Finite-connectivity spin-glass phase diagrams and low-density parity check codes

We obtain phase diagrams of regular and irregular finite-connectivity spin glasses. Contact is first established between properties of the phase diagram and the performance of low-density parity check (LDPC) codes within the replica symmetric (RS) ansatz. We then study the location of the dynamical and critical transition points of these systems within the one step replica symmetry breaking theory (RSB), extending similar calculations that have been performed in the past for the Bethe spin-glass problem. We observe that the location of the dynamical transition line does change within the RSB theory, in comparison with the results obtained in the RS case. For LDPC decoding of messages transmitted over the binary erasure channel we find, at zero temperature and rate R=14, an RS critical transition point at pc 0.67 while the critical RSB transition point is located at pc 0.7450±0.0050, to be compared with the corresponding Shannon bound 1-R. For the binary symmetric channel we show that the low temperature reentrant behavior of the dynamical transition line, observed within the RS ansatz, changes its location when the RSB ansatz is employed; the dynamical transition point occurs at higher values of the channel noise. Possible practical implications to improve the performance of the state-of-the-art error correcting codes are discussed. © 2006 The American Physical Society.

Average and reliability error exponents in low-density parity-check codes

We present a theoretical method for a direct evaluation of the average and reliability error exponents in low-density parity-check error-correcting codes using methods of statistical physics. Results for the binary symmetric channel are presented for codes of both finite and infinite connectivity.

Analysis of common attacks in public-key cryptosystems based on low-density parity-check codes

The security and reliability of a class of public-key cryptosystems against attacks by unauthorized parties, who had acquired partial knowledge of one or more of the private key components and/or of the message, were discussed. The standard statistical mechanical methods of dealing with diluted spin systems with replica symmetric considerations were analyzed. The dynamical transition which defined decryption success in practical situation was studied. The phase diagrams which showed the dynamical threshold as a function of the partial acquired knowledge of the private key were also presented.

Statistical mechanics of broadcast channels using low-density parity-check codes

We investigate the use of Gallager's low-density parity-check (LDPC) codes in a degraded broadcast channel, one of the fundamental models in network information theory. Combining linear codes is a standard technique in practical network communication schemes and is known to provide better performance than simple time sharing methods when algebraic codes are used. The statistical physics based analysis shows that the practical performance of the suggested method, achieved by employing the belief propagation algorithm, is superior to that of LDPC based time sharing codes while the best performance, when received transmissions are optimally decoded, is bounded by the time sharing limit.

Finite-size effects in low-density parity-check codes applied to cryptography

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Hypercholesterolaemia-induced oxidative stress at the blood-brain barrier

Blood cholesterol levels are not consistently elevated in subjectswith age-related cognitive decline, although epidemiological studies suggest that Alzheimer's disease and cardiovascular diseases share common risk factors. These include the presence of an unusual genetic variant, the APOE4 (apolipoprotein E4) allele, which modulates LDL (low-density lipoproteins) metabolism, increases free radical formation and reduces plasma antioxidant concentrations. Together, these risk factors support a mechanism for increased LDL circulation time and free radical modification of LDL. Plasma oxycholesterols, hydroxylated metabolites of cholesterol, are carried by oxidized LDL, and elevated lipids in mid-life are associated with increased longterm risk of dementia. Although brain cholesterol metabolism is segregated from the systemic circulation, during oxidative stress, plasma oxycholesterols could have damaging effects on BBB (blood-brain barrier) function and consequently on neuronal cells. Cholesterol-lowering drugs such as statins may prevent the modifications to LDL in mid-life and might show beneficial effects in later life. © The Authors Journal compilation © 2014 Biochemical Society.

Typical performance of regular low-density parity-check codes over general symmetric channels

Typical performance of low-density parity-check (LDPC) codes over a general binary-input output-symmetric memoryless channel is investigated using methods of statistical mechanics. Relationship between the free energy in statistical-mechanics approach and the mutual information used in the information-theory literature is established within a general framework; Gallager and MacKay-Neal codes are studied as specific examples of LDPC codes. It is shown that basic properties of these codes known for particular channels, including their potential to saturate Shannon's bound, hold for general symmetric channels. The binary-input additive-white-Gaussian-noise channel and the binary-input Laplace channel are considered as specific channel models.

Critical noise levels for low-density parity check decoding

We determine the critical noise level for decoding low-density parity check error-correcting codes based on the magnetization enumerator (M), rather than on the weight enumerator (W) employed in the information theory literature. The interpretation of our method is appealingly simple, and the relation between the different decoding schemes such as typical pairs decoding, MAP, and finite temperature decoding (MPM) becomes clear. In addition, our analysis provides an explanation for the difference in performance between MN and Gallager codes. Our results are more optimistic than those derived using the methods of information theory and are in excellent agreement with recent results from another statistical physics approach.

Top-down lipidomics of low density lipoprotein reveal altered lipid profiles in advanced chronic kidney disease

This study compared the molecular lipidomic profi le of LDL in patients with nondiabetic advanced renal disease and no evidence of CVD to that of age-matched controls, with the hypothesis that it would reveal proatherogenic lipid alterations. LDL was isolated from 10 normocholesterolemic patients with stage 4/5 renal disease and 10 controls, and lipids were analyzed by accurate mass LC/MS. Top-down lipidomics analysis and manual examination of the data identifi ed 352 lipid species, and automated comparative analysis demonstrated alterations in lipid profi le in disease. The total lipid and cholesterol content was unchanged, but levels of triacylglycerides and N -acyltaurines were signifi cantly increased, while phosphatidylcholines, plasmenyl ethanolamines, sulfatides, ceramides, and cholesterol sulfate were signifi cantly decreased in chronic kidney disease (CKD) patients. Chemometric analysis of individual lipid species showed very good discrimination of control and disease sample despite the small cohorts and identifi ed individual unsaturated phospholipids and triglycerides mainly responsible for the discrimination. These fi ndings illustrate the point that although the clinical biochemistry parameters may not appear abnormal, there may be important underlying lipidomic changes that contribute to disease pathology. The lipidomic profi le of CKD LDL offers potential for new biomarkers and novel insights into lipid metabolism and cardiovascular risk in this disease. -Reis, A., A. Rudnitskaya, P. Chariyavilaskul, N. Dhaun, V. Melville, J. Goddard, D. J. Webb, A. R. Pitt, and C. M. Spickett. Topdown lipidomics of low density lipoprotein reveal altered lipid profi les in advanced chronic kidney disease. J. Lipid Res. 2015.

Differential effects of chlorinated and oxidized phospholipids in vascular tissue:implications for neointima formation

The presence of inflammatory cells and MPO (myeloperoxidase) in the arterial wall after vascular injury could increase neointima formation by modification of phospholipids. The present study investigates how these phospholipids, in particular oxidized and chlorinated species, are altered within injured vessels and how they affect VSMC (vascular smooth muscle cell) remodelling processes. Vascular injury was induced in C57BL/6 mice and high fat-fed ApoE-/- (apolipoprotein E) mice by wire denudation and ligation of the left carotid artery (LCA). Neointimal and medial composition was assessed using immunohistochemistry and ESI-MS. Primary rabbit aortic SMCs (smooth muscle cells) were utilized to examine the effects of modified lipids on VSMC proliferation, viability and migration at a cellular level. Neointimal area, measured as intima-to-media ratio, was significantly larger in wire-injured ApoE-/- mice (3.62±0.49 compared with 0.83±0.25 in C57BL/6 mice, n=3) and there was increased oxidized low-density lipoprotein (oxLDL) infiltration and elevated plasma MPO levels. Relative increases in lysophosphatidylcholines and unsaturated phosphatidylcholines (PCs) were also observed in wire-injured ApoE-/- carotid arteries. Chlorinated lipids had no effect on VSMC proliferation, viability or migration whereas chronic incubation with oxidized phospholipids stimulated proliferation in the presence of fetal calf serum [154.8±14.2% of viable cells at 1 μM PGPC (1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphocholine) compared with control, n=6]. In conclusion, ApoE-/- mice with an inflammatory phenotype develop more neointima in wire-injured arteries and accumulation of oxidized lipids in the vessel wall may propagate this effect.

Bilirubin is independently associated with oxidized LDL levels in young obese patients

BACKGROUND: Bilirubin can prevent lipid oxidation in vitro, but the association in vivo with oxidized low-density lipoprotein (Ox-LDL) levels has been poorly explored. Our aim is to the association of Ox-LDL with total bilirubin (TB) levels and with variables related with metabolic syndrome and inflammation, in young obese individuals. FINDINGS: 125 obese patients (13.4 years; 53.6% females) were studied. TB, lipid profile including Ox-LDL, markers of glucose metabolism, and levels of C-reactive protein (CRP) and adiponectin were determined. Anthropometric data was also collected. In all patients, Ox-LDL correlated positively with BMI, total cholesterol, LDLc, triglycerides (TG), CRP, glucose, insulin and HOMAIR; while inversely with TB and HDLc/Total cholesterol ratio (P < 0.05 for all). In multiple linear regression analysis, LDLc, TG, HDLc and TB levels were significantly associated with Ox-LDL (standardized Beta: 0.656, 0.293, -0.283, -0.164, respectively; P < 0.01 for all). After removing TG and HDLc from the analysis, HOMAIR was included in the regression model. In this new model, LDLc remained the best predictor of Ox-LDL levels (β = 0.665, P < 0.001), followed by TB (β = -0.202, P = 0.002) and HOMAIR (β = 0.163, P = 0.010). CONCLUSIONS: Lower bilirubin levels may contribute to increased LDL oxidation in obese children and adolescents, predisposing to increased cardiovascular risk.

The creation of a new tourist destination in low density areas: the Boticas case

CIEO-Research Centre for Spatial and Organizational Dynamics, University of Algarve

O papel da lisofosfatidilcolina na ativação do inflamassoma NLRP3 e sua relação com a formação de células gordurosas

Dissertação (mestrado)—Universidade de Brasília, Instituto de Ciências Biológicas, Programa de Pós-Graduação em Biologia Molecular, 2016.