1,377 research outputs found
Unconventional magnetism in all-carbon nanofoam
We report production of nanostructured carbon foam by a high-repetition-rate,
high-power laser ablation of glassy carbon in Ar atmosphere. A combination of
characterization techniques revealed that the system contains both sp2 and sp3
bonded carbon atoms. The material is a novel form of carbon in which
graphite-like sheets fill space at very low density due to strong hyperbolic
curvature, as proposed for ?schwarzite?. The foam exhibits ferromagnetic-like
behaviour up to 90 K, with a narrow hysteresis curve and a high saturation
magnetization. Such magnetic properties are very unusual for a carbon
allotrope. Detailed analysis excludes impurities as the origin of the magnetic
signal. We postulate that localized unpaired spins occur because of topological
and bonding defects associated with the sheet curvature, and that these spins
are stabilized due to the steric protection offered by the convoluted sheets.Comment: 14 pages, including 2 tables and 7 figs. Submitted to Phys Rev B 10
September 200
Bioethanol production from <em>Chara globularis</em> using yeast and yield improvement by optimization of conditions
The rising population, depletion of petroleum-based fossil fuel and atmospheric contaminations by combustion of fossil fuel have opened avenues for alternative, eco-friendly and renewable energy sources. Bioethanol is an alternative and renewable source that has drawn attention due environmental concerns and energy security with non-renewable sources. This study was aimed at determining the potential bioethanol producing freshwater flora that are abundantly available in the Northern Province of Sri Lanka using Saccharomyces cerevisiae and to optimize the fermentation conditions to enhance the ethanol yield from Chara globularis. Freshwater flora such as C. globularis, Cabomba caroliniana, Spirodela polyrhiza, Salvinia minima, Salvinia natans, Wolffia arrhiza and Wolffia globosa were hydrolysed with 1M sulfuric acid solution to determine the reducing sugar and bioethanol yields. C. globularis produced a higher amount of reducing sugar and bioethanol than other species tested. When C. globularis was pre-treated with 1 M acid solutions (sulfuric acid, nitric acid, and hydrochloric acid) and alkaline solutions (sodium hydroxide and potassium hydroxide), a higher reducing sugar and bioethanol yields were obtained with sulfuric acid. When bioethanol was produced from C. globularis using S. cerevisiae following three different hydrolysis methods viz., acid hydrolysis (1 M sulfuric acid), enzymatic hydrolysis (1% alphaamylase) and combination of chemical and enzymatic hydrolysis (1 M sulfuric acid and 1% alpha-amylase), the combination of chemical and enzymatic hydrolysis gave a higher yield, thus was selected. The conditions for fermentation of C. globularis substrate using S. cerevisiae were optimized sequentially by changing one factor at a time while keeping the other variables constant. After the optimization of fermentation time (24 hours), operating temperature (35 °C), rotation speed (200 rpm) and sulfuric acid concentration for combined pre-treatment (0.75 M) with an inoculum size of 100 g l-1, bioethanol yield was increased
The Origin of the Mass--Metallicity Relation: Insights from 53,000 Star-Forming Galaxies in the SDSS
We utilize Sloan Digital Sky Survey imaging and spectroscopy of ~53,000
star-forming galaxies at z~0.1 to study the relation between stellar mass and
gas-phase metallicity. We derive gas-phase oxygen abundances and stellar masses
using new techniques which make use of the latest stellar evolutionary
synthesis and photoionization models. We find a tight (+/-0.1 dex) correlation
between stellar mass and metallicity spanning over 3 orders of magnitude in
stellar mass and a factor of 10 in metallicity. The relation is relatively
steep from 10^{8.5} - 10^{10.5} M_sun, in good accord with known trends between
luminosity and metallicity, but flattens above 10^{10.5} M_sun. We use indirect
estimates of the gas mass based on the H-alpha luminosity to compare our data
to predictions from simple closed box chemical evolution models. We show that
metal loss is strongly anti-correlated with baryonic mass, with low mass dwarf
galaxies being 5 times more metal-depleted than L* galaxies at z~0.1. Evidence
for metal depletion is not confined to dwarf galaxies, but is found in galaxies
with masses as high as 10^{10} M_sun. We interpret this as strong evidence both
of the ubiquity of galactic winds and of their effectiveness in removing metals
from galaxy potential wells.Comment: ApJ accepted, 15 pages, 9 figures, emulateapj.st
The proton and deuteron F_2 structure function at low Q^2
Measurements of the proton and deuteron structure functions are
presented. The data, taken at Jefferson Lab Hall C, span the four-momentum
transfer range GeV, and Bjorken values from 0.009 to
0.45, thus extending the knowledge of to low values of at low .
Next-to-next-to-leading order calculations using recent parton distribution
functions start to deviate from the data for GeV at the low and
high -values. Down to the lowest value of , the structure function is
in good agreement with a parameterization of based on data that have been
taken at much higher values of or much lower values of , and which is
constrained by data at the photon point. The ratio of the deuteron and proton
structure functions at low remains well described by a logarithmic
dependence on at low .Comment: 3 figures, submitted pape
A precise extraction of the induced polarization in the 4He(e,e'p)3H reaction
We measured with unprecedented precision the induced polarization Py in
4He(e,e'p)3H at Q^2 = 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2. The induced polarization
is indicative of reaction-mechanism effects beyond the impulse approximation.
Our results are in agreement with a relativistic distorted-wave impulse
approximation calculation but are over-estimated by a calculation with strong
charge-exchange effects. Our data are used to constrain the strength of the
spin independent charge-exchange term in the latter calculation.Comment: submitted to Physical Review Letter
Polarization Transfer in the 4He(e,e'p)3H Reaction at Q^2 = 0.8 and 1.3 (GeV/c)^2
Proton recoil polarization was measured in the quasielastic 4He(e,e'p)3H
reaction at Q^2 = 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2 with unprecedented precision.
The polarization-transfer coefficients are found to differ from those of the
1H(e,e' p) reaction, contradicting a relativistic distorted-wave approximation,
and favoring either the inclusion of medium-modified proton form factors
predicted by the quark-meson coupling model or a spin-dependent charge-exchange
final-state interaction. For the first time, the polarization-transfer ratio is
studied as a function of the virtuality of the proton
Longitudinal-Transverse Separations of Structure Functions at Low for Hydrogen and Deuterium
We report on a study of the longitudinal to transverse cross section ratio,
, at low values of and , as determined from
inclusive inelastic electron-hydrogen and electron-deuterium scattering data
from Jefferson Lab Hall C spanning the four-momentum transfer range 0.06 GeV. Even at the lowest values of , remains
nearly constant and does not disappear with decreasing , as expected. We
find a nearly identical behaviour for hydrogen and deuterium.Comment: 4 pages, 2 gigure
Asymptotic normalization coefficients (nuclear vertex constants) for and the direct astrophysical S-factors at solar energies
A new analysis of the precise experimental astrophysical S-factors for the
direct capture reaction [A.J.Junghans et al.Phys.Rev. C
68 (2003) 065803 and L.T. Baby et al. Phys.Rev. C 67 (2003) 065805] is carried
out based on the modified two - body potential approach in which the direct
astrophysical S-factor, , is expressed in terms of the
asymptotic normalization constants for and two additional
conditions are involved to verify the peripheral character of the reaction
under consideration. The Woods-Saxon potential form is used for the bound
()- state wave function and for the - scattering wave function.
New estimates are obtained for the ^{\glqq}indirectly measured\grqq values of
the asymptotic normalization constants (the nuclear vertex constants) for the
and at E 115 keV, including =0. These
values of and asymptotic normalization constants have been used for
getting information about the ^{\glqq}indirectly measured\grqq values of the
wave average scattering length and the wave effective range parameters
for - scattering.Comment: 27 pages, 6 figure
Measurements of electron-proton elastic cross sections for
We report on precision measurements of the elastic cross section for
electron-proton scattering performed in Hall C at Jefferson Lab. The
measurements were made at 28 unique kinematic settings covering a range in
momentum transfer of 0.4 5.5 . These measurements
represent a significant contribution to the world's cross section data set in
the range where a large discrepancy currently exists between the ratio of
electric to magnetic proton form factors extracted from previous cross section
measurements and that recently measured via polarization transfer in Hall A at
Jefferson Lab.Comment: 17 pages, 18 figures; text added, some figures replace
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