60 research outputs found
North Atlantic marine <sup>14</sup>C reservoir effects: implications for late-Holocene chronological studies
We investigated surface ocean–atmosphere 14C offsets for the later Holocene at eight locations in the eastern North Atlantic. This resulted in 11 new ΔR assessments for the west coast of Ireland, the Outer Hebrides, the north coast of the Scottish mainland, the Orkney Isles and the Shetland Isles over the period 1300–500 BP. Assessments were made using a robust Multiple Paired Sample (MPS) approach, which is designed to maximize the accuracy of ΔR determinations. Assessments are placed in context with other available data to enable reconstruction of a realistic picture of surface ocean 14C activity over the Holocene period within the North Atlantic region
The Functional Nasal Anatomy of the Pike, <i>Esox lucius</i> L.
Olfactory flow in fishes is a little-explored area of fundamental and applied importance. We investigated olfactory flow in the pike, Esox lucius, because it has an apparently simple and rigid nasal region. We characterised olfactory flow by dye visualisation and computational fluid dynamics, using models derived from X-ray micro-computed tomography scans of two preserved specimens. An external current induced a flow of water through the nasal chamber at physiologically relevant Reynolds numbers (200 – 300). We attribute this externally-induced flow to: the location of the incurrent nostril in a region of high static pressure; the nasal bridge deflecting external flow into the nasal chamber; an excurrent nostril normal to external flow; and viscous entrainment. A vortex in the incurrent nostril may be instrumental in viscous entrainment. Flow was dispersed over the olfactory sensory surface when it impacted on the floor of the nasal chamber. Dispersal may be assisted by: the radial array of nasal folds; a complementary interaction between a posterior nasal fold and the ventral surface of the nasal bridge; and the incurrent vortex. The boundary layer could delay considerably (up to ~ 3 s) odorant transport from the external environment to the nasal region. The drag incurred by olfactory flow was almost the same as the drag incurred by models in which the nasal region had been replaced by a smooth surface. The boundary layer does not detach from the nasal region. We conclude that the nasal bridge and the incurrent vortex are pivotal to olfaction in the pike
Status of the UCNτ experiment
The neutron is the simplest nuclear system that can be used to probe the structure of the weak interaction and search for physics beyond the standard model. Measurements of neutron lifetime and β-decay correlation coefficients with precisions of 0.02% and 0.1%, respectively, would allow for stringent constraints on new physics. The UCNτ experiment uses an asymmetric magneto-gravitational UCN trap with in situ counting of surviving neutrons to measure the neutron lifetime, τ_n = 877.7s (0.7s)_(stat) (+0.4/−0.2s)_(sys). We discuss the recent result from UCNτ, the status of ongoing data collection and analysis, and the path toward a 0.25 s measurement of the neutron lifetime with UCNτ
Light-flavor sea-quark distributions in the nucleon in the SU(3) chiral quark soliton model (I) -- phenomenological predictions --
Theoretical predictions are given for the light-flavor sea-quark
distributions including the strange quark ones on the basis of the flavor SU(3)
version of the chiral quark soliton model. Careful account is taken here of the
SU(3) symmetry breaking effects due to the mass difference between the strange
and nonstrange quarks. This effective mass difference between the
strange and nonstrange quarks is the only one parameter necessary for the
flavor SU(3) generalization of the model. A particular emphasis of study is put
on the {\it light-flavor sea-quark asymmetry} as exemplified by the observables
as well as on the {\it particle-antiparticle asymmetry} of
the strange quark distributions represented by etc. As for the unpolarized
sea-quark distributions, the predictions of the model seem qualitatively
consistent with the available phenomenological information provided by the NMC
data for , the E866 data for , the CCFR data and Barone et al.'s fit for etc. The
model is shown to give several unique predictions also for the spin-dependent
sea-quark distribution, such that and , although the verification
of these predictions must await more elaborate experimental investigations in
the near future.Comment: 36 pages, 20 EPS figures. The revised version accepted for
publication in Phys. Rev. D. The title has been changed, and the body of the
paper has been divided into two pieces, i.e.. the present one which discusses
the main phenomenological predictions of the model and the other one which
describes the detailed formulation of the flavor SU(3) chiral quark soliton
model to predict light-flavor quark and antiquark distribution functions in
the nucleo
Physics Opportunities with the 12 GeV Upgrade at Jefferson Lab
This white paper summarizes the scientific opportunities for utilization of
the upgraded 12 GeV Continuous Electron Beam Accelerator Facility (CEBAF) and
associated experimental equipment at Jefferson Lab. It is based on the 52
proposals recommended for approval by the Jefferson Lab Program Advisory
Committee.The upgraded facility will enable a new experimental program with
substantial discovery potential to address important topics in nuclear,
hadronic, and electroweak physics.Comment: 64 page
Strong evidences of hadron acceleration in Tycho's Supernova Remnant
Very recent gamma-ray observations of G120.1+1.4 (Tycho's) supernova remnant
(SNR) by Fermi-LAT and VERITAS provided new fundamental pieces of information
for understanding particle acceleration and non-thermal emission in SNRs. We
want to outline a coherent description of Tycho's properties in terms of SNR
evolution, shock hydrodynamics and multi-wavelength emission by accounting for
particle acceleration at the forward shock via first order Fermi mechanism. We
adopt here a quick and reliable semi-analytical approach to non-linear
diffusive shock acceleration which includes magnetic field amplification due to
resonant streaming instability and the dynamical backreaction on the shock of
both cosmic rays (CRs) and self-generated magnetic turbulence. We find that
Tycho's forward shock is accelerating protons up to at least 500 TeV,
channelling into CRs about the 10 per cent of its kinetic energy. Moreover, the
CR-induced streaming instability is consistent with all the observational
evidences indicating a very efficient magnetic field amplification (up to ~300
micro Gauss). In such a strong magnetic field the velocity of the Alfv\'en
waves scattering CRs in the upstream is expected to be enhanced and to make
accelerated particles feel an effective compression factor lower than 4, in
turn leading to an energy spectrum steeper than the standard prediction
{\propto} E^-2. This latter effect is crucial to explain the GeV-to-TeV
gamma-ray spectrum as due to the decay of neutral pions produced in nuclear
collisions between accelerated nuclei and the background gas. The
self-consistency of such an hadronic scenario, along with the fact that the
concurrent leptonic mechanism cannot reproduce both the shape and the
normalization of the detected the gamma-ray emission, represents the first
clear and direct radiative evidence that hadron acceleration occurs efficiently
in young Galactic SNRs.Comment: Minor changes. Accepted for publication in Astronomy & Astrophysic
Best practice methodology for 14C calibration of marine and mixed terrestrial/marine samples
There is a lack of detailed guidance in the published literature on how to calibrate 14C measurements made on marine or mixed marine/terrestrial (primarily human remains) samples. We describe what we consider to be the best approach towards achieving the most accurate calibrated age ranges, using the most appropriate ΔR and percentage marine diet estimates, and associated, realistic error terms on these values. However, this approach will increase the calibrated age range(s) by fully accounting for the variability in both the model and the material. While the discussion is based on examples from the UK and Iceland, the same fundamental arguments can be applied in any geographic location largely devoid of C4 plants as the high δ13C values from such plants can make identification of marine intake difficult to determine
Prognostic Tools in Patients with Advanced Cancer: A Systematic Review
Purpose:
In 2005, the European Association for Palliative Care (EAPC) made recommendations for prognostic markers in advanced cancer. Since then, prognostic tools have been developed, evolved and validated. The aim of this systematic review was to examine the progress in the development and validation of prognostic tools.
Methods:
Medline, Embase Classic + and Embase were searched. Eligible studies met the following criteria: patients with incurable cancer; >18 years; original studies; population n>100; published after 2003. Descriptive and quantitative statistical analyses were performed.
Results:
Forty-nine studies were eligible, assessing seven prognostic tools across different care settings, primary cancer types and statistically assessed survival prediction. The (PPS) Palliative Performance Scale was the most studied (n=21,082), composed of 6 parameters (6 subjective), was externally validated and predicted survival. The Palliative Prognostic Score (PaP) composed of 6 parameters (4 subjective, 2 objective), the Palliative Prognostic Index (PPI) composed of 9 parameters (9 subjective), and the Glasgow Prognostic Score (GPS) composed of 2 parameters (2 objective), and were all externally validated in more than 2000 patients with advanced cancer and predicted survival.
Conclusion:
Various prognostic tools have been validated, but vary in their complexity, subjectivity and therefore clinical utility. The GPS would seem the most favourable as it uses only two parameters (both objective) and has prognostic value complementary to the gold standard measure, which is performance status. Further studies comparing all proven prognostic markers in a single cohort of patients with advanced cancer, are needed to determine the optimal prognostic tool
Strange Hadronic Loops of the Proton: A Quark Model Calculation
Nontrivial sea effects have their origin in the low- dynamics
of strong QCD. We present here a quark model calculation of the contribution of
pairs arising from a {\it complete} set of OZI-allowed strong
hadronic loops to the net spin of the proton, to its charge radius,
and to its magnetic moment. The calculation is performed in an ``unquenched
quark model" which has been shown to preserve the spectroscopic successes of
the naive quark model and to respect the OZI rule. We speculate that an
extension of the calculation to the nonstrange sea will show that most of the
``missing spin" of the proton is in orbital angular momenta.Comment: revtex, 34 pages, 4 figure
History of clinical transplantation
How transplantation came to be a clinical discipline can be pieced together by perusing two volumes of reminiscences collected by Paul I. Terasaki in 1991-1992 from many of the persons who were directly involved. One volume was devoted to the discovery of the major histocompatibility complex (MHC), with particular reference to the human leukocyte antigens (HLAs) that are widely used today for tissue matching.1 The other focused on milestones in the development of clinical transplantation.2 All the contributions described in both volumes can be traced back in one way or other to the demonstration in the mid-1940s by Peter Brian Medawar that the rejection of allografts is an immunological phenomenon.3,4 © 2008 Springer New York
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