664 research outputs found
A tunable radiation source by coupling laser-plasma-generated electrons to a periodic structure
Near-infrared radiation around 1000 nm generated from the interaction of a high-density MeV electron beam, obtained by impinging an intense ultrashort laser pulse on a solid target, with a metal grating is observed experimentally. Theoretical modeling and particle-in-cell simulation suggest that the radiation is caused by the Smith-Purcell mechanism. The results here indicate that tunable terahertz radiation with tens GV=m field strength can be achieved by using appropriate grating parameter
BTZ-copolymer loaded graphene aerogel as new type Green and metal-freevisible light photocatalyst
This paper reports a new class of efficient, green and metal-free visible-light photocatalyst made from graphene aerogel (GA) doped with a conjugated porous polymer (CMPs). Hence, we report the synthesis of a benzothiadiazole (BTZ)-based CMP loaded into GA via a one-step hydrothermal reaction between 2D graphene oxide (GO) and the CMP, performed through a green process and under mild conditions. The as-prepared GA showed a bathochromic shift in the UV–vis diffraction reflectance spectroscopy (DRS) absorption edge to 628.5 nm, demonstrating its ability to absorb light in the visible region. SEM, TEM, XPS, EDX mapping results further showed the successful loading of the BTZ-based CMP in the GA array. The synthesized GA was used as a 3D structured photocatalyst for the visible-light-driven photodecomposition of methyl orange (MO) with an efficiency of 89.2% (5 wt% CMP). When compared to that of the pure CMP (86.9%), a comparable yet small increase in the efficiency was observed. This is due to a synergistic effect between GO and loaded polymer in GA array upon the formation of CMPGA hybrid structure via chemical interaction between BTZ-Py and GO throughout the mild hydrothermal reaction, and the enhanced photocatalytic activity exhibited from 1 mg equivalent polymer in the CMPGA2 hybrid when compared to the 20 mg pure polymer. Upon repeated use, the depreciation in photocatalytic activity was low with a <5% drop over 3 cycles. These results showed the CMP-loaded GA as an efficient metal-free photocatalyst and a promising material for further investigation into other photocatalytic applications
Implicações das prioridades de gasto do estado sobre a dinâmica econômica brasileira
XX Encontro Nacional de Economia Política: desenvolvimento Latino-Americano, Integração e Inserção Internacional - UNILA, Foz do Iguaçu, 26 a 29 de maio de 2015A sociedade brasileira tem passado, nas últimas décadas, por
transformações importantes em seu contexto político e econômico. Este
artigo trata principalmente de dois fatos que ainda, atualmente, impactam
na dinâmica do gasto público. O processo de redemocratização, em
fi nais dos anos de 1980 e a globalização econômica com a consequente
fi nanceirização dos mercados. Estas transformações infl uenciam a
forma de atuação do Estado na economia, principalmente no que se
refere à defi nição de alocação de recursos públicos. Assim, este artigo
aprofunda o entendimento da evolução das despesas públicas na esfera
federal, pela análise dos gastos sociais bem como da dívida pública,
constatando os impactos econômicos destas despesas e levantando
conclusões sobre a viabilidade de determinados gastos governamentais
sob a dinâmica econômica e social do país. A realização deste estudo
contribui para o debate sobre as estratégias de política fi scal que vêm
sendo adotadas e o impacto de priorização de determinados gastos,
sobre o crescimento econômico do paísBanco Nacional de Desenvolvimento Econômico e Social (BNDES); Usina Hidrelétrica de Itaipu (ITAIPU); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) e Universidade Federal da Integração Latino-Americana (UNILA
A switchable pH-differential unitized regenerative fuel cell with high performance
Regenerative fuel cells are a potential candidate for future energy storage, but their applications are limited by the high cost and poor round-trip efficiency. Here we present a switchable pH-differential unitized regenerative fuel cell capable of addressing both the obstacles. Relying on a membraneless laminar flow-based design, pH environments in the cell are optimized independently for different electrode reactions and are switchable together with the cell process to ensure always favorable thermodynamics for each electrode reaction. Benefiting from the thermodynamic advantages of the switchable pH-differential arrangement, the cell allows water electrolysis at a voltage of 0.57 V, and a fuel cell open circuit voltage of 1.89 V, rendering round-trip efficiencies up to 74%. Under room conditions, operating the cell in fuel cell mode yields a power density of 1.3 W cm¯², which is the highest performance to date for laminar flow-based cells and is comparable to state-of-the-art polymer electrolyte membrane fuel cells
Structure Formation, Melting, and the Optical Properties of Gold/DNA Nanocomposites: Effects of Relaxation Time
We present a model for structure formation, melting, and optical properties
of gold/DNA nanocomposites. These composites consist of a collection of gold
nanoparticles (of radius 50 nm or less) which are bound together by links made
up of DNA strands. In our structural model, the nanocomposite forms from a
series of Monte Carlo steps, each involving reaction-limited cluster-cluster
aggregation (RLCA) followed by dehybridization of the DNA links. These links
form with a probability which depends on temperature and particle
radius . The final structure depends on the number of monomers (i. e. gold
nanoparticles) , , and the relaxation time. At low temperature, the
model results in an RLCA cluster. But after a long enough relaxation time, the
nanocomposite reduces to a compact, non-fractal cluster. We calculate the
optical properties of the resulting aggregates using the Discrete Dipole
Approximation. Despite the restructuring, the melting transition (as seen in
the extinction coefficient at wavelength 520 nm) remains sharp, and the melting
temperature increases with increasing as found in our previous
percolation model. However, restructuring increases the corresponding link
fraction at melting to a value well above the percolation threshold. Our
calculated extinction cross section agrees qualitatively with experiments on
gold/DNA composites. It also shows a characteristic ``rebound effect,''
resulting from incomplete relaxation, which has also been seen in some
experiments. We discuss briefly how our results relate to a possible sol-gel
transition in these aggregates.Comment: 12 pages, 10 figure
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
Measurements of the observed cross sections for exclusive light hadron production in e^+e^- annihilation at \sqrt{s}= 3.773 and 3.650 GeV
By analyzing the data sets of 17.3 pb taken at GeV
and 6.5 pb taken at GeV with the BESII detector at the
BEPC collider, we have measured the observed cross sections for 12 exclusive
light hadron final states produced in annihilation at the two energy
points. We have also set the upper limits on the observed cross sections and
the branching fractions for decay to these final states at 90%
C.L.Comment: 8 pages, 5 figur
Measurements of psi(2S) decays to octet baryon-antibaryon pairs
With a sample of 14 million psi(2S) events collected by the BESII detector at
the Beijing Electron Positron Collider (BEPC), the decay channels psi(2S)->p
p-bar, Lambda Lambda-bar, Sigma0 Sigma0-bar, Xi Xi-bar are measured, and their
branching ratios are determined to be (3.36+-0.09+-0.24)*10E-4,
(3.39+-0.20+-0.32)*10E-4, (2.35+-0.36+-0.32)*10E-4, (3.03+-0.40+-0.32)*10E-4,
respectively. In the decay psi(2S)->p p-bar, the angular distribution parameter
alpha is determined to be 0.82+-0.17+-0.04.Comment: 8 pages, 8 figure
Measurements of J/psi Decays into 2(pi+pi-)eta and 3(pi+pi-)eta
Based on a sample of 5.8X 10^7 J/psi events taken with the BESII detector,
the branching fractions of J/psi--> 2(pi+pi-)eta and J/psi-->3(pi+pi-)eta are
measured for the first time to be (2.26+-0.08+-0.27)X10^{-3} and
(7.24+-0.96+-1.11)X10^{-4}, respectively.Comment: 11 pages, 6 figure
BESII Detector Simulation
A Monte Carlo program based on Geant3 has been developed for BESII detector
simulation. The organization of the program is outlined, and the digitization
procedure for simulating the response of various sub-detectors is described.
Comparisons with data show that the performance of the program is generally
satisfactory.Comment: 17 pages, 14 figures, uses elsart.cls, to be submitted to NIM
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