Planar Expansion Research Articles

Characterization of material ablation driven by laser generated intense extreme ultraviolet light

We present a comparative study on the hydrodynamic behaviour of plasmas generated by material ablation by the irradiation of nanosecond extreme ultraviolet (EUV or XUV) or infrared laser pulses on solid samples. It was clarified that the difference in the photon energy deposition and following material heating mechanism between these two lights result in the difference in the plasma parameters and plasma expansion characteristics. Silicon plate was ablated by either focused intense EUV pulse (λ = 9–25 nm, 10 ns) or laser pulse (λ = 1064 nm, 10 ns), both with an intensity of ∼109 W/cm2. Both the angular distributions and energy spectra of the expanding ions revealed that the photoionized plasma generated by the EUV light differs significantly from that produced by the laser. The laser-generated plasma undergoes spherical expansion, whereas the EUV-generated plasma undergoes planar expansion in a comparatively narrow angular range. It is presumed that the EUV radiation is transmitted through the expanding plasma and directly photoionizes the samples in the solid phase, consequently forming a high-density and high-pressure plasma. Due to a steep pressure gradient along the direction of the target normal, the EUV plasma expands straightforward resulting in the narrower angular distribution observed.

Porous composite with negative thermal expansion obtained by photopolymer additive manufacturing

Additive manufacturing (AM) could be a novel method of fabricating composite and porous materials having various effective performances based on mechanisms of their internal geometries. Materials fabricated by AM could rapidly be used in industrial application since they could easily be embedded in the target part employing the same AM process used for the bulk material. Furthermore, multi-material AM has greater potential than usual single-material AM in producing materials with effective properties. Negative thermal expansion is a representative effective material property realized by designing a composite made of two materials with different coefficients of thermal expansion. In this study, we developed a porous composite having planar negative thermal expansion by employing multi-material photopolymer AM. After measurement of the physical properties of bulk photopolymers, the internal geometry was designed by topology optimization, which is the most effective structural optimization in terms of both minimizing thermal stress and maximizing stiffness. The designed structure was converted to a three-dimensional stereolithography (STL) model, which is a native digital format of AM, and assembled as a test piece. The thermal expansions of the specimens were measured using a laser scanning dilatometer. Negative thermal expansion corresponding to less than −1 × 10−4 K−1 was observed for each test piece of the N = 3 experiment.

Radius of curvature analysis of oscillating follower cylindrical cam’s expansion pitch curve

The currently used method to calculate radius of curvature of a cylindrical cam’s planar expansion pitch curve produces errors. Therefore, there is an urgent need to find an accurate method for cylindrical cam design. This research utilizes the three-dimensional expansion curve coordinates of the follower’s motion track and establishes the planar expansion pitch curve equation with the consideration of deviation angle, which can be easily used to analyze and design an oscillating follower cylindrical cam. The deduced equation of radius of curvature is based on motion law of the mechanism and prime cylinder radius of the cam. The relation curve between minimum radius of curvature and prime cylinder radius, which takes into consideration that planar expansion pitch curve varies with prime cylinder radius in the event of certain motion law, is described by MATLAB, and specific minimum radius of prime cylinder is generated for each allowable radius of curvature according to the relation curve. Thus, geometric parameters of a cylindrical cam can be designed. The feasibility of our methodology is validated with a specific example.

Temporal Hyporheic Zone Response to Water Table Fluctuations.

Expansion and contraction of the hyporheic zone due to temporal hydrologic changes between stream and riparian aquifer influence the biogeochemical cycling capacity of streams. Theoretical studies have quantified the control of groundwater discharge on the depth of the hyporheic zone; however, observations of temporal groundwater controls are limited. In this study, we develop the concept of groundwater-dominated differential hyporheic zone expansion to explain the temporal control of groundwater discharge on the hyporheic zone in a third-order stream reach flowing through glacially derived terrain typical of the Great Lakes region. We define groundwater-dominated differential expansion of the hyporheic zone as: differing rates and magnitudes of hyporheic zone expansion in response to seasonal vs. storm-related water table fluctuation. Specific conductance and vertical hydraulic gradient measurements were used to map changes in the hyporheic zone during seasonal water table decline and storm events. Planar and riffle beds were monitored in order to distinguish the cause of increasing hyporheic zone depth. Planar bed seasonal expansion of the hyporheic zone was of a greater magnitude and longer in duration (weeks to months) than storm event expansion (hours to days). In contrast, the hyporheic zone beneath the riffle bed exhibited minimal expansion in response to seasonal groundwater decline compared to storm related expansion. Results indicated that fluctuation in the riparian water table controlled seasonal expansion of the hyporheic zone along the planar bed. This groundwater induced hyporheic zone expansion could increase the potential for biogeochemical cycling and natural attenuation.

Semi-analytical model of thin plasma layer expansion into vacuum

A practical model of a thin planar plasma layer expansion into vacuum is proposed, which makes it possible to rather simply determine spatiotemporal and spectral characteristics of accelerated ions for an arbitrary plasma electron temperature.

Investigation of pulse shape characteristics on the laser ablation dynamics of TiN coatings in the ns regime

In this work, the ablation dynamics of TiN coating with a ns-pulsed fibre laser in a wide range of pulse durations were studied. Critical time instances within the pulse duration were assessed by reflected pulse analysis. Digital holography was employed to investigate the shock wave expansion dynamics within and beyond the pulse duration. The results depict that the absorption behaviour changes as a function of the pulse rise time. Moreover, planar expansion of the shock wave is observed, which is generally linked to higher machining quality and absence of excessive plasma. The results of the study are interpreted to depict the required characteristics of optimized pulse shapes in the ns-region for improved micromachining performance.

A Planar Wobble Motor with a XY Compliant Mechanism Driven by Shape Memory Alloy

This paper describes the design concept, operating principle, analytical design, fabrication of a functional prototype, and experimental performance verification of a novel wobble motor with a XY compliant mechanism driven by shape memory alloy (SMA) wires. With the aim of realizing an SMA based motor which could generate bidirectional high-torque motion, the proposed motor is devised with wobble motor driving principle widely utilized for speed reducers. As a key mechanism which functions to guide wobbling motion, a planar XY compliant mechanism is designed and applied to the motor. Since the mechanism has monolithic flat structure with the planar mirror symmetric configuration, cyclic expansion and contraction of the SMA wires could be reliably converted into high-torque rotary motion. For systematic design of the motor, a characterization of electro-thermomechanical behavior of the SMA wire is experimentally carried out, and the design parametric analysis is conducted to determine parametric values of the XY compliant mechanism. The designed motor is fabricated as a functional prototype to experimentally investigate its operational feasibility and working performances. The observed experimental results obviously demonstrate the unique driving characteristics and practical applicability of the proposed motor.

Expansion wave diffraction over a 90 degree corner

AbstractThe diffraction of an initially one-dimensional plane expansion wave over a 90° corner was explored using experiment and numerical simulation. Unlike studies of shock diffraction, expansion wave diffraction has hardly been documented previously. The planar expansion wave was produced in a shock tube by bursting a diaphragm. Two independent parameters were identified for study: (i) the initial diaphragm shock tube pressure ratio, which determines the strength (pressure ratio) of the expansion, and (ii) the position of the diaphragm from the apex of the 90° corner, which determines the width of the wave. The experimentation only considered variation in the shock tube pressure ratio whereas the simulation varied both parameters. A Navier–Stokes solver with Menter’s shear stress transport $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}k\mbox{--}\omega $ turbulence model was found to adequately model the overall flow field. A number of major flow features were identified occurring in the vicinity of the corner. These were: a shear layer that originated by flow separation at the apex of the corner; a vortex within a separation bubble that remained attached to the wall, in sharp contrast to what happens in the shock wave diffraction case, where the vortex convects downstream; and a reflected compression wave arising from perturbation signals generated by the diffraction. For a narrow-width expansion wave existing prior to diffraction, the reflected compression wave steepens into an outwardly propagating, weak cylindrical shock wave. Regions of supersonic flow are identified surrounding the bubble and can extend downstream depending on the pressure ratio. Another major flow feature identified in some cases was an oblique shock located near the separation bubble. A large wake region is evident immediately downstream of the bubble and appears to consist of two distinct layers. The experimental results showed large-scale turbulent structures within the separation bubble, and shear layer instability and vortex shedding from the separation bubble were also evident.

The Effect of Bacterial Cellulose (BC) Fiber Content on the Properties of BC Fiber Reinforced Nanocomposites

Optically transparent nanocomposites were prepared by epoxy resin reinforced with bacterial cellulose nanofibers in volume fraction from 2.6 to 32.7wt%. The transparence, surface smoothness, thermal expansion and mechanic properties of the nanocomposites with different BC fiber content were characterized. It was found that the nanocomposites display high visible light transparence (84% at 600nm) even at high fiber content (32.7 wt%). The coefficient of planar thermal expansion (CTE) was reduced from 83.8 ppm/K (Epoxy resin) to 40.6 ppm/K at low fiber content (2.6 wt%). The high transparence was insensitive to the change of temperature from room temperature to 90 oC.

Gauge theories, D-branes and holography

Based on a generalization of the string theoretic concept of D-brane probe, we propose a new approach to large N gauge theories which makes the holographic properties manifest. For any gauge theory, we define from first principles an effective action for a fixed number of “probe” D-branes in the presence of N “background” D-branes on which the gauge theory lives. This effective action is shown to encode all the information about the large N gauge theory. The analysis of the planar diagram expansion which computes the effective action yields a simple and generic mechanism explaining the emergence of holographic space dimensions: the probe D-branes move in a higher dimensional dual holographic space–time. The construction yields a new perspective on the notion of bulk space–time locality and draws unexpected links with some aspects of the 't Hooft Abelian projection ideas. It also provides a new non-perturbative approximation scheme, able to capture both the weak and strong coupling regimes. We sketchily illustrate the basic ideas on a few examples, including the pure four dimensional Yang–Mills theory.

High-resolution infrared spectra of vibrationally excited HC4H in a supersonic hydrocarbon plasma jet

High-resolution infrared spectra of diacetylene (HC4H) are recorded in the 3μm CH stretch region using continuous wave cavity ring-down spectroscopy (cw-CRDS). The HC4H molecules are generated in a pulsed and supersonic planar plasma expansion by discharging a C2H2/He/Ar gas mixture. The jet-cooling realizes a low rotational temperature of Trot∼17K. Vibrational temperatures are found to be relatively high, allowing the detection of vibrationally excited HC4H in direct absorption with energies up to 1800cm−1. In total, sixteen ro-vibrational bands are identified, where nine of them were not reported before. Detailed and systematic rotational analyses are presented, yielding spectroscopic parameters for a series of vibrational levels over energy regions of 0–1800 and 3300–5100cm−1. Using the observed infrared band intensities, two vibrational excitation temperatures of HC4H in the plasma jet, ∼570(50) K for the ν6, ν7 and ν8 bending vibrations, and ∼125(10) K for the ν9 bending vibration, are deduced.

Flow of elasto-viscoplastic liquids through a planar expansion–contraction

The steady flow of incompressible elasto-viscoplastic liquids through a planar expansion–contraction is investigated. A novel constitutive model is employed to describe the mechanical behavior of the flowing liquids. Numerical solutions of the constitutive and conservation equations were obtained via a finite element method to investigate the role of elasticity, yield stress, and inertia. The fields of velocity, stress, elastic strain, and rate of strain were obtained for different combinations of the governing parameters. It was observed that these fields, as well as the shape and position of the yield surface, are all strong functions of elasticity, yield stress, and inertia. The trends observed agree well with previous numerical and visualization results available in the literature. The present work offers a detailed study on the effects of elasticity, presenting, in particular, the fields of elastic strain.

Allogeneic cell therapy bioprocess economics and optimization: Single‐use cell expansion technologies

For allogeneic cell therapies to reach their therapeutic potential, challenges related to achieving scalable and robust manufacturing processes will need to be addressed. A particular challenge is producing lot-sizes capable of meeting commercial demands of up to 109 cells/dose for large patient numbers due to the current limitations of expansion technologies. This article describes the application of a decisional tool to identify the most cost-effective expansion technologies for different scales of production as well as current gaps in the technology capabilities for allogeneic cell therapy manufacture. The tool integrates bioprocess economics with optimization to assess the economic competitiveness of planar and microcarrier-based cell expansion technologies. Visualization methods were used to identify the production scales where planar technologies will cease to be cost-effective and where microcarrier-based bioreactors become the only option. The tool outputs also predict that for the industry to be sustainable for high demand scenarios, significant increases will likely be needed in the performance capabilities of microcarrier-based systems. These data are presented using a technology S-curve as well as windows of operation to identify the combination of cell productivities and scale of single-use bioreactors required to meet future lot sizes. The modeling insights can be used to identify where future R&D investment should be focused to improve the performance of the most promising technologies so that they become a robust and scalable option that enables the cell therapy industry reach commercially relevant lot sizes. The tool outputs can facilitate decision-making very early on in development and be used to predict, and better manage, the risk of process changes needed as products proceed through the development pathway. Biotechnol. Bioeng. 2014;111: 69–83. © 2013 Wiley Periodicals, Inc.

Broadband Cavity Enhanced Absorption Spectroscopy: A New Approach to Search for DIB Carriers

AbstractA new and sensitive set-up to swiftly test proposed carriers of the diffuse interstellar bands (DIBs), over a relatively broad spectral range, is described. The instrument utilizes broad-band cavity enhanced absorption spectroscopy (BBCEAS) and incorporates an optomechanical shutter to modulate light from a continuous incoherent light source. A pulsed supersonically expanding planar plasma expansion is used to mimic conditions in translucent interstellar clouds. Measurements of plasma durations as low as 400 μs are possible. The sensitivity is estimated to be better than 10 ppm/pass, measured with an effective exposure time of only ca. 1 s. The performance and potential of the instrument is demonstrated on spectra of C5H, C6H and C9H3 recorded through expanding hydrocarbon plasma.

Steady flow of power-law fluids in a 1:3 planar sudden expansion

The laminar flow of inelastic non-Newtonian fluids, obeying the power-law model, through a planar sudden expansion with a 1:3 expansion ratio was investigated numerically using a finite volume method. A broad range of power-law indices in the range 0.2⩽n⩽4 was considered. Shear-thinning, Newtonian and shear-thickening fluids are analyzed, with particular emphasis on the flow patterns and bifurcation phenomenon occurring at high Reynolds number laminar flows. The effect of the generalized Reynolds number (based on power-law index, n, and the inflow channel height, h) on the main vortex characteristics and Couette correction are examined in detail in the range 0.01⩽Regen⩽600. Values for the critical generalized Reynolds number for the onset of steady flow asymmetry and the appearance of a third main vortex are also included. We found that the shear-thinning behavior increases the critical Regen, while shear-thickening has the opposite effect. Comparison with available literature and with predictions using a commercial software (Fluent® 6.3.26) are also presented and discussed. It was found that both results are in good agreement, and that our code is able to achieve converged solutions for a broad range of flow conditions, providing new benchmark quality data.

Mid-infrared continuous wave cavity ring-down spectroscopy of a pulsed hydrocarbon plasma

We describe an ultra-sensitive method to record high-resolution mid-IR spectra of hydrocarbon-chain species and other astrophysically relevant molecular transients in a pulsed planar plasma expansion. The method uses an all fiber-laser-based optical parametric oscillator (OPO) light source, in combination with continuous wave cavity ring-down spectroscopy (cw-CRDS) as a direct absorption detection tool. A hardware based multi-trigger concept is introduced to apply cw-CRDS to pulsed plasma. The performance and potential of the method are illustrated and discussed, based on extended and fully rotationally resolved sample spectra of HC4H and HC6H, generated in the discharge of an expanding C2H2/He/Ar gas mixture.

Modeling Asymmetric Flow of Viscoelastic Fluid in Symmetric Planar Sudden Expansion Geometry Based on User-Defined Function in FLUENT CFD Package

Through embedding an in-house subroutine into FLUENT code by utilizing the functionalization of user-defined function provided by the software, a new numerical simulation methodology on viscoelastic fluid flows has been established. In order to benchmark this methodology, numerical simulations under different viscoelastic fluid solution concentrations (with solvent viscosity ratio varied from 0.2 to 0.9), extensibility parameters ([Formula: see text]), Reynolds numbers (0.1 ≤ Re ≤ 100), and Weissenberg numbers (0 ≤ Wi ≤ 20) are conducted on unsteady laminar flows through a symmetric planar sudden expansion with expansion ratio of 1: 3 for viscoelastic fluid flows. The constitutive model used to describe the viscoelastic effect of viscoelastic fluid flow is FENE-P (finitely extensive nonlinear elastic-Peterlin) model. The numerical simulation results show that the influences of elasticity, inertia, and concentration on the flow bifurcation characteristics are more significant than those of extensibility. The present simulation results including the critical Reynolds number for which the flow becomes asymmetric, vortex size, bifurcation diagram, velocity distribution, streamline, and pressure loss show good agreements with some published results. That means the newly established method based on FLUENT software platform for simulating peculiar flow behaviors of viscoelastic fluid is credible and suitable for the study of viscoelastic fluid flows.

New large-Nlimit and the planar equivalence outside the planar limit

We consider a new large-$N$ limit, in which the 't Hooft coupling grows with $N$. We argue that a class of large-$N$ equivalences, which is known to hold in the 't Hooft limit, can be extended to this very strongly coupled limit. Hence this limit may lead to a new way of studying corrections to the 't Hooft limit, while keeping nice properties of the latter. As a concrete example, we describe large-$N$ equivalences between the Aharony, Bergman, Jafferis and Maldacena theory and its orientifold projection. The equivalence implies that operators neutral under the projection symmetry have the same correlation functions in two theories at large $N$. Usual field theory arguments are valid when 't Hooft coupling $\ensuremath{\lambda}\ensuremath{\sim}N/k$ is fixed and observables can be computed by using a planar diagrammatic expansion. With the help of the AdS/CFT correspondence, we argue that the equivalence extends to stronger coupling regions, $N\ensuremath{\gg}k$, including the M-theory region $N\ensuremath{\gg}{k}^{5}$. We further argue that the orbifold/orientifold equivalences between certain Yang-Mills theories can also be generalized. Such equivalences can be tested both analytically and numerically. Based on calculations of the free energy, we conjecture that the equivalences hold because planar dominance persists beyond the 't Hooft limit.

Transmission of near-limit detonation wave through a planar sudden expansion in a narrow channel

Transmission of single-cell and spinning detonation waves in C2H4+3(O2+βN2) mixtures through a 2-D sudden expansion experimentally studied using high-speed cinematography and soot film visualization. Nitrogen dilution ratio, β, is utilized to control cell size and detonation mode. Detonation wave of ethylene/oxygen/nitrogen mixture was initiated via DDT in the 1mm×1mm cross-section and 250mm long initiator channel before propagating into the 3mm×1mm receptor channel. Visualizations show that detonation waves were extinct and accompanied with abrupt decrease in visible reaction front propagating velocities right after passing through the sudden expansion. However, re-acceleration of the reaction front and re-initiation of the detonation wave were observed downstream in the expanded receptor section. Two re-initiation modes with large disparity in the re-initiation distance were experimentally characterized. For mixtures with nitrogen dilution ratio equals 0.3 or less, the cellular detonation front propagated with single cell in the initiator section before entering the sudden expansion. The re-initiation distance was less than 50mm and was likely achieved via shock reflection. Velocity characterization shows that steady propagating speed of the detonation wave is ∼100m/s higher in receptor section than in the initiator section. Since the cell size became larger than 1mm for mixtures with β⩾0.3, the detonation wave propagated in spinning detonation mode before transmitting into the expanded section. The reaction front would have to go through another DDT process to reach detonation state in the receptor section, and the re-initiation distance was increased to more than 150mm. Moreover, step height of the sudden expansion was proposed as the characteristic length scale to obtain a unified non-dimensional correlation between re-initiation distance and detonation cell size.

Optic tectum morphogenesis: A step-by-step model based on the temporal-spatial organization of the cell proliferation. Significance of deterministic and stochastic components subsumed in the spatial organization

Cell proliferation plays an important morphogenetic role. This work analyzes the temporal-spatial organization of cell proliferation as an attempt to understand its contribution to the chick optic tectum (OT) morphogenesis. A morphogenetic model based on space-dependent differences in cell proliferation is presented. Step1: a medial zone of high mitotic density (mZHMD) appears at the caudal zone. Step2: the mZHMD expands cephalically forming the dorsal curvature and then duplicates into two bilateral ZHMDs (bZHMD). Step3: the bZHMDs move toward the central region of each hemitectum. Step4: the planar expansion of both bZHMD and a relative decrement in the dorsal midline growth produces a dorsal medial groove separating the tectal hemispheres. Step5: a relative caudal displacement of the bZHMDs produces the OT caudal curvature. Numerical sequences derived from records of mitotic cells spatial coordinates, analyzed as stochastic point processes, show that they correspond to 1/f((β)) processes. The spatial organization subsumes deterministic and stochastic components. The deterministic component describes the presence of a long-range influence that installs an asymmetric distribution of cell proliferation, i.e., an asymmetrically located ZHMD that print space-dependent differences onto the tectal corticogenesis. The stochastic component reveals short-range anti-correlations reflecting spatial clusterization and synchronization between neighboring cells.