First-passage theory of exciton population loss in single-walled carbon nanotubes reveals micron-scale intrinsic diffusion lengths

One-dimensional crystals have long range translational invariance which manifests as long exciton diffusion lengths, but such intrinsic properties are often obscured by environmental perturbations. We use a first-passage approach to model single-walled carbon nanotube (SWCNT) exciton dynamics (including exciton-exciton annihilation and end effects) and compare it to results from both continuous-wave and multi-pulse ultrafast excitation experiments to extract intrinsic SWCNT properties. Excitons in suspended SWCNTs experience macroscopic diffusion lengths, on the order of the SWCNT length, (1.3-4.7 um) in sharp contrast to encapsulated samples. For these pristine samples, our model reveals intrinsic lifetimes (350-750 ps), diffusion constants (130-350 cm^2/s), and absorption cross-sections (2.1-3.6 X 10^-17 cm^2/atom) among the highest previously reported.and diffusion lengths for SWCNTs.Comment: 6 pages, 3 figure

Antigen-driven T-cell turnover.

A mathematical model is developed to characterize the distribution of cell turnover rates within a population of T lymphocytes. Previous models of T-cell dynamics have assumed a constant uniform turnover rate; here we consider turnover in a cell pool subject to clonal proliferation in response to diverse and repeated antigenic stimulation. A basic framework is defined for T-cell proliferation in response to antigen, which explicitly describes the cell cycle during antigenic stimulation and subsequent cell division. The distribution of T-cell turnover rates is then calculated based on the history of random exposures to antigens. This distribution is found to be bimodal, with peaks in cell frequencies in the slow turnover (quiescent) and rapid turnover (activated) states. This distribution can be used to calculate the overall turnover for the cell pool, as well as individual contributions to turnover from quiescent and activated cells. The impact of heterogeneous turnover on the dynamics of CD4(+) T-cell infection by HIV is explored. We show that our model can resolve the paradox of high levels of viral replication occurring while only a small fraction of cells are infected

Soil Nitrification Inhibition with Plantain (\u3ci\u3ePlantago lanceolata\u3c/i\u3e)

One strategy to reduce nitrogen losses from intensively grazed forage systems is to slow the first stage of soil nitrification, specifically inhibiting the microbial oxidation of ammonium to nitrite. Plantain (Plantago lanceolata) leaves and roots are known to contain several bioactive compounds (e.g., aucubin, catalpol and verbascoside) that may contribute to this inhibition. Recent laboratory studies indicate that this inhibition occurs via consumption by grazing animals of precursor bioactive compounds in aboveground biomass and their subsequent excretion as secondary metabolites in urine and/or via active exudation from the roots. Different cultivars of plantain have been shown to impart differing nitrification inhibition activity via both mechanisms. The urinary effect was assessed by determination of net soil nitrification in soil microcosms treated with urine from sheep fed a diet containing either perennial ryegrass or plantain. Analyses showed significant treatment effects on the rate of net nitrification and microbial community structure over time. A preliminary evaluation of the root exudate effect involved the collection of root exudates from six plantain cultivars grown in a hydroponic system. The assay of the root exudates against a pure culture of an ammonium-oxidising bacterium indicated differences in the amount of inhibition imparted by the exudates of each cultivar. The exact means of soil nitrification inhibition by either mechanism is as yet unconfirmed. However, it is likely that these compounds (or derivatives thereof) inhibit the first enzymatic step of nitrification directly, without harm to the soil microbiome as a whole

A comparative study of Type II-P and II-L supernova rise times as exemplified by the case of LSQ13cuw

We report on our findings based on the analysis of observations of the Type II-L supernova LSQ13cuw within the framework of currently accepted physical predictions of core-collapse supernova explosions. LSQ13cuw was discovered within a day of explosion, hitherto unprecedented for Type II-L supernovae. This motivated a comparative study of Type II-P and II-L supernovae with relatively well-constrained explosion epochs and rise times to maximum (optical) light. From our sample of twenty such events, we find evidence of a positive correlation between the duration of the rise and the peak brightness. On average, SNe II-L tend to have brighter peak magnitudes and longer rise times than SNe II-P. However, this difference is clearest only at the extreme ends of the rise time versus peak brightness relation. Using two different analytical models, we performed a parameter study to investigate the physical parameters that control the rise time behaviour. In general, the models qualitatively reproduce aspects of the observed trends. We find that the brightness of the optical peak increases for larger progenitor radii and explosion energies, and decreases for larger masses. The dependence of the rise time on mass and explosion energy is smaller than the dependence on the progenitor radius. We find no evidence that the progenitors of SNe II-L have significantly smaller radii than those of SNe II-P.Comment: 19 pages, 10 figures, accepted by A&

On the multiple supernova population of Arp 299: constraints on progenitor properties and host galaxy star formation characteristics

Throughout the last 20 years 7 supernovae (SNe) have been discovered within Arp 299. One of these is unclassified, leaving 6 core-collapse events; 2 type II, 2 type Ib, a type IIb and one object of indistinct type; Ib/IIb. We analyse the relative numbers of these types, together with their positions with respect to host galaxy properties, to investigate implications for both progenitor characteristics and star formation (SF) properties. Our findings are: 1) the ratio of 'stripped envelope' (SE) events to other type II is higher than that found in the local Universe. 2) All SE SNe are more centrally concentrated within the system than the other type II. 3) All SN environments have similar metallicities and there are no significant metallicity gradients across the system. 4) The SE SNe all fall on bright SF regions while the other type II are found to occur away from bright HII regions. We draw two different -but non-mutually exclusive- interpretations on the system and its supernovae: 1) The distribution of SNe, and the relatively high fraction of types Ib and IIb events over other type II can be explained by the young age of the most recent SF in the system, where insufficient time has expired for the observed to match the 'true' relative SN rates. This explanation provides additional independent evidence that both types Ib and IIb SNe arise from progenitors of shorter stellar lifetime and hence higher mass than other type II. 2) Given the assumption that types Ib and IIb trace higher mass progenitor stars, the relatively high frequency of types Ib and IIb to other type II, and also the centralisation of the former over the latter with respect to host galaxy light implies that in the centrally peaked and enhanced SF within this system, the initial mass function is biased towards the production of high mass stars.Comment: 13 pages, 4 figures. Accepted for publication in MNRAS. The abstract has been edited to fit within arXiv.org submission requirement

Associations between Adverse Childhood Experiences and the novel inflammatory marker glycoprotein acetyls in two generations of the Avon Longitudinal Study of Parents and Children birth cohort

BACKGROUND: Adverse childhood experiences (ACEs) are associated with increased risk of non-communicable diseases in adulthood, potentially mediated by chronic low-grade inflammation. Glycoprotein acetyls (GlycA) is a marker of chronic and cumulative inflammation. We investigated associations between ACEs and GlycA at different ages, in two generations of the population-based Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort. METHODS: ALSPAC offspring's total ACE scores were generated for two age periods using prospectively collected data: 0-7y and 0-17y. GlycA was measured using high-resolution proton nuclear magnetic resonance at mean ages 8y, 18y, and 24y. Sample sizes ranged from: n = 5116 (8y) to n = 3085 (24y). ALSPAC mothers (n = 4634) retrospectively reported ACEs experienced before age 18y and GlycA was assessed at mean age 49y. We used multivariable linear regression to estimate associations between ACEs (total ACE score and individual ACEs) and subsequent GlycA in both samples, adjusting for key confounders. RESULTS: Mean GlycA levels were similar in offspring and mothers and over time. In offspring, there was no evidence that ACEs (total score or individual ACE) were associated with GlycA at age 8y or 18y, or 24y after adjustment for maternal age at birth and parity, maternal marital status, household occupational social class, maternal education, maternal smoking, own ethnicity, sex, and age in months. In mothers, there was evidence of a positive association between the total ACE score and GlycA at age 49y (adjusted mean difference 0.007 mmol/L; 95%CI: 0.003, 0.01). Emotional neglect was the only individual ACE associated with higher GlycA after adjusting for confounders and other ACEs. CONCLUSION: Results suggest the association between ACEs and GlycA may emerge in middle age. Future research should explore the extent to which inflammation in adulthood mediates well-documented associations between ACEs and adverse health outcomes in later life

Epidemiological determinants of spread of causal agent of severe acute respiratory syndrome in Hong Kong.

BACKGROUND: Health authorities worldwide, especially in the Asia Pacific region, are seeking effective public-health interventions in the continuing epidemic of severe acute respiratory syndrome (SARS). We assessed the epidemiology of SARS in Hong Kong. METHODS: We included 1425 cases reported up to April 28, 2003. An integrated database was constructed from several sources containing information on epidemiological, demographic, and clinical variables. We estimated the key epidemiological distributions: infection to onset, onset to admission, admission to death, and admission to discharge. We measured associations between the estimated case fatality rate and patients' age and the time from onset to admission. FINDINGS: After the initial phase of exponential growth, the rate of confirmed cases fell to less than 20 per day by April 28. Public-health interventions included encouragement to report to hospital rapidly after the onset of clinical symptoms, contact tracing for confirmed and suspected cases, and quarantining, monitoring, and restricting the travel of contacts. The mean incubation period of the disease is estimated to be 6.4 days (95% CI 5.2-7.7). The mean time from onset of clinical symptoms to admission to hospital varied between 3 and 5 days, with longer times earlier in the epidemic. The estimated case fatality rate was 13.2% (9.8-16.8) for patients younger than 60 years and 43.3% (35.2-52.4) for patients aged 60 years or older assuming a parametric gamma distribution. A non-parametric method yielded estimates of 6.8% (4.0-9.6) and 55.0% (45.3-64.7), respectively. Case clusters have played an important part in the course of the epidemic. INTERPRETATION: Patients' age was strongly associated with outcome. The time between onset of symptoms and admission to hospital did not alter outcome, but shorter intervals will be important to the wider population by restricting the infectious period before patients are placed in quarantine

The progenitor and early evolution of the Type IIb SN 2016gkg

We report initial observations and analysis on the Type IIb SN~2016gkg in the nearby galaxy NGC~613. SN~2016gkg exhibited a clear double-peaked light curve during its early evolution, as evidenced by our intensive photometric follow-up campaign. SN~2016gkg shows strong similarities with other Type IIb SNe, in particular with respect to the \he~emission features observed in both the optical and near infrared. SN~2016gkg evolved faster than the prototypical Type~IIb SN~1993J, with a decline similar to that of SN~2011dh after the first peak. The analysis of archival {\it Hubble Space Telescope} images indicate a pre-explosion source at SN~2016gkg's position, suggesting a progenitor star with a $\sim$mid F spectral type and initial mass $15-20$\msun, depending on the distance modulus adopted for NGC~613. Modeling the temperature evolution within $5\,\rm{days}$ of explosion, we obtain a progenitor radius of $\sim\,48-124$\rsun, smaller than that obtained from the analysis of the pre-explosion images ($240-320$\rsun).Comment: 7 pages, 5 figures. Submitted to ApJ Letter

Transmission dynamics of the etiological agent of SARS in Hong Kong: impact of public health interventions.

We present an analysis of the first 10 weeks of the severe acute respiratory syndrome (SARS) epidemic in Hong Kong. The epidemic to date has been characterized by two large clusters-initiated by two separate "super-spread" events (SSEs)-and by ongoing community transmission. By fitting a stochastic model to data on 1512 cases, including these clusters, we show that the etiological agent of SARS is moderately transmissible. Excluding SSEs, we estimate that 2.7 secondary infections were generated per case on average at the start of the epidemic, with a substantial contribution from hospital transmission. Transmission rates fell during the epidemic, primarily as a result of reductions in population contact rates and improved hospital infection control, but also because of more rapid hospital attendance by symptomatic individuals. As a result, the epidemic is now in decline, although continued vigilance is necessary for this to be maintained. Restrictions on longer range population movement are shown to be a potentially useful additional control measure in some contexts. We estimate that most currently infected persons are now hospitalized, which highlights the importance of control of nosocomial transmission