5,670 research outputs found
UV-B induced changes of phenol composition and antioxidant activity in black currant fruit (Ribes nigrum L.)
Information on UV-B elicitor mediated changes on phenolic composition and antioxidant activity of black currant (Ribes nigrum L.) are scanty. In the present study physiological ripe black currant fruits were harvested and exposed to UV-B radiation with different exposure and adaptation times. The influence of UV-B on phenolic profile and quantitative composition as well as on the corresponding antioxidant activity was investigated. Antioxidant activity was screened with electron spin resonance spectrometry (ESR), while phenolic compound composition was conducted by HPLC analysis. Total phenol content and phenolic composition (flavonols, anthocyanins, hydroxycinnamic and hydroxybenzoic acids) increased to a large extent during UV-B treatment, irrespective of the adaptation time. Anthocyanins are concluded to absorb UV radiation within a short time, meanwhile flavonols and phenolic acids are assumed to have an impact on antioxidant protection of UV-B mediated tissue damage. Moreover, antioxidant activity significantly correlated with different phenolic compounds and increased to a similar extent by UV-B exposure
Influence of location and fertilization on antioxidant acitivity in highbush blueberries (Vaccinium corymbosum L.)
Highbush blueberry cultivars ‘Bluecrop’ and ‘Reka’ were growing in two variants of mulching and fertilizing systems on formerly used farmland. Fruits were harvested at two picking dates and analyzed for their content of phenolic compounds and antioxidant activity. These data were compared with samples of two forest soil locations from the Brandenburg region (Beelitz and Klaistow). The results showed significant differences between cultivars, both harvest times and different locations. The variations in fertilization and ground cover (with or without mulch) showed significant differences. Moreover, it is demonstrated that without ground cover and commercial fertilization higher contents of total phenolic compounds and an increase in antioxidant activity tendentiously occurred. This result paralleled the decline in vegetative growth and was associated with drought stress
Geometric potential and transport in photonic topological crystals
We report on the experimental realization of an optical analogue of a quantum
geometric potential for light wave packets constrained on thin dielectric
guiding layers fabricated in silica by the femtosecond laser writing
technology. We further demonstrate the optical version of a topological
crystal, with the observation of Bloch oscillations and Zener tunneling of
purely geometric nature
Two-dimensional solitons at interfaces between binary superlattices and homogeneous lattices
We report on the experimental observation of two-dimensional surface solitons
residing at the interface between a homogeneous square lattice and a
superlattice that consists of alternating "deep" and "shallow" waveguides. By
exciting single waveguides in the first row of the superlattice, we show that
solitons centered on deep sites require much lower powers than their respective
counterparts centered on shallow sites. Despite the fact that the average
refractive index of the superlattice waveguides is equal to the refractive
index of the homogeneous lattice, the interface results in clearly asymmetric
output patterns.Comment: 16 pages, 5 figures, to appear in Physical Review
Neutrino Coherent Scattering Rates at Direct Dark Matter Detectors
Neutrino-induced recoil events may constitute a background to direct dark
matter searches, particularly for those detectors that strive to reach the
ton-scale and beyond. This paper discusses the expected neutrino-induced
background spectrum due to several of the most important sources, including
solar, atmospheric, and diffuse supernova neutrinos. The largest rate arises
from B produced solar neutrinos, providing upwards of events
per ton-year over all recoil energies for the heaviest nuclear targets. However
the majority of these B events are expected to be below the recoil
threshold of modern detectors. The remaining neutrino sources are found to
constitute a background to the WIMP-induced recoil rate only if the
WIMP-nucleon cross section is less than pb. Finally the sensitivity
to diffuse supernova neutrino flux for non-electron neutrino flavors is
discussed, and projected flux limits are compared with existing flux limits
NP-hardness of the cluster minimization problem revisited
The computational complexity of the "cluster minimization problem" is
revisited [L. T. Wille and J. Vennik, J. Phys. A 18, L419 (1985)]. It is argued
that the original NP-hardness proof does not apply to pairwise potentials of
physical interest, such as those that depend on the geometric distance between
the particles. A geometric analog of the original problem is formulated, and a
new proof for such potentials is provided by polynomial time transformation
from the independent set problem for unit disk graphs. Limitations of this
formulation are pointed out, and new subproblems that bear more direct
consequences to the numerical study of clusters are suggested.Comment: 8 pages, 2 figures, accepted to J. Phys. A: Math. and Ge
A Fresh Look at Axions and SN 1987A
We re-examine the very stringent limits on the axion mass based on the
strength and duration of the neutrino signal from SN 1987A, in the light of new
measurements of the axial-vector coupling strength of nucleons, possible
suppression of axion emission due to many-body effects, and additional emission
processes involving pions. The suppression of axion emission due to nucleon
spin fluctuations induced by many-body effects degrades previous limits by a
factor of about 2. Emission processes involving thermal pions can strengthen
the limits by a factor of 3-4 within a perturbative treatment that neglects
saturation of nucleon spin fluctuations. Inclusion of saturation effects,
however, tends to make the limits less dependent on pion abundances. The
resulting axion mass limit also depends on the precise couplings of the axion
and ranges from 0.5x10**(-3) eV to 6x10**(-3) eV.Comment: 32 latex pages, 13 postscript figures included, uses revtex.sty,
submitted to Physical Review
Hemodynamic and ADH responses to central blood volume shifts in cardiac-denervated humans
Hemodynamic responses and antidiuretic hormone (ADH) were measured during body position changes designed to induce blood volume shifts in ten cardiac transplant recipients to assess the contribution of cardiac and vascular volume receptors in the control of ADH secretion. Each subject underwent 15 min of a control period in the seated posture, then assumed a lying posture for 30 min at 6 deg head down tilt (HDT) followed by 20 min of seated recovery. Venous blood samples and cardiac dimensions (echocardiography) were taken at 0 and 15 min before HDT, 5, 15, and 30 min of HDT, and 5, 15, and 30 min of seated recovery. Blood samples were analyzed for hematocrit, plasma osmolality, plasma renin activity (PRA), and ADH. Resting plasma volume (PV) was measured by Evans blue dye and percent changes in PV during posture changes were calculated from changes in hematocrit. Heart rate (HR) and blood pressure (BP) were recorded every 2 min. Results indicate that cardiac volume receptors are not the only mechanism for the control of ADH release during acute blood volume shifts in man
Nucleon Spin Fluctuations and the Supernova Emission of Neutrinos and Axions
In the hot and dense medium of a supernova (SN) core, the nucleon spins
fluctuate so fast that the axial-vector neutrino opacity and the axion
emissivity are expected to be significantly modified. Axions with
m_a\alt10^{-2}\,{\rm eV} are not excluded by SN~1987A. A substantial transfer
of energy in neutrino-nucleon () collisions is enabled which may alter
the spectra of SN neutrinos relative to calculations where energy-conserving
collisions had been assumed near the neutrinosphere.Comment: 8 pages. REVTeX. 2 postscript figures, can be included with epsf.
Small modifications of the text, a new "Note Added", and three new
references. To be published in Phys. Rev. Let
Mu and Tau Neutrino Thermalization and Production in Supernovae: Processes and Timescales
We investigate the rates of production and thermalization of and
neutrinos at temperatures and densities relevant to core-collapse
supernovae and protoneutron stars. Included are contributions from electron
scattering, electron-positron annihilation, nucleon-nucleon bremsstrahlung, and
nucleon scattering. For the scattering processes, in order to incorporate the
full scattering kinematics at arbitrary degeneracy, the structure function
formalism developed by Reddy et al. (1998) and Burrows and Sawyer (1998) is
employed. Furthermore, we derive formulae for the total and differential rates
of nucleon-nucleon bremsstrahlung for arbitrary nucleon degeneracy in
asymmetric matter. We find that electron scattering dominates nucleon
scattering as a thermalization process at low neutrino energies
( MeV), but that nucleon scattering is always faster
than or comparable to electron scattering above MeV. In
addition, for g cm, MeV, and
neutrino energies MeV, nucleon-nucleon bremsstrahlung always
dominates electron-positron annihilation as a production mechanism for
and neutrinos.Comment: 29 pages, LaTeX (RevTeX), 13 figures, submitted to Phys. Rev. C. Also
to be found at anonymous ftp site http://www.astrophysics.arizona.edu; cd to
pub/thompso
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