66,925 research outputs found
BES Recent Results and Future Plans
We report the preliminary R values for all the 85 energy points scanned in
the energy region of 2-5 GeV with the upgraded Beijing Spectrometer (BESII) at
Beijing Electron Positron Collider (BEPC). Preliminary results from the J/psi
data collected with both BESI and BESII are presented. Measurements of the
branching fraction of the psi(2S) decays and the psi(2S) resonance parameters
are reported. The future plans, i.e. significantly upgrade the machine and
detector are also discussed.Comment: Talk given at APPAC2000, 6 pages, 8 figure
Recent BES measurements and the hadronic contribution to the QED vacuum polarization
We have updated our evaluation of the hadronic contribution to the running of
the QED fine structure constant using the recent precise measurements of the
e+e- annihilation at the center-of-mass (c.m.s.) energy region between 2.6 and
3.65 GeV performed by the BES collaboration. In the low energy region, around
the rho resonance, we include the recent measurements from the BABAR, CDM-2,
KLOE and SND collaborations. We obtain Delta alpha (5)_had (s) = 0.02750 +/-
0.00033 at s = m_Z^2.Comment: 3 pages, 1 figur
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Comparison of wind turbine tower failure modes under seismic and wind loads
This paper studies the structural responses and failure modes of a 1.5-MW horizontal-axis wind turbine under strong ground motions and wind loading. Ground motions were selected and scaled to match the two design response spectra given by the seismic code, and wind loads were generated considering tropical cyclone scenarios. Nonlinear dynamic time-history analyses were conducted and structural performances under wind loads as well as short- and long-period ground motions compared. The results show that under strong wind loads the collapse of the wind turbine tower is driven by the formation of a plastic hinge at the lower section of the tower. This area is also critical when the tower is subject to most ground motions. However, some short-period earthquakes trigger the collapse of the middle and upper parts of the tower due to the increased contribution of high-order vibration modes. Although long-period ground motions tend to result in greater structural responses, short-period earthquakes may cause brittle failure modes in which the full plastic hinge develops quickly in regions of the tower with only a moderate energy dissipation capacity. Based on these results, recommendations for future turbine designs are proposed
Analytical considerations of flow boiling heat transfer in metal-foam filled tubes
Flow boiling in metal-foam filled tube was analytically investigated based on a modified microstructure model, an original boiling heat transfer model and fin analysis for metal foams. Microstructure model of metal foams was established, by which fiber diameter and surface area density were precisely predicted. The heat transfer model for flow boiling in metal foams was based on annular pattern, in which two phase fluid was composed by vapor region in the center of the tube and liquid region near the wall. However, it was assumed that nucleate boiling performed only in the liquid region. Fin analysis and heat transfer network for metal foams were integrated to obtain the convective heat transfer coefficient at interface. The analytical solution was verified by its good agreement with experimental data. The parametric study on heat transfer coefficient and boiling mechanism was also carried out
A Model for Abundances in Metal-Poor Stars
It is argued that the abundances of r-process related elements in stars with
-3<[Fe/H]<-1 can be explained by the contributions of three sources. The
sources are: the first generations of very massive (>100 solar masses) stars
that are formed from Big Bang debris and are distinct from SNII, and two types
of SNII, the H and L events, which can occur only at [Fe/H]>-3. The H events
are of high frequency and produce dominantly heavy (A>130) r-elements but no Fe
(presumably leaving behind black holes). The L events are of low frequency and
produce Fe and dominantly light (A<130) r-elements (essentially none above Ba).
By using the observed abundances in two ultra-metal-poor stars and the solar
r-abundances, the initial or prompt inventory of elements produced by the first
generations of very massive stars and the yields of H and L events can be
determined. The abundances of a large number of elements in a star can then be
calculated from the model by using only the observed Eu and Fe abundances. To
match the model results and the observational data for stars with -3<[Fe/H]<-1
requires that the solar r-abundances for Sr, Y, Zr, and Ba must be
significantly increased from the standard values. Whether the solar
r-components of these elements used here to obtain a fit to the stellar data
can be reconciled with those obtained from solar abundances by subtracting the
s-components calculated from models is not clear.Comment: 47 pages, 19 figures, to appear in Ap
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