801 research outputs found
Applying a Dynamical Systems Model and Network Theory to Major Depressive Disorder
Mental disorders like major depressive disorder can be seen as complex
dynamical systems. In this study we investigate the dynamic behaviour of
individuals to see whether or not we can expect a transition to another mood
state. We introduce a mean field model to a binomial process, where we reduce a
dynamic multidimensional system (stochastic cellular automaton) to a
one-dimensional system to analyse the dynamics. Using maximum likelihood
estimation, we can estimate the parameter of interest which, in combination
with a bifurcation diagram, reflects the expectancy that someone has to
transition to another mood state. After validating the proposed method with
simulated data, we apply this method to two empirical examples, where we show
its use in a clinical sample consisting of patients diagnosed with major
depressive disorder, and a general population sample. Results showed that the
majority of the clinical sample was categorized as having an expectancy for a
transition, while the majority of the general population sample did not have
this expectancy. We conclude that the mean field model has great potential in
assessing the expectancy for a transition between mood states. With some
extensions it could, in the future, aid clinical therapists in the treatment of
depressed patients.Comment: arXiv admin note: text overlap with arXiv:1610.0504
Inhibition of Brevibacterium linens by Probiotics from Dairy Products
Brevibacterium linens is an important species in dairy products rendering a specific taste and aroma to numerous smear ripened and blue veined cheeses due to proteolysis. However, the presence of the species in South African blue veined cheeses is undesirable and consumers demand the product void of the species. Accordingly, numerous methods including microbial inhibition using fungi and bacterial probiotic cultures with possible inhibitory effects were applied in an attempt to inhibit the species. None of the fungi, however, proved to be successful, whereas Lactobacillus rhamnosus and Bifidobacterium lactis, two typical probiotic species applied in dairy products, showed inhibitory effects against B. linens when tested using the spot-on-lawn assay
Structural and synthetic studies of sesquiterpenoids and flavonoids isolated from Helichrysum species
Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2008.The genus Helichrysum (Asteraceae) consists of approximately 500 species worldwide,
with 245 indigenous to South Africa. As a result of the large number of species, the
chemistry and biological activity of several species have not yet been investigated. The aim
of this project was to investigate the phytochemistry of three species and propose a
synthetic route to one of the antibacterial compounds isolated.
An extensive literature review regarding the widespread traditional uses, biological activity
and phytochemistry of the South African Helichrysum species is provided.
From Helichrysum splendidum, a plant used traditionally to treat rheumatism, two
monomeric guaianolides and a dimeric guaianolide, helisplendidilactone, were isolated.
The stereochemistry of these known compounds was confirmed and the NMR assignments
for certain peaks of helisplendidilactone were corrected. An X-ray structure for
helisplendidilactone was obtained for the first time.
The phytochemistry of Helichrysum montanum was investigated for the first time and new
diastereoisomers of known guaianolides were isolated. The phytochemistry of H.
splendidum and H. montanum is remarkably similar and supports their morphological
classification in the same taxonomic group. The chloroform:methanol extract of H.
montanum yielded a new dimeric guaianolide, 13’-epihelisplendidilactone, which is related
to helisplendidilactone, as well as three monomeric guaianolides (of which one is a new
diastereomer of a known compound). The extract also yielded spathulenol (a
sesquiterpene), umbelliferone (a coumarin) and 4’,5,7-trihydroxy-3,3’,8-trimethoxyflavone
(a flavonoid).
Thirty-five Helichrysum species were screened for antimicrobial activity against six microorganisms
and a preliminary cytotoxic assay, which included the use of “normal” and
cancer cell lines, was performed. H. excisum was selected for further study based on the
fact that it exhibited promising antimicrobial activity and relative low toxicity.
Furthermore, with the exception of the essential oil, the phytochemistry of this species has
not been investigated. From the aerial parts of H. excisum, five flavonoids, identified as pinocembrin, gnaphaliin,
lepidissipyrone, 5-hydroxy-7,8-dimethoxyflavone and isoscutellarein 7-O-b-glucoside
were isolated. Four of these flavonoids have an unsubstituted B-ring, a phenomenon often
observed in flavonoids isolated from Helichrysum species. The active antimicrobial
component of H. excisum has been identified as lepidissipyrone.
Owing to the interesting biological activities reported for phloroglucinol a-pyrones and the
synthetic challenges associated with these molecules, lepidissipyrone was selected for a
synthetic study. Both the flavanone and pyrone moieties present in lepidissipyrone have
been successfully synthesised. A successful strategy towards the CH2 linker between the
two units has been illustrated. The strategy could be used to synthesise similar
phloroglucinol-derived pyrones
On the Cause of the Mid‐Pleistocene Transition
The Mid-Pleistocene Transition (MPT), where the Pleistocene glacial cycles changed from 41 to ∼100 kyr periodicity, is one of the most intriguing unsolved issues in the field of paleoclimatology. Over the course of over four decades of research, several different physical mechanisms have been proposed to explain the MPT, involving non-linear feedbacks between ice sheets and the global climate, the solid Earth, ocean circulation, and the carbon cycle. Here, we review these different mechanisms, comparing how each of them relates to the others, and to the currently available observational evidence. Based on this discussion, we identify the most important gaps in our current understanding of the MPT. We discuss how new model experiments, which focus on the quantitative differences between the different physical mechanisms, could help fill these gaps. The results of those experiments could help interpret available proxy evidence, as well as new evidence that is expected to become available
On the Cause of the Mid-Pleistocene Transition
The Mid-Pleistocene Transition (MPT), where the Pleistocene glacial cycles changed from 41 to ∼100 kyr periodicity, is one of the most intriguing unsolved issues in the field of paleoclimatology. Over the course of over four decades of research, several different physical mechanisms have been proposed to explain the MPT, involving non-linear feedbacks between ice sheets and the global climate, the solid Earth, ocean circulation, and the carbon cycle. Here, we review these different mechanisms, comparing how each of them relates to the others, and to the currently available observational evidence. Based on this discussion, we identify the most important gaps in our current understanding of the MPT. We discuss how new model experiments, which focus on the quantitative differences between the different physical mechanisms, could help fill these gaps. The results of those experiments could help interpret available proxy evidence, as well as new evidence that is expected to become available
On the duration of magnetochrons C24r and C25n and the timing of early Eocene global warming events: Implications from the Ocean Drilling Program Leg 208 Walvis Ridge depth transect
Five sections drilled in multiple holes over a depth transect of more than 2200 m at the Walvis Ridge (SE Atlantic) during Ocean Drilling Program (ODP) Leg 208 resulted in the first complete early Paleogene deep-sea record. Here we present high-resolution stratigraphic records spanning a ~4.3 million yearlong interval of the late Paleocene to early Eocene. This interval includes the Paleocene-Eocene thermal maximum (PETM) as well as the Eocene thermal maximum (ETM) 2 event. A detailed chronology was developed with nondestructive X-ray fluorescence (XRF) core scanning records and shipboard color data. These records were used to refine the shipboard-derived spliced composite depth for each site and with a record from ODP Site 1051 were then used to establish a continuous time series over this interval. Extensive spectral analysis reveals that the early Paleogene sedimentary cyclicity is dominated by precession modulated by the short (100 kyr) and long (405 kyr) eccentricity cycles. Counting of precession-related cycles at multiple sites results in revised estimates for the duration of magnetochrons C24r and C25n. Direct comparison between the amplitude modulation of the precession component derived from XRF data and recent models of Earth’s orbital eccentricity suggests that the onset of the PETM and ETM2 are related to a 100-kyr eccentricity maximum. Both events are approximately a quarter of a period offset from a maximum in the 405-kyr eccentricity cycle, with the major difference that the PETM is lagging and ETM2 is leading a 405-kyr eccentricity maximum. Absolute age estimates for the PETM, ETM2, and the magnetochron boundaries that are consistent with recalibrated radiometric ages and recent models of Earth’s orbital eccentricity cannot be precisely determined at present because of too large uncertainties in these methods. Nevertheless, we provide two possible tuning options, which demonstrate the potential for the development of a cyclostratigraphic framework based on the stable 405-kyr eccentricity cycle for the entire Paleogene
Case studies: Tuberculination in pig herds suspected of infection with Mycobacterium avium
Mycobacterium avium, both subspecies hominissuis (MAH) and subsp avium (MAA), are considered a significant zoonotic hazard in pigs. Therefore special attention is given to detect the presence of this hazard in pigs during post mortem meat inspection. Herds delivered at slaughter were monitored on blood antibodies against MAH. Herds with an antibody response against a MAH infection were visited. Initially a questionnaire assessing relevant risk factors for MAH was applied
Orbitally Paced Carbon and Deep-Sea Temperature Changes at the Peak of the Early Eocene Climatic Optimum
Inhibition of Brevibacterium linens by Probiotics from Dairy Products
Brevibacterium linens is an important species in dairy products rendering a specific taste and aroma to numerous smear ripened and blue veined cheeses due to proteolysis. However, the presence of the species in South African blue veined cheeses is undesirable and consumers demand the product void of the species. Accordingly, numerous methods including microbial inhibition using fungi and bacterial probiotic cultures with possible inhibitory effects were applied in an attempt to inhibit the species. None of the fungi, however, proved to be successful, whereas Lactobacillus rhamnosus and Bifidobacterium lactis, two typical probiotic species applied in dairy products, showed inhibitory effects against B. linens when tested using the spot-on-lawn assay
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