This is the first book to comprehensively cover chromatic polynomials of graphs. It includes most of the known results and unsolved problems in the area of chromatic polynomials. Dividing the book ...into three main parts, the authors take readers from the rudiments of chromatic polynomials to more complex topics: the chromatic equivalence classes of graphs and the zeros and inequalities of chromatic polynomials. The early material is well suited to a graduate level course while the latter parts will be an invaluable resource for postgraduate students and researchers in combinatorics and graph theory.
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•A synchronous sensing scheme for mass perturbation and driving force is proposed.•Output voltage, sensing range and anti-driving fluctuation performance are improved.•The proposed ...synchronous sensing scheme is universal and practical.
This paper, the second of two companion papers, mainly reports a synchronous sensing scheme for both mass perturbation and driving force, via the internal resonance phenomena in various coupled Duffing oscillators. The mass perturbation, applied on the low frequency oscillator, is sensed by the dip frequency of the low frequency oscillator caused by modal interaction, and further detected by the corresponding multiplied response frequency of the high frequency oscillator, while the driving force, applied on the low frequency oscillator, is directly detected by measuring the multiplied jump frequency of the high frequency oscillator. A magnetically coupled orthogonal beams with a frequency ratio of two to one, is taken as an example for both theoretical and experimental demonstration. The results show that the synchronous sensing of both mass perturbation and driving amplitude are achievable with a mass sensitivity of −21.5 Hz/g in the range of 0 mg to 314 mg and a force sensitivity of 8.84 Hz/V in the range of 0.5 V to 2.0 V. Compared to the double amplification mass sensing one proposed in the companion paper, the output voltage, the mass sensing range, and the anti-driving fluctuation performance of the proposed scheme in this paper, are improved or amplified by about 167%, 388%, and 3470% times respectively. It is thus more universal and applicable to various micro and nano resonators, when the Duffing nonlinearity is practically considered.
In order to study the temporal and spatial variations of PM2.5 and its chemical compositions in the region of Beijing, Tianjin, and Hebei (BTH), PM2.5 samples were collected at four urban sites in ...Beijing (BJ), Tianjin (TJ), Shijiazhuang (SJZ), and Chengde (CD), and also one site at Shangdianzi (SDZ) regional background station over four seasons from 2009 to 2010. The samples were weighted for mass concentrations and analyzed in the laboratory for chemical profiles of 19 elements (Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Ni, P, Pb, Sr, Ti, V, and Zn), eight water-soluble inorganic ions (Na+ , NH4+ , K+ , Mg2+ , Ca2+ , Cl- , NO3- , and SO42- , and carbon fractions (OC and EC). The concentrations of PM2.5 and its major chemical species were season dependent and showed spatially similar characteristics in the plain area of BTH. The average annual concentrations of PM2.5 were 71.8-191.2 μg m-3 at the five sites, with more than 90% of sampling days exceeding 50 μg m-3 at BJ, TJ, and SJZ. PM2.5 pollution was most serious at SJZ, and the annual concentrations of PM2.5 , secondary inorganic ions, OC, EC, and most crustal elements were all highest. Due to stronger photochemical oxidation, the sum of concentrations of secondary inorganic ions (NH4+ , NO3- , and SO42- was highest in the summer at SDZ, BJ, TJ, and CD. Analysis of electric charges of water-soluble inorganic ions indicated the existence of nitric acid or hydrochloric acid in PM2.5 . For all five sites, the concentrations of OC, EC and also secondary organic carbon (SOC) in the spring and summer were lower than those in the autumn and winter. SOC had more percentages of increase than primary organic carbon (POC) during the winter. The sums of crustal elements (Al, Ca, Fe, Mg, Ti, Ba, and Sr) were higher in the spring and autumn owing to more days with blowing or floating dust. The concentrations of heavy metals were at higher levels in the BTH area by comparison with other studies. In Shijiazhuang and Chengde, the PM2.5 pollution was dominated by coal combustion. Motor vehicle exhausts and coal combustion emissions both played important roles in Tianjin PM2.5 pollution. However, motor vehicle exhausts had played a more important role in Beijing owing to the reduction of coal consumption and sharp increase of cars in recent years. At SDZ, regional transportation of air pollutants from southern urban areas was significant.
► The pH plays important roles in 2205 DSS passive film composition and occurrence of pitting. ► The passive film of 2205 DSS in the alkaline solution, presenting a bilayer structure, composed of an ...outer and inner layer. ► As the pH increases, there is a gradual enrichment in chromium and nitrogen in the surface film. ► The peak of NH3/NH4+ is disappeared in the pH 10.5 solutions. ► The pit initiated at inclusions or in austenite phase near the γ/δ boundaries.
The electrochemical behaviour of 2205 duplex stainless steel in alkaline solutions with different pH values in the presence of NaCl was evaluated by different techniques: potentiodynamic measurements, electrochemical impedance spectroscopy and capacitance measurements (Mott–Schottky approach). The chemical composition was studied by X-ray photoelectron spectroscopy (XPS). In addition, the site of pitting nucleated preferentially on the duplex stainless steel had been confirmed by scanning electron microscopy (SEM). The results indicated that both the pH and immersion time play important roles in the evolution of the film resistance, charge transfer processes and the occurrence of pitting. The composition of the surface film changes with the pH value. The film formed in the alkaline solution, presenting a bilayer structure, predominantly contained Fe species and Cr-oxide. The NH3/NH4+ species in the passive film are disappeared in the pH 10.5 solution. The pit initiation sites occurred in austenite phase near the γ/δ boundaries or at inclusions. The number and size of the pits increases with the decrease of pH value after long time immersion.
Glaucoma is the most prevalent neurodegenerative disease and a leading cause of blindness worldwide. The mechanisms causing glaucomatous neurodegeneration are not fully understood. Here we show, ...using mice deficient in T and/or B cells and adoptive cell transfer, that transient elevation of intraocular pressure (IOP) is sufficient to induce T-cell infiltration into the retina. This T-cell infiltration leads to a prolonged phase of retinal ganglion cell degeneration that persists after IOP returns to a normal level. Heat shock proteins (HSP) are identified as target antigens of T-cell responses in glaucomatous mice and human glaucoma patients. Furthermore, retina-infiltrating T cells cross-react with human and bacterial HSPs; mice raised in the absence of commensal microflora do not develop glaucomatous T-cell responses or the associated neurodegeneration. These results provide compelling evidence that glaucomatous neurodegeneration is mediated in part by T cells that are pre-sensitized by exposure to commensal microflora.
A deep learning (DL) approach for improving detection accuracy and efficiency is conducted in this paper based on a mass-position sensing scheme. In the scheme, masses and positions of multiple ...spheres can be determined using a length-adjustable cantilever with lower modes. Four DL networks, including two simple MLP (multi-layer perceptron), an inverted triangle MLP and a residual network, are constructed to process the data sets obtained by experimentally verified physics-based model. Comparing to iteration with the non-negative linear least squares, the detection accuracy is increased by 80%, and the calculation efficiency is improved by more than 4000 times. The conducted DL approach does not rely on the modal shape functions of the cantilever which is essential for the iteration method. The size of the data set has almost no impact on the predicted accuracy while more input dimensions can make significant improvement. If the principle of a physical sensor can be verified by simulation and experiment simultaneously, a data set can be established with simulation and then the DL neural network can be trained to learn the relationship between input and output of the sensors. This is especially useful when it is difficult to reverse the input from the output of the sensor by traditional mathematical means. So our approach that training DL networks with the data set obtained by experimentally verified physics-based model is expected to be applicable to physical sensors besides resonant one.
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•Mass sensitivity is double-amplified via differential internal resonance.•Effect of driving amplitude fluctuation is also greatly suppressed.•Driving threshold and sensing range are ...adjustable by changing damping.
This paper, the first of two companion papers, mainly reports a double amplification scheme for mass sensitivity, via a differential phenomenon in various non-Duffing internal resonance systems with even power nonlinearities and coupling. Both frequency sum and amplitude difference of the two symmetrical peaks, in response amplitude of the basic mode, are capable of differentially amplifying the sensitivity as well as greatly suppressing the effect of noise caused by driving amplitude fluctuation. Combining frequency up-conversion to further amplify the sensitivity, double amplified mass sensitivity is thus achieved via frequency shift. Magnetically coupled orthogonal beams with a frequency ratio of two to one, is adopted as an example for both theoretical and experimental demonstration. Experimental results show effect of driving voltage fluctuating in the range of 200 mV to 600 mV is reduced by 360%, as well as the sensitivity for mass perturbation in the range of 0 g to 10 g is 332% amplified. Lower driving threshold and wider sensing range are further obtained through adjusting modal damping. Compared to those based on synchronization or internal resonance under the same frequency ratios, the proposed amplification scheme, not only enhances the mass sensitivity up to about 166%, but also suppresses the effect of driving amplitude fluctuation down to about 27.8%, indicating a potential possibility to break through the sensing limit.
This article clarifies a high-sensitivity mass sensing mechanism, intrinsically correlated with energy relocalization. A sensing theory is derived to predict the amplitude-frequency curve with ...respect to the effect of mass perturbation, where high linearity is observed for both amplitude changes and frequency shifts. A localization factor is defined to characterize the degree of the energy localization, and its physical rationality is demonstrated with a coupled three-beam array as an example. A higher detection sensitivity via energy relocalization, increased by about 123.8% based on the amplitude change and by 250% based on the localization factor, is experimentally obtained with a high vibration amplitude compared to a low one. A mass sensing-warning scheme is further proposed for low-concentration monitoring and high-concentration warning, applicable to the detection and warning of a gas leak, dust pollution, harmful chemicals, and so on.
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•A new mass multi-warning scheme with physical realization is proposed.•Both range of 1st warning and threshold of 2nd warning are adjustable.•The scheme satisfies complex warning and ...sensing requirements for applications.
A new mass multi-warning scheme via integrating duffing nonlinearity with 1:3 internal resonance is proposed in this paper, which can achieve the sensing, the first time warning and the second time warning with the increment of mass perturbation. A nonlinear low frequency mode and another linear high frequency mode with a frequency ratio of 1:3 are coupled via cubic nonlinearities. A theoretical expression is established and derived by multi-scale method to predict the amplitude-frequency curve with respect to the effect of mass perturbation. On one hand, both the range of the first time warning and the threshold of the second time warning can be adjusted for different applications through changing the eigen-state frequency value of the high frequency mode. On the other hand, the linearity of mass sensing can be greatly improved by reversing the sign of the coupling term of the high frequency mode to the low frequency mode. A П-shaped coupled beam structure, consisting of a П-shaped beam and a rectangular beam that coupled by two overhangs, is further proposed for preliminarily physical realization. Compared to conventional bifurcation-based single warning scheme, the multi-warning scheme proposed in this paper is more capable of satisfying complex warning and sensing requirements in various applications, such as both the detection and the multi-warning of gas leak, dust pollution, harmful chemicals and so on.
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