On-line learning algorithm for dynamic sensitivity control in IEEE 802. 11ax network

The popularity of IEEE 802. 11 based wireless local area network（ WLAN） increased significantly in recent years and resulted in the dense deployment of WLANs. While densification can contribute to increasing coverage,it could also lead to increasing interference and cannot insure high spatial reuse due to the current physical carrier sensing of IEEE 802. 11. To tackle these challenges,the dynamic sensitivity control（ DSC） is considered in IEEE802. 11 ax,which dynamically selects the appropriate carrier sensing threshold（ CST） to improve spectrum efficiency and enhance spatial reuse in densely deployed network. A dynamic Q-learning based CST selection method is proposed to enable a network to select the optimal CST according to the channel condition. Simulation results show that the proposed scheme provides 40% aggregate throughput gain of a dense network when compared with legacy IEEE 802. 11.

Studies on sensitivity to tension and gating pathway of MscL by molecular dynamic simulation

Mechanosensitive（MS） ion channels play an important role in various physiological processes.Although the determination of the structure of mechanosensitive channel of large conductance（MscL） makes the simulation study possible,it has not so far been possible to directly simulate the gating mechanism of MscL in atomic detail.In this article,MscL has been studied via molecular dynamic（MD） simulations to gain a detailed description of the sensitivity to lateral tension and the gating pathway.MscL undergoes conformational rearrangement in sustaining lateral tension,and the open state is obtained when 2.0 MPa lateral tension is directly applied on the pure protein.During the opening process,Loop region responds to tension first,and the mechanical sensitivity is followed by S1 domain.Transmembrane（TM） bundle is the key position for channel opening,and the motion of TM1 helices finally realizes the significant expansion of the constricted gating pore.C-terminus domain presents expansion later during the TM opening.In our study,return of the whole protein to the initial closed state is achieved only in the early opening stage.During the relaxation from the open state,the TM helices are the most mobile domain,which is different from the opening process.

Strain-rate Sensitivity of Aluminum 2024-T6/TiB_2 Composites and Aluminum 2024-T6

Strain-rate sensitivities of 55vol%-65vol% aluminum 2024-T6/TiB2 composites and the corresponding aluminum 2024-T6 matrix were investigated using split Hopkinson pressure bar method. The experimental results showed that 55vol%-65vol% aluminum 2024-T6/TiB2 composites exhibited significant strain-rate sensitivities, which were three times higher than the strain-rate sensitivity of the aluminum 2024-T6 matrix. The strain-rate sensitivity of the aluminum 2024-T6 matrix composites rose obviously with increasing reinforcement content（up to 60%）, which agreed with that from the previous researches. But it decreased as the ceramic reinforcement content reached 65%. After high strain rates compression, a large number of dislocations and micro-cracks were found inside the matrix and the Ti B2 particles, respectively. These micro-cracks can accelerate the brittle fracture of the composites. The aluminum 2024-T6/Ti B2 composites showed various fracture characteristics and shear instability was the predominant failure mechanism under dynamic loading.

Parametrical analysis of the railways dynamic response at high speed moving loads

The paper introduces some findings about a sensitivity analysis conducted on every geometrical and mechanical parameters which characterize the use of a railway superstructure at the high velocity. This analysis was carried out by implementing a forecast model that is derived from the simplified Gazetas and Dobry one. This model turns out to be particularly appropriate in the explication of problems connected to high velocity, since it evaluates both inertial and viscous effects activated by the moving load speed. The model implementation requires the transfer function determination that represents the action occurred by the bed surfaces on the railway and it therefore contains information concerning the geometrical and the mechanical characteristics of the embankment, of the ballast and of the sub-ballast. The transfer function H has been evaluated with the finite elements method and particularly, by resorting the ANSYS code with a harmonic structural analysis in the frequencies field. The authors, from the critic examination of the system＇s dynamics response in its entirety, glean a series of observations both of a general and a specific character, finally attaining a propose of a design modification of the standard railway superstructure at the high velocity of train operation adopted today especially in Italy.

Light weight analysis of a skeleton vehicle frame using BS960 super-high-strength steel

Static strength finite element analysis was conducted to decrease the weight of a skeleton vehicle＇s frame. Results indicated that the maximum stress occurs on the front beam ＇s variable section area. Dynamic sensitivity analysis elucidated the relationship between the maximum stress and the thickness of a particular beam,e. g.,top,middle,and bottom beam. Displacement was analyzed by the key part that influenced the maximum stress. Finally,the new plan using BS960 super-high-strength beam steel and the preferred beam thickness was compared with the original plan. New combinations of beam thickness were introduced on the basis of different purposes; the maximum responding light w eight ratio was 21%.

Optimal design of vibration absorber using minimax criterion with simplified constraints

In this paper, a minimax design of damped dynamic vibration absorber for a damped primary system is investigated to minimize the vibration magnitude peaks. Moreover, to reduce the sensitivity of the primary system response to variations of the forcing frequency for a two- degree-of-freedom system, the primary system should have two equal resonance magnitude peaks. To meet this re- quirement, a set of simplified constraint equations includ- ing distribution characteristics of the resonant frequencies of the primary system is established for the minimax objective function. The modified constraint equations have less un- known variables than those by other authors, which not only simplifies the computation but also improves the accuracy of the optimal values. The advantage of the proposed method is illustrated through numerical simulations.

Theoretical Insight into the Influence of Molecular Ratio on the Stability, Mechanical Property, Solvent Effect and Cooperativity Effect of HMX/DMI Cocrystal Explosive

Molecular dynamics method was employed to study the binding energies of the selected crystal planes of the 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane（HMX）/1,3-dimethyl-2-imidazolidinone（DMI） cocrystal in different molecular molar ratios. The mechanical properties were estimated in different molar ratios. Solvent effects were evaluated and the cooperativity effects were discussed in the HMX···HF···DMI ternary by using the M06-2x/6-311＋G（2df,2p） and MP2（full）/6-311＋G（2df,2p） methods. The results indicate that the substituted patterns（020） and（100） own the highest binding energies. The stabilities of cocrystals in the 1：1 and 2：1 ratios are the greatest, and thus the HMX/DMI cocrystals prefer cocrystallizing in the 1：1 and 2：1 molar ratios, which have good mechanical properties. The sensitivity change of cocrystal originates from not only the formation of intermolecular interaction but also the increment of bond dissociation energy of the N–NO2 bond. The cooperativity effect appears in the linear complex while the anti-cooperativity effect is found in the cyclic system. DMI binding to HMX is not energetically and structurally favored in the presence of HF. This is perhaps the reason that the solvent with large dielectric constant weakens the stability of the HMX/DMI cocrystals. Therefore, the solvents with low dielectric constants should be chosen in the preparation of HMX/DMI cocrystals.

Optical properties and dynamic process in metal ions doped on CdSe quantum dots sensitized solar cells

In recent years, the nanostructure for solar cells have attracted considerable attention from scientists as a result of a promising candidate for low cost devices. In this work, quantum dots sensitized solar cells with effective performance based on a co-sensitized Cd S∕Cd Se：Mn2＋（or Cu2＋） nanocrystal, which was made by successive ionic layer absorption and reaction, are discussed. The optical, physical, chemical, and photovoltaic properties of quantum dots sensitized solar cells were sensitized to Mn2＋and Cu2＋dopants. Therefore, the short current（JSC）of the quantum dot sensitized solar cells is boosted dramatically from 12.351 mA∕cm2 for pure Cd Se nanoparticles to 18.990 mA∕cm2 for Mn2＋ions and 19.915 mA∕cm2 for Cu2＋ions. Actually, metal dopant extended the band gap of pure Cd Se nanoparticles, reduced recombination, enhanced the efficiency of devices, and improved the charge transfer and collection. In addition, Mn2＋and Cu2＋dopants rose to the level of the conduction band of pure Cd Se nanoparticles, which leads to the reduction of the charge recombination, enhances the lightharvesting efficiency, and improves the charge diffusion and collection. The results also were confirmed by the obtained experimental data of photoluminescence decay and electrochemical impedance spectroscopy.

Impact of Climate Change on Maize Potential Productivity and the Potential Productivity Gap in Southwest China

The impact of climate change on maize potential productivity and the potential productivity gap in Southwest China（SWC） are investigated in this paper.We analyze the impact of climate change on the photosynthetic,light-temperature,and climatic potential productivity of maize and their gaps in SWC,by using a crop growth dynamics statistical method.During the maize growing season from 1961 to 2010,minimum temperature increased by 0.20℃ per decade（p 〈 0.01） across SWC.The largest increases in average and minimum temperatures were observed mostly in areas of Yunnan Province.Growing season average sunshine hours decreased by 0.2 h day^（-1） per decade（p 〈 0.01） and total precipitation showed an insignificant decreasing trend across SWC.Photosynthetic potential productivity decreased by 298 kg ha^（-1）per decade（p 〈 0.05）.Both light-temperature and climatic potential productivity decreased（p 〈 0.05） in the northeast of SWC,whereas they increased（p 〈 0.05） in the southwest of SWC.The gap between lighttemperature and climatic potential productivity varied from 12 to 2729 kg ha^（-1）,with the high value areas centered in northern and southwestern SWC.Climatic productivity of these areas reached only 10%-24%of the light-temperature potential productivity,suggesting that there is great potential to increase the maize potential yield by improving water management in these areas.In particular,the gap has become larger in the most recent 10 years.Sensitivity analysis shows that the climatic potential productivity of maize is most sensitive to changes in temperature in SWC.The findings of this study are helpful for quantification of irrigation water requirements so as to achieve maximum yield potentials in SWC.