Expansion Mode Research Articles

Buckling behavior of circular steel tubes infilled with C170/185 ultra-high-strength concrete under fire

Modern building codes do not cover the use of ultra-high strength concrete (UHSC) in design of composite columns. This paper investigates the structural fire performance of UHSC filled steel tubular (CFST) columns. Experimental studies were carried out on 9 CFST columns with C170/185 concrete under standard ISO fire. The columns were subjected to concentrated or eccentric compressions and then heated to failure to record the fire resistance time. The simple calculation model in EC 4 was examined by predicting the fire resistance time and comparing them with the test results; the axial force–moment (N-M) interaction strength model for room temperature design was extended to predict the fire resistance. The test results showed that the CFST columns with UHSC exhibited similar fire performance to those with normal/high strength concrete with respect to thermal expansion, axial contraction and failure modes. Adding 0.1% polypropylene fibers in UHSC was found to be effective in preventing explosive spalling especially when it was heated rapidly under the standard fire. The N-M interaction strength model gave better predictions than the EC 4 model as it gave less scattered results when compared to the test data. EC 4 buckling curve “c” was found to be conservative in predicting the fire resistance time of CFST columns with UHSC subjected to pure compression. Parametric study showed that the fire resistance of CFST columns with UHSC reduced faster than those with normal strength concrete (NSC) and high strength concrete (HSC) in early stage of heating but slower at the later heating stage. Within the practical range of load level (i.e.,≤0.7), the CFST columns with UHSC employed by this study had better fire resistance than those columns infilled with NSC and HSC.

A multiscale analysis of the effect of urban expansion on PM2.5 concentrations in China: Evidence from multisource remote sensing and statistical data

The timely and effective evaluation of the effect of urban expansion on PM2.5 concentrations is highly important for an understanding of urban-environment sustainability in China. However, studies examining the effect of urban expansion on PM2.5 concentrations at multiple administrative scales from different perspectives are still lacking. In this study, multisource remote sensing data were used to define urban spatial expansion and urban socioeconomic expansion, respectively. The effect of urban expansion on PM2.5 concentrations was then evaluated and compared at the regional, urban agglomeration, and metropolitan scales. The results showed that China's economic urban expansion lagged far behind urban spatial expansion from 2000 to 2015. There is a bidirectional long-term Granger causal relationship between urban expansion and PM2.5 concentrations across different scales. A short-term Granger causality test proved that urban expansion is still at the stage of aggravating PM2.5 concentrations. Variance decomposition analysis results indicated that the contribution of urban socioeconomic expansion in explaining PM2.5 concentrations was higher than urban spatial expansion with the increase in scales. The aggregation effect has become an important means for urban socioeconomic expansion to affect PM2.5 concentrations. In addition, PM2.5 concentrations can be reduced by the technical progress effect of urban spatial expansion across different scales. The Chinese government should consider the impact of different urban expansion modes on PM2.5 concentrations. Moreover, the technical progress effect will play an important role in decoupling urban spatial expansion and PM2.5 concentrations in China.

A review of exact solutions for conversion of a surface wave into a propagating wave

In this paper, we summarize our recent theoretical and numerical studies of conversion of a surface wave to a propagating wave (and vice versa) with maximized conversion efficiency. We show that the exact solution for the homogeneous plane wave to surface wave conversion in a homogeneous medium by a point-wise lossless metasurface is restricted by Maxwell’s equations. Such performance is possible only with approximations and implies some limitations, including impossibility to fully avoid unwanted scatterings. Nevertheless, an inhomogeneous plane wave can be converted into a surface wave perfectly, and it is described by an exact solution formed by a superposition of only two modes of the Floquet expansion. The results of the studies are expected to be of fundamental importance for leaky-wave antennas efficiency improvement. Besides, they can lead to novel applications in various research areas.

High frequency thickness expansion mode bulk acoustic wave resonator using LN single crystal thin plate

In this report, a thickness expansion mode film bulk acoustic resonator (FBAR) was fabricated using 4 μm thick 36°Y-LiNbO3(LN) single crystal thin plate. The LN thin plate was made by polishing after bonded to a Si bare wafer. The LN FBAR showed a bandwidth of 10.3% and an impedance ratio of 45 dB at 800 MHz. The spurious response due to a thickness shear (TS) mode was much smaller than the main mode, because the optimal cut angle was chosen. The quality factor of anti-resonance is poor probably due to acoustic loss caused by a misalignment of the upper and lower electrodes, the series connection of two resonators etc. By minimizing the acoustic loss, the impedance ratio can be improved up to 60 dB.

Deterministic and Random Response Evaluation of a Straight Beam with Nonlinear Boundary Conditions

Deterministic and random responses of one-dimensional continuous structures with nonlinear boundary conditions are evaluated in this article. Dynamic behaviors (i.e., the time-domain response for the deterministic case and mean-square response for the stochastic case) of a straight beam with a cubic nonlinear elastic boundary is investigated numerically. The nonlinear vibration problem is discretized by a new global spatial discretization method, and its responses are compared with those from the finite element method and assumed mode method. The effects of selected various types of linear homogeneous boundary conditions and the number of expansion modes on the accuracy of the responses under harmonic excitation are discussed. Detailed discussions on the influence of nonlinear boundary conditions on dynamic behaviors uncover a counter-intuitive phenomenon: with the increase of the nonlinear spring stiffness, the stationary mean-square displacement of the mid-point descends first and then ascends slightly. Numerical results show that the present procedure possesses high precision for evaluating harmonic responses for both low-frequency and high-frequency excitations. Furthermore, it can be directly generalized to two-dimensional continuous systems and various types of nonlinear boundary conditions.

Constructing reduced model for complex physical systems via interpolation and neural networks* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11871400 and 11971386) and the Natural Science Foundation of Shaanxi Province, China (Grant No. 2017JM1019).

The work studies model reduction method for nonlinear systems based on proper orthogonal decomposition (POD) and discrete empirical interpolation method (DEIM). Instead of using the classical DEIM to directly approximate the nonlinear term of a system, our approach extracts the main part of the nonlinear term with a linear approximation before approximating the residual with the DEIM. We construct the linear term by Taylor series expansion and dynamic mode decomposition (DMD), respectively, so as to obtain a more accurate reconstruction of the nonlinear term. In addition, a novel error prediction model is devised for the POD-DEIM reduced systems by employing neural networks with the aid of error data. The error model is cheaply computable and can be adopted as a remedy model to enhance the reduction accuracy. Finally, numerical experiments are performed on two nonlinear problems to show the performance of the proposed method.

Fault Diagnosis of Distribution Terminal Units’ Measurement System Based on Generative Adversarial Network Combined with Convolutional Neural Network

As the condition monitoring and control device in the distribution automation system, the abnormal or fault state of distribution terminal units’ measurement system will negatively affect the quality of measured electrical quantities, and therefore, the fast and accurate discrimination of the abnormal state’s data will improve the reliability of distribution automation system. This paper proposes a method, which is based on generative adversarial network (GAN) combined with convolutional neural network (CNN), to discriminate the specific fault category of distribution terminals’ measuring electrical data. Firstly, four fault state characteristic time-frequency domain graph models of terminals’ AC voltage sampling data are established, which based on Fourier transform (STFT). Then, take advantage of GAN’s reconstruction of input graph data, to generate additional time-frequency sample graphs expanding the sample size of training set, which will be used to train a CNN to diagnosis and classify the fault state of terminals from measuring data. Finally, three training sets with different capacity expansion modes are set up to compare and verify that the method of GAN combined with CNN proposed in this paper improves the discrimination accuracy on the fault data, and the validation of diagnosis terminals’ measurement system.

Performance Assessment of a Hybrid Vapor Compression and Evaporative Cooling Fresh-Air-Handling Unit Operating in Hot Climates

Evaporative cooling can be integrated into fresh-air-handling units, to reduce cooling demand. This study considers a hybrid fresh-air-handling unit which incorporates a vapor-compression cooling cycle and indirect evaporative cooling to condition an ambient primary airstream to a desired supply air state. The cooling effects of using various modes (vapor compression only; direct expansion with mist; direct expansion with water shower; and direct expansion with mist and water shower) are compared when the fresh-air-handling unit operates in harsh (hot and humid) climatic conditions experienced in Qatar. Experimental analysis is based on actual ambient conditions measured from August 2018 to July 2019. It is found that the best-performing wet mode of operation saves more than 60% of the energy required by a conventional direct expansion cooling system operating under the same ambient conditions. In hot, dry conditions, the coefficient of performance of the fresh-air-handling unit when using the indirect evaporative mode of operation is double the coefficient of performance when operating with direct expansion mode only.

Deformation and Compressive Strength of Steel Fiber Reinforced MgO Concrete.

To reduce the cracking caused by shrinkage and avoid the brittle behavior of concrete, MgO expansion agent and steel fibers were used in this paper. Firstly, the effect of MgO and steel fibers on the compressive strength of concrete was compared. The results showed that the compressive strength of steel fibers reinforced concrete (SC) and steel fiber reinforced MgO concrete (SMC) was significantly improved. Compared with ordinary concrete (OC), SMC’s 28 days compressive strength increased by 19.8%. Secondly, the influence of MgO and steel fibers with different contents on the self-volumetric deformation of concrete was compared through the experiment. The results showed that as a result of the hydration expansion of MgO, MC and SMC both showed obvious expansion, and their 190 days expansion was 335 and 288 , respectively. Lastly, through a scanning electron microscope (SEM) test, it was found that the constraint effect of steel fibers changed the expansion mode of MgO from outward expansion to inward extrusion, thus improving the interfacial bond strength of concrete.

Muriel Rukeyser and the Security of the Imagination: Poetry and Propaganda in 1940s America

This article begins by situating Muriel Rukeyser's call for ‘the security of the imagination’ within the highly charged historical contexts of the 1940s, a decade bracketed not only by war but by America's growing obsession with security – from President Roosevelt's ‘Four Freedoms’ speech of 1941 to the rise of McCarthyism at the end of the forties. It then examines how Rukeyser's work as a propagandist, a poet and an essayist in the 1940s was deeply shaped by her involvement with the American security services. It further shows how Rukeyser sought to combine words and images in both her war posters and her poems in an attempt to forge an expansive, inclusive and antifascist mode of representation. In a significant departure from other studies of this period, this article brings original archival sources into contact with Rukeyser's poetry, and reads these literary and archival documents through the theoretical lens of security studies. In the face of an increasingly paranoid, repressive political climate, Rukeyser's wartime propaganda work and poetry offers ways of thinking past dominant assumptions structuring the discourse of security.

Plasma expansion accompanying superthermal electrons in over-picosecond relativistic laser-foil interactions

We study the plasma expansion dynamics in over-picosecond relativistic laser-foil interactions using one-dimensional particle-in-cell (PIC) simulations. A new expansion mode ‘isofield expansion’ appears after the well-known isothermal expansion due to the continuous energy input from the laser light to the plasma. The blowout of the heated plasma at the front surface triggers the transition from the isothermal mode to the new mode. In the new expansion mode, electrons and ions expand quasi-neutrally with a constant sheath electric field, and a large scale low density plasma is formed where superthermal electrons are produced efficiently. A two-dimensional PIC simulation confirms the appearance of the isofield expansion mode after the plasma blowout for a large focal spot laser.

Consequences of Holographic Dark Energy Cosmological Model in Gravity

We have investigated the dynamics of spatially homogeneous Bianchi type-I (LRS) space-time filled with two minimally interacting fields-matter and holographic dark energy components with volumetric power laws expansion towards the gravitational field equations for the linear form of gravity. Solving the set of field equation we obtained the exact solution andobserved that the mode of expansion of the model is accelerating throughout the evolution due to destructive assessment of deceleration parameter. Also it has found that the Gauss-Bonnet invariantand the function of Gauss-Bonnet invariant both are not occur for , the equation of state parameter admits the different values for different values of n whichare relevantin the standard range provided by recent theoretical and experimental data along with the model has a Big-Bang type of singularity at singular point.

Three-Dimensional Urban Expansion Analysis of Valley-Type Cities: A Case Study of Chengguan District, Lanzhou, China

The development of cities in the vertical dimension is important in valley-type cities where physical growth is limited by terrain. However, little research has focused on three-dimensional urban expansion of valley-type cities. Lanzhou is a typical valley-type city in China and Chengguan District is the core area of Lanzhou City. This research is aimed at understanding the development of valley-type cities through the analysis of the three-dimensional urban expansion of Lanzhou Chengguan District and providing a reference for urban planning. We extracted five periods of architectural contours and height information between 1975 to 2018 with the support of multi-source remote sensing and network data. We used overlay analysis and mathematical statistical methods to analyze urban horizontal expansion and used the building density, floor area ratio, vertical expansion speed, fluctuation degree, and skyline to analyze urban vertical expansion. We found that the mode of horizontal expansion of Chengguan District shifted from adjacency to enclave through mountain area reclamation. The area with the fastest vertical expansion speed first appeared in the horizontal expansion completed area, and then in both the rapid horizontal expansion area and in the horizontal expansion completed area. Before 2007, the speed of horizontal expansion increased and reached its peak while the vertical expansion speed was relatively stable. After that, the former decreased, and the vertical expansion increased rapidly and dominated the urban development. The vertical expansion of the valley-type city gradually dominates urban development. Urban planning should consider the three-dimensional expansion, especially in the vertical dimension.

2D Mechanical Metamaterials with Widely Tunable Unusual Modes of Thermal Expansion.

Most natural materials expand uniformly in all directions upon heating. Artificial, engineered systems offer opportunities to tune thermal expansion properties in interesting ways. Previous reports exploit diverse design principles and fabrication techniques to achieve a negative or ultralow coefficient of thermal expansion, but very few demonstrate tunability over different behaviors. This work presents a collection of 2D material structures that exploit bimaterial serpentine lattices with micrometer feature sizes as the basis of a mechanical metamaterials system capable of supporting positive/negative, isotropic/anisotropic, and homogeneous/heterogeneous thermal expansion properties, with additional features in unusual shearing, bending, and gradient modes of thermal expansion. Control over the thermal expansion tensor achieved in this way provides a continuum-mechanics platform for advanced strain-field engineering, including examples of 2D metamaterials that transform into 3D surfaces upon heating. Integrated electrical and optical sources of thermal actuation provide capabilities for reversible shape reconfiguration with response times of less than 1 s, as the basis of dynamically responsive metamaterials.

Spatiotemporal cytoskeleton organizations determine morphogenesis of multicellular trichomes in tomato.

Plant trichomes originate from epidermal cell, forming protective structure from abiotic and biotic stresses. Different from the unicellular trichome in Arabidopsis, tomato trichomes are multicellular structure and can be classified into seven different types based on cell number, shape and the presence of glandular cells. Despite the importance of tomato trichomes in insect resistance, our understanding of the tomato trichome morphogenesis remains elusive. In this study, we quantitatively analyzed morphological traits of trichomes in tomato and further performed live imaging of cytoskeletons in stably transformed lines with actin and microtubule markers. At different developmental stages, two types of cytoskeletons exhibited distinct patterns in different trichome cells, ranging from transverse, spiral to longitudinal. This gradual transition of actin filament angle from basal to top cells could correlate with the spatial expansion mode in different cells. Further genetic screen for aberrant trichome morphology led to the discovery of a number of independent mutations in SCAR/WAVE and ARP2/3 complex, which resulted in actin bundling and distorted trichomes. Disruption of microtubules caused isotropic expansion while abolished actin filaments entirely inhibited axial extension of trichomes, indicating that microtubules and actin filaments may control distinct aspects of trichome cell expansion. Our results shed light on the roles of cytoskeletons in the formation of multicellular structure of tomato trichomes.

Bandwidth Expansion Mode Under Component Carrier based scheme in LTE Networks

This paper reflects the bandwidth expansion using component carrier scheme in LTE networks by using different OFDM’s i.e. bandwidth allocation algorithm and resource allocation algorithm are observed. Wireless cellular networks are an underlying for mobile phones, personal communication systems etc. There is a dramatic growth of wireless cellular networks in number of mobile phones. As a result, there is a significant increase in base station power consumption and data requirements. In competitive cellular industry, the power consumption in the base station has therefore become a major challenge to the vendors. Through component carrier based scheme the energy efficient LTE networks can be realized and energy efficiency can be improved to some extent through component carrier based scheme.

Wideband Active Region Metasurface Antennas

Modulated metasurface (MTS) antennas with broadside beam rely on the interaction between a radially modulated equivalent impedance and a surface wave (SW) with cylindrical wavefront, launched by a point source. At the frequency where the SW wavelength matches the period of the impedance modulation, the −1 indexed (leaky) mode of the Floquet-mode expansion in cylindrical coordinates provides a broadside beam. The mismatch between the SW wavelength and the period of the modulation imposes a limitation on the product bandwidth–gain. Here, we overcome this limitation by exponentially stretching the radial period of the impedance modulation. Doing so, an annular active region is generated on the antenna aperture, which moves from the antenna center to the circular rim as the frequency decreases. This mechanism enables a broadside beam over an extreme large bandwidth. We, therefore, significantly extend the applicability of these antennas, e.g., to requirements of 30±1.5dB gain over 30% bandwidths. Here, an analytical formulation is proposed to treat the active region migration and edge outgoing by a Fresnel-type transition function. This function predicts in closed form the antenna bandwidth and average gain. A more accurate gain versus frequency response is also introduced by an integral formula that accounts for the frequency-dependent amplitude distribution of the aperture fields. The theory is validated by full-wave simulations and by measurements of a prototype realized by subwavelength elliptical patches. The presented results show that these antennas can provide a performance difficult to reach by any other flat antennas based on printed technology.

Investigation on the Edge Chipping in Ultrasonic Assisted Sawing of Monocrystalline Silicon

Monocrystalline silicon is an important semiconductor material and occupies a large part of the market demand. However, as a hard-brittle material, monocrystalline silicon is extremely prone to happen edge chipping during sawing processing. The edge chipping seriously affects the quality and performance of silicon wafers. In this paper, both conventional and ultrasonicassisted sawing tests were carried out on monocrystalline silicon to study the formation mechanism of edge chipping. The shape and size of edge chipping after sawing process were observed and measured. The experimental results demonstrated that different sawing processes present different material removal modes and edge quality. The mode of crack propagation was continuous cracks in conventional sawing process, while the expansion mode in ultrasonic assisted sawing was blasting microcracks. This results in the cutting force of ultrasonic assisted sawing becomes much smaller than that of conventional sawing process, which can reduce the size of edge chipping and improve the quality of machined surface.

Innovative Design of Intervention Module for Vessel Intervention Surgery Robot Based on TRIZ Theory

Functional model of interventional surgery robot system is obtained based on the analysis of interventional surgery needs. Combining the original design results, functional models are further analyzed. An innovative design method of interventional surgery robot based on TRIZ theory is proposed to simply the mechanism and perfect function. The problem model is defined by using TRIZ method. System tailoring strategy based on functional model and invention principle based on conflict resolution theory are combined for solving the design problem. Then, the new structural scheme is given based on the above analyses. The synthesized structural scheme has been greatly simplified. Finally, the TRIZ theory is used to evaluate the innovative design scheme. It is concluded that the improvement of the new scheme relative to the original scheme follows the evolutionary mode of expansion and simplification of the technical system, and conforms to the evolutionary rule of the technical system.

Effect of crystal orientation on initiation and propagation of crack: Phase field crystal model study

The crystal phase field (PFC) method is used to simulate the propagation of the nano-crack of samples with different crystal orientations under the strain of the uniaxial tensile. The results show that the different crystal orientations have a significant effect on the initiation and propagation of the cracks. For the samples with the orientation angles of 5° and 20°, the notch is directly cracked due to the strain concentration at the dislocation of the crack tip. The cracks mainly show a mode of the brittle expansion, and its edges show smooth planar features. For the samples with the orientation angles of 10° and 15°, the dislocation is firstly emitted at the notch to generate vacancies by dislocation slipping. The vacancies grow and connect to form cracks. This process of the crack propagation belongs to the mode of the ductile crack with the rough edges. The results are consistent with that of the molecular dynamic and experimental results.