97 research outputs found
Thermal inactivation and conformational lock studies on glucose oxidase
In this study, the dissociative thermal inactivation
and conformational lock theories are applied for the
homodimeric enzyme glucose oxidase (GOD) in order to
analyze its structure. For this purpose, the rate of activity
reduction of glucose oxidase is studied at various temperatures
using b-D-glucose as the substrate by incubation of
enzyme at various temperatures in the wide range between
40 and 70 �C using UV–Vis spectrophotometry. It was
observed that in the two ranges of temperatures, the
enzyme has two different forms. In relatively low temperatures,
the enzyme is in its dimeric state and has normal
activity. In high temperatures, the activity almost disappears
and it aggregates. The above achievements are confirmed
by dynamic light scattering. The experimental
parameter ‘‘n’’ as the obvious number of conformational
locks at the dimer interface of glucose oxidase is obtained
by kinetic data, and the value is near to two. To confirm the
above results, the X-ray crystallography structure of the
enzyme, GOD (pdb, 1gal), was also studied. The secondary
and tertiary structures of the enzyme to track the thermal
inactivation were studied by circular dichroism and
fluorescence spectroscopy, respectively. We proposed a
mechanism model for thermal inactivation of GOD based
on the absence of the monomeric form of the enzyme by
circular dichroism and fluorescence spectroscopy
The N-P-K soil nutrient balance of portuguese cropland in the 1950s: the transition from organic to chemical fertilization
Agricultural nutrient balances have been receiving increasing attention in both historical and
nutrient management research. The main objectives of this study were to further develop balance
methodologies and to carry out a comprehensive assessment of the functioning and nutrient cycling
of 1950s agroecosystems in Portugal. Additionally, the main implications for the history of agriculture
in Portugal were discussed from the standpoint of soil fertility. We used a mass balance approach
that comprises virtually all nitrogen (N), phosphorus (P) and potassium (K) inputs and outputs from
cropland topsoil for average conditions in the period 1951–56. We found a consistent deficit in N, both
for nationwide (−2.1 kg.ha−1.yr−1) and arable crops (−1.6 kg.ha−1.yr−1) estimates, that was rectified
in the turn to the 1960 decade. P and K were, in contrast, accumulating in the soil (4.2–4.6 kg.ha−1.yr−1
and 1.0–3.0 kg.ha−1.yr−1, respectively). We observed that the 1950s is the very moment of inflection
from an agriculture fertilized predominantly through reused N in biomass (livestock excretions plus
marine, plant and human waste sources) to one where chemical fertilizers prevailed. It is suggested that
N deficiency played an important role in this transitioninfo:eu-repo/semantics/publishedVersio
First measurement of the nuclear-recoil ionization yield in silicon at 100 eV
We measured the nuclear--recoil ionization yield in silicon with a cryogenic
phonon-sensitive gram-scale detector. Neutrons from a mono-energetic beam
scatter off of the silicon nuclei at angles corresponding to energy depositions
from 4\,keV down to 100\,eV, the lowest energy probed so far. The results show
no sign of an ionization production threshold above 100\,eV. These results call
for further investigation of the ionization yield theory and a comprehensive
determination of the detector response function at energies below the keV
scale
Ionization yield measurement in a germanium CDMSlite detector using photo-neutron sources
Two photo-neutron sources, YBe and SbBe, have been
used to investigate the ionization yield of nuclear recoils in the CDMSlite
germanium detectors by the SuperCDMS collaboration. This work evaluates the
yield for nuclear recoil energies between 1 keV and 7 keV at a temperature of
50 mK. We use a Geant4 simulation to model the neutron spectrum assuming
a charge yield model that is a generalization of the standard Lindhard model
and consists of two energy dependent parameters. We perform a likelihood
analysis using the simulated neutron spectrum, modeled background, and
experimental data to obtain the best fit values of the yield model. The
ionization yield between recoil energies of 1 keV and 7 keV is shown to be
significantly lower than predicted by the standard Lindhard model for
germanium. There is a general lack of agreement among different experiments
using a variety of techniques studying the low-energy range of the nuclear
recoil yield, which is most critical for interpretation of direct dark matter
searches. This suggests complexity in the physical process that many direct
detection experiments use to model their primary signal detection mechanism and
highlights the need for further studies to clarify underlying systematic
effects that have not been well understood up to this point
Search for low-mass dark matter via bremsstrahlung radiation and the Migdal effect in SuperCDMS
We present a new analysis of previously published SuperCDMS data using a profile likelihood framework to search for sub-GeV dark matter (DM) particles through two inelastic scattering channels: bremsstrahlung radiation and the Migdal effect. By considering these possible inelastic scattering channels, experimental sensitivity can be extended to DM masses that are undetectable through the DM-nucleon elastic scattering channel, given the energy threshold of current experiments. We exclude DM masses down to 220 MeV/c2 at 2.7×10−30 cm2 via the bremsstrahlung channel. The Migdal channel search provides overall considerably more stringent limits and excludes DM masses down to 30 MeV/c2 at 5.0×10−30 cm2
A Search for Low-mass Dark Matter via Bremsstrahlung Radiation and the Migdal Effect in SuperCDMS
We present a new analysis of previously published of SuperCDMS data using a
profile likelihood framework to search for sub-GeV dark matter (DM) particles
through two inelastic scattering channels: bremsstrahlung radiation and the
Migdal effect. By considering these possible inelastic scattering channels,
experimental sensitivity can be extended to DM masses that are undetectable
through the DM-nucleon elastic scattering channel, given the energy threshold
of current experiments. We exclude DM masses down to at
via the bremsstrahlung channel. The Migdal
channel search provides overall considerably more stringent limits and excludes
DM masses down to at .Comment: Submitted to PR
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