Low-complexity soft-output signal detector based on adaptive pre-conditioned gradient descent method for uplink multiuser massive MIMO systems

In multiuser massive Multiple Input Multiple Output(MIMO)systems,a large amount of antennas are deployed at the Base Station(BS).In this case,the Minimum Mean Square Error(MMSE)detector with soft-output can achieve the near-optimal performance at the cost of a large-scale matrix inversion operation.The optimization algorithms such as Gradient Descent(GD)method have received a lot of attention to realize the MMSE detection efficiently without a large scale matrix inversion operation.However,they converge slowly when the condition number of the MMSE filtering matrix(the coefficient matrix)increases,which can compromise the efficiency of their implementation.Moreover,their soft information computation also involves a large-scale matrix-matrix multiplication operation.In this paper,a low-complexity soft-output signal detector based on Adaptive Pre-conditioned Gradient Descent(APGD-SOD)method is proposed to realize the MMSE detection with soft-output for uplink multiuser massive MIMO systems.In the proposed detector,an Adaptive Pre-conditioner(AP)matrix obtained through the Quasi-Newton Symmetric Rank One(QN-SR1)update in each iteration is used to accelerate the convergence of the GD method.The QN-SR1 update supports the intuitive notion that for the quadractic problem one should strive to make the pre-conditioner matrix close to the inverse of the coefficient matrix,since then the condition number would be close to unity and the convergence would be rapid.By expanding the signal model of the massive MIMO system and exploiting the channel hardening property of massive MIMO systems,the computational complexity of the soft information is simplified.The proposed AP matrix is applied to the GD method as a showcase.However,it also can be used by Conjugate Gradient(CG)method due to its generality.It is demonstrated that the proposed detector is robust and its convergence rate is superlinear.Simulation results show that the proposed detector converges at most four iterations.Simulation results also show that the proposed approach achieves a better trade-off between the complexity and the performance than several existing detectors and achieves a near-optimal performance of the MMSE detector with soft-output at four iterations without a complicated large scale matrix inversion operation,which entails a big challenge for the efficient implementation.

Hypoxic pre-conditioned adipose-derived stem/progenitor cells embedded in fibrin conduits promote peripheral nerve regeneration in a sciatic nerve graft model

Recent results emphasize the supportive effects of adipose-derived multipotent stem/progenitor cells(ADSPCs)in peripheral nerve recovery.Cultivation under hypoxia is considered to enhance the release of the regenerative potential of ADSPCs.This study aimed to examine whether peripheral nerve regeneration in a rat model of autologous sciatic nerve graft benefits from an additional custom-made fibrin conduit seeded with hypoxic pre-conditioned(2%oxygen for 72 hours)autologous ADSPCs(n=9).This treatment mode was compared with three others:fibrin conduit seeded with ADSPCs cultivated under normoxic conditions(n=9);non-cell-carrying conduit(n=9);and nerve autograft only(n=9).A 16-week follow-up included functional testing(sciatic functional index and static sciatic index)as well as postmortem muscle mass analyses and morphometric nerve evaluations(histology,g-ratio,axon density,and diameter).At 8 weeks,the hypoxic pre-conditioned group achieved significantly higher sciatic functional index/static sciatic index scores than the other three groups,indicating faster functional regeneration.Furthermore,histologic evaluation showed significantly increased axon outgrowth/branching,axon density,remyelination,and a reduced relative connective tissue area.Hypoxic pre-conditioned ADSPCs seeded in fibrin conduits are a promising adjunct to current nerve autografts.Further studies are needed to understand the underlying cellular mechanism and to investigate a potential application in clinical practice.

Experimental investigation of shale breakdown pressure under liquid nitrogen pre-conditioning before nitrogen fracturing

Cryogenic fracturing with liquid nitrogen(LN_(2))offers the benefits of reducing the water consumption and adverse environmental impacts induced by water-based fracturing,as well as potentially enhancing the fracture complexity.We performed a series of laboratory experiments to explore the key mechanisms governing the breakdown pressures of shale during cryogenic fracturing.In this study,cylindrical shale samples were pre-conditioned by exposing a borehole to low-temperature LN_(2) for a certain time period,and then,the samples were fractured using gaseous N_(2) under triaxial stress and a high reservoir temperature.The effects of various key parameters on the breakdown pressure were investigated,including the duration of the low-temperature LN_(2) treatment,the confining pressure,the reservoir temperature,and the direction of the shale bedding relative to the borehole axis.The results demonstrate that the injection of low-temperature LN_(2) as a pre-fracturing fluid into a borehole can significantly reduce the breakdown pressure of the shale during subsequent nitrogen fracturing.This reduction in breakdown pressure can be further intensified by increasing the duration of the LN_(2) pre-conditioning.Without LN_(2) pre-conditioning,the breakdown pressure initially increases and then decreases with increasing reservoir temperature.When LN_(2) pre-conditioning is applied,the breakdown pressure keeps decreasing with increasing reservoir temperature.As the confining pressure increased,the breakdown pressure increased linearly in the tests with and without LN_(2) pre-conditioning.The experimental results demonstrate that LN_(2) preconditioning before N_(2) fracturing is a promising waterless fracturing technique that reduces the breakdown pressure and enhances the fracture complexity.

Numerical and experimental analyses of rock failure mechanisms due to microwave treatment

Despite the extensive studies conducted on the effectiveness of microwave treatment as a novel rock preconditioning method,there is yet to find reliable data on the rock failure mechanisms due to microwave heating.In addition,there is no significant discussion on the energy efficiency of the method as one of the important factors among the mining and geotechnical engineers in the industry.This study presents a novel experimental method to evaluate two main rock failure mechanisms due to microwave treatment without applying any mechanical forces,i.e.distributed and concentrated heating.The result shows that the existence of a small and concentrated fraction of a strong microwave absorbing mineral will change the failure mechanism from the distributed heating to the concentrated heating,which can increase the weakening over microwave efficiency(WOME)by more than 10 folds.This observation is further investigated using the developed coupled numerical model.It is shown that at the same input energy,the existence of microwave absorbing minerals can cause major heat concentration inside the rock and increase the maximum temperature by up to three times.

Heme oxygenase system in hepatic ischemia-reperfusion injury

Hepatic ischemia-reperfusion injury (IRI) limits access to transplantation. Heme oxygenase-1 (HO-1) is a powerful antioxidant enzyme which degrades free heme into biliverdin,free iron and carbon monoxide. HO-1 and its metabolites have the ability to modulate a wide variety of inflammatory disorders including hepatic IRI. Mechanisms of this protective effect include reduction of oxygen free radicals,alteration of macrophage and T cell phenotype. Further work is required to understand the physiological importance of the many actions of HO-1 identified experimentally,and to harness the protective effect of HO-1 for therapeutic potential.

Redox therapeutics in hepatic ischemia reperfusion injury

Ischemia-reperfusion plays a major role in the injury experienced by the liver during transplantation. Much work has been done recently investigating the role of redox species in hepatic ischemia-reperfusion. As animal models are better characterized and developed, and more insights are gained into the pathophysiology of hepatic ischemia reperfusion injury in humans the questions into exactly how oxidants participate in this injury are becoming more refined. These questions include effects of cellular location, timing of injury, and ability of therapeutics to access this site are increasing our appreciation of the complexity of ischemia reperfusion and improving attempts to ameliorate its effects. In this review, we aim to discuss the various methods to alter redox chemistry during ischemia reperfusion injury and future prospects for preventing organ injury during hepatic ischemia reperfusion.

Study of the Optimal Precursors for Blocking Events

The precursors of dipole blocking are obtained by a numerical approach based upon a quasi-geostrophic barotropic planetary- to synoptic-scale interaction model without topography and with a localized synoptic-scale wave-maker. The optimization problem related to the precursors of blocking is formulated and the nonlinear optimization method is used to examine the optimal synoptic-scale initial field successfully. The results show that the prominent characteristics of the optimal synoptic-scale initial field are that the synoptic-scale wave train structures exist upstream of the incipient blocking. In addition, the large-scale low/high eddy-forcing pattern upstream of the incipient blocking is an essential precondition for the onset of dipole blocking.

Mesenchymal stem cell-derived exosomes: The dawn of diabetic wound healing

Chronic wound healing has long been an unmet medical need in the field of wound repair,with diabetes being one of the major etiologies.Diabetic chronic wounds(DCWs),especially diabetic foot ulcers,are one of the most threatening chronic complications of diabetes.Although the treatment strategies,drugs,and dressings for DCWs have made great progress,they remain ineffective in some patients with refractory wounds.Stem cell-based therapies have achieved specific efficacy in various fields,with mesenchymal stem cells(MSCs)being the most widely used.Although MSCs have achieved good feedback in preclinical studies and clinical trials in the treatment of cutaneous wounds or other situations,the potential safety concerns associated with allogeneic/autologous stem cells and unknown long-term health effects need further attention and supervision.Recent studies have reported that stem cells mainly exert their trauma repair effects through paracrine secretion,and exosomes play an important role in intercellular communication as their main bioactive component.MSC-derived exosomes(MSC-Exos)inherit the powerful inflammation and immune modulation,angiogenesis,cell proliferation and migration promotion,oxidative stress alleviation,collagen remodeling imbalances regulation of their parental cells,and can avoid the potential risks of direct stem cell transplantation to a large extent,thus demonstrating promising performance as novel"cell-free"therapies in chronic wounds.This review aimed to elucidate the potential mechanism and update the progress of MSC-Exos in DCW healing,thereby providing new therapeutic directions for DCWs that are difficult to be cured using conventional therapy.

Stem Cell Therapy of Ischemic Heart Disease

Ischemic heart disease (IHD) accelerates death of cardiomyocytes and leads to the onset of cardiac failure. Due to the application of stem cells, there exists a potential for the regeneration of a damaged myocardium. Here we present a brief review of the modern data on the application of various types of stem cells for the IHD therapy. We consider different types of stem cells, which are most preferable for the clinical application, including mesenchymal stem cells, cardiac stem cells, embryonic stem cells, iPS cells and others. In particular, we discuss their advantages and strategies which can be applied in order to boost their regenerative potential, as well as optimization of their delivery. Besides, our review refers to the contemporary achievements in the field of tissue engineering of heart, using both polymer scaffolds and scaffold-free constructs. We also discuss the most prominent known clinical trials on stem cell therapy of ischemic heart disease.

On Numerical methods for determination of Earth gravity field model using mass satellite gravity gradiometry data

On the basis of Space-Wise Least Square method, three numerical methods including Cholesky de- composition, pre-conditioned conjugate gradient and Open Multi-Processing parallel algorithm are applied into the determination of gravity field with satellite gravity gradiometry data. The results show that, Cholesky de- composition method has been unable to meet the requirements of computation efficiency when the computer hardware is limited. Pre-conditioned conjugate gradient method can improve the computation efficiency of huge matrix inversion, but it also brings a certain loss of precision. The application of Open Multi-Processing parallel algorithm could achieve a good compromise between accuracy and computation efficiency.

Cryptanalysis of the Double-Moduli Cryptosystem

In this article we present a lattice attack done on a NTRU-like scheme introduced by Verkhovsky in [1]. We show how, based on the relation between the public and private key, we can construct an attack which allows any passive adversary to decrypt the encrypted messages. We explain, step by step, how an attacker can construct an equivalent private key and guess what the original plaintext was. Our attack is efficient and provides good experimental results.

EFFECT OF MECHANICAL PRE-CONDITIONING ON FRACTURE RESISTANCE OF POLYPROPYLENE

The effect of externally applied mechanical pre-conditioning, i.e. pre-impact treatment, on the fracture resistance was investigated for polypropylene （PP）. Impact strength was obtained via notched and/or unnotched samples. It has been shown that the pre-impact treatment is favorable to the improvement of the fracture resistance. The impact strength increases linearly with the applied pre-impact energy. Both optical and SEM results show that there are at least two possible mechanisms for the improvement of the fracture resistance. One is the crack blunting effect which is introduced to notched sample by pre-impact treatment, reducing the sensitivity of PP to the applied notch. The other is the formation of large amount of microvoids induced by pre-impact treatment, which changes the stress distribution and induces intensive plastic deformation of PP at the second impact measurement, leading to the improvement of the fracture resistance.

Short-term memory of danger signals or environmental stimuli in mesenchymal stem cells： implications for therapeutic potential

Mesenchymal stem/stromal cells （MSCs） possess some characteristics of immune cells, including a pro-inflammatory phenotype, an immunosuppressive phenotype, antibacterial properties and the expression of Toll-like receptor proteins. Here we show that, similar to immune cells, MSCs retain information from danger signals or environmental stimuli for a period of time. When treated with the pro-inflammatory factors lipopolysaccharide （LPS） or tumor necrosis factor-a （TNF-a）, MSCs display increased expression of IL-6, IL-8 and MCP-1. Following re-plating and several rounds of cell division in the absence of stimulating factors, the expression of IL-6, IL-8 and MCP-1 remained higher than in untreated cells for over 7 days. A spike in cytokine secretion occurred when cells were exposed to a second round of stimulation. We primed MSCs with LPS and LPS-primed MSCs had better therapeutic efficacy at promoting skin flap survival in a diabetic rat model than did unprimed MSCs. Finally, we found that several microRNAs, including miR146a, miR150 and miR155, along with the modification of DNA by 5-hydroxymethylcytosine （5hmC）, mediate the MSC response to LPS and TNF-e stimulation. Collectively, our data suggest that MSCs have a short-term memory of environmental signals, which may impact their therapeutic potential.

A RELAXED HSS PRECONDITIONER FOR SADDLE POINT PROBLEMS FROM MESHFREE DISCRETIZATION＊

In this paper, a relaxed Hermitian and skew-Hermitian splitting （RHSS） preconditioner is proposed for saddle point problems from the element-free Galerkin （EFG） discretization method. The EFG method is one of the most widely used meshfree methods for solving partial differential equations. The RHSS preconditioner is constructed much closer to the coefficient matrix than the well-known HSS preconditioner, resulting in a RHSS fixed-point iteration. Convergence of the RHSS iteration is analyzed and an optimal parameter, which minimizes the spectral radius of the iteration matrix is described. Using the RHSS pre- conditioner to accelerate the convergence of some Krylov subspace methods （like GMRES） is also studied. Theoretical analyses show that the eigenvalues of the RHSS precondi- tioned matrix are real and located in a positive interval. Eigenvector distribution and an upper bound of the degree of the minimal polynomial of the preconditioned matrix are obtained. A practical parameter is suggested in implementing the RHSS preconditioner. Finally, some numerical experiments are illustrated to show the effectiveness of the new preconditioner.

Regular transient limb ischemia prevents atherosclerosis progression in hypercholesterolemic rabbits

Background:Endothelial dysfunction,the initial pathogenic factor in atherosclerosis,can be alleviated via transient limb ischemia.We observed the effects of regular transient limb ischemia (RTLI) on atherosclerosis in hypercholesterolemic rabbits.Methods:Twenty-eight rabbits were randomized to control,cholesterol,sham,ischemia groups (n=7 each) between October 2010 and March 2011.They were fed a normal diet in the control group and hypercholesterolemic diet in other groups for 12 weeks.Six cycles of RTLI were performed once per day on the ischemia group.Serum samples were prepared to measure the total cholesterol (TC),high-density lipoprotein cholesterol (HDL-C),low-density lipoprotein cholesterol (LDL-C) before the experiment (W0),at the end of weeks 4,8,12 (W4,W8,W12).The whole aorta was harvested at W12 and stained using Sudan IV to identify the plaque.The plaque area was measured using Image J.Results were analyzed by analysis of variance or rank sum test.Results:Concentrations of TC in the cholesterol group were higher than those in the control group at W4 (29.60 [23.75,39.30] vs.1.00 [0.80,1.55],Z =–2.745,P = 0.006),W8 (41.78 [28.08,47.37] vs.0.35 [0.10,0.68],Z =–2.739,P = 0.006),W12 (48.32 [40.04,48.95] vs.0.61 [0.50,0.86],Z =–2.739,P = 0.006).Similar results were obtained for HDL-C and LDL-C.Serum concentrations of TC,HDL-C,and LDL-C in the hypercholesterolemic groups had no differences (all P > 0.05).The percentage of plaque area in the cholesterol group was higher than that in the control group (47.22 ± 23.89% vs.0,Z =–2.986,P = 0.003).Square root of the percentage of plaque area was smaller in the ischemia group than that in the cholesterol (0.44 ± 0.13 vs.0.67 ± 0.18,P = 0.014) or sham groups (0.44 ± 0.13 vs.0.61 ± 0.12,P = 0.049).Conclusion:In hypercholesterolemic rabbits,RTLI might prevent atherosclerosis progression by reducing the percentage of plaque area.