基于UMHexagenS的快速运动估计算法优化

结合JM12.4的源代码对UMHexagens算法进行了理论与数据的分析,并对该算法进行改进,能够在保证视频序列各分量信噪比的情况下有效地缩短运动估计时间.通过改进UMHexagonS算法中的帧间模式选择,使搜索算法避开了一部分多余的搜索点.实验结果表明,在保证PSNR和码率基本不变的前提下,可以减少运动估计时间10%...     

基于比例公平原则的多用户MIMO-OFDM系统资源分配

提出了一种基于比例公平原则提高MIMO-OFDM系统吞吐量的子载波和功率分配算法.它在总功率和误比特率的约束下,以获取最大系统吞吐量为目标,同时为兼顾用户间资源享用的公平性,根据用户速率成比例推导出了子载波分配限制准则.仿真结果表明,本算法不仅可满足不同用户的速率要求,而且平衡了容量最大化和用户间公平性的矛盾,同时计算...     

Surfactant-controlled morphology and magnetic property of manganese ferrite nanocrystal contrast agent

MnFe(2)O(4) nanocrystals (NCs) coated with three different surfactants (oleic acid, oleylamine or 1,2-hexadecanediol) and their mixtures, with sizes in range 6-12 nm, were synthesized by high-temperature decomposition of organometallic precursors. The effects of morphology and surface chemistry of MnFe(2)O(4) NCs on the magnetic properties were systematically investigated by comparing their saturation magnetization values and their capability to improve the negative contrast for magnetic resonance imaging (MRI) after converting the hydrophobic NCs to hydrophilic ones by a ligand exchange protocol. An important finding is that the magnetization values and proton relaxivity rates of MnFe(2)O(4) NCs are strongly dependent on the size and surface state of the particles that covalently bonded with different hydrophobic ligands before ligand exchange. In particular, monodisperse cubic MnFe(2)O(4) NCs could be obtained when oleylamine and 1,2-hexadecanediol were used as mixed stabilizers, and showed excellent morphology and magnetic properties. Furthermore, the low cytotoxicity and good cell uptake MR imaging of the dopamine capped MnFe(2)O(4) NCs make them promising candidates for use as bio-imaging probes.     

A Hollow‐Core,Magnetic, and Mesoporous Double‐Shell Nanostructure: In Situ Decomposition/Reduction Synthesis,Bioimaging, and Drug‐Delivery Properties

A novel in situ decomposition/reduction approach is developed to manu­facture hollow core, magnetic, and mesoporous double‐shell nanostructures (HMMNSs) via in situ decomposition and reduction of a β‐FeOOH nanorod core and organosilicate‐incorporated silica‐shell precursor. The formed HMMNSs are then aminated by silanization for further covalent conjugation to rhodamine B isothiocyanate (RBITC) and poly(ethylene glycol) (PEG) chains. The resultant RBITC‐grafted and PEGylated nanocomposites (HMMNS–R/Ps) have excellent blood compatibility and very low cytotoxicity towards HeLa and MCF‐7 cells, and can be taken up by cancer cells effectively in a dose‐dependent manner, as confirmed by in vitro flow cytometry, confocal luminescence imaging, and magnetic resonance imaging (MRI) studies. In vivo MRI studies coupled with Prussian blue staining of slides from different organs show that the nanocomposites preferentially accumulate in liver and spleen after intravenous injection, which suggests a potential application of the nanocomposites as MRI contrast agents. Importantly, the HMMNS–R/P nanocomposites show high loading capacity for water‐insoluble anticancer drugs (docetaxel or camptothecin) owing to the presence of a large inner cavity and enhanced surface area and pore volume. Furthermore, the drug‐loaded nanocomposites exhibit greater cytotoxicity than the corresponding free drugs. These results confirm that the HMMNS–R/P nanocomposites are promising candidates for simultaneous bioimaging and drug delivery.     

Large strain response in acceptor- and donor-doped Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-based lead-free ceramics

Effects of Fe and La addition on the dielectric, ferroelectric, and piezoelectric properties of Bi_0.5Na_0.5TiO₃–Bi_0.5Li_0.5TiO₃–BaTiO₃–Mn ceramics were investigated. Similar to the doping effect in lead-based piezoelectric materials, here the Fe-doped ceramic created a hard effect with an improved mechanical quality factor (Q _m) ~ 160, coercive field (E _c) ~ 2.9 kV/mm, decreased dielectric constant ( e₃₃^T /e₀ ) ~ 80 3, \left( {\varepsilon_{33}^{T} /\varepsilon_{0} } \right)\sim 80 3, and loss (tanδ) ~ 0.024 while the La-doped one indicated a soft feature with improved piezoelectric constant (d ₃₃) ~ 184 pC/N, e₃₃^T /e₀   ~ 983, \varepsilon_{33}^{T} /\varepsilon_{0} \,\sim { 983}, tanδ ~ 0.033, and decreased E _c ~ 2.46 kV/mm. In addition, the temperature dependence of the ferroelectric hysteresis loops and strain response under unipolar electric field was also studied. Around the depolarization temperature T _d, large strain value was obtained with the normalized d₃₃^* d_{33}^{*} up to ~1,000 pC/N, which was suggested originated from the development of the short-range order or non-polar phases in the ferroelectric matrix. All these would provide a new way to realize high piezoelectric response for practical application in different temperature scale.     

Modification of cellulose acetate nanofibers with PVP/Ag addition

In this work cellulose acetate (CA) nanostructures were synthesized using electrospinning process. Silver nanoparticles (Ag NPs) were synthesized using silver nitrate as the starting precursor, ethanol as solvent and polyvinyl pyrolydone (PVP) as capping agent. The Ag NPs were added to the cellulose acetate (CA) nanostructures before and after CA electrospinning. The obtained CA and Ag-CA composite were characterized by various techniques such as, Fourier Transform Infrared (FTIR) spectroscopy, Raman Spectroscopy, Scanning electron microscopy (SEM) and Differential Scanning Calorimetry (DSC). It was found that Ag NPs can be effectively coated on or embedded into the electrospun CA and the PVP can lead to noticeable change in morphology and structure.     

Spherical Harmonic–Generalized Laguerre Spectral Method for Exterior Problems

In this paper, we propose the mixed spherical harmonic-generalized Laguerre spectral method for three-dimensional exterior problems. Some approximation results are established. As an example, a model problem is considered. The convergence of proposed scheme is proved. Numerical results demonstrate the efficiency of this approach.     

Polymer electrolyte membrane resistance model

A model and an analytical solution for the model are presented for the resistance of the polymer electrolyte membrane of a H₂/O₂ fuel cell. The solution includes the effect of the humidity of the inlet gases and the gas pressure at the anode and the cathode on the membrane resistance. The accuracy of the solution is verified by comparison with experimental data. The experiments were carried out with a Nafion 112 membrane in a homemade fuel cell test station. The membrane resistances predicted by the model agree well with those obtained during the experiments.     

Strong localization of microwave in photonic fractals with Menger-sponge structure

Photonic fractal with self-similar structure of dielectric medium can strongly localize the electromagnetic wave energy in the three-dimensional fractal structure. We have fabricated Menger-sponge fractal structures of epoxy by using stereolithography. Titania–silica particles were dispersed into the epoxy to increase the dielectric constant and decrease the dielectric loss. The samples have square holes of 1, 3, 9 and 27 mm in edge length through the cubic body of 81 mm. Four types of Menger-sponge samples with fractal stages 1–4 were subjected for measurement of microwave responses. The both reflection and transmission amplitudes were attenuated simultaneously at frequencies of 9.5, 10.5, 12.0 and 13.5 GHz for each sample with fractal stages 1, 2, 3 and 4, respectively. The electromagnetic field amplitudes in the air holes measured by inserting a mono-pole antenna probe confirmed the strong localization of the electromagnetic wave in the central air cavity. The localized mode frequency can be calculated using the sample size, number of stage, and the effective dielectric constant. The localization efficiency increased according to the fractal stage number.