Best Estimate Of Age Research Articles

Risk factors for relapse after discontinuation of tenofovir or entecavir in hepatitis B e antigen-negative patients.

This study aimed to define the relapse frequency and risk determinants in chronic hepatitis B (CHB) patients who discontinued nucleoside analog (NA) treatment, were HBeAg-negative, and had achieved both a virological and biochemical response. This retrospective cohort study reviewed patients with HBeAg-negative CHB who received antiviral therapy for at least 65 months between January 1, 2013, and December 31, 2020. These patients discontinued treatment after demonstrating a biochemical and virological response and were evaluated at 6, 12, and 24 months post-treatment discontinuation. Sixty-seven patients with CHB who received NA therapy for at least 65 months, discontinued treatment, and had undetectable HBV DNA and normal ALT values were evaluated. After cessation of NA therapy, a relapse was observed in 38 patients (56.7%). The relapse rate was 71.0% in patients treated with tenofovir disoproxil fumarate (TDF) as the last NA type and 37.9% in patients treated with entecavir (ETV) (p=0.017). The cutoff value for the best estimate of age for predicting relapse was 42 years. The relapse rate was 69.2% in patients aged ≥42 years and 39.2% in patients aged <42 years (p=0.007). The relapse rate was 51.3% in patients with a pre-treatment fibrosis score of 2, 56.0% in those with a fibrosis score of 3, and 100% in those with a fibrosis score of 4 (p=0.089). Among HBeAg-negative CHB patients who achieved a virological and biochemical response to long-term antiviral therapy, those aged 42 years and older, those with high fibrosis scores before treatment, and those who used TDF before treatment cessation should be closely monitored for relapse, especially in the first 12 months after stopping NA treatment.

From the forests to teeth: Visual crossdating to refine age estimates in marine mammals

Estimation of the age of individuals is a fundamental parameter for understanding the biology of individuals and ecology of populations. Incremental growth deposits in tooth dentine or cementum, known as growth layer groups (GLGs), have been used to estimate the age of toothed marine mammals (odontocetes, pinnipeds) since the 1950s (Scheffer and Myrick 1980). In most species, it is assumed that GLGs are deposited annually (Hohn 2009). Validation of this assumption has only been possible in a small number of marine mammal species (e.g., Bowen et al. 1983, Myrick et al. 1984, Hohn et al. 1989, Lockyer 1993, Oosthuizen 1997), due to impracticalities in obtaining validated ages (Evans et al. 2002, Hohn 2009). For species in which validation of age is not possible, absolute age or the accuracy of age estimates cannot be confirmed (Campana 2001). Further, the precision of estimates (i.e., the closeness of repeat counts from an individual tooth) may not necessarily reflect the best estimate of age and, at present, an objective method to assist with identification of GLGs for age estimation purposes has not been established (Evans et al. 2002, Campana and Stewart 2014).

Definition of a Global Stratotype Section and Point (GSSP) for the base of the Upper (Late) Pleistocene Subseries (Quaternary System/Period)

Following the precedence already established during the INQUA Congress in 1932, the Middle/Upper (Late) Pleistocene boundary is defined at the base of the Last Interglacial, the Eemian Stage. It is proposed that a high-resolution core sequence from the Amsterdam Terminal (the Eemian Stage parastratotype) should constitute the Global Stratotype Section and Point (GSSP) for the base of the Upper (Late) Pleistocene Subseries (Quaternary System/Period). The core contains a proxy climate record across the Middle/Upper (Late) Pleistocene boundary as indicated by different biotic and abiotic parameters reflecting the first signs of climate warming at the end of the Saalian cold Stage. For the beginning of the Eemian Stage in Europe, the date of 127.2 ka from the varved-dated record of Monticchio in Italy can be taken as the best estimate of age.

Precise geochronology of phoscorites and carbonatites:: The critical role of U-series disequilibrium in age interpretations

We present the results of a comparative study of several geochronometer minerals (baddeleyite, zircon, apatite, phlogopite and tetraferriphlogopite) and isotopic systems (U-Pb, Th-Pb and Rb-Sr) from phoscorites (magnetite-forsterite-apatite-calcite rocks) and carbonatites of the Kovdor ultramafic-alkaline-carbonatite massif, Kola Peninsula, Russia. Uranium, thorium and their decay products are extremely fractionated by minerals that crystallise from carbonatite and phoscorite magma. We obtain high-precision ages from different chronometers, compare their accuracy, and evaluate the role of geochronological pitfalls of initial radioactive disequilibrium, differential migration of radiogenic isotopes, and inaccurate decay constants. Apatite yielded concordant U-Th-Pb ages between 376 and 380 Ma. The accuracy of the apatite 238U- 206Pb ages is, however, compromised by uncertainty in the amount of radiogenic 206Pb produced from initial excess 230Th. The 235U- 207Pb ages are relatively imprecise due to large common Pb correction and the uncertainty in the initial Pb isotopic composition. The Th-Pb system yields a more precise age of 376.4 ± 0.6 Ma. Zircon from two carbonatite samples is characterised by moderate to low U contents, high Th contents, and very high Th/U ratios up to 9000. The 206Pb*/ 238U systems in the zircon are strongly affected by the presence of excess 206Pb*, produced by decay of initial 230Th. The 208Pb*/ 232Th ages of zircon from both carbonatite samples are uniform and yield a weighted average of 377.52 ± 0.94 Ma. Baddeleyite U-Pb analyses are 3 to 6% normally discordant and have variable 207Pb*/ 206Pb* apparent ages. Eleven alteration-free baddeleyite fractions from three samples with no evidence for Pb loss yield uniform 206Pb*/ 238U ages with a weighted average of 378.54±0.23 Ma (378.64 Ma after correction for initial 230Th deficiency), which we consider the best estimate for age of the phoscorite-carbonatite body of the Kovdor massif. The 206Pb*/ 238U ages of baddeleyite fractions from five other samples spread between 378.5 and 373 Ma, indicating a variable lead loss up to 1.5%. The anomalously old 207Pb/ 235U and 207Pb/ 206Pb ages are consistent with the presence of excess radiogenic 207Pb* in the baddeleyite. We interpret this as a result of preferential partitioning of 231Pa to baddeleyite. Fifteen phlogopite and tetraferriphlogopite fractions from five carbonatite and phoscorite samples yielded precise Rb-Sr isochron age of 372.2 ± 1.5 Ma, which is 5 to 7 m.y. younger than our best estimate based on U-Th-Pb age values. This difference is unlikely to be a result of the disturbance or late closure of Rb-Sr system in phlogopite, but rather suggests that the accepted decay constant of 87Rb is too high. Comparative study of multiple geochronometer minerals from the Kovdor massif has revealed an exceptional complexity of isotopic systems. Reliable ages can be understood through systematic analysis of possible sources of distortion. No single geochronometer is sufficiently reliable in these rocks. Th-Pb and Rb-Sr can be a very useful supplement to U-Pb geochronometry, but the routine use of these geochronometers together will require more precise and accurate determination of decay constants for 232Th and 87Rb.

The age of the universe

Globular clusters are the oldest objects in the Galaxy whose age may be accurately determined. As such globular cluster ages provide the best estimate for the age of the universe. The age of a globular cluster is determined by a comparison between theoretical stellar evolution models and observational data. Current uncertainties in the stellar models and age dating process are discussed in detail. The best estimate for the absolute age of the globular clusters is 14.6 ± 1.7 Gyr. The one-sided, 95% confidence limit on the lower age of the universe is 12.2 Gyr.

Growth and Development of Nestling Brown Goshawks Accipiter Fasciatus, with Details of Breeding Biology

The nesting chronology of one captive (5 nestings) and two wild pairs of Brown Goshawk Accipiter fasciatus, and the growth and development of twelve captive-bred and five wild-bred nestlings are described. Nest building commenced three to four weeks before egg-laying and involved both partners. Moult in the female started, at the innermost primary, about five days before the first egg was laid. Clutch size was two to four (median 3) and eggs were laid at two to four day intervals (median 2) with incubation usually commencing with the second egg. Incubation, by both sexes, lasted thirty days (range 29-31). amongst the shortest recorded for accipiters. Nestlings hatched in a coat of sparse white down which was gradually replaced by a thicker, browner, down by twelve days of age. At six days wing pins had emerged and at eight days tail pins. Fledging occurred at thirty to thirty-one days (range 28-37). Males usually reached various developmental and plumage stages a day or so before females. Wing length increased linearly between the emergence of the wing pins and thirty-five days of age and gave the best estimate of age. Weight increase was more or less sigmoid; adult weight was reached by fledging in males and slightly after fledging in females. Females were not consistently separable from males by weight until about three weeks of age, and their wing and tail length were similar to those of males until about seven weeks of age. Some methods for the estimation of age and sex are given. Growth rates were rapid in relation to body size.

Observations on Development, Nesting Chronolgy, and Clutch and Brood Size in the Australian Kestrel, Falco cenchroides (Aves : Falconidae)

The nesting chronology of three captive and two wild pairs of Australian kestrels and the development of nine captive-bred and five wild-bred nestlings are presented. Clutch and brood sizes and dates when eggs and young were found in nests, collected from a number of sources, are discussed. Breeding biology was similar to that of other species of kestrel. Wing length of nestlings gave the best estimate of age up to about 6 weeks, and the pulling of a rectrix was found to have potential as a method of sexing nestlings and first-year birds.