Ejection Mechanism Research Articles

(Invited) Energetic Hole Ejection Involved in Plasmon-Induced Charge Separation: Local Oxidation and an Application to Near IR Photovoltaics

Plasmon-induced charge separation (PICS)1-3 involves electron transfer from plasmonic nanoparticles of Au, Ag, or Cu to a semiconductor such as TiO2.1-4 PICS of Ag-TiO2 systems often involve oxidation of Ag to Ag+,5 and that this reaction occurs preferentially at resonance sites, at which optical near fields are localized.6-8 This cannot be ascribed to thermal acceleration of reaction,9 but can be explained in terms of ejection of energetic holes from the nanoparticles as Ag+ ions. This hole ejection has been investigated further for Au nanocubes on TiO2 by using other reactions; Pb2+ oxidation to PbO2 and pyrrole oxidation to polypyrrole. Au nanocubes on TiO2 show distal mode, in which electron oscillation is localized at the top face of the nanocube, and proximal mode, in which electron oscillation is localized at the bottom face. In the case of Pb2+ oxidation, PICS for the distal mode and proximal mode resulted in PbO2 deposition at around the top face and the bottom face, respectively.10 However, in the case of pyrrole oxidation, both of the distal mode PICS and proximal mode PICS resulted in polypyrrole deposition at the whole surface of the nanocube. On the basis of those results, we conclude that the localized oxidation and the delocalized oxidation are ascribed to energetic hole ejection mechanism and positive charge accumulation mechanism, respectively. We have applied energetic hole ejection to fabrication of chiral plasmonic nanostructures11 and near IR photovoltaics.12 Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005).Y. Tian and T. Tatsuma, Chem. Commun., 2004, 1810.T. Tatsuma, H. Nishi, and T. Ishida, Chem. Sci., 8, 3325 (2017) [review].E. Kazuma and T. Tatsuma, Adv. Mater. Interfaces, 1, 1400066 (2014).Y. Ohko, T. Tatsuma, T. Fujii, K. Naoi, C. Niwa, Y. Kubota, and A. Fujishima, Nat. Mater., 2, 29 (2003).E. Kazuma, N. Sakai, and T. Tatsuma, Chem. Commun., 47, 5777 (2011).I. Tanabe and T. Tatsuma, Nano Lett., 12, 5418 (2012).K. Saito, I. Tanabe, and T. Tatsuma, J. Phys. Chem. Lett., 7, 4363 (2016).K. Saito, K. Setoura, S. Ito, H. Miyasaka, Y. Mitsuda, and T. Tatsuma, ACS Appl. Mater. Interfaces, 9, 11064 (2017).H. Nishi, M. Sakamoto, and T. Tatsuma, Chem. Commun., 54, 11741 (2018).K. Saito and T. Tatsuma, Nano Lett., 18, 3209 (2018).S. H. Lee, H. Nishi, and T. Tatsuma, Nanoscale, 10, 2841 (2018).

Structures of T7 bacteriophage portal and tail suggest a viral DNA retention and ejection mechanism

Double-stranded DNA bacteriophages package their genome at high pressure inside a procapsid through the portal, an oligomeric ring protein located at a unique capsid vertex. Once the DNA has been packaged, the tail components assemble on the portal to render the mature infective virion. The tail tightly seals the ejection conduit until infection, when its interaction with the host membrane triggers the opening of the channel and the viral genome is delivered to the host cell. Using high-resolution cryo-electron microscopy and X-ray crystallography, here we describe various structures of the T7 bacteriophage portal and fiber-less tail complex, which suggest a possible mechanism for DNA retention and ejection: a portal closed conformation temporarily retains the genome before the tail is assembled, whereas an open portal is found in the tail. Moreover, a fold including a seven-bladed β-propeller domain is described for the nozzle tail protein.

Electronic properties of vacancies in bilayer graphane

We have performed the ab initio hybrid density functional theory (DFT) calculations to investigate the electronic structure of various neutral and charged vacancies (VH, VCH, VC, VC−CH and VC−C) in a diamond-like bilayer graphane. In the neutral state, the identified vacancies create the energetically unfavorable dangling bonds which are significantly stabilize by electron ejection (+1 state) mechanism. The studied vacancies introduce the electronic states within the band gap, which are either metallic or semiconducting in nature. The metallic vacancies posses a magnetic moment of 1.00 μB. The charge states modulation alters the electronic character of the vacancies and suppresses the induced magnetic moment. Our study demonstrates that the vacancies in a diamond-like bilayer graphane structure could have potential applications in nanoelectronics and band gap related energy storage devices.

PG 1610+062: a runaway B star challenging classical ejection mechanisms

Hypervelocity stars are rare objects, mostly main-sequence (MS) B stars, traveling so fast that they will eventually escape from the Milky Way. Recently, it has been shown that the popular Hills mechanism, in which a binary system is disrupted via a close encounter with the supermassive black hole at the Galactic center, may not be their only ejection mechanism. The analyses of Gaia data ruled out a Galactic center origin for some of them, and instead indicated that they are extreme disk runaway stars ejected at velocities exceeding the predicted limits of classical scenarios (dynamical ejection from star clusters or binary supernova ejection). We present the discovery of a new extreme disk runaway star, PG 1610+062, which is a slowly pulsating B star bright enough to be studied in detail. A quantitative analysis of spectra taken with ESI at the Keck Observatory revealed that PG 1610+062 is a late B-type MS star of 4–5 M⊙ with low projected rotational velocity. Abundances (C, N, O, Ne, Mg, Al, Si, S, Ar, and Fe) were derived differentially with respect to the normal B star HD 137366 and indicate that PG 1610+062 is somewhat metal rich. A kinematic analysis, based on our spectrophotometric distance (17.3 kpc) and on proper motions from Gaia’s second data release, shows that PG 1610+062 was probably ejected from the Carina-Sagittarius spiral arm at a velocity of 550 ± 40 km s−1, which is beyond the classical limits. Accordingly, the star is in the top five of the most extreme MS disk runaway stars and is only the second among the five for which the chemical composition is known.

A novel variable topology design for a multi-flexible ejection mechanism

The airborne missile launch mechanism often subjects to significant deformations induced by the large ejection force during high-speed actuations in missile ejection process, leading to a substantial deviation of separation parameters from designed values that threats safety of the carrier. This study proposes a novel variable topology design for launch mechanism, achieved via a Prismatic-Revolute-Revolute pair (PR-R) motion formed by the structural gap with a specific direction. It enables launch mechanism variability during missile ejection process and optimizes the ejection force given by the front and back ejection arms, and greatly optimizes the separation parameters during missile ejection. The kinetics simulation analysis is conducted under working conditions of the original ejection mechanism and the novel mechanism with variable topology design, respectively. The results show that the novel variable topology design is more befitting for the launch process in terms of system safety and controllability, effectively improving the separation posture, restraining the flexible effect of the mechanism, and fulfilling the effectiveness of the design value of multi-rigid body.

Thermal Conduction Effects on the Accretion–Ejection Mechanism. I. Accretion Flow Investigation

Abstract Understanding the accretion of matter around compact objects such as young stars or black holes remains one of the most interesting problems in astrophysics. Recent observations detected the accretion of matter of several young stars from their circumstellar disk and proposed the existence of the X-ray emission at very high temperature. The hot gases surrounding these systems are likely to proceed under the collisionless regime, which indicates that the thermal conduction has a relevant contribution in the transport of energy along the accretion disks. Notwithstanding its importance, this physical ingredient is largely neglected in previous time-dependent studies of accretion–ejection structure. More research is still necessary before obtaining a complete picture of such a phenomenon. In this series, we have included the three nonideal effects together, viscosity, resistivity, and thermal conduction, to explore the physical mechanism of the disk–jet system. We carry out extensive time-dependent simulations of the accretion disk and jet using the PLUTO code. The mean field approach is used in this work by taking into account the evolution of the disk and jet simultaneously. We show in this first paper how the thermal conduction plays a crucial role in the accretion disk dynamics by presenting a detailed discussion of its effects on the evolution of basic facets of the inflow properties with a special emphasis on the equatorial plane and disk surface. Our model also shows strong indications of the ejection efficiency improvement in the presence of thermal conduction.

The propulsion mechanism and tiny particles removal investigation based on the “micro-gun” propulsion system

A “micro-gun” propulsion system is proposed in this work, by which a directional laser pulse can be generated and subsequently emitted through a system tip to excite a shockwave (or plasma). Noteworthily, the excited shockwave yields a directional force in the same way as its actuator does, which was investigated experimentally by propelling a micro-particle along a predefined trajectory. To best understand the physical mechanism behind the experimental phenomena, a physical model of “micro-gun” propulsion system was established. Analysis of the experimental and the simulation results demonstrate that the laser pulse propulsion was dominated by shockwave ejection mechanism. An agreement between the experimental results and simulation results is obtained, and which enables us to accurately determine the particle removal efficiency, and to identify the performance dependencies, namely the laser pulse energy, particle types as well as particle dimensions. The particle transport feature makes the “micro-gun” propulsion system promising for applications in particle screen and separation.

Unseen companions of V Hya inferred from periodic ejections

ABSTRACT A recent study using Hubble Space Telescope observations found periodic, high-speed, collimated ejections (or ‘bullets’) from the star V Hya. The authors of that study proposed a model associating these bullets with the periastron passage of an unseen, substellar companion in an eccentric orbit and with an orbital period of ∼8 yr. Here we propose that V Hya is part of a triple system, with a substellar companion having an orbital period of ∼8 yr, and a tertiary object on a much wider orbit. In this model, the more distant object causes high-eccentricity excitations on the substellar companion’s orbit via the Eccentric Kozai–Lidov mechanism. These eccentricities can reach such high values that they lead to Roche-lobe crossing, producing the observed bullet ejections via a strongly enhanced accretion episode. For example, we find that a ballistic bullet ejection mechanism can be produced by a brown-dwarf-mass companion, while magnetically driven outflows are consistent with a Jovian-mass companion. Finally, we suggest that the distant companion may reside at few a hundred astronomical units on an eccentric orbit.

Motion of Enzyme-Powered Microshell Motors.

Microshells are attractive in constructing bubble-propelled micromotors due to the lower energy consumption for bubbles forming on a concave surface. In this work, enzyme-powered microshell motors were fabricated on multimetallic (Au/Ag/Au) microshells along with the modification of catalase on its concave surface. The catalase triggered the decomposition of hydrogen peroxide to oxygen gas, hence propelling the autonomous motion of microshell motors. A size-dependent motion behaviour was observed for the microshell motors in the form of slow tremble and fast translation motion for a size smaller and larger than 5 μm, respectively, according to the size, generation efficiency and ejection mechanism of bubbles and the intensity of Brownian motion. In addition, the effect of fuel concentration on the motion speed of microshells was dependent on whether the bubble generation was affected by the limited mass transfer in the microshell space. These findings play an important role for the design of microshell motors.

Role of intra-ventricular vortex in left ventricular ejection elucidated by echo-dynamography.

From the correlation between the blood flow dynamics and wall dynamics in the left ventriocle (LV) analyzed using echo-dynamography, the ejection mechanisms and role of the intra-ventricular vortex in the LV were elucidated in detail during the pre-ejection transitional period (pre-ETP), the very short period preceding LV ejection. The study included 10 healthy volunteers. Flow structure was analyzed using echo-dynamography, and LV wall dynamics were measured using both high-frame-rate two-dimensional echocardiography and a phase difference tracking method we developed. A large accelerated vortex occurred at the central basal area of the LV during this period. The main flow axis velocity line of the LV showed a linearly increasing pattern. The slope of the velocity pattern reflected the deformity of the flow route induced by LV contraction during the pre-ETP. The centrifugal force of the vortex at its junction with the main outflow created a stepwise increase of about 50% of the ejection velocity. Ejection of blood from the LV was accomplished by the extruding action of the ventricular wall and the centrifugal force of the accelerated vortex during this period. During ejection, acceralated outflow was considered to create a spiral flow in the aorta with help from the spherical structure of the Valsalva sinus.

Relation between winds and jets in radio-loud AGN

We have investigated the relation between the two modes of outflow (wind and jet) in radio-loud active galactic nuclei (AGN). For this study we have carried out a systematic and homogeneous analysis of XMM-Newton spectra of a sample of 16 suitable radio-loud Seyfert-1 AGN. The ionised winds in these AGN are parameterised through high-resolution X-ray spectroscopy and photoionisation modelling. We discover a significant inverse correlation between the column density NH of the ionised wind and the radio-loudness parameter R of the jet. We explored different possible explanations for this NH-R relation and find that ionisation, inclination, and luminosity effects are unlikely to be responsible for the observed relation. We argue that the NH-R relation is rather a manifestation of the magnetic driving mechanism of the wind from the accretion disc. Change in the magnetic field configuration from toroidal to poloidal, powering either the wind or the jet mode of the outflow, is the most feasible explanation for the observed decline in the wind NH as the radio jet becomes stronger. Our findings provide evidence for a wind-jet bimodality in radio-loud AGN and shine new light on the link between these two modes of outflow. This has far-reaching consequences for the accretion disc structure and the wind ejection mechanism.

Interaction of short laser pulses with model contamination microparticles on a high reflector.

The response of model contamination particles located on the surface of a multilayer dielectric mirror when exposed to 1053nm laser pulses of 10ps or 0.6ps duration is investigated. Four different particle types were studied: stainless steel, borosilicate glass, polyethylene, and polytetrafluoroethylene, all having an average diameter of about 40μm. Irradiation with one laser pulse caused particles to eject from the surface with an onset fluence in the range 5× to 100×, depending on the particle type, below the particle-free, laser-induced damage threshold of the mirror. Morphological analysis showed, however, that the ejection process always generated ablation craters and/or secondary contamination, both of which can degrade the performance of the optic during subsequent pulses. Ejection and damage mechanisms are discussed for each particle type.

Dust properties of double-tailed active asteroid (6478) Gault

Context. Asteroid (6478) Gault was discovered to exhibit a comet-like tail in observations from December 2018, becoming a new member of the so-called active asteroid population in the main asteroid belt. Aims. We seek to investigate the grain properties of the dust ejected from asteroid (6478) Gault and to give insight into the activity mechanism(s). Methods. We use a Monte Carlo dust tail brightness code to retrieve the dates of dust ejection, the physical properties of the grains, and the total dust mass losses during each event. The code takes into account the brightness contribution of the asteroid itself. The model is applied to a large data set of images spanning the period from 2019 January 11 to 2019 March 13. In addition, we carried out both short- and long-term photometric measurements of the asteroid. Results. It is shown that, to date, asteroid (6478) Gault has experienced two episodes of impulsive dust ejection, which took place around 2018 November 5 and 2019 January 2. These two episodes released at least 1.4 × 107 kg and 1.6 × 106 kg of dust, respectively, at escape speeds. The size distribution, consisting of particles in the 1 μm–1 cm radius range, follows a broken power law with bending points near 15 μm and 870 μm. On the other hand, the photometric series indicate a nearly constant magnitude over several 5–7.3 h periods, which is a possible effect of the masking of a rotational light curve by the dust. Conclusions. The dust particles forming Gault’s tails were released from the asteroid at escape speeds, but the specific ejection mechanism is unclear until photometry of the dust-free asteroid are conducted to assess whether this was related to rotational disruption or to other possible causes.

Laminar-to-transitional evolution of three-dimensional vortical structures in a low-aspect-ratio rectangular synthetic jet

A time-resolved single-camera volumetric particle image velocimetry (SV-PIV) method was used to measure three-dimensional (3D) vortical structures in a transitional rectangular synthetic jet with aspect ratio (AR) of 3 at a Reynolds number of 332. Compared to a laminar circular synthetic jet, the rectangular case displayed more complicated vortical evolution associated with axis switching of the vortex ring and the formation of streamwise vortex (SV-I), arc-like vortex (AV), Λ-like vortex, and their interactions. The differences in the vortical structures between the rectangular synthetic jets and rectangular continuous jets (AR ≥ 2) were discussed in detail. The joint induction of the vortex ring, SV-I, and AV produced an ejection and injection mechanism, suggesting an enhanced mixing property. In addition, the interactions of SV-I and AV with the vortex ring could promote early flow transition, and result in the rapid decay of the enstrophy for the rectangular case. The start of transition could be determined from the power spectrum. Then the velocity triple-decomposition method was applied to reveal different contributions of the large-scale coherent and small-scale turbulent structures to the flow field. The rectangular case displayed an earlier increase in the random turbulence kinetic energy compared to the circular case.

A Compact Quick-Release Solid Target System for the TRIUMF TR13 Cyclotron

A new solid target system for the TRIUMF TR13 cyclotron that can accommodate target discs with a 1-2-mm thickness and a 28-mm diameter has been developed. The target system design is based on a modified clamping mechanism of a KF-40 vacuum connector, and comprises an easy and quick ejection mechanism for the target plate. The new quick-release target system decreases the retrieval time of the irradiated target to less than 1 minute and is expected to reduce the radiation burden to operating staff by a factor of ~10.

Investigation of the Pentathiepin Functionality as an Inhibitor of Feline Immunodeficiency Virus (FIV) via a Potential Zinc Ejection Mechanism, as a Model for HIV Infection.

A small diverse library of pentathiepin derivatives were prepared to evaluate their efficacy against the nucleocapsid protein function of the feline immunodeficiency virus (FIV) as a model for HIV, using an in vitro cell culture approach. This study led to the development of nanomolar active compounds with low toxicity.

Photochemical Etching of Carbonyl Groups from a Carbon Matrix: The (001) Diamond Surface.

The surface of diamond is reported to undergo nonablative photochemical etching when exposed to ultraviolet (UV) radiation which allows controlled single and partial layer removal of lattice layers. Oxygen termination of surface dangling bonds is known to be crucial for the etching process; however, the exact mechanism of carbon ejection remains unclear. We investigate the interaction of UV laser pulses with oxygen-terminated diamond surfaces using atomic-scale surface characterization combined with first-principles time-dependent density functional theory calculations. We present evidence for laser-induced desorption (LID) from carbonyl functional groups at the diamond {001} surface. The doubly bonded carbonyl group is photoexcited into a triply bonded CO-like state, including scission of the underlying C─C bonds. The carbon removal process in LID is atom by atom; therefore, this mechanism provides a novel "top-down" approach for creating nanostructures on the surface of diamond and other carbon-containing semiconductors.

Study of the thermal erosion, ejection and solidification processes of electrode materials during EDM

Due to the complexity of electrical discharge machining (EDM), there is no perfect theory to explain the mechanisms of material erosion, ejection and solidification during the machining process. Therefore, this paper analyzed the micro-process of a single-pulse discharge during EDM and studied the thermal erosion, ejection and solidification processes of the electrode materials. A thermal-fluid simulation model that considered melting-solidification was established. A mathematical model of vapor flow considering the impact pressure was developed, and it was compiled and loaded as a material ejection force in simulations with a user defined function (UDF). The changes in the material ejection, crater formation and material solidification processes at different discharge times were studied. Finally, the simulation results were verified by single-pulse material discharge experiments, which provided a reference for additional understanding of the micro material discharge processes during EDM.

纳秒激光诱导铜箔喷射机制的研究

纳秒激光诱导铜箔喷射机制的研究

Optimizing the substrate-mediated laser ablation of biological tissues: Quest for the best substrate material

Laser micro-sampling is a promising tool for ambient pressure chemical imaging of biological material by mass spectrometry. Conventional approaches use laser energy coupling into the analyzed sample through electronic (UV) or vibrational (IR) channels. In a recent study [B. Fatou, M. Wisztorski, C. Focsa, M. Salzet, M. Ziskind, I. Fournier, Sci. Rep. 5:18135, 2015], we have demonstrated efficient micro-sampling of biological material through a substrate-mediate laser ablation (SMLA) mechanism using non-resonant visible radiation. Taking advantage of this effect, a large-scale proteomic analysis of micro-sampled tissue sections was performed, demonstrating the possible identification of about 400 proteins, including minor species, from an irradiated surface of 400 μm diameter. Fundamental investigations on biological standards revealed the role of the substrate optical properties in the ejection process. In the present work, we extend these studies by considering the substrate thermal properties. A systematic investigation on the sampling efficiency of homogeneous tissue sections placed on top of various selected substrates was performed. Two ejection mechanisms are clearly evidenced and interpreted in the frame of a simple model based on the substrate properties and the laser beam profile. Improvement of the ejection yield and spatial resolution is also discussed in this frame, in view of the practical application of this technique in the field of (bio)chemical mass spectrometry imaging.