30,673 research outputs found
Empowering a helper cluster through data-width aware instruction selection policies
Narrow values that can be represented by less number of bits than the full machine width occur very frequently in programs. On the other hand, clustering mechanisms enable cost- and performance-effective scaling of processor back-end features. Those attributes can be combined synergistically to design special clusters operating on narrow values (a.k.a. helper cluster), potentially providing performance benefits. We complement a 32-bit monolithic processor with a low-complexity 8-bit helper cluster. Then, in our main focus, we propose various ideas to select suitable instructions to execute in the data-width based clusters. We add data-width information as another instruction steering decision metric and introduce new data-width based selection algorithms which also consider dependency, inter-cluster communication and load imbalance. Utilizing those techniques, the performance of a wide range of workloads are substantially increased; helper cluster achieves an average speedup of 11% for a wide range of 412 apps. When focusing on integer applications, the speedup can be as high as 22% on averagePeer ReviewedPostprint (published version
Some observations about the components of transonic fan noise from narrow-band spectral analysis
Qualitative and quantitative spectral analyses are presented that give the broadband-noise, discrete-tone, and multiple-tone properties of the noise generated by a full-scale high-bypass single-stage axial-flow transonic fan (fan B, NASA Quiet Engine Program). The noise components were obtained from narrow-band spectra in conjunction with 1/3-octave-band spectra. Variations in the pressure levels of the noise components with fan speed, forward-quadrant azimuth angle, and frequency are presented and compared. The study shows that much of the apparent broadband noise on 1/3-octave-band plots consists of a complex system of shaft-order tones. The analyses also indicate the difficulties in determining or defining noise components, especially the broadband level under the discrete tones. The sources which may be associated with the noise components are discussed
Chemical propulsion research at MSFC
Chemical propulsion research reviews at Marshall Space Flight Cente
Improvements in the X-ray luminosity function and constraints on the Cosmological parameters from X-ray luminous clusters
We show how to improve constraints on \Omega_m, \sigma_8, and the dark-energy
equation-of-state parameter, w, obtained by Mantz et al. (2008) from
measurements of the X-ray luminosity function of galaxy clusters, namely MACS,
the local BCS and the REFLEX galaxy cluster samples with luminosities L> 3
\times 10^{44} erg/s in the 0.1--2.4 keV band. To this aim, we use Tinker et
al. (2008) mass function instead of Jenkins et al. (2001) and the M-L
relationship obtained from Del Popolo (2002) and Del Popolo et al. (2005).
Using the same methods and priors of Mantz et al. (2008), we find, for a
\Lambda while the result of Mantz et al. (2008) gives
less tight constraints and
\sigma_8=0.78^{+0.11}_{-0.13}. In the case of a wCDM model, we find
\Omega_m=0.27^{+0.07}_{-0.06}, and
, while in Mantz et al. (2008) they are again less tight
\Omega_m=0.24^{+0.15}_{-0.07}, \sigma_8=0.85^{+0.13}_{-0.20} and
w=-1.4^{+0.4}_{-0.7}. Combining the XLF analysis with the f_{gas}+CMB+SNIa data
set results in the constraint \Omega_m=0.269 \pm 0.012, \sigma_8=0.81 \pm 0.021
and w=-1.02 \pm 0.04, to be compared with Mantz et al. (2008), \Omega_m=0.269
\pm 0.016, \sigma_8=0.82 \pm 0.03 and w=-1.02 \pm 0.06. The tightness of the
last constraints obtained by Mantz et al. (2008), are fundamentally due to the
tightness of the +CMB+SNIa constraints and not to their XLF analysis.
Our findings, consistent with w=-1, lend additional support to the
cosmological-constant model.Comment: 9 pages, 4 Figures. A&A accepted. Paper Subitted Previously To Mantz
et al 2009, arXiv:0909.3098 and Mantz et al 2009b, arXiv:0909.309
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