电信运营的发展方向

亚洲电信业的市场正随着经济的蓬勃发展而迅速增大,然而大多数电信运营部门没能尽快更新设备以跟上商业需求增长的步伐。本文在分析用户业务需求的变化和对现有电信基础设施进行评估之后,提出应加强或采用叠加、并行的网络设施来为增长中的用户服务。同时认为通信资费应根据用户实际业务量的情况进行调整。这些做法将有助于电信经营部门处于更有竞争力的地位并从不断扩大的市场中赢得更多份额。     

A case study validation of a knowledge-based approach for the selection of requirements engineering techniques

Requirements engineering (RE) is a critical phase in the software engineering process and plays a vital role in ensuring the overall quality of a software product. Recent research has shown that industry increasingly recognizes the importance of good RE practices and the use of appropriate RE techniques. However, due to the large number of RE techniques, requirements engineers find it challenging to select suitable techniques for a particular project. Unfortunately, technique selection based on personal experience has limitations with regards to the scope, effectiveness and suitability of the RE techniques for the project at hand. In this paper, a Knowledge-based Approach for the Selection of Requirements Engineering Techniques (KASRET) is proposed that helps during RE techniques selection. This approach has three major features. First, a library of requirements techniques was developed which includes detailed knowledge about RE techniques. Second, KASRET integrates advantages of different knowledge representation schemata and reasoning mechanisms. Thus, KASRET provides mechanisms for the management of knowledge about requirements techniques and support for RE process development. Third, as a major decision support mechanism, an objective function evaluates the overall ability and cost of RE techniques, which is helpful for the selection of RE techniques. This paper makes not only a contribution to RE but also to research and application of knowledge management and decision support in process development. A case study using an industrial project shows the support of KASRET for RE techniques selection.

Liquid–liquid equilibria of aqueous two-phase systems composed of TritonX-100 and sodium citrate or magnesium sulfate salts

Liquid–liquid phase diagrams of surfactant-based aqueous two-phase systems (ATPS) composed of TritonX-100, as a non-ionic surfactant, and two different salts have been studied at 298.15 K. The salts used were an inorganic salt, magnesium sulfate (MgSO₄), and an organic salt, sodium citrate (Na₃C₆H₅O₇). The results show that the salt MgSO₄ is more capable of inducing ATPS formation than the salt Na₃C₆H₅O₇. The experimental liquid–liquid equilibrium data were correlated using a modified virial model. Good agreement was obtained with the experimental data.     

Adipose-derived stem cells could sense the nano-scale cues as myogenic-differentiating factors

Microenvironmental cues, such as surface topography and substrate stiffness, may affect stem cells adhesion, morphology, alignment, proliferation and differentiation. Adipose derived stem cells (ASCs) have attracted considerable interest in regenerative medicine due to their easy isolation, extensive in vitro expandability and ability to differentiate along a number of different tissue-specific lineages. The aim of this work was to investigate ASCs adhesion, alignment and differentiation into myogenic lineage on nanofibrous polymeric scaffolds with anisotropic topography. Nanostructured scaffolds with randomized or parallel fibers were fabricated by electrospinning using polycaprolactone (PCL) and the polycarbonate-urethane ChronoFlex AL 80A (CFAL). Cells expressed myosin (fast skeletal) and tropomyosin in all surface topographies 7 days after seeding but myotube formation was only observed on CFAL scaffolds and only few myotubes were formed on PCL scaffolds. The different cell behavior could be ascribed to two main parameters: fibers dimensions and fibers orientation of the substrates that could result in a better myotube formation on CFAL scaffolds.     

MOFs 材料金属位点设计及沼气纯化应用研究

改变MOFs材料的中心金属能影响其气体的亲和性和双组份气体的吸附选择性（如比表面积,孔道结构,内部电场等）,本文合成并表征了M－DABCO系列（M＝Ni, Co, Cu, Zn） MOFs材料。并应用理想吸附溶液理论（Ideal Adsorbed Solution Theory,简称IAST）量化模拟了环境条件下双组分混合气体（组分比CO2：CH4＝40％：60％）的吸附选择性。 Ni－DABCO材料具有良好的CO2吸附性能和在环境条件下对CO2／CH4混合气体的吸附选择性。本文通过实验、表征及计算等来讨论中心金属对M－DABCO系列吸附位点的影响。     

Microstructure and corrosion behaviour of plain carbon steel–B4C composite produced by GTAW method in 3·5 wt-%NaCl solution

In this work, the corrosion behaviour of metal matrix composite plain carbon steel–B₄C was studied in 3·5 wt-%NaCl solution. The composite was locally produced as weld band on plain carbon steel by means of gas tungsten arc welding process and using nickel as wetting agent. Samples from weld band, heat affected zone and base regions were extracted precisely, and electrochemical techniques including open circuit potential, linear polarisation resistance, electrochemical impedance spectroscopy, potentiodynamic polarisation in combination with SEM-EDX surface analysis and microhardness were used for characterisation. The results showed that hardness value of made composite increased significantly to 642 HV10. However, the corrosion resistance of composite region during 7 days (168 h) of exposure to 3·5 wt-%NaCl solution was slightly reduced. This was attributed to the fact that B₄C particles play as cathode site for oxygen reduction; therefore, they increase the corrosion rate slightly.     

Structure and properties of lead and lead sulfide nanoparticles in natural zeolite

We have synthesized lead and lead sulfide nanoparticles embedded in a natural zeolite (clinoptilolite) matrix by a simple hydrothermal process. The process steps involve the partial removing of the natural cations in clinoptilolite, the ion-exchange process to enclose Pb ions and nanoparticles and finally a sulfuration process at different temperatures to obtain lead sulfide phases in the zeolite matrix. The samples were studied by X-ray diffraction, diffuse reflectance spectroscopy, energy dispersive X-ray spectroscopy, X-ray photon spectroscopy and transmission electron microscopy. The experimental results show the inclusion of three Pb species with different valence states after the Pb ion-exchange step, namely Pb²⁺, Pb⁴⁺, and Pb⁰. At the end of the process, two simultaneous lead sulfide crystalline phases, PbS (Galena) and PbS₂ (tetragonal) were synthesized in the clinoptilolite matrix. The optical absorption spectra of the samples show the exciton absorption peaks typical of colloidal PbS nanoparticles. The average size of the PbS nanoparticles was about 10 nm and their crystalline structure was determined from diffraction electron patterns. The high-pressure phase PbS₂ was also identified and its formation was attributed to the influence of the special conditions of clinoptilolite matrix as crystallization media to induce some selective nucleation process of this crystalline phase.     

Adaptive maximum windowed likelihood multicomponent AM-FM signal decomposition

Considering a real signal as the sum of a number of sinusoidal signals in the presence of additive noise, maximum windowed likelihood (MWL) criterion is introduced and applied to construct an adaptive algorithm in order to estimate the amplitude and frequency of these components. The amplitudes, phases and frequencies are assumed to be slowly time varying. Employing MWL an adaptive algorithm is obtained in two steps. First, assuming some initial values for the frequency of each component, a closed form is derived to estimate the amplitudes. Then, the gradient of MWL is used to adaptively track the frequencies, using the latter values of amplitudes. The proposed algorithm has a parallel structure in which each branch estimates parameters of one of the components. The proposed multicomponent phase locked loop (MPLL) algorithm is implemented employing low complexity blocks. It is adjustable to be used in different conditions. The mean squared error of the algorithm is studied to analyze the effect of the window length and type and the step size. Simulations have been conducted to illustrate the efficiency and the performance of the algorithm in different conditions including: the effect of the initialization, the frequency resolution, for chirp components, for components during frequency crossover and for speech signals. Simulations illustrate that the method efficiently tracks slowly time-varying components of the signals such as voiced speech segments.     

Evaluation of bacterial RNase P RNA as a drug target

RNA has gained increasing importance as a therapeutic target. However, so far mRNAs rather than stable cellular RNAs have been considered in such studies. In bacteria, the tRNA-processing enzyme RNase P has a catalytic RNA subunit. Fundamental differences in structure and function between bacterial and eukaryotic RNase P, and its indispensability for cell viability make the bacterial enzyme an attractive drug target candidate. Herein we describe two approaches utilized to evaluate whether the catalytic RNA subunit of bacterial RNase P is amenable to inactivation by antisense-based strategies. In the first approach, we rationally designed RNA hairpin oligonucleotides targeted at the tRNA 3'-CCA binding site (P15 loop region) of bacterial RNase P RNA by attempting to include principles derived from the natural CopA-CopT antisense system. Substantial inactivation of RNase P RNA was observed for Type A RNase P RNA (such as that in Escherichia coli) but not for Type B (as in Mycoplasma hyopneumoniae). Moreover, only an RNA oligonucleotide (Eco 3') complementary to the CCA binding site and its 3' flanking sequences was shown to be an efficient inhibitor. Mutation of Eco 3' and analysis of other natural RNase P RNAs with sequence deviations in the P15 loop region showed that inhibition is due to interaction of Eco 3' with this region and occurs in a highly sequence-specific manner. A DNA version of Eco 3' was a less potent inhibitor. The potential of Eco 3' to form an initial kissing complex with the P15 loop did not prove advantageous. In a second approach, we tested a set of oligonucleotides against E. coli RNase P RNA which were designed by algorithms developed for the selection of suitable mRNA targets. This approach identified the P10/11-J11/12 region of bacterial RNase P RNA as another accessible region. In conclusion, both the P15 loop and P10/11-J11/12 regions of Type A RNase P RNAs seem to be promising antisense target sites since they are easily accessible and sufficiently interspersed with nonhelical sequence elements, and oligonucleotide binding directly interferes with substrate docking to these two regions.