11,058 research outputs found
Precise measurement of the 222Rn half-life: a probe to monitor the stability of radioactivity
We give the results of a study on the 222Rn decay we performed in the Gran
Sasso Laboratory (LNGS) by detecting the gamma rays from the radon progeny. The
motivation was to monitor the stability of radioactivity measuring several
times per year the half-life of a short lifetime (days) source instead of
measuring over a long period the activity of a long lifetime (tens or hundreds
of years) source. In particular, we give a possible reason of the large
periodical fluctuations in the count rate of the gamma rays due to radon inside
a closed canister which has been described in literature and which has been
attributed to a possible influence of a component in the solar irradiation
affecting the nuclear decay rates. We then provide the result of four half-life
measurements we performed underground at LNGS in the period from May 2014 to
January 2015 with radon diffused into olive oil. Briefly, we did not measure
any change of the 222Rn half-life with a 8*10^-5 precision. Finally, we provide
the most precise value for the 222Rn half-life: 3.82146(16){stat}(4){syst}
days.Comment: Accepted for publication in Physics Letters B, 6 pages, 6 figure
Search for correlations between solar flares and decay rate of radioactive nuclei
The deacay rate of three different radioactive sources 40K, 137Cs and natTh
has been measured with NaI and Ge detectors. Data have been analyzed to search
for possible variations in coincidence with the two strongest solar flares of
the years 2011 and 2012. No significant deviations from standard expectation
have been observed, with a few 10-4 sensitivity. As a consequence, we could not
find any effect like that recently reported by Jenkins and Fischbach: a few per
mil decrease in the decay rate of 54Mn during solar flares in December 2006.Comment: 5 pages, 3 figure
Thermal effects on chaotic directed transport
We study a chaotic ratchet system under the influence of a thermal
environment. By direct integration of the Lindblad equation we are able to
analyze its behavior for a wide range of couplings with the environment, and
for different finite temperatures. We observe that the enhancement of the
classical and quantum currents due to temperature depend strongly on the
specific properties of the system. This makes difficult to extract universal
behaviors. We have also found that there is an analogy between the effects of
the classical thermal noise and those of the finite size. These results
open many possibilities for their testing and implementation in kicked BECs and
cold atoms experiments.Comment: 5 pages, 4 figure
How to detect an anti-spacetime
Is it possible, in principle, to measure the sign of the Lapse? We show that
fermion dynamics distinguishes spacetimes having the same metric but different
tetrads, for instance a Lapse with opposite sign. This sign might be a physical
quantity not captured by the metric. We discuss its possible role in quantum
gravity.Comment: Article awarded with an "Honorable Mention" from the 2012 Gravity
Foundation Award. 6 pages, 8 (pretty) figure
Discrete Symmetries in Covariant LQG
We study time-reversal and parity ---on the physical manifold and in internal
space--- in covariant loop gravity. We consider a minor modification of the
Holst action which makes it transform coherently under such transformations.
The classical theory is not affected but the quantum theory is slightly
different. In particular, the simplicity constraints are slightly modified and
this restricts orientation flips in a spinfoam to occur only across degenerate
regions, thus reducing the sources of potential divergences.Comment: 8 pages, v2: Minor change
Search for time modulations in the decay rate of 40K and 232Th
Time modulations at per mil level have been reported to take place in the
decay constant of about 15 nuclei with period of one year (most cases) but also
of about one month or one day. In this paper we give the results of the
activity measurement of a 40K source and a 232Th one. The two experiments have
been done at the Gran Sasso Laboratory during a period of about 500 days, above
ground (40K) and underground (232Th) with a target sensitivity of a few parts
over 10^5. We also give the results of the activity measurement at the time of
the X-class solar flares which took place in May 2013. Briefly, our
measurements do not show any evidence of unexpected time dependence in the
decay rate of 40K and 232Th.Comment: version accepted for publication (Astroparticle Physics
On approximate solutions of semilinear evolution equations
A general framework is presented to discuss the approximate solutions of an
evolution equation in a Banach space, with a linear part generating a semigroup
and a sufficiently smooth nonlinear part. A theorem is presented, allowing to
infer from an approximate solution the existence of an exact solution.
According to this theorem, the interval of existence of the exact solution and
the distance of the latter from the approximate solution can be evaluated
solving a one-dimensional "control" integral equation, where the unknown gives
a bound on the previous distance as a function of time. For example, the
control equation can be applied to the approximation methods based on the
reduction of the evolution equation to finite-dimensional manifolds: among
them, the Galerkin method is discussed in detail. To illustrate this framework,
the nonlinear heat equation is considered. In this case the control equation is
used to evaluate the error of the Galerkin approximation; depending on the
initial datum, this approach either grants global existence of the solution or
gives fairly accurate bounds on the blow up time.Comment: 33 pages, 10 figures. To appear in Rev. Math. Phys. (Shortened
version; the proof of Prop. 3.4. has been simplified
Matching Seeds to Needs - female farmers adapt to a changing climate in Ethiopia
Between 2010 and 2012 Bioversity International worked with partners and stakeholders in Ethiopia to develop an innovative low-cost strategy for managing risks to agricultural systems posed by the adverse effects of climate change. The objective, which the project indeed achieved, was to decrease vulnerability and enhance adaptive capacity in smallholder farming communities by increasing the intraspecific diversity of important food security crops using barley and durum wheat
Confocal laser scanning microscope, raman microscopy and western blotting to evaluate inflammatory response after myocardial infarction
Cardiac muscle necrosis is associated with inflammatory cascade that clears the infarct from dead
cells and matrix debris, and then replaces the damaged tissue with scar, through three overlapping phases: the
inflammatory phase, the proliferative phase and the maturation phase.
Western blotting, laser confocal microscopy, Raman microscopy are valuable tools for studying the inflammatory
response following myocardial infarction both humoral and cellular phase, allowing the identification and
semiquantitative analysis of proteins produced during the inflammatory cascade activation and the topographical distribution
and expression of proteins and cells involved in myocardial inflammation. Confocal laser scanning microscopy
(CLSM) is a relatively new technique for microscopic imaging, that allows greater resolution, optical sectioning of the
sample and three-dimensional reconstruction of the same sample. Western blotting used to detect the presence of a specific
protein with antibody-antigen interaction in the midst of a complex protein mixture extracted from cells, produced
semi-quantitative data quite easy to interpret. Confocal Raman microscopy combines the three-dimensional optical resolution
of confocal microscopy and the sensitivity to molecular vibrations, which characterizes Raman spectroscopy.
The combined use of western blotting and confocal microscope allows detecting the presence of proteins in the sample
and trying to observe the exact location within the tissue, or the topographical distribution of the same. Once demonstrated
the presence of proteins (cytokines, chemokines, etc.) is important to know the topographical distribution, obtaining in this
way additional information regarding the extension of the inflammatory process in function of the time stayed from the
time of myocardial infarction. These methods may be useful to study and define the expression of a wide range of inflammatory
mediators at several different timepoints providing a more detailed analysis of the time course of the infarct
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