Shallow water acoustic networks

Underwater acoustic networks are generally formed by acoustically connected ocean bottom sensor nodes, autonomous underwater vehicles (AUVs), and surface stations that serve as gateways and provide radio communication links to on-shore stations. The quality of service of such networks is limited by the low bandwidth of acoustic transmission channels, high latency resulting from the slow propagation of sound, and elevated noise levels in some environments. The long-term goal in the design of underwater acoustic networks is to provide for a self-configuring network of distributed nodes with network links that automatically adapt to the environment through selection of the optimum system parameters. This article considers several aspects in the design of shallow water acoustic networks that maximize throughput and reliability while minimizing power consumption     

PAM decomposition of M-ary multi-h CPM

It is known that any multilevel continuous phase-modulated (CPM) signal with a single modulation index can be exactly represented by a sum of pulse-amplitude modulated (PAM) waveforms. In this paper, we show how multi-h CPM signals can also be represented in this manner. The decomposition is presented in general terms as a function of the alphabet size, modulation indexes, and phase pulse of the CPM scheme. The number of pulses required to exactly construct the signal is shown to increase over that previously given for single-h schemes; this increase is in proportion to the number of modulation indexes. We propose an approximation which significantly reduces the number of signal pulses and which minimizes the mean-squared error for an arbitrary set of modulation indexes. We show that this approximation can have two objectives: 1) to reduce the number of pulses in the same manner as has been proposed for single-h schemes; and/or 2) to reduce the number of multi-h pulses; we also show the conditions where this latter objective is most practical. We compare this minimum mean-squared error approximation with another method which was recently proposed for CPM. We also give numerical results on detection performance which demonstrate the practicality of the proposed approximation.     

Organizational Media Affordances: Operationalization and Associations with Media Use

The concept of affordances has been increasingly applied to the study of information and communication technologies (ICTs) in organizational contexts. However, almost no research operationalizes affordances, limiting comparisons and programmatic research. This article briefly reviews conceptualizations and possibilities of affordances in general and for media, then introduces the concept of organizational media affordances as organizational resources. Analysis of survey data from a large Nordic media organization identified six reliable and valid organizational media affordances: pervasiveness, editability, self-presentation, searchability, visibility, and awareness. Eight media scales based on frequency of use of 10 media within each of three organization levels were differentially associated with these affordances. The conceptualization, measurement approach, and results from this study provide the foundation for considerable future organizational communication and ICT research.     

Interference canceller for a single-wavelength bidirectional optical-fibre link

A simple and practical electronic technique is presented that provides interchannel-crosstalk isolation to better than a 10?9 BER for a 20 Mbit/s single-wavelength single-fibre full-duplex transmission system.     

Cross-cultural comparison of organizational media evaluation and choice

Managers working in four countries reported the richness of five media, equivocality of 11 situations, preferred media for each situation, and cultural values. The richness and equivocality measures were reliable and unidimensional. Face-to-face was ranked as most, and business memos least, rich. Only E-mail and telephone preferences were significantly correlated with richness. Media preferences for face-to-face and telephone for each situation were highly correlated with the situations' equivocality. Respondents from collectivist countries rated the telephone as less rich, and the business memo as richer, than did respondents from individualist countries.     

Organic Materials and Thin‐Film Structures for Cross‐Point Memory Cells Based on Trapping in Metallic Nanoparticles

Non‐volatile solid‐state memory cells based on composites of metal nanoparticles and polymers are embedded in organic semiconducting host materials. This paper presents data from a wide range of materials and device structures and shows that the switching phenomenon is commonly observed.     

Cramer-Rao lower bounds for QAM phase and frequency estimation

In this paper, we present the true Cramer-Rao lower bounds (CRLBs) for the estimation of phase offset for common quadrature amplitude modulation (QAM), PSK, and PAM signals in AWGN channels. It is shown that the same analysis also applies to the QAM, FSK, and PAM CRLBs for frequency offset estimation. The ratio of the modulated to the unmodulated CRLBs is derived for all QAM, PSK, and PAM signals and calculated for specific cases of interest. This is useful to determine the limiting performance of synchronization circuits for coherent receivers without the need to simulate particular algorithms. The hounds are compared to the existing true CRLBs for an unmodulated carrier wave (CW), BPSK, and QPSK. We investigated new and existing QAM phase estimation algorithms in order to verify the new phase CRLB. This showed that new minimum distance estimator performs close to the QAM bound and provides a large improvement over the power law estimator at moderate to high signal-to-noise ratios     

Effects of Thermal Expansion Mismatch Stresses on th Room-Temperature Fracture of Boron Carbid

Calculation of apparent fracture energies (γ_a) using the applied failure stress and fractographically determined flaw sizes (C) in B₄ C shows γ_a decreasing with C , once C < 100 μm. This is attributed to increasing contributions of microstructural stresses (σ_i) due to thermal expansion anisotropy ( 1 × 10⁻⁶°C⁻¹). Extrapolation of this σ_i contribution to C ∼ G (the grain size) and calculation from maximum thermal expansion mismatch are in reasonable agreement. e.g., giving σ∼ 1000 MPa. Strength-mirror size data also show deviations at higher strengths-smaller mirror sizes consistent with both the occurrence and estimated level of such microstructural stress contributions to failure.     

Terminal residues of hog pancreatic amylase

We have considered a differential diagnosis of clinical hyperkalemia. The clinical signs and symptoms of patients with hyperkalemia are manifold and can involve many organ systems. The nonoliguric chronic renal failure patient with hyporeninemia and hypoaldosteronemia may have as one of his principal problems recurrent hyperkalemia. Treatment of this condition includes well-known modalities such as administration of calcium salts, NaHCO3, removal of potassium with resin or dialysis as well as placement of a transvenous pacemaker in anticipation of bradyarrhythmias or asystole.     

Hartnup disease. Clinical, pathological, and biochemical observations

Hartnup disease is a rare genetic disorder of amino acid transport associated with variable and intermittent clinical abnormalities. A family is described in which three siblings had an intermittently progressive neurological disease and two of the affected siblings had the Hartnup-pattern aminoaciduria. Neuropathological examination of one case showed severe diffuse atrophy, generalized neuronal loss in the cortex, and Purkinje cell loss in the cerebellum. In vivo and in vitro studies of intestinal amino acid transport in the surviving sibling indicated a partial defect in the transport of several neutral amino acids (tryptophan, alanine, serine, and methionine) with normal transport of other neutral amino acids (threonine, phenylalanine, histidine, tyrosine, and isoleucine). Transport of glycine, proline, hydroxyproline, and the basic amino acids appeared normal.