Quantum simulations of time travel can power nonclassical metrology

Gambling agencies forbid late bets, placed after the winning horse crosses the finish line. A time-traveling gambler could cheat the system. We construct a gamble that one can win by simulating time travel with experimentally feasible entanglement manipulation. Our gamble echoes a common metrology protocol: A gambler must prepare probes to input into a metrology experiment. The goal is to infer as much information per probe as possible about a parameter's value. If the input is optimal, the information gained per probe can exceed any value achievable classically. The gambler chooses the input state analogously to choosing a horse. However, only after the probes are measured does the gambler learn which input would have been optimal. The gambler can "place a late bet" by effectively teleporting the optimal input back in time, via entanglement manipulation. Our Gedankenexperiment demonstrates that not only true time travel, but even a simulation offers a quantum advantage in metrology.Comment: 5+1 pages. 2 figures. Comments are welcomed

Wear and Friction Behaviour of Additive Manufactured PEEK under Non-conformal Contact

Tribological properties of laser sintered polyether-ether-ketone (EOS PEEK HP3) were investigated using a rolling-sliding test rig. This investigation aimed to study the wear and friction failure mechanism of EOS PEEK HP3. The main objectives included to conduct wear and friction tests under non-conformal contact, to monitor surface temperature, to carry out surface characterization with microscopy. With this rolling-sliding test rig, tests were carried out on an EOS PEEK HP3 specimen running against a steel disc unlubricated, with various slip-ratios under a contact pressure of 56 MPa, 48 MPa and 39 MPa respectively. Both wear and friction were measured. The results have shown that both friction and wear were increased with an increase of either slip-ratios or the contact pressures, exacerbated by high surface temperatures. It has also been observed that both friction and wear failures were associated with the degradation of the non-conformal contact surfaces due to crystallinity changes that correlated well with working conditions. Using microscopy it was found that such failures as pitting, fatigue and surface cracking were affected by the surfaces in contact, including the degree of melting of the surface. Based on the observation on the contact surfaces, the failure mechanisms of EOS PEEK HP3 include surface melting and contact fatigue failures with the high slip-ratio and the high contact pressure conditions. The findings of this investigation have the potential to help to design & develop additive manufacturing PEEK products. Typically, these results can be used in a design process for a more effective polymeric gear system

Variational quantum chemistry requires gate-error probabilities below the fault-tolerance threshold

The variational quantum eigensolver (VQE) is a leading contender for useful quantum advantage in the NISQ era. The interplay between quantum processors and classical optimisers is believed to make the VQE noise resilient. Here, we probe this hypothesis. We use full density-matrix simulations to rank the noise resilience of leading gate-based VQE algorithms in ground-state computations on a range of molecules. We find that, in the presence of noise: (i) ADAPT-VQEs that construct ansatz circuits iteratively outperform VQEs that use "fixed" ansatz circuits; and (ii) ADAPT-VQEs perform better when circuits are constructed from gate-efficient elements rather than physically-motivated ones. Our results show that, for a wide range of molecules, even the best-performing VQE algorithms require gate-error probabilities on the order of $10^{-6}$ to $10^{-4}$ to reach chemical accuracy. This is significantly below the fault-tolerance thresholds of most error-correction protocols. Further, we estimate that the maximum allowed gate-error probability scales inversely with the number of noisy (two-qubit) gates. Our results indicate that useful chemistry calculations with current gate-based VQEs are unlikely to be successful on near-term hardware without error correction.Comment: 17 pages, 8 figure

Compressive behaviour of tin slag polymer concrete confined with glass fibre reinforced epoxy under various loading speeds

Polymer concrete reinforced tin slag is predicted to replace Portland cement as the major building material. The objective of this study was to analyze the compressive behaviour of tin slag polymer concrete (TSPC) confined with glass fibre reinforced polymer (GFRP) composites under various loading speeds. Compressive test was performed according to ATSM C579-01. Result shows that TSPC confined with five layers of GFRP achieved the highest compressive strength of 148.19 MPa at a loading speed of 7 mm/min. Comparable results were obtained by TSPC with four layers of GFRP at three and five mm/min, and TSPC with three layers of GFRP at ten mm/min loading speed. Meanwhile, a low loading speed increases compressive strength slightly, but neither the number of confinement layers nor the loading speed has a prominent effect on the modulus of elasticity. Energy absorption has increased significantly between unconfined and confined TSPC. TSPC confined with four layers of GFRP achieves the highest energy absorption when evaluated at 3 mm/min, with a 297.9% increase over the unconfined specimen. The application of confinement layers has greatly improved the compressive strength of TSPC confined with GFRP, allowing for higher loading capabilities

Critical care service delivery across healthcare systems in low-income and low-middle-income countries: protocol for a systematic review

Introduction- Critical care in low-income and low-middle income countries (LLMICs) is an underdeveloped component of the healthcare system. Given the increasing growth in demand for critical care services in LLMICs, understanding the current capacity to provide critical care is imperative to inform policy on service expansion. Thus, our aim is to describe the provision of critical care in LLMICs with respect to patients, providers, location of care and services and interventions delivered. Methods and analysis- We will search PubMed/MEDLINE, Web of Science and EMBASE for full-text original research articles available in English describing critical care services that specify the location of service delivery and describe patients and interventions. We will restrict our review to populations from LLMICs (using 2016 World Bank classifications) and published from 1 January 2008 to 1 January 2020. Two-reviewer agreement will be required for both title/abstract and full text review stages, and rate of agreement will be calculated for each stage. We will extract data regarding the location of critical care service delivery, the training of the healthcare professionals providing services, and the illnesses treated according to classification by the WHO Universal Health Coverage Compendium. Ethics and dissemination- Reviewed and exempted by the Stanford University Office for Human Subjects Research and IRB on 20 May 2020. The results of this review will be disseminated through scholarly publication and presentation at regional and international conferences. This review is designed to inform broader WHO, International Federation for Emergency Medicine and partner efforts to strengthen critical care globally

The causal nexus of government spending and revenue in Finland: a bootstrap approach

Applying VAR(5), a bootstrap simulation approach and a multivariate Rao's F-test indicate that government revenue Granger-causes spending in Finland. This does not agree with Barr's tax smoothing hypothesis. This explanation of this is due to the institutional factors that are specific for Finland.

The small sample properties of the reset test as applied to systems of equations

The RESET test for functional misspecification is generalised to cover systems of equations, and the properties of 7 versions are studied using Monte Carlo methods. The Rao F -test clearly exhibits the best performance as regards correct size, whilst the commonly used LRT (uncorrected for degrees-of-freedom), and LM and Wald tests (both corrected and uncorrected) behave badly even in single equations. The Rao test exhibits correct size even in ten equation systems, which is better than previous research concerning autocorrelation tests. The power of the test is low, however, when the number of equations grows and the correlation between the omitted variables and the RESET proxies is small