17,076 research outputs found
Effects of a finite size reflecting disk in sound power measurements
© 2018 Elsevier Ltd In practical sound power measurements in an anechoic room, a baffle sometimes has to be used to support the sound source under test so that the anechoic room can be used as a hemi-anechoic room by laying a reflecting plane. To understand the effects of a finite size reflecting plane on measurements quantitatively, this paper investigates the effects of a disk on sound power measurements by formulating an exact solution to the problem based on the spheroidal wave functions. Three practical measurement cases are considered and the correction terms for the cases are presented based on numerical simulations. Experiments are conducted to validate the analytical solutions and numerical results
A large sample of low surface brightness disk galaxies from the SDSS. I: The sample and the stellar populations
We present the properties of a large sample (12,282) of nearly face-on low
surface brightness (LSB) disk galaxies selected from the main galaxy sample of
SDSS-DR4. These properties include B-band central surface brightness mu_0(B),
scale lengths h, integrated magnitudes, colors, and distances D. This sample
has mu_0(B) values from 22 to 24.5 mag arcsec^{-2} with a median value of 22.42
mag arcsec^{-2}, and disk scale lengths ranging from 2 to 19 kpc. They are
quite bright with M_B taking values from -18 to -23 mag with a median value of
-20.08 mag. There exist clear correlations between logh and M_B, logh and logD,
logD and M_B. However, no obvious correlations are found between mu_0(B) and
logh, colors etc. The correlation between colors and logh is weak even though
it exists. Both the optical-optical and optical-NIR color-color diagrams
indicate that most of them have a mixture of young and old stellar populations.
They also satisfy color-magnitude relations, which indicate that brighter
galaxies tend generally to be redder. The comparison between the LSBGs and a
control sample of nearly face-on disk galaxies with higher surface brightness
(HSB) with mu_0(B) from 18.5 to 22 mag arcsec^{-2} show that, at a given
luminosity or distance, the observed LSB galaxies tend to have larger scale
lengths. These trends could be seen gradually by dividing both the LSBGs and
HSBGs into two sub-groups according to surface brightness. A volume-limited
sub-sample was extracted to check the incompleteness of surface brightness. The
only one of the property relations having an obvious change is the relation of
logh versus mu_0(B), which shows a correlation in this sub-sample.Comment: 14 pages, 18 figures, accepted for publication in MNRA
HyBIS: Windows Guest Protection through Advanced Memory Introspection
Effectively protecting the Windows OS is a challenging task, since most
implementation details are not publicly known. Windows has always been the main
target of malwares that have exploited numerous bugs and vulnerabilities.
Recent trusted boot and additional integrity checks have rendered the Windows
OS less vulnerable to kernel-level rootkits. Nevertheless, guest Windows
Virtual Machines are becoming an increasingly interesting attack target. In
this work we introduce and analyze a novel Hypervisor-Based Introspection
System (HyBIS) we developed for protecting Windows OSes from malware and
rootkits. The HyBIS architecture is motivated and detailed, while targeted
experimental results show its effectiveness. Comparison with related work
highlights main HyBIS advantages such as: effective semantic introspection,
support for 64-bit architectures and for latest Windows (8.x and 10), advanced
malware disabling capabilities. We believe the research effort reported here
will pave the way to further advances in the security of Windows OSes
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