scholarly journals Prospects for High Angular Resolution Instrumentation at Millimeter and Submillimeter Wavelengths

2001 ◽  
Vol 205 ◽  
pp. 432-437
Author(s):  
Karl M. Menten
Keyword(s):  
Spatial Resolution ◽  
Angular Resolution ◽  
Diffraction Limit ◽  
High Angular Resolution ◽  
Submillimeter Wavelength ◽  
Millimeter Astronomy ◽  
Short Summary ◽  
Submillimeter Wavelengths ◽  
Millimeter And Submillimeter Wavelengths ◽  
Infrared Telescopes

Millimeter- and submillimeter wavelength interferometry is a powerful technique allowing imaging of dust and molecules in a multitude of astronomical environments. With the arrival of the Atacama Large Millimeter Array (ALMA), such studies will be possible with unprecedented sensitivity and a spatial resolution similar to the diffraction limit of large optical/infrared telescopes. In this paper, we mention a few aspects of (sub) millimeter astronomy and provide a short summary of ALMA's capabilities.

scholarly journals High spatial resolution multiwavelength observations of star and planet formation

2001 ◽  
Vol 205 ◽  
pp. 236-243
Author(s):  
Mark J. McCaughrean
Keyword(s):  
Spatial Resolution ◽  
Planet Formation ◽  
Angular Resolution ◽  
High Spatial Resolution ◽  
High Angular Resolution ◽  
Multiwavelength Observations

We discuss the importance of multiwavelength (optical, infrared, millimetre, and radio), high angular resolution (arcsec to subarcsec) observations in studying star and planet formation. We provide a few illustrative examples, and briefly discuss how future observational facilities will allow a yet more detailed view of the important processes at work.

scholarly journals 7.2. 12.5μ imaging of Sgr A West with the Keck Telescope

1998 ◽  
Vol 184 ◽  
pp. 293-294
Author(s):  
E. E. Becklin ◽  
M. Morris ◽  
D. F. Figer ◽  
A. M. Ghez ◽  
R. Puetter ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Central Region ◽  
Angular Resolution ◽  
Diffraction Limit ◽  
Mosaic Pattern ◽  
Long Wavelength ◽  
The Galaxy ◽  
Sgr A ◽  
Better Than ◽  
Atmospheric Seeing

We have used the 10-meter Keck I telescope and the camera mode of the long wavelength spectrometer to observe the central region of the Galaxy at 12.5 μm. The 96×70 As:Si array used had a scale of 0.114 arcsec per pixel. The filter was centered at 12.5 μm and had a bandwidth of about 1 μm. The array was flat-fielded using sky flats from the background. We observed the central 20×20 arcsec region (about 1pc × 1pc) by using a mosaic pattern of the 11×8 arcsec array in approximately half-array steps. The position of the array was determined after the fact by using structure in the flux in the overlap regions. The accuracy of the positioning was better than 0.1 arcsec. The resultant spatial resolution of the final map was about 0.7 arcsec FWHM based on the size of IRS 7 and IRS 3. The demonstrated diffraction limit of the phased Keck telescope at 12.5 microns is just over 0.3 arcsec FWHM, so that the final resolution is a result of atmospheric seeing and chopper smear. The final map is shown in Figure 1. The map is similar, but of much higher angular resolution, to the 12.5 μm map of Gezari (1992, The Center, Bulge and Disk of the Galaxy, ed. Blitz, Dordrecht: Kluwer, 23).

scholarly journals Resolving the mass loss from red supergiants by high angular resolution

2016 ◽  
Vol 12 (S329) ◽  
pp. 97-103
Author(s):  
Keiichi Ohnaka
Keyword(s):  
Mass Loss ◽  
Spatial Resolution ◽  
Angular Resolution ◽  
High Spatial Resolution ◽  
Spatial Scales ◽  
High Angular Resolution ◽  
Circumstellar Envelope ◽  
Long Baseline ◽  
Red Supergiants ◽  
Late Stages

AbstractDespite its importance on late stages of the evolution of massive stars, the mass loss from red supergiants (RSGs) is a long-standing problem. To tackle this problem, it is essential to observe the wind acceleration region close to the star with high spatial resolution. While the mass loss from RSGs is often assumed to be spherically symmetric with a monotonically accelerating wind, there is mounting observational evidence that the reality is much more complex. I review the recent progress in high spatial resolution observations of RSGs, encompassing from the circumstellar envelope on rather large spatial scales (~100 stellar radii) to milliarcsecond-resolution aperture-synthesis imaging of the surface and the atmosphere of RSGs with optical and infrared long-baseline interferometers.

scholarly journals Spatial versus angular resolution for tractography-assisted planning of deep brain stimulation

2019 ◽  
Author(s):  
Luka C. Liebrand ◽  
Guido A. van Wingen ◽  
Frans M. Vos ◽  
Damiaan Denys ◽  
Matthan W.A. Caan
Keyword(s):  
Deep Brain Stimulation ◽  
Spatial Resolution ◽  
Brain Stimulation ◽  
Diffusion Mri ◽  
Angular Resolution ◽  
Internal Capsule ◽  
High Angular Resolution ◽  
Scanning Time ◽  
Mri Protocol ◽  
Deep Brain

AbstractGiven the restricted total scanning time for clinical neuroimaging, it is unclear whether clinical diffusion MRI protocols would benefit more from higher spatial resolution or higher angular resolution. In this work, we investigated the relative benefit of improving spatial or angular resolution in diffusion MRI to separate two parallel running white matter tracts that are targets for deep brain stimulation: the anterior thalamic radiation and the supero-lateral branch of the medial forebrain bundle. Both these tracts are situated in the ventral anterior limb of the internal capsule, and recent studies suggest that targeting a specific tract could improve treatment efficacy. Therefore, we scanned 19 healthy volunteers at 3T and 7T according to three diffusion MRI protocols with respectively standard clinical settings, increased spatial resolution of 1.4 mm, and increased angular resolution (64 additional gradient directions at b=2200s/mm2). We performed probabilistic tractography for all protocols and quantified the separability of both tracts. The higher spatial resolution protocol improved separability by 41% with respect to the clinical standard, presumably due to decreased partial voluming. The higher angular resolution protocol resulted in increased apparent tract volumes and overlap, which is disadvantageous for application in precise treatment planning. We thus recommend to increase the spatial resolution for deep brain stimulation planning to 1.4 mm while maintaining angular resolution. This recommendation complements the general advice to aim for high angular resolution to resolve crossing fibers, confirming that the specific application and anatomical considerations are leading in clinical diffusion MRI protocol optimization.

scholarly journals Resolution and b value dependent Structural Connectome in ex vivo Mouse Brain

2022 ◽  
Author(s):  
Stephanie Crater ◽  
Surendra Maharjan ◽  
Yi Qi ◽  
Qi Zhao ◽  
Gary Cofer ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Mouse Brain ◽  
Diffusion Mri ◽  
Angular Resolution ◽  
Ex Vivo ◽  
B Value ◽  
High Angular Resolution ◽  
Preclinical Studies ◽  
High Quality ◽  
Structural Connectome

Diffusion magnetic resonance imaging has been widely used in both clinical and preclinical studies to characterize tissue microstructure and structural connectivity. The diffusion MRI protocol for the Human Connectome Project (HCP) has been developed and optimized to obtain high-quality, high-resolution diffusion MRI (dMRI) datasets. However, such efforts have not been fully explored in preclinical studies, especially for rodents. In this study, high quality dMRI datasets of mouse brains were acquired at 9.4T system from two vendors. In particular, we acquired a high-spatial resolution dMRI dataset (25 um isotropic with 126 diffusion encoding directions), which we believe to be the highest spatial resolution yet obtained; and a high-angular resolution dMRI dataset (50 um isotropic with 384 diffusion encoding directions), which we believe to be the highest angular resolution compared to the dMRI datasets at the microscopic resolution. We systematically investigated the effects of three important parameters that affect the final outcome of the connectome: b value (1000 s/mm2 to 8000 s/mm2), angular resolution (10 to 126), and spatial resolution (25 um to 200 um). The stability of tractography and connectome increase with the angular resolution, where more than 50 angles are necessary to achieve consistent results. The connectome and quantitative parameters derived from graph theory exhibit a linear relationship to the b value (R2 > 0.99); a single-shell acquisition with b value of 3000 s/mm2 shows comparable results to the multi-shell high angular resolution dataset. The dice coefficient decreases and both false positive rate and false negative rate gradually increase with coarser spatial resolution. Our study provides guidelines and foundations for exploration of tradeoffs among acquisition parameters for the structural connectome in ex vivo mouse brain.

Small-Angle Electron Scattering (SAES) of Polymers

1985 ◽  
Vol 43 ◽  
pp. 78-79
Author(s):  
Ralph Oralor ◽  
Pamela Lloyd ◽  
Satish Kumar ◽  
W. W. Adams
Keyword(s):  
Electron Scattering ◽  
Small Angle ◽  
Angular Resolution ◽  
Structural Features ◽  
Objective Lens ◽  
High Angular Resolution ◽  
Push Button ◽  
First Case ◽  
Diffraction Mode ◽  
Very High

Small angle electron scattering (SAES) has been used to study structural features of up to several thousand angstroms in polymers, as well as in metals. SAES may be done either in (a) long camera mode by switching off the objective lens current or in (b) selected area diffraction mode. In the first case very high camera lengths (up to 7Ø meters on JEOL 1Ø ØCX) and high angular resolution can be obtained, while in the second case smaller camera lengths (approximately up to 3.6 meters on JEOL 1Ø ØCX) and lower angular resolution is obtainable. We conducted our SAES studies on JEOL 1ØØCX which can be switched to either mode with a push button as a standard feature.

Large-angle convergent-beam electron-diffraction study of coherent precipitates and decorated dislocations

1996 ◽  
Vol 54 ◽  
pp. 1002-1004
Author(s):  
J.M.K. Wiezorek ◽  
H.L. Fraser
Keyword(s):  
Electron Diffraction ◽  
Angular Resolution ◽  
Large Angle ◽  
Electron Diffraction Study ◽  
Convergent Beam Electron Diffraction ◽  
Crystal Defects ◽  
High Angular Resolution ◽  
Beam Electron ◽  
Diffraction Plane ◽  
Convergent Beam

Conventional methods of convergent beam electron diffraction (CBED) use a fully converged probe focused on the specimen in the object plane resulting in the formation of a CBED pattern in the diffraction plane. Large angle CBED (LACBED) uses a converged but defocused probe resulting in the formation of ‘shadow images’ of the illuminated sample area in the diffraction plane. Hence, low-spatial resolution image information and high-angular resolution diffraction information are superimposed in LACBED patterns which enables the simultaneous observation of crystal defects and their effect on the diffraction pattern. In recent years LACBED has been used successfully for the investigation of a variety of crystal defects, such as stacking faults, interfaces and dislocations. In this paper the contrast from coherent precipitates and decorated dislocations in LACBED patterns has been investigated. Computer simulated LACBED contrast from decorated dislocations and coherent precipitates is compared with experimental observations.

Binary Cepheids From High-Angular Resolution

2015 ◽  
Vol 71-72 ◽  
pp. 187-188
Author(s):  
A. Gallenne ◽  
A. Mérand ◽  
P. Kervella
Keyword(s):  
Angular Resolution ◽  
High Angular Resolution
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