Wah-keat Lee - Academia.edu (original) (raw)

Papers by Wah-keat Lee

A direct measurement of three-dimensional X-ray velocimetry with micrometer spatial resolution is... more A direct measurement of three-dimensional X-ray velocimetry with micrometer spatial resolution is presented. The key to this development is the use of a Laue crystal as an X-ray beam splitter and mirror. Three-dimensional flow velocities in a 0.4 mm-diameter tubing were recorded, with <5 mm spatial resolution and speeds of 0.7 mm s 1. This development paves the way for three-dimensional velocimetry in many cases where visible-light techniques are not effective, such as multiphase flow or flow of optically opaque liquids. Keywords: X-ray imaging; 3D velocimetry; stereo imaging; 3D particle tracking; 3D flow velocimetry. 1.

Energy Storage Materials, 2020

LiCoO 2 (LCO) possess a high theoretical specific capacity of 274 mAh g À1 , and currently LCO ch... more LiCoO 2 (LCO) possess a high theoretical specific capacity of 274 mAh g À1 , and currently LCO charged to 4.48 V with a capacity of~190-195 mAh g À1 is penetrating the commercial markets. Scalable strategies to further enhance the performance of LCO are highly attractive. Here, we develop a scalable ball-milling and sintering method to tackle this long-standing challenge by modifying LCO surface with only 1.5-3.5% ceramic solid electrolyte nanoparticles, specifically Li 1.5 Al 0.5 Ge 1.5 (PO 4) 3 (LAGP) as an example. Consequently, the atomic-tomeso multiscale structural stabilities have been significantly improved, even with a high cutoff voltage of 4.5 V vs. Li/Li þ , leading to excellent electrochemical stabilities. The nano-LAGP modified Li|LCO cell exhibits high discharge capacity of 196 mAh g À1 at 0.1 C, capacity retention of 88% over 400 cycles, and remarkably enhanced rate capability (163 mAh g À1 at 6 C). These results show significant improvement compared to the Li|LCO cells. The as-prepared graphite|LAGP-LCO full cells also show steady cycling with 80.4% capacity retention after 200 cycles with a voltage cutoff of 4.45 V. This work provides a simple and scalable approach to achieve stable cycling of LCO at high voltage with high energy density.

Fluids, 2017

Improved knowledge of the magnetic field dependent flow properties of nanoparticle-based magnetic... more Improved knowledge of the magnetic field dependent flow properties of nanoparticle-based magnetic fluids is critical to the design of biomedical applications, including drug delivery and cell sorting. To probe the rheology of ferrofluid on a sub-millimeter scale, we examine the paths of 550 µm diameter glass spheres falling due to gravity in dilute ferrofluid, imposing a uniform magnetic field at an angle with respect to the vertical. Visualization of the spheres' trajectories is achieved using high resolution X-ray phase-contrast imaging, allowing measurement of a terminal velocity while simultaneously revealing the formation of an array of long thread-like accumulations of magnetic nanoparticles. Drag on the sphere is largest when the applied field is normal to the path of the falling sphere, and smallest when the field and trajectory are aligned. A Stokes drag-based analysis is performed to extract an empirical tensorial viscosity from the data. We propose an approximate physical model for the observed anisotropic drag, based on the resistive force theory drag acting on a fixed non-interacting array of slender threads, aligned parallel to the magnetic field.

Advances in experimental medicine and biology, 2016

Insects are small relative to vertebrates, and were larger in the Paleozoic when atmospheric oxyg... more Insects are small relative to vertebrates, and were larger in the Paleozoic when atmospheric oxygen levels were higher. The safety margin for oxygen delivery does not increase in larger insects, due to an increased mass-specific investment in the tracheal system and a greater use of convection in larger insects. Prior studies have shown that the dimensions and number of tracheal system branches varies inversely with rearing oxygen in embryonic and larval insects. Here we tested whether rearing in 10, 21, or 40 kPa atmospheric oxygen atmospheres for 5-7 generations affected the tracheal dimensions and diffusing capacities of pupal and adult Drosophila. Abdominal tracheae and pupal snorkel tracheae showed weak responses to oxygen, while leg tracheae showed strong, but imperfect compensatory changes. The diffusing capacity of leg tracheae appears closely matched to predicted oxygen transport needs by diffusion, perhaps explaining the consistent and significant responses of these trache...

National Synchrotron Light Source II (NSLS-II) is a new state-of-the-art 3rd generation synchrotr... more National Synchrotron Light Source II (NSLS-II) is a new state-of-the-art 3rd generation synchrotron. The NSLS-II facility is shielded up to 3 GeV electron beam energy at 500 mA. When the gas bremsstrahlung (GB) from the storage ring is scattered by the beamline components in the first optical enclosure (FOE), the scattered radiation will pose additional radiation hazard (bypassing primary GB collimators and stops) and challenge the FOE shielding. The scattered GB radiation hazard can be mitigated by supplementary shielding or with an exclusion zone downstream of the FOE.

Here, the assumption is that the MTDwater::: 3 MTDgallium. This assumption comes from past empiri... more Here, the assumption is that the MTDwater::: 3 MTDgallium. This assumption comes from past empirical observations. Theoretical calculations [2,3] suggest that, depending on the actual geometry, MTDwater ::: 1.5-2.5 tv1TD ga liium. Thus, for example, in figure 26, the MTD for the liquid-galliumcooled slotted crystal ranges from 4-7 0 C. We assume then, that if water were used as a coolant instead, the MTD ranges would be from 12-2P C, as shown in figure 27.

SPIE Proceedings, 1998

A beam chopper together with the temporal structure of x-rays emitted by a synchrotrons storage r... more A beam chopper together with the temporal structure of x-rays emitted by a synchrotrons storage ring can be utilized to generate x-ray bursts of variable length and time separation. A Si cube, cut for diffraction from the (220) planes, was mounted to a low-speed motor to produce abeam chopper based upon the Darwin width of the crystal. An x-ray puke, consisting of an envelope of individual pulses characterizing the loading pattern of the storage ring, was transmitted. The width of the transmitted pulse and the time between pukes was varied by varying the rotation frequency of the Si cube. Pulses as short as = 75 ps or as long as = 4 ps were transmitted with pulse separation spanning from 4 ms to 167 ms.

MRS Proceedings, 2004

ABSTRACTInterpenetrating Al2O3/Al composites were created by liquid-metal infiltration of alumina... more ABSTRACTInterpenetrating Al2O3/Al composites were created by liquid-metal infiltration of alumina preforms with three-dimensional periodicity produced by a robotic deposition method. Volume-averaged lattice strains in the alumina phase were measured by synchrotron x-ray diffraction at various uniaxial compression stresses up to 350 MPa. Load transfer, which is experimentally found to occur between the aluminum and the alumina phase, is in agreement with simple rule of mixtures models. Spatially resolved measurements showed variations in load transfer at different positions within the composite for the elastic-, plastic-, and damage-deformation regimes. Using phase-enhanced imaging, the extent of damage within the composites was observed.

Physical Review E, 2010

Deformation and aggregation of bubbles in magnetic fluid ͑ferrofluid͒ can be observed at high res... more Deformation and aggregation of bubbles in magnetic fluid ͑ferrofluid͒ can be observed at high resolution by x-ray phase-contrast imaging. Images of gas bubbles in water-based ferrofluid ͑EMG-607/707͒ reveal that bubbles with diameters of a few hundreds of microns deform only slightly in applied fields up to 0.2 T, becoming prolate along the field direction. Also, neighboring bubbles readily attract one another along the field direction, forming linear chains of two or more bubbles. Comparison of experimentally measured bubble trajectories with direct numerical simulations and theoretical predictions shows that aggregation of bubbles under an externally applied field is driven by the attractive magnetophoretic force resulting from the induced fields of the bubbles. Direct numerical simulations were performed with a volume-of-fluid code that incorporates a multiple-color function scheme, to suppress numerical bubble merger, as well as Maxwell stresses as an interfacial force.

SPIE Proceedings, 1996

This paper describes the design, expected performance, and preliminary test results of a contact-... more This paper describes the design, expected performance, and preliminary test results of a contact-cooled monochromator for use on high heat load x-ray beamlines. The monochromator has a cross section in the shape of the letter U. This monochromator should be suitable for handing heat fluxes up to 5 W/rnm2. As such,fur the present application, it is compatible with the best internally cooled crystal monochromators. There are three key features in the design of this monochromator. First, it is contact cooled, thereby eliminating fabrication of cooling channels, bonding, and undesirable strains in the monochromator due to coolant-manifold-to-crystal-interface. Second, by illuminating the entire length of the crystal and extracting the central part of the reflected beam, sharp slope changes in the beam profile and thus slope errors are avoided. Last, by appropriate cooling of the crystal, tangential slope error can be substantially reduced.

Journal of Experimental Biology, 2013

Summary Abdominal pumping in caterpillars has only been documented during molting. Using synchrot... more Summary Abdominal pumping in caterpillars has only been documented during molting. Using synchrotron x-ray imaging in conjunction with high-speed flow-through respirometry, we show that Manduca sexta L. caterpillars cyclically contract their bodies in response to hypoxia, resulting in significant compressions of the tracheal system. Compression of tracheae induced by abdominal pumping drives external gas exchange, as evidenced by the high correlation between CO2 emission peaks and body movements. During abdominal pumping, both the frequency and percent diameter change of tracheae increased with body mass. However, abdominal pumping and tracheal compression were only observed in larger, older caterpillars (>0.2 g body mass), suggesting that this hypoxic response increases during ontogeny. The diameters of major tracheae in the thorax increased isometrically with body mass. However, tracheae in the head did not scale with mass, suggesting that there is a large safety margin for oxy...

Soft Matter, 2014

In a non-uniform magnetic field, the droplets of colloids of nickel nanorods and nanoparticles ag... more In a non-uniform magnetic field, the droplets of colloids of nickel nanorods and nanoparticles aggregate to form a cusp at the droplet surface not deforming the entire droplet shape. When the field is removed, nanorods diffuse away and cusp disappears. Spherical particles can form cusps in a similar way, but they stay aggregated after release of the field; finally, the aggregates settle down to the bottom of the drop. X-ray phase contrast imaging reveals that nanorods in the cusps stay parallel to each other without visible spatial order of their centers of mass. Formation of cusps can be explained with a model that includes magnetostatic and surface tension forces. The discovered possibility of controlled assembly and quenching of nanorod orientation under the cusped liquid surface offers vast opportunities for alignment of carbon nanotubes, nanowires and nanoscrolls, prior to spinning them into superstrong and multifunctional fibers. Magneto and electrostatic analogy suggests that similar ideal alignment can be achieved with the rod-like dipoles subject to a strong electric filed.

Science, 2003

Insects are known to exchange respiratory gases in their system of tracheal tubes by using either... more Insects are known to exchange respiratory gases in their system of tracheal tubes by using either diffusion or changes in internal pressure that are produced through body motion or hemolymph circulation. However, the inability to see inside living insects has limited our understanding of their respiration mechanisms. We used a synchrotron beam to obtain x-ray videos of living, breathing insects. Beetles, crickets, and ants exhibited rapid cycles of tracheal compression and expansion in the head and thorax. Body movements and hemolymph circulation cannot account for these cycles; therefore, our observations demonstrate a previously unknown mechanism of respiration in insects analogous to the inflation and deflation of vertebrate lungs.

Proceedings of the National Academy of Sciences, 2007

Recent studies have suggested that Paleozoic hyperoxia enabled animal gigantism, and the subseque... more Recent studies have suggested that Paleozoic hyperoxia enabled animal gigantism, and the subsequent hypoxia drove a reduction in animal size. This evolutionary hypothesis depends on the argument that gas exchange in many invertebrates and skin-breathing vertebrates becomes compromised at large sizes because of distance effects on diffusion. In contrast to vertebrates, which use respiratory and circulatory systems in series, gas exchange in insects is almost exclusively determined by the tracheal system, providing a particularly suitable model to investigate possible limitations of oxygen delivery on size. In this study, we used synchrotron x-ray phase–contrast imaging to visualize the tracheal system and quantify its dimensions in four species of darkling beetles varying in mass by 3 orders of magnitude. We document that, in striking contrast to the pattern observed in vertebrates, larger insects devote a greater fraction of their body to the respiratory system, as tracheal volume s...

PLoS ONE, 2009

Although the biochemical correlates of freeze tolerance in insects are becoming well-known, the p... more Although the biochemical correlates of freeze tolerance in insects are becoming well-known, the process of ice formation in vivo is subject to speculation. We used synchrotron x-rays to directly visualise real-time ice formation at 3.3 Hz in intact insects. We observed freezing in diapausing 3 rd instar larvae of Chymomyza amoena (Diptera: Drosophilidae), which survive freezing if it occurs above 214uC, and non-diapausing 3 rd instar larvae of C. amoena and Drosophila melanogaster (Diptera: Drosophilidae), neither of which survive freezing. Freezing was readily observed in all larvae, and on one occasion the gut was seen to freeze separately from the haemocoel. There were no apparent qualitative differences in ice formation between freeze tolerant and non-freeze tolerant larvae. The time to complete freezing was positively related to temperature of nucleation (supercooling point, SCP), and SCP declined with decreasing body size, although this relationship was less strong in diapausing C. amoena. Nucleation generally occurred at a contact point with the thermocouple or chamber wall in nondiapausing larvae, but at random in diapausing larvae, suggesting that the latter have some control over ice nucleation. There were no apparent differences between freeze tolerant and non-freeze tolerant larvae in tracheal displacement or distension of the body during freezing, although there was markedly more distension in D. melanogaster than in C. amoena regardless of diapause state. We conclude that although control of ice nucleation appears to be important in freeze tolerant individuals, the physical ice formation process itself does not differ among larvae that can and cannot survive freezing. This suggests that a focus on cellular and biochemical mechanisms is appropriate and may reveal the primary adaptations allowing freeze tolerance in insects.

Optics Express, 2011

Fresnel zone plates (450 nm thick Au, 25 nm outermost zone width) used as objective lenses in a f... more Fresnel zone plates (450 nm thick Au, 25 nm outermost zone width) used as objective lenses in a full field transmission reached a spatial resolution better than 20 nm and 1.5% efficiency with 8 keV photons. Zernike phase contrast was also realized without compromising the resolution. These are very significant achievements in the rapid progress of high-aspect-ratio zone plate fabrication by combined electron beam lithography and electrodeposition.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1992

This report was prepared as an account of work sponsored by an agency of the United States Govern... more This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their ,_ _.,.._-_,, ;_ _)_ employees, makes any warranty, express or implied, or assumes any legal liability or responsi-_tt_ ___,f_' '_.._ _ t_,' un% bility for the accuracy, completeness, or usefulness of any information, apparatus, product, or _]_| _'_.%j_ process disclosed, or represents that its use would not infringe privately owned rights. Rcfcr.. ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitutc or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed hcrcin do not necessarily state or rcflect those of the United States Government or any agency thereof.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1992

C Z The submitted manuscript has been authored by a contractor of the U.S. Governmerlt under cont... more C Z The submitted manuscript has been authored by a contractor of the U.S. Governmerlt under contract No, W-31-109-ENG-38. Accordingly, the U. S. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U. S. Government purposes.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1992

CZ This report was prepared as an account of work sponsored by an agency of the United States Gov... more CZ This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer-cnc¢ herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise dots not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Energy Storage Materials, 2020

Fluids, 2017

Advances in experimental medicine and biology, 2016

SPIE Proceedings, 1998

MRS Proceedings, 2004

Physical Review E, 2010

SPIE Proceedings, 1996

Journal of Experimental Biology, 2013

Soft Matter, 2014

Science, 2003

Proceedings of the National Academy of Sciences, 2007

PLoS ONE, 2009

Optics Express, 2011

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1992