8,080 research outputs found
Model-independent Analyses of Dark-Matter Particle Interactions
A model-independent treatment of dark-matter particle elastic scattering has
been developed, yielding the most general interaction for WIMP-nucleon
low-energy scattering, and the resulting amplitude has been embedded in the
nucleus, taking into account the selection rules imposed by parity and
time-reversal. One finds that, in contrast to the usual
spin-independent/spin-dependent (SI/SD) formulation, the resulting cross
section contains six independent nuclear response functions, three of which are
associated with possible velocity-dependent interactions. We find that current
experiments are four orders of magnitude more sensitive to derivative couplings
than is apparent in the standard SI/SD treatment, which necessarily associates
such interactions with cross sections proportional to the square of the WIMP
velocity relative to the nuclear center of mass.Comment: 10 pages, 2 figures; talk presented at TAUP201
Model-independent WIMP Scattering Responses and Event Rates: A Mathematica Package for Experimental Analysis
The community's reliance on simplified descriptions of WIMP-nucleus
interactions reflects the absence of analysis tools that integrate general
theories of dark matter with standard treatments of nuclear response functions.
To bridge this gap, we have constructed a public-domain Mathematica package for
WIMP analyses based on our effective theory formulation. Script inputs are 1)
the coefficients of the effective theory, through which one can characterize
the low-energy consequences of arbitrary ultraviolet theories of WIMP
interactions; and 2) one-body density matrices for commonly used targets, the
most compact description of the relevant nuclear physics. The generality of the
effective theory expansion guarantees that the script will remain relevant as
new ultraviolet theories are explored; the use of density matrices to factor
the nuclear physics from the particle physics will allow nuclear structure
theorists to update the script as new calculations become available,
independent of specific particle-physics contexts. The Mathematica package
outputs the resulting response functions (and associated form factors) and also
the differential event rate, once a galactic WIMP velocity profile is
specified, and thus in its present form provides a complete framework for
experimental analysis. The Mathematica script requires no a priori knowledge of
the details of the non-relativistic effective field theory or nuclear physics,
though the core concepts are reviewed here and in arXiv:1203.3542.Comment: 30+6 page
New Perspective on Galaxy Clustering as a Cosmological Probe: General Relativistic Effects
We present a general relativistic description of galaxy clustering in a FLRW
universe. The observed redshift and position of galaxies are affected by the
matter fluctuations and the gravity waves between the source galaxies and the
observer, and the volume element constructed by using the observables differs
from the physical volume occupied by the observed galaxies. Therefore, the
observed galaxy fluctuation field contains additional contributions arising
from the distortion in observable quantities and these include tensor
contributions as well as numerous scalar contributions. We generalize the
linear bias approximation to relate the observed galaxy fluctuation field to
the underlying matter distribution in a gauge-invariant way. Our full formalism
is essential for the consistency of theoretical predictions. As our first
application, we compute the angular auto correlation of large-scale structure
and its cross correlation with CMB temperature anisotropies. We comment on the
possibility of detecting primordial gravity waves using galaxy clustering and
discuss further applications of our formalism.Comment: 10 pages, 2 figures, accepted for publication in Physical Review
XO-2b: a hot Jupiter with a variable host star that potentially affects its measured transit depth
The transiting hot Jupiter XO-2b is an ideal target for multi-object
photometry and spectroscopy as it has a relatively bright (-mag = 11.25) K0V
host star (XO-2N) and a large planet-to-star contrast ratio
(R/R). It also has a nearby (31.21") binary stellar
companion (XO-2S) of nearly the same brightness (-mag = 11.20) and spectral
type (G9V), allowing for the characterization and removal of shared systematic
errors (e.g., airmass brightness variations). We have therefore conducted a
multiyear (2012--2015) study of XO-2b with the University of Arizona's 61"
(1.55~m) Kuiper Telescope and Mont4k CCD in the Bessel U and Harris B
photometric passbands to measure its Rayleigh scattering slope to place upper
limits on the pressure-dependent radius at, e.g., 10~bar. Such measurements are
needed to constrain its derived molecular abundances from primary transit
observations. We have also been monitoring XO-2N since the 2013--2014 winter
season with Tennessee State University's Celestron-14 (0.36~m) automated
imaging telescope to investigate stellar variability, which could affect
XO-2b's transit depth. Our observations indicate that XO-2N is variable,
potentially due to {cool star} spots, {with a peak-to-peak amplitude of ~R-mag and a period of ~days for the 2013--2014
observing season and a peak-to-peak amplitude of ~R-mag and
~day period for the 2014--2015 observing season. Because of}
the likely influence of XO-2N's variability on the derivation of XO-2b's
transit depth, we cannot bin multiple nights of data to decrease our
uncertainties, preventing us from constraining its gas abundances. This study
demonstrates that long-term monitoring programs of exoplanet host stars are
crucial for understanding host star variability.Comment: published in ApJ, 9 pages, 11 figures, 3 tables; updated figures with
more ground-based monitoring, added more citations to previous work
Effects of CO2 Concentration on Leaf Photosynthesis and Stomatal Conductance of Potatoes Grown Under Different Irradiance Levels and Photoperiods
Potato (Solanum tuberosum L.) cvs. Russet Burbank, Denali, and Norland, were grown in environmental rooms controlled at approx 350 micro mol/mol (ambient during years 1987/1988) and 1000 micro mol/mol (enriched) CO2 concentrations. Plants and electric lamps were arranged to provide two irradiance zones, 400 and 800 micro mol/mol/square m/S PPF and studies were repeated using two photoperiods (12-h light / 12-h dark and continuous light). Leaf photosynthetic rates and leaf stomatal conductance were measured using fully expanded, upper canopy leaves at weekly intervals throughout growth (21 through 84 days after transplanting). Increasing the CO2 from approx 350 to 1000 micro mol/mol under the 12-h photoperiod increased leaf photosynthetic rates by 39% at 400 micro mol/mol/square m/S PPF and 27% at 800 micro mol/mol/square m/S PPF. Increasing the CO2 from approx 350 to 1000 micro mol/mol under continuous light decreased leaf photosynthetic rates by 7% at 400 micro mol/mol/square m/S PPF and 13% at 800 micro mol/mol/square m/S PPF. Increasing the CO2 from approx 350 to 1000 micro mol/mol under the 12-h photoperiod plants decreased stomatal conductance by an average of 26% at 400 micro mol/mol/square m/S PPF and 42% at 800 micro mol/mol/square m/S PPF. Under continuous light, CO2 enrichment resulted in a small increase (2%) of stomatal conductance at 400 micro mol/mol/square m/S PPF, and a small decrease (3%) at 800 micro mol/mol/square m/S PPF. Results indicate that CO2 enrichment under the 12-h photoperiod showed the expected increase in photosynthesis and decrease in stomatal conductance for a C3 species like potato, but the decreases in leaf photosynthetic rates and minimal effect on conductance from CO2 enrichment under continuous light were not expected. The plant leaves under continuous light showed more chlorosis and some rusty flecking versus plants under the 12-h photoperiod, suggesting the continuous light was more stressful on the plants. The increased rates of leaf photosynthesis with increased CO2 concentration paralleled trends in biomass production (published previously) but were not proportional to the biomass yields
CARETS: A prototype regional environmental information system. Volume 5: Interpretation, compilation and field verification procedures in the CARETS project
The author has identified the following significant results. Level 2 land use mapping from high altitude aircraft photography at a scale of 1:100,000 required production of a photomosaic mapping base for each of the 48, 50 x 50 km sheets, and the interpretation and coding of land use polygons on drafting film overlays. To enhance the value of the land use sheets, a series of overlays was compiled, showing cultural features, county boundaries and census tracts, surface geology, and drainage basins. In producing level 1 land use maps from LANDSAT imagery, at a scale of 1:250,000 drafting film was directly overlaid on LANDSAT color composite transparencies. Numerous areas of change were identified, but extensive areas of false changes were also noted
Relationships between Larval and Juvenile Abundance of Winter-Spawned Fishes in North Carolina, USA
We analyzed the relationships between the larval and juvenile abundances of selected estuarine-dependent fishes that spawn during the winter in continental shelf waters of the U.S. Atlantic coast. Six species were included in the analysis based on their ecological and economic importance and relative abundance in available surveys: spot Leiostomus xanthurus, pinfish Lagodon rhomboides, southern flounder Paralichthys lethostigma, summer flounder Paralichthys dentatus, Atlantic croaker Micropogonias undulatus, and Atlantic menhaden Brevoortia tyrannus. Cross-correlation analysis was used to examine the relationships between the larval and juvenile abundances within species. Tests of synchrony across species were used to find similarities in recruitment dynamics for species with similar winter shelf-spawning life-history strategies. Positive correlations were found between the larval and juvenile abundances for three of the six selected species (spot, pinfish, and southern flounder). These three species have similar geographic ranges that primarily lie south of Cape Hatteras. There were no significant correlations between the larval and juvenile abundances for the other three species (summer flounder, Atlantic croaker, and Atlantic menhaden); we suggest several factors that could account for the lack of a relationship. Synchrony was found among the three southern species within both the larval and juvenile abundance time series. These results provide support for using larval ingress measures as indices of abundance for these and other species with similar geographic ranges and winter shelf-spawning life-history strategies
Antilocalization of Coulomb Blockade in a Ge-Si Nanowire
The distribution of Coulomb blockade peak heights as a function of magnetic
field is investigated experimentally in a Ge-Si nanowire quantum dot. Strong
spin-orbit coupling in this hole-gas system leads to antilocalization of
Coulomb blockade peaks, consistent with theory. In particular, the peak height
distribution has its maximum away from zero at zero magnetic field, with an
average that decreases with increasing field. Magnetoconductance in the
open-wire regime places a bound on the spin-orbit length ( < 20 nm),
consistent with values extracted in the Coulomb blockade regime ( < 25
nm).Comment: Supplementary Information available at http://bit.ly/19pMpd
Kimberley Research Station progress report, 1964 : climate
A review of recent research in climate, soils, tropical crops and pastures, weeds, insect pests and cattle husbandry at the Kimberley Research Station.
EXTENSIVE climatic data are recorded at the Station and analysed in relation to crop performance, irrigation requirements, and farm management practices
The fundamental problem of command : plan and compliance in a partially centralised economy
When a principal gives an order to an agent and advances resources for its implementation, the temptations for the agent to shirk or steal from the principal rather than comply constitute the fundamental problem of command. Historically, partially centralised command economies enforced compliance in various ways, assisted by nesting the fundamental problem of exchange within that of command. The Soviet economy provides some relevant data. The Soviet command system combined several enforcement mechanisms in an equilibrium that shifted as agents learned and each mechanism's comparative costs and benefits changed. When the conditions for an equilibrium disappeared, the system collapsed.Comparative Economic Studies (2005) 47, 296–314. doi:10.1057/palgrave.ces.810011
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