114 research outputs found
Optimization of xylanase production by filamentous fungi in solid state fermentation and scale-up to horizontal tube bioreactor
Five microorganisms, namely Aspergillus niger CECT 2700, A. niger CECT 2915, A. niger CECT 2088, Aspergillus terreus CECT 2808, and Rhizopus stolonifer CECT 2344, were grown on corncob to produce cell wall polysaccharide-degrading enzymes, mainly xylanases, by solid-state fermentation (SSF). A. niger CECT 2700 produced the highest amount of xylanases of 504±7 U/g dry corncob (dcc) after 3 days of fermentation. The optimization of the culture broth (5.0 g/L NaNO3, 1.3 g/L (NH4)2SO4, 4.5 g/L KH2PO4, and 3 g/L yeast extract) and operational conditions (5 g of bed loading, using an initial substrate to moistening medium of 1:3.6 (w/v)) allowed increasing the predicted maximal xylanase activity up to 2,452.7 U/g dcc. However, different pretreatments of materials, including destarching, autoclaving, microwave, and alkaline treatments, were detrimental.
Finally, the process was successfully established in a laboratory-scale horizontal tube biore- actor, achieving the highest xylanase activity (2,926 U/g dcc) at a flow rate of 0.2 L/min. The result showed an overall 5.8-fold increase in xylanase activity after optimization of culture media, operational conditions, and scale-up.We are grateful to the Spanish Ministry of Science and Innovation for the financial support of this work (project CTQ2011-28967), which has partial financial support from the FEDER funds of the European Union; to the Leonardo da Vinci Programme for founding the stay of Felisbela Oliveira in Vigo University; to MAEC-AECID (Spanish Government) for the financial support for Perez-Bibbins, B. and to Spanish Ministry of Education, Culture and Sports for Perez-Rodriguez's FPU; and to Solla E. and Mendez J. (CACTI-University of Vigo) for their excellent technical assistance in microscopy
Advances in estimation by the item sum technique using auxiliary information in complex surveys
To collect sensitive data, survey statisticians have designed many strategies to reduce
nonresponse rates and social desirability response bias. In recent years, the item count
technique (ICT) has gained considerable popularity and credibility as an alternative mode
of indirect questioning survey, and several variants of this technique have been proposed as
new needs and challenges arise. The item sum technique (IST), which was introduced by
Chaudhuri and Christofides (2013) and Trappmann et al. (2014), is one such variant, used
to estimate the mean of a sensitive quantitative variable. In this approach, sampled units are
asked to respond to a two-list of items containing a sensitive question related to the study
variable and various innocuous, nonsensitive, questions. To the best of our knowledge,
very few theoretical and applied papers have addressed the IST. In this article, therefore,
we present certain methodological advances as a contribution to appraising the use of the
IST in real-world surveys. In particular, we employ a generic sampling design to examine
the problem of how to improve the estimates of the sensitive mean when auxiliary information on the population under study is available and is used at the design and estimation
stages. A Horvitz-Thompson type estimator and a calibration type estimator are proposed
and their efficiency is evaluated by means of an extensive simulation study. Using simulation experiments, we show that estimates obtained by the IST are nearly equivalent to those
obtained using “true data” and that in general they outperform the estimates provided by a
competitive randomized response method. Moreover, the variance estimation may be considered satisfactory. These results open up new perspectives for academics, researchers and
survey practitioners, and could justify the use of the IST as a valid alternative to traditional
direct questioning survey modes.Ministerio de Economía y Competitividad of SpainMinisterio de Educacion, Cultura y Deporteproject PRIN-SURWE
Extending Procedural Justice Theory: A Fiducia Report on the Design of New Survey Indicators
Estimation of population proportion in randomized response sampling using weighted confidence interval construction
[[abstract]]This paper considers the problem of estimation for binomial proportions of sensitive attributes in the population of interest. Randomized response techniques are suggested for protecting the privacy of respondents and reducing the response bias while eliciting information on sensitive attributes. By applying the Wilson (J Am Stat Assoc 22:209–212, 1927) score approach for constructing confidence intervals, various probable point estimators and confidence interval estimators are suggested for the common structures of randomized response procedures. In addition, efficiency comparisons are carried out to study the performances of the proposed estimators for both the cases of direct response surveys and randomized response surveys. Circumstances under which each proposed estimators is better are also identified.[[notice]]補正完畢[[journaltype]]國外[[incitationindex]]SCI[[booktype]]電子版[[booktype]]紙本[[countrycodes]]DE
Vertical coupling of atmospheres: dependence on strength of sudden stratospheric warming and solar activity
Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents
A simplified model for A. Niger FS3 growth during phytase formation in solid State fermentation
Solid-State Fermentation of Soybean and Corn Processing Coproducts for Potential Feed Improvement
Farmers’ Preferences for Future Agricultural Land Use Under the Consideration of Climate Change
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