Tuning terahertz transitions in a double-gated quantum ring

We theoretically investigate the optical functionality of a semiconducting quantum ring manipulated by two electrostatic lateral gates used to induce a double quantum well along the ring. The well parameters and corresponding inter-level spacings, which lie in the THz range, are highly sensitive to the gate voltages. Our analysis shows that selection rules for inter-level dipole transitions, caused by linearly polarized excitations, depend on the polarization angle with respect to the gates. In striking difference from the conventional symmetric double well potential, the ring geometry permits polarization-dependent transitions between the ground and second excited states, allowing the use of this structure in a three-level lasing scheme.Comment: 7 pages, 6 figure

A new population of terrestrial gamma-ray flashes in the RHESSI data

Terrestrial gamma-ray flashes (TGFs) are the most energetic photon phenomenon occurring naturally on Earth. An outstanding question is as follows: Are these flashes just a rare exotic phenomenon or are they an intrinsic part of lightning discharges and therefore occurring more frequently than previously thought? All measurements of TGFs so far have been limited by the dynamic range and sensitivity of spaceborne instruments. In this paper we show that there is a new population of weak TGFs that has not been identified by search algorithms. We use the World Wide Lightning Location Network (WWLLN) to identify lightning that occurred in 2006 and 2012 within the 800 km field of view of Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). By superposing 740,210 100 ms RHESSI data intervals, centered at the time of the WWLLN detected lightning, we identify at least 141 and probably as many as 191 weak TGFs that were not part of the second RHESSI data catalogue. This supports the suggestion that the global TGF production rate is larger than previously reported

A Study of the Effect of Blended Cements on the Durability of Concrete Incorporating an Inferior Coarse Aggregate

Research Project C-13 was set up for the purpose of studying the effect of blended cement, with air-entraining properties, on the durability of concrete incorporating an inferior grade of limestone as the coarse aggregate. This investigation is not correlated with any Department of Highways field project, being entirely a laboratory study. The tests were begun April 12, 1945, and were completed February 6, 1946

Durability of Concrete as Affected by Absorbed Moisture in Tennessee River Gravel Aggregate

This project is more or less a preliminary investigation of Tennessee River gravel relative to the effect of the moisture condition of the aggregates upon the durability of concrete. Certain observations made in the field indicated that absorbed moisture in the aggregate could have a marked effect on concrete, so this study was made in an attempt to give quantitative significance to the observation

Cooperative Investigation of Joint Spacing in Concrete Pavements

During the summer of 1940 the Kentucky Department of Highways, with the Public Roads Administration participating, constructed 6.27 miles of investigational pavement as a cooperative research project on joint spacing. This project was one of six planned by the Public Roads Administration and the Portland Cement Association in cooperation with six highway departments. The five other states participating were California, Michigan, Hinnesota, Missouri, and Oregon. The project selected for this jointing study in Kentucky is in Daviess County, approximately six miles southeast of Owensboro, on Kentucky Route No. 71 (Layout map in Figure 1). The experimental program was outlined for the purpose of evaluating the relative merits of varying intervals in expansion joint spacing and of dummy contraction joints with and without dowel bars for load transfer. A complete discussion of the scope and purpose has been given in a paper by Mr. E. F. Kelly of the Public Roads Administration

A Study of the Effect of Blended Coarse Aggregate on Air-Entrained Concrete Progress Report 3

The purpose of this investigetion was to study the durability characteristics of a river gravel, used as coarse aggregate for concrete, with respect to four major fractions separated in accordance to their general mineralogical classification. This aggregate was from the same stock of Ohio River gravel that was used in earlier phases of this Project reported in 1947. Since this gravel consisted of several rock types varying in mineralogic constituents, it was conceivable that poor performance could possibly be attributed to some undesirable fraction or fractions, rather than to the aggregate as a whole. The separation of this aggregate was rather general yet satisfactory for the purposes of this study and was confined to four fractions in each of which there was a preponderance of one general rock type. These four fractions were designated, for convenience, as limestone, chert, quartzite, and granite. Evaluation of durability characteristics was made by means of freezing and thawing tests on like samples of concrete made with the different gravel components. All other features of the concrete were kept as constant as possible

Progress Report on Experimental Jointing Installations for Concrete Pavements

Combined in this report are descriptions of the progress of three individual experimental joint installations. Each of these includes a series of two or more experimental joints of special design, installed in concrete pavement in lieu of the conventional types employed in their respective construction projects. These experimental joints included at one location a prefabricated neoprene seal; and, at two locations, aluminum load transfer devices, All installations were contraction joints only, Periodic inspections of these have been made and will be continued on two of the projects until adequate performance records are established. The condition of concrete about the joints with neoprene seals has reached the stage where there would be little value in additional observations

An Investigation of Lean Concrete Mixes as Base Courses for Bituminous Surfaces [Jan. 1951]

Cement concrete bases for pavements with bituminous surfaces are, of course, not new. However, it has been many years since concrete has served this purpose except as a pavement itself ultimately resurfaced after years of service. The outstanding qualities of many roads which developed in this way were obvious without any particular tests, and for many years there apparently was no attempt to evaluate them. Probably structural value was first investigated in tests on airfields in Florida, Ohio and California. Although the original concrete pavements in all cases were heavy in comparison with highway sections, the results of the tests have some bearing on highway considerations. In beefing up rigid pavements that had failed under heavy loads and running subsequent tests under moving wheels, the Army Engineers came to the conclusion that --treatments of as little as 3 inches of asphaltic concrete give astounding structural benefits. Accelerated traffic tests have shown overlays of less rigid material to be so beneficial that original designs utilizing a rigid slab of moderate thickness covered with a flexible type surface can and probably will be in cost competition where conditions are favorable