Similarity of Near-Threshold Energy Dependence of Positronium Formation and Photoionization in Molecules.

High-resolution measurements of the positronium formation cross sections for positron energies from threshold to 10 eV are presented for aniline (C_{6}H_{5}NH_{2}), pyridine (C_{5}H_{5}N), and cyclopentane (C_{5}H_{10}). The data reveal that the measured energy dependence of the cross sections on the excess energy in the near-threshold region (1-2 eV) is nearly identical to that of the corresponding photoionization cross sections. This similarity occurs despite the difference between the basic threshold laws for processes without and with a Coulomb interaction between the final-state particles. It is proposed here that the near-threshold behavior of these two different ionization processes is governed by the vibrational dynamics of the final-state cation. This is supported by comparison of the data with the calculated spectrum of vibronic intensities for the pyridine cation [Trofimov et al., J. Chem. Phys. 153, 164307 (2020)JCPSA60021-960610.1063/5.0024446].

Resonant Annihilation and Positron Bound States in Benzene.

Positrons attach to molecules in vibrationally resonant two-body collisions that result in greatly enhanced annihilation rates. Measurements of annihilation as a function of positron energy are presented for benzene using a cryogenic, trap-based beam. They establish a positron binding energy of 132±3 meV to test state-of-the-art theoretical calculations, and they exhibit many unexpected resonances, likely due to combination and overtone vibrational modes. The relationship of these results to the unique π-bonded structure of benzene is discussed.

Enhanced Resonant Positron Annihilation due to Nonfundamental Modes in Molecules.

Positrons attach to most molecules through Feshbach resonant excitation of fundamental vibrational modes, and this leads to greatly enhanced annihilation rates. In all but the smallest molecules, vibrational energy transfer further enhances these annihilation rates. Evidence is presented that in alkane and cycloalkane molecules, this can occur by the excitation of other than fundamental vibrations and produce roughly comparable annihilation rates. These features are compared to infrared absorption spectra. A possible mechanism is discussed that involves combination and overtone vibrations.

First Measurement of the Total Neutron Cross Section on Argon between 100 and 800 MeV.

We report the first measurement of the neutron cross section on argon in the energy range of 100-800 MeV. The measurement was obtained with a 4.3-h exposure of the Mini-CAPTAIN detector to the WNR/LANSCE beam at LANL. The total cross section is measured from the attenuation coefficient of the neutron flux as it traverses the liquid argon volume. A set of 2631 candidate interactions is divided in bins of the neutron kinetic energy calculated from time-of-flight measurements. These interactions are reconstructed with custom-made algorithms specifically designed for the data in a time projection chamber the size of the Mini-CAPTAIN detector. The energy averaged cross section is 0.91±0.10(stat)±0.09(syst) b. A comparison of the measured cross section is made to the GEANT4 and FLUKA event generator packages, where the energy averaged cross sections in this range are 0.60 and 0.68 b, respectively.

Lossless Positron Injection into a Magnetic Dipole Trap.

The high-efficiency injection of a low-energy positron beam into the confinement volume of a magnetic dipole has been demonstrated experimentally. This was accomplished by tailoring the three-dimensional guiding-center drift orbits of positrons via optimization of electrostatic potentials applied to electrodes at the edge of the trap, thereby producing localized and essentially lossless cross-field particle transport by means of the E×B drift. The experimental findings are reproduced and elucidated by numerical simulations, enabling a comprehensive understanding of the process. These results answer key questions and establish methods for use in upcoming experiments to create an electron-positron plasma in a levitated dipole device.

Confinement of Positrons Exceeding 1 s in a Supported Magnetic Dipole Trap.

An ensemble of low-energy positrons injected into a supported magnetic dipole trap can remain trapped for more than a second. Trapping experiments with and without a positive magnet bias yield confinement times up to τ_{A}=(1.5±0.1) and τ_{B}=(0.28±0.04) s, respectively. Supported by single-particle simulations, we conclude that the dominant mechanism limiting the confinement in this trap is scattering off of neutrals, which can lead to both radial transport and parallel losses onto the magnet surface. These results provide encouragement for plans to confine an electron-positron plasma in a levitated dipole trap.

Vibrational Feshbach Resonances Mediated by Nondipole Positron-Molecule Interactions.

Measurements of energy-resolved positron-molecule annihilation show the existence of positron binding and vibrational Feshbach resonances. The existing theory describes this phenomenon successfully for the case of infrared-active vibrational modes that allow dipole coupling between the incident positron and the vibrational motion. Presented here are measurements of positron-molecule annihilation made using a recently developed cryogenic positron beam capable of significantly improved energy resolution. The results provide evidence of resonances associated with infrared-inactive vibrational modes, indicating that positron-molecule bound states may be populated by nondipole interactions. The anticipated ingredients for a theoretical description of such interactions are discussed.

Evolution of a Vortex in a Strain Flow.

Experiments and vortex-in-cell simulations are used to study an initially axisymmetric, spatially distributed vortex subject to an externally imposed strain flow. The experiments use a magnetized pure electron plasma to model an inviscid two-dimensional fluid. The results are compared to a theory assuming an elliptical region of constant vorticity. For relatively flat vorticity profiles, the dynamics and stability threshold are in close quantitative agreement with the theory. Physics beyond the constant-vorticity model, such as vortex stripping, is investigated by studying the behavior of nonflat vorticity profiles.

Electron plasma orbits from competing diocotron drifts.

The perpendicular dynamics of a pure electron plasma column are investigated when the plasma spans two Penning-Malmberg traps with noncoinciding axes. The plasma executes noncircular orbits described by competing image-charge electric-field (diocotron) drifts from the two traps. A simple model is presented that predicts a set of nested orbits in agreement with observed plasma trajectories.

Role of vibrational dynamics in resonant positron annihilation on molecules.

Vibrational Feshbach resonances are dominant features of positron annihilation for incident positron energies in the range of the molecular vibrations. Studies in relatively small molecules are described that elucidate the role of intramolecular vibrational energy redistribution into near-resonant multimode states, and the subsequent coupling of these modes to the positron continuum, in suppressing or enhancing these resonances. The implications for annihilation in other molecular species, and the necessary ingredients of a more complete theory of resonant positron annihilation, are discussed.

Efficacy and quality of life 2 years after treatment for faecal incontinence with injectable bulking agents.

BACKGROUND: Stabilized non-animal hyaluronic acid/dextranomer (NASHA Dx) gel as injectable bulking therapy has been shown to decrease symptoms of faecal incontinence, but the durability of treatment and effects and influence on quality of life (QoL) is not known. The aim of this study was to assess the effects on continence and QoL and to evaluate the relationship between QoL and efficacy up to 2 years after treatment. METHODS: Thirty-four patients (5 males, mean age 61, range 34-80) were injected with 4 × 1 ml NASHA Dx in the submucosal layer. The patients were followed for 2 years with registration of incontinence episodes, bowel function and QoL questionnaires. RESULTS: Twenty-six patients reported sustained improvement after 24 months. The median number of incontinence episodes before treatment was 22 and decreased to 10 at 12 months (P = 0.0004) and to 7 at 24 months (P = 0.0026). The corresponding Miller incontinence scores were 14, 11 (P = 0.0078) and 10.5 (P = 0.0003), respectively. There was a clear correlation between the decrease in the number of leak episodes and the increase in the SF-36 Physical Function score but only patients with more than 75 % improvement in the number of incontinence episodes had a significant improvement in QoL at 24 months. CONCLUSIONS: Anorectal injection of NASHA Dx gel induces improvement of incontinence symptoms for at least 2 years. The treatment has a potential to improve QoL. A 75 % decrease in incontinence episodes may be a more accurate threshold to indicate a successful incontinence treatment than the more commonly used 50 %.

Ubiquitous nature of multimode vibrational resonances in positron-molecule annihilation.

Positron annihilation on many molecules occurs via positron capture into vibrational Feshbach resonances, with annihilation rates often further enhanced by energy transfer to vibrational excitations weakly coupled to the positron continuum. Data presented here uncover another scenario in which the positron couples directly to a quasicontinuum of multimode vibrational states. A model that assumes excitation and escape from a statistically complete ensemble of multimode vibrations is presented that reproduces key features of the data.

Comparisons of positron and electron binding to molecules.

Positron binding to molecules is compared to the analogous electron-molecule bound states. For both, the bound lepton density is diffuse and remains outside the valence shell. Positron binding energies are found to be one to two orders of magnitude larger than those of the negative ions due to two effects: the orientation of the molecular dipole moment allows the positron to approach it more closely and, for positrons, lepton correlations (e.g., via dipole polarizability) contribute more strongly.

Non-neutral plasma manipulation techniques in development of a high-capacity positron trap.

Preliminary experiments have been performed toward the development of a multi-cell Penning-Malmberg trap for the storage of large numbers of positrons (≥1010 e+). We introduce the master-cell test trap and the diagnostic tools for first experiments with electrons. The usage of a phosphor screen to measure the z-integrated plasma distribution and the number of confined particles is demonstrated, as well as the trap alignment to the magnetic field (B = 3.1 T) using the m = 1 diocotron mode. The plasma parameters and expansion are described along with the autoresonant excitation of the diocotron mode using rotating dipole fields and frequency chirped sinusoidal drive signals. We analyze the reproducibility of the excitation and use these findings to settle on the path for the next generation multi-cell test device.

Dipole enhancement of positron binding to molecules.

Measurements of positron-molecule binding energies are made for molecules with large permanent dipole moments (>2.7 D), by studying vibrational-Feshbach-mediated annihilation resonances as a function of incident positron energy. The binding energies are relatively large (e.g., ≥90 meV) as compared to those for similar sized molecules studied previously and analogous weakly bound electron-molecule (negative ion) states. Comparisons with existing theoretical predictions are discussed.

Shifts in perception of size after adaptation to gratings.

After viewing a suitable grating of vertical stripes for 5 minutes, subjects overestimated the width of a rectangle by 6 percent. The shifts in perception of size occurred whether individual stripes in the grating were narrower than, equal to, or wider than the rectangle. Rectangle width was underestimated only if the grating stripes were extremely wide, with a spatial frequency lower than most of the effective amplitude spectrum of the rectangle. These findings (and complementary ones with horizontal gratings) suggest that the visual system codes size on the basis of spatial frequency components, rather than directly in terms of width.

Banking North American buffalo semen.

The purpose of this study was to develop a procedure to collect and preserve semen from wood bison (Bison bison athabascae) and plains bison (Bison bison bison). Semen samples from three wood and three plains bison bulls were collected by electroejaculation from June through October. In addition, sperm was collected from the cauda epididymis of seven plains bison. Semen was cryopreserved using two commercially available cryopreservation media, an egg yolk-based medium (Triladyl), and a medium free of products of animal origin (Andromed). Sperm morphology and motility were recorded on fresh and post-thawed semen samples. Total sperm motility was not different between plains and wood bison for the months of June (50%), July (69%) and October (54%). However, total sperm motility for wood bison was higher (P<0.05) than plains bison for the months of August and September (August: 80% vs 55%; September: 73% vs 40%). Plains and wood bison did not differ in mean total and mean progressive motility (35 and 15%, respectively) of frozen-thawed sperm samples. The post-thaw motility of Triladyl-treated sperm was higher (P<0.05) than Andromed-treated sperm (35% vs 13%, respectively). Interestingly, post-thawed epididymal spermatozoa had higher total motility (P<0.05) than post-thawed electroejaculated sperm when cryopreserved with a medium free of products of animal origin (Andromed; 35% vs 9%, respectively). In conclusion, we used electroejaculation to collect high quality bison semen, and cryopreserved it for future needs.

Characterization of formylpeptide chemoattractant binding on neutrophils and monocytes from patients with head and neck cancer.

Monocytes from patients with head and neck tumors display a marked chemotactic deficiency in response to formylpeptide chemoattractants. Normal leukocytes possess receptors known to bind to chemotactic formylpeptides such as the hexapeptide N-formyl-nor-leucyl-leucyl-phenylalanyl-nor-leucyl-tyrosyl-lysine, with high specificity and great avidity. Light microscopic autoradiography was used to visualize the binding and subsequent cellular processing of the formylhexapeptide N-formyl-nor-leucyl-leucyl-phenylalanyl-nor-leucyl-[125I]tyrosyl-lysine to polymorphonuclear leukocytes (PMN) and monocytes from patients with epidermoid tumors of the head and neck. Surface-adherent leukocytes were exposed to 5 nM 125I-labeled hexapeptide for 15 minutes at 4 degrees C and were either fixed immediately or rinsed and then further incubated for 20 minutes at 37 degrees C prior to fixation. Cells underwent autoradiography, and silver grains associated with 400 cells were counted. There were no significant differences between the numbers of formylpeptide receptors on control and cancer patient PMN. However, there were significantly larger numbers of formylpeptide receptors (P less than .02) on cancer patient monocytes than on control monocytes. Cells that were allowed to process bound hexapeptide at 37 degrees C prior to fixation showed large decreases in the number of cell-associated silver grains. However, the amount of hexapeptide associated with PMN and monocytes treated in this way was the same for both control and tumor patients. In addition, histograms were plotted showing the amount of hexapeptide bound versus the frequency of cells at each level of binding. Examination of these histograms revealed that two major peaks or subpopulations occurred in each for neutrophils and monocytes from control patients. Histograms of grain counts for neutrophils and monocytes from tumor patients did not display two separate peaks of formylhexapeptide binding; instead, only one broad peak was evident. These observations indicated that: Tumor patient PMN expressed as many formylpeptide receptors as did control PMN, and tumor patient monocytes possessed significantly more receptors than did control monocytes. The disposition of formylpeptide initially bound to control and tumor patient leukocytes appeared to be essentially the same. Subpopulations existed in each control neutrophil and monocyte sample, one exhibiting approximately 30% more formylpeptide binding than the other. However, in the leukocytes obtained from tumor patients, the distinction between these two subpopulations had become obscured such that only one cell population was evident.

Batch-swirl method for detoxification of isopropyl myristate used for sterility testing of oils and ointments: membrane selection.

A 1-hr batch-swirl method was developed for the preparation of isopropyl myristate to be used in the sterility testing of oils and ointments. The method is simpler and faster than that in USP XX. Flow rates of various membrane filters were tested. Cellulose acetate filters increased the filtration rate of oils and ointments and, thus, reduced the exposure time of possible microbial contaminants to the toxicity of isopropyl myristate.

Characterization of a chemotactic defect in patients with Kartagener syndrome.

Kartagener syndrome (KS) is an autosomally inherited recessive condition characterized by situs inversus, bronchiectasis, and chronic sinusitis. Ciliary dynein, the mechanochemical force generator in ciliary movement, is deficient in patients with KS. We examined blood samples from two patients and tissue biopsy specimens from five patients and found: (1) no significant defect in neutrophil or monocyte chemotaxis in response to formylpeptide chemoattractant; (2) no alterations in centriolar structure, but significantly more centriole-associated microtubules in KS neutrophils and monocytes than in control leukocytes; and (3) a marked reduction in KS fibroblast chemotaxis in response to fibronectin compared with control fibroblasts. The significance of these cellular defects in KS is described.