315 research outputs found
Orientation of drill core by use of borehole geophysical imaging
Borehole core must be orientated relative to a geographic coordinate system if meaningful geological, structural and geotechnical information is to be derived from it. This can be achieved by matching core features with features revealed by geophysical images of the borehole wall. The orientation of a reference line marked on the drill core can thereby be calculated, along with the dip and azimuth of any significant features found in the core. A technique developed by the British Geological Survey (BGS) on the basis of borehole imaging is described here and evaluated in the light of results obtained in the orientation of core extracted on behalf of United Kingdom Nirex, Ltd (Nirex)
Fitness declines toward range limits and local adaptation to climate affect dispersal evolution during climate-induced range shifts
Sherpa Romeo yellow journal (pre-print only, accepted for publication)Dispersal
ability
will
largely
determine
whether
species
track
their
climatic
niches
during
climate
change,
a
process
especially
important
for
populations
at
contracting
(low-Âlatitude/low-Âelevation)
range
limits
that
otherwise
risk
extinction.
We
investigate
whether
dispersal
evolution
at
contracting
range
limits
is
facilitated
by
two
processes
that
potentially
enable
edge
populations
to
experience
and
adjust
to
the
effects
of
climate
deterioration
before
they
cause
extinction:
a)
climate-Ââinduced
fitness
declines
toward
range
limits,
and
b)
local
adaptation
to
a
shifting
climate
gradient.
We
simulate
a
species
distributed
continuously
along
a
temperature
gradient
using
a
spatially
explicit,
individual-Ââ
based
model.
We
compare
range-Ââwide
dispersal
evolution
during
climate
stability
vs.
directional
climate
change,
with
uniform
fitness
vs.
fitness
that
declines
toward
range
limits
(RLs),
and
for
a
single
climate
genotype
vs.
multiple
genotypes
locally
adapted
to
temperature.
Dispersal
decreased
toward
stable
RLs
when
range-Ââwide
fitness
was
uniform,
but
increased
when
fitness
declined
toward
RLs,
due
to
highly
dispersive
genotypes
maintaining
sink
populations
at
RLs,
increased
kin
selection
in
smaller
populations,
and
an
emergent
fitness
asymmetry
that
favoured
dispersal
in
low-Ââquality
habitat.
However,
this
initial
dispersal
advantage
at
low-Ââfitness
RLs
did
not
facilitate
climate
tracking,
as
it
was
outweighed
by
an
increased
probability
of
extinction.
Locally-Ââadapted
genotypes
benefited
from
staying
close
to
their
climate
optima;
this
selected
against
dispersal
under
stable
climates
but
for
increased
dispersal
throughout
shifting
ranges,
compared
to
cases
without
local
adaptation.
Dispersal
increased
at
expanding
RLs
in
most
scenarios,
but
only
increased
at
the
range
centre
and
contracting
RLs
given
local
adaptation
to
climate
Growing Income Inequality Threatens American Education
The first of two articles in consecutive months describes the origins and nature of growing income inequality, and some of its consequences for American children. It documents the increased family income inequality that's occurred over the past 40 years and shows that the increased income disparity has been more than matched by an expanding gap between the amounts of money that low- and high-income parents spend on enrichment activities for their children. It also shows that the growth in income inequality has been accompanied by increasing gaps in academic achievement. The article draws from the first part of the author's recent book, Restoring Opportunity: The Crisis of Inequality and the Challenge for American Education (Harvard Education Press and the Russell Sage Foundation, 2014). The second part to the series, also drawn from Restoring Opportunity, describes ideas based on proven policy approaches that will enable the country to make progress on the enormous task of restoring the educational opportunities that children from low-income families need if they are to lead productive and fulfilling lives. © 2014
Transverse Beam Spin Asymmetries in Forward-Angle Elastic Electron-Proton Scattering
We have measured the beam-normal single-spin asymmetry in elastic scattering
of transversely-polarized 3 GeV electrons from unpolarized protons at Q^2 =
0.15, 0.25 (GeV/c)^2. The results are inconsistent with calculations solely
using the elastic nucleon intermediate state, and generally agree with
calculations with significant inelastic hadronic intermediate state
contributions. A_n provides a direct probe of the imaginary component of the
2-gamma exchange amplitude, the complete description of which is important in
the interpretation of data from precision electron-scattering experiments.Comment: 5 pages, 3 figures, submitted to Physical Review Letters; shortened
to meet PRL length limit, clarified some text after referee's comment
Strange Quark Contributions to Parity-Violating Asymmetries in the Forward G0 Electron-Proton Scattering Experiment
We have measured parity-violating asymmetries in elastic electron-proton
scattering over the range of momentum transfers 0.12 < Q^2 < 1.0 GeV^2. These
asymmetries, arising from interference of the electromagnetic and neutral weak
interactions, are sensitive to strange quark contributions to the currents of
the proton. The measurements were made at JLab using a toroidal spectrometer to
detect the recoiling protons from a liquid hydrogen target. The results
indicate non-zero, Q^2 dependent, strange quark contributions and provide new
information beyond that obtained in previous experiments.Comment: 5 pages, 2 figure
The G0 Experiment: Apparatus for Parity-Violating Electron Scattering Measurements at Forward and Backward Angles
In the G0 experiment, performed at Jefferson Lab, the parity-violating
elastic scattering of electrons from protons and quasi-elastic scattering from
deuterons is measured in order to determine the neutral weak currents of the
nucleon. Asymmetries as small as 1 part per million in the scattering of a
polarized electron beam are determined using a dedicated apparatus. It consists
of specialized beam-monitoring and control systems, a cryogenic hydrogen (or
deuterium) target, and a superconducting, toroidal magnetic spectrometer
equipped with plastic scintillation and aerogel Cerenkov detectors, as well as
fast readout electronics for the measurement of individual events. The overall
design and performance of this experimental system is discussed.Comment: Submitted to Nuclear Instruments and Method
Double-Spin Asymmetry in the Cross Section for Exclusive rho^0 Production in Lepton-Proton Scattering
Evidence for a positive longitudinal double-spin asymmetry = 0.24
+-0.11 (stat) +-0.02 (syst) in the cross section for exclusive diffractive
rho^0(770) vector meson production in polarised lepton-proton scattering was
observed by the HERMES experiment. The longitudinally polarised 27.56 GeV HERA
positron beam was scattered off a longitudinally polarised pure hydrogen gas
target. The average invariant mass of the photon-proton system has a value of
= 4.9 GeV, while the average negative squared four-momentum of the virtual
photon is = 1.7 GeV^2. The ratio of the present result to the
corresponding spin asymmetry in inclusive deep-inelastic scattering is in
agreement with an early theoretical prediction based on the generalised vector
meson dominance model.Comment: 10 pages, 4 embedded figures, LaTe
Towards evolutionary predictions:Current promises and challenges
Evolution has traditionally been a historical and descriptive science, and predicting future evolutionary processes has long been considered impossible. However, evolutionary predictions are increasingly being developed and used in medicine, agriculture, biotechnology and conservation biology. Evolutionary predictions may be used for different purposes, such as to prepare for the future, to try and change the course of evolution or to determine how well we understand evolutionary processes. Similarly, the exact aspect of the evolved population that we want to predict may also differ. For example, we could try to predict which genotype will dominate, the fitness of the population or the extinction probability of a population. In addition, there are many uses of evolutionary predictions that may not always be recognized as such. The main goal of this review is to increase awareness of methods and data in different research fields by showing the breadth of situations in which evolutionary predictions are made. We describe how diverse evolutionary predictions share a common structure described by the predictive scope, time scale and precision. Then, by using examples ranging from SARS-CoV2 and influenza to CRISPR-based gene drives and sustainable product formation in biotechnology, we discuss the methods for predicting evolution, the factors that affect predictability and how predictions can be used to prevent evolution in undesirable directions or to promote beneficial evolution (i.e. evolutionary control). We hope that this review will stimulate collaboration between fields by establishing a common language for evolutionary predictions
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