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We report the transverse phase space diagnostics for electron beams generated through ionization injection in a laser-plasma accelerator. Single-shot measurements of both ultimate emittance and Twiss parameters are achieved by means of permanent magnetic quadrupole. Beams with emittance of μm rad level are obtained in a typical ionization injection scheme, and the dependence on nitrogen concentration and charge density is studied experimentally and confirmed by simulations. A key feature of the transverse phase space, matched beams with Twiss parameter αT ≃ 0, is identified according to the measurement. Numerical simulations that are in qualitative agreement with the experimental results reveal that a sufficient phase mixing induced by an overlong injection length leads to the matched phase space distribution. [ABSTRACT FROM AUTHOR]

Low emittance (sub-100 nm rad) measurement of electron beams in plasma accelerators has been a challenging issue for a while. Among various measurement schemes, measurements based on single-shot quad-scan using permanent magnetic quadrupoles (PMQs) has been recently reported with emittance as low as ∼200 nm Weingartner (2012 Phys. Rev. Spec. Top. Accel. Beams15 111302). However, the accuracy and reliability of this method have not been systematically analyzed. Such analysis is critical for evaluating the potential of sub-100 nm rad emittance measurement using any scheme. In this paper, we analyze the effects of various nonideal physical factors on the accuracy and reliability using the PMQ method. These factors include aberration induced by a high order field, PMQ misalignment and angular fluctuation of incoming beams. Our conclusions are as follows: (i) the aberrations caused by high order fields of PMQs are relatively weak for low emittance measurement as long as the PMQs are properly constructed. A series of PMQs were manufactured and measured at Tsinghua University, and using numerical simulations their high order field effects were found to be negligible . (ii) The largest measurement error of emittance is caused by the angular misalignment between PMQs. For low emittance measurement of ∼100 MeV beams, an angular alignment accuracy of 0.1° is necessary. This requirement can be eased for beams with higher energies. (iii) The transverse position misalignment of PMQs and angular fluctuation of incoming beams only cause a translational and rotational shift of measured signals, respectively, therefore, there is no effect on the measured value of emittance. (iv) The spatial resolution and efficiency of the detection system need to be properly designed to guarantee the accuracy of sub-100 nm rad emittance measurement. [ABSTRACT FROM AUTHOR]

Piezoelectric materials possess excellent electromechanical coupling characteristics, which are functional and suitable in structural vibration control. This study investigates the active control of free and forced vibration for piezoelectric-integrated functionally graded carbon nanotube reinforced composite (FG-CNTRC) plate using the finite element method (FEM). Based on the first-order shear deformation theory (FSDT), the governing equations of the motion of a piezoelectric-integrated FG-CNTRC plate are derived by Hamilton’s principle. The convergence and accuracy of the numerical method is verified through the results of natural frequencies. The influences of CNT volume fraction, CNT distribution type, piezoelectric layer thickness-to-plate thickness ratio, and boundary condition on the natural frequencies are investigated. A constant gain velocity feedback algorithm is used to achieve the dynamic response control of the piezoelectric-integrated FG-CNTRC plate. In addition, the effects of dynamic load, feedback control gain, and boundary condition on the dynamic response of the plate are studied. Numerical results indicate that active control is promising for practical applications in civil and mechanical engineering.

We demonstrated a novel and widely accessible method for determining the electron effective mass and scattering time of ZnO films with different carrier concentrations by combining terahertz time-domain spectroscopy with Hall measurement. The terahertz time domain spectroscopy (THz-TDS) transmission spectra (0.1-2THz) were well described by Drude model. It is found that electron effective mass varied from 0.23m0 to 0.26m0 as the electron concentration changes from 5.9 x 1017 cm-3 to 4.0 x 1019 cm-3. The carrier concentration dependent characteristic is ascribed to the non-parabolicity of conduction band. Free carrier localization mechanism explained the discrepancy in mobilities obtained from THz-TDS and Hall measurements. [ABSTRACT FROM AUTHOR]

The layered MoS2 films have been prepared by the chemical vapor deposition (CVD) method, which shows numerous MoS2 convex flakes (i.e., MoS2 nanosheets) on SiO2/Si substrates. The convex flake islands form a uniform layered film and the single flake corresponds to one small piece of monolayer MoS2 film; they show a strong photoluminescence (PL) radiation as a whole. The thickness of the layered MoS2 films increases with the increases of growth time, the effect of diverse growth time on the properties of layered MoS2 films has been discussed, and the PL enhancement effect is due to the PL intensity accumulation from each of the convex flakes. The strong PL radiation has been found by annealing the samples and the reason has been analyzed. The layered MoS2 films could provide more photon energy than both the monolayer MoS2 film and the bulk MoS2. This work provides a fundamental study about the device fabrication based on layered MoS2 films. The optoelectronic devices based on this study will be more energy efficient.

Novel three-dimensional (3D) continuously graded phononic crystals (CGPCs) have been designed, and fabricated by 3D printing. Each of the CGPCs is an entity instead of a combination of several other samples, and the porosity distribution of the CGPC along the incident direction is nearly linear. The sound absorption characteristics of CGPCs were experimentally investigated and compared with those of uniform phononic crystals (UPCs) and discretely stepped phononic crystals (DSPCs). Experimental results show that CGPCs demonstrate excellent sound absorption performance because of their continuously graded structures. CGPCs have higher sound absorption coefficients in the large frequency range and more sound absorption coefficient peaks in a specific frequency range than UPCs and DSPCs. In particular, the sound absorption coefficients of the CGPC with a porosity of 0.6 and thickness of 30 mm are higher than 0.56 when the frequency is 1350–6300 Hz and are all higher than 0.2 in the studied frequency range (1000–6300 Hz). CGPCs are expected to have potential application in noise control, especially in the broad frequency and low-frequency ranges.

A new heavy-ion linac within a continuous-wave (CW) 4-rod radio-frequency quadrupole (RFQ) was designed and constructed as the injector for the separated-sector cyclotron (SSC) at the Heavy Ion Research Facility at Lanzhou (HIRFL). In this paper, we present the development of and the beam commissioning results for the 53.667 MHz CW RFQ. In the beam dynamics design, the transverse phase advance at zero current, σ_{0⊥}, is maintained at a relatively high level compared with the longitudinal phase advance (σ_{0∥}) to avoid parametric resonance. A quasi-equipartitioning design strategy was applied to control the emittance growth and beam loss. The installation error of the electrodes was checked using a FARO 3D measurement arm during the manufacturing procedure. This method represents a new approach to measuring the position shifts of electrodes in a laboratory environment and provides information regarding the manufacturing quality. The experimental results of rf measurements exhibited general agreement with the simulation results obtained using CST code. During on-line beam testing of the RFQ, two kinds of ion beams (^{40}Ar^{8+} and ^{16}O^{5+}) were transported and accelerated to 142.8 keV/u, respectively. These results demonstrate that the SSC-Linac has made a significant progress. And the design scheme and technology experiences developed in this work can be applied to other future CW RFQs.

Microbial communities in coastal seas experience strong environmental disturbances, yet their response patterns, especially regarding differently abundant subcommunities, remain poorly understood. Here, through 16S rRNA gene amplicon sequencing, we investigated the diversity, time-decay pattern, and assembly process of abundant, conditionally rare taxa (CRT) and rare microbial subcommunities in temperate coastal waters over 60 consecutive weeks. The abundant (50.9%) and CRT (46.1%) communities each comprised approximately half of the planktonic community, while the CRT and rare communities contributed to the extremely high species diversity. Distinct temporal heterogeneity was observed among the three fractions and was associated with taxonomic level. The abundant subcommunity exhibited time-decay patterns at all taxonomic levels, while for CRT, the pattern was found only at finer levels. In contrast, variations of the rare community loosely followed a temporal rhythm and were largely confined within a specific taxonomic range, likely raised from turnovers among closely related taxa. Determinism dominated the community assembly of the abundant fraction, while the rare one was more controlled by stochasticity that may be related to pulse terrigenous inputs and anthropogenic disturbances. The rare subcommunity with narrow niche widths likely represented a stable repository to offer episodic specialists, while the abundant taxa that exhibited broader niche widths were considered the generalists in fluctuating environments. Our study revealed the distinct strategies that abundant and rare communities adopt to maintain community stability in temporal dynamics of prokaryotic plankton in the coastal seawater., Importance: The relative importance of rare and abundant taxa in microbial temporal patterns remains debated. Here, we identified taxonomically associated distinct diversity modes of abundant and rare subcommunities from a year-round time-series study in dynamic coastal seawater. We highlighted the significance of the rare subcommunity in maintaining community stability by serving as a repository to offer specialists driven by stochastic processes over time. The abundant subcommunity, by contrast, contributed mainly to temporal rhythmic variations. This study expands the current understanding of the temporal dynamics and stability of coastal microbial communities by revealing distinct variation patterns of subcommunities with different abundances.