Precision Neutron Polarimetry for Neutron Beta Decay

The abBA collaboration is developing a new type of field-expansion spectrometer for a measurement of the three correlation coefficients a, A, and B and the shape parameter b. The measurement of A and B requires precision neutron polarimetry. We will polarize a pulsed cold neutron beam from the SNS using a ³He neutron spin filter. The well-known polarizing cross section for n-³He has a 1/v dependence, where v is the neutron velocity, which is used to determine the absolute beam polarization through a time-of-flight (TOF) measurement. We show that by measuring the TOF dependence of A and B, the coefficients and the neutron polarization can be determined with a small loss of the statistical precision and with negligible systematic error. We conclude that it is possible to determine the neutron polarization averaged over a long run in the neutron beta decay experiment with a statistical error less than 10⁻⁴. We discuss various sources of systematic uncertainty in the measurement of A and B and conclude that the fractional systematic errors are less than 2 × 10⁻⁴.     

Differential equations determining the function that describes precatastrophic behavior of a system

Based on an analysis of the experimental data obtained for various catastrophic phenomena, Malinetskii et al. [1] considered the main parameters of a process preceding the catastrophe and proposed the following function of time that describes this process: I(t) = A + B(t _c ? t)^α[1 + Ccos(θ log(t _c ? t) ? ?)]. The passage to complex quantities and substitution of variables reveal a power-law character of this approximation. Using this approach, differential equations determining the function that describes the precatastrophic behavior are obtained.     

Monte Carlo Study of the abBA Experiment: Detector Response and Physics Analysis

The abBA collaboration proposes to conduct a comprehensive program of precise measurements of neutron β-decay coefficients a (the correlation between the neutrino momentum and the decay electron momentum), b (the electron energy spectral distortion term), A (the correlation between the neutron spin and the decay electron momentum), and B (the correlation between the neutron spin and the decay neutrino momentum) at a cold neutron beam facility. We have used a GEANT4-based code to simulate the propagation of decay electrons and protons in the electromagnetic spectrometer and study the energy and timing response of a pair of Silicon detectors. We used these results to examine systematic effects and find the uncertainties with which the physics parameters a, b, A, and B can be extracted from an over-determined experimental data set.     

Bioresorbable,heparinized polymers for stent coating:in vitro studies on heparinization efficiency,maintenance of anticoagulant properties and improvement of stent haemocompatibility

Biodegradable poly-(D,L-lactide) RESOMER^® R208 and poly(D,L-lactide-co-glycolide) RESOMER^® RG756 were heparinized to improve the blood contacting properties of the materials. The immobilization of heparin was performed with glutaraldehyde as coupling agent. The efficacy of the surface modification was monitored with respect to the total amount of bound heparin measured by a toluidine blue assay, the anticoagulant potential estimated by a factor Xa assay, and the activation of platelets estimated by a GMP140 assay. It was found that a reaction at ambient temperature for 2h resulted in optimal heparin binding, with high anticoagulant activity and low thrombogenicity. The storage of heparinized polylactide in saline solutions up to 8 days demonstrated the release of small quantities of heparin into the fluid. A further finding was that with prolonged storage the anticoagulant potential was improved, whereas the thrombogenicity decreased. Comparison of platelet activation on RESOMER^® R208 as unmodified and heparinized material with polypropylene and Pellethane^® revealed that heparinization of R208 substantially improved the haemocompatibility. Coating and subsequent heparinization of intravascular stents were carried out with RESOMER^® RG756 because of its more appropriate mechanical properties.In vitro studies with blood under flow conditions demonstrated that platelet activation on Palmaz stents was considerably diminished after polymer coating and heparinization.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials, Oporto, Portugal, 10–13 September.     

Electrical conductivity of Sc2O3-ZrO2 compositions by 4-probe d.c. and 2-probe complex impedance techniques

The ionic conductivities of several samples in the Sc₂O₃-ZrO₂ system (Sc₂O₃: ～ 8 mol %) have been measured using 4-probe d.c. and 2-probe complex impedance dispersion techniques. Samples which contained monoclinic zirconia showed hysteresis effects and S-shaped Arrhenius conductivity plots. This behaviour was assigned to the m-ZrO₂ ? t-ZrO₂ transformation. In samples which were free of monoclinic ZrO₂, contributions from the grain boundary resistance were relatively small. The Arrhenius plots of their conductivity showed a distinct change in the slope around 600° C towards higher activation energy and this was attributed to vacancy trapping. The 4-probe d.c. data could be fitted to an equation of the formρ=A ₁ T exp (E ₁/RT)+A ₂ T exp (E ₂/RT). The process which dominated the conduction mechanism at lower temperatures had an activation energy of 130 to 140 kJ mol^?1. The activation energy for the migration of oxygen ion vacancies within the bulk of the grain was 64 to 70 kJ mol^?1.     

Viscous dissipation effects on mixed convection about a rotating sphere

The effect of viscous dissipation on mixed convection flow about a rotating sphere is investigated analytically. A method based on Merk's type of series expansions is used to obtain the heat transfer rate and the skin-friction coefficients. Numerical computations were carried out for Eckert number Ec ranging from 0 to 0.1, rotation parameter B = 0, 1, 4 and buoyancy parameter ranging from 0 to 1 at various angular positions. As viscous dissipation increases heat transfer rate decreases. It is found that for Ec > 0, a critical value of B (say B_cri) exist such that $\text{Nu Re}{}_{\mathrm{R}}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ increases as B increases up to B = B_cri and then decreases. B_cri decreases with Ec when the angle is fixed or decreases with angle when Ec is fixed. When Ec > 0, possibly there exist a λ, say λ_cri, such that $\text{Nu Re}{}_{\mathrm{R}}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ increases with λ up to λ = λ_cri and then decreases. Also the effect of viscous dissipation on skin friction is investigated.     

Measurement of Neutron Decay Parameters—The abBA Experiment

We are developing an experiment to measure the correlations a, A, and B, and the Fierz interference term b in neutron decay, with a precision of approximately 10⁻⁴. The experiment uses an electromagnetic spectrometer in combination with two large-area segmented silicon detectors to detect the proton and electron from the decay in coincidence, with 4π acceptance for both particles. For the neutron-polarization-dependent observables A and B, precision neutron polarimetry is achieved through the combination of a pulsed neutron beam, under construction at the SNS, and a polarized ³He neutron polarizer. Measuring a and A in the same apparatus provides a redundant determination of λ = g_A/g_V. Uncertainty in λ dominates the uncertainty of CKM unitarity tests.     

Acidic Potassium Dichromate Solutions as Ultraviolet Absorbance Standards

The absorbances of five concentrations of potassium dichromate in 0.001 M perchloric acid have been determined at eight wavelengths in the ultraviolet on the National Bureau of Standards Institute for Materials Research high-accuracy spectrophotometer. Four of the wavelengths—235, 257, 313, and 350 nm—correspond to absorbance maxima or minima in the HCrO₄^– spectrum and are useful wavelengths for checking the accuracy of the absorbance scale of narrow bandpass spectrophotometers. Although partial dimerization of HCrO₄^– to Cr₂O₇⁼ produces small positive deviations from Beer’s law at these wavelengths, the apparent absorptivities calculated for each concentration are reproducible to one part in a thousand. The estimated uncertainties in the absorptivity values are ± 0.7 percent at 0.1 absorbance (A) and ± 0.2 percent near A = 1. These uncertainties include all known sources of possible systematic error and the 95 percent confidence level for the mean. The remaining four wavelengths used for measurement are near two predicted isosbestic points in the HCr0₄^–/Cr₂O₇⁼ spectra. The absorptivities at 345 nm are sufficiently independent of concentration that this wavelength can be used for checking absorbance linearity to one part in a thousand over the range A = 0.2–1.     

Sound Spectroscopy of the Superfluid Phases of 3He in Aerogel in Zero Magnetic Field

Low-frequency sound is used to study phase transitions of ³He confined in 98% open aerogel. Superfluidity is manifested by the onset of the low frequency (slow) mode whose velocity (as a function of pressure and temperature) was used to map out the phase diagram of the B-phase and the metastable A-phase of ³He in aerogel. Analysis of the slow mode's evolution with temperature allows the development of the superfluid fraction in the A and B phases to be determined. The metastable A-phase and the equilibrium B-phase can co-exist in a properly prepared sample. Both the superfluid transition and the A→B transition exhibit a finite width of ～20–25 µK.     

Franck-Condon Factors to High Vibrational Quantum Numbers III: CN

Franck-Condon factor arrays have been computed numerically to high vibrational quantum numbers for the red (A²II_i–X²Σ⁺) and violet (B²Σ⁺ – X²Σ⁺) band systems of CN.     

Kinetics of Competitive Sorption in Decontamination of Materials from Radionuclides

kinetic model of the mass transfer of a microcomponent in the simplest competitive system from the sorbed state (A) into a solution (B) and then into a sorbent (C) in accordance with the scheme A ? B ? C was formulated within the framework of competitive sorption statics. The kinetic equations were solved numerically. The influence exerted by the weight of competing sorbents А and С and by the degree of reversibility of linear reactions on the nonequilibrium decontamination factor K_dec(t) was determined. The time in which the equilibrium decontamination factor is attained for the model of chemical sorption kinetics was estimated from the experimental data on the rate constants of direct and reverse heterogeneous reactions and on the distribution coefficients of Cs(I) in the SiO₂ (A)–CsCl solution (B)–Prussian Blue (C) system.     

Nonlinear interdiffusion in binary nanometer-scale multilayers submitted to thermal annealing

The concentration profile in binary A-B nanometer-scale multilayers submitted to thermal annealing was calculated based on the Martin's kinetic discrete model for one-dimension nonlinear interdiffusion by a diffusion asymmetry coefficient m′ and an ordering energy V between A and B atoms. With decreasing the diffusion asymmetry coefficient m′ from 0 to − 6, the concentration profile of the multilayers deviated from symmetrical distribution, and their interfaces became sharp and shifted towards the side of the sublayer with lower pair interaction energy. The difference of diffusion coefficient of A and B atoms caused by the diffusion asymmetry coefficient m′ led to the difference of net fluxes of A and B atoms in the multilayers. When the ordering energy V changed from − 0.001 eV to − 0.05 eV, change in the concentration profile and interface structure was same for the multilayers with a given diffusion asymmetry coefficient m′, but the calculated diffusion time decreased correspondently. The lower ordering energy V makes the A and B atoms aggregating more easily during the interdiffusion. It is found that the nonlinear interdiffusion of a series of binary nanometer-scale multilayers can be characterized by the diffusion asymmetry coefficient m′ and the ordering energy V, to explore the solid state reaction between the sublayers of nanometer-scale multilayers.     

Applications of grain boundary diffusion studies to soldering and thermocompression bonding

This paper describes the application of grain boundary diffusion and oxidation to the technologically important topics of solderability and thermocompression bondability. Copper leads plated with 0.73 μm of gold were studied. Arrhenius plots were constructed and extrapolated to expected storage conditions. A storage life of greater than 2 a at 50°C is predicted for both properties. The time to loss of solderability is given by t_s = 1.6 x 10^-7 exp(0.8 eV/kT) h and the time to loss of bondability by t_B = 4 x 10^-10 exp(1.0 eV/kT) h. The effective activation energies 0.8 and 1.0 eV compare with 0.91 eV for the grain boundary diffusion of copper through gold. Loss of solderability and loss of bondability were modeled as a two-step series event. First the copper diffuses to the gold surface via its grain boundaries. The copper then oxidizes. Auger analysis indicates that the surface oxide is Cu₂O.     

Effect of mechanical activation pretreatment on the properties of sugarcane bagasse/poly(vinyl chloride) composites

This current work is concerned with the pretreatment of sugarcane bagasse (SCB) by mechanical activation (MA) using a self-designed stirring ball mill and surface modification of SCB using aluminate coupling agent (ACA). The untreated and differently treated SCBs were used to produce composites with poly(vinyl chloride) (PVC) as polymer matrix. The activation grade (A_g) measurement and Fourier transform infrared (FTIR) analysis of SCB showed that MA enhanced the condensation reaction between ACA and hydroxyl groups of the SCB fibres, which obviously increased the hydrophobicity of SCB. It was found that the mechanical properties of both the PVC composites reinforced by SCB with and without ACA modification increased with increasing milling time (t_M). Scanning electron microscopy (SEM) analysis showed that MA pretreatment significantly improved the dispersion of SCB in the composites and interfacial adhesion between SCB and PVC matrix, resulting in better mechanical properties of the composites.     

Characterization of temperature-dependent carrier transport in disordered indium-tin-oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/polyfluorene/Ca/Al polymer structures

The temperature-dependent electrical characteristics of polyfluorene-based polymer structures over a temperature range from 200 to 300 K are systematically investigated in this study. Initially, using the definitions of the Berthelot-type model, it is found that the sample exhibits a higher Berthelot-type temperature T_B with high driving voltage, indicating that carrier transport in a disordered system manifests Berthelot-type behaviors. The ideal current density-voltage curve for the polymer structures given the carrier transmit mechanism is further elucidated by taking into account the ohmic conduction, trap charge limited current, and Mott and Gurney model of space charge limited current. The proposed procedure is simple and can be used to characterize the material with reasonable accuracy. We also study the density of the traps H_t, and the characteristic energy of the distribution E_t to better understand the carrier-transport process in organic materials and structures.     

Adjuvant properties of a biocompatible thermo-responsive polymer of N-isopropylacrylamide in autoimmunity and arthritis

To evaluate the thermo-responsive poly(N-isopropylacrylamide) (PNiPAAm) polymer as an adjuvant, we synthesized PNiPAAm through free radical polymerization and characterized it both in vitro and in vivo. The polymer when mixed with collagen type II (CII) induced antigen-specific autoimmunity and arthritis. Mice immunized with PNiPAAm–CII developed significant levels of CII-specific IgG response comprising major IgG subclasses. Antigen-specific cellular recall response was also enhanced in these mice, while negligible level of IFN-γ was detected in splenocyte cultures, in vitro. PNiPAAm–CII-immunized arthritic mouse paws showed massive infiltration of immune cells and extensive damage to cartilage and bone. As determined by immunostaining, most of the CII protein retained its native configuration after injecting it with PNiPAAm in naive mice. Physical adsorption of CII and the high-molecular-weight form of moderately hydrophobic PNiPAAm induced a significant anti-CII antibody response. Similar to CII, mice immunized with PNiPAAm and ovalbumin (PNiPAAm–Ova) induced significant anti-ovalbumin antibody response. Comparable levels of serum IFN-γ, IL-1β and IL-17 were observed in ovalbumin-immunized mice with complete Freund, incomplete Freund (CFA and IFA) or PNiPAAm adjuvants. However, serum IL-4 levels were significantly higher in PNiPAAm–Ova and CFA–Ova groups compared with the IFA–Ova group. Thus, we show for the first time, biocompatible and biodegradable thermo-responsive PNiPAAm can be used as an adjuvant in several immunological applications as well as in better understanding of the autoimmune responses against self-proteins.     

Project of Neutron Beta-Decay A-Asymmetry Measurement With Relative Accuracy of (1–2)×10?3

We are going to use a polarized cold neutron beam and an axial magnetic field in the shape of a bottle formed by a superconducting magnetic system. Such a configuration of magnetic fields allows us to extract the decay electrons inside a well-defined solid angle with high accuracy. An electrostatic cylinder with a potential of 25 kV defines the detected region of neutron decays. The protons, which come from this region will be accelerated and registered by a proton detector. The use of coincidences between electron and proton signals will allow us to considerably suppress the background. The final accuracy of the A-asymmetry will be determined by the uncertainty of the neutron beam polarization measurement which is at the level of (1–2) × 10⁻³, as shown in previous studies.     

A systems approach to model the relationship between aflatoxin gene cluster expression,environmental factors,growth and toxin production by Aspergillus flavus

A microarray analysis was used to examine the effect of combinations of water activity (a_w, 0.995–0.90) and temperature (20–42°C) on the activation of aflatoxin biosynthetic genes (30 genes) in Aspergillus flavus grown on a conducive YES (20 g yeast extract, 150 g sucrose, 1 g MgSO₄·7H₂O) medium. The relative expression of 10 key genes (aflF, aflD, aflE, aflM, aflO, aflP, aflQ, aflX, aflR and aflS) in the biosynthetic pathway was examined in relation to different environmental factors and phenotypic aflatoxin B₁ (AFB₁) production. These data, plus data on relative growth rates and AFB₁ production under different a_w × temperature conditions were used to develop a mixed-growth-associated product formation model. The gene expression data were normalized and then used as a linear combination of the data for all 10 genes and combined with the physical model. This was used to relate gene expression to a_w and temperature conditions to predict AFB₁ production. The relationship between the observed AFB₁ production provided a good linear regression fit to the predicted production based in the model. The model was then validated by examining datasets outside the model fitting conditions used (37°C, 40°C and different a_w levels). The relationship between structural genes (aflD, aflM) in the biosynthetic pathway and the regulatory genes (aflS, aflJ) was examined in relation to a_w and temperature by developing ternary diagrams of relative expression. These findings are important in developing a more integrated systems approach by combining gene expression, ecophysiological influences and growth data to predict mycotoxin production. This could help in developing a more targeted approach to develop prevention strategies to control such carcinogenic natural metabolites that are prevalent in many staple food products. The model could also be used to predict the impact of climate change on toxin production.     

The nosocomial transmission rate of animal-associated ST398 meticillin-resistant Staphylococcus aureus

The global epidemiology of meticillin-resistant Staphylococcus aureus (MRSA) is characterized by different clonal lineages with different epidemiological behaviour. There are pandemic hospital clones (hospital-associated (HA-)MRSA), clones mainly causing community-acquired infections (community-associated (CA-)MRSA, mainly USA300) and an animal-associated clone (ST398) emerging in European and American livestock with subsequent spread to humans. Nosocomial transmission capacities (R_A) of these different MRSA types have never been quantified. Using two large datasets from MRSA outbreaks in Dutch hospitals (dataset 1, the UMC Utrecht for 144 months; dataset 2, 51 hospitals for six months) and a recently developed mathematical model, we determined the genotype-specific R_A for ST398 and non-ST398 isolates (categorized as HA-MRSA), using observational data, the detection rate of MRSA carriage and the discharge rate from hospital as the input. After detection of 42 MRSA index cases in dataset 1 (all non-ST398 MRSA) 5076 people were screened, yielding 30 secondary cases. In dataset 2, 75 index cases (51 non-ST398 MRSA and 24 ST398) resulted in 7892 screened individuals and 56 and three secondary cases for non-ST398 MRSA and ST398, respectively. The ratio between discharge and the detection rate was 2.7. R_A values (95% confidence interval (CI)) were 0.68 (0.47–0.95) for non-ST398 MRSA in dataset 1, 0.93 (0.71–1.21) for non-ST398 MRSA in dataset 2 and 0.16 (0.04–0.40) for ST398. The R_A ratio between non-ST398 MRSA and ST398 was 5.90 (95% CI 2.24–23.81). ST398 is 5.9 times less transmissible than non-ST398 MRSA in Dutch hospitals, which may allow less stringent transmission-control measures for ST398 MRSA.     

Linear differential-algebraic equations with properly stated leading term: B -critical points

We examine in this article so-called B-critical points of linear, time-varying differential-algebraic equations (DAEs) of the form A(t)(D(t)x(t))′ + B(t)x(t) = q(t). These critical or singular points, which cannot be handled by classical projector methods, require adapting a recently introduced framework based on Π-projectors. Via a continuation of certain invariant spaces through the singularity, we arrive at a scenario which accommodates both A- and B-critical DAEs. The working hypotheses apply in particular to standard-form analytic systems although, in contrast to other approaches to critical problems, the scope of our approach extends beyond the analytic setting. Some examples illustrate the results.