for in situ monitoring of the surface quality during wafer processing steps. Our results demonstrate that only HF contacts can be used for in situ monitoring because ns ≈ ps. For NH4F or BHF contacts, low recombination rates were observed only because ns >> ps, and NT,s cannot be inferred from these measurements.

Quantum computers with tens to hundreds of noisy qubits are being developed today. To be useful for real-world applications, we believe that these near-term systems cannot simply be scaled-down non-error-corrected versions of future fault-tolerant large-scale quantum computers. These near-term systems require specific architecture and design attributes to realize their full potential. To efficiently execute an algorithm, the quantum coprocessor must be designed to scale with respect to qubit number and to maximize useful computation within the qubits' decoherence bounds. In this work, we employ an application-system-qubit co-design methodology to architect a near-term quantum coprocessor. To support algorithms from the real-world application area of simulating the quantum dynamics of a material system, we design a (parameterized) arbitrary single-qubit rotation instruction and a two-qubit entangling controlled-Z instruction. We introduce dynamic gate set and paging mechanisms to implement the instructions. To evaluate the functionality and performance of these two instructions, we implement a two-qubit version of an algorithm to study a disorder-induced metal-insulator transition and run 60 random instances of it, each of which realizes one disorder configuration and contains 40 two-qubit instructions (or gates) and 104 single-qubit instructions. We observe the expected quantum dynamics of the time-evolution of this system.

As evidenced by past climatic refugia, locations projected to harbor remnants of present-day climates may serve as critical refugia for current biodiversity in the face of modem climate change. We mapped potential climatic refugia in the future across North America, defined as locations with increasingly rare climatic conditions. We identified these locations by trackingprojected changes in the size and distribution of climate analogs over time. We used biologically derived thresholds to define analogs and tested the impacts of dispersal limitation with 4 distances to limit analog searches. We identified at most 12% of North America as potential climatic refugia. Refugia extent varied depending on the analog threshold, dispersal distance, and climate projection. However, in all cases refugia were concentrated at high elevations and in topographically complex regions. Refugia identified using different climate projections were largely nested, suggesting that identified refugia were relatively robust to climate-projection selection. Existing conservation areas cover approximately 10% of North America and yet protected up to 25% of identified refugia, indicating that protected areas disproportionately include refugia. Refugia located at lower latitudes (≤40°N) and slightly lower elevations (approximately 2500 m ) were more likely to be unprotected. Based on our results, a 23% expansion of the protected-area network would be sufficient to protect the refugia present under all 3 climate projections we explored. We believe these refugia are high conservation priorities due to their potential to harbor rare species in the future. However, these locations are simultaneously highly vulnerable to climate change over the long term. These refugia contracted substantially between the 2050s and the 2080s, which supports the idea that the pace of climate change will strongly determine the availability and effectiveness of refugia for protecting today's biodiversity. Los refugios climáticos pasados han evidenciado que las localidades proyectadas para albergar remanentes de los climas actuales pueden fungir como refugios importantes para la biodiversidad contemporánea de frente al cambio climático actual. Mapeamos los refugios climáticos potenciales en el futuro a lo largo de América del Norte, definidos como localidades con condiciones climáticas cada vez más raras. Identificamos estas localidades rastreando los cambios proyectados en el tamaño y distribución de los análogos climáticos en el transcurso del tiempo. Usamos umbrales derivados biológicamente para definir estos análogos y probamos los impactos de la limitación de la dispersión con cuatro distancias para limitar las búsquedas análogas. Identificamos, cuando mucho, el 12% de América del Norte como refugios climáticos potenciales. La extensión de los refugios varió dependiendo del umbral análogo, la distancia de dispersión y la proyección climática. Sin embargo, los refugios estuvieron concentrados en elevaciones altas y en regiones complejas topográficamente en todos los casos. Los refugios que fueron identificados usando diferentes proyecciones climáticas estuvieron anidados en general, lo que sugiere que estos refugios identificados fueron relativamente sólidos con respecto a la selección de proyección climática. Las áreas de conservación existentes cubren aproximadamente el 10% de América del Norte y aun así protegieron hasta el 25% de los refugios identificados, lo que indica que las áreas protegidas incluyen desproporcionada mente refugios climáticos. Los refugios localizados a latitudes menores (≤40°N) y a elevaciones ligeramente menores (aproximadamente 2500 m) tuvieron una mayor probabilidad de no estar protegidos. Con base en nuestros resultados, una expansión del 23% de la red de áreas protegidas debería ser suficiente para proteger los refugios presentes en las tresproyecciones climáticas que exploramos. Creemos que estos refugios climáticos son de prioridad alta para la conservación debido a su potencial para albergar especies raras en el futuro. Sin embargo, estas localidades también son altamente vulnerables al cambio climático a largo plazo. Estos refugios se redujeron sustancialmente entre las décadas de 2050 y 2080, lo que refuerza la idea de que el paso del cambio climático determinará con fuerza la disponibilidad y efectividad de los refugios climáticos para proteger a la biodiversidad contemporánea. 过去的气候庇护所数据可以证明，在现代气候变化的情况下,那些 被预测可以保留残存物种的地区可能是当前生物多祥性的重要庇护所。我们绘制了北美地区未来潜在的气候庇 护所地图, 对气候庇护所的定义是那些罕见气候条件日益増加的地区, 我们主要是通过追踪相似气候在大小和分 布上随时间的预计变化确定了这些地区。我们用生物学的临界值来定义相似气候，并通过分析四种、不同扩散距 离限制的影响来限定对相似气候的搜寻范围。本研究发现北美洲至多有12%的地区是潜在气候庇护所。庇护所 的范围随相似气候的临界值.、扩散距离和气候预测模型而变化。然而，在所有案例中，庇护所都集中在那些海 拔高、地形复杂的地区。用不同气候预测模型确定的庇护所很大程度上是相互嵌套的，这表明它们对气候预测 模型的选择相对稳健。目前，现有的保护地覆盖了北美约10%的地区，保护着髙达25%经确定的庇护所，这说明 保护地不成比例地囊括了庇护所, 而那些位于低纬度地区 (≤40°N) 和较低海拔(约2500米)的庇护所更有可能 仍未受到保护。根据我们的结果，保护地网络扩大23% 就足以保护我们分析的三种气候预测模型下存在的庇护 所。我们相信这些庇护所应得到优先保护, 因为它们有潜力在未来为珍稀物种提供栖息地。然而，从长期来看，这些地区同时非常容易受到气候变化的影响。它们可能在21世纪50到80年代大幅度縮小，这支持了气候变化的 速度将大大影响庇护所对于保护当前生物多祥性的可用性及有效性的观点。

In 2011, Lake Erie experienced the largest harmful algal bloom in its recorded history, with a peak intensity over three times greater than any previously observed bloom. Here we show that long-term trends in agricultural practices are consistent with increasing phosphorus loading to the western basin of the lake, and that these trends, coupled with meteorological conditions in spring 2011, produced record-breaking nutrient loads. An extended period of weak lake circulation then led to abnormally long residence times that incubated the bloom, and warm and quiescent conditions after bloom onset allowed algae to remain near the top of the water column and prevented flushing of nutrients from the system. We further find that all of these factors are consistent with expected future conditions. If a scientifically guided management plan to mitigate these impacts is not implemented, we can therefore expect this bloom to be a harbinger of future blooms in Lake Erie.

Interleukin 15 (IL-15) promotes the survival of natural killer (NK) cells by preventing apoptosis through mechanisms unknown at present. Here we identify Bim, Noxa and Mcl-1 as key regulators of IL-15-dependent survival of NK cells. IL-15 suppressed apoptosis by limiting Bim expression through the kinases Erk1 and Erk2 and mechanisms dependent on the transcription factor Foxo3a, while promoting expression of Mcl-1, which was necessary and sufficient for the survival of NK cells. Withdrawal of IL-15 led to upregulation of Bim and, accordingly, both Bim-deficient and Foxo3a −/− NK cells were resistant to cytokine deprivation. Finally, IL-15-mediated inactivation of Foxo3a and cell survival were dependent on phosphotidylinositol-3-OH kinase. Thus, IL-15 regulates the survival of NK cells at multiple steps, with Bim and Noxa being key antagonists of Mcl-1, the critical survivor factor in this process.

Unlike for advanced liver fibrosis, the practical rules for the early non-invasive diagnosis of cirrhosis in NAFLD remain not well defined. Here, we report the derivation and validation of a stepwise diagnostic algorithm in 1568 patients with NAFLD and liver biopsy coming from four independent cohorts. The study algorithm, using first the elastography-based tests Agile3+ and Agile4 and then the specialized blood tests FibroMeter V3G and CirrhoMeter V3G , provides stratification in four groups, the last of which is enriched in cirrhosis (71% prevalence in the validation set). A risk prediction chart is also derived to allow estimation of the individual probability of cirrhosis. The predicted risk shows excellent calibration in the validation set, and mean difference with perfect prediction is only −2.9%. These tools improve the personalized non-invasive diagnosis of cirrhosis in NAFLD. The practical rules for the early non-invasive diagnosis of cirrhosis in NAFLD are not well defined. Here, the authors develop and validate two diagnostic tools: a stepwise stratification algorithm including a cirrhosis group, and a risk prediction chart providing a personalized assessment of the individual probability of cirrhosis.