Modeling of nonlinearity-compensated optical communication systems considering second-order signal-noise interactions.

An analytical model considering modulation-dependent nonlinear effects and second-order interactions between signal and optical amplifier noise is presented for Nyquist-spaced wavelength-division-multiplexing optical communication systems. System performance of dual-polarization modulation formats, such as DP-QPSK, DP-16QAM, and DP-64QAM, is investigated using both the analytical model and numerical simulations. A good agreement between analytical and numerical results shows that, in the case of full-field nonlinearity compensation, accounting for second-order interactions becomes essential to predict system performance of both single- and multi-channel systems at optimum launched powers and beyond. This effect is validated via numerical simulations for signal bandwidths up to ∼1 THz.

Abnormal intelligibility of speech in competing speech and in noise in a frequency region where audiometric thresholds are near-normal for hearing-impaired listeners.

The ability to identify syllables in the presence of speech-shaped noise and a single-talker background was measured for 18 normal-hearing (NH) listeners, and for eight hearing-impaired (HI) listeners with near-normal audiometric thresholds for frequencies up to 1.5 kHz and a moderate to severe hearing loss above 2 kHz. The stimulus components were restricted to the low-frequency (≤1.5 kHz) region, where audiometric thresholds were classified clinically as normal or near normal for all listeners. Syllable identification in a speech background was measured as a function of the fundamental-frequency (F0) difference between competing voices (ranging from 1 semitone to ∼1 octave). HI listeners had poorer syllable intelligibility than NH listeners in all conditions. Intelligibility decreased by about the same amount for both groups when the F0 difference between competing voices was reduced. The results suggest that the ability to identify speech against noise or an interfering talker was disrupted in frequency regions of near-normal hearing for HI listeners, but that the ability to benefit from the tested F0 differences was not disrupted. This deficit was not predicted by the elevated absolute thresholds for speech in speech, but it was for speech in noise. It may result from supra-threshold auditory deficits associated with aging.

Differential carrier phase recovery for QPSK optical coherent systems with integrated tunable lasers.

The performance of a differential carrier phase recovery algorithm is investigated for the quadrature phase shift keying (QPSK) modulation format with an integrated tunable laser. The phase noise of the widely-tunable laser measured using a digital coherent receiver is shown to exhibit significant drift compared to a standard distributed feedback (DFB) laser due to enhanced low frequency noise component. The simulated performance of the differential algorithm is compared to the Viterbi-Viterbi phase estimation at different baud rates using the measured phase noise for the integrated tunable laser.

Temporal-envelope reconstruction for hearing-impaired listeners.

Recent studies suggest that normal-hearing listeners maintain robust speech intelligibility despite severe degradations of amplitude-modulation (AM) cues, by using temporal-envelope information recovered from broadband frequency-modulation (FM) speech cues at the output of cochlear filters. This study aimed to assess whether cochlear damage affects this capacity to reconstruct temporal-envelope information from FM. This was achieved by measuring the ability of 40 normal-hearing listeners and 41 listeners with mild-to-moderate hearing loss to identify syllables processed to degrade AM cues while leaving FM cues intact within three broad frequency bands spanning the range 65-3,645 Hz. Stimuli were presented at 65 dB SPL for both normal-hearing listeners and hearing-impaired listeners. They were presented as such or amplified using a modified half-gain rule for hearing-impaired listeners. Hearing-impaired listeners showed significantly poorer identification scores than normal-hearing listeners at both presentation levels. However, the deficit shown by hearing-impaired listeners for amplified stimuli was relatively modest. Overall, hearing-impaired data and the results of a simulation study were consistent with a poorer-than-normal ability to reconstruct temporal-envelope information resulting from a broadening of cochlear filters by a factor ranging from 2 to 4. These results suggest that mild-to-moderate cochlear hearing loss has only a modest detrimental effect on peripheral, temporal-envelope reconstruction mechanisms.

Development of a variable launch attenuation and isolation measurement system for optical waveguides.

In this paper we describe a system that measures the attenuation and isolation of optical waveguides and has the capability to fully explore these properties over a range of reproducible launch conditions. The system allows both the launch signal spot size and numerical aperture to be varied and can be correlated to the actual operating conditions of the board. Characterization of the optical system, including the magnification factor as well as the linearity, sensitivity, spatial uniformity of the charge-coupled device cameras, is shown. Initial results from a variety of waveguides, including planar, radii, and crossover designs, are discussed and an assessment of the key uncertainty contributions of the system is presented.

Estimating OSNR of equalised QPSK signals.

We propose and demonstrate a technique to estimate the OSNR of an equalised QPSK signal based on the radial moments of the complex signal constellation. The technique is compared through simulation with maximum likelihood estimation and the effect of the block size used in the estimation is also assessed. The technique is verified experimentally and when combined with a single point calibration the OSNR of the input signal was estimated to within 0.5 dB.

Bihemispheric foundations for human speech comprehension.

Emerging evidence from neuroimaging and neuropsychology suggests that human speech comprehension engages two types of neurocognitive processes: a distributed bilateral system underpinning general perceptual and cognitive processing, viewed as neurobiologically primary, and a more specialized left hemisphere system supporting key grammatical language functions, likely to be specific to humans. To test these hypotheses directly we covaried increases in the nonlinguistic complexity of spoken words [presence or absence of an embedded stem, e.g., claim (clay)] with variations in their linguistic complexity (presence of inflectional affixes, e.g., play+ed). Nonlinguistic complexity, generated by the on-line competition between the full word and its onset-embedded stem, was found to activate both right and left fronto-temporal brain regions, including bilateral BA45 and -47. Linguistic complexity activated left-lateralized inferior frontal areas only, primarily in BA45. This contrast reflects a differentiation between the functional roles of a bilateral system, which supports the basic mapping from sound to lexical meaning, and a language-specific left-lateralized system that supports core decompositional and combinatorial processes invoked by linguistically complex inputs. These differences can be related to the neurobiological foundations of human language and underline the importance of bihemispheric systems in supporting the dynamic processing and interpretation of spoken inputs.

Intensity and phase measurements of asymmetric mode profiles and the transform in the near- to far-field transitions.

A fast and accurate measurement technique employing a calibrated CCD array is described to measure the intensity and phase distributions of the asymmetric mode profiles associated with optical waveguides. A Shack-Hartmaan wavefront sensor incorporated in the system provides the phase information. The transform describing the near-field (NF) to far-field (FF) transitions of the asymmetric mode profiles is investigated both experimentally and theoretically. The simulated NF to FF transitions using the transform are compared with the measured profiles at different positions from the end face of the waveguide. Good agreement is obtained between the measured and the computed profiles proving the accuracy of the measurement technique and also the transform used for propagation of the asymmetric mode profiles.

A case of fever, eosinophilia, and pneumonia.

There is a broad differential for patients presenting with fever, eosinophilia, and pneumonia. We present a case of a 48-year-old man who presented with recurrent fever, pleuritic chest pain, and cough. His medical history was significant for a recent trip to Arizona. A chest X ray showed a right lower lobe infiltrate and CT examination of the chest showed extensive mediastinal lymphadenopathy. Tissue culture from a biopsy specimen of the mediastinal lymph nodes revealed growth of Coccidioides immitis and a diagnosis of coccidioidomycosis was made. He was treated with a total of a 9-month course of itraconazole and has remained disease free for >2 years. This case shows how a careful history and evaluation will direct the clinician to the correct diagnosis.

Mutations within the putative active site of heterodimeric deoxyguanosine kinase block the allosteric activation of the deoxyadenosine kinase subunit.

Replacement of the Asp-84 residue of the deoxyguanosine kinase subunit of the tandem deoxyadenosine kinase/ deoxyguanosine kinase (dAK/dGK) from Lactobacillus acidophilus R-26 by Ala, Asn, or Glu produced increased Km values for deoxyguanosine on dGK. However, it did not seem to affect the binding of Mg-ATP. The Asp-84 dGK replacements had no apparent effect on the binding of deoxyadenosine by dAK. However, the mutant dGKs were no longer inhibited by dGTP, normally a potent distal endproduct inhibitor of dGK. Moreover, the allosteric activation of dAK activity by dGTP or dGuo was lost in the modified heterodimeric dAK/dGK enzyme. Therefore, it seems very likely that Asp-84 participates in dGuo binding at the active site of the dGK subunit of dAK/dGK from Lactobacillus acidophilus R-26.