313 research outputs found
Very fast formation of superconducting MgB2/Fe wires with high Jc
In this paper we have investigated the effects of sintering time and
temperature on the formation and critical current densities of Fe-clad MgB2
wires. MgB2 wires were fabricated using the powder-in-tube process and sintered
for different periods of time at predetermined temperatures. All the samples
were examined using XRD, SEM and magnetisation measurements. In contrast to the
common practice of sintering for several hours, the present results show that
there is no need for prolonged heat treatment in the fabrication of Fe-clad
MgB2 wires. A total time in the furnace of several minutes is more than enough
to form nearly pure MgB2 with high performance characteristics. The results
from Tc, Jc and Hirr show convincingly that the samples which were sintered for
3 minutes above 800 oC are as good as those sintered for longer times. In fact,
the Jc field performance for the most rapidly sintered sample is slightly
better than for all other samples. Jc of 4.5 times 10 ^5 A/cm2 in zero field
and above 10 ^5 A/cm2 in 2T at 15 K has been achieved for the best Fe-clad MgB2
wires. As a result of such a short sintering there is no need for using high
purity argon protection and it is possible to carry out the heat treatment in a
much less protective atmosphere or in air. These findings substantially
simplify the fabrication process, making it possible to have a continuous
process for fabrication and reducing the costs for large-scale production of
MgB2 wires.Comment: 15 pages, one table, 9 figures, submitted to Physica C on June 8,
200
Experimental Investigation on the Tensile Strength of Composite Laminates Containing Open and Filled Holes
An experimental study is performed to evaluate
the effects of clamping pressure, friction, and
washer size on the static performance of composite
laminates with open and bolt-filled holes.
The static tensile strength and failure behavior
of composite laminates with an open hole and a
bolt-filled hole are analyzed and compared. Experimental
results show that the static tensile
strength of composite laminates is sensitive to
pre-existing damage of both open- or filled-hole
laminates. In contrast, a comparison between
the experimental results of open- and filled-hole
specimens proved that whether the hole is open
or filled has a feeble influence on the tensile-tensile
fatigue strength of studied composite laminates.
In comparison, however, it is found that
the inserted washer size, bolt clamping force,
and friction force strongly affect the tensile
strength of open- and filled-hole composite laminates.
Moreover, application of thicker washers
and hi-lock bolt will significantly increase
the static strength and fatigue life of composite
laminates with a bolt-filled hole.Экспериментально оценено влияние силы зажима, трения и размера шайбы на статические
характеристики слоистых композитов со сквозными и болтовыми отверстиями. Проведено
сравнение статического предела прочности при растяжении и характера разрушения слоистых композитов со сквозным и болтовым отверстиями. Результаты экспериментальных
исследований показали, что на статический предел прочности при растяжении слоистых
композитов влияет изначальное повреждение независимо от наличия сквозного или болтового
отверстия. Сравнительный анализ результатов исследований образцов со сквозным и болтовым отверстиями подтвердил тот факт, что вид отверстия (сквозное или болтовое)
незначительно влияет на усталостную прочность при растяжении исследуемых слоистых
композитов. Установлено, что такие факторы, как размер шайбы, сила зажима болта и
сила трения, существенно влияют на предел прочности при растяжении слоистых композитов со сквозным или болтовым отверстием. Использование утолщенных шайб между
слоистым материалом и болтом-заклепкой значительно увеличивает статическую прочность и долговечность слоистых композитов с болтовыми отверстиями.Експериментально досліджено вплив сили затиску, тертя і розміру шайби на статичні
характеристики шаруватих композитів із наскрізними і болтовими отворами. Проведено порівняння статичної границі міцності при розтязі і характера руйнування
шаруватих композитів із наскрізними і болтовими отворами. Результати експериментальних досліджень показали, що на статичну границю міцності при розтязі
шаруватих композитів впливає початкове пошкодження незалежно від наявності
наскрізного чи болтового отвору. Порівняльний аналіз результатів досліджень зразків із наскрізними і болтовими отворами підтвердив той факт, що вид отвору
(наскрізне чи болтове) незначно впливає на міцність від утомленості при розтязі
досліджуваних шаруватих композитів. Установлено, що такі чинники, як розмір
шайби, сила затиску болта і сила тертя, суттєво впливають на границю міцності при
розтязі шаруватих композитів із наскрізним чи болтовим отвором. Використання
стовщених шайб між шаруватим матеріалом і болтом-заклепкою значно збільшує
статичну міцність і довговічність шаруватих композитів із болтовими отворам
Significant enhancement of flux pinning in MgB2 superconductor through nano-Si addition
Polycrystalline MgB2 samples with 10 wt % silicon powder addition were
prepared by an in-situ reaction process. Two different Si powders, one with
coarse (44 mm) and the other with nano-size (<100 nm) particles were used for
making samples. The phases, microstructures, and flux pinning were
characterized by XRD, TEM, and magnetic measurements. It was observed that the
samples doped with nano-sized Si powder showed a significantly improved field
dependence of the critical current over a wide temperature range compared with
both undoped samples and samples with coarse Si added. Jc is as high as 3000
A/cm2 in 8 T at 5 K, one order of magnitude higher than for the undoped MgB2.
X-ray diffraction results indicated that Si had reacted with Mg to form Mg2Si.
Nano-particle inclusions and substitution, both observed by transmission
electron microscopy, are proposed to be responsible for the enhancement of flux
pinning in high fields. However, the samples made with the coarse Si powders
had a poorer pinning than the undoped MgB2.Comment: 3 pages, 6 figure
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 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
Measurement of branching fractions for the inclusive Cabibbo-favored ~K*0(892) and Cabibbo-suppressed K*0(892) decays of neutral and charged D mesons
The branching fractions for the inclusive Cabibbo-favored ~K*0 and
Cabibbo-suppressed K*0 decays of D mesons are measured based on a data sample
of 33 pb-1 collected at and around the center-of-mass energy of 3.773 GeV with
the BES-II detector at the BEPC collider. The branching fractions for the
decays D+(0) -> ~K*0(892)X and D0 -> K*0(892)X are determined to be BF(D0 ->
\~K*0X) = (8.7 +/- 4.0 +/- 1.2)%, BF(D+ -> ~K*0X) = (23.2 +/- 4.5 +/- 3.0)% and
BF(D0 -> K*0X) = (2.8 +/- 1.2 +/- 0.4)%. An upper limit on the branching
fraction at 90% C.L. for the decay D+ -> K*0(892)X is set to be BF(D+ -> K*0X)
< 6.6%
Study of
New data are presented on from a sample of 58M
events in the upgraded BES II detector at the BEPC. There is a
conspicuous signal for and a peak at higher mass which
may be fitted with . From a combined analysis with
data, the branching ratio
is at the 95%
confidence level.Comment: 11 pages, 5 figures. Submitted to Phys. Lett.
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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