PubMed | Institute for Bioengineering of Catalonia IBEC, University of Lisbon, CEA Grenoble, Laue Langevin Institute and 2 more.
Type: Evaluation Studies | Journal: Journal of synchrotron radiation | Year: 2015
A fast atomic force microscope (AFM) has been developed that can be installed as a sample holder for grazing-incidence X-ray experiments at solid/gas or solid/liquid interfaces. It allows a wide range of possible investigations, including soft and biological samples under physiological conditions (hydrated specimens). The structural information obtained using the X-rays is combined with the data gathered with the AFM (morphology and mechanical properties), providing a unique characterization of the specimen and its dynamics in situ during an experiment. In this work, lipid monolayers and bilayers in air or liquid environment have been investigated by means of AFM, both with imaging and force spectroscopy, and X-ray reflectivity. In addition, this combination allows the radiation damage induced by the beam on the sample to be studied, as has been observed on DOPC and DPPC supported lipid bilayers under physiological conditions.
News Article | April 20, 2016
The 2007–2014 excavations at Liang Bua, including eight 2 × 2 m and two 1 × 2 m areas (referred to as Sectors), proceeded in 10 cm intervals (referred to as spits) while following stratigraphic units. Timber shoring of the baulks was installed after ~2.5 m depth for safety. In situ findings (for example, bones, artefacts and charcoal) were plotted in three dimensions and the sediments from each spit were sieved by hand, followed by wet sieving (2 mm mesh). All recovered findings were cleaned, catalogued and transported to Pusat Penelitian Arkeologi Nasional (Jakarta, Indonesia) for curation and further study. Bulk samples of four tephras were wet sieved at >32 μm and then dry sieved into 32–63 μm, 63–125 μm, 125–250 μm, 250–500 μm and 500 μm–1 mm fractions. Depending on the grain-size distribution of the sample, the dominant dry fraction containing the most glass material was mounted into an epoxy resin. Glass from bubble-wall shards or vesiculated pumice fragments was analysed as individual grains (>63 μm) using an electron microprobe. Major element determinations were made using a JEOL Superprobe (JXA-8230) housed at Victoria University of Wellington, New Zealand, using the ZAF correction method31. Analyses were performed with 15 kV accelerating voltage, 8 nA beam current, and an electron beam defocused to 10–20 μm. Standardization was achieved by means of mineral and glass standards. Rhyolitic glass standard ATHO-G (ref. 32) was routinely used to monitor calibration in all analytical runs and to evaluate any day-to-day differences in calibration. All analyses were normalized to 100% (by weight) anhydrous and total iron was calculated as FeO (Supplementary Information section 1). The major element compositions of the four tephras and the Youngest Toba Tuff33 are displayed as bivariate plots in Extended Data Fig. 3c–e. Sediment samples were collected using opaque plastic tubes hammered horizontally into cleaned stratigraphic sections and wrapped in black plastic after removal. Field measurements of the gamma dose rate at each sample location were made using a portable gamma-ray detector (Exploranium GR-320) inserted into the emptied tube holes. Sediment samples were also collected from the tube holes for laboratory determinations of water content and beta dose rate at the University of Wollongong. The environmental dose rate of each sample was calculated as the sum of the beta dose rate (estimated from beta-counting of dried and powdered sediment samples using a Risø low-level beta multicounter system and allowing for beta-dose attenuation and other factors34), the in situ gamma dose rate, and the estimated cosmic-ray dose rate35. The latter took account of the burial depth of each sample, the thickness of cave roof overhead, the zenith-angle dependence of cosmic rays, and the latitude, longitude and altitude of Liang Bua. Each of these external dose rate contributors were adjusted for long-term water content. The measured (field) water contents of the seven samples collected in 2012 range from 26 to 35%, but higher and lower field water contents have been reported for other sediment samples collected at Liang Bua: 15–30% (ref. 2), 3–22% (ref. 7) and 24–39% (Supplementary Information section 2). We used a value of 20 ± 5% as a mid-range estimate of the long-term water content, with the standard error sufficient to cover (at 2σ) most of the field measurements. The total dose rate of each sample also includes an estimate of the internal beta dose rate due to the radioactive decay of 40K and 87Rb. This estimate was based on a K concentration of 12 ± 1%, determined from energy- and wavelength-dispersive X-ray spectroscopic measurements of individual feldspar grains36, 37 (see Supplementary Information section 2), and an assumed Rb concentration of 400 ± 100 μg g–1 (ref. 38). Potassium-rich feldspar (K-feldspar) grains of 90–212 or 180–212 μm diameter were extracted from the sediment samples under dim red illumination and prepared using standard procedures39, including the use of a sodium polytungstate solution of 2.58 g cm–3 density to separate the feldspar grains from heavier minerals. The separated grains were also washed in 10% hydrofluoric acid for 40 min to clean their surfaces and reduce the thickness of the alpha-irradiated outer layer by ~15 μm, which was taken into account in the dose rate calculation. For each sample, single aliquots composed of a few hundred grains were measured using an automated Risø TL/OSL reader equipped with infrared (875 nm) light-emitted diodes (LEDs) for stimulation40 and a calibrated 90Sr/90Y source for beta irradiations. We also made measurements of individual K-feldspar grains (180–212 μm diameter) from two samples collected in 2012 (LB12-OSL3 and -OSL4) and the two original sediment samples (LBS7-40a and LBS7-42a) collected from above and alongside the remains of LB1 (ref. 2). Infrared stimulation of individual K-feldspar grains was achieved using a focused laser beam (830 nm)40. The IRSL emissions from the single aliquots and single grains were detected using an Electron Tubes Ltd 9235B photomultiplier tube fitted with Schott BG-39 and Corning 7-59 filters to transmit wavelengths of 320–480 nm. To estimate the equivalent dose (D ) for each aliquot or grain39, 41, we initially used the multiple elevated temperature post-infrared IRSL (MET-pIRIR) regenerative-dose procedure21, 30, 42, in which the IRSL signals are measured by progressively increasing the stimulation temperature from 50 °C to 250 °C in 50 °C increments. The samples yielded very dim signals, however, so we used a two-step pIRIR procedure21, 43 to improve the signal-to-noise ratio. Grains were preheated at 320 °C for 60 s before infrared stimulation of the natural, regenerative and test doses at 50 °C for 200 s. The pIRIR signal was then measured at 290 °C for either 200 s (single aliquots) or 1 s (single grains), followed by an infrared bleach at 325 °C for 100 s at the end of each regenerative-dose cycle. Example pIRIR decay and dose–response curves are shown in Extended Data Fig. 7a–c. Performance tests of the regenerative-dose procedure and details of residual dose measurements21, 44 and anomalous fading tests45, 46 are described in Supplementary Information section 2. We estimated the pIRIR age of each sample from the weighted mean D (calculated using the central age model47, 48) divided by the environmental dose rate, and applied corrections for residual dose and anomalous fading. For the latter corrections, we used the weighted mean fading rate (0.9 ± 0.3% per decade) measured for five of the seven samples collected in 2012. Sediment samples were taken in the same manner as the IRSL samples, as were the in situ gamma dose rate measurements (made using an ORTEC digi-DART gamma-ray detector). Additional sediment samples were also collected for determinations of water content and beta dose rate at Macquarie University. The environmental dose rate of each sample consists of three external components, each adjusted for long-term water content (20 ± 5%): the beta dose rate (estimated from beta-counting and allowing for beta-dose attenuation), the in situ gamma dose rate, and the estimated cosmic-ray dose rate. An assumed internal dose rate of 0.03 ± 0.01 Gy kyr–1 was also included in the total dose rate. Quartz grains were separated from the sediment samples under dim red illumination and prepared using standard procedures39, including mineral separations using 2.70 and 2.62 g cm–3 density solutions of sodium polytungstate to isolate the quartz and a 40% hydrofluoric acid etch for 45 min to remove the alpha-irradiated outer ~20 μm of each grain. Aliquots composed of about 10,000 quartz grains were measured using a dual-aliquot regenerative-dose TL protocol22 to isolate the light-sensitive red emissions49. This procedure was originally developed for application at Liang Bua2 and requires two aliquots of each sample: one to estimate the D associated with the heat-reset TL traps and the other to measure the total TL signal, from which the D associated with the light-sensitive TL traps is estimated by subtraction. Measurements were made on a Risø TL/OSL reader fitted with an Electron Tubes Ltd 9658B photomultiplier tube and Schott BG-39 and Kopp 2-63 filters designed to transmit red emissions (peak transmission in the 600–620 nm range, with minimum and maximum wavelengths of 580 and 670 nm), and cooled to –22 °C to reduce the background count rate. Bleaching was performed using a halogen lamp and light guide integrated into the reader, and laboratory doses were given using a 90Sr/90Y source mounted on the reader. The quartz grains were first heated to 260 °C at a heating rate of 5 K s–1 and then held at this temperature for 1,000 s to induce an isothermal TL signal and reduce the unwanted glow from incandescence. Following ref. 22, D values were estimated from the 20–30 s interval of isothermal TL (which was shown to be light-sensitive) and the final 160 s was used as background. Two of the samples contained abundant quantities of quartz, so problems associated with inter-aliquot variability50, 51 were reduced by measuring 12 replicates of each pair of aliquots (Supplementary Information section 2). As prolonged sunlight exposure is required the empty the light-sensitive TL traps, the ages obtained should be regarded as maximum estimates of the time elapsed since sediment deposition22. Samples of bone from three specimens of Homo floresiensis (LB1, LB2 and LB6), one Homo sapiens and eight Stegodon florensis insularis were analysed using laser ablation uranium-series isotope measurement analysis procedures and instruments similar to those described previously23, 52. Cuts were made perpendicular to the bone surface using a rotatory tool equipped with a thin (100 μm wide) diamond saw blade. The cut samples were mounted into aluminium cups, aligning the cross-sectioned surfaces with the outer rim of the sample holder to position the samples on the focal plane of the laser in the sampling cell. Sequential laser spot analyses were undertaken along 1–5 parallel tracks per sample, starting from the interior of each cross-sectioned bone (Extended Data Figs 8 and 9 and Supplementary Information section 3). Uranium and thorium isotopes were measured at the Australian National University using a Finnigan MAT Neptune multi-collector inductively-coupled plasma mass spectrometer (MC-ICP-MS) equipped with multiple Faraday cups and ion counters. Two ion counters were set to masses of 230.1 and 234.1, while the Faraday cups measured the masses 232, 235 and 238. Samples were ablated using a Lambda Physik LPFPro ArF excimer laser (193 nm) coupled to the MC-ICP-MS through a custom-designed Helex ablation cell. The analyses were made at regular spacing (typically 2–3 mm) along each track, using a laser spot size of 265 μm and a 5 Hz pulse rate. The samples were initially cleaned for 5 s and ablation pits were measured for 50 s. These measurements were bracketed by analyses of reference standards to correct for instrument drift. Semi-quantitative estimates of uranium and thorium concentrations were made from repeated measurements of the SRM NIST-610 glass standard (U: 461.5 μg g–1, Th: 457.2 μg g–1) and uranium-isotope (activity) ratios from repeated measurements of rhinoceros tooth dentine from Hexian sample 1118 (ref. 53). Apparent 234U/230Th ages were estimated for each track using a diffusion–adsorption–decay (DAD) model24, which uses the entire set of isotope measurements made along the track to calculate the rate of diffusion of 238U and 234U into the bone. Bones behave as geochemically ‘open’ systems, so the diffusion of uranium into a bone may have occurred soon after it was deposited or much later. The original isotopic signature may also be overprinted by secondary uranium uptake that is hard to recognize. As such, uranium-series ages for bones are most likely to be minimum estimates of time since deposition, with the extent of age underestimation being very difficult or impossible to evaluate23. The modelled ages were calculated after rejecting data points associated with detrital contamination (U/Th elemental ratios of ≤ 300) and data points at the surface of the bones where secondary overprinting was suspected. Results are tabulated in Supplementary Information section 3, with all errors given at 2σ. Samples of calcite deposited as speleothems (flowstones and a 1 cm-tall stalagmite) were collected during excavation. Unlike bone, speleothems commonly behave as geochemically ‘closed’ systems, with no loss or gain of uranium after calcite crystallization54. The cleanest portion of each sample was selected, ground to the size of a rice grain, cleaned ultrasonically and then handpicked, avoiding pieces that appeared to be porous or contaminated. Age determinations were made at the University of Queensland using a Nu Plasma MC-ICP-MS. Uranium and thorium separation procedures, MC-ICP-MS analytical protocols, details of spike calibrations, blank and ‘memory’ assessments, and repeat measurements of standards have been described previously55, 56. The 234U/230Th ages were calculated using Isoplot 3.75 (ref. 57) and half-lives of 245.25 kyr (234U) and 75.69 kyr (230Th) (ref. 58). As most samples consist of impure calcite with some degree of detrital contamination, a correction for non-radiogenic 230Th was applied to the measured 230Th/232Th activity ratio of each sample using an assumed bulk-Earth 230Th/232Th activity ratio of 0.825 (with a relative error of ± 50% and assuming secular equilibrium in the 238U–234U–230Th decay chain), as is typical of most other studies59. This non-radiogenic 230Th correction reduces the calculated ages of the samples and increases the age uncertainties by an amount dependent on the extent of detrital contamination. All ten dated samples have measured 230Th/232Th activity ratios of >20 (Supplementary Information section 4), so the detritally-corrected 234U/230Th ages are only slightly younger than the uncorrected (measured) ages. Crystals of hornblende were obtained for the 100–150 and 150–250 μm size fractions of the T1 tephra using standard heavy liquid and magnetic separation techniques. Crystals were loaded into wells in 18 mm-diameter aluminium sample discs for neutron irradiation, along with the 1.185 million year-old Alder Creek sanidine26 as the neutron fluence monitor. Neutron irradiation was carried out for 4 min in the cadmium-shielded CLICIT facility at the Oregon State University TRIGA reactor. Argon isotopic analyses of gas released from 6 hornblende aliquots during CO laser step-heating, including a final fusion step (‘fuse’ in Supplementary Information section 5), were made on a fully automated, high-resolution, Nu Instruments Noblesse multi-collector noble-gas mass spectrometer, using procedures documented previously25. One set of four experiments (Lab IDs 2598 and 2599 in Supplementary Information section 5) consisted of strong degassing of 10 mg hornblende aliquots in square pits in the laser disc, using a beam integrator lens that gives a ‘top hat’ 6 × 6 mm energy profile at the focal plane. The laser was then operated at 32 W and this high-temperature, pre-fusion step measured (‘D’ in Supplementary Information section 5). The fusion step was performed using a conventional focus lens. In the second set of experiments, 20 mg hornblende aliquots were loaded into 5 mm-wide channels in the laser disc and a defocused laser beam was programmed to raster in 50 traverses, each 30 mm in length and separated by 0.1 mm. Low power (<1 W) steps were performed initially to remove loosely trapped argon. At 1 W of laser power (step ‘C’), the hornblende crystals began to glow and release significant amounts of 39Ar. This and subsequent steps, including the final fusion, are reported in Supplementary Information section 5 as Lab IDs 2584-03C to -03O (fuse) and 2584-04C to -04I (fuse). Sample gas clean-up was through an all-metal extraction line, equipped with a –130 °C cold trap (to remove H O) and two water-cooled SAES GP-50 getter pumps (to absorb reactive gases). Argon isotopic analyses of unknowns, blanks and monitor minerals were carried out in identical fashion during a fixed period of 400 s in 14 data acquisition cycles. 40Ar and 39Ar were measured on the high-mass ion counter, 38Ar and 37Ar on the axial ion counter and 36Ar on the low-mass ion counter, with baselines measured every third cycle. Measurement of the 40Ar, 38Ar and 36Ar ion beams was carried out simultaneously, followed by sequential measurement of 39Ar and 37Ar. Beam switching was achieved by varying the field of the mass spectrometer magnet and with minor adjustment of the quad lenses. Data acquisition and reduction was performed using the program ‘Mass Spec’ (A. Deino, Berkeley Geochronology Center). Detector intercalibration and mass fractionation corrections were made using the weighted mean of a time series of measured atmospheric argon aliquots delivered from a calibrated air pipette25. The accuracy of the primary air pipette measurements was verified by cross-referencing to data produced from a newly charged second air pipette. Decay and other constants, including correction factors for interference isotopes produced by nucleogenic reactions, are as reported in ref. 25. An isotope correlation (inverse isochron) plot of the data for all 28 aliquots is shown in Extended Data Fig. 3f. The age determined from the inverse isochron is 85 ± 13 kyr for all 28 aliquots, or 79 ± 12 kyr (errors at 1σ) if the data point on the far right-hand side of the plot is excluded. In both cases, the 40Ar/36Ar intercept value is statistically indistinguishable from the atmospheric ratio of 298.6 ± 0.3 (ref. 60), indicating the absence of significant excess 40Ar in the hornblende crystals. Three charcoal samples recovered during excavation were sent to DirectAMS Radiocarbon Dating Service in Bothell, Washington (Supplementary Information section 6). Samples were pretreated using acid–base–acid (ABA) procedures and the 14C content was measured using accelerator mass spectrometry61. Conventional 14C ages in radiocarbon years before present (bp) were converted to calendar-year age ranges at the 68% and 95% confidence intervals using the SHCal13 calibration data set62 and CALIB 7.1 (http://calib.qub.ac.uk/calib/). One of these three samples yielded an ‘old’ radiocarbon age (>40 kyr bp), so we submitted the remaining charcoal to the Oxford Radiocarbon Accelerator Unit (ORAU) for a harsher cleaning protocol known as ABOx-SC63, 64. This pretreatment is known to improve charcoal decontamination and has been shown repeatedly to produce more reliable results for ‘old’ charcoal. However, the harshness of the ABOx-SC procedure often results in large material loss and sample failure, so a new preparative method (AOx-SC) has been developed and tested at the ORAU (K. Douka, personal communication). The AOx-SC procedure does not include a NaOH step and produces identical results to ABOx-SC, but with much higher yields and reduced sample failure. For the Liang Bua sample, ~100 mg and ~50 mg of hand-picked charcoal underwent ABOx-SC and AOx-SC pretreatments, respectively. Only the AOx-treated charcoal survived the wet chemistry, yielding sufficient carbon for stepped combustion, first at 630 °C and then at 1,000 °C, with the latter fraction collected for graphitization and measurement by accelerator mass spectrometry.
News Article | April 27, 2016
4,4′-Dichlorodiphenylsulfone (DCDPS), 4,4′-difluorodiphenylsulfone (DFDPS), 4,4′-dihydroxybiphenyl (BP) and tetramethyl bisphenol A (TMBP) (Sigma-Aldrich) were purified by recrystallization with ethanol, and dried at 60 °C for one day under vacuum. 3,3′-Disulfonate-4,4′-dichlorodiphenylsulfone (SDCDPS) was prepared via direct sulfonation with fuming sulfuric acid. Fuming sulfuric acid, toluene, dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), potassium carbonate (K CO ), methanol (MeOH), 1,1,2,2,-tetrachloroethane, toluene and acrylic acid (Sigma-Aldrich) were used as received. N-bromosuccinimide (NBS) and benzoyl peroxide (BPO) (Sigma-Aldrich) were used as received for bromination of tetramethylated poly(arlyene ether sulfone) (TMBPS). Sodium chloride (NaCl) (Daejung Hwageum Chemical) was used as received. Sulfonated poly(arylene ether sulfone) (BPS) with 40% and 60% degrees of sulfonation was synthesized via polycondensation polymerization of SDCDPS (4 mmol, 3.93 g for BPSH40; 6 mmol, 5.90 g for BPSH60), DCDPS (6 mmol, 3.45 g for BPSH40; 4 mmol, 2.3 g for BPSH60), K CO (11.5 mmol, 3.1787 g), BP (10 mmol, 3.7242 g) in 40 ml DMAc and 20 ml toluene mixture. The mixture was heated at 140 °C and refluxed from 140 °C to 155 °C for 3 h to remove water as a byproduct in the form of an azeotropic mixture with toluene. The reaction was maintained at 165 °C for 20 h and the solution was precipitated in cold deionized water. The precipitate was washed several times with deionized water, boiled in deionized water to remove K CO , and then dried at 120 °C for 12 h under vacuum. BPS membranes in sodium form (BPSNa) were prepared by casting solutions of ~15 wt% polymer in NMP, followed by evaporation under ambient conditions at 40 °C for 12 h, 60 °C for 2 h, 100 °C for 2 h and 120 °C in vacuo for 2 h. The subsequent drying protocol was in a vacuum oven sequentially at 45 °C for 24 h, 60 °C for 2 h and 120 °C for 6 h. The resulting BPSNa membrane was transformed to cationic-exchange membrane in sodium form (CBPS; C40 and C60) for reverse electrodialysis by immersing it in 1 M NaCl. The resulting BPSNa membranes were also immersed in boiling deionized water for 2 h to remove the residual solvent, and then treated in boiling 1 M sulfuric acid for 2 h. After washing in boiling deionized water for 4 h, BPS membranes in the protonated form (BPSH) were dried at 120 °C for 12 h under vacuum. The approximate thickness of the membranes was 50 μm. Tetramethylated poly(arylene ether sulfone) (TMBPS) was synthesized via condensation polymerization of DFDPS (30 mmol, 7.6275 g), TMBP (12 mmol, 2.9077 g) for tetrabrominated poly(arylene ether sulfone) with degree of functionalization 40 (TBrBPS40) and 18 mmol, 4.3616 g for TBrBPS60, BP (18 mmol, 3.3518 g for TBrBPS40; 12 mmol, 2.2345 g for TBrBPS60) and K CO (45 mmol, 6.2195 g) in 85 ml DMAc and 80 ml toluene mixture. The mixture was heated at 120 °C and refluxed for 4 h to remove water with toluene via the azeotropic method. The reaction temperature was increased to 160 °C and maintained for 2 h. After cooling to room temperature, the mixture was precipitated in cold deionized water. The resulting TMBPS precipitate was washed several times with deionized water and dried at 60 °C in vacuo. TMBPS polymer (14.1300 g), NBS (60.14 mmol, 7.1674 g for aminated poly(arylene ether sulfone) copolymer with degree of functionalization 40 (ABPS40); 87.8837 mmol, 10.4723 g for ABPS60) and BPO (4.010 mmol, 1.2950 g for ABPS40; 5.8589 mmol, 1.8923 g for ABPS60) were introduced in 127 ml of 1,1,2,2-tetracholoroethane under an argon atmosphere for the brominated TMBPS (TBrBPS). The mixture was heated to 80 °C and was maintained at that temperature for 12 h. After cooling to room temperature, the mixture was precipitated with methanol and washed several times. The resulting TBrBPS polymer was dried and dissolved in 15 wt% NMP and the solution was cast onto a glass plate. The polymer solution was evaporated slowly in an oven as the temperature was increased to 40 °C for 24 h, to 60 °C for 2 h, and to 120 °C for 2 h in vacuo. The resulting membrane was immersed in trimethylamine 45% (w/w) aqueous solution for 24 h to substitute bromide with tetramethyl ammonium functional groups, which allow conduction of hydrated chloride ions through the polymer membranes. The resulting membrane was transformed to its chloride form (ABPS; A40 and A60) for reverse electrodialysis by immersing it in 1 M NaCl. Atmospheric non-equilibrium plasma treatment can be employed to deposit a thin polymeric layer on the membrane via plasma polymerization for hydrophobic surface modification16, 17, 18. Electric discharge powered by radio frequency generates various monomer fragment species such as neutral molecules, ions and radicals, which are grafted or adsorbed onto the surface. Grafted oligomers and radicals grow from the polymer surface as the plasma discharge continues via plasma polymerization. Plasma-enhanced chemical vapour deposition imparts various chemical properties originating from different precursors, creating hydrophobicity and ion conductive and physical membrane properties compared to non-treated membranes. In this work, an atmospheric plasma discharge system (SHP-1000, APP) with a 13.56-MHz radio frequency discharger was used for hydrophobic plasma surface coating. Dried BPSH membrane film (10 cm × 10 cm) was attached onto an aluminium plate. The aluminium plate traverse speed was controlled to 30 mm s−1 along the y axis under the plasma glow discharging source (18 cm × 2 cm) with the gap set at about 2.5 mm, which allowed homogeneously coated surfaces to be obtained. Atmospheric plasma treatment (input power of 150 W) was performed under controlled chamber conditions of atmospheric pressure at 25 °C and 40% RH, with gas flow rates of 10 ml min−1 of octafluorocyclobutane (c-C F ) and 20 litres per minute of He as coating cycles increased from 3 cycles to 40 cycles (Extended Data Fig. 2a). For graft plasma polymerization, the radio-frequency discharger excites the He carrier gas, which lowers the surface energy of the BPSH, CBPS or ABPS membrane (Extended Data Fig. 2c) and c-C F gas molecules are also excited and fragment into various types of species including neutral molecules, radicals and ions of C F in the plasma field (Extended Data Fig. 2b). The generated monomer fragments undergo plasma polymerization, including radical polymerization, on the excited surface of BPSH or CBPS and ABPS, which continues to grow fluorocarbon graft branches with additional coating cycles (Extended Data Fig. 2b). The thickness of the deposited polymer layer as well as the hydrophobicity of the membrane surface is controlled by the number of coating cycles. X-ray photoelectron spectroscopy was acquired using a Sigma Probe (Thermo VG Scientific) equipped with an Al Kα monochromatic X-ray source under a base chamber pressure of 5 × 10−8 mbar. The spectrum for each atom (such as C, S, O and F) was fitted using the Spectral Data Processor Version 7 program (http://xpsdata.com) in order to estimate the atomic composition change on the membrane surface. The spectra for sulfur and fluorine atoms were scanned from 155 eV to 185 eV and from 679 eV to 699 eV, respectively, in stepwise increases of 0.10 eV. AFM images were obtained using a Digital Instruments MultiMode 8 AFM (Veeco) with a NanoScope V controller (Veeco). A silicon probe (Nanosensors) with a force contact of 1.2–29 N m−1 was used to scan surface morphology. Samples were conditioned at different hydration conditions to present the surface morphology changes of the membranes. Plasma-coated samples were dried immediately after treatment at 120 °C in vacuo for 12 h before AFM measurement. Assist scan tapping mode was performed in a fluid cell filled with deionized water in order to scan the surface of fully hydrated plasma-coated membranes, which were immersed in deionized water for 24 h at room temperature. Hydrated samples were allowed to air-dry on the piezo-scanner of the microscope for at least 30 min to obtain the surface morphology of partially dehydrated membranes. AFM was performed in a fluid cell filled with deionized water using the assist scan tapping mode and under atmospheric conditions with 30% to ~45% RH using the tapping mode. Surface topological depths were estimated from AFM height images. DVS was performed using a DVS Advantage (Surface Measurement Systems, UK) with Cahn balance D-200 to investigate water vapour sorption and desorption behaviour. The RH was controlled by changing the ratio of dry and wet gases in the range of 0%–90%. All membrane samples were dried at 120 °C under vacuum for 12 h to remove absorbed water before measurements. Water contact angles were measured on an Easy Drop Standard (Krüss) instrument equipped with a charge-coupled device camera by the sessile-drop method. The average volume of water droplet was about 2 μl for contact angle measurements. Field-emission scanning electron microscopy (JSM-7900F, JEOL, Japan) was performed to investigate the morphology of the hydrophobic coated surface layer. PALS is a nuclear technique used to measure the free volume of bulk polymer materials. The lifetime of the ortho-positronium (o-Ps, the bound state of a positron and an electron of the same spin) is related to the size of the free volume elements within the polymer. The o-Ps will preferentially locate within the pore spaces and will then annihilate with an electron from the pore wall of the sample. The size of the pore determines how long it takes for an annihilation event; larger pores result in longer lifetimes. The Tao–Eldrup equation is a quantum model used to calculate the average spherical pore size from the o-Ps lifetime20. The lifetime has an associated intensity value which is related to the relative number of pores within the sample. The samples were stacked 2 mm thick each side of a positron point source (30 μCi of 22NaCl enclosed in a Mylar envelope). The volume of plasma surface coating in the 2 mm film stack (for a 100 nm coating) is 0.4%, to ensure that the o-Ps is probing the bulk membrane. The samples were run under a nitrogen atmosphere with humidity control. The spectra were detected using an automated ORTEC EG&G instrument (Oak Ridge) and analysed using LT version 9 software24. The first lifetime was fixed to 0.125 ns owing to para-positronium annihilation (a bound state of an electron and a positron of opposite spin) and the second lifetime was ~0.4 ns owing to free annihilation with an electron. The third component, o-Ps, was used to calculate the lifetime, which is related to pore size, and intensity, which is related to the relative number of pores within membranes. The results show that there is no change in the bulk properties of the membranes caused by the surface coating. The intensity consistently drops with increasing RH owing to the uptake of water and hence a decrease in the number of empty pores. The lifetimes show a more complex trend. The initial drop (0%–30% RH) is probably due to a pore-filling effect and then the increase is due to swelling above 40% RH. The membrane electrode assembly with an active area of 5 cm2 and Pt loading of 0.5 mg cm−2 was fabricated via the screen printing method25. The membrane electrode assembly was set into a single cell test fixture and mounted in a commercial fuel-cell testing station (SMART PEMFC test system, WonATech) which was supplied with temperature- and humidity-controlled gases. The test system was operated at 80 °C under various RH conditions with hydrogen and oxygen/air gases under ambient pressure. Additionally, membrane electrode assembly electrochemical performance was evaluated at 80 °C (100% RH), 100 °C (85% RH) and 120 °C (35% RH) under 1.5 atm pressure. Hydrogen gas and oxygen/air gas were supplied at a flow rate considering the stoichiometry ratio on the increased current load. A single cell stability test was performed by measuring the variation of current density at constant 0.7 V as a function of time at 120 °C and 35% RH. The stability tests were performed three times for each type of membrane. Other conditions were as described above. The plasma-coated membranes and uncoated membranes in sodium chloride salt form were soaked in distilled water for at least 24 h to allow complete hydration before measuring permselectivity and membrane resistances in aqueous NaCl solution (0.1 M and 0.5 M) at 20 °C. Permselectivity was measured by a static potential method in a two-compartment cell separated by the membrane, where each cell contained 0.1 M and 0.5 M NaCl solution, respectively. Membrane resistances were tested by using an electrochemical impedance spectroscopy analyser in a two-compartment cell equipped with Ag/AgCl reference electrodes (RE-1B, ALS) in 0.5 M aqueous NaCl solution at 20 °C.
Keyser R.M.,ORTEC |
Journal of Radioanalytical and Nuclear Chemistry | Year: 2013
The need to perform gamma-ray spectroscopy measurements at high count rates with HPGe detectors is more common than many believe. Examples exist in safeguards, radiochemistry, nuclear medicine, and neutron activation analysis. In other applications wide dynamic ranges in count rate may be encountered, for example samples taken after a nuclear accident are counted on a system normally used for environmental monitoring. In a real situation, it may not be possible to reduce count-rates by increasing the distance or using collimators. The challenge is to obtain the "best" data possible in the given measurement situation. "Best" is a combination of statistical (number of counts) and spectral quality (peak width and position) considerations over a wide range of count rates. The development of multichannel analyzers (MCA) using digital signal processing (DSP) has made possible a much wider range of values for shaping times as well as the processing of the detector signal in various ways to improve performance with pulse-by-pulse adjustments. The pulse processing time is directly related to the shaping time. The throughput is related to the pulse processing time and the duration of the detector signal. Longer shaping times generally produce better peak resolution. However, the longer shaping times mean larger dead times and lower throughput. The ability to select the best compromise between throughput and resolution is possible with DSP MCAs. In addition, the dead-time-per-pulse can be reduced by changing the digital filter without significant impact on the full-width at half-maximum. To evaluate the improvements and to suggest an approach to optimization of system performance, a small and a large GEM (p-type) coaxial HPGe detector were selected for measurements to determine the performance at various input count rates and wide range of rise times and flattops in the DSPEC 50 MCA. Results will be presented for the throughput measured at dead times from 30 to 99.9 % with and without the use of the ORTEC Enhanced Throughput Mode. © 2012 Akadémiai Kiadó, Budapest, Hungary.
Keyser R.M.,ORTEC |
Twomey T.R.,ORTEC |
Webster N.A.,Thermo Fisher Scientific |
Belbot M.D.,Thermo Fisher Scientific
Proceedings of the International Conference on Radioactive Waste Management and Environmental Remediation, ICEM | Year: 2011
Several different types of detectors, software, and hardware designs are employed in instruments used to monitor radioactive content of freight shipments in order to detect illicit trafficking of nuclear materials. The instruments can be container monitors, hand-held radiation detectors, mobile analysis systems, or fixed radiation portal monitors. However, within the various groupings (e.g., portal monitors), all instruments are expected to solve the same problem, that is, to detect and identify any radioactive material present according to the prescribed investigative procedure or CONOPS. The best way to compare the performance of different instruments is with a numerical score or Figure of Merit (FOM). The FOM must quantify the performance of the instrument with respect to true positives (TP), false positives (FP), and false negatives (FN). The minimization of FN for certain radionuclides (e.g., uranium and plutonium or other Special Nuclear Material (SNM)) is more important than the minimization of FN for non-threat nuclides (e.g., low level NORM). In a similar way, the minimization of FP for SNM is more important than falsely reporting the common NORM nuclides which represent no threat. System performance depends on the measurement detail (e.g., transit speed through a portal, measurement time in general, amount and distribution of NORM), therefore the test conditions should also be included in the statement of the FOM. The FOM is expected to vary significantly with the above measurement details. A FOM has been developed based on the number of true positives (TP), the number of false important positives (FIP), the number of FP, the number of true positives for SNM (TPSNM), and the number of false positives for SNM (FPSNM). This formula rates the overall performance with extra weight given to FP and FN for SNM. Examples will be shown for testing of portal monitors. Copyright © 2011 by ASME.
Meuffels W.J.M.,ORTEC |
Meuffels W.J.M.,University of Tilburg |
Fleuren H.A.,University of Tilburg |
Cruijssen F.C.A.M.,Wageningen University |
Van Dam E.R.,University of Tilburg
Flexible Services and Manufacturing Journal | Year: 2010
Express service carriers provide time-guaranteed deliveries of parcels via a network consisting of nodes and hubs. In this, nodes take care of the collection and delivery of parcels, and hubs have the function to consolidate parcels in between the nodes. The tactical network design problem assigns nodes to hubs, determines arcs between hubs, and routes parcels through the network. Afterwards, fleet scheduling creates a schedule for vehicles operated in the network. The strong relation between flow routing and fleet scheduling makes it difficult to optimise the network cost. Due to this complexity, fleet scheduling and network design are usually decoupled. We propose a new tactical network design model that is able to include fleet scheduling characteristics (like vehicle capacities, vehicle balancing, and drivers' legislations) in the network design. The model is tested on benchmark data based on instances from an express provider, resulting in significant cost reductions. © 2010 The Author(s).
van der Veen E.,ORTEC |
van der Veen E.,University of Twente |
Hans E.W.,University of Twente |
Post G.F.,ORTEC |
And 3 more authors.
Journal of Scheduling | Year: 2015
This paper introduces a shift rostering problem that surprisingly has not been studied in the literature: the weekend shift rostering problem. It is motivated by our experience that employees’ shift preferences predominantly focus on the weekends, since many social activities happen during weekends. The weekend rostering problem (WRP) addresses the rostering of weekend shifts, for which we design a problem-specific heuristic. We consider the WRP as the first phase of the shift rostering problem. To complete the shift roster, the second phase assigns the weekday shifts. This decomposition reflects how shift rosters are often created manually in practice, which makes the decomposition method proposed in this paper a more intuitive approach for business users compared to approaches without this decomposition. We believe that such approaches enable business users to effectively analyze and steer the outcomes of algorithms for shift rostering especially on criteria that are relevant to them such as those concerning weekends. We analyze and discuss effects of this two-phase approach both on the weekend shift roster and on the roster as a whole. We demonstrate that our first-phase weekend rostering heuristic is effective both on generated instances and real-life instances. For situations where the weekend shift roster is one of the key determinants of the quality of the complete roster, our two-phase approach is shown to be effective. © 2014, Springer Science+Business Media New York.
Gromicho J.,VU University Amsterdam |
Van Hoorn J.J.,VU University Amsterdam |
Kok A.L.,ORTEC |
Schutten J.M.J.,University of Twente
Computers and Operations Research | Year: 2012
Most successful solution methods for solving large vehicle routing and scheduling problems are based on local search. These approaches are designed and optimized for specific types of vehicle routing problems (VRPs). VRPs appearing in practice typically accommodate restrictions that are not accommodated in classical VRP models, such as time-dependent travel times and driving hours regulations. We present a new construction framework for solving VRPs that can handle a wide range of different types of VRPs. In addition, this framework accommodates various restrictions that are not considered in classical vehicle routing models, but that regularly appear in practice. Within this framework, restricted dynamic programming is applied to the VRP through the giant-tour representation. This algorithm is a construction heuristic which for many types of restrictions and objective functions leads to an optimal algorithm when applied in an unrestricted way. We demonstrate the flexibility of the framework for various restrictions appearing in practice. The computational experiments demonstrate that the framework competes with state of the art local search methods when more realistic constraints are considered than in classical VRPs. Therefore, this new framework for solving VRPs is a promising approach for practical applications. © 2011 Elsevier Ltd. All rights reserved.
PubMed | ORTEC
Type: Journal Article | Journal: Health care management science | Year: 2015
We propose a mathematical programming formulation that incorporates annualized hours and shows to be very flexible with regard to modeling various contract types. The objective of our model is to minimize salary cost, thereby covering workforce demand, and using annualized hours. Our model is able to address various business questions regarding tactical workforce planning problems, e.g., with regard to annualized hours, subcontracting, and vacation planning. In a case study for a Dutch hospital two of these business questions are addressed, and we demonstrate that applying annualized hours potentially saves up to 5.2% in personnel wages annually.
News Article | December 5, 2016
NPI, a leading spend management consulting firm, has appointed Don Addington as President. A dynamic and recognized leader in the technology industry, Addington was previously President and CEO of Mobile Labs, a provider of automated, cross-platform mobile application testing solutions. “It’s rare to find a leader that has the experience, enthusiasm and track record that Don brings to the table. His ability to help companies achieve their full growth potential is remarkable. Don will help us take NPI to the next level of success and we are honored to have him join our team,” said Jon Winsett, CEO of NPI. Addington brings more than 35 years of enterprise information technology and business leadership to NPI, and a long track record of growing successful companies. As President and CEO of Mobile Labs, Addington was responsible for taking the business from start-up to an established market leader in mobile application testing. He previously served as President, Americas at ORTEC, a global supply chain software provider, and as President and CEO at Seagull Software where his vision and leadership established the company as one of the world’s leading providers of legacy evolution IT solutions. He was President and COO of KnowledgeWare, an innovative application development tools provider, and has served as Chairman and Vice Chair of the Technology Association of Georgia’s (TAG) board of directors. “Taking companies to their next level of growth is something I’m very passionate about and I’m thrilled to be joining NPI to achieve that objective,” said Addington. “All of the right elements are in place – a strong commitment to excellence, a talented team and a terrific company culture. IT sourcing is also at an interesting inflection point where transformation is happening, but companies need a roadmap and the tools to get there. The sky is the limit.” Addington will focus on client acquisition and revenue growth strategies. CEO Jon Winsett will focus on the company’s business direction and portfolio expansion. Winsett added: “Don and I have worked together before in rapid growth companies so we know how to get things done together, and I couldn’t be more excited about NPI’s future.” For more information on NPI’s IT, telecom and transportation spend management services, visit http://www.npifinancial.com. About NPI NPI is a spend management consulting firm that protects companies from overspending in three cost categories where pricing is opaque, complex and inconsistent – information technology, telecommunication and transportation. Using price benchmark data and vendor-specific cost reduction expertise, NPI helps clients assure that each purchase is priced at or below fair market value and program selection, licensing and business terms are cost-optimized. Reviewing more than 14,000 purchases annually, NPI provides objective oversight for billions of dollars of strategic spend for its clients. To learn more about how NPI can help your company start saving today, visit http://www.npifinancial.com or call 404-591-7500