Modelling of glass-like carbon structure and its experimental verification by neutron and X-ray diffraction

Glass-like carbon is a well known carbon form that still poses many challenges for structural characterization owing to a very complex internal atomic organization. Recent research suggests that glassy carbon has a fullerene-related structure that evolves with the synthesis temperature. This article reports on direct evidence of curved planes in glassy carbons using neutron and X-ray diffraction measurements and their analysis in real space using the atomic pair distribution function formalism. Changes in the structure including the degree of curvature of the non-graphitizing glassy carbons as a function of the pyrolysis temperature in the range 800–2500°C (1073–2773 K) are studied using optimized models of the atomic structure. Averaged models of single coherent scattering domains as well as larger structural fragments consisting of thousands of atoms were relaxed using classical molecular dynamics. For such models the diffraction intensities and the pair distribution functions were computed. The compatibility of the computer-generated models was verified by comparison of the simulations with the experimental diffraction data in both reciprocal and real spaces. On the basis of features of the developed structural models for glass-like carbons, the origin of the properties such as high strength and hardness and low gas permeability can be better understood.

What Is the Actual Local Crystalline Structure of Uranium Dioxide, UO2? A New Perspective for the Most Used Nuclear Fuel

Up to now, uranium dioxide, the most used nuclear fuel, was said to have a Fm3̅m crystalline structure from 30 to 3000 K, and its behavior was modeled under this assumption. However, recently X-ray diffraction experiments provided atomic pair-distribution functions of UO₂, in which UO distance was shorter than the expected value for the Fm3̅m space group. Here we show neutron diffraction results that confirm this shorter UO bond, and we also modeled the corresponding pair-distribution function showing that UO₂ has a local Pa3̅ symmetry. The existence of a local lower symmetry in UO₂ could explain some unexpected properties of UO₂ that would justify UO₂ modeling to be reassessed. It also deserves more study from an academic point of view because of its good thermoelectric properties that may originate from its particular crystalline structure.

Structural Changes in the Local Environment of Uranium Atoms in the Three Phases of U4O9

The crystal structure of U4O9 remains an enigma because of its differences with U(4+) and U(5+) coordination polyhedral mixtures, as shown in the XANES experimental results. To better understand this crystal structure, its diffraction pattern was measured at seven different temperatures using neutron diffraction before being independently refined by Rietveld's method and pair distribution function analysis. The O cuboctahedron-a structural element consisting of 13 oxygen atoms-is a specific feature of the U4O9 crystal structure. The volume of the cuboctahedron decreases when the temperature increases, whereas the overall volume of the crystal cell increases. This feature can be correlated with the two U4O9 phase transitions that induce sharp changes in the cuboctahedron geometry, suggesting that this structural element has internal dynamics. In particular, these structural modifications in the γ phase suggest that the high-temperature phase can be described as a mixture of U(4+) and U(5+) coordination polyhedra, the latter having U-O distances shorter than 2.2 Å, that are absent in the former. These changes in uranium polyhedra as a function of temperature are tentatively interpreted using steric arguments. They also raise the question of charge localization on the different U ion sites in the low-temperature phases of U4O9.

Thermal Properties of Boron-Rich Borides

The specific heats of β-B and of B4C have been reviewed, and measurements of a different sample of B4C have been carried out below 80 K. A specific heat anomaly observed previously in boron carbides has been shown to be extrinsic in origin. The thermal conductivity of B1−x Cx, for x < 0.20, between 0.2 and 2000 K has also been reviewed, and recent measurements have been added. The magnitude and temperature dependence of the conductivity are somewhat similar to what is expected for amorphous boron, except for the characteristic plateau which is not clearly discernible. A possible explanation for the strong phonon scattering is discussed.

Magnetic critical scattering in solid Co80Pd20

Using small-angle neutron scattering combined with a containerless aerodynamic levitation technique for high temperatures, we have measured the temperature dependence of the correlation length ξ of near-critical magnetic fluctuations in the solid phase of the completely miscible fcc alloy Co₈₀Pd₂₀. A fit to our data yields a critical exponent ν = 0.76 ± 0.05 for the divergence of ξ(T) above the ferromagnetic transition temperature T_c. This value of ν is consistent with the prediction of the three-dimensional Heisenberg model for magnetic critical scattering.

Structure of molten yttrium aluminates: a neutron diffraction study

We used the aerodynamic levitation technique combined with CO₂ laser heating to study the structure of liquid yttrium aluminates above their melting point with neutron diffraction. For various yttria contents, we determined the structure factors and corresponding pair correlation functions describing the short-range order in the liquids. In particular, we derived Al-O and Y-O bond distances and coordination numbers. Experimental data are compared with ab initio molecular dynamics, carried out using the VASP code where the interatomic forces are obtained from density functional theory. In particular, partial pair correlation functions have been calculated and are in relatively good agreement with the experimental observations.

Europium Palladium Hydrides

The first fully structurally characterized ternary europium palladium hydrides (deuterides) are reported. The most Eu rich compound is Eu(2)PdD(4). Its beta-K(2)SO(4) type structure (space group Pnma, a = 749.47(1) pm, b = 543.34(1) pm, c = 947.91(1) pm, Z = 4) contains tetrahedral 18-electron [PdD(4)](4)(-) complex anions and divalent Eu cations. The compound is presumably nonmetallic and shows paramagnetic behavior (mu(eff) = 8.0(2) mu(B)) with ferromagnetic ordering at T(C) = 15.1(4) K. A metallic compound at intermediate Eu content is EuPdD(3). It crystallizes with the cubic perovskite structure (space group Pm3m, a = 380.01(2) pm, Z = 1) in which palladium is octahedrally surrounded by fully occupied deuterium sites. Metallic hydrides at low Eu content form by reversible hydrogen absorption of intermetallic EuPd(2) (Fd3m, a = 775.91(1) pm, Z = 8). Depending on the experimental conditions at least three phases with distinctly different hydrogen contents x exist: EuPd(2)H(x) ( approximately )(0.1) (a = 777.02(2) pm, Z = 8, T = 298 K, p(H(2)) = 590 kPa), EuPd(2)H(x) ( approximately )(1.5) (a = 794.47(5) pm, Z = 8, T = 298 K, p(H(2)) = 590 kPa), and EuPd(2)H(x) ( approximately )(2.1) (a = 802.1(1) pm, Z = 8, T = 350 K, p(H(2)) = 610 kPa). All crystallize with cubic Laves phase derivative structures and have presumably disordered hydrogen distributions.

First solvation shell of the Cu(II) aqua ion: evidence for fivefold coordination

We determined the structure of the hydrated Cu(II) complex by both neutron diffraction and first-principles molecular dynamics. In contrast with the generally accepted picture, which assumes an octahedrally solvated Cu(II) ion, our experimental and theoretical results favor fivefold coordination. The simulation reveals that the solvated complex undergoes frequent transformations between square pyramidal and trigonal bipyramidal configurations. We argue that this picture is also consistent with experimental data obtained previously by visible near-infrared absorption, x-ray absorption near-edge structure, and nuclear magnetic resonance methods. The preference of the Cu(II) ion for fivefold instead of sixfold coordination, which occurs for other cations of comparable charge and size, results from a Jahn-Teller destabilization of the octahedral complex.

Defects in a disordered world: the structure of glassy GeSe2

The full set of partial structure factors for the prototypical network glass GeSe2 was measured using the method of isotopic substitution in neutron diffraction. The basic building block of the network is the Ge(Se(1/2))(4) tetrahedron in which 34(5)% of the Ge reside in edge-sharing configurations. The intrinsic chemical order of the glass is, however, broken with a maximum of 25(5)% Ge and 20(5)% Se being involved in homopolar bonds at distances of 2.42(2) and 2.32(2) A, respectively.

Implications of human T-lymphotropic virus type-I and type-II testing in donors and patients

The retroviruses known as Human T-Lymphotropic Virus Types I and II (HTLV-I and -II) were recognized before the human immunodeficiency virus (HIV-1). Associated diseases of HTLV-I infection, including a particular kind of leukemia or the development of a specific demyelinating disease, have also been observed. Screening of blood donors for antibodies to HTLV was mandated in November of 1988. This paper examines the biology of HTLV-I and HTLV-II and reviews the testing methods for HTLV-I/II. Data from 39,908 blood donations of volunteer donors at The University of Texas M. D. Anderson Cancer Center (UTMDACC), Division of Laboratory Medicine, Section of Transfusion Medicine are presented. Initially reactive specimens for HTLV antibodies were 158 (0.4 percent). Of these 0.26 percent or 105 of 39,908 were repeatedly reactive. Eight hundred and sixty-seven cancer patients were also tested for HTLV antibodies. Eight or 0.9 percent were repeatedly reactive for HTLV antibodies by enzyme immunoassays (EIA), but only one could be confirmed as positive. HTLV-I/II has a very low incidence in the ambulatory population. The relationship of clinical sequelae and the rate of transmission of these viruses remain unclear. A readily applicable confirmatory test is not yet available. Even significant improvements in the sensitivity and specificity of testing will present ongoing problems for identification of true HTLV carriers. The clinical decision-making process related to the meaning of these results continues to be difficult.

Autologous transfusions for cancer patients undergoing elective ablative surgery

Patients who have cancer are exposed to the adverse consequences of blood transfusions, such as transmissible diseases. This study presents an examination of a program of autologous blood deposit for cancer patients undergoing elective surgical procedures. Over a 3-year period, 235 patients deposited 388 units of autologous blood: 6 for head and neck tumor surgery, 8 for neurosurgical tumors, 8 for gastrointestinal and colorectal tumor surgery, 14 for adrenal tumor surgery, 16 for gynecologic tumor surgery, 23 for soft tissue and bone tumor surgery, 25 for mastectomies and reconstructive breast surgery, 42 for genitourinary tumor surgery, and 93 for bone marrow aspirations for autologous transplants. One hundred eighty-two patients (77.4%) used 278 units (71.6%) of their autologous blood units during the operations, 50/182 required additional homologous blood, and 53 did not require transfusions with autologous blood. Our study shows that a majority of these patients (132/182) underwent surgery using only autologous transfusions. Therefore, we believe that predeposited autologous blood is a viable alternative to homologous blood for cancer patients undergoing surgery.

Plasma fibronectin values in patients with acquired immunodeficiency syndrome (AIDS) and AIDS-related complex

The authors studied the circulating fibronectin concentrations in the plasma of 24 patients with acquired immunodeficiency syndrome (AIDS) or AIDS-related complex (ARC) and of 74 age- and sex-matched healthy blood donors. They adapted a commercially available turbidimetric immunoassay for use with a centrifugal analyzer. The assay showed within-run precision of 2.1%, 2.3%, 1.8%, and 1.1%, and an accuracy of 90%, 99%, 98%, and 98% at fibronectin concentrations of 126 mg/L, 200 mg/L, 293 mg/L, and 317 mg/L, respectively. Between-run precision was 5%, 3%, and 2% for 66 mg/L, 218 mg/L, and 283 mg/L concentrations, respectively. Plasma fibronectin values obtained from the healthy blood donors were in good agreement with those values reported by other investigators using various methods. No significant differences between the plasma fibronectin values of the patient population (mean +/- 2 SD = 294 mg/L +/- 110 mg/L) and of the control group (mean +/- 2 SD = 311 mg/L +/- 130 mg/L) were noted. The authors conclude that the measurement of fibronectin concentrations in patients with AIDS or ARC does not contribute significantly to the diagnosis and therapeutic management of these patients.

Expression of Rh0(D) antigen in choriocarcinoma of the uterus in an Rh0(D)-negative patient: report of a case

Choriocarcinoma of the uterus developed in an Rh0(D)-negative woman six weeks after delivery of a normal Rh0(D)-positive child. Although the patient's medical history did not show any previous sensitization, a strong anti-Rh0(D) antibody was detected during evaluation preceding surgical removal of the tumor. The tumor was considered the most probable cause of the Rh0(D) sensitization, since large Rh0(D)-positive areas of tumor were demonstrated by the immunoperoxidase method. This finding indicates that the Rh0(D) antigen is not restricted to erythrocytes, as commonly assumed, but can also be expressed on other tissue, such as tumor tissue.

Steroid metabolism by endometrial and conceptus tissues during early pregnancy and pseudopregnancy in gilts

Endometrial and conceptus tissues were obtained on Days 10.5, 11, 12, 16 and 25 of pregnancy and Day 25 of pseudopregnancy of gilts and incubated for 6 h in Minimal Essential Medium (5 ml) containing 35 ng [3H]progesterone. Metabolism of [3H]progesterone to oestrone, oestradiol and oestriol was determined by gas and high-pressure liquid chromatography and successive recrystallizations with unlabelled standards. Conceptuses collected between Days 10.5 and 12 were spherical, tubular or filamentous and incubated with 500 mg endometrium and [3H]progesterone. Production of oestrone by spherical conceptuses was not detected, but was 44-47 pg/tubular conceptus and 21 pg/filamentous conceptus. A similar trend was observed for oestradiol. Conceptus tissues from Days 16 and 25 (chorion) were most active in producing oestrone (123 and 520 pg/mg tissue, respectively) and oestradiol (277 and 876 pg/mg tissue, respectively). Endometrial oestrogen production was less than that for conceptus tissue for oestrone and oestradiol on Days 16 and 25 of gestation. Coincubations of endometrium and conceptus tissues had lower oestrogen production than conceptus alone. Endometrium from Day 25 of pseudopregnancy metabolized [3H]progesterone to several non-polar metabolites, but no oestrogens were detected. An unidentified phenolic metabolite of [3H]progesterone was detected in higher quantities than either oestrone or oestradiol; 445 to 461 pg/conceptus at the tubular stage. These results indicate temporal changes in the conversion of [3H]progesterone to oestrogens by conceptus and endometrial tissue from pregnant gilts, but not endometrium from pseudopregnant gilts.

Pneumonia caused by a previously undescribed bacterium

A new and as yet unidentified bacterium was isolated from the lung tissue of a cancer patient with bilateral pneumonia. Clinically, the pneumonia was consistent with legionellosis; the organism cultured from the lung grew only on the charcoal-yeast extract agar routinely used for Legionella isolation. Subsequent testing, however, showed the organism to be quite distinct from the known Legionella species in its biochemical, antigenic, and growth characteristics.

T and B Cell Populations in Platelet Donors

T and B lymphocyte populations were monitored in the peripheral blood of two long-term plateletpheresis donors. The studies showed minimal fluctuation of both populations compared to the normal controls. The evidence so far accumulated seems to indicate that long-term manual plateletpheresis has no appreciable effect on the level of the T and B cell population of the peripheral blood. Further studies are needed to evaluate larger donor pools.