Open-Loop Woofer-Tweeter Control on the LAO Multi-Conjugate Adaptive Optics Testbed

Advances in micro deformable mirror (DM) technologies such as MEMs, have stimulated interest in the characteristics of systems that include a high stroke mirror in series with a high actuator count mirror. This arrangement is referred to as a woofer-tweeter system. In certain situations it may be desirable or necessary to operate the woofer DM in open-loop. We present a simple method for controlling a woofer DM in open loop provided the device behaves in an approximately linear fashion. We have tested a mirror that we believe meets our criterion, the ALPAO DM52 mirror. Using our open-loop method we fit several test Kolmogorov wavefronts with the mirror and have achieved an accuracy of approximately 25 nm rms surface deviation over the whole clear aperture, and 20 nm rms over 90% of the aperture. We have also flattened the mirror in open loop to approximately 11 nm rms residual.Comment: 5 pages, 3 figures, to be published in proceedings of The 6th International Workshop on Adaptive Optics for Industry and Medicin

Stroke saturation on a MEMS deformable mirror for woofer-tweeter adaptive optics

High-contrast imaging of extrasolar planet candidates around a main-sequence star has recently been realized from the ground using current adaptive optics (AO) systems. Advancing such observations will be a task for the Gemini Planet Imager, an upcoming "extreme" AO instrument. High-order "tweeter" and low-order "woofer" deformable mirrors (DMs) will supply a >90%-Strehl correction, a specialized coronagraph will suppress the stellar flux, and any planets can then be imaged in the "dark hole" region. Residual wavefront error scatters light into the DM-controlled dark hole, making planets difficult to image above the noise. It is crucial in this regard that the high-density tweeter, a micro-electrical mechanical systems (MEMS) DM, have sufficient stroke to deform to the shapes required by atmospheric turbulence. Laboratory experiments were conducted to determine the rate and circumstance of saturation, i.e. stroke insufficiency. A 1024-actuator 1.5-um-stroke MEMS device was empirically tested with software Kolmogorov-turbulence screens of r_0=10-15cm. The MEMS when solitary suffered saturation ~4% of the time. Simulating a woofer DM with ~5-10 actuators across a 5-m primary mitigated MEMS saturation occurrence to a fraction of a percent. While no adjacent actuators were saturated at opposing positions, mid-to-high-spatial-frequency stroke did saturate more frequently than expected, implying that correlations through the influence functions are important. Analytical models underpredict the stroke requirements, so empirical studies are important.Comment: 16 pages, 10 figure

A propos de l' ü souletin

Hay dos tesis sobre el origen de la ü suletina: viene del dialecto del Béarn o es una evolución espontánea. En el texto se estudian algunos ejemplos de palabras que contienen la üThere are two thesis on the origin of the "ü" from the Soule: either it comes from the dialect from the Béarn or it is a spontaneous evolution. Some words that contain this "ü" are studied in the tex

Towards optimization of pulsed sodium laser guide stars

Pulsed sodium laser guide stars (LGS) are useful because they allow for Rayleigh blanking and fratricide avoidance in multiple-LGS systems. Bloch-equation simulations of sodium-light interactions show that these may be able to achieve photon returns nearly equal to, and in some cases greater than, what is seen from continuous-wave (CW) excitation. In this work, we study the time-dependent characteristics of sodium fluorescence, and investigate the optimal format for the new fiber laser LGS that will be part of the upgraded adaptive optics (AO) system on the Shane telescope at Mt. Hamilton. Results of this analysis are examined in the context of their general applicability to other LGS systems and the potential benefits of uplink correction are considered. Comparisons of simulation predictions with measurements from existing LGS are also presented and discussed.Comment: 9 pages, 7 figures, accepted by JOSA

More Than Mere Synonyms: Examining The Differences Between Criminogenic Thinking And Criminogenic Attitudes

More than 75% of prison inmates are arrested for a new crime within five years of being released from prison. Known as recidivism, this trend of repeated criminal activity accounts for more than half of annual prison admissions, and rehabilitative programs demonstrate varying degrees of success in reducing recidivism. Andrews, Bonta, and Hoge (1990) demonstrated that offenders are less likely to recidivate when they receive services that match their assessed level of risk factors (e.g., history of violence), intervention needs (e.g., mental health diagnosis), and responsivity (e.g., ideal learning environment). Criminogenic cognition, mental events (e.g., thoughts, attitudes, and beliefs) often exhibited by criminal offenders and thought to promote antisocial behavior, are among the greatest needs that must be addressed to decrease recidivism; however, the distinction between thought content and thought process is not sufficiently clear in the literature. The current study aimed to distinguish these two domains of criminogenic cognition and examine their relationship to one another. Specifically, four common measures of criminogenic thinking and attitudes were compared. Correlational analyses provided support for the prediction that the two constructs are related yet quantitatively distinct. Problems with the data prevented the successful completion of the primary data analysis, leading to inconclusive results. Possible explanations for these results and suggestions for future research are discussed

Patterns of growth in first grade reading

Thesis (Ed.D.)--Boston University.PROBLEM: The purpose of this study was to investigate the levels of reading achievement at the end of grade one in relation to status and growth of various word perception abilities measured several times during the year. PROCEDURES: Many first grade reading series in use today delay instruction of perceptual abilities until an extensive sight vocabulary has been acquired. Since research has indicated that such instruction might well be begun earlier in the year, the language arts staff at Boston University designed a program that would include the regular work in word recognition plus early training in perceptual abilities. During the first week of school in September 1955, a meeting explaining the program and services offered was held with the teachers in four communities. Participation was put on a voluntary basis; 64 classrooms took part in the program. [TRUNCATED

Evaluation of Sprinkler Systems in Northern Utah

Sprinkling as a method of irrigation has been expanding rapidly in the United States, with acreages irrigated by this method increasing every year. One of the major reasons for the expansion is the great improvements that have been made in sprinkler irrigation equipment. Lightweight aluminum pipe, with quick couplers, improved pump and motor efficiencies have all made sprinkler irrigation more desirable. High efficiency of water application, labor requirements, and favorable plant response have also favored the expansion

Evidence of Empathy in Animals Across Time

Empathetic behaviors are characterized by a three-tiered hierarchical organization involving arousal, emotional contagion, and cognitive empathy. In the current study, we define each step in this hierarchy in order to build toward a paradigm that represents true cognitive empathy. We then examine the levels of empathy displayed by rats in previous paradigms and classify prior studies by level of arousal, emotional contagion, or cognitive empathy. Finally, we present two studies which examine the potential for empathetic display in rats