18,524 research outputs found
The Carriers of the Interstellar Unidentified Infrared Emission Features: Constraints from the Interstellar C-H Stretching Features at 3.2-3.5 Micrometers
The unidentified infrared emission (UIE) features at 3.3, 6.2, 7.7, 8.6, and
11.3 micrometer, commonly attributed to polycyclic aromatic hydrocarbon (PAH)
molecules, have been recently ascribed to mixed aromatic/aliphatic organic
nanoparticles. More recently, an upper limit of <9% on the aliphatic fraction
(i.e., the fraction of carbon atoms in aliphatic form) of the UIE carriers
based on the observed intensities of the 3.4 and 3.3 micrometer emission
features by attributing them to aliphatic and aromatic C-H stretching modes,
respectively, and assuming A_34./A_3.3~0.68 derived from a small set of
aliphatic and aromatic compounds, where A_3.4 and A_3.3 are respectively the
band strengths of the 3.4 micrometer aliphatic and 3.3 micrometer aromatic C-H
bonds.
To improve the estimate of the aliphatic fraction of the UIE carriers, here
we analyze 35 UIE sources which exhibit both the 3.3 and 3.4 micrometer C-H
features and determine I_3.4/I_3.3, the ratio of the power emitted from the 3.4
micrometer feature to that from the 3.3 micrometer feature. We derive the
median ratio to be ~ 0.12. We employ density functional theory
and second-order perturbation theory to compute A_3.4/A_3.3 for a range of
methyl-substituted PAHs. The resulting A_3.4/A_3.3 ratio well exceeds 1.4, with
an average ratio of ~1.76. By attributing the 3.4 micrometer
feature exclusively to aliphatic C-H stretch (i.e., neglecting anharmonicity
and superhydrogenation), we derive the fraction of C atoms in aliphatic form to
be ~2%. We therefore conclude that the UIE emitters are predominantly aromatic.Comment: 14 pages, 5 figures, 1 table; accepted for publication in The
Astrophysical Journa
The Carriers of the "Unidentified" Infrared Emission Features: Clues from Polycyclic Aromatic Hydrocarbons with Aliphatic Sidegroups
The "unidentified" infrared emission (UIE) features at 3.3, 6.2, 7.7, 8.6,
and 11.3 m are ubiquitously seen in various astrophysical regions. The UIE
features are characteristic of the stretching and bending vibrations of
aromatic hydrocarbons. The 3.3 m feature resulting from aromatic C--H
stretches is often accompanied by a weaker feature at 3.4 m often
attributed to aliphatic C--H stretches. The ratio of the observed intensity of
the 3.3 m aromatic C--H feature () to that of the 3.4 m
aliphatic C--H feature () allows one to estimate the aliphatic
fraction (i.e. , the number of C atoms in
aliphatic units to that in aromatic rings) of the UIE carriers, provided the
intrinsic oscillator strengths of the 3.3 m aromatic C--H stretch
() and the 3.4 m aliphatic C--H stretch () are known.
In this article we summarize the computational results on and
and their implications for the aromaticity and aliphaticity of the
UIE carriers. We use density functional theory and second-order perturbation
theory to derive and from the infrared vibrational spectra
of seven PAHs with various aliphatic substituents (e.g., methyl-, dimethyl-,
ethyl-, propyl-, butyl-PAHs, and PAHs with unsaturated alkyl-chains). The mean
band strengths of the aromatic () and aliphatic () C--H
stretches are derived and then employed to estimate the aliphatic fraction of
the UIE carriers by comparing / with /. We
conclude that the UIE emitters are predominantly aromatic, as revealed by the
observationally-derived ratio ~ 0.12 and the
computationally-derived ratio ~ 1.76 which suggest an
upper limit of ~ 0.02 for the aliphatic
fraction of the UIE carriers.Comment: 67 pages, 18 figures, 8 tables; invited article accepted for
publication in "New Astronomy Review"; a considerable fraction of this
article is concerned with the computational techniques and results, readers
who are mainly interested in astrophysics may wish to only read
"Introduction", and "Astrophysical Implications
Aperiodic Quantum Random Walks
We generalize the quantum random walk protocol for a particle in a
one-dimensional chain, by using several types of biased quantum coins, arranged
in aperiodic sequences, in a manner that leads to a rich variety of possible
wave function evolutions. Quasiperiodic sequences, following the Fibonacci
prescription, are of particular interest, leading to a sub-ballistic
wavefunction spreading. In contrast, random sequences leads to diffusive
spreading, similar to the classical random walk behaviour. We also describe how
to experimentally implement these aperiodic sequences.Comment: 4 pages and 4 figure
A Hierarchical Emotion Regulated Sensorimotor Model: Case Studies
Inspired by the hierarchical cognitive architecture and the perception-action
model (PAM), we propose that the internal status acts as a kind of
common-coding representation which affects, mediates and even regulates the
sensorimotor behaviours. These regulation can be depicted in the Bayesian
framework, that is why cognitive agents are able to generate behaviours with
subtle differences according to their emotion or recognize the emotion by
perception. A novel recurrent neural network called recurrent neural network
with parametric bias units (RNNPB) runs in three modes, constructing a
two-level emotion regulated learning model, was further applied to testify this
theory in two different cases.Comment: Accepted at The 5th International Conference on Data-Driven Control
and Learning Systems. 201
Salvia miltiorrhiza treatment during early reperfusion reduced postischemic myocardial injury in the rat
Oxidative stress may play a causative role in myocardial ischemia-reperfusion injury. However, it is a relatively understudied aspect regarding an optimal timing of antioxidant intervention during ischemia-reperfusion. The present study investigates the effect of different treatment regimens of Salvia miltiorrhiza (SM) herb extracts containing phenolic compounds that possess potent antioxidant properties on postischemic myocardial functional recovery in the setting of global myocardial ischemia and reperfusion. Langendorff-perfused rat hearts were subjected to 40 min of global ischemia at 37°C followed by 60 min of reperfusion, and were randomly assigned into the untreated control and 2 SM-treated groups (n = 7 per group). In treatment 1 (SM1), 3 mg/mL of water soluble extract of SM was given for 10 min before ischemia and continued during ischemia through the aorta at a reduced flow rate of 60 μL/min, but not during reperfusion. In treatment 2 (SM2), SM (3 mg/mL) was given during the first 15 min of reperfusion. During ischemia, hearts in the control and SM2 groups were given physiological saline at 60 μL/min. The SM1 treatment reduced the production of 15-F2t- isoprostane, a specific index of oxidative stress-induced lipid peroxidation, during ischemia (94 ± 20, 43 ± 6, and 95 ± 15 pg/mL in the coronary effluent in control, SM1, and SM2 groups, respectively; p < 0.05, SM1 vs. control or SM2) and post-poned the onset of ischemic contracture. However, SM2, but not the SM1 regimen, significantly reduced 15-F 2t-isoprostane production during early reperfusion and led to optimal postischemic myocardial functional recovery (left ventricular developed pressure 51 ± 4, 46 ± 4, and 60 ± 6 mmHg in the control, SM1, and SM2 groups, respectively, at 60 min of reperfusion; p < 0.05, SM2 vs. control or SM1) and reduced myocardial infarct size as measured by triphenyltetrazolium chloride staining (26% ± 2%, 22% ± 2%, and 20% ± 2% of the total area in the control, SM1, and SM2 groups, respectively, p < 0.05, SM2 vs. control). It is concluded that S. miltiorrhiza could be beneficial in the treatment of myocardial ischemic injury and the timing of administration seems important. © 2007 NRC.published_or_final_versio
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
Bis(4-phenylpyridinium) tetrakis(nitrato-κ2 O,O′)stannate(IV). Retraction
Retraction of Acta Cryst. (2007), E63, m1567
Bis(4,4′-bipyridine-κN)tetrakis(nitrato-κ2 O,O′)tin(IV). Retraction
Retraction of Acta Cryst. (2007), E63, m1566
Networking Effects on Cooperation in Evolutionary Snowdrift Game
The effects of networking on the extent of cooperation emerging in a
competitive setting are studied. The evolutionary snowdrift game, which
represents a realistic alternative to the well-known Prisoner's Dilemma, is
studied in the Watts-Strogatz network that spans the regular, small-world, and
random networks through random re-wiring. Over a wide range of payoffs, a
re-wired network is found to suppress cooperation when compared with a
well-mixed or fully connected system. Two extinction payoffs, that characterize
the emergence of a homogeneous steady state, are identified. It is found that,
unlike in the Prisoner's Dilemma, the standard deviation of the degree
distribution is the dominant network property that governs the extinction
payoffs.Comment: Changed conten
Reflection of audio sounds generated by a parametric array loudspeaker.
The reflection of audio sounds generated by a parametric array loudspeaker (PAL) is investigated in this paper. The image source method and the non-paraxial PAL radiation model under the quasilinear approximation are used to calculate the reflected audio sound from an infinitely large surface with an arbitrary incident angle. The effects of the surface absorption in the ultrasound frequency range are studied, and the simulation and experiment results show that the reflection behavior of audio sounds generated by a PAL is different from those generated by traditional audio sources. The reason is that the reflected sound generated by the PAL consists of the reflection of audio sounds generated by incident ultrasounds and the audio sounds generated by the reflected ultrasound, and it is the latter that determines the directivity of the reflected audio sound
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