A Cold-Strontium Laser in the Superradiant Crossover Regime

Recent proposals suggest that lasers based on narrow dipole-forbidden transitions in cold alkaline earth atoms could achieve linewidths that are orders of magnitude smaller than linewidths of any existing lasers. Here, we demonstrate a laser based on the 7.5 kHz linewidth dipole forbidden $^3$P$_1$ to $^1$S$_0$ transition in laser-cooled and tightly confined $^{88}$Sr. We can operate this laser in the bad-cavity regime, where coherence is primarily stored in the atoms, or continuously tune to the more conventional good-cavity regime, where coherence is primarily stored in the light field. We show that the cold-atom gain medium can be repumped to achieve quasi steady-state lasing, and demonstrate up to an order of magnitude suppression in the sensitivity of laser frequency to changes in cavity length, the primary limitation for the most frequency stable lasers today.Comment: 5 pages, 4 figure

A New \u3ci\u3eFlexamia\u3c/i\u3e (Homoptera: Cicadellidae: Deltocephalinae) From Southern Michigan

A new species, Flexamia huroni, is described from a prairie fen in south- eastern Michigan. This leafhopper is closely related to the western F. serrata B & T, a specialist on mat muhly (Muhlenbergia richardsonis). Like its sister species, F. huroni was found only in close association with mat muhly, a grass listed as a threatened species in Michigan and Wisconsin. The regional rarity of mat muhly, its association with a globally imperiled plant commnity (prairie fen) and the absence of F. huroni from several fens known to contain this grass, make this new Flexamia a strong candidate for listing as endangered in Michigan

Determinants of household choice of breakfast cereals: healthy or unhealthy?

We studied consumer demand for more and less healthy breakfast cereals. Using ACNielsen Homescan database and USDA food nutrition data, we developed three cereal nutrition indexes for each household in the data. In addition to the standard demographic characteristics of households and prices, we included variables representing differences between private labels and national brands. We found that the structure of the industry, through its effect on the product mix produced, affects consumer choice of nutritious foods. Some households buy fewer healthy cereals simply through reluctance to trust private labels. Among all factors expected to influence consumer purchases, the prices appear to have the strongest effect on the healthiness of the choice of breakfast cereals, which is a relatively inexpensive product. Households with children and teens buy less healthy cereals, while older and more educated households make healthier choices.consumer demand, healthy and unhealthy food, breakfast cereals, Consumer/Household Economics,

Fault tolerant control of a quadrotor using L-1 adaptive control

Purpose – The growing use of small unmanned rotorcraft in civilian applications means that safe operation is increasingly important. The purpose of this paper is to investigate the fault tolerant properties to faults in the actuators of an L1 adaptive controller for a quadrotor vehicle. Design/methodology/approach – L1 adaptive control provides fast adaptation along with decoupling between adaptation and robustness. This makes the approach a suitable candidate for fault tolerant control of quadrotor and other multirotor vehicles. In the paper, the design of an L1 adaptive controller is presented. The controller is compared to a fixed-gain LQR controller. Findings – The L1 adaptive controller is shown to have improved performance when subject to actuator faults, and a higher range of actuator fault tolerance. Research limitations/implications – The control scheme is tested in simulation of a simple model that ignores aerodynamic and gyroscopic effects. Hence for further work, testing with a more complete model is recommended followed by implementation on an actual platform and flight test. The effect of sensor noise should also be considered along with investigation into the influence of wind disturbances and tolerance to sensor failures. Furthermore, quadrotors cannot tolerate total failure of a rotor without loss of control of one of the degrees of freedom, this aspect requires further investigation. Practical implications – Applying the L1 adaptive controller to a hexrotor or octorotor would increase the reliability of such vehicles without recourse to methods that require fault detection schemes and control reallocation as well as providing tolerance to a total loss of a rotor. Social implications – In order for quadrotors and other similar unmanned air vehicles to undertake many proposed roles, a high level of safety is required. Hence the controllers should be fault tolerant. Originality/value – Fault tolerance to partial actuator/effector faults is demonstrated using an L1 adaptive controller