371 research outputs found
Spectroscopic characterization of 1.3µm GaInNAs quantum-well structures grown by metal-organic vapor phase epitaxy
We report optical studies of high-quality 1.3 μm strain-compensated GaInNAs/GaAs single-quantum-well structures grown by metalorganic vapor phase epitaxy. Photoluminescence excitation (PLE) spectroscopy shows clearly the electronic structure of the two-dimensional quantum well. The transition energies between quantized states of the electrons and holes are in agreement with theoretical calculations based on the band anti-crossing model in which the localized N states interact with the extended states in the conduction band. We also investigated the polarization properties of the luminescence by polarized edge-emission measurements. Luminescence bands with different polarization characters arising from the electron to heavy-hole and light-hole transitions, respectively, have been identified and verify the transition assignment observed in the PLE spectrum
Measurement of Ultra-Low Potassium Contaminations with Accelerator Mass Spectrometry
Levels of trace radiopurity in active detector materials is a subject of
major concern in low-background experiments. Among the radio-isotopes, \k40
is one of the most abundant and yet whose signatures are difficult to reject.
Procedures were devised to measure trace potassium concentrations in the
inorganic salt CsI as well as in organic liquid scintillator (LS) with
Accelerator Mass Spectrometry (AMS), giving, respectively, the
\k40-contamination levels of and g/g.
Measurement flexibilities and sensitivities are improved over conventional
methods. The projected limiting sensitivities if no excess of potassium signals
had been observed over background are g/g and g/g for the CsI and LS, respectively. Studies of the LS samples
indicate that the radioactive contaminations come mainly in the dye solutes,
while the base solvents are orders of magnitude cleaner. The work demonstrate
the possibilities of measuring naturally-occurring isotopes with the AMS
techniques.Comment: 18 pages, 4 figures, 3 table
Effect of the SiC Particle Orientation Anisotropy on the Tensile Properties of a Spray-Formed SiCp/Al-Si Composite
The effects of the SiC particle orientation anisotropy
on the tensile properties of spray-formed
SiCp/Al-Si composites was investigated and
compared with that of the unreinforced matrix alloy.
The addition of SiC particles increased the
elastic modulus but decreased ultimate tensile
strength and elongation of an Al–Si alloy under
peak-aged conditions. Microstructure disolayed a
preferred orientation of the reinforcement particles,
which were inclined to align parallel to the
extrusion axis. Meanwhile, the degree of orientation
anisotropy turned to be higher with larger reinforcement
sizes particle. The elastic modulus,
tensile strength and elongation in the longitudinal
orientation (parallel to the extrusion axis) were
higher than those in the transverse orientation
(perpendicular to the extrusion axis). The fracture
mechanism in a composite with 4.5 m particles
was attributed to interfacial debonding
between SiC and matrix in the two orientations.
However, in case of aluminum reinforced wild
20 m particles, both cracking of SiC particles in
the longitudinal orientation and the interfacial
debonding in the transverse orientation played an
important role in fracture.Исследовано влияние анизотропии, определяемой ориентацией SiC частиц, на механические
свойства при растяжении SiCp/Al-Si композита, полученного методом напыления. Результаты
исследования SiCp/Al-Si композита сопоставлены с таковыми сплава с неупрочненной матрицей. При растяжении Аl-Si сплава в условиях максимального старения благодаря введению SiC
частиц модуль упругости увеличивается, а предел прочности и удлинение уменьшаются. При
определении характеристик микроструктуры было установлено, что упрочняющие частицы
преимущественно ориентированы в направлении, параллельном оси экструзии. При значительном упрочнении степень анизотропии, определяемой ориентацией частиц, более высокая.
Значения модуля упругости, предела прочности и удлинения при растяжении в продольном
направлении (параллельно оси экструзии) оказываются выше, чем в поперечном (перпендикулярно оси экструзии). Признаком механизма разрушения композита с частицами размером
4,5 мкм полагают граничное разделение между SiC частицами и матрицей в двух направлениях. В случае упрочненного алюминия с частицами размером 20 мкм растрескивание SiC
частиц в продольном направлении и граничное разделение в поперечном направлении играют
важную роль в процессе разрушения.Досліджено вплив анізотропії, що визначається орієнтацією SiC частинок, на механічні властивості при розтязі SiCp/Al-Si композита, отриманого методом напилення.
Результати дослідження SiCp/Al-Si композита зіставляли з такими сплава, що має
незміцнювану матрицю. При розтязі Al-Si сплаву в умовах максимального старіння
завдяки введенно SiC частинок модуль пружності збільшується, а границя міцності і
подовження зменшуються. Визначення характеристик мікроструктури показало, що
зміцнювані частинки переважно орієнтовані у напрямку, паралельному осі екструзії.
При значному зміцненні ступінь анізотропії, що визначається орієнтацією частинок,
значно вища. Значення модуля пружності, границі міцності і подовження при розтязі
в поздовжньому напрямку (паралельно осі екструзії) більші, аніж у поперечному
(перпендикулярно до осі екструзії). Ознакою механізму руйнування композита з
частинками розміром 4,5 мкм вважають граничний розподіл між SiC частинками і
матрицею у двох напрямках. У випадку зміцненого алюмінію з частинками розміром
20 мкм розтріскування SiC частинок у поздовжньому напрямку і граничний розподіл
у поперечному напрямку відіграють важливу роль у процесі руйнування
Measurement of Trace I-129 Concentrations in CsI Powder and Organic Liquid Scintillator with Accelerator Mass Spectrometry
Levels of trace radiopurity in active detector materials is a subject of
major concern in low-background experiments. Procedures were devised to measure
trace concentrations of I-129 in the inorganic salt CsI as well as in organic
liquid scintillator with Accelerator Mass Spectrometry (AMS) which leads to
improvement in sensitivities by several orders of magnitude over other methods.
No evidence of their existence in these materials were observed. Limits of < 6
X 10^{-13} g/g and < 2.6 X 10^{-17} g/g on the contaminations of I-129 in CsI
and liquid scintillator, respectively, were derived.These are the first results
in a research program whose goals are to develop techniques to measure trace
radioactivity in detector materials by AMS.Comment: Proceedings of 10th International Conference on Accelerator Mass
Spectrometr
Effects of Long-term Exposure on E-glass Composite Material Subjected to Stress Corrosion in a Saline Medium
[EN] This work provides an insight on very long-term degradation of polyester-fiber glass composites immersed more than 30,000 h in saline medium under service stresses. Samples were loaded under bending conditions with stresses both in the elastic and plastic fields, with the result that characteristics in a flexural mode were able to be determined and the ensuing decrease in characteristics was fitted to an exponential model. The degree of losses ranged from 25 to 31% for the bending modulus, from 28 to 35% for the flexural strength, and from 40 to 51% for the specific fracture energy. The most notable losses were for specimens immersed in artificial sea water under a continuous stress of 140 MPa, corresponding to the plastic behavior of the material. Although the existence of matrix plasticization is doubtful, the osmotic effects of the diffusion on the matrix and the junction to the fibers, the presence of microcracks, and the effects of chemical ions in the medium on the surface fiber composition became evident in the strength degradation of the material.Segovia López, EF.; Salvador Moya, MD.; Sahuquillo Navarro, O.; Vicente Escuder, Á. (2007). Effects of Long-term Exposure on E-glass Composite Material Subjected to Stress Corrosion in a Saline Medium. Journal of Composite Materials. 41(17):2119-2128. doi:10.1177/0021998307074134S21192128411
Direct Measurements of the Branching Fractions for and and Determinations of the Form Factors and
The absolute branching fractions for the decays and
are determined using singly
tagged sample from the data collected around 3.773 GeV with the
BES-II detector at the BEPC. In the system recoiling against the singly tagged
meson, events for and events for decays are observed. Those yield
the absolute branching fractions to be and . The
vector form factors are determined to be
and . The ratio of the two form
factors is measured to be .Comment: 6 pages, 5 figure
Measurements of the Mass and Full-Width of the Meson
In a sample of 58 million events collected with the BES II detector,
the process J/ is observed in five different decay
channels: , , (with ), (with
) and . From a combined fit of all five
channels, we determine the mass and full-width of to be
MeV/ and
MeV/.Comment: 9 pages, 2 figures and 4 table. Submitted to Phys. Lett.
The pole in
Using a sample of 58 million events recorded in the BESII detector,
the decay is studied. There are conspicuous
and signals. At low mass, a large
broad peak due to the is observed, and its pole position is determined
to be - MeV from the mean of six analyses.
The errors are dominated by the systematic errors.Comment: 15 pages, 6 figures, submitted to PL
Search for the Lepton Flavor Violation Processes and
The lepton flavor violation processes and are
searched for using a sample of 5.8 events collected with
the BESII detector. Zero and one candidate events, consistent with the
estimated background, are observed in and
decays, respectively. Upper limits on the branching ratios are determined to be
and at the 90% confidence level (C.L.).Comment: 9 pages, 2 figure
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