Measurements of differential scattering cross section using a ring transducer

A procedure for the measurement of intrinsic scattering object properties is presented and used to obtain illustrative results. The procedure is based on the measurement of the scattered acoustic field as a function of scattering angle and frequency. Measurements are normalized using analytically determined expressions for emitter and detector beams resulting from a combination of unfocused linear elements arranged in a circular configuration. The spatial effects of finite emitter pulse length and detector gate length are represented by a convolution formula valid for narrow-band transmitted signals and long receiver gates. The normalization includes correction for target absorption as well as measurement of the directly transmitted acoustic power in the free field and yields the average differential scattering cross section per unit volume. Under the Born approximation, this quantity is directly proportional to the spatial-frequency spectrum of the scattering medium inhomogeneities. Measured results are reported for two phantoms consisting of glass microspheres embedded in a weakly absorbing agar background medium. For the phantoms employed, scattering effects, rather than increased absorption, are shown to account for most of the difference in transmission loss between pure agar and agar with glass spheres. The measured differential scattering cross sections are compared with theoretical cross sections for distributions of glass spheres measured experimentally. The measured values show good relative agreement with theory for varying angle, frequency, and phantom properties. The results are interpreted in terms of wave space resolution and the potential for tissue characterization using similar fixed transducer configurations.     

铝(Ⅲ)-铝试剂-溴化十六烷基三甲胺体系共振瑞利散射法测定痕量铝

铝是广泛应用于工业生产各个领域的重要金属材料,愈来愈多的铝化合物随废水排入水体,因此测定水中铝的含量很有必要。研究了铝(Ⅲ)-铝试剂-溴化十六烷基三甲铵体系的共振瑞利散射光谱,优化了体系的最佳条件,考察了体系的其他离子干扰情况,初步探讨了反应机理,并据此建立了共振瑞利散射法测定铝的方法。试验表明,在弱酸性介质中,铝与铝试剂(ATA)形成配阴离子,然后再与溴化十六烷基三甲胺(CTMAB)通过静电引力及疏水作用力形成离子缔合物,从而引起体系的共振瑞利散射强度增加。在598.1nm处,Al(Ⅲ)的质量浓度在0.02~0.16μg/mL范围内与其对应的共振瑞利散射强度呈良好的线性关系,相关系数为0.998 9。方法检出限为1.8ng/mL。对实际水样进行了分析检测,铝测定结果的相对标准偏差(RSD,n=6)均不大于1.1%,回收率为93.5%~100.8%,测定值与原子吸收光谱法(AAS)测定值基本一致。     

Characterization of 9Cr-1MoVNb steel by anomalous small-angle X-ray scattering

The size distribution and volume fraction of Cr₂₃C₆ precipitates in 9Cr-1MoVNb steel have been isolated from the distributions of all other precipitates by the technique of anomalous small-angle X-ray scattering. Three X-ray wavelengths near the Cr K absorption edge were used to vary the scattering contrast of Cr₂₃C₆ while that of the other precipitates was left unchanged. Size distributions calculated from each scattering curve using a maximum entropy method were combined by a scattering contrast gradient analysis to isolate the volume-fraction size distribution of the chromium carbides. Behavior of these carbides was studied as a function of isothermal aging temperature. Mean diameter is smallest and Cr₂₃C₆ number density is highest after aging at 811 K. Above 811 K, the mean diameter of the chromium carbides increases with increasing aging temperature.     

Determination of dispersoid size distributions in Inconel MA 754 by small-angle X-ray scattering

The dispersoid size frequency distribution and volume fraction of the nickel based oxide dispersion strengthened alloy Inconel MA 754 have been determined using small-angle X-ray scattering (SAXS). Two methods of determining dispersoid size distributions from the SAXS spectra are utilized. One method involves a calculation of log-normal distribution parameters from the integrated intensity, forward scattering and the Porod radius. A second method employs an integral transform of the data to calculate the size distribution. Dispersoid size distributions from the transform method exhibit close agreement with histograms obtained from thin foil transmission electron microscopy. Measurement of dispersoid volume fractions from the integrated intensity, coupled with dispersoid size frequency distributions allow a calculation of the average planar separation distance of the dispersoids. The results for two heats of MA 754 lead to predicted dislocation creep strengths which are in reasonable agreement with short time creep data at 1000 and 1093°C. The effect of the presence of mixed aluminum-yttrium oxides in MA 754 is considered.     

Measurement of smoothed Wigner phase-space distributions for small-angle scattering in a turbid medium

We study Wigner phase-space distributions W (x, p) in position (x) and momentum (p) for light undergoing multiple small-angle scattering in a turbid medium. Smoothed Wigner phase-space distributions are measured by using a heterodyne technique that achieves position and momentum resolution determined by the width and the diffraction angle of the local oscillator beam. The sample consists of 5.7-micron-radius polystyrene spheres suspended in a water-glycerol mixture. The momentum distribution of the transmitted light is found to contain a ballistic peak, a narrow diffractive pedestal, and a broad background. The narrow diffractive pedestal is found to decay more slowly than the ballistic peak as the concentration of scatterers is increased. The data are in excellent agreement with a simple theoretical model that explains the behavior of the narrow pedestal by including multiple diffractive scattering and treating large-angle scattering as a loss.     

Frequency dependence of acoustic backscatter from 5 to 65 MHz (0.06 < ka < 4.0) of polystyrene beads in agarose

Attenuation and compensated backscatter from suspensions of random distributions of polystyrene beads in agarose are reported across a broad, continuous range of frequencies including frequencies which are currently of interest in the emerging fields of acoustic backscatter microscopy and intravascular imaging. Data are reported over the range of ka from 0.06 to 4, where k is the magnitude of the ultrasonic wave vector and a is the radius of the beads. The attenuation coefficient exhibits a linear dependence on frequency for ka < < 1 and more complex behaviour at larger values of ka. The measured frequency dependence of the compensated backscatter was consistent with the frequency dependence of the differential backscatter cross section for a single polystyrene sphere throughout the range of ka investigated.     

Calculation accuracy of volumes for evaluating dose-volume histograms. Comparison of various radiation planning systems

BACKGROUND: Modern 3-dimensional treatment planning systems on the basis of sectional imaging allow the calculation of volumes for organs of interest. The aim of this study is to investigate systematically the accuracy of calculations of volumes by the use of a phantom for 4 different treatment planning systems. MATERIAL AND METHOD: The tests were done with a phantom with 5 cylindrical structures and 6 spherical shaped structures. After performing a CT-scan and reading the data into the planning systems the structures were contoured and the volumes were calculated in order to compare these values with the values calculated by mathematical equations. This was systematically done as a function of different parameters. RESULTS: Comparing different methods of contouring showed notable influence on the result. Parameters as number of calculation points or length of cylinders showed no significant differences. In summary, the mean deviations for cylinders were +7% for system A, -2% for B, -17% for C, and 0% for D. For larger spheres (radii between 5 and 2.5 cm) the mean deviations were -5% for A, +3% for B, +1% for C, and +5% for D. For smaller spheres (radii between 1.75 and 1.25 cm) the mean deviations were -14% for A, -2% for B, -10% for C, and -4% for D. CONCLUSION: Verifying results of planning systems is important for the daily routine, but it has to be taken into account, that small changes of the radius of a cylinder or sphere cause substantial volume changes. The differences are also caused by inaccuracies of the whole procedure, e.g., the CT study, the shape and dimensions of the cylinders and the spheres and the CT information and the delineariation of the structures.     

Characterization of Open Volume Regions in a Simulated Cu-Zr Metallic Glass

Optimizing the structural reliability of bulk metallic glass (BMG) components demands a detailed understanding of the atomic structure of the glass, particularly the defects that control plastic flow. These defects are thought to be associated with regions of low atomic density, which facilitate the required diffusion-like atomic rearrangement processes. In the present article, the distribution of low-density regions in a simulated Cu-Zr glass is studied with two different techniques. Using a hard-sphere model, the interstitial volume distribution was obtained by constructing Voronoi polyhedra around each atom and inserting spheres into the unoccupied regions at the vertices. The volumes of touching spheres were summed and corrected for any overlap to obtain the size distribution of the unoccupied sites. The resulting distribution is in good agreement with Cohen and Turnbull’s free volume model and provides insight into how a single free volume site may be described. However, this model depends significantly on the somewhat arbitrary selection of the hard-sphere atomic radii and may not give a realistic indication of the shape or connectivity of the low atomic-density regions. Recent experimental studies of the open volume distribution using positron annihilation spectroscopy probe the electron and not the atomic density. We therefore propose a novel method to identify low-density regions from ab initio calculated radially averaged electron-density distributions, which allows a more physical and less ambiguous identification of low-density areas and, at the same time, connects atomic and electron distributions. Our results show that the qualitative volume distribution from the electron-density model agrees well with the hard-sphere model, while allowing a more physical quantitative analysis. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.     

Chain Orientation in Block Copolymers Exhibiting Cylindrically Confined Crystallization

The orientation of the crystal stems in diblock copolymers, where crystallization occurs within the cylindrical microdomains present in the melt mesophase, is investigated via X-ray scattering on flow-aligned specimens. A series of ethylene-b-(3-methyl-1-butene) diblocks (E/MB) is compared with an ethylene-b-(vinylcyclohexane) diblock (E/VCH), where MB is rubbery (Tg < Troom) and VCH is vitreous (Tg = 134 degreesC) at the freezing point of the E block. All of the diblocks contain 26-28 wt % E, leading to a morphology of hexagonally-packed E cylinders. Crystallization in all of these materials can be confined to the cylindrical microdomains. Not only do the crystals align preferentially within the semicrystalline cylinders, but this orientation varies depending on the ability of chains to diffuse during the crystallization process. When chain diffusion is most rapid, alignment is observed with the chain axis in the crystals perpendicular to the cylinder axis and the b axis (fast growth axis) coincident with the cylinder axis. However, when the chain mobility is limited, the crystal stems tilt with respect to a plane which is normal to the cylinder axis, allowing better accommodation of amorphous material at the crystallite surface.     

Protein interactions in solution characterized by light and neutron scattering: comparison of lysozyme and chymotrypsinogen

The effects of pH and electrolyte concentration on protein-protein interactions in lysozyme and chymotrypsinogen solutions were investigated by static light scattering (SLS) and small-angle neutron scattering (SANS). Very good agreement between the values of the virial coefficients measured by SLS and SANS was obtained without use of adjustable parameters. At low electrolyte concentration, the virial coefficients depend strongly on pH and change from positive to negative as the pH increases. All coefficients at high salt concentration are slightly negative and depend weakly on pH. For lysozyme, the coefficients always decrease with increasing electrolyte concentration. However, for chymotrypsinogen there is a cross-over point around pH 5.2, above which the virial coefficients decrease with increasing ionic strength, indicating the presence of attractive electrostatic interactions. The data are in agreement with Derjaguin-Landau-Verwey-Overbeek (DLVO)-type modeling, accounting for the repulsive and attractive electrostatic, van der Waals, and excluded volume interactions of equivalent colloid spheres. This model, however, is unable to resolve the complex short-ranged orientational interactions. The results of protein precipitation and crystallization experiments are in qualitative correlation with the patterns of the virial coefficients and demonstrate that interaction mapping could help outline new crystallization regions.     

均匀散射介质参与体系辐射换热分析

在辐射换热网络法基础上，定义了容积散射热阻并导出其表达式，区别容积辐射体对不同表面段的发射率及逸散系数，分析了均匀散射介质参与辐射换热时空间热阻的变化，并绘制出散射介质参与的三元体系辐射换热网络图．介质的散射使得容积段与表面段之间的总热阻增大，因而削弱了容积段与表面段之间的辐射热交换．     

Vesicle size distributions measured by flow field-flow fractionation coupled with multiangle light scattering

The separation method, flow field-flow fractionation (flow FFF), is coupled on-line with multiangle laser light scattering (MALLS) for simultaneous measurement of the size and concentration of vesicles eluting continuously from the fractionator. These size and concentration data, gathered as a function of elution time, may be used to construct both number- and mass-weighted vesicle size distributions. Unlike most competing, noninvasive methods, this flow FFF/MALLS technique enables measurement of vesicle size distributions without a separate refractive index detector, calibration using particle size standards, or prior assumptions about the shape of the size distribution. Experimentally measured size distributions of vesicles formed by extrusion and detergent removal are non-Gaussian and are fit well by the Weibull distribution. Flow FFF/MALLS reveals that both the extrusion and detergent dialysis vesicle formation methods can yield nearly size monodisperse populations with standard deviations of approximately 8% about the mean diameter. In contrast to the rather low resolution of dynamic light scattering in analyzing bimodal systems, flow FFF/MALLS is shown to resolve vesicle subpopulations that differ by much less than a factor of two in mean size.     

Ordering of human bone marrow B lymphocyte precursors by single-cell polymerase chain reaction analyses of the rearrangement status of the immunoglobulin H and L chain gene loci

CD19+CD10+ human B lineage bone marrow cells were separated into cycling or resting cells, which differ in their expression of CD34, VpreB, recombination activating gene (RAG-1), and terminal deoxynucleotidyl transferase (TdT). Polymerase chain reaction analyses developed for DHJH and VkJk, VkJkK(de) and VkK(de) rearrangements with DNA of single cells and a comparison with B lineage cell development in mouse bone marrow, allow to delineate the human B lymphocyte pathway of development as follows: CD34+VpreB+RAG-1+TdT+, DHJH-rearranged, kL germline cycling pre-B I cells-->CD34-VpreB+microH chain+ (pre-B receptor+) RAG-1-TdT-, VHDHJH-rearranged, kL germline, cycling pre-B II cells-->CD34-VpreB-, intracytoplasmic microH chain+ (pre-B receptor-) RAG-1+/-TdT-, VHDHJH-rearranged, mainly kL germline cycling pre-B II cells-->CD34-VpreB-intracytoplasmic microH chain+, RAG-1+TdT-, VHDHJH-rearranged, VkJk-rearranged, IgM-, resting pre-B II cells CD34+VpreB-, sIgM+, RAG-1+TdT-, VHDHJH- and VkJk-rearranged IgM+ immature B cells-->CD34-, CD10-, sIgM+/sIgD+ mature B cells. This order, for the first time established for human B lineage cells, shows striking similarities with that established for mouse B lineage cells in bone marrow.     

A model of the quaternary structure of the Escherichia coli F1 ATPase from X-ray solution scattering and evidence for structural changes in the delta subunit during ATP hydrolysis

The shape and subunit arrangement of the Escherichia coli F1 ATPase (ECF1 ATPase) was investigated by synchrotron radiation x-ray solution scattering. The radius of gyration and the maximum dimension of the enzyme complex are 4.61 +/- 0.03 nm and 15.5 +/- 0.05 nm, respectively. The shape of the complex was determined ab initio from the scattering data at a resolution of 3 nm, which allowed unequivocal identification of the volume occupied by the alpha3beta3 subassembly and further positioning of the atomic models of the smaller subunits. The delta subunit was positioned near the bottom of the alpha3beta3 hexamer in a location consistent with a beta-delta disulfide formation in the mutant ECF1 ATPase, betaY331W:betaY381C:epsilonS108C, when MgADP is bound to the enzyme. The position and orientation of the epsilon subunit were found by interactively fitting the solution scattering data to maintain connection of the two-helix hairpin with the alpha3beta3 complex and binding of the beta-sandwich domain to the gamma subunit. Nucleotide-dependent changes of the delta subunit were investigated by stopped-flow fluorescence technique at 12 degrees C using N-[4-[7-(dimethylamino)-4-methyl]coumarin-3-yl]maleimide (CM) as a label. Fluorescence quenching monitored after addition of MgATP was rapid [k = 6.6 s-1] and then remained constant. Binding of MgADP and the noncleavable nucleotide analog AMP . PNP caused an initial fluorescent quenching followed by a slower decay back to the original level. This suggests that the delta subunit undergoes conformational changes and/or rearrangements in the ECF1 ATPase during ATP hydrolysis.     

Comparison of nuclear magnetic resonance spectroscopy with dual-photon absorptiometry and dual-energy X-ray absorptiometry in the measurement of thoracic vertebral bone mineral density: compressive force versus bone mineral

31P nuclear magnetic resonance spectroscopy (NMRS) measurements were made on human T2 and T3 vertebral bodies. The bone mineral content (BMC) of isolated vertebral bodies minus the posterior elements and disks was measured using (1) NMRS on a 3.5 T, 85 mm bore GE Medical Systems NT-150 superconducting spectrometer, (2) a Lunar Corporation DPX-L dual-energy X-ray absorptiometry (DXA) scanner in an anterior-posterior (AP) orientation, (3) a Norland Corporation XR26 DXA scanner, also in an AP direction, and (4) a Norland Corporation model 2600 dual-photon absorptiometry (DPA) densitometer in both the AP and superior-inferior (SI) directions. Vertebral body volumes were measured using a water displacement technique to determine volume bone mineral densities (VBMD). They were then compressed to failure using an electrohydraulic testing device, followed by ashing in a muffle furnace at 700 degrees C for 18 h. Correlations of BMC between NMRS and DPA, DXA and ashing were excellent (0.96 < or = r < or = 0.99); in a one-way analysis of variance (ANOVA) test, means were not statistically different at a p level of 0.757. The correlations of VBMD between NMRS and the other methods were not as good (0.83 < or = r < or = 0.95); in a one-way ANOVA test, means were not statistically different at a p level of 0.089. BMC was a better predictor of ultimate compressive failure than VBMD for all six methods. For NMRS, the regression coefficient for BMC was r2 = 0.806, compared with r2 = 0.505 for VBMD. NMRS may prove an alternative to present methods of determining bone mineral.     

SiC对粉碎烧结法制备P型Bi0.5Sb1.5Te3合金热电性能的影响

向粉碎法制备的Bi_0.5Sb_1.5Te₃+5%Te(质量分数)合金粉体中混入不同体积分数的SiC颗粒,利用放电等离子体烧结法制备SiC复合块体材料,探究块体材料组织和热电性能的变化规律。研究发现：随着SiC体积分数的增加,块体材料的取向性弱化,组织细化,载流子浓度增加,迁移率降低;由于取向性弱化及组织细化,加强了声子散射,降低了晶格热导率。由于SiC复合块体材料的电学性能恶化,块体材料的无量纲热电优值(ZT)并未获得显著的提升;当SiC体积分数为0.40%时,SiC复合块体材料在322 K时具有最优的无量纲热电优值(ZT=～0.81)。     

Recovery of neonatal head turning to decreased sound pressure level.

Human newborns' responses to decreased sound pressure level (SPL) were investigated with a localized head-turning habituation procedure. Recovery to a decrement in volume contradicts a selective receptor adaptation view because a lower intensity stimulus does not engage a separate set of receptor cells. Ninety-six infants (mean age 41 hrs) were presented with the same sound for 2 infant-controlled phases. After criterion orientation (3 head turns toward the sound in 4 consecutive trials) and criterion habituation (3 consecutive trials with no head turns or head turns away) to 1 of 2 stimulus intensities (72 or 78 dB [SPL]), infants were randomly assigned to test trials at an intensity of 66, 72, or 78 dB (SPL). Planned comparisons of percentage of test trials with head turns toward the sound revealed that decreased SPL produced recovery of localized head turning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Salt-dependent DNA superhelix diameter studied by small angle neutron scattering measurements and Monte Carlo simulations

Using small angle neutron scattering we have measured the static form factor of two different superhelical DNAs, p1868 (1868 bp) and pUC18 (2686 bp), in dilute aqueous solution at salt concentrations between 0 and 1.5 M Na+ in 10 mM Tris at 0% and 100% D2O. For both DNA molecules, the theoretical static form factor was also calculated from an ensemble of Monte Carlo configurations generated by a previously described model. Simulated and measured form factors of both DNAs showed the same behavior between 10 and 100 mM salt concentration: An undulation in the scattering curve at a momentum transfer q = 0.5 nm-1 present at lower concentration disappears above 100 mM. The position of the undulation corresponds to a distance of approximately 10-20 nm. This indicated a change in the DNA superhelix diameter, as the undulation is not present in the scattering curve of the relaxed DNA. From the measured scattering curves of superhelical DNA we estimated the superhelix diameter as a function of Na+ concentration by a quantitative comparison with the scattering curve of relaxed DNA. The ratio of the scattering curves of superhelical and relaxed DNA is very similar to the form factor of a pair of point scatterers. We concluded that the distance of this pair corresponds to the interstrand separation in the superhelix. The computed superhelix diameter of 16.0 +/- 0.9 nm at 10 mM decreased to 9.0 +/- 0.7 nm at 100 mM salt concentration. Measured and simulated scattering curves agreed almost quantitatively, therefore we also calculated the superhelix diameter from the simulated conformations. It decreased from 18.0 +/- 1.5 nm at 10 mM to 9.4 +/- 1.5 nm at 100 mM salt concentration. This value did not significantly change to lower values at higher Na+ concentration, in agreement with results obtained by electron microscopy, scanning force microscopy imaging in aqueous solution, and recent MC simulations, but in contrast to the observation of a lateral collapse of the DNA superhelix as indicated by cryo-electron microscopy studies.     

The influence of premedication on heart rate variability

Analysis of heart rate variability has been used to study the effects of midazolam, morphine and clonidine on the autonomic nervous system, when administered to patients for premedication. Ninety-five patients were studied 60 min before and 60 min after premedication. Normal saline (n = 25), midazolam 0.08 mg.kg-1 (n = 24), morphine 0.15 mg.kg-1 (n = 23), or clonidine 2 micrograms.kg-1 (n = 23) were administered intramuscularly by random allocation. A Holter device was connected to the patient during the study period. Using power spectral analysis the low-frequency and high-frequency components were calculated from the Holter recordings. These are markers for sympathetic and parasympathetic activity respectively; the low- to high-frequency ratio was also calculated, a ratio of > 1 signifying sympathetic dominance. A significant reduction was noticed in both low-frequency and high-frequency power in the three premedicated groups, whereas no changes were observed in the normal saline group. In the case of midazolam, both the low and high frequencies were decreased but the low- to high-frequency ratio did not change significantly. Morphine and clonidine depressed the low-frequency component more than the high-frequency component and the low- to high-frequency ratio was decreased, suggesting parasympathetic dominance. We conclude that heart rate variability may be a useful tool for investigating the effect of drugs on the autonomic nervous system.     

Sediment Monitoring Bias by Automatic Sampler in Comparison with Large Volume Sampling for Parking Lot Runoff

A field study was conducted to assess biases of suspended sediment concentration (SSC) analyses (ASTM Standard D3977-97) performed on discrete samples obtained by automatic sampler in comparison with actual sediment concentrations from large volume sampling. Research results indicate that the biases attributed to the monitoring of sediment event mean concentration (EMC) and median particle size in parking lot runoff by automated samplers (nonisokinetic) were minimal. Large volume samples ( ～ 15,000??L) of the first-flush event runoff were taken from a storm-water sewer system for eighteen storm events over two years. The intent was to obtain a complete portion of a storm to accurately determine EMCs and particle size distributions (PSDs). Concurrently, flow-weighted discrete samples were obtained by automatic samplers for the same portion of the events. Thus, characteristics of sediments from a whole-storm sample were compared with those of subsamples obtained by an automatic sampler using nonisokinetic sampling. SSCs and PSDs were compared for the two respective field sampling methods. The two methods showed a strong correlation for median sediment EMCs (R2 = 0.98, n = 18). Biases to particle size distributions were found to be both for the large particles (>75–150??μm) and smaller fines (<25??μm). Specific sediment size fractions captured by the large volume sampling and automatic sampler were not significantly different (α = 0.05) for D50, which = 58 and 46??μm, respectively.