20,859 research outputs found
A time of flight method to measure the speed of sound using a stereo sound card
We present an inexpensive apparatus for measuring the speed of sound, with a
time of flight method, using a computer with a stereo sound board. Students
measure the speed of sound by timing the delay between the arrivals of a pulse
to two microphones placed at different distances from the source. It can serve
as a very effective demonstration, providing a quick measurement of the speed
of sound in air; we have used it with great success in Open Days in our
Department. It can also be used for a full fledged laboratory determination of
the speed of sound in air.Comment: Accepted for publication in The Physics Teache
Produção de mudas de palma-forrageira utilizando fragmentos de cladódios.
A palma (Opuntia ficus-indica L.) é uma das principais alternativas para alimentação de caprinos, ovinos e bovinos no Semiárido brasileiro. Contudo, o ataque da cochonilhado-carmim (Dactylopius opuntiae Cockerel) erradicou grande parte da área plantada, já que a maioria das variedades cultivadas são suscetíveis à praga. Três novas variedades resistentes à praga foram identificadas: Orelha-de-elefante mexicana, Miúda ou Doce e a variedade Mão-de-moça (clones IPA-Sertânea e PALMEPA-PB1). Contudo, a disponibilidade de material propagativo (cladódios ou raquetes) ainda é baixa, aumentando o preço da palma-semente. Assim, desenvolveu-se uma metodologia utilizando-se fragmentos (pedaços) de raquetes para a obtenção de novas mudas
Non-parametric comparison of histogrammed two-dimensional data distributions using the Energy Test
When monitoring complex experiments, comparison is often made between regularly acquired histograms of data and reference histograms which represent the ideal state of the equipment. With the larger HEP experiments now ramping up, there is a need for automation of this task since the volume of comparisons could overwhelm human operators. However, the two-dimensional histogram comparison tools available in ROOT have been noted in the past to exhibit shortcomings. We discuss a newer comparison test for two-dimensional histograms, based on the Energy Test of Aslan and Zech, which provides more conclusive
discrimination between histograms of data coming from different distributions than methods provided in a recent ROOT release.The Science and Technology Facilities Council, U
GeMs/GSAOI observations of La Serena 94: an old and far open cluster inside the solar circle
Physical properties were derived for the candidate open cluster La Serena 94,
recently unveiled by the VVV collaboration. Thanks to the exquisite angular
resolution provided by GeMS/GSAOI, we could characterize this system in detail,
for the first time, with deep photometry in JHK - bands. Decontaminated
JHK diagrams reach about 5 mag below the cluster turnoff in H. The locus
of red clump giants in the colour - colour diagram, together with an extinction
law, was used to obtain an average extinction of . The
same stars were considered as standard - candles to derive the cluster
distance, kpc. Isochrones were matched to the cluster colour -
magnitude diagrams to determine its age, , and
metallicity, . A core radius of pc was
found by fitting King models to the radial density profile. By adding up the
visible stellar mass to an extrapolated mass function, the cluster mass was
estimated as M, consistent with an
integrated magnitude of and a tidal radius of
pc. The overall characteristics of La Serena 94 confirm that
it is an old open cluster located in the Crux spiral arm towards the fourth
Galactic quadrant and distant kpc from the Galactic centre. The
cluster distorted structure, mass segregation and age indicate that it is a
dynamically evolved stellar system.Comment: 16 pages, 24 figures, 2 Tables, accepted by MNRAS; corrected typo
Spatial patterns of mango malformation in irrigated areas of the brazilian semi-arid.
There are over 18.000 ha of irrigated mango in the São Francisco River Valley, and 90% of the fruit produced in this semi-arid region is exported to the european and american markets. With the expansion of the mango areas in the last decade, the intensity of malformation has been increasing, and there are many unresolved questions on the dynamics of the disease in the region, such as the role of the mango bud mite (Aceria mangiferae) or mechanical transmission in the dissemination of the disease. This study aimed to characterize the spatial patterns of mango malformation in commercial orchards, of the brazilian semi-arid
Ensaio comparativo avançado de arroz irrigado (várzea) em Belém, Pará - ano agrícola 1998/1999.
bitstream/item/52944/1/PesquisaAnd0180001.pd
Jaburu: cultivar de arroz lançada para o ecossistema de várzea no Estado do Pará.
bitstream/item/28011/1/com.tec.73.pd
BRS Biguá: cultivar de arroz para as várzeas do Estado do Pará.
bitstream/item/18743/1/com.tec.91.pdfDisponível também on-line
Spectrally narrow exciton luminescence from monolayer MoS2 exfoliated onto epitaxially grown hexagonal BN
The strong light-matter interaction in transition Metal dichalcogenides
(TMDs) monolayers (MLs) is governed by robust excitons. Important progress has
been made to control the dielectric environment surrounding the MLs, especially
through hexagonal boron nitride (hBN) encapsulation, which drastically reduces
the inhomogeneous contribution to the exciton linewidth. Most studies use
exfoliated hBN from high quality flakes grown under high pressure. In this
work, we show that hBN grown by molecular beam epitaxy (MBE) over a large
surface area substrate has a similarly positive impact on the optical emission
from TMD MLs. We deposit MoS and MoSe MLs on ultrathin hBN films (few
MLs thick) grown on Ni/MgO(111) by MBE. Then we cover them with exfoliated hBN
to finally obtain an encapsulated sample : exfoliated hBN/TMD ML/MBE hBN. We
observe an improved optical quality of our samples compared to TMD MLs
exfoliated directly on SiO substrates. Our results suggest that hBN grown
by MBE could be used as a flat and charge free substrate for fabricating
TMD-based heterostructures on a larger scale.Comment: 5 pages, 3 figure
- …