Multiple Independent Channels Research Articles

Inbreeding–stress interactions: evolutionary and conservation consequences

The effect of environmental stress on the magnitude of inbreeding depression has a long history of intensive study. Inbreeding-stress interactions are of great importance to the viability of populations of conservation concern and have numerous evolutionary ramifications. However, such interactions are controversial. Several meta-analyses over the last decade, combined with omic studies, have provided considerable insight into the generality of inbreeding-stress interactions, its physiological basis, and have provided the foundation for future studies. In this review, we examine the genetic and physiological mechanisms proposed to explain why inbreeding-stress interactions occur. We specifically examine whether the increase in inbreeding depression with increasing stress could be due to a concomitant increase in phenotypic variation, using a larger data set than any previous study. Phenotypic variation does usually increase with stress, and this increase can explain some of the inbreeding-stress interaction, but it cannot explain all of it. Overall, research suggests that inbreeding-stress interactions can occur via multiple independent channels, though the relative contribution of each of the mechanisms is unknown. To better understand the causes and consequences of inbreeding-stress interactions in natural populations, future research should focus on elucidating the genetic architecture of such interactions and quantifying naturally occurring levels of stress in the wild.

Equation of motion for multiqubit entanglement in multiple independent noisy channels

We investigate the possibility and conditions to factorize the entanglement evolution of a multiqubit system passing through multi-sided noisy channels. By means of a lower bound of concurrence (LBC) as an entanglement measure, we derive an explicit formula of the LBC evolution of the N-qubit generalized Greenberger–Horne–Zeilinger (GGHZ) state under some typical noisy channels, based on which two kinds of factorizing conditions for the LBC evolution are presented. In this case, the time-dependent LBC can be determined by a product of initial LBC of the system and the LBC evolution of a maximally entangled GGHZ state under the same multi-sided noisy channels. We analyze the realistic situations where these two kinds of factorizing conditions can be satisfied. In addition, we also discuss the dependence of entanglement robustness on the number of qubits and that of the noisy channels.

Diversity analysis for energy detection-based spectrum sensing

In this study the authors perform a diversity analysis for an energy detection-based non-coherent spectrum sensing scheme and benchmark it against a genie aided coherent spectrum sensing scheme, which has full knowledge of the fading channel. In both cases the sensor has access to multiple independent channel observations. Results show that both schemes achieve full diversity. However, the authors find that the coherent scheme approaches this asymptotic limit faster than the non-coherent scheme. Through analysis the authors determine the penalty of the non-coherent scheme over the coherent scheme in converging to the asymptotic limit as a function of the SNR and the number of diversity branches. With these results the authors substantiate analysis, previously made, and thus provide further insights into the trade-off between complexity and performance for spectrum sensing schemes.

Crosstalk Elimination in Dense Wavelength Division Multiplexing Networks: Implementation and Theory

Data traffic for multiple independent data channels can be simultaneously transmitted over a dense wavelength division multiplexing network with complete segregation. A limiting amplifier applied to each channel after the optical to electrical conversion eliminates crosstalk.

Choosing the right multiple channel system to minimize transaction costs

This paper proposes that firms can use a transaction cost approach to make multiple channel system design related decisions. The author differentiates between two types of multiple channel systems and hypothesizes that transaction asset specificity, behavioral uncertainty and environmental uncertainty lead manufacturers to adopt either a dual channel system or a multiple independent channel system. Furthermore, the author proposes that when all three transaction cost variables match with the type of multiple channel system used, firms can minimize their transaction costs and eventually increase their channel system performance in terms of contribution to firm profitability. The author tests the hypotheses with survey data collected from 229 firms. The results support that the fit between the type of multiple channel mix and the three transaction-cost theory variables results in lower transaction costs and higher contribution to profit. The author presents theoretical and managerial implications.

Multiple‐channel and cross‐channel shopping behavior: role of consumer shopping orientations

PurposeThe purpose of this paper is to examine the role of consumer shopping orientations on consumer's channel choice, cross‐channel shopping behavior, and shopping outcomes.Design/methodology/approachUsing multiple sources of data including surveys of store, web, and cross‐channel shoppers and their transaction information, the impact of consumer shopping orientations on comparison‐shopping, likelihood of cross‐channel usage, purchase outcomes including unplanned purchasing, retailer satisfaction, intent to return/abandon purchases, and share of category purchases are investigated.FindingsResults suggest that high‐thrift customers patronizing a cross‐channel retailer are less likely to search for competitive offerings online or offline than customers patronizing a multiple channel retailer. Further, retailer satisfaction is higher for cross‐channel compared to multi‐channel retailers irrespective of the transaction channel used by consumers.Research limitations/implicationsThe data have external validity; however, they lack the control possible in laboratory experiments. Future research should examine if the findings can be replicated in multiple retail sectors.Practical implicationsThese results suggest that brick‐and‐click retailers can exploit synergies between their channels through order online and pick up in store strategies for greater profitability than those who operate multiple independent channels.Originality/valueThis paper examines managerial implications of multiple independent channel vs cross‐channel strategies by retailers using data from customers of a commercial retailer.

PAC vs. MAC for Decentralized Detection Using Noncoherent Modulation

In decentralized detection, local sensor observations have to be communicated to a fusion center through the wireless medium, inherently a multiple-access channel (MAC). As communication is bandwidth- and energy-constrained, it has been suggested to use the properties of the MAC to combine the sensor observations directly on the channel. Although this leads to an array-processing gain if the sensors' transmissions combine coherently on the channel, it has been shown that this is not the case when they combine noncoherently. We review known results for the coherent case and then analyze the noncoherent case based on a simple on/off scheme combined with optimal sensor ldquocensoring.rdquo Since the optimal forwarding function is not available, we also bound the performance using an equivalent communication problem and a centralized estimator to verify trends. We find that for noncoherent modulation, there is no processing gain using the MAC for decentralized detection, but compared to parallel-access channels (PACs) the MAC avoids the noncoherent combining loss. Still the performance of the MAC approach is only of diversity one, as the output of the MAC is approximately a zero-mean complex Gaussian random variable for a large number of sensor. The MAC performance can be increased by using multiple independent channels, each used as a MAC by all sensors, which we term diversity-MAC. This approach always outperforms the PAC scheme on Rayleigh fading channels, where the output is exactly Gaussian, but has inferior performance across random phase channels when few sensors are used, as the PAC does not create ldquoartificialrdquo fading.

Scalable time-correlated photon counting system with multiple independent input channels

Time-correlated single photon counting continues to gain importance in a wide range of applications. Most prominently, it is used for time-resolved fluorescence measurements with sensitivity down to the single molecule level. While the primary goal of the method used to be the determination of fluorescence lifetimes upon optical excitation by short light pulses, recent modifications and refinements of instrumentation and methodology allow for the recovery of much more information from the detected photons, and enable entirely new applications. This is achieved most successfully by continuously recording individually detected photons with their arrival time and detection channel information (time tagging), thus avoiding premature data reduction and concomitant loss of information. An important property of the instrumentation used is the number of detection channels and the way they interrelate. Here we present a new instrument architecture that allows scalability in terms of the number of input channels while all channels are synchronized to picoseconds of relative timing and yet operate independent of each other. This is achieved by means of a modular design with independent crystal-locked time digitizers and a central processing unit for sorting and processing of the timing data. The modules communicate through high speed serial links supporting the full throughput rate of the time digitizers. Event processing is implemented in programmable logic, permitting classical histogramming, as well as time tagging of individual photons and their temporally ordered streaming to the host computer. Based on the time-ordered event data, any algorithms and methods for the analysis of fluorescence dynamics can be implemented not only in postprocessing but also in real time. Results from recently emerging single molecule applications are presented to demonstrate the capabilities of the instrument.

Power Allocation for Amplify-and-Forward Cooperative Transmission Over Rayleigh-Fading Channels

Cooperative transmission has been used to achieve diversity gain through partner to create multiple independent fading channels. It has attracted lots of research attention in recent years. An important question in cooperative communication is power allocation. Given the same total power, how much should be allocated to self-information transmission and how much to relayinginformation transmission. In this paper, we investigate power allocation problem using amplify-and-forward (AF) protocol considering bit error rate (BER) performance of both users and the work region of two cooperative users. We solve cooperative ratio, which is defined as the ratio of power used for cooperative transmission over the total power. We first consider both users applying the same ratio, and then extend to two-dimensional cooperative ratio problem. Our results show that it is sufficient to allocate both users the same ratio. This value is specified by the user with a weaker channel gain to the destination, i.e., bottleneck link.With appropriate selection of the cooperative ratio, the BER performance of both users can be improved significantly. User fairness is also considered in the analysis.

Low complexity MIMO scheduling with channel decomposition using capacity upperbound

In multiuser MIMO systems, the base station schedules transmissions to a group of users simultaneously. Since the data transmitted to each user are different, in order to avoid the inter-user interference, a transmit preprocessing technique which decomposes the multiuser MIMO downlink channel into multiple parallel independent single-user MIMO channels can be used. When the number of users is larger than the maximum that the system can support simultaneously, the base station selects a subset of users who have the best instantaneous channel quality to maximize the system throughput. Since the exhaustive search for the optimal user set is computationally prohibitive, a low complexity scheduling algorithm which aims to maximize the capacity upper bound is proposed. Simulation results show that the proposed scheduling algorithm achieves comparable total throughput as the optimal algorithm with much lower complexity.

Multi-channel counter-current chromatography for high-throughput fractionation of natural products for drug discovery

A multi-channel counter-current chromatography (CCC) method has been designed and fabricated for the high-throughput fractionation of natural products without complications sometimes encountered with other conventional chromatographic systems, such as irreversible adsorptive constituent losses and deactivation, tailing of solute peaks and contamination. It has multiple independent CCC channels and each channel connects independent separation column(s) by parallel flow tubes, and thus the multi-channel CCC apparatus can achieve simultaneously two or more independent chromatographic processes. Furthermore, a high-throughput CCC fractionation method for natural products has been developed by a combination of a new three-channel CCC apparatus and conventional parallel chromatographic devices including pumps, sample injectors, effluent detectors and collectors, and its performance has been displayed on the fractionation of ethyl acetate extracts of three natural materials Solidago canadensis, Suillus placidus, and Trichosanthes kirilowii, which are found to be potent cytotoxic to tumor cell lines in the course of screening the antitumor candidates. By combination of biological screening programs and preparative high-performance liquid chromatography (HPLC) purification, 22.8 mg 6β-angeloyloxykolavenic acid and 29.4 mg 6β-tigloyloxykolavenic acid for S. canadensis, 25.3 mg suillin for S. placidus, and 6.8 mg 23,24-dihydrocucurbitacin B for T. Kirilowii as their major cytotoxic principles were isolated from each 1000 mg crude ethyl acetate exctract. Their chemical structures were characterized by electrospray ionization mass spectrometry, one- and two-dimensional nuclear magnetic resonance. The overall results indicate the multi-channel CCC is very useful for high-throughput fractionation of natural products for drug discovery in spite of the solvent balancing requirement and the lower resolution of the shorter CCC columns.

Resource Allocation for Wireless Fading Relay Channels: Max-Min Solution

Resource allocation is investigated for fading relay channels under separate power constraints at the source and relay nodes. As a basic information-theoretic model for fading relay channels, the parallel relay channel is first studied, which consists of multiple independent three-terminal relay channels as subchannels. Lower and upper bounds on the capacity are derived, and are shown to match, and thus establish the capacity for the parallel relay channel with degraded subchannels. This capacity theorem is further demonstrated via the Gaussian parallel relay channel with degraded subchannels, for which the synchronized and asynchronized capacities are obtained. The capacity-achieving power allocation at the source and relay nodes among the subchannels is partially characterized for the synchronized case and fully characterized for the asynchronized case. The fading relay channel is then studied, which is based on the three-terminal relay channel with each communication link being corrupted by a multiplicative fading gain coefficient as well as an additive Gaussian noise term. For each link, the fading state information is assumed to be known at both the transmitter and the receiver. The source and relay nodes are allowed to allocate their power adaptively according to the instantaneous channel state information. The source and relay nodes are assumed to be subject to separate power constraints. For both the full-duplex and half-duplex cases, power allocations that maximize the achievable rates are obtained. In the half-duplex case, the power allocation needs to be jointly optimized with the channel resource (time and bandwidth) allocation between the two orthogonal channels over which the relay node transmits and receives. Capacities are established for fading relay channels that satisfy certain conditions.

A multi-channel architecture for high-performance NAND flash-based storage system

Many mobile devices demand a large-capacity and high-performance storage system in order to store, retrieve, and process large multimedia data quickly. In this paper, we present a high-performance NAND flash-based storage system based on a multi-channel architecture. The proposed system consists of multiple independent channels, where each channel has multiple NAND flash memory chips. On this hardware, we investigate three optimization techniques to exploit I/O parallelism: striping, interleaving, and pipelining. By combining all the optimization techniques carefully, our system has shown 3.6 times higher overall performance compared to the conventional single-channel architecture.

DCMA: A Label Switching MAC for Efficient Packet Forwarding in Multihop Wireless Networks

This paper addresses the problem of efficient packet forwarding in a multihop, wireless "mesh" network. We present an efficient interface contained forwarding (ICF) architecture for a "wireless router," i.e., a forwarding node with a single wireless network interface card (NIC) in a multihop wireless network that allows a packet to be forwarded entirely within the NIC of the forwarding node without requiring per-packet intervention by the node's CPU. To effectively forward packets in a pipelined fashion without incurring the 802.11-related overheads of multiple independent channel accesses, we specify a slightly modified version of the 802.11 MAC, called data driven cut-through multiple access (DCMA) that uses multiprotocol label switching (MPLS)-like labels in the control packets, in conjunction with a combined ACK/RTS packet, to reduce 802.11 channel access latencies. Our proposed technique can be used in combination with "frame bursting" as specified by the IEEE 802.11e standard to provide an end-to-end cut-through channel access. Using extensive simulations, we compare the performance of DCMA with 802.11 DCF MAC with respect to throughput and latency and suggest a suitable operating region to get maximum benefits using our mechanism as compared to 802.11

A Transmit Preprocessing Technique for Multiuser MIMO Systems Using a Decomposition Approach

We introduce a transmit preprocessing technique for the downlink of multiuser multiple-input multiple-output (MIMO) systems. It decomposes the multiuser MIMO downlink channel into multiple parallel independent single-user MIMO downlink channels. Some key properties are that each equivalent single-user MIMO channel has the same properties as a conventional single-user MIMO channel, and that increasing the number of transmit antennas of the multiuser system by one increases the number of spatial channels to each user by one. Simulation results are also provided and these results demonstrate the potential of our technique in terms of performance and capacity.

Simultaneous label swapping and wavelength conversion of multiple independent WDM channels in an all-optical MPLS network using PPLN waveguides as wavelength converters

This paper presents the demonstration of all-optical simultaneous label swapping and wavelength conversion of multiple independent wavelength-division multiplexed (WDM) channels using periodically poled lithium niobate (PPLN) waveguides as wavelength converters. Label swapping is one of the required functions in the physical layer for efficient data flow control in the proposed multiprotocol label switching (MPLS) networks. The technique operates directly on the optical signal without optoelectronic (O/E) conversion; therefore, it is bit-rate, label length, and protocol/format independent. Experimental results are presented for the label swapping of distinct 8-b-long labels in a system with 2 WDM data channels at 10 Gb/s. There is a guard time of 400 ps between the payload and the label. The power penalty introduced by the method is less than 3 dB. This method can potentially accommodate 10 WDM channels simultaneously over the PPLN waveguide's ∼40 nm /spl lambda/-shifting bandwidth.

Sound processing circuit

A sound processing circuit for distributing low frequency signal components of multichannel audio signals. The sound processing circuit filters low frequency signal components from the digital audio signals of m (m≦n) specified channels using an exclusive channel having low frequency signals and n (n>1) multiple independent channels, and outputs the filtered low frequency signal components as part of a low frequency signal channel. The sound processor circuit comprises m high-pass filters to receive digital audio signals from m of specified channels, and allows the signal components having a frequency higher than a cut-off frequency fc to pass; m first coefficient multipliers receive the digital audio signals of the m of specified channels and multiply the signals by a multiplication coefficient ai (0<ai<1); a second coefficient multiplier receives the digital audio signal of the exclusive channel, and multiplies the signal by a multiplication coefficient aL (0<aL<1); an adder for adding each output of the m first coefficient multipliers and the output of the second coefficient multiplier to produce a synthetic audio signal; and a low pass filter which receives the synthetic audio signal from the adder, and allows the signal components having a frequency lower than the cut-off frequency fc to pass.

Exact pairwise error probability of space-time codes

We describe a simple technique for the numerical calculation, within any desired degree of accuracy, of the pairwise error probability (PEP) of space-time codes over fading channels. This method applies also to the calculation of E[Q(/spl radic//spl xi/)] for any nonnegative random variable /spl xi/ whose moment-generating function /spl Phi//sub /spl xi//(s)=E[exp(-s/spl xi/)] is known. Its application to the multiple antenna independent Rayleigh-fading channel and to the Rayleigh block fading channel is discussed, and illustrated by two simple examples.

Gating and permeability of ion channels produced by botulinum toxin types A and E in PC12 cell membranes

Botulinum neurotoxin (BoNT) is known to produce cationic channels in artificial bilayers. This study examined ion channels formed by BoNT in native membranes from cultured PC12 cells under conditions approximating those thought to occur during toxin internalization. Membrane patches were excised from PC12 cells using patch electrodes and exposed to symmetrical solutions containing either 200 mM CsCl, RbCl or KCl. The patch pipettes also contained 1–5 μg/ml BoNT buffered to pH 5.3 while the bath solutions were buffered to pH 7.0. In the presence of toxin, bursts of ion channel openings were observed. These toxin-induced channels were most active with a negative voltage applied to the same side as the toxin (cis). The increased activity at negative voltages was due to an increase in mean open time of e-fold per 120 mV and a decrease in mean closed time between bursts of e-fold per 110 mV. The shorter mean closed time within a burst was independent of membrane voltage. While BoNT-induced ion channels started as a single conductance level of 27 pS (KCl), 34 pS (RbCl) or 46 pS (CsCl) they typically increased in roughly equal steps to five or more times the original channel conductance. These higher conductance BoNT `channels' opened and closed synchronously and could be distinguished from superposition of multiple independent channels. Despite differences in putative transmembrane sequences between BoNT/A and BoNT/E, both serotypes evidenced the same channel conductance and mean open time.

Optical demultiplexing for subcarrier multiplexed systems

Subcarrier multiplexing (SCM) is an attractively simple technique for establishing multiple independent channels over a single fiber. At the receiver, electrical mixing converts a selected channel to baseband. The photodiode, oscillator, mixer, and preamplifier must, however, operate up to the highest subcarrier frequency. The use of an optical filter for channel selection allows any subcarrier to be accessed with only baseband electronics. To obtain the best performance with this approach, sub-subcarrier modulation is needed. In this paper we propose a method suitable for externally modulated CATV systems and show that the sensitivity is comparable to the best conventional receivers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>