Long-lasting Emissions Research Articles

Investigating short-term dynamics and long-term trends of SO 4 in the runoff of a forested catchment using artificial neural networks

The impact of long-lasting non-point emissions on groundwater and streamwater in remote watersheds has been studied at numerous sites. In spite of substantially decreasing emissions in the last decade, recovery has not yet been observed in all cases. This trend might be masked by the considerable short-term variability of the chemical hydrographs. In this study, artificial neural networks are applied to investigate the SO 4 dynamics in the runoff of a small forested catchment susceptible to SO 4 deposition. Empirical models are fitted to the short-term dynamics at a time step of one day. About 75% of the variance of the SO 4 data is explained by the instantaneous discharge, short-term history of discharge and the moving average of SO 4 concentration in throughfall. In contrast, neither air temperature as an indicator for biological activity nor a snowmelt indicator based on the temperature sum increase the performance of the model. The model is used to investigate long-term trends in sub-regions of the phase space spanned by the identified input variables. According to the model, decreasing emissions have a significant effect on runoff SO 4 concentration only during the first severe storms at the end of the vegetation period. This suggests to focus on these events as indicators for recovery of the topsoil layers.

Spontaneous otoacoustic emissions and relaxation dynamics of long decay time OAEs in audiometrically normal and impaired subjects.

The relationship between hearing loss, detected by measuring the audiometric threshold shift, and the presence of long-lasting otoacoustic emissions, has been studied in a population of 66 adult males, by analyzing the cochlear response in the 80 ms following the subministration of a click stimulus. Most long-lasting OAEs are also recognizable as Synchronized Spontaneous OAEs (SSOAEs). The OAE characteristic decay times were evaluated according to the model by Sisto and Moleti [J. Acoust. Soc. Am. 106, 1893 (1999)]. The starting hypothesis, confirmed by the results, is that long decay time and large equilibrium amplitude are both manifestations of the effectiveness of the active feedback mechanism. The prevalence and frequency distribution of long-lasting OAEs, and of their SSOAE subset, have been separately analyzed for normal and impaired ears. No long-lasting OAE was found within the hearing loss frequency range, but several were found in impaired ears outside the hearing loss range, both at lower and higher frequencies. This result suggests that the correlation between the presence of long-lasting OAEs and good cochlear functionality be local in the frequency domain. The monitor of the OAE decay time is proposed as a new possible method for early detecting hearing loss in populations exposed to noise.

Generation of electrostatic emissions by lightning-induced whistler-mode radiation above thunderstorms

Data from two separate thunderstorm sounding rocket experiments – Thunderstorm-II (T-II), which involved two rockets, and Thunderstorm-III (T-III) – are compared. In both cases, the sounding rockets over-flew active storm cells, but the bottomside of the ionosphere had a lower density and was much more structured for the first experiment than for the second. Electric field measurements on the flight through a structured ionosphere (T-II) show a triggered emission that has a height variation with altitude that seems to track the lower hybrid resonance frequency (LHR). Theories and other experimental data are presented supporting the concept that LH waves can be stimulated by intense whistlers when density gradients are present, and we interpret these T-II data in just such a context. We believe these emissions may be responsible for the irregularities causing the remote-sensing phenomenon called explosive spread F. The T-III flight had no such height-dependent emissions, which we attribute to the smoothness of the medium during that flight. Curiously, long-lasting emissions also occurred during T-III, but at frequencies that were constants with height and harmonics of the cut-off frequency for the earth-ionosphere wave guide. To our knowledge, there is no existing theory against which to test the T-III emissions.