MultiView High Precision VLBI Astrometry at Low Frequencies

AbstractObservations at low frequencies (<8GHz) are dominated by distinct direction dependent ionospheric propagation errors, which place a very tight limit on the angular separation of a suitable phase referencing calibrator and astrometry. To increase the capability for high precision astrometric measurements an effective calibration strategy of the systematic ionospheric propagation effects that is widely applicable is required. The MultiView technique holds the key to the compensation of atmospheric spatial-structure errors, by using observations of multiple calibrators and two dimensional interpolation. In this paper we present the first demonstration of the power of MultiView using three calibrators, several degrees from the target, along with a comparative study of the astrometric accuracy between MultiView and phase-referencing techniques. MultiView calibration provides an order of magnitude improvement in astrometry with respect to conventional phase referencing, achieving ~100micro-arcseconds astrometry errors in a single epoch of observations, effectively reaching the thermal noise limit.

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EFFECT OF CELLULAR MEMBRANE RESISTIVITY INHOMOGENEITY ON THE THERMAL NOISE-LIMIT

JOURNAL OF ADVANCES IN PHYSICS ◽

10.24297/jap.v11i3.6859 ◽

2015 ◽

Vol 11 (3) ◽

pp. 3171-3183

Author(s):

Gyula Vincze

Keyword(s):

Field Strength ◽

Thermal Noise ◽

Cellular Membrane ◽

Thermal Limit ◽

Low Frequencies ◽

Membrane Resistivity ◽

Noise Limit ◽

The Asymmetry ◽

Characteristic Field

Our objective is to generalize the Weaver-Astumian (WA) and Kaune (KA) models of thermal noise limit to the case ofcellular membrane resistivity asymmetry. The asymmetry of resistivity causes different effects in the two models. In the KAmodel, asymmetry decreases the characteristic field strength of the thermal limit over and increases it below the breakingfrequency (10ï· ï€½ï´ mï€), while asymmetry decreases the spectral field strength of the thermal noise limit at all frequencies.We show that asymmetry does not change the character of the models, showing the absence of thermal noise limit at highand low frequencies in WA and KA models, respectively.

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High-Density Memristor-CMOS Ternary Logic Family

10.36227/techrxiv.12598559 ◽

2020 ◽

Author(s):

Xiaoyuan Wang ◽

Pengfei Zhou ◽

Jason Eshraghian ◽

Chih-Yang Lin ◽

Herbert Ho-Ching Iu ◽

...

Keyword(s):

Indium Tin Oxide ◽

Practical Implementation ◽

Switching Speed ◽

High Data ◽

Fast Switching ◽

Data Density ◽

Order Of Magnitude ◽

High Transconductance ◽

Logic Functions ◽

Magnitude Improvement

<div>This paper presents the first experimental demonstration</div><div>of a ternary memristor-CMOS logic family. We systematically</div><div>design, simulate and experimentally verify the primitive</div><div>logic functions: the ternary AND, OR and NOT gates. These are then used to build combinational ternary NAND, NOR, XOR and XNOR gates, as well as data handling ternary MAX and MIN gates. Our simulations are performed using a 50-nm process which are verified with in-house fabricated indium-tin-oxide memristors, optimized for fast switching, high transconductance, and low current leakage. We obtain close to an order of magnitude improvement in data density over conventional CMOS logic, and a reduction of switching speed by a factor of 13 over prior state-of-the-art ternary memristor results. We anticipate extensions of this work can realize practical implementation where high data density is of critical importance.</div>

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Nano-Kelvin Thermometry and Temperature Control: Beyond the Thermal Noise Limit

Physical Review Letters ◽

10.1103/physrevlett.112.160801 ◽

2014 ◽

Vol 112 (16) ◽

Cited By ~ 39

Author(s):

Wenle Weng ◽

James D. Anstie ◽

Thomas M. Stace ◽

Geoff Campbell ◽

Fred N. Baynes ◽

...

Keyword(s):

Temperature Control ◽

Thermal Noise ◽

Noise Limit

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Incremental Construction of Generalized Voronoi Diagrams on Pointerless Quadtrees

Mathematical Problems in Engineering ◽

10.1155/2014/456739 ◽

2014 ◽

Vol 2014 ◽

pp. 1-14 ◽

Cited By ~ 1

Author(s):

Quanjun Yin ◽

Long Qin ◽

Xiaocheng Liu ◽

Yabing Zha

Keyword(s):

Voronoi Diagrams ◽

Surrounding Area ◽

Repair Mechanism ◽

Local Repair ◽

Order Of Magnitude ◽

Generalized Voronoi Diagrams ◽

Incremental Construction ◽

Coarse To Fine ◽

Multiple Granularities ◽

Magnitude Improvement

In robotics, Generalized Voronoi Diagrams (GVDs) are widely used by mobile robots to represent the spatial topologies of their surrounding area. In this paper we consider the problem of constructing GVDs on discrete environments. Several algorithms that solve this problem exist in the literature, notably the Brushfire algorithm and its improved versions which possess local repair mechanism. However, when the area to be processed is very large or is of high resolution, the size of the metric matrices used by these algorithms to compute GVDs can be prohibitive. To address this issue, we propose an improvement on the current algorithms, using pointerless quadtrees in place of metric matrices to compute and maintain GVDs. Beyond the construction and reconstruction of a GVD, our algorithm further provides a method to approximate roadmaps in multiple granularities from the quadtree based GVD. Simulation tests in representative scenarios demonstrate that, compared with the current algorithms, our algorithm generally makes an order of magnitude improvement regarding memory cost when the area is larger than210×210. We also demonstrate the usefulness of the approximated roadmaps for coarse-to-fine pathfinding tasks.

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Use of the Leksell Gamma Knife for Localized Small Field Lens Irradiation in Rodents

Technology in Cancer Research & Treatment ◽

10.1177/153303460300200510 ◽

2003 ◽

Vol 2 (5) ◽

pp. 449-454 ◽

Cited By ~ 30

Author(s):

Colleen DesRosiers ◽

Marc S. Mendonca ◽

Craig Tyree ◽

Vadim Moskvin ◽

Morris Bank ◽

...

Keyword(s):

Gamma Knife ◽

High Precision ◽

Small Animal ◽

Small Animals ◽

Small Field ◽

Thermoluminescent Dosimeters ◽

Ion Chamber ◽

Order Of Magnitude ◽

Contralateral Eye

For most basic radiobiological research applications involving irradiation of small animals, it is difficult to achieve the same high precision dose distribution realized with human radiotherapy. The precision for irradiations performed with standard radiotherapy equipment is ±2 mm in each dimension, and is adequate for most human treatment applications. For small animals such as rodents, whose organs and tissue structures may be an order of magnitude smaller than those of humans, the corresponding precision required is closer to ±0.2 mm, if comparisons or extrapolations are to be made to human data. The Leksell Gamma Knife is a high precision radiosurgery irradiator, with precision in each dimension not exceeding 0.5 mm, and overall precision of 0.7 mm. It has recently been utilized to treat ocular melanoma and induce targeted lesions in the brains of small animals. This paper describes the dosimetry and a technique for performing irradiation of a single rat eye and lens with the Gamma Knife while allowing the contralateral eye and lens of the same rat to serve as the “control”. The dosimetry was performed with a phantom in vitro utilizing a pinpoint ion chamber and thermoluminescent dosimeters, and verified by Monte Carlo simulations. We found that the contralateral eye received less than 5% of the administered dose for a 15 Gy exposure to the targeted eye. In addition, after 15 Gy irradiation 15 out of 16 animals developed cataracts in the irradiated target eyes, while 0 out of 16 contralateral eyes developed cataracts over a 6-month period of observation. Experiments at 5 and 10 Gy also confirmed the lack of cataractogenesis in the contralateral eye. Our results validate the use of the Gamma Knife for cataract studies in rodents, and confirmed the precision and utility of the instrument as a small animal irradiator for translational radiobiology experiments.

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Thermal noise limit in measuring the gravitational constant G using the angular acceleration method and the dynamic deflection method

Physics Letters A ◽

10.1016/j.physleta.2013.04.016 ◽

2013 ◽

Vol 377 (21-22) ◽

pp. 1397-1401 ◽

Cited By ~ 7

Author(s):

Jie Luo ◽

Cheng-Gang Shao ◽

Yuan Tian ◽

Dian-Hong Wang

Keyword(s):

Thermal Noise ◽

Gravitational Constant ◽

Angular Acceleration ◽

Noise Limit ◽

Acceleration Method

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The Array of Long Baseline Antennas for Taking Radio Observations from the Sub-Antarctic

Journal of Astronomical Instrumentation ◽

10.1142/s2251171720500191 ◽

2020 ◽

Vol 09 (04) ◽

pp. 2050019

Author(s):

H. C. Chiang ◽

T. Dyson ◽

E. Egan ◽

S. Eyono ◽

N. Ghazi ◽

...

Keyword(s):

Low Frequency ◽

Neutral Hydrogen ◽

Radio Frequency Interference ◽

Marion Island ◽

Radio Observations ◽

Long Baseline ◽

Galactic Emission ◽

Operating Frequency Range ◽

Order Of Magnitude ◽

Magnitude Improvement

Measurements of redshifted 21[Formula: see text]cm emission of neutral hydrogen at [Formula: see text][Formula: see text]MHz have the potential to probe the cosmic “dark ages,” a period of the universe’s history that remains unobserved to date. Observations at these frequencies are exceptionally challenging because of bright Galactic foregrounds, ionospheric contamination, and terrestrial radio-frequency interference. Very few sky maps exist at [Formula: see text][Formula: see text]MHz, and most have modest resolution. We introduce the Array of Long Baseline Antennas for Taking Radio Observations from the Sub-Antarctic (ALBATROS), a new experiment that aims to image low-frequency Galactic emission with an order-of-magnitude improvement in resolution over existing data. The ALBATROS array will consist of antenna stations that operate autonomously, each recording baseband data that will be interferometrically combined offline. The array will be installed on Marion Island and will ultimately comprise 10 stations, with an operating frequency range of 1.2–125[Formula: see text]MHz and maximum baseline lengths of [Formula: see text][Formula: see text]km. We present the ALBATROS instrument design and discuss pathfinder observations that were taken from Marion Island during 2018–2019.

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