12,087 research outputs found
Star Formation and the Interstellar Medium In Nearby Tidal Streams (SAINTS): Spitzer Mid-infrared Spectroscopy and Imaging of Intergalactic Star-forming Objects
A spectroscopic analysis of 10 intergalactic star forming objects (ISFOs) and
a photometric analysis of 67 ISFOs in a sample of 14 interacting systems is
presented. The majority of the ISFOs have relative polycyclic aromatic
hydrocarbon (PAH) band strengths similar to those of nearby spiral and
starburst galaxies. In contrast to what is observed in blue compact dwarfs
(BCDs) and local giant HII regions in the Milky Way (NGC 3603) and the
Magellanic Clouds (30 Doradus and N 66), the relative PAH band strengths in
ISFOs correspond to models with a significant PAH ion fraction (<50%) and
bright emission from large PAHs (~100 carbon atoms). The [NeIII]/[NeII] and
[SIV]/[SIII] line flux ratios indicate moderate levels of excitation with an
interstellar radiation field that is harder than the majority of the Spitzer
Infrared Nearby Galaxies Survey and starburst galaxies, but softer than BCDs
and local giant HII regions. The ISFO neon line flux ratios are consistent with
a burst of star formation < 6 million years ago. Most of the ISFOs have
~million solar masses of warm molecular hydrogen with a likely origin in
photo-dissociation regions (PDRs). Infrared Array Camera photometry shows the
ISFOs to be bright at 8 um, with one third having [4.5] - [8.0] > 3.7, i.e.,
enhanced non-stellar emission, most likely due to PAHs, relative to normal
spirals, dwarf irregulars and BCD galaxies. The relative strength of the 8 um
emission compared to that at 3.6 um or 24 um separates ISFOs from dwarf
galaxies in Spitzer two color diagrams. The infrared power in two thirds of the
ISFOs is dominated by emission from grains in a diffuse interstellar medium.
One in six ISFOs have significant emission from PDRs, contributing ~30 % - 60 %
of the total power. ISFOs are young knots of intense star formation.Comment: Accepted in ApJ. 49 pages 9 figure
Advancing imaging technologies for patients with spinal pain : with a focus on whiplash injury
Background: Radiological observations of soft-tissue changes that may relate to clinical symptoms in patients with traumatic and non-traumatic spinal disorders are highly controversial. Studies are often of poor quality and findings are inconsistent. A plethora of evidence suggests some pathoanatomical findings from traditional imaging applications are common in asymptomatic participants across the life span, which further questions the diagnostic, prognostic, and theranostic value of traditional imaging. Although we do not dispute the limited evidence for the clinical importance of most imaging findings, we contend that the disparate findings across studies may in part be due to limitations in the approaches used in assessment and analysis of imaging findings.
Purpose: This clinical commentary aimed to (1) briefly detail available imaging guidelines, (2) detail research-based evidence around the clinical use of findings from advanced, but available, imaging applications (eg, fat and water magnetic resonance imaging and magnetization transfer imaging), and (3) introduce how evolving imaging technologies may improve our mechanistic understanding of pain and disability, leading to improved treatments and outcomes.
Study Design/Setting: A non-systematic review of the literature is carried out.
Methods: A narrative summary (including studies from the authors' own work in whiplash injuries) of the available literature is provided.
Results: An emerging body of evidence suggests that the combination of existing imaging sequences or the use of developing imaging technologies in tandem with a good clinical assessment of modifiable risk factors may provide important diagnostic information toward the exploration and development of more informed and effective treatment options for some patients with traumatic neck pain.
Conclusions: Advancing imaging technologies may help to explain the seemingly disconnected spectrum of biopsychosocial signs and symptoms of traumatic neck pain
Correlation Receivers Minimizing Intersymbol Interference
The problem considered here is that of binary pulse communication operating in a white noise environment -wherein interfering signal pulses are generated by any of the following causes t (1) A signaling rate larger than channel bandwidths, causing pulse spill over into succeeding bands. (2) Go-channel interference or cross talk on carrier systems. (3) Signal echoes or reflections due to antenna location or mismatch of high frequency components. The optimum correlation receiver is found to be a linear combination of the desired signal pulse plus the interfering pulse. In severe cases significant improvement can be had over a correlation receiver using only the desired signal pulse. For the cause (l) above, prior receiver decisions may be used to improve the design. In particular, the immediately preceding overall receiver decision is used to select one of two parallel component correlation operations whose designs are based on a priori knowledge of the preceding transmission. It can then be shown that this is equivalent to a single correlation operation with dual decision levels, wherein the preceding receiver output controls the selection of the decision level to be utilized next. The resulting performance of this type of receiver is superior t© the correlator composed of the linear sum of signal plus interference pulses. A similar investigation was performed for the ease of Rayleigh fading on the interfering pulse. Analytical equations are established for determining the necessary solutions; however, numerical complexity precludes definitive results at this tim
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