Gregory Wright - Academia.edu (original) (raw)

Papers by Gregory Wright

Publications of the Astronomical Society of the Pacific, May 1, 2001

Consider the scenario of FIGURE A. The energy used to send an electromagnetic message is PT where... more Consider the scenario of FIGURE A. The energy used to send an electromagnetic message is PT where P is the radiated power. A receiver at some distance D will capture some fraction of this power ν D P where ν D is defined as the energy capture coefficient of the receiver. We assume square law isotropic propagation loss with transmitting antenna gain

2016 IEEE International Conference on Communications (ICC), 2016

Proceedings of the IEEE, 2016

Large arrays of radios have been exploited for beamforming and null steering in both radar and co... more Large arrays of radios have been exploited for beamforming and null steering in both radar and communication applications, but cost and form factor limitations have precluded their use in commercial systems. This paper discusses how to build arrays that enable multiuser massive MIMO and aggressive spatial multiplexing with many users sharing the same spectrum. The focus of the paper is the energy and cost efficient realization of these arrays in order to enable new applications. Distributed algorithms for beamforming are proposed, and the optimum array size is considered as a function of the performance of the receiver, transmitter, frequency synthesizer and signal distribution within the array. The effects of errors such as phase noise and synchronization skew across the array are analyzed. The paper discusses both RF frequencies below 10 GHz, where fully digital techniques are preferred, and operation at mm-wave bands where a combination of digital and analog techniques are needed to keep cost and power low.

2015 IEEE International Conference on Communication Workshop (ICCW), 2015

Conference Record of the Thirty-Eighth Asilomar Conference on Signals, Systems and Computers, 2004.

We consider the energy requirements of information carriage using physical transport of inscribed... more We consider the energy requirements of information carriage using physical transport of inscribed matter and compare it to that using electromagnetic radiation when delivery delay beyond light transit time can be tolerated. Somewhat counter-intuitively, physical transport of inscribed matter is often more energy efficient than electromagnetic broadcast by many orders of magnitude over a wide range of scenarios-from chipto-chip computer communications to interstellar signaling. In fact, the efficiencies are so enormous that it may even be more likely for initial contact by extraterrestrial civilizations to occur using physical artifacts-essentially messages in a bottle-than via electromagnetic communication.

[

IEEE Signal Processing Magazine, 2010

The Astrophysical Journal Supplement Series, 2009

Fully sampled degree-scale maps of the 13 CO 2-1 and CO 4-3 transitions toward three members of t... more Fully sampled degree-scale maps of the 13 CO 2-1 and CO 4-3 transitions toward three members of the Lupus Molecular Cloud Complex-Lupus I, III, and IV-trace the column density and temperature of the molecular gas. Comparison with IR extinction maps from the c2d project requires most of the gas to have a temperature of 8-10 K. Estimates of the cloud mass from 13 CO emission are roughly consistent with most previous estimates, while the line widths are higher, around 2 km s −1. CO 4-3 emission is found throughout Lupus I, indicating widespread dense gas, and toward Lupus III and IV. Enhanced line widths at the NW end and along the edge of the B 228 ridge in Lupus I, and a coherent velocity gradient across the ridge, are consistent with interaction between the molecular cloud and an expanding H I shell from the Upper-Scorpius subgroup of the Sco-Cen OB Association. Lupus III is dominated by the effects of two HAe/Be stars, and shows no sign of external influence. Slightly warmer gas around the core of Lupus IV and a low line width suggest heating by the Upper-Centaurus-Lupus subgroup of Sco-Cen, without the effects of an H I shell.

Astronomy and Astrophysics, 2001

We report measurements of the 12 C/ 13 C abundance ratio in the three galactic regions G 333.0-0.... more We report measurements of the 12 C/ 13 C abundance ratio in the three galactic regions G 333.0-0.4, NGC 6334 A and G 351.6-1.3 from observations of the 12 Ci 3 P2 → 3 P1 transition and the hyperfine components of the corresponding 13 Ci transition near 809 GHz. These transitions were observed simultaneously with the CO 7-6 line emission at 806 GHz with the AST/RO telescope located at the South Pole. From a simultaneous fit to the 12 Ci 3 P2 → 3 P1 transition and the HF components of the corresponding 13 Ci transition and an independent estimate of an upper limit to the optical depth of the 12 Ci emission we determine intrinsic 12 Ci/ 13 Ci column density ratios of 23 ± 1 for G 333.0-0.4, 56 ± 14 for NGC 6334 A and 69 ± 12 for G 351.6-1.3. As the regions observed are photon dominated, we argue that the apparent enhancement in the abundance of 13 C towards G 333.0-0.4 may be due to strong isotope-selective photodissociation of 13 CO, outweighing the effects of chemical isotopic fractionation as suggested by models of PDRs. Towards NGC 6334 A and G 351.6-1.3 these effects appear to be balanced, similar to the situation for the Orion Bar region observed by Keene et al. (1998).

IEEE Transactions on Communications, 2003

We consider information flow via physical transport of inscribed mass through space and compare i... more We consider information flow via physical transport of inscribed mass through space and compare it to information flow via electromagnetic radiation. Counterintuitively, for point to point links physical transport of inscribed mass is often more energy efficient than electromagnetic broadcast by many orders of magnitude. Perhaps more surprising, in a broadcast setting inscribed mass transport may still be more energy efficient. We discuss the implications of these results for terrestrial telecommunications networks as well as point to point and broadcast communication over great distances with loose delay constraints.

Annals of the New York Academy of Sciences, 1992

Publications of the Astronomical Society of the Pacific, May 1, 2001

Consider the scenario of FIGURE A. The energy used to send an electromagnetic message is PT where... more Consider the scenario of FIGURE A. The energy used to send an electromagnetic message is PT where P is the radiated power. A receiver at some distance D will capture some fraction of this power ν D P where ν D is defined as the energy capture coefficient of the receiver. We assume square law isotropic propagation loss with transmitting antenna gain

2016 IEEE International Conference on Communications (ICC), 2016

Proceedings of the IEEE, 2016

Large arrays of radios have been exploited for beamforming and null steering in both radar and co... more Large arrays of radios have been exploited for beamforming and null steering in both radar and communication applications, but cost and form factor limitations have precluded their use in commercial systems. This paper discusses how to build arrays that enable multiuser massive MIMO and aggressive spatial multiplexing with many users sharing the same spectrum. The focus of the paper is the energy and cost efficient realization of these arrays in order to enable new applications. Distributed algorithms for beamforming are proposed, and the optimum array size is considered as a function of the performance of the receiver, transmitter, frequency synthesizer and signal distribution within the array. The effects of errors such as phase noise and synchronization skew across the array are analyzed. The paper discusses both RF frequencies below 10 GHz, where fully digital techniques are preferred, and operation at mm-wave bands where a combination of digital and analog techniques are needed to keep cost and power low.

2015 IEEE International Conference on Communication Workshop (ICCW), 2015

Conference Record of the Thirty-Eighth Asilomar Conference on Signals, Systems and Computers, 2004.

We consider the energy requirements of information carriage using physical transport of inscribed... more We consider the energy requirements of information carriage using physical transport of inscribed matter and compare it to that using electromagnetic radiation when delivery delay beyond light transit time can be tolerated. Somewhat counter-intuitively, physical transport of inscribed matter is often more energy efficient than electromagnetic broadcast by many orders of magnitude over a wide range of scenarios-from chipto-chip computer communications to interstellar signaling. In fact, the efficiencies are so enormous that it may even be more likely for initial contact by extraterrestrial civilizations to occur using physical artifacts-essentially messages in a bottle-than via electromagnetic communication.

[

IEEE Signal Processing Magazine, 2010

The Astrophysical Journal Supplement Series, 2009

Fully sampled degree-scale maps of the 13 CO 2-1 and CO 4-3 transitions toward three members of t... more Fully sampled degree-scale maps of the 13 CO 2-1 and CO 4-3 transitions toward three members of the Lupus Molecular Cloud Complex-Lupus I, III, and IV-trace the column density and temperature of the molecular gas. Comparison with IR extinction maps from the c2d project requires most of the gas to have a temperature of 8-10 K. Estimates of the cloud mass from 13 CO emission are roughly consistent with most previous estimates, while the line widths are higher, around 2 km s −1. CO 4-3 emission is found throughout Lupus I, indicating widespread dense gas, and toward Lupus III and IV. Enhanced line widths at the NW end and along the edge of the B 228 ridge in Lupus I, and a coherent velocity gradient across the ridge, are consistent with interaction between the molecular cloud and an expanding H I shell from the Upper-Scorpius subgroup of the Sco-Cen OB Association. Lupus III is dominated by the effects of two HAe/Be stars, and shows no sign of external influence. Slightly warmer gas around the core of Lupus IV and a low line width suggest heating by the Upper-Centaurus-Lupus subgroup of Sco-Cen, without the effects of an H I shell.

Astronomy and Astrophysics, 2001

We report measurements of the 12 C/ 13 C abundance ratio in the three galactic regions G 333.0-0.... more We report measurements of the 12 C/ 13 C abundance ratio in the three galactic regions G 333.0-0.4, NGC 6334 A and G 351.6-1.3 from observations of the 12 Ci 3 P2 → 3 P1 transition and the hyperfine components of the corresponding 13 Ci transition near 809 GHz. These transitions were observed simultaneously with the CO 7-6 line emission at 806 GHz with the AST/RO telescope located at the South Pole. From a simultaneous fit to the 12 Ci 3 P2 → 3 P1 transition and the HF components of the corresponding 13 Ci transition and an independent estimate of an upper limit to the optical depth of the 12 Ci emission we determine intrinsic 12 Ci/ 13 Ci column density ratios of 23 ± 1 for G 333.0-0.4, 56 ± 14 for NGC 6334 A and 69 ± 12 for G 351.6-1.3. As the regions observed are photon dominated, we argue that the apparent enhancement in the abundance of 13 C towards G 333.0-0.4 may be due to strong isotope-selective photodissociation of 13 CO, outweighing the effects of chemical isotopic fractionation as suggested by models of PDRs. Towards NGC 6334 A and G 351.6-1.3 these effects appear to be balanced, similar to the situation for the Orion Bar region observed by Keene et al. (1998).

IEEE Transactions on Communications, 2003

We consider information flow via physical transport of inscribed mass through space and compare i... more We consider information flow via physical transport of inscribed mass through space and compare it to information flow via electromagnetic radiation. Counterintuitively, for point to point links physical transport of inscribed mass is often more energy efficient than electromagnetic broadcast by many orders of magnitude. Perhaps more surprising, in a broadcast setting inscribed mass transport may still be more energy efficient. We discuss the implications of these results for terrestrial telecommunications networks as well as point to point and broadcast communication over great distances with loose delay constraints.

Annals of the New York Academy of Sciences, 1992