Bounce Conditions in f(R) Cosmologies

We investigate the conditions for a bounce to occur in Friedmann-Robertson-Walker cosmologies for the class of fourth order gravity theories. The general bounce criterion is determined and constraints on the parameters of three specific models are given in order to obtain bounces solutions. It is found that unlike the case of General Relativity, a bounce appears to be possible in open and flat cosmologies.Comment: 11 pages LaTe

A Solution to the Graceful Exit Problem in Pre-Big Bang Cosmology

We examine the string cosmology equations with a dilaton potential in the context of the Pre-Big Bang Scenario with the desired scale factor duality, and give a generic algorithm for obtaining solutions with appropriate evolutionary properties. This enables us to find pre-big bang type solutions with suitable dilaton behaviour that are regular at $t=0$, thereby solving the graceful exit problem. However to avoid fine tuning of initial data, an `exotic' equation of state is needed that relates the fluid properties to the dilaton field. We discuss why such an equation of state should be required for reliable dilaton behaviour at late times.Comment: 16 pages LaTeX, 5 figures. To appear in Physical Review

Seizure outcomes and survival in adult low-grade glioma over 11 years: living longer and better

Background: There has been a trend toward earlier and more aggressive resection for low-grade gliomas (LGGs). This study set out to compare seizure control and survival of adults with LGG seen in the same neuro-oncology clinic over 11 years and to determine whether a change in surgical philosophy has led to a corresponding improvement in outcomes. / Methods: We conducted a retrospective analysis using case-note review of 153 adults with histologically verified or radiologically suspected LGG, collecting data on patient, tumor, and seizure characteristics between 2006 and 2017. / Results: We studied 79 patients in 2006 and 74 patients in 2017. There was no significant difference between the 2 groups in age at presentation, tumor location, or integrated pathological diagnosis. The numbers of complete or partial resections increased from 21.5% in 2006 to 60.8% in 2017 (P < .05). Five- and 10-year overall survival increased from 81.8% and 51.7% in 2006 to 100% and 95.8% in 2017 (P < .001); similarly, 5- and 10-year progression-free survival increased from 47.0% and 30.7% in 2006 to 93.1% and 68.7% in 2017. The proportion of patients with intractable epilepsy declined from 72.2% in 2006 to 43.2% in 2017 (P < .05). The neurosurgical morbidity rate was identical in both groups (11.8% in 2006 vs 11.1% in 2017). / Conclusion: Management of LGG over the last 11 years has led to substantial improvements in survival and seizure control. This is most likely thanks to a change in surgical philosophy, with early resection now favored over watchful waiting where possible

Bounce behaviour in Kantowski-Sachs and Bianchi Cosmologies

Many cosmological scenarios envisage either a bounce of the universe at early times, or collapse of matter locally to form a black hole which re-expands into a new expanding universe region. Energy conditions preclude this happening for ordinary matter in general relativistic universes, but scalar or dilatonic fields can violate some of these conditions, and so could possibly provide bounce behaviour. In this paper we show that such bounces cannot occur in Kantowski-Sachs models without violating the {\it reality condition} $\dot{\phi}^2\geq 0$. This also holds true for other isotropic spatially homogenous Bianchi models, with the exception of closed Friedmann-Robertson-Walker and Bianchi IX models; bounce behaviour violates the {\em weak energy condition} $\rho\geq 0$ and $\rho+p\geq 0$. We turn to the Randall-Sundrum type braneworld scenario for a possible resolution of this problem.Comment: Matches published versio

Caustics of Compensated Spherical Lens Models

We consider compensated spherical lens models and the caustic surfaces they create in the past light cone. Examination of cusp and crossover angles associated with particular source and lens redshifts gives explicit lensing models that confirm previous claims that area distances can differ by substantial factors from angular diameter distances even when averaged over large angular scales. `Shrinking' in apparent sizes occurs, typically by a factor of 3 for a single spherical lens, on the scale of the cusp caused by the lens; summing over many lenses will still leave a residual effect.Comment: 21 pages, 5 ps figures, eps

Observational signatures of a non-singular bouncing cosmology

We study a cosmological scenario in which inflation is preceded by a bounce. In this scenario, the primordial singularity, one of the major shortcomings of inflation, is replaced by a non-singular bounce, prior to which the universe undergoes a phase of contraction. Our starting point is the bouncing cosmology investigated in Falciano et al. (2008), which we complete by a detailed study of the transfer of cosmological perturbations through the bounce and a discussion of possible observational effects of bouncing cosmologies. We focus on a symmetric bounce and compute the evolution of cosmological perturbations during the contracting, bouncing and inflationary phases. We derive an expression for the Mukhanov-Sasaki perturbation variable at the onset of the inflationary phase that follows the bounce. Rather than being in the Bunch-Davies vacuum, it is found to be in an excited state that depends on the time scale of the bounce. We then show that this induces oscillations superimposed on the nearly scale-invariant primordial spectra for scalar and tensor perturbations. We discuss the effects of these oscillations in the cosmic microwave background and in the matter power spectrum. We propose a new way to indirectly measure the spatial curvature energy density parameter in the context of this model.Comment: 40 pages, 5 figures, typos corrected and reference adde

Tuberculous meningitis in children: a forgotten public health emergency

Tuberculous meningitis (TBM) remains a major cause of morbidity and mortality in children with tuberculosis (TB), yet there are currently no estimates of the global burden of paediatric TBM. Due to frequent non-specific clinical presentation and limited and inadequate diagnostic tests, children with TBM are often diagnosed late or die undiagnosed. Even when diagnosed and treated, 20% of children with TBM die. Of survivors, the majority have substantial neurological disability with significant negative impact on children and their families. Surveillance data on this devastating form of TB can help to quantify the contribution of TBM to the overall burden, morbidity and mortality of TB in children and the epidemiology of TB more broadly. Paediatric TBM usually occurs shortly after primary infection with Mycobacterium tuberculosis and reflects ongoing TB transmission to children. In this article we explain the public health importance of paediatric TBM, discuss the epidemiology within the context of overall TB control and health system functioning and the limitations of current surveillance strategies. We provide a clear rationale for the benefit of improved surveillance of paediatric TBM using a TB care cascade framework to support monitoring and evaluation of paediatric TB, and TB control more broadly. Considering the public health implications of a diagnosis of TBM in children, we provide recommendations to strengthen paediatric TBM surveillance and outline how improved surveillance can help us identify opportunities for prevention, earlier diagnosis and improved care to minimize the impact of TBM on children globally

Cutting Ties with Pro-Ana: A Narrative Inquiry Concerning the Experiences of Pro-Ana Disengagement from Six Former Site Users.

Websites advocating the benefits of eating disorders (“Pro-Ana”) tend to reinforce and maintain restrictive eating and purging behaviors. Yet remarkably, no study has explored individual accounts of disengagement from these sites and the associated meanings. Using narrative inquiry, this study sought to address this gap. From the interviews of six women, two overarching storylines emerged. The first closely tied disengagement to recovery with varying positions of personal agency claimed: this ranged from enforced and unwelcomed breaks that ignited change, to a personal choice that became viable through the development of alternative social and personal identities. A strong counternarrative to “disengagement as recovery” also emerged. Here, disengagement from Pro-Ana was storied alongside a need to retain an ED lifestyle. With “recovery” being just one reason for withdrawal from Pro-Ana sites, clinicians must remain curious about the meanings individuals ascribe to this act, without assuming it represents a step toward recovery.Peer reviewedFinal Accepted Versio