Aerosol‐planetary boundary layer (PBL) interactions have been found to enhance air pollution in megacities in China. We show that black carbon (BC) aerosols play the key role in modifying the PBL ...meteorology and hence enhancing the haze pollution. With model simulations and data analysis from various field observations in December 2013, we demonstrate that BC induces heating in the PBL, particularly in the upper PBL, and the resulting decreased surface heat flux substantially depresses the development of PBL and consequently enhances the occurrences of extreme haze pollution episodes. We define this process as the “dome effect” of BC and suggest an urgent need for reducing BC emissions as an efficient way to mitigate the extreme haze pollution in megacities of China.
Key Points
BC plays an important role in enhancing surface haze pollution in megacities in China
Upper PBL heating and surface cooling by BC are two comparable processes in the PBL feedback
Reducing BC emission cobenefits the mitigations of haze pollution and global warming
Bifurcations and quasi-periodic motions of high-dimensional nonlinear models of a translating beam with a stationary load subsystem under harmonic boundary excitation, where there are combined ...parametric and forcing excitations, are investigated. It is demonstrated that by adjusting the frequency of the boundary excitation beyond bifurcation points, the nonlinear system exhibits quasi-periodic motion rather than the periodic response reported in an earlier publication. Particular attention is paid to the nonlinear dynamics of models with five and six included trial functions, where quantitative and qualitative results of frequency responses and quasi-periodic motions are significantly different from each other. The nonlinear governing equations of motion of the translating beam are established by using the Newton's second law. The Galerkin method is used to truncate the governing partial differential equation into a set of nonlinear ordinary differential equations. The incremental harmonic balance (IHB) method is used to solve for periodic responses of the high-dimensional models of the translating beam. The Floquet theory along with the precise Hsu's method is used to investigate stability of the periodic responses. The IHB method with two time scales developed earlier is extended to analyze quasi-periodic motion of the nonlinear system with combined parametric and forcing excitations whose spectrum contains uniformly spaced sideband frequencies. Quasi-periodic motion obtained from the IHB method with two time scales is in excellent agreement with that from numerical integration using the fourth-order Runge-Kutta method.
•A new type of vibration shapes called a free response shape (FRS) is introduced.•FRSs can be obtained using a continuously scanning laser Doppler vibrometer system.•An analytical expression of FRSs ...of a damped beam structure is derived.•A damage identification methodology using FRSs is proposed and investigated.•The methodology has been numerically and experimentally validated.
Spatially dense operating deflection shapes and mode shapes can be rapidly obtained by use of a continuously scanning laser Doppler vibrometer (CSLDV) system, which sweeps its laser spot over a vibrating structure surface. This paper introduces a new type of vibration shapes called a free response shape (FRS) that can be obtained by use of a CSLDV system, and a new damage identification methodology using FRSs is developed for beam structures. An analytical expression of FRSs of a damped beam structure is derived, and FRSs from the analytical expression compare well with those from a finite element model. In the damage identification methodology, a free-response damage index (FRDI) is proposed, and damage regions can be identified near neighborhoods with consistently high values of FRDIs associated with different modes; an auxiliary FRDI is defined to assist identification of the neighborhoods. A FRDI associated with a mode consists of differences between curvatures of FRSs associated with the mode in a number of half-scan periods of a CSLDV system and those from polynomials that fit the FRSs with properly determined orders. A convergence index is proposed to determine the proper order of a polynomial fit. One advantage of the methodology is that the FRDI does not require any baseline information of an undamaged beam structure, if it is geometrically smooth and made of materials that have no stiffness and mass discontinuities. Another advantage is that FRDIs associated with multiple modes can be obtained using free response of a beam structure measured by a CSLDV system in one scan. The number of half-scan periods for calculation of the FRDI associated with a mode can be determined by use of the short-time Fourier transform. The proposed methodology was numerically and experimentally applied to identify damage in beam structures; effects of the scan frequency of a CSLDV system on qualities of obtained FRSs were experimentally investigated.
Metal and its oxide nanoparticles show ideal pharmacological activity, especially in anti-tumor therapy. Our previous study demonstrated that cuprous oxide nanoparticles (CONPs) selectively induce ...apoptosis of tumor cells in vitro. To explore the anti-tumor properties of CONPs in vivo, we used the particles to treat mouse subcutaneous melanoma and metastatic lung tumors, based on B16-F10 mouse melanoma cells, by intratumoral and systemic injections, respectively. The results showed that CONPs significantly reduced the growth of melanoma, inhibited the metastasis of B16-F10 cells and increased the survival rate of tumor-bearing mice. Importantly, the results also indicated that CONPs were rapidly cleared from the organs and that these particles exhibited little systemic toxicity. Furthermore, we observed that CONPs targeted the mitochondria, which resulted in the release of cytochrome C from the mitochondria and the activation of caspase-3 and caspase-9 after the CONPs entered the cells. In conclusion, CONPs can induce the apoptosis of cancer cells through a mitochondrion-mediated apoptosis pathway, which raises the possibility that CONPs could be used to cure melanoma and other cancers.
•Continuous Scanning LDV techniques, A Raison d’être.•Continuous Scanning LDV techniques, Applications to Vibration Measurements.•The past and present of continuous scanning techniques.•Guidance for ...new researchers.
Continuous Scanning Laser Doppler Vibrometry (CSLDV) methods first appeared in the literature in the early 1990s and over the past three decades they have undergone an evolution in terms of procedures and applications which constitute a new state-of-the-art now described in this review paper. The advances in vibration measurement performed by Scanning Laser Doppler Vibrometers augmented the capability of measuring vibration data from a grid of a few hundred measurement points to a single scan which traverses and measures at many thousands of points on the same structure. The deflection shapes of vibration modes can be created by assembling two pieces of information from a scanning measurement - temporal and spatial - and the more measurement ‘points’, the better the spatial density and resolution of the deflection shape(s). The introduction of Continuous Scanning techniques challenged the traditional principle that the number of measurement points defines the spatial definition of the deflection shape. Thereafter, high definition deflection shapes could be achieved by measuring a single time series from a continuously sweeping trajectory covering the same surface area that would traditionally be covered by a set of fixed-point measurements, each of which spans a range of frequencies. The CSLDV approach compresses both the temporal oscillation and the spatial distribution of the deflection shape into one LDV output-modulated signal, whereby the harmonic oscillation and the spatial distribution across a swept area were now defined by a central response harmonic and its sidebands. This change of perspective in vibration measurements from the conventional stepped-scan method to the continuous-scan approach allowed several researchers to exploit and expand the potential of the scanning vibrometer further than its initial design specifications. This paper starts with the raison d’être, with a brief historical account of how vibration measurements have developed over the past decades, and then moves to the theoretical background and applications of the CSLDV approach. Finally, the paper presents a philosophical and technical account of the research work carried out by several colleagues over the past thirty years and aims to provide a chronological order to the various advancements that CSLDV techniques offer in engineering structural dynamics.
Abstract
According to the principle of Euler similarity between laboratory and astrophysical plasmas, laboratory plasmas driven by high-power lasers have been used to simulate some aspects of ...astrophysical phenomena. And in doing so, they aid our understanding of shock heating, interaction structures, and the consequential evolution for astrophysical outflows within a short timescale (∼ns). In this work, we experimentally investigated the mechanism of X-ray emission originating from a hot outflow (plasma) with a velocity of around 330 km s
−1
, impinging on a cold medium. A hybrid model was set up to understand the high-resolution X-ray spectra taken at the interaction region and to deduce that charge exchange takes place in such a laboratory miniature of astrophysical outflow interacting with dense molecular clouds, as in the cases of HH 248 and Cap in M82, for example. Effects from targets with multiple electrons are also explored. A brief analysis has been performed for our laboratory analog and astrophysical objects by a dimensionless ratio of the length scale between X-ray-emitting and charge-exchange regions.
A coordinate-transformation method can be used to design invisibility cloaks for many types of waves, including acoustic waves. The traditional method for designing a cloak depends on a ...transformation from a virtual space to a physical space. Previous acoustic cloaks that are mainly designed with linear-transformation-based acoustics have drawbacks that acoustic wave trajectories in the cloaks cannot be controlled and tuned. This work uses a nonlinear mapping from a ray trajectory perspective to construct acoustic cloaks with tunable non-singular material properties. Use of a ray trajectory equation is a straightforward and alternate way to study propagation characteristics of different types of waves, which allows more flexibility in controlling the waves. A broadband cylindrical cloak for acoustic waves in an inviscid fluid is realized with layered non-singular, homogeneous, and isotropic materials based on a nonlinear transformation. Some advantages and improvements of the invisibility nonlinear-transformation cloak over a traditional linear-transformation cloak are analyzed. The invisibility capability of the nonlinear-transformation cloak can be tuned by adjusting a design parameter that is shown to have influence on the acoustic wave energy flowing into the region inside the cloak. Numerical examples show that the nonlinear-transformation cloak is more effective for making a domain undetectable by acoustic waves in an inviscid fluid and shielding acoustic waves from outside the cloak than the linear-transformation cloak in a broad frequency range. The methodology developed here can be used to design nonlinear-transformation cloaks for other types of waves.
To develop a green primary explosive, we prepare an Al@KIO
4
nano-thermite using spray co-precipitation and then mix it with pentaerythritol tetranitrate (PETN) to form a PETN/Al@KIO
4
composite as ...a primary explosive. The thermite structure is characterized using X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy, which indicates that the thermite is about 200 nm and well distributed. The combustion performance is investigated using high-speed photography and confined combustion experiments. The results show that the detonation time of PETN/Al@KIO
4
composites is 60
s earlier than that of pure PETN, indicating that the thermite accelerates the process of the deflagration-to-detonation transition of PETN. The detonation performance of the composites is investigated, and it is verified that PETN/Al@KIO
4
can initiate RDX successfully and be used as a primary explosive. Moreover, the safety performance and long-term storage performance of the composite are evaluated, which shows that the PETN/Al@KIO
4
composite performance is steady and the initiation effect does not change after 20 years of storage.
An efficient Galerkin averaging-incremental harmonic balance (EGA-IHB) method is developed for steady-state nonlinear dynamic analysis of index-3 differential algebraic equations (DAEs) for general ...rigid multibody systems. The multibody dynamic modeling theory has made significant advances in generality and simplicity, and multibody systems are usually governed by DAEs. The bridge between the multibody dynamic modeling theory and nonlinear dynamic analysis theory is built for the first time in this work, and the EGA-IHB method can be used as a universal solver for obtaining steady-state periodic responses of DAEs for general multibody systems. Since the fast Fourier transform and EGA are used, the EGA-IHB method has excellent robustness. Since the Floquet theory cannot be directly used for stability analysis of periodic responses of DAEs, a new stability analysis procedure is developed, where perturbed, linearized DAEs are reduced to ordinary differential equations with use of independent generalized coordinates. A modified arc-length continuation method with a scaling strategy is proposed for calculating response curves and conducting parameter studies. Several examples are used to show the performance and capability of the current method. Periodic solutions of DAEs from the EGA-IHB method show excellent agreement with those from numerical integration methods. Amplitude–frequency and amplitude–parameter response curves are generated, and stability and period-doubling bifurcations are analyzed. The current method shows excellent computational efficiency and robustness in solving high-dimensional DAEs.
One of the most promising approaches to reach a high gain in inertial confinement fusion is the fast ignition scheme. In this scheme, a relativistic electron beam is generated; this passes through ...the imploded plasma and deposits parts of its energy in the core. However, the large angular spread of the relativistic electron beam and the poorly controlled compression of the target affect realization of the fast ignition technique. Here, we demonstrate that indirectly driven (that is, driven by X-rays generated inside a gold hohlraum) implosions with a ‘high-foot’ and a short-coast time of less than 200 ps allow us to tightly compress the shell. Furthermore, we show the ability to optimize the symmetry of the imploding shell by changing the hohlraum length, successfully tuning a suitable tube-shaped shell to compensate for the large angular spread of the relativistic electron beam and to enhance the electron-to-core coupling efficiency via resistive magnetic fields. Benefiting from those experimental techniques, a significant enhancement in neutron yield was achieved in our indirectly driven fast ignition experiments. These results pave the way towards high-coupling fast ignition experiments with indirectly driven targets similar to those at the National Ignition Facility.Experiments realizing the indirect-drive fast ignition scheme for inertial confinement fusion are reported. Enabled by a tightly compressed target, an increase of neutron yield is observed.
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