Open timelike curves violate Heisenberg's uncertainty principle

Toy models for quantum evolution in the presence of closed timelike curves (CTCs) have gained attention in the recent literature due to the strange effects they predict. The circuits that give rise to these effects appear quite abstract and contrived, as they require non-trivial interactions between the future and past which lead to infinitely recursive equations. We consider the special case in which there is no interaction inside the CTC, referred to as an open timelike curve (OTC), for which the only local effect is to increase the time elapsed by a clock carried by the system. Remarkably, circuits with access to OTCs are shown to violate Heisenberg's uncertainty principle, allowing perfect state discrimination and perfect cloning of coherent states. The model is extended to wave-packets and smoothly recovers standard quantum mechanics in an appropriate physical limit. The analogy with general relativistic time-dilation suggests that OTCs provide a novel alternative to existing proposals for the behaviour of quantum systems under gravity

Linking employee burnout to medical aid provider expenditure

Background. Healthcare has become a major expense. Burnout and its connection with psychological and physical health is well researched,yet little research has been done on the connection between burnout and financial outcomes, specifically as indicated by the costs incurredby medical aid providers as a result of members’ claims.Objective. To investigate the connection between employee burnout and medical aid claims and expenditure data in a sample from theprivate sector.Method. A cross-sectional design was used. The sample comprised 3 182 participants. The available objective medical aid expendituredata connected with each participant were: total insured benefits, general practitioner visits, specialist visits, general practitioner insuredbenefits, and claims for medicine. A low and a high burnout group were extracted, based on comorbidity of the two core components ofburnout. Analysis of covariance (ANCOVA) was then applied to investigate the differences in estimated marginal means of the expenditureson the low and the high burnout contrast groups, while controlling for age and gender.Results. The high burnout group frequented a general practitioner more often, and the medical aid provider expenditure was nearly doublethat of the low burnout group, on all the variables. Specialist visits did not show a significant result.Conclusion. High burnout is associated with a higher expenditure by a medical aid provider, compared with low burnout, per member.Stakeholders should therefore address burnout to reduce expenditure and promote health

Human brucellosis in South Africa: Public health and diagnostic pitfalls

Human brucellosis in South Africa (SA) is under-diagnosed and under-reported. This is because many clinicians have little or no experience in managing affected patients, and in part because of the nonspecific and insidious nature of the disease. A case of human brucellosis caused by Brucella melitensis in a patient from the Western Cape Province of SA is described, and the resulting exposure of staff members at two medical microbiology laboratories, as well as the public health investigation that was conducted, are discussed. The objective of this article is to highlight the need for strengthening integration between public health, medical and veterinary services and exposing deficiencies in public health, veterinary and laboratory practices

Hard choices: Ethical challenges in phase 1 of COVID-19 vaccine roll-out in South Africa

Access to COVID-19 vaccines has raised concerns globally. Despite calls for solidarity and social justice during the pandemic, vaccine nationalism, stockpiling of limited vaccine supplies by high-income countries and profit-driven strategies of global pharmaceutical manufacturers have brought into sharp focus global health inequities and the plight of low- and middle-income countries (LMICs) as they wait in line for restricted tranches of vaccines. Even in high-income countries that received vaccine supplies first, vaccine roll-out globally has been fraught with logistic and ethical challenges. South Africa (SA) is no exception. Flawed global institutional strategies for vaccine distribution and delivery have undermined public procurement platforms, leaving LMICs facing disproportionate shortages necessitating strict criteria for vaccine prioritisation. In anticipation of our first consignment of vaccines, deliberations around phase 1 roll-out were intense and contentious. Although the first phase focuses on healthcare personnel (HCP), the devil is in the detail. Navigating the granularity of prioritising different categories of risk in healthcare sectors in SA is complicated by definitions of risk in personal and occupational contexts. The inequitable public-private divide that characterises the SA health system adds another layer of complexity. Unlike other therapeutic or preventive interventions that are procured independently by the private health sector, COVID-19 vaccine procurement is currently limited to the SA government only, leaving HCP in the private sector dependent on central government allocation. Fair distribution among tertiary, secondary and primary levels of care is another consideration. Taking all these complexities into account, procedural and substantive ethical principles supporting a prioritisation approach are outlined. Within the constraints of suboptimal global health governance, LMICs must optimise progressive distribution of scarce vaccines to HCP at highest risk

Quantum fields on closed time-like curves

Recently, there has been much interest in the evolution of quantum particles on closed time-like curves (CTCs). However, such models typically assume point-like particles with only two degrees of freedom - a very questionable assumption given the relativistic setting of the problem. We show that it is possible to generalise the Deutsch model of CTCs to fields using the equivalent circuit formalism. We give examples for coherent, squeezed and single-photon states interacting with the CTC via a beamsplitter. The model is then generalised further to account for the smooth transition to normal quantum mechanics as the CTC becomes much smaller than the size of the modes interacting on it. In this limit, we find that the system behaves like a standard quantum mechanical feedback loop.Comment: 12 pages, 10 figures. Minor corrections, added reference

Space-time qubits

We construct a qubit algebra from field creation and annihilation operators acting on a global vacuum state. Particles to be used as qubits are created from the vacuum by a near-deterministic single particle source. Our formulation makes the space-time dependence of the qubits explicit, preparing the way for quantum computation within a field framework. The method can be generalized to deal with interacting qubits whose wavepackets are not perfectly matched to each other. We give an example of how to calculate the Heisenberg evolution of a simple two-qubit circuit, taking expectation values in the field vacuum state.Comment: 8 pages, 7 figures, added references, added appendix, moved some text from introduction to conclusion, made minor corrections to text and figure

Single-cell approaches for studying the role of mitochondrial DNA in neurodegenerative disease

In light of accumulating evidence suggestive of cell type-specific vulnerabilities as a result of normal aging processes that adversely affect the brain, as well as age-related neurodegenerative disorders such as Parkinson's disease (PD), the current chapter highlights how we study mitochondrial DNA (mtDNA) changes at a single-cell level. In particular, we comment on increasing questioning of the narrow neurocentric view of such pathologies, where microglia and astrocytes have traditionally been considered bystanders rather than players in related pathological processes. Here we review the contribution made by single-cell mtDNA alterations towards neuronal vulnerability seen in neurodegenerative disorders, focusing on PD as a prominent example. In addition, we give an overview of methodologies that support such experimental investigations. In considering the significant advances that have been made in recent times for developing mitochondria-specific therapies, investigations to account for cell type-specific mitochondrial patterns and how these are altered by disease hold promise for delivering more effective disease-modifying therapeutics

Aggregation, impaired degradation and immunization targeting of amyloid-beta dimers in Alzheimer’s disease: a stochastic modelling approach

Background Alzheimer’s disease (AD) is the most frequently diagnosed neurodegenerative disorder affecting humans, with advanced age being the most prominent risk factor for developing AD. Despite intense research efforts aimed at elucidating the precise molecular underpinnings of AD, a definitive answer is still lacking. In recent years, consensus has grown that dimerisation of the polypeptide amyloid-beta (Aß), particularly Aß42, plays a crucial role in the neuropathology that characterise AD-affected post-mortem brains, including the large-scale accumulation of fibrils, also referred to as senile plaques. This has led to the realistic hope that targeting Aß42 immunotherapeutically could drastically reduce plaque burden in the ageing brain, thus delaying AD onset or symptom progression. Stochastic modelling is a useful tool for increasing understanding of the processes underlying complex systems-affecting disorders such as AD, providing a rapid and inexpensive strategy for testing putative new therapies. In light of the tool’s utility, we developed computer simulation models to examine Aß42 turnover and its aggregation in detail and to test the effect of immunization against Aß dimers. Results Our model demonstrates for the first time that even a slight decrease in the clearance rate of Aß42 monomers is sufficient to increase the chance of dimers forming, which could act as instigators of protofibril and fibril formation, resulting in increased plaque levels. As the process is slow and levels of Aβ are normally low, stochastic effects are important. Our model predicts that reducing the rate of dimerisation leads to a significant reduction in plaque levels and delays onset of plaque formation. The model was used to test the effect of an antibody mediated immunological response. Our results showed that plaque levels were reduced compared to conditions where antibodies are not present. Conclusion Our model supports the current thinking that levels of dimers are important in initiating the aggregation process. Although substantial knowledge exists regarding the process, no therapeutic intervention is on offer that reliably decreases disease burden in AD patients. Computer modelling could serve as one of a number of tools to examine both the validity of reliable biomarkers and aid the discovery of successful intervention strategies

Diagnosis of childhood tuberculosis and host RNA expression in Africa

Improved diagnostic tests for tuberculosis in children are needed. We hypothesized that transcriptional signatures of host blood could be used to distinguish tuberculosis from other diseases in African children who either were or were not infected with the human immunodeficiency virus (HIV