3,734 research outputs found
DC and high-frequency conductivity of the organic metals beta"-(BEDT-TTF)2SF5RSO3 (R = CH2CF2 and CHF)
The temperature dependences of the electric-transport properties of the
two-dimensional organic conductors beta"-(BEDT-TTF)2SF5CH2CF2SO3,
beta"-(d8-BEDT-TTF)2SF5CH2CF2SO3, and beta"-(BEDT-TTF)2SF5CHFSO3 are measured
by dc methods in and perpendicular to the highly-conducting plane. Microwave
measurements are performed at 24 and 33.5 GHz to probe the high-frequency
behavior from room temperature down to 2 K. Superconductivity is observed in
beta"-(BEDT-TTF)2SF5CH2CF2SO3 and its deuterated analogue. Although all the
compounds remain metallic down to low-temperatures, they are close to a
charge-order transition. This leads to deviations from a simple Drude behavior
of the optical conductivity which become obvious already in the microwave
range. In beta"-(BEDT-TTF)2SF5CH2CF2SO3, for instance, charge fluctuations
cause an increase in microwave resistivity for T < 20 K which is not detected
in dc measurements. beta"-(BEDT-TTF)2SF5CHFSO3 exhibits a simple metallic
behavior at all frequencies. In the dc transport, however, we observe
indications of localization in the perpendicular direction.Comment: 8 pages, 9 figure
Using poststratification to improve abundance estimates from multispecies surveys: a study of juvenile flatfishes
Population assessments seldom incorporate habitat information or use previously observed distributions of fish density. Because habitat affects the spatial distribution of fish density and overall abundance, the use of habitat information and previous estimates of fish density can produce more precise and less biased
population estimates. In this study, we describe how poststratification can be applied as an unbiased estimator
to data sets that were collected under a probability sampling design, typical of many multispecies trawl surveys.
With data from a multispecies survey of juvenile flatfish, we show how poststratification can be applied to a data set that was not collected under a probability sampling design,
where both the precision and the bias are unknown. For each of four species, three estimates of total abundance were compared: 1) unstratified; 2) poststratified by habitat; and 3) poststratified by habitat and fish density (high fish density and low fish density) in nearby years. Poststratification by habitat gave more precise and (or) less design-biased estimates than an unstratified estimator for all species in all years. Poststratification by habitat and fish density produced the most precise and representative estimates when the sample size in the high fish-density and low fish-density strata were sufficient (in this study, n≥20 in the high fish-density stratum,
n≥9 in the low fish-density stratum). Because of the complexities of statistically testing the annual stratified
data, we compared three indices of abundance for determining statistically significant changes in annual
abundance. Each of the indices closely approximated the annual differences of the poststratified estimates. Selection of the most appropriate index was dependent upon the species’ density distribution within habitat and the
sample size in the different habitat areas. The methods used in this study are particularly useful for estimating
individual species abundance from multispecies surveys and for retrospective s
Alternative sampling and estimation methods for multispecies trawl surveys
Thesis (Ph.D.) University of Alaska Fairbanks, 2004Multispecies demersal trawl surveys are used in the United States and internationally to estimate the relative abundance of commercial and non-commercial fish species. Their usefulness for estimating species' abundance is often limited by the variance associated with estimates. This study implemented and evaluated alternative sampling and estimation methods, with the goal to incorporate additional sources of information for increased precision of individual species' estimates from multispecies trawl surveys. First, habitat characteristics and past spatial distributions of four flatfish species' density were incorporated into a multispecies trawl survey design conducted in Kalsin and Middle Bays, Kodiak Island, Alaska. Stratification by depth and percent sand produced estimates of relative abundance with lower CV s than those from unstratified sampling. Additional decreases in relative precision were generally not achieved by estimating the relative abundance of multiple species from regions of species-specific suboptimal habitat. Second, a poststratification technique was used to incorporate species-specific habitat characteristics and previous distributions of species' density into the estimation of species' abundance from the Kalsin and Middle Bays' trawl survey. Poststratification by habitat gave estimates with lower variance and/or less design-bias than an unstratified estimator for all species in all years. Poststratification by habitat and fish density produced estimates with the least design-bias for all species in all years and the lowest variance when stratum sample sizes were sufficient. Third, mixed model linear regression (MMLR), empirical Bayes (EB) and hierarchical Bayes (HB) estimation methods were used to incorporate historical trends of yellowfin sole, Limanda aspera biomass from the eastern Bering Sea trawl survey into annual biomass estimates. Using MMLR, EB, and HB methods resulted in biomass estimates that were less anomalous than survey estimates with respect to a linear regression trend. Estimates for all three methods had lower CV s than surveys in most years. The results of this thesis suggest that incorporating additional information into survey design and estimation can decrease the variability of survey estimates and/or correct for possible bias. Methods that can incorporate additional information, therefore, have the potential to improve survey assessments for management use.Introduction -- Multispecies survey designs with habitat and fish density information -- Using poststratification to improve multispecies survey assessments : case study of juvenile flatfishes -- A comparison of models for incorporating multiple years of information into annual estimates of biomass from multispecies trawl surveys -- Conclusions
Responsible Government: Investing in the Well-Being of Black Fathers, Families and Communities
Beginning with a summary of the history of public policy contributions to poverty and racial inequity in America, the report describes how this context impacts black fathers, and how their circumstances and choices in turn affect black children. It concludes with an overview of the Julia Carson Responsible Fatherhood and Healthy Families Act of 2009 (which subsequently died and was re-introduced in 2011 and 2013)
Certainty in Heisenberg's uncertainty principle: Revisiting definitions for estimation errors and disturbance
We revisit the definitions of error and disturbance recently used in
error-disturbance inequalities derived by Ozawa and others by expressing them
in the reduced system space. The interpretation of the definitions as
mean-squared deviations relies on an implicit assumption that is generally
incompatible with the Bell-Kochen-Specker-Spekkens contextuality theorems, and
which results in averaging the deviations over a non-positive-semidefinite
joint quasiprobability distribution. For unbiased measurements, the error
admits a concrete interpretation as the dispersion in the estimation of the
mean induced by the measurement ambiguity. We demonstrate how to directly
measure not only this dispersion but also every observable moment with the same
experimental data, and thus demonstrate that perfect distributional estimations
can have nonzero error according to this measure. We conclude that the
inequalities using these definitions do not capture the spirit of Heisenberg's
eponymous inequality, but do indicate a qualitatively different relationship
between dispersion and disturbance that is appropriate for ensembles being
probed by all outcomes of an apparatus. To reconnect with the discussion of
Heisenberg, we suggest alternative definitions of error and disturbance that
are intrinsic to a single apparatus outcome. These definitions naturally
involve the retrodictive and interdictive states for that outcome, and produce
complementarity and error-disturbance inequalities that have the same form as
the traditional Heisenberg relation.Comment: 15 pages, 8 figures, published versio
- …