Evaluation of jet engine noise

Three basic equations, acoustic mode and two Mach modes, characterize jet noise environments. These equations are used to predict noise generation magnitude

Phase diagram of asymmetric Fermi gas across Feshbach resonance

We study the phase diagram of the dilute two-component Fermi gas at zero temperature as a function of the polarization and coupling strength. We map out the detailed phase separations between superfluid and normal states near the Feshbach resonance. We show that there are three different coexistence of superfluid and normal phases corresponding to phase separated states between: (I) the partially polarized superfluid and the fully polarized normal phases, (II) the unpolarized superfluid and the fully polarized normal phases and (III) the unpolarized superfluid and the partially polarized normal phases from strong-coupling BEC side to weak-coupling BCS side. For pairing between two species, we found this phase separation regime gets wider and moves toward the BEC side for the majority species are heavier but shifts to BCS side and becomes narrow if they are lighter.Comment: 4 pages, 3 figures. Submitted to LT25 on June 200

Spectral techniques in jet noise theory

Spectral analysis techniques applied to Lighthill aerodynamic sound equation for unified jet noise theor

Some applications of jet noise theory

Some applications of jet noise theorie

Completing incomplete cohort fertility schedules

This paper develops a simple age-period-cohort framework in completing incomplete cohort fertility schedules, and makes full use of 1917--2005 U.S. data to obtain robust outcomes. Empirically, we indicate that the period effect is the key to transforming a fertility level into a fertility schedule. Accompanied by the smoothed version of tempo-variance-adjusted total fertility rates proposed in Kohler and Philipov (2001), we approximate the cohort fertility schedules fairly well and the estimates of all distributional parameters can be thereby obtained. Our approach is easy to implement and the data requirement is relatively light, indicating that the proposed method is readily applicable to countries whose data lengths are insufficiently long, and would be helpful for further empirical investigation of the relationship between cohort fertility behavior and other cohort-specific socioeconomic factors.APC model, cohort fertility schedule, fertility forecast

Effects of keyword generation and peer collaboration on metacomprehension accuracy in middle school students

Metacomprehension refers to the ability to judge one's own comprehension. Studies in the literature have shown that generating keywords after reading helps adults and children make comprehension judgments that are better correlated with their actual comprehension. Researchers have also found that when metacomprehension is framed in terms of confidence, there is an effect of ability, where individuals with low ability tend to be overconfident in their judgments, while those with high ability tend to be underconfident. This paper describes two experiments investigating metacomprehension in seventh graders. Experiment 1 sought to replicate and extend the finding that generating keywords after reading improves the accuracy of comprehension judgments and the effectiveness of study choices. To account for potential effects of time on task, participants in the control condition were asked to read passages twice in lieu of generating keywords. Two measures of metacomprehension accuracy (signed differences and gamma correlations) were based on comprehension judgments taken at two time points (pre-test and post-test). The moderating effects of reading ability were also examined. The results of Experiment 1 showed that participants were overconfident in their judgments of their own comprehension. Overconfidence was greater for pre-test predictions than for post-test reflections, and it was also greater for participants with lower reading ability. Generating keywords caused participants to become significantly less overconfident- or more accurate- from pre-test to post-test in their comprehension judgments, but it did not actually boost comprehension scores. In other words, generating keywords helped participants know that they did not know; it did not, however, help them know more. In Experiment 2, the investigation of generating keywords and rereading text was situated within a new context incorporating practice test questions. Studies have shown that practice testing is an effective study strategy. Additionally, since researchers have found that learners can use information about peer performance as a basis for making judgments about themselves, Experiment 2 also asked whether peer collaboration might increase metacomprehension accuracy. Participants were randomly assigned to four conditions: individual/keyword, individual/reread, collaborate/keyword, and collaborate/reread. All participants answered practice test questions; participants in the individual conditions worked on the questions alone, while participants in the collaborative conditions discussed the questions with a partner. As in Experiment 1, participants in Experiment 2 were also overconfident in judging their own comprehension. Again, there was an effect for time of judgment, such that predictions were more overconfident than were reflections. Surprisingly, peer collaboration was found to lead to greater overconfidence in comprehension judgments. Participants who collaborated with a peer were more overconfident than participants who worked alone. Experiment 2 showed that in the presence of practice testing and peer collaboration, the interactive effect of keyword generation and time of judgment was minimized. Within the keyword group, participants who collaborated and participants who worked alone did not differ in overconfidence. Within the reread group, however, participants who collaborated were significantly more overconfident than those who worked alone. Taken together, these two studies suggest that middle school students are generally overconfident in their judgments of comprehension. However, the results indicate that study strategies designed to enhance comprehension and learning can be effective in reducing students' overconfidence about themselves

Phase diagram of a dilute fermion gas with density imbalance

We map out the phase diagram of a dilute two-component atomic fermion gas with unequal populations and masses under a Feshbach resonance. As in the case of equal masses, no uniform phase is stable for an intermediate coupling regime. For majority component heavier, the unstable region moves towards the BEC side. When the coupling strength is increased from the normal phase, there is an increased parameter space where the transition is into the FFLO state. The converse is true if the majority is light.Comment: Proceeding for M$^2$S-HTSC VIII meeting, July 9-14 2006, Dresden; To appear in Physica

Recent Langley helicopter acoustics contributions

The helicopter acoustics program at NASA Langley has included technology for elements of noise control ranging from sources of noise to receivers of noise. The scope of Langley contributions for about the last decade is discussed. Specifically, the resolution of two certification noise quantification issues by subjective acoustics research, the development status of the helicopter system noise prediction program ROTONET are reviewed and the highlights from research on blade rotational, broadband, and blade vortex interaction noise sources are presented. Finally, research contributions on helicopter cabin (or interior) noise control are presented. A bibliography of publications from the Langley helicopter acoustics program for the past 10 years is included

VORCOR: A computer program for calculating characteristics of wings with edge vortex separation by using a vortex-filament and-core model

A computer code base on an improved vortex filament/vortex core method for predicting aerodynamic characteristics of slender wings with edge vortex separations is developed. The code is applicable to camber wings, straked wings or wings with leading edge vortex flaps at subsonic speeds. The prediction of lifting pressure distribution and the computer time are improved by using a pair of concentrated vortex cores above the wing surface. The main features of this computer program are: (1) arbitrary camber shape may be defined and an option for exactly defining leading edge flap geometry is also provided; (2) the side edge vortex system is incorporated