1,217 research outputs found
Limits on Electron Neutrino Disappearance from the KARMEN and LSND electron neutrino - Carbon Cross Section Data
This paper presents a combined analysis of the KARMEN and LSND nu_e-carbon
cross section measurements within the context of a search for nu_e
disappearance at high Delta m^2. KARMEN and LSND were located at 17.7 m and
29.8 m respectively from the neutrino source, so the consistency of the two
measurements, as a function of antineutrino energy, sets strong limits on
neutrino oscillations. Most of the allowed region from the nu_e disappearance
analysis of the Gallium calibration data is excluded at >95% CL and the best
fit point is excluded at 3.6. Assuming CPT conservation, comparisons
are also made to the oscillation analyses of reactor antineutrino data.Comment: Published versio
Using Reactors to Measure
A next-generation neutrino oscillation experiment using reactor neutrinos
could give important information on the size of mixing angle . The
motivation and goals for a new reactor measurement are discussed in the context
of other measurements using off-axis accelerator neutrino beams. The reactor
measurements give a clean measure of the mixing angle without ambiguities
associated with the size of the other mixing angles, matter effects, and
effects due to CP violation. The key question is whether a next-generation
experiment can reach the needed sensitivity goals to make a measurement for
at the 0.01 level. The limiting factors associated with
a reactor disappearance measurement are described with some ideas of how
sensitivities can be improved. Examples of possible experimental setups are
presented and compared with respect to cost and sensitivity
Comparisons and Combinations of Reactor and Long-Baseline Neutrino Oscillation Measurements
We investigate how the data from various future neutrino oscillation
experiments will constrain the physics parameters for a three active neutrino
mixing model. The investigations properly account for the degeneracies and
ambiguities associated with the phenomenology as well as estimates of
experimental measurement errors. Combinations of various reactor measurements
with the expected J-PARC (T2K) and NuMI offaxis (Nova) data, both with and
without the increased flux associated with proton driver upgrades, are
considered. The studies show how combinations of reactor and offaxis data can
resolve degeneracies (e.g. the theta23 degeneracy) and give more precise
information on the oscillation parameters. A primary purpose of this
investigation is to establish the parameter space regions where CP violation
can be discovered and where the mass hierarchy can be determined. It is found
that such measurements, even with the augmented flux from proton driver
upgrades, demand sin^2 (2 theta13) be fairly large and in the range where it is
measurable by reactor experiments.Comment: 25 pages, 13 figures, fixed typos; 25 pages, 13 figures, updated
content, references; previous 22 pages, 12 figures, added references and
fixed reference display proble
Confronting the short-baseline oscillation anomalies with a single sterile neutrino and non-standard matter effects
We examine the MiniBooNE neutrino, MiniBooNE antineutrino and LSND
antineutrino data sets in a two-neutrino
oscillation approximation subject to non-standard matter effects. We assume
those effects can be parametrized by an -independent effective potential,
, experienced only by an intermediate, non-weakly-interacting
(sterile) neutrino state which we assume participates in the oscillation, where
corresponds to neutrino/antineutrino propagation. We discuss the
mathematical framework in which such oscillations arise in detail, and derive
the relevant oscillation probability as a function of the vacuum oscillation
parameters and , and the matter effect
parameter . We are able to successfully fit all three data sets, including
the MiniBooNE low energy excess, with the following best-fit model parameters:
eV, , and
eV. The -probability for the best fit
corresponds to 21.6%, to be compared to 6.8% for a fit where has been set
to zero, corresponding to a (3+1) sterile neutrino oscillation model. We find
that the compatibility between the three data sets corresponds to 17.4%, to be
compared to 2.3% for . Finally, given the fit results, we examine
consequences for reactor, solar, and atmospheric oscillations. For this paper,
the presented model is empirically driven, but the results obtained can be
directly used to investigate various phenomenological interpretations such as
non-standard matter effects.Comment: 19 pages, 11 figures, 1 tabl
Collective force generation by groups of migrating bacteria
From biofilm and colony formation in bacteria to wound healing and embryonic
development in multicellular organisms, groups of living cells must often move
collectively. While considerable study has probed the biophysical mechanisms of
how eukaryotic cells generate forces during migration, little such study has
been devoted to bacteria, in particular with regard to the question of how
bacteria generate and coordinate forces during collective motion. This question
is addressed here for the first time using traction force microscopy. We study
two distinct motility mechanisms of Myxococcus xanthus, namely twitching and
gliding. For twitching, powered by type-IV pilus retraction, we find that
individual cells exert local traction in small hotspots with forces on the
order of 50 pN. Twitching of bacterial groups also produces traction hotspots,
however with amplified forces around 100 pN. Although twitching groups migrate
slowly as a whole, traction fluctuates rapidly on timescales <1.5 min. Gliding,
the second motility mechanism, is driven by lateral transport of substrate
adhesions. When cells are isolated, gliding produces low average traction on
the order of 1 Pa. However, traction is amplified in groups by a factor of ~5.
Since advancing protrusions of gliding cells push on average in the direction
of motion, we infer a long-range compressive load sharing among sub-leading
cells. Together, these results show that the forces generated during twitching
and gliding have complementary characters and both forces are collectively
amplified in groups
Predictability and hierarchy in Drosophila behavior
Even the simplest of animals exhibit behavioral sequences with complex
temporal dynamics. Prominent amongst the proposed organizing principles for
these dynamics has been the idea of a hierarchy, wherein the movements an
animal makes can be understood as a set of nested sub-clusters. Although this
type of organization holds potential advantages in terms of motion control and
neural circuitry, measurements demonstrating this for an animal's entire
behavioral repertoire have been limited in scope and temporal complexity. Here,
we use a recently developed unsupervised technique to discover and track the
occurrence of all stereotyped behaviors performed by fruit flies moving in a
shallow arena. Calculating the optimally predictive representation of the fly's
future behaviors, we show that fly behavior exhibits multiple time scales and
is organized into a hierarchical structure that is indicative of its underlying
behavioral programs and its changing internal states
Curvature and torsion in growing actin networks
Intracellular pathogens such as Listeria monocytogenes and Rickettsia
rickettsii move within a host cell by polymerizing a comet-tail of actin fibers
that ultimately pushes the cell forward. This dense network of cross-linked
actin polymers typically exhibits a striking curvature that causes bacteria to
move in gently looping paths. Theoretically, tail curvature has been linked to
details of motility by considering force and torque balances from a finite
number of polymerizing filaments. Here we track beads coated with a prokaryotic
activator of actin polymerization in three dimensions to directly quantify the
curvature and torsion of bead motility paths. We find that bead paths are more
likely to have low rather than high curvature at any given time. Furthermore,
path curvature changes very slowly in time, with an autocorrelation decay time
of 200 seconds. Paths with a small radius of curvature, therefore, remain so
for an extended period resulting in loops when confined to two dimensions. When
allowed to explore a 3D space, path loops are less evident. Finally, we
quantify the torsion in the bead paths and show that beads do not exhibit a
significant left- or right-handed bias to their motion in 3D. These results
suggest that paths of actin-propelled objects may be attributed to slow changes
in curvature rather than a fixed torque
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