Many urban areas have elevated soil lead concentrations due to prior large-scale use of lead in products such as paint and automobile gasoline. This presents a potential problem for the growing ...numbers of wildlife living in urbanized areas as lead exposure is known to affect multiple physiological systems, including the nervous system, in vertebrate species. In humans and laboratory animals, low-level lead exposure is associated with neurological impairment, but less is known about how lead may affect the behavior of urban wildlife. We focused on the Northern Mockingbird Mimus polyglottos, a common, omnivorous North American songbird, to gain insights into how lead may affect the physiology and behavior of urban wildlife. We predicted that birds living in neighborhoods with high soil lead concentrations would (a) exhibit elevated lead concentrations in their blood and feathers, (b) exhibit lower body condition, (c) exhibit less diverse and consistent vocal repertoires, and (d) behave more aggressively during simulated conspecific territorial intrusions compared to birds living in neighborhoods with lower soil lead concentrations. Controlling for other habitat differences, we found that birds from areas of high soil lead had elevated lead concentrations in blood and feathers, but found no differences in body condition or vocal repertoires. However, birds from high lead areas responded more aggressively during simulated intrusions. These findings indicate that sub-lethal lead exposure may be common among wildlife living in urban areas, and that this exposure is associated with increased aggression. Better understanding of the extent of the relationship between lead exposure and aggression and the consequences this could have for survival and reproduction of wild animals are clear priorities for future work in this and other urban ecosystems.
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•Sub-lethal lead exposure of urban wildlife is widespread, but effects are unknown.•We evaluated exposure and behavioral correlates in the Northern Mockingbird.•Birds in high lead areas had higher blood and feather lead and were more aggressive.•No differences were observed in vocal repertoire or body condition.•Behavioral consequences of lead exposure to urban wildlife deserve more attention.
Multicarrier signals are known to suffer from a high peak-to-average power ratio, caused by the addition of a large number of independently modulated subcarriers in parallel at the transmitter. When ...subjected to a peak-limiting channel, such as a nonlinear power amplifier, these signals may undergo significant spectral distortion, leading to both in-band and out-of-band interference, and an associated degradation in system performance. This paper characterizes the distortion caused by the clipping of multicarrier signals in a peak-limiting (nonlinear) channel. Rather than modeling the effects of distortion as additive noise, as is widespread in the literature, we identify clipping as a rare event and focus on evaluating system performance based on the conditional probability of bit error given the occurrence of such an event. Our analysis is based on the asymptotic properties of the large excursions of a stationary Gaussian process, and offers important insights into both the true nature of clipping distortion, as well as the consequent design of schemes to alleviate this problem.
The effect of the companding process on QAM signals has been under investigation for the past several years. The compander, included in the PCM telephone network to improve voice performance, has an ...unusual affect on digital QAM data signals which are transmitted over the same channel. The quantization noise, generated by the companding process which is multiplicative (and asymmetric), degrades the detectability performance of the outermost points of the QAM constellation more than that of the inner points. The combined effect of the companding noise and the inherent white Gaussian noise of the system, leads to a re-examination of signal constellation design. The authors investigate the detectability performance of a number of candidates for signal constellations including, a typical rectangular QAM constellation, the same constellation with the addition of a smear-desmear operation, and two new improved QAM constellation designs with two-dimensional warping
Error-burst detection with tandem CRCs Mazo, J.E.; Saltzberg, B.R.
IEEE transactions on communications,
08/1991, Letnik:
39, Številka:
8
Journal Article
Recenzirano
The authors investigate the efficacy of using two different cyclic redundancy check (CRC) codes in tandem to increase error-burst detecting capability. For a set of pairs of CRCs which are used in ...standards, it is found that the guaranteed detectable burst length is less than the sum of the individual guaranteed detectable burst lengths, but not much less. Thus strengthened CRC codes can readily be obtained using existing devices.< >
The encoding and decoding schemes presented are aimed at enabling the transfer of data through a channel in which two types of interference are added to the transmitted signal and the sum is ...quantized. One of these interferences is known (or can be estimated), whereas the second is an additive white Gaussian noise (AWGN). Since the input of the quantizer is not accessible, the known interference can not be removed from the received signal. We show that the error rate for an uncoded transmission through this channel is unacceptably large, even for low noise levels and linear quantization. It is also shown that the problem becomes even more severe when a nonlinear quantization is present. Therefore, coding is essential and a huge coding gain is achievable in this application. An upper-bound on the error rate, contributed by the component codes of a multilevel code, has been developed for multistage decoding. Results of computer simulations of a practical case with optimal and suboptimal decoding algorithms, both developed in this paper, are presented.
When a QAM (quadrature amplitude modulation) data signal is transmitted over a channel that includes PCM codecs, it has frequently been observed and shown that the resulting noise around the final ...received constellation points grows with the distance of the point from the origin. The authors extend the analysis of this effect, and further show that the noise distribution about each point is elliptical, with greater variance in the radial direction. Formulas giving the signal-dependent noise components as a function of the channel characteristics of the analog transmit and receive access legs are derived. Experimental results confirm the analysis.< >
Lucent Technologies is well positioned to create the elements required for its customers to offer a wide array of future services to their customers. A vision of these services includes richly ...detailed and personalized multimedia environments used to conduct transactions and to communicate, integrate, and investigate information from applications created across a set of independent components in a geographically and functionally diverse network. Creation of such environments requires development of new network elements, architectures, and tools for ongoing individualized service creation. A particularly critical element is access to customers. This can be provided over a wide variety of transmission media, such as paired cable, coaxial cable, optical fiber, and wireless networks.
Electroencephalographic (EEG) studies of lateralized cognitive functions have primarily relied upon measures of averaged evoked potentials (AEP) and power spectra (PS) to demonstrate hemispheric ...differences. The nature of the tasks appropriate to each of these methods of signal analysis generally require different cognitive activities and suggest different assumptions about cerebral specialization. This study investigated whether the tasks associated with either method were more likely to produce EEG asymmetries. Eighteen right-handed subjects participated in a three phase experiment which varied the amount of subject involvement in task performance. Phase I entailed passive listening to speech and nonspeech sounds. Phase II required active attention to speech and nonspeech sounds. Phase III involved a verbal matching task, a spatial rotations task, and a noncognitive control task. Auditory AEPs were measured in Phases I and II, and PS were measured in Phase II and III. EEG recordings were obtained from frontal and parietal areas of both hemispheres (F3, F4, P3, P4) referred to linked ears. Power spectra were derived from the 4-8, 8-13, and 13-20 Hz frequency bands at each lead. Despite statistically significant task and/or stimuli differences found in all three phases of study, essentially no task by lead interactions were obtained. That is, interhemispheric activity did not covary with differing stimuli and tasks. The absence of such interactions calls into question uncritical acceptance of a simple direct relation between task performance, EEG activity, and hemisphere specialization.
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