Numerical studies on channel formation and growth during solidification: Effect of process parameters

In the present work, solidification of a hyper-eutectic ammonium chloride solution in a bottom-cooled cavity (i.e. with stable thermal gradient) is numerically studied. A Rayleigh number based criterion is developed, which determines the conditions favorable for freckles formation. This criterion, when expressed in terms of physical properties and process parameters, yields the condition for plume formation as a function of concentration, liquid fraction, permeability, growth rate of a mushy layer and thermophysical properties. Subsequently, numerical simulations are performed for cases with initial and boundary conditions favoring freckle formation. The effects of parameters, such as cooling rate and initial concentration, on the formation and growth of freckles are investigated. It was found that a high cooling rate produced larger and more defined channels which are retained for a longer durations. Similarly, a lower initial concentration of solute resulted in fewer but more pronounced channels. The number and size of channels are also found to be related to the mushy zone thickness. The trends predicted with regard to the variation of number of channels with time under different process conditions are in accordance with the experimental observations reported in the literature.

Robust joint precoder/receive filter designs for multiuser MIMO downlink

In this paper, we consider robust joint linear precoder/receive filter designs for multiuser multi-input multi-output (MIMO) downlink that minimize the sum mean square error (SMSE) in the presence of imperfect channel state information at the transmitter (CSIT). The base station (BS) is equipped with multiple transmit antennas, and each user terminal is equipped with one or more receive antennas. We consider a stochastic error (SE) model and a norm-bounded error (NBE) model for the CSIT error. In the case of CSIT error following SE model, we compute the desired downlink precoder/receive filter matrices by solving the simpler uplink problem by exploiting the uplink-downlink duality for the MSE region. In the case of the CSIT error following the NBE model, we consider the worst-case SMSE as the objective function, and propose an iterative algorithm for the robust transceiver design. The robustness of the proposed algorithms to imperfections in CSIT is illustrated through simulations.

Uplink Power Control and Base Station Association in Multichannel Cellular Networks

A combined base station association and power control problem is studied for the uplink of multichannel multicell cellular networks, in which each channel is used by exactly one cell (i.e., base station). A distributed association and power update algorithm is proposed and shown to converge to a Nash equilibrium of a noncooperative game. We consider network models with discrete mobiles (yielding an atomic congestion game), as well as a continuum of mobiles (yielding a population game). We find that the equilibria need not be Pareto efficient, nor need they be system optimal. To address the lack of system optimality, we propose pricing mechanisms. It is shown that these mechanisms can be implemented in a distributed fashion.

The impact of communication technologies on life and relationship satisfaction

Previous studies have shown a relationship between the use of communications technology and well-being, particularly mediated through its effect on personal relationships. However, there is some debate over whether this effect is positive or negative. The present study explored this issue further, examining whether the effect varies depending on the type of communications technology, and the nature of the personal relationship. An online survey was conducted with 3,421 participants in three countries (Australia, UK and US). It examined the use of ten communication methods, overall satisfaction with life and satisfaction with four different kinds of relationships (close and extended family, and close and distant friends). Results indicate that richer communication methods, which include non-verbal cues, were positively associated with both overall satisfaction with life and satisfaction with relationships. These methods included face-to-face communication, and phone and video calls. Conversely, more restricted methods, such as text messaging and instant messaging, were negatively associated with both variables. Social networking was negatively associated with overall satisfaction, but not with satisfaction with relationships. The strength of the association between a communications method and satisfaction with a relationship varied depending on the type of relationship, but whether it was positive or negative did not change.

Performance of Quantized Equal Gain Transmission With Noisy Feedback Channels

In this paper, new results and insights are derived for the performance of multiple-input, single-output systems with beamforming at the transmitter, when the channel state information is quantized and sent to the transmitter over a noisy feedback channel. It is assumed that there exists a per-antenna power constraint at the transmitter, hence, the equal gain transmission (EGT) beamforming vector is quantized and sent from the receiver to the transmitter. The loss in received signal-to-noise ratio (SNR) relative to perfect beamforming is analytically characterized, and it is shown that at high rates, the overall distortion can be expressed as the sum of the quantization-induced distortion and the channel error-induced distortion, and that the asymptotic performance depends on the error-rate behavior of the noisy feedback channel as the number of codepoints gets large. The optimum density of codepoints (also known as the point density) that minimizes the overall distortion subject to a boundedness constraint is shown to be the same as the point density for a noiseless feedback channel, i.e., the uniform density. The binary symmetric channel with random index assignment is a special case of the analysis, and it is shown that as the number of quantized bits gets large the distortion approaches the same as that obtained with random beamforming. The accuracy of the theoretical expressions obtained are verified through Monte Carlo simulations.

Communication and Political Crisis: Media, Politics and Governance in a Globalized Public Sphere

Communication and Political Crisis explores the role of the global media in a period of intensifying geopolitical conflict. Through case studies drawn from domestic and international political crises such as the conflicts in the Middle East and Ukraine, leading media scholar Brian McNair argues that the digitized, globalized public sphere now confronted by all political actors has produced new opportunities for social progress and democratic reform, as well as new channels for state propaganda and terrorist spectaculars such as those performed by the Islamic State and Al Qaeda. In this major work, McNair argues that the role of digital communication will be crucial in determining the outcome of pressing global issues such as the future of feminism and gay rights, freedom of speech and media, and democracy itself.

Comprehending adverbs of doubt and certainty in health communication: A multidimensional scaling approach

This research explored the feasibility of using multidimensional scaling (MDS) analysis in novel combination with other techniques to study comprehension of epistemic adverbs expressing doubt and certainty (e.g., evidently, obviously, probably) as they relate to health communication in clinical settings. In Study 1, Australian English speakers performed a dissimilarity-rating task with sentence pairs containing the target stimuli, presented as "doctors' opinions". Ratings were analyzed using a combination of cultural consensus analysis (factor analysis across participants), weighted-data classical-MDS, and cluster analysis. Analyses revealed strong within-community consistency for a 3-dimensional semantic space solution that took into account individual differences, strong statistical acceptability of the MDS results in terms of stress and explained variance, and semantic configurations that were interpretable in terms of linguistic analyses of the target adverbs. The results confirmed the feasibility of using MDS in this context. Study 2 replicated the results with Canadian English speakers on the same task. Semantic analyses and stress decomposition analysis were performed on the Australian and Canadian data sets, revealing similarities and differences between the two groups. Overall, the results support using MDS to study comprehension of words critical for health communication, including in future studies, for example, second language speaking patients and/or practitioners. More broadly, the results indicate that the techniques described should be promising for comprehension studies in many communicative domains, in both clinical settings and beyond, and including those targeting other aspects of language and focusing on comparisons across different speech communities.

Slogans of Change : Three Outlooks on Finnish Television

The study Slogans of Change. Three Outlooks on Finnish Television Contents is concerned with alleged changes of television contents during the 1990s and 2000s, such as dumbing down, tabloidisation, entertainisation , and the like. Specifically, the focus is on the ways these changes might manifest in Finnish television. The aim of the study has been threefold: 1. To operationalise public and academic discussions about changes via specific slogans emerging from the debates; 2. Consequently, to study the slogans empirically and reflect on the findings with earlier research, including studies on institutional and audience-related aspects; 3. Finally, to suggest what the findings might mean regarding discussions about television s role, and what kinds of slogans or concepts might best serve future discussions and research. The empirical outlooks presented in this study offer analyses with three different sets of opposing slogans of change. The outlooks also follow three different traditions of the study of television. The first outlook focuses on quantity, as it gives a longitudinal (1993-2004), macro-level view on programme structures. The methodological approach is derived from media economic and policy studies. The claims that frame the analysis are convergence versus diversification of programme structures. The second outlook provides quantitative and qualitative views on the characteristics and quality  the term signifying essence as well as worth  of Finnish television journalism during sample weeks from the years 2002 and 2003. This outlook follows the traditions of quantitative content analysis found in journalism studies coupled with descriptive qualitative content analyses. The slogans reflected in this section are the lightening or widening of journalism. The third outlook narrows down the material and focuses at a micro-level on form; that is, communicative conventions in a small array of selected programmes in 1993, 2000 and during 2002-2004. The analyses have been inspired by the method of conversation analysis of verbal interaction, and coupled with qualitative close readings, with the focus of different communicative situations in the programmes. The catchphrases employed in this part are emotainment versus democratainment, coupled with more specific claims of discursive hybridisation and conversationalisation. The findings depict that, empirically, changes in Finnish television contents are not clear linear trends and cannot easily be moulded into neat slogans. The quantitative outlook on programme output during 1993-2004 depicts a tendency towards differentiation of channels, paving the way for the multi-channel digital system. The change in programme structures, however, is not dramatic on the level of total output. The second outlook suggests that the dualistic concepts, such as the pair information-entertainment, are not sufficient in understanding the array and changes of programmes that could be called journalism. The outlook on communicative conventions highlights hybridisation in the manner of television talk and its relation to broader debates on contents. Despite the three dissimilar empirical approaches, unifying aspects emerge. The outlooks suggest, albeit in different ways, tendencies toward distinction and polarisation. This study proposes that in order to facilitate a more nuanced understanding of the changes in television contents, dualistic slogans should be replaced with a multi-dimensional understanding of the concept of diversity.

A novel iterative frequency offset estimation in an OFDM system

The Orthogonal Frequency Division Multiplexing (OFDM) is a form of Multi-Carrier Modulation where the data stream is transmitted over a number of carriers which are orthogonal to each other i.e. the carrier spacing is selected such that each carrier is located at the zeroes of all other carriers in the spectral domain. This paper proposes a new novel iterative frequency offset estimation algorithm for an OFDM system in order to receive the OFDM data symbols error-free over the noisy channel at the receiver and to achieve frequency synchronization between the transmitter and the receiver. The performance of this algorithm has been studied in AWGN, ADSL and SUI channels successfully.

Effects of membrane channel-forming polypeptides on mitochondrial oxidative phosphorylation. A comparison of alamethicin, gramicidin A, melittin and tetraacetyl melittin

Transmembrane channel-forming polypeptides can function as uncouplers of mitochondrial oxidative phosphorylation. The observed effects are dependent on the phosphate ion (Pi) concentration in the medium. At low Pi (2.5 mM) the order of uncoupling efficiencies is gramicidin A much greater than alamethicin greater than tetraacetyl melittin greater than melittin. The remarkably high activity of gramicidin A suggests insertion of preformed channel dimers into the membrane. It is also suggested that lipid phase association of peptides is necessary in the other cases. At Pi = 100 mM inhibitory effects are observed for alamethicin and tetraacetyl melittin. Less pronounced inhibition is seen for melittin, while no such effect is noted for gramicidin A. The site of inhibition is shown to be complex IV, and the differences in the behavior of the peptides are rationalized in terms of channel structures.

A novel fractional sampling offset estimation in an OFDM system

The Orthogonal Frequency Division Multiplexing (OFDM) is a form of Multi-Carrier Modulation where the data stream is transmitted over a number of carriers which are orthogonal to each other i.e. the carrier spacing is selected such that each carrier is located at the zeroes of all other carriers in the spectral domain. This paper proposes a new novel sampling offset estimation algorithm for an OFDM system in order to receive the OFDM data symbols error-free over the noisy channel at the receiver and to achieve fine timing synchronization between the transmitter and the receiver. The performance of this algorithm has been studied in AWGN, ADSL and SUI channels successfully.

A systematic design of high-rate full-diversity space-frequency codes for MIMO-OFDM systems

This paper presents a systematic construction of high-rate and full-diversity space-frequency block codes for MIMO-OFDM systems. While all prior constructions offer only a maximum rate of one complex symbol per channel use, our construction yields rate equal to the number of transmit antennas and simultaneously achieves full-diversity. The proposed construction works for arbitrary number of transmit antennas and arbitrary channel power delay profile. A key step in this construction is the generalization of the stacked matrix code design criteria given by Bolcskei et.al., (IEEE WCNC 2000). Explicit equivalence of our generalized code design criteria with the Hadamard-product based criteria of W. Su et.al., (lEEE Trans. Sig. Proc. Nov 2003) is established and new high-rate codes are constructed using our criteria.

A unified construction of space-time codes with optimal rate-diversity tradeoff

The problem of constructing space-time (ST) block codes over a fixed, desired signal constellation is considered. In this situation, there is a tradeoff between the transmission rate as measured in constellation symbols per channel use and the transmit diversity gain achieved by the code. The transmit diversity is a measure of the rate of polynomial decay of pairwise error probability of the code with increase in the signal-to-noise ratio (SNR). In the setting of a quasi-static channel model, let n(t) denote the number of transmit antennas and T the block interval. For any n(t) <= T, a unified construction of (n(t) x T) ST codes is provided here, for a class of signal constellations that includes the familiar pulse-amplitude (PAM), quadrature-amplitude (QAM), and 2(K)-ary phase-shift-keying (PSK) modulations as special cases. The construction is optimal as measured by the rate-diversity tradeoff and can achieve any given integer point on the rate-diversity tradeoff curve. An estimate of the coding gain realized is given. Other results presented here include i) an extension of the optimal unified construction to the multiple fading block case, ii) a version of the optimal unified construction in which the underlying binary block codes are replaced by trellis codes, iii) the providing of a linear dispersion form for the underlying binary block codes, iv) a Gray-mapped version of the unified construction, and v) a generalization of construction of the S-ary case corresponding to constellations of size S-K. Items ii) and iii) are aimed at simplifying the decoding of this class of ST codes.

Effects of membrane channel-forming polypeptides on mitochondrial oxidative phosphorylation. A comparison of alamethicin, gramicidin A, melittin and tetraacetyl melittin.

Transmembrane channel-forming polypeptides can function as uncouplers of mitochondrial oxidative phosphorylation. The observed effects are dependent on the phosphate ion (Pi) concentration in the medium. At low Pi (2.5 mM) the order of uncoupling efficiencies is gramicidin A much greater than alamethicin greater than tetraacetyl melittin greater than melittin. The remarkably high activity of gramicidin A suggests insertion of preformed channel dimers into the membrane. It is also suggested that lipid phase association of peptides is necessary in the other cases. At Pi = 100 mM inhibitory effects are observed for alamethicin and tetraacetyl melittin. Less pronounced inhibition is seen for melittin, while no such effect is noted for gramicidin A. The site of inhibition is shown to be complex IV, and the differences in the behavior of the peptides are rationalized in terms of channel structures.

Ion channel formation by zervamicin-IIB. A molecular modelling study.

Zervamicin-IIB (Zrv-IIB) is a 16 residue peptaibol which forms voltage-activated, multiple conductance level channels in planar lipid bilayers. A molecular model of Zrv-IIB channels is presented. The structure of monomeric Zrv-IIB is based upon the crystal structure of Zervamicin-Leu. The helical backbone is kinked by a hydroxyproline residue at position 10. Zrv-IIB channels are modelled as helix bundles of from 4 to 8 parallel helices surrounding a central pore. The monomers are packed with their C-terminal helical segments in close contact, and the bundles are stabilized by hydrogen bonds between glutamine 11 and hydroxyproline 10 of adjacent helices. Interaction energy profiles for movement of three different probes species (K+, Cl- and water) through the central pore are analyzed. The conformations of: (a) the sidechain of glutamine 3; (b) the hydroxyl group of hydroxyproline 10; and (c) the C-terminal hydroxyl group are "optimized" in order to maximize favourable interactions between the channel and the probes, resulting in favourable interaction energy profiles for all three. This suggests that conformational flexibility of polar sidechains enables the channel lining to mimic an aqueous environment.