Dynamic random-access memory (DRAM) is the building block of modern main memory systems. DRAM cells must be periodically refreshed to prevent loss of data. These refresh operations waste energy and degrade system performance by interfering with memory accesses. The negative effects of DRAM refresh increase as DRAM device capacity increases. Existing DRAM devices refresh all cells at a rate determined by the leakiest cell in the device. However, most DRAM cells can retain data for significantly longer. Therefore, many of these refreshes are unnecessary.In this paper, we propose RAIDR (Retention-Aware Intelligent DRAM Refresh), a low-cost mechanism that can identify and skip unnecessary refreshes using knowledge of cell retention times. Our key idea is to group DRAM rows into retention time bins and apply a different refresh rate to each bin. As a result, rows containing leaky cells are refreshed as frequently as normal, while most rows are refreshed less frequently. RAIDR uses Bloom filters to efficiently implement retention time bins. RAIDR requires no modification to DRAM and minimal modification to the memory controller. In an 8-core system with 32 GB DRAM, RAIDR achieves a 74.6% refresh reduction, an average DRAM power reduction of 16.1%, and an average system performance improvement of 8.6% over existing systems, at a modest storage overhead of 1.25 KB in the memory controller. RAIDR's benefits are robust to variation in DRAM system configuration, and increase as memory capacity increases.

This paper attempts to provide some new understanding of the mechanical as well as thermal effects of the Tibetan Plateau (TP) on the circulation and climate in Asia through diagnosis and numerical experiments. The air column over the TP descends in winter and ascends in summer and regulates the surface Asian monsoon flow. Sensible heating on the sloping lateral surfaces appears from the authors’ experiments to be the major driving source. The retarding and deflecting effects of the TP in winter generate an asymmetric dipole zonal-deviation circulation, with a large anticyclone gyre to the north and a cyclonic gyre to the south. Such a dipole deviation circulation enhances the cold outbreaks from the north over East Asia, results in a dry climate in south Asia and a moist climate over the Indochina peninsula and south China, and forms the persistent rainfall in early spring (PRES) in south China. In summer the TP heating generates a cyclonic spiral zonal-deviation circulation in the lower troposphere, which converges toward and rises over the TP. It is shown that because the TP is located east of the Eurasian continent, in summertime the meridional winds and vertical motions forced by the Eurasian continental-scale heating and the TP local heating are in phase over the eastern and central parts of the continent. The monsoon in East Asia and the dry climate in middle Asia are therefore intensified.

This paper presents a method for evaluating multiple feature spaces while tracking, and for adjusting the set of features used to improve tracking performance. Our hypothesis is that the features that best discriminate between object and background are also best for tracking the object. We develop an on-line feature ranking mechanism based on the two-class variance ratio measure, applied to log likelihood values computed from empirical distributions of object and background pixels with respect to a given feature. This feature ranking mechanism is embedded in a tracking system that adaptively selects the top-ranked discriminative features for tracking. Examples are presented to illustrate how the method adapts to changing appearances of both tracked object and scene background.

Photoresponsive nanoporous membranes, composed of monosized pores modified with azobenzene ligands, were prepared on an ITO working electrode using an evaporation-induced self-assembly procedure. They exhibited the size-selective photoregulated mass transport of two ferrocene-based molecular probes through the membrane to the electrode surface as determined using a chronoamperometry technique. The measured oxidative current increased and decreased in response to alternating UV and visible light exposure correlating strongly with the photoisomerization state of the azobenzene ligands. This indicates that the optically switchable conformation (trans or cis) of azobenzene ligands controls the effective pore size and, correspondingly, transport behavior on the nanoscale.

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Background: Gold nanoparticle toxicity research is currently leading towards the in vivo experiment. Most toxicology data show that the surface chemistry and physical dimensions of gold nanoparticles play an important role in toxicity. Here, we present the in vivo toxicity of 5, 10, 30, and 60 nm PEG-coated gold nanoparticles in mice. Methods: Animal survival, weight, hematology, morphology, organ index, and biochemistry were characterized at a concentration of 4000 µg/kg over 28 days. Results:The PEG-coated gold particles did not cause an obvious decrease in body weight or appreciable toxicity even after their breakdown in vivo. Biodistribution results show that 5 nm and 10 nm particles accumulated in the liver and that 30 nm particles accumulated in the spleen, while the 60 nm particles did not accumulate to an appreciable extent in either organ. Transmission electron microscopic observations showed that the 5, 10, 30, and 60 nm particles located in the blood and bone marrow cells, and that the 5 and 60 nm particles aggregated preferentially in the blood cells. The increase in spleen index and thymus index shows that the immune system can be affected by these small nanoparticles. The 10 nm gold particles induced an increase in white blood cells, while the 5 nm and 30 nm particles induced a decrease in white blood cells and red blood cells. The biochemistry results show that the 10 nm and 60 nm PEG-coated gold nanoparticles caused a significant increase in alanine transaminase and aspartate transaminase levels, indicating slight damage to the liver. Conclusion: The toxicity of PEG-coated gold particles is complex, and it cannot be concluded that the smaller particles have greater toxicity. The toxicity of the 10 nm and 60 nm particles was obviously higher than that of the 5 nm and 30 nm particles. The metabolism of these particles and protection of the liver will be more important issues for medical applications of gold-based nanomaterials in future.

Introduction. Currently, amphiphilic copolymers with nonlinear and noncentrosymmetric architectures start to attract much interest due to the synthetic challenges and their unprecedented properties. [1][2][3] The particular asymmetric character of amphiphilic particles having two faces was termed as "Janus". [4][5][6] Depending on their shape, Janus particles can be divided into Janus spheres, cylinders, and sheets (Figure 1). These amphiphilic nanoparticles should have novel properties in solution, at interfaces, or in the bulk. Because of their amphiphilic nature, the formation of structures of higher hierarchical order is expected. Proteins in the shape of "amphiphilic helices" are observed in nature, and they form oligomeric superstructures. 7 Various strategies can be designed to construct the structures in Figure 1. One strategy is based on the selfassembly of block terpolymers (i.e., ABC triblock copolymers) in the bulk. [8][9][10] Depending on their composition, they can form, for example, lamellae-sphere, lamellae-cylinder, or lamellae-lamellar morphologies in the bulk. Selective cross-linking of the central block and redissolution leads to nanoscopic particles where the corona is forced to be compartmentalized. This approach was used by Erhardt et al. in order to synthesize spherical Janus micelles with polystyrene (PS) and poly(methyl methacrylate) (PMMA) hemicoronas. 3 These micelles form larger aggregates in nonselective organic solvents, on a silicon surface, and at the air/water interface. 3,11 Hydrolysis of the PMMA ester groups led to amphiphilic Janus micelles with PS and poly(methacrylic acid) hemicoronas which again lead to superstructures and giant particles. 12 Another strategy to form Janus micelles is based on the self-assembly of block copolymers in solution. 13 In one approach, block terpolymers can form micellar solutions in a solvent that dissolves the outer blocks but is a nonsolvent for the middle block. Cross-linking of the core again should form Janus micelles. 14 However, phase separation of the outer blocks may not be as pronounced as in the bulk approach. Another selfassembly approach is based on the electrostatic interactions of AB and CD diblock copolymers where B and C form insoluble complexes, e.g., inter-polyelectrolyte complexes, in a solvent for blocks A and D. The first reported approach has led to nonsymmetric vesicles rather than to Janus spheres. 15 Alternatively, great efforts have been taken into the synthesis of Janus-like particles through pure organic synthetic approaches in recent years. Hadjichristidis et al. and other groups investigated the synthesis of miktoarm star copolymers through living anionic polymerization, 1,2 controlled radical polymerization, 16 or

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