Velocity Spread Research Articles

Effect of Ignition Position on Pre-chamber Jet Combustion

This study focused on the effect of ignition position in the pre-chamber on front chamber jet combustion. To investigate the effect of ignition position, we designed a pre-chamber visualized cylinder head with multiple ignition positions that can capture the pre-chamber combustion. From the visualized images, it was found that two different jet morphologies, a pre-existing jet and a pre-existing unburned mixed gas jet, are produced depending on the ignition position. In the case of the pre-existing jet, it was confirmed that the combustion pattern of the sub-chamber affects the main chamber flame spread velocity.

Effect of Fuel Chemical Compositions on Combustion and Autoignition Characteristics in Gasoline Surrogate Fuel

In this study, three types of gasoline surrogate fuels were used to investigate the effect of fuel chemical composition on combustion and auto-ignition characteristics. For the study, an optically accessible engine capable of velocity analysis was used to observe the combustion and auto-ignition behavior. The results showed that the knock intensity of TRF with high toluene content was lower than that of S5R due to the OH consumption effect during combustion, but the knock suppression effect of toluene weakened at higher temperature and pressure conditions. Next, as the reason why auto-ignition did not occur only for PRF 82.6, the combustion rate analysis and chemical reaction numerical analysis indicate that the cold flame reaction and H2O2 reaction loop are more active in PRF 82.6 than in the other fuels, resulting in a shorter ignition delay and faster flame spread speed, and thus no auto-ignition occurred. Conversely, in TRF and S5R, the OH consumption effect by toluene and the suppression of the cold flame reaction and H2O2 reaction loop resulted in a slower flame spread velocity than in PRF 82.6, which created a time delay before auto-ignition and thus auto-ignition occurred. In addition, it can be inferred that the main reason for the frequent occurrence of wall auto-ignition in S5R is that, unlike PRF 82.6, this fuel does not have an NTC region.

The growth and the decay of a visco-elastocapillary ridge by localized forces.

A soft solid layer develops a ridge-like deformation below the contact line due to the pulling force of the liquid-air surface tension when a droplet is in contact with it. We investigate the growth and the decay of a viscoelastic wetting ridge. The global features, e.g. the ridge height, evolve with time scales corresponding to the relaxation of the viscoelastic material. In contrast, we show that locally around the tip of the ridge, the surface tensions not only determine the equilibrium shape, but also have a significant impact on the dynamics, for which the relaxation has a characteristic spreading velocity depending on the solid surface tension. The relaxation time to an equilibrium state depends on the distance from the contact line, which can be much smaller than the long-term relaxation time scale of the viscoelastic material. The different dynamics between the global features of the ridge and the tip morphology suggests an alternative focus when investigating the contact line dynamics in soft wetting, such as stick-slip motion.

Ambient-air in situ fabrication of high-surface-area, superhydrophilic, and microporous few-layer activated graphene films by ultrafast ultraviolet laser for enhanced energy storage

Microporous graphene-based (MPG) films have attracted tremendous attention in micro-energy storage devices due to their unique characteristics of high specific surface area (SSA), high flexibility and high conductivity. However, current fabrication technologies generally provide overall activation in the form of powder in the bulky tube furnace, and multi-stepped thin film forming process, hurdling their practical utilizations that require efficient, cost-effective and controllable methods for large-area MPG films. Herein, a one-step and scalable laser induction & activation technique is reported for in situ fabrication of decimeter-level few-layer MPG films by utilizing ultrafast ultraviolet laser as a mobile heat source acting on microstructured polyimide film coated with KOH in air, which enable directly regulating the activation area on a flexible substrate. The resulting laser-induced and activated graphene (LIAG) films have interconnected hierarchical porous structures containing ultra- (0.5–0.8 nm) and super-micropores (~1.2 nm), high SSA (>1300 m2 g−1), small amount of doped potassium (~0.50 wt%), and super-hydrophilicity (maximum droplet spreading velocity reaches 424.7 mm s−1). With the well-balanced properties of SSA, heteroatom doping, bulk density, and crystalline size, the LIAG micro-supercapacitors with interdigital electrodes of 35 µm width gap achieve a maximum areal capacitance of 128.4 mF cm−2, which outperforms state-of-the-art laser-processed carbon-based micro-supercapacitors. Additionally, it achieves almost the highest comprehensive evaluation considering processing precision, efficiency, cost and environmental friendliness. The facile, efficient, binder-free fabricability and roll-to-roll process compatibility would provide a rapid route for high-performance flexible energy storage devices.

Crown evolution kinematics of a camellia oil droplet impacting on a liquid layer

The phenomenon of droplet impact on an immiscible liquid is encountered in a variety of scenarios in nature and industrial production. Despite exhaustive research, it is not fully clear how the immiscibility of the liquid on which a droplet impacts affects the crown evolution. The present work experimentally investigates the evolution kinematics of a crown formed by the normal impact of a camellia oil droplet on an immiscible water layer. Based on discussion of dynamic impact behaviors for three critical Weber numbers (We), the radius of the crown and its average spreading velocity are compared with those of previous theoretical models to discuss their applicability to the immiscible liquid. The evolution kinematics (morphology and velocity) are analyzed by considering the effects of the We and layer thickness. Furthermore, the ability of crown expansion in radial and vertical directions is characterized by a velocity ratio. The results show that our experimental crown radius still follows a square-root function of evolution time, which agrees with the theoretical predictions. The dimensionless average spreading velocity decreases with We and follows a multivariate power law, while the dimensionless average rising velocity remains constant. The velocity ratio is shown to linearly increase with We, demonstrating that the rising movement in crown evolution gradually enhances with We. These results are helpful for further investigation on the droplet impact on an immiscible liquid layer.

Microfluidic water flow on laser-patterned MicroCoat® - coated steel surface

A series of hybrid textures with variable topography and chemical composition were obtained on a hydrophilic steel (AISI 304) substrate with a hydrophobic MicroCoat® coating at the increasing incident nanosecond laser fluence from 1.4 J/cm2 to 5.6 J/cm2. The microtopography of the textured surface was studied by laser microscopy and scanning electron microscopy (SEM), while the chemical composition of the surface was determined by IR spectroscopy. The contact angles of water wetting in the textured areas varied versus laser fluence from about 100° to 10°, which was explained by both ablative removal of the hydrophobic polymer coating and the increase in roughness of the hydrophilic steel surface. The time dependence of the contact angle on the different textures, which demonstrated hydrophobization at different time scales depending on the texturing conditions, was analyzed. Autonomous directional flow was observed on laser-patterned wetting-gradient structures of various shapes, and the flow velocity of water droplets on these structures were measured. It was shown that the velocity of water drop spreading on the gradient structures depends on the difference in contact angles on adjacent spots. The various modules fabricated can be harnessed in chemical and biomedical microfluidic devices.

The characteristics of ventilated pool fires of Daegok-Sosa subway lines using Model-Scale tunnels and stations

The characteristics of ventilated pool fires for Daegok-Sosa subway lines with a length of 15.12 km in Seoul, South Korea were studied. The model-scale tunnels and stations were built in scale 1:50 and temperature distribution, smoke (Carbon Monoxide (CO)) spreading, back-layering phenomenon and longitudinal ventilated flow velocity were systematically investigated. Present subscale model was based on the Froude number similitude and a heptane pool fire was used as the heat source. Heat release rate of pool fire in model-scale tunnel was 1.13 kW corresponding to an equivalent 20 MW in full scale. The occurrence of smoke back-layering phenomenon could be observed by whether the upstream temperature rose at a certain position during the whole process of the fire test. In the single line parallel tunnel, the smoke was restricted to downstream of fire source, however, in the double track tunnel the smoke back layering slightly occurred in upstream region of fire source and then it soon disappeared. The smoke propagated far downstream side and the tunnel safety measures should be taken for passenger’s safe evacuation from the CO toxic gas. The longitudinal air velocities in upstream side near the fire source were accelerated and were about 11% higher than the downstream velocities in single line parallel tunnel and more than 20% higher in double track tunnel caused by the blocking effect of fire source. A generalized quasi one-dimensional flow network solver was employed to calculate the longitudinal air velocity in tunnels using the finite volume Ghost Junction Method (GJM) which were compared with the present experimental data. The required minimum longitudinal air velocities (2.0 m/sec for single line parallel tunnel and 2.5 m/sec for double track tunnel) specified in the Korean railway facility technical standards were well satisfied in this experiment.

Cortical depth-dependent modeling of visual hemodynamic responses

A physiologically based three-dimensional (3D) hemodynamic model is developed to predict the experimentally observed blood oxygen level dependent (BOLD) responses versus the cortical depth induced by visual stimuli. Prior 2D approximations are relaxed in order to analyze 3D blood flow dynamics as a function of cortical depth. Comparison of the predictions with experimental data for evoked stimuli demonstrates that the full 3D model performs at least as well as previous approaches while remaining parsimonious. In particular, the 3D model requires significantly fewer assumptions and model parameters than previous models such that there is no longer need to define depth-specific parameter values for spatial spreading, peak amplitude, and hemodynamic velocity.

Gα13 Mediates Transendothelial Migration of Neutrophils by Promoting Integrin-Dependent Motility without Affecting Directionality.

Neutrophil migration requires β2 integrins and chemoattractant receptor signaling for motility and directionality. G protein subunit Gα13 can facilitate cell migration by mediating RhoA activation induced by G protein-coupled receptors. However, the possible role of Gα13-integrin interaction in migration is unclear. In this study, we show that Gα13 -/- neutrophils are deficient in transendothelial migration and migration on β2 integrin ligand ICAM-1. However, unlike G protein-coupled receptors and integrin inside-out signaling pathways, Gα13 is important in migration velocity and neutrophil spreading but not in directionality nor cell adhesion. Importantly, neutrophil recruitment in vivo was also inhibited in Gα13 -/- mice, suggesting the importance of Gα13 in transendothelial migration of neutrophils in vitro and in vivo. Furthermore, a synthetic peptide (MB2mP6) derived from the Gα13 binding site of β2 inhibited Gα13-β2 interaction and Gα13-mediated transient RhoA inhibition in neutrophils, suggesting that this peptide inhibited integrin outside-in signaling. MB2mP6 inhibited migration of control neutrophils through endothelial cell monolayers or ICAM-1-coated filters, but was without further effect on Gα13 -/- neutrophils. It also inhibited integrin-dependent neutrophil migration velocity without affecting directionality. In vivo, MB2mP6 markedly inhibited neutrophil infiltration into the cardiac tissues induced by ischemia/reperfusion injury. Thus, Gα13-dependent outside-in signaling enables integrin-dependent neutrophil motility without affecting directionality and may be a new therapeutic target for inhibiting neutrophil trafficking but not adhesion.

Porcine Reproductive and Respiratory Syndrome (PRRS) Epidemiology in an Integrated Pig Company of Northern Italy: A Multilevel Threat Requiring Multilevel Interventions.

Porcine reproductive and respiratory syndrome (PRRS) is probably the most relevant viral disease affecting pig farming. Despite the remarkable efforts paid in terms of vaccination administration and biosecurity, eradication and long-term control have often been frustrated. Unfortunately, few studies are currently available that objectively link, using a formal statistical approach, viral molecular epidemiology to the risk factors determining the observed scenario. The purpose of the present study is to contribute to filling this knowledge gap taking advantage of the advancements in the field of phylodynamics. Approximately one-thousand ORF7 sequences were obtained from strains collected between 2004 and 2021 from the largest Italian pig company, which implements strict compartmentalization among independent three-sites (i.e., sow herds, nurseries and finishing units) pig flows. The history and dynamics of the viral population and its evolution over time were reconstructed and linked to managerial choices. The viral fluxes within and among independent pig flows were evaluated, and the contribution of other integrated pig companies and rurally risen pigs in mediating such spreading was investigated. Moreover, viral circulation in Northern Italy was reconstructed using a continuous phylogeographic approach, and the impact of several environmental features on PRRSV strain persistence and spreading velocity was assessed. The results demonstrate that PRRSV epidemiology is shaped by a multitude of factors, including pig herd management (e.g., immunization strategy), implementation of strict-independent pig flows, and environmental features (e.g., climate, altitude, pig density, road density, etc.) among the others. Small farms and rurally raised animals also emerged as a potential threat for larger, integrated companies. These pieces of evidence suggest that none of the implemented measures can be considered effective alone, and a multidimensional approach, ranging from individual herd management to collaboration and information sharing among different companies, is mandatory for effective infection control.

Disentangling cadherin-mediated cell-cell interactions in collective cancer cell migration

Cell dispersion from a confined area is fundamental in a number of biological processes, including cancer metastasis. To date, a quantitative understanding of the interplay of single-cell motility, cell proliferation, and intercellular contacts remains elusive. In particular, the role of E- and N-cadherin junctions, central components of intercellular contacts, is still controversial. Combining theoretical modeling with in vitro observations, we investigate the collective spreading behavior of colonies of human cancer cells (T24). The spreading of these colonies is driven by stochastic single-cell migration with frequent transient cell-cell contacts. We find that inhibition of E- and N-cadherin junctions decreases colony spreading and average spreading velocities, without affecting the strength of correlations in spreading velocities of neighboring cells. Based on a biophysical simulation model for cell migration, we show that the behavioral changes upon disruption of these junctions can be explained by reduced repulsive excluded volume interactions between cells. This suggests that in cancer cell migration, cadherin-based intercellular contacts sharpen cell boundaries leading to repulsive rather than cohesive interactions between cells, thereby promoting efficient cell spreading during collective migration.

Development of a Magnetic Cusp Gun for a 1-THz Harmonic Gyrotron

High-quality axis-encircling electron beam is essential to drive a high-harmonic gyrotron. A magnetic cusp gun that can generate a low-spread axis-encircling electron beam at an extremely high magnetic-compression ratio was developed for a 1-THz fourth-harmonic gyrotron toward continuous-wave operation. The optimized gun could generate an axis-encircling electron beam with 80-kV voltage, 1-A current, and a nearly constant pitch factor of about 1.5 in a wide range of magnetic field strength. The transverse velocity spread was less than 2.1% and the guiding center radius was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$26.6 ~\mu \text{m}$ </tex-math></inline-formula> . The design was verified by using MAGIC, EGUN, and CST simulations and good agreements were achieved.

Carnegie Supernova Project: The First Homogeneous Sample of Super-Chandrasekhar-mass/2003fg-like Type Ia Supernovae

Abstract We present a multiwavelength photometric and spectroscopic analysis of 13 super-Chandrasekhar-mass/2003fg-like Type Ia supernovae (SNe Ia). Nine of these objects were observed by the Carnegie Supernova Project. The 2003fg-like SNe have slowly declining light curves (Δm 15(B) &lt; 1.3 mag), and peak absolute B-band magnitudes of −19 &lt; M B &lt; −21 mag. Many of the 2003fg-like SNe are located in the same part of the luminosity–width relation as normal SNe Ia. In the optical B and V bands, the 2003fg-like SNe look like normal SNe Ia, but at redder wavelengths they diverge. Unlike other luminous SNe Ia, the 2003fg-like SNe generally have only one i-band maximum, which peaks after the epoch of the B-band maximum, while their near-IR (NIR) light-curve rise times can be ≳40 days longer than those of normal SNe Ia. They are also at least 1 mag brighter in the NIR bands than normal SNe Ia, peaking above M H = −19 mag, and generally have negative Hubble residuals, which may be the cause of some systematics in dark-energy experiments. Spectroscopically, the 2003fg-like SNe exhibit peculiarities such as unburnt carbon well past maximum light, a large spread (8000–12,000 km s−1) in Si ii λ6355 velocities at maximum light with no rapid early velocity decline, and no clear H-band break at +10 days. We find that SNe with a larger pseudo-equivalent width of C ii at maximum light have lower Si ii λ6355 velocities and more slowly declining light curves. There are also multiple factors that contribute to the peak luminosity of 2003fg-like SNe. The explosion of a C–O degenerate core inside a carbon-rich envelope is consistent with these observations. Such a configuration may come from the core-degenerate scenario.

Universal dynamical scaling laws in three-state quantum walks.

We perform a finite-time scaling analysis over the detrapping point of a three-state quantum walk on the line. The coin operator is parametrized by ρ that controls the wave packet spreading velocity. The input state prepared at the origin is set as a symmetric linear combination of two eigenstates of the coin operator with a characteristic mixing angle θ, one of them being the component that results in full spreading occurring at θ_{c}(ρ) for which no fraction of the wave packet remains trapped near the initial position. We show that relevant quantities, such as the survival probability and the participation ratio assume single parameter scaling forms at the vicinity of the detrapping angle θ_{c}. In particular, we show that the participation ratio grows linearly in time with a logarithmic correction, thus, shedding light on previous reports of sublinear behavior.

Superwicking Functionality of Femtosecond Laser Textured Aluminum at High Temperatures.

An advanced superwicking aluminum material based on a microgroove surface structure textured with both laser-induced periodic surface structures and fine microholes was produced by direct femtosecond laser nano/microstructuring technology. The created material demonstrates excellent wicking performance in a temperature range of 23 to 120 °C. The experiments on wicking dynamics show a record-high velocity of water spreading that achieves about 450 mm/s at 23 °C and 320 mm/s at 120 °C when the spreading water undergoes intensive boiling. The lifetime of classic Washburn capillary flow dynamics shortens as the temperature increases up to 80 °C. The effects of evaporation and boiling on water spreading become significant above 80 °C, resulting in vanishing of Washburn’s dynamics. Both the inertial and visco-inertial flow regimes are insignificantly affected by evaporation at temperatures below the boiling point of water. The boiling effect on the inertial regime is small at 120 °C; however, its effect on the visco-inertial regime is essential. The created material with effective wicking performance under water boiling conditions can find applications in Maisotsenko cycle (M-cycle) high-temperature heat/mass exchangers for enhancing power generation efficiency that is an important factor in reducing CO2 emissions and mitigation of the global climate change.

Efficiency Enhancement of a High Power Radial-Line Relativistic Klystron Amplifier Driven by Disk Intense Electron Beam

The power conversion efficiency of relativistic klystron amplifiers (RKAs) is severely limited by the strong space-charge repulsion force caused by the intense electron beam. A radial-line RKA (RL-RKA) driven by the disk beam may provide great potentials to alleviate this issue due to its radially propagating characteristic of the electron beam. However, such potential advantage of high efficiency has not been fully exploited in previous research due to the insufficient beam modulation and relatively low beam-wave coupling strength. In this article, an initial RL-RKA is improved significantly by utilizing a three-stage cascaded bunching link, a four-gap output cavity, and a lengthened drift tube. The three-stage cascaded bunching link plays a role in increasing the fundamental harmonic current and decreasing the velocity spread of the electron beam simultaneously. The four-gap output cavity is designed to improve the coupling impedance and strengthen the beam-wave power conversion. Moreover, a drift tube is lengthened suitably to boost the fundamental harmonic current further. Eventually, the power conversion efficiency of the RL-RKA is enhanced up to 67% by these measures, which indicates a significant advance over the initial state of 38%.

Cyclotron Resonance Maser With Zigzag Quasi-Optical Transmission Line: Concept and Modeling

A microwave system in the form of a quasi-optical (QO) transmission line is proposed as an interaction circuit of an amplifier or an oscillator based on the cyclotron resonance maser (CRM) instability. The circuit consists of periodically spaced along the horizontal <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${z}$ </tex-math></inline-formula> -axis focusing mirrors, which transport the Gaussian wave beam along a zigzag path with vertical and inclined segments. A beam of electrons having sufficiently high perpendicular velocities is guided by a static B-field along the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${z}$ </tex-math></inline-formula> -axis so that the e-beam periodically crosses the wave beam. The CRM instability occurs in regions where an electromagnetic wave having a Bz-component, as in a gyrotron, propagates strictly across the e-beam resulting in the interaction with minimal sensitivity to particle velocity spread. Three-dimensional Particle-In-Cell (3-D PIC) simulations demonstrate the attractiveness of this “zigzag” CRM for the implementation of relatively broadband amplifiers or oscillators with unique (more than an octave bandwidth) frequency tunability at wavelengths of 1–2 mm.

Deceleration and Trapping of SrF Molecules.

We report on the electrostatic trapping of neutral SrF molecules. The molecules are captured from a cryogenic buffer-gas beam source into the moving traps of a 4.5-m-long traveling-wave Stark decelerator. The SrF molecules in X^{2}Σ^{+}(v=0,N=1) state are brought to rest as the velocity of the moving traps is gradually reduced from 190 m/s to zero. The molecules are held for up to 50ms in multiple electric traps of the decelerator. The trapped packets have a volume (FWHM) of 1 mm^{3} and a velocity spread of 5(1) m/s, which corresponds to a temperature of 60(20)mK. Our result demonstrates a factor 3 increase in the molecular mass that has been Stark decelerated and trapped. Heavy molecules (mass>100 amu) offer a highly increased sensitivity to probe physics beyond the standard model. This work significantly extends the species of neutral molecules of which slow beams can be created for collision studies, precision measurement, and trapping experiments.

Design and Simulation Investigations of W-Band Second Harmonic Periodically Dielectric-Loaded Gyro-TWT

ABSTRACT In this article, the complete design and beam-wave interaction studies of W-band gyro-TWT amplifier have been presented. The gyro-TWT has been designed to operate at second harmonic TE 02 mode to reduce the magnetic field requirement. A triode-type magnetron injection gun has been designed and optimized for low-velocity spread using E-GUN. A novel, mode selective input coupler with a gradually tapered slotted waveguide has been used to feed the desired TE 02 mode and suppress the reflection and spurious oscillations at the input end (upstream). To abridge the absolute instability of the operating mode and backward wave oscillations caused by spurious modes, a periodic lossy dielectric-loaded RF structure has been adopted. The particle-in-cell simulation of the amplifier predicted a peak RF output power of ∼500 kW with ∼3.6 GHz bandwidth, ∼20% efficiency, and ∼32.2 dB saturated gain for the DC input of 100 kV, ∼25 A with 4% axial velocity spread and velocity ratio of 1.22. Further, to extract the output power with minimum reflection, a double-disc window has been studied. An undepressed curved collector is also designed using E-GUN and its simulation predicted a maximum heat wall loading of ∼0.39 kW /cm2.

Investigation of a Multibeam Magnetron Injection Gun for a W-Band Sectorial-Tunnel Gyro-TWT

In order to enhance the power capacity of gyro-traveling wave tube (Gyro-TWT), a novel multisectorial-tunnel circuit is presented in this article. The multisectorial tunnel could extend the transverse dimension of RF circuit for higher power electron beam transportation. The azimuthal drifting and transportation distortion performance for rotated electron beam are analyzed. A multibeam magnetron injection gun (MIG) is designed. The electron beam with pitch factor of 1.09 and axial velocity spread of 3.5% is obtained. And the designed cathode was fabricated and temperature distribution was measured. It provides a possible method to enhance the power capacity of Gyro-TWT.