This paper summarizes key findings in single-photon generation from deep level defects in silicon carbide (SiC) and highlights the significance of these individually addressable centers for emerging ...quantum applications. Single photon emission from various defect centers in both bulk and nanostructured SiC are discussed as well as their formation and possible integration into optical and electrical devices. The related measurement protocols, the building blocks of quantum communication and computation network architectures in solid state systems, are also summarized. This includes experimental methodologies developed for spin control of different paramagnetic defects, including the measurement of spin coherence times. Well established doping, and micro- and nanofabrication procedures for SiC may allow the quantum properties of paramagnetic defects to be electrically and mechanically controlled efficiently. The integration of single defects into SiC devices is crucial for applications in quantum technologies and we will review progress in this direction.
Abstract
We use very long baseline interferometry to measure the proper motions of three black hole X-ray binaries (BHXBs). Using these results together with data from the literature and Gaia DR2 to ...collate the best available constraints on proper motion, parallax, distance, and systemic radial velocity of 16 BHXBs, we determined their three-dimensional Galactocentric orbits. We extended this analysis to estimate the probability distribution for the potential kick velocity (PKV) a BHXB system could have received on formation. Constraining the kicks imparted to BHXBs provides insight into the birth mechanism of black holes (BHs). Kicks also have a significant effect on BH–BH merger rates, merger sites, and binary evolution, and can be responsible for spin–orbit misalignment in BH binary systems. 75 per cent of our systems have potential kicks $\gt 70\, \rm {km\,s^{-1}}$. This suggests that strong kicks and hence spin–orbit misalignment might be common among BHXBs, in agreement with the observed quasi-periodic X-ray variability in their power density spectra. We used a Bayesian hierarchical methodology to analyse the PKV distribution of the BHXB population, and suggest that a unimodal Gaussian model with a mean of 107 $\pm \,\,16\, \rm {km\,s^{-1}}$ is a statistically favourable fit. Such relatively high PKVs would also reduce the number of BHs likely to be retained in globular clusters. We found no significant correlation between the BH mass and PKV, suggesting a lack of correlation between BH mass and the BH birth mechanism. Our python code allows the estimation of the PKV for any system with sufficient observational constraints.
To assess heterogeneity in the influence of genetic variation on educational attainment across environmental contexts, we present a meta-analysis of heritability estimates in fifteen samples and ...thirty-four subgroups differing by nationality, sex, and birth cohort. We find that heritability, shared environment, and unshared environment each explain a substantial percentage of the variance in attainment across all countries, with between-sample heterogeneity in all three variance components. Although we observe only meager differences in the total family effect by cohort or sex, we observe large cohort and sex differences in the composition of the family effect, consistent with a history of higher heritability of educational attainment for males and for individuals born in the latter half of the twentieth century. Heritability also varies significantly by nation, with the direction of variation specific by sample. We find a markedly larger impact of shared environment on attainment than has been found for other social outcomes, with the percent of variation in attainment attributable to shared environment exceeding the percent attributable to heritability in one-third of the studies in our sample. Our findings demonstrate the heritability of educational attainment to be environmentally contingent, affirm the widespread and enduring role of shared environment in determining ultimate socioeconomic attainment, and emphasize the importance of considering behavioral genetics techniques in models of social mobility.
The precise measurement of mechanical stress at the nanoscale is of fundamental and technological importance. In principle, all six independent variables of the stress tensor, which describe the ...direction and magnitude of compression/tension and shear stress in a solid, can be exploited to tune or enhance the properties of materials and devices. However, existing techniques to probe the local stress are generally incapable of measuring the entire stress tensor. Here, we make use of an ensemble of atomic-sized in situ strain sensors in diamond (nitrogen-vacancy defects) to achieve spatial mapping of the full stress tensor, with a submicrometer spatial resolution and a sensitivity of the order of 1 MPa (10 MPa) for the shear (axial) stress components. To illustrate the effectiveness and versatility of the technique, we apply it to a broad range of experimental situations, including mapping the stress induced by localized implantation damage, nanoindents, and scratches. In addition, we observe surprisingly large stress contributions from functional electronic devices fabricated on the diamond and also demonstrate sensitivity to deformations of materials in contact with the diamond. Our technique could enable in situ measurements of the mechanical response of diamond nanostructures under various stimuli, with potential applications in strain engineering for diamond-based quantum technologies and in nanomechanical sensing for on-chip mass spectroscopy.
Formation of an r8-Dominant Si Material Wong, S; Haberl, B; Johnson, B C ...
Physical review letters,
2019-Mar-15, Letnik:
122, Številka:
10
Journal Article
Recenzirano
Odprti dostop
The rhombohedral phase of Si (r8-Si), a promising semiconducting material, is formed by indentation together with the body-centered cubic phase (bc8-Si). Using a novel sample preparation method, ...x-ray diffraction is used to determine the relative volume of these phases in indented Si and allow observation of a distorted unit cell along the direction of indentation loading. Theoretical calculations together with these observations suggest the indent contains an intrinsic compression of ∼4 GPa that stabilizes the r8 phase.
•Cassava diseases have broad social and economic impacts for subsistence farmers.•Clean planting material and better disease control will improve disease outcomes.•Climate change may reduce cassava ...disease impacts in many regions across Africa.•Accelerated breeding and transgenic technologies will improve disease resistance.
Cassava is an important staple food crop for millions of people in tropical regions across Africa, South America and Asia. Viral, bacterial and fungal diseases impact cassava yield in all three regions. The viruses causing cassava mosaic disease and cassava brown streak disease have been particularly devastating to cassava production in Africa. Improved farming practices and disease monitoring can reduce the impact of cassava diseases in the field. The availability of disease resistant cassava varieties developed through breeding or genetic engineering is key to tackling disease incidence and severity.
Objective To determine the relative effects of open healing compared with primary closure for pilonidal sinus and optimal closure method (midline v off-midline).Design Systematic review and ...meta-analyses of randomised controlled trials.Data sources Cochrane register of controlled trials, Cochrane Wounds Group specialised trials register, Medline (1950-2007), Embase, and CINAHL bibliographic databases, without language restrictions.Data extraction Primary outcomes were time (days) to healing, surgical site infection, and recurrence rate. Secondary outcomes were time to return to work, other complications and morbidity, cost, length of hospital stay, and wound healing rate.Study selection Randomised controlled trials evaluating surgical treatment of pilonidal sinus in patients aged 14 years or more. Data were extracted independently by two reviewers and assessed for quality. Meta-analyses used fixed and random effects models, dichotomous data were reported as relative risks or Peto odds ratios and continuous data are given as mean differences; all with 95% confidence intervals.Results 18 trials (n=1573) were included. 12 trials compared open healing with primary closure. Time to healing was quicker after primary closure although data were unsuitable for aggregation. Rates of surgical site infection did not differ; recurrence was less likely to occur after open healing (relative risk 0.42, 0.26 to 0.66). 14 patients would require their wound to heal by open healing to prevent one recurrence. Six trials compared surgical closure methods (midline v off-midline). Wounds took longer to heal after midline closure than after off-midline closure (mean difference 5.4 days, 95% confidence interval 2.3 to 8.5), rate of infection was higher (relative risk 4.70, 95% confidence interval 1.93 to 11.45), and risk of recurrence higher (Peto odds ratio 4.95, 95% confidence interval 2.18 to 11.24). Nine patients would need to be treated by an off-midline procedure to prevent one surgical site infection and 11 would need to be treated to prevent one recurrence.Conclusions Wounds heal more quickly after primary closure than after open healing but at the expense of increased risk of recurrence. Benefits were clearly shown with off-midline closure compared with midline closure. Off-midline closure should become standard management for pilonidal sinus when closure is the desired surgical option.
Building upon the demonstration of coherent control and single-shot readout of the electron and nuclear spins of individual 31P atoms in silicon, we present here a systematic experimental estimate of ...quantum gate fidelities using randomized benchmarking of 1-qubit gates in the Clifford group. We apply this analysis to the electron and the ionized 31P nucleus of a single P donor in isotopically purified 28Si. We find average gate fidelities of 99.95% for the electron and 99.99% for the nuclear spin. These values are above certain error correction thresholds and demonstrate the potential of donor-based quantum computing in silicon. By studying the influence of the shape and power of the control pulses, we find evidence that the present limitation to the gate fidelity is mostly related to the external hardware and not the intrinsic behaviour of the qubit.
Analyzing groundwater systems in transient state is essential for understanding the response of groundwater recharge to changing environments. Radioactive isotopes have long been used to track ...recharge behavior, typically under steady state conditions. This study tests the limitations of using radioactive isotopes in confined aquifers and under transient conditions to sense changes in groundwater recharge rates over time. Four system parameters determine the bounds of this approach: the isotope half‐life, the Péclet number (Pe), and mobile‐immobile zone interactions. This study revealed that in confined groundwater systems where Pe ≥ 10, isotopes reflect transience when the half‐life matches the water travel time down the flow path or the time elapsed from the change in velocity. This response is evident regardless of mobile‐immobile interaction, suggesting that appropriate isotope selection is key to establishing past recharge regardless of aquifer lithology or geometry.
Plain Language Summary
Changes in groundwater recharge are linked to environmental stimuli. Defining these changes helps inform a holistic understanding of the system, and guides sustainable approaches to groundwater use. The use of radioactive elements for examining long‐term groundwater behavior is common due to their time‐related quality. However, this is rarely done in the context of changing recharge conditions. The main purpose of this study was to observe the radioactive elements' response under a variety of groundwater flow and subsurface geometry settings to determine under which conditions they uncover past changes in groundwater recharge. The physical parameters of the system are often simplified, but robust enough to explore where the limitations of this application lie. Radioactive elements reflect change when the half‐life is equal to the time it takes the groundwater to travel down the flow path, regardless of the physical subsurface settings. This makes the framework highly useful for interpreting real data sets.
Key Points
Radioactive isotopes preserve transient groundwater behavior with timeframes consistent with their half‐life
Transient behavior can be identified using a visual interpretation of a log‐scaled change in concentration with distance plot
Graphical interpretation allows determination of the timing of an environmental change influencing groundwater recharge
As sessile organisms, plants have to endure a wide variety of biotic and abiotic stresses, and accordingly they have evolved intricate and rapidly inducible defense strategies associated with the ...activation of a battery of genes. Among other mechanisms, changes in chromatin structure are thought to provide a flexible, global, and stable means for the regulation of gene transcription. In support of this idea, we demonstrate here that the Arabidopsis (Arabidopsis thaliana) histone methyltransferase SET DOMAIN GROUP8 (SDG8) plays a crucial role in plant defense against fungal pathogens by regulating a subset of genes within the jasmonic acid (JA) and/or ethylene signaling pathway. We show that the loss-of-function mutant sdg8-1 displays reduced resistance to the necrotrophic fungal pathogens Alternaria brassicicola and Botrytis cinerea. While levels of JA, a primary phytohormone involved in plant defense, and camalexin, a major phytoalexin against fungal pathogens, remain unchanged or even above normal in sdg8-1, induction of several defense genes within the JA/ethylene signaling pathway is severely compromised in response to fungal infection or JA treatment in mutant plants. Both downstream genes and, remarkably, also upstream mitogen-activated protein kinase kinase genes MKK3 and MKK5 are misregulated in sdg8-1. Accordingly, chromatin immunoprecipitation analysis shows that sdg8-1 impairs dynamic changes of histone H3 lysine 36 methylation at defense marker genes as well as at MKK3 and MKK5, which normally occurs upon infection with fungal pathogens or methyl JA treatment in wild-type plants. Our data indicate that SDG8-mediated histone H3 lysine 36 methylation may serve as a memory of permissive transcription for a subset of defense genes, allowing rapid establishment of transcriptional induction.
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