Ps Intensity Research Articles

Crystal Structure Defects in Titanium Nickelide after Abc Pressing at Lowered Temperature.

The experimental results regarding the effect of warm (573 K) abc pressing with an increase in the specified true strain, e, up to 9.55, on the microstructure and crystal structure defects (dislocations, vacancies) of the Ti49.8Ni50.2 (at %) alloy are presented. It is shown that all samples (regardless of e) have a two-level microstructure. The grains–subgrains of the submicrocrystalline scale level are in the volumes of large grains. The average sizes of both large grains and subgrain grains decrease with increasing e to 9.55 (from 27 to 12 µm and from 0.36 to 0.13 µm, respectively). All samples had a two-phase state (rhombohedral R and monoclinic B19′ martensitic phases) at 295 K. The full-profile analysis of X-ray reflections of the B2 phase obtained at 393 K shows that the dislocation density increases from 1014 m−2 to 1015 m−2 after pressing with e = 1.84 and reaches 2·1015 m−2 when e increases to 9.55. It has been established by positron annihilation lifetime spectroscopy that dislocations are the main type of defects in initial samples and the only type of defects in samples after abc pressing. The lifetime of positrons trapped by dislocations is 166 ps, and the intensity of this component increases from 83% in the initial samples to 99.4% after pressing with e = 9.55. The initial samples contain a component with a positron lifetime of 192 ps (intensity 16.4%), which corresponds to the presence of monovacancies in the nickel sublattice of the B2 phase (concentration ≈10−5). This component is absent in the positron lifetime spectra in the samples after pressing. The results of the analysis of the Doppler broadening spectroscopy correlate with the data obtained by the positron annihilation lifetime spectroscopy.

Practice Patterns and Predictors of Severe Toxicity Among Older Adults with Diffuse Large B Cell Lymphoma Treated with Frontline Chemoimmunotherapy

Introduction:Chemoimmunotherapy with R-CHOP is the standard of care for newly diagnosed diffuse large B cell lymphoma (DLBCL) leading to high cure rates although treatment-related toxicities are significant among older adults. Reduced dose R-CHOP has been proposed to balance efficacy and safety, but there is considerable ambiguity in “whom” and “by how much” with the best available data on those >80y [Peyrade et al 2011]. In this study, we sought to document the variability in chemotherapy dosing among unselected older adults with DLBCL treated with R-CHOP at a large, urban academic center in the Deep South. In addition, we sought to determine how baseline clinical features impacted tolerance of treatment.Methods:We conducted a single-institution retrospective review of all adults with newly diagnosed DLBCL initiating chemoimmunotherapy, predominantly R-CHOP, between 1/2015 and 2/2021 at the University of Alabama at Birmingham. For the current analysis, the cohort was limited to patients >70y. We extracted information on baseline clinico-demographic variables (age, sex, race, albumin, ECOG performance status [ECOG PS], Charlson comorbidity index [CCI], cancer type, stage, Revised International Prognostic Index score) and treatment intensity (type and dose of chemotherapy at 1 st cycle). Dose reduction was defined as any pre-planned reduction in cyclophosphamide, vincristine, or doxorubicin from standard CHOP dosing for cycle 1 of treatment. The primary outcome of interest was ≥grade 3 treatment-related toxicity (using CTCAE v5.0) occurring up to 30 days from the last dose of R-CHOP; secondary outcomes included dose modifications (dose delays >7d, dose reductions and treatment discontinuation) and health care utilization (unplanned emergency department visits and hospitalizations). Given high missingness for ECOG PS, we performed multiple imputation with chained equations producing 10 imputed datasets. Finally, we built a multivariate logistic regression model to identify baseline characteristics associated with severe toxicity; putative risk factors included age, sex, ECOG PS, CCI, albumin and treatment intensity. We pooled regression coefficients across imputed datasets using Rubin's rules. All hypothesis testing were two-sided, and the level of significance was chosen as 0.05.Results:Of 287 patients with DLBCL initiating R-CHOP during the study period, 101 (35%) patients were included in our cohort. The median age was 76y (IQR 73-79), with 55% males and 85% whites. Stage IV disease was present in 33% of patients, and 11% had double or triple-hit subtype. Of those with non-missing ECOG PS (55%), 38% had ECOG PS ≥2, and 29% had a CCI ≥2 [Table 1].Overall, 55% of patients received planned reduced dose treatment. Interestingly, 51% of patients <80y received reduced dose R-CHOP, whereas 32% of patients ≥80y still received full dose R-CHOP. Over half of patients (54%) experienced ≥grade 3 toxicity (42% hematologic toxicity, 27% non-hematologic toxicity). Dose delays (12%), reductions (12%), or discontinuations (17%) were frequent, and over a third (35%) of patients had unplanned hospitalizations during treatment. In a multivariate logistic regression model, reduced dose R-CHOP (Odds Ratio, OR 0.34; 95% CI 0.12-0.94; p value 0.038) was associated with decreased risk of ≥grade 3 toxicity, and CCI ≥2 (OR 5.35; 95% CI 1.58-18.25; p value 0.007) was associated with increased risk of ≥grade 3 toxicity. Age, albumin, and ECOG PS were not associated with risk of toxicity [Table 2]. Overall, only 11% of the observed inter-individual variability in toxicity could be explained by the above potential risk factors.Conclusions:Among older adults >70y with DLBCL, planned dose reductions based on anticipated tolerability were frequent, yet over half of patients experienced severe treatment-related toxicity. Treatment intensity and comorbidity burden were significantly associated with increased risk of toxicity, but age, albumin, and performance status were not. Overall, pre-treatment factors only explained about 11% of the observed variability in toxicity suggesting that a significant proportion of inter-individual variability in severe toxicity is unexplained by traditional evaluation. Future studies should examine the role of geriatric assessment and altered body composition in older adults to identify those at increased risk of severe toxicity from chemoimmunotherapy. [Display omitted] DisclosuresNarkhede: Genentech/Roche: Research Funding; Genmab: Other: Medical writing support, Research Funding; TG Therapeautics: Research Funding; Gilead: Research Funding. Mehta: Affirmed; Kite/Gilead; Roche-Genetech; Celgene/BMS; Oncotartis; Innate Pharmaceuticals; Seattle Genetics; Incyte; Takeda; Fortyseven Inc/Gilead; TG Therapeutics; Merck; Juno Pharmaceuticals/Bristol Myers Squibb: Research Funding; Seattle Genetics; Incyte; TG Therapeutics: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Seattle Genetics; Incyte; TG Therapeutics: Consultancy. Giri: PackHealth: Research Funding; CareVive: Honoraria, Research Funding.

Enhanced ion acceleration in the relativistic transparent regime due to the laser rising edge

We investigate the impacts of the laser contrast on ion acceleration when an ultra-intense laser pulse irradiates on a sub-micron foil target. In high-intensity laser driven ion acceleration experiments, the rising edge of the pulse could significantly preheat the target, which is likely to cause premature relativistic induced transparency of the target before the pulse peak. In this case, our particle-in-cell simulations show that the breakout afterburner (BOA) mechanism has obvious advantages over the radiation pressure acceleration (RPA). With the ATLAS laser contrast of 10−8.8 in 2 ps and peak intensity, the optimized target thickness is increased to 0.27 µm, where BOA works well and the maximum proton energy can reach 250 MeV. The proton energy is higher than that generated via RPA in a nanometer thin target either with and without the rising edge. Besides, the BOA appears robust against the laser contrast.

Reinforcing involvement of NK cells in psoriasiform dermatitis animal model.

Psoriasis (Ps) is a chronic inflammatory immune-mediated disease with skin and joint manifestations, characterized by abnormal and rapid proliferation of keratinocytes and infiltration of psoriatic lesions with immune cells. Extensive literature suggests that Ps is a T-cell mediated disease its pathogenesis being highly related to innate and adaptative immune cells. Although natural killer (NK) cells are involved in the inflammatory process of Ps through pro-inflammatory cytokine secretion (tumor necrosis factor α, interferon γ), their role in this pathology is not yet fully elucidated. In order to study the involvement of NK subpopulations in the pathogenesis of Ps we used the imiquimod-based mouse model of psoriasiform dermatitis and NK cells complex phenotype patterns from peripheral blood (PB) and spleen were investigated. Skin inflammation and the disease severity were assessed using in vivo measurements (erythema, desquamation and induration parameters, PASI modified score), splenomegaly assessment and histopathological evaluation. Phenotypic characterization of NK cells in imiquimod (IMQ)-treated mice was performed by flow cytometry, for both PB and spleen cell suspension. A large panel of surface markers was used: maturation and activation markers [cluster of differentiation (CD)49b, CD11b, CD43, CD27, KLRG1, CD335, CD69, CD28, gp49R, CD45R, CD11c] and markers for cytokine receptors (CD25, CD122, CD132). Our experimental data showed important differences in IMQ-treated mouse NK cell phenotype as compared to control group. The maturation markers (CD11b, CD43, CD27, KLRG1) were found increased on NK cells, in periphery and spleen, while CD49b+NK1.1+ was significantly lower, and the alterations correlated with the severity of the disease. Our findings reflect the immune engagement toward activatory profile of NK cells and draw attention to evaluating Ps intensity correlated with the mature profile of circulating NK cells.

Developing a Tool for the Detection of the Relative Amount of Water in Shale Cores Using Positron Annihilation Lifetime Spectroscopy

Recent investigation of positron lifetime in Barnett Shale samples has shown a small intensity of positronium (Ps) formation. The samples studied have XRF information on 35 elements and chemical information on total organic carbon (TOC). Previous research has shown that Ps is not formed in dry quartz-rich sandstone, calcite-rich limestone or dolomite-rich rocks, which contain minerals that also constitute a significant part of most shale samples. Recent study of twenty-five different common rock-forming minerals has helped to clarify the Ps contribution of different minerals commonly found in shale and the effect of hydration of some minerals on Ps formation. As a result, a better understanding of how Ps is formed in the shale samples is now available. It is suggested that the observed variation in Ps intensity in shale is due to variation in water content in the samples. While there is still no information about the possible Ps contribution of organic carbon in the sample, it is expected to be small. Development of a novel laboratory tool for the characterization of the amount of water in shale core using Positron Annihilation Lifetime Spectroscopy is discussed.

Positron annihilation studies of 4-n-butyl-4′-isothiocyanato-1,1′-biphenyl

Positron annihilation lifetime spectroscopy (PALS) measurements were performed between 93 and 293 K in order to study the supercooled smectic-E (Sm-E) phase of 4-n-butyl-4'-isothiocyanato-1,1'-biphenyl (4TCB), the ordered molecular crystal of 4TCB, and the phase transition between the Sm-E phase and the ordered molecular crystal of 4TCB. The phase transition was well reflected in the abrupt increase of the ortho-positronium (o-Ps) lifetime and intensity. The value of the o-Ps lifetime in the Sm-E liquid crystalline phase of 4TCB, i.e., 2.21 ns at room temperature, was explained by the formation of bubbles induced by Ps atoms, which are created due to a liquidlike state of the butyl chains of 4TCB molecules in the Sm-E phase. The temperature dependence of the o-Ps intensity for the supercooled Sm-E phase can be explained by thermal generation of sites where bubbles are formed; an activation energy equal to 0.30±0.02 eV was estimated. This value was compared with the activation energies of molecular motions. The o-Ps lifetime in the ordered molecular crystal was interpreted as originating from the annihilation of o-Ps confined in molecular vacancy-type imperfections in the crystal lattice. The value of the o-Ps pickoff annihilation between 1.8 and 1.9 ns is in accordance with the size of the molecular vacancy for the 4TCB crystal lattice. Its intensity is lower than 5%. The isothermal crystallization of the 4TCB Sm-E phase was observed by PALS. The low-dimensional crystal growth was concluded from the Avrami equation fitted to the time dependence of the o-Ps intensity, which resulted in an Avrami exponent equal to 1.73.

The Influence of Admixtures in n-Alkanes on Electron Traps

The distribution of electron trap depths in hydrocarbons seems to be continuous in the range from 0.6 eV to 2.2 eV. However, it seems that among the deepest traps in n-heptane also the discrete ones appear as well. The influence of the admixture of other alkane on Ps intensity in alkanes was examined. As far as the admixture of an alkane with a shorter chain is concerned, the depth of the traps and their amount remain almost the same like in the case of the pure solvent. When it comes to essentially non-miscible solid heptane and nonane, a total lack of electron accumulation effects was observed. It is an exception among the mixed alkanes investigated here and needs a careful study.

Order‐disorder transitions in self‐assembled polymers: A positron annihilation study

AbstractWe report here the first results of order‐disorder transition (ODT) in a self‐assembled comb‐like polymer‐amphiphile supramolecular system as identified from the change in positron lifetime parameters. We have used poly(4‐vinyl pyridine) hydrogen bonded with 3‐pentadecyl phenol, which upon heating showed a stepwise reduction in o ‐Ps intensity at the ODT from lamellar self‐assembled state to the disordered state. The ODT temperature was confirmed by differential scanning calorimetry and small angle X‐ray scattering. The free volume “holes” in this polymer‐amphiphile system are proposed to be near the chain ends of the polymer backbones. We suggest that positron lifetime spectroscopy can serve as a technique to identify ODTs in self‐assembled lamellar structured supramolecular systems. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Positron annihilation lifetime data and actual porosity of polymers

AbstractApplication of the three‐component LT9.0 analyses and discrete four‐component PATFIT analysis to PAL distribution in some porous polymers, such as PIM‐1, AF2400, AF1600, PTMSP, give practically the same good fitting. In the conditions of this uncertainty, some additional experiments (thermomechanical tests, NMR on the protons of the absorbed water, thermo‐stimulated luminescence TSL, low temperature gas sorption BET, mathematic molecular‐dynamic simulation) give some arguments in favour of non‐Gaussian distribution of elementary free volumes EFV in some porous polymers and their possible heterogeneity. Furthermore, a comparison of PAL and TSL data confirm the idea on the interconnection between the rigidity of the polymer chains and effective size of the EFV. This interconnection is illustrated by the correlation of the o ‐Ps lifetime and intensity of the high‐temperature peak in the TSL glow curve. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Depth-dependent positronium formation in γ-irradiated polymers after 30-month aging

Depth-dependent positronium (Ps) formation and annihilation study of Co-60 γ-irradiated polyethylene and polytetrafluorethylene were performed. After 30-month aging, no free radicals effect on Ps formation was detected for the studied polymers. Efficient trapping of back-diffusion positrons was observed in heavily irradiated samples, where Ps formation probability near polymer surface and in the bulk turns to be equivalent to each other. Results shown that positron annihilation Doppler broadening in polytetrafluorethylene is prevailingly influenced by high momentum electrons of fluorine atoms instead of Ps intensity.

Positronium formation on trapped electrons in n-heptadecane

Positronium (Ps) formation on trapped electrons as a function of positron irradiation time by high-energy positrons and temperature were investigated in the case of n-heptadecane, as a representative of odd-numbered alkanes. It was found that the rise of Ps intensity with temperature in the range below 200 K results from an increasing positron mobility, at constant trapped electron density. Thermal collapse of the traps is responsible for reduction of Ps intensity at higher temperatures.

Hydrodynamic Investigations of Intense Subpicosecond Laser–Matter Interaction

A model for the interaction of a short laser with matter is presented. The model is based on the solution of wave-propagation equations in a medium with complex dielectric constant. The model is coupled with multigroup radiation hydrodynamics to take into account the space and time evolution of plasma parameters. The complete code is used to analyze various experiments with laser pulse duration varying from 150 fs to 5 ps and laser intensity varying from 1012 W/cm2 to 1017 W/cm2. The model is also used to study the enhancement in absorption with prepulse

Comments on electric field experiments of positronium formation

Validity of using static electric field in studying Ps formation mechanism is tested experimentally. At the present experimental condition, Ps intensity in low-density polyethylene was decreased seemingly in a similar way as a function of the strength of static and alternating electric fields. However, a time-dependent screening effect, possibly caused by accumulated charge, was apparent. By using an alternating field, it was possible to eliminate the screening effect. It is highly recommended to use alternating fields in the forthcoming electric field experiments. In another experiment, while applying alternating electric field, PAL was measured only when the polarity was positive or negative with respect to the positron implantation trajectory. The results showed that positive and negative fields have the same effect, indicating that the structure of terminal positron spur is symmetric, unlike the asymmetric structure at the end of muon track.

Effects of electric field on positronium formation in polyethylene at various temperatures

Effects of electric field on the positronium (Ps) formation probability have been studied at various temperatures. At 250 K, at which Ps intensity is the smallest, there was no electric field effect. At 150 K, where Ps intensity becomes large due to recombination of e + and trapped electrons, the electric field effect was also not observed. The reason for the absence of electric field is different for these two cases. At and above room temperature Ps intensity was decreased by the electric field, and the efficiency was larger at lower temperatures. This latter observation has been explained in terms of the temperature dependence of energy loss processes of e + and e − in the terminal positron spur. With this view, it is also possible to explain the fact around room temperature that the zero-field Ps intensity becomes larger with temperature. It seems that at least three different Ps formation mechanisms are involved in the present system.

Positronium trapping in free volume of polymers

Positronium trapping process caused by slow thermalization of Ps inside intermolecular spaces of polymer is considered. The pickoff annihilation rate of Ps decreases from an initial value, characteristic for the delocalized Ps, to a final value, relating to its localized state. The elastic thermalization lifetime analysis of polymers spectra with a new ETLT program is proposed to determine the total Ps intensity ( I Ps), Ps trapping rate ( γ), its initial ( τ 0) and final ( τ ∞) pickoff lifetimes as well as the relative e +–e − contact density ( η). The model is tested through the analysis of polyurethane spectra measured in a wide range of temperature, containing the glass transition point ( T g). In contrast to the conventional analysis, I Ps does not display any change at T g. The results indicated slow trapping rate (about 1 ns −1) of Ps in the cavities.

A positron annihilation study of the tensile behaviour of bivoltine silk fibers

The influence of longitudinal stress on the microstructure of bivoltine silk fibers has been investigated by the Positron Lifetime Technique (PLT). The variation of o–Ps (ortho–positronium atom) pick-off lifetime and intensity as a function of stress (0–240 kPa) reveals that the free volume size and its number density remains unchanged within the elastic limit (60 kPa). Thereafter, the free volume size decreases from 67 to 57 Å 3. Owing to the loose helix structure, the chain alignment in the crystalline regions starts prior to that in the amorphous regions, leading to a more ordered silk-II type. The estimated low activation energy in the disordered regions suggests a folded chain conformation for the more ordered silk-II type.

The study of the positron states in CS2

Mogensen reported that CS2 was the only liquid which showed large decrease of the positronium (Ps) intensity with lowering the temperature. The ratio between the intensity of the longest lifetime and the width of the narrowest component on the angular correlation measurement was not 3∶1 in CS2 liquids. Here I measured the change of intensity and lifetime of the longest lifetime component caused by varying the surface tension, the dielectric constant, and the temperature to clarify the positron state in CS2. I also measured the angular correlation of the positron annihilation γ-rays in CS2. High surface tension and high electron and positron affinities of CS2 cause many phenomena which can not be seen in other liquids.

Effect of CCl4 on positronium formation in isooctane

The effect of CCl4 on positronium (Ps) formation is examined in isooctane through positron lifetime spectroscopy experiments, in the framework of a series of studies on AOT-based reverse micellar systems. This solute appears as a rather strong Ps formation inhibitor, as expected in view of its well-known electron scavenging properties. The reciprocal of the triplet Ps intensity (1/I3) varies linearly with CCl4 concentration (C), up to about 0.08M, allowing to derive a high inhibition constant,k=36.6M−1. Above 0.08M, however, the inhibition slackens out, which is attributed to an anti-inhibition effect. On the basis of previous reports on halocompounds, a general scheme of reactions is proposed to occur in the positron spur, including, besides the primary Ps formation through thee+/e− reaction and the recombination reactions, electron scavenging by CCl4 as the direct inhibiting reaction, followed by the reaction of the thus formed anion with the positron. The latter reaction may lead either to a [CCl4Ps] bound-state or, if the positron picks off the electron from the anion, to some additional Ps formation. By using a simple quantitative approach to this scheme, an equation descriptive of the variation ofI3 withC is derived which agrees well with the experimental data.

The Study of the Electron–Positron Pair in CS2

Abstract Ole E. Mogensen reported that CS2 was the only liquid which showed large decrease of the Ps intensity with lowering the temperature, even though electron and positron could encounter with each other at low temperatures such as −100 °C. The intensity change by the positron annihilation lifetime was observed at a little lower temperature by the positron annihilation angular correlation. Here I measured the change of intensity and lifetime of the longest lifetime component caused by varying the surface tension, the dielectric constant, and the temperature, to clarify the positron state in CS2. These experimental results confirm the ideas of the “fourth positron state” and the “squeezed positronium state” which were proposed by Ole E. Mogensen.

Structure of the adsorbed ethyl xanthate monolayer on copper

AbstractXPS intensity calculations from completely oriented and randomly oriented ethyl xanthate on copper have been made as a function of electron take‐off angle. Corresponding experiments also were carried out using the variable‐angle XPS (VAXPS) method. The results show that the completely oriented ethyl xanthate layer model at a certain stage of adsorption seems to be valid, as originally proposed by Mielczarski et al. However, there are systematic errors in the calculations, which are mainly due to uncertainties in calculated electron mean free paths and absolute values of parameters characterizing the assumed adsorption layer structure.