5,484 research outputs found
Measurement of the ratio h/e with a photomultiplier tube and a set of LEDs
We propose a laboratory experience aimed at undergraduate physics students to
understand the main features of the photoelectric effect and to perform a
measurement of the ratio h/e, where h is the Planck's constant and e is the
electron charge. The experience is based on the method developed by Millikan
for his measurements on the photoelectric effect in the years from 1912 to
1915. The experimental setup consists of a photomultiplier tube (PMT) equipped
with a voltage divider properly modified to set variable retarding potentials
between the photocathode and the first dynode, and a set of LEDs emitting at
different wavelengths. The photocathode is illuminated with the various LEDs
and, for each wavelength of the incident light, the output anode current is
measured as a function of the retarding potential applied between the cathode
and the first dynode. From each measurement, a value of the stopping potential
for the anode current is derived. Finally, the stopping potentials are plotted
as a function of the frequency of the incident light, and a linear fit is
performed. The slope and the intercept of the line allow respectively to
evaluate the ratio h/e and the ratio W/e, where W is the work function of the
photocathode.Comment: 14 pages, 4 figure
Agnostic cosmology in the CAMEL framework
Cosmological parameter estimation is traditionally performed in the Bayesian
context. By adopting an "agnostic" statistical point of view, we show the
interest of confronting the Bayesian results to a frequentist approach based on
profile-likelihoods. To this purpose, we have developed the Cosmological
Analysis with a Minuit Exploration of the Likelihood ("CAMEL") software.
Written from scratch in pure C++, emphasis was put in building a clean and
carefully-designed project where new data and/or cosmological computations can
be easily included.
CAMEL incorporates the latest cosmological likelihoods and gives access from
the very same input file to several estimation methods: (i) A high quality
Maximum Likelihood Estimate (a.k.a "best fit") using MINUIT ; (ii) profile
likelihoods, (iii) a new implementation of an Adaptive Metropolis MCMC
algorithm that relieves the burden of reconstructing the proposal distribution.
We present here those various statistical techniques and roll out a full
use-case that can then used as a tutorial. We revisit the CDM
parameters determination with the latest Planck data and give results with both
methodologies. Furthermore, by comparing the Bayesian and frequentist
approaches, we discuss a "likelihood volume effect" that affects the optical
reionization depth when analyzing the high multipoles part of the Planck data.
The software, used in several Planck data analyzes, is available from
http://camel.in2p3.fr. Using it does not require advanced C++ skills.Comment: Typeset in Authorea. Online version available at:
https://www.authorea.com/users/90225/articles/104431/_show_articl
Optical emission investigation of laser-produced MgB2 plume expanding in an Ar buffer gas
Optical emission spectroscopy is used to study the dynamics of the plasma
generated by pulsed-laser irradiation of a MgB2 target, both in vacuum and at
different Ar buffer gas pressures. The analysis of the time-resolved emission
of selected species shows that the Ar background gas strongly influences the
plasma dynamics. Above a fixed pressure, plasma propagation into Ar leads to
the formation of blast waves causing both a considerable increase of the
fraction of excited Mg atoms and a simultaneous reduction of their kinetic flux
energy. These results can be particularly useful for optimizing MgB2 thin film
deposition processes.Comment: 11 pages,4 figures, Applied Physics Letters in pres
Relieving tensions related to the lensing of CMB temperature power spectra
The angular power spectra of the cosmic microwave background (CMB)
temperature anisotropies reconstructed from Planck data seem to present too
much gravitational lensing distortion. This is quantified by the control
parameter that should be compatible with unity for a standard cosmology.
With the Class Boltzmann solver and the profile-likelihood method, for this
parameter we measure a 2.6 shift from 1 using the Planck public
likelihoods. We show that, owing to strong correlations with the reionization
optical depth and the primordial perturbation amplitude , a
tension on also appears between the results obtained with
the low () and high () multipoles
likelihoods. With Hillipop, another high- likelihood built from Planck
data, this difference is lowered to . In this case, the value
is still in disagreement with unity by , suggesting a non-trivial
effect of the correlations between cosmological and nuisance parameters. To
better constrain the nuisance foregrounds parameters, we include the very high
measurements of the Atacama Cosmology Telescope (ACT) and South Pole
Telescope (SPT) experiments and obtain . The
Hillipop+ACT+SPT likelihood estimate of the optical depth is
which is now fully compatible with the low
likelihood determination. After showing the robustness of our results with
various combinations, we investigate the reasons for this improvement that
results from a better determination of the whole set of foregrounds parameters.
We finally provide estimates of the CDM parameters with our combined
CMB data likelihood.Comment: accepted by A&
Testicular endocrine activity is upregulated by D-Aspartic acid in the green frog Rana esculenta
This study investigated the involvement of D-aspartic acid (D-Asp) in testicular steroidogenesis of the green frog Rana esculenta and its effect on stimulation of thumb pad morphology and glandular activity, a typical testosterone-dependent secondary sexual characteristic in this amphibian species. In the testis, D-Asp concentrations vary significantly during the reproductive cycle: they are low in pre- and post-reproductive periods, but reach peak levels in the reproductive period (140-236 nmol/g wet tissue). Moreover, the concentrations of D-Asp in the testis through the sexual cycle positively match the testosterone levels in the gonad and the plasma. The racemase activity evaluated during the cycle expresses its peak when D-Asp and testosterone levels are highest, that is, during the reproductive period, confirming the synthesis of D-Asp from L-Asp by an aspartate racemase. Short-term in vivo experiments consisting of a single injection of D-Asp (2.0 micro mol/g body weight) demonstrated that this amino acid accumulates significantly in the testis, and after 3 h its uptake is coupled with a testosterone increase in both testis and plasma. Moreover, within 18 h of amino acid administration, the D-Asp concentration in the testis decreased along with the testosterone titer to prestimulation levels. Other amino acids (L-Asp, D-Glu and L-Glu) used instead of D-Asp were ineffective, confirming that the significant increase in testicular testosterone was a specific feature of this amino acid. In long-term experiments, D-Asp had been administered chronically to frogs caught during the three phases of the reproductive cycle, inducing testosterone increase and 17beta-estradiol decrease in the gonad during the pre- and post-reproductive period, and vice versa during the reproductive period
Stress in Context: Morpho-Syntactic Properties Affect Lexical Stress Assignment in Reading Aloud
Recent findings from English and Russian have shown that grammatical category plays a key role in stress assignment. In these languages, some grammatical categories have a typical stress pattern and this information is used by readers. However, whether readers are sensitive to smaller distributional differences and other morpho-syntactic properties (e.g., gender, number, person) remains unclear. We addressed this issue in word and non-word reading in Italian, a language in which: (1) nouns and verbs differ in the proportion of words with a dominant stress pattern; (2) information specified by words sharing morpho-syntactic properties may contrast with other sources of information, such as stress neighborhood. Both aspects were addressed in two experiments in which context words were used to induce the desired morpho-syntactic properties. Experiment 1 showed that the relatively different proportions of stress patterns between grammatical categories do not affect stress processing in word reading. In contrast, Experiment 2 showed that information specified by words sharing morpho-syntactic properties outweighs stress neighborhood in non-word reading. Thus, while general information specified by grammatical categories may not be used by Italian readers, stress neighbors with morpho-syntactic properties congruent with those of the target stimulus have a primary role in stress assignment. These results underscore the importance of expanding investigations of stress assignment beyond single words, as current models of single-word reading seem unable to account for our results
A meta-learning approach for training explainable graph neural networks
In this article, we investigate the degree of explainability of graph neural networks (GNNs). The existing explainers work by finding global/local subgraphs to explain a prediction, but they are applied after a GNN has already been trained. Here, we propose a meta-explainer for improving the level of explainability of a GNN directly at training time, by steering the optimization procedure toward minima that allow post hoc explainers to achieve better results, without sacrificing the overall accuracy of GNN. Our framework (called MATE, MetA-Train to Explain) jointly trains a model to solve the original task, e.g., node classification, and to provide easily processable outputs for downstream algorithms that explain the model's decisions in a human-friendly way. In particular, we meta-train the model's parameters to quickly minimize the error of an instance-level GNNExplainer trained on-the-fly on randomly sampled nodes. The final internal representation relies on a set of features that can be ``better'' understood by an explanation algorithm, e.g., another instance of GNNExplainer. Our model-agnostic approach can improve the explanations produced for different GNN architectures and use any instance-based explainer to drive this process. Experiments on synthetic and real-world datasets for node and graph classification show that we can produce models that are consistently easier to explain by different algorithms. Furthermore, this increase in explainability comes at no cost to the accuracy of the model
Identification of GABA receptor genes and evidence of GABA signaling during embryogenesis of the sea urchin
Gamma-aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the
mammalian central nervous system and acts via ionotropic (GABAA-Rs) and metabotropic
(GABAB-Rs) receptors. GABAA-Rs are Cl- selective hetero-pentameric channels assembled by
combinations of 19 distinct gene products. Instead, GABAB-Rs are bi-subunit G-protein coupled
receptors linked to K+ or Ca2+ channels. Dysfunctions of GABA-signaling (GS) cause psychotic
disorders and correlate with epigenetic alterations, such as over-expression of DNA methyl
transferase-1 which in turn imposes iper-methylation of GABA-regulated genes. The sea urchin
embryo, which presents a rudimentary nervous system, offers a big opportunity to study the GS
and its potential epigenetic implications in a simple eukaryote model. To this purpose, we
performed a comprehensive in silico analysis of the sea urchin genome and identified a 450 Kb
long cluster containing two genes encoding for the GABAB-R subunits, and two genes
respectively encoding for a \u3b1/\u3b3/\u3b5-type and a \u3b2/\u3c1/\u3b4/\u3c4/\u3c0-type GABA
B
A-R subunit. From an
evolutionary perspective, this result revealed a unique genomic organization of these genes in
sea urchin. Next, to preliminarily evaluate the role of GS during development, Paracentrotus
lividus embryos were cultured in the presence of GABA at concentrations ranging from 0.01 to
1.0 mM. Compared to controls, treated embryos showed aberrations in axial patterning, with a
dose-dependent effect. In particular, at 48 hours post-fertilization control embryos were normal
bilateral symmetric plutei whereas GABA-treated embryos displayed a radial organization with
supranumerary spicules. Washout experiments allowed to determine that the period of
sensitivity is restricted from the blastula to the gastrula stage. Altogether, these results suggest
that dysregulation of GS affects the polarization of the ectoderm. Although preliminary, this
study provide the first evidence of GS activity during development of echinoderms
Optical Absorption and Scattering Phenomena in 'Jubileum' Plums in Relation to Their Colour Properties
Absorption and scattering of laser light pulse passing through the fruit determine among others, the optical properties of the product. Efforts have been made in the recent past to utilize innovative techniques such as time-resolved reflectance spectroscopy (TRS) to study the quality aspects of different fruit such as nectarines. These optical properties have been well related to firmness, sugars, acids and other quality attributes. TRS measurements were performed on âJubileumâ plums at two different wavelengths: 670 nm and 758 nm. The fruit were harvested in Norway and brought to Italy under protected conditions. After sorting the fruit by size, TRS measurements were made and the fruit were randomized for different examinations of quality aspects. It was observed that the absorption coefficient (”a) increased for both wavelengths as ripening progressed towards the melting stage of the fruit. The ”a values at 670 nm were higher than those at 758 nm. The higher rate in the ”a was distinguishable from the third day onwards as the fruit ripened. Similarly, it was interesting to note that the internal colour measured after destructing the fruit related well with the TRS absorption coefficient (”a), i.e., a decrease in the CIE L* (towards darker region) and b* (towards blue) value along with an increase in a* (towards red) from third day of storag
- âŠ