152 research outputs found
Broadband NIR-emitting Te cluster-doped glass for smart light source towards night-vision and NIR spectroscopy applications
Broadband near-infrared (NIR)-emitting materials are crucial components of the next generation of smart NIR light sources based on blue light-emitting diodes (LEDs). Here, we report a Te cluster-doped borate glass, which exhibits ultra-broadband emission around 980 nm with a full-width at half-maximum (FWHM) of 306 nm under blue light excitation. We propose adjustments of glass chemistry and processing condition as a means for topo-chemical tailoring of the NIR photoemission characteristics in such materials. Through implementing strongly reducing conditions during glass melting, Te clusters with broad NIR photoluminescence can be generated and stabilized once the melt is vitrified to the glassy state. Tunability of the NIR emission peak over the wavelength range of 904 to 1026 nm is possible in this way, allowing for fine adjustments of spectral properties relative to the stretching vibrations of common chemical bonds, for example, in water, proteins, and fats. This potentially enables high sensitivity in NIR spectroscopy. We further demonstrate potential application of glass-converted LEDs in night vision.</p
Determination of oxygen stoichiometry in the mixed-valent manganites
The possible redox (oxidation reduction) chemical methods for precisely
determining the oxygen content in the perovskite manganites including
hole-doped La1-xCaxMnOy and electron-doped La1-xTexMnOy compounds are
described. For manganites annealed at different temperatures, the oxygen
content of the samples was determined by a redox back titration in which the
powder samples taken in a quartz crucible were dissolved in (1+1) sulfuric acid
containing an excess of sodium oxalate, and the excess sodium oxalate was
titrated with permanganate standard solution. The results indicate that the
method is effective and highly reproducible. Moreover, the variation of oxygen
content is also reflected in significantly affecting the electrical transport
property of the samples, which is mainly considered to be closely related to
introduce oxygen vacancies in the Mn-O-Mn network.Comment: 13 pages, 1 figure. J. Magn. Magn .Mater (accepted
Parallelization of a DEM/CFD code for the numerical simulation of particle-laden turbulent flows
The interaction between a turbulent fluid flow and particle motion is investigated
numerically. A complete direct numerical simulation (DNS) is carried out to solve the governing equations of the fluid phase, to investigate the behavior of inter-particle collision and its effects on particle dispersion, the discrete element method (DEM) is employed to calculate the particle motion.The parallelization strategy of the DNS part is based on a domain decomposition method and uses a hybrid MPI+OpenMP approach. On the other hand, the OpenMP is used for the parallelization of DEM: the total number of particles to be tracked are equally distributed among processors. Finally, the method is tested for a turbulent flow through a square duct.Peer ReviewedPostprint (author’s final draft
The effect of grain size on electrical transport and magnetic properties of La0.9Te0.1MnO3
The effect of grain size on structural, magnetic and transport properties in
electron-doped manganites La0.9Te0.1MnO3 has been investigated. All samples
show a rhombohedral structure with the space group at room temperature. It
shows that the Mn-O-Mn bond angle decreases and the Mn-O bond length increases
with the increase of grain size. All samples undergo paramagnetic
(PM)-ferromagnetic (FM) phase transition and an interesting phenomenon that
both magnetization and the Curie temperature decrease with increasing grain
size is observed, which is suggested to mainly originate from the increase of
the Mn-O bond length . Additionally, obviously increases with decreasing grain
size due to the increase of both the height and width of tunneling barriers
with decreasing the grain size. The results indicate that both the intrinsic
colossal magnetoresistance (CMR) and the extrinsic the extrinsic interfacial
magnetoresistance (IMR) can be effectively tuned in La0.9Te0.1MnO3 by changing
grain size.Comment: 15 pages,4 figures. Solid state communications 132(2004)83-8
The effect of oxygen stoichiometry on electrical transport and magnetic properties of La0.9Te0.1MnOy
The effect of the variation of oxygen content on structural, magnetic and
transport properties in the electron-doped manganites La0.9Te0.1MnOy has been
investigated. All samples show a rhombohedral structure with the space group .
The Curie temperature decreases and the paramagnetic-ferromagnetic (PM-FM)
transition becomes broader with the reduction of oxygen content. The
resistivity of the annealed samples increases slightly with a small reduction
of oxygen content. Further reduction in the oxygen content, the resistivity
maximum increases by six orders of magnitude compared with that of the
as-prepared sample, and the r(T) curves of samples with y = 2.86 and y = 2.83
display the semiconducting behavior () in both high-temperature PM phase and
low-temperature FM phase, which is considered to be related to the appearance
of superexchange ferromagnetism (SFM) and the localization of carriers. The
results are discussed in terms of the combined effects of the increase in the
Mn2+/(Mn2++Mn3+) ratio, the partial destruction of double exchange (DE)
interaction, and the localization of carriers due to the introduction of oxygen
vacancies in the Mn-O-Mn network.Comment: 20 pages, 8 figure
The ARGO-YBJ Experiment Progresses and Future Extension
Gamma ray source detection above 30TeV is an encouraging approach for finding
galactic cosmic ray origins. All sky survey for gamma ray sources using wide
field of view detector is essential for population accumulation for various
types of sources above 100GeV. To target the goals, the ARGO-YBJ experiment has
been established. Significant progresses have been made in the experiment. A
large air shower detector array in an area of 1km2 is proposed to boost the
sensitivity. Hybrid detection with multi-techniques will allow a good
discrimination between different types of primary particles, including photons
and protons, thus enable an energy spectrum measurement for individual specie.
Fluorescence light detector array will extend the spectrum measurement above
100PeV where the second knee is located. An energy scale determined by balloon
experiments at 10TeV will be propagated to ultra high energy cosmic ray
experiments
Search for the Rare Decays J/Psi --> Ds- e+ nu_e, J/Psi --> D- e+ nu_e, and J/Psi --> D0bar e+ e-
We report on a search for the decays J/Psi --> Ds- e+ nu_e + c.c., J/Psi -->
D- e+ nu_e + c.c., and J/Psi --> D0bar e+ e- + c.c. in a sample of 5.8 * 10^7
J/Psi events collected with the BESII detector at the BEPC. No excess of signal
above background is observed, and 90% confidence level upper limits on the
branching fractions are set: B(J/Psi --> Ds- e+ nu_e + c.c.)<4.8*10^-5, B(J/Psi
--> D- e+ nu_e + c.c.) D0bar e+ e- + c.c.)<1.1*10^-5Comment: 10 pages, 4 figure
Study of J/psi decays to Lambda Lambdabar and Sigma0 Sigma0bar
The branching ratios and Angular distributions for J/psi decays to Lambda
Lambdabar and Sigma0 Sigma0bar are measured using BESII 58 million J/psi.Comment: 11 pages, 5 figure
ARGO-YBJ constraints on very high energy emission from GRBs
The ARGO-YBJ (Astrophysical Radiation Ground-based Observatory at YangBaJing)
experiment is designed for very high energy -astronomy and cosmic ray
researches. Due to the full coverage of a large area () with
resistive plate chambers at a very high altitude (4300 m a.s.l.), the ARGO-YBJ
detector is used to search for transient phenomena, such as Gamma-ray bursts
(GRBs). Because the ARGO-YBJ detector has a large field of view (2 sr)
and is operated with a high duty cycle (90%), it is well suited for GRB
surveying and can be operated in searches for high energy GRBs following alarms
set by satellite-borne observations at lower energies. In this paper, the
sensitivity of the ARGO-YBJ detector for GRB detection is estimated. Upper
limits to fluence with 99% confidence level for 26 GRBs inside the field of
view from June 2006 to January 2009 are set in the two energy ranges 10100
GeV and 10 GeV1 TeV.Comment: accepted for publication in Astroparticle Physic
Measurement of \chi_cJ--> K+K-K+K-
Using 14M psi(2S) events taken with the BES-II detector, chi_cJ-->K+K-K+K-
decays are studied. For the four-kaon final state, the branching fractions are
B(chi_c0,1,2 -->K+K-K+K-)=(3.48\pm 0.23\pm 0.47)\times 10^{-3}, (0.70\pm
0.13\pm 0.10)\times 10^{-3}, and (2.17\pm 0.20\pm 0.31)\times 10^{-3}. For the
\phi K+K- final state, the branching fractions, which are measured for the
first time, are B(chi_c0,1,2-->\phi K+K-)=(1.03\pm 0.22\pm 0.15)\times 10^{-3},
(0.46\pm 0.16\pm 0.06)\times 10^{-3}, and (1.67\pm 0.26\pm 0.24)\times 10^{-4}.
For the \phi\phi final state, B(chi_{c0,2}-->\phi\phi)=(0.94\pm 0.21\pm
0.13)\times 10^{-3} and (1.70\pm 0.30\pm 0.25)\times 10^{-3}.Comment: 7 pages, 7 figure
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