13,803 research outputs found
Detection of equine atypical myopathy-associated hypoglycin A in plant material: Optimisation and validation of a novel LC-MS based method without derivatisation
Hypoglycin A (HGA) toxicity, following ingestion of material from certain plants, is linked to an acquired multiple acyl-CoA dehydrogenase deficiency known as atypical myopathy, a commonly fatal form of equine rhabdomyolysis seen worldwide. Whilst some plants are known to contain this toxin, little is known about its function or the mechanisms that lead to varied HGA concentrations between plants. Consequently, reliable tools to detect this amino acid in plant samples are needed. Analytical methods for HGA detection have previously been validated for the food industry, however, these techniques rely on chemical derivatisation to obtain accurate results at low HGA concentrations. In this work, we describe and validate a novel method, without need for chemical derivatisation (accuracy = 84–94%; precision = 3–16%; reproducibility = 3–6%; mean linear range R2 = 0.999). The current limit of quantitation for HGA in plant material was halved (from 1μg/g in previous studies) to 0.5μg/g. The method was tested in Acer pseudoplatanus material and other tree and plant species. We confirm that A. pseudoplatanus is most likely the only source of HGA in trees found within European pastures
Antioxidant activity of alkyl gallates and glycosyl alkyl gallates in fish oil in water emulsions: Relevance of their surface active properties and of the type of emulsifier
The antioxidant activity of gallic acid and a series of alkyl gallates (C4-C18) and glycosylated alkyl gallates (C4-C18) on fish oil-in-water emulsions was studied. Three types of emulsifiers, lecithin, Tween-20 and sodium dodecyl sulphate (SDS) were tested. A nonlinear behavior of the antioxidant activity of alkyl gallates when increasing alkyl chain length was observed for emulsions prepared with lecithin. Medium-size alkyl gallates (C6-C12) were the best antioxidants. In contrast, for emulsions prepared with Tween-20, the antioxidants seem to follow the polar paradox. Glucosyl alkyl gallates were shown previously to be better surfactants than alkyl gallates. Nevertheless, they exhibited a worse antioxidant capacity than their corresponding alkyl gallates, in emulsions prepared with lecithin or Tween-20, indicating the greater relevance of having three OH groups at the polar head in comparison with having improved surfactant properties but just a di-ortho phenolic structure in the antioxidant
The energy spectrum observed by the AGASA experiment and the spatial distribution of the sources of ultra-high energy cosmic rays
Seven and a half years of continuous monitoring of giant air showers
triggered by ultra high-energy cosmic rays have been recently summarized by the
AGASA collaboration. The resulting energy spectrum indicates clearly that the
cosmic ray spectrum extends well beyond the Greisen-Zatsepin-Kuzmin (GZK)
cut-off at eV. Furthermore, despite the small number
statistics involved, some structure in the spectrum may be emerging. Using
numerical simulations, it is demonstrated in the present work that these
features are consistent with a spatial distribution of sources that follows the
distribution of luminous matter in the local Universe. Therefore, from this
point of view, there is no need for a second high-energy component of cosmic
rays dominating the spectrum beyond the GZK cut-off.Comment: 14 pages, 4 figures, Astrophys. J. Letters (submitted
Chiral molecular films as electron polarizers and polarization modulators
Recent experiments on electron scattering through molecular films have shown
that chiral molecules can be efficient sources of polarized electrons even in
the absence of heavy nuclei as source of a strong spin-orbit interaction. We
show that self-assembled monolayers (SAMs) of chiral molecules are strong
electron polarizers due to the high density effect of the monolayers and
explicitly compute the scattering amplitude off a helical molecular model of
carbon atoms. Longitudinal polarization is shown to be the signature of chiral
scattering. For elastic scattering, we find that at least double scattering
events must take place for longitudinal polarization to arise. We predict
energy windows for strong polarization, determined by the energy dependences of
spin-orbit strength and multiple scattering probability. An incoherent
mechanism for polarization amplification is proposed, that increases the
polarization linearly with the number of helix turns, consistent with recent
experiments on DNA SAMs.Comment: 5 Pages, 4 figure
Universal Magnetic-Field-Driven Metal-Insulator-Metal Transformations in Graphite and Bismuth
Applied magnetic field induces metal - insulator and re-entrant
insulator-metal transitions in both graphite and rhombohedral bismuth. The
corresponding transition boundaries plotted on the magnetic field - temperature
(B - T) plane nearly coincide for these semimetals and can be best described by
power laws T ~ (B - B_c)^k, where B_c is a critical field at T = 0 and k = 0.45
+/- 0.05. We show that insulator-metal-insulator (I-M-I) transformations take
place in the Landau level quantization regime and illustrate how the IMT in
quasi-3D graphite transforms into a cascade of I-M-I transitions, related to
the quantum Hall effect in quasi-2D graphite samples. We discuss the possible
coupling of superconducting and excitonic correlations with the observed
phenomena, as well as the signatures of quantum phase transitions associated
with the M-I and I-M transformations.Comment: 23 pages including 14 figure
Galactic Planetary Nebulae with Wolf-Rayet Nuclei III. Kinematical Analysis of a Large Sample of Nebulae
Expansion velocities (Vexp) of different ions and line widths at the base of
the lines are measured and analyzed for 24 PNe with [WC]-type nuclei (WRPNe), 9
PNe ionized by WELS (WLPNe) and 14 ordinary PNe. A comparative study of the
kinematical behavior of the sample clearly demonstrates that WRPNe have in
average 40-45% larger Vexp, and possibly more turbulence than WLPNe and
ordinary PNe. WLPNe have velocity fields very much alike the ones of ordinary
PNe, rather than the ones of WRPNe. All the samples (WRPNe, WLPNe and ordinary
PNe) show expansion velocities increasing with age indicators, for example
is larger for low-density nebulae and also it is larger for nebulae
around high-temperature stars. This age effect is much stronger for evolved
WRPNe, suggesting that the [WC] winds have been accelerating the nebulae for a
long time, while for non-WRPNe the acceleration seems to stop at some point
when the star reaches a temperature of about 90,000-100,000 K. Non-WR nebulae
reach a maximum Vexp < 30 km/s while evolved WRPNe reach maximum Vexp of about
40 km/s. For all kind of objects (WRPNe and non-WRPNe) it is found that in
average Vexp(N+) is slightly larger than Vexp(O++), indicating that the nebulae
present acceleration of the external shells.Comment: 20 pages, 11 fig. To appear in Revista Mexicana de Astronomia y
Astrofisica, April 200
Directed paths on hierarchical lattices with random sign weights
We study sums of directed paths on a hierarchical lattice where each bond has
either a positive or negative sign with a probability . Such path sums
have been used to model interference effects by hopping electrons in the
strongly localized regime. The advantage of hierarchical lattices is that they
include path crossings, ignored by mean field approaches, while still
permitting analytical treatment. Here, we perform a scaling analysis of the
controversial ``sign transition'' using Monte Carlo sampling, and conclude that
the transition exists and is second order. Furthermore, we make use of exact
moment recursion relations to find that the moments always determine,
uniquely, the probability distribution $P(J)$. We also derive, exactly, the
moment behavior as a function of $p$ in the thermodynamic limit. Extrapolations
($n\to 0$) to obtain for odd and even moments yield a new signal for
the transition that coincides with Monte Carlo simulations. Analysis of high
moments yield interesting ``solitonic'' structures that propagate as a function
of . Finally, we derive the exact probability distribution for path sums
up to length L=64 for all sign probabilities.Comment: 20 pages, 12 figure
Developing a Model for Slow Hypoxic Injury and Vascular Degeneration in Amyloid Burdened Brains
The breakdown of neurovascular systems may play a crucial role in the pathogenesis of Alzheimer’s
disease. However whether this breakdown initiates a degenerative mechanism or is the consequence of
some other deleterious process remains unknown. We examined hippocampal pathology in double
transgenic mice overexpressing a human mutant gene encoding the amyloid precursor protein
(APPSwe/Ind) using a combination of histochemistry and stereologic techniques. Expression of
APPSwe/Ind in these mice is driven by a tetracycline-sensitive promoter. Tetracycline transcriptional
activator (tTA), the second transgene, is driven in turn by a CAM KIIa promoter that is only active in
neurons. Thus this double transgenic construct allows us to control expression of APPSwe/Ind with
doxycycline. Utilizing this characteristic, we created three distinct experimental groups: A, display abeta
plaque pathology and express APPSwe/Ind at time of sacrifice; B, display abeta plaque pathology but do
not express APPSwe/Ind at time of sacrifice; and C, do not display abeta plaque pathology but do
express APPSwe/Ind at time of sacrifice. Stereologic investigation revealed decreased hippocampal
volume in groups A(n=5) and B(n=5) when compared to group C(n=5) and age-matched wildtype (n=9)
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