The pitches of the harmonics (numbers 1, 2, 3, 4, 5, 7, 9, and 11) of a complex tone were measured in a matching experiment. The harmonics to be matched were mistuned (8% or less) either positively, or negatively, or not at all. For all mistuned harmonics and all listeners the matching pitches were found to be exaggerations of the mistunings, i.e., the data exhibited pitch shifts with the same sign as the mistunings. This result is shown to be contrary to place models of pitch perception, such as the spectral pitch algorithm of Terhardt, in which pitch shifts are caused by the interaction of excitation patterns for the individual harmonics. An alternative model, in which pitch is determined by neural timing, also fails to account for the data. However, a hybrid model, combining effects of excitation pattern interaction with neural timing, does agree with most of the data.
We consider models for the observed ro-vibrational absorption lines of acetylene toward NGC 7538 IRS9. The data are fit with multiple screens, each having separate column densities, rotational and vibrational excitation temperatures, and filling factors. The best fit was determined using a chi-squared minimization scheme. We find that only one screen is necessary-multiple screens gave rise to either making one of the screens transparent, or very occasionally making the two screens the same. As a result, we can place constraints on Trot, Tvib, NC2H2, and the filling factor, f. In particular we find 0.03 < f < 0.3 with a best fit of f ~ 0.1. We also find Tvib < 200 K, with a best fit of Tvib < 20 K. We find NC2H2 = 2.4 +/− 0.6 × 10 16 cm −2 , or that N × f ~ 2 × 10 15 cm −2 . Lastly, we find 80 < Trot < 140 K, with a best fit of Trot ~ 100 K. Physically, this can be interpreted as: (1) no vibrational excitation, (2) the warm region only fills a small fraction of the beam, (3) the C2H2 arises very near a region of 100 K. Chemically, this is in consistent with a model where the C2H2 is formed in the gas phase. It is however consistent with a scenario where the C2H2 is evaporated at 100 K from the grain surface, suggesting either a grain-surface origin or earlier origin followed by condensation. Finally, the C2H2 column density is consistent with a disk geometry.
Recent experimental work on harmonic modelocking shows constraints on temporal spacing and frequency spectra can produce highly uniform trains of solitons. In addition, recent numerical simulation and analytical work predict: (1) solitons on the separate cores of dual core fiber can exhibit both repulsive and attractive interactions, and (2) individual solitons, satisfying certain threshold conditions, can propagate primarily on one core of dual core fiber despite significant coupling between guides. We use numerical simulation and analytical techniques to study the consequences of these findings for simple soliton arrays propagating in dual guide structures. In particular, we examine the case where strong constraints are imposed on the temporal spacing, amplitude, and frequency spectra of solitons in a given core, but weaker, or no constraints are imposed on solitons in the adjacent core. We find conditions, e.g., where a uniform train of solitons propagates primarily in the core where the strong constraints are imposed. We also find interesting dynamics for a “free” soliton in the second core that result from the interaction of the “free” soliton with the periodic potential produced by presence of the uniform soliton train on the first core. We examine routes to stability of this coupled system.
We present a study of the pre-protostellar core (PPC) L1498. A series of self-consistent, threedimensional continuum radiative transfer models are constructed. The outputs of these models are convolved with appropriate telescope beam responses, including the effect of beam chopping to simulate SCUBA observations. The simulated observations are compared with existing observational data. An automated search is conducted in the multi-dimensional parameter space to identify the best-fit model. Grids of models are constructed in the vicinity of the best fit in order to understand the sensitivity/uncertainty of the results. We find that the source is well fit by a prolate spheroid of cutoff (and thus approximately outer) radius rcut = 0.073 ± 0.005 pc, axis ratio q = 2.0 ± 0.2, a central luminosity L* < 10 −3 Lsun, and an optical depth in the visible of τv = 20 ± 5. We find that the PPC is illuminated by two external radiation fields: a uniform ISRF of strength sISRF = 0.5 ± 0.25 and a local plane-parallel radiation field sPPRF = 1.0 ± 0.5. Both of these radiation fields are locally attenuated, with τISRF = 1.0 ± 0.25, and τPPRF = 1.25 ± 0.75, consistent with the fact that L1498 is embedded in a larger cloud. Most interestingly, the density fall-off at the outer edge is extremely steep, having a power law of m > 10. This is effectively a "sharp edge" to the PPC, and together with the constant density interior, is interpreted as potential signs of a pressure-confined core.
Satisfying the research requirements for tenure and promotion at a small, predominantly undergraduate teaching institution can be daunting. This is especially true since the time involved with effective teaching, another key requirement to promotion, typically surpasses a full time commitment. Moreover, the fiscal, facility, and expertise constraints of a small institute limit viable projects, particularly experimental endeavors. To meet the research requirements for promotion, three junior, untenured faculty members (an electrical engineer and two physicists) took the initiative to form a cross-discipline, off-campus collaborative research effort with a senior, tenured physiologist at a mid-sized research university. The junior faculty members contribute their time and technical skills to the project. The physiologist provides mentoring, direction, laboratory space and supplies. The collaboration involves the waveform analysis of electroretinograms (ERG) in rats. At this early stage of the project, the junior faculty are spending time in the lab learning how to record ERG's and the biochemistry involved in the visual process. They have also upgraded the ERG recording scheme from a strip chart recorder to a digital oscilloscope with a front-end computer. Their technical skills will be instrumental in later stages of the project. The collaboration addresses many issues simultaneously. These issues include lack of time, funding, facilities and guidance. We will present details of the formation, difficulties and rewards of this cross-discipline, off-campus collaboration.
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