The Impact of CSI and Power Allocation on Relay Channel Capacity and Cooperation Strategies

Capacity gains from transmitter and receiver cooperation are compared in a relay network where the cooperating nodes are close together. Under quasi-static phase fading, when all nodes have equal average transmit power along with full channel state information (CSI), it is shown that transmitter cooperation outperforms receiver cooperation, whereas the opposite is true when power is optimally allocated among the cooperating nodes but only CSI at the receiver (CSIR) is available. When the nodes have equal power with CSIR only, cooperative schemes are shown to offer no capacity improvement over non-cooperation under the same network power constraint. When the system is under optimal power allocation with full CSI, the decode-and-forward transmitter cooperation rate is close to its cut-set capacity upper bound, and outperforms compress-and-forward receiver cooperation. Under fast Rayleigh fading in the high SNR regime, similar conclusions follow. Cooperative systems provide resilience to fading in channel magnitudes; however, capacity becomes more sensitive to power allocation, and the cooperating nodes need to be closer together for the decode-and-forward scheme to be capacity-achieving. Moreover, to realize capacity improvement, full CSI is necessary in transmitter cooperation, while in receiver cooperation optimal power allocation is essential.Comment: Accepted for publication in IEEE Transactions on Wireless Communication

The Magnetic Field of L1544: I. Near-Infrared Polarimetry and the Non-Uniform Envelope

The magnetic field (B-field) of the starless dark cloud L1544 has been studied using near-infrared (NIR) background starlight polarimetry (BSP) and archival data in order to characterize the properties of the plane-of-sky B-field. NIR linear polarization measurements of over 1,700 stars were obtained in the H-band and 201 of these were also measured in the K-band. The NIR BSP properties are correlated with reddening, as traced using the RJCE (H-M) method, and with thermal dust emission from the L1544 cloud and envelope seen in Herschel maps. The NIR polarization position angles change at the location of the cloud and exhibit their lowest dispersion of position angles there, offering strong evidence that NIR polarization traces the plane-of-sky B-field of L1544. In this paper, the uniformity of the plane-of-sky B-field in the envelope region of L1544 is quantitatively assessed. This allowed evaluating the approach of assuming uniform field geometry when measuring relative mass-to-flux ratios in the cloud envelope and core based on averaging of the envelope radio Zeeman observations, as in Crutcher et al. (2009). In L1544, the NIR BSP shows the envelope B-field to be significantly non-uniform and likely not suitable for averaging Zeeman properties without treating intrinsic variations. Deeper analyses of the NIR BSP and related data sets, including estimates of the B-field strength and testing how it varies with position and gas density, are the subjects of later papers in this series.Comment: 16 pages, 9 figures; accepted for publication in The Astrophysical Journa

Distortion Minimization in Gaussian Layered Broadcast Coding with Successive Refinement

A transmitter without channel state information (CSI) wishes to send a delay-limited Gaussian source over a slowly fading channel. The source is coded in superimposed layers, with each layer successively refining the description in the previous one. The receiver decodes the layers that are supported by the channel realization and reconstructs the source up to a distortion. The expected distortion is minimized by optimally allocating the transmit power among the source layers. For two source layers, the allocation is optimal when power is first assigned to the higher layer up to a power ceiling that depends only on the channel fading distribution; all remaining power, if any, is allocated to the lower layer. For convex distortion cost functions with convex constraints, the minimization is formulated as a convex optimization problem. In the limit of a continuum of infinite layers, the minimum expected distortion is given by the solution to a set of linear differential equations in terms of the density of the fading distribution. As the bandwidth ratio b (channel uses per source symbol) tends to zero, the power distribution that minimizes expected distortion converges to the one that maximizes expected capacity. While expected distortion can be improved by acquiring CSI at the transmitter (CSIT) or by increasing diversity from the realization of independent fading paths, at high SNR the performance benefit from diversity exceeds that from CSIT, especially when b is large.Comment: Accepted for publication in IEEE Transactions on Information Theor

Building Morphological Chains for Agglutinative Languages

In this paper, we build morphological chains for agglutinative languages by using a log-linear model for the morphological segmentation task. The model is based on the unsupervised morphological segmentation system called MorphoChains. We extend MorphoChains log linear model by expanding the candidate space recursively to cover more split points for agglutinative languages such as Turkish, whereas in the original model candidates are generated by considering only binary segmentation of each word. The results show that we improve the state-of-art Turkish scores by 12% having a F-measure of 72% and we improve the English scores by 3% having a F-measure of 74%. Eventually, the system outperforms both MorphoChains and other well-known unsupervised morphological segmentation systems. The results indicate that candidate generation plays an important role in such an unsupervised log-linear model that is learned using contrastive estimation with negative samples.Comment: 10 pages, accepted and presented at the CICLing 2017 (18th International Conference on Intelligent Text Processing and Computational Linguistics

What is the impact of psychiatric decision units on mental health crisis care pathways? Protocol for an interrupted time series analysis with a synthetic control study

Background The UK mental health system is stretched to breaking point. Individuals presenting with mental health problems wait longer at the ED than those presenting with physical concerns and finding a bed when needed is difficult – 91% of psychiatric wards are operating at above the recommended occupancy rate. To address the pressure, a new type of facility – psychiatric decision units (also known as mental health decision units) – have been introduced in some areas. These are short-stay facilities, available upon referral, targeted to help individuals who may be able to avoid an inpatient admission or lengthy ED visit. To advance knowledge about the effectiveness of this service for this purpose, we will examine the effect of the service on the mental health crisis care pathway over a 4-year time period; the 2 years proceeding and following the introduction of the service. We use aggregate service level data of key indicators of the performance of this pathway. Methods Data from four mental health Trusts in England will be analysed using an interrupted time series (ITS) design with the primary outcomes of the rate of (i) ED psychiatric presentations and (ii) voluntary admissions to mental health wards. This will be supplemented with a synthetic control study with the same primary outcomes, in which a comparable control group is generated for each outcome using a donor pool of suitable National Health Service Trusts in England. The methods are well suited to an evaluation of an intervention at a service delivery level targeting population-level health outcome and the randomisation or ‘trialability’ of the intervention is limited. The synthetic control study controls for national trends over time, increasing our confidence in the results. The study has been designed and will be carried out with the involvement of service users and carers. Discussion This will be the first formal evaluation of psychiatric decision units in England. The analysis will provide estimates of the effect of the decision units on a number of important service use indicators, providing much-needed information for those designing service pathways

Outage Capacity of Incremental Relaying at Low Signal-to-Noise Ratios

We present the \epsilon-outage capacity of incremental relaying at low signal-to-noise ratios (SNR) in a wireless cooperative network with slow Rayleigh fading channels. The relay performs decode-and-forward and repetition coding is employed in the network, which is optimal in the low SNR regime. We derive an expression on the optimal relay location that maximizes the \epsilon-outage capacity. It is shown that this location is independent of the outage probability and SNR but only depends on the channel conditions represented by a path-loss factor. We compare our results to the \epsilon-outage capacity of the cut-set bound and demonstrate that the ratio between the \epsilon-outage capacity of incremental relaying and the cut-set bound lies within 1/\sqrt{2} and 1. Furthermore, we derive lower bounds on the \epsilon-outage capacity for the case of K relays.Comment: 5 pages, 4 figures, to be presented at VTC Fall 2009 in Anchorage, Alask

The Tumor Microenvironment Regulates Retinoblastoma Cell Survival

Retinoblastoma (Rb) is the most common intraocular malignancy in children comprising 4% of all pediatric tumors. Early intervention increases survival rates up to 95% in developed countries; being survival rates associated to socio-economic status. Despite the high survival rates in developed countries, preservation of the eye and vision are continuing challenges in the management of Rb. Vitreous seeds constitute the greatest challenge in treatment of Rb. The unique location of these seeds within the vitreous makes them difficult to treat. Viable seeds showed reduced proliferative capacity and metabolism. making the majority refractory to current chemotherapeutics. This prompted the development of new delivery routes for chemotherapeutics, such as intra-ophthalmic artery, intravitreal, and subconjunctival administration. Still ocular salvage rates have not exceeded 70% in over two decades. Novel, safer therapies are required but there is a fundamental lack of knowledge about the biology of the tumor for the development of targeted therapies; the vitreous, as it surrounds the seeds; and the interactions between the vitreous and the seeds. Despite the current understanding of how cancer is a multifaceted disease full of complex cellular and protein interactions (commonly referred to as the tumor microenvironment, TME), the immunology of the vitreous microenvironment and the role it plays in the sustainment of seeds in Rb disease is poorly understood. In this study, we begin investigating Rb tumor cells and how they alter the TME by examination of matrix metalloproteinases, a family of enzymes involved in degradation of the extracellular matrix and tissue remodeling heavily implicated in tumor migration and survival. We identified two gelatinases, MMP-2 and MMP-9, to be expressed in Rb cell lines and demonstrated by pharmacological inhibition and genetic knockdown, a role for these gelatinases in Rb cell migration, invasion, and survival. Additionally, we demonstrated how secretion of VEGF, involved in angiogenesis, and TGFβ, involved in metastasis, were altered by MMP-2 and MMP-9 pharmacological inhibition. As MMPs are pivotal for the tumor and extracellular matrix interactions within the TME leading to tissue invasion, we then transitioned to the vitreous, investigating the vitreous as a TME and how it sustains Rb. Multiple proteins are found within the soluble phase of the vitreous that are associated with ocular pathological processes, including diabetes retinopathy and proliferative vitreoretinopathy. Therefore, we compared the presence of a small cohort of proteins associated to ocular pathologies, to healthy vitreous and to Rb patients’ vitreous samples, identifying high expression of Platelet-Derived Growth Factor Receptor β (PDGFRβ) and its ligand PDGFBB in the Rb samples. Additional studies of ex vivo healthy human vitreous, murine Rb xenografts, and patient-derived Rb xenograft tissues, measured high activity of the PDGF-PDGFRβ signaling pathway in diseased, but not healthy tissue. We focused the next part of this work on the role PDGFRβ plays in vitreous seeds. To investigate this pathway in depth we used established Rb cell lines, namely Y79-the metastatic and aggressive model, and Weri-1 Rb, the non-metastatic model. Our work demonstrated PDGFRβ was overexpressed in Y79 cells, the metastatic model of Rb, in vitro. To provide mechanistic insight, we utilized the tyrosine kinase inhibitor imatinib mesylate (IM), and demonstrated PDGF-PDGFRβ signaling pathway regulates Rb cell proliferation, invasion, and survival. We found increased PDGF-PDGFRβ signaling resulted in higher activity of the p53-inactivator, MDM2, as well as the pro-inflammatory NFβB pathway, both of which are involved in tumor survival. As there is a lack of models for vitreous seeding, we utilized magnetic nanoparticles to generate the first in vitro vitreous seed model and demonstrated similar features between an ex vivo seed and one of our in vitro magnet-generated 3D tumor spheroids, validating our system. Using this novel technology, we recapitulated our in vitro 2D work and demonstrated that inhibition of the PDGF-PDGFRβ signaling pathway results in decreased spheroid size. PDGFRB gene knockdown by siRNA confirmed the results with the pharmacological agent showing these results were PDGF-PDGFRβ signaling-specific. Next, we tested the effects of IM, as a potential Rb therapy, in retinal endothelial cells h(RECs) as retinal endothelial cell-associated toxicities are one of the challenges with conventional chemotherapies in Rb. We measured the capacity of hREC to proliferate and for tube formation in the presence of the therapy. Our results demonstrated neither proliferation nor tube formation of hRECs changed when exposed to IM. Upon further examination, we demonstrated the absence of PDGFRB mRNA expression in hRECs. Taken together these results illustrate the potential use of anti-PDGFRβ therapy as a targeted therapy in Rb. The last section of the study investigated the expression and function of members of the ATP-binding cassette (ABC) transporters as well as the multifunctional glycoprotein CD44 in Rb, as one of the properties of vitreous seeds is their resistance to chemotherapy. We discovered heterogeneous expression of multiple ABC transporters in vitro using Y79 Rb cell line and ex vivo using Rb vitreous samples. In addition to expression, the transporters efflux activity was determined. CD44 mRNA, whose protein is considered a promoter of chemoresistance, was highly expressed in naïve vitreous from Rb patients. These results illustrate that chemoresistance is not induced by treatment and is, instead, an innate feature of vitreous seeds. Flow cytometry analyses established (1) a high correlation between active, or phosphorylated PDGFRβ (p-PDGFRβ) and CD44; and (2) inhibition of p-PDGFRβ resulted in decreased CD44, as well. Collectively, this study demonstrated the Rb TME plays a crucial role in Rb tumor properties. MMP-2 and MMP-9 are highly expressed in Rb and allow degradation of the ECM in tissue, increasing migration and invasion of Rb. Additional work focused on vitreous seeds and identified increasing signaling activity of the PDGF-PDGFRβ signaling pathway in multiple Rb models, including in vitro cell lines, ex vivo Rb patient vitreous samples and tissue, as well as in a murine xenograft system. Next, we identified this pathway as a potential target, as pharmacological and genomic inhibition of the PDGF-PDGFRβ signaling pathway by IM and PDGFRB siRNA resulted in decreased proliferation, invasion, resistance, and survival. These cellular functions appear to be mediated by the downstream targets MDM2 and NFβB. Our initial studies demonstrated a lack of drug-associated toxicity on hRECs with IM. This work is a further step in our quest for targeting vitreous seeding

Minimum Expected Distortion in Gaussian Layered Broadcast Coding with Successive Refinement

A transmitter without channel state information (CSI) wishes to send a delay-limited Gaussian source over a slowly fading channel. The source is coded in superimposed layers, with each layer successively refining the description in the previous one. The receiver decodes the layers that are supported by the channel realization and reconstructs the source up to a distortion. In the limit of a continuum of infinite layers, the optimal power distribution that minimizes the expected distortion is given by the solution to a set of linear differential equations in terms of the density of the fading distribution. In the optimal power distribution, as SNR increases, the allocation over the higher layers remains unchanged; rather the extra power is allocated towards the lower layers. On the other hand, as the bandwidth ratio b (channel uses per source symbol) tends to zero, the power distribution that minimizes expected distortion converges to the power distribution that maximizes expected capacity. While expected distortion can be improved by acquiring CSI at the transmitter (CSIT) or by increasing diversity from the realization of independent fading paths, at high SNR the performance benefit from diversity exceeds that from CSIT, especially when b is large.Comment: To appear in the proceedings of the 2007 IEEE International Symposium on Information Theory, Nice, France, June 24-29, 200