A Communication Monitor for Wireless Sensor Networks Based on Software Defined Radio

Link quality estimation of reliability-crucial wireless sensor networks (WSNs) is often limited by the observability and testability of single-chip radio transceivers. The estimation is often based on collection of packer-level statistics, including packet reception rate, or vendor-specific registers, such as CC2420's Received Signal Strength Indicator (RSSI) and Link Quality Indicator (LQI). The speed or accuracy of such metrics limits the performance of reliability mechanisms built in wireless sensor networks. To improve link quality estimation in WSNs, we designed a powerful wireless communication monitor based on Software Defined Radio (SDR). We studied the relations between three implemented link quality metrics and packet reception rate under different channel conditions. Based on a comparison of the metrics' relative advantages, we proposed using a combination of them for fast and accurate estimation of a sensor network link

Link Quality Estimation for Future Cooperating Objects

ReSens

Scientific elite revisited: Patterns of productivity, collaboration, authorship and impact

Throughout history, a relatively small number of individuals have made a profound and lasting impact on science and society. Despite long-standing, multi-disciplinary interests in understanding careers of elite scientists, there have been limited attempts for a quantitative, career-level analysis. Here, we leverage a comprehensive dataset we assembled, allowing us to trace the entire career histories of nearly all Nobel laureates in physics, chemistry, and physiology or medicine over the past century. We find that, although Nobel laureates were energetic producers from the outset, producing works that garner unusually high impact, their careers before winning the prize follow relatively similar patterns as ordinary scientists, being characterized by hot streaks and increasing reliance on collaborations. We also uncovered notable variations along their careers, often associated with the Nobel prize, including shifting coauthorship structure in the prize-winning work, and a significant but temporary dip in the impact of work they produce after winning the Nobel. Together, these results document quantitative patterns governing the careers of scientific elites, offering an empirical basis for a deeper understanding of the hallmarks of exceptional careers in science

Mixed convection flow near a non-orthogonal stagnation point towards a stretching vertical plate

An analysis of the steady two-dimensional mixed convection flow of an incompressible viscous fluid near an oblique stagnation point on a heated or cooled stretching vertical flat plate has been studied. It is assumed that the plate is stretched with a velocity proportional to the distance from a fixed point and the temperature of the plate is constant. Both the cases of the assisting and opposing flows are considered. It is shown that the velocity increases as the shear parameter γ increases with the increase of the straining parameter a/c. These flows have a boundary layer structure near the stagnation region. It is also found that the flow has an inverted boundary layer structure when the stretching velocity of the surface exceeds the stagnation velocity of the free stream (a/c < 1). It is shown that the position of the point xs of zero skin friction (shear stress on the wall) is shifted to the left or to the right of the origin and it depends upon the balance between obliqueness, straining motion and buoyancy effect

Synthesis and Characterization of Novel Functional Materials based on Cellulose and Graphene Oxide

This thesis focused on the synthesis and characterization of novel functional materials based on cellulose and graphene derivatives. Cellulose/GO hydrogels were produced as the starting material by dissolving cellulose and dispersing GO in NaOH/urea solution. This method is considered as an efficient, simple, environmentally friendly, and low-cost method. Novel functionalities, such as sensing, catalytic and EMI shielding properties have been “built-in” to cellulose/GO hydrogels. Cellulose/rGO composite films and aerogels were successfully fabricated by dissolving cellulose and dispersing GO in NaOH/urea solution, followed by the chemical reduction with vitamin C as the reducing agent. The cellulose/rGO films and aerogels with various rGO contents were prepared by air-drying and freeze-drying of the prepared cellulose/rGO composite hydrogels. The resultant cellulose/rGO composites prepared by this efficient and simple method show high resistance sensitivity to environmental stimuli like temperature, humidity, liquids, vapours, and strain stress. Thus, the cellulose/rGO films can be applied in detecting human motions and human breath cycles. Liquid temperature, liquid type, and ion concentration also be determined by our cellulose/rGO films. Moreover, the composite aerogels are fast responding and extremely sensitive sensors for vapour detection and testing with good repeatability. It was also revealed that discriminating and quantitative responses can be obtained when analyzing various vapours and different vapour concentrations. For methanol vapour, the aerogel shows linear response to the vapour concentration. Thus cellulose/rGO composite aerogel can be used to quantify methanol vapour concentrations. The efficient, scalable, and environmentally friendly preparation of novel and high-performance of vapour sensing materials with well reproducibility is promising to achieve practical vapour sensing applications. We have successfully presented an effective, facial, simple, and scalable method to form Fe3O4 nanoparticles onto cellulose/GO hydrogels. XRD, FTIR, XPS and TEM indicated that Fe3O4 nanoparticles with good dispersion and uniform size are successfully coated on cellulose matrix and GO sheets. This material was tested as catalyst for the cleaning of dye-contaminated water by oxidation with H2O2.The optimized experiment conditions for AO7 degradation are: [AO7] = 0.1 mM, T = 298 K, [H2O2] = 22 mM, and pH = 3. Under these conditions, the resulting hydrogels display 97 % AO7 removal within 120 min and retained strong degradation performance after twenty consecutive cycles of reuse. Especially, the detailed XPS analysis of cellulose/GO/Fe3O4 and cellulose/Fe3O4 composites indicated that the cellulose/GO/Fe3O4 hydrogel retain its high degradation activity by keeping the ratio of Fe3+/Fe2+ at 2 during the 20 heterogeneous Fenton-like reaction cycles. Therefore, the cellulose/GO/Fe3O4 hydrogel is recommended to test the treatment of other dye-contaminated wastewaters. Cellulose/rGO/Fe3O4 films and aerogels were successfully fabricated by the in-situ grown of Fe3O4 nanoparticles within a cellulose matrix containing rGO sheets. Cellulose/rGO (8 wt.%)/Fe3O4 aerogels with the thickness of 0.5 mm exhibited high EMI shielding performance with the EMI SE value at 32.4-40.1 dB in the 8.2-12.4 GHz frequency range. High loading of rGO and large thickness of the composites are beneficial for the excellent EMI shielding performance of our aerogels. The lightweight aerogel is suitable for the practical application as EMI shielding materials such as spacecraft, aircraft, energy conversion application, and energy storage