Optimal strategies for sending information through a quantum channel

Quantum states can be used to encode the information contained in a direction, i.e., in a unit vector. We present the best encoding procedure when the quantum state is made up of N spins (qubits). We find that the quality of this optimal procedure, which we quantify in terms of the fidelity, depends solely on the dimension of the encoding space. We also investigate the use of spatial rotations on a quantum state, which provide a natural and less demanding encoding. In this case we prove that the fidelity is directly related to the largest zeros of the Legendre and Jacobi polynomials. We also discuss our results in terms of the information gain.

s-wave charmed baryon resonances from a coupled-channel approach with heavy quark symmetry

We study charmed baryon resonances that are generated dynamically within a unitary meson-baryon coupled-channel model that treats the heavy pseudoscalar and vector mesons on equal footing as required by heavy-quark symmetry. It is an extension of recent SU(4) models with t-channel vector-meson exchanges to an SU(8) spin-flavor scheme, but differs considerably from the SU(4) approach in how the strong breaking of the flavor symmetry is implemented. Some of our dynamically generated states can be readily assigned to recently observed baryon resonances, while others do not have a straightforward identification and require the compilation of more data as well as an extension of the model to d-wave meson-baryon interactions and p-wave coupling in the neglected s- and u-channel diagrams. Of several novelties, we find that the Delta c(2595), which emerged as a ND quasibound state within the SU(4) approaches, becomes predominantly a ND* quasibound state in the present SU(8) scheme.

Blind channel deconvolution of real world signals using source separation techniques

In this paper we present a method for blind deconvolution of linear channels based on source separation techniques, for real word signals. This technique applied to blind deconvolution problems is based in exploiting not the spatial independence between signals but the temporal independence between samples of the signal. Our objective is to minimize the mutual information between samples of the output in order to retrieve the original signal. In order to make use of use this idea the input signal must be a non-Gaussian i.i.d. signal. Because most real world signals do not have this i.i.d. nature, we will need to preprocess the original signal before the transmission into the channel. Likewise we should assure that the transmitted signal has non-Gaussian statistics in order to achieve the correct function of the algorithm. The strategy used for this preprocessing will be presented in this paper. If the receiver has the inverse of the preprocess, the original signal can be reconstructed without the convolutive distortion.

Solid-Phase Synthesis of New Trp(Nps)-Containing Dipeptide Derivatives as TRPV1 Channel Blockers

Trp(Nps)-Lys-NH2 derivatives, bearing alkyl or guanidine groups either at the N-terminus or on the Lys side-chain or at both positions were conveniently prepared on solid-phase and evaluated as TRPV1 channel antagonists.

Joint physical-MAC layer design of the broadcast channel protocol in adhoc networks

Broadcast transmission mode in ad hoc networks is critical to manage multihop routing or providing medium accesscontrol (MAC)-layer fairness. In this paper, it is shown that ahigher capacity to exchange information among neighbors may beobtained through a physical-MAC cross-layer design of the broadcastprotocol exploiting signal separation principles. Coherentdetection and separation of contending nodes is possible throughtraining sequences which are selected at random from a reducedset. Guidelines for the design of this set are derived for a lowimpact on the network performance and the receiver complexity.

ML approaches to channel estimation for pilot-aided multi-rate DS/CDMA systems

This paper analyzes the asymptotic performance of maximum likelihood (ML) channel estimation algorithms in wideband code division multiple access (WCDMA) scenarios. We concentrate on systems with periodic spreading sequences (period larger than or equal to the symbol span) where the transmitted signal contains a code division multiplexed pilot for channel estimation purposes. First, the asymptotic covariances of the training-only, semi-blind conditional maximum likelihood (CML) and semi-blind Gaussian maximum likelihood (GML) channelestimators are derived. Then, these formulas are further simplified assuming randomized spreading and training sequences under the approximation of high spreading factors and high number of codes. The results provide a useful tool to describe the performance of the channel estimators as a function of basicsystem parameters such as number of codes, spreading factors, or traffic to training power ratio.

On the inclusion of channel's time dependence in a hidden Markov model for blind channel estimation

In this paper, the theory of hidden Markov models (HMM) isapplied to the problem of blind (without training sequences) channel estimationand data detection. Within a HMM framework, the Baum–Welch(BW) identification algorithm is frequently used to find out maximum-likelihood (ML) estimates of the corresponding model. However, such a procedureassumes the model (i.e., the channel response) to be static throughoutthe observation sequence. By means of introducing a parametric model fortime-varying channel responses, a version of the algorithm, which is moreappropriate for mobile channels [time-dependent Baum-Welch (TDBW)] isderived. Aiming to compare algorithm behavior, a set of computer simulationsfor a GSM scenario is provided. Results indicate that, in comparisonto other Baum–Welch (BW) versions of the algorithm, the TDBW approachattains a remarkable enhancement in performance. For that purpose, onlya moderate increase in computational complexity is needed.

Blind channel estimation and data detection using hidden Markov models theory

In this correspondence, we propose applying the hiddenMarkov models (HMM) theory to the problem of blind channel estimationand data detection. The Baum–Welch (BW) algorithm, which is able toestimate all the parameters of the model, is enriched by introducingsome linear constraints emerging from a linear FIR hypothesis on thechannel. Additionally, a version of the algorithm that is suitable for timevaryingchannels is also presented. Performance is analyzed in a GSMenvironment using standard test channels and is found to be close to thatobtained with a nonblind receiver.

Linear transceiver design in nonregenerative relays with channel state information

This paper deals with the design of nonregenerativerelaying transceivers in cooperative systems where channel stateinformation (CSI) is available at the relay station. The conventionalnonregenerative approach is the amplify and forward(A&F) approach, where the signal received at the relay is simplyamplified and retransmitted. In this paper, we propose an alternativelinear transceiver design for nonregenerative relaying(including pure relaying and the cooperative transmission cases),making proper use of CSI at the relay station. Specifically, wedesign the optimum linear filtering performed on the data to beforwarded at the relay. As optimization criteria, we have consideredthe maximization of mutual information (that provides aninformation rate for which reliable communication is possible) fora given available transmission power at the relay station. Threedifferent levels of CSI can be considered at the relay station: onlyfirst hop channel information (between the source and relay);first hop channel and second hop channel (between relay anddestination) information, or a third situation where the relaymay have complete cooperative channel information includingall the links: first and second hop channels and also the directchannel between source and destination. Despite the latter beinga more unrealistic situation, since it requires the destination toinform the relay station about the direct channel, it is useful as anupper benchmark. In this paper, we consider the last two casesrelating to CSI.We compare the performance so obtained with theperformance for the conventional A&F approach, and also withthe performance of regenerative relays and direct noncooperativetransmission for two particular cases: narrowband multiple-inputmultiple-output transceivers and wideband single input singleoutput orthogonal frequency division multiplex transmissions.

Measurement of a Structured Backflow in an Open Small Channel Induced by Surface-Tension Gradients

We present experiments in which the laterally confined flow of a surfactant film driven by controlled surface tension gradients causes the subtended liquid layer to self-organize into an inner upstream microduct surrounded by the downstream flow. The anomalous interfacial flow profiles and the concomitant backflow are a result of the feedback between two-dimensional and three-dimensional microfluidics realized during flow in open microchannels. Bulk and surface particle image velocimetry data combined with an interfacial hydrodynamics model explain the dependence of the observed phenomena on channel geometry.

Observations on the feeding habits of the narrow mouthed cat shark Schroederichthys bivius (Chondrichthyes, Scyliorhinidae) in the Beagle Channel

The study of the stomach contents of 97 specimens of the narrow mouthed cat shark Schroederichthys bivius shows that their basic food consists of crabs, mainly Munida subrugosa. No significant variations were observed between size classes. The strongly developed sexual dimorphism in Touch morphology and mouth shape was not correlated with the diet of males and females

Increased voltage-dependent K+ channel Kv1.3 and Kv1.5 expression correlates with leiomyosarcoma aggressiveness

Voltage-dependent K+ channels (Kv) are involved in the proliferation and differentiation of mammalian cells, since Kv antagonists impair cell cycle progression. Although myofibers are terminally differentiated, some myoblasts may re-enter the cell cycle and proliferate. Since Kv1.3 and Kv1.5 expression is remodeled during tumorigenesis and is involved in smooth muscle proliferation, the purpose of this study was to analyze the expression of Kv1.3 and Kv1.5 in smooth muscle neoplasms. In the present study, we examined human samples of smooth muscle tumors together with healthy speci­mens. Thus, leiomyoma (LM) and leiomyosarcoma (LMS) tumors were analyzed. Results showed that Kv1.3 was poorly expressed in the healthy muscle and indolent LM specimens, whereas aggressive LMS showed high levels of Kv1.3 expression. Kv1.5 staining was correlated with malignancy. The findings show a remodeling of Kv1.3 and Kv1.5 in human smooth muscle sarcoma. A correlation of Kv1.3 and Kv1.5 expression with tumor aggressiveness was observed. Thus, our results indicate Kv1.5 and Kv1.3 as potential tumorigenic targets for aggressive human LMS.

The L-type voltage-gated calcium channel modulates microglial pro-inflammatory activity

Under pathological conditions, microglia, the resident CNS immune cells, become reactive and release pro-inflammatory cytokines and neurotoxic factors. We investigated whether this phenotypic switch includes changes in the expression of the L-type voltage-gated calcium channel (VGCC) in a rat model of N-methyl-d-aspartate-induced hippocampal neurodegeneration. Double immunohistochemistry and confocal microscopy evidenced that activated microglia express the L-type VGCC. We then analyzed whether BV2 microglia express functional L-type VGCC, and investigated the latter's role in microglial cytokine release and phagocytic capacity. Activated BV2 microglia express the CaV1.2 and CaV1.3 subunits of the L-type VGCC determined by reverse transcription-polymerase chain reaction, Western blot and immunocytochemistry. Depolarization with KCl induced a Ca2+ entry facilitated by Bay k8644 and partially blocked with nifedipine, which also reduced TNF-α and NO release by 40%. However, no nifedipine effect on BV2 microglia viability or phagocytic capacity was observed. Our results suggest that in CNS inflammatory processes, the L-type VGCC plays a specific role in the control of microglial secretory activity.