2,558 research outputs found
Water quality between the Barron River/Trinity Inlet and Green Island and the effect of seasonal change
Nutrients and related water quality characteristics were measured at six sites along
a transect from the Barron River estuary to Green Island over a twenty-month
period.
The water column was generally well mixed and so depth was not a significant
source of variation. Overall, slightly higher nutrient concentrations tended to be
found at the two most inshore sites. FUrthermore, some elevated nutrient levels
were recorded right across the transect after periods of heavy rain and/or rough
weather. This elevation was most noticeable at the two inshore sites, suggesting
input from the Barron River discharge.· At Green Island there was no significant
increase over background levels in the mean levels of nutrients in the vicinity of the
sewage outfall, however relatively high chlorophyll a levels were recorded near to
the sewage discharge. These high chlorophyll a levels could indeed result from the
discharge of sewage effluent but further studies will need to be carried out in order
to confirm this
Transcriptional factor influence on OTA production and the quelling attribute of Sirna on the OTA producing strains of Aspergillus section Nigri
This study determined the influence of some transcriptional factors on ochratoxin A production as well as investigates the quelling attributes of some designed siRNA on the OTA producing Aspergillus section Nigri using standard recommended techniques. Results obtained following comparison of the pks gene promoter sequences from 15 isolates depicts differences in length and homology with the pks gene ranging from 218bp in a strain of the Aspergillus niger to 700bp in Aspergillus carbonarius. The alignment of the pks gene promoter region revealed that six and two of the aligned genes have Aba A binding site corresponding to CATTCT and CATTCC respectively while Brl A binding site was absent in all the isolates. Pac C binding site corresponding to CCTGGC and GCCAAG was also found in two and three of the pks gene promoter region respectively. The three designed siRNA shows significant impact on OTA inhibitions with no significant statistical differences (80.9, 74.4 and 75.3% for pks_Ia, pks_Ib and pks_Ic respectively) (F= 3.830, p>0.05). It can be concluded that Are A and Aba A are potential enhancers for ochratoxin A biosynthesis and none of the investigated transcriptional factors is enough for the activation of ochratoxin A production. However, pks gene was seen as a good target gene for inactivation in order to develop efficient means for ochratoxin A control using RNA silencing technology.Key words: Transcriptional factors, Ochratoxin A, siRNA, Quelling , Aspergillus section Nigr
Genetic diversity of ochratoxigenic Aspergillus section Nigri, using RAPD and VCG techniques
This study evaluates the genetic diversity of ochratoxigenic Aspergillus section Nigri using RAPD and VCG techniques. Results obtained revealed OPX 07 as the most informative of the tested RAPD markers generating 12 polymorphic bands while the least bands were generated by OPR 19. Of the 40 Aspergillus section Nigri (20 each of Aspergillus niger and Aspergillus carbonarius), 22 VCGs and 27 RAPD haplotypes were delineated. The two techniques demonstrated similar resolution except in few cases where the RAPD technique further sub divided some VCGs into simpler haplotypes. The average percentage of variable VCG and RAPD reactions were 25 and 50% in that order of sequence while 75 and 50% of the isolates were resolved as same isolates by these techniques respectively. It was also found that the Simpson index of genetic diversity approached one for the isolates from the four geopolitical zones of Ogun State, Nigeria with the mean genetic diversity within isolates (GL) contributing significantly approximately 89% of the total diversity observed within the isolates (F=22.23, p<0.05). The remaining 11% of variation could only be allotted to diversity among isolates (GS). On the whole, the total genetic diversity (HT) was found to be approximately 48%. In conclusion, RAPD markers provided better resolution than the classical VCG typing technique.Keywords; Genetic Diversity, Ochratoxigenic Aspergillus, RAPD and VC
Improved brain PET quantification using partial volume correction techniques
Positron emission tomography (PET) suffers from a degradation in quantitative accuracy due
to a phenomenon known as the partial volume effect (PVE). The effects are due to the limited
spatial resolution of the scanner. Methods that correct for PVEs are known as partial
volume correction (PVC) techniques and are either data-driven or make use of anatomical
information from other modalities such as magnetic resonance (MR) imaging. This thesis reports
investigations into PVC techniques for improving the quantification of brain amyloid
PET tracers. These tracers image amyloid plaque aggregation in-vivo, which is a pathological
hallmark of Alzheimer’s disease.
An extension to existing anatomy-based PVC methods is reported. Region-based voxelwise
(RBV) correction has been shown to reduce PVE-induced regional bias and variance
when compared to commonly applied PVC techniques. This has been proven in phantom
studies and observed in clinical data. In addition, RBV has been used to demonstrate that
white matter variability exists in two different amyloid tracers. This finding has implications
for the application of PVC in amyloid imaging and also how scans should be normalised.
Alternative reference regions were investigated in two amyloid PET tracers. The brain stem,
in combination with PVC, was found to result in the strongest agreement between tracers.
Anatomy-based PVC techniques rely on parcellations of structural images. These parcellations
are not necessarily representative of the PET data. A further extension to RBV is
proposed which iteratively modifies the parcellations to find an optimal PVC in terms of the
observed PET data. This novel technique reduces quantification errors due to PET-MR mismatch
and has the potential to provide an additional parameter of ‘functional volume change’
in longitudinal studies
The Exact MSSM Spectrum from String Theory
We show the existence of realistic vacua in string theory whose observable
sector has exactly the matter content of the MSSM. This is achieved by
compactifying the E_8 x E_8 heterotic superstring on a smooth Calabi-Yau
threefold with an SU(4) gauge instanton and a Z_3 x Z_3 Wilson line.
Specifically, the observable sector is N=1 supersymmetric with gauge group
SU(3)_C x SU(2)_L x U(1)_Y x U(1)_{B-L}, three families of quarks and leptons,
each family with a right-handed neutrino, and one Higgs-Higgs conjugate pair.
Importantly, there are no extra vector-like pairs and no exotic matter in the
zero mode spectrum. There are, in addition, 6 geometric moduli and 13 gauge
instanton moduli in the observable sector. The holomorphic SU(4) vector bundle
of the observable sector is slope-stable.Comment: 15 pages, LaTeX; v2: Hidden sector is unstable, symbol typesetting
error corrected, clarifications and references added; v3: New discussion of
hidden secto
Identification and utilization of informative EST-SSR markers for genetic purity testing of coconut hybrids
Coconut palms are categorized into two forms, viz., ‘talls’ and ‘dwarfs’ which are being utilized to produce hybrids through the process of inter-varietal or intra-varietal crosses. Hybrid coconut seedlings are generally identified and selected based on morphological traits by plant breeders, which is quite difficult and requires expertise. Even minor errors in identification may adversely affect breeding programs in coconut, which is spread over many decades. In this study, we have utilized thirty EST-SSR markers, derived from existing coconut leaf transcriptome data, for screening polymorphism between eighteen coconut parental lines. The polymorphic primers capable of differentiating the parental palms were then utilized successfully for assessment of purity of hybrids derived from these parents. Thus, the current study demonstrates the utility of EST-SSR markers in determiningthe genetic purity of hybrids in coconut
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A sticky business: the status of the conjectured viscosity/entropy density bound
There have been a number of forms of a conjecture that there is a universal
lower bound on the ratio, eta/s, of the shear viscosity, eta, to entropy
density, s, with several different domains of validity. We examine the various
forms of the conjecture. We argue that a number of variants of the conjecture
are not viable due to the existence of theoretically consistent
counterexamples. We also note that much of the evidence in favor of a bound
does not apply to the variants which have not yet been ruled out.Comment: 23 pages, 4 figures, added references, corrected typos, added
subsection in response to Son's comments in arXiv:0709.465
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Applications of Solid Freeform Fabrication at the Naval Research Laboratory
Solid Freeform Fabrication (SFF) and related techniques are used at the Naval Research
Laboratory (NRL) for a variety of materials related investigations. Research and applications
conducted over the past few years are described including: Helisys Laminated Object
Manufacturing System (LOMS) fabrication of: ceramic piezoelectric actuators, tooling for
multifunctional materials, and anatomical prototypes for surgical visualization; fabrication of
mesoscale electronic and sensor components using a laser forward transfer direct write
technique; and visualization of complex, 3-D microstructures using a Stratasys Fused-Deposition
Modeler. The paper closes with a brief overview of future SFF related work at the NRL.Support for this work from DARPA, Office of Naval Research, and the Naval Research
Laboratory Core Research Program is gratefully acknowledged.Mechanical Engineerin
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