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Browsing Duke Faculty Scholarship by Duke-affiliated Author

Browsing Duke Faculty Scholarship by Duke-affiliated Author "Cummer, Steven A."

Now showing items 1-13 of 13

Contrasting the efficiency of radiation belt losses caused by ducted and nonducted whistler-mode waves from ground-based transmitters

Cummer, Steven (AMER GEOPHYSICAL UNION, 2010)

It has long been recognized that whistler-mode waves can be trapped in plasmaspheric whistler ducts which guide the waves. For nonguided cases these waves are said to be "nonducted", which is dominant for L < 1.6. Wave-particle ...
Design of layered transformation-optics devices of arbitrary shape

Popa, Bogdan; Cummer, Steven (AMER PHYSICAL SOC, 2010)

Transformation-optics devices of arbitrary shapes usually result in material parameters inside the device that feature level sets of different shapes. Consequently, these devices cannot easily be implemented using a layered ...
Gigantic jets with negative and positive polarity streamers

Cummer, Steven; Li, Jingbo (AMER GEOPHYSICAL UNION, 2010)

The ISUAL gigantic jets (GJs) are categorized into three types from their generating sequence and spectral properties. Generating sequence of the type I GJs resembles that reported previously; after the fully developed jet ...
A lightning discharge producing a beam of relativistic electrons into space

Cummer, Steven (AMER GEOPHYSICAL UNION, 2010)

Strong electric fields associated with lightning generate brief (similar to 1 ms) but intense Terrestrial Gamma-ray Flashes (TGFs), detected by spacecrafts. A few events are thought to be the signature of a relativistic ...
Lightning mapping observation of a terrestrial gamma-ray flash

Lu, Gaopeng; Li, Jingbo; Cummer, Steven (AMER GEOPHYSICAL UNION, 2010)

We report the observation with the North Alabama Lightning Mapping Array (LMA) related to a terrestrial gamma-ray flash (TGF) detected by RHESSI on 26 July 2008. The LMA data explicitly show the TGF was produced during the ...
Midlatitude daytime D region ionosphere variations measured from radio atmospherics

Han, Feng; Cummer, Steven (AMER GEOPHYSICAL UNION, 2010)

We measured the midlatitude daytime ionospheric D region electron density profile height variations in July and August 2005 near Duke University by using radio atmospherics (or sferics for short), which are the high-power, ...
Midlatitude nighttime D region ionosphere variability on hourly to monthly time scales

Han, Feng; Cummer, Steven (AMER GEOPHYSICAL UNION, 2010)

Significant temporal variability of the nighttime D region is well known, but its inaccessibility means that the time scales, magnitudes, and sources for that variability are not well understood. We probed the ionospheric ...
Multi-instrumental observations of a positive gigantic jet produced by a winter thunderstorm in Europe

Li, Jingbo; Cummer, Steven (AMER GEOPHYSICAL UNION, 2010)

At 2336:56 UTC on 12 December 2009, a bright gigantic jet (GJ) was recorded by an observer in Italy. Forty-nine additional sprites, elves, halos and two cases of upward lightning were observed that night. The location of ...
Observations of prolific transient luminous event production above a mesoscale convective system in Argentina during the Sprite2006 Campaign in Brazil

Cummer, Steven (AMER GEOPHYSICAL UNION, 2010)

On the night of 22-23 February 2006, 444 transient luminous events (TLEs), 86% sprites, were observed above a prolific mesoscale convective system (MCS) over Argentina, as part of the third sprite campaign in Brazil. GOES ...
Phase Conjugation and Negative Refraction using Nonlinear Active Metamaterials

Katko, Alexander R.; Gu, Shi; Barrett, John P.; Popa, Bogdan; Cummer, Steven (AMER PHYSICAL SOC, 2010)

We present an experimental demonstration of phase conjugation using nonlinear metamaterial elements. Active split-ring resonators loaded with varactor diodes are demonstrated theoretically to act as phase-conjugating or ...
Polarity and energetics of inner core lightning in three intense North Atlantic hurricanes

Cummer, Steven (AMER GEOPHYSICAL UNION, 2010)

We use the World Wide Lightning Location Network (WWLLN), low-frequency magnetic fields measured at Duke University, and storm intensity data (winds and central pressure) to examine the polarity and energetics of lightning ...
A survey of ELF and VLF research on lightning-ionosphere interactions and causative discharges

Cummer, Steven (AMER GEOPHYSICAL UNION, 2010)

Extremely low frequency (ELF) and very low frequency (VLF) observations have formed the cornerstone of measurement and interpretation of effects of lightning discharges on the overlying upper atmospheric regions, as well ...
Transient luminous events above two mesoscale convective systems: Storm structure and evolution

Cummer, Steven (AMER GEOPHYSICAL UNION, 2010)

Two warm-season mesoscale convective systems (MCSs) were analyzed with respect to their production of transient luminous events (TLEs), mainly sprites. The 20 June 2007 symmetric MCS produced 282 observed TLEs over a 4 h ...