836 research outputs found
The Self Model and the Conception of Biological Identity in Immunology
The self/non-self model, first proposed by F.M. Burnet, has dominated immunology for sixty years now. According to this model, any foreign element will trigger an immune reaction in an organism, whereas endogenous elements will not, in normal circumstances, induce an immune reaction. In this paper we show that the self/non-self model is no longer an appropriate explanation of experimental data in immunology, and that this inadequacy may be rooted in an excessively strong metaphysical conception of biological identity. We suggest that another hypothesis, one based on the notion of continuity, gives a better account of immune phenomena. Finally, we underscore the mapping between this metaphysical deflation from self to continuity in immunology and the philosophical debate between substantialism and empiricism about identity
A statistical mechanics approach to autopoietic immune networks
The aim of this work is to try to bridge over theoretical immunology and
disordered statistical mechanics. Our long term hope is to contribute to the
development of a quantitative theoretical immunology from which practical
applications may stem. In order to make theoretical immunology appealing to the
statistical physicist audience we are going to work out a research article
which, from one side, may hopefully act as a benchmark for future improvements
and developments, from the other side, it is written in a very pedagogical way
both from a theoretical physics viewpoint as well as from the theoretical
immunology one.
Furthermore, we have chosen to test our model describing a wide range of
features of the adaptive immune response in only a paper: this has been
necessary in order to emphasize the benefit available when using disordered
statistical mechanics as a tool for the investigation. However, as a
consequence, each section is not at all exhaustive and would deserve deep
investigation: for the sake of completeness, we restricted details in the
analysis of each feature with the aim of introducing a self-consistent model.Comment: 22 pages, 14 figur
Age and growth of longfinned eels (Anguilla dieffenbachii) in pastoral and forested streams in the Waikato River basin, and in two hydro-electric lakes in the North Island, New Zealand
Growth rates of New Zealand endemic longfinned eels (Anguilla dieffenbachii) from streams in pasture and indigenous forest, and from two hydroelectric lakes (Lakes Karapiro and Matahina), were estimated by otolith examination. Habitat-specific growth was further investigated with measurement of widths of annual bands in otoliths. Longfinned eels 170-1095 mm in length ranged between 4 and 60 years old (N=252). Eels in pastoral streams grew faster (mean annual length increment ±95% CL = 24 ± 3 mm to 36 ± 7 mm) than eels in streams in indigenous forest (annual length increment 12 ± 2 mm to 15 ± 3 mm). Eels from the hydro-electric lakes had growth rates (annual length increments 19 ± 4 and 19 + 7 mm) similar to eels from pastoral streams. Otoliths of most eels showed annual band widths that indicated growth in several different habitats, corresponding to growth during upstream migration, and limited movement among adult habitats. Estimated age at marketable size (220 g) ranged between 7 and 26 years. The particularly slow growth of longfinned eels in streams in indigenous forest has considerable implications for management. The fast growth rates of eels in hydro-electric lakes provides evidence for the potential of increased eel production by stocking. The probable selective production of female eels in these lakes may be nationally important to allow enhancement of breeding stocks
Ancient Origins of a Modern Anthropic Cosmological Argument
Ancient origins of a modern anthropic argument against cosmologies involving
infinite series of past events are considered. It is shown that this argument -
which in modern times has been put forward by distinguished cosmologists like
Paul C. W. Davies and Frank J. Tipler - originates in pre-Socratic times and is
implicitly present in the cyclical cosmology of Empedocles. There are traces of
the same line of reasoning throughout the ancient history of ideas, and the
case of a provocative statement of Thucydides is briefly analyzed. Moreover,
the anthropic argument has been fully formulated in the epic of Lucretius,
confirming it as the summit of ancient cosmology. This is not only of
historical significance but presents an important topic for the philosophy of
cosmology provided some of the contemporary inflationary models, particularly
Linde's chaotic inflation, turn out to be correct.Comment: 11 pages, no figures; Astronomical and Astrophysical Transactions,
accepte
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'Tipping the Balance': Karl Friedrich Meyer, Latent Infections, and the Birth of Modern Ideas of Disease Ecology
The Swiss-born medical researcher Karl Friedrich Meyer (1884â1974) is best known as a âmicrobe hunterâ who pioneered investigations into diseases at the intersection of animal and human health in California in the 1920s and 1930s. In particular, historians have singled out Meyerâs 1931 Ludwig Hektoen Lecture in which he described the animal kingdom as a âreservoir of diseaseâ as a forerunner of âone medicineâ approaches to emerging zoonoses. In so doing, however, historians risk overlooking Meyerâs other intellectual contributions. Developed in a series of papers from the mid-1930s onwards, these were ordered around the concept of latent infections and sought to link microbial behavior to broader bio-ecological, environmental, and social factors that impact hostpathogen interactions. In this respect Meyerâlike the comparative pathologist Theobald Smith and the immunologist Frank Macfarlane Burnetâcan be seen as a pioneer of modern ideas of disease ecology. However, while Burnetâs and Smithâs contributions to this scientific field have been widely acknowledged, Meyerâs have been largely ignored. Drawing on Meyerâs published writings and private correspondence, this paper aims to correct that lacuna while contributing to a reorientation of the historiography of bacteriological epidemiology. In particular I trace Meyerâs intellectual exchanges with Smith, Burnet and the animal ecologist Charles Elton, over brucellosis, psittacosis and plagueâexchanges that not only showed how environmental and ecological conditions could âtip the balanceâ in favor of parasites but which transformed Meyer thinking about resistance to infection and disease
Multifrequency Radiation of Extragalactic Large-Scale Jets
Large-scale extragalactic jets, observed to extend from a few to a few
hundred kiloparsecs from active galactic nuclei, are now studied over many
decades in frequency of electromagnetic spectrum, from radio until (possibly)
TeV gamma rays. For hundreds of known radio jets, only about 25 are observed at
optical frequencies. Most of them are relatively short and faint, with only a
few exceptions, like 3C 273 or M 87, allowing for detailed spectroscopic and
morphological studies. Somewhat surprisingly, the large-scale jets can be very
prominent in X-rays. Up to now, about 25 jets were detected within the 1 - 10
keV energy range, although the nature of this emission is still under debate.
In general, both optical and X-ray jet observations present serious problems
for standard radiation models for the considered objects. Recent TeV
observations of M 87 suggest the possibility of generating large photon fluxes
at these high energies by its extended jet.
In this paper we summarize information about multiwavelength emission of the
large-scale jets, and we point out several modifications of the standard jet
radiation models (connected with relativistic bulk velocities, jet radial
stratification and particle energization all the way along the jet), which can
possibly explain some of the mentioned puzzling observations. We also comment
on gamma-ray emission of the discussed objects.Comment: 29 pages. Modified version, accepted for publication in Chinese
Journal of Astronomy and Astrophysic
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Introduction: microbes, networks, knowledgeâdisease ecology and emerging infectious diseases in time of COVID-19
This is an introduction to the topical collection Microbes, Networks, Knowledge: Disease Ecology in the twentieth Century, based on a workshop held at Queen Mary, University London on July 6â7 2016. More than twenty years ago, historian of science and medicine Andrew Mendelsohn asked, âWhere did the modern, ecological understanding of epidemic disease come from?â Moving beyond Mendelsohnâs answer, this collection of new essays considers the global history of disease ecology in the past century and shows how epidemics and pandemics have made âmicrobes complexâ
Direct constraint on the distance of y2 Velorum from AMBER/VLTI observations
In this work, we present the first AMBER observations, of the Wolf-Rayet and
O (WR+O) star binary system y2 Velorum. The AMBER instrument was used with the
telescopes UT2, UT3, and UT4 on baselines ranging from 46m to 85m. It delivered
spectrally dispersed visibilities, as well as differential and closure phases,
with a resolution R = 1500 in the spectral band 1.95-2.17 micron. We interpret
these data in the context of a binary system with unresolved components,
neglecting in a first approximation the wind-wind collision zone flux
contribution. We show that the AMBER observables result primarily from the
contribution of the individual components of the WR+O binary system. We discuss
several interpretations of the residuals, and speculate on the detection of an
additional continuum component, originating from the free-free emission
associated with the wind-wind collision zone (WWCZ), and contributing at most
to the observed K-band flux at the 5% level. The expected absolute separation
and position angle at the time of observations were 5.1±0.9mas and
66±15° respectively. However, we infer a separation of
3.62+0.11-0.30 mas and a position angle of 73+9-11°. Our analysis thus
implies that the binary system lies at a distance of 368+38-13 pc, in agreement
with recent spectrophotometric estimates, but significantly larger than the
Hipparcos value of 258+41-31 pc
Kinetic Luminosity and Composition of Active Galactic Nuclei Jets
We present a new method how to discriminate the matter content of
parsec-scale jets of active galactic nuclei. By constraining the kinetic
luminosity of a jet from the observed core size at a single very long baseline
interferometry frequency, we can infer the electron density of a radio-emitting
component as a function of the composition. Comparing this density with that
obtained from the theory of synchrotron self-absorption, we can determine the
composition. We apply this procedure to the five components in the 3C~345 jet
and find that they are likely pair-plasma dominated at 11 epochs out of the
total 21 epochs, provided that the bulk Lorentz factor is less than 15
throughout the jet. We also investigate the composition of the 3C~279 jet and
demonstrate that its two components are likely pair-plasma dominated at three
epochs out of four epochs, provided that their Doppler factors are less than
10, which are consistent with observations. The conclusions do not depend on
the lower cutoff energy of radiating particles.Comment: 6 figures, 2 tables; accepted to Astroph.
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