1,028 research outputs found
Immunological techniques in the study of biochemical problems
For many years now serological differentiation of bacterial strains and determination of blood groups have been standard methods in hospital laboratories. More recently a great deal of research effort has been directed towards investigating the many protein components of serum and their relation to disease. This work has been very dependent on immunological techniques. Because of their high specificity and sensitivity, such methods have become useful tools to biochemists and protein chemists. In this laboratory immunological methods have been used to investigate problems of comparative biochemistry, to obtain estimates of the size of proteins, and to gauge the effect on protein structure produced by procedures which chemically alter the amino acids of the protein. The work in this laboratory is concerned with the study of copper-containing proteins from the blood of invertebrates (haemocyanins), and from humans (caeruloplasmin). Some of this work is described in this article. The principles behind the techniques are described in some detail in the hope of stimulating their use in other fields of research.peer-reviewe
The isolation and study of mammalian islets of langherhans
The study of metabolism of isolated tissues is of remarkable importance in biochemistry and physiology. The main objective of this article is to review some of the methods used to isolate mammalian islets of Langerhans from mammalian pancreas. There are two methods by which these can be isolated, namely, micro-dissection, and the selective enzyme treatment to loosen or remove much of the acinar tissue. The results obtained by these methods are indicated, whereby it is evident that isolated islets of Langerhans are amenable to study by suitable micro-methods. It is encouraging that the results obtained correspond with the knowledge of endocrine pancreatic function.peer-reviewe
Exclusive 16O(γ,π-p) reaction in the Δ resonance region
We report the first exclusive (γ,π-p) measurements on a complex nucleus. The 16O(γ,π-p) reaction was measured at pion laboratory angles of 64° and 120°. Coincident protons were detected over the quasifree angular correlation range using a vertical array of seven plastic scintillator detectors spanning ±33° about the scattering plane. The cross sections are compared to factorized distorted-wave impulse approximation calculations; these provide a good description of the backward angle data, but are in serious disagreement with the forward angle data
The Local Bubble and Interstellar Material Near the Sun
The properties of interstellar matter (ISM) at the Sun are regulated by our
location with respect to the Local Bubble (LB) void in the ISM. The LB is
bounded by associations of massive stars and fossil supernovae that have
disrupted natal ISM and driven intermediate velocity ISM into the LB interior
void. The Sun is located in such a driven ISM parcel. The Local Fluff has a
bulk velocity of 19 km/s in the LSR, and an upwind direction towards the center
of the gas and dust ring formed by the Loop I supernova remnant interaction
with the LB. When the ram pressure of the LIC is included in the total LIC
pressure, and if magnetic thermal and cosmic ray pressures are similar, the LIC
appears to be in pressure equilibrium with the local hot bubble plasma.Comment: Proceedings of Symposium on the Composition of Matter, honoring
Johannes Geiss on the occasion of his 80th birthday. Space Science Reviews
(in press
Assessing the risk of bluetongue to UK livestock: uncertainty and sensitivity analyses of a temperature-dependent model for the basic reproduction number
Since 1998 bluetongue virus (BTV), which causes bluetongue, a non-contagious, insect-borne infectious disease of ruminants, has expanded northwards in Europe in an unprecedented series of incursions, suggesting that there is a risk to the large and valuable British livestock industry. The basic reproduction number, R0, provides a powerful tool with which to assess the level of risk posed by a disease. In this paper, we compute R0 for BTV in a population comprising two host species, cattle and sheep. Estimates for each parameter which influences R0 were obtained from the published literature, using those applicable to the UK situation wherever possible. Moreover, explicit temperature dependence was included for those parameters for which it had been quantified. Uncertainty and sensitivity analyses based on Latin hypercube sampling and partial rank correlation coefficients identified temperature, the probability of transmission from host to vector and the vector to host ratio as being most important in determining the magnitude of R0. The importance of temperature reflects the fact that it influences many processes involved in the transmission of BTV and, in particular, the biting rate, the extrinsic incubation period and the vector mortality rate
Three-body non-additive forces between spin-polarized alkali atoms
Three-body non-additive forces in systems of three spin-polarized alkali
atoms (Li, Na, K, Rb and Cs) are investigated using high-level ab initio
calculations. The non-additive forces are found to be large, especially near
the equilateral equilibrium geometries. For Li, they increase the three-atom
potential well depth by a factor of 4 and reduce the equilibrium interatomic
distance by 0.9 A. The non-additive forces originate principally from chemical
bonding arising from sp mixing effects.Comment: 4 pages, 3 figures (in 5 files
Charged pion form factor between Q^2=0.60 and 2.45 GeV^2. II. Determination of, and results for, the pion form factor
The charged pion form factor, Fpi(Q^2), is an important quantity which can be
used to advance our knowledge of hadronic structure. However, the extraction of
Fpi from data requires a model of the 1H(e,e'pi+)n reaction, and thus is
inherently model dependent. Therefore, a detailed description of the extraction
of the charged pion form factor from electroproduction data obtained recently
at Jefferson Lab is presented, with particular focus given to the dominant
uncertainties in this procedure. Results for Fpi are presented for
Q^2=0.60-2.45 GeV^2. Above Q^2=1.5 GeV^2, the Fpi values are systematically
below the monopole parameterization that describes the low Q^2 data used to
determine the pion charge radius. The pion form factor can be calculated in a
wide variety of theoretical approaches, and the experimental results are
compared to a number of calculations. This comparison is helpful in
understanding the role of soft versus hard contributions to hadronic structure
in the intermediate Q^2 regime.Comment: 18 pages, 11 figure
Extragalactic neutrino background from very young pulsars surrounded by supernova envelopes
We estimate the extragalactic muon neutrino background which is produced by
hadrons injected by very young pulsars at an early phase after supernova
explosion. It is assumed that hadrons are accelerated in the pulsar wind zone
which is filled with thermal photons captured below the expanding supernova
envelope. In collisions with those thermal photons hadrons produce pions which
decay into muon neutrinos. At a later time, muon neutrinos are also produced by
the hadrons in collisions with matter of the expanding envelope. We show that
extragalactic neutrino background predicted by such a model should be
detectable by the planned 1 km neutrino detector if a significant part of
pulsars is born with periods shorter than ms. Since such population
of pulsars is postulated by the recent models of production of extremely high
energy cosmic rays, detection of neutrinos with predicted fluxes can be used as
their observational test.Comment: 4 pages, 2 figures, A&A style, accepted to A&A Let
Phenomenology of the Deuteron Electromagnetic Form Factors
A rigorous extraction of the deuteron charge form factors from tensor
polarization data in elastic electron-deuteron scattering, at given values of
the 4-momentum transfer, is presented. Then the world data for elastic
electron-deuteron scattering is used to parameterize, in three different ways,
the three electromagnetic form factors of the deuteron in the 4-momentum
transfer range 0-7 fm^-1. This procedure is made possible with the advent of
recent polarization measurements. The parameterizations allow a
phenomenological characterization of the deuteron electromagnetic structure.
They can be used to remove ambiguities in the form factors extraction from
future polarization data.Comment: 18 pages (LaTeX), 2 figures Feb. 25: minor changes of content and in
Table
Is the evidence for dark energy secure?
Several kinds of astronomical observations, interpreted in the framework of
the standard Friedmann-Robertson-Walker cosmology, have indicated that our
universe is dominated by a Cosmological Constant. The dimming of distant Type
Ia supernovae suggests that the expansion rate is accelerating, as if driven by
vacuum energy, and this has been indirectly substantiated through studies of
angular anisotropies in the cosmic microwave background (CMB) and of spatial
correlations in the large-scale structure (LSS) of galaxies. However there is
no compelling direct evidence yet for (the dynamical effects of) dark energy.
The precision CMB data can be equally well fitted without dark energy if the
spectrum of primordial density fluctuations is not quite scale-free and if the
Hubble constant is lower globally than its locally measured value. The LSS data
can also be satisfactorily fitted if there is a small component of hot dark
matter, as would be provided by neutrinos of mass 0.5 eV. Although such an
Einstein-de Sitter model cannot explain the SNe Ia Hubble diagram or the
position of the `baryon acoustic oscillation' peak in the autocorrelation
function of galaxies, it may be possible to do so e.g. in an inhomogeneous
Lemaitre-Tolman-Bondi cosmology where we are located in a void which is
expanding faster than the average. Such alternatives may seem contrived but
this must be weighed against our lack of any fundamental understanding of the
inferred tiny energy scale of the dark energy. It may well be an artifact of an
oversimplified cosmological model, rather than having physical reality.Comment: 12 pages, 5 figures; to appear in a special issue of General
Relativity and Gravitation, eds. G.F.R. Ellis et al; Changes: references
reformatted in journal style - text unchange
- …