Optically exciting a magnetic memory - A feasibility study

Rare earth iron garnets were used in experiments to determine the feasibility of optically pumping a magnetic material to effect the switching process. It was found that rare earth garnets are limited by an absorption edge, only terbium and dysprosium offer a possibility of pumping at energies below the conduction band edge

Methods and costs associated with outfitting light aircraft for remote sensing applications

This document was designed to provide the potential user of a light aircraft remote sensor platform/data gathering system with general information on aircraft definition, implementation complexity, costs, scheduling and operational factors involved in this type of activity. Most of the subject material was developed from actual situations and problem areas encountered during the build-up cycle and early phases of flight operations

Pixelation effects in weak lensing

Weak gravitational lensing can be used to investigate both dark matter and dark energy but requires accurate measurements of the shapes of faint, distant galaxies. Such measurements are hindered by the finite resolution and pixel scale of digital cameras. We investigate the optimum choice of pixel scale for a space-based mission, using the engineering model and survey strategy of the proposed Supernova Acceleration Probe as a baseline. We do this by simulating realistic astronomical images containing a known input shear signal and then attempting to recover the signal using the Rhodes, Refregier, & Groth algorithm. We find that the quality of shear measurement is always improved by smaller pixels. However, in practice, telescopes are usually limited to a finite number of pixels and operational life span, so the total area of a survey increases with pixel size. We therefore fix the survey lifetime and the number of pixels in the focal plane while varying the pixel scale, thereby effectively varying the survey size. In a pure trade-off for image resolution versus survey area, we find that measurements of the matter power spectrum would have minimum statistical error with a pixel scale of 0.09 '' for a 0.14 '' FWHM point-spread function (PSF). The pixel scale could be increased to similar to 0.16 '' if images dithered by exactly half-pixel offsets were always available. Some of our results do depend on our adopted shape measurement method and should be regarded as an upper limit: future pipelines may require smaller pixels to overcome systematic floors not yet accessible, and, in certain circumstances, measuring the shape of the PSF might be more difficult than those of galaxies. However, the relative trends in our analysis are robust, especially those of the surface density of resolved galaxies. Our approach thus provides a snapshot of potential in available technology, and a practical counterpart to analytic studies of pixelation, which necessarily assume an idealized shape measurement method

Can Arhats Attain Buddhahood?

The Lotus Sutra is well known for its teaching of the One Vehicle. According to this teaching, although the Buddha preached that there are three paths to buddhahood (the paths of the śrāvakas, pratyekabuddhas and bodhisattva), there is in fact only one path of practice in Buddhism: the teaching of the bodhisattva leading to complete enlightenment. This implies that those who have attained the goal of arhathood through the practice of the śrāvaka path must ultimately convert to the bodhisattva path and continue their practices until they attain buddhahood. However, there is a problem since arhats are said to have destroyed all the defilements binding them to continued existence within the realms of transmigration, meaning that they must necessarily enter nirvāṇa at the end of their lives and are therefore prevented from continuing their practices to reach buddhahood. In this paper, I will introduce the theories of Kumārajīva and Fayun who argued, on the basis of the Dazhidulum and the Śrīmālā-simhanāda Sūtra respectively, that arhats are indeed capable of attaining buddhahood since they have not yet destroyed their defilements completely and still retain a subtle form of defilement. The Lotus Sutra is well known for its teaching of the One Vehicle. According to this teaching, although the Buddha preached that there are three paths to buddhahood (the paths of the śrāvakas, pratyekabuddhas and bodhisattva), there is in fact only one path of practice in Buddhism: the teaching of the bodhisattva leading to complete enlightenment. This implies that those who have attained the goal of arhathood through the practice of the śrāvaka path must ultimately convert to the bodhisattva path and continue their practices until they attain buddhahood. However, there is a problem since arhats are said to have destroyed all the defilements binding them to continued existence within the realms of transmigration, meaning that they must necessarily enter nirvāṇa at the end of their lives and are therefore prevented from continuing their practices to reach buddhahood. In this paper, I will introduce the theories employed by Kumārajīva and Fayun to explain this conundrum. Kumārajīva, a noted translator of Buddhist texts into Chinese, engaged in an exchange of letters with Huiyuan of Mt. Lu, one of the most respected Chinese Buddhist of his age. In one exchange, Kumārajīva specifically deals with the question of how arhats can attain buddhahood and argues that, although arhats believe they have eradicated all defilements, they have not actually done so. Taking his cue from the Dazhidulum, Kumārajīva argues they still possess what he terms “love towards nirvāṇa and the buddha dharma.” Hence, he concludes, arhats have not actually rid themselves of all defilements but must still remain within the cycle of transmigration undertaking bodhisattva practices until they extinguish these subtle forms of defilements and achieve buddhahood. Fayun, who lived approximately a century after Kumārajīva, was a noted scholar monk who wrote an influential commentary on the Lotus Sutra. In this commentary, Fayun also argues that arhats are capable of achieving buddhahood since they are still encumbered by defilements. However, in making his argument, Fayun relies on the theory of five levels of defilements taken from the Śrīmālā-simhanāda Sūtra. According to this theory, arhats have destroyed the latent defilements, the first four of the five levels of defilements described in the sūtra, but have yet to eradicate the defilements of fundamental ignorance, the final and most profound form of defilements. By availing himself to this theory, Fayun argues that arhats are indeed capable of attaining buddhahood since they still possess the defilements of fundamental ignorance which prevents them from entering extinction in nirvāṇa, allowing them to continue their practices as bodhisattvas until they achieve complete buddhahood

Observation of a possible superflare on Proxima Centauri

We report the observation on UT 2017 July 1 of an unusually powerful flare detected in near-infrared continuum photometry of Proxima Centauri. During a campaign monitoring the star for possible exoplanet transits, we identified an increase in Sloan i' flux leading to an observed peak at BJD 2457935.996 that was at least 10 per cent over pre-flare flux in this band. It was followed by a two-component rapid decline in the first 100 s that became a slower exponential decay with time constant of 1350 s. A smaller flare event 1300 s after the first added an incremental peak flux increase of 1 per cent of pre-flare flux. Since the onset of the flare was not fully time resolved at a cadence of 62 s, its actual peak value is unknown but greater than the time average over a single exposure of 20 s. The i' band is representative of broad optical and near-IR continuum flux over which the integrated energy of the flare is 100 times the stellar luminosity. This meets the criteria that established the concept of superflares on similar stars. The resulting implied ultraviolet flux and space weather could have had an extreme effect on the atmospheres of planets within the star's otherwise habitable zone

Pyrotechnic shock at the orbiter/external tank forward attachment

During the initial certification test of the forward structural attachment of the space shuttle orbiter to the external tank, pyrotechnic shock from actuation of the separation device resulted in structural failure of the thermal protection tiles surrounding the attachment. Because of the high shock associated with the separation bolt, the development of alternative low shock separation designs was initiated. Two concepts that incorporate a 5.08 centimeter frangible nut as the release device were developed and tested

Preliminary rotor wake measurements with a laser velocimeter

A laser velocimeter (LV) was used to determine rotor wake characteristics. The effect of various fuselage widths and rotor-fuselage spacings on time averaged and detailed time dependent rotor wake velocity characteristics was defined. Definition of time dependent velocity characteristics was attempted with the LV by associating a rotor azimuth position with each velocity measurement. Results were discouraging in that no apparent time dependent velocity characteristics could be discerned from the LV measurements. Since the LV is a relatively new instrument in the rotor wake measurement field, the cause of this lack of periodicity is as important as the basic research objectives. An attempt was made to identify the problem by simulated acquisition of LV-type data for a predicted rotor wake velocity time history. Power spectral density and autocorrelation function estimation techniques were used to substantiate the conclusion that the primary cause of the lack of time dependent velocity characteristics was the nonstationary flow condition generated by the periodic turbulence level that currently exists in the open throat configuration of the wind tunnel