Bio

Bio


Dr Skinner is a Board certified therapeutic medical physicist with interests in novel 3D printed devices and a research background in synchrotron x-ray scattering, neutron scattering, molecular dynamics and Monte Carlo computational modelling.

Academic Appointments


Administrative Appointments


  • AAPM Northern California, Chapter Secretary (2019 - Present)
  • Chief Physics Resident, Stanford University (2018 - 2018)

Professional Education


  • Residency, Stanford University, Therapeutic Medical Physics (2018)
  • Pg. Cert., University of Chicago, Medical Physics (CAMPEP) (2016)
  • PhD, Bristol University (UK), Physics (condensed matter) (2009)
  • MSci, Bristol University (UK), Physics (2005)

Patents


  • Lawrie Skinner. "United States Patent S19-067/PROV -- ID:3935 Tungsten filled 3D printed field shaping devices for electron beam radiation therapy", Leland Stanford Junior University, Aug 10, 2019
  • Lawrie Skinner. "United States Patent PID:26564 A NOVEL INTEGRATED MULTI-MODAL PHANTOM FOR COMBINED DOSIMETRY AND POSITIONING VERIFICATION", Leland Stanford Junior Universit, Nov 19, 2018

Publications

All Publications


  • Impact of Audio-Visual Assisted Therapeutic Ambience in Radiotherapy (AVATAR) on Anesthesia Use, Payer Charges, and Treatment Time in Pediatric Patients. Practical radiation oncology Balazy, K. E., Gutkin, P. M., Skinner, L., von Eyben, R., Fowler, T., Pinkham, D. W., Rodriguez, S., Maxim, P. G., Donaldson, S. S., Loo, B. W., Bush, K., Hiniker, S. M. 2020

    Abstract

    PURPOSE: Pediatric radiotherapy requires optimal immobilization that often necessitates daily anesthesia. To decrease anesthesia use, we implemented a novel XXX system which projects video onto a radiolucent screen within the child's line of vision to provide attentional diversion. We investigated its reduction on anesthesia use, payer charges, and treatment time, as well as its impact on radiation delivery.METHODS AND MATERIALS: A 6-year retrospective analysis was performed among children undergoing radiotherapy (n=224), 3 years before and 3 after introduction of XXX. The frequency of anesthesia use before and after XXX implementation, as well as radiotherapy treatment times were compared. The number of spared anesthesia treatments allowed for a charge to payer analysis. To document lack of surface dose perturbation by XXX, a phantom craniospinal treatment course was delivered both with and without XXX. Additionally, an ion chamber course was delivered to document changes to dose at depth.RESULTS: More children were able to avoid anesthesia use entirely in the post-XXX cohort, compared to the pre-XXX cohort (73.2% vs 63.4%, p=0.03) and fewer required anesthesia for each treatment (18.8% vs 33%; p = 0.03). XXX introduction reduced anesthesia use for all ages studied. Treatment time per session was reduced by 38% using XXX compared to anesthesia. There were 326 fewer anesthesia sessions delivered over three years after XXX was introduced, with an estimated savings of > $500,000. OSLDs revealed a small increase in dose of 0.8%-9.5% with XXX, while the use of a thermomolded face mask increased skin dose as much as 58%.CONCLUSIONS: XXX introduction decreased anesthesia use in children undergoing radiotherapy; more avoided anesthesia entirely, and fewer needed it for every treatment. This resulted in a reduction in treatment time, and savings of nearly $550,000 in approximately 3 years, with minimal perturbation of radiotherapy dose delivery.

    View details for DOI 10.1016/j.prro.2019.12.009

    View details for PubMedID 31935524

  • An integrated quality assurance phantom for frameless single-isocenter multitarget stereotactic radiosurgery. Physics in medicine and biology Capaldi, D. P., Skinner, L. B., Dubrowski, P., Yu, A. S. 2020

    Abstract

    Purpose:Brain stereotactic-radiosurgery (SRS) treatments require multiple quality-assurance (QA) procedures to ensure accurate and precise treatment delivery. As single-isocenter multitarget SRS treatments become more popular, the quantification of off-axis accuracy of the linear-accelerator is crucial. In this study, a novel brain SRS integrated phantom was developed and validated to enable SRS QA with a single phantom to facilitate implementation of a frameless single-isocenter, multitarget SRS program. This phantom combines the independent verification of each positioning system, the Winston-Lutz, off-axis accuracy evaluation (i.e. off-axis Winston-Lutz), and the dosimetric accuracy utilizing both point-dose-measurements as well as film-measurement, without moving the phantom.Methods and Materials:A novel 3D-printed phantom, coinedOneIso, was designed with a movable insert which can switch between the Winston-Lutz test target and dose measurement without moving the phantom itself. For dose verification, eight brain SRS clinical-treatment-plans with 10MV Flattening-Filter-Free (FFF) beams were delivered on a Varian TrueBeam with a high-definition-multi-leaf-collimator (HD-MLC). Radiochromic film and pinpoint ion chamber comparison measurements were made between the OneIso and solid water (SW) phantom setups. For the off-axis Winston-Lutz measurements, a row of off-axis ball-bearings (BBs) was integrated into the OneIso. To quantify the spatial accuracy versus distance from isocenter, two-dimensional displacements were calculated between the planned and delivered BB locations relative to their respective MLC defined field border.Results:OneIso and the SW phantoms agree within 1%, for both film and point-dose measurements. OneIso identified a reduction in spatial accuracy further away from isocenter. Differences increased as distance from isocenter increased exceeding recommended SRS accuracy tolerances at 3-4cm away from isocenter.Conclusions:OneIso provides a streamlined, single-setup workflow for single-isocenter multitarget frameless linac-based SRS QA. Additionally, with the ability to quantify off-axis spatial-discrepancies, we can determine limitations on the maximum distance between targets to ensure a single-isocenter multitarget SRS program meets recommended guidelines.

    View details for DOI 10.1088/1361-6560/ab8534

    View details for PubMedID 32235050

  • Patient motion tracking for non-isocentric and non-coplanar treatments via fixed frame-of-reference 3D camera. Journal of applied clinical medical physics Gasparyan, S., Ko, K., Skinner, L. B., Ko, R. B., Loo, B. W., Fahimian, B. P., Yu, A. S. 2020

    Abstract

    As C-arm linac radiation therapy evolves toward faster, more efficient delivery, and more conformal dosimetry, treatments with increasingly complex couch motions are emerging. Monitoring the patient motion independently of the couch motion during non-coplanar, non-isocentric, or dynamic couch treatments is a key bottleneck to their clinical implementation. The goal of this study is to develop a prototype real-time monitoring system for unconventional beam trajectories to ensure a safe and accurate treatment delivery.An in-house algorithm was developed for tracking using a couch-mounted three-dimensional (3D) depth camera. The accuracy of patient motion detection on the couch was tested on a 3D printed phantom created from the body surface contour exported from the treatment planning system. The technique was evaluated against a commercial optical surface monitoring system with known phantom displacements of 3, 5, and 7mm in lateral, longitudinal, and vertical directions by placing a head phantom on a dynamic platform on the treatment couch. The stability of the monitoring system was evaluated during dynamic couch trajectories, at speeds between 10.6 and 65cm/min.The proposed monitoring system agreed with the ceiling mounted optical surface monitoring system in longitudinal, lateral, and vertical directions within 0.5mm. The uncertainty caused by couch vibration increased with couch speed but remained sub-millimeter for speeds up to 32cm/min. For couch speeds of 10.6, 32.2, and 65cm/min, the uncertainty ranges were 0.27- 0.73mm, 0.15-0.87mm, and 0.28-1.29mm, respectively.By mounting a 3D camera in the same frame-of-reference as the patient and eliminating dead spots, this proof of concept demonstrates real-time patient monitoring during couch motion. For treatments with non-coplanar beams, multiple isocenters, or dynamic couch motion, this provides additional safety without additional radiation dose and avoids some of the complexity and limitations of room mounted systems.

    View details for DOI 10.1002/acm2.12842

    View details for PubMedID 32107845

  • Volumetric Modulated Arc Therapy and 3-Dimensional Printed Bolus in the Treatment of Refractory Primary Cutaneous Gamma Delta Lymphoma of the Bilateral Legs PRACTICAL RADIATION ONCOLOGY Obeid, J., Gutkin, P. M., Lewis, J., Skinner, L., Wang, E. B., Khodadoust, M. S., Kim, Y. H., Weng, W., Hoppe, R. T., Hiniker, S. M. 2019; 9 (4): 220?25
  • Factor 10 Expedience of Monthly Linac Quality Assurance via an Ion Chamber Array and Automation Scripts. Technology in cancer research & treatment Skinner, L. B., Yang, Y., Hsu, A., Xing, L., Yu, A. S., Niedermayr, T. 2019; 18: 1533033819876897

    Abstract

    PURPOSE: While critical for safe and accurate radiotherapy, monthly quality assurance of medical linear accelerators is time-consuming and takes physics resources away from other valuable tasks. The previous methods at our institution required 5 hours to perform the mechanical and dosimetric monthly linear accelerator quality assurance tests. An improved workflow was developed to perform these tests with higher accuracy, with fewer error pathways, in significantly less time.METHODS: A commercial ion chamber array (IC profiler, Sun Nuclear, Melbourne, Florida) is combined with automation scripts to consolidate monthly linear accelerator QA. The array was used to measure output, flatness, symmetry, jaw positions, gated dose constancy, energy constancy, collimator walkout, crosshair centering, and dosimetric leaf gap constancy. Treatment plans were combined with automation scripts that interface with Sun Nuclear's graphical user interface. This workflow was implemented on a standard Varian clinac, with no special adaptations, and can be easily applied to other C-arm linear accelerators.RESULTS: These methods enable, in 30 minutes, measurement and analysis of 20 of the 26 dosimetric and mechanical monthly tests recommended by TG-142. This method also reduces uncertainties in the measured beam profile constancy, beam energy constancy, field size, and jaw position tests, compared to our previous methods. One drawback is the increased uncertainty associated with output constancy. Output differences between IC profiler and farmer chamber in plastic water measurements over a 6-month period, across 4 machines, were found to have a 0.3% standard deviation for photons and a 0.5% standard deviation for electrons, which is sufficient for verifying output accuracy according to TG-142 guidelines. To minimize error pathways, automation scripts which apply the required settings, as well as check the exported data file integrity were employed.CONCLUSIONS: The equipment, procedure, and scripts used here reduce the time burden of routine quality assurance tests and in most instances improve precision over our previous methods.

    View details for DOI 10.1177/1533033819876897

    View details for PubMedID 31707931

  • Cost Analysis of Audiovisual-Assisted Therapeutic Ambiance in Radiation Therapy (AVATAR) Aided Omission of Anesthesia in Radiation for Pediatric Malignancies. Practical radiation oncology McClelland, S., Overton, K. W., Overshiner, B., Bush, K., Loo, B. W., Skinner, L. B., Watson, G. A., Holmes, J. A., Hiniker, S. M., Maxim, P. G. 2019

    View details for DOI 10.1016/j.prro.2019.09.011

    View details for PubMedID 31574319

  • Optimizing efficiency and safety in external beam radiotherapy using automated plan check (APC) tool and six sigma methodology. Journal of applied clinical medical physics Liu, S., Bush, K. K., Bertini, J., Fu, Y., Lewis, J. M., Pham, D. J., Yang, Y., Niedermayr, T. R., Skinner, L., Xing, L., Beadle, B. M., Hsu, A., Kovalchuk, N. 2019; 20 (8): 56?64

    Abstract

    To develop and implement an automated plan check (APC) tool using a Six Sigma methodology with the aim of improving safety and efficiency in external beam radiotherapy.The Six Sigma define-measure-analyze-improve-control (DMAIC) framework was used by measuring defects stemming from treatment planning that were reported to the departmental incidence learning system (ILS). The common error pathways observed in the reported data were combined with our departmental physics plan check list, and AAPM TG-275 identified items. Prioritized by risk priority number (RPN) and severity values, the check items were added to the APC tool developed using Varian Eclipse Scripting Application Programming Interface (ESAPI). At 9months post-APC implementation, the tool encompassed 89 check items, and its effectiveness was evaluated by comparing RPN values and rates of reported errors. To test the efficiency gains, physics plan check time and reported error rate were prospectively compared for 20 treatment plans.The APC tool was successfully implemented for external beam plan checking. FMEA RPN ranking re-evaluation at 9 months post-APC demonstrated a statistically significant average decrease in RPN values from 129.2 to 83.7 (P<.05). After the introduction of APC, the average frequency of reported treatment-planning errors was reduced from 16.1% to 4.1%. For high-severity errors, the reduction was 82.7% for prescription/plan mismatches and 84.4% for incorrect shift note. The process shifted from 4? to 5? quality for isocenter-shift errors. The efficiency study showed a statistically significant decrease in plan check time (10.17.3min, P=.005) and decrease in errors propagating to physics plan check (80%).Incorporation of APC tool has significantly reduced the error rate. The DMAIC framework can provide an iterative and robust workflow to improve the efficiency and quality of treatment planning procedure enabling a safer radiotherapy process.

    View details for DOI 10.1002/acm2.12678

    View details for PubMedID 31423729

  • Tungsten filled 3D printed field shaping devices for electron beam radiation therapy. PloS one Skinner, L., Fahimian, B. P., Yu, A. S. 2019; 14 (6): e0217757

    Abstract

    PURPOSE: Electron radiotherapy is a labor-intensive treatment option that is complicated by the need for field shaping blocks. These blocks are typically made from casting Cerrobend alloys containing lead and cadmium. This is a highly toxic process with limited precision. This work aims to provide streamlined and more precise electron radiotherapy by 3D using printing techniques.METHODS: The 3D printed electron cutout consists of plastic shells filled with 2 mm diameter tungsten ball bearings. Five clinical Cerrobend defined field were compared to the planned fields by measuring the light field edge when mounted in the electron applicator on a linear accelerator. The dose transmitted through the 3D printed and Cerrobend cutouts was measured using an IC profiler ion chamber array with 6 MeV and 16 MeV beams. Dose profiles from the treatment planning system were also compared to the measured dose profiles. Centering and full width half maximum (FWHM) metrics were taken directly from the profiler software.RESULTS: The transmission of a 16MeV beam through a 12 mm thick layer of tungsten ball bearings agreed within 1% of a 15 mm thick Cerrobend block (measured with an ion chamber array). The radiation fields shaped by ball bearing filled 3D printed cutout were centered within 0.4 mm of the planned outline, whereas the Cerrobend cutout fields had shift errors of 1-3 mm, and shape errors of 0.5-2 mm. The average shift of Cerrobend cutouts was 2.3 mm compared to the planned fields (n = 5). Beam penumbra of the 3D printed cutouts was found to be equivalent to the 15 mm thick Cerrobend cutout. The beam profiles agreed within 1.2% across the whole 30 cm profile widths.CONCLUSIONS: This study demonstrates that with a proper quality assurance procedure, 3D-printed cutouts can provide more accurate electron radiotherapy with reduced toxicity compared to traditional Cerrobend methods.

    View details for DOI 10.1371/journal.pone.0217757

    View details for PubMedID 31216296

  • Beyond sixfold coordinated Si in SiO2 glass at ultrahigh pressures PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Prescher, C., Prakapenka, V. B., Stefanski, J., Jahn, S., Skinner, L. B., Wang, Y. 2017; 114 (38): 10041?46

    Abstract

    We investigated the structure of SiO2 glass up to 172 GPa using high-energy X-ray diffraction. The combination of a multichannel collimator with diamond anvil cells enabled the measurement of structural changes in silica glass with total X-ray diffraction to previously unachievable pressures. We show that SiO2 first undergoes a change in Si-O coordination number from fourfold to sixfold between 15 and 50 GPa, in agreement with previous investigations. Above 50 GPa, the estimated coordination number continuously increases from 6 to 6.8 at 172 GPa. Si-O bond length shows first an increase due to the fourfold to sixfold coordination change and then a smaller linear decrease up to 172 GPa. We reconcile the changes in relation to the oxygen-packing fraction, showing that oxygen packing decreases at ultrahigh pressures to accommodate the higher than sixfold Si-O coordination. These results give experimental insight into the structural changes of silicate glasses as analogue materials for silicate melts at ultrahigh pressures.

    View details for DOI 10.1073/pnas.1708882114

    View details for Web of Science ID 000411157100045

    View details for PubMedID 28874582

    View details for PubMedCentralID PMC5617297

  • The temperature dependence of intermediate range oxygen-oxygen correlations in liquid water JOURNAL OF CHEMICAL PHYSICS Schlesinger, D., Wikfeldt, K. T., Skinner, L. B., Benmore, C. J., Nilsson, A., Pettersson, L. G. 2016; 145 (8)

    Abstract

    We analyze the recent temperature dependent oxygen-oxygen pair-distribution functions from experimental high-precision x-ray diffraction data of bulk water by Skinner et al. [J. Chem. Phys. 141, 214507 (2014)] with particular focus on the intermediate range where small, but significant, correlations are found out to 17 . The second peak in the pair-distribution function at 4.5 is connected to tetrahedral coordination and was shown by Skinner et al. to change behavior with temperature below the temperature of minimum isothermal compressibility. Here we show that this is associated also with a peak growing at 11 which strongly indicates a collective character of fluctuations leading to the enhanced compressibility at lower temperatures. We note that the peak at ?13.2 exhibits a temperature dependence similar to that of the density with a maximum close to 277 K or 4?C. We analyze simulations of the TIP4P/2005 water model in the same manner and find excellent agreement between simulations and experiment albeit with a temperature shift of ?20 K.

    View details for DOI 10.1063/1.4961404

    View details for Web of Science ID 000383875500037

    View details for PubMedID 27586931

  • X-ray and Neutron Scattering of Water CHEMICAL REVIEWS Amann-Winkel, K., Bellissent-Funel, M., Bove, L. E., Loerting, T., Nilsson, A., Paciaroni, A., Schlesinger, D., Skinner, L. 2016; 116 (13): 7570-7589

    Abstract

    This review article focuses on the most recent advances in X-ray and neutron scattering studies of water structure, from ambient temperature to the deeply supercooled and amorphous states, and of water diffusive and collective dynamics, in disparate thermodynamic conditions and environments. In particular, the ability to measure X-ray and neutron diffraction of water with unprecedented high accuracy in an extended range of momentum transfers has allowed the derivation of detailed O-O pair correlation functions. A panorama of the diffusive dynamics of water in a wide range of temperatures (from 400 K down to supercooled water) and pressures (from ambient up to multiple gigapascals) is presented. The recent results obtained by quasi-elastic neutron scattering under high pressure are compared with the existing data from nuclear magnetic resonance, dielectric and infrared measurements, and modeling. A detailed description of the vibrational dynamics of water as measured by inelastic neutron scattering is presented. The dependence of the water vibrational density of states on temperature and pressure, and in the presence of biological molecules, is discussed. Results about the collective dynamics of water and its dispersion curves as measured by coherent inelastic neutron scattering and inelastic X-ray scattering in different thermodynamic conditions are reported.

    View details for DOI 10.1021/acs.chemrev.5b00663

    View details for Web of Science ID 000379794000006

    View details for PubMedID 27195477

  • Low-Dimensional Network Formation in Molten Sodium Carbonate SCIENTIFIC REPORTS Wilding, M. C., Wilson, M., Alderman, O. G., Benmore, C., Weber, J. R., Parise, J. B., Tamalonis, A., Skinner, L. 2016; 6: 24415

    Abstract

    Molten carbonates are highly inviscid liquids characterized by low melting points and high solubility of rare earth elements and volatile molecules. An understanding of the structure and related properties of these intriguing liquids has been limited to date. We report the results of a study of molten sodium carbonate (Na2CO3) which combines high energy X-ray diffraction, containerless techniques and computer simulation to provide insight into the liquid structure. Total structure factors (F(x)(Q)) are collected on the laser-heated carbonate spheres suspended in flowing gases of varying composition in an aerodynamic levitation furnace. The respective partial structure factor contributions to F(x)(Q) are obtained by performing molecular dynamics simulations treating the carbonate anions as flexible entities. The carbonate liquid structure is found to be heavily temperature-dependent. At low temperatures a low-dimensional carbonate chain network forms, at T?=?1100?K for example ~55% of the C atoms form part of a chain. The mean chain lengths decrease as temperature is increased and as the chains become shorter the rotation of the carbonate anions becomes more rapid enhancing the diffusion of Na(+) ions.

    View details for DOI 10.1038/srep24415

    View details for Web of Science ID 000374166300001

    View details for PubMedID 27080401

    View details for PubMedCentralID PMC4832186

  • Exploring the structure of high temperature, iron-bearing liquids Wilding, M., Benmore, C., Weber, R., Parise, J., Lazareva, L., Skinner, L., Alderman, O., Tamalonis, A. ELSEVIER SCIENCE BV. 2015: 358?63
  • The structure of water around the compressibility minimum JOURNAL OF CHEMICAL PHYSICS Skinner, L. B., Benmore, C. J., Neuefeind, J. C., Parise, J. B. 2014; 141 (21): 214507

    Abstract

    Here we present diffraction data that yield the oxygen-oxygen pair distribution function, g(OO)(r) over the range 254.2-365.9 K. The running O-O coordination number, which represents the integral of the pair distribution function as a function of radial distance, is found to exhibit an isosbestic point at 3.30(5) . The probability of finding an oxygen atom surrounding another oxygen at this distance is therefore shown to be independent of temperature and corresponds to an O-O coordination number of 4.3(2). Moreover, the experimental data also show a continuous transition associated with the second peak position in g(OO)(r) concomitant with the compressibility minimum at 319 K.

    View details for DOI 10.1063/1.4902412

    View details for Web of Science ID 000346014200032

    View details for PubMedID 25481152

  • Molten uranium dioxide structure and dynamics SCIENCE Skinner, L. B., Benmore, C. J., Weber, J. R., Williamson, M. A., Tamalonis, A., Hebden, A., Wiencek, T., Alderman, O. G., Guthrie, M., Leibowitz, L., Parise, J. B. 2014; 346 (6212): 984?87

    Abstract

    Uranium dioxide (UO2) is the major nuclear fuel component of fission power reactors. A key concern during severe accidents is the melting and leakage of radioactive UO2 as it corrodes through its zirconium cladding and steel containment. Yet, the very high temperatures (>3140 kelvin) and chemical reactivity of molten UO2 have prevented structural studies. In this work, we combine laser heating, sample levitation, and synchrotron x-rays to obtain pair distribution function measurements of hot solid and molten UO2. The hot solid shows a substantial increase in oxygen disorder around the lambda transition (2670 K) but negligible U-O coordination change. On melting, the average U-O coordination drops from 8 to 6.7 0.5. Molecular dynamics models refined to this structure predict higher U-U mobility than 8-coordinated melts.

    View details for DOI 10.1126/science.1259709

    View details for Web of Science ID 000345696000041

    View details for PubMedID 25414311

  • Structure of Ba-Ti-Al-O glasses produced by aerodynamic levitation and laser heating PHYSICAL REVIEW B Kidkhunthod, P., Skinner, L. B., Barnes, A. C., Klysubun, W., Fischer, H. E. 2014; 90 (9)
  • Packing and the structural transformations in liquid and amorphous oxides from ambient to extreme conditions PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Zeidler, A., Salmon, P., Skinner, L. 2014; 111 (28): 10045?48

    Abstract

    Liquid and glassy oxide materials play a vital role in multiple scientific and technological disciplines, but little is known about the part played by oxygen-oxygen interactions in the structural transformations that change their physical properties. Here we show that the coordination number of network-forming structural motifs, which play a key role in defining the topological ordering, can be rationalized in terms of the oxygen-packing fraction over an extensive pressure and temperature range. The result is a structural map for predicting the likely regimes of topological change for a range of oxide materials. This information can be used to forecast when changes may occur to the transport properties and compressibility of, e.g., fluids in planetary interiors, and is a prerequisite for the preparation of new materials following the principles of rational design.

    View details for DOI 10.1073/pnas.1405660111

    View details for Web of Science ID 000338985700020

    View details for PubMedID 24982151

    View details for PubMedCentralID PMC4104877

  • Ultrafast X-ray probing of water structure below the homogeneous ice nucleation temperature NATURE Sellberg, J. A., Huang, C., McQueen, T. A., Loh, N. D., Laksmono, H., Schlesinger, D., Sierra, R. G., Nordlund, D., Hampton, C. Y., Starodub, D., DePonte, D. P., Beye, M., Chen, C., Martin, A. V., Barty, A., Wikfeldt, K. T., Weiss, T. M., Caronna, C., Feldkamp, J., Skinner, L. B., Seibert, M. M., Messerschmidt, M., Williams, G. J., Boutet, S., Pettersson, L. G., Bogan, M. J., Nilsson, A. 2014; 510 (7505): 381-?

    Abstract

    Water has a number of anomalous physical properties, and some of these become drastically enhanced on supercooling below the freezing point. Particular interest has focused on thermodynamic response functions that can be described using a normal component and an anomalous component that seems to diverge at about 228 kelvin (refs 1-3). This has prompted debate about conflicting theories that aim to explain many of the anomalous thermodynamic properties of water. One popular theory attributes the divergence to a phase transition between two forms of liquid water occurring in the 'no man's land' that lies below the homogeneous ice nucleation temperature (TH) at approximately 232 kelvin and above about 160 kelvin, and where rapid ice crystallization has prevented any measurements of the bulk liquid phase. In fact, the reliable determination of the structure of liquid water typically requires temperatures above about 250 kelvin. Water crystallization has been inhibited by using nanoconfinement, nanodroplets and association with biomolecules to give liquid samples at temperatures below TH, but such measurements rely on nanoscopic volumes of water where the interaction with the confining surfaces makes the relevance to bulk water unclear. Here we demonstrate that femtosecond X-ray laser pulses can be used to probe the structure of liquid water in micrometre-sized droplets that have been evaporatively cooled below TH. We find experimental evidence for the existence of metastable bulk liquid water down to temperatures of 227(-1)(+2) kelvin in the previously largely unexplored no man's land. We observe a continuous and accelerating increase in structural ordering on supercooling to approximately 229 kelvin, where the number of droplets containing ice crystals increases rapidly. But a few droplets remain liquid for about a millisecond even at this temperature. The hope now is that these observations and our detailed structural data will help identify those theories that best describe and explain the behaviour of water.

    View details for DOI 10.1038/nature13266

    View details for Web of Science ID 000337350200031

  • Low Cation Coordination in Oxide Melts PHYSICAL REVIEW LETTERS Skinner, L. B., Benmore, C. J., Weber, J. R., Du, J., Neuefeind, J., Tumber, S. K., Parise, J. B. 2014; 112 (15): 157801

    Abstract

    The complete set of partial pair distribution functions for a rare earth oxide liquid are measured by combining aerodynamic levitation, neutron and x-ray diffraction on Y2O3, and Ho2O3 melts at 2870K. The average Y-O (or Ho-O) coordination of these isomorphic melts is measured to be 5.5(2), which is significantly less than the octahedral coordination of crystalline Y2O3 (or Ho2O3). Investigation of La2O3, ZrO2, and Al2O3 melts by x-ray diffraction and molecular dynamics simulations also show lower-than-crystal cation-oxygen coordination. These measurements suggest a general trend towards lower coordination compared to their crystalline counterparts. It is found that the coordination drop is larger for lower field strength, larger radius cations and is negligible for high field strength (network forming) cations, such as SiO2. These findings have broad implications for predicting the local structure and related physical properties of metal-oxide melts and oxide glasses.

    View details for DOI 10.1103/PhysRevLett.112.157801

    View details for Web of Science ID 000334597300014

    View details for PubMedID 24785072

  • Atomistic insight into viscosity and density of silicate melts under pressure NATURE COMMUNICATIONS Wang, Y., Sakamaki, T., Skinner, L. B., Jing, Z., Yu, T., Kono, Y., Park, C., Shen, G., Rivers, M. L., Sutton, S. R. 2014; 5: 3241

    Abstract

    A defining characteristic of silicate melts is the degree of polymerization (tetrahedral connectivity), which dictates viscosity and affects compressibility. While viscosity of depolymerized silicate melts increases with pressure consistent with the free-volume theory, isothermal viscosity of polymerized melts decreases with pressure up to ~3-5?GPa, above which it turns over to normal (positive) pressure dependence. Here we show that the viscosity turnover in polymerized liquids corresponds to the tetrahedral packing limit, below which the structure is compressed through tightening of the inter-tetrahedral bond angle, resulting in high compressibility, continual breakup of tetrahedral connectivity and viscosity decrease with increasing pressure. Above the turnover pressure, silicon and aluminium coordination increases to allow further packing, with increasing viscosity and density. These structural responses prescribe the distribution of melt viscosity and density with depth and play an important role in magma transport in terrestrial planetary interiors.

    View details for DOI 10.1038/ncomms4241

    View details for Web of Science ID 000331143500001

    View details for PubMedID 24476847

  • Benchmark oxygen-oxygen pair-distribution function of ambient water from x-ray diffraction measurements with a wide Q-range JOURNAL OF CHEMICAL PHYSICS Skinner, L. B., Huang, C., Schlesinger, D., Pettersson, L. G., Nilsson, A., Benmore, C. J. 2013; 138 (7)

    Abstract

    Four recent x-ray diffraction measurements of ambient liquid water are reviewed here. Each of these measurements represents a significant development of the x-ray diffraction technique applied to the study of liquid water. Sources of uncertainty from statistical noise, Q-range, Compton scattering, and self-scattering are discussed. The oxygen-hydrogen contribution to the measured x-ray scattering pattern was subtracted using literature data to yield an experimental determination, with error bars, of the oxygen-oxygen pair-distribution function, g(OO)(r), which essentially describes the distribution of molecular centers. The extended Q-range and low statistical noise of these measurements has significantly reduced truncation effects and related errors in the g(OO)(r) functions obtained. From these measurements and error analysis, the position and height of the nearest neighbor maximum in g(OO)(r) were found to be 2.80(1) A? and 2.57(5) respectively. Numerical data for the coherent differential x-ray scattering cross-section I(X)(Q), the oxygen-oxygen structure factor S(OO)(Q), and the derived g(OO)(r) are provided as benchmarks for calibrating force-fields for water.

    View details for DOI 10.1063/1.4790861

    View details for Web of Science ID 000315263500038

    View details for PubMedID 23445023

  • Joint diffraction and modeling approach to the structure of liquid alumina PHYSICAL REVIEW B Skinner, L. B., Barnes, A. C., Salmon, P. S., Hennet, L., Fischer, H. E., Benmore, C. J., Kohara, S., Weber, J., Bytchkov, A., Wilding, M. C., Parise, J. B., Farmer, T. O., Pozdnyakova, I., Tumber, S. K., Ohara, K. 2013; 87 (2)
  • Structure and diffusion of ZnO-SrO-CaO-Na2O-SiO2 bioactive glasses: a combined high energy X-ray diffraction and molecular dynamics simulations study RSC ADVANCES Xiang, Y., Du, J., Skinner, L. B., Benmore, C. J., Wren, A. W., Boydd, D. J., Towler, M. R. 2013; 3 (17): 5966?78

    View details for DOI 10.1039/c3ra23231j

    View details for Web of Science ID 000316965800034

  • Structure of the floating water bridge and water in an electric field PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Skinner, L. B., Benmore, C. J., Shyam, B., Weber, J. R., Parise, J. B. 2012; 109 (41): 16463?68

    Abstract

    The floating water bridge phenomenon is a freestanding rope-shaped connection of pure liquid water, formed under the influence of a high potential difference (approximately 15 kV). Several recent spectroscopic, optical, and neutron scattering studies have suggested that the origin of the bridge is associated with the formation of anisotropic chains of water molecules in the liquid. In this work, high energy X-ray diffraction experiments have been performed on a series of floating water bridges as a function of applied voltage, bridge length, and position within the bridge. The two-dimensional X-ray scattering data showed no direction-dependence, indicating that the bulk water molecules do not exhibit any significant preferred orientation along the electric field. The only structural changes observed were those due to heating, and these effects were found to be the same as for bulk water. These X-ray scattering measurements are supported by molecular dynamics (MD) simulations which were performed under electric fields of 10(6) V/m and 10(9) V/m. Directional structure factor calculations were made from these simulations parallel and perpendicular to the E-field. The 10(6) V/m model showed no significant directional-dependence (anisotropy) in the structure factors. The 10(9) V/m model however, contained molecules aligned by the E-field, and had significant structural anisotropy.

    View details for DOI 10.1073/pnas.1210732109

    View details for Web of Science ID 000310280300025

    View details for PubMedID 23010930

    View details for PubMedCentralID PMC3478597

  • Comment on 'Molecular arrangement in water: random but not quite' JOURNAL OF PHYSICS-CONDENSED MATTER Skinner, L. B., Benmore, C. J., Parise, J. B. 2012; 24 (33): 338001; discussion 338002

    Abstract

    Accurate high energy x-ray diffraction data are presented on liquid water measured at room temperature. Sources of both systematic and statistical errors within the experiment are considered and data consistency checks are discussed. It is found that the resulting x-ray pair distribution function is smoothly varying in real space and shows no evidence of small peaks in the 3-5 region. Our results are in contrast to the recent findings reported in Petkov et al 2012 J. Phys.: Condens. Matter 24 155102.

    View details for DOI 10.1088/0953-8984/24/33/338001

    View details for Web of Science ID 000306997300024

    View details for PubMedID 22824868

  • Structure and triclustering in Ba-Al-O glass PHYSICAL REVIEW B Skinner, L. B., Barnes, A. C., Salmon, P. S., Fischer, H. E., Drewitt, J. E., Honkimaeki, V. 2012; 85 (6)
  • Area detector corrections for high quality synchrotron X-ray structure factor measurements NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT Skinner, L. B., Benmore, C. J., Parise, J. B. 2012; 662 (1): 61?70
  • Nanostructure of Calcium Silicate Hydrates in Cements PHYSICAL REVIEW LETTERS Skinner, L. B., Chae, S. R., Benmore, C. J., Wenk, H. R., Monteiro, P. M. 2010; 104 (19): 195502

    Abstract

    Calcium silicate hydrate (CSH) is the major volume phase in the matrix of Portland cement concrete. Total x-ray scattering measurements with synchrotron x rays on synthetic CSH(I) shows nanocrystalline ordering with a particle diameter of 3.5(5) nm, similar to a size-broadened 1.1 nm tobermorite crystal structure. The CSH component in hydrated tricalcium silicate is found to be similar to CSH(I). Only a slight bend and additional disorder within the CaO sheets is required to explain its nanocrystalline structure.

    View details for DOI 10.1103/PhysRevLett.104.195502

    View details for Web of Science ID 000277699600029

    View details for PubMedID 20866975

  • Liquid-Liquid Phase Transition in Supercooled Yttria-Alumina PHYSICAL REVIEW LETTERS Barnes, A. C., Skinner, L. B., Salmon, P. S., Bytchkov, A., Pozdnyakova, I., Farmer, T. O., Fischer, H. E. 2009; 103 (22): 225702

    Abstract

    The structure and thermal characteristics of aerodynamically levitated samples of yttria-alumina in the liquid, supercooled liquid and solid phases were explored in an extensive series of high energy x-ray diffraction, small angle neutron scattering, and pyrometric cooling measurements. Particular focus was placed on the compound (Y2O3)(x)(Al2O3)(1-x) with x = 0.2 for which a liquid-liquid phase transition at a temperature of 1788 K has recently been reported. No structural or thermal signature in support of this metastable phase transition could be found.

    View details for DOI 10.1103/PhysRevLett.103.225702

    View details for Web of Science ID 000272182000034

    View details for PubMedID 20366109

  • Phase separation, crystallization and polyamorphism in the Y2O3-Al2O3 system Skinner, L. B., Barnes, A. C., Salmon, P. S., Crichton, W. A. IOP PUBLISHING LTD. 2008: 205103

    Abstract

    A detailed study of glass formation from aerodynamically levitated liquids in the (Y(2)O(3))(x)(Al(2)O(3))(1-x) system for the composition range 0.21?x?0.41 was undertaken by using pyrometric, optical imaging and x-ray diffraction methods. Homogeneous and clear single-phase glasses were produced over the composition range [Formula: see text]. For Y(2)O(3)-rich compositions ([Formula: see text]), cloudy materials were produced which contain inclusions of crystalline yttrium aluminium garnet (YAG) of diameter up to 40m in a glassy matrix. For Y(2)O(3)-poor compositions around x = 0.24, cloudy materials were also produced, but it was not possible to deduce whether this resulted from (i) sub-micron inclusions of a nano-crystalline or glassy material in a glassy matrix or (ii) a glass formed by spinodal decomposition. For x = 0.21, however, the sample cloudiness results from crystallization into at least two phases comprising yttrium aluminium perovskite and alumina. The associated pyrometric cooling curve shows slow recalescence events with a continuous and slow evolution of excess heat which contrasts with the sharp recalescence events observed for the crystallization of YAG at compositions near x = 0.375. The materials that are the most likely candidates for demonstrating homogeneous nucleation of a second liquid phase occur around x = 0.25, which corresponds to the limit for formation of a continuous random network of corner-shared AlO(4) tetrahedra.

    View details for DOI 10.1088/0953-8984/20/20/205103

    View details for Web of Science ID 000255661500058

    View details for PubMedID 21694284

  • An oscillating coil system for contactless electrical conductivity measurements of aerodynamically levitated melts REVIEW OF SCIENTIFIC INSTRUMENTS Skinner, L., Barnes, A. C. 2006; 77 (12)

    View details for DOI 10.1063/1.2403939

    View details for Web of Science ID 000243159100021

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