Significance of the Difference between Two Means when the Population Variances may be Unequal

Weir, J. B. De V.

doi:10.1038/187438a0

Cited by 28 publications

(5 citation statements)

References 3 publications

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“…The components were divided into the hydrocarbon class (CH-class), sulfur-containing classes (S x -class), nitrogencontaining classes (N x -class), and their corresponding oxidation products (O x -class, S x O y -class, and N x O y -class). Aging-related trends were statistically validated at 95% statistical certainty applying the Weir t-test, 64 which is specially designed for a limited number of replicates.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Investigation of Aging Processes in Bitumen at the Molecular Level with High-Resolution Fourier-Transform Ion Cyclotron Mass Spectrometry and Two-Dimensional Gas Chromatography Mass Spectrometry

et al. 2020

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Bitumen is a highly viscous and chemically complex petroleum-derived material, which is applied as a binder in road construction. However, the asphalt undergoes hardening, cracking, and embrittlement not only due to oxidative short-term aging during the mixing and paving process but also due to long-term aging during the service time of the pavement. In this study, chemical changes occurring during short-term aging, mimicked by a prolonged rotating flask procedure, are investigated for an artificial bitumen model at the molecular level. The model bitumen enables the application of two complementary analytical techniques for obtaining a comprehensive insight into the aging effects: high-resolution Fourier-transform ion cyclotron mass spectrometry (FT-ICR MS) coupled to thermogravimetry was applied to investigate the aging effects on polar to semipolar high-molecular-weight compounds ionized by atmospheric pressure chemical ionization. Aromatic core structures were analyzed by alternating collision-induced dissociation. In order to support structural assignments from FT-ICR MS data in the semivolatile region, comprehensive two-dimensional gas chromatography mass spectrometry (GC × GC–HRTOFMS) with electron ionization at 70 eV was applied for the group-type analysis and the investigation of particular chemical functionalities. Oxidation processes were revealed to be the prevalent reactions caused by short-term aging of the hydrocarbons (CH-class) and sulfur-containing classes. Aromatic species with low steric hindrance or activated carbon positions as well as high aromatic core structures are favorably oxidized, forming carbonyl functionalities. For molecules with one sulfur atom (S1-class), nonaromatic species such as tetrahydrothiophenes decrease, whereas aromatic S1-compounds remain constant. Nonaromatic S1O1-species tend to further oxidize, while higher aromatic species are formed with ongoing aging time. Moreover, this study highlights the aging behavior of nitrogen-containing compounds, such as carbazoles. A significant reduction of the N-classes was observed during aging, indicating thermal-induced condensation reactions as well as favored oxidation of highly aromatic core structures.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Investigation of Aging Processes in Bitumen at the Molecular Level with High-Resolution Fourier-Transform Ion Cyclotron Mass Spectrometry and Two-Dimensional Gas Chromatography Mass Spectrometry

et al. 2020

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“…As a second step these normalized raw spectra were averaged and blank-value corrected. Statistical analyses of bacterial metabolites on NB and NBG were performed by using a variant of the T-test, with a 5% confidence level [71]. …”

Section: Methodsmentioning

confidence: 99%

Volatile organic compounds produced by the phytopathogenic bacterium Xanthomonas campestris pv. vesicatoria 85-10

Weise

Kai

Gummesson³

et al. 2012

Beilstein J. Org. Chem.

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Xanthomonas campestrisis a phytopathogenic bacterium and causes many diseases of agricultural relevance. Volatiles were shown to be important in inter- and intraorganismic attraction and defense reactions. Recently it became apparent that also bacteria emit a plethora of volatiles, which influence other organisms such as invertebrates, plants and fungi. As a first step to study volatile-based bacterial–plant interactions, the emission profile ofXanthomonas c.pv.vesicatoria85-10 was determined by using GC/MS and PTR–MS techniques. More than 50 compounds were emitted by this species, the majority comprising ketones and methylketones. The structure of the dominant compound, 10-methylundecan-2-one, was assigned on the basis of its analytical data, obtained by GC/MS and verified by comparison of these data with those of a synthetic reference sample. Application of commercially available decan-2-one, undecan-2-one, dodecan-2-one, and the newly synthesized 10-methylundecan-2-one in bi-partite Petri dish bioassays revealed growth promotions in low quantities (0.01 to 10 μmol), whereas decan-2-one at 100 μmol caused growth inhibitions of the fungusRhizoctonia solani. Volatile emission profiles of the bacteria were different for growth on media (nutrient broth) with or without glucose.

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“…For 3 L benchtop reactor trials, an F-test was used to confirm the variances were not significantly different between treatments [16]. A two-sample t-test was conducted if variances were not significantly different and a welch two-sample t-test was performed if variances were significantly different [20,21].…”

Section: Discussionmentioning

confidence: 99%

Assessing Various Types of Fungal Strains to Convert Soybean Processing Industry Wastewater into Protein-Rich Animal Feed

Zahler¹,

Karki²,

Isaac³

et al. 2018

J Microb Biochem Technol

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Significance of the Difference between Two Means when the Population Variances may be Unequal

Cited by 28 publications

References 3 publications

Investigation of Aging Processes in Bitumen at the Molecular Level with High-Resolution Fourier-Transform Ion Cyclotron Mass Spectrometry and Two-Dimensional Gas Chromatography Mass Spectrometry

Investigation of Aging Processes in Bitumen at the Molecular Level with High-Resolution Fourier-Transform Ion Cyclotron Mass Spectrometry and Two-Dimensional Gas Chromatography Mass Spectrometry

Volatile organic compounds produced by the phytopathogenic bacterium Xanthomonas campestris pv. vesicatoria 85-10

Assessing Various Types of Fungal Strains to Convert Soybean Processing Industry Wastewater into Protein-Rich Animal Feed

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