Journal articles on the topic 'Elongated beam systems'
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1
Kuriakose, Akhil, Monica Bollani, Paolo Di Trapani, and Ottavia Jedrkiewicz. "Study of Through-Hole Micro-Drilling in Sapphire by Means of Pulsed Bessel Beams." Micromachines 13, no. 4 (April 15, 2022): 624. http://dx.doi.org/10.3390/mi13040624.
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Ultrashort Bessel beams have been used in this work to study the response of a 430-μm-thick monocrystalline sapphire sample to laser–matter interaction when injecting the beam orthogonally through the whole sample thickness. We show that with a 12° Bessel beam cone angle, we are able to internally modify the material and generate tailorable elongated microstructures while preventing the formation of surface cracks, even in the picosecond regime, contrary to what was previously reported in the literature. On the other hand, by means of Bessel beam machining combined with a trepanning technique where very high energy pulses are needed, we were able to generate 100 μm diameter through-holes, eventually with negligible cracks and very low taper angles thanks to an optimization achieved by using a 60-μm-thick layer of Kapton Polyimide removable tape.
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Kim, Wook-Bae, and Sol-Yi Han. "Microinjection Molding of Out-of-Plane Bistable Mechanisms." Micromachines 11, no. 2 (January 30, 2020): 155. http://dx.doi.org/10.3390/mi11020155.
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We present a novel fabrication technique of a miniaturized out-of-plane compliant bistable mechanism (OBM) by microinjection molding (MM) and assembling. OBMs are mostly in-plane monolithic devices containing delicate elastic elements fabricated in metal, plastic, or by a microelectromechanical system (MEMS) process. The proposed technique is based on stacking two out-of-plane V-beam structures obtained by mold fabrication and MM of thermoplastic polyacetal resin (POM) and joining their centers and outer frames to construct a double V-beam structure. A copper alloy mold insert was machined with the sectional dimensions of the V-beam cavities. Next, the insert was re-machined to reduce dimensional errors caused by part shrinkage. The V-beam structure was injection-molded at a high temperature. Gradually elongated short-shots were obtained by increasing pressure, showing the symmetrical melt filling through the V-beam cavities. The as-molded structure was buckled elastically by an external-force load but showed a monostable behavior because of a higher unconstrained buckling mode. The double V-beam device assembled with two single-molded structures shows clear bistability. The experimental force-displacement curve of the molded structure is presented for examination. This work can potentially contribute to the fabrication of architected materials with periodic assembly of the plastic bistable mechanism for diverse functionalities, such as energy absorption and shape morphing.
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Carta, G., M. Brun, and A. B. Movchan. "Dynamic response and localization in strongly damaged waveguides." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, no. 2167 (July 8, 2014): 20140136. http://dx.doi.org/10.1098/rspa.2014.0136.
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In this paper, we investigate the formation of band-gaps and localization phenomena in an elastic strip nearly disintegrated by an array of transverse cracks. We analyse the eigenfrequencies of finite, strongly damaged, elongated solids with reference to the propagation bands of an infinite strip with a periodic damage. Subsequently, we determine analytically the band-gaps of the infinite strip by using a lower-dimensional model, represented by a periodically damaged beam in which the small ligaments between cracks are modelled as ‘elastic junctions’. The effective rotational and translational stiffnesses of the elastic junctions are obtained from an ad hoc asymptotic analysis. We show that, for a finite frequency range, the dispersion curves for the reduced beam model agree with the dispersion data determined numerically for the two-dimensional elastic strip. Exponential localization, boundary layers and standing waves in strongly damaged systems are discussed in detail.
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Fu, Jia, Ian Richardson, and Marcel Hermans. "Microstructure Study of Pulsed Laser Beam Welded Oxide Dispersion-Strengthened (ODS) Eurofer Steel." Micromachines 12, no. 6 (May 28, 2021): 629. http://dx.doi.org/10.3390/mi12060629.
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Oxide dispersion-strengthened (ODS) Eurofer steel was laser welded using a short pulse duration and a designed pattern to minimise local heat accumulation. With a laser power of 2500 W and a duration of more than 3 ms, a full penetration can be obtained in a 1 mm thick plate. Material loss was observed in the fusion zone due to metal vaporisation, which can be fully compensated by the use of filler material. The solidified fusion zone consists of an elongated dual phase microstructure with a bimodal grain size distribution. Nano-oxide particles were found to be dispersed in the steel. Electron backscattered diffraction (EBSD) analysis shows that the microstructure of the heat-treated joint is recovered with substantially unaltered grain size and lower misorientations in different regions. The experimental results indicate that joints with fine grains and dispersed nano-oxide particles can be achieved via pulsed laser beam welding using filler material and post heat treatment.
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Pantillon, Florian, Bianca Adler, Ulrich Corsmeier, Peter Knippertz, Andreas Wieser, and Akio Hansen. "Formation of Wind Gusts in an Extratropical Cyclone in Light of Doppler Lidar Observations and Large-Eddy Simulations." Monthly Weather Review 148, no. 1 (December 19, 2019): 353–75. http://dx.doi.org/10.1175/mwr-d-19-0241.1.
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Abstract Damaging gusts in windstorms are represented by crude subgrid-scale parameterizations in today’s weather and climate models. This limitation motivated the Wind and Storms Experiment (WASTEX) in winter 2016–17 in the Upper Rhine Valley over southwestern Germany. Gusts recorded at an instrumented tower during the passage of extratropical cyclone “Thomas” on 23 February 2017 are investigated based on measurements of radial wind with ≈70-m along-beam spacing from a fast-scanning Doppler lidar and realistic large-eddy simulations with grid spacings down to 78 m using the Icosahedral Nonhydrostatic model. Four wind peaks occur due to the storm onset, the cold front, a precipitation line, and isolated showers. The first peak is related to a sudden drop in dewpoint and results from the downward mixing of a low-level jet and a dry layer within the warm sector characterized by extremely high temperatures for the season. While operational convection-permitting forecasts poorly predict the storm onset overall, a successful ensemble member highlights the role of upstream orography. Lidar observations reveal the presence of long-lasting wind structures that result from a combination of convection- and shear-driven instability. Large-eddy simulations contain structures elongated in the wind direction that are qualitatively similar but too coarse compared to the observed ones. Their size is found to exceed the effective model resolution by one order of magnitude due to their elongation. These results emphasize the need for subkilometer-scale measuring and modeling systems to improve the representation of gusts in windstorms.
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Mitchell, R. L., M. Coleman, P. Davies, L. North, E. C. Pope, C. Pleydell-Pearce, W. Harris, and R. Johnston. "Macro-to-nanoscale investigation of wall-plate joints in the acorn barnacle Semibalanus balanoides : correlative imaging, biological form and function, and bioinspiration." Journal of The Royal Society Interface 16, no. 157 (August 2019): 20190218. http://dx.doi.org/10.1098/rsif.2019.0218.
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Correlative imaging combines information from multiple modalities (physical–chemical–mechanical properties) at various length scales (centimetre to nanometre) to understand the complex biological materials across dimensions (2D–3D). Here, we have used numerous coupled systems: X-ray microscopy (XRM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), optical light microscopy (LM) and focused ion beam (FIB-SEM) microscopy to ascertain the microstructural and crystallographic properties of the wall-plate joints in the barnacle Semibalanus balanoides . The exoskeleton is composed of six interlocking wall plates, and the interlocks between neighbouring plates (alae) allow barnacles to expand and grow while remaining sealed and structurally strong. Our results indicate that the ala contain functionally graded orientations and microstructures in their crystallography, which has implications for naturally functioning microstructures, potential natural strengthening and preferred oriented biomineralization. Elongated grains at the outer edge of the ala are oriented perpendicularly to the contact surface, and the c -axis rotates with the radius of the ala. Additionally, we identify for the first time three-dimensional nanoscale ala pore networks revealing that the pores are only visible at the tip of the ala and that pore thickening occurs on the inside (soft bodied) edge of the plates. The pore networks appear to have the same orientation as the oriented crystallography, and we deduce that the pore networks are probably organic channels and pockets, which are involved with the biomineralization process. Understanding these multiscale features contributes towards an understanding of the structural architecture in barnacles, but also their consideration for bioinspiration of human-made materials. The work demonstrates that correlative methods spanning different length scales, dimensions and modes enable the extension of the structure–property relationships in materials to form and function of organisms.
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Oi, Takao, Sakiko Enomoto, Tomoyo Nakao, Shigeo Arai, Koji Yamane, and Mitsutaka Taniguchi. "Three-dimensional ultrastructural change of chloroplasts in rice mesophyll cells responding to salt stress." Annals of Botany 125, no. 5 (November 27, 2019): 833–40. http://dx.doi.org/10.1093/aob/mcz192.
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Abstract Background and Aims Excess salinity inhibits the metabolism of various systems and induces structural changes, especially in chloroplasts. Although the chloroplast body seems to swell under salinity stress as observed by conventional transmission electron microscopy, previous studies are limited to 2-D data and lack quantitative comparisons because specimens need to be sliced into ultrathin sections. This study shows three-dimensionally the structural changes in a whole mesophyll cell responding to salinity stress by serial sectioning with a focused ion beam scanning electron microscope (FIB-SEM) and compares the differences in chloroplast structures based on reconstructed models possessing accurate numerical voxel values. Methods Leaf blades of rice plants treated with 100 mm NaCl or without (control) for 4 d were fixed chemically and embedded in resin. The specimen blocks were sectioned and observed using the FIB-SEM, and then the sliced image stacks were reconstructed into 3-D models by image processing software. Key Results On the transverse sections of rice mesophyll cells, the chloroplasts in the control leaves appeared to be elongated meniscus lens shaped, while those in the salt-treated leaves appear to be expanded oval shaped. The 3-D models based on serial sectioning images showed that the chloroplasts in the control cells spread like sheets fitted to the shape of the cell wall and in close contact with the adjacent chloroplasts. In contrast, those in the salt-stressed cells curled up into a ball and fitted to cell protuberances without being in close contact with adjacent chloroplasts. Although the shapes of chloroplasts were clearly different between the two treatments, their volumes did not differ. Conclusions The 3-D reconstructed models of whole rice mesophyll cells indicated that chloroplasts under salt stress conditions were not swollen but became spherical without increasing their volume. This is in contrast to findings of previous studies based on 2-D images.
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Chesnokov, Yury, Andrey Shibaev, Roman Kamyshinsky, Vyacheslav Kralin, Olga Philippova, and Anton Orekhov. "Abstract P-3: The Structure of Self-Assembled Surfactant Micellar Networks by in situ Cryo-Electron Tomography." International Journal of Biomedicine 11, Suppl_1 (June 1, 2021): S12. http://dx.doi.org/10.21103/ijbm.11.suppl_1.p3.
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Background: Surfactant molecules can form various self-assembled structures in aqueous solutions, including spherical and cylindrical micelles, lamellae, vesicles, etc. Elongated cylindrical (wormlike) micelles can entangle and form a dense network. The study of the un-perturbed native structure of wormlike micelles in such networks presents a great challenge, since the micelles are formed due to weak non-covalent interactions and may easily break when external conditions are changed. In this work in situ cryo-electron tomography (cryo-ET) was applied to reveal the relaxed structure of such entangled systems. Methods: To prepare samples for the cryo-ET study 1 µl of the aqueous surfactant-containing solution was applied to the glow discharged grid, blotted with filter paper for 10 sec, drained for 60 sec to allow for the relaxation of the system and plunge-frozen with Vitrobot Mark IV. The vitrified sample was transferred to Versa 3D cryo-focused ion beam / scanning electron microscope (cryo-FIB/SEM) to prepare thin (100-150 nm) sections of the sample. Cryo-ET study was conducted using Titan Krios. IMOD and Avizo software packages were used for data processing. Results: In this work, wormlike micelles formed by a mixture of an anionic and a cationic surfactant were investigated at the excess of the anionic surfactant. Cryo-ET study of the obtained lamellae demonstrated the formation of two different phases, consisting of straight rods oriented along the grid substrate (phase 1) and isotropic network formed by wormlike micelles (phase 2) above it. The topology of the second phase corresponded to the branched saturated network or entangled network depending on cation/anion ratio of the sample. However, the analysis of the thin samples obtained without cryo-FIB demonstrated only the presence of the metastable phase (phase 1), which could lead to false conclusions regarding the morphology of the micelles. Conclusion: Here we discuss the influence of different sample preparation approaches on the sample structure and demonstrate that the native un-perturbed conformation of charged cylindrical surfactant micelles in the dense network is that of a slightly bent rod or a wormlike chain with high persistence length.
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Xu, Menghua, Yali Qin, Kailai Ji, and Hongshun Zhang. "Primary aberrations in tightly focused polarized anomalous vortex beams." Laser Physics 32, no. 3 (January 21, 2022): 035401. http://dx.doi.org/10.1088/1555-6611/ac4912.
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Abstract Based on the Richards Wolf vector diffraction theory, the intensity profiles of the radially and azimuthally polarized anomalous vortex beams focused by a high numerical aperture (NA) lens in the presence of primary aberration are obtained. The effects of the primary aberration coefficient on the intensity distribution, longitudinal field and the quality of the aberrated focused field through calculating the Strehl ratio under various polarized input beams are analyzed. The results show that spherical aberration destroys the rotational symmetry of the focused intensity about the optical axis. Coma will shift the focal spot which gradually presents an obvious comet shape. Astigmatism will elongate the focal spot. Meanwhile, defocus technology on compensating aberrations is studied. The results have potential applications in the design and assembly of high NA systems or overcoming aberrations in the future.
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Heisser, Ronald H., Vishal P. Patil, Norbert Stoop, Emmanuel Villermaux, and Jörn Dunkel. "Controlling fracture cascades through twisting and quenching." Proceedings of the National Academy of Sciences 115, no. 35 (August 13, 2018): 8665–70. http://dx.doi.org/10.1073/pnas.1802831115.
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Fracture fundamentally limits the structural stability of macroscopic and microscopic matter, from beams and bones to microtubules and nanotubes. Despite substantial recent experimental and theoretical progress, fracture control continues to present profound practical and theoretical challenges. While bending-induced fracture of elongated rod-like objects has been intensely studied, the effects of twist and quench dynamics have yet to be explored systematically. Here, we show how twist and quench protocols may be used to control such fracture processes, by revisiting Feynman’s observation that dry spaghetti typically breaks into three or more pieces when exposed to large pure bending stresses. Combining theory and experiment, we demonstrate controlled binary fracture of brittle elastic rods for two distinct protocols based on twisting and nonadiabatic quenching. Our experimental data for twist-controlled fracture agree quantitatively with a theoretically predicted phase diagram, and we establish asymptotic scaling relations for quenched fracture. Due to their general character, these results are expected to apply to torsional and kinetic fracture processes in a wide range of systems.
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Fang, Congqi, Wenyan Dong, and Mohammad Parsaeimaram. "Seismic performance of double skin semi-base-isolated structures." E3S Web of Conferences 143 (2020): 01048. http://dx.doi.org/10.1051/e3sconf/202014301048.
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Base isolation technology is a popular and powerful isolation technology. This technique can greatly reduce the seismic response of the structure, so as to reduce the damage to the structure. Base isolation method decouples the superstructure from the base by installing a flexible layer under each column to reduce dynamic response in the earthquake and elongate the time period of structures due to its inherent flexibility. However, the long time period causes large displacement. In addition, base isolation devices are highly vulnerable due to uplift forces produced by lateral force resisting systems (LFRS). In this study, an adjustable structure with a new configuration, namely double skin semi-base-isolated (SBI) structure is presented to solve the above problems. The LFRS is omitted in the proposed SBI structure and the time period and displacement are reduced compared to the conventional base-isolated structure. The forcedeformation behavior of an isolator is modeled as bi-linear hysteretic behavior which can be effectively used to model all isolation system in practice. This study investigates the seismic performance of 10-story double skin SBI reinforced concrete (RC) structure under far-fault earthquake ground motion by numerical method. Results demonstrate that the SBI system is significantly adjustable with the use of RC coupling beams between the inner core and outer frames. By increasing or reducing the number of connected floors in the SBI system, dynamic behaviors of the SBI system can be changed. The adjusted structure can be created by adding and removing RC coupling beams at every arbitrary floor level.
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Kislyuk, Alexander M., Tatiana S. Ilina, Ilya V. Kubasov, Dmitry A. Kiselev, Alexander A. Temirov, Andrei V. Turutin, Mikhail D. Malinkovich, Andrey A. Polisan, and Yury N. Parkhomenko. "Tailoring of stable induced domains near a charged domain wall in lithium niobate by probe microscopy." Modern Electronic Materials 5, no. 2 (June 1, 2019): 51–60. http://dx.doi.org/10.3897/j.moem.5.2.51314.
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Ferroelectric lithium niobate (LiNbO3) crystals with an engineered domain structure have a number of applications in optical systems for generation of multiple laser radiation harmonics, acoustooptics, precision actuators, vibration and magnetic field sensors, including those for high-temperature applications, and prospectively, in non-volatile computer memory. We have studied the effect of charged domain boundary on the formation of induced domain structures in congruent lithium niobate (LiNbO3) crystals at the non-polar x-cut. Bi- and polydomain ferroelectric structures containing charged “head-to-head” and “tail-to-tail” type domain boundaries have been formed in the specimens using diffusion annealing in air ambient close to the Curie temperature and infrared annealing in an oxygen free environment. The surface potential near the charged domain wall has been studied using an atomic force microscope (AFM) in Kelvin mode. We have studied surface wedge-shaped induced microscopic domains formed at the charged domain boundary and far from that boundary by applying electric potential to the AFM cantilever which was in contact with the crystal surface. We have demonstrated that the morphology of the induced domain structure depends on the electrical conductivity of the crystals. The charged “head-to-head” domain boundary has a screening effect on the shape and size of the domain induced at the domain wall. Single wedge-shaped domains forming during local repolarization of reduced lithium niobate crystals at the AFM cantilever split into families of microscopic domains in the form of codirectional beams emerging from a common formation site. The charged domain wall affects the topography of the specimens by inducing the formation of an elongated trench, coincident with the charged boundary, during reduction annealing.
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Som, Tirtha, and Basudeb Karmakar. "Novel Plasmonic Nanometal - Rare-Earth Ions co-doped Antimony Glasses for Nanophotonic Applications." MRS Proceedings 1788 (2015): 1–6. http://dx.doi.org/10.1557/opl.2015.626.
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ABSTRACTGlasses are recognized as the ideal hosts to incorporate plasmonic metal nanoparticles (NPs), semiconductor NPs, and luminescent rare-earth (RE3+) ions. This is due to their unique optical properties, stability, absence of high energy bond vibrations and inertness towards the incorporated NPs. However, conventional methods of metal-glass nanocomposite fabrication involve ion-implantation or sputtering and subsequent heat-treatment under H2, UV-light/X-ray/γ- or laser irradiation. They are (i) multi-step, (ii) require expensive set-up, (iii) bear risk of sample damage and (iv) the formation of NPs occurs only in surface layers. Here we develop two novel glass-systems K2O-B2O3-Sb2O3 and K2O-B2O3-Sb2O3-ZnO. Using the selective reducing property of the main component Sb2O3 in these hosts, here we demonstrate for the first time the strategy for single-step in-situ fabrication of metal (M0) NPs and RE3+ ions co-embedded within bulk glasses. This new series of novel composites co-embedding metal NPs (elliptical Au, elongated Ag NPs and Aucore-AuAgshell NPs) and RE3+ ions exhibit enhanced upconversion for solar panels, advanced displays and other nanophotonic applications. Metal NPs exhibit surface plasmons resonance results in concentration and enhancement of the local electromagnetic field (LFE) around them. The luminescent RE3+ ion in the vicinity experiences the local field effect. We observe that the LFE effect is stronger on electric dipole transitions of the RE3+ than the magnetic dipole ones. LFE induced by nano Au enhance the (i) 4G7/2 → 4I9/2 540 nm green and 4G7/2 → 4I15/2 650 nm red upconversion emissions of Nd3+ by 9 and 11 fold, (ii) electric dipole 4G5/2 → 6H9/2 636 nm red upconversion of Sm3+ by about 7 fold and (ii) 4S3/2 → 4I15/2 536 nm green and 4F9/2 →4I15/2 645 nm red emissions of Er3+ by 2 and 5 fold respectively. LFE induced by nano Ag enhance both the green and red upconversion emission of Er3+ by 8 fold. The Aucore-AuAgshell NPs enhance the red upconversion of Sm3+ only by 2 fold due to smaller LFE effect of bimetallic NPs. All the Au-doped antimony glasses are dichroic. They transmit the blue light and reflect the brown light, which make them very interesting material comparable to the historic Lycurgus Cup.
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Yao, Su, Xiaolong Yang, Minfeng Gu, Tao An, Jun Yang, Luis C. Ho, Xiang Liu, Ran Wang, Xue-Bing Wu, and Weimin Yuan. "Detection of a Parsec-Scale Jet in a Radio-Quiet Narrow-Line Seyfert 1 Galaxy with Highly Accreting Supermassive Black Hole." Monthly Notices of the Royal Astronomical Society, September 16, 2021. http://dx.doi.org/10.1093/mnras/stab2651.
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Abstract The jet in active galactic nuclei (AGN) is a key ingredient in understanding the co-evolution of galaxies and their central supermassive black holes (SMBHs). Unfortunately, the mechanism of jet launching and collimation is still elusive. The observational evidence of decreasing radio loudness with increasing Eddington ratio implies that the jet should be coupled with the accretion process. To further explore the relationship between the jet and accretion, it is necessary to extend our knowledge of the jet to an extreme end of the Eddington ratio distribution of AGN. Using Very Long Baseline Array (VLBA), we report the detection of the parsec-scale radio structure in Mrk 335, a radio-quiet narrow-line Seyfert 1 galaxy with an Eddington ratio close to/above unity. The VLBA image at 1.5 GHz reveals an elongated structure extending ∼20 parsec in north-south direction with a peak flux density of 1.98 ± 0.05 mJy/beam and radio brightness temperatures as high as 6 × 107 K. This feature provides a strong evidence of a parsec-scale (bipolar) jet launched from a highly accreting SMBH. We discuss the result by comparing Mrk 335 with other highly accreting systems, e.g. Galactic black holes and tidal disruption events, and recall the discovery of collimated corona in the vicinity of SMBH in Mrk 335 by previous X-ray observations, whose relation to the parsec-scale radio jet should be explored by future simultaneous X-ray spectroscopy and high resolution radio observations.
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Zhang, Xi-Cheng, and Fabrizio Buccheri. "Terahertz photonics of microplasma and beyond." Lithuanian Journal of Physics 58, no. 1 (March 28, 2018). http://dx.doi.org/10.3952/physics.v58i1.3647.
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THz air photonics using laser-induced air plasma is one of the leading frontiers in the THz community. Ambient air, when excited with an intense femtosecond laser beam, exhibits the remarkable ability to generate and detect pulsed THz waves through a nonlinear optical process. Significant advances in the use of air plasma for emitting, controlling, enhancing and measuring broadband THz waves have opened up a range of research opportunities. However, one of the major challenges for the research community and in real world applications is that plasma formation requires the use of an intense laser (mJ pulse energy), but most femtosecond laser oscillators only have pulse energies in the range of pJ to tens of nJ. The investigation of THz photonics, specifically the exploration of laserinduced plasmas at the micro-nano scale and beyond, is a frontier. Microplasmas generated by tightly focused optical excitation beams with controlled polarization serve as a new THz source with its unique radiation pattern and easy operation. The laser energy threshold for THz wave generation, the power scaling and the generation efficiency from microplasmas are significantly different from those of elongated plasmas. Our estimation indicates that the micronano plasma approach could reduce the necessary optical pulse energy by five orders of magnitude, while still obtaining a comparable or better signal-to-noise ratio for THz time-domain spectroscopy. This would be made possible by the high electron density (1019 cm–3 or more) achievable with a tight focus laser excitation, which correlates with the THz generation efficiency, and the use of laser oscillators with a much higher pulse repetition rate, as compared to the currently employed amplified laser systems (100 MHz vs 1 kHz). The THz micro-nano plasma is expected to lead to key technologies that will enable further interdisciplinary research and continued advancements of numerous THz wave sensing and spectroscopy developments. It serves as a vehicle for studying the extreme THz science.
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Castaño, Maria L., and Xiaobo Tan. "Model Predictive Control-Based Path-Following for Tail-Actuated Robotic Fish." Journal of Dynamic Systems, Measurement, and Control 141, no. 7 (April 9, 2019). http://dx.doi.org/10.1115/1.4043152.
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There has been an increasing interest in the use of autonomous underwater robots to monitor freshwater and marine environments. In particular, robots that propel and maneuver themselves like fish, often known as robotic fish, have emerged as mobile sensing platforms for aquatic environments. Highly nonlinear and often under-actuated dynamics of robotic fish present significant challenges in control of these robots. In this work, we propose a nonlinear model predictive control (NMPC) approach to path-following of a tail-actuated robotic fish that accommodates the nonlinear dynamics and actuation constraints while minimizing the control effort. Considering the cyclic nature of tail actuation, the control design is based on an averaged dynamic model, where the hydrodynamic force generated by tail beating is captured using Lighthill's large-amplitude elongated-body theory. A computationally efficient approach is developed to identify the model parameters based on the measured swimming and turning data for the robot. With the tail beat frequency fixed, the bias and amplitude of the tail oscillation are treated as physical variables to be manipulated, which are related to the control inputs via a nonlinear map. A control projection method is introduced to accommodate the sector-shaped constraints of the control inputs while minimizing the optimization complexity in solving the NMPC problem. Both simulation and experimental results support the efficacy of the proposed approach. In particular, the advantages of the control projection method are shown via comparison with alternative approaches.
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Bouhouche, K., M. S. Valentine, P. Le Borgne, M. Lemullois, J. Yano, S. Lodh, A. Nabi, A. M. Tassin, and J. L. Van Houten. "Paramecium, a Model to Study Ciliary Beating and Ciliogenesis: Insights From Cutting-Edge Approaches." Frontiers in Cell and Developmental Biology 10 (March 14, 2022). http://dx.doi.org/10.3389/fcell.2022.847908.
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Cilia are ubiquitous and highly conserved extensions that endow the cell with motility and sensory functions. They were present in the first eukaryotes and conserved throughout evolution (Carvalho-Santos et al., 2011). Paramecium has around 4,000 motile cilia on its surface arranged in longitudinal rows, beating in waves to ensure movement and feeding. As with cilia in other model organisms, direction and speed of Paramecium ciliary beating is under bioelectric control of ciliary ion channels. In multiciliated cells of metazoans as well as paramecia, the cilia become physically entrained to beat in metachronal waves. This ciliated organism, Paramecium, is an attractive model for multidisciplinary approaches to dissect the location, structure and function of ciliary ion channels and other proteins involved in ciliary beating. Swimming behavior also can be a read-out of the role of cilia in sensory signal transduction. A cilium emanates from a BB, structurally equivalent to the centriole anchored at the cell surface, and elongates an axoneme composed of microtubule doublets enclosed in a ciliary membrane contiguous with the plasma membrane. The connection between the BB and the axoneme constitutes the transition zone, which serves as a diffusion barrier between the intracellular space and the cilium, defining the ciliary compartment. Human pathologies affecting cilia structure or function, are called ciliopathies, which are caused by gene mutations. For that reason, the molecular mechanisms and structural aspects of cilia assembly and function are actively studied using a variety of model systems, ranging from unicellular organisms to metazoa. In this review, we will highlight the use of Paramecium as a model to decipher ciliary beating mechanisms as well as high resolution insights into BB structure and anchoring. We will show that study of cilia in Paramecium promotes our understanding of cilia formation and function. In addition, we demonstrate that Paramecium could be a useful tool to validate candidate genes for ciliopathies.
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Luecke, Noah Carr, Kerri Crawford, Hanane Stanghellini, Alyssa Burkhard, and Steve Koike. "First report of root rot caused by (Pythium dissotocum) on hydroponically grown collard greens (Brassica oleracea var. acephala)." Plant Disease, September 13, 2021. http://dx.doi.org/10.1094/pdis-07-21-1584-pdn.
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Collards (Brassica oleracea var. acephala) are grown throughout the United States. Hydroponic greens are more common now due to technological advances lowering the cost and increasing the efficacy of production. In January 2021, a 325 m2 indoor hydroponic farm opened to provide fresh produce for a school in Los Angeles County, CA. Three week old collard seedlings were purchased from a local nursery, rinsed of their rooting media, and transplanted into deep water culture beds (1.2 m x 2.5 m x 0.3 m). Two weeks later, symptoms including plant stunting, chlorosis, leaf curling and wilting, and brown necrotic roots appeared. By and by 80-100% of usable plants were lost to disease. Symptomatic roots were plated on corn meal agar (CMA) amended with 2 ml of 25% lactic acid and CMA amended with pimaricin, ampicillin, rifampicin, and pentachloronitrobenzene (PARP) (Kannwischer et al. 1978). After 2 days a single colony type emerged on PARP but no growth occurred on acidified CMA. Representative isolates were transferred to CMA and to filtered (0.02 µm) soil extract solution with boiled grass blades (Martin 1992), both of which were incubated at 22 C and ambient light conditions. On CMA, isolates produced coenocytic mycelium with minimal aerial hyphae. After 24 h in soil extract, isolates developed filamentous sporangia, elongated discharge tubes with slightly inflated tips, and zoospores. Oospores were not observed. Pathogenicity was confirmed by soaking the roots of five day old collard seedlings in beakers containing zoospores (1 x 102 zoospores/ml) in filtered soil extract. Four isolates were tested on 15 seedlings each. After 24 h at 22 C in ambient light conditions, plants were transferred to new beakers with roots placed on filter paper at the bottom and saturated with sterile distilled water. Three days after this transfer, leaves on all plants turned chlorotic and roots developed brown lesions from which morphologically identical colonies were isolated. Control plants, soaked in filtered soil extract, developed no root or foliar symptoms. To molecularly identify the collard isolates, DNA was extracted from mycelial original and re-isolated isolates and was amplified by PCR using mitochondrial primers for the cytochrome oxidase I (COI) gene (Robideau et al. 2011) and the cytochrome oxidase II (COX2) gene (Martin 2000). The only species that matched both loci from the original and re-isolated isolates with a high percent identity was Pythium dissotocum. The COI locus from the original isolate (MZ027311) matched P. dissotocum with 99% identity and with 332/334 base pairs matching the isolate with Sequence ID MT981134.1. From the re-isolated isolate (MZ027313), the COIequence perfectly matched 657/657 base pairs of P. dissotocum (Sequence ID MT981147.1). The COX2 locus from the original isolate (MZ027312) matched P. dissotocum (Sequence ID MG719859.1) with a 99% identity and 517/518 matching base pairs and the re-isolated isolate (MZ027314) perfectly matched P. dissotocum (Sequence ID MG719859.1) with 515/515 matching base pairs. Based on these molecular and morphological data, the isolates were identified as Pythium dissotocum. To our knowledge, this is the first report of P. dissotocum causing root rot on collards. At this same facility, P. dissotocum was also confirmed as the cause of declining bean (Phaseolus vulgaris) plants. As hydroponics will be necessary to feed a growing population – especially in urban areas -- and because leafy greens are a main crop of the hydroponics industry, we anticipate this issue may become common. Hydroponic systems are highly conducive to the persistence of Oomycetes and a record of infection and plan of action will be necessary to preserve crop health.