1,248 research outputs found
Gravitationally enhanced depolarization of ultracold neutrons in magnetic-field gradients
Trapped ultracold neutrons (UCN) have for many years been the mainstay of experiments to search for the electric dipole moment (EDM) of the neutron, a critical parameter in constraining scenarios of new physics beyond the Standard Model. Because their energies are so low, UCN preferentially populate the lower region of their physical enclosure, and do not sample uniformly the ambient magnetic field throughout the storage volume. This leads to a substantial increase in the rate of depolarization, as well as to shifts in the measured frequency of the stored neutrons. Consequences for EDM measurements are discussed
What did HERA teach us about the structure of the proton?
Starting in 2008 the H1 and ZEUS experiments have been combining their data
in order to provide the most complete and accurate set of deep-inelastic data
as the legacy of HERA. The present review presents these combinations, both
published and preliminary, and explores how they have been used to give
information on the structure of the proton. The HERAPDF parton distribution
functions (PDFs) are presented and compared with other current PDFs and with
data from the Tevatron and LHC colliders.Comment: 49 pages, 49 figures, to be published in J.Phys.
Estimating ecological metrics for holistic conservation management in a biodiverse but information‐poor tropical region
Conservation ecologists face the dual challenge of working with difficult‐to‐study species and providing ecological metrics that support conservation management at global, regional, and local levels. We present metrics identifying distributions, site‐level and global abundance, site‐contextualized habitat requirements, and threats for seven dry forest endemic birds (two threatened, one Near Threatened) in the globally important Tumbes region of Peru. Extents of occurrence ranged from 36,000 to 152,000 km2, and while broad distributions were generally congruent, nearly half of species overlapped 150,000. Site‐level population estimates varied hugely, reflecting size of site and extreme variation in local abundances. Large tree girths and dense low cover generally promoted bird abundance, but stem density acted in opposite directions for different species, implying the need for site‐ and species‐specific habitat management. Habitat quality varied across sites, further complicating management options at the local level (e.g., reduced grazing). We highlight the suitability of our methods in providing useful conservation metrics for data‐poor regions, and demonstrate their application. Importantly, we propose key sites and priority actions for the region, including extensions of existing protected areas
Electron Beam Nano-Etching in Oxides, Fluorides, Metals and Semiconductors
Etching, lithography, hole formation, surface restructuring and external machining can all be performed on a nanometre scale using an intense electron beam. Results are presented for a range of different materials which demonstrate the variety of mechanisms by which electron beam nano-etching can occur. For example, in crystalline 13-alumina hole formation occurs by surface indentations growing inwards to join up and form a nanometre diameter hole. In amorphous alumina, on the other hand, hole formation is from the inside-out: oxygen gas bubbles form under the electron beam, coalesce, and burst to leave a well defined nanometre diameter hole. In MgO and Si, holes develop from the electron exit surface: whereas in Al voids form along the irradiated volume, leading eventually to the development of a hole at the electron entrance surface. The potential of electron beam nano-etching to lithography and information storage is demonstrated by showing that the entire contents of the Encyclopaedia Britannica can be written on a pinhead
The production, purification and crystallization of a pocilloporin pigment from a reef-forming coral
Reef-building corals contain fluorescent pigments termed pocilloporins that function by regulating the light environment of coral and acting as a photoprotectant in excessive sunlight. These pocilloporins are related to the monomeric green fluorescent protein and the tetrameric DsRed fluorescent proteins, which have widespread use as biotechnological tools. An intensely blue-coloured pocilloporin, termed Rtms5, was expressed in Escherichia coli, purified and crystallized. Rtms5 was shown to be tetrameric, with deep blue crystals that diffract to 2.2 Angstrom resolution and belong to space group I4(1)22. The colour of this pocilloporin was observed to be sensitive to pH and a yellow (pH 3.5) and a red form (pH 4.5) of Rtms5 were also crystallized. These crystals belong to space group P4(2)22 and diffract to 2.4 Angstrom resolution or better
Fully Unintegrated Parton Correlation Functions and Factorization in Lowest Order Hard Scattering
Motivated by the need to correct the potentially large kinematic errors in
approximations used in the standard formulation of perturbative QCD, we
reformulate deeply inelastic lepton-proton scattering in terms of gauge
invariant, universal parton correlation functions which depend on all
components of parton four-momentum. Currently, different hard QCD processes are
described by very different perturbative formalisms, each relying on its own
set of kinematical approximations. In this paper we show how to set up
formalism that avoids approximations on final-state momenta, and thus has a
very general domain of applicability. The use of exact kinematics introduces a
number of significant conceptual shifts already at leading order, and tightly
constrains the formalism. We show how to define parton correlation functions
that generalize the concepts of parton density, fragmentation function, and
soft factor. After setting up a general subtraction formalism, we obtain a
factorization theorem. To avoid complications with Ward identities the full
derivation is restricted to abelian gauge theories; even so the resulting
structure is highly suggestive of a similar treatment for non-abelian gauge
theories.Comment: 44 pages, 69 figures typos fixed, clarifications and second appendix
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Protocol to determine antibody affinity and concentration in complex solutions using microfluidic antibody affinity profiling
The Color Dipole Picture of low-x DIS: Model-Independent and Model-Dependent Results
We present a detailed examination of the color-dipole picture (CDP) of
low- deep inelastic scattering. We discriminate model-independent results,
not depending on a specific parameterization of the dipole cross section, from
model-dependent ones. The model-independent results include the ratio of the
longitudinal to the transverse photoabsorption cross section at large , or
equivalently the ratio of the longitudinal to the unpolarized proton structure
function, , as well as the low- scaling
behavior of the total photoabsorption cross section as for
, and as for .
Here, denotes the low- scaling variable, with being
the saturation scale. The model-independent analysis also implies
at any for asymptotically
large energy, . Consistency with pQCD evolution determines the underlying
gluon distribution and the numerical value of in the expression
for the saturation scale, . In the
model-dependent analysis, by restricting the mass of the actively contributing
fluctuations by an energy-dependent upper bound, we extend the
validity of the color-dipole picture to . The
theoretical results agree with the world data on DIS for .Comment: 77 pages, 30 figure
The Optical Alignment System of the ZEUS MicroVertex Detector
The laser alignment system of the ZEUS microvertex detector is described. The
detector was installed in 2001 as part of an upgrade programme in preparation
for the second phase of electron-proton physics at the HERA collider. The
alignment system monitors the position of the vertex detector support structure
with respect to the central tracking detector using semi-transparent
amorphous-silicon sensors and diode lasers. The system is fully integrated into
the general environmental monitoring of the ZEUS detector and data has been
collected over a period of 5 years. The primary aim of defining periods of
stability for track-based alignment has been achieved and the system is able to
measure movements of the support structure to a precision around m.Comment: 38 pages; 17 figure
Invasive ants take and squander native seeds: implications for native plant communities
Seed dispersal is a fundamental process in the lifecycle of all flowering plants. Many plant species have evolved specialist associations with biotic vectors to facilitate dispersal. Such specialised interactions mean that these associations are potentially highly sensitive to disruption, e.g. from invasive species. However, despite this threat we still understand remarkably little about how such perturbations affect the dynamics and efficiency of the seed-dispersal process. In this study we quantify the impacts of an invasive ant across three key phases of the seed dispersal process: seed removal, distribution and placement, in order to determine the stages of seed dispersal most vulnerable to disruption by invaders. Using the Argentine ant (Linepithema humile) as a model, we show that invaded sites exhibited a significant decrease in seed dispersal services across all three phases of the dispersal process, relative to non-invaded sites. Seeds dispersed in invaded sites were: (a) less likely to be transported; (b) potentially distributed over a smaller spatial area, and (c) less likely to be placed at soil depths favourable for germination and establishment compared to those dispersed in non-invaded sites. These results reveal that ant-mediated seed dispersal services are significantly reduced by an invasive species at multiple stages in the dispersal process. Reductions in the efficacy of seed dispersal, combined with shifts in the ecological and geographical patterns of dispersal, may lead to cascading impacts on plant species composition and community structure. This study shows how an invasive ant can affect seed dispersal at several stages in the dispersal process
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