Search results for "Principal component"
showing 4 items of 514 documents
Online anomaly detection using dimensionality reduction techniques for HTTP log analysis
2015
Modern web services face an increasing number of new threats. Logs are collected from almost all web servers, and for this reason analyzing them is beneficial when trying to prevent intrusions. Intrusive behavior often differs from the normal web traffic. This paper proposes a framework to find abnormal behavior from these logs. We compare random projection, principal component analysis and diffusion map for anomaly detection. In addition, the framework has online capabilities. The first two methods have intuitive extensions while diffusion map uses the Nyström extension. This fast out-of-sample extension enables real-time analysis of web server traffic. The framework is demonstrated using …
Determining the number of sources in high-density EEG recordings of event-related potentials by model order selection
2011
To high-density electroencephalography (EEG) recordings, determining the number of sources to separate the signal and the noise subspace is very important. A mostly used criterion is that percentage of variance of raw data explained by the selected principal components composing the signal space should be over 90%. Recently, a model order selection method named as GAP has been proposed. We investigated the two methods by performing independent component analysis (ICA) on the estimated signal subspace, assuming the number of selected principal components composing the signal subspace is equal to the number of sources of brain activities. Through examining wavelet-filtered EEG recordings (128…
Agronomical evaluation of Sicilian biotypes of Lavandula stoechas L. spp. stoechas and analysis of the essential oils
2015
The aim of this study was to characterize wild lavender, which was collected in three different areas of Sicily (Italy),according to agronomic and chemical evaluation. The collection sites were located in Pantelleria island, Partinico (a warm sub-area of Lauretum) and Castelbuono (a middle sub-area of Lauretum). All the populations were identified as Lavandula stoechas L. ssp. stoechas. Essential oils were extracted by hydrodistillation and analyzed by gas chromatography– flame ionization detector (GC–FID) and GC–mass spectrometry (GC–MS). GC–FID and GC–MS analyses permitted the identification of 101 components from the essential oils. We analyzed only the flowers and leaves of L. stoechas …
Study of quantitative and qualitative variations in essential oils of Sicilian oregano biotypes
2015
Essential oil (EO) was extracted using hydrodistillation from samples of Origanum vulgare subspecies hirtum (Link) Ietswaart, gathered from the wild in various parts of Sicily, Italy; GC-FID and GC-MS analyses were subsequently performed. The aim of the study was to analyze the relationship between essential oil yields and the geographical distribution of oregano wild populations based on variations in environmental factors as collection sites. Moreover, the purpose was to group Origanum vulgare subspecies hirtum biotypes according to the chemical composition of the EO. The seven principal components in the EO was thymol (24.0–54.4%), γ-terpinene (9.8–30.5%), ρ-cymene (5.2–18.7%), α-terpine…