Mean Coherence Length Research Articles

Coherence Metrics for Reader-Independent Differentiation of Cystic From Solid Breast Masses in Ultrasound Images.

Traditional breast ultrasound imaging is a low-cost, real-time and portable method to assist with breast cancer screening and diagnosis, with particular benefits for patients with dense breast tissue. We previously demonstrated that incorporating coherence-based beamforming additionally improves the distinction of fluid-filled from solid breast masses, based on qualitative image interpretation by board-certified radiologists. However, variable sensitivity (range: 0.71-1.00 when detecting fluid-filled masses) was achieved by the individual radiologist readers. Therefore, we propose two objective coherence metrics, lag-one coherence (LOC) and coherence length (CL), to quantitatively determine the content of breast masses without requiring reader assessment. Data acquired from 31 breast masses were analyzed. Ideal separation (i.e., 1.00 sensitivity and specificity) was achieved between fluid-filled and solid breast masses based on the mean or median LOC value within each mass. When separated based on mean and median CL values, the sensitivity/specificity decreased to 1.00/0.95 and 0.92/0.89, respectively. The greatest sensitivity and specificity were achieved in dense, rather than non-dense, breast tissue. These results support the introduction of an objective, reader-independent method for automated diagnoses of cystic breast masses.

Polycrystalline texture causes magnetic instability in greigite

Magnetic stability of iron mineral phases is a key for their use as paleomagnetic information carrier and their applications in nanotechnology, and it critically depends on the size of the particles and their texture. Ferrimagnetic greigite (Fe3S4) in nature and synthesized in the laboratory forms almost exclusively polycrystalline particles. Textural effects of inter-grown, nano-sized crystallites on the macroscopic magnetization remain unresolved because their experimental detection is challenging. Here, we use ferromagnetic resonance (FMR) spectroscopy and static magnetization measurements in concert with micromagnetic simulations to detect and explain textural effects on the magnetic stability in synthetic, polycrystalline greigite flakes. We demonstrate that these effects stem from inter-grown crystallites with mean coherence length (MCL) of about 20 nm in single-domain magnetic state, which generate modifiable coherent magnetization volume (CMV) configurations in the flakes. At room temperature, the instability of the CVM configuration is exhibited by the angular dependence of the FMR spectra in fields of less than 100 mT and its reset by stronger fields. This finding highlights the magnetic manipulation of polycrystalline greigite, which is a novel trait to detect this mineral phase in Earth systems and to assess its fidelity as paleomagnetic information carrier. Additionally, our magneto-spectroscopic approach to analyse instable CMV opens the door for a new more rigorous magnetic assessment and interpretation of polycrystalline nano-materials.

Effect of increasing disorder on superconductivity of Mo/Nb superlattices

We investigated the superconducting properties of Nb/Mo superlattices (SLs). The structural changes as a function of Nb and Mo layer thickness allow us to investigate the effect of disorder on the superconducting properties in a controlled fashion. Systematic structural studies provide quantitative measures of disorder parameters, such as roughness, interdiffusion, and strain, which allow separating their effect on the individual superconducting layers. The Mo critical temperature does not change as the layer thickness decreases below its coherence length. Thus, the SL critical temperatures in the presence of disorder and proximity effects can be modeled by considering only the effects of the Nb mean free path and coherence length. With increasing layer thickness, the SL critical temperatures approach Nb bulk values. Contrary to expectations the Tc of Mo remains below the Nb Tc. We discuss the results using existing theories based on Coulomb repulsion or changes in the density of states at the Fermi surface as a function of disorder. Questions about current understanding of the effect of disorder on superconductivity arise from the results.

Pairing versus quarteting coherence length

We systematically analyse the coherence length in even-even nuclei. The pairing coherence length in the spin-singlet channel for the effective density dependent delta (DDD) and Gaussian interaction is estimated. We consider in our calculations bound states as well as narrow resonances. It turns out that the pairing gaps given by the DDD interaction are similar to those of the Gaussian potential if one renormalizes the radial width to the nuclear radius. The correlations induced by the pairing interaction have in all considered cases a long range character inside the nucleus and decrease towards the surface. The mean coherence length is larger than the geometrical radius for light nuclei and approaches this value for heavy nuclei. The effect of the temperature and states in continuum is investigated. Strong shell effects are evidenced, especially for protons. We generalize this concept to quartets by considering similar relations, but between proton and neutron pairs. The quartet coherence length has a similar shape, but with larger values on the nuclear surface. We evidence the important role of proton-neutron correlations by estimating the so-called alpha coherence length, which takes into account the overlap with the proton-neutron part of the $\alpha$-particle wave function. It turns out that it does not depend on the nuclear size and has a value comparable to the free $\alpha$-particle radius. We have shown that pairing correlations are mainly concentrated inside the nucleus, while quarteting correlations are connected to the nuclear surface.

Characterization of the effects of silicon on the formation of goethite

Goethite samples were synthesised with different sodium silicate concentrations (0, 10 −5, 10 −4, 10 −3 and 10 −2 M) in the initial aqueous solution. X-ray diffraction (XRD), Mössbauer spectrometry, inductively coupled plasma mass spectrometry (ICP-MS) and transmission electron microscopy (TEM) were used to investigate the influence of Si content on the formation and physical characteristics of goethite. Mössbauer spectroscopy and TEM results demonstrate that the particle size changes as the sodium silicate content increases. XRD results (lattice parameters, line width and mean coherence length values) do not show any indication that Si species would substitute for Fe in the goethite structure.

Acid‐tolerant microaerophilic Fe(II)‐oxidizing bacteria promote Fe(III)‐accumulation in a fen

The ecological importance of Fe(II)-oxidizing bacteria (FeOB) at circumneutral pH is often masked in the presence of O(2) where rapid chemical oxidation of Fe(II) predominates. This study addresses the abundance, diversity and activity of microaerophilic FeOB in an acidic fen (pH ∼ 5) located in northern Bavaria, Germany. Mean O(2) penetration depth reached 16 cm where the highest dissolved Fe(II) concentrations (up to 140 µM) were present in soil water. Acid-tolerant FeOB cultivated in gradient tubes were most abundant (10(6) cells g(-1) peat) at the 10-20 cm depth interval. A stable enrichment culture was active at up to 29% O(2) saturation and Fe(III) accumulated 1.6 times faster than in abiotic controls. An acid-tolerant, microaerophilic isolate (strain CL21) was obtained which was closely related to the neutrophilic, lithoautotrophic FeOB Sideroxydans lithotrophicus strain LD-1. CL21 oxidized Fe(II) between pH 4 and 6.0, and produced nanoscale-goethites with a clearly lower mean coherence length (7 nm) perpendicular to the (110) plane than those formed abiotically (10 nm). Our results suggest that an acid-tolerant population of FeOB is thriving at redox interfaces formed by diffusion-limited O(2) transport in acidic peatlands. Furthermore, this well-adapted population is successfully competing with chemical oxidation and thereby playing an important role in the microbial iron cycle.

Preparation and Properties of Various Magnetic Nanoparticles

The fabrications of iron oxides nanoparticles using co-precipitation and gadolinium nanoparticles using water in oil microemulsion method are reported in this paper. Results of detailed phase analysis by XRD and Mössbauer spectroscopy are discussed. XRD analysis revealed that the crystallite size (mean coherence length) of iron oxides (mainly γ-Fe2O3) in the Fe2O3 sample was 30 nm, while in Fe2O3/SiO2 where the ε-Fe2O3 phase dominated it was only 14 nm. Gd/SiO2 nanoparticles were found to be completely amorphous, according to XRD. The samples showed various shapes of hysteresis loops and different coercivities. Differences in the saturation magnetization (MS) correspond to the chemical and phase composition of the sample materials. However, we observed that MS was not reached in the case of Fe2O3/SiO2, while for Gd/SiO2 sample the MS value was extremely low. Therefore we conclude that only unmodified Fe2O3 nanoparticles are suitable for intended biosensing application in vitro (e.g. detection of viral nucleic acids) and the phase purification of this sample for this purpose is not necessary.

Mixed oxides obtained from Co and Mn containing layered double hydroxides: Preparation, characterization, and catalytic properties

Co–Mn–Al layered double hydroxides (LDHs) with various Co:Mn:Al molar ratios (4:2:0, 4:1.5:0.5, 4:1:1, 4:0.5:1.5, and 4:0:2) were prepared and characterized. Magnesium containing LDHs Co–Mg–Mn (2:2:2), Co–Mg–Mn–Al (2:2:1:1), and Co–Mg–Al (2:2:2) were also studied. Thermal decomposition of prepared LDHs and formation of related mixed oxides were studied using high-temperature X-ray powder diffraction and thermal analysis. The thermal decomposition of Mg-free LDHs starts by their partial dehydration accompanied by shrinkage of the lattice parameter c from ca. 0.76 to 0.66 nm. The dehydration temperature of the Co–Mn–Al LDHs decreases with increasing Mn content from 180 °C in Co–Al sample to 120 °C in sample with Co:Mn:Al molar ratio of 4:1.5:0.5. A subsequent step is a complete decomposition of the layered structure to nanocrystalline spinel, the complete dehydration, and finally decarbonation of the mixed oxide phase. Spinel-type oxides were the primary crystallization products. Mg-containing primary spinels had practically empty tetrahedral cationic sites. A dramatic increase of the spinel cell size upon heating and analysis by Raman spectroscopy revealed a segregation of Co-rich spinel in Co–Mn and Co–Mn–Al specimens. In calcination products obtained at 500 °C, the spinel mean coherence length was 5–10 nm, and the total content of the X-ray diffraction crystalline portion was 50–90%. These calcination products were tested as catalysts in the total oxidation of ethanol and decomposition of N 2O. The catalytic activity in ethanol combustion was enhanced by increasing (Co+Mn) content while an optimum content of reducible components was necessary for high activity in N 2O decomposition, where the highest conversions were found for calcined Co–Mn–Al sample with Co:Mn:Al molar ratio of 4:1:1.

Controls on Fe reduction and mineral formation by a subsurface bacterium

The reductive dissolution of FeIII (hydr)oxides by dissimilatory iron-reducing bacteria (DIRB) could have a large impact on sediment genesis and Fe transport. If DIRB are able to reduce FeIII in minerals of high structural order to carry out anaerobic respiration, their range could encompass virtually every O 2-free environment containing FeIII and adequate conditions for cell growth. Previous studies have established that Shewanella putrefaciens CN32, a known DIRB, will reduce crystalline Fe oxides when initially grown at high densities in a nutrient-rich broth, conditions that poorly model the environments where CN32 is found. By contrast, we grew CN32 by batch culture solely in a minimal growth medium. The stringent conditions imposed by the growth method better represent the conditions that cells are likely to encounter in their natural habitat. Furthermore, the expression of reductases necessary to carry out dissimilatory Fe reduction depends on the method of growth. It was found that under anaerobic conditions CN32 reduced hydrous ferric oxide (HFO), a poorly crystalline FeIII mineral, and did not reduce suspensions containing 4 mM FeIII in the form of poorly ordered nanometer-sized goethite (α-FeOOH), well-ordered micron-sized goethite, or nanometer-sized hematite (α-Fe 2O 3) crystallites. Transmission electron microscopy (TEM) showed that all minerals but the micron-sized goethite attached extensively to the bacteria and appeared to penetrate the outer cellular membrane. In the treatment with HFO, new FeII and FeIII minerals formed during reduction of HFO-Fe in culture medium containing 4.0 mmol/L P i (soluble inorganic P), as observed by TEM with energy-dispersive X-ray spectroscopy, selected area electron diffraction, and X-ray diffraction. The minerals included magnetite (Fe 3O 4), goethite, green rust, and vivianite [Fe 3(PO 4) 2 · 8H 2O]. Vivianite appeared to be the stable end product and the mean coherence length was influenced by the rate of FeIII reduction. When P i was 0.4 mol/L under otherwise identical conditions, goethite was the only mineral observed to form, and less Fe 2+ was produced overall. Hence, the ability of DIRB to reduce Fe (hydr)oxides may be limited when the bacteria are grown under nutrient-limited conditions, and the minerals that result depend on the vigor of FeIII reduction.

Coherence lengths and anisotropy inMgB2superconductor

Field and temperature microwave measurements have been carried out on MgB2 thin film grown on Al2O3 substrate. The analysis reveals the mean field coherence length xi_{MF} in the mixed state and a temperature independent anisotropy ratio gamma_{MF} = xi_{MF}^{ab} / xi_{MF}^c approximately 2. At the superconducting transition, the scaling of the fluctuation conductivity yields the Ginzburg-Landau coherence length with a different anisotropy ratio gamma_{GL} = 2.8, also temperature independent.

Lensing of ultra-high energy cosmic rays in turbulent magnetic fields

We consider the propagation of ultra high energy cosmic rays through turbulent magnetic fields and study the transition between the regimes of single and multiple images of point-like sources. The transition occurs at energies around Ec Z 41 EeV(Brms/5 μG)(L/2 kpc)3/2(50 pc/Lc)1/2, where L is the distance traversed by the CR's with electric charge Ze in the turbulent magnetic field of root mean square strength Brms and coherence length Lc. We find that above 2Ec only sources located in a fraction of a few % of the sky can reach large amplifications of its principal image or start developing multiple images. New images appear in pairs with huge magnifications, and they remain amplified over a significant range of energies. At decreasing energies the fraction of the sky in which sources can develop multiple images increases, reaching about 50% for E > Ec/2. The magnification peaks become however increasingly narrower and for E < Ec/3 their integrated effect becomes less noticeable. If a uniform magnetic field component is also present it would further narrow down the peaks, shrinking the energy range in which they can be relevant. Below E Ec/10 some kind of scintillation regime is reached, where many demagnified images of a source are present but with overall total magnification of order unity. We also search for lensing signatures in the AGASA data studying two-dimensional correlations in angle and energy and find some interesting hints.

Mineralogical and (sub)microscopic aspects of iron oxides in polygenetic Oxisols from Minas Gerais, Brazil

Iron oxides are known to be useful paleo-environmental indicators, and their properties may give information about past and present circumstances of weathering and soil formation. Iron oxides from polygenetic Oxisols developed on saprolites of metamorphic rocks (soil-saprolite sequences) and on sediments (soil-sediment sequences) from Minas Gerais, Brazil, were studied by X-ray diffraction, Mössbauer spectroscopy, micromorphology, and electron microscopy to establish the connection between their properties and circumstances of formation. Hematite and goethite are the only iron oxides found in the clay and silt fractions. Micromorphology and mineralogy indicated the presence of three genetically different forms of hematite and four forms of goethite. XRD and Mössbauer spectroscopy indicate that these forms have differences in mean coherence length (MCL) and Al substitution. In soil-saprolite sequences, hematite is mainly formed during saprolite formation, while goethite formed mainly during soil formation. Microscopic hematite formed in the saprolite has low Al substitution and uniform MCL. In response to soil formation, it diminishes to submicroscopic size and goethite is formed towards toposoils. Goethite formed in yellow surface soils reflects recent soil formation and has high Al substitution. Hematites and goethites related to gley phenomena have low Al substitution and large MCLs. Different coexisting forms of either goethite or hematite point to varying pedo-environments, either in time, corroborating the polygenetic nature of the studied soils, or at micron-scale.

Short-Range Coherence in the Energy Transfer of Photosynthetic Light-Harvesting Systems

We employ a simple model for the electronic excitations and the exciton-vibration coupling characterizing the B850 ring of the light-harvesting complex in photosynthetic bacteria to investigate the possibility of coherence in the energy transfer within the system. The structure of the equilibrium density matrix is studied using the path integral formulation of quantum statistical mechanics. The calculated mean coherence length is computed from the average root-mean-square deviation of closed imaginary time paths that are sampled via a Monte Carlo procedure. This procedure allows simultaneous examination of the effects of thermal averaging and dynamic and static disorder in a single calculation. The mean coherence length is found to be about two to three chlorophyll monomers at room temperature. The principal factor responsible for this localization is thermal averaging, although static and dynamic disorder further destabilize extended states. At low temperatures the circular arrangement of the pigments favors coherence with respect to the situation in a linear aggregate. Visual inspection of typical paths offers an intuitive picture of the extent of coherent energy delocalization in biological antenna systems.

Kinetic Instability of Nanocrystalline Aluminum Prepared by Chemical Synthesis; Facile Room-Temperature Grain Growth

Nanocrystalline aluminum (nano-Al) is synthesized by two chemical methods. Method A consists of the following: reaction of LiAlH4 and AlCl3 at 164 °C in 1,3,5-trimethylbenzene produces nano-Al with an average mean coherence length (crystallite size) of 160 ± 50 nm. The byproduct LiCl is removed by washing with MeOH at −25 or 0 °C. Method B consists of the following: nano-Al is produced by decomposition of H3Al(NMe2Et) under reflux in 1,3,5-trimethylbenzene (ca. 100−164 °C), with or without added decomposition catalyst Ti(O-i-Pr)4. Here the mean particle size (40−180 nm) and degree of aggregation of the nano-Al depend on the mole percent of decomposition catalyst used (0−1%). The nano-Al produced by method A contains 3−4 wt % each of C, O, and Cl; whereas that produced by method B contains only ≤0.25 wt % each of C, O, and Cl and is ≥99 wt % Al. nano-Al produced by both methods has been consolidated by uniaxial pressing at 350 MPa for 1 h at 25, 100, or 300 °C. Rapid grain growth is observed at each pressing temperature in method-B powders. The mean grain size doubles at 25 °C within 1 h and continues to increase beyond the nanometer-size regime over longer periods. The low-temperature grain-size instability of the chemically synthesized (method-B) nano-Al contrasts markedly with the high-temperature stability (≥300 °C) of nano-Al prepared by gas condensation or mechanical attrition. Facile grain growth in the chemically synthesized (method-B) nano-Al is attributed to higher grain-boundary purity and to aggregate structures that minimize adventitious oxidation. The results establish that barriers to grain growth in pure nano-Al are intrinsically low.

Morphological and genetic relations between siderite, calcite and goethite in a Low Moor Peat from southern Germany

Siderite, calcite and goethite occur in a Low Moor Peat near Freising, southern Germany. Siderite is present mainly as microcrystalline ovoids which have a lamellar structure and are less than 5 μm long. Selected area electron diffraction and X‐ray diffraction data suggest a crystal size less than that of the ovoids, probably as small as 20–50 nm. Siderite occurs interstitially between plant materials, predominantly of the genus Equisetum. Calcite, which is subordinate to siderite, occurs as pseudomorphs of plant cells. This suggests an earlier crystallization for calcite predating that of the siderite.The distribution of mineral morphologies and pH and Eh data suggest that siderite weathers by oxidation to goethite under mildly alkaline conditions, despite the probable production of protons. This process initially involves a pseudomorphism of the siderite ovoids by goethite. However, the goethite, comprising poorly acicular crystals with a mean coherence length of 11 nm normal to the 111 plane, eventually develops into a massive fabric.Calcite occurs with goethite in oxidized samples in the same location as in the unoxidized samples, but in decreased amount. Thus, calcite dissolution may act as a buffer to siderite oxidation.

Measurements of r_0 and θ_0: two decades and 18 sites

We present a statistical analysis of r (0) and theta(0) measurements collected over the last 2 decades at 18 different sites. Although the site altitudes varied from sea level to 3 km, the major distinguishing feature between average r(0) values was the presence or absence of a turbulent, atmospheric boundary layer above the surface. For locations without a strong boundary-layer inversion, the mean coherence length, r(0), was 93 +/- 6 mm and the mean isoplanatic angle, theta(0), was 9.4 +/- 0.5 murad. Where a boundary-layer inversion was present, the corresponding values for r(0) and theta(0) were 53 +/- 2 mm and 6.5 +/- 0.5 murad, respectively.

Effects of crystallinity of goethite: I. Preparation and properties of goethites of differing crystallinity

SummaryWe prepared five samples of pure goethite and three samples of aluminous goethite with mole fractions of aluminium ranging from 0·05 to 0·20. One of the samples of pure goethite was repeatedly heated in an autoclave at 150°C. We studied the samples using transmission electron microscopy and XRD and we measured the surface area (BET), rate of dissolution of the samples in acid, the surface charge in four concentrations of sodium nitrate from pH 4–10, and the sorption of calcium and chloride from a dilute solution of calcium chloride. Surface areas ranged from 18 to 132 m2 g−1. The BET adsorption‐desorption isotherms had hysteresis loops which increased as the surface area increased. These showed that there were pores present with diameters smaller than 2 nm and that the number of pores increased as the surface area increased. All samples of goethite showed typical X‐ray diffraction patterns but with peak heights decreasing, and width increasing, as surface area increased. Mean coherence lengths, as determined by XRD line broadening, were smaller than those determined by transmission electron microscopy. This was because each crystal was composed of several domains, and the XRD data reflect the size of the domains. Heating one of the goethite samples in an autoclave caused most of the domains to coalesce and slightly decreased the surface area. As the surface area of the eight goethite samples increased, the mean coherence length in the direction of the a, b and c axes decreased. The better crystallized samples dissolved more slowly in acid and the dissolution curves were sigmoid because the acid was able to penetrate between the domains allowing access to a larger surface area and consequently accelerated dissolution. The points of zero charge increased with increasing surface area of the goethite. The charge carried by the goethite at pH values distant from the point of zero charge increased as the surface area increased. This may indicate movement of protons or hydroxyl ions into pores or other defects in the crystal. The effects of pH and of salt concentration on surface charge were closely described by the variable‐charge/variable‐potential model. This model also closely described adsorption of Ca2+ and Cl− from calcium chloride solutions requiring only the allocation of constants for these ions. The substitution of aluminium for iron did not affect the charge properties of goethite.

Aluminium influence on iron oxides: XVIII. The effect of Al substitution and crystal size on magnetic hyperfine fields of natural goethites

AbstractTwo sets of natural Al-substituted goethites from contrasting surface environments (24 tropical and subtropical soils vs. ten lake iron ores from Finland) were characterized by Mössbauer spectra obtained at room temperature and 4.2 K. A negative correlation between Bhf and Al substitution (R2 = 0.751) was found by combining the data of all the samples, which was slightly improved (R2 = 0.779) by taking the mean coherence length perpendicular to 111 (MCL111) into account. The effect of Al on lowering Bhf was, however, stronger for the tropical soil goethites than for those of the lake ores. This is parallelled by a corresponding difference in the unit-cell decrease per unit Al substitution. These differences are believed to result from the crystallization conditions in the two different environments.

Evidence of biogenic greigite (ferrimagnetic Fe3S4) in soil

SummaryThe occurrence of greigite (Fe3S4) in soils is reported for the first time. It forms irregularly‐shaped aggregations within plant cells in the Gr2 horizon of a gley soil developed from colluvial material. Greigite was identified by X‐ray diffraction and magnetic measurements and was investigated by optical and transmission electron microscopy. Biogenic formation is proposed, based on the elongated shape of single greigite crystals, and sulphur isotope analyses, which showed a depletion in 34S relative to the soil‐water sulphate. The cell‐edge length of 0.98639±0.00003 nm is significantly smaller than values reported for sedimentary greigite. The mean coherence length of 27 nm agrees with TEM observations and indicates that the single greigite crystals lie in the superparamagnetic region. However, the fine aggregates show magnetically single‐domain behaviour. Greigite is the only carrier of a stable magnetic remanence in the soil profile studied.