Valley interference and spin exchange at the atomic scale in silicon.

Tunneling is a fundamental quantum process with no classical equivalent, which can compete with Coulomb interactions to give rise to complex phenomena. Phosphorus dopants in silicon can be placed with atomic precision to address the different regimes arising from this competition. However, they exploit wavefunctions relying on crystal band symmetries, which tunneling interactions are inherently sensitive to. Here we directly image lattice-aperiodic valley interference between coupled atoms in silicon using scanning tunneling microscopy. Our atomistic analysis unveils the role of envelope anisotropy, valley interference and dopant placement on the Heisenberg spin exchange interaction. We find that the exchange can become immune to valley interference by engineering in-plane dopant placement along specific crystallographic directions. A vacuum-like behaviour is recovered, where the exchange is maximised to the overlap between the donor orbitals, and pair-to-pair variations limited to a factor of less than 10 considering the accuracy in dopant positioning. This robustness remains over a large range of distances, from the strongly Coulomb interacting regime relevant for high-fidelity quantum computation to strongly coupled donor arrays of interest for quantum simulation in silicon.

Association of transcription factor 7-like 2 gene (TCF7L2) polymorphisms with stress-related hyperglycaemia (SRH) in intensive care and resulting outcomes: The READIAB study.

OBJECTIVE: The study aimed to evaluate the impact of the single nucleotide polymorphism (SNP) rs7903146 on the transcription factor 7-like 2 (TCF7L2) gene in stress-related hyperglycaemia (SRH), defined as blood glucose≥11mmol/L in at least two blood samples during the first 3 days in the intensive care unit (ICU), and on 28-day and 1-year mortality, and incidence of type 2 diabetes (T2D) at 6 months and 1 year in patients hospitalized in the ICU. METHODS: This prospective observational (non-interventional) multicentre READIAB study, carried out during 2012-2016 in six French ICUs, involved adult patients admitted to ICUs for at least two organ failures; patients admitted for<48h were excluded. During the 3-day ICU observational period, genetic testing, blood glucose values and insulin treatment were recorded. MAIN RESULTS: The association of rs7903146 with SRH was assessed using logistic regression models. Cox proportional hazards regression models assessed the associations between rs7903146 and mortality and between SRH and mortality, both at 28 days and 1 year. A total of 991 of the 1000 enrolled patients were included in the READIAB-G4 cohort, but 242 (24.4%) had preexisting diabetes and were excluded from the analyses. SRH occurred within the first 3 days in the ICU for one-third of the non-diabetes patients. The association between the rs7903146 polymorphism and SRH did not reach significance (P=0.078): OR(peroneTcopy): 1.24, 95% CI: 0.98-1.58. A significant association was found between rs7903146 and 28-day mortality after adjusting for severity scores (P=0.026), but was no longer significant at 1 year (P=0.61). At 28 days, mortality was increased in patients with SRH (HR: 2.09, 95% CI: 1.43-3.06; P<0.001), and remained significant at 1 year after adjusting for severity scores (HR: 1.73, 95% CI: 1.32-2.28; P<0.001). On admission, non-diabetes patients with SRH had a higher incidence of T2D at 6 months vs. those without SRH (16.0% vs. 7.6%, RR: 2.11, 95% CI: 1.07-4.20; P=0.030). At 1 year, these figures were 13.4% vs. 9.2%, RR: 1.45, 95% CI: 0.71-2.96; P=0.31). Moreover, the rs7903146 polymorphism was not significantly associated with T2D development at either 6 months (P=0.72) or 1 year (P=0.64). CONCLUSION: This study failed to demonstrate any significant association between rs7903146 and SRH. Nevertheless, the issue remains an important challenge, as SRH may be associated with increased rates of both mortality and T2D development.

Dynamic platelet function on von Willebrand factor is different in preterm neonates and full-term neonates: changes in neonatal platelet function.

Essentials It is unclear if platelet function differs between preterm and full-term neonates. Platelet behavior was characterized using a flow-based assay on von Willebrand Factor (VWF). Preterms had increased platelet interaction with VWF and glycoprotein Ibα expression. Platelets from preterm neonates behave differently on VWF compared to full-term neonates. SUMMARY: Background Very low birth weight (VLBW) preterm neonates have an increased risk of hemorrhage-related morbidity and mortality as compared with their full-term counterparts. It is unclear whether platelet function differs between preterm and full-term neonates. This is partly because of the large volumes of blood required to perform standard platelet function tests, and the difficulty in obtaining such samples in neonates. Objectives This study was designed to characterize platelet behavior in neonates with a physiologic flow-based assay that quantifies platelet function in microliter volumes of blood under arterial shear. Methods Blood from VLBW preterm neonates of ≤ 32 weeks' gestation (n = 15) and full-term neonates (n = 13) was perfused under arterial shear over surface-immobilized von Willebrand factor (VWF). Platelet behavior was recorded by digital-image microscopy and analyzed. Surface expression of platelet glycoprotein (GP) Ibα and GPIIIa of VLBW preterm and full-term neonates was also measured. Results VLBW preterm neonates had increased numbers of platelets interacting with VWF, and increased GPIbα expression on the platelet surface. Despite the increased numbers of VWF interactions as reflected by flow-driven platelet translocation along the protein surface, no significant differences were observed in the numbers of platelets that adhered in a stationary fashion to VWF. Platelets from VLBW preterm neonates and those from full-term neonates behaved differently on VWF. Conclusions These differences in platelet function may contribute to the higher incidence of bleeding observed in VLBW preterm neonatal populations, or may represent a compensatory mechanism to counteract this risk of bleeding.

Spatial metrology of dopants in silicon with exact lattice site precision.

Scaling of Si-based nanoelectronics has reached the regime where device function is affected not only by the presence of individual dopants, but also by their positions in the crystal. Determination of the precise dopant location is an unsolved problem in applications from channel doping in ultrascaled transistors to quantum information processing. Here, we establish a metrology combining low-temperature scanning tunnelling microscopy (STM) imaging and a comprehensive quantum treatment of the dopant-STM system to pinpoint the exact coordinates of the dopant in the Si crystal. The technique is underpinned by the observation that STM images contain atomic-sized features in ordered patterns that are highly sensitive to the STM tip orbital and the absolute dopant lattice site. The demonstrated ability to determine the locations of P and As dopants to 5 nm depths will provide critical information for the design and optimization of nanoscale devices for classical and quantum computing applications.

Electrical Control of g-Factor in a Few-Hole Silicon Nanowire MOSFET.

Hole spins in silicon represent a promising yet barely explored direction for solid-state quantum computation, possibly combining long spin coherence, resulting from a reduced hyperfine interaction, and fast electrically driven qubit manipulation. Here we show that a silicon-nanowire field-effect transistor based on state-of-the-art silicon-on-insulator technology can be operated as a few-hole quantum dot. A detailed magnetotransport study of the first accessible hole reveals a g-factor with unexpectedly strong anisotropy and gate dependence. We infer that these two characteristics could enable an electrically driven g-tensor-modulation spin resonance with Rabi frequencies exceeding several hundred mega-Hertz.

The coupled atom transistor.

We describe the first implementation of a coupled atom transistor where two shallow donors (P or As) are implanted in a nanoscale silicon nanowire and their electronic levels are controlled with three gate voltages. Transport spectroscopy through these donors placed in series is performed both at zero and microwave frequencies. The coherence of the charge transfer between the two donors is probed by Landau-Zener-Stückelberg interferometry. Single-charge transfer at zero bias (electron pumping) has been performed and the crossover between the adiabatic and non-adiabatic regimes is studied.

Spatially resolved resonant tunneling on single atoms in silicon.

The ability to control single dopants in solid-state devices has opened the way towards reliable quantum computation schemes. In this perspective it is essential to understand the impact of interfaces and electric fields, inherent to address coherent electronic manipulation, on the dopants atomic scale properties. This requires both fine energetic and spatial resolution of the energy spectrum and wave-function, respectively. Here we present an experiment fulfilling both conditions: we perform transport on single donors in silicon close to a vacuum interface using a scanning tunneling microscope (STM) in the single electron tunneling regime. The spatial degrees of freedom of the STM tip provide a versatility allowing a unique understanding of electrostatics. We obtain the absolute energy scale from the thermal broadening of the resonant peaks, allowing us to deduce the charging energies of the donors. Finally we use a rate equations model to derive the current in presence of an excited state, highlighting the benefits of the highly tunable vacuum tunnel rates which should be exploited in further experiments. This work provides a general framework to investigate dopant-based systems at the atomic scale.

Coherent coupling of two dopants in a silicon nanowire probed by Landau-Zener-Stückelberg interferometry.

We report on microwave-driven coherent electron transfer between two coupled donors embedded in a silicon nanowire. By increasing the microwave frequency we observe a transition from incoherent to coherent driving revealed by the emergence of a Landau-Zener-Stückelberg quantum interference pattern of the measured current through the donors. This interference pattern is fitted to extract characteristic parameters of the double-donor system. In particular we estimate a charge dephasing time of 0.3±0.1 ns, comparable to other types of charge-based two-level systems. The demonstrated coherent coupling between two dopants is an important step towards donor-based quantum computing devices in silicon.

A two-atom electron pump.

With the development of single-atom transistors, consisting of single dopants, nanofabrication has reached an extreme level of miniaturization. Promising functionalities for future nanoelectronic devices are based on the possibility of coupling several of these dopants to each other. This already allowed to perform spectroscopy of the donor state by d.c. electrical transport. The next step, namely manipulating a single electron over two dopants, remains a challenge. Here we demonstrate electron pumping through two phosphorus donors in series implanted in a silicon nanowire. While quantized pumping is achieved in the low-frequency adiabatic regime, we observe remarkable features at higher frequency when the charge transfer is limited either by the tunnelling rates to the electrodes or between the two donors. The transitions between quantum states are modelled involving a Landau-Zener transition, allowing to reproduce in detail the characteristic signatures observed in the non-adiabatic regime.

Detection of a large valley-orbit splitting in silicon with two-donor spectroscopy.

We measure a large valley-orbit splitting for shallow isolated phosphorus donors in a silicon gated nanowire. This splitting is close to the bulk value and well above previous reports in silicon nanostructures. It was determined using a double dopant transport spectroscopy which eliminates artifacts induced by the environment. Quantitative simulations taking into account the position of the donors with respect to the Si/SiO2 interface and electric field in the wire show that the values found are consistent with the device geometry.

[Management of acute asthma]. / Asthme aigu: orientation et prise en charge.

INTRODUCTION: All patients with asthma are at risk of exacerbations. Mortality is often associated with failure to identify patients at risk and/or to appreciate the severity of acute episode, resulting in inadequate initial treatment, delay in referring to emergency care and inappropriate hospitalization rates, including delayed transfer to intensive care units. This review focuses on the management of acute severe and near fatal asthma. STATE OF ART: Lung mechanics and cardiopulmonary interactions associated with airflow obstruction explain the physical presentation and severity criteria for exacerbations. The past and recent medical history, the initial evaluation of severity and the assessment of response to treatment direct the in-hospital management: emergency department visit, transfer to ward or intensive care unit. In any cases, the goals of therapy are summarized as oxygenation, repetitive inhalations of bronchodilators and early administration of systemic corticosteroids. Mechanical ventilation is required in a few patients with near fatal attacks resulting in asphyxia or progressive exhaustion despite maximal therapy. Controlled hypoventilation with permissive hypercapnia is the best strategy to avoid barotrauma. The role of adjunctive therapies, mainly halogenated agents and heliox, is discussed. PERSPECTIVES AND CONCLUSION: During the last decade, asthma related mortality has decreased in France (<1000/year). The majority of deaths occur at home or during transport to the hospital but some deaths occur suddenly. Most deaths could be preventable if one adopts the approach that every exacerbation is potentially fatal. This practice should be more vigorously included in patient and general practitioner educational programs.

[Anaesthetic management for caesarean delivery and acute myocardial infarction by spontaneous coronary dissection]. / Anesthésie pour césarienne à la phase aiguë d'un infarctus du myocarde par dissection coronaire.

Myocardial infarction is rare during pregnancy and is associated with a high maternal and foetal mortality rate. We report the case of a 32-year-old woman at 38 weeks gestation who developed a myocardial infarction with spontaneous coronary dissection treated with coronary angioplasty and who needed an emergency caesarean section. We discuss the anaesthetic management of urgent caesarean section in this context.