Blue Stragglers After the Main Sequence

We study the post-main sequence evolution of products of collisions between main sequence stars (blue stragglers), with particular interest paid to the horizontal branch and asymptotic giant branch phases. We found that the blue straggler progeny populate the colour-magnitude diagram slightly blueward of the red giant branch and between 0.2 and 1 magnitudes brighter than the horizontal branch. We also found that the lifetimes of collision products on the horizontal branch is consistent with the numbers of so-called "evolved blue straggler stars" (E-BSS) identified by various authors in a number of globular clusters, and is almost independent of mass or initial composition profile. The observed ratio of the number of E-BSS to blue stragglers points to a main sequence lifetime for blue stragglers of approximately 1-2 Gyr on average.Comment: accepted by the Astrophysical Journa

The Hunt for Missing Tornadoes: Using Satellite Imagery to Detect and Document Historical Tornado Damage in Canadian Forests

Historical tornado events from 1982 to 2020 were documented within Canada’s forested regions using high-resolution satellite imagery. Tornado forest disturbances were identified using a three-step process: 1) detecting, 2) assessing, and 3) dating each event. A grid of 120 km 3 120 km boxes was created covering Canada (excluding the extreme north). Of the 484 boxes, 367 were manually searched. Once a long, narrow region of tree damage was detected, it was first cross-referenced with known tornado databases to ensure it was a unique event. Once events were classified as either tornadic or downburst, the coordinates of the start, worst damage, and end locations were documented, as well as the direction of motion, damage indicators, degree of damage, estimated maximum wind speed, and F/EF-scale rating. In total, 231 previously unknown tornadoes were identified. In Ontario, 103 events were discovered, followed by 98 in Quebec, 9 in Manitoba, 6 in Saskatchewan, 9 in Alberta, 5 in British Columbia, and 1 in New Brunswick. The largest number of discovered tornadoes occurred in 2015, and the largest number of strong F2 tornadoes occurred in 2005. Most of the discovered tornadoes occurred in July for both F/EF1 and F/EF2 ratings. Most tornado tracks had widths between 200 and 400 m, and more than 50% of the tornadoes had a pathlength of less than 10 km. Of all the events that were discov-ered, 125 events could be fully dated, 19 were dated only by month, 41 were dated only by year, and 46 remained undated

Experimental Seizure Models and New Antiepileptic Drugs

The objective of this programme of work was to study experimental seizure models and new antiepileptic drugs. Initial investigations addressed the contribution of basic animal models of epilepsy to its experimental study. Next, an attempt was made to emphasise the crucial role of neuronal inhibition and excitation in epileptogenesis and to relate these phenomena to the study of novel antiepileptic agents. Finally, the future of epilepsy research, in terms of appropriate strategies for AED development and innovative experimental paradigms was examined. Investigation of basic animal seizure models Of all the experimental seizure models in current laboratory employment, the pentylenetetrazol (PTZ) test, and the maximal (MES) and minimal (Min-ES) electroshock tests are among the most popular by virtue of their simplicity and economy. The primary aim of these studies was to afford a familiarity with these three basic animal seizure models and to validate them as techniques for subsequent use. These studies also incorporated an investigation of concentration-effect relationships with PTZ which attempted to delineate previously observed efficacy problems with this compound in our laboratory. Validation of all three experimental models was satisfactory, with results reflecting those reported in the literature. Although the concentration-effect studies with PTZ afforded a degree of insight into its pharmacokinetics, attempts to provide a suitable explanation for its lack of convulsant action in some animals proved unsuccessful. Antiepileptic drug enhancement of neuronal inhibition Impairment of gamma-aminobutyric acid (GABA)-mediated neuronal inhibition is believed to be one of the fundamental aetiological mechanisms of epileptogenesis. These investigations compared and contrasted the experimental anticonvulsant profiles and mechanisms of action of vigabatrin (VGB) and tiagabine (TGB), two novel AEDs which have been proposed to enhance GABA-mediated inhibition. VGB raised the threshold for induction of tonic seizures, determined by the Min-ES test, but was without effect in the PTZ and MES tests. TGB, in contrast, exhibited anticonvulsant effects against both PTZ- and MES-induced seizures. Drug mechanisms were investigated in isolated brain tissue and in primary cultures of cerebral cortical astrocytes and neurones. Previously reported mechanisms of action of the two drugs were confirmed, with VGB inhibiting GAB A metabolism by an action on GABA-aminotransferase (GABA-T), and TGB blocking GAB A uptake in a non-cell-specific manner. An inhibitory effect of VGB on glutamic acid decarboxylase (GAD) was also verified, and an additional, previously unreported action of the drug on GABA uptake was proposed. Antiepileptic drug attenuation of neuronal excitation Glutamate-induced neuronal excitability and voltage-sensitive calcium influx are believed to be inexorably entwined at all stages of epileptogenesis. These studies compared and contrasted the experimental anticonvulsant profiles and mechanisms of action of nimodipine (NMD) and amlodipine (AML), members of the dihydropyridine (DHP) class of calcium channel blockers which have been proposed as putative AEDs. In single dose, NMD was effective against MES-induced seizures and also raised the tonic seizure threshold, determined by the Min-ES test. Its effects in the MES test appeared to extend Novel strategies for antiepileptic drug development It has been proposed that to satisfactorily address the problem of refractory epilepsy the development of novel antiepileptic agents with similarly novel mechanisms of action is required. Nicotinylalanine (NA) is a newly-synthesised neuroactive compound which is believed to exert its effects by inhibition of the kynurenine pathway, resulting in increased brain concentrations of kynurenic acid, an endogenous antagonist at the glycine recognition site on the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. This study explored the anticonvulsant profile of NA in three standard animal models of seizure. NA protected against PTZ induced seizures in mice in a dose and time dependent manner and was also active in the maximal and minimal electroshock tests. These preliminary results would suggest that NA warrants further investigation as a putative AED. Development of a novel animal model of epilepsy It is now recognised that few, if any, of the existing "animal models of the epilepsies" mirror the condition of chronically recurrent spontaneous seizures which is characteristic of human epilepsy. This study followed the preliminary development of an innovative model of partial epilepsy, proposed to more closely mimic the human condition. This model was characterised by a laser-induced lesion in the rat somatosensory cortex. Production of cortical laser lesions in the rat proved to be a feasible procedure. Histological investigation proposed the lesions to be highly reproducible and to possess cellular characteristics similar to those of disruptive brain insults in man. The lesion did not appear to be intrinsically epileptogenic, nor did the procedure influence the latency to generalised PTZ-induced seizures. Preliminary autoradiographical studies suggested that brain damage associated with the procedure was confined to the lesion tract itself, and that cerebral glucose metabolism was additionally altered in adjacent, otherwise healthy, tissue. Despite possessing several attractive features, the full potential of this model for use in epilepsy research remains to be evaluated

Monte Carlo Simulations of Globular Cluster Evolution. V. Binary Stellar Evolution

We study the dynamical evolution of globular clusters containing primordial binaries, including full single and binary stellar evolution using our Monte Carlo cluster evolution code updated with an adaptation of the single and binary stellar evolution codes SSE/BSE from Hurley et. al (2000, 2002). We describe the modifications we have made to the code. We present several test calculations and comparisons with existing studies to illustrate the validity of the code. We show that our code finds very good agreement with direct N-body simulations including primordial binaries and stellar evolution. We find significant differences in the evolution of the global properties of the simulated clusters using stellar evolution compared to simulations without any stellar evolution. In particular, we find that the mass loss from stellar evolution acts as a significant energy production channel simply by reducing the total gravitational binding energy and can significantly prolong the initial core contraction phase before reaching the binary-burning quasi steady state of the cluster evolution as noticed in Paper IV. We simulate a large grid of clusters varying the initial cluster mass, binary fraction, and concentration and compare properties of the simulated clusters with those of the observed Galactic globular clusters (GGCs). We find that our simulated cluster properties agree well with the observed GGC properties. We explore in some detail qualitatively different clusters in different phases of their evolution, and construct synthetic Hertzprung-Russell diagrams for these clusters.Comment: 46 preprint pages, 18 figures, 3 tables, submitted to Ap

NRSF and BDNF polymorphisms as biomarkers of cognitive dysfunction in adults with newly-diagnosed epilepsy

Cognitive dysfunction is a common comorbidity in people with epilepsy, but its causes remain unclear. It may be related to the etiology of the disorder, the consequences of seizures, or the effects of antiepileptic drug treatment. Genetics may also play a contributory role. We investigated the influence of variants in the genes encoding neuron-restrictive silencer factor (NRSF) and brain-derived neurotrophic factor (BDNF), proteins previously associated with cognition and epilepsy, on cognitive function in people with newly diagnosed epilepsy. A total of 82 patients who had previously undergone detailed neuropsychological assessment were genotyped for single nucleotide polymorphisms (SNPs) across the NRSF and BDNF genes. Putatively functional SNPs were included in a genetic association analysis with specific cognitive domains, including memory, psychomotor speed, and information processing. Cross-sectional and longitudinal designs were used to explore genetic influences on baseline cognition at diagnosis and change from baseline over the first year since diagnosis, respectively. We found a statistically significant association between genotypic variation and memory function at both baseline (NRSF: rs1105434, rs2227902 and BDNF: rs1491850, rs2030324, rs11030094) and in our longitudinal analysis (NRSF: rs2227902 and BDNF: rs12273363). Psychomotor speed was also associated with genotype (NRSF rs3796529) in the longitudinal assessment. In line with our previous work on general cognitive function in the healthy aging population, we observed an additive interaction between risk alleles for the NRSF rs2227902 (G) and BDNF rs6265 (A) polymorphisms which was again consistent with a significantly greater decline in delayed recall over the first year since diagnosis. These findings support a role for the NRSF–BDNF pathway in the modulation of cognitive function in patients with newly diagnosed epilepsy

A comparison of HMGB1 concentrations between cerebrospinal fluid and blood in patients with neurological disease

AIMS: To determine whether a correlation exists between paired cerebrospinal fluid (CSF) and serum levels of a novel inflammatory biomarker, high-mobility group box 1 (HMGB1), in different neurological conditions. METHODS: HMGB1 was measured in the serum and CSF of 46 neurological patients (18 idiopathic intracranial hypertension [IIH], 18 neurological infection/inflammation [NII] and 10 Rasmussen's encephalitis [RE]). RESULTS: Mean serum (± SD) HMGB1 levels were 1.43 ± 0.54, 25.28 ± 27.9 and 1.89 ± 1.49 ng/ml for the patients with IIH, NII and RE, respectively. Corresponding mean (± SD) CSF levels were 0.35 ± 0.22, 4.48 ± 6.56 and 2.24 ± 2.35 ng/ml. Both CSF and serum HMGB1 was elevated in NII. Elevated CSF HMGB1 was demonstrated in RE. There was no direct correlation between CSF and serum levels of HMGB1. CONCLUSION: Serum HMGB1 cannot be used as a surrogate measure for CSF levels. CSF HMGB1 was elevated in NII and RE, its role as a prognostic/stratification biomarker needs further study

Rotational velocities of low-mass stars in the Pleiades and Hyades

We have obtained high-resolution spectra of 89 M dwarf members of the Pleiades and Hyades and have derived radial velocities, H-alpha equivalent widths, and spectroscopic rotational velocities for these stars. Typical masses of the newly-observed Pleiades and Hyades stars are ~ 0.4 M_{\sun} and ~ 0.2 M_{\sun}, respectively. We combine our new observations with previously published data to explore the rotational evolution of young stars with M < 0.4 M_\sun. The average rotation rate in the Hyades (age 600 Myr) is about 0.4 that of the Pleiades (110 Myr), and the mean equivalent widths of H-alpha are also lower. As found in previous studies, the correlation between rotation and chromospheric activity is identical in both clusters, implying that the lower activity in the Hyades is a result of the lower rotation rates. We show that a simple scaling of the Pleiades rotational distribution for M \leq 0.4 M_{\sun}, corrected for the effects of structural evolution, matches that of the Hyades if the average angular momentum loss from the Pleiades to the Hyades age is factor of \approx 6. This suggests that the distribution of initial angular momenta and disk-locking lifetimes for the lowest mass stars was similar in both clusters. We argue that this result provides further evidence for a saturation of the angular momentum loss rate at high rotational velocities.Comment: 22 pages, 11 figures, accepted for publication in The Astronomical Journal, tentatively scheduled for March 200

The effect of massive binaries on stellar populations and supernova progenitors

We compare our latest single and binary stellar model results from the Cambridge STARS code to several sets of observations. We examine four stellar population ratios, the number of blue to red supergiants, the number of Wolf-Rayet stars to O supergiants, the number of red supergiants to Wolf-Rayet stars and the relative number of Wolf-Rayet subtypes, WC to WN stars. These four ratios provide a quantitative measure of nuclear burning lifetimes and the importance of mass loss during various stages of the stars' lifetimes. In addition we compare our models to the relative rate of type Ib/c to type II supernovae to measure the amount of mass lost over the entire lives of all stars. We find reasonable agreement between the observationally inferred values and our predicted values by mixing single and binary star populations. However there is evidence that extra mass loss is required to improve the agreement further, to reduce the number of red supergiants and increase the number of Wolf-Rayet stars.Comment: Accepted for publication in MNRAS, 11 pages, 10 figure

An analysis of clinical process measures for acute healthcare delivery in Appalachia: The Roane Medical Center experience

OBJECTIVE: To survey management of selected emergency healthcare needs in a Tennessee community hospital. MATERIALS AND METHODS: In this descriptive report, discharges and associated standard process measures were retrospectively studied for Roane Medical Center (RMC) in Harriman, Tennessee (pop. 6,757). Hospital data were extracted from a nationwide database of short-term acute care hospitals to measure 16 quality performance measures in myocardial infarction (MI), heart failure, and pneumonia during the 14 month interval ending March 2005. The data also permitted comparisons with state and national reference groups. RESULTS: Of RMC patients with myocardial infarction (MI), 94% received aspirin on arrival, a figure higher than both state (85%) and national (91%) averages. Assessment of left ventricular dysfunction among heart failure patients was also higher at RMC (98%) than the state (74%) or national (79%) average. For RMC pneumonia patients, 79% received antibiotics within 4 h of admission, which compared favorably with State (76%) and national (75%) average. RMC scored higher on 13 of 16 clinical process measures (p<0.01, sign test analysis, >95% CI) compared to state and national averages. DISCUSSION: Although acute health care needs are often met with limited resources in medically underserved regions, RMC performed above state and national average for most process measures assessed in this review. Our data were derived from one facility and the associated findings may not be applicable in other healthcare settings. Further studies are planned to track other parameters and specific clinical outcomes at RMC, as well as to identify specific institutional policies that facilitate attainment of target quality measures