[Show abstract][Hide abstract] ABSTRACT: For the last decade, a propagation-based X-ray imaging technique has been used for analysis of in- and near-nozzle flow characteristics of high-pressure fuel injectors. Despite remarkable progress has been made in the near-nozzle jet flow analysis, the structure and dynamics of in-nozzle flow have been difficult to be ana-lyzed due to severe X-ray absorption from the steel nozzle enclosure. In this study, we investigate the structure and dynamics of in-nozzle and emerging jet flow of a multi-hole GDI injector using a single-shot high-speed X-ray imaging technique. The multi-hole GDI injector was equipped with the aluminum (Al) nozzles containing the holes with different geometries. The high X-ray transmittance of the Al nozzles enabled the single-shot high-speed imaging of the in-nozzle flow using an ultra-short X-ray pulse with a 150 ps duration. At first, the transient characteristics of the in-nozzle flows were discussed using the X-ray images. Liquid fuel and bubbles coexisted inside the nozzle before the start of injection. As the needle lifts up, the geometric cavitation was formed inside the nozzle hole that reached nozzle outside, like a hydraulic flip. After the needle close, the bubbles were formed inside the sac, and they survived until the next injection event. Second, we characterized the effects of nozzle hole geometry on the structure and dynamics of in-nozzle and emerging jet flow at the steady-state of fuel in-jection. The geometric cavitations were usually formed at which the nozzle hole inlet angle is less than 90o. Two main flows were associated with the formation of geometric cavitation inside the nozzle hole, one directly ap-proaching from needle upstream and the other approaching from the sac that caused flow branching outside the nozzle. The flow branching was promoted as the nozzle hole inclination angle increased which resulted in an increase in the flow dispersion angle outside the nozzle. The initial jet flow characteristics of the multi-hole GDI injector seemed predominated by the bulk flow motion inside the nozzle rather than the formation of geometric cavitation inside the nozzle hole.
[Show abstract][Hide abstract] ABSTRACT: Despite the fact that all modern diesel engines use multi-hole injectors, single-hole injectors are frequently used to understand the fundamental properties of high-pressure diesel injections due to their axisymmetric design of the injector nozzles. A multi-hole injector accommodates many holes around the nozzle axis to deliver adequate amount of fuel with small orifices. The off-axis arrangement of the multi-hole injectors significantly alters the inter- and near-nozzle flow patterns compared to those of the single-hole injectors. This study compares the transient needle motion and near-nozzle flow characteristics of the single- and multi-hole (3-hole and 6-hole) diesel injectors to understand how the difference in hole arrangement and number affects the initial flow development of the diesel injectors. A propagation-based X-ray phase-contrast imaging technique was applied to compare the transient needle motion and near-nozzle flow characteristics of the single- and multi-hole injectors. The comparisons were made by dividing the entire injection process by three sub-stages: opening-transient, quasi-steady and closing-transient.
[Show abstract][Hide abstract] ABSTRACT: Self-assembly of nanoparticles at fluid interfaces has emerged as a simple yet efficient way to create two-dimensional membranes with tunable properties. In these membranes, inorganic nanoparticles are coated with a shell of organic ligands that interlock as spacers and provide tensile strength. Although curvature due to gradients in lipid-bilayer composition and protein scaffolding is a key feature of many biological membranes, creating gradients in nanoparticle membranes has been difficult. Here, we show by X-ray scattering that nanoparticle membranes formed at air/water interfaces exhibit a small but significant ∼6 Å difference in average ligand-shell thickness between their two sides. This affects surface-enhanced Raman scattering and can be used to fold detached free-standing membranes into tubes by exposure to electron beams. Molecular dynamics simulations elucidate the roles of ligand coverage and mobility in producing and maintaining this asymmetry. Understanding this Janus-like membrane asymmetry opens up new avenues for designing nanoparticle superstructures.
No preview · Article · Jun 2015 · Nature Materials
[Show abstract][Hide abstract] ABSTRACT: Photonic microsystems played an essential role in the development of integrated photonic devices, thanks to their unique spatiotemporal control and spectral shaping capabilities. Similar capabilities to markedly control and manipulate X-ray radiation are highly desirable but practically impossible due to the massive size of the silicon single-crystal optics currently used. Here we show that micromechanical systems can be used as X-ray optics to create and preserve the spatial, temporal and spectral correlation of the X-rays. We demonstrate that, as X-ray reflective optics they can maintain the wavefront properties with nearly 100% reflectivity, and as a dynamic diffractive optics they can generate nanosecond time windows with over 100-kHz repetition rates. Since X-ray photonic microsystems can be easily incorporated into lab-based and next-generation synchrotron X-ray sources, they bring unprecedented design flexibility for future dynamic and miniature X-ray optics for focusing, wavefront manipulation, multicolour dispersion, and pulse slicing.
Full-text · Article · May 2015 · Nature Communications
[Show abstract][Hide abstract] ABSTRACT: The current study takes a morphological approach to interpret the emerging jet flows from multi-hole
diesel injectors. Several types of multi-hole injectors, a six-hole injector and two two-hole injectors with
different needle control mechanisms, were used to investigate the emerging jet flows and related flow
breakup at different needle lifts. A short X-ray pulse with 150 ps duration was used to visualize the nearfield
morphologies of the emerging jet flows using an ultrafast X-ray phase-contrast imaging technique.
A few X-ray pulses with 68 ns periodicity were also used to analyze the dynamics of the emerging jet
flows by tracking the movement of the structures inside the spray. At first, the effects of needle lift on
emerging flow pattern and breakup were investigated using a six-hole injector under practical injection
conditions. A highly expanding spray was observed at the low needle lifts. The degree of flow expansion
was however suppressed with an increase in the needle lift. The higher degree of flow expansion at the
low needle lifts promoted the flow breakup and increased the spray deceleration rate with an increase
in the axial distance. Then, a detailed morphological study of the emerging flows was performed using
two-hole nozzles under low injection pressures to slow down the flow breakup in order to figure out
the intrinsic nature of the emerging flows associated with the nozzle internal flow. The phase-contrast
images revealed clear morphologies of several branching flows inside the spray having different flowing
directions and stretching the spray three-dimensionally that originate from complex nozzle internal flow
pattern. The degree of flow expansion associated with the branching flows appeared differently with the
needle lift with formation of various flow structures: cone shaped, stretched thin, and cylindrical. At
certain needle lifts, the branching flows sometimes formed a couple of microwavelets inside the spray
having different instability frequencies, indicating different origins of each flow associated with nozzle
internal flow. Increasing ambient gas density did not alter the branching characteristics of the flows
significantly, while increasing injection pressure and reducing the fuel viscosity significantly altered the
branching flow characteristics.
No preview · Article · May 2015 · Atomization and Sprays
[Show abstract][Hide abstract] ABSTRACT: Grazing-Incidence Small Angle X-ray Scattering (GISAXS) offers the ability to probe large sample areas, providing three-dimensional structural information at high detail in a thin film geometry. In this study we exploit the application of GISAXS to structures formed at one step of the LiNe (Liu-Nealey) flow using chemical patterns for directed self-assembly of block copolymer films. Experiments conducted at the Argonne National Laboratory provided scattering patterns probing film characteristics at both parallel and normal directions to the surface. We demonstrate the application of new computational methods to construct models based on scattering measured. Such analysis allows for extraction of structural characteristics at unprecedented detail.
No preview · Article · Mar 2015 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: Despite the fact that all modern diesel engines use multi-hole injectors, single-hole injectors are frequently used to understand the fundamental properties of high-pressure diesel injections due to their axisymmetric design of the injector nozzles. A multi-hole injector accommodates many holes around the nozzle axis to deliver adequate amount of fuel with small orifices. The off-axis arrangement of the multi-hole injectors significantly alters the inter- and near-nozzle flow patterns compared to those of the single-hole injectors. This study compares the transient needle motion and near-nozzle flow characteristics of the single- and multi-hole (3-hole and 6-hole) diesel injectors to understand how the
difference in hole arrangement and number affects the initial flow development of the diesel injectors. A propagation-based X-ray phase-contrast imaging technique was applied to compare the transient needle motion and near-nozzle flow characteristics of the single- and multi-hole injectors. The comparisons were made by dividing the entire injection process by three sub-stages: opening-transient, quasi-steady and closing-transient.
[Show abstract][Hide abstract] ABSTRACT: The thermoreversible self-assembly of poly(methyl methacrylate)-b-poly(tert-butyl methacrylate) (PMMA–PtBMA) diblock copolymers in 2-ethylhexanol has been studied in the transition regime between spherical and cylindrical morphologies. In these materials the PMMA block exhibits a strong temperature dependence of the solvent quality that leads to reversible micelle formation, and the PtBMA block is a versatile polymer that can be hydrolyzed for further use as a polyelectrolyte. Self-consistent field theory was used in combination with a variety of experimental techniques to develop a simple criterion for the location of the sphere/cylinder transition in solutions with concentrations above the micelle overlap threshold. It is shown that the effective volume fraction of PMMA core, accounting for solvent swelling of the micelle core, is equal to ≈0.27 at the sphere/cylinder transition. For the spherical domain morphologies, a transition between disorded micelles and micelles packed on a body-centered-cubic lattice occurs when the micelle hydrodynamic radius of the micelle is comparable to the intermicelle spacing in the ordered micellar structure.
[Show abstract][Hide abstract] ABSTRACT: Selective mitochondrial clearance by autophagy is crucial for maintaining proper cellular function and cellular homeostasis. Reticulocytes, which completely remove their mitochondria during terminal maturation, provide a good physiological model to study the mechanisms of such clearance. Nip-like protein X (Nix, also known as Bnip3L), an atypical BH3-only member of the Bcl-2 family, plays an essential role in mitochondrial autophagy occurring during erythroid maturation. Nix-/- reticulocytes show an abnormal retention of mitochondria and a defect in the sequestration of mitochondria by autophagosomes. Nix is not required for autophagosome formation; instead, its role in mitochondrial clearance during erythroid maturation likely involves both dissipation of mitochondrial membrane potential (δψm) and interaction with autophagosomes. Given that mitochondria are important organelles for energy production and regulation of cell death, elucidating the mechanisms underlying selective mitochondrial autophagy not only will help us to understand the mechanisms for erythroid maturation, but also may provide insights into mitochondrial quality control by autophagy in protection against aging, cancer, and neurodegenerative diseases.
[Show abstract][Hide abstract] ABSTRACT: Unveiling the near-field dynamics of high-speed and optically dense liquid fuel jets and sprays, such as velocity and turbulence intensity fields, is of great importance for successful interpretation and modeling of the spraying and combustion process in internal combustion engines. Characterizing the dynamics using conventional laser optical techniques have been difficult in the near-nozzle region where the fuel jet, ligaments, and droplets interact with visible light strongly producing severe multiple scattering and optical opacity. Here, we use a novel technique to characterize the velocity and turbulence intensity fields of the high-speed diesel sprays in the near-field by multi-exposed X-ray phase-contrast images. With the X-ray-imaging data, the effects of the orifice inlet geometry and injection pressure on the near-field dynamics of the diesel sprays are investigated. Notable features of the spray dynamics in the near-nozzle region and beyond are discussed by comparing the measurement results with the predictions of conventional gas jet theories.
[Show abstract][Hide abstract] ABSTRACT: Polymers that are thermally insulating in bulk forms have been found to exhibit higher thermal conductivities when stretched under tension. This enhanced heat transport performance is believed to arise from the orientational alignment of the polymer chains induced by tensile stretching. In this work, a novel high-sensitivity micro-device platform was employed to determine the axial thermal conductivity of individual Nylon-11 polymer nanofibers fabricated by electrospinning and post-stretching. Their thermal conductivity showed a correlation with the crystalline morphology measured by high-resolution wide-angle X-ray scattering. The relationship between the nanofiber internal structures and thermal conductivities could provide insights into the understanding of phonon transport mechanisms in polymeric systems and also guide future development of the fabrication and control of polymer nanofibers with extraordinary thermal performance and other desired properties.
[Show abstract][Hide abstract] ABSTRACT: Vaccination has been the most widely used strategy to protect against viral infections for centuries. However, the molecular mechanisms governing the long-term persistence of immunological memory in response to vaccines remain unclear. Here we show that autophagy has a critical role in the maintenance of memory B cells that protect against influenza virus infection. Memory B cells displayed elevated levels of basal autophagy with increased expression of genes that regulate autophagy initiation or autophagosome maturation. Mice with B cell-specific deletion of Atg7 (B/Atg7(-/-) mice) showed normal primary antibody responses after immunization against influenza but failed to generate protective secondary antibody responses when challenged with influenza viruses, resulting in high viral loads, widespread lung destruction and increased fatality. Our results suggest that autophagy is essential for the survival of virus-specific memory B cells in mice and the maintenance of protective antibody responses required to combat infections.
[Show abstract][Hide abstract] ABSTRACT: Cavitation is an intricate multiphase phenomenon that interplays with turbulence in fluid flows. It exhibits clear duality in characteristics, being both destructive and beneficial in our daily lives and industrial processes. Despite the multitude of occurrences of this phenomenon, highly dynamic and multiphase cavitating flows have not been fundamentally well understood in guiding the effort to harness the transient and localized power generated by this process. In a microscale, multiphase flow liquid injection system, we synergistically combined experiments using time-resolved x-radiography and a novel simulation method to reveal the relationship between the injector geometry and the in-nozzle cavitation quantitatively. We demonstrate that a slight alteration of the geometry on the micrometer scale can induce distinct laminar-like or cavitating flows, validating the multiphase computational fluid dynamics simulation. Furthermore, the simulation identifies a critical geometric parameter with which the high-speed flow undergoes an intriguing transition from non-cavitating to cavitating.
[Show abstract][Hide abstract] ABSTRACT: Improvement of spray atomization and penetration characteristics of the gasoline direct-injection (GDi) multihole injector is a critical component of the GDi combustion developments, especially in the context of engine downsizing and turbo-charging trend that is adopted in order to achieve the European target CO2, US CAFE, and concomitant stringent emissions standards. Significant R&D efforts are directed towards optimization of the nozzle designs, in order to improve the GDi multi-hole spray characteristics.
This publication reports VOF-LES analyses of GDi singlehole skew-angled nozzles, with β=30° skew (bend) angle and different nozzle geometries. The objective is to extend previous works to include the effect of nozzle-hole skew angle on the nozzle flow and spray primary breakup. VOFLES simulations of a single nozzle-hole of a purposedesigned
GDi multi-hole seat geometry, with three identical nozzle-holes per 120° seat segment, are performed. The simulations are complemented by comparison with the spray
near-field breakup structure obtained through optical shadowgraphy and phase-contrast x-ray imaging techniques.
The spray shadographic and X-ray imaging data reveal the jet primary breakup in the immediate vicinity of the nozzle, representative of the “atomization regime”. The jet
morphology indicate the effect of injector valve-group hydraulic pressure oscillations. The VOFLES simulations show fully-attached nozzle flow, and an “atomization regime” spray primary breakup in close agreement with the spray imaging data. The simulations highlight the effect of nozzle counter-bore on the jet primary atomization, through influence on the jet interface instability and, more notable, the physical interaction with the atomizing spray plume. Overall, the comparison of VOF-LES simulations with the spray imaging data shows good predictive capability with respect to the jet primary breakup, the plume macroscale features (trajectory, cone angle) and the observed effect of nozzle geometry.
[Show abstract][Hide abstract] ABSTRACT: Dendritic cells (DCs) are professional antigen-presenting cells that can regulate both innate and adaptive immune responses. Programmed cell death of DCs plays an important role in maintaining the homeostasis of DCs and in the regulation of immune responses. Methods to measure the rate of spontaneous and T cell-mediated cell death of DCs are described here. These procedures can be adapted to study the -induction of dendritic cell death in different settings of immune responses.
No preview · Article · Feb 2013 · Methods in molecular biology (Clifton, N.J.)
[Show abstract][Hide abstract] ABSTRACT: The pathway of interfacial self-assembly of large-scale, highly-ordered 2D nanoparticle/polymer monolayer or bilayer arrays from a toluene solution at an air/water interface was investigated using grazing-incidence small-angle scattering at a synchrotron source. Interfacial-assembly of the ordered nanoparticle/polymer array was found to occur through two stages: formation of an incipient randomly close-packed interfacial monolayer followed by compression of the monolayer to form a close-packed lattice driven by solvent evaporation from the polymer. Because the nanoparticles are hydrophobic, they localize exclusively to the polymer-air interface during self-assembly, creating a through thickness asymmetric film as confirmed by x-ray reflectivity. The interfacial self-assembly approach can be extended to form binary NP/polymer arrays. It is anticipated that by understanding the interfacial self-assembly pathway, this simple evaporative procedure could be conducted as a continuous process amenable to large area nanoparticle-based manufacturing needed for emerging energy technologies.
[Show abstract][Hide abstract] ABSTRACT: Engagement of the TCR induces activation-induced cell death (AICD) of T cells that have been previously stimulated. However, a portion of these T cells can survive and undergo further activation. The molecular mechanism that decides whether a T cell will live or die after TCR re-engagement is unclear. We found that cross-linking of TCR in preactivated primary mouse T cells led to the cleavage of anti-apoptotic Bcl-2 and Bcl-xL in dying cells. Cleavage-resistant Bcl-2 and Bcl-xL were more efficient than their wild-type counterparts in the inhibition of apoptosis in primary mouse T cells and in the H9 T cell line after TCR cross-linking. In contrast, the surviving T cells after TCR re-engagement displayed upregulation of Bcl-xL, and knockdown of Bcl-xL promoted AICD. This indicates that caspase-mediated cleavage of anti-apoptotic Bcl-2 or Bcl-xL facilitates AICD in T cells, whereas upregulation of Bcl-xL promotes T cell survival and allows further T cell activation. Our data suggest that cleavage of anti-apoptotic Bcl-2 and Bcl-xL contributes to the decision between T cell activation and apoptosis after TCR re-engagement.
No preview · Article · Nov 2012 · The Journal of Immunology
[Show abstract][Hide abstract] ABSTRACT: We demonstrate the use of electrostatically driven
micro-electromechanical systems (MEMS) devices to control and deliver
synchrotron x-ray pulses at high repetition rates. Torsional MEMS
micromirrors, rotating at duty cycles of 2 kHz and higher, were used to
modulate grazing-incidence x rays, producing x-ray bunches shorter than
10 μs. We find that dynamic deformation of the oscillating
micromirror is a limiting factor in the duration of the x-ray pulses
produced, and we describe plans for reaching higher operating
frequencies using mirrors designed for minimal deformation.
No preview · Article · Oct 2012 · Proceedings of SPIE - The International Society for Optical Engineering