Asymptotic Performance of Linear Receivers in MIMO Fading Channels

Linear receivers are an attractive low-complexity alternative to optimal processing for multi-antenna MIMO communications. In this paper we characterize the information-theoretic performance of MIMO linear receivers in two different asymptotic regimes. For fixed number of antennas, we investigate the limit of error probability in the high-SNR regime in terms of the Diversity-Multiplexing Tradeoff (DMT). Following this, we characterize the error probability for fixed SNR in the regime of large (but finite) number of antennas. As far as the DMT is concerned, we report a negative result: we show that both linear Zero-Forcing (ZF) and linear Minimum Mean-Square Error (MMSE) receivers achieve the same DMT, which is largely suboptimal even in the case where outer coding and decoding is performed across the antennas. We also provide an approximate quantitative analysis of the markedly different behavior of the MMSE and ZF receivers at finite rate and non-asymptotic SNR, and show that while the ZF receiver achieves poor diversity at any finite rate, the MMSE receiver error curve slope flattens out progressively, as the coding rate increases. When SNR is fixed and the number of antennas becomes large, we show that the mutual information at the output of a MMSE or ZF linear receiver has fluctuations that converge in distribution to a Gaussian random variable, whose mean and variance can be characterized in closed form. This analysis extends to the linear receiver case a well-known result previously obtained for the optimal receiver. Simulations reveal that the asymptotic analysis captures accurately the outage behavior of systems even with a moderate number of antennas.Comment: 48 pages, Submitted to IEEE Transactions on Information Theor

Performance of MMSE MIMO Receivers: A Large N Analysis for Correlated Channels

Linear receivers are considered as an attractive low-complexity alternative to optimal processing for multi-antenna MIMO communications. In this paper we characterize the performance of MMSE MIMO receivers in the limit of large antenna numbers in the presence of channel correlations. Using the replica method, we generalize our results obtained in arXiv:0810.0883 to Kronecker-product correlated channels and calculate the asymptotic mean and variance of the mutual information of a MIMO system of parallel MMSE subchannels. The replica method allows us to use the ties between the optimal receiver mutual information and the MMSE SIR of Gaussian inputs to calculate the joint moments of the SIRs of the MMSE subchannels. Using the methodology discussed in arXiv:0810.0883 it can be shown that the mutual information converges in distribution to a Gaussian random variable. Our results agree very well with simulations even with a moderate number of antennas.Comment: Invited article at the IEEE Vehicular Technology Conference, Barcelona 200

Colors and K-Band Counts of Extremely Faint Field Galaxies

We combine deep K-band (Keck) with V- and I-band (NTT) observations of two high-Galactic latitude fields, surveying a total of ~2 sq. arcmin. The K-band galaxy counts continue to rise above K=22, reaching surface densities of few x 10^5 per sq. degree. The slope for the counts is (d log(N) per mag per sq. degree) = 0.23 +/- 0.02 between K=18-23, consistent with other deep K surveys. The numbers of galaxies in each mag bin is about two times greater than the galaxy counts of Djorgovski et al. (1995). The optical and near infrared magnitudes of all objects detected in the V+I+K image are discussed in the context of grids of isochrone synthesis galaxy evolutionary models (Bruzual & Charlot 1993, 1995). The colors of most of the observed galaxies are consistent with a population drawn from a broad redshift distribution. A few galaxies at K=19-20 are red in both colors (V-I>3; I-K>2), consistent with being early-type galaxies having undergone a burst of star formation at z>5 and viewed at z~1. At K>20, we find ~8 ``red outlier'' galaxies with I-K>4 and V-I<2.5, whose colors are difficult to mimic by a single evolving or non-evolving stellar population at any redshift. They are likely either low-metallicity, dusty dwarf galaxies, or old galaxies at high redshift (z>1.2). Their surface density is several per square arcminute, which is so high that they are probably common objects of low luminosity $L<L_*$.Comment: 28 pages, 9 Figures (2 Plates), uses aaspp4.sty. The complete paper (including large figures and the plates) are available via anonymous ftp at ftp://coma.berkeley.edu/pub/lmoustakas/ . To appear in the Astrophysical Journal, Feb 1 1997, vol. 47

Etiopathogenesis of Insulin Autoimmunity

Autoimmunity against pancreatic islet beta cells is strongly associated with proinsulin, insulin, or both. The insulin autoreactivity is particularly pronounced in children with young age at onset of type 1 diabetes. Possible mechanisms for (pro)insulin autoimmunity may involve beta-cell destruction resulting in proinsulin peptide presentation on HLA-DR-DQ Class II molecules in pancreatic draining lymphnodes. Recent data on proinsulin peptide binding to type 1 diabetes-associated HLA-DQ2 and -DQ8 is reviewed and illustrated by molecular modeling. The importance of the cellular immune reaction involving cytotoxic CD8-positive T cells to kill beta cells through Class I MHC is discussed along with speculations of the possible role of B lymphocytes in presenting the proinsulin autoantigen over and over again through insulin-carrying insulin autoantibodies. In contrast to autoantibodies against other islet autoantigens such as GAD65, IA-2, and ZnT8 transporters, it has not been possible yet to standardize the insulin autoantibody test. As islet autoantibodies predict type 1 diabetes, it is imperative to clarify the mechanisms of insulin autoimmunity

The Origin And Loss Of Periodic Patterning In The Turtle Shell

The origin of the turtle shell over 200 million years ago greatly modified the amniote body plan, and the morphological plasticity of the shell has promoted the adaptive radiation of turtles. The shell, comprising a dorsal carapace and a ventral plastron, is a layered structure formed by basal endochondral axial skeletal elements (ribs, vertebrae) and plates of bone, which are overlain by keratinous ectodermal scutes. Studies of turtle development have mostly focused on the bones of the shell; however, the genetic regulation of the epidermal scutes has not been investigated. Here, we show that scutes develop from an array of patterned placodes and that these placodes are absent from a soft-shelled turtle in which scutes were lost secondarily. Experimentally inhibiting Shh, Bmp or Fgf signaling results in the disruption of the placodal pattern. Finally, a computational model is used to show how two coupled reaction-diffusion systems reproduce both natural and abnormal variation in turtle scutes. Taken together, these placodal signaling centers are likely to represent developmental modules that are responsible for the evolution of scutes in turtles, and the regulation of these centers has allowed for the diversification of the turtle shell

Local Heavy Quasiparticle in Four-Level Kondo Model

An impurity four-level Kondo model, in which an ion is tunneling among 4-stable points and interacting with surrounding conduction electrons, is investigated using both perturbative and numerical renormalization group methods. The results of numerical renormalization group studies show that it is possible to construct the ground state wavefunction including the excited ion states if we take into account the interaction between the conduction electrons and the ion. The resultant effective mass of quasiparticles is moderately enhanced. This result offers a good explanation for the enhanced and magnetically robust Sommerfeld coefficient observed in SmOs$_4$Sb$_{12}$, some other filled-skutterudites, and clathrate compounds.Comment: 9 pages, 7 figures. Added references and "Note added

Sustainable production of pure silica from rice husk waste in Kazakhstan

This study aimed at developing a new synthesis method for the production of high purity silica from rice husks originated from different regions of Kazakhstan. The proposed eco-friendly method is compared with the conventional one reported in the literature which is accompanied by the use of significant amount of inorganic alkali and acids and direct combustion. In order to reduce the environmental impact, the mineral acid pre-treatment stage was either removed or replaced with organic acid pre-treatment, which reduced the amount of chemicals used during the synthesis and treatment process. The calcination temperature of 600 °C was selected based on thermogravimetric analysis. The average purity of silica samples obtained via different methods ranged from 84.81 to 99.66 wt%. The purity of the produced silica by use of the greener method was high reaching 98.67% with surface area up to 625 m 2 /g

'They're battle scars, I wear them well': A phenomenological exploration of young women's experiences of building resilience following adversity in adolescence

This is an Author's Accepted Manuscript of an article published in Journal of Youth Studies, 13(3), 273 - 290, 2010 [copyright Taylor & Francis], available online at: http://www.tandfonline.com/10.1080/13676260903520886.This phenomenological study explored young women's accounts of building resilience following chains of adverse life experiences in adolescence. Six participants were interviewed, aged 20–25 years. Most had, or were receiving, a university education. They described their recovery from adversity as starting with certain pivotal moments, followed by both short-term and longer-term strategies. Short-term strategies tended to offer respite from distress and emotional comfort, increased clarity about their experiences and social affirmation. Recovery involved gaining new perspectives on their adverse situation and recovering a positive self-image through three longer-term strategies. These involved making visible progress in their education, rebuilding relationships with family and friends, and participating in the ‘normalizing’ activities and developmental projects of adolescence. Participants believed that they were stronger and more compassionate although positive achievements co-existed with some regrets. Most perceived the adversity as catalyzing personal growth. These accounts of resilience revealed the complex psychosocial processes and resources available to some adolescents

Effects of Cadmium (Cd) on Dry Matter and on Cd Concentration in Leaves and Roots of Purple Coneflower (Echinacea purpurea L.)

The aim of this research was to examine the effect of Cd on leaves dry matter (LDM), root dry matter (RDM) and on Cd concentration in leaves (Cd-leaves) and roots (Cd-roots) of purple coneflower (E. purpurea) grown in an acid and in a neutral substrate. A completely randomized block design with four treatments (0-control, 1, 2, and 5 mg Cd L-1) and six replications for each treatment and each substrate (acid, neutral) was conducted in pot experiments. Cd concentration in leaves grown in acid substrate as well as in roots of plants grown in neutral substrate increased at Cd rates greater than 2 mg Cd L-1. Cd concentration in roots of the plants grown in neutral substrate raised with increasing doses of Cd. In general Cd concentration in the roots and leaves of purple coneflower grown either in acid or in neutral substrate was affected by Cd applications