10 research outputs found
Methods for Combining Probability and Nonprobability Samples Under Unknown Overlaps
Nonprobability (convenience) samples are increasingly sought to stabilize
estimations for one or more population variables of interest that are performed
using a randomized survey (reference) sample by increasing the effective sample
size. Estimation of a population quantity derived from a convenience sample
will typically result in bias since the distribution of variables of interest
in the convenience sample is different from the population. A recent set of
approaches estimates conditional (on sampling design predictors) inclusion
probabilities for convenience sample units by specifying reference
sample-weighted pseudo likelihoods. This paper introduces a novel approach that
derives the propensity score for the observed sample as a function of
conditional inclusion probabilities for the reference and convenience samples
as our main result. Our approach allows specification of an exact likelihood
for the observed sample. We construct a Bayesian hierarchical formulation that
simultaneously estimates sample propensity scores and both conditional and
reference sample inclusion probabilities for the convenience sample units. We
compare our exact likelihood with the pseudo likelihoods in a Monte Carlo
simulation study.Comment: 32 pages, 8 figure
Manganese Content Control in Weld Metal During MAG Welding
The influence of the welding current and method of gas shielding in MAG welding on the content of manganese is considered in the paper. Results of study of the welded specimens of steels 45 when applying welding wire of different formulas and different types of gas shielding (traditional shielding and double-jet shielding) are given. It is found that in MAG welding the value of the welding current and the speed of the gas flow from the welding nozzle have a considerable impact on the chemical composition of the weld metal. The consumable electrode welding under double-jet gas shielding provides the directed gas-dynamics in the welding area and enables controlling the electrode metal transfer and the chemical composition of a weld
Lyngbyaureidamides A and B, two anabaenopeptins from the cultured freshwater cyanobacterium Lyngbya sp. (SAG 36.91)
Responses of freshwater mussel (Elliptio complanata) hemocytes exposed in vitro to crude extracts of Microcystis aeruginosa and Lyngbya wollei
Aplicação-teste da medida de atitude à área de atuação de um centro de saúde do Município de São Paulo, Brasil
Assessment of microcystin distribution and biomagnification in tissues of aquatic food web compartments from a shallow lake and evaluation of potential risks to public health
The objectives of this study were: (1) to examine the distribution and bioaccumulation of microcystins in the main components of the food web (phytoplankton, zooplankton, crayfish, shrimp, mussel, snail, fish, frog) of Lake Pamvotis (NW Greece), (2) to investigate the possibility of microcystin biomagnification and (3) to evaluate the potential threat of the contaminated aquatic organisms to human health. Significant microcystin concentrations were detected in all the aquatic organisms during two different periods, with the higher concentrations observed in phytoplankton and the lower in fish species and frogs. This is the first study reporting microcystin accumulation in the body of the freshwater shrimp Atyaephyra desmsaresti, in the brain of the fish species common carp (Cyprinus carpio) and in the skin of the frog Rana epirotica. Although there was no evidence for microcystin biomagnification, the fact that microcystins were found in lake water and in the tissues of aquatic organisms, suggests that serious risks to animal and public health are possible to occur. In addition, it is likely to be unsafe to consume aquatic species harvested in Lake Pamvotis due to the high-concentrations of accumulated microcystins